Cytochrome P450 mono-oxygenase gene expression and protein activity in cultures of adult cardiomyocytes of the rat

The Challenges of Predicting Drug-Induced QTc Prolongation in Humans

The content of this article derives from a Health and Environmental Sciences Institute (HESI) consortium with a focus to improve cardiac safety during drug development. A detailed literature review was conducted to evaluate the concordance between nonclinical repolarization assays and the clinical thorough QT (TQT) study. Food and Drug Administration and HESI developed a joint database of nonclinical and clinical data, and a retrospective analysis of 150 anonymized drug candidates was reviewed to compare the performance of 3 standard nonclinical assays with clinical TQT study findings as well as investigate mechanism(s) potentially responsible for apparent discrepancies identified. The nonclinical assays were functional (IKr) current block (Human ether-a-go-go related gene), action potential duration, and corrected QT interval in animals (in vivo corrected QT). Although these nonclinical assays demonstrated good specificity for predicting negative clinical QT prolongation, they had relatively poor sensitivity for predicting positive clinical QT prolongation. After review, 28 discordant TQT-positive drugs were identified. This article provides an overview of direct and indirect mechanisms responsible for QT prolongation and theoretical reasons for lack of concordance between clinical TQT studies and nonclinical assays. We examine 6 specific and discordant TQT-positive drugs as case examples. These were derived from the unique HESI/Food and Drug Administration database. We would like to emphasize some reasons for discordant data including, insufficient or inadequate nonclinical data, effects of the drug on other cardiac ion channels, and indirect and/or nonelectrophysiological effects of drugs, including altered heart rate. We also outline best practices that were developed based upon our evaluation.

Diallyl sulfide protects against dilated cardiomyopathy via inhibition of oxidative stress and apoptosis in mice

Cytochrome P450 family 2 subfamily E member 1 (CYP2E1) is a member of the cytochrome P450 enzyme family and catalyzes the metabolism of various substrates. CYP2E1 is upregulated in multiple heart diseases and causes damage mainly via the production of reactive oxygen species (ROS). In mice, increased CYP2E1 expression induces cardiac myocyte apoptosis, and knockdown of endogenous CYP2E1 can attenuate the pathological development of dilated cardiomyopathy (DCM). Nevertheless, targeted inhibition of CYP2E1 via the administration of drugs for the treatment of DCM remains elusive. Therefore, the present study aimed to investigate whether diallyl sulfide (DAS), a competitive inhibitor of CYP2E1, can be used to inhibit the development of the pathological process of DCM and identify its possible mechanism. Here, cTnT^R141W transgenic mice, which developed typical DCM phenotypes, were used. Following treatment with DAS for 6 weeks, echocardiography, histological analysis and molecular marker detection were conducted to investigate the DAS-induced improvement on myocardial function and morphology. Biochemical analysis, western blotting and TUNEL assays were used to detected ROS production and myocyte apoptosis. It was found that DAS improved the typical DCM phenotypes, including chamber dilation, wall thinning, fibrosis, poor myofibril organization and decreased ventricular blood ejection, as determined using echocardiographic and histopathological analyses. Furthermore, the regulatory mechanisms, including inhibition both of the oxidative stress levels and the mitochondria-dependent apoptosis pathways, were involved in the effects of DAS. In particular, DAS showed advantages in terms of improved chamber dilation and dysfunction in model mice, and the improvement occurred in the early stage of the treatment compared with enalaprilat, an angiotensin-converting enzyme inhibitor that has been widely used in the clinical treatment of DCM and HF. The current results demonstrated that DAS could protect against DCM via inhibition of oxidative stress and apoptosis. These findings also suggest that inhibition of CYP2E1 may be a valuable therapeutic strategy to control the development of heart diseases, especially those associated with CYP2E1 upregulation. Moreover, the development of DAS analogues with lower cytotoxicity and metabolic rate for CYP2E1 may be beneficial.

6β-Hydroxytestosterone Promotes Angiotensin II-Induced Hypertension via Enhanced Cytosolic Phospholipase A2α Activity

Supplemental Digital Content is available in the text.

This study was conducted to test the hypothesis that the CYP1B1 (cytochrome P450 1B1)-testosterone metabolite 6β-hydroxytestosterone contributes to angiotensin II-induced hypertension by promoting activation of group IV cPLA₂α (cytosolic phospholipase A₂α) and generation of prohypertensive eicosanoids in male mice. Eight-week-old male intact or orchidectomized cPLA₂α^+/+/Cyp1b1^+/+ and cPLA₂α^–/–/Cyp1b1^+/+ and intact cPLA₂α^+/+/Cyp1b1^–/– mice were infused with angiotensin II (700 ng/kg/min, subcutaneous) for 2 weeks and injected with 6β-hydroxytestosterone (15 μg/g/every third day, intraperitoneal). Systolic blood pressure was measured by tail-cuff and confirmed by radiotelemetry. Angiotensin II-induced increase in systolic blood pressure, cardiac and renal collagen deposition, and reactive oxygen species production were reduced by disruption of the cPLA₂α or Cyp1b1 genes or by administration of the arachidonic acid metabolism inhibitor 5,8,11,14-eicosatetraynoic acid to cPLA₂α^+/+/Cyp1b1^+/+ mice. 6β-hydroxytestosterone treatment restored these effects of angiotensin II in cPLA₂α^+/+/Cyp1b1^–/– mice but not in orchidectomized cPLA₂α^–/–/Cyp1b1^+/+ mice, which were lowered by 5,8,11,14-eicosatetraynoic acid in cPLA₂α^+/+/Cyp1b1^–/– mice. Antagonists of prostaglandin E₂-EP1/EP3 receptors and thromboxane A₂-TP receptors decreased the effect of 6β-hydroxytestosterone in restoring the angiotensin II-induced increase in systolic blood pressure, cardiac and renal collagen deposition, and reactive oxygen species production in cPLA₂α^+/+/Cyp1b1^–/– mice. These data suggest that 6β-hydroxytestosterone promotes angiotensin II-induced increase in systolic blood pressure and associated pathogenesis via cPLA₂α activation and generation of eicosanoids, most likely prostaglandin E₂ and thromboxane A₂ that exerts prohypertensive effects by stimulating EP1/EP3 and TP receptors, respectively. Therefore, agents that selectively block these receptors could be useful in treating testosterone exacerbated angiotensin II-induced hypertension and its pathogenesis.

Fluconazole Represses Cytochrome P450 1B1 and Its Associated Arachidonic Acid Metabolites in the Heart and Protects Against Angiotensin II-Induced Cardiac Hypertrophy

Cytochrome P450 1B1 (CYP1B1) has been reported to have a major role in metabolizing arachidonic acid (AA) into cardiotoxic metabolites, mid-chain hydroxyeicosatetraenoic acids (HETEs). Recently, we have shown that fluconazole decreases the level of mid-chain HETEs in human liver microsomes. Therefore, the objectives of this study were to investigate the effect of fluconazole on CYP1B1 mediated mid-chain HETEs and to explore its potential protective effect against angiotensin II- (Ang II)-induced cellular hypertrophy. To do this, Sprague Dawley rats were injected intraperitoneally with a single dose of fluconazole (20 mg/kg) for 24 h. Also, H9c2 and RL-14 cells were treated with 10 μM Ang II in the presence and absence of 50 μM fluconazole for 24 h. Our results demonstrated that treatment of rats with fluconazole significantly decreased the expression of CYP1B1 enzyme and the level of mid-chain HETEs in the heart. Furthermore, fluconazole was able to attenuate Ang-II-induced cellular hypertrophy as evidenced by a significant down-regulation of hypertrophic markers; β-myosin heavy chain (MHC)/α-MHC and brain natriuretic peptide (BNP) as well as cell surface area. In conclusion, our findings indicate that fluconazole protects against Ang II-induced cellular hypertrophy by repressing CYP1B1 and its associated mid-chain HETEs.

