IKKβ inhibition prevents fat-induced beta cell dysfunction in vitro and in vivo in rodents.

Abstract

We have previously shown that oxidative stress plays a causal role in beta cell dysfunction induced by fat. Here, we address whether the proinflammatory kinase inhibitor of (nuclear factor) κB kinase β (IKKβ), which is activated by oxidative stress, is also implicated. Fat (oleate or olive oil) was infused intravenously in Wistar rats for 48h with or without the IKKβ inhibitor salicylate. Thereafter, beta cell function was evaluated in vivo using hyperglycaemic clamps or ex vivo in islets isolated from fat-treated rats. We also exposed rat islets to oleate in culture, with or without salicylate and 4(2'-aminoethyl)amino-1,8-dimethylimidazo(1,2-a)quinoxaline; BMS-345541 (BMS, another inhibitor of IKKβ) and evaluated beta cell function in vitro. Furthermore, oleate was infused in mice treated with BMS and in beta cell-specific Ikkb-null mice. 48h infusion of fat impaired beta-cell function in vivo, assessed using the disposition index (DI), in rats (saline: 1.41±0.13; oleate: 0.95±0.11; olive oil [OLO]: 0.87±0.15; p<0.01 for both fats vs saline) and in mice (saline: 2.51±0.39; oleate: 1.20±0.19; p<0.01 vs saline) and ex vivo (i.e., insulin secretion, units are pmol insulin islet-1h-1) in rat islets (saline: 1.51±0.13; oleate: 1.03±0.10; OLO: 0.91±0.13; p<0.001 for both fats vs saline) and the dysfunction was prevented by co-infusion of salicylate in rats (oleate+salicylate: 1.30±0.09; OLO+salicylate: 1.33±0.23) or BMS in mice (oleate+BMS: 2.25±0.42) in vivo and by salicylate in rat islets ex vivo (oleate+salicylate: 1.74±0.31; OLO+salicylate: 1.54±0.29). In cultured islets, 48h exposure to oleate impaired beta-cell function ([in pmol insulin islet-1h-1] control: 0.66±0.12; oleate: 0.23±0.03; p<0.01 vs saline), an effect prevented by both inhibitors (oleate+salicylate: 0.98±0.08; oleate+BMS: 0.50±0.02). Genetic inhibition of IKKβ also prevented fat-induced beta-cell dysfunction ex vivo ([in pmol insulin islet-1h-1] control saline: 0.16±0.02; control oleate: 0.10±0.02; knockout oleate: 0.17±0.04; p<0.05 control saline vs. control oleate) and in vivo (DI: control saline: 3.86±0.40; control oleate: 1.95±0.29; knockout oleate: 2.96±0.24; p<0.01 control saline vs control oleate). Our results demonstrate a causal role for IKKβ in fat-induced beta cell dysfunction in vitro, ex vivo and in vivo.