Dietary restriction, Rapamycin, α-ketoglutarate (AKG), and Carglumic Acid influence aging-related processes through nutrient availability, mTOR signaling, central metabolism, and nitrogen metabolism, respectively. Their effects involve autophagy, proteostasis, mitochondrial function, and chronic inflammation, although the underlying mechanisms and maturity of the supporting evidence differ substantially among these interventions.

Keywords: aging; dietary restriction; Rapamycin; mTOR; AMPK; autophagy; α-ketoglutarate; AKG; Carglumic Acid; CPS1

1 Aging-Related Nutrient Sensing and Metabolic Homeostasis

1.1 Nutrient Sensing and Cellular Homeostasis

Cells sense nutrient availability, energy status, and redox conditions through systems such as insulin/IGF-1, mTOR, AMPK, and Sirtuins. Under nutrient-rich conditions, mTORC1 promotes protein and lipid synthesis. When energy availability declines, pathways such as AMPK enhance substrate utilization, autophagy, and stress adaptation. During aging, coordination among biosynthesis, damage clearance, and homeostatic maintenance gradually deteriorates, making dysregulated nutrient sensing an important molecular feature of aging.

1.2 Autophagy, Mitochondria, and Chronic Inflammation

The autophagy–lysosome system removes abnormal proteins and damaged organelles, while mTORC1 and AMPK regulate autophagy initiation through nodes such as ULK1. Aging is accompanied by reduced autophagic efficiency and mitochondrial quality control. Accumulation of dysfunctional mitochondria can increase oxidative stress and promote inflammatory signaling, creating an interconnected regulatory network involving proteostasis, autophagy, mitochondrial function, and chronic inflammation.

1.3 Lifespan and Healthspan

Lifespan reflects the length of survival, whereas healthspan focuses on the period during which mobility, metabolism, immunity, and tissue functions remain preserved. Some interventions reduce frailty and disease burden without producing a comparable extension of lifespan. Evaluation of aging interventions therefore requires integrated assessment of lifespan, frailty, tissue function, and disease burden rather than substitution of the overall aging phenotype with a single metabolic indicator.

2 Mechanisms by Which Dietary Restriction Regulates Aging

2.1 Nutrient Restriction Remodels mTOR–AMPK Signaling

(1) Reduced mTORC1 Signaling

Caloric restriction (CR) and other forms of dietary restriction can reduce sustained glucose, insulin, and amino acid availability. As support for mTORC1 from insulin/IGF-1–PI3K–AKT signaling and amino acid sensing declines, S6K- and 4E-BP-regulated protein translation and anabolic metabolism are reduced, decreasing the allocation of cellular resources toward continuous growth and biosynthesis.

(2) Enhanced AMPK Signaling

Reduced nutrient availability can alter cellular energy status and promote AMPK activation. AMPK restricts mTORC1 activity while promoting fatty acid oxidation and regulating ULK1-mediated autophagy. Reduced mTORC1 activity and enhanced AMPK signaling jointly redirect metabolic resources from energy-intensive biosynthetic processes toward substrate utilization, damage clearance, and homeostatic maintenance.

2.2 Autophagy and Mitochondrial Quality Control

(1) Enhanced Autophagic Clearance

Reduced mTORC1 activity and AMPK activation can promote ULK1-associated autophagy, directing abnormal proteins and damaged organelles into the autophagy–lysosome degradation pathway. Amino acids, fatty acids, and other substrates generated through degradation can be reused in metabolism, reducing the cellular damage burden while improving resource utilization under nutrient-limited conditions.

(2) Improved Mitochondrial Homeostasis

Dietary restriction can regulate substrate oxidation, mitochondrial biogenesis, and the clearance of damaged mitochondria, helping maintain oxidative phosphorylation and redox homeostasis. Improved mitochondrial quality control can also reduce reactive oxygen species and inflammatory stimuli produced by dysfunctional mitochondria, coordinating energy metabolism with cellular quality control.

