Cytochrome P450 and Lipoxygenase Metabolites on Renal Function

Arachidonic acid metabolism as a therapeutic target in AKI-to-CKD transition

Arachidonic acid (AA) is a main component of cell membrane lipids. AA is mainly metabolized by three enzymes: cyclooxygenase (COX), lipoxygenase (LOX) and cytochrome P450 (CYP450). Esterified AA is hydrolysed by phospholipase A2 into a free form that is further metabolized by COX, LOX and CYP450 to a wide range of bioactive mediators, including prostaglandins, lipoxins, thromboxanes, leukotrienes, hydroxyeicosatetraenoic acids and epoxyeicosatrienoic acids. Increased mitochondrial oxidative stress is considered to be a central mechanism in the pathophysiology of the kidney. Along with increased oxidative stress, apoptosis, inflammation and tissue fibrosis drive the progressive loss of kidney function, affecting the glomerular filtration barrier and the tubulointerstitium. Recent studies have shown that AA and its active derivative eicosanoids play important roles in the regulation of physiological kidney function and the pathogenesis of kidney disease. These factors are potentially novel biomarkers, especially in the context of their involvement in inflammatory processes and oxidative stress. In this review, we introduce the three main metabolic pathways of AA and discuss the molecular mechanisms by which these pathways affect the progression of acute kidney injury (AKI), diabetic nephropathy (DN) and renal cell carcinoma (RCC). This review may provide new therapeutic targets for the identification of AKI to CKD continuum.

Broadening horizons: ferroptosis as a new target for traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of death and disability worldwide, with ~50 million people experiencing TBI each year. Ferroptosis, a form of regulated cell death triggered by iron ion-catalyzed and reactive oxygen species-induced lipid peroxidation, has been identified as a potential contributor to traumatic central nervous system conditions, suggesting its involvement in the pathogenesis of TBI. Alterations in iron metabolism play a crucial role in secondary injury following TBI. This study aimed to explore the role of ferroptosis in TBI, focusing on iron metabolism disorders, lipid metabolism disorders and the regulatory axis of system Xc-/glutathione/glutathione peroxidase 4 in TBI. Additionally, we examined the involvement of ferroptosis in the chronic TBI stage. Based on these findings, we discuss potential therapeutic interventions targeting ferroptosis after TBI. In conclusion, this review provides novel insights into the pathology of TBI and proposes potential therapeutic targets.

A preliminary study on the pathology and molecular mechanism of fumonisin B1 nephrotoxicity in young quails

Fumonisin B1 (FB1) is a widely present mycotoxin that accumulates in biological systems and poses a health risk to animals. However, few studies have reported the molecular mechanism by which FB1 induces nephrotoxicity. The aim of this study was to assess the extent of nephrotoxicity during FB1 exposure and the possible molecular mechanisms behind it. Therefore, 180 young quails were equally divided into two groups. The control group was fed typical quail food, while the experimental group was fed quail food containing 30 mg·kg-1 FB1. Various parameters were assessed, which included histopathological, ultrastructural changes, levels of biochemical parameters, oxidative indicators, inflammatory factors, possible target organelles mitochondrial and endoplasmic reticulum (ER)-related factors, nuclear xenobiotic receptors (NXR) response, and cytochrome P450 system (CYP450s)-related factors in the kidneys on days 14, 28, and 42. The results showed that FB1 can induce oxidative stress through NXR response and disorder of the CYP450s system, leading to mitochondrial dysfunction and ER stress, promoting the expression of inflammatory factors (including IL-1β, IL-6, and IL-8) and causing kidney damage. This study elucidated the possible molecular mechanism by which FB1 induces nephrotoxicity in young quails.

