Interactions between vitamin E and glucose on B-cell functions in the rat: an in vivo and in vitro study

Pancreas. 1999 Apr;18(3):274-81. doi: 10.1097/00006676-199904000-00009.

Abstract

Hyperglycemia exerts negative effects on B-cell functions that may involve oxidative stress. This was tested for by investigating effects of D-alpha-tocopherol (vitamin E), known as a free radical scavenger, on B-cell functions. For in vivo testing, rat pancreatic islets were transplanted syngeneically under the kidney capsule in streptozotocin-induced diabetic rats. Transplanted rats were treated with D-alpha-tocopherol (40 mg/kg, intraperitoneally injected every other day) or soybean oil for 2 or 6 weeks. Graft-bearing kidneys were then perfused and insulin release was measured after stimulation sequentially with glucose (27 mmol/L) and L-arginine (10 mmol/L). D-alpha-tocopherol treatment for 2 or 6 weeks failed to restore glucose-induced insulin secretion, whereas treatment for 2 but not for 6 weeks enhanced basal insulin release (by 24%, p < 0.05) and arginine-induced release (by 79%, p < 0.05). Treatment did not affect graft content of preproinsulin mRNA. The presence of D-alpha-tocopherol (50 microg/ml) in vitro enhanced glucose (27 mmol/L)-stimulated insulin release from batch-type incubated islets by 33% (p < 0.05). Exposing islets to D-alpha-tocopherol for 1 day in the presence of 38 mmol/L glucose enhanced glucose-stimulated insulin release (by 25%, p < 0.05), L-arginine-stimulated release (by 37%, p < 0.05) and elevated islet insulin content (by 20%, p < 0.05). These effects of exposure to D-alpha tocopherol were lost when the culture period was extended up to 3 weeks. It is concluded that D-alpha-tocopherol exerts moderate beneficial effects on B-cell functions during short to intermediate length of high glucose exposure. These effects are, however, insufficient to support a major role for oxidative stress behind glucotoxicity toward B cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Arginine / pharmacology
  • Cells, Cultured
  • Diabetes Mellitus, Experimental
  • Drug Interactions
  • Female
  • Glucose / pharmacology*
  • Insulin / metabolism
  • Insulin Secretion
  • Islets of Langerhans / drug effects*
  • Islets of Langerhans / metabolism*
  • Islets of Langerhans Transplantation
  • Kidney
  • Male
  • Proinsulin / genetics
  • Protein Precursors / genetics
  • RNA / analysis
  • RNA, Messenger / analysis
  • Rats
  • Rats, Inbred WF
  • Rats, Wistar
  • Transplantation, Heterotopic
  • Vitamin E / pharmacology*

Substances

  • Insulin
  • Protein Precursors
  • RNA, Messenger
  • Vitamin E
  • preproinsulin
  • RNA
  • Proinsulin
  • Arginine
  • Glucose