Eman Fatima and His Research
Ketone Bodies and Autophagy: Synergistic Approach to luminating Neurotoxic Aggregates in Alzheimer Disease.
Abstract:
Alzheimer disease (AD) is a progressive condition that exhibits cerebral glucose hypometabolism, accumulation of amyloid-b(ab) and tau tangles, and derailing of proteostatic responses. β-hydroxybutyrate (BHB), the major blood-borne ketone body, can replace glucose as an alternative cerebral energy source, and pleiotropic neuroprotective effects. BHB is shown to restore mitochondrial metabolism, reduce neuroinflammation, and regulate the unfolded-protein response to preserve lysosomal integrity and maintain autophagic flux. With experimental evidence. Simultaneously, BHB facilitates lysine b-hydroxybutyrylation (Kbhb) of metabolic enzymes, histone acetylation, as well as clearance of aggregation-prone proteins by both macroautophagy and chaperone-mediated autophagy. Preclinical AD models also show that BHB treatment lowers Aβ and tau pathology, enhances cognitive functions and displays synergistic effects in conjunction with pharmacologic activators of autophagy as AMPK agonists and TFEB inducers. All these findings reinforce a mechanistic model where ketones induced metabolic re-programming and autophagy regulation intersect to recover proteostasis and can serve as the disease-modifying approach in AD.
Introduction
The brain is a very energy consuming organ. Despite the fact that it comprises only 2 percent of the total body mass, it consumes approximately 20 percent-23 percent of the total body energy, which is about 110 percent-140 grams of glucose per day. The energy is necessary to sustain their resting potentials, develop action and post-synaptic potentials, as well as to normalize pre-synaptic calcium levels and to restore neurotransmitter levels, especially that of glutamate. The brain mostly utilizes glucose in the fed state but when the body is in fasting, both ketone bodies are co-utilized with the most prominent in normal consumption of glucose and the secondary one acetone. The lactate produced by anaerobic glycolysis can also be seen as another energy source; it is used when there are basal and hyperlactatemia conditions.
Alzheimer disease (AD) is a neurodegenerative condition that develops as a result of the deposition of neurotoxic protein aggregates including amyloid-beta (Aβ) plaques and tau tangles which cause impairment of synapses, neuronal degeneration and cognitive impairment. As a person ages, the rate of cerebral glucose uptake becomes lower, which frequently occurs without any clinical manifestation decades before the indicators appear [1]. Even though there is a lot of research, there is still no disease-modifying treatment that could be effective. New literature has highlighted cellular impaired clarification and metabolic illness as major AD pathogenic factors [2]. The consumption of energy substrates is altered in both a diffuse and regional way around the world and locally in the brain through ageing and neurodegeneration especially in glucose. These modifications are either causal or consequential. It is critical to learn the mechanisms of normal and pathological brain metabolism to come up with anti-aging and anti-neuro degenerative measures [3].
The purpose of the current review is to discuss the therapeutic perspective of β-hydroxybutyrate-mediated reprogramming of metabolism and activation of autophagy in Alzheimer disease. The review, in particular, summarizes available data about the association of cerebral glucose hypometabolism with the steps of the development of AD, analyses the capacity of BHB as an alternative energy source and its impact on mitochondrial and lysosomal functions, and outlines the molecular pathways by which BHB induces Kbhb, controls the unfolded-protein response, and improves autophagic clearance of Aβ and tau. Moreover, it critically discusses preclinical evidence that assesses the synergies of BHB with pharmacologic autophagy enhancers and outlines current gaps in knowledge that determine the further experimental and clinical research to translate ketone-based interventions to AD treatment.
1.1. Reducing Glucose Metabolism and Sparing Ketone Metabolism in AD.
A decrease in glucose metabolism is coupled with the Aβ plaques. Aβ plaques has a direct destructive effect on mitochondria via electron transport complex III, cytochrome c and TCA cycle enzymes as well as reactive oxygen and nitrogen species (ROS / RNS) damage of cell membranes, glucose transporters, and NMDA receptors. These molecular effects help in reduction in body glucose usage. It is interesting to note that Aβ deposition takes place an average of 15 years prior to the AD manifestation whereas cerebral hypometabolism comes at around 10 years of age [4].
2. Ketone Body Metabolism and its role in the Alzheimer Disease (AD)
In the fasting process, the adipocytes release the free fatty acids which are carried to the liver where they are converted to ketones. Diabetic patients have low insulin concentrations that facilitate lipolysis by desensitizing the inhibition of hormone-sensitive lipase, leading to β-oxidation in hepatocytes, and causing ketogenesis. Long chain fatty acids have to be transported to mitochondria, so the process of ketosis might be restricted during ketogenic diets, but medium-chain fatty acids (MCFA) could reach the mitochondria without the involvement of transport proteins [5].
Ketogenic interventions are postulated to achieve improvements in cognitive and behavior of AD models and some patients with significant improvements in energy deficits through clinical and preclinical studies [6,7,8].
2.1. β hydroxybutyrate (BHB) production
The production of β-Hydroxybutyrate (BHB) occurs in the liver during the process of metabolic acidosis. The main ketone is β-hydroxybutyrate. On decreased glucose metabolism β-OHB ketolysis to generate acetyl-CoA, which enters the TCA cycle where it gives rise to the production of ATP. In liver mitochondria ketogenesis is performed when the production of acetyl-CoA using fatty acids is more than the oxidative power of the TCA cycle and the excess of acetyl-CoA is changed into ketones [9]. The liver cells are the primary producers of ketones with little input by the kidney and astrocytes. This process and the production of acetoacetate are regulated by three enzymes, mitochondrial acetoacetyl-CoA thiolase, HMGCS2 (controlled by insulin/glucagon through FOXA2), and HMG-CoA lyase. The production of acetone occurs either spontaneously or through the change of acetoacetate into BHB (most abundant ketone in the blood) through β-hydroxybutyrate dehydrogenase which requires NADH as a cofactor [5].
Ketone bodies are soluble and transporter acetyl compounds (oxygenated to CO2 and water) that act as a source of energy to the peripheral tissues, but are not carried out by albumin or lipoproteins [9]. Ketogenic diets with calories limited stimulate the expression of HMGCS2 in the liver and brain of rodents [5]. β-hydroxybutyric acid also enhances the metabolism of mitochondria, signaling molecule regulation, histone acetylation, and neuroinflammation and clearance of Aβ and Tau proteins in AD rodent models. H3K9 Kbhb and other Kbhb lysine β-hydroxybutylation (Epigenetic) regulation affects the expression of genes and liver metabolism, but their involvement in AD progression has not been published yet [10].
2.2. Uptake of Ketones in the Brain using Monocarboxylate Transporters (MCTs)
The uptake of ketone over the BBB through MCTs is concentration-dependent and not dependent on the neuronal activity. BBB endothelium/astroglia expresses MCT1, the astrocytes express the MCT4 (low affinity) and the neurons express MCT2 (high affinity). In human beings and rodents, expression patterns are similar. MCTs are stimulated with fasting, ketogenic diets, or exercise, and these efforts have increased the transport of ketones [5].
2.3. The Ketone Bodies: Proteostasis Regulators
Other than fuel, BHB regulates proteostasis. Proteomic research suggests that BHB selectively changes the solubility of pathological proteins including A beta. BHB or ketone ester treatment induces aggregation-prone proteins turnover, presumably through autophagy in mice [11]. BHB is also useful in promoting the lysine 1, β-hydroxybutyrylation (Kbhb) of proteins, such as TCA cycle enzymes. Pathological stages of APP/PS1 mice exhibit a reduction in Kbhb on citrate synthase and SUCLG1; BHB or ketogenic diets replenish Kbhb, increasing activity, ATP generation, and decreasing Aβ-plaque pathology and microgliosis [10].
2.4. Ketone-Uptake and Oxidation Conservation in the Alzheimer Disease
PET images depict that AD patients possess less than 25 percent down of frontal, parietal, temporal lobes, cingulate gyrus CMRGlu combined with a reduction of glucose uptake rate constants (KGlu) of around 15 percent when compared to healthy older people [4]. There are no significant differences in CMRAcAc and AcAc uptake rates in healthy adults, MCI, and AD groups [4,11]. This denotes that glucose metabolism reduces with age/with cognitive impairment whereas there is no effect on ketone metabolism.