New Molecular Mechanism Underlying Myc-Mediated Cytochrome P450 2E1 Upregulation in Apoptosis and Energy Metabolism in the Myocardium

Background

Canonical studies indicate that cytochrome P450 2E1 (CYP2E1) plays a critical role in the metabolism of xenobiotics and ultimately participates in tissue damage. CYP2E1 upregulates in the pathophysiological development of multiple diseases; however, the mechanism of CYP2E1 upregulation, particularly in heart disease, remains elusive.

Methods and Results

We found that the level of CYP2E1 increased in heart tissues from patients with hypertrophic cardiomyopathy; multiple mouse models of heart diseases, including dilated cardiomyopathy, hypertrophic cardiomyopathy, and myocardial ischemia; and HL‐1 myocytes under stress. We determined that Myc bound to the CYP2E1 promoter and activated its transcription by bioinformatics analysis, luciferase activity, and chromatin immunoprecipitation, and Myc expression was modulated by extracellular signal–regulated kinases 1/2 and phosphatidylinositol 3 kinase/protein kinase B pathways under stress or injury in myocardium by signal transduction analysis. In addition, the level of oxidative stress and apoptosis gradually worsened with age in transgenic mice overexpressing CYP2E1, which was significantly inhibited with CYP2E1 knockdown.

Conclusions

Our results demonstrated that CYP2E1 is likely a sensor of diverse pathophysiological factors and states in the myocardium. Upregulated CYP2E1 has multiple pathophysiological roles in the heart, including increased oxidative stress and apoptosis as well as energy supply to meet the energy demand of the heart in certain disease states. Our discovery thus provides a basis for a therapeutic strategy for heart diseases targeting Myc and CYP2E1.

Overview of the Components of Cardiac Metabolism

Metabolism in organs other than the liver and kidneys may play a significant role in how a specific organ responds to chemicals. The heart has metabolic capability for energy production and homeostasis. This homeostatic machinery can also process xenobiotics. Cardiac metabolism includes the expression of numerous organic anion transporters, organic cation transporters, organic carnitine (zwitterion) transporters, and ATP-binding cassette transporters. Expression and distribution of the transporters within the heart may vary, depending on the patient's age, disease, endocrine status, and various other factors. Several cytochrome P450 (P450) enzyme classes have been identified within the heart. The P450 hydroxylases and epoxygenases within the heart produce hydroxyeicosatetraneoic acids and epoxyeicosatrienoic acids, metabolites of arachidonic acid, which are critical in regulating homeostatic processes of the heart. The susceptibility of the cardiac P450 system to induction and inhibition from exogenous materials is an area of expanding knowledge, as are the metabolic processes of glucuronidation and sulfation in the heart. The susceptibility of various transcription factors and signaling pathways of the heart to disruption by xenobiotics is not fully characterized but is an area with implications for disruption of normal postnatal development, as well as modulation of adult cardiac health. There are knowledge gaps in the timelines of physiologic maturation and deterioration of cardiac metabolism. Cross-species characterization of cardiac-specific metabolism is needed for nonclinical work of optimum translational value to predict possible adverse effects, identify sensitive developmental windows for the design and conduct of informative nonclinical and clinical studies, and explore the possibilities of organ-specific therapeutics.

Development of cellular hypertrophy by 8-hydroxyeicosatetraenoic acid in the human ventricular cardiomyocyte, RL-14 cell line, is implicated by MAPK and NF-κB

Recent studies have established the role of mid-chain hydroxyeicosatetraenoic acids (mid-chain HETEs) in the development of cardiovascular disease. Among these mid-chains, 8-HETE has been reported to have a proliferator and proinflammatory action. However, whether 8-HETE can induce cardiac hypertrophy has never been investigated before. Therefore, the overall objectives of the present study are to elucidate the potential hypertrophic effect of 8-HETE in the human ventricular cardiomyocytes, RL-14 cells, and to explore the mechanism(s) involved. Our results showed that 8-HETE induced cellular hypertrophy in RL-14 cells as evidenced by the induction of cardiac hypertrophy markers ANP, BNP, α-MHC, and β-MHC in a concentration- and time-dependent manner as well as the increase in cell surface area. Mechanistically, 8-HETE was able to induce the NF-κB activity as well as it significantly induced the phosphorylation of ERK1/2. The induction of cellular hypertrophy was associated with a proportional increase in the formation of dihydroxyeicosatrienoic acids (DHETs) parallel to the increase of soluble epoxide hydrolase (sEH) enzyme activity. Blocking the induction of NF-κB, ERK1/2, and sEH signaling pathways significantly inhibited 8-HETE-induced cellular hypertrophy. Our study provides the first evidence that 8-HETE induces cellular hypertrophy in RL-14 cells through MAPK- and NF-κB-dependent mechanism

Soluble epoxide hydrolase inhibitor, TUPS, protects against isoprenaline-induced cardiac hypertrophy

BACKGROUND AND PURPOSE

We have previously shown that isoprenaline-induced cardiac hypertrophy causes significant changes in the expression of cytochromes P450 (CYP) and soluble epoxide hydrolase (sEH) genes. Therefore, it is important to examine whether the inhibition of sEH by 1-(1-methanesulfonyl-piperidin-4-yl)-3-(4-trifluoromethoxy-phenyl)-urea (TUPS) will protect against isoprenaline-induced cardiac hypertrophy.

EXPERIMENTAL APPROACH

Male Sprague-Dawley rats were treated with TUPS (0.65 mg kg(-1) day(-1), p.o.), isoprenaline (5 mg kg(-1) day(-1), i.p.) or the combination of both. In vitro H9c2 cells were treated with isoprenaline (100 μM) in the presence and absence of either TUPS (1 μM) or 11,12 EET (1 μM). The expression of hypertrophic, fibrotic markers and different CYP genes were determined by real-time PCR.

KEY RESULTS

Isoprenaline significantly induced the hypertrophic, fibrotic markers as well as the heart to body weight ratio, which was significantly reversed by TUPS. Isoprenaline also caused an induction of CYP1A1, CYP1B1, CYP2B1, CYP2B2, CYP4A3 and CYP4F4 gene expression and TUPS significantly inhibited this isoprenaline-mediated effect. Moreover, isoprenaline significantly reduced 5,6-, 8,9-, 11,12- and 14,15-EET and increased their corresponding 8,9-, 11,12- and 14,15-dihydroxyeicosatrienoic acid (DHET) and the 20-HETE metabolites. TUPS abolished these isoprenaline-mediated changes in arachidonic acid (AA) metabolites. In H9c2 cells, isoprenaline caused a significant induction of ANP, BNP and EPHX2 mRNA levels. Both TUPS and 11,12-EET significantly decreased this isoprenaline-mediated induction of ANP, BNP and EPHX2.

CONCLUSIONS AND IMPLICATIONS

TUPS partially protects against isoprenaline-induced cardiac hypertrophy, which confirms the role of sEH and CYP enzymes in the development of cardiac hypertrophy.

