Interleukin-6 affects insulin secretion and glucose metabolism of rat pancreatic islets in vitro.
Recently it has been postulated that interleukin-1 (IL-1) locally released by infiltrating mononuclear cells may destroy the pancreatic B cells during the development of insulin-dependent diabetes mellitus. Since IL-1 is a potent inducer of interleukin-6 (IL-6) in various cells, it is conceivable that IL-6 is a second mediator of the IL-1 action. In the present study the effects of IL-6 alone or in combination with IL-1 were studied on pancreatic islet function in vitro after tissue culture and compared with the effects observed after exposure to IL-1 only. Rat pancreatic islets were cultured in medium RPMI 1640 + 10% calf serum with or without the addition of human recombinant IL-6 (500-5000 pg/ml) for 48 h. The medium insulin accumulation was increased by 40-50% after culture with 500-2000 pg/ml IL-6, but was similar to the controls at 5000 pg/ml. When islets were cultured for 18 h only, also 5000 pg/ml IL-6 stimulated the medium insulin accumulation. IL-6 did not affect the islet insulin content and the rates of islet (pro)insulin and total protein biosynthesis. It inconsistently decreased the islet DNA content. In short-term experiments after 48-h culture with IL-6, there was a dose-dependent inhibition of the glucose-stimulated insulin release. On the other hand, islets cultured with IL-6 (5000 pg/ml) exhibited an elevated glucose oxidation and oxygen uptake, but a lower ATP content at 16.7 mM glucose and an unaffected glucose utilization and glutamine oxidation compared to the controls. This raises the possibility that IL-6 had induced a condition with an increased energy expenditure, resulting in an enhanced mitochondrial metabolism of glucose. Islets cultured with human recombinant IL-1 beta (25 units/ml) showed a strong inhibition of the insulin accumulation in the culture medium and of glucose-stimulated insulin release and a marked decrease in the islet DNA and insulin content. A combination of IL-1 (25 U/ml) + IL-6 (1000 pg/ml) did not alter the inhibitory action of IL-1 alone. The present findings thus show that IL-6 induces a dissociation between insulin secretion and glucose oxidation in islets in vitro. This has not been observed in islets exposed to IL-1, which suggests that IL-6 does not solely mediate the inhibitory effects of IL-1 on islet function.(ABSTRACT TRUNCATED AT 250 WORDS)
Sandler
S
S
Department of Medical Cell Biology, Uppsala University, Sweden.
Bendtzen
K
K
Eizirik
D L
DL
Welsh
M
M
D000227:Adenine Nucleotides / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D004247:DNA / Q000378:metabolism; D004734:Energy Metabolism; D005947:Glucose / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007375:Interleukin-1 / Q000494:pharmacology; D015850:Interleukin-6 / Q000494:pharmacology*; D007515:Islets of Langerhans / Q000378:metabolism*; D008297:Male; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D011384:Proinsulin / Q000096:biosynthesis; D014176:Protein Biosynthesis; D051381:Rats; D011919:Rats, Inbred Strains; D011994:Recombinant Proteins
D000227:Adenine Nucleotides; D007328:Insulin; D007375:Interleukin-1; D015850:Interleukin-6; D011994:Recombinant Proteins; D000255:Adenosine Triphosphate; D004247:DNA; D011384:Proinsulin; D005947:Glucose