Ayman O.S. El-Kadi

Effect of cytochrome P450 polymorphism on arachidonic acid metabolism and their impact on cardiovascular diseases

Cardiovascular diseases (CVDs) remain the leading cause of death in the developed countries. Taking into account the mounting evidence about the role of cytochrome P450 (CYP) enzymes in cardiovascular physiology, CYP polymorphisms can be considered one of the major determinants of individual susceptibility to CVDs. One of the important physiological roles of CYP enzymes is the metabolism of arachidonic acid. CYP epoxygenases such as CYP1A2, CYP2C, and CYP2J2 metabolize arachidonic acid to epoxyeicosatrienoic acids (EETs) which generally possess vasodilating, anti-inflammatory, anti-apoptotic, anti-thrombotic, natriuretic, and cardioprotective effects. Therefore, genetic polymorphisms causing lower activity of these enzymes are generally associated with an increased risk of several CVDs such as hypertension and coronary artery disease. EETs are further metabolized by soluble epoxide hydrolase (sEH) to the less biologically active dihydroxyeicosatrienoic acids (DHETs). Therefore, sEH polymorphism has also been shown to affect arachidonic acid metabolism and to be associated with CVDs. On the other hand, CYP omega-hydroxylases such as CYP4A11 and CYP4F2 metabolize arachidonic acid to 20-hydroxyeicosatetraenoic acid (20-HETE) which has both vasoconstricting and natriuretic effects. Genetic polymorphisms causing lower activity of these enzymes are generally associated with higher risk of hypertension. Nevertheless, some studies have denied the association between polymorphisms in the arachidonic acid pathway and CVDs. Therefore, more research is needed to confirm this association and to better understand the pathophysiologic mechanisms behind it.

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.

Role of NF-κB in the Regulation of Cytochrome P450 Enzymes

Abstract Nuclear factor kappa B (NF-kappaB) is an important transcription factor that regulates a wide spectrum of genes including cytochrome P450 (CYP), the most important family of drug metabolizing enzymes. Therefore, in this review, we addressed the potential role of NF-kappaB in CYP regulation. We proposed three mechanisms by which NF-kappaB can regulate CYP expression and activity. First, NF-kappaB can directly regulate the expression of CYP1A1, CYP2B1/2, CYP2C11, CYP2D5, CYP2E1, CYP3A7, and CYP27B1 through binding to the promoter region of these genes. Second, NF-kappaB indirectly regulates the transcription of CYP genes through mutual repression with some nuclear receptors that are involved in CYP regulation such as AhR, CAR, GR, PXR, RXR, PPAR, FXR, and LXR. Finally, NF-kappaB can regulate CYP activity at post-transcriptional level by inducing heme oxygenase or by affecting the CYP protein stability. In addition, increased inflammatory mediators, oxidative stress, and subsequent NF-kappaB activation have been demonstrated in many conditions such as inflammatory bowel diseases, rheumatoid arthritis, psychological stress, diabetes, aging, cancer, renal diseases, and congestive heart failure. Meanwhile, there is a significant alteration of CYP expression and activity in these diseases. Therefore, we propose that NF-kappaB could be one of the links between inflammation, oxidative stress, and CYP regulation in these diseases. In conclusion, NF-kappaB plays a crucial role in the regulation of CYP through several mechanisms and this role can explain the altered CYP regulation in many conditions.

The induction of tumor apoptosis in B16 melanoma following STAT3 siRNA delivery with a lipid-substituted polyethylenimine

