Comparative induction of CYP1A1 expression by pyridine and its metabolites

Antithrombotic effects of pyridinium compounds formed from trigonelline upon coffee roasting

Coffee may exert a preventive effect on arterial thrombosis. Trigonelline is one of the most abundant compounds in coffee that undergoes pyrolysis upon roasting of coffee beans. The aim of the present study was to identify pyridinium compounds formed upon trigonelline pyrolysis and coffee roasting and to investigate the effect of three of them, i.e., 1-methylpyridine and 1,3- and 1,4-dimethylpyridine, on experimentally induced arterial thrombosis in rats. 1,3- and 1,4-dimethylpyridine but not 1-methylpyridine inhibited arterial thrombus formation. 1,3-Dimethylpyridine inhibited platelet aggregation and reduced fibrin formation in platelet-rich plasma, whereas 1,4-dimethylpyridine increased the plasma level of 6-keto-PGF1α. 1,4-Dimethylpyridine slightly increased rat tissue plasminogen activator plasma activity. In summary, we demonstrated that pyridinium compounds display mild antithrombotic properties due to stimulation by prostacyclin release (1,4-dimethylpyridine) and inhibition of platelet aggregation (1,3-dimethylpyridine). Those pyridinium compounds may, to some extent, be responsible for the beneficial effects of coffee drinking.

2,3,7,8-Tetrachlorodibenzo-p-dioxin enhances CCl4-induced hepatotoxicity in an aryl hydrocarbon receptor-dependent manner

Cytochrome P4502E1 (CYP2E1) is involved in the biotransformation of several low molecular weight chemicals and plays an important role in the metabolic activation of carcinogens and hepatotoxins such as CCl(4). Induction of CYP2E1 is exerted mainly at posttranscriptional levels through mRNA and protein stabilization, and there is little evidence of xenobiotic induction at the transcriptional level. Previously, we reported microarray analysis data suggesting a decrease in Cyp2e1 gene expression on Ahr-null livers when compared to wild-type mouse livers. The goal of the present study was to determine whether 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) increased mouse CYP2E1 levels in an AhR-dependent manner and the impact on CCl(4)-induced hepatotoxicity. TCDD treatment induced CYP2E1 mRNA and protein levels in mouse liver, and this effect was aryl hydrocarbon receptor (AhR)-dependent. Moreover, TCDD pre-treatment increased the CCl(4)-induced alanine aminotransferase (ALT) activity, the extent of CCl(4)-induced necrosis, and the number of sinusoidal cells in wild-type animals, while this potentiating effect was not observed in Ahr-null mice. In conclusion, this study revealed that TCDD, probably in an AhR-dependent manner, exacerbated CCl(4)-induced hepatotoxicity through induction of CYP2E1.

Induction of micronuclei by 2-hydroxypyridine in water and elimination of solution genotoxicity by UVC (254 nm) photolysis

2-Hydroxypyridine (2-HPY) is a major first-stage product formed upon the photolytic destruction of 2-halogenated pyridines. Genotoxicity of 2-HPY in water was studied as a function of concentration. Aqueous solutions of 2-HPY were irradiated by ultraviolet (UV) at 254 nm. 2-HPY concentration, solution total organic carbon (TOC) concentration and solution genotoxicity were measured as a function of treatment time and their profile as a function of time is presented in this work. 2-HPY was found to be genotoxic at all concentrations in the range of 5-400 μg ml(-1). 2-HPY mineralises completely upon prolonged UV irradiation. All untreated and irradiated