Impact of Cyp1a2 or Ahr gene knockout in mice: Implications for biomonitoring studies

The role of the cytochrome P450 superfamily in the skin

In mammals, the skin acts as a barrier to prevent harmful environmental stimuli from entering the circulation. CYP450s are involved in drug biotransformation, exogenous and endogenous substrate metabolism, and maintaining the normal physiological function of the skin, as well as facilitating homeostasis of the internal environment. The expression pattern of CYP450s in the skin is tissue-specific and thus differs from the liver and other organs. The development of skin topical medications, and knowledge of the toxicity and side effects of these medications require a detailed understanding of the expression and function of skin-specific CYP450s. Thus, we summarized the expression of CYP450s in the skin, their function in endogenous metabolic physiology, aberrant CYP450 expression in skin diseases and the influence of environmental variables and medications. This information will serve as a crucial foundation for future studies on the skin, as well as for the design and development of new drugs for skin diseases including topical medications.

Characterization of Five Natural Anthraquinone Compounds as Potent Inhibitors against CYP1B1: Implications for Cancer Treatment

BACKGROUND

Human cytochrome P450 1B1 (CYP1B1) is an extrahepatic enzyme that is overexpressed in many tumors and is associated with tumor development and acquired resistance. Few studies have reported that anthraquinone compounds have inhibitory activity against the CYP1B1 enzyme. Cassiae semen (Leguminosae) is a well-known traditional Chinese medicine containing more than 70 compounds. The crude extracts and pure compounds of Cassiae semen have been widely used in preclinical and clinical practice for their beneficial effects, such as neuroprotective, hepatoprotective, antimicrobial, antioxidant, and hypotensive effects. Aloe-emodin, chrysophanol, obtusifolin, aurantio-obtusin, and rhein are important active natural anthraquinones in Cassiae semen.

OBJECTIVE

Aloe-emodin, chrysophanol, obtusifolin, aurantio-obtusin, and rhein have a wide range of pharmacological activities and have been found to have good anti-tumor and antioxidant effects. However, the underlying mechanisms of these pharmacological activities remain poorly understood. This study aimed to investigate the inhibitory effects of five natural anthraquinones on the activity of CYP1B1 and to analyze the structure- activity relationship of these compounds.

MATERIALS AND METHODS

In this study, 7-ethoxyresorufin O-deethylation (EROD) was used as the fluorescent substrate of CYP1B1 to investigate the inhibition effect, and molecular docking was performed to further determine the structural-activity relationship of the compound molecules.

RESULTS

We found that aloe-emodin and chrysophanol had strong inhibitory effects on CYP1B1 with IC50 values of 0.28 and 0.34μM, respectively, while obtusifolin and aurantio-obtusin had IC50 values of 0.77μM and 9.11μM, respectively. The structural activity analysis showed that the inhibition strength was related to the position of the hydroxyl group substitution and the number of methoxy group substitutions. Rhein containing one carboxyl group showed the weakest inhibition of 23.72μM. The inhibition kinetics showed that all five compounds belonged to the non-competitive inhibition model. The inhibition kinetics revealed that all five compounds exhibited the non-competitive inhibition model.

CONCLUSION

The present study provided a comprehensive analysis of the inhibitory effects of five natural anthraquinones, namely aloe-emodin, chrysophanol, obtusifolin, aurantio-obtusin and rhein, on CYP1B1 activity, and elucidated the structure-activity relationship. Molecular docking simulations further revealed the specific amino acid residues within the active site of CYP1B1, where these compounds exerted their actions. These findings offer novel insights into investigating the potential antitumor properties of natural anthraquinones.

7H-Dibenzo[c,g]carbazole: Metabolic pathways and toxicity

7H-Dibenzo[c,g]carbazole (DBC), a local and systemic carcinogen in animal studies, is a common environmental pollutant. It generally co-occurs in a variety of organic complex mixtures derived from incomplete combustion of organic matter. Despite high lipophilicity, DBC is more water-soluble and faster metabolized than the homocyclic aromatics. Moreover, greater polarity, high bioaccumulation potential, and persistence in the environment may imply DBC's higher biological significance and impact on human health, even at lower concentrations. The biotransformation pathways of DBC are incompletely known and the ultimate carcinogenic metabolite(s) are not clearly identified as yet. Structure-biological studies suggest two ways of activation: at the ring carbon atoms and at the pyrrole nitrogen. It is supposed that the particular pathway of biotransformation might be connected with the tissue/organ specificity of DBC. Cytochrome P450 (CYP) family of enzymes plays a pivotal role in the metabolism of DBC; though, the one-electron activation and the aldo-keto reductase-catalyzed oxidation are also involved in metabolic activation. Additionally, DBC can be photoactivated even at physiologically relevant doses of UVA light due to the extended aromatic ring system resulting in strong genotoxicity and oxidative stress. The goal of this review is to summarize current knowledge on mechanisms of DBC activation and possible implications for toxicity, genotoxicity, and carcinogenicity.