The whole-brain CMRAcAc and CMRGlc were found to increase by 28 and 44 percent respectively with ketogenic diets in old 14-day-old rats [12]. CMRAcAc increased (p = 0.005) and CMRGlu reduced 20% (p = 0.014) in human adults [13]. Whether the KD interventions can change the glucose uptake is still to be established [12].
2.5. Regulation of Ketone Metabolism during Autophagy
There is the crosstalk in the metabolism of ketones and autophagy. BHB controls the unfolded protein response (UPR), lysosomal integrity, and autophagic flux and keeps proteostasis valid. There is in vivo stroke research that demonstrates D-BHB inhibits maladadaptive UPR, decreases the activation of PERK-eIF2α-ATF4 arm and IRE1α phosphorylation, suppresses chronic ER stress, and abates cell death [14]. BHB lowers the expression of ATF6, PERK, and CHOP, alleviates the occurrence of inflammasome and pyroptosis, and boosts the survival of SH-SY5Y neurons when confronted by Aβ and LPS, facilitating adaptive, but not pro-apoptotic/pro-inflammatory cascade reactions [15]. D-BHB preserves lysosomal-autophagic vacuoles, inhibits cleavage of LAMP2, restores ATG5, ATG7, Beclin 1, LC3, and p62 indicators, and decreases the quantity of lesion volume, preserving fruitful autophagic flux [16]. Prolonged nutritional ketosis of the mouse biosphere increases the markers and proteins of hippocampal autophagy (SIRT2-regulated FOXO1/3a, PGC1a, TFEB), enhancing autophagy, mitophagy and lysosomal biogenesis [17]. This coupling of elevated ketone utilization with stronger autophagy-lysosomal machinery and fine-tuned UPR signaling supports the concept that ketone metabolism and autophagy are part of a unified adaptive response that promotes clearance of damaged proteins and organelles and may be especially relevant for limiting aggregate accumulation in aging and Alzheimer's disease [17,18,14].
BHB therapy enhances memory, reduces Aβ deposits and phospho-tau, elevates CMA target proteins (LAMP2A, Hsp70), and suppresses NLRP3 inflammasome activation in sporadic AD animals [19]. It enhances mitochondrial and lysosomal integrity, decreases lysosomal acidification, decreases fibrillar vesicle accumulation, and improves lifespan and memory in Drosophila AD models [20].
Ketone bodies, especially BHB are used as alternative fuels and signaling molecules to: (1) support neuronal ATP in glucose hypometabolism, (2) remodel proteome solubility/ post-translational modifications, and (3) increase autophagy/CMA and lysosomal activity. This is because ketone metabolism is a major factor that contributes to proteostasis and aggregate clearance in AD.
3. Autophagic Dysregulation in Alzheimer's Disease
Quality checkpoint of proteins and organelles in neurons is dependent on autophagy-lysosomal mechanisms. There is a malfunction of this system at several stages in AD mechanisms: initiation, cargo trafficking, autophagosome-lysosome fusion, and lysosomal proteolysis. It leads to impaired autophagy, intracellular 86 -amyloid and tau retention, neurotic dystrophy, and cell death.
3.1. Abnormal Autophagy-Lysosomal Flux in AD
The electron microscopy and neuropathology show that autophagic vacuoles (AVs) and autolysosomes are present in the dystrophic neurites, which are signs of autophagic stasis and not normal turnover [21,22,23]. Autophagosomes and amphisomes in neurites and synaptic areas and incompleteness of substances in autolysosomes, upsurge of LC3-positive vesicles, and LAMP1-positive lysosomes but decrease in clearance capacity are consistently demonstrated in post-mortem experiments and animal models [24,22,25]. As these results indicate, lysosomal clearance failure, but not complete constriction of autophagy inductance, is a significant abnormality in AD [21,24,26].
3.2. Imbalanced Autophagosomal Presence and Formation
A number of studies portray altered autophagy initiation. In AD mTORC1 hyperactivity (high amounts of p-mTOR, p-RPS6KA1, p-RPTOR, RRAGC) in the hippocampus prevents the initiation of autophagy [27]. Significant constituents of autophagosome-formation, such as Beclin 1, NRBF2, ULK1/2, are also reduced in AD hippocampus and models, which is in line with impaired biogenesis [27,28,23].
Nonetheless, transcriptomic and protein studies of CA1 neurons demonstrate that the gene expression and LC3 puncta increase, which suggests an increase in autophagosome formation in vulnerable neurons [24,21]. The intensive autophagy triggering at the initial stages may be compensated by these conflicting data, yet dysregulation of mTOR and depletion of necessary ATG machinery eventually damage autophagy initiation [27,24,22,23].
3.3. Alterations in Autophagosome Transport and Fusion
The autophagosomes are usually formed distally and being conveyed in a retrograde manner to the soma where it fuses to a lysosome. The degenerative neurons in AD contain undeveloped autophagosomes in the dystrophic neurites, especially in the dendrite and axons of the nervous system, suggesting the loss of transport and maturation [23]. A-beta and APP C-terminal flakes interfere with endosome-lysosome and autophagosome-lysosome fusion. PS1/APP mice and A-beta aggregation prevent fusion and decrease the lysosomal membrane and lysosome markers (cathepsin B and Lamp1) [29].
Accumulation of cholesterol in AD/Niemann-Pick C-like models does not change autophagosome formation but interferes with endosomal-lysosomal vesicle fusion through an abnormal distribution of RAB7 and SNARE, which does not allow A-beta /tau degradation in autophagosomes, but leads to autophagosome secretion of A-beta [30]. The dysfunction of SNARE complexes and malfunctioning lysosomal acidification negatively affect fusion and AV accumulation even more [31,32].
3.4. Failure of Lysosomal Abnormality and Proteolysis
The lysosomal/autolysosomal stage is considered to be a prime suspect of primary blocks. Structured analyses of CA1 neurons depict more autophagosomes produce and lysosomes in the cells (MiTF/TFE activation), yet the LC3 II protein and p62 accumulate in the enlarged autophagosomes and lysosomes (substrate degradation breakdown). PSEN1 and APP mutations that cause familial AD affect the functioning of the lysosome, rendering it unable to acidify and to degrade proteins, the lysosome is unable to clear autophagosomes, but APP knockout can repair lysosomal/autophagy impairment in human neurons [33]. Swollen deacidified autolysosomal accumulation of A-beta/APP- betaCTF, in AD mice, leads to PANTHOS patterns in which effected neurons become key contributors of senile plaques [34,35]. Human AD brains and models have been reported to have lysosomal PH defects, cathepsin B/D activity decrease and membrane integrity damage, frequently prelude overt plaque pathology [27,26,36].
3.5. Consequences for A-beta and Tau
Autophagy-lysosomal defects have direct effects on AD core proteins. AVs and autolysosomes include APP, beta-secretase and gamma-secretase, which facilitates the synthesis of A-beta and decreases its degradation [22,37,38]. Hyperphosphorylated tau is localized with LC3-positive vesicles and aggregates of tau form with autophagy defects; LAMP1 and cathepsin D defects suggest failures of tau turnover [25,39]. Genetic or pharmacologic neuronal inhibition of Atg5, Atg7 and Beclin 1 causes ubiquitin aggregation, p62 aggregation, neurodegeneration and exacerbated AD pathology, highlighting the protective properties of autophagy [27,39].
3.6. Dynamic and Stage-Dependent Dynamicity of Autophagy.
AD Autophagy is not a static process, but instead, an early period of compensatory induction and bio-genesis, followed by chronic lysosomal impairment, AV overload and neuritic dystrophy are observed during AD progression [27,24,22,26,35]. Autophagy encouragement (e.g., mTOR suppression, TFEB stimulation) could be used therapeutically to decrease A-beta/tau, if lysosomal function is intact, and as well as to enhance the cognition. Nevertheless, in late lysosomal failure, subjecting the person to further induction may increase substrate deposition and toxicity [22].
3.7. Epidiagnostic evidence of AD Autophagy collapse in the lab.
1) Pathology of human brain and mouse model.
The post-mortem evidence demonstrates that the pools of AVs and autolysosomes are huge in the brains of AD and mouse models indicating autophagic flux blockage [27,28,34,39]. Functional imaging of neuron-specific LC3 pH sensors shows early autolysosome acidification decline than extracellular plaque loss due to impaired v-ATPase activity [34]. A-beta/APP-betaCTF is deposited in enlarged deacidified autolysosomes that produce PANTHOS rosettes, one of the principal forms of senile plaques [34,35]. The broken connexon between autophagosomes and lysosomes, defective retrograde transporting, and dysfunctional lysosomes are verified as primary AD autophagy defects [27,39,40].
