title: Dietary resistant starch prevents urinary excretion of vitamin D metabolites and maintains circulating 25-hydroxycholecalciferol concentrations in Zucker diabetic fatty rats.
abstract: BACKGROUND
  Type 2 diabetes (T2D) is the leading cause of nephropathy in the United States. Renal complications of T2D include proteinuria and suboptimal serum 25-hydroxycholecalciferol (25D) concentrations. 25D is the major circulating form of vitamin D and renal reabsorption of the 25D-vitamin D-binding protein (DBP) complex via megalin-mediated endocytosis is believed to determine whether 25D can be activated to 1,25-dihydroxycholecalciferol (1,25D) or returned to circulation. We previously demonstrated that excessive urinary excretion of 25D-DBP and albuminuria occurred in rats with type 1 diabetes (T1D) and T2D. Moreover, feeding rats with T1D high-amylose maize partially resistant to digestion [resistant starch (RS)] prevented excretion of 25D-DBP without significantly affecting hyperglycemia.
  
  
  OBJECTIVE
  We used Zucker diabetic fatty (ZDF) rats, a model of obesity-related T2D, to determine whether feeding RS could similarly prevent loss of vitamin D and maintain serum 25D concentrations.
  
  
  METHODS
  Lean control Zucker rats (n = 8) were fed a standard semi-purified diet (AIN-93G) and ZDF rats were fed either the AIN-93G diet (n = 8) or the AIN-93G diet in which cornstarch was replaced with RS (550 g/kg diet; 35% resistant to digestion) (n = 8) for 6 wk.
  
  
  RESULTS
  RS attenuated hyperglycemia by 41% (P < 0.01) and prevented urinary DBP excretion and albuminuria, which were elevated 3.0- (P < 0.01) and 3.6-fold (P < 0.01), respectively, in control diet-fed ZDF rats. Additionally, urinary excretion of 25D (P = 0.01) and 1,25D (P = 0.03) was higher (89% and 97%, respectively), whereas serum 25D concentrations were 31% lower (P < 0.001) in ZDF rats fed the control diet compared with RS-fed ZDF rats. Histopathologic scoring of the kidney revealed that RS attenuated diabetes-mediated damage by 21% (P = 0.12) despite an ∼50% decrease in megalin protein abundance.
  
  
  CONCLUSIONS
  Taken together, these data provide evidence that suggests vitamin D balance can be maintained by dietary RS through nephroprotective actions in T2D, which are independent of vitamin D supplementation and renal expression of megalin.
authors.affiliation: Department of Food Science and Human Nutrition, Interdepartmental Graduate Program in Nutritional Sciences, and.
authors.forename: Gar Yee
authors.initials: GY
authors.lastname: Koh
authors.affiliation: Department of Veterinary Pathology, College of Veterinary Medicine, Iowa State University, Ames, IA.
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Whitley
authors.affiliation: Department of Food Science and Human Nutrition.
authors.forename: Kirsten
authors.initials: K
authors.lastname: Mancosky
authors.affiliation: Department of Food Science and Human Nutrition.
authors.forename: Yi Ting
authors.initials: YT
authors.lastname: Loo
authors.affiliation: Department of Food Science and Human Nutrition.
authors.forename: Kelly
authors.initials: K
authors.lastname: Grapentine
authors.affiliation: Department of Food Science and Human Nutrition.
authors.forename: Emily
authors.initials: E
authors.lastname: Bowers
authors.affiliation: Department of Food Science and Human Nutrition, Interdepartmental Graduate Program in Nutritional Sciences, and.
authors.forename: Kevin L
authors.initials: KL
authors.lastname: Schalinske
authors.affiliation: Department of Food Science and Human Nutrition, Interdepartmental Graduate Program in Nutritional Sciences, and mrowling@iastate.edu.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Rowling
mesh_terms: D000821:Animal Feed / Q000032:analysis*; D000818:Animals; D002112:Calcifediol / Q000097:blood*; D004040:Dietary Carbohydrates / Q000008:administration & dosage; D004063:Digestion; D005786:Gene Expression Regulation / Q000502:physiology; D007668:Kidney / Q000378:metabolism; D008297:Male; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011897:Random Allocation; D051381:Rats; D011924:Rats, Zucker; D014807:Vitamin D / Q000378:metabolism* / Q000652:urine; D003313:Zea mays / Q000737:chemistry / Q000378:metabolism
chemical_list: D004040:Dietary Carbohydrates; D012333:RNA, Messenger; D014807:Vitamin D; D002112:Calcifediol