title: gamma-tocopherol partially protects insulin-secreting cells against functional inhibition by nitric oxide.
abstract: 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.
authors.affiliation: Cancer Research Center of Hawaii, Molecular Carcinogenesis Program, University of Hawaii at Manoa, 1236 Lauhala Street, Honolulu, Hawaii, 96813-2424, USA. ake@ehk.ks.se
authors.forename: A
authors.initials: A
authors.lastname: Sjöholm
authors.forename: P O
authors.initials: PO
authors.lastname: Berggren
authors.forename: R V
authors.initials: RV
authors.lastname: Cooney
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D018679:Cholinergic Agonists / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D006152:Cyclic GMP / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007340:Insulinoma / Q000378:metabolism; D007375:Interleukin-1 / Q000494:pharmacology; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism; D008956:Models, Chemical; D009569:Nitric Oxide / Q000378:metabolism / Q000494:pharmacology*; D009589:Nitrogen Oxides; D010069:Oxadiazoles / Q000494:pharmacology; D010703:Phorbol Esters / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D013096:Spermine / Q000031:analogs & derivatives / Q000494:pharmacology; D010738:Type C Phospholipases / Q000378:metabolism; D014810:Vitamin E / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology*
chemical_list: C095284:1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one; D015220:Calcium Channels; D018679:Cholinergic Agonists; D004791:Enzyme Inhibitors; D007328:Insulin; D007375:Interleukin-1; D009589:Nitrogen Oxides; D010069:Oxadiazoles; D010703:Phorbol Esters; D011810:Quinoxalines; C091861:spermine nitric oxide complex; D014810:Vitamin E; D005576:Colforsin; D013096:Spermine; D009569:Nitric Oxide; D002217:Carbachol; D011493:Protein Kinase C; D010738:Type C Phospholipases; D000262:Adenylyl Cyclases; D006152:Cyclic GMP; D002118:Calcium