Cancer chemoprevention revisited: Cytochrome P450 family 1B1 as a target in the tumor and the microenvironment

Cancer chemoprevention is the use of synthetic, natural or biological agents to prevent or delay the development or progression of malignancies. Intriguingly, many phytochemicals with anti-inflammatory and anti-angiogenic effects, recently proposed as chemoprevention strategies, are inhibitors of Cytochrome P450 family 1B1 (CYP1B1), an enzyme overexpressed in a wide variety of tumors and associated with angiogenesis. In turn, pro-inflammatory cytokines were reported to boost CYP1B1 expression, suggesting a key role of CYP1B1 in a positive loop of inflammatory angiogenesis. Other well-known pro-tumorigenic activities of CYP1B1 rely on metabolic bioactivation of xenobiotics and steroid hormones into their carcinogenic derivatives. In contrast to initial in vitro observations, in vivo studies demonstrated a protecting role against cancer for the other CYP1 family members (CYP1A1 and CYP1A2), suggesting that the specificity of CYP1 family inhibitors should be carefully taken into account for developing potential chemoprevention strategies. Recent studies also proposed a role of CYP1B1 in multiple cell types found within the tumor microenvironment, including fibroblasts, endothelial and immune cells. Overall, our review of the current literature suggests a positive loop between inflammatory cytokines and CYP1B1, which in turn may play a key role in cancer angiogenesis, acting on both cancer cells and the tumor microenvironment. Strategies aiming at specific CYP1B1 inhibition in multiple cell types may translate into clinical chemoprevention and angioprevention approaches.

Comparative chronic liver toxicity of benzo[a]pyrene in two populations of the atlantic killifish (Fundulus heteroclitus) with different exposure histories

BACKGROUND

The Atlantic Wood Industries Superfund site on the Elizabeth River (ER) in Portsmouth, Virginia, is contaminated with polycyclic aromatic hydrocarbons (PAHs) derived from creosote. Embryos and larvae of ER killifish (Fundulus heteroclitus) are refractory to the induction of enzymes regulated by the aryl hydrocarbon receptor including cytochrome P4501A (CYP1A) and are resistant to PAH-induced lethality and teratogenicity. However, adult ER killifish show a greater prevalence of hepatic and pancreatic tumors compared with those from reference sites.

OBJECTIVES

We used controlled laboratory studies to determine if ER killifish are more or less sensitive to PAH-induced chronic hepatic toxicity than killifish from an uncontaminated site.

METHODS

Larvae from the ER and a reference site on King's Creek (KC) were subjected to two 24-hr aqueous exposures of benzo[a]pyrene (BaP; 0-400 µg/L). At various time points, larvae were analyzed for CYP1A activity, BaP concentrations, nuclear and mitochondrial DNA damage, and liver pathology.

RESULTS

CYP1A activity was induced by BaP in KC but not ER larvae, and KC larvae demonstrated a greater reduction in whole-body concentrations of BaP over time. Mitochondrial and nuclear DNA lesion frequency increased significantly in BaP-exposed KC larvae, but not in ER larvae. Nine months postexposure, KC juveniles exhibited significantly more hepatic foci of cellular alteration and only KC juveniles developed hepatocellular carcinomas.

CONCLUSIONS

In addition to acquiring the heritable resistance to the acute teratogenic effects of PAHs, ER fish appear to have concomitantly developed resistance to chronic effects, including cancer.

Differences between human slow N-acetyltransferase 2 alleles in levels of 4-aminobiphenyl-induced DNA adducts and mutations

