Altered leukotriene B4 metabolism in CYP4F18-deficient mice does not impact inflammation following renal ischemia

Abstract

Inflammatory responses to infection and injury must be restrained and negatively regulated to minimize damage to host tissue. One proposed mechanism involves enzymatic inactivation of the pro-inflammatory mediator leukotriene B4, but it is difficult to dissect the roles of various metabolic enzymes and pathways. A primary candidate for a regulatory pathway is omega oxidation of leukotriene B4 in neutrophils, presumptively by CYP4F3A in humans and CYP4F18 in mice. This pathway generates ω, ω-1, and ω-2 hydroxylated products of leukotriene B4, depending on species. We created mouse models targeting exons 8 and 9 of the Cyp4f18 allele that allows both conventional and conditional knockout of Cyp4f18. Neutrophils from wild-type mice convert leukotriene B4 to 19-hydroxy leukotriene B4, and to a lesser extent 18-hydroxy leukotriene B4, whereas these products were not detected in neutrophils from conventional Cyp4f18 knockouts. A mouse model of renal ischemia-reperfusion injury was used to investigate the consequences of loss of CYP4F18 in vivo. There were no significant changes in infiltration of neutrophils and other leukocytes into kidney tissue as determined by flow cytometry and immunohistochemistry, or renal injury as assessed by histological scoring and measurement of blood urea nitrogen. It is concluded that CYP4F18 is necessary for omega oxidation of leukotriene B4 in neutrophils, and is not compensated by other CYP enzymes, but loss of this metabolic pathway is not sufficient to impact inflammation and injury following renal ischemia-reperfusion in mice.

20-Hydroxy- and 20-carboxy-leukotriene (LT) B4 downregulate LTB4-mediated responses of human neutrophils and eosinophils

“…In that regard, we provide significant evidence that LTB 4 metabolites from the CYP4F3A pathway impair LTB 4 ‐mediated functions, while having no impact on BLT 1 ‐independant functions. Of note, the deletion of CYP4F18, the mouse ortholog of CYP4F3A, did not affect neutrophil recruitment in a model of ischemia‐reperfusion injury while it increased the C5a‐induced neutrophil recruitment . However, CYP4F18 does not metabolize LTB 4 into 20‐OH‐LTB 4 but into 19‐OH‐LTB 4 , and 18‐OH‐LTB 4 .…”

Role of Cytochrome P450s in Inflammation

“…In addition, mouse neutrophils have an alternative pathway of LTB 4 metabolism that involves a 12-hydroxydehydrogenase. Knockout of Cyp4f18 does not impact inflammation in a mouse model of renal ischemia-reperfusion (Winslow et al, 2014), although knockout of the genes for LTB 4 synthesis does have observable effects in this model (Patel et al, 2004). It would appear that mice have redundant pathways of LTB 4 inactivation in neutrophils, and it is possible that Cyp4f18 has an alternative function in these cells.…”

“…It has lower activity for LTB 4 and higher activity for arachidonic acid, compared to CYP4F3A. The mouse homologue of CYP4F3A was identified as Cyp4f18 (Christmas et al, 2006), and knockout of Cyp4f18 abolishes LTB 4 hydroxylase activity in mouse neutrophils (Winslow et al, 2014). However, there are significant differences between mice and humans.…”

Negative Regulation of TGFβ Signaling by Stem Cell Antigen-1 Protects against Ischemic Acute Kidney Injury

“…Tissue injury was scored on a 1–6 scale by adding parameters for severity and extent of tubular injury, as previously published [ 25 ]. The scores were assigned as follows.…”