Epoxyeicosatrienoic acids improve glucose homeostasis by preventing NF-κB-mediated transcription of SGLT2 in renal tubular epithelial cells

TPPU inhibits inflammation-induced excessive autophagy to restore the osteogenic differentiation potential of stem cells and improves alveolar ridge preservation

Inflammation-induced autophagy is a double-edged sword. Dysfunction of autophagy impairs the differentiation capacity of mesenchymal stem cells and enhances inflammation-induced bone loss. Tooth extraction with periodontal and/or endodontic lesions exacerbates horizontal and vertical resorption of alveolar bone during the healing period. Alveolar socket preservation (ASP) procedure following tooth extraction has important clinical implications for future prosthodontic treatments. Studies have shown that epoxyeicosatrienoic acids (EETs) have significant anti-inflammatory effects and participate in autophagy. However, whether EETs can minimize alveolar bone resorption and contribute to ASP by regulating autophagy levels under inflammatory conditions remain elusive. Here, we figured out that LPS-induced inflammatory conditions increased the inflammatory cytokine and inhibited osteogenic differentiation of human dental pulp stem cells (hDPSCs), and led to excessive autophagy of hDPSCs. Moreover, we identified that increased EETs levels using TPPU, a soluble epoxide hydrolase inhibitor, reversed these negative outcomes. We further demonstrated the potential of TPPU to promote early healing of extraction sockets and ASP, and speculated that it was related to autophagy. Taken together, these results suggest that targeting inhibition of soluble epoxide hydrolase using TPPU plays a protective role in the differentiation and autophagy of mesenchymal stem cells and provides potential feasibility for applying TPPU for ASP, especially under inflammatory conditions.

Mechanism study of Cordyceps sinensis alleviates renal ischemia–reperfusion injury

Cordyceps sinensis (C. sinensis) is a kind of traditional Chinese medicine commonly used to protect renal function and relieve kidney injury. This study aimed to reveal the renal protective mechanism of C. sinensis in renal ischemia–reperfusion injury (RIRI). First, we obtained 8 active components and 99 common targets of C. sinensis against RIRI from public databases. Second, we have retrieved 38 core targets through STRING database analysis. Third, Gene Ontology analysis of 38 core targets is indicated that C. sinensis treatment RIRI may related hormone regulation, oxidative stress, cell proliferation, and immune regulation. Kyoto Encyclopedia of Genes and Genomes enrichment analysis of 38 core targets is indicated that C. sinensis treatment RIRI may involve in PI3K–Akt, HIF-1, and MAPK signaling pathways, as well as advanced glycation end product (AGE)–receptor for AGE (RAGE) signaling pathway in diabetic complications. Lastly, molecular docking was used to detect the binding activity and properties of active components and core target using molecular docking. And the results showed that eight active components of C. sinensis had low affinity with core targets. In conclusion, C. sinensis may improve RIRI by regulating oxidative stress and immunity through PI3K–Akt, HIF-1, and MAPK pathways.

CYP450 Epoxygenase Metabolites, Epoxyeicosatrienoic Acids, as Novel Anti-Inflammatory Mediators

Inflammation plays a crucial role in the initiation and development of a wide range of systemic illnesses. Epoxyeicosatrienoic acids (EETs) are derived from arachidonic acid (AA) metabolized by CYP450 epoxygenase (CYP450) and are subsequently hydrolyzed by soluble epoxide hydrolase (sEH) to dihydroxyeicosatrienoic acids (DHETs), which are merely biologically active. EETs possess a wide range of established protective effects on many systems of which anti-inflammatory actions have gained great interest. EETs attenuate vascular inflammation and remodeling by inhibiting activation of endothelial cells and reducing cross-talk between inflammatory cells and blood vessels. EETs also process direct and indirect anti-inflammatory properties in the myocardium and therefore alleviate inflammatory cardiomyopathy and cardiac remodeling. Moreover, emerging studies show the substantial roles of EETs in relieving inflammation under other pathophysiological environments, such as diabetes, sepsis, lung injuries, neurodegenerative disease, hepatic diseases, kidney injury, and arthritis. Furthermore, pharmacological manipulations of the AA-CYP450-EETs-sEH pathway have demonstrated a contribution to the alleviation of numerous inflammatory diseases, which highlight a therapeutic potential of drugs targeting this pathway. This review summarizes the progress of AA-CYP450-EETs-sEH pathway in regulation of inflammation under different pathological conditions and discusses the existing challenges and future direction of this research field.

