Discover how lithocholic acid, a key calorie-restriction metabolite, unlocks the secret to improved health, stronger muscles, and longer life.
Study: Lithocholic acid phenocopies anti-ageing effects of calorie restriction. Image Credit: Shutterstock AI / Shutterstock.com
Calorie restriction (CR) is a dietary intervention that promotes various metabolic changes. CR-induced lithocholic acid (LCA) production has been associated with improved life expectancy and many other health-related benefits.
A recent Nature study used metabolomics to investigate how CR induces metabolic changes that promote physiological benefits.
How does CR affect aging?
CR is a non-pharmacological dietary intervention that induces several metabolic changes, such as alterations in cholesterol, free fatty acid, short-chain organic acid, and vitamin levels. Multiple studies have associated CR with improved lifespan and health status in many organisms, including yeast, mice, flies, nematodes, and primates.
Modifications in serum metabolite levels can mitigate age-related conditions, including homeostasis of cellular proteins, oxidative damage, and inflammation. Randomized clinical trials have indicated that CR also improves age-related frailty and diseases, such as insulin resistance, central obesity, dyslipidemia, and muscle deterioration.
CR activates adenosine monophosphate (AMP)-activated protein kinase (AMPK), an enzyme that helps cells maintain energy balance. AMPK regulates several signalling pathways that delay aging, such as forkhead box O (FOXO) proteins, and rapamycin complex 1 (TORC1). AMPK also induces nicotinamide adenine dinucleotide (NAD+) production that induces transcription factor EB (TFEB), activates sirtuins, and inhibits cyclic adenosine monophosphate response element binding protein (CREB)-regulated transcriptional co-activators.
AMPK is associated with many anti-aging-related cellular processes, such as proteostasis, mitochondrial biogenesis, autophagy, mitohormesis, inflammation, and neurodegeneration. Therefore, AMPK is a prime mediator of the health benefits associated with CR.
Metformin and resveratrol are two CR mimetics (CRMs) that induce AMPK activation and contribute to an extended lifespan in many organisms. Thus, it is important to understand how CR-mediated metabolic adaptations in the body enable AMPK activation to promote good health and longevity.
About the study
The current study hypothesized that serum metabolites that undergo modifications due to CR might be responsible for its beneficial effects at the cellular and organismal levels. To test this hypothesis, metabolite levels were assessed in serum cells, tissues, flies, and nematodes.
Study findings
Serum analysis revealed that four months of CR treatment in mice (CR serum) activated AMPK in mouse embryonic fibroblasts (MEFs), primary hepatocytes, human embryonic kidney 293T (HEK293T) cells, and primary myocytes. This activation was determined by estimating the phosphorylation levels of AMPKα (pAMPKα) and substrate acetyl coenzyme A carboxylases (pACC).
Perfusing CR serum into mice on an ad libitum diet led to the activation of AMPK in the liver and muscle. Experimental findings also indicated the presence of heat-stable and low-molecular-weight metabolites in CR serum that could activate AMPK.
Metabolomics and various mass spectrometry-based analyses were conducted on serum samples from CR-treated and non-CR-treated mice. A total of 1,215 metabolites were identified, 695 of which were found to undergo modification in CR serum. Furthermore, compared to the control serum, CR serum exhibited reduced phenylalanine, long-chain fatty acids, and tyrosine levels and increased short-chain fatty acids, bile acids, and acyl-carnitine levels.
Initial screening assays identified six metabolites that could activate AMPK, of which LCA activated AMPK at a concentration of one μM in HEK293T cells, MEFs, primary hepatocytes, and primary myocytes. In addition to AMPK activation, mTORC1 was inhibited, and pACC was increased. LCA-treated MEFs exhibited reduced phosphoAMPKα2(S345) levels, along with TFEB translocation into the nucleus.
After four months of CR treatment, 1.1 μM of LCA was estimated in serum, which remained stable in mice before and after feeding. Comparatively, 0.3 μM LCA was measured in ad libitum-fed mice. Experimental findings indicated that the CR-induced increase in LCA was independent of muricholate.
LCA treatment did not induce any change in energy levels in all studied cell types, nor the liver and muscle tissue of CR-treated mice. LCA treatment did not activate AMPK through TGR5 in MEFs or cause bulk calcium increases that may induce CaMKK2-mediated AMPK activation. Thus, LCA appears to be a specific metabolite in CR serum that activates AMPK at physiological concentrations.
Administration of LCA in aged male and female mice for one month revealed improved muscle performance, as demonstrated by a rise in the number of oxidative muscle fibers and reduced glycolytic fibers. This treatment also improved muscle regeneration after damage in aged mice. In LCA-treated mice, significant upregulation of plasma glucagon-like peptide 1 (GLP-1) levels was observed.
LCA-treated aged mice exhibited improvements in running distance, duration, and grip strength. This treatment also alleviated age-associated glucose intolerance and insulin resistance.
Conclusions
LCA was identified as a CR-induced metabolite that can activate AMPK and improve the lifespan of many organisms, including hermaphroditic nematodes, flies, and mice. Thus, LCA's anti-aging effects were demonstrated.
Journal reference:
- Qu, Q., Chen, Y., Wang, Y., et al. (2024) Lithocholic acid phenocopies anti-ageing effects of calorie restriction. Nature 1-9. doi:10.1038/s41586-024-08329-5