2) Molecular and mechanistic Evidances
The genetic and molecular research shows that the alterations in familial AD are autophagy-lysosomal defects (e.g., PSEN1, APP, lysosomal genes) that disrupt lysosomal acidification and proteolysis and result in the accumulation of APP, A-beta and tau and neurodegeneration [27,35,39]. A-beta and phosphorylated tau disrupt autophagy/mitophagy and decrease clearance of impaired mitochondria and protein aggregates [41]. Increase tau accumulation in the presence of lysosomal inhibitors (chloroquine, NH 4 Cl, 3 -methyladenine) is also a confirmatory that tau is removed via autophagy-lysosome mechanisms [42].
3) Signaling changes within damaged autophagy.
The imbalance of nutrient-sensing and transcriptional pathways occurs in autophagy-lysosomal collapse in AD. Constant mTORC1 stimulation in the human AD hippocampi suppresses autophagy and lysosomal biogenesis and genetic mTOR deficit in Tg2576 results in autophagy restore and cognitive ability in mice [37]. Mutated AMPK, TFEB, and associated signaling also worsens neuron autophagy-lysosome flux, initiating a vicious cycle of low clearance, A-beta /Tau and mitochondrial dysfunction and cell death [27,35,37,39,41,43].
4. Therapeutic implication of Autophagy Collapse in Alzheimer disease.
Because the autophagy impairment is mechanistically linked to A-beta and tau aggregates, synaptic demise, and cell demise, the restoration of autophagic flux, especially the lysosomal activity, is an important treatment approach.
4.1. Activation of mTOR-Independent Autophagy
mTORC1 inhibitors like rapamycin enhance autophagy and lower A-beta and tau pathology, as well as learning and memory in various mouse models of AD [27,23,37,39,44]. Genetic blockage of mTOR improves autophagy in Tg2576 mice and prevents cognitive impairment, which is a good argument that lowering mTORC1 levels are therapeutic [37]. Moreover, memantine and carbamazepine, both used clinically, could induce autophagy either through mTOR dependent or independent mechanism, and carbamazepine can reduce the amyloid load and enhance cognition in 3xTg AD mice [23].
4.2. TFEB and Lysosomal Activation
The transcriptional master of lysosomal biogenesis is TFEB. TFEB can be pharmacologically or genetically activated to increase the activity of the lysosome, facilitate the breakdown of A-beta and tau, and improve pathology of AD models [32,27]. To illustrate, intermittent hypoxia of APP/PS1 mice restores the nuclear TFEB positioning in plaque-engaging microglia, augmenting autophagy-lysosomal legislation, amplifying A-beta clearance result, decreasing load and neuroinflammation of plaques, and indicates the functional advantages of TFEB-mediated lysosomal rehabilitation [44].
4.3. Small-Molecule Enhancers and Repurposed Drugs
Various agents, including rapalogs, metformin, resveratrol, nilotinib, spermidine, curcumin, and more, stimulate autophagy with either mTOR-dependent or independent pathways and reduce A-beta and tau pathology as well as improve cognition in preclinical AD models [23,27,28,39,40,46]. Reviews of clinical trials show that the majority of clinical autophagy-targeted therapies are at an early stage of pharmacological development with no autophagy modulator approved specifically in AD. The serious issues are penetration of the brain, optimal dosing option, as well as the danger of excessive autophagic activation in circumstances of late-stage lysosomal failure [23,47,48].
4.4. Attacking the Upstream and Parallel Pathways
Activators of AMPK, PDE4 inhibitors, TRIB3 modulator, Nmnat, and BAG3 have been shown to repair autophagic flux, minimize protein aggregates, and enhance cognitive deficits in experimental systems [37,39,49,50]. By inducing autophagy and senolytic approaches, the burden of senescent cells, neuroinflammation, A-beta and tau deposition, and memory rescue in AD models in rodents, the autophagy senescence axis is of great significance [37].
There is a strong stage dependency to autophagy at early stages of disease autophagy is a protective process, but at late stages in AD there is evidence of severe lysosomal impairment and autophagosome overproduction, which may increase the vacuolar accumulation [27,34,35,39]. Therapeutic studies with co-targeted lysosomal acidification and biogenesis (e.g., TFEB, v-ATPase) along with induced autophagy should also be tested together, and the latter needs demonstration in human research [27,32,34,35,47].
5. Molecular Interaction of BHB with Autophagy, AMPK, beta-Hydroxybutyrylation, Lysosomal pH, and NLRP3 Inhibition.
BHB is an energy source and a signaling molecule that controls autophagy and inflammation by converging on various mechanisms that are involved in neurodegeneration and aging [51,52].
5.1. Autophagy and Mitophagy Plasticity.
BHB causes AMPK and ULK1 activation in brain cells and other cell types which stimulate autophagy and mitophagy events. D-BHB enhances phosphorylation of AMPK Thr172 and ULK1 Ser317, and raises the level of LC3-II, as well as LC3-positive autophagic vesicles in cultured neurons, which indicates the presence of an AMPK-dependent but mTOR-independent process of autophagic flux [17]. BHB enhances ULK1 ser317 phosphorylation and inhibits mTORC1 activity, shown by decreased p-S6K1 Thr389 in HGPS fibroblasts, and prevents BHB-induced p62/SQSTM1 degradation, progerin degradation is prevented by inhibiting AMPK or ULK1 showing that BHB enhances autophagy via the AMPK-mTOR-ULK1 pathway in order to clean up toxic intricate proteins [52].
In addition to autophagy, BHB rebates mitophagy and ATP generation in osteoarthritic chondrocytes, and BHB antioxidative, anti-senescence and anti-apoptotic actions are canceled by knockout of HCAR2, or AMPK inhibition, suggesting that it acts through the HCAR2-AMPK-PINK1/PARK2 pathway [53]. D-BHB inhibits superfluous LC3-II accumulation and p62 accumulation and suppresses AMPK-ULK1 Ser317 activation to restore autophagic flux and mitigate neuronal death in rats with severe hypoglycemia and coma, which is probably through the enhancement of mitochondrial energetics [54].
All these results suggest that BHB is either able to up- or down-regulate AMPK-dependent autophagy in response to physiological conditions, but can always improve mitochondrial energetics and mitophagy to reestablish autophagic flux in various cellular and in vivo systems [17,51,52,53,54]. Despite the fact that this data implies mechanistic interrelationships between ketone metabolism, mitochondrial quality regulation, and proteostasis, they have been yet to be confirmed in human neurodegenerative systems.
5.2. Epigenetic Control and beta-Hydroxybutyrylation of Autophagy Genes.
BHB is an epigenetic signaling metabolite which inhibits the activity of the class I histone deacetylases and is a precursor of lysine beta-hydroxybutyrylation (Kbhb), a histone mark that promotes stress resistance, mitochondrial metabolism, and autophagy gene activation [51,55]. A number of studies indicate that BHB-induced histone changes increase the levels of autophagy-related and antioxidant genes, which adds to cellular resistance to metabolic and neurodegeneration disorders [51,55,56].
Even though the direct mapping of the beta-hydroxybutyrylated regulatory elements that mediate autophagy has not been fully accomplished yet, there is current evidence of BHB as an epigenetic promoter of autophagy and mitochondrial homeostasis [51,55].
5.3. Lysosomal Biogenesis, Function, and PH
BHB also regulates the autophagylysosomal system and lysosomal capacity. D-BHB uses TFEB-dependent lysosomal biogenesis and SIRT2-FOXO1/FOXO3a-PGC 1alpha signaling in neurons to synchronize autophagy, mitophagy and mitochondrial biogenesis [17]. BHB recovers the impaired autophagy state of HGPS fibroblasts and triggers p62 degradation, which is prevented by AMPK or ULK1 inhibition, and the effect reveals that a repressed autophagy-lysosomal route has been reinstated [52]. D-BHB has been shown to rescue LAMP2 expression and lysosomal membrane integrity, LC3-II accumulation and p62 accumulation, and increase autophagy and degrade lysosomal function, respectively, and improve autophagic degradation in models of NMDA excitotoxicity and hypoglycemic coma, which is also evidence of the stabilization of lysosomal activity and autophagy under stress conditions [16,54].