Aromatic amines such as 4-aminobiphenyl (ABP) require biotransformation to exert their carcinogenic effects. Genetic polymorphisms in biotransformation enzymes such as N-acetyltransferase 2 (NAT2) may modify cancer risk following exposure. Nucleotide excision repair-deficient Chinese hamster ovary (CHO) cells stably transfected with human cytochrome P4501A1 (CYP1A1) and a single copy of either NAT2*4 (rapid acetylator), NAT2*5B (common Caucasian slow acetylator), or NAT2*7B (common Asian slow acetylator) alleles (haplotypes) were treated with ABP to test the effect of NAT2 polymorphisms on DNA adduct formation and mutagenesis. ABP N-acetyltransferase catalytic activities were detectable only in cell lines transfected with NAT2 and were highest in cells transfected with NAT2*4, lower in cells transfected with NAT2*7B, and lowest in cells transfected with NAT2*5B. Following ABP treatment, N-(deoxyguanosin-8-yl)-4-aminobiphenyl (dG-C8-ABP) was the primary adduct formed. Cells transfected with both CYP1A1 and NAT2*4 showed the highest concentration-dependent cytotoxicity, hypoxanthine phosphoribosyl transferase (hprt) mutants, and dG-C8-ABP adducts. Cells transfected with CYP1A1 and NAT2*7B showed lower levels of cytotoxicity, hprt mutagenesis, and dG-C8-ABP adducts. Cells transfected with CYP1A1 only or cells transfected with both CYP1A1 and NAT2*5B did not induce cytotoxicity, hprt mutagenesis or dG-C8-ABP adducts. ABP-DNA adduct levels correlated very highly (r>0.96) with ABP-induced hprt mutant levels following each treatment. The results of the present study suggest that investigations of NAT2 genotype or phenotype associations with disease or toxicity could be more precise and reproducible if heterogeneity within the "slow" NAT2 acetylator phenotype is considered and incorporated into the study design.

Antipsychotic drugs alter neuronal development including ALM neuroblast migration and PLM axonal outgrowth in Caenorhabditis elegans

Antipsychotic drugs are increasingly being prescribed for children and adolescents, and are used in pregnant women without a clear demonstration of safety in these populations. Global effects of these drugs on neurodevelopment (e.g., decreased brain size) have been reported in rats, but detailed knowledge about neuronal effects and mechanisms of action are lacking. Here we report on the evaluation of a comprehensive panel of antipsychotic drugs in a model organism (Caenorhabditis elegans) that is widely used to study neuronal development. Specifically, we examined the effects of the drugs on neuronal migration and axonal outgrowth in mechanosensory neurons visualized with green fluorescent protein expressed from the mec-3 promoter. Clozapine, fluphenazine, and haloperidol produced deficits in the development and migration of ALM neurons and axonal outgrowth in PLM neurons. The defects included failure of neuroblasts to migrate to the proper location, and excessive growth of axons past their normal termination point, together with abnormal morphological features of the processes. Although the antipsychotic drugs are potent antagonists of dopamine and serotonin receptors, the neurodevelopmental deficits were not rescued by co-incubation with serotonin or the dopaminergic agonist, quinpirole. Other antipsychotic drugs, risperidone, aripiprazole, quetiapine, trifluoperazine and olanzapine, also produced modest, but detectable, effects on neuronal development. This is the first report that antipsychotic drugs interfere with neuronal migration and axonal outgrowth in a developing nervous system.

Interaction between CYP1A2-T2467DELT polymorphism and smoking in adenocarcinoma and squamous cell carcinoma of the lung

This study aimed to identify new genetic characteristics contributing to individual susceptibility to smoke-induced lung cancer. Despite functional evidence of a possible role of cytochrome P450 1A2 (CYP1A2) in lung cancer susceptibility, no studies have evaluated the influence of CYP1A2 genotypes on lung cancer risk. We investigated the interaction between CYP1A2-T2467delT (allele*1D) polymorphism and smoking in Tunisian lung cancer cases (n=101 male smokers) separately for the histological types squamous cell carcinoma (SCC) (n=60) and adenocarcinoma (n=41), and in controls (n=98 male smokers) using a case-only study design. A significant interaction between CYP1A2-T/delT or delT/delT genotypes and tobacco consumption (pack-years) adjusted for age was evident (OR (95% CI) 7.78 (1.52-42.8)) in the SCC cases who smoked relatively less (< or =33 pack-years, I quartile value), but not in adenocarcinoma and controls. Our results suggest that CYP1A2-T2467delT polymorphism has an important role in lung carcinogenesis, especially SCC, among smokers.

Toxicogenomics in Drug Discovery and Drug Development: Potential Applications and Future Challenges

Despite the massive investments made by pharmaceutical companies on drug research and development, the number of new drug approvals has remained stagnant in the past decades. It is well known that developing safe and effective new drugs is a long, difficult, and expensive process. While the cost of developing new drugs is increasing rapidly, withdrawals of drugs from the marketplace due to adverse drug reactions (ADR) and/or toxicity is increasing concurrently. The recent advent of high-throughput in silico (computer softwares) and in vitro (cell cultures) screenings have somewhat alleviated some, but not all, of these challenges by providing an efficient and effective way for developing safer and better drugs. This emerging technology, known as toxicogenomics, has great potential to facilitate the development of methodologies that could predict the long-term toxic effects of compounds using relatively short-term bioassays. This review is aimed at discussing the potential applications and future challenges of toxicogenomics in drug discovery and drug development.