Role of interleukin 1 beta in the regulation of rat intestinal multidrug resistance-associated protein 2 under conditions of experimental endotoxemia.

Multidrug resistance-associated protein 2 (Mrp2), expressed at the brush border membrane (BBM) of the enterocyte, is an ABC transporter with relevant intestinal barrier function. Its toxicological relevance lies in preventing absorption and tissue accumulation of dietary contaminants, drugs, and potentially harmful endogenous metabolites. Expression and activity of intestinal Mrp2 is downregulated in LPS-induced endotoxemia. In addition, confocal microscopy studies demonstrated internalization of the transporter to endocytic vesicles. Since IL-1β plays an important role as early mediator of LPS-inflammatory responses, we evaluated whether IL-1β mediates LPS-induced impairment of Mrp2 function. Two protocols were used: I) In vivo administration of LPS (5 mg/kg b.wt., i.p., single dose) to rats in simultaneous with administration of anti-IL-1β (25 μg/kg b.wt., i.p., 4 doses), followed by studies of Mrp2 expression, localization and activity, 24 h after LPS administration; II) In vitro incubation of isolated intestinal sacs with IL-1β (10 ng/mL) for 30 min, followed by analysis of Mrp2 activity and localization. We found that in vivo immunoneutralization of IL-1β partially prevented the decrease of Mrp2 protein expression and activity as well as its internalization to intracellular domains induced by LPS. Involvement of IL-1β in the alteration of Mrp2 localization and activity was more directly demonstrated in isolated intestinal sacs, as incubation with IL-1β resulted in detection of Mrp2 in intracellular regions of the enterocyte in simultaneous with alteration of transport activity. In conclusion, IL-1β induces early internalization of intestinal Mrp2, which could partially explain loss of expression at the BBM under conditions of experimental endotoxemia. Concomitant impairment of Mrp2-dependent barrier function may have pathophysiological relevance since IL-1β mediates the effect of many local and systemic inflammatory processes.