6β-hydroxytestosterone, a cytochrome P450 1B1 metabolite of testosterone, contributes to angiotensin II-induced hypertension and its pathogenesis in male mice

Previously, we showed that Cyp1b1 gene disruption minimizes angiotensin II-induced hypertension and associated pathophysiological changes in male mice. This study was conducted to test the hypothesis that cytochrome P450 1B1-generated metabolites of testosterone, 6β-hydroxytestosterone and 16α-hydroxytestosterone, contribute to angiotensin II-induced hypertension and its pathogenesis. Angiotensin II infusion for 2 weeks increased cardiac cytochrome P450 1B1 activity and plasma levels of 6β-hydroxytestosterone, but not 16α-hydroxytestosterone, in Cyp1b1(+/+) mice without altering Cyp1b1 gene expression; these effects of angiotensin II were not observed in Cyp1b1(-/-) mice. Angiotensin II-induced increase in systolic blood pressure and associated cardiac hypertrophy, and fibrosis, measured by intracardiac accumulation of α-smooth muscle actin, collagen, and transforming growth factor-β, and increased nicotinamide adenine dinucleotide phosphate oxidase activity and production of reactive oxygen species; these changes were minimized in Cyp1b1(-/-) or castrated Cyp1b1(+/+) mice, and restored by treatment with 6β-hydroxytestoterone. In Cyp1b1(+/+) mice, 6β-hydroxytestosterone did not alter the angiotensin II-induced increase in systolic blood pressure; the basal systolic blood pressure was also not affected by this agent in either genotype. Angiotensin II or castration did not alter cardiac, angiotensin II type 1 receptor, angiotensin-converting enzyme, Mas receptor, or androgen receptor mRNA levels in Cyp1b1(+/+) or in Cyp1b1(-/-) mice. These data suggest that the testosterone metabolite, 6β-hydroxytestosterone, contributes to angiotensin II-induced hypertension and associated cardiac pathogenesis in male mice, most probably by acting as a permissive factor. Moreover, cytochrome P450 1B1 could serve as a novel target for developing agents for treating renin-angiotensin and testosterone-dependent hypertension and associated pathogenesis in males.

Human fetal ventricular cardiomyocyte, RL-14 cell line, is a promising model to study drug metabolizing enzymes and their associated arachidonic acid metabolites

INTRODUCTION

RL-14 cells, human fetal ventricular cardiomyocytes, are a commercially available cell line that has been established from non-proliferating primary cultures derived from human fetal heart tissue. However, the expression of different drug metabolizing enzymes (DMEs) in RL-14 cells has not been elucidated yet. Therefore, the main objectives of the current work were to investigate the capacity of RL-14 cells to express different cytochrome P450 (CYP) isoenzymes and correlate this expression to primary cardiomyocytes.

METHODS

The expression of CYP isoenzymes was determined at mRNA, protein and catalytic activity levels using real time-PCR, Western blot analysis and liquid chromatography-electron spray ionization-mass spectrometry (LC-ESI-MS), respectively.

RESULTS

Our results showed that RL-14 cells constitutively express CYP ω-hydroxylases, CYP1A, 1B, 4A and 4F; CYP epoxygenases, CYP2B, 2C and 2J; in addition to soluble epoxide hydrolayse (EPHX2) at mRNA and protein levels. The basal expression of CYP ω-hydroxylases, epoxygenases and EPHX2 was supported by the ability of RL-14 cells to convert arachidonic acid to its biologically active metabolites, 20-hydroxyeicosatetraenoic acids (20-HETEs), 14,15-epoxyeicosatrienoic acids (14,15-EET), 11,12-EET, 8,9-EET, 5,6-EET, 14,15-dihydroxyeicosatrienoic acid (14,15-DHET), 11,12-DHET, 8,9-DHET and 5,6-DHET. Furthermore, RL-14 cells express CYP epoxygenases and ω-hydroxylase at comparable levels to those expressed in adult and fetal human primary cardiomyocytes cells implying the importance of RL-14 cells as a model for studying DMEs in vitro. Lastly, different CYP families were induced in RL-14 cells using 2,3,7,8-tetrachlorodibenzo-p-dioxin and fenofibrate at mRNA and protein levels.

DISCUSSION

The current study provides the first evidence that RL-14 cells express CYP isoenzymes at comparable levels to those expressed in the primary cells and thus offers a unique in vitro model to study DMEs in the heart.

Analysis of the cytotoxic effects of ruthenium-ketoconazole and ruthenium-clotrimazole complexes on cancer cells

Ruthenium-based compounds have intriguing anti-cancer properties, and some of these novel compounds are currently in clinical trials. To continue the development of new metal-based drug combinations, we coupled ruthenium (Ru) with the azole compounds ketoconazole (KTZ) and clotrimazole (CTZ), which are well-known antifungal agents that also display anticancer properties. We report the activity of a series of 12 Ru-KTZ and Ru-CTZ compounds against three prostate tumor cell lines with different androgen sensitivity, as well as cervical cancer and lymphoblastic lymphoma cell lines. In addition, human cell lines were used to evaluate the toxicity against non-transformed cells and to establish selectivity indexes. Our results indicate that the combination of ruthenium and KTZ/CTZ in a single molecule results in complexes that are more cytotoxic than the individual components alone, displaying in some cases low micromolar CC50 values and high selectivity indexes. Additionally, all compounds are more cytotoxic against prostate cell lines with lower cytotoxicity against non-transformed epidermal cell lines. Some of the compounds were found to primarily induce cell death via apoptosis yet weakly interact with DNA. Our studies also demonstrate that the cytotoxicity induced by our Ru-based compounds is not directly related to their ability to interact with DNA.

Activity, inhibition, and induction of cytochrome P450 2J2 in adult human primary cardiomyocytes

Cytochrome P450 2J2 plays a significant role in the epoxidation of arachidonic acid to signaling molecules important in cardiovascular events. CYP2J2 also contributes to drug metabolism and is responsible for the intestinal clearance of ebastine. However, the interaction between arachidonic acid metabolism and drug metabolism in cardiac tissue, the main expression site of CYP2J2, has not been examined. Here we investigate an adult-derived human primary cardiac cell line as a suitable model to study metabolic drug interactions (inhibition and induction) of CYP2J2 in cardiac tissue. The primary human cardiomyocyte cell line demonstrated similar mRNA-expression profiles of P450 enzymes to adult human ventricular tissue. CYP2J2 was the dominant isozyme with minor contributions from CYP2D6 and CYP2E1. Both terfenadine and astemizole oxidation were observed in this cell line, whereas midazolam was not metabolized suggesting lack of CYP3A activity. Compared with recombinant CYP2J2, terfenadine was hydroxylated in cardiomyocytes at a similar K(m) value of 1.5 μM. The V(max) of terfenadine hydroxylation in recombinant enzyme was found to be 29.4 pmol/pmol P450 per minute and in the cells 6.0 pmol/pmol P450 per minute. CYP2J2 activity in the cell line was inhibited by danazol, astemizole, and ketoconazole in submicromolar range, but also by xenobiotics known to cause cardiac adverse effects. Of the 14 compounds tested for CYP2J2 induction, only rosiglitazone increased mRNA expression, by 1.8-fold. This cell model can be a useful in vitro model to investigate the role of CYP2J2-mediated drug metabolism, arachidonic acid metabolism, and their association to drug induced cardiotoxicity.