[Fatty acid epoxides in the regulation of the inflammation]

Cyclooxygenase and lipoxygenase derived lipid metabolites of polyunsaturated fatty acids (PUFAs), as well as their role in the inflammation, have been studied quite thoroughly. However, cytochrome P450 derived lipid mediators, as well as their participation in the regulation of the inflammation, need deeper understanding. In recent years, it has become known that PUFAs are oxidized by cytochrome P450 epoxygenases to epoxy fatty acids, which act as the extremely powerful lipid mediators involved in resolving inflammation. Recent studies have shown that the anti-inflammatory mechanisms of ω-3 PUFAs are also mediated by their conversion to the endocannabinoid epoxides. Thus, it is clear that a number of therapeutically relevant functions of PUFAs are due to their conversion to PUFA epoxides. However, with the participation of cytochrome P450 epoxygenases, not only PUFA epoxides, but also other metabolites are formed. They are further are converted by epoxide hydrolases into pro-inflammatory dihydroxy fatty acids and anti-inflammatory dihydroxyeicosatrienoic acids. The study of the role of PUFA epoxides in the regulation of the inflammation and pharmacological modeling of the activity of epoxide hydrolases are the promising strategies for the treatment of the inflammatory diseases. This review systematizes the current literature data of the fatty acid epoxides, in particular, the endocannabinoid epoxides. Their role in the regulation of inflammation is discussed.

The Pathophysiological Basis of Diabetic Kidney Protection by Inhibition of SGLT2 and SGLT1

SGLT2 inhibitors can protect the kidneys of patients with and without type 2 diabetes mellitus and slow the progression towards end-stage kidney disease. Blocking tubular SGLT2 and spilling glucose into the urine, which triggers a metabolic counter-regulation similar to fasting, provides unique benefits, not only as an anti-hyperglycemic strategy. These include a low hypoglycemia risk and a shift from carbohydrate to lipid utilization and mild ketogenesis, thereby reducing body weight and providing an additional energy source. SGLT2 inhibitors counteract hyperreabsorption in the early proximal tubule, which acutely lowers glomerular pressure and filtration and thereby reduces the physical stress on the filtration barrier, the filtration of tubule-toxic compounds, and the oxygen demand for tubular reabsorption. This improves cortical oxygenation, which, together with lesser tubular gluco-toxicity and improved mitochondrial function and autophagy, can reduce pro-inflammatory, pro-senescence, and pro-fibrotic signaling and preserve tubular function and GFR in the long-term. By shifting transport downstream, SGLT2 inhibitors more equally distribute the transport burden along the nephron and may mimic systemic hypoxia to stimulate erythropoiesis, which improves oxygen delivery to the kidney and other organs. SGLT1 inhibition improves glucose homeostasis by delaying intestinal glucose absorption and by increasing the release of gastrointestinal incretins. Combined SGLT1 and SGLT2 inhibition has additive effects on renal glucose excretion and blood glucose control. SGLT1 in the macula densa senses luminal glucose, which affects glomerular hemodynamics and has implications for blood pressure control. More studies are needed to better define the therapeutic potential of SGLT1 inhibition to protect the kidney, alone or in combination with SGLT2 inhibition.

Orally active epoxyeicosatrienoic acid analogs in hypertension and renal injury

Epoxyeicosatrienoic acids (EETs) are arachidonic acid metabolites synthesized by cytochrome P450 epoxygenases. Biological activities for EETs include vasodilation, decreasing inflammation, opposing apoptosis, and inhibiting renal sodium reabsorption. These actions are beneficial in lowering blood pressure and slowing kidney disease progression. Furthermore, evidence in human and experimental animal studies have found that decreased EET levels contribute to hypertension and kidney diseases. Consequently, EET mimics/analogs have been developed as a potential therapeutic for hypertension and acute and chronic kidney diseases. Their development has resulted in EET analogs that are orally active with favorable pharmacological profiles. Analogs for 8,9-EET, 11,12-EET, and 14,15-EET have been tested in several hypertension and kidney disease animal models. More recently, kidney targeted EET analogs have been synthesized and tested against drug-induced nephrotoxicity. Experimental evidence has demonstrated compelling therapeutic potential for EET analogs to oppose cardiovascular and kidney diseases. These EET analogs lower blood pressure, decrease kidney inflammation, improve vascular endothelial function, and decrease kidney fibrosis and apoptosis. Overall, these preclinical studies support the likelihood that EET analogs will advance to clinical trials for hypertension and associated comorbidities or acute and chronic kidney diseases.

