Rationalizing the Use of Polyphenol Nano-formulations in the Therapy of Neurodegenerative Diseases

Neurodegenerative diseases are a heterogeneous group of disorders among aging populations worldwide characterized by the progressive degeneration of the structure and function of brain cells and the nervous system. Alzheimer's disease and Parkinson's disease are common neurodegenerative diseases (NDs). Classic pathological features of AD are the accumulation of the amyloid betaprotein and aggregates of hyperphosphorylated tau protein around the brain cells. Dopaminergic neuronal death in the midbrain and accumulation of α- synuclein in the neurons are the hallmark of Parkinson's disease. The pathogenesis is multifactorial, and both neurodegenerative disorders have complex etiology. Oxidative stress closely linked with mitochondrial dysfunction, excitotoxicity, nitric oxide toxicity, and neuro-inflammation, is anticipated to trigger neuronal death. Ample evidence has implicated that oxidative stress and inflammation contribute to the pathology of neurodegeneration in AD and PD. Currently, acetylcholinesterase inhibitors are the main treatment option for AD, while L-DOPA is the gold standard therapy for PD. Along with the main therapy, many endogenous antioxidants, like vitamin E, selenium, etc., are also given to the patients to combat oxidative stress. Current treatment for these NDs is limited due to the blood-brain barrier (BBB) that hinders drug targeting towards neurons. In this review, we emphasize adjunct treatment with anti-inflammatory agents that act at the site of the disease and can halt the disease progression by attenuating the effect of ROS triggering neuro-inflammatory response. Polyphenols, either as purified compounds or extracts from various natural plant sources, have been well studied and documented for anti-inflammatory effects, but their use for ND is limited due to their physicochemical attributes. Nanoparticle-mediated drug delivery system exhibits immense potential to overcome these hurdles in drug delivery to the CNS, enabling nanoparticle-based therapies to directly target the inflammation and release bioactive compounds with anti-inflammatory properties to the site of action.