Role of cytochrome P450-mediated arachidonic acid metabolites in the pathogenesis of cardiac hypertrophy

A plethora of studies have demonstrated the expression of cytochrome P450 (CYP) and soluble epoxide hydrolase (sEH) enzymes in the heart and other cardiovascular tissues. In addition, the expression of these enzymes is altered during several cardiovascular diseases (CVDs), including cardiac hypertrophy (CH). The alteration in CYP and sEH expression results in derailed CYP-mediated arachidonic acid (AA) metabolism. In animal models of CH, it has been reported that there is an increase in 20-hydroxyeicosatetraenoic acid (20-HETE) and a decrease in epoxyeicosatrienoic acids (EETs). Further, inhibiting 20-HETE production by CYP ω-hydroxylase inhibitors and increasing EET stability by sEH inhibitors have been proven to protect against CH as well as other CVDs. Therefore, CYP-mediated AA metabolites 20-HETE and EETs are potential key players in the pathogenesis of CH. Some studies have investigated the molecular mechanisms by which these metabolites mediate their effects on cardiomyocytes and vasculature leading to pathological CH. Activation of several intracellular signaling cascades, such as nuclear factor of activated T cells, nuclear factor kappa B, mitogen-activated protein kinases, Rho-kinases, Gp130/signal transducer and activator of transcription, extracellular matrix degradation, apoptotic cascades, inflammatory cytokines, and oxidative stress, has been linked to the pathogenesis of CH. In this review, we discuss how 20-HETE and EETs can affect these signaling pathways to result in, or protect from, CH, respectively. However, further understanding of these metabolites and their effects on intracellular cascades will be required to assess their potential translation to therapeutic approaches for the prevention and/or treatment of CH and heart failure.

Cytochrome P450 epoxygenase metabolite, 14,15-EET, protects against isoproterenol-induced cellular hypertrophy in H9c2 rat cell line

We have previously shown that isoproterenol-induced cardiac hypertrophy causes significant changes to cytochromes P450 (CYPs) and soluble epoxide hydrolase (sEH) gene expression. Therefore, in this study, we examined the effect of isoproterenol in H9c2 cells, and the protective effects of 14,15-EET against isoproterenol-induced cellular hypertrophy. Isoproterenol was incubated with H9c2 cells for 24 and 48 h. To determine the protective effects of 14,15-EET, H9c2 cells were incubated with isoproterenol in the absence and presence of 14,15-EET. Thereafter, the expression of hypertrophic markers and different CYP genes were determined by real time-PCR. Our results demonstrated that isoproterenol significantly increased the expression of hypertrophic marker, atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), parallel to a significant increase in cell surface area. Also, isoproterenol increased the mRNA expression of CYP1A1, CYP1B1, CYP2J3, CYP4F4 and CYP4F5, as well as the gene encoding sEH, EPHX2. On other hand, 14,15-EET significantly attenuated the isoproterenol-mediated induction of ANP, BNP, CYP1A1, CYP2J3, CYP4F4, CYP4F5 and EPHX2. Moreover 14,15-EET prevented the isoproterenol-mediated increase in cell surface area. Interestingly, 20-hydroxyeicosatetraenoic acid (20-HETE) treatment caused similar effects to that of isoproterenol treatment and induced cellular hypertrophy in H9c2 cells. In conclusion, isoproterenol induces cellular hypertrophy and modulates the expression of CYPs and EPHX2 in H9c2 cells. Furthermore, 14,15-EET exerts a protective effect against isoproterenol-induced cellular hypertrophy whereas, 20-HETE induced cellular hypertrophy in H9c2 cells.

ROS regulation of microdomain Ca(2+) signalling at the dyads

Reactive oxygen species (ROS) are emerging as centre-stage players in cardiac functional regulation. ROS and Ca(2+) signals converge at dyads, the structural and functional units of cardiac excitation-contraction coupling. These two prominent signalling systems are intertwined with ROS modulation of the entire Ca(2+)-signalling network, and vice versa. While constitutively generated homoeostatic ROS are important in setting the redox potential of the intracellular milieu, dynamic signalling ROS shape microdomain and global Ca(2+) signals on both the beat-to-beat and greater time scales. However, ROS effects are complex and subtle, characterized by multiphasic and bidirectional Ca(2+) responses; and sustained oxidative stress may lead to compromised contractility and arrhythmogenicity. These new understandings should be leveraged to harness ROS for their beneficial roles while avoiding deleterious effects in the heart.

Murine atrial HL-1 cell line is a reliable model to study drug metabolizing enzymes in the heart

HL-1 cells are currently the only cells that spontaneously contract while maintaining a differentiated cardiac phenotype. Thus, our objective was to examine murine HL-1 cells as a new in vitro model to study drug metabolizing enzymes. We examined the expression of cytochrome P450s (Cyps), phase II enzymes, and nuclear receptors and compared their levels to mice hearts. Our results demonstrated that except for Cyp4a12 and Cyp4a14 all Cyps, phase II enzymes: glutathione-S-transferases (Gsts), heme oxygenase-1 (HO-1), and NAD(P)H: quinone oxidoreductase (Nqo1), nuclear receptors: aryl hydrocarbon receptor (AhR), constitutive androstane receptor (CAR), pregnane X receptor (PXR), and peroxisome proliferator activated receptor (PPAR-alpha) were all constitutively expressed in HL-1 cells. Cyp2b19, Cyp2c29, Cyp2c38, Cyp2c40, and Cyp4f16 mRNA levels were higher in HL-1 cells compared to mice hearts. Cyp2b9, Cyp2c44, Cyp2j9, Cyp2j11, Cyp2j13, Cyp4f13, Cyp4f15 mRNA levels were expressed to the same extent to that of mice hearts. Cyp1a1, Cyp1a2, Cyp1b1, Cyp2b10, Cyp2d10, Cyp2d22, Cyp2e1, Cyp2j5, Cyp2j6, Cyp3a11, Cyp4a10, and Cyp4f18 mRNA levels were lower in HL-1 cells compared to mice hearts. Moreover, 3-methylcholanthrene induced Cyp1a1 while fenofibrate induced Cyp2j9 and Cyp4f13 mRNA levels in HL-1 cells. Examining the metabolism of arachidonic acid (AA) by HL-1 cells, our results demonstrated that HL-1 cells metabolize AA to epoxyeicosatrienoic acids, dihydroxyeicosatrienoic acids, and 20-hydroxyeicosatetraenoic acids. In conclusion, HL-1 cells provide a valuable in vitro model to study the role of Cyps and their associated AA metabolites in addition to phase II enzymes in cardiovascular disease states.

Expression and inducibility of CYP1A1, 1A2, 1B1 by β-naphthoflavone and CYP2B22, CYP3As by rifampicin in heart regions and coronary arteries of pig

In this study, the constitutive and inducible expression of the CYP genes (1A1, 1A2, 1B1, 2B22, 3A22, 3A29 and 3A46), related transcriptional factors (AhR, CAR, PXR, and Nrf2) and the antioxidant enzymes SOD, catalase, GSSH-reductase and GSH-peroxidase were investigated in the liver, heart regions and coronary arteries of control pigs and pigs treated with β-naphthoflavone (βNF) or with rifampicin (RIF). Real-time PCR experiments and enzymatic or immunoblot assays showed that CYP1A1 was predominantly enhanced by βNF in a similar manner in all the heart regions, whereas antioxidant enzyme activity was not affected. The rifampicin treatment resulted in an induction of CYP2B22 and CYP3As, at the transcriptional, activity and protein level in liver but not in heart nor in the coronary arteries, despite the expression of CAR and PXR in the cardiac tissues. These results obtained in vivo suggest that pig cardiac tissues may represent a useful model for humans.

