gamma-tocopherol partially protects insulin-secreting cells against functional inhibition by nitric oxide

Biochem Biophys Res Commun. 2000 Oct 22;277(2):334-40. doi: 10.1006/bbrc.2000.3650.


Preceding the onset of type 1 diabetes mellitus, pancreatic islets are infiltrated by macrophages secreting interleukin-1beta (IL-1beta) which induces beta-cell apoptosis and exerts inhibitory actions on islet beta-cell insulin secretion. IL-1beta seems to act chiefly through induction of nitric oxide (NO) synthesis. Hence, IL-1beta and NO have been implicated as key effector molecules in type 1 diabetes mellitus. In this paper, the influence of endogenously produced and exogenously delivered NO on the regulation of cell proliferation, cell viability and discrete parts of the stimulus-secretion coupling in insulin-secreting RINm5F cells was investigated. Because vitamin E may delay diabetes onset in animal models, we also investigated whether tocopherols may protect beta-cells from the suppressive actions of IL-1 and NO in vitro. To this end, the impact of NO on insulin secretory responses to activation of phospholipase C (by carbamylcholine), protein kinase C (by phorbol ester), adenylyl cyclase (by forskolin), and Ca(2+) influx through voltage-activated Ca(2+) channels (by K(+)-induced depolarization) was monitored in culture after treatment with IL-1beta or by co-incubation with the NO donor spermine-NONOate. It was found that cell proliferation, viability, insulin production and the stimulation of insulin release evoked by carbamylcholine and phorbol ester were impeded by IL-1beta or spermine-NONOate, whereas the hormone output by the other secretagogues was not altered by NO. Pretreatment with gamma-tocopherol (but not alpha-tocopherol) afforded a partial protection against the inhibitory effects of NO, whereas specifically inhibiting inducible NO synthase with N-nitro-L-arginine completely reversed the IL-1beta effects. In contrast, inhibiting guanylyl cyclase with ODQ (1H-[1,2, 4]oxadiazolo[4,3-alpha]-quinoxaline-1-one) or blocking low voltage-activated Ca(2+) channels with NiCl(2) failed to influence the actions of NO. In conclusion, our data show that NO inhibits growth and insulin secretion in RINm5F cells, and that gamma-tocopherol may partially prevent this. The results suggest that phospholipase C or protein kinase C may be targeted by NO. In contrast, cGMP or low voltage-activated Ca(2+) channels appear not to mediate the toxicity of NO in these cells. These adverse effects of NO on the beta-cell, and the protection by gamma-tocopherol, may be of importance for the development of the impaired insulin secretion characterizing type 1 diabetes mellitus, and offer possibilities for intervention in this process.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenylyl Cyclases / metabolism
  • Animals
  • Calcium / metabolism
  • Calcium Channels / metabolism
  • Carbachol / pharmacology
  • Cell Division / drug effects
  • Cell Line
  • Cell Survival / drug effects
  • Cholinergic Agonists / pharmacology
  • Colforsin / pharmacology
  • Cyclic GMP / metabolism
  • Enzyme Inhibitors / pharmacology
  • Insulin / metabolism*
  • Insulin Secretion
  • Insulinoma / metabolism
  • Interleukin-1 / pharmacology
  • Islets of Langerhans / drug effects
  • Islets of Langerhans / metabolism
  • Models, Chemical
  • Nitric Oxide / metabolism
  • Nitric Oxide / pharmacology*
  • Nitrogen Oxides
  • Oxadiazoles / pharmacology
  • Phorbol Esters / pharmacology
  • Protein Kinase C / metabolism
  • Quinoxalines / pharmacology
  • Rats
  • Spermine / analogs & derivatives
  • Spermine / pharmacology
  • Type C Phospholipases / metabolism
  • Vitamin E / chemistry
  • Vitamin E / metabolism*
  • Vitamin E / physiology*


  • 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one
  • Calcium Channels
  • Cholinergic Agonists
  • Enzyme Inhibitors
  • Insulin
  • Interleukin-1
  • Nitrogen Oxides
  • Oxadiazoles
  • Phorbol Esters
  • Quinoxalines
  • spermine nitric oxide complex
  • Vitamin E
  • Colforsin
  • Spermine
  • Nitric Oxide
  • Carbachol
  • Protein Kinase C
  • Type C Phospholipases
  • Adenylyl Cyclases
  • Cyclic GMP
  • Calcium