Pharmacological inhibition of soluble epoxide hydrolase provides cardioprotection in hyperglycemic rats

Epoxyeicosatrienoic acid: A potential therapeutic target of heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) reduces the quality of life, costs substantial medical resources, and has a high mortality. However, we lack an effective therapy for HFpEF due to our limited knowledge of its mechanism. Therefore, it is crucial to explore novel therapeutics, such as those with endogenous protective roles, and seek new targeted therapies. Epoxyeicosatrienoic acids (EETs) are endogenous bioactive metabolites of arachidonic acids produced by cytochrome P450 (CYP) epoxygenases. EETs can function as endogenous cardioprotective factors with potent inhibitory roles in inflammation, endothelial dysfunction, cardiac remodeling, and fibrosis, which are the fundamental mechanisms of HFpEF. This suggests that EETs have the potential function to protect against HFpEF. Therefore, we present an overview of the ever-expanding world of EETs and how they might help alleviate the pathophysiology underlying HFpEF to provide new insights for research in this field.

17β-Estradiol Treatment Improves Acetylcholine-Induced Relaxation of Mesenteric Arteries in Ovariectomized UC Davis Type 2 Diabetes Mellitus Rats in Prediabetic State

We recently reported sex differences in mesenteric arterial function of the UC Davis type-2 diabetes mellitus (UCD-T2DM) rats as early as the prediabetic state. We reported that mesenteric arteries (MA) from prediabetic male rats exhibited a greater impairment compared to that in prediabetic females. However, when females became diabetic, they exhibited a greater vascular dysfunction than males. Thus, the aim of this study was to investigate whether the female sex hormone, estrogen preserves mesenteric arterial vasorelaxation in UCD-T2DM female rats at an early prediabetic state. Age-matched female Sprague Dawley and prediabetic (PD) UCD-T2DM rats were ovariectomized (OVX) and subcutaneously implanted with either placebo or 17β-estradiol (E_2, 1.5 mg) pellets for 45 days. We assessed the contribution of endothelium-derived relaxing factors (EDRF) to acetylcholine (ACh)-induced vasorelaxation, using pharmacological inhibitors. Responses to sodium nitroprusside (SNP) and phenylephrine (PE) were also measured. Additionally, metabolic parameters and expression of some targets associated with vascular and insulin signaling were determined. We demonstrated that the responses to ACh and SNP were severely impaired in the prediabetic state (PD OVX) rats, while E₂ treatment restored vasorelaxation in the PD OVX + E₂. Moreover, the responses to PE was significantly enhanced in MA of PD OVX groups, regardless of placebo or E₂ treatment. Overall, our data suggest that 1) the impairment of ACh responses in PD OVX rats may, in part, result from the elevated contractile responses to PE, loss of contribution of endothelium-dependent hyperpolarization (EDH) to vasorelaxation, and a decreased sensitivity of MA to nitric oxide (NO), and 2) the basis for the protective effects of E₂ may be partly attributed to the elevation of the NO contribution to vasorelaxation and its interaction with MA as well as potential improvement of insulin signaling. Here, we provide the first evidence of the role of E₂ in protecting MA from early vascular dysfunction in prediabetic female rats.

Adeno-associated virus-mediated in vivo suppression of expression of EPHX2 gene modulates the activity of paraventricular nucleus neurons in spontaneously hypertensive rats

BACKGROUND

Hypertension can be attributed to increased sympathetic activities. Presympathetic neurons in the paraventricular nucleus (PVN) of the hypothalamus are capable of modulating sympathetic outflow, thus contributing to the pathogenesis of neurogenic hypertension. Epoxyeicosatrienoic acids (EETs) were reported to have anti-hypertensive effects, which could be degraded by soluble epoxide hydrolase (sEH), encoded by EPHX2. However, the potential effect of EETs on PVN neuron activity and the underlying molecular mechanism are largely unknown.

METHODS

Knockdown of EPHX2 in spontaneously hypertensive rats (SHRs) was achieved by tail-intravenous injection of AAV plasmid containing shRNA targeting EPHX2. Whole-cell patch clamp was used to record action potentials of PVN neurons. An LC-MS/MS System was employed to determine 14,15-EET levels in rat cerebrospinal fluid. qPCR and western blotting were applied to examine the expression level of EPHX2 in various tissues. ELISA and immunofluorescence staining were applied to examine the levels of ATP, D-serine and glial fibrillary acidic protein (GFAP) in isolated astrocytes.