EET Analog Treatment Improves Insulin Signaling in a Genetic Mouse Model of Insulin Resistance

We previously showed that global deletion of the cytochrome P450 epoxygenase Cyp2c44, a major epoxyeicosatrienoic acid (EET) producing enzyme in mice, leads to impaired hepatic insulin signaling resulting in insulin resistance. This finding led us to investigate whether administration of a water soluble EET analog restores insulin signaling in vivo in Cyp2c44(-/-) mice and investigated the underlying mechanisms by which this effect is exerted. Cyp2c44(-/-) mice treated with the analog EET-A for 4 weeks improved fasting glucose and glucose tolerance compared to Cyp2c44(-/-) mice treated with vehicle alone. This beneficial effect was accompanied by enhanced hepatic insulin signaling, decreased expression of gluconeogenic genes and increased expression of glycogenic genes. Mechanistically, we show that insulin-stimulated phosphorylation of insulin receptor β (IRβ) is impaired in primary Cyp2c44(-/-) hepatocytes and this can be restored by cotreatment with EET-A and insulin. Plasma membrane fractionations of livers indicated that EET-A enhances the retention of IRβ in membrane rich fractions, thus potentiating its activation. Altogether, EET analogs ameliorate insulin signaling in a genetic model of hepatic insulin resistance by stabilizing membrane-associated IRβ and potentiating insulin signaling.

Epoxyeicosatrienoic Acids and Fibrosis: Recent Insights for the Novel Therapeutic Strategies

Organ fibrosis often ends in eventual organ failure and leads to high mortality. Although researchers have identified many effector cells and molecular pathways, there are few effective therapies for fibrosis to date and the underlying mechanism needs to be examined and defined further. Epoxyeicosatrienoic acids (EETs) are endogenous lipid metabolites of arachidonic acid (ARA) synthesized by cytochrome P450 (CYP) epoxygenases. EETs are rapidly metabolized primarily via the soluble epoxide hydrolase (sEH) pathway. The sEH pathway produces dihydroxyeicosatrienoic acids (DHETs), which have lower activity. Stabilized or increased EETs levels exert several protective effects, including pro-angiogenesis, anti-inflammation, anti-apoptosis, and anti-senescence. Currently, intensive investigations are being carried out on their anti-fibrotic effects in the kidney, heart, lung, and liver. The present review provides an update on how the stabilized or increased production of EETs is a reasonable theoretical basis for fibrosis treatment.

Inhibition of soluble epoxide hydrolase alleviates insulin resistance and hypertension via downregulation of SGLT2 in the mouse kidney

The epoxyeicosatrienoic acid (EET) exerts beneficial effects on insulin resistance and/or hypertension. EETs could be readily converted to less biological active diols by soluble epoxide hydrolase (sEH). However, whether sEH inhibition can ameliorate the comorbidities of insulin resistance and hypertension and the underlying mechanisms of this relationship are unclear. In this study, C57BL/6 mice were rendered hypertensive and insulin resistant through a high-fat and high-salt (HF–HS) diet. The sEH inhibitor, 1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea (TPPU), was used to treat mice (1 mg/kg/day) for 8 weeks, followed by analysis of metabolic parameters. The expression of sEH and the sodium–glucose cotransporter 2 (SGLT2) was markedly upregulated in the kidneys of mice fed an HF–HS diet. We found that TPPU administration increased kidney EET levels, improved insulin resistance, and reduced hypertension. Furthermore, TPPU treatment prevented upregulation of SGLT2 and the associated increased urine volume and the excretion of urine glucose and urine sodium. Importantly, TPPU alleviated renal inflammation. In vitro, human renal proximal tubule epithelial cells (HK-2 cells) were used to further investigate the underlying mechanism. We observed that 14,15-EET or sEH knockdown or inhibition prevented the upregulation of SGLT2 upon treatment with palmitic acid or NaCl by inhibiting the inhibitory kappa B kinase α/β/NF-κB signaling pathway. In conclusion, sEH inhibition by TPPU alleviated insulin resistance and hypertension induced by an HF–HS diet in mice. The increased urine excretion of glucose and sodium was mediated by decreased renal SGLT2 expression because of inactivation of the inhibitory kappa B kinase α/β/NF-κB–induced inflammatory response.