5-lipoxygenase (5-LOX) inhibition by zileuton reduces the amount of neutrophils that reaches the liver during liver regeneration after partial hepatectomy (PH)

Abstract

5-LOX is the first and main enzyme that participates in the synthesis of leukotrienes. LTB4 is a leukotriene involved in inflammation and also is a potent chemoattractant of neutrophils. Previous studies from our lab showed that treatment with a 5-LOX inhibitor produces a decrease in hepatic LTB4 content and a reduction in liver proliferation after 70% PH in rats, indicating that LTB4 is necessary for liver regeneration. Additionally, it was reported that liver regeneration was impaired after neutrophils depletion. Objective: To study if the reduction in hepatic LTB4 reduces the levels of polymorphonuclear leukocytes (PMNs) post-PH which could be necessary to trigger liver regeneration at early times after PH. Methods and results: Adult male Wistar rats were subjected to sham surgery or PH (70 % liver removal). Two hours before surgery, animals received a specific inhibitor of 5-LOX, zileuton (Zi) 40 mg/kg BW or the drug vehicle. Liver samples were obtained at 3 and 5h post-PH. We studied by immunohistochemistry and qRT-PCR the myeloperoxidase (MPO) levels (marker of neutrophils) and we found a significant increment in the levels of MPO-positive cells in the hepatectomized animals treated with vehicle (control PH) respect to the sham (+300%*). On the other hand, the animals that received the 5-LOX inhibitor showed a decrease in MPO-positive cells (-62,5%# 5h post-PH) and MPO mRNA levels (-38,48%# 3h post-PH) respect to control PH rats. Also, by immunofluorescence and confocal microscopy we analyzed a specific marker of rat neutrophil leukocytes (using anti-neutrophil antibody LS C348005, LSBio) and we observed a significant reduction in the number of positive cells in PH rats treated with Zi compared with control PH rats at 3h post-PH (-36,6%#) (*p<0,05 vs. sham, # p<0,05 vs. control PH). Conclusion: Inhibition of 5-LOX by zileuton reduces the levels of LTB4 that attract PMNs cells into the liver. This phenomenon can mediate the inhibitory effect of 5-LOX inhibition on liver regeneration post PH.