RESULTS

The expression level of EPHX2 was higher, while the level of 14,15-EET was lower in SHRs than normotensive Wistar-Kyoto rats (WKY) rats. The spike firing frequency of PNV neurons in SHRs was higher than in WKY rats at a given stimulus current, which could be reduced by either EPHX2 downregulation or 14,15-EET administration. In isolated hypothalamic astrocytes, the elevated intracellular ATP or D-serine induced by Angiotensin II (Ang II) treatment could be rescued by 14,15-EET addition or 14,15-EET combing serine racemase (SR) downregulation by siRNA, respectively. Furthermore, 14,15-EET treatment reduced the Ang II-induced elevation of GFAP immunofluorescence.

CONCLUSIONS

The elevation of EET levels by EPHX2 downregulation reduced presympathetic neuronal activity in the PVN of SHRs, leading to a reduced sympathetic outflow in hypertension rats. The ATP/SR/D-serine pathway of astrocytes is involved in EET-mediated neuroprotection.

Zucker Diabetic Sprague Dawley rat (ZDSD): type 2 diabetes translational research model

New Findings

What is the topic of this review?

The Zucker Diabetic‐Sprague Dawley (ZDSD) rat is in the early adoption phase of use by researchers in the fields of diabetes, including prediabetes, obesity and metabolic syndrome. It is essential that physiology researchers choose preclinical models that model human type 2 diabetes appropriately and are aware of the limitations on experimental design.

What advances does it highlight?

Our review of the scientific literature finds that although sex, age and diets contribute to variability, the ZDSD phenotype and disease progression model the characteristics of humans who have prediabetes and diabetes, including co‐morbidities.

Abstract

Type 2 diabetes (T2D) is a prevalent disease and a significant concern for global population health. For persons with T2D, clinical treatments target not only the characteristics of hyperglycaemia and insulin resistance, but also co‐morbidities, such as obesity, cardiovascular and renal disease, neuropathies and skeletal bone conditions. The Zucker Diabetic‐Sprague Dawley (ZDSD) rat is a rodent model developed for experimental studies of T2D. We reviewed the scientific literature to highlight the characteristics of T2D development and the associated phenotypes, such as metabolic syndrome, cardiovascular complications and bone and skeletal pathologies in ZDSD rats. We found that ZDSD phenotype characteristics are independent of leptin receptor signalling. The ZDSD rat develops prediabetes, then progresses to overt diabetes that is accelerated by introduction of a timed high‐fat diet. In male ZDSD rats, glycated haemoglobin (HbA1c) increases at a constant rate from 7 to >30 weeks of age. Diabetic ZDSD rats are moderately hypertensive compared with other rat strains. Diabetes in ZDSD rats leads to endothelial dysfunction in specific vasculatures, impaired wound healing, decreased systolic and diastolic cardiac function, neuropathy and nephropathy. Changes to bone composition and the skeleton increase the risk of bone fractures. Zucker Diabetic‐Sprague Dawley rats have not yet achieved widespread use by researchers. We highlight sex‐related differences in the ZDSD phenotype and gaps in knowledge for future studies. Overall, scientific data support the premise that the phenotype and disease progression in ZDSD rats models the characteristics in humans. We conclude that ZDSD rats are an advantageous model to advance understanding and discovery of treatments for T2D through preclinical research.

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.

Pharmacological regulation of cytochrome P450 metabolites of arachidonic acid attenuates cardiac injury in diabetic rats

