Short exposure of rat pancreatic islets to interleukin-1 beta induces a sustained but reversible impairment in beta-cell function: influence of protease activation, gene transcription, and protein synthesis

Abstract

In an attempt to gain further knowledge about the mechanism of action of recombinant interleukin-1 beta (rIL-1 beta) on rat pancreatic beta-cells, we studied the effects of short term rIL-1 beta exposure (50 U/ml for 1 h) on islet function over the next 72 h. There was an initial increase in glucose-induced insulin release, followed by a decrease in islet function, reaching a nadir (values of insulin release about 20% of those observed in control islets) 10-12 h after treatment with the cytokine. Thereafter, the islets recovered their function, reaching levels of insulin secretion similar to the control values after 72 h. Short term exposure to rIL-1 beta did not induce a decrease in either islet DNA or islet insulin content. Using this experimental approach, we tested whether 1-h incubation of islets in the presence of various agents plus rIL-1 beta could counteract the inhibitory effects of the cytokine 10-12 h later. Both actinomycin-D (5 micrograms/ml), an inhibitor of DNA transcription, and N alpha-p-tosyl-L-lysine chloromethyl ketone (0.1 mM), a protease inhibitor, could protect the islets. There was also a weak protection by dimethyl urea (61 mM), a free radical scavenger, but no protection by cycloheximide (10 micrograms/ml), an inhibitor of protein synthesis, or amiloride (12.5 microM), a blocker of Na+/H+ exchange. In a subsequent series of experiments, the islets were exposed for 6 h to different test agents after the initial 1-h exposure to rIL-1 beta. In this context, there was a clear protection by cycloheximide and actinomycin-D and a lesser protection by N alpha-p-tosyl-L-lysine chloromethyl ketone. These data suggest that early steps of the actions of rIL-1 beta on rat pancreatic islets are mediated by protease activation and gene transcription, followed by protein synthesis. The identity of the protein(s) remains to be clarified.