Knockdown of Cytochrome P450 2E1 Inhibits Oxidative Stress and Apoptosis in the cTnT R141W Dilated Cardiomyopathy Transgenic Mice

Cytochrome P450 2E1 (CYP2E1) is a cytochrome P450 enzyme that catalyzes the metabolism of toxic substrates. CYP2E1 is upregulated in heart disease, including the dilated cardiomyopathy (DCM) mouse model. Here, knockdown of CYP2E1 significantly ameliorated the dilated left ventricle, thin wall, and dysfunctional contraction in the cTnT R141W and adriamycin-induced DCM mouse models. Interstitial fibrosis, poorly organized myofibrils, and swollen mitochondria with loss of cristae were improved in the myocardium of α-myosin heavy chain (MHC)-cTnT R141W ×CYP2E1-silence double-transgenic mice when compared with the cTnT R141W transgenic mice. Oxidative stress, the activation of caspase 3 and caspase 9, the release of cytochrome c , and the apoptosis in the myocardium were significantly decreased in double-transgenic mice compared with the cTnT R141W transgenic mice. In summary, the expression of CYP2E1 is upregulated in heart disease and might be induced by hypoxemia in cardiomyopathy. The overexpression of CYP2E1 can enhance the metabolism of endogenous ketones to meet the energy demand of the heart in certain disease states, but the overexpression of CYP2E1 can also increase oxidative stress and apoptosis in the DCM heart. Knockdown or downregulation of CYP2E1 might be a therapeutic strategy to control the development of DCM after mutations of cTnT R141W or other factors, because DCM is the third most common cause of heart failure and the most frequent cause of heart transplantation.

Myocardial pharmacokinetics of ebastine, a substrate for cytochrome P450 2J, in rat isolated heart

BACKGROUND AND PURPOSE

It is well established that cytochrome P450 2J (CYP2J) enzymes are expressed preferentially in the heart, and that ebastine is a substrate for CYP2J, but it is not known whether ebastine is metabolized in myocardium. Therefore, we investigated its pharmacokinetics in the rat isolated perfused heart.

EXPERIMENTAL APPROACH

Rat isolated hearts were perfused in the recirculating mode with ebastine for 130 min. The concentrations of ebastine and its metabolites, hydroxyebastine and carebastine, were measured using liquid chromatography with a tandem mass spectrometry. The data were analysed by a compartmental model. The time course of negative inotropic response was linked to ebastine concentration to determine the concentration-effect relationship.

KEY RESULTS

Ebastine was metabolized to an intermediate compound, hydroxyebastine, which was subsequently further metabolized to carebastine. No desalkylebastine was found. The kinetics of the sequential metabolism of ebastine was well described by the compartmental model. The EC(50) of the negative inotropic effect of ebastine in rat isolated heart was much higher than free plasma concentrations in humans after clinical doses.

CONCLUSIONS AND IMPLICATIONS

The kinetics of ebastine conversion to carebastine via hydroxyebastine resembled that observed in human liver microsomes. The results may be of interest for functional characterization of CYP2J activity in rat heart.

Metabolic activity and mRNA levels of human cardiac CYP450s involved in drug metabolism

Background

Tissue-specific expression of CYP450s can regulate the intracellular concentration of drugs and explain inter-subject variability in drug action. The overall objective of our study was to determine in a large cohort of samples, mRNA levels and CYP450 activity expressed in the human heart.

Methodology

CYP450 mRNA levels were determined by RTPCR in left ventricular samples (n = 68) of explanted hearts from patients with end-stage heart failure. Samples were obtained from ischemic and non-ischemic hearts. In some instances (n = 7), samples were available from both the left and right ventricles. A technique for the preparation of microsomes from human heart tissue was developed and CYP450-dependent activity was determined using verapamil enantiomers as probe-drug substrates.

Principal Findings

Our results show that CYP2J2 mRNA was the most abundant isoform in all human heart left ventricular samples tested. Other CYP450 mRNAs of importance were CYP4A11, CYP2E1, CYP1A1 and CYP2C8 mRNAs while CYP2B6 and CYP2C9 mRNAs were present at low levels in only some of the hearts analyzed. CYP450 mRNAs did not differ between ischemic and non-ischemic hearts and appeared to be present at similar levels in the left and right ventricles. Incubation of verapamil with heart microsomes led to the formation of nine CYP450-dependent metabolites: a major finding was the observation that stereoselectivity was reversed compared to human liver microsomes, in which the R-enantiomer is metabolized to a greater extent.

Conclusions

This study determined cardiac mRNA levels of various CYP450 isozymes involved in drug metabolism and demonstrated the prevalent expression of CYP2J2 mRNA. It revealed that cardiomyocytes can efficiently metabolize drugs and that cardiac CYP450s are highly relevant with regard to clearance of drugs in the heart. Our results support the claim that drug metabolism in the vicinity of a drug effector site can modulate drug effects.

Induction of CYP1A1, 2B, 2E1 and 3A in rat liver by organochlorine pesticide dicofol

The present study has determined the ability of dicofol, an organochlorine pesticide, to induce cytochrome P450 using rats treated with 1, 10, and 25mg/kg dicofol intraperitoneally for 4 days. Treatments with 10 and 25mg/kg dicofol produced dose-related increases of cytochrome P450 and cytochrome b(5) contents and NADPH-cytochrome c reductase, 7-ethoxyresorufin O-deethylase, pentoxyresorufin O-dealkylase, aniline hydroxylase, and erythromycin N-demethylase activities in liver microsomes. The treatments also increased glutathione S-transferase and superoxide dismutase activities in liver cytosol. Dicofol at 1mg/kg produced a general trend towards increases of the aforementioned enzyme levels. The results of immunoblot analyses showed that 10 and 25mg/kg dicofol increased protein levels of CYP1A1, CYP2B, CYP2E1, and 3A in liver. RT-PCR data indicated that dicofol induced mRNA expression of liver CYP1A1, CYP2B, and CYP3A. Pretreatments of rats with 10 and 25mg/kg dicofol decreased phenobarbital-induced sleeping time by 34% and 39%, respectively. Dicofol pretreatment at 25mg/kg increased CCl4-induced serum alanine aminotransferase activity by 4.3-fold and aspartate aminotransferase activity by 4.1-fold. The present study demonstrates that dicofol has the ability to induce CYP1A1, CYP2B, CYP2E1, and CYP3A in the liver and increase phenobarbital metabolism and CCl4 toxicity in rats.

Effect of 2-amino-9H-pyrido[2,3-b]indole (AalphaC), a carcinogenic heterocyclic amine present in food, on atherosclerotic plaque development in apoE deficient mice

There is experimental and epidemiological evidence demonstrating that polycyclic aromatic hydrocarbons (PAHs) are involved in the pathogenesis of cardiovascular diseases. However, heterocyclic amines (HAs), a class of carcinogenic compounds present in food, which share many biochemical features with PAHs, have not received much attention. Previous reports have shown that the heterocyclic amine 2-amino-9H-pyrido[2,3-b]indole (AalphaC) binds and metabolically affects endothelial cells in animal models suggesting a potential role in vascular remodeling. The present study investigates the effect of exposure to HAs on atherosclerotic plaque development in the apoE(-/-) mice. We observed that animals treated with AalphaC developed atherosclerotic lesions characterized by lower lipid content but richer in inflammatory cells and collagen content when compared with control animals. Moreover, atherosclerotic plaques from AalphaC-treated apoE(-/-) mice were also smaller with a marked reduction in the tunica media thickness. Furthermore, total cholesterol levels were significantly reduced in AalphaC-treated apoE(-/-) mice. In contrast to what has been previously reported for PAHs, we provide for the first time evidence that HAs may protect against cardiovascular disease by inducing stable atherosclerotic plaques and reducing circulating cholesterol levels. These results open new avenues to further investigate the role of these food-borne carcinogens in cardiovascular physiology and pathology.