2.3 NAD⁺–Sirtuin-Mediated Metabolic Adaptation

Dietary restriction can alter NAD⁺ metabolism across different tissues and metabolic states and influence NAD⁺-dependent deacetylases such as SIRT1 and SIRT3. Sirtuins regulate FOXO, PGC-1α, and multiple metabolic enzymes and participate in oxidative metabolism, antioxidant responses, and maintenance of mitochondrial function. Together with mTOR and AMPK, this pathway forms a nutrient- and energy-adaptation network induced by dietary restriction.

2.4 Individual Variation in the Effects of Dietary Restriction

The effects of dietary restriction on lifespan and healthspan are influenced by the extent of restriction, feeding schedule, nutrient composition, age, sex, and genetic background. More intensive caloric restriction can produce greater lifespan effects in some animal models but may also reduce lean body mass and alter immune status. The relationship between restriction intensity and improvement in aging phenotypes is therefore not simply linear.

3 Rapamycin-Mediated Regulation of Aging Through mTOR

3.1 The FKBP12–Rapamycin Complex Inhibits mTORC1

After entering cells, Rapamycin binds FKBP12 to form a complex that subsequently interacts with the FRB domain of mTOR and allosterically inhibits mTORC1. Reduced mTORC1 signaling suppresses downstream pathways such as S6K that promote protein translation and cell growth. Unlike ATP-competitive mTOR inhibitors, classical Rapamycin does not inhibit all mTORC1 substrates to an equivalent extent, resulting in selective downstream effects.

Figure 1. Rapamycin Modulation of Aging through the mTORC1 Pathway

3.2 mTORC1 Inhibition Remodels Proteostasis

(1) Reduced Protein Synthesis Burden

Aging is accompanied by declining efficiency of protein folding, proteasomal degradation, autophagy, and other quality-control systems. Reduced mTORC1 signaling lowers the burden of sustained protein translation and decreases the demand placed on nascent protein folding and quality control, thereby supporting the stability of existing proteins and cellular structures.

(2) Enhanced Autophagy-Mediated Damage Clearance

mTORC1 is an important negative regulator of autophagy. Reduced mTORC1 activity partially releases the inhibition of ULK1-associated autophagy initiation and promotes the delivery of abnormal proteins, protein aggregates, and damaged organelles to the autophagy–lysosome pathway. Reduced protein synthesis and enhanced damage clearance jointly contribute to Rapamycin-mediated regulation of proteostasis.

3.3 mTOR Inhibition, Inflammation, and Tissue Homeostasis

(1) Regulation of Chronic Inflammation

mTORC1 participates in immune cell metabolism, inflammatory mediator production, and certain components of the senescence-associated secretory phenotype. Reducing mTORC1 activity can alter immune cell metabolic states, while enhanced autophagy may decrease endogenous inflammatory stimuli such as damaged mitochondria, linking mTOR regulation with aging-associated chronic inflammation.

(2) Boundaries of Long-Term Inhibition

mTOR also participates in normal immunity, glucose metabolism, and tissue homeostasis. Prolonged or intensive exposure to Rapamycin may affect mTORC2-associated functions. Current research increasingly focuses on intermittent administration, appropriate dosing, and more selective regulation of mTORC1 to reduce the long-term metabolic consequences of broad mTOR inhibition.

4 Regulation of Aging Metabolism by AKG and Carglumic Acid

4.1 AKG Connects Central Metabolism with Cellular Regulation

AKG is an important intermediate in the TCA cycle and amino acid metabolism and also functions as a metabolic signal and enzymatic cosubstrate. Changes in AKG levels can influence mitochondrial energy metabolism and connect nutrient sensing with epigenetic regulation through TOR-associated signaling and α-KG-dependent dioxygenases.

