Increased Epoxyeicosatrienoic Acid Formation in the Rat Kidney during Liver Cirrhosis

Abstract

Abstract. Vascular complications during liver cirrhosis are often severe, particularly in the kidney. These complications are the result of complex and poorly understood interactions between the injured liver and other organs such as the lungs, heart, and kidney. The purpose of this study was to investigate the alterations to renal hemodynamics during cirrhosis, focusing on the actions of epoxyeicosatrienoic acids (EET), known to be potent regulators of renal hemodynamics. Cirrhosis was induced in rats by common bile duct ligation (CBDL), and they were compared with sham rats. Experiments were conducted 4 wk after either the sham or CBDL surgery. Vasoreactivity was assessed in isolated perfused kidneys. cPLA 2 expression and cytochrome P450 (CYP450) expression were measured using Western blot. cPLA 2 enzymatic activity was measured by radioenzymatic assay. EET production was measured using rpHPLC analysis. The major findings were that kidneys from CBDL rats had significantly greater acetylcholine-induced vasodilation that was partially blocked by nitric oxide (NO) and prostaglandin inhibition and fully blocked by the combined inhibition of NO, prostaglandins, and CYP450 metabolites. Expression and activity of cPLA 2 in CBDL kidneys was increased, providing arachidonic acid substrate to the CYP450 enzymes. Finally, expression and activity of CYP450 enzymes was elevated in CBDL kidneys, resulting in significantly greater production of the vasodilating 11,12-EET and 14,15-EET. While it is well documented that renal vasoconstriction leading to impaired renal function occurs during cirrhosis, our data clearly demonstrate that endogenous production of EET is increased in cirrhotic kidneys. This may be a homeostatic response to preserve renal perfusion.Endothelium-dependent vasodilation is an important regulatory mechanism in the kidney. Many studies indicate that peripheral vasodilation of splanchnic organs may be the leading factor causing the renal dysfunction of cirrhosis (for review, see reference 1). Endothelial cells produce a wide array of biologic active agents that regulate vascular tone. These agents include NO, prostaglandin, and an unidentified substance that hyperpolarizes vascular smooth muscle called endothelium-derived hyperpolarizing factor (EDHF). The biologic actions of epoxyeicosatrienoic acids (EET) make them a strong candidate for being EDHF, because EET dilate blood vessels by activating vascular smooth muscle calcium-activated K ϩ (K Ca ) channels resulting in membrane hyperpolarization. EET are produced from arachidonic acid cleaved from membrane-associated phospholipid pools by phospholipase-A2 (cPLA 2 ) (2-4) and are further metabolized by specific cytochrome P450 (CYP450) enzymes (5-9). It is known that CYP450 2C isoforms are responsible for the majority of EET biosynthesis in the rat kidney, and CYP 2C11, 2C23, and 2C24 are the predominant 2C isoforms expressed in the male rat kidney (10 -12). However, the vascular sites of action responsible for the CYP component in cirrhotic rat kidney a...

The effect of albumin administration on renal dysfunction after experimental surgical obstructive jaundice in male rats

“…The oxidative stress and generation of reactive oxygen species (ROS) secondary to cholestasis could give rise to the involvement of remote organs other than the liver, such as the kidney with alterations in its function [4]; antioxidant administration improves these alterations [5]. Experimentally, the in vitro addition of excess bile acids or bilirubin to a mixture of reactive enzymes inhibited mitochondrial oxidative enzymes.…”

Human CYP4F3s are the main catalysts in the oxidation of fatty acid epoxides

“…EETs are products of cytochrome P450 epoxygenase, mainly CYP2C8 in human liver (20,21); they are endowed with important vasodilatating and antiinflammatory properties and serve as components of cell signaling cascades (22)(23)(24)(25)(26). EETs were shown to accumulate in alcoholic liver disease in rat (27) and increased in the rat kidney during liver cirrhosis (28). Cytochrome P450 monooxygenases are involved in both the epoxidation and hydroxylation of fatty acids (FAs).…”

Effects of chronic L-NAME on nitrotyrosine expression and renal vascular reactivity in rats with chronic bile-duct ligation

“…As the disease advances, there is progressive sodium retention and eventual development of ascites, hepatorenal syndrome and death [5,6,28]. The time course of these events is variable depending on several factors, including the strain of rats, gender and even the laboratory [15,28,30,[32][33][34]. The animals used in the present study, in the 4th week of BDL, had typical signs of cirrhosis, such as decreased growth, jaundice, coluria and haematocrit.…”

“…Taken together with our present study, these results suggest that during BDL the NO excess in the presence of elevated oxidative stress damages renal vascular and excretory function. Although different substances may potentially alter vascular reactivity in the kidney [15,41], in cirrhosis elevated levels of NO and O 2 − can greatly favour the formation of peroxynitrite. Peroxynitrite may alter the vasoactive responses to several substances in several ways.…”

“…Previous studies have also suggested that an increased generation of ROS (reactive oxygen species) participates in the systemic and renal functional alterations of experimental cirrhosis [13][14][15][16][17][18], and that antioxidant administration, which quenches O 2 − (superoxide anion), improves these alterations [19][20][21][22][23]. During cirrhosis, increased levels of NO and O 2 − could easily react to form peroxynitrite (ONOO − ), a RNOS (reactive nitroxy species).…”