Kupffer Cell-Mediated Downregulation of Hepatic Transporter Expression in Rat Hepatic Ischemia-Reperfusion

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Abstract
Background. Hepatic ischemia-reperfusion (IR) injury is frequently followed by cholestatic liver disease. Cytokines released by Kupffer cells following hepatic IR injury may subsequently regulate hepatic transporter expression. The purpose of this study was to determine whether hepatic IR injury and the resultant Kupffer cell activation alters hepatic transporter expression. Methods. Rats were subjected to 60 minutes of partial hepatic ischemia followed by 0, 3, 6, 24, or 48 hours of reperfusion. After IR surgery, the following were determined: 1) serum bilirubin and bile acid levels; 2) serum levels of cytokines, such as tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL6; 3) expression of several hepatic transporters; and 4) nuclear protein levels of hepatocyte nuclear factor (HNF)-1α and retinoid X receptor (RXR)-α to investigate whether altered expression of hepatic transporters following IR is associated with decreases in these transcription factors. Results. After reperfusion: 1) serum bilirubin and bile acids increased; 2) levels of all three cytokines increased; 3) mRNA expression of hepatic transporters organic anion transporting polypeptide (Oatp) 1a1, Oatp1a4, Oatp1b2, sodium taurocholate cotransporting polypeptide, multidrug resistance-associated protein (Mdr) 2, and bile salt export pump decreased, whereas Mdr1b expression increased; and 4) nuclear protein levels of HNF1α decreased, whereas RXRα was not altered. Pretreatment with gadolinium chloride to deplete Kupffer cells before IR: 1) blocked the increase in serum bile acids, 2) attenuated TNFα but not IL1β/IL6 levels, 3) inhibited the altered hepatic transporter expression, and 4) blocked the decrease in HNF1α nuclear protein levels. Conclusions. These results suggest that alterations in hepatic transporter expression during IR occur through Kupffer cell-mediated events, possibly involving a decrease in nuclear HNF1α.