Arachidonic acid metabolism in health and disease

Arachidonic acid (AA), an n-6 essential fatty acid, is a major component of mammalian cells and can be released by phospholipase A2. Accumulating evidence indicates that AA plays essential biochemical roles, as it is the direct precursor of bioactive lipid metabolites of eicosanoids such as prostaglandins, leukotrienes, and epoxyeicosatrienoic acid obtained from three distinct enzymatic metabolic pathways: the cyclooxygenase pathway, lipoxygenase pathway, and cytochrome P450 pathway. AA metabolism is involved not only in cell differentiation, tissue development, and organ function but also in the progression of diseases, such as hepatic fibrosis, neurodegeneration, obesity, diabetes, and cancers. These eicosanoids are generally considered proinflammatory molecules, as they can trigger oxidative stress and stimulate the immune response. Therefore, interventions in AA metabolic pathways are effective ways to manage inflammatory-related diseases in the clinic. Currently, inhibitors targeting enzymes related to AA metabolic pathways are an important area of drug discovery. Moreover, many advances have also been made in clinical studies of AA metabolic inhibitors in combination with chemotherapy and immunotherapy. Herein, we review the discovery of AA and focus on AA metabolism in relation to health and diseases. Furthermore, inhibitors targeting AA metabolism are summarized, and potential clinical applications are discussed.

Bioactive lipids in hypertension

Hypertension is a major healthcare issue that afflicts one in every three adults worldwide and contributes to cardiovascular diseases, morbidity and mortality. Bioactive lipids contribute importantly to blood pressure regulation via actions on the vasculature, kidney, and inflammation. Vascular actions of bioactive lipids include blood pressure lowering vasodilation and blood pressure elevating vasoconstriction. Increased renin release by bioactive lipids in the kidney is pro-hypertensive whereas anti-hypertensive bioactive lipid actions result in increased sodium excretion. Bioactive lipids have pro-inflammatory and anti-inflammatory actions that increase or decrease reactive oxygen species and impact vascular and kidney function in hypertension. Human studies provide evidence that fatty acid metabolism and bioactive lipids contribute to sodium and blood pressure regulation in hypertension. Genetic changes identified in humans that impact arachidonic acid metabolism have been associated with hypertension. Arachidonic acid cyclooxygenase, lipoxygenase and cytochrome P450 metabolites have pro-hypertensive and anti-hypertensive actions. Omega-3 fish oil fatty acids eicosapentaenoic acid and docosahexaenoic acid are known to be anti-hypertensive and cardiovascular protective. Lastly, emerging fatty acid research areas include blood pressure regulation by isolevuglandins, nitrated fatty acids, and short chain fatty acids. Taken together, bioactive lipids are key contributors to blood pressure regulation and hypertension and their manipulation could decrease cardiovascular disease and associated morbidity and mortality.

Drug-drug-gene interactions as mediators of adverse drug reactions to diclofenac and statins: a case report and literature review

Concomitant treatment with drugs that inhibit drug metabolising enzymes and/or transporters, such as commonly prescribed statins and nonsteroidal anti-inflammatory drugs (NSAIDs), has been associated with prolonged drug exposure and increased risk of adverse drug reactions (ADRs) due to drug-drug interactions. The risk is further increased in patients with chronic diseases/comorbidities who are more susceptible because of their genetic setup or external factors. In that light, we present a case of a 46-year-old woman who had been experiencing acute renal and hepatic injury and myalgia over two years of concomitant treatment with diclofenac, atorvastatin, simvastatin/fenofibrate, and several other drugs, including pantoprazole and furosemide. Our pharmacogenomic findings supported the suspicion that ADRs, most notably the multi-organ toxicity experienced by our patient, may be owed to drug-drug-gene interactions and increased bioavailability of the prescribed drugs due to slower detoxification capacity and decreased hepatic and renal elimination. We also discuss the importance of CYP polymorphisms in the biotransformation of endogenous substrates such as arachidonic acid and their modulating role in pathophysiological processes. Yet even though the risks of ADRs related to the above mentioned drugs are substantially evidenced in literature, pre-emptive pharmacogenetic analysis has not yet found its way into common clinical practice.

