A Pre-Post Study of Vitamin D Supplement Effects on Urinary Megalin: The Emerging Predictive Role of Megalin in Diabetic Nephropathy Progression

Introduction: Megalin is a renal proximal tubular protein that reabsorbs vitamin D from glomerular filtrates. Previous studies found significantly higher levels of urinary megalin in chronic microvascular complications of diabetes with associated metabolic derangements. This study aimed at testing the effect of vitamin D supplements on urinary megalin levels in diabetic nephropathy (DN) patients with vitamin D hypovitaminosis. Methods: Sixty-three participants with vitamin D deficiency and diabetic nephropathy (DN) were enrolled in the pre-post study; urinary megalin levels with various clinical parameters and serum levels of vitamin D3 were measured and compared to the baseline at 3- and 6-month intervals. Results: Interestingly, a supplementation related increase in serum vitamin D3 levels at 3- and 6- month interventions affected a constellation of ameliorations in the DN progression of clinical and metabolic factors. There was a decrease in ACR with a concomitant decrease in urinary megalin and a decrease in blood pressure, fasting plasma glucose (FPG), and low-density lipoprotein – cholesterol (LDL-C) – but an increase in glomerular filtration rate (GFR). Principally, pellet urinary megalin associated positively (p < 0.05) with vitamin D hypovitaminosis and the albumin-to-creatinine ratio (ACR) but negatively (p < 0.05) with Ca2+ and body mass index (BMI). Conclusion: Vitamin D supplementation could elucidate underlying pathophysiological mechanisms and a prognostic significance of urinary megalin association with DN, obesity/MetS-related dyslipidemia, and hyperglycemia modification. Megalin is a putative sensitive and precise predictive marker and an emerging therapeutic target of renal anomalies.