Dietary Resistant Starch Prevents Urinary Excretion of 25-Hydroxycholecalciferol and Vitamin D-Binding Protein in Type 1 Diabetic Rats1,2

Abstract

Diabetes is a rapidly growing epidemic affecting millions of Americans and has been implicated in a number of devastating secondary complications. We previously demonstrated that type 2 diabetic rats exhibit vitamin D deficiency due to aberrant megalin-mediated endocytosis and excessive urinary excretion of 25-hydroxycholecalciferol (25D3) and vitamin D-binding protein (DBP). Here, we examined whether a model of type 1 diabetes [T1D; streptozotocin (STZ)-treated Sprague-Dawley rats] would similarly excrete abnormally high concentrations of 25D3 and DBP due to renal damage and compromised expression of megalin and its endocytic partner, disabled-2 (Dab2). Moreover, we tested whether feeding diabetic rats starch that is resistant to digestion could alleviate these abnormalities. Control (n = 12) rats were fed a standard, semipurified diet (AIN-93G) containing 55% total dietary starch and STZ-treated rats were fed the AIN-93G diet (n = 12) or a diet containing 55% high-amylose maize that is partially resistant to digestion [20% total dietary resistant starch (RS); n = 12] for 2 and 5 wk. The RS diet attenuated weight loss and polyuria in STZ-treated rats. Histology and immunohistochemistry revealed that dietary RS also attenuated the loss of Dab2 expression in renal proximal tubules. Moreover, urinary concentrations of both 25D3 and DBP were elevated ∼10-fold in STZ-treated rats (5 wk post STZ injection), which was virtually prevented by the RS. We also observed a ∼1.5-fold increase in megalin mRNA expression in STZ-treated rats, which was attenuated by feeding rats the RS diet for 2 wk. Taken together, these studies indicate that consumption of low-glycemic carbohydrates can attenuate disruption of vitamin D homeostasis in T1D through the rescue of megalin-mediated endocytosis in the kidney.

Urine and plasma concentrations of amino acids and plasma vitamin status differ, and are differently affected by salmon intake, in obese Zucker fa/fa rats with impaired kidney function and in Long-Evans rats with healthy kidneys

“…The higher plasma concentration of all fat-soluble vitamins and the majority of water-soluble vitamins in Zucker fa/fa rats compared to Long-Evans rats was clearly demonstrated in the PCA, despite similar energy intake between the two groups. This was an unexpected finding since the loss of both fat-soluble and water-soluble vitamins in urine has been demonstrated to be higher in rats with tubular injury (47,48) and since vitamin D insufficiency is highly prevalent in patients with chronic kidney disease (20) . Transport proteins for fat-soluble vitamins, including retinol-binding protein and vitamin D-binding protein, and water-soluble vitamins are filtered in the glomeruli and reabsorbed in the renal tubule or secreted in urine (49,50) .…”

Epigenetics in Adipose Tissue, Obesity, Weight Loss, and Diabetes

“…Subsequently, this new knowledge may be used in future dietary and therapeutic recommendations regarding the control of diabetes and its complications. For example, numerous recent reports have demonstrated that dietary resistant starch or probiotics have an important beneficial impact on diabetes and obesity (102,103), suggesting that intervention strategies that target the gut microbiota represent a viable approach for disease prevention or treatment.…”

Resistant Starch Regulates Gut Microbiota: Structure, Biochemistry and Cell Signalling

“…Consumption of resistant starch can attenuate disruption of vitamin D homeostasis in type I diabetes through the rescue of megalin-mediated endocytosis in kidney in the absence of visible side effects [56]. …”