Diabetic cardiomyopathy (DCM) is a well-established complication of type 1 and type 2 diabetes associated with a high rate of morbidity and mortality. DCM is diagnosed at advanced and irreversible stages. Therefore, it is of utmost need to identify novel mechanistic pathways involved at early stages to prevent or reverse the development of DCM. In vivo experiments were performed on type 1 diabetic rats (T1DM). Functional and structural studies of the heart were executed and correlated with mechanistic assessments exploring the role of cytochromes P450 metabolites, the 20-hydroxyeicosatetraenoic acids (20-HETEs) and epoxyeicosatrienoic acids (EETs), and their crosstalk with other homeostatic signaling molecules. Our data displays that hyperglycemia results in CYP4A upregulation and CYP2C11 downregulation in the left ventricles (LV) of T1DM rats, paralleled by a differential alteration in their metabolites 20-HETEs (increased) and EETs (decreased). These changes are concomitant with reductions in cardiac outputs, LV hypertrophy, fibrosis, and increased activation of cardiac fetal and hypertrophic genes. Besides, pro-fibrotic cytokine TGF-ß overexpression and NADPH (Nox4) dependent-ROS overproduction are also correlated with the observed cardiac functional and structural modifications. Of interest, these observations are attenuated when T1DM rats are treated with 12-(3-adamantan-1-yl-ureido) dodecanoic acid (AUDA), which blocks EETs metabolism, or N-hydroxy-N'-(4-butyl-2-methylphenol)Formamidine (HET0016), which inhibits 20-HETEs formation. Taken together, our findings confer pioneering evidence about a potential interplay between CYP450-derived metabolites and Nox4/TGF-β axis leading to DCM. Pharmacologic interventions targeting the inhibition of 20-HETEs synthesis or the activation of EETs synthesis may offer novel therapeutic approaches to treat DCM.

Epoxy Fatty Acids: From Salt Regulation to Kidney and Cardiovascular Therapeutics: 2019 Lewis K. Dahl Memorial Lecture

Epoxyeicosatrienoic acids (EETs) are epoxy fatty acids that have biological actions that are essential for maintaining water and electrolyte homeostasis. An inability to increase EETs in response to a high-salt diet results in salt-sensitive hypertension. Vasodilation, inhibition of epithelial sodium channel, and inhibition of inflammation are the major EET actions that are beneficial to the heart, resistance arteries, and kidneys. Genetic and pharmacological means to elevate EETs demonstrated antihypertensive, anti-inflammatory, and organ protective actions. Therapeutic approaches to increase EETs were then developed for cardiovascular diseases. sEH (soluble epoxide hydrolase) inhibitors were developed and progressed to clinical trials for hypertension, diabetes mellitus, and other diseases. EET analogs were another therapeutic approach taken and these drugs are entering the early phases of clinical development. Even with the promise for these therapeutic approaches, there are still several challenges, unexplored areas, and opportunities for epoxy fatty acids.

Role of cytochrome P450-derived, polyunsaturated fatty acid mediators in diabetes and the metabolic syndrome

Over the last decade, cases of metabolic syndrome and type II diabetes have increased exponentially. Exercise and ω-3 polyunsaturated fatty acid (PUFA)-enriched diets are usually prescribed but no therapy is effectively able to restore the impaired glucose metabolism, hypertension, and atherogenic dyslipidemia encountered by diabetic patients. PUFAs are metabolized by different enzymes into bioactive metabolites with anti- or pro-inflammatory activity. One important class of PUFA metabolizing enzymes are the cytochrome P450 (CYP) enzymes that can generate a series of bioactive products, many of which have been attributed protective/anti-inflammatory and insulin-sensitizing effects in animal models. PUFA epoxides are, however, further metabolized by the soluble epoxide hydrolase (sEH) to fatty acid diols. The biological actions of the latter are less well understood but while low concentrations may be biologically important, higher concentrations of diols derived from linoleic acid and docosahexaenoic acid have been linked with inflammation. One potential application for sEH inhibitors is in the treatment of diabetic retinopathy where sEH expression and activity is elevated as are levels of a diol of docosahexaenoic acid that can induce the destabilization of the retina vasculature.

Empagliflozin normalizes the size and number of mitochondria and prevents reduction in mitochondrial size after myocardial infarction in diabetic hearts