Regulation of Tissue Inflammation by 12-Lipoxygenases

Lipoxygenases (LOXs) are lipid metabolizing enzymes that catalyze the di-oxygenation of polyunsaturated fatty acids to generate active eicosanoid products. 12-lipoxygenases (12-LOXs) primarily oxygenate the 12th carbon of its substrates. Many studies have demonstrated that 12-LOXs and their eicosanoid metabolite 12-hydroxyeicosatetraenoate (12-HETE), have significant pathological implications in inflammatory diseases. Increased level of 12-LOX activity promotes stress (both oxidative and endoplasmic reticulum)-mediated inflammation, leading to damage in these tissues. 12-LOXs are also associated with enhanced cellular migration of immune cells-a characteristic of several metabolic and autoimmune disorders. Genetic depletion or pharmacological inhibition of the enzyme in animal models of various diseases has shown to be protective against disease development and/or progression in animal models in the setting of diabetes, pulmonary, cardiovascular, and metabolic disease, suggesting a translational potential of targeting the enzyme for the treatment of several disorders. In this article, we review the role of 12-LOXs in the pathogenesis of several diseases in which chronic inflammation plays an underlying role.

Deletion of Alox15 improves kidney dysfunction and inhibits fibrosis by increased PGD2 in the kidney

BACKGROUND

Lipid-metabolizing enzymes and their metabolites affect inflammation and fibrosis, but their roles in chronic kidney disease (CKD) have not been completely understood.

METHODS

To clarify their role in CKD, we measured the mRNA levels of major lipid-metabolizing enzymes in 5/6 nephrectomized (Nx) kidneys of C57BL/6 J mice. Mediator lipidomics was performed to reveal lipid profiles of CKD kidneys.

RESULTS

In 5/6 Nx kidneys, both mRNA and protein levels of Alox15 were higher when compared with those in sham kidneys. With respect to in situ hybridization, the mRNA level of Alox15 was higher in renal tubules of 5/6 Nx kidneys. To examine the role of Alox15 in CKD pathogenesis, we performed 5/6 Nx on Alox15-/- mice. Alox15-/- CKD mice exhibited better renal functions than wild-type mice. Interstitial fibrosis was also inhibited in Alox15-/- CKD mice. Mediator lipidomics revealed that Alox15-/- CKD mouse kidneys had significantly higher levels of PGD2 than the control. To investigate the effects of PGD2 on renal fibrosis, we administered PGD2 to TGF-β1-stimulated NRK-52E cells and HK-2 cells, which lead to a dose-dependent suppression of type I collagen and αSMA in both cell lines.

CONCLUSION

Increased PGD2 in Alox15-/- CKD mouse kidneys could inhibit fibrosis, thereby resulting in CKD improvement. Thus, Alox15 inhibition and PGD2 administration may be novel therapeutic targets for CKD.

Eicosanoid blood vessel regulation in physiological and pathological states

Arachidonic acid can be metabolized in blood vessels by three primary enzymatic pathways; cyclooxygenase (COX), lipoxygenase (LO), and cytochrome P450 (CYP). These eicosanoid metabolites can influence endothelial and vascular smooth muscle cell function. COX metabolites can cause endothelium-dependent dilation or constriction. Prostaglandin I2 (PGI2) and thromboxane (TXA2) act on their respective receptors exerting opposing actions with regard to vascular tone and platelet aggregation. LO metabolites also influence vascular tone. The 12-LO metabolite 12S-hydroxyeicosatrienoic acid (12S-HETE) is a vasoconstrictor whereas the 15-LO metabolite 11,12,15-trihydroxyeicosatrienoic acid (11,12,15-THETA) is an endothelial-dependent hyperpolarizing factor (EDHF). CYP enzymes produce two types of eicosanoid products: EDHF vasodilator epoxyeicosatrienoic acids (EETs) and the vasoconstrictor 20-HETE. The less-studied cross-metabolites generated from arachidonic acid metabolism by multiple pathways can also impact vascular function. Likewise, COX, LO, and CYP vascular eicosanoids interact with paracrine and hormonal factors such as the renin-angiotensin system and endothelin-1 (ET-1) to maintain vascular homeostasis. Imbalances in endothelial and vascular smooth muscle cell COX, LO, and CYP metabolites in metabolic and cardiovascular diseases result in vascular dysfunction. Restoring the vascular balance of eicosanoids by genetic or pharmacological means can improve vascular function in metabolic and cardiovascular diseases. Nevertheless, future research is necessary to achieve a more complete understanding of how COX, LO, CYP, and cross-metabolites regulate vascular function in physiological and pathological states.

