Endogenous Epoxygenases Are Modulators of Monocyte/Macrophage Activity

Background: Arachidonic acid is metabolized through three major metabolic pathways, the cyclooxygenase, lipoxygenase and CYP450 enzyme systems. Unlike cyclooxygenase and lipoxygenases, the role of CYP450 epoxygenases in monocyte/macrophage-mediated responses is not known.Methodology/Principal Findings: When transfected in vitro, CYP2J2 is an efficient activator of anti-inflammatory pathways through the nuclear receptor peroxisome proliferator-activated receptor (PPAR) alpha. Human monocytes and macrophages contain PPAR alpha and here we show they express the epoxygenases CYP2J2 and CYP2C8. Inhibition of constitutive monocyte epoxygenases using the epoxygenase inhibitor SKF525A induces cyclooxygenase (COX)-2 expression and activity, and the release of TNF alpha, and can be reversed by either add back of the endogenous epoxygenase products and PPAR alpha ligand 11,12-epoxyeicosatrienoic acid (EET) or the addition of the selective synthetic PPAR alpha ligand GW7647. In alternatively activated (IL-4-treated) monocytes, in contrast to classically activated cells, epoxygenase inhibition decreased TNF alpha release. Epoxygenases can be pro-inflammatory via superoxide anion production. The suppression of TNF alpha by SKF525A in the presence of IL-4 was associated with a reduction in superoxide anion generation and reproduced by the superoxide dismutase MnCl2. Similar to these acute activation studies, in monocyte derived macrophages, epoxygenase inhibition elevates M1 macrophage TNF alpha mRNA and further decreases M2 macrophage TNF alpha.Conclusions/Significance: In conclusion, epoxygenase activity represents an important endogenous pathway which limits monocyte activation. Moreover endogenous epoxygenases are immuno-modulators regulating monocyte/macrophage activation depending on the underlying activation state

The Epoxygenases CYP2J2 Activates the Nuclear Receptor PPARα In Vitro and In Vivo

Peroxisome proliferator-activated receptors (PPARs) are a family of three (PPARalpha, -beta/delta, and -gamma) nuclear receptors. In particular, PPARalpha is involved in regulation of fatty acid metabolism, cell growth and inflammation. PPARalpha mediates the cardiac fasting response, increasing fatty acid metabolism, decreasing glucose utilisation, and is the target for the fibrate lipid-lowering class of drugs. However, little is known regarding the endogenous generation of PPAR ligands. CYP2J2 is a lipid metabolising cytochrome P450, which produces anti-inflammatory mediators, and is considered the major epoxygenase in the human heart.Expression of CYP2J2 in vitro results in an activation of PPAR responses with a particular preference for PPARalpha. The CYP2J2 products 8,9- and 11-12-EET also activate PPARalpha. In vitro, PPARalpha activation by its selective ligand induces the PPARalpha target gene pyruvate dehydrogenase kinase (PDK)4 in cardiac tissue. In vivo, in cardiac-specific CYP2J2 transgenic mice, fasting selectively augments the expression of PDK4.Our results establish that CYP2J2 produces PPARalpha ligands in vitro and in vivo, and suggests that lipid metabolising CYPs are prime candidates for the integration of global lipid changes to transcriptional signalling events

The influence of sub-optimal protein nutrition on insulin hypersecretion evoked by high-energy/high-fat feeding in rats

AbstractLow (8%) protein feeding during pregnancy impairs the functional development of the fetal endocrine pancreas. Continued low-protein feeding post-natally decreases pancreatic insulin content and secretion, whereas transfer to standard diet evoked β-cell recuperation. Glucose-stimulated insulin secretion (GSIS) and insulin action were examined in vivo at 28 days after transfer from 8% protein diet to a high-energy/high-fat/standard (20%)-protein diet (HEF diet). HEF feeding dramatically enhanced GSIS after intravenous glucose in control rats, but not in rats previously maintained on the low-protein diet. However, glucose disappearance after intravenous glucose, and glucose production and whole-body glucose disposal during euglycaemic-hyperinsulinaemic clamps were unaffected by prior protein malnutrition. In conclusion, impaired insulin secretion after protein malnutrition is exacerbated by high-energy/high-fat feeding, but this response is not linked to enhanced whole-body insulin resistance