Altogether, these data indicate that BHB promotes autophagic accumulation of the lysosome and its functional stability and mitigates the stress-related bottlenecks of autophagosome traffic formation instead of intensifying autophagosome formation [16,17,51,52,54].
5.4. NLRP3 Inflammasomes and Autophagy Crosstalk
BHB has great anti-inflammatory properties that are direct inhibitors of the NLRP3 inflammasome and indirect instigators of autophagic homeostasis. BHB, but not acetoacetate or short-chain fatty acids, dose-dependently inhibits NLRP3 activation and IL-1beta/IL-18 release in macrophages through the inhibition of potassium efflux and ASC oligomerization and is independent of AMPK, reactive oxygen species, autophagy, GPR109A/HCAR2, SIRT2 and glycolytic inhibition [57].
Against cellular evidence, in vivo BHB or ketogenic diets suppress caspase-1 activation and IL-1beta release in a number of NLRP3-mediated inflammatory systems and validate systemic inflammasome inhibition [57]. Exogenous BHB in a 5XFAD AD model decreases the plaque burden, microglial proliferation, ASC speck, and activates caspase-1, which suggests that neuropathology is inhibited by NLRP3 inhibition [58]. On the same note, BHB suppresses hippocampal NLRP3, cleaved caspase-1, IL-1beta/IL-18, pyroptosis markers and enhances chaperone-mediated autophagy markers LAMP2A, Hsp70 in an unpredictable AD-like rat model, correlating the hippocampal inflammasome inhibition with heterogenized proteostasis and resultant decreased neuroinflammation [19]. BHB also has an anti-NLRP3-activated effect in the hepatocytes (AMPK-FOXO3a-antioxidant enzyme) in response to ER-stress, and the effect is independent of central nervous system activity, and is another evidence that AMPK-regulates pathway [59]. Due to the ability of BHB to protect lysosomal activity and prevent inflammasome activation, the subsequent mechanism of its protective properties in metabolic, inflammatory, and neurodegenerative diseases is that chronic NLRP3 activation disrupts the autophagic flux and leads to pyroptotic cell death [19,51,57,58,59].
Combined, these data indicate that BHB mediates inflammatory suppressive and proteostatic stabilizing responses to convergent metabolic signals as opposed to linear response, and NLRP3 inhibition and autophagy stabilization are direct consequences of cellular reprogramming under the influence of ketones.
6. Role of BHB-induced Autophagy and Complementary Synergies in clearing A-beta and Tau in AD.
BHB modulates multiple autophagy arms (macroautophagy, chaperone mediated autophagy, lysosomal function) and inflammation, which can functionally cooperate to induce A-beta and tau clearance and can mechanistically interact with other autophagy-based interventions.
6.1 BHB-induced Autophagy and Proteostasis in AD models.
a) Chaperone-Mediated Autophagy (CMA), Hsp70 and A-beta/Tau Clearance.
Systemic administration of BHB (125 mg/kg) enhanced cognitive functions, decreased amyloid plaque burden and phosphorylated tau in the hippocampal in a high-fat/fructose with LPS induced sporadic AD-like rat model, and also preserved neuronal architecture. BHB stimulated several BHB pathway elements, which was mechanistic. In particular, BHB elevated the level of hippocampal LAMP2A, the CMA rate-limiting receptor on the lysosome, and Hsp70, a cytosolic chaperone that recognizes and delivers substrates with KFERQ motifs to CMA [19]. Simultaneously, A-beta decatenation and phosphorylated tau were found to decrease, and CMA upregulate, as expected by the fact that tau and a subset of APP/ A-beta related proteins are CMA substrates, and that increased CMA can directly induce their lysosomal degradation [19,27,37].
Taken together, these results suggest that BHB restores the activity of CMA and Hsp70-dependent proteostatic quality control, which facilitates the selective degradation of misfolded tau and A-beta related species.
b) Macroautophagy/Mitophagy: The Escher Not-AD Systems.
Non-AD models also provide the mechanistic understanding of the BHB-driven autophagy. BPH activates the AMPK -ULK1 pathway and inhibits mTORC1 in Hutchinson Gilford progeria fibroblasts, which reinstate the autophagic flux and facilitates the clearance of toxic progerin protein, pharmacological inhibition of either ULK1 or AMPK ablates the effect, which confirms the autophagic clearance [52]. This model is not AD-specific, but it gives the mechanistic model of how BHB can trigger autophagy-induced clearance of aggregation-prone proteins, a principle that is directly applicable to the A-beta and tau protein clearance [27,37].
Additional evidence is provided by proteomic studies of a C99 expressing Drosophila AD model, which supports the mitochondrial fragmentation caused by C99, enhances lysosomal acidification, lowers the number of dense degradative vesicles, and prolongs lifespan and memory. These effects suggest that the mitochondrial-autophagy-lysosome homeostasis is restored at an A-beta production higher-order level [20].
6.2. Anti-Inflammatory Synergy: NLRP3, Autophagy, and BHB.
BHB also strongly inhibits the activity of the NLRP3 inflammasome, which is one of the key contributors to Alzheimer disease (AD)-related neuroinflammation, which, in turn, undermines both microglial autophagy and mitophagy [58,60]. Exogenous BHB minimized A-beta plaque burden, microgliosis, ASC speck or caspase-1 activation in 5XFAD mice, showing that not only NLRP3 but also AD pathology is attenuated [58]. Correspondingly, in a sporadic AD rat model, BHB reduced hippocampal levels of NLRP3, cleaved caspase-1, IL-1beta/IL-18, caspase-11 and gasdermin-N, and simultaneously augmented CMA markers (LAMP2A and Hsp70) and a transition to the neuroprotective M2-type microglial phenotype, compared to the pro-inflammatory M1-type microglial phenotype [19]. Taken together, these results associate NLRP3 inhibition with decreased pyroptosis and SASP-like cytokine signatures, and improved microglial functioning and CMA, which in combination, enhance extracellular A-beta handling and minimized phosphorylated tau aggregation [19,37,60].
At mechanistic level, recovery of autophagy and mitophagy suppresses the build-up of dysfunctional mitochondria and mitochondrial ROS, which in turn suppresses NLRP3 further. This forms a positive feedback mechanism between BHB-induced autophagic recovery and inflammasome-inhibition [37,39,60].
6.3. Autophagy-Mediated Tau and A-beta clearance: General mechanisms.
Several reviews manage to agree on the opinion that macroautophagy, chaperone-mediated autophagy (CMA), aggrephagy, and mitophagy are the major intracellular activities that lead to A1BB and tau species clearance [27,23,28,40,43]. Autophagy-lysosomal pathway Aggregates of A-beta as well as tau inclusions are degraded by the autophagy-lysosomal pathway and genetic expression of autophagy (e.g., knock-in of Beclin-1 F121A) or pharmacological activation with rapamycin, metformin, and other small molecules reduces amyloid burden, tau pathology, and improves cognitive functions in models of AD [23,27,28,37,40,47].
On the other hand, defects in the fusion of autophagosomes and lysosomes and lysosomal acidification are the cause of pathological accumulation in AD, since perturbation of autophagic flux to accumulate vesicles of APP, beta-secretase, A-beta, and tau accumulates the aggregates, and thus fixing lysosomal activity is necessary to clear both proteins effectively. Together, all those results confirm that autophagy-lysosomal pathways are the predominant intracellular processes controlling A-beta and tau clearance, and that reconstitution of lysosomal function and autophagic flux is a key to effective proteostasis in AD [27,40,43]. In that regard, the ability of BHB to re-initiate lysosomal pathways such as CMA and macroautophagy along with restoring a normal lysosomal activity is consistent with the prevailing proteolytic processes of eliminating A-beta and tau [19,20,27,37,43]. This mechanistic overlap creates a rational basis to thinking whether BHB can cooperate with complementary nodes of the same proteostatic network of other autophagy-based interventions without suggesting any additive effects other than those experimentally proven.
7. Additional Autophagy-Based Strategies that would be Complementary to BHB.
This will discuss the autophagy-modulating interventions that have been established to converge mechanistically with the pathways that BHB has already activated, such as the activation of AMPK-ULK1, mTORC1 inhibition, lysosomal biogenesis, and inflammatory limitations on autophagic flux. It is meant to map mechanistic overlap and possible compatibility and not to place therapeutic advantage or additive effect on top of the available experimental evidence [19,23,27,37,47,52].
(a) Rapamycin, Metformin and autophagy enhancers.
