Dietary Genistein Rescues Reduced Basal Chloride Secretion in Diabetic Jejunum via Sex-Dependent Mechanisms

Abstract

Background/Aims: The goal of this study was to determine the effect of dietary genistein (naturally occurring phytoestrogen) on jejunal secretory function in a clinically relevant model of diabetes and obesity, the leptin-defIcient ob/ob mouse. Methods: We measured transepithelial short circuit current (I_sc), across freshly isolated segments of jejunum from 12-week old male and female ob/ob and lean C57Bl/6J mice fed a genistein diet (600 mg genistein/kg diet) for 4-weeks. Separate segments of jejunum were frozen for western blot determination of key proteins involved in secretory transport. Results: Basal I_sc was signifIcantly decreased (by 33%, P<0.05) in ob/ob females versus leans, and genistein-diet reversed this. Similarly, in males, basal I_sc was decreased (by 47%, P<0.05) in ob/ob mice versus leans, and genistein-diet reversed this. Inhibition with either clotrimazole (100 µM, bilateral) or ouabain (100 µM, basolateral) was signifIcantly reduced in ob/ob mice compared to leans (P<0.05), and genistein-diet reversed clotrimazole-sensitive inhibition in ob/ob females, and reversed the ouabain-sensitive inhibition in males (indicating sex-dependent mechanisms). Our data suggested that PDE3 levels were dysregulated in ob/ob females and genistein reversed this. Expression of total CFTR (normalized to actin) was signifIcantly decreased ∼80% (P<0.05) in all ob/ob mice compared to leans, and genistein-diet was without effect. Expression of total NKCC1 (normalized to actin) was signifIcantly decreased ∼80% (P<0.05) in ob/ob male mice versus leans, and genistein-diet reversed this. Conclusions: Our data suggests that the reduced basal jejunal I_sc in ob/ob female mice is a consequence of reduced CFTR expression, decreased activities of the basolateral K_Ca channel and Na⁺/K⁺-ATPase, and in male mice reduced basal jejunal I_sc is a consequence of reduced CFTR and NKCC1 expression, along with decreased activities of the basolateral K_Ca channel and Na⁺/K⁺-ATPase. Genistein-diet has beneficial effects on basal I_sc mediated by sex-dependent mechanisms in diabetic mice: in females via increased K_Ca-sensitive I_sc and in males via increased Na⁺/K⁺-ATPase activity and increased NKCC1 expression. Improved understanding of intestinal dysfunctions in the ob/ob jejunum, may allow for the development of novel drug targets to treat obesity and diabetes, and may also be of benefit in CF-related diabetes.