Renal metabolism and hypertension

Hypertension is a leading risk factor for disease burden worldwide. The kidneys, which have a high specific metabolic rate, play an essential role in the long-term regulation of arterial blood pressure. In this review, we discuss the emerging role of renal metabolism in the development of hypertension. Renal energy and substrate metabolism is characterized by several important and, in some cases, unique features. Recent advances suggest that alterations of renal metabolism may result from genetic abnormalities or serve initially as a physiological response to environmental stressors to support tubular transport, which may ultimately affect regulatory pathways and lead to unfavorable cellular and pathophysiological consequences that contribute to the development of hypertension.

Factors associated with platelet reactivity during dual antiplatelet therapy in patients with diabetes after acute coronary syndrome

Antiplatelet drugs are prescribed without considering the diabetic status of the patient. The objective of the current investigation was to determine the impact of clinical factors, CYP4F2 enzyme and 20-hydroxyeicosatetraenoic acid (20-HETE) concentrations on high on-treatment platelet reactivity in patients with diabetes treated with antiplatelet drugs following acute coronary syndromes. A total of 667 patients were included in the study. Dual antiplatelet drug loading dosages with aspirin (300 mg) and ticagrelor (180 mg) or clopidogrel (600 mg) were prescribed to all the studied patients. Testing of platelet aggregation was performed the day after loading antiplatelet drug dosages. Platelet aggregation test was done according to the classical Born method. Multivariate binary regression analysis demonstrated that insulin use and higher 20-HETE concentration increased the odds of high on-treatment platelet reactivity during the initiation of antiplatelet drug therapy (OR: 3.968, 95% CI: 1.478-10.656, p = 0.006 and OR: 1.139, 95% CI: 1.073-1.210, respectively, p < 0.001). Ticagrelor use decreased the odds of developing high on-treatment platelet reactivity (OR: 0.238, 95% CI: 0.097-0.585, p = 0.002). Data from this study revealed that high on-treatment platelet reactivity during dual antiplatelet therapy in patients with diabetes may depend on such factors as insulin prescription and 20-HETE concentration.

Diurnal Regulation of Renal Electrolyte Excretion: The Role of Paracrine Factors

Many physiological processes, including most kidney-related functions, follow specific rhythms tied to a 24-h cycle. This is largely because circadian genes operate in virtually every cell type in the body. In addition, many noncanonical genes have intrinsic circadian rhythms, especially within the liver and kidney. This new level of complexity applies to the control of renal electrolyte excretion. Furthermore, there is growing evidence that paracrine and autocrine factors, especially the endothelin system, are regulated by clock genes. We have known for decades that excretion of electrolytes is dependent on time of day, which could play an important role in fluid volume balance and blood pressure control. Here, we review what is known about the interplay between paracrine and circadian control of electrolyte excretion. The hope is that recognition of paracrine and circadian factors can be considered more deeply in the future when integrating with well-established neuroendocrine control of excretion.

