Non-polar metabolites of green beans (Phaseolus vulgaris L.) potentiate the antidiabetic activity of mesenchymal stem cells in streptozotocin-induced diabetes in rats

Abstract

Green beans (Phaseolus vulgaris L.) are consumed as pods or mature seeds (common beans). The pods were extracted with 95% ethanol and processed to prepare non- polar and polar fractions. Comparing the antihyperglycemic activity of both fractions, non-polar fraction (NPF, 200 mg kg−1 day−1) lowered blood glucose in streptozotocin diabetic rats by 65% compared to 57% for the polar fraction at the same dose. When NPF treatment was combined with injection of mesenchymal stem cells (MSC) a 4.4- fold increase in serum insulin and a 73.6% reduction in blood glucose were observed compared to untreated control. Additionally, a significant decrease in malondialde- hyde (76.2%), nitric oxide (68.2%), cholesterol (76.1%), and triglycerides (69.5%) and a 1.75-fold increase in HDL concentrations were observed in the group treated with this combination compared to diabetic animals. Interestingly, NPF increased homing of MSC in pancreas potentiating their antidiabetic activity. Finally, 26 compounds were identified in NPF using LC/MS analysis and four were isolated in pure form. The isolated compounds namely calotroproceryl acetate, fridelin, calotroproceryl A, and stigmasterol showed good inhibitory activity against pancreatic lipase with IC50 at 1.93, 1.07, 1.34 and 1.44–1 μg/ml, respectively. Additionally, these compounds inhib- ited α-amylase, albeit at higher concentration, with IC50 at 248, 212, 254, and 155 μg/ ml for calotroproceryl acetate, fridelin, calotroproceryl A, and stigmasterol, respec- tively. Our results suggest that green beans extract can potentiate effect of MSC in diabetes directly due to its own antidiabetic effect and indirectly by increasing MSC homing in pancreatic tissues. Practical applications It has been suggested in this study that green beans can improve hyperglycemia, oxi- dative balance in diabetes, so green beans can be promoted as a healthy nutrient for diabetic patients. Green beans also can enhance homing and differentiation of mesn- chymal stem cells in the pancreas for future stem cell therapy of type I diabetes.