To explore mechanisms by which SGLT2 inhibitors protect diabetic hearts from heart failure, we examined the effect of empagliflozin (Empa) on the ultrastructure of cardiomyocytes in the noninfarcted region of the diabetic heart after myocardial infarction (MI). OLETF, a rat model of type 2 diabetes, and its nondiabetic control, LETO, received a sham operation or left coronary artery ligation 12 h before tissue sampling. Tissues were sampled from the posterior ventricle (i.e., the remote noninfarcted region in rats with MI). The number of mitochondria was larger and small mitochondria were more prevalent in OLETF than in LETO. Fis1 expression level was higher in OLETF than in LETO, while phospho‐Ser637‐Drp1, total Drp1, Mfn1/2, and OPA1 levels were comparable. MI further reduced the size of mitochondria with increased Drp1‐Ser616 phosphorylation in OLETF. The number of autophagic vacuoles was unchanged after MI in LETO but was decreased in OLETF. Lipid droplets in cardiomyocytes and tissue triglycerides were increased in OLETF. Empa administration (10 mg/kg per day) reduced blood glucose and triglycerides and paradoxically increased lipid droplets in cardiomyocytes in OLETF. Empa suppressed Fis1 upregulation, increased Bnip3 expression, and prevented reduction in both mitochondrial size and autophagic vacuole number after MI in OLETF. Together with the results of our parallel study showing upregulation of SOD2 and catalase by Empa, the results indicate that Empa normalizes the size and number of mitochondria in diabetic hearts and that diabetes‐induced excessive reduction in mitochondrial size after MI was prevented by Empa via suppression of ROS and restoration of autophagy.

Lower sarcoplasmic reticulum Ca2+ threshold for triggering afterdepolarizations in diabetic rat hearts

BACKGROUND

Type 2 diabetes (T2D) increases arrhythmia risk through incompletely elucidated mechanisms. Ventricular arrhythmias could be initiated by delayed afterdepolarizations (DADs) resulting from elevated spontaneous sarcoplasmic reticulum (SR) Ca2+ release (SR Ca2+ leak).

OBJECTIVE

The purpose of this study was to test the role of DADs and SR Ca2+ leak in triggering arrhythmias in T2D hearts.

METHODS

We compared rats with late-onset T2D that display pancreatic and cardiac phenotypes similar to those in humans with T2D (HIP rats) and their nondiabetic littermates (wild type [WT]).

RESULTS

HIP rats showed higher propensity for premature ventricular complexes and ventricular tachyarrhythmias, whereas HIP myocytes displayed more frequent DADs and had lower SR Ca2+ content than WT. However, the threshold SR Ca2+ at which depolarizing transient inward currents (Itis) are generated was also significantly decreased in HIP myocytes and was below the actual SR Ca2+ load, which explains the increased DAD incidence despite reduced Ca2+ in SR. In agreement with these findings, Ca2+ spark frequency was augmented in myocytes from HIP vs WT rats, which suggests activation of ryanodine receptors (RyRs) in HIP hearts. Indeed, RyR phosphorylation (by CaMKII and protein kinase A) and oxidation are enhanced in HIP hearts, whereas there is no RyR O-GlcNAcylation in either HIP or control hearts. CaMKII inhibition dissipated the difference in Ca2+ spark frequency between HIP and WT myocytes.

CONCLUSION

The threshold SR Ca2+ for generating depolarizing Itis is lower in T2D because of RyR activation after hyperphosphorylation and oxidation, which favors the occurrence of DADs despite low SR Ca2+ loads.

The Role of Epoxyeicosatrienoic Acids in Diabetes Mellitus-Induced Impaired Vascular Relaxation of Aortic Rings in Ovariectomized Sprague-Dawley Rats

AIM

The present study was aimed at determining if type 1 diabetes mellitus (DM) affects vascular function and at elucidating the mechanisms mediating vasorelaxation in both nonovariectomized and ovariectomized Sprague-Dawley (SD) rats.

MATERIALS AND METHODS

Eighty female SD rats were divided into four groups: nonovariectomized healthy (non-OVX-CTR) and diabetic (non-OVX-DM) rats and ovariectomized healthy (OVX-CTR) and diabetic (OVX-DM) rats. Bilateral ovariectomy was performed at the age of 5 weeks, and type 1 DM was induced by streptozotocin at the age of 6 weeks. At the age of 12 weeks, acetylcholine-induced relaxation (AChIR) was assessed in aortic rings in the absence/presence of L-NAME, Indomethacin, and MS-PPOH. Aortic tissue mRNA expression of eNOS, iNOS, COX-1, COX-2, thromboxane synthase 1 (TBXAS1), CYP4A1, CYP4A3, and CYP2J3, as well as plasma oxidative stress, was measured.