Persistent activation of signal transducer and activator of transcription 3 (STAT3) has been shown to impart several oncogenic features in many solid and blood tumors. In this study, we investigated the potential of nanoparticles based on polyethylenimine (PEI) modified with stearic acid (StA), to deliver siRNA for efficient STAT3 downregulation in B16 melanoma cells. The B16 cells were targeted with approximately 6-200 nm of siRNA complexes for 36 h. Compared to the PEI complexes, the PEI-StA complexes showed higher potency in STAT3 silencing in B16 cells accompanied by a significant induction of IL-6 secretion and a reduction of VEGF production. Moreover, with PEI-StA complexes, the level of the cellular Caspase 3 activity (an indicator of apoptotic activity) was found to be 2.5 times higher than that of PEI complexes. When the cells were treated with 50 nm of siRNA complexes on a daily basis, the cell viability was dramatically reduced reaching only to 16% after the third daily dose of PEI-StA complexes, as compared to the 69% viability observed with the PEI complexes at an equivalent time period. Consistently, in vivo results indicated significant regression in tumor growth and tumor weight after siRNA/PEI-StA treatment as compared to the siRNA/PEI. This was accompanied with significant increase in IL-6 levels and Caspase 3 activity, and a significant decrease in VEGF level and STAT3 activity in the tumor tissue. The lipid-modified PEI is a promising carrier for siRNA delivery and downregulation of STAT3 by polymer-mediated siRNA delivery is an effective strategy for cancer treatment especially when an optimum delivery system can potentiate the silencing activity of siRNA.

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 μM 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.

Acute doxorubicin cardiotoxicity alters cardiac cytochrome P450 expression and arachidonic acid metabolism in rats

Doxorubicin (DOX) is a potent anti-neoplastic antibiotic used to treat a variety of malignancies; however, its use is limited by dose-dependent cardiotoxicity. Moreover, there is a strong correlation between cytochrome P450 (CYP)-mediated arachidonic acid metabolites and the pathogenesis of many cardiovascular diseases. Therefore, in the current study, we have investigated the effect of acute DOX toxicity on the expression of several CYP enzymes and their associated arachidonic acid metabolites in the heart of male Sprague-Dawley rats. Acute DOX toxicity was induced by a single intraperitoneal injection of 15 mg/kg of the drug. Our results showed that DOX treatment for 24 h caused a significant induction of CYP1A1, CYP1B1, CYP2C11, CYP2J3, CYP4A1, CYP4A3, CYP4F1, CYP4F4, and EPHX2 gene expression in the heart of DOX-treated rats as compared to the control. Similarly, there was a significant induction of CYP1A1, CYP1B1, CYP2C11, CYP2J3, CYP4A, and sEH proteins after 24 h of DOX administration. In the heart microsomes, acute DOX toxicity significantly increased the formation of 20-HETE which is consistent with the induction of the major CYP omega-hydroxylases: CYP4A1, CYP4A3, CYP4F1, and CYP4F4. On the other hand, the formation of 5,6-, 8,9-, 11,12-, and 14,15-epoxyeicosatrienoic acids (EETs) was significantly reduced, whereas the formation of their corresponding dihydroxyeicosatrienoic acids was significantly increased. The decrease in the cardioprotective EETs can be attributed to the increase of sEH activity parallel to the induction of the EPHX2 gene expression in the heart of DOX-treated rats. In conclusion, acute DOX toxicity alters the expression of several CYP and sEH enzymes with a consequent alteration in arachidonic acid metabolism. These results may represent a novel mechanism by which this drug causes progressive cardiotoxicity.

STAT3 Silencing in Dendritic Cells by siRNA Polyplexes Encapsulated in PLGA Nanoparticles for the Modulation of Anticancer Immune Response

In dendritic cells (DCs), the induction of signal transducer and activator of transcription 3 (STAT3) by tumor-derived factors (TDFs) renders DCs tolerogenic and suppresses their antitumor activity. Therefore, silencing STAT3 in DCs is beneficial for cancer immunotherapy. We have shown that STAT3 knockdown in B16 murine melanoma by siRNA polyplexes of polyethylenimine (PEI) or its stearic acid derivative (PEI-StA) induces B16 cell death in vitro and in vivo. Here, we investigated the physical encapsulation of siRNA/PEI and PEI-StA polyplexes in poly(d,l-lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) for STAT3 knockdown in DCs. PLGA NPs containing siRNA polyplexes of PEI (PLGA-P) and PEI-StA (PLGA-PS) had an average diameter of ~350 to 390 nm and a zeta potential of ∼-13 to -19 mV, respectively. The encapsulation efficiency (E.E.) of siRNA in PLGA-P and PLGA-PS was 26% and 43%, respectively. In both NP types, siRNA release followed a triphasic pattern, but it was faster in PLGA-PS. Our uptake study by fluorescence microscopy confirmed DC uptake and endosomal localization of both NP types. After exposure to B16.F10 conditioned medium, DCs showed high STAT3 and low CD86 expression indicating impaired function. STAT3 silencing by PLGA-P and PLGA-PS of STAT3 siRNA restored DC maturation and functionality as evidenced by the upregulation of CD86 expression, high secretion of TNF-α and significant allogenic T cell proliferation. Moreover, encapsulation in PLGA NPs significantly reduced PEI-associated toxicity on DCs. We propose this formulation as a strategy for targeted siRNA delivery to DCs. The potential of this approach is not limited to STAT3 downregulation in DCs but can be used to target the expression of other proteins as well. Moreover, it can be combined with other means for cancer immunotherapy like cancer vaccine strategies.

