S-methyl-L-thiocitrulline counteracts interleukin 1 beta induced suppression of pancreatic islet function in vitro, but does not protect against multiple low-dose streptozotocin-induced diabetes in vivo.
Nitric oxide, induced by pancreatic islet exposure to cytokines, has been implicated in beta-cell destruction in insulin-dependent diabetes mellitus. In this context it could be worthwhile to characterize inhibitors of the nitric oxide generating enzyme. For this purpose rat pancreatic islets were cultured for 48 h in medium supplemented without or with 10, 100 or 500 microM of S-methyl-L-thiocitrulline, in the absence or presence of 25 U/ml of interleukin 1 beta (IL-1 beta). S-methyl-L-thiocitrulline alone did not affect the islet glucose oxidation rate, but all concentrations of S-methyl-L-thiocitrulline prevented IL-1 beta induced suppression of the islet glucose metabolism. Moreover, S-methyl-L-thiocitrulline (100 microM) completely protected against cytokine mediated inhibition of medium insulin accumulation, glucose-stimulated insulin release and (pro)insulin biosynthesis. IL-1 beta caused a more than 10-fold increase in medium nitrite production, an indication of nitric oxide production, which was blocked by S-methyl-L-thiocitrulline. Acutely in the absence of IL-1 beta, islet glucose-stimulated insulin release was enhanced by S-methyl-L-thiocitrulline (100 microM). The efficacy of S-methyl-L-thiocitrulline, NG-monomethyl-L-arginine and aminoguanidine in counteracting IL-1 beta induced nitrite formation was also compared. When estimating the half-maximal inhibitory concentration for this effect, it was approximately 10 microM for S-methyl-L-thiocitrulline and about 1000 microM for NG-monomethyl-L-arginine and aminoguanidine. Next, the efficacy of S-methyl-L-thiocitrulline was tested in an animal model of insulin-dependent diabetes mellitus i.e. multiple low-dose streptozotocin-induced diabetes in male C57BL/Ks mice (40 mg/kg body weight/day for 5 days). It was found that all groups of mice treated with streptozotocin injections gradually developed hyperglycaemia. Administration of S-methyl-L-thiocitrulline (15 mg/kg body weight/day) either for 6-13 days or for 5-11 days after the first STZ injection could not prevent this effect. Moreover, S-methyl-L-thiocitrulline did not appear to influence the evolution of mononuclear cell infiltration and pancreatic insulitis. Thus the present study shows that S-methyl-L-thiocitrulline can potently block cytokine induced activation of nitric oxide synthase in pancreatic islets, but using the presently adopted administration protocol failed to protect against development of insulin-dependent diabetes mellitus in vivo.
Sternesjö
J
J
Department of Medical Cell Biology, Uppsala University, Sweden.
Welsh
N
N
Sandler
S
S
D000818:Animals; D002478:Cells, Cultured; D002956:Citrulline / Q000031:analogs & derivatives* / Q000494:pharmacology; D003921:Diabetes Mellitus, Experimental / Q000517:prevention & control*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005947:Glucose / Q000378:metabolism; D007328:Insulin / Q000378:metabolism; D007375:Interleukin-1 / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D007515:Islets of Langerhans / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D013311:Streptozocin; D013890:Thiourea / Q000031:analogs & derivatives* / Q000494:pharmacology
D004791:Enzyme Inhibitors; D007328:Insulin; D007375:Interleukin-1; D002956:Citrulline; D013311:Streptozocin; D019001:Nitric Oxide Synthase; D013890:Thiourea; D005947:Glucose; C086717:S-methylthiocitrulline