RESULTS

AChIR did not differ in non-OVX-DM rats compared to non-OVX-CTR ones. AChIR was significantly reduced in the OVX-DM group compared to the OVX-CTR group. MS-PPOH did not reduce AChIR in OVX-DM rats as it did in OVX-CTR ones. CYP4a3 mRNA expression in OVX-DM rats was significantly lower compared to that in the OVX-CTR group.

CONCLUSIONS

Female sex hormones may protect vasorelaxation in type 1 diabetic rats. Type 1 diabetes impairs vasorelaxation in response to ACh in ovariectomized rats (but not in nonovariectomized rats) by affecting vasorelaxation pathways mediated by EETs.

INDICATORS OF THE ELEMENT RANGE OF RAT’S BLOOD IN TERM ARTIFICIAL HYPOBYOSIS

The promising method of anesthesia and anesthesia is the state of artificial hypobiosis. Hypercapnia is a prerequisite for creating an artificial carbon dioxide hypobiosis, along with hypoxia and hypothermia. Adhering to the conditions under which the state of artificial carbon dioxide hypobiosis is created, animals reduce the level and intensity of metabolic processes both in the body as a whole and in separate organs. In order to investigate the safety of the hypobiological state and evaluate its applicability in clinical practice, it is necessary to investigate the functional characteristics of the blood. One of the most important indicators is the change of elemental composition. After all, the set of micro-and macro-elements is involved in the enzymatic reactions of the organism, its metabolic processes. Therefore, the aim of the study was to investigate the elemental changes in the blood of rats for artificial hypobiosis. In experiments, white non-breeding male rats weighing 180–200 g were used, which were maintained under standard vivarium conditions. Animals were divided into 2 groups: control and experimental (the state of artificial hypobiosis). Each group had 7 animals. Measurement of the content of macro- and micronutrients was carried out using a mass spectrometric ionization method in an inductively coupled plasma on an IRIS Interband II XSP device manufactured by Thermo Scientific, USA. The results of the study were processed and presented using the methods of statistical analysis, namely: the method of descriptive statistics; Shapiro-Wielka's criterion for choosing a statistical criterion for comparing groups; Student's criterion; Mann-Whitney's criterion. Results of evaluation of dynamics in the experimental (hypobiotic) group using the criterion of sign-marks of Wilcoxon. As a result of the studies, increased levels of Sodium, Ferrum, Calcium were observed, while the content of Nickel and Barium reduced. The results of the analysis of the dynamics of blood parameters in the experimental group by the methods of descriptive statistics showed significant changes in such elements as: Potassium, Sodium, Ferrum, Calcium, Magnesium. The heterogeneity of the results of the experimental and control groups according to the Mann-Whitney criterion was demonstrated in the following elements: Potassium, Sodium, Ferrum, Calcium, Chromium, Strontium.

Soluble epoxide hydrolase inhibitors, t-AUCB, downregulated miR-133 in a mouse model of myocardial infarction

Background

It has been demonstrated that soluble epoxide hydrolase inhibitors (sEHIs) are protective against ischemia-induced lethal arrhythmias, but the mechanisms involved are unknown. Previously, we showed that sEHIs might reduce the incidence of ischemic arrhythmias by suppressing microRNA-1 (miR-1) in the myocardium. As miR-1 and miR-133 have the same proarrhythmic effects in the heart, we assumed that the beneficial effects of sEHIs might also relate to the regulation of miR-133.

Methods

A mouse model of myocardial infarction (MI) was established by ligating the coronary artery. The sEHI t-AUCB (trans-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid) was administered daily for 7 days before MI. Myocardial infarct size and cardiac function was assessed at 24 h post-MI. The miRNA expression profiles of sham and MI mice treated with or without t-AUCB were determined by microarray and verified by real-time PCR. The incidence of arrhythmias was assessed by in vivo electrophysiologic studies. The mRNA levels of miR-133, its target genes (KCNQ1 [potassium voltage-gated channel subfamily Q member 1] and KCNH2 [potassium voltage-gated channel subfamily H member 2]), and serum response factor (SRF) were measured by real-time PCR; KCNQ1, KCNH2, and SRF protein levels were assessed by western blotting.

