The role of nitric oxide in IL-1 beta-mediated dysfunction of rodent islets of Langerhans. Implications for the function of intrahepatic islet grafts.

Products of inflammation, such as interleukin-1 beta (IL-1 beta) and nitric oxide (NO), may impair early function of pancreatic islet grafts. In in vitro studies, freshly isolated rat islets of Langerhans cultured for 24 hr (10 islets/well) in the presence of 20 IU/ml of IL-1 beta released 57% less insulin (mean +/- S.E. of 151 +/- 61 microU) on the average than control (385 +/- 89 microU) cultures (n = 9, P = 0.08). Nitrite levels in the medium (indirect measure of NO) after islets were cultured for a 24-hr period were nearly 3-fold greater in IL-1 beta-exposed islets than control islet cultures (5.8 +/- 1.0 microM vs. 2.2 +/- 0.3 microM, P = 0.03). Production of nitrite by islet cells in the presence of IL-1 beta was inhibited in cultures also containing 2 mM L-NG-monomethyl-Arginine (L-NMMA) (3.4 +/- 0.4 microM, n = 9, P = 0.09 vs. control). When islets were maintained for 1 hr in 30 mg/dl glucose followed by 300 mg/dl for 1 hr, insulin release (stimulated) increased 6-fold (from 7 +/- 2 to 45 +/- 11 microU) in control cultures but only 3-fold (from 4 +/- 2 to 12 +/- 4 microU) in IL-1 beta-exposed cultures (n = 9, P = .01). Addition of 2 mM L-NMMA to islet cultures in the presence of IL-1 beta (20 IU/ml) (n = 9) restored insulin release to normal (from 6 +/- 2 to 38 +/- 9 microU, P > or = 0.6), suggesting that NO mediates the inhibitory effect of IL-1 beta on beta-cell function. In in vivo studies, rats with streptozotocin-induced diabetes (blood glucose > 400 mg/dl) received minimal (750 hand-picked islets) intraportal beta cell mass isografts with (n = 5) or without (n = 9) treatment with 100 mg/7 days of L-NMMA from 3 days before transplantation to 4 days after transplantation (POD -3 to +4). L-NMMA-treated rats became euglycemic (glucose < 200 mg/dl) earlier than nontreated rats (mean +/- SD of 6.4 +/- 2.5 vs. 16.7 +/- 4.7 days posttransplant, P = 0.001). These findings support the hypothesis that NO is a mediator of beta cell dysfunction after intraportal transplantation of freshly isolated islets of Langerhans.