Expression and regulation of leukotriene-synthesis enzymes in rat liver cells

The liver plays a major role in metabolism and elimination of leukotrienes (LT). It produces cysteinyl leukotrienes (cLT), and cLT have been implicated in hepatocellular toxicity in several models of lipopolysaccharide (LPS)associated liver injury. However, the liver cell types responsible for cLT production are poorly defined, and the expression of the LT-synthesis enzymes, 5-lipoxygenase (5-LO) and LTC₄ synthase (LTC₄- S), in liver cells has never been demonstrated. The aim of the present study was to examine the ability of rat liver cells to produce cLT by determining whether hepatocytes, Kupffer cells, and sinusoidal endothelial cells express mRNA and enzyme activities of the LT-synthesis enzymes and whether expression is altered by LPS. 5-LO mRNA was expressed in whole liver, and expression was enhanced by LPS. Cell fractionation studies demonstrated that expression was present in Kupffer cells and sinusoidal endothelial cells, but not in hepatocytes. LTC₄-S mRNA was detected in whole liver, hepatocytes, and sinusoidal endothelial cells, but not in Kupffer cells. Semiquantitative reverse-transcriptase polymerase chain reaction (RT-PCR) showed that LPS increased LTC₄-S expression in hepatocytes by a factor of 3 (n = 3; P < .03). LTC₄-S enzyme activity in the microsomal fraction of hepatocytes was also increased from 0.52 ± 0.13 to 1.90 ± 0.66 nmol · mg protein^-1·5 min^-1 (n = 6; P < .015) after LPS treatment. These results indicate that hepatocytes do not possess the ability for de novo synthesis of cLT from arachidonic acid, but they may actively participate in cLT production by conjugation of LTA₄ with glutathione to produce LTC₄. LPS enhances LTC₄-S expression in hepatocytes. This intrinsic cLT production may contribute to hepatocellular injury during inflammation.