Characteristics of sinusoidal uptake and biliary excretion of cysteinyl leukotrienes in perfused rat liver

Abstract

In single-pass perfused rat liver, the sinusoidal uptake ofinfused 3H-labelled leukotriene (LT) C4 (10 nmol . 1-') was inhibited by sulfobromophthalein. Inhibition was half-maximal at sulfobromophthalein concentrations of approximately 1.2 pmol . 1-' in the influent perfusate and leukotriene uptake was inhibited by maximally 34%.Sulfobromophthalein (20 pmol . 1-I) also decreased the uptake of infused [3H]LTE4 (10 nmol . I-') by 31%.Indocyanine green (10 pmol . 1-') inhibited the sinusoidal [3H]LTC4 uptake by 19%.Replacement of sodium in the perfusion medium by choline decreased the uptake of infused [3H]LTC4(10 nmol . 1-') by 56%, but was without effect on the uptake of sulfobromophthalein.The canalicular excretion of LTC4, LTD4 and N-acetyl-LTE, was inhibited by sulfobromophthalein. In contrast, the proportion of polar w-oxidation metabolites recovered in bile following the infusion of [3H]LTC4 was increased. Taurocholate, which had no effect on the sinusoidal leukotriene uptake, increased bile flow and also the biliary elimination of the radioactivity taken up. With increasing taurocholate additions, the amount of LTD, recovered in bile increased at the expense of LTC4.Following the infusion of [3H]LTD4 (10 nmol . 1-I), a major biliary metabolite was LTC4 indicating a reconversion of LTD, to LTC,. In the presence of taurocholate (40 pmol . 1-I), however, this reconversion was completely inhibited.The findings suggest the involvement of different transport systems in the sinusoidal uptake of cysteinyl leukotrienes. LTC4 uptake is not affected by bile acids and has a sodium-dependent and a sodium-independent component, the latter probably being shared with organic dyes. Sulfobromophthalein also interferes with the canalicular transport of LTC4, LTD4 and N-acetyl-LTE4, but not with the excretion of w-oxidized cysteinyl leukotrienes. The data may be relevant for the understanding of hepatic leukotriene processing in conditions like hyperbilirubinemia or cholestasis.The cysteinyl leukotrienes (LT) LTC4, LTD4 and LTE4, potent lipid mediators of inflammation, are effectively eliminated from circulating blood [l]. In a variety of species the liver is the major site of leukotriene uptake [2-51, whereas in ximates both biliary and urinary excretion contribute to the :limination of cysteinyl leukotrienes [6, 71. Hepatic processing of leukotrienes includes extracellular degradation of LTC4 to LTD4 and LTE4 catalyzed by the ectoenzymes y-glutamyltransferase and y-glutamyldipeptidase [S], uptake into the hepatocytes, intracellular metabolism and biliary excretion. In rat livers, LTE4 is intracellularly Nacetylated [9, lo], followed by w-oxidation and subsequent chain shortening by /?-oxidation from the w-carboxyl end [l 1 -131. The biliary compartment most likely also contributes to leukotriene metabolism by interconverting biliary LTC4 and LTD4 due to the high activity of y-glutamyltransferase in the canalicular and bile duct membranes ~4 1 .

Leukotriene uptake by hepatocytes and hepatoma cells

“…LTC4 uptake by the isolated perfused rat liver was decreased in the absence of sodium ions [19]. However, a sodium dependence of the cysteinyl leukotriene or of LTB4 uptake was not detected in our experiments with isolated rat hepatocytes.…”

Identification of Glutathione as a Driving Force and Leukotriene C4 as a Substrate for oatp1, the Hepatic Sinusoidal Organic Solute Transporter

“…The cysteinyl leukotrienes are potent mediators of inflammatory responses (15), and the liver is the major site of their removal from the blood (15-18). The mechanism for their hepatic uptake is unknown, although evidence from isolated hepatocytes and perfused rat liver studies indicate that uptake is mediated by oapt1 (17)(18)(19). LTC 4 uptake into isolated rat hepatocytes and plasma membrane vesicles is independent of the Na ϩ gradient, is inhibited by substrates of oatp1, and exhibits an apparent K m of 0.20 M (19).…”

Molecular Identification of a Rat Novel Organic Anion Transporter moat1, Which Transports Prostaglandin D2, Leukotriene C4, and Taurocholate

“…However, precise characterization is unclear because the oatp1-mediated leukotriene C 4 uptake reported was not saturated at their indicated value (38). Leukotrienes are the potent lipid mediator of inflammation and are effectively eliminated from the circulation through the biliary and urinary pathway (39,40). The expression of moat1 mRNAs in such organs may suggest its role in eliminating inflammatory leukotrienes.…”