Metformin Alleviates Diabetes-Associated Hypertension by Attenuating the Renal Epithelial Sodium Channel

Diabetic nephropathy is the primary cause of morbidity in type 2 diabetes mellitus (T2DM) patients. New data indicate that hypertension, a common comorbidity in T2DM, can worsen outcomes of diabetic nephropathy. While metformin is a commonly prescribed drug for treating type 2 diabetes, its blood pressure regulating ability is not well documented. The aim of this study was to investigate the effect of metformin on normalizing blood pressure in salt-loaded hypertensive diabetic db/db mice. Sixteen-week-old male and female diabetic db/db mice were individually placed in metabolic cages and then randomized to a control vehicle (saline) or metformin treatment group. We evaluated the blood pressure reducing ability of metformin in salt-induced hypertension and progression of nephropathy in db/db mice. We observed that metformin- normalized systolic blood pressure in hypertensive diabetic mice. Mechanistically, metformin treatment reduced renal cathepsin B expression. Low cathepsin B expression was associated with reduced expression and activity of the epithelial sodium channel (ENaC), sodium retention, and thus control of hypertension. In addition, we identified that urinary extracellular vesicles (EVs) from the diabetic mice are enriched in cathepsin B. Compared to treatment with urinary EVs of vehicle-treated hypertensive diabetic mice, the amiloride-sensitive transepithelial current was significantly attenuated upon exposure of renal collecting duct cells to urinary EVs isolated from metformin-treated db/db mice or cathepsin B knockout mice. Collectively, our study identifies a novel blood pressure reducing role of metformin in diabetic nephropathy by regulating the cathepsin B-ENaC axis.

SAT-LB126 Metformin Attenuates Sodium Retention and Blood Pressure in Hypertensive Diabetic Mice by Reducing the Phosphorylation of Renal NCC and Its Association With the Actin Cytoskeleton

Metformin is the first-line drug in the treatment of type 2 diabetes mellitus. The aim of this work was to evaluate the efficacy of metformin treatment in reducing blood pressure and investigate the molecular mechanism using a preclinical animal model. Adult male and female diabetic db/db mice with a blood glucose of greater than 300 mg/dl were salt-loaded (8% NaCl) for 10 days to induce hypertension. The mice were subject to metabolic cage studies for 24 hour urine collections in order to measure urinary electrolytes, albumin, and creatinine. Blood pressure was measured weekly by the tail-cuff method to assess the effect of metformin or vehicle given by oral gavage (dose of 60 mg/kg of body weight per day). At the end of the study the mice was euthanized and the left kidney was formalin-fixed and paraffin-embedded for immunohistochemistry while the right kidney was homogenized for Western blotting. Western blotting showed attenuation of total NCC and phospho-NCC in diabetic db/db mice given an oral gavage of metformin (Pearson correlation coefficient: 0.9470 +/- 2.52e^-3) compared to vehicle (Pearson correlation coefficient: 0.9800 +/- 2.86e^-3). Immunohistochemical analysis showed less co-localization of the actin cytoskeleton protein filamin and phosphorylated NCC in the metformin treated group compared to the control group. Taken together, we show metformin decreases sodium retention and blood pressure by reducing the density of renal NCC at the luminal membrane and the association between NCC and the actin cytoskeleton.

Cholecystokinin, gastrin, cholecystokinin/gastrin receptors, and bitter taste receptor TAS2R14: trophoblast expression and signaling

We investigated expression of cholecystokinin (CCK) in humans and mice, and the bitter taste receptor TAS2R14 in the human placenta. Because CCK and gastrin activate the CCKBR receptor, we also explored placental gastrin expression. Finally, we investigated calcium signaling by CCK and TAS2R14. By RT-PCR, we found CCK/Cck and GAST/Gast mRNA expression in both normal human and mouse placentas, as well as in human trophoblast cell lines (TCL). Although both Cckar and -br mRNA were expressed in the mouse placenta, only CCKBR mRNA was detected in the human placenta and TCL. mRNA expression for TAS2R14 was also observed in the human placenta and TCL. Using immunohistochemistry, CCK protein was localized to the syncytiotrophoblast (ST) and extravillous trophoblast (EVT) in the human term placenta, and to trophoblast glycogen cells in mouse and human placentas. Gastrin and TAS2R14 proteins were also observed in ST and EVT of the human placenta. Both sulfated and nonsulfated CCK elicited a comparable rise in intracellular calcium in TCL, consistent with CCKBR expression. Three TAS2R14 agonists, flufenamic acid, chlorhexidine, and diphenhydramine, also evoked rises in intracellular calcium in TCL. These results establish CCK, gastrin, and their receptor(s) in both human and mouse placentas, and TAS2R14 in the human placenta. Both CCK and TAS2R14 agonists increased intracellular calcium in human TCL. Although the roles of these ligands and receptors, and their potential cross talk in normal and pathological placentas, are currently unknown, this study opens new avenues for placental research.