The Role of Cytochrome P450 Epoxygenase Enzymes in Renal Injury and Inflammation with Salt Sensitive Hypertension

Abstract

Impaired cytochrome p450 epoxygenase enzyme (Cyp2c) regulation with salt sensitive hypertension may contribute to renal damage. Firstly, we hypothesized that both renal injury as well as Cyp2c regulation by salt are improved in interleukin-6 knockout (IL6-/-) hypertensive mice fed a high salt diet. Wild type (WT) and IL-6 -/- mice were given a high salt (4%) diet and implanted with osmotic pumps to deliver angiotensin for 14 days. Systolic blood pressure increased to a greater extent in angiotensin high salt hypertension (ANG/HS) as compared to angiotensin hypertension alone but did not differ between WT and IL6-/- groups. Albuminuria increased significantly with ANG/HS WT (5113±1050 μg/day)) and was attenuated in the ANG/HS IL6-/- group (1306±385 μg/day). Urinary monocyte chemottractant protein 1 (MCP-1) also increased significantly with ANG/HS WT (36±5 pg/day) and was significantly less in the ANG/HS IL6-/- mice (11±4 pg/day). Renal Cyp2c protein expression significantly decreased with ANG/HS WT as compared to high salt alone; however, Cyp2c expression remained unchanged ANG/HS IL6-/- group. Soluble epoxide hydrolase (sEH) protein expression significantly increased in WT ANG/HS and was significantly less in the ANG/HS IL6-/- group. 2 Secondly, we hypothesized that targeted disruption of the sEH gene (Ephx2 -/-) prevents both renal inflammation and injury in mice treated with deoxycorticosterone acetate (DOCA) and NaCl. Mean arterial blood pressure increased significantly in the DOCA-salt groups from baseline (145±2 vs 109±1 in WT and 129±3 vs 107±1 in Ephx2-/-, p<0.05). Ephx2- /- DOCA-salt mice demonstrated a lower mean arterial pressure as compared to WT DOCA-salt (p<0.05). To determine the renal inflammatory status, urinary MCP-1 excretion and renal macrophage infiltration were examined. Following 21 days of treatment, WT DOCA-salt urinary MCP-1 excretion increased from control (9±4 vs 504±91 pg/day, respectively, p<0.05) which was attenuated in the Ephx2-/-DOCA-salt group (285±77 pg/day, p<0.05). Macrophage infiltration within the kidney was examined by histology using ED-1 staining. Ephx2-/- DOCA-salt mice demonstrated reduced macrophage infiltration compared to WT DOCAsalt (20±5 vs 34±2 positive cells per mm2, respectively, p<0.05). Assessment of renal injury was examined with microalbuminuria and nephrin immunofluorescence. Albuminuria increased in WT DOCA-salt compared to control (18±1 vs 235±48 μg/day respectively, p<0.05) and was blunted in the Ephx2-/- DOCA-salt group (116±23 μg/day, p<0.05). Glomerular nephrin expression measured by immunofluorescence was inversely related to albuminuria. Nephrin immunofluorescence was greater in the Ephx2-/- DOCA-salt group compared to WT DOCA-salt (1.72±0.14 vs 1.18±0.03 RFU respectively, p<0.05). 3 These data suggest that upregulation of Cyp450 epoxygenase enzymes and prevention of epoxyeicosatrienoic acids (EET) degradation may abrogate renal injury associated with salt sensitive hypertension and may provide possible therapeutic benefit to patients with end stage renal disease.