COPPER ADDITION PREVENTS THE INHIBITORY EFFECTS OF INTERLEUKIN-1-BETAON RAT PANCREATIC-ISLETS

Since copper [Cu(II)] is a necessary cofactor for both intra-mitochond rial enzymes involved in energy production and hydroxyl scavenger enzy mes, two hypothesised mechanisms for action of interleukin-I beta (IL- 1 beta), we studied whether Cu(II) addition could prevent the inhibito ry effect of IL-1 beta on insulin release and glucose oxidation in rat pancreatic islets. Islets were incubated with or without 50 U/ml IL-1 beta, in the presence or absence of various concentrations of Cu(II)- GHL (Cu(II) complexed with glycyl-L-histidyl-L-lysine, a tripeptide kn own to enhance copper uptake into cultured cells). CuSO4 (1-1000 ng/ml ) was used as a control for Cu(II) effect when present as an inorganic salt. At the end of the incubation period, insulin secretion was eval uated in the presence of either 2.8 mmol/l (basal insulin secretion) o r 16.7 mmol/l glucose (glucose-induced release). In control islets bas al insulin secretion was 92.0 +/- 11.4 pg.islet(-1).h(-1) (mean +/- SE M, n = 7) and glucose-induced release was 2824.0 +/- 249.0 pg islet(-1 ).h(-1). In islets pre-exposed to 50 U/ml IL-1 beta, basal insulin rel ease was not significantly affected but glucose-induced insulin releas e was greatly reduced (841.2 +/- 76.9, M = 7, p < 0.005). In islets in cubated with IL-1 beta and Cu-GHL (0.4 mu mol/l, maximal effect) basal secretion was 119.0 +/- 13.1 pg.islet(-1).h(-1) and glucose-induced r elease was 2797.2 +/- 242.2, (n = 7, p < 0.01 in respect to islets exp osed to IL-1 beta alone). In contrast to data obtained with Cu(II)-GHL , increasing concentrations of CuSO4 (up to 10 mu mol/l) did not influ ence the inhibitory effect of IL-1 beta on glucose-stimulated insulin release. Glucose oxidation (in the presence of 16.7 mmol/l glucose) wa s 31.5 +/- 2.4 pmol.islet(-1).90min(-1) in control islets and 7.0 +/- 0.9 (p < 0.01) in IL-1 beta-exposed islets. In islets exposed to IL-1 beta and Cu-GHL glucose oxidation was similar to control islets (31.9 +/- 1.9). In contrast, Cu-GHL did not prevent the IL-1 beta-induced in crease in nitric oxide production. Nitrite levels were 5 +/- 1.7, 26 /- 5 and to 29 +/- 4 pmol.islet(-1) 48 h(-1) (mean +/- SEM, n = 5) in the culture medium from control, IL-1 beta and IL-1 beta + Cu-GHL expo sed islets, respectively. These data indicate that the Cu(II) complexe d to GHL is able to prevent the inhibitory effects of IL-1 beta on ins ulin secretion and glucose oxidation, but not on NO production. The me chanism of action of Cu-GHL is still unclear, but it might restore the activity of the enzymatic systems inhibited by IL-1 beta.