4.2 AKG Regulates the ATP Synthase–TOR–Autophagy Axis

(1) The ATP Synthase–TOR Mechanism

A classical study in Caenorhabditis elegans showed that AKG can bind the β subunit of mitochondrial ATP synthase and partially inhibit ATP synthase activity, reducing ATP levels and oxygen consumption while suppressing TOR signaling and enhancing autophagy. Genetic and pharmacological evidence supported the involvement of ATP synthase and TOR in AKG-mediated lifespan extension, establishing a direct mechanistic connection between a central metabolite, energy sensing, and autophagy.

(2) Multifactorial Regulation in Mammals

Direct causal evidence for the ATP synthase–TOR longevity pathway is derived primarily from C. elegans. Although CaAKG studies in mice have reported reduced frailty, improved healthspan, and effects on lifespan, these changes cannot be attributed entirely to ATP synthase inhibition. Mitochondrial metabolism, immune regulation, chronic inflammation, and epigenetic mechanisms may jointly contribute to the effects of AKG in mammals.

4.3 AKG and Epigenetic Regulation

AKG is an important cosubstrate for TET family DNA dioxygenases, JmjC-domain histone demethylases, and certain prolyl hydroxylases, linking cellular metabolic status with DNA and histone modifications, hypoxic responses, and cell differentiation. These enzymes are also influenced by succinate, fumarate, oxygen availability, and iron status, making the epigenetic effects of AKG strongly dependent on the surrounding metabolic environment.

4.4 AKG, Chronic Inflammation, and Healthspan

Studies involving CaAKG supplementation in mice have shown that intervention beginning in middle age can reduce frailty and systemic inflammatory factors, with some experiments also detecting changes in T-cell IL-10. Current evidence suggests that the effects of AKG on mammalian healthspan may involve coordinated changes in central metabolism, mitochondrial function, immune regulation, and epigenetics.

4.5 Carglumic Acid and the CPS1–Urea Cycle

(1) CPS1 Activation

Carglumic Acid, also known as N-Carbamyl-L-glutamic acid, is a structural analog of N-acetylglutamate (NAG). NAG is an essential allosteric activator of carbamoyl phosphate synthetase 1 (CPS1). Carglumic Acid mimics NAG and activates CPS1, promoting the entry of ammonia into the urea cycle and its eventual excretion as urea.

(2) Nitrogen Metabolic Homeostasis

Protein and amino acid degradation continuously generates nitrogen-containing metabolites, whose clearance depends on hepatic mitochondria and the urea cycle. Aging is accompanied by remodeling of muscle protein metabolism, hepatic function, and mitochondrial metabolism, potentially altering nitrogen production, transport, and clearance. The CPS1–urea cycle has consequently become an important component of research on age-related metabolism.

4.6 Boundaries of Carglumic Acid Research in Aging

A drug-screening study in rotifers showed that exogenous Carglumic Acid could extend lifespan and improve certain healthspan-related parameters. A subsequent multi-organ metabolic aging study identified Carglumic Acid as a potential aging-driving metabolite and found that human cells can synthesize it. Exogenous pharmacological intervention and age-related changes in an endogenous metabolite do not necessarily produce effects in the same direction, and direct evidence that CPS1 activation extends lifespan in normal mammals remains lacking.

5 Research Progress in Delaying Aging

5.1 Dietary Restriction in Genetically Heterogeneous Mice

A 2024 study compared 20% and 40% caloric restriction with fasting for one or two days per week in 960 genetically heterogeneous female mice. The dietary restriction regimens produced different degrees of lifespan extension, with caloric restriction showing a greater overall effect. Genetic background exerted a stronger influence on lifespan differences than the dietary regimens themselves, while intensive caloric restriction was accompanied by changes in lean body mass and immune cell composition. These findings indicate that improvements in health-related phenotypes and lifespan extension are not always completely aligned.

