Cobalt-protoporphyrin treatment renders islets tolerant to interleukin-1 beta suppression

This study examined whether treating donor mice with a single dose of cobalt protoporphyrin (CoPP) induced heme oxygenase-1 (HO-1) and protected islet cells from interleukin-1 beta (IL-1β) suppression. Islets were isolated from mice receiving a single dose of either CoPP (20 mg/kg of body weight, CoPP islets) or isotonic NaCl solution vehicle (control islets), 24 hours before isolation. Glucose-stimulated insulin secretion (GSIS) and insulin content (IC) of the islets were determined following incubation in the presence versus absence of murine IL-1β for 21 or 65 hours. The HO-1 protein level of CoPP-induced islets, as determined by an enzyme immunoassay, was significantly higher than that of control islets at 12 hours (P < .01) and 30 hours (P < .05), and returned to basal levels at 56 hours (P = NS). Following a 21-hour incubation with IL-1β, CoPP islets secreted significantly more insulin upon glucose stimulation and preserved significantly more IC than control islets. After 65-hour incubation with IL-1β, CoPP islets secreted significantly less insulin upon glucose stimulation than control islets and preserved significantly less IC compared to islets incubated without IL-1β. In conclusion, treatment with cobalt-protoporphyrin to induce heme oxygenase-1 protects islets against the suppressive effects of IL-1β.