Results

We demonstrated that the treatment with sEHIs could reduce infarct size, improve cardia function, and prevent the development of cardiac arrhythmias in MI mice. The expression levels of 14 miRNAs differed between the sham and MI groups. t-AUCB treatment altered the expression of eight miRNAs: two were upregulated and six were downregulated. Of these, the muscle-specific miR-133 was downregulated in the ischemic myocardium. In line with this, up-regulation of miR-133 and down-regulation of KCNQ1 and KCNH2 mRNA/protein were observed in ischemic myocaridum, whereas administration of sEHIs produced an opposite effect. In addition, miR-133 overexpression inhibited expression of the target mRNA, whereas t-AUCB reversed the effects. Furthermore, SRF might participate in the negative regulation of miR-133 by t-AUCB.

Conclusions

In MI mice, sEHI t-AUCB can repress miR-133, consequently stimulating KCNQ1 and KCNH2 mRNA and protein expression, suggesting a possible mechanism for its potential therapeutic application in ischemic arrhythmias.

Electronic supplementary material

The online version of this article (10.1186/s12944-018-0780-y) contains supplementary material, which is available to authorized users.

Liraglutide protects cardiac function in diabetic rats through the PPARα pathway

Increasing evidence shows that diabetes causes cardiac dysfunction. We hypothesized that a glucagon-like peptide-1 analogue, liraglutide, would attenuate cardiac dysfunction in diabetic rats. Twenty-four Sprague Dawley (SD) rats were divided into 2 groups fed either a normal diet (normal, n = 6) or a high-fat diet (HFD, n = 18) for 4 weeks. Then, the HFD rats were injected with streptozotocin (STZ) to create a diabetic rat model. Diabetic rats were divided into 3 subgroups receiving vehicle (diabetic, n = 6), a low dose of liraglutide (Llirag, 0.2 mg/kg/day, n = 6) or a high dose of liraglutide (Hlirag, 0.4 mg/kg/day, n = 6). Metabolic parameters, systolic blood pressure, heart rate, left ventricular (LV) function, and whole genome expression of the heart were determined. Diabetic rats developed insulin resistance, increased blood lipid levels and oxidative stress, and impaired LV function, serum adiponectin, NO. Liraglutide improved insulin resistance, serum adiponectin, NO, heart rate and LV function and reduced blood triglyceride, total cholesterol levels and oxidative stress. Moreover, liraglutide increased heart Nr1h3 , Ppar-α and Srebp expression and reduced Dgat , and Angptl3 expression. Liraglutide prevented in cardiac dysfunction by activating the PPARα pathway to inhibit Dgat expression and oxidative stress in diabetic rats.

Soluble epoxide hydrolase inhibitors, t-AUCB, regulated microRNA-1 and its target genes in myocardial infarction mice

Purpose

Soluble epoxide hydrolase inhibitors (sEHIs) had been demonstrated to produce cardioprotective effects against ischemia-induced lethal arrhythmias, but the exact mechanisms remain unknown. The present study was designed to investigate whether the beneficial effects of sEHIs are related to regulation of microRNA-1, which was a proarrhythmic factor in the ischemic heart.

Methods

A mousemyocardial infarction (MI) model was established by ligating the coronary artery. sEHI t-AUCB (0.2, 1, 5 mg/L in drinking-water) was administered daily seven days before MI. The incidence of arrhythmias was assessed by in vivo electrophysiologic studies. miR-1, KCNJ2 (encoding the K⁺ channel subunit Kir2.1), and GJA1 (encoding connexin 43 [Cx43]) mRNA were measured by real-time PCR; Kir2.1 and Cx43 protein were assessed by western blotting and immunohistochemistry.

Results

We demonstrated that sEHIs reduced the myocardium infarct size and incidence of inducible arrhythmias in MI mice. Up-regulation of miR-1 and down-regulation of KCNJ2/Kir2.1 and GJA1/Cx43 mRNA/protein were observed in ischemic myocaridum, whereas administration of sEHIs produced an opposite effect. In addition, miR-1 overexpression inhibited expression of the target mRNA and their corresponding proteins, whereas t-AUCB reversed the effects. Our results further revealed that PI3K/Akt signaling pathway might participate in the negatively regulation of miR-1 by sEHi.

Conclusions

We conclude that sEHIs can repress miR-1, thus stimulate expression of KCNJ2/Kir2.1 and GJA1/Cx43 mRNA/protein in MI mice, suggesting a possible mechanism for its potential therapeutic application in ischemic arrhythmias.

