Role of hepatocytes in direct clearance of lipopolysaccharide in rats

Background & Aims: The liver is the clearance organ for lipopolysaccharide (LPS). The aim of this study was to investigate the biliary excretion of LPS using fluorescein isothiocyanate (FITC)-labeled LPS. Methods: After FITC-LPS was injected intravenously into rats, the cellular localization of fluorescence in the liver was examined and the biliary excretion of fluorescence was measured. The effects of gadolinium chloride, a blocker of Kupffer cells, and colchicine, an inhibitor of microtubules, on the biliary excretion of fluorescence was investigated, and bile was analyzed using high-performance liquid chromatography. Results: Laser scanning confocal microscopy showed that fluorescence was taken up by hepatocytes 5 minutes after injection of FITC-LPS into the portal vein. When FITC-LPS was injected into the portal vein, fluorescence was rapidly secreted into bile, peaking at 20 minutes, and 25.1% of the injected dose appeared in bile within 60 minutes. When the same dose of FITC-LPS was injected into the tail vein, 15.8% appeared in bile within 60 minutes. Chromatography showed that FITC-LPS was excreted into bile in an unchanged form over a period of 20 minutes after injection. Colchicine significantly reduced the biliary excretion of fluorescence, but gadolinium chloride had no effect. Conclusions: LPS was directly and effectively processed by hepatocytes and secreted into the bile canalicular system via a microtubule-dependent vesicular pathway.