Characterization of supported liquid extraction as a sample pretreatment method for eicosanoids and related metabolites in biological fluids

Sample pretreatment is an important process in liquid chromatography-mass spectrometry-based quantitative lipidomics. Reversed-phase solid phase extraction (RP-SPE) has been widely used for analyzing various types of samples, including aqueous samples such as cell culture media, plasma, serum, urine, and other biological fluids. Because lipid mediators are often protein-bound, prior deproteinization is necessary for their effective recovery. Deproteinization is typically performed by the addition of organic solvents, which requires time-consuming evaporation-reconstitution, or dilution with aqueous solvents before RP-SPE; however, both of these approaches compromise the analytical performance. As a potential alternative, we attempted to utilize supported liquid extraction (SLE), an automation-compatible variant of liquid-liquid extraction, for the determination of eicosanoids and related metabolites in aqueous samples. We screened 81 different sample diluent-eluent conditions and found that the use of 0.1% formic acid-water as the diluent and 0.1% formic acid-methyl acetate as the eluent enabled the optimum recovery of a variety of eicosanoids, except for peptide leukotrienes. The optimized SLE method efficiently removed protein from human plasma, while phospholipids and neutral lipids were modestly recovered. Moreover, the proposed method exhibited a quantitative performance comparable to that of typical ordinary RP-SPE method in the analysis of human platelets stimulated with thrombin receptor-activating peptide 6. Thus, we propose SLE as an attractive option for rapid lipid mediator extraction from aqueous samples.

Extracts from guava fruit protect renal tubular endothelial cells against acetaminophen‑induced cytotoxicity

Acetaminophen (APAP) is an analgesic and antipyretic agent primarily used in the clinical setting. However, high doses of APAP can cause oxidative stress. Guavas have been reported to provide anti‑inflammatory, anti‑microbial, anti‑oxidative and anti‑diarrheal functions. In addition, guavas have been reported to prevent renal damage due to progression of diabetes mellitus. Therefore, the aim of the present study was to investigate whether guavas can reduce APAP‑induced renal cell damage. In the present study, extracts from guavas were obtained and added to APAP‑treated renal tubular endothelial cells. The present results demonstrated that APAP induces cytotoxicity in renal tubular endothelial cells, while guava extracts inhibited this cytotoxicity. In addition, the study demonstrated that the protective effects of guava extracts against APAP‑induced cytotoxicity may be associated with inhibition of oxidative stress and caspase‑3 activation.

Lipoxygenases modulate the effect of glutoxim on Na+ transport in the frog skin epithelium

Using voltage-clamp technique, the involvement of lipoxygenases in the effect of immunomodulatory drug glutoxim on Na⁺ transport in frog skin was investigated. It was shown for the first time that preincubation of the skin with lipoxygenase inhibitors caffeic acid, baicalein, and nordihydroguaiaretic acid significantly decreases the stimulatory effect of glutoxim on Na⁺ transport. The data suggest the involvement of lipoxygenase oxidation pathway of arachidonic acid metabolism in the glutoxim effect on Na⁺ transport in frog skin epithelium.

Effect of Cytochrome P450 Metabolites of Arachidonic Acid in Nephrology

Thirty-five years ago, a third pathway for the metabolism of arachidonic acid by cytochrome P450 enzymes emerged. Subsequent work revealed that 20-hydroxyeicosatetraenoic and epoxyeicosatrienoic acids formed by these pathways have essential roles in the regulation of renal tubular and vascular function. Sequence variants in the genes that produce 20-hydroxyeicosatetraenoic acid are associated with hypertension in humans, whereas the evidence supporting a role for variants in the genes that alter levels of epoxyeicosatrienoic acids is less convincing. Studies in animal models suggest that changes in the production of cytochrome P450 eicosanoids alter BP. However, the mechanisms involved remain controversial, especially for 20-hydroxyeicosatetraenoic acid, which has both vasoconstrictive and natriuretic actions. Epoxyeicosatrienoic acids are vasodilators with anti-inflammatory properties that oppose the development of hypertension and CKD; 20-hydroxyeicosatetraenoic acid levels are elevated after renal ischemia and may protect against injury. Levels of this eicosanoid are also elevated in polycystic kidney disease and may contribute to cyst formation. Our review summarizes the emerging evidence that cytochrome P450 eicosanoids have a role in the pathogenesis of hypertension, polycystic kidney disease, AKI, and CKD.

