Sodium Bicarbonate Supplementation and Urinary TGF-β1 in Nonacidotic Diabetic Kidney Disease

Abstract

Background and objectivesIn early-phase studies of individuals with hypertensive CKD and normal serum total CO2, sodium bicarbonate reduced urinary TGF-β1 levels and preserved kidney function. The effect of sodium bicarbonate on kidney fibrosis and injury markers in individuals with diabetic kidney disease and normal serum total CO2 is unknown.Design, setting, participants, & measurementsWe conducted a randomized, double-blinded, placebo-controlled study in 74 United States veterans with type 1 or 2 diabetes mellitus, eGFR of 15–89 ml/min per 1.73 m2, urinary albumin-to-creatinine ratio (UACR) ≥30 mg/g, and serum total CO2 of 22–28 meq/L. Participants received oral sodium bicarbonate (0.5 meq/kg lean body wt per day; n=35) or placebo (n=39) for 6 months. The primary outcome was change in urinary TGF-β1-to-creatinine from baseline to months 3 and 6. Secondary outcomes included changes in urinary kidney injury molecule-1 (KIM-1)-to-creatinine, fibronectin-to-creatinine, neutrophil gelatinase-associated lipocalin (NGAL)-to-creatinine, and UACR from baseline to months 3 and 6.ResultsKey baseline characteristics were age 72±8 years, eGFR of 51±18 ml/min per 1.73 m2, and serum total CO2 of 24±2 meq/L. Sodium bicarbonate treatment increased mean total CO2 by 1.2 (95% confidence interval [95% CI], 0.3 to 2.1) meq/L, increased urinary pH by 0.6 (95% CI, 0.5 to 0.8), and decreased urinary ammonium excretion by 5 (95% CI, 0 to 11) meq/d and urinary titratable acid excretion by 11 (95% CI, 5 to 18) meq/d. Sodium bicarbonate did not significantly change urinary TGF-β1/creatinine (difference in change, 13%, 95% CI, −10% to 40%; change within the sodium bicarbonate group, 8%, 95% CI, −10% to 28%; change within the placebo group, −4%, 95% CI, −19% to 13%). Similarly, no significant effect on KIM-1-to-creatinine (difference in change, −10%, 95% CI, −38% to 31%), fibronectin-to-creatinine (8%, 95% CI, −15% to 37%), NGAL-to-creatinine (−33%, 95% CI, −56% to 4%), or UACR (1%, 95% CI, −25% to 36%) was observed.ConclusionsIn nonacidotic diabetic kidney disease, sodium bicarbonate did not significantly reduce urinary TGF-β1, KIM-1, fibronectin, NGAL, or UACR over 6 months.