Medicinal plants for diabetes associated neurodegenerative diseases: A systematic review of preclinical studies.

Diabetes mellitus is a metabolic defect with many complications for the patients. Deaths due to diabetes and its complications are increasing, and one of the most serious consequences are the neurological disorders. Chemical treatments have irreversible side effect and therefore the aim of this study is to evaluate the medicinal plants used for treatment of cognitive impairments and neurodegenerative diseases associated with diabetes in 2004-2020 period. Electronic databases used were PubMed, Scopus and Cochrane library. The keywords used were "diabetes," "plant," "herb," "neurodegenerative," "neurodegeneration," "cognitive," "cognition," "Alzheimer," "dementia." The non-English articles, repetitive articles and review studies were excluded. From total of 3,590 results, 58 articles are included in the study. The results show that many chemical treatments considered for this disease simply control hyperglycemia, but cannot improve the complications of diabetes. Herbal medicine could be more effective due to the high antioxidant activity of some medicinal plants. Biologically active substances of medicinal plants can improve the neurological disorders caused by diabetes via several pathways. The most important pathway is related to antioxidant properties. Other pathways include antiinflammatory, anti-apoptotic, neurotoxicity inhibition, neuronal death, increasing the uptake of glucose by cells and improve neurotransmitters levels involved in learning and memory.