Modulation of cytochrome P450 gene expression and arachidonic acid metabolism during isoproterenol-induced cardiac hypertrophy in rats

Several cytochrome P450 (P450) enzymes have been identified in the heart, and their levels have been reported to be altered during cardiac hypertrophy. Moreover, there is a strong correlation between P450-mediated arachidonic acid metabolites and the pathogenesis of cardiac hypertrophy. Therefore, we investigated the effect of isoproterenol-induced cardiac hypertrophy on the expression of several P450 genes and their associated P450-derived metabolites of arachidonic acid. Cardiac hypertrophy was induced by seven daily i.p. injections of 5 mg/kg isoproterenol. Thereafter, the heart, lung, liver, and kidney were harvested, and the expression of different genes was determined by real-time polymerase chain reaction. Heart microsomal protein from control or isoproterenol treated rats was incubated with 50 microM arachidonic acid, and arachidonic acid metabolites were determined by liquid chromatography-electron spray ionization-mass spectrometry. Our results show that isoproterenol treatment significantly increased the heart/body weight ratio and the hypertrophic markers. In addition, there was a significant induction of CYP1A1, CYP1B1, CYP4A3, and soluble epoxide hydrolase and a significant inhibition of CYP2C11 and CYP2E1 in the hypertrophied hearts as compared with the control. CYP1A1, CYP2E1, and CYP4A3 gene expression was induced in the kidney, and CYP4A3 was induced in the liver of isoproterenol-treated rats. Isoproterenol treatment significantly reduced 5,6-, 8,9-, 11,12-, and 14,15-epoxyeicosatrienoic acid formation and significantly increased their corresponding 8,9-, and 14,15-dihydroxyeicosatrienoic acid and the 20-hydroxyeicosatetraenoic acid metabolite. In conclusion, isoproterenol-induced cardiac hypertrophy alters arachidonic acid metabolism and its associated P450 enzymes, suggesting their role in the development and/or progression of cardiac hypertrophy.

Constitutive expression and inducibility of CYP1A1 in the H9c2 rat cardiomyoblast cells

Cardiomyocytes are a valuable tool for studying the drug metabolizing enzymes in the heart. However, isolated cardiomyocytes are rather fragile and difficult to isolate. Therefore, there is an urgent need for an in vitro cell line model. The H9c2 cells are commonly used as an in vitro model for studying the cellular mechanisms and signaling pathways involved in drug-induced cardiotoxicity. These cells maintain many molecular markers of cardiomyocytes and show morphological characteristics of immature embryonic cardiomyocytes. Therefore, in the present study we examined the expression and inducibility of CYP1A1 in the H9c2 rat cardiomyoblast cells. Our results showed that treatment of H9c2 cells with the CYP1A1 inducer, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) significantly induced CYP1A1 at mRNA, protein, and activity levels in a concentration-dependent manner. The RNA synthesis inhibitor, actinomycin D, completely blocked the CYP1A1 mRNA induction by TCDD, indicating the requirement of de novo RNA synthesis through transcriptional activation. In conclusion, we demonstrated for the first time the constitutive expression and inducibility of CYP1A1 in H9c2 cells. Therefore, this cell line offers a unique in vitro model to study the role of CYP1A1 in the pathogenesis of various cardiovascular diseases.

H9c2 cell line is a valuable in vitro model to study the drug metabolizing enzymes in the heart

INTRODUCTION

Recent studies demonstrated that cultured primary cardiomyocytes are a valuable tool for studying the metabolic capacity of the heart. However, a major limitation for isolated cardiomyocytes is that they are rather fragile and difficult to isolate. Therefore, there is an urgent need for an in vitro cell line model.

METHODS

Expression of different cytochrome P450 (CYP) genes were examined in a rat H9c2 cell line in comparison with that of rat heart. RNAs from H9c2 cells, rat heart as well as rat liver were isolated and CYP mRNA expression was determined by reverse transcription-polymerase chain reaction.

RESULTS

Our results showed that CYP1A1 and 1B1 are constitutively expressed in both H9c2 cells and the heart. CYP1A1 was induced by beta-naphthoflavone in H9c2 cells and the heart, whereas CYP1B1 was only induced in the heart. CYP2B1, 2B2, 2E1 and 2J3 were expressed in H9c2 cells and the heart at a comparable level but significantly lower than that detected in the liver. Expression of CYP2C11, 2C13, and 2C23 appeared to be greater in the cell line than in heart. On the other hand, CYP2A1, 3A1, and 3A2 were not expressed either in H9c2 cells or in the heart.

DISCUSSION

Our findings provide the first evidence for the expression of multiple CYPs in H9c2 cells at comparable levels to those expressed in the rat heart. Therefore, this cell line offers a valuable in vitro model to study the metabolic capacity of the heart.

Induction and inhibition of cytochrome P450-dependent monooxygenases of rats by fungicide bitertanol

The effects of fungicide bitertanol on cytochrome P450-dependent monooxygenases were studied using rats treated intraperitoneally with the N-substituted triazole for 4 days. Treatment with 10, 25, and 100 mg/kg bitertanol produced 2-, 4-, and 14-fold increases of 7-ethoxyresorufin O-deethylation activity in liver microsomes, respectively. Immunoblot analysis of microsomal proteins revealed that 25 mg/kg bitertanol increased CYP1A1 protein in the liver, kidney, and lung by 10-, 13-, and 17-fold, respectively. Bitertanol produced smaller increases of CYP2B and CYP3A catalytic activity and protein than that of CYP1A1 in liver. RT-PCR analysis of total RNA indicated that bitertanol-induced CYP1A1, CYP2B, and CYP3A mRNA. Additions of 0.01-100 microM bitertanol to liver microsomes from rats treated with 25 mg/kg bitertanol or 3-methylcholanthrene inhibited microsomal 7-ethoxyresorufin O-deethylation activity (IC(50)=0.8 or 0.9 microM). Bitertanol at 100 mg/kg increased liver UDP-glucuronosyltransferase and glutathione S-transferase activities by 2-fold. Bitertanol at 25 mg/kg produced a minor increase in metabolic activation of benzo[a]pyrene by liver S-9 fraction in the Ames mutagenicity test while the increase was blocked by addition of 100 microM bitertanol. These findings show that bitertanol is an inducer of CYP1A1, CYP2B, and CYP3A in vivo and an inhibitor of CYP1A catalytic activity in vitro.

Cytochrome P450 enzymes: Central players in cardiovascular health and disease

Cardiovascular disease (CVD) is a human health crisis that remains the leading cause of death worldwide. The cytochrome P450 (CYP) class of enzymes are key metabolizers of both xenobiotics and endobiotics. Many CYP enzyme families have been identified in the heart, endothelium and smooth muscle of blood vessels. Furthermore, mounting evidence points to the role of endogenous CYP metabolites, such as epoxyeicosatrienoic acids (EETs), hydroxyeicosatetraenoic acids (HETEs), prostacyclin (PGI(2)), aldosterone, and sex hormones, in the maintenance of cardiovascular health. Emerging science and the development of genetic screening have provided us with information on the differences in CYP expression among populations and groups of individuals. With this information, a link between CYP expression and activity and CVD, such as hypertension, coronary artery disease (CAD), myocardial infarction, heart failure, stroke, and cardiomyopathy and arrhythmias, has been established. In fact many currently used therapeutic modalities in CVD owe their therapeutic efficacy to their effect on CYP metabolites. Thus, the evidence for the involvement of CYP in CVD is numerous. Concentrating on treatment modalities that target the CYP pathway makes ethical sense for the affected individuals and decreases the socioeconomic burden of this disease. However, more research is needed to allow the integration of this information into a clinical setting.

