Having a heart attack? Avoid the “HETE”!

Mitochondrial activity and oxidative stress functions are influenced by the activation of AhR-induced CYP1A1 overexpression in cardiomyocytes

There is an endemic cardiomyopathy currently occurring in China, termed, Keshan disease (KD). The authors previously compared mitochondrial-associated gene expression profiles of peripheral blood mononuclear cells (PBMCs) derived from KD patients and normal controls, using mitochondria-focused cDNA microarray technology. The results detected an upregulation of the enzyme-associated CYP1A1 gene, (ratios ≥2.0). The aryl hydrocarbon receptor (AhR) regulates the expression of numerous cytochrome P450 (CYP) genes including members of the CYP1 family; CYP1A1 and CYP1A2. Several previous studies have suggested roles for the aryl hydrocarbon receptor (AhR) and the genes that it regulates. An example involves cytochrome P4501A1 (CYP1A1), in the pathogenesis of heart failure, cardiac hypertrophy and other cardiomyopathies. Mitochondria comprise ~30% of the intracellular volume in mammalian cardiomyocytes, and subtle alterations in mitochondria can markedly influence cardiomyopathies. The present study investigated alterations in the activity and functions of mitochondria following AhR-induced overexpression of CYP1A1. AC16 cells were treated with the CYP1A1 inducer 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and cytotoxicity was then evaluated in MTT assays. Reverse transcription-quantitative polymerase chain reactions, western blot analysis and 7-ethoxyresorufin O-deacylase assays were performed to analyze the mRNA and protein levels, and the enzymatic activity of CYP1A1. Mitochondrial activity and mass were analyzed using an inverted fluorescence microscope and a fluorescence microplate reader. Reactive oxygen species (ROS) activity was analyzed using flow cytometry. The results of the current study demonstrated that TCDD gradually increased mRNA and protein levels of AhR and CYP1A1, in addition to the enzymatic activity. Mitochondrial activity and the quality of mitochondrial membranes were also significantly attenuated, and mitochondrial ROS levels were elevated in the TCDD-induced cardiomyocytes. The results indicate the involvement of the AhR/CYP1A1 signaling pathway in the mechanism of action of TCDD in human cardiomyocytes. The present findings may provide an explanation for myocardial injuries caused by polycyclic aromatic hydrocarbons. The authors conclude that exposure to TCDD results in regulatory alteration to the expression of detoxification genes that ultimately affect the metabolic activation and function of cardiomyocytes.

Inflammation in myocardial diseases

Inflammatory processes underlie a broad spectrum of conditions that injure the heart muscle and cause both structural and functional deficits. In this article, we address current knowledge regarding 4 common forms of myocardial inflammation: myocardial ischemia and reperfusion, sepsis, viral myocarditis, and immune rejection. Each of these pathological states has its own unique features in pathogenesis and disease evolution, but all reflect inflammatory mechanisms that are partially shared. From the point of injury to the mobilization of innate and adaptive immune responses and inflammatory amplification, the cellular and soluble mediators and mechanisms examined in this review will be discussed with a view that both beneficial and adverse consequences arise in these human conditions.

Cytosolic phospholipase A(2)α protects against ischemia/reperfusion injury in the heart

Studies with sPLA(2) Group X, and cPLA(2) α gene-targeted mice suggest that absence of sPLA(2) Group X results in protection from ischemia/reperfusion (I/R) injury in the heart, and absence of cPLA(2) α Group IV is protective in the brain. Although latter studies might suggest a similar deleterious role for cPLA(2) α in I/R injury in the heart, the pathophysiology of stroke is intricately related to excitotoxicity and cannot necessarily be extrapolated to the heart. We report here that unlike findings in the brain, cPLA(2) α((-/-)) mice have exaggerated injury following I/R in vivo. In contrast, there is no difference in injury induced by simulated ischemia in cardiomyocytes isolated from cPLA(2) α((-/-)) versus cPLA(2) α((+/+)) mice. This suggests that cPLA(2) α does not have an important cardiomyocyte autonomous effect on ischemic injury. Prostaglandin E(2) (PGE(2) ) levels are significantly reduced in the hearts of the cPLA(2) α((-/-)) mice, and the enhanced injury is ameliorated by treatment with the PGE analog, misoprostol. We demonstrate that cPLA(2) α is cardioprotective in vivo, and this is likely via cPLA(2) α-mediated production of cardioprotective eicosanoids. These studies are the first to identify a protective role for cPLA(2) in I/R injury in any organ and raise concerns over long-term inhibition of cPLA(2).

Different patterns of oxidized lipid products in plasma and urine of dengue fever, stroke, and Parkinson's disease patients: cautions in the use of biomarkers of oxidative stress

Many products of lipid oxidation have been associated with human diseases. These include F2-isoprostanes (F2-IsoPs), hydroxyeicosatetraenoic acid products (HETEs), and cholesterol oxidation products (COPs). Here we present measurements of F2-IsoPs, HETEs, COPs, and arachidonate in single plasma samples of patients with acute (dengue fever and ischemic stroke) and chronic (Parkinson's) diseases, and in age-matched study controls. Urine samples were collected for F2-IsoPs analysis. Our analysis demonstrated elevated F2-IsoPs levels in ischemic stroke, HETEs in Parkinson's disease, dengue fever, and ischemic stroke, and COPs in Parkinson's disease and dengue fever patients, as compared with those in age-matched study controls. Strong but complex correlations were observed between levels of certain oxidized lipid products and age. The relations between various oxidized lipids and dengue fever, stroke, and Parkinson's disease are discussed in relation to the selection and application of biomarkers of oxidative lipid damage, in particular the need for corrections for age and lipid levels.

20-HETE increases renal sympathetic nerve activity via activation of chemically and mechanically sensitive muscle afferents

Arachidonic acid and its metabolites produced via cyclooxygenase (COX) and lipoxygenase pathways have been reported to contribute to the cardiovascular reflexes evoked by stimulating thin fibre muscle afferents during muscle contraction. 20-Hydroxyeicosatetraenoic acid (20-HETE), a primarily metabolized product of arachidonic acid by cytochrome P450 enzymes, can be accumulated in contracting muscles. Thus, the purpose of this study was to determine the role of 20-HETE in modulating the reflex sympathetic responses to activation of chemically and mechanically sensitive muscle afferents. The renal sympathetic nerve activity (RSNA) and cardiovascular responses were examined after injections of 20-HETE into the arterial blood supply of the hindlimb muscles of decerebrated rats. This induced a dose-dependent increases in RSNA and mean arterial pressure (MAP). We also tested the hypothesis that 20-HETE would sensitize muscle afferents and, thereby, augment the RSNA and blood pressure response to muscle stretch. The results show that arterial infusion of 20-HETE significantly enhanced the RSNA and MAP responses to muscle stretch. In contrast, N-hydroxy-N'-(4-butyl-2-methylphenyl)formamidine, a potent inhibitor of 20-HETE production, attenuated the reflex muscle responses. Furthermore, the sensitizing effect of 20-HETE on the muscle reflex was significantly attenuated after blocking COX activity with indomethacin. Our data suggest that 20-HETE plays a role in modulating muscle afferent-mediated sympathetic responses, probably through engagement of a COX-dependent mechanism.