The Role of Cytochrome P450 Epoxygenases, Soluble Epoxide Hydrolase, and Epoxyeicosatrienoic Acids in Metabolic Diseases

Metabolic diseases are associated with an increased risk of developing cardiovascular disease. The features comprising metabolic diseases include obesity, insulin resistance, hyperglycemia, hyperlipidemia, and hypertension. Recent evidence has emerged showcasing a role for cytochrome P450 epoxygenases, soluble epoxide hydrolase, and epoxyeicosatrienoic acids (EETs) in the development and progression of metabolic diseases. This review discusses the current knowledge related to the modulation of cytochrome P450 epoxygenases and soluble epoxide hydrolase to alter concentrations of biologically active EETs, resulting in effects on insulin resistance, lipid metabolism, obesity, and diabetes. Future areas of research to address current deficiencies in the understanding of these enzymes and their eicosanoid metabolites in various aspects of metabolic diseases are also discussed.

Hyperamylinemia Increases IL-1β Synthesis in the Heart via Peroxidative Sarcolemmal Injury

Hypersecretion of amylin is common in individuals with prediabetes, causes amylin deposition and proteotoxicity in pancreatic islets, and contributes to the development of type 2 diabetes. Recent studies also identified amylin deposits in failing hearts from patients with obesity or type 2 diabetes and demonstrated that hyperamylinemia accelerates the development of heart dysfunction in rats expressing human amylin in pancreatic β-cells (HIP rats). To further determine the impact of hyperamylinemia on cardiac myocytes, we investigated human myocardium, compared diabetic HIP rats with diabetic rats expressing endogenous (nonamyloidogenic) rat amylin, studied normal mice injected with aggregated human amylin, and developed in vitro cell models. We found that amylin deposition negatively affects cardiac myocytes by inducing sarcolemmal injury, generating reactive aldehydes, forming amylin-based adducts with reactive aldehydes, and increasing synthesis of the proinflammatory cytokine interleukin-1β (IL-1β) independently of hyperglycemia. These results are consistent with the pathological role of amylin deposition in the pancreas, uncover a novel contributing mechanism to cardiac myocyte injury in type 2 diabetes, and suggest a potentially treatable link of type 2 diabetes with diabetic heart disease. Although further studies are necessary, these data also suggest that IL-1β might function as a sensor of myocyte amylin uptake and a potential mediator of myocyte injury.

Soluble epoxide hydrolase inhibition improves coronary endothelial function and prevents the development of cardiac alterations in obese insulin-resistant mice

This study addressed the hypothesis that inhibiting the soluble epoxide hydrolase (sEH)-mediated degradation of epoxy-fatty acids, notably epoxyeicosatrienoic acids, has an additional impact against cardiovascular damage in insulin resistance, beyond its previously demonstrated beneficial effect on glucose homeostasis. The cardiovascular and metabolic effects of the sEH inhibitor trans-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid (t-AUCB; 10 mg/l in drinking water) were compared with those of the sulfonylurea glibenclamide (80 mg/l), both administered for 8 wk in FVB mice subjected to a high-fat diet (HFD; 60% fat) for 16 wk. Mice on control chow diet (10% fat) and nontreated HFD mice served as controls. Glibenclamide and t-AUCB similarly prevented the increased fasting glycemia in HFD mice, but only t-AUCB improved glucose tolerance and decreased gluconeogenesis, without modifying weight gain. Moreover, t-AUCB reduced adipose tissue inflammation, plasma free fatty acids, and LDL cholesterol and prevented hepatic steatosis. Furthermore, only the sEH inhibitor improved endothelium-dependent relaxations to acetylcholine, assessed by myography in isolated coronary arteries. This improvement was related to a restoration of epoxyeicosatrienoic acid and nitric oxide pathways, as shown by the increased inhibitory effects of the nitric oxide synthase and cytochrome P-450 epoxygenase inhibitors l-NA and MSPPOH on these relaxations. Moreover, t-AUCB decreased cardiac hypertrophy, fibrosis, and inflammation and improved diastolic function, as demonstrated by the increased E/A ratio (echocardiography) and decreased slope of the end-diastolic pressure-volume relation (invasive hemodynamics). These results demonstrate that sEH inhibition improves coronary endothelial function and prevents cardiac remodeling and diastolic dysfunction in obese insulin-resistant mice.