Meloxicam fails to augment the reno-protective effects of soluble epoxide hydrolase inhibition in streptozotocin-induced diabetic rats via increased 20-HETE levels

The pro-inflammatory cyclooxygenase (COX)-derived prostaglandins and the anti-inflammatory cytochrome P450 epoxygenase-derived epoxyeicosatrienoic acids (EETs) play an important role in the regulation of renal injury. The current study examined whether COX inhibition augments the reno-protective effects of increased EETs levels via inhibiting EETs degradation by soluble epoxide hydrolase (sEH) in diabetic rats. Streptozotocin (50mg/kg, i.v) was used to induce diabetes in male Sprague Dawley rats. Rats were then divided into 5 groups (n=6-8); control non diabetic, diabetic, diabetic treated with the sEH inhibitor trans-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid (t-AUCB), diabetic treated with the COX inhibitor meloxicam and diabetic treated with meloxicam plus t-AUCB for 2 months. Glomerular albumin permeability and urinary albumin and nephrin excretion levels were significantly elevated in diabetic rats together with decreased glomerular α3 integrin and nephrin expression levels. Inhibition of sEH reduced glomerular albumin permeability, albumin and nephrin excretion levels and restored the decrease in glomerular α3 integrin and nephrin expression in diabetic rats. Meloxicam failed to reduce renal injury or even to synergize the reno-protective effects of sEH inhibition in diabetic rats. Furthermore, inhibition of sEH reduced the elevation in renal collagen deposition and urinary MCP-1 excretion levels together with a reduction in the number of renal TUNEL positive cells in diabetic vs. control rats (P<0.05). Meloxicam did not reduce renal inflammation or apoptosis in diabetic rats or even exacerbate the anti-inflammatory and anti-apoptotic effects of sEH inhibition. Renal 20-hydroxyeicosatetranoic acid (20-HETE) levels were elevated in diabetic rats and meloxicam further exacerbated this elevation. In conclusion, our study suggests that inhibition of COX failed to provide renal protection or to augment the reno-protective effects of sEH inhibition in diabetic rats, at least in part, via increased inflammatory 20-HETE levels.

Molecular mechanisms and cell signaling of 20-hydroxyeicosatetraenoic acid in vascular pathophysiology

Cytochrome P450s enzymes catalyze the metabolism of arachidonic acid to epoxyeicosatrienoic acids (EETs), dihydroxyeicosatetraenoic acid and hydroxyeicosatetraeonic acid (HETEs). 20-HETE is a vasoconstrictor that depolarizes vascular smooth muscle cells by blocking K+ channels. EETs serve as endothelial derived hyperpolarizing factors. Inhibition of the formation of 20-HETE impairs the myogenic response and autoregulation of renal and cerebral blood flow. Changes in the formation of EETs and 20-HETE have been reported in hypertension and drugs that target these pathways alter blood pressure in animal models. Sequence variants in CYP4A11 and CYP4F2 that produce 20-HETE, UDP-glucuronosyl transferase involved in the biotransformation of 20-HETE and soluble epoxide hydrolase that inactivates EETs are associated with hypertension in human studies. 20-HETE contributes to the regulation of vascular hypertrophy, restenosis, angiogenesis and inflammation. It also promotes endothelial dysfunction and contributes to cerebral vasospasm and ischemia-reperfusion injury in the brain, kidney and heart. This review will focus on the role of 20-HETE in vascular dysfunction, inflammation, ischemic and hemorrhagic stroke and cardiac and renal ischemia reperfusion injury.