The role of aryl hydrocarbon receptor in the pathogenesis of cardiovascular diseases

Numerous experimental and epidemiological studies have demonstrated that polycyclic aromatic hydrocarbons (PAHs), which are major constituents of cigarette tobacco tar, are strongly involved in the pathogenesis of the cardiovascular diseases (CVDs). Knowing that PAH-induced toxicities are mediated by the activation of a cytosolic receptor, aryl hydrocarbon receptor (AhR), which regulates the expression of a group of xenobiotic metabolizing enzymes (XMEs) such as CYP1A1, CYP1A2, CYP1B1, NQO1, and GSTA1, suggests a direct link between AhR-regulated XMEs and CVDs. Therefore, identifying the localization and expression of the AhR and its regulated XMEs in the cardiovascular system (CVS) is of major importance in understanding their physiological and pathological roles. Generally, it was believed that the levels of AhR-regulated XMEs are lower in the CVS than in the liver; however, it has been shown that similar or even higher levels of expression are demonstrated in the CVS in a tissue- and species-specific manner. Moreover, most, if not all, AhR-regulated XMEs are differentially expressed in most of the CVS, particularly in the endothelium cells, aorta, coronary arteries, and ventricles. Although the exact mechanisms of PAH-mediated cardiotoxicity are not fully understood, several mechanisms are proposed. Generally, induction of CYP1A1, CYP1A2, and CYP1B1 is considered cardiotoxic through generating reactive oxygen species (ROS), DNA adducts, and endogenous arachidonic acid metabolites. However the cardioprotective properties of NQO1 and GSTA1 are mainly attributed to the antioxidant effect by decreasing ROS and increasing the levels of endogenous antioxidants. This review provides a clear understanding of the role of AhR and its regulated XMEs in the pathogenesis of CVDs, in which imbalance in the expression of cardioprotective and cardiotoxic XMEs is the main determinant of PAH-mediated cardiotoxicity.

Are hERG channel inhibition and QT interval prolongation all there is in drug-induced torsadogenesis? A review of emerging trends

Contemporary preclinical in vitro and in vivo methods have been imperfect in predicting drug-induced Torsades de Pointes (TdP) in humans. A better understanding of additional relevant factors in the genesis of drug-induced TdP is necessary. New sophisticated in vitro techniques, such as arterially perfused ventricular wedge preparations or isolated perfused hearts, potentially offer a better understanding of torsadogenic mechanisms and a refinement of drug testing. Of particular interest are the dispersion of repolarization and the refractoriness of different cell types across the ventricular wall, triangulation of the action potential, reverse use dependence and instability of the action potential duration. In vivo models are currently refined by establishing parameters such as beat-to-beat variability and T-wave morphology as derived from the in vitro proarrhythmia indices. Animal models of proarrhythmia are to date not recommended for routine evaluation. A pharmacodynamic interaction with combinations of torsadogenic compounds is another area to be considered. Little is known about channel/receptor cross talk, although considerable evidence exists that cardiac G protein-coupled receptors can modulate hERG channel function. More investigations are necessary to further evaluate the role of altered gene expression, mutations, and polymorphisms in drug-induced TdP. A novel mechanism of drug-induced torsadogenesis is the reduced expression of hERG channel protein on the plasma membrane due to a trafficking defect. Pharmacokinetic and metabolism data are crucial for calculating the risk of a torsadogenic potential in man. Consideration of intracardiac accumulation can help in delineating pharmacokinetic-pharmacodyamic relationships. In silico virtual screening procedures with new chemical entities to predict hERG block may develop as a promising tool. The role of in silico modeling of TdP arrhythmia is likely to become increasingly important for organizing and integrating the vast amount of generated data. At present, however, in silico methods cannot replace existing preclinical in vitro and in vivo models.

Metabolic fate of the Ah receptor ligand 6-formylindolo[3,2-b]carbazole

The physiological role of the aryl hydrocarbon receptor (AhR), a member of the basic helix-loop-helix PER-ARNT-SIM (PAS) transcription factor family is not known. We have suggested that the AhR is involved in light signaling through binding of photoproducts with high AhR affinity. This suggestion is based on (i) the high AhR affinity of the tryptophan photoproduct formylindolo[3,2-b]carbazole (FICZ), (ii) the induction of rapid and transient expression of AhR-regulated genes by FICZ and by extracts of UV-irradiated tryptophan as well as (iii) the fact that light induces the AhR-regulated cytochrome P450s CYP1A1, CYP1B1 and CYP2S1. The transient mRNA expression caused by light and tryptophan photoproducts suggests that the biotransformation enzymes induced by AhR activation take part in a metabolic degradation of the natural AhR ligand. This study aimed at identifying the involvement of phase I and phase II enzymes in the metabolic degradation of FICZ. A cytochrome P450-dependent metabolism of FICZ giving rise to preferentially mono- and di-hydroxylated derivatives has earlier been reported. In the present study, rat and human hepatic S9 mixes were employed together with specific enzyme inhibitors and cofactors. Compared to the Aroclor-induced rat liver S9, the non-induced rat liver S9 and the human liver S9 caused a more complex metabolite profile of FICZ. The CYP1A1 enzyme was confirmed to be the most important enzyme for the first step in the metabolism. CYP1A2 was found to have overlapping specificity with CYP1A1 being able to form the same major metabolites although with different kinetics. CYP1B1 turned out to be preferentially involved in the further metabolism of dihydroxylated metabolites. Microsomal epoxide hydrolase, and as yet not identified forms of sulphotransferases and glucuronosyltransferases were also found to take part in the metabolic degradation of FICZ. Thus, tryptophan photoproducts fit into a model in which the ligand-activated AhR signaling is autoregulated by the induced metabolic enzymes.

Androgen metabolism in thymus of fetal and adult rats

Cytochrome P450 (P450) monooxygenases play a role in target tissue metabolic activation of xenobiotics and/or endogenous compounds, such as vasoactive molecules or hormones. Indeed, tissue-specific metabolism of steroids is important in a variety of organs, including thymus, and may alter tissue-specific functions. Steroids have been shown to regulate thymus growth and function, but surprisingly little is known about expression of the responsible enzyme systems in thymus tissue, nor is the thymus-specific biotransformation of testosterone known. We therefore investigated gene and protein expression, total protein content, and enzyme activity of major P450 isoforms and other key steroid-metabolizing enzymes in thymus tissue of adult and fetal rats. We detected 6 beta-hydroxytestosterone (HT), 7 alpha-HT, 16 alpha-HT, 2 alpha-HT, and androstenedione to be major testosterone metabolites in the adult thymus. The high production of 7 alpha-HT and 16 alpha-HT correlated well with the gene and protein expression of CYP2A1/2 and CYP2B1/2 in thymus of adult animals. When compared with fetal thymic tissue, CYP2A1/2, 17beta-hydroxysteroid dehydrogenase isoform 1 (17 beta-HSDH1) and the androgen receptor were 8-, 3-, and 3-fold more highly expressed in adult rats, whereas 17 beta-HSDH2, 17 beta-HSDH3, and 5 alpha-reductase were reduced to 12%, 0%, and 32% of those in fetal thymus. In conclusion, we demonstrated that rat thymus expresses a variety of cytochrome P450 monooxygenases and other steroid-metabolizing enzymes, and it successfully metabolizes testosterone. Changes of the underlying steroid-metabolizing enzyme systems may aid in understanding the role of androgens in altering biological functions of the thymus.

