Valeric Acid: A Gut-Derived Metabolite as a Potential Epigenetic Modulator of Neuroinflammation in the Gut–Brain Axis

The gut-brain axis (GBA) is a critical area of research for understanding the pathogenesis of neuroinflammatory and neurodegenerative diseases. Metabolites produced by the gut microbiota, particularly short-chain fatty acids (SCFAs), act as key mediators in this bidirectional communication. While the roles of acetate, propionate, and butyrate are well-established, valeric acid (VA), a five-carbon SCFA, is poorly understood. This comprehensive review explores VA as a gut-derived physiological epigenetic modulator, examining its microbial biosynthesis and systemic effects. This review discusses how VA acts as a selective histone deacetylase inhibitor (HDACi), particularly targeting Class I HDACs, to modulate gene expression and exert neuroprotective and anti-inflammatory effects. The analysis compares VA with its pharmacological analog, valproic acid (VPA), a well-known but non-selective HDACi. This comparison highlights how VA's physiological nature may offer a more targeted and safer intervention. In conclusion, elucidating VA's role as a microbiome-derived epigenetic regulator would open promising avenues for therapeutic strategies that directly connect gut and CNS health within the GBA.