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 n itric oxide (NO), may impair early function of pancreatic islet grafts . In in vitro studies, freshly isolated rat islets of Langerhans cultu red for 24 hr (10 islets/well) in the presence of 20 IU/ml of IL-IP re leased 57% less insulin (mean +/- S.E. of 151+/-61 mu U) on the averag e than control (385+/-89 mu U) 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 S fold greater in IL-1 beta-exposed islets than control islet cultures (5.8+/-1.0 mu M vs. 2.2+/-0.3 mu M, P=0.03 ). Production of nitrite by islet cells in the presence of IL-1 beta w as inhibited in cultures also containing 2 mM L-NG-monomethyl-Arginine (L-NMMA) (3.4+/-0.4 mu M, 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 mu U) in control cultures but only 3-fold (from 4+/-2 to 12+/-4 mu U) in IL-1 beta-exposed cultures (n=9, P=.01). Addition of 2 mM L-NMMA t o islet cultures in the presence of IL-1 beta (20 IU/ml) (n=9) restore d insulin release to normal (from 6+/-2 to 38+/-9 mu U, P greater than or equal to 0.6), suggesting that NO mediates the inhibitory effect o f IL-1 beta on beta-cell function. In in vuv studies, rats with strept ozotocin-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 t han nontreated rats (mean a SD of 6.4+/-2.5 vs. 16.7+/-4.7 days posttr ansplant, P=0.001). These findings support the hypothesis that NO is a mediator of beta cell dysfunction after intraportal transplantation o f freshly isolated islets of Langerhans.