Equol as a Multitarget Agent Against Neurodegeneration: Mechanistic Insights into Its Molecular Modulation

Neurodegenerative diseases consist of a group of progressive disorders characterized by the gradual decline in the structure or function of neurons, which ultimately results in neuronal death. The occurrence and societal effects of these disorders have been consistently rising, presenting considerable public health challenges globally. Multiple interconnected pathways, including oxidative stress, neuroinflammation, nitrosative stress, and apoptosis, drive their progression. NOX-induced ROS disrupts neuronal function, impairs mitochondrial activity, and triggers lipid peroxidation, contributing to neuronal death. Activation of the TLR-4/MAPK/NF-κB pathway triggers neuroinflammation and NLRP3 inflammasome activation. This inflammasome-driven inflammation accelerates neuronal injury and death. Moreover, reduced estrogen receptor expression weakens neuronal defenses, impairing synaptic function, thereby worsening neurodegeneration. Neurodegenerative diseases continue to be without a cure, as existing treatments focus on alleviating symptoms and modifying the disease. Due to their intricate and multifactorial pathophysiology, there is a pressing need for agents capable of targeting multiple pathological mechanisms to effectively combat these disorders. Various phytomolecules have shown promise in tackling different neurodegenerative diseases by modulating key molecular targets. Equol (4',7-isoflavandiol) is a metabolite of daidzein, a soy isoflavone present in soybeans and various other plant sources. Equol has shown significant promise in combating neurodegeneration by modulating mediators involved in oxidative stress, neuroinflammation, nitrosative stress, and apoptosis. Key signaling molecules influenced by equol include TLR-4, MAPKs, NLRP3 inflammasome, ROS, and inflammatory mediators, among others. Considering equol's ability to modulate these signaling mediators, this review explores the mechanistic pathways through which equol confers neuroprotection.