AMPK-ULK1 signalling and/or mTORC1 inhibition can be stimulated by metformin and rapamycin and can reverse autophagic flux, A-beta and tau pathology, and improve cognition in various AD models, and early clinical trials are currently being conducted [23,27,28,37,47]. BHB activates intersecting AMPK -ULK1 and lysosomal regulated axes [37,52]. which implies mechanistic strengthening of autophagy initiation and degradative power. Nevertheless, it should be carefully dosed not to cause excessive autophagosome build-up and dysfunctional flux [27,23,47].
(b) TFEB, benimidazoles and aspirin mediate the lysosomal biogenesis.
Flubendazole decreases the A-beta burden and tau hyperphosphorylation in APP/PS1 mice by stimulating autophagy via PPARgamma and inhibiting GSK3 beta, and synergistic aggregating clearance by increasing autophagic flux. Aspirin enhances A-beta clearance through the PPARalpha-TFEB axis, which activates lysosomal biogenesis and autophagy-lysosome activity with cognitive benefit [61]. In isolation, the intermittent hypoxia treatment enhances TFEB nuclear translocation in plaque microglia, boosts lysosomal and autophagy genes, promotes A-beta catabolic activity and decreases the plaque load and neuronal damage [44]. Convergence with TFEB-activation or PPAR-driven therapies due to the effect of BHB on lysosomal functional enhancements on degradation of A-beta will subsequently increase lysosomal capacity to degrade tau [19,20,37].
(c) Nanochaperones and targeted autophagy in case of tau.
Selective pathogenic tau binding with a tau-targeted nanochaperone, microtubules stabilization, and local activation of autophagy by a tau-targeted nanochaperone leads to improved autophagic flux and robust tau clearance and cognitive functions in AD mice [62]. BHB in an integrated system promotes mitochondrial health, autophagy, and CMA [19,20,37,52] and inhibitory autophagy by NLRP3 [19,58,60]. The BHB thus offers substrate specificity to tau, but the degradative potential and anti-inflammatory environment needed to ensure an efficient clearance is maintained by nanochaperones.
(d) Small molecules with autophagy and anti-inflammatory /ferroptosis properties.
Berberine induces autophagy and inhibits ferroptosis by down regulating JNK-38 MAPK signaling and reducing A beta plaques, neuroinflammation and neuron damage, and enhancing memory in 5xFAD mice [63]. Isobavachalcone stimulates CAMKK2 -AMPK signaling, autophagy, and inhibition of NLRP3 inflammasomes to promote extracellular A -clearance and cognitive enhancement in 5xFAD mice [64]. These analogs mechanistically converge the AMPK activation and inflammasome suppression and upregulate autophagy similar to BHB in conceptual compatibility in the same regulatory framework [19,37,58,60,62,64].
8. Mechanistic Integration: The BHB and Autophagy-Directed Therapies Cooperatively Clear A-beta and Tau.
Altogether, the above-mentioned studies can be said to support a combined mechanistic model:
8.1. Recovery of autophagic cell lysosome and lysosome capacity.
BHB (through CMA and macroautophagy) in tandem with metformin/rapamycin, TFEB activators and nano-/ small-molecule autophagy enhancers all induce autophagosome formation, intracellular trafficking, lysosomal fusion and acidification to be restored. Such a coordinated restoration can help with the degradation of intraneuronal A-beta and tau [19,23,27,37,43,45,61,62].
8.2. Selective elimination of A-beta/tau species.
BHB-prompted upregulation of the CMA components (LAMP2A and Hsp70) identically promotes cleansing of particular misfolded tau species and substrates associated with the APP [43]. Simultaneously, aggrephagy and programmed nanochaperones can target insoluble A-beta aggregates and tau aggregates (resistant to proteasomal degradation) with aggrephagy and engineered nanochaperones, respectively [23,40,62].
8.3. The peripheral integration and microglial.
BHB and other NLRP3 modulators facilitate a partial re-differentiating of microglia to phagocytic, low-inflammasome, phenotypes, which facilitates increased extracellular A-beta uptake and trafficking of A-beta to autophagic and lysosomal degradation routes [19,44,45,60]. There is also growing evidence that hepatic autophagy plays a role in the peripheral A piece of evidence; the previously mentioned signal of systemic metabolism could assist this axis of inter-organ proteasolysis, but direct experimental evidence of this has not been confirmed so far [43].
9. Translational landscape and Continued Trials. KD, Exogenous Ketones, Combinatorial Therapeutics.
Ketone-based and autophagy-targeting approaches in the clinical translation of Alzheimer disease are still ongoing concepts, yet in their initial development stages. Numerous randomized controlled clinical trials and small clinical studies prove that ketogenic interventions, such as or including classic ketogenic diets, modified Atkins diets, medium-chain triglyceride (MCT) formulas, and ketone drinks, consistently increase blood ketone levels, boost brain ketone uptake levels, and produce profile improvements in global and episodic cognition in patients with mild to moderate AD or mild cognitive impairment, especially in APOE4-negative individuals [8,65,66,67,68,69]. Cerebral ketone metabolism is improved by ketone therapies on PET imaging, and some cerebrospinal fluid and FDG-PET biomarkers of brain metabolism fluctuate with ketone therapies [8,66,67,68,70]. Translational reviews and systematic reviews highlight that ketogenic diets and ketone supplement are a viable but varied option in terms of their arrangement and that intervention periods can be as short as 45 days and as long as 180 days of intervention, the formulations they used can be MCT oils, powders, enriched meals, and ketone jet [8,65,68,70]. Consumption of ketogenic diet in frail AD patients is limited by adherence issues, gastrointestinal side-effects, weight loss and dietary complexity, but exogenous ketones and MCTs seem more acceptable to have on chronic use [8,65,66,69,70]. Ketone therapies also are getting tested in not only symptomatic AD but also prodromal and preclinical AD populations with high amyloid burden, and are aimed at modulating the pathology before significant degrees of neurodegeneration [66,67].
The use of autophagy activity as a major biomarker is not yet tested in clinical trials of ketones, but mechanistic reviews have linked ketone metabolism to processes that involve autophagy (such as better mitochondrial function, reduced oxidative stress, reduced neuroinflammation, and AB and tau pathology modulation) [8,23,27,38,71,72,73]. Drug trials that target autophagy, mTOR inhibitors, AMPK activators, TFEB-related agonists and repurposed small molecules, are currently in early phases of clinical development, mainly as monotherapies [27,47,72,74]. No published phase II direct combination trials of ketone therapies with autophagy modulators have been undertaken as yet; but concept papers have explicitly outlined combined strategies of using ketogenic strategies in combination with antioxidants, neuroprotective drugs or disease-modulating drugs to attack multiple nodes of AD pathophysiology [47,67,71,72].
Identified Gaps, Challenges and Future Research - Dose, Specificity, Biomarkers, Combination Therapy.
There is no definition of optimal ketone levels and diet, no real definition of duration of intervention because different trials vary with regard to fat sources, carbohydrate levels and aim BHB levels. As much as benefits seem to be best at early or prodromal AD grade, there are limited robust long-term outcomes [8,65,66,67,68,69,71]. The autophagy activators are no exception since the uncertainties with respect to dose windows capable of increasing protein clearance without leading to excessive catabolism and toxicity have been expressed [276,48,72,74].
The mechanism of action of mTOR-targeting drugs affects many other pathways of the cell, such as glucose metabolism, lipid regulation and protein synthesis, and this puts systemic safety risks when used chronically in the elderly [27,4772,74]. The reviews identify the need of brain-targeted delivery plans and type of cell design, and more specifically, neuronal and microglial effects to minimize off-target effects [47,72,74,75]. One of the greatest barriers to translation is the lack of validated in vivo biomarkers of autophagy, where assays have been done based on the tissue levels of LC3 and p62, or reporter constructs being introduced into animal models and cannot be used regularly in humans [27,47,75]. There is an urgent necessity of PET tracers or cerebrospinal fluid markers reflecting autophagic flux, lysosomal functioning or clearance of aggregates to connect ketone interventions to autophagy adjustments in patients [27,47,75]. Other standardized bioenergetic and inflammatory biomarker panel, such as plasma, and cerebrospinal fluid ketones, inflammatory cytokines, and multi-tracer PET imaging are also needed to establish the responders and to understand the mechanisms [8,66,67,68,69,71].
