Neuroprotective effects of ursodeoxycholic acid in Parkinson's disease and Alzheimer's disease.

Neurodegenerative diseases (NDDs) including Parkinson's disease (PD) and Alzheimer's disease (AD), are progressive disorders characterised by shared pathological features, including mitochondrial dysfunction, oxidative stress, apoptosis, neuroinflammation, neurotoxic protein buildup, and impaired protein clearance. Current treatments can only relieve disease symptoms but cannot delay the disease progression. Ursodeoxycholic acid (UDCA), a hydrophilic bile acid traditionally used in hepatology, has recently gained attention for its neuroprotective properties. This review critically evaluates UDCA's mechanisms of action, including the restoration of mitochondrial function, inhibition of apoptosis, reduction of oxidative stress and neuroinflammation, and enhancement of autophagy in both PD and AD models. In vitro and in vivo studies demonstrate UDCA's ability to preserve neuronal integrity, improve motor and cognitive outcomes, and reduce toxic protein aggregates. Although early-phase clinical trials, such as the UDCA for Parkinson's (UP) study in PD, show promising mitochondrial benefits and safety, clinical evidence in AD remains limited. Future directions emphasise the need for large-scale trials, personalised medicine, improved central nervous system (CNS) delivery strategies, or dietary interventions to modulate UDCA production from the gut microbiome. While not a first-line treatment, UDCA represents a compelling mitochondrial stabiliser with disease-modifying potential in NDDs.