The brain renin-angiotensin system in Parkinson's disease: Friend or foe? mechanistic insights and therapeutic implications.

The renin-angiotensin system (RAS), classically known for its role in cardiovascular and fluid homeostasis, also regulates neuronal homeostasis in the central nervous system (CNS), where its dysregulation contributes to PD pathogenesis. The emerging evidence links excessive activation of the brain RAS in PD, where sustained activation of the angiotensin II (Ang II)/angiotensin type-1 receptor (AT1R) axis promotes oxidative stress, neuroinflammation, mitochondrial dysfunction, and blood-brain barrier (BBB) disruption that leads to progressive dopaminergic neurodegeneration. This AngII-AT1R signaling increases the production of reactive oxygen species (ROS) mediated by NADPH oxidase, primes microglia to a chronic pro-inflammatory state, disrupts the proteostatic regulation of nigrostriatal neuronal α-synuclein clearance, and intensifies the selective vulnerability of nigrostriatal neurons. The counter-regulatory ACE2/angiotensin (1-7)/Mas and AT2R pathway seems to have neuroprotective effects; however, it reverses the negative effects of Ang II. In preclinical, epidemiological, and emerging clinical evidence, pharmacological modulation of the RAS, particularly BBB-penetrant angiotensin receptor blockers (ARBs) and angiotensin-converting enzyme inhibitors (ACEIs), has shown promise as neuroprotective agents. In the current area of research, RAS-targeted interventions represent a promising and mechanistically grounded strategy for disease modification rather than symptomatic management alone. This review explores molecular, cellular, and system-level insights into RAS dysregulation in PD, integrates translational evidence supporting RAS-modulating therapies, and highlights emerging biomarkers and precision medicine approaches that may guide therapeutic optimization. This review also highlights the brain RAS as a key mediator linking redox imbalance, neuroinflammation, and multisystem dysfunction in PD and makes it a promising therapeutic axis for slowing the disease progression.