5.2 Late-Life Rapamycin Intervention

Studies in genetically heterogeneous mice showed that Rapamycin administration beginning at approximately 600 days of age could still extend lifespan in both male and female mice, demonstrating that mTOR intervention late in life can alter lifespan trajectories. Subsequent research has increasingly focused on dosage, intermittent administration, and mTORC1 selectivity. Human studies currently evaluate immune, metabolic, and age-related functional endpoints, but direct evidence of human lifespan extension is not available.

5.3 CaAKG and Healthspan in Mice

Following CaAKG supplementation beginning in middle age, both male and female C57BL/6 mice showed reduced frailty and improved healthspan, accompanied by reductions in systemic inflammatory factors. The lifespan effect showed sex-related differences and was more evident in females. This study extended AKG research from the ATP synthase–TOR mechanism identified in model organisms to mammalian healthspan.

5.4 Carglumic Acid in Aging Research

A 2018 drug-repurposing study found that 5 μM Carglumic Acid extended lifespan in rotifers and improved certain measures of mitochondrial activity and mobility. A 2026 multi-organ metabolic aging study subsequently identified Carglumic Acid as a potential aging-driving metabolite and found that human cells can synthesize it. Its direction of action and effects on lifespan in normal mammals require further investigation.

6 Products

6.1 Products for Rapamycin, AKG, and Carglumic Acid Research

6.2 Products for mTOR–AMPK, NAD⁺, and Autophagy Research

6.3 Products for Evaluating AKG Mechanisms and Mitochondrial Function

Dietary restriction, Rapamycin, and AKG regulate aging-related homeostasis through nutrient sensing, mTOR signaling, and central metabolism, respectively, whereas Carglumic Acid extends this research to the CPS1–urea cycle and age-related nitrogen metabolism. Because the evidence supporting these interventions differs substantially, their value in aging regulation should be evaluated through both mechanistic evidence and long-term healthspan outcomes.

References

[1] López-Otín C, Blasco MA, Partridge L, Serrano M, Kroemer G. Hallmarks of aging: An expanding universe. Cell. 2023;186(2):243–278.

[2] Green CL, Lamming DW, Fontana L. Molecular mechanisms of dietary restriction promoting health and longevity. Nat Rev Mol Cell Biol. 2022;23:56–73.

[3] Di Francesco A, Deighan AG, Litichevskiy L, et al. Dietary restriction impacts health and lifespan of genetically diverse mice. Nature. 2024;634:684–692.

[4] Saxton RA, Sabatini DM. mTOR signaling in growth, metabolism, and disease. Cell. 2017;168(6):960–976.

[5] Harrison DE, Strong R, Sharp ZD, et al. Rapamycin fed late in life extends lifespan in genetically heterogeneous mice. Nature. 2009;460:392–395.

[6] Mannick JB, Lamming DW. Targeting the biology of aging with mTOR inhibitors. Nat Aging. 2023;3:642–660.

[7] Chin RM, Fu X, Pai MY, et al. The metabolite α-ketoglutarate extends lifespan by inhibiting ATP synthase and TOR. Nature. 2014;510:397–401.

[8] Asadi Shahmirzadi A, Edgar D, Liao CY, et al. Alpha-ketoglutarate, an endogenous metabolite, extends lifespan and compresses morbidity in aging mice. Cell Metab. 2020;32(3):447–456.e6.

[9] Snell TW, Johnston RK, Matthews AB, Zhou H, Gao M, Skolnick J. Repurposed FDA-approved drugs targeting genes influencing aging can extend lifespan and healthspan in rotifers. Biogerontology. 2018;19(2):145–157.

[10] Pilley SE, Awad D, Latumalea D, et al. A metabolic atlas of mouse aging. Cell Metab. 2026;38(2):399–418.e7.

[11] Häberle J. Carglumic acid for the treatment of N-acetylglutamate synthase deficiency and acute hyperammonemia. Expert Rev Endocrinol Metab. 2012;7(3):263–271.

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