The preclinical evidence indicates that concurrently augmenting bioenergetics by using ketones and autophagic clearance using rapalogs, AMPK activators, and aggrephagy/mitophagy inducers has a potential to synergistically decrease A-beta and tau burden [23,27,40,48,72]. Nevertheless, families of ketone and autophagy modulators as adjuncts to AD to date lack large randomized controlled trials and characteristic drug-diet and long-term tolerability of ketone and autophagy modulators in multimorbid and polypharmacy geriatric patients [8,72,74, (Fernandes, et al., 2025). The next round of trials should use the factorial or multi-arm design, i.e. ketogenic diet versus autophagy drug versus combinations, combine precision stratification with APOE genotype, metabolic status, and disease stage, and provide a follow-up time that would capture structural and biomarker outcomes [47,66,68,69,71,75].
10.4. Potential Future and Future Work Recommendations
There is convergent data that both ketone-based strategies and autophagy modulation show mechanistically consistent but small effects in Alzheimer disease: ketones increase cerebral energy metabolism and reduce oxidative and inflammatory stress, and autophagy-targeted strategies maximize the clearance of A-beta, and damaged organelles [8,47,71,72]. Though there is promising clinical evidence available, much is still in small fragments with small sample sizes, shorter durations of the trials and heterogeneous design of the studies prevailing in the literature today.
The initial step in advancing research directed at Ketone Bodies and Autophagy: Synergistic Approaches is standardized large, multicenter randomized controlled trials with adequately powered cohorts, and harmonized protocols to support parallel randomized trials assessing autophagic-based or exogenous intervention based on ketones, expressly the measurement of autophagic and lysosomal dynamics of processing [68]. The second urgent goal is the production and confirmation of noninvasive biomarkers of autophagy and aggrophagy, which can be used in longitudinal studies of humans, preferably on the basis of PET tracers or cerebrospinal fluid and plasma molecular signatures [27,44,47].
Emerging combination therapies such as ketotherapies and mTOR-independent autophagy activators, mitophagy activators, or anti-amyloid and anti-tau therapies will have to be systematically optimized on dose, evaluated in terms of safety, and stratified based on genetic background and metabolic phenotype [27,44,47,71,72,74]. Simultaneously, the concept of ketone and autophagy should be applied in multidomain prevention paradigms that combine diet, physical activity, and cognitive training, with an emphasis on early or preclinical Alzheimer diseases, in this case the most probable target of metabolic and proteolytic regulation [8,62,66,68,69,71]. Overall, despite the promising clinical potential, it has not yet been properly investigated, and it needs strictly designed, mechanistically guided translational research, which must help to establish to what degree the ketone-induced autophagy modulation can play a significant role in the development of the Alzheimer disease.
References:
Avgerinos, K. I., Mullins, R. J., Egan, J. M., and Kapogiannis, D. (2022). Ketone Ester Effects on Biomarkers of Brain Metabolism and Cognitive Performance in Cognitively Intact Adults ≥ 55 Years Old. A Study Protocol for a Double-Blinded Randomized Controlled Clinical Trial. The journal of prevention of Alzheimer's disease, 9(1), 54-66.
Ramezani, M., Fernando, M., Eslick, S., Asih, P. R., Shadfar, S., Bandara, E., and Martins, R. N. (2023). Ketone bodies mediate alterations in brain energy metabolism and biomarkers of Alzheimer's disease. Frontiers in Neuroscience, 17, 1297984. https://doi.org/10.3389/fnins.2023.1297984.
Kapogiannis D, and Mattson MP. (2011). Disrupted energy metabolism and neuronal circuit dysfunction in cognitive impairment and Alzheimer's disease. The Lancet Neurology, 10(2), 187-198.
Croteau, E., Castellano, C.A., Fortier, M., Bocti, C., Fulop, T., Paquet, N., and Cunnane, S.C. (2018). A cross-sectional comparison of brain glucose and ketone metabolism in cognitively healthy older adults, mild cognitive impairment and early Alzheimer's disease. Experimental Gerontology, 107, 18-26. https://doi.org/10.1016/j.exger.2017.07.004.
Jensen, N. J., Wodschow, H. Z., Nilsson, M., and Rungby, J. (2020). Effects of Ketone Bodies on Brain Metabolism and Function in Neurodegenerative Diseases. International Journal of Molecular Sciences, 21(22), 8767.
Hertz, L., Chen, Y., and Waagepetersen, H. (2015). Effects of ketone bodies in Alzheimer's disease in relation to neural hypometabolism, beta-amyloid toxicity, and astrocyte function. Journal of Neurochemistry, 134(1), 7-20.
Jang, J., Kim, S.R., Lee, J.E., Lee, S., Son, H.J., Choe, W., Yoon, K.-S., Kim, S.S., Yeo, E.-J., and Kang, I. (2023). Molecular Mechanisms of Neuroprotection by Ketone Bodies and Ketogenic Diet in Cerebral Ischemia and Neurodegenerative Diseases. International Journal of Molecular Sciences, 25(1), 124.
Rusek, M., Pluta, R., Ulamek-Koziol, M., and Czuczwar, S. (2019). Ketogenic Diet in Alzheimer's Disease. International Journal of Molecular Sciences, 20(16), 3892.
Akram, M. (2013). A Focused Review of the Role of Ketone Bodies in Health and Disease. Journal of Medicinal Food, 16(11), 965-967.
Han, W., Zhang, B., Zhao, W., Zhao, W., He, J., Qiu, X., Zhang, L., Wang, X., Wang, Y., Lu, H., Zhang, Y., Xie, Y., Geng, Y., Zhao, W., Huang, Q., and Wang, Z. (2024). Ketogenic beta-hydroxybutyrate regulates beta-hydroxybutyrylation of TCA cycle-associated enzymes and attenuates disease-associated pathologies in Alzheimer's mice. Aging Cell, 24(1), 14368.
Castellano, C.A., Nugent, S., Paquet, N., Tremblay, S., Bocti, C., Lacombe, G., Imbeault, H., Turcotte, E., Fulop, T., and Cunnane, S.C. (2015). Lower brain 18F-fluorodeoxyglucose uptake but normal 11C-acetoacetate metabolism in mild Alzheimer's disease dementia. Journal of Alzheimer's Disease, 43(4), 1343-1353.
Takeishi, J., Tatewaki, Y., Nakase, T., Takano, Y., Tomita, N., Yamamoto, S., Mutoh, T., and Taki Y. (2021). Alzheimer's Disease and Type 2 Diabetes Mellitus: The Use of MCT Oil and a Ketogenic Diet. International Journal of Molecular Sciences, 22(22), 12310.
Courchesne-Loyer, A., Croteau, E., Castellano, C.A., St-Pierre, V., Hennebelle, M., and Cunnane, S.C. (2017). Inverse relationship between brain glucose and ketone metabolism in adults during short-term moderate dietary ketosis: A dual tracer quantitative positron emission tomography study. Journal of Cerebral Blood Flow & Metabolism, 37(7), 2485-2493.
Montiel, T., Gomora-Garcia, J., Geronimo-Olvera, C., Heras-Romero, Y., Bernal-Vicente, B., Perez-Martinez, X., Tovar-Y-Romo, L., and Massieu, L. (2023). Modulation of the autophagy-lysosomal pathway and endoplasmic reticulum stress by ketone bodies in experimental models of stroke. Journal of Neurochemistry, 166(1), 106 - 87.
Maleki, M., Omidi, F., Javanshir, Z., Bagheri, M., Tanhadoroodzani, Z., Dastghaib, S., Shams, M., Akbari, M., and Dastghaib, S. (2024). beta-Hydroxybutyrate and melatonin suppress maladaptive UPR, excessive autophagy and pyroptosis in A-beta 1-42 and LPS-Induced SH-SY5Y cells. Molecular Biology Reports, 51, 802.
Montiel, T., Montes-Ortega, L., Flores-Yanez, S., and Massieu, L. (2020). Treatment with the Ketone Body D-beta-hydroxybutyrate Attenuates Autophagy Activated by NMDA and Reduces Excitotoxic Neuronal Damage in the Rat Striatum in Vivo. Current Pharmaceutical Design, 26(12), 1377-1387.
Gomora-Garcia, J., Montiel, T., Huttenrauch, M., Salcido-Gomez, A., Garcia-Velazquez, L., Ramiro-Cortes, Y., Gomora, J., Castro-Obregon, S., and Massieu, L. (2023). Effect of the Ketone Body, D-beta-Hydroxybutyrate, on Sirtuin2-Mediated Regulation of Mitochondrial Quality Control and the Autophagy-Lysosomal Pathway. Cells, 12(3), 486.
