Insulin-like plant proteins as potential innovative drugs to treat diabetes—The Moringa oleifera case study

•Plant proteins with in vitro and in vivo insulin-mimetic effects.•Insulin-like proteins are found in leaves, fruits and seeds.•Insulin-like plant proteins have the potential for therapeutic use in diabetes.•Moringa oleifera is a source of insulin-like proteins. Various plant species have long been used in traditional medicine worldwide to treat diabetes. Among the plant-based compounds with hypoglycemic properties, studies on insulin-like proteins isolated from leaves, fruits and seeds are rarely reported in the relevant literature. Our research group has been investigating the presence of insulin-like proteins in Moringa oleifera, a plant species native to India, and we have obtained a leaf protein isolate and semi-purified derived fractions, as well as a seed coat protein fraction (Mo-SC), with hypoglycemic activity in chemically induced diabetic mice that have increased tolerance to orally administered glucose. Equally importantly, Mo-SC possesses insulin-like antigenic epitopes. In this context, the present review aims to highlight that prospection of insulin-like proteins in plants is of the utmost importance both for finding new drugs for the treatment of diabetes and for shedding light on the mechanisms involved in diabetes.