Role and mechanism of herbal bioactives in treatment of Parkinson disease: A promising therapeutic approach

Parkinson's disease is a complex chronic neurodegenerative disorder characterized by loss of dopaminergic neurons in the substantia nigra and possesses characteristic motor symptoms including bradykinesia, rigidity, tremor, postural instability, and dystonia, resulting in nerve cell damage that further leads to reduction in the dopamine level. However, the symptomatology of Parkinson disease is diverse, including clinically significant non-motor characteristic symptoms such as anxiety, depression, pain, insomnia, restless leg syndrome, gastrointestinal disturbance, difficulty in walking and fatigue. Although there are various conventional treatment approaches used for Parkinson disease such as monoamine oxidase-B inhibitors, catecholamine-O-methyl transferase inhibitors, dopamine agonist, and anticholinergics but are associated with various side effects. In Asian countries, herbal products are being used as an alternative approach for treating neurogenerative diseases. Herbal medicines are used worldwide as these have fewer side effects than that of allopathic drugs. In this review, we will summarize recent studies demonstrating use of herbs in treating parkinsonism. A search for possibly relevant literature was done using four electronic databases: Google, Pub Med, Web of Science, and Scopus. Several key phrases were used to conduct the search, including “Parkinson Disease”, “Herbal Drugs”, “Etiology of PD”, “Conventional treatment for PD”, “motor/non-motor symptoms”, Clinical trials”, “Symptomatology”, Natural products” etc. More research was conducted by examining the abstracts, reference lists, and consulting previously published review articles. A large number of herbal medicines and their formulations are currently in use for treatment of Parkinson disease. Some of these include Bacopa monnieri (L.) Wettst., Mucuna pruriens (L.) DC., Withania somnifera (L.) Dunal, Curcuma longa L., Gingko biloba L., and Camellia sinensis (L.) Kuntze, Alpinia oxyphyll Miq, Hypericum perforatum L., Panax ginseng C.A. Mey. and Crocus sativus L. Although, many preclinical trials have been already reported that signifies the importance of herbal products in Parkinson disease, however, further investigation is demanded to prove their usefulness in clinics.