Garcia-Velazquez L and Massieu L (2023) The proteomic effects of ketone bodies: implications for proteostasis and brain proteinopathies. Frontiers in Molecular Neuroscience, 16, 1214092. doi: 10.3389/fnmol.2023.1214092.
Mohamed, R., Abdallah, D., and El-Abhar, H. (2025). Chaperone-mediated autophagy, heat shock protein 70, and serotonin: novel targets of beta-hydroxybutyrate in HFFD/LPS-induced sporadic Alzheimer's disease model. Inflammopharmacology, 33, 3461 - 3477.
Huang, H., Xu, K., and Lardelli, M. (2025). beta Hydroxybutyrate Targets C99 Driven Organelle Disruption in a Drosophila Model of Alzheimers Disease. http://dx.doi.org/10.2139/ssrn.5778200
Nixon, R., and Yang, D. (2011). Autophagy failure in Alzheimer's disease—locating the primary defect. Neurobiology of Disease, 43(1), 38-45.
Orr, M., and Oddo, S. (2013). Autophagic/lysosomal dysfunction in Alzheimer's disease. Alzheimer's Research & Therapy, 5(53). https://doi.org/10.1186/alzrt217.
Zhang, Z., Yang, X., Song, Y., and Tu, J. (2020). Autophagy in Alzheimer's disease pathogenesis: Therapeutic potential and future perspectives. Ageing Research Reviews, 72, 101464.
Bordi, M., Berg, M. J., Mohan, P. S., Peterhoff, C. M., Alldred, M. J., Che, S., ... and Nixon, R. A. (2016). Autophagy flux in CA1 neurons of Alzheimer hippocampus: Increased induction overburdens failing lysosomes to propel neuritic dystrophy. Autophagy, 12(12), 2467-2483.
Piras, A., Collin, L., Gruninger, F., Graff, C., and Ronnback, A. (2016). Autophagic and lysosomal defects in human tauopathies: analysis of post-mortem brain from patients with familial Alzheimer disease, corticobasal degeneration and progressive supranuclear palsy. Acta Neuropathologica Communications, 4(1), 22.
Nixon, R. A., & Rubinsztein, D. C. (2024). Mechanisms of autophagy-lysosome dysfunction in neurodegenerative diseases. Nature Reviews Molecular Cell Biology, 25(11), 926-946.
Zhang, W., Xu, C., Sun, J., Shen, H. M., Wang, J., and Yang, C. (2022). Impairment of the autophagy-lysosomal pathway in Alzheimer's diseases: pathogenic mechanisms and therapeutic potential. Acta Pharmaceutica Sinica B, 12(3), 1019-1040.
Uddin, M. S., Stachowiak, A., Mamun, A. A., Tzvetkov, N. T., Takeda, S., Atanasov, A. G., and Stankiewicz, A. M. (2018). Autophagy and Alzheimer's disease: from molecular mechanisms to therapeutic implications. Frontiers in Aging Neuroscience, 10, 04. https://doi.org/10.3389/fnagi.2018.00004.
Long, Z., Chen, J., Zhao, Y., Zhou, W., Yao, Q., Wang, Y., and He, G. (2020). Dynamic changes of autophagic flux induced by Abeta in the brain of postmortem Alzheimer's disease patients, animal models and cell models. Aging (Albany NY), 12(11), 10912.
Barbero-Camps, E., Roca-Agujetas, V., Bartolessis, I., de Dios, C., Fernandez-Checa, J. C., Mari, M., and Colell, A. (2018). Cholesterol impairs autophagy-mediated clearance of amyloid beta while promoting its secretion. Autophagy, 14(7), 1129-1154.
Li, S., Wang, Y., Liang, X., and Li, Y. (2025). Autophagy intersection: Unraveling the role of the SNARE complex in lysosomal fusion in Alzheimer's disease. Journal of Alzheimer's Disease, 103(4), 979-993.
Kim, Y., Ha, T. Y., Lee, M. S., and Chang, K. A. (2025). Regulatory mechanisms and therapeutic implications of lysosomal dysfunction in Alzheimer's disease. International Journal of Biological Sciences, 21(3), 1014.
Hung, C. O., and Livesey, F. J. (2018). Altered gamma-secretase processing of APP disrupts lysosome and autophagosome function in monogenic Alzheimer's disease. Cell Reports, 25(13), 3647-3660.
Lee, J. H., Yang, D. S., Goulbourne, C. N., Im, E., Stavrides, P., Pensalfini, A., ... and Nixon, R. A. (2022). Faulty autolysosome acidification in Alzheimer's disease mouse models induces autophagic build-up of A-beta in neurons, yielding senile plaques. Nature Neuroscience, 25(6), 688-701.
Nixon, R. A. (2024). Autophagy-lysosomal-associated neuronal death in neurodegenerative disease. Acta Neuropathologica, 148(1), 42.
Whyte, L. S., Lau, A. A., Hemsley, K. M., Hopwood, J. J., and Sargeant, T. J. (2017). Endo-lysosomal and autophagic dysfunction: a driving factor in Alzheimer's disease? Journal of Neurochemistry, 140(5), 703-717.
Hussain, M. S., Agrawal, N., Ilma, B., MM, R., Nayak, P. P., Kaur, M., and Dua, K. (2025). Autophagy and Cellular Senescence in Alzheimer's Disease: Key Drivers of Neurodegeneration. CNS Neuroscience & Therapeutics, 31(7), e70503.
Di Meco, A., Curtis, M. E., Lauretti, E., and Pratico, D. (2020). Autophagy dysfunction in Alzheimer's disease: mechanistic insights and new therapeutic opportunities. Biological Psychiatry, 87(9), 797-807.
Uddin, M. S., Mamun, A. A., Labu, Z. K., Hidalgo-Lanussa, O., Barreto, G. E., and Ashraf, G. M. (2019). Autophagic dysfunction in Alzheimer's disease: cellular and molecular mechanistic approaches to halt Alzheimer's pathogenesis. Journal of Cellular Physiology, 234(6), 8094-8112.
Rahman, M. A., Rahman, M. S., Rahman, M. H., Rasheduzzaman, M., Mamun-Or-Rashid, A. N. M., Uddin, M. J., and Rhim, H. (2020). Modulatory effects of autophagy on APP processing as a potential treatment target for Alzheimer's disease. Biomedicines, 9(1), 5.
Reddy, P. H., and Oliver, D. M. (2019). Amyloid beta and phosphorylated tau-induced defective autophagy and mitophagy in Alzheimer's disease. Cells, 8(5), 488.
Hamano, T., Enomoto, S., Shirafuji, N., Ikawa, M., Yamamura, O., Yen, S. H., and Nakamoto, Y. (2021). Autophagy and tau protein. International Journal of Molecular Sciences, 22(14), 7475.
Hein, Z. M., Vishnumukkala, T., Karikalan, B., Alkatiri, A., Hussan, F., Jagadeesan, S., and Gopalakrishna, P. K. (2025). Autophagy and Alzheimer's disease: mechanisms and impact beyond the brain. Cells, 14(12), 911.
Menzies, F. M., Fleming, A., Caricasole, A., Bento, C. F., Andrews, S. P., Ashkenazi, A., and Rubinsztein, D. C. (2017). Autophagy and neurodegeneration: pathogenic mechanisms and therapeutic opportunities. Neuron, 93(5), 1015-1034.
Wang, X., Xie, Y., Chen, G., Lu, Y., Wang, D., and Zhu, L. (2023). Intermittent hypoxia therapy ameliorates beta-amyloid pathology via TFEB-mediated autophagy in murine Alzheimer's disease. Journal of Neuroinflammation, 20(1), 240.
Park, H., Kang, J. H., and Lee, S. (2020). Autophagy in neurodegenerative diseases: a hunter for aggregates. International Journal of Molecular Sciences, 21(9), 3369.
Fernandes, S. M., Mayer, J., Nilsson, P., and Shimozawa, M. (2025). How close is autophagy-targeting therapy for Alzheimer's disease to clinical use? A summary of autophagy modulators in clinical studies. Frontiers in Cell and Developmental Biology, 12, 1520949. https://doi.org/10.3389/fcell.2024.1520949.