Sulforaphane induces CYP1A1 mRNA, protein, and catalytic activity levels via an AhR-dependent pathway in murine hepatoma Hepa 1c1c7 and human HepG2 cells

Recent reports have proposed that some naturally occurring phytochemicals can function as anticancer agents mainly through inducing phase II drug detoxification enzymes. Of these phytochemicals, isothiocyanates sulforaphane (SUL), present in broccoli, is by far the most extensively studied. In spite of its positive effect on phase II drug metabolizing enzymes, its effect on the phase I bioactivating enzyme cytochrome P450 1a1 (Cyp1a1) is still a matter of debate. As a first step to investigate this effect, Hepa 1c1c7 and HepG2 cells were treated with various concentration of SUL. Our results showed that SUL-induced CYP1A1 mRNA in a dose- and time-dependent manner. Furthermore, this induction was further reflected on the protein and catalytic activity levels. Investigating the effect of SUL at the transcriptional level revealed that SUL increases the Cyp1a1 mRNA as early as 1h. The RNA polymerase inhibitor actinomycin D (Act-D) completely abolished the SUL-induced Cyp1a1 mRNA. Furthermore, SUL successfully activated AhR transformation and its subsequent binding to the XRE. At the post-transcriptional level, SUL did not affect the levels of existing Cyp1a1 mRNA transcripts. This is the first demonstration that the broccoli-derived SUL can directly induce Cyp1a1 gene expression in an AhR-dependent manner and represents a novel mechanism by which SUL induces this enzyme.

The impact of experimental hyperlipidemia on the distribution and metabolism of amiodarone in rat

The tissue distribution and hepatic microsomal metabolism of amiodarone were studied in a hyperlipidemic rat model. Rats were rendered hyperlipidemic by the intraperitoneal injection of poloxamer 407. Other normolipidemic animals given saline in place of poloxamer 407 were used as control animals. After single intravenous injection of amiodarone HCl (25mg/kg) rats were anesthetized and plasma and tissue specimens were obtained. Liver microsomal protein was harvested and used to measure velocity of desethylamiodarone formation from amiodarone and cytochrome P450 (CYP) protein expression. Hyperlipidemia caused large increases in plasma concentrations of amiodarone. In tissues, however, concentrations of drug selectively increased, decreased or did not change. In heart, the site of action of the drug, as well as liver and spleen, amiodarone concentrations increased. In other tissues such as kidney, lung and brain, concentrations decreased. No changes were seen in fat or thyroid. Decreases were observed in liver metabolic efficiency, and expression of CYP3A1/2 and 2C11. No changes were seen in CYP2B1/2, 2C6, 2D1 or 1A2. This experimental hyperlipidemia caused a complex pattern of changes in tissue distribution of AM. In addition, there are decreases in the expression of some important rat CYP isoenzymes.

3-methylcholanthrene and benzo(a)pyrene modulate cardiac cytochrome P450 gene expression and arachidonic acid metabolism in male Sprague Dawley rats.

Background and purpose:  There is a strong correlation between cytochrome P450 (P450)‐dependent arachidonic acid metabolism and the pathogenesis of cardiac hypertrophy. Several aryl hydrocarbon receptor (AhR) ligands were found to alter P450‐dependent arachidonic acid metabolism. Here, we have investigated the effect of 3‐methylcholanthrene (3‐MC) and benzo(a)pyrene (BaP), two AhR ligands, on the development of cardiac hypertrophy.