Cardioprotection by controlling hyperamylinemia in a "humanized" diabetic rat model

BACKGROUND

Chronic hypersecretion of the pancreatic hormone amylin is common in humans with obesity or prediabetic insulin resistance and induces amylin aggregation and proteotoxicity in the pancreas. We recently showed that hyperamylinemia also affects the cardiovascular system. Here, we investigated whether amylin aggregates interact directly with cardiac myocytes and whether controlling hyperamylinemia protects the heart.

METHODS AND RESULTS

By Western blot, we found abundant amylin aggregates in lysates of cardiac myocytes from obese patients, but not in controls. Aggregated amylin was elevated in failing hearts, suggesting a role in myocyte injury. Using rats overexpressing human amylin in the pancreas (HIP rats) and control myocytes incubated with human amylin, we show that amylin aggregation at the sarcolemma induces oxidative stress and Ca(2+) dysregulation. In time, HIP rats developed cardiac hypertrophy and left-ventricular dilation. We then tested whether metabolites with antiaggregation properties, such as eicosanoid acids, limit myocardial amylin deposition. Rats were treated with an inhibitor of soluble epoxide hydrolase, the enzyme that degrades endogenous eicosanoids. Treatment doubled the blood concentration of eicosanoids, which drastically reduced incorporation of aggregated amylin in cardiac myocytes and blood cells, without affecting pancreatic amylin secretion. Animals in the treated group showed reduced cardiac hypertrophy and left-ventricular dilation. The cardioprotective mechanisms included the mitigation of amylin-induced cardiac oxidative stress and Ca(2+) dysregulation.

CONCLUSIONS

The results suggest blood amylin as a novel therapeutic target in diabetic heart disease and elevating blood levels of antiaggregation metabolites as a pharmacological strategy to reduce amylin aggregation and amylin-mediated cardiotoxicity.

A systematic review of fetal genes as biomarkers of cardiac hypertrophy in rodent models of diabetes

Pathological cardiac hypertrophy activates a suite of genes called the fetal gene program (FGP). Pathological hypertrophy occurs in diabetic cardiomyopathy (DCM); therefore, the FGP is widely used as a biomarker of DCM in animal studies. However, it is unknown whether the FGP is a consistent marker of hypertrophy in rodent models of diabetes. Therefore, we analyzed this relationship in 94 systematically selected studies. Results showed that diabetes induced with cytotoxic glucose analogs such as streptozotocin was associated with decreased cardiac weight, but genetic or diet-induced models of diabetes were significantly more likely to show cardiac hypertrophy (P<0.05). Animal strain, sex, age, and duration of diabetes did not moderate this effect. There were no correlations between the heart weight:body weight index and mRNA or protein levels of the fetal genes α-myosin heavy chain (α-MHC) or β-MHC, sarco/endoplasmic reticulum Ca²⁺-ATPase, atrial natriuretic peptide (ANP), or brain natriuretic peptide. The only correlates of non-indexed heart weight were the protein levels of α-MHC (Spearman's ρ = 1, P<0.05) and ANP (ρ = −0.73, P<0.05). These results indicate that most commonly measured genes in the FGP are confounded by diabetogenic methods, and are not associated with cardiac hypertrophy in rodent models of diabetes.

Mechanisms of epoxyeicosatrienoic acids to improve cardiac remodeling in chronic renal failure disease

Both clinical and basic science studies have demonstrated that cardiac remodeling in patients with chronic renal failure (CRF) is very common. It is a key feature during the course of heart failure and an important risk factor for subsequent cardiac mortality. Traditional drugs or therapies rarely have effects on cardiac regression of CRF and cardiovascular events are still the first cause of death. Epoxyeicosatrienoic acids (EETs) are the products of arachidonic acids metabolized by cytochrome P450 epoxygenases. It has been found that EETs have important biological effects including anti-hypertension and anti-inflammation. Recent data suggest that EETs are involved in regulating cardiomyocyte injury, renal dysfunction, chronic kidney disease (CKD)-related risk factors and signaling pathways, all of which play key roles in cardiac remodeling induced by CRF. This review analyzes the literature to identify the possible mechanisms for EETs to improve cardiac remodeling induced by CRF and indicates the therapeutic potential of EETs in it.