Zhang, X. W., Zhu, X. X., Tang, D. S., and Lu, J. H. (2023). Targeting autophagy in Alzheimer's disease: Animal models and mechanisms. Zoological Research, 44(6), 1132.
Dhapola, R., Kumari, S., Sharma, P., Vellingiri, B., and Harikrishnareddy, D. (2025). Advancements in autophagy perturbations in alzheimer's disease: molecular aspects and therapeutics. Brain Research, 1851, 149494. https://doi.org/10.1016/j.brainres.2025.149494.
Banerjee, A., Thekkekkara, D., Manjula, S. N., Nair, S. P., and Lalitha, M. S. (2025). Correlation of autophagy and Alzheimer's disease with special emphasis on the role of phosphodiesterase-4. 3 Biotech, 15(5), 1-16.
Ehtiati, S., Hatami, B., Khatami, S. H., Tajernarenj, K., Abdi, S., Sirati-Sabet, M., and Karima, S. (2025). The Multifaceted Influence of Beta-Hydroxybutyrate on Autophagy, Mitochondrial Metabolism, and Epigenetic Regulation. Journal of Cellular Biochemistry, 126(6), e70050.
Monterrubio-Ledezma, F., Salcido-Gomez, A., Zavaleta-Vasquez, T., Navarro-Garcia, F., Cisneros, B., and Massieu, L. (2025). The anti-senescence effect of D-beta-hydroxybutyrate in Hutchinson-Gilford progeria syndrome involves progerin clearance by the activation of the AMPK-mTOR-autophagy pathway. GeroScience, 47, 3849 - 3871. https://doi.org/10.1007/s11357-024-01501-9.
Zhuang, H., Ren, X., Zhang, Y., Li, H., and Zhou, P. (2024). beta-Hydroxybutyrate enhances chondrocyte mitophagy and reduces cartilage degeneration in osteoarthritis via the HCAR2/AMPK/PINK1/Parkin pathway. Aging Cell, 23(11), e14294.
Torres-Esquivel, C., Montiel, T., Flores-Mendez, M., and Massieu, L. (2020). Effect of beta-hydroxybutyrate on autophagy dynamics during severe hypoglycemia and the hypoglycemic coma. Frontiers in Cellular Neuroscience, 14, 547215. https://doi.org/10.3389/fncel.2020.547215.
Pali, D. V., Kim, S., Mantik, K. E. K., Lee, J. B., So, C. Y., Moon, S., and Kang, J. H. (2025). Unraveling the translational relevance of beta-hydroxybutyrate as an intermediate metabolite and signaling molecule. International Journal of Molecular Sciences, 26(15), 7362.
Vergara Nieto, A. A., Diaz, A. H., Hernandez, M., and Sagredo, D. (2025). A Narrative Review about Metabolic Pathways, Molecular Mechanisms and Clinical Implications of Intermittent Fasting as Autophagy Promotor. Current Nutrition Reports, 14(1), 78.
Youm, Y. H., Nguyen, K. Y., Grant, R. W., Goldberg, E. L., Bodogai, M., Kim, D., and Dixit, V. D. (2015). The ketone metabolite beta-hydroxybutyrate blocks NLRP3 inflammasome-mediated inflammatory disease. Nature Medicine, 21(3), 263-269.
Shippy, D. C., Wilhelm, C., Viharkumar, P. A., Raife, T. J., and Ulland, T. K. (2020). beta-Hydroxybutyrate inhibits inflammasome activation to attenuate Alzheimer's disease pathology. Journal of Neuroinflammation, 17(1), 280.
Bae, H. R., Kim, D. H., Park, M. H., Lee, B., Kim, M. J., Lee, E. K., and Chung, H. Y. (2016). beta-Hydroxybutyrate suppresses inflammasome formation by ameliorating endoplasmic reticulum stress via AMPK activation. Oncotarget, 7(41), 66444.
Ayyubova, G., and Madhu, L. N. (2025). Microglial NLRP3 inflammasomes in alzheimer's disease pathogenesis: from interaction with autophagy/mitophagy to therapeutics. Molecular Neurobiology, 62, 1-20. https://doi.org/10.1007/s12035-025-04758-z.
Cordos, B., Tero-Vescan, A., Hampson, I. N., Oliver, A. W., and Slevin, M. (2025). Synergistic Autophagy-Related Mechanisms of Protection Against Brain Aging and AD: Cellular Pathways and Therapeutic Strategies. Pharmaceuticals, 18(6), 829.
Xu, L., Wu, X., Zhao, S., Hu, H., Wang, S., Zhang, Y., and Shi, L. (2024). Harnessing Nanochaperone-Mediated Autophagy for Selective Clearance of Pathogenic Tau Protein in Alzheimer's Disease. Advanced Materials, 36(39), 2313869.
Sun, C., Gao, X., Sha, S., Wang, S., Shan, Y., Li, L., and Du, H. (2025). Berberine alleviates Alzheimer's disease by activating autophagy and inhibiting ferroptosis through the JNK-p38MAPK signaling pathway. International Immunopharmacology, 155, 114550. https://doi.org/10.1016/j.intimp.2025.114550.
Kour, D., Khajuria, P., Sharma, K., Sharma, A., Sharma, A., Ali, S. M., and Kumar, A. (2025). Isobavachalcone ameliorates Alzheimer disease pathology by autophagy-mediated clearance of amyloid beta and inhibition of NLRP3 inflammasome in primary astrocytes and 5x-FAD mice. Frontiers in Pharmacology, 16, 1525364. https://doi.org/10.3389/fphar.2025.1525364.
Lilamand, M., Porte, B., Cognat, E., Hugon, J., Mouton-Liger, F., and Paquet, C. (2020). Are ketogenic diets promising for Alzheimer's disease? A translational review. Alzheimer's Research & Therapy, 12(1), 42.
Lange, K. W., Lange, K. M., Makulska-Gertruda, E., Nakamura, Y., Reissmann, A., Kanaya, S., and Hauser, J. (2017). Ketogenic diets and Alzheimer's disease. Food Science and Human Wellness, 6(1), 1-9.
Taylor, M. K., Sullivan, D. K., Keller, J. E., Burns, J. M., and Swerdlow, R. H. (2022). Potential for ketotherapies as amyloid-regulating treatment in individuals at risk for Alzheimer's Disease. Frontiers in Neuroscience, 16, 899612. https://doi.org/10.3389/fnins.2022.899612.
Grammatikopoulou, M. G., Goulis, D. G., Gkiouras, K., Theodoridis, X., Gkouskou, K. K., Evangeliou, A., and Bogdanos, D. P. (2020). To keto or not to keto? A systematic review of randomized controlled trials assessing the effects of ketogenic therapy on Alzheimer disease. Advances in Nutrition, 11(6), 1583-1602.
Hersant, H., and Grossberg, G. (2022). The ketogenic diet and Alzheimer's disease. The Journal of Nutrition, Health & Aging, 26(6), 606-614.
Lilamand, M., Mouton-Liger, F., Di Valentin, E., Sanchez Ortiz, M., and Paquet, C. (2022). Efficacy and safety of ketone supplementation or ketogenic diets for Alzheimer's disease: a mini review. Frontiers in Nutrition, 8, 807970.
Pawlowska, M., Kruszka, J., Porzych, M., Garbarek, J., and Nuszkiewicz, J. (2025). Ketogenic metabolism in neurodegenerative diseases: mechanisms of action and therapeutic potential. Metabolites, 15(8), 508.
Deng, Z., Dong, Y., Zhou, X., Lu, J. H., and Yue, Z. (2022). Pharmacological modulation of autophagy for Alzheimer's disease therapy: opportunities and obstacles. Acta Pharmaceutica Sinica B, 12(4), 1688-1706.
Xu, Y., Zheng, F., Zhong, Q., & Zhu, Y. (2023). Ketogenic diet as a promising non-drug intervention for Alzheimer's disease: Mechanisms and clinical implications. Journal of Alzheimer's Disease, 92(4), 1173-1198.
Liu, J., and Li, L. (2019). Targeting autophagy for the treatment of Alzheimer's disease: challenges and opportunities. Frontiers in Molecular Neuroscience, 12, 203.
Wang, T., Jiang, H., Zheng, R., Zhang, C., Ma, X., & Liu, Y. (2025). Trends and research focus on autophagy in Alzheimer's disease (2003-2023): A bibliometric study. Journal of Alzheimer's Disease, 106(1), 13872877251336442.