A synthetic epoxyeicosatrienoic acid analogue prevents the initiation of ischemic acute kidney injury

AIM

Imbalances in cytochrome P450 (CYP)-dependent eicosanoid formation may play a central role in ischemic acute kidney injury (AKI). We reported previously that inhibition of 20-hydroxyeicosatetraenoic acid (20-HETE) action ameliorated ischemia/reperfusion (I/R)-induced AKI in rats. Now we tested the hypothesis that enhancement of epoxyeicosatrienoic acid (EET) actions may counteract the detrimental effects of 20-HETE and prevent the initiation of AKI.

METHODS

Male Lewis rats underwent right nephrectomy and ischemia was induced by 45 min clamping of the left renal pedicle followed by up to 48 h of reperfusion. Circulating CYP-eicosanoid profiles were compared in patients who underwent cardiac surgery with (n = 21) and without (n = 38) developing postoperative AKI.

RESULTS

Ischemia induced an about eightfold increase of renal 20-HETE levels, whereas free EETs were not accumulated. To compensate for this imbalance, a synthetic 14,15-EET analogue was administered by intrarenal infusion before ischemia. The EET analogue improved renal reoxygenation as monitored by in vivo parametric MRI during the initial 2 h reperfusion phase. The EET analogue improved PI3K- as well as mTORC2-dependent rephosphorylation of Akt, induced inactivation of GSK-3β, reduced the development of tubular apoptosis and attenuated inflammatory cell infiltration. The EET analogue also significantly alleviated the I/R-induced drop in creatinine clearance. Patients developing postoperative AKI featured increased preoperative 20-HETE and 8,9-EET levels.

CONCLUSIONS

Pharmacological interventions targeting the CYP-eicosanoid pathway could offer promising new options for AKI prevention. Individual differences in CYP-eicosanoid formation may contribute to the risk of developing AKI in clinical settings.

Novel signalling mechanisms and targets in renal ischaemia and reperfusion injury

Acute kidney injury (AKI) induced by ischaemia and reperfusion (I/R) injury is a common and severe clinical problem. Vascular dysfunction, immune system activation and tubular epithelial cell injury contribute to functional and structural deterioration. The search for novel therapeutic interventions for I/R-induced AKI is a dynamic area of experimental research. Pharmacological targeting of injury mediators and corresponding intracellular signalling in endothelial cells, inflammatory cells and the injured tubular epithelium could provide new opportunities yet may also pose great translational challenge. Here, we focus on signalling mediators, their receptors and intracellular signalling pathways which bear potential to abrogate cellular processes involved in the pathogenesis of I/R-induced AKI. Sphingosine 1 phosphate (S1P) and its respective receptors, cytochrome P450 (CYP450)-dependent vasoactive eicosanoids, NF-κB- and protein kinase-C (PKC)-related pathways are representatives of such 'druggable' pleiotropic targets. For example, pharmacological agents targeting S1P and PKC isoforms are already in clinical use for treatment for autoimmune diseases and were previously subject of clinical trials in kidney transplantation where I/R-induced AKI occurs as a common complication. We summarize recent in vitro and in vivo experimental studies using pharmacological and genomic targeting and highlight some of the challenges to clinical application of these advances.

High temporal resolution parametric MRI monitoring of the initial ischemia/reperfusion phase in experimental acute kidney injury

Ischemia/reperfusion (I/R) injury, a consequence of kidney hypoperfusion or temporary interruption of blood flow is a common cause of acute kidney injury (AKI). There is an unmet need to better understand the mechanisms operative during the initial phase of ischemic AKI. Non-invasive in vivo parametric magnetic resonance imaging (MRI) may elucidate spatio-temporal pathophysiological changes in the kidney by monitoring the MR relaxation parameters T₂* and T₂, which are known to be sensitive to blood oxygenation. The aim of our study was to establish the technical feasibility of fast continuous T₂*/T₂ mapping throughout renal I/R. MRI was combined with a remotely controlled I/R model and a segmentation model based semi-automated quantitative analysis. This technique enabled the detailed assessment of in vivo changes in all kidney regions during ischemia and early reperfusion. Significant changes in T₂* and T₂ were observed shortly after induction of renal ischemia and during the initial reperfusion phase. Our study demonstrated for the first time that continuous and high temporal resolution parametric MRI is feasible for in-vivo monitoring and characterization of I/R induced AKI in rats. This technique may help in the identification of the timeline of key events responsible for development of renal damage in hypoperfusion-induced AKI.

Abstract 655: Ischemia-induced Epoxyeicosatrienoic Acid Release Protects Female Rats From Acute Kidney Injury

Females are naturally protected against ischemia/reperfusion (I/R)-induced acute kidney injury (AKI) in various clinical and experimental settings. However, the underlying mechanisms are unknown. We hypothesized that female protection may be conferred by enhanced production of cytochrome P450 (CYP)-dependent epoxyeicosatrienoic acids (EETs) that promote vasodilation as well as antiinflammatory and antiapoptotic pathways in the kidney. To test this hypothesis, we first analyzed the renal CYP-eicosanoid profile by liquid chromatography tandem mass spectrometry in male and female Lewis rats. Ischemia was induced through 45 min of left renal vessel clamping after right nephrectomy (n=6-8 per group). In non-ischemic controls, male and female kidneys stored almost identical amounts of EETs as well as 20-hydroxyeicosatetraenoic acid (20-HETE), both predominantly esterified into phospholipids, under basal non-ischemic conditions. 45 min of ischemia induced a massive release of EETs from membrane stores in females but not males. The free renal EET-levels reached 70.2±20.1 in females compared to only 4.6±1.3 ng/g in males. After ischemia, the ratio of free EETs to free 20-HETE was about 1:1 in females and 1:3 in males. Next, we proved the functional importance of EETs in renal protection by pretreating males with a synthetic EET-agonist (12-HUDE) and females with a selective EET-antagonist (14,15-EEZE-mSI). As analyzed two days after reperfusion, the EET-agonist protected males against loss of creatinine clearance (1.03±0.18 vs. 0.26±0.02 ml/min, p<0.01 vs. vehicle, compared to 1.28±0.06 ml/min in sham control). Females were rendered susceptible to I/R-injury by the EET-antagonist (creatinine clearance: 0.25±0.05 vs. 0.67±0.04; p<0.01 vs. vehicle, compared to 0.81±0.04 ml/min in sham control). Changes in inflammatory cell infiltration and tubular apoptosis paralleled these effects on renal function. Our results indicate that female rats are protected against renal I/R-injury by enhanced ischemia-induced EET-release and demonstrate that renal protection can be transferred to males using synthetic EET-agonists.