Tubular NHE3 is a determinant of the acute natriuretic and chronic blood pressure lowering effect of the SGLT2 inhibitor empagliflozin

The sodium glucose cotransporter 2 (SGLT2) inhibitor, empagliflozin, is a new antihyperglycemic drug that also lowers blood pressure and has beneficial effects in patients with heart failure (EMPA-REG OUTCOME). These effects may relate at least in part to its natriuretic effect. In the brush border of the early proximal tubule, SGLT2 may interact with the Na+-H+-exchanger NHE3, which reabsorbs about 30% of Na+ in the proximal convoluted tubule. Here we determine whether the acute or chronic natriuretic effect of empagliflozin depends on intact tubular NHE3. Methods We generated mice with NHE3 knock-down in the tubular system (NHE3-KO; using Pax8-Cre) and compared them with littermate controls (WT). In a first series, we determined acute effects of empagliflozin (0.3 mg/kg, given by oral gavage together with a water load to facilitate quantitative urine collection over 3 hours) or vehicle on urinary pH and excretion of fluid, Na, and bicarbonate in metabolic cage studies (n=9–11/group). In a second series, we treated mice for 4 months with empagliflozin (150 mg/kg of diet) or vehicle and measured systolic blood pressure (SBP) by automated tail cuff in trained awake mice and renal renin mRNA expression by RT-qPCR (n=10/group for renin mRNA and 15–26/group for SBP). Results Series 1 In WT, empagliflozin significantly enhanced urinary pH and the excretion of glucose, fluid, Na and bicarbonate compared with vehicle control. In NHE3-KO, urine pH and bicarbonate excretion were significantly greater than in WT in response to vehicle; however, these two parameters were not significantly changed in response to empagliflozin. Moreover, empagliflozin actually reduced urine Na excretion in NHE3-KO. Series 2 In WT, empagliflozin lowered SBP and enhanced renal renin mRNA expression, consistent with a sustained natriuretic effect. In vehicle-treated NHE3-KO, SBP was lower and renal renin mRNA higher compared with WT; however, these two parameters were not significantly changed in response to empagliflozin. Conclusion The data are consistent with the notion that the acute natriuretic and the chronic blood pressure lowering effect of the SGLT2 inhibitor empagliflozin involve a functional interaction with tubular NHE3, and can occur in the absence of hyperglycemia. The chosen dose of empagliflozin only induced a mild glucosuria, i.e. glucose reabsorption through downstream SGLT1 had just been fully saturated. Since SGLT1 transports Na and glucose in a ratio of 2:1 versus 1:1 for SGLT2, shifting glucose reabsorption from SGLT2 to downstream SGLT1 can explain an anti-natriuretic effect of empagliflozin that has been unmasked by the absence of tubular NHE3. Support or Funding Information NIH R01DK112042, R01DK106102, P30DK079337, the Department of Veterans Affairs, Boehringer Ingelheim Pharma GmbH & Co.KG This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.