Potential of Medicinal Plants to Ameliorate Retinopathy Events in Diabetes: A Systematic Review

Diabetic Retinopathy (DR) is one of the most common diabetic complications which can lead to vision loss if left unattended. Medicinal plants are considered as a treatment option for its lesser side effects. Given the overwhelming number of studies on various medicinal plants using different subjects, this systematic review aims to update the current status of the potential of medicinal plants in ameliorating DR. Literature from the years 2011 to 2020 was retrieved from PubMed, ScienceDirect and Scopus databases using the search terms: Medicinal plants AND (diabetes OR hyper glycaemia) AND retinopathy. The PRISMA guidelines were adhered to for reporting the systematic review, while the SYRCLE tool was used to assess the risk of bias in animal studies. Inclusion and exclusion criteria were established for selecting compatible studies. Based on these criteria, four out of 439 studies were selected: Studies on DR in rats included three or more assays for measuring retinal vascular permeability, VEGF protein and gene expressions and body weight. An additional six studies from a manual search brought the total to ten selected studies. All studied medicinal plants demonstrated potential in ameliorating DR, based on their downregulation of diabetes-induced retinal vascular leakage and VEGF expressions. Medicinal plants with significant potential in attenuating DR included Zingiber zerumbet rhizomes and its active ingredient, zerumbone; Lycium barbarum; Plantaginis semen; and apocynin. The aqueous extracts of Radix astragali, Radix angelica sinensis, Panax notoginseng, Lycopus lucidus Turcz and total lignans from Fructus arctii can be further evaluated in future studies.