Is Urolithin A(UA) a pharmacologically credible neuro-nutraceutical? A critical review of mechanisms, brain exposure, and evidence gaps in Alzheimer's and Parkinson's disease.

Urolithin A(UA) is a gut microbiota-derived metabolite of dietary ellagitannins and ellagic acid, generated by specific gut bacterial species and absent from food in free form. Preclinical evidence indicates that UA restores PINK1/Parkin-mediated mitophagy, attenuates NF-κB, NLRP3 inflammasome and cGAS-STING-driven neuroinflammation, and preserves synaptic and cognitive function across rodent and cell-culture models of Alzheimer's disease, Parkinson's disease, and age-related cognitive decline. However, circulating UA in humans exists predominantly as phase II glucuronide and sulfate conjugates rather than free aglycone, and human clinical evidence to date establishes UA's safety, favorable pharmacokinetics, mitochondrial target engagement, and benefits to muscle strength and physical function in middle-aged and older adults, with no completed trial yet evaluating cognitive or neurodegenerative disease-modifying outcomes. This review critically examines whether UA's neuroprotective mechanisms are pathway-specific and supported by convergent preclinical and human data, while explicitly separating mechanistic plausibility from demonstrated clinical efficacy.UA therefore represents a promising but still investigational neuro-nutraceutical candidate, with a mechanistic foundation strong enough to justify dedicated, CNS-endpoint-focused clinical trials as the next logical step toward establishing its neuroprotective potential in humans.