Experimental Assessment of the Role of Acetaldehyde in Alcoholic Cardiomyopathy

Alcoholism is one of the major causes of non-ischemic heart damage. The myopathic state of the heart due to alcohol consumption, namely alcoholic cardiomyopathy, is manifested by cardiac hypertrophy, compromised ventricular contractility and cardiac output. Several mechanisms have been postulated for alcoholic cardiomyopathy including oxidative damage, accumulation of triglycerides, altered fatty acid extraction, decreased myofilament Ca(2+ )sensitivity, and impaired protein synthesis. Despite intensive efforts to unveil the mechanism and ultimate toxin responsible for alcohol-induced cardiac toxicity, neither has been clarified thus far. Primary candidates for the specific toxins are ethanol, its first and major metabolic product - acetaldehyde (ACA) and fatty acid ethyl esters. Evidence from our lab suggests that ACA directly impairs cardiac function and promotes lipid peroxidation resulting in oxidative damage. The ACA-induced cardiac contractile depression may be reconciled with inhibitors of Cytochrome P-450 oxidase, xanthine oxidase and lipid peroxidation Unfortunately, the common methods to investigate the toxicity of ACA have been hampered by the fact that direct intake of ACA is toxic and unsuitable for chronic study, which is unable to provide direct evidence of direct cardiac toxicity for ACA. In order to overcome this obstacle associated with the chemical properties of ACA, our laboratory has used the chronic ethanol feeding model in transgenic mice with cardiac over-expression of alcohol dehydrogenase (ADH) and an in vitro ventricular myocyte culture model. The combination of both in vivo and in vitro approaches allows us to evaluate the role of ACA in ethanol-induced cardiac toxicity and certain cellular signaling pathways leading to alcoholic cardiomyopathy.

PCBs alter gene expression of nuclear transcription factors and other heart-specific genes in cultures of primary cardiomyocytes: possible implications for cardiotoxicity

1. Polychlorinated biphenyls (PCBs) are well-known environmental pollutants that bioaccumulate mainly in the fatty tissue of animals and humans. Although contamination occurs primarily via the food chain, waste combustion leads to airborne PCBs. From epidemiological studies, there is substantial evidence that cardiovascular disease is linked to air pollution, but little is known about the underlying molecular events. 2. We investigated the effects of Aroclor 1254, a complex mixture of >80 PCB isomers and congeners, on the expression of nuclear transcription factors (GATA-4, Nkx-2.5, MEF-2c, OCT-1) and of downstream target genes (atrial and brain natriuretic peptide, alpha- and beta-myosin heavy chain, alpha-cardiac and alpha-skeletal actin), which play an important role in cardiac biology. 3. We treated cultures of primary cardiomyocytes of adult rats with Aroclor 1254 (10.0 micro M) and found significant induction of the transcription factor genes GATA-4 and MEF-2c and of genes regulated by these factors, i.e. atrial natriuretic peptide, brain-type natriuretic peptide, alpha- and beta-myosin heavy chain, and skeletal alpha actin. 4. We have shown PCBs to modulate expression of genes coding for programmes of cellular differentiation and stress (e.g. atrial natriuretic peptide, brain-type natriuretic peptide) and these alterations may be important in the increase of cardiovascular disease in polluted areas.

Testosterone, cytochrome P450, and cardiac hypertrophy

Cytochrome P450 mono-oxygenases (CYP) play an essential role in steroid metabolism, and there is speculation that sex hormones might influence cardiac mass and physiology. As CYP mono-oxygenases activity is frequently altered during disease, we tested our hypothesis that CYP mono-oxygenase expression and testosterone metabolism are altered in cardiac hypertrophy. We investigate major CYP mono-oxygenase isoforms and other steroid-metabolizing enzymes and the androgen receptor in normal, hypertrophic, and assist device-supported human hearts and in spontaneously hypertensive rats (SHR). We show increased and idiosyncratic metabolism of testosterone in hypertrophic heart and link these changes to altered CYP mono-oxygenase expression. We show significant induction of 5-alpha steroid reductase and P450 aromatase gene expression and enhanced production of dihydrotestosterone, which can be inhibited by the 5-alpha reductase inhibitor finasteride. We show increased gene expression of the androgen receptor and increased levels of lipid peroxidation in diseased hearts, the latter being markedly inhibited by CYP mono-oxygenase inactivation. We show alpha-MHC to be significantly repressed in cardiac hypertrophy and restored to normal on testosterone supplementation. We conclude that heart-specific steroid metabolism is of critical importance in cardiac hypertrophy

Verapamil: new insight into the molecular mechanism of drug oxidation in the human heart

Verapamil is a commonly prescribed cardiovascular drug, but surprisingly its metabolism in the target tissue of pharmacotherapy is basically unknown. We therefore investigated its biotransformation in human heart tissue and correlate the production of metabolites with the gene expression of major drug metabolising enzymes. Using electrospray LC-MS-MS and LC-MS3 experiments, a total of nine metabolites were observed in incubation experiments with verapamil and microsomes isolated from the human heart tissue, and this included a carbinolamine-, N-formyl-, ahemiacetale-, and formate-intermediate of N-demethyl- and O-demethylverapamil. We also observed a hydroxylation product at the benzylic position of atom C-7 (M9). Metabolites M5-M9 are novel and were not observed in previous studies with liver or other human tissues. A fine example of the considerable metabolic competence of human heart is the formation of M1-M4, e.g. dealkylverapamil, norverapamil and isomers of O-demethylverapamil, which were believed to be exclusively produced by the liver.

Cardiovascular protective effects of 17beta-estradiol metabolites

17beta-estradiol (estradiol), the most abundant endogenous estrogen, affords cardiovascular protection. However, in a given cohort of postmenopausal women, estradiol replacement therapy provides cardiovascular protection in only a subset. The reasons for this variable action can only be understood once the mechanisms by which estradiol induces its cardiovascular protective effects are known. Because most biological effects of estradiol are mediated via estrogen receptors (ERs) and the heart and blood vessels contain both ER-alpha and ER-beta, the prevailing view is that ERs mediate estradiol-induced cardiovascular protection. However, recent findings that estradiol protects against vascular injury in arteries of mice lacking either ER-alpha or ER-beta seriously challenges this concept. Thus other non-ER mechanisms may be operative. Endogenous estradiol is enzymatically converted to several nonestrogenic metabolites, and some of these metabolites induce potent biological effects via ER-independent mechanisms. Therefore, it is conceivable that the cardiovascular protective effects of estradiol are mediated via its endogenous metabolites. On the basis of the evidence cited in this review, the cardiovascular protective effects of estradiol are both ER dependent and independent. The purpose of this article is to review the evidence regarding the cardiovascular protective effects of estradiol metabolites and to discuss the cellular, biochemical, and molecular mechanisms involved.

Isolation and cultivation of Ca2+ tolerant cardiomyocytes from the adult rat: improvements and applications

1. Primary cultures of cardiomyocytes provide a valuable tool for the study of the pharmacological and toxicological properties of drugs and chemicals, but for several technical reasons cardiomyocytes from adult animals are not routinely used in long-term culture. Because of significant advances in cardiovascular research, tissue engineering and cell transplantation, the need to isolate primary cells from adult animal and/or human tissue is likely to increase in the future. 2. The most common protocols for the isolation and cultivation of cardiomyocytes have been reviewed and the various approaches have been compared. The recent advances in cell culture techniques and the use of the cytoprotective agent, e.g. 2,3-butanedione monoxime greatly increases cell yield and cell viability of isolated and cultured cardiomyocytes. New concepts emerge that enabled an assessment of cellular differentiation in cultured cardiomyocytes and certain specific nuclear transcription factors may play a pivotal role in this process.