Inhibition of 5‐lipoxygenase induces cell growth arrest and apoptosis in rat Kupffer cells: implications for liver fibrosis

Abstract

The existence of an increased number of Kupffer cells is recognized as critical in the initiation of the inflammatory cascade leading to liver fibrosis. Because 5-lipoxygenase (5-LO) is a key regulator of cell growth and survival, in the current investigation we assessed whether inhibition of the 5-LO pathway would reduce the excessive number of Kupffer cells and attenuate inflammation and fibrosis in experimental liver disease. Kupffer cells were the only liver cell type endowed with a metabolically active 5-LO pathway (i.e., expressed mRNAs for 5-LO, 5-LO-activating protein [FLAP], and leukotriene [LT] C4 synthase and generated LTB4 and cysteinyl-LTs). Both the selective 5-LO inhibitor AA861 and the FLAP inhibitor BAY-X-1005 markedly reduced the number of Kupffer cells in culture. The antiproliferative properties of AA861 and BAY-X-1005 were associated with the occurrence of condensed nuclei, fragmented DNA, and changes in DNA content and cell cycle frequency distribution consistent with an apoptotic process. In vivo, in carbon tetrachloride-treated rats, BAY-X-1005 had a significant antifibrotic effect and reduced liver damage and the hepatic content of hydroxyproline. Together, these findings indicate a novel mechanism by which inactivation of the 5-LO pathway could disrupt the sequence of events leading to liver inflammation and fibrosis.

Regulatory effects of arachidonate 5-lipoxygenase on hepatic microsomal TG transfer protein activity and VLDL-triglyceride and apoB secretion in obese mice

“…3), suggesting a lack of effect of these compounds in tissues carrying low 5-LO activity. This finding is consistent with previous studies showing no effects of inhibitors of the 5-LO pathway in lean control animals (16,22,23).…”

“…7). The finding that 5-LO inhibition exerts antisteatotic effects in a murine model of obesity-related fatty liver disease adds more weight to the evidence obtained in previous studies demonstrating a protective effect of 5-LO inhibition against liver inflammation and fibrosis (16,22,23). Fig.…”

“…The presence of a metabolically active 5-LO pathway in the liver has been ascribed to Kupffer cells, and these macrophages are the only hepatic cell type endowed with a complete enzymatic machinery for the biosynthesis of 5-LO products (22,23,42). On the other hand, many of the known biological effects of 5-LO products are mediated through interaction with specific G-protein coupled receptors (33).…”

“…Liver sections of about 40 mg were incubated with 0.5 ml of Ringer buffer containing arachidonic acid (50 mM) (Cayman Chemical, Ann Arbor, MI) and ionophore A23187 (5mM) (Sigma) for 15 min at 37°C in a 24-well plate. At the end of the incubation period, supernatants were collected, centrifuged for 5 min at 3000 rpm at 4°C, and frozen at 280°C until the determination of 5-LO products by enzyme immunoassay (22,23). 5-LO activity was calculated as the sum of LTB 4 and cysteinyl-LTs produced per time unit and expressed as ng/min.…”

“…5-LO activity was calculated as the sum of LTB 4 and cysteinyl-LTs produced per time unit and expressed as ng/min. The accumulation of LTB 4 and cysteinyl-LTs in the liver of wildtype mice and ob/ob mice was determined in samples of about 0.2-0.4 g that were individually homogenized with a Ultra-Turrax T25 (Ika, Werke Staufen, Germany) in 2 ml of cold DPBS 21 and extracted with Sep Pak C 18 columns, prior to enzyme immunoassay analysis (22,23).…”