TY - JOUR
T1 - γ-Tocopherol partially protects insulin-secreting cells against functional inhibition by nitric oxide
AU - Sjöholm, Åke
AU - Berggren, Per Olof
AU - Cooney, Robert V.
N1 - Funding Information:
We thank Drs. Yuichiro Tanaka and Terrilea S. Burnett for helpful advice and Ms. Elvi Sandberg for skillful insulin measurements. Financial support was received from the European Foundation for the Study of Diabetes, Torsten and Ragnar Söderberg’s Foundations, Barndiabetesfonden, Karolinska Institutet, the Swedish Society of Medicine, the Nordic Insulin Foundation Committee, Åke Wiberg’s Foundation, the Swedish Medical Research Council (72X-12550, 72X-00034, 72X-09890, 72XS-12708), the Swedish Diabetes Association, Fredrik and Inger Thuring’s Foundation, Novo-Nordisk Sweden Pharma AB, Harald Jeansson’s and Harald and Greta Jeans-son’s Foundations, Tore Nilsson’s Foundation for Medical Research, Magn. Bergvall’s Fund, Syskonen Svensson’s Fund, Berth von Kant-zow’s Foundation, and the American Cancer Society (Grant CN-158, to R.V.C.).
PY - 2000/10/22
Y1 - 2000/10/22
N2 - Preceding the onset of type 1 diabetes mellitus, pancreatic islets are infiltrated by macrophages secreting interleukin-1β (IL-1β) which induces β-cell apoptosis and exerts inhibitory actions on islet β-cell insulin secretion. IL-1β seems to act chiefly through induction of nitric oxide (NO) synthesis. Hence, IL-1β 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 β-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 Ca2+ influx through voltage-activated Ca2+ channels (by K+-induced depolarization) was monitored in culture after treatment with IL-1β 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-1β or spermine-NONOate, whereas the hormone output by the other secretagogues was not altered by NO. Pretreatment with γ-tocopherol (but not α-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-1β effects. In contrast, inhibiting guanylyl cyclase with ODQ (1H-[1,2,4]oxadiazolo[4,3-α]-quinoxaline-1-one) or blocking low voltage-activated Ca2+ channels with NiCl2 failed to influence the actions of NO. In conclusion, our data show that NO inhibits growth and insulin secretion in RINm5F cells, and that γ-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 Ca2+ channels appear not to mediate the toxicity of NO in these cells. These adverse effects of NO on the β-cell, and the protection by γ-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. (C) 2000 Academic Press.
AB - Preceding the onset of type 1 diabetes mellitus, pancreatic islets are infiltrated by macrophages secreting interleukin-1β (IL-1β) which induces β-cell apoptosis and exerts inhibitory actions on islet β-cell insulin secretion. IL-1β seems to act chiefly through induction of nitric oxide (NO) synthesis. Hence, IL-1β 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 β-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 Ca2+ influx through voltage-activated Ca2+ channels (by K+-induced depolarization) was monitored in culture after treatment with IL-1β 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-1β or spermine-NONOate, whereas the hormone output by the other secretagogues was not altered by NO. Pretreatment with γ-tocopherol (but not α-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-1β effects. In contrast, inhibiting guanylyl cyclase with ODQ (1H-[1,2,4]oxadiazolo[4,3-α]-quinoxaline-1-one) or blocking low voltage-activated Ca2+ channels with NiCl2 failed to influence the actions of NO. In conclusion, our data show that NO inhibits growth and insulin secretion in RINm5F cells, and that γ-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 Ca2+ channels appear not to mediate the toxicity of NO in these cells. These adverse effects of NO on the β-cell, and the protection by γ-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. (C) 2000 Academic Press.
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U2 - 10.1006/bbrc.2000.3650
DO - 10.1006/bbrc.2000.3650
M3 - Article
C2 - 11032727
AN - SCOPUS:0034703623
VL - 277
SP - 334
EP - 340
JO - Biochemical and Biophysical Research Communications
JF - Biochemical and Biophysical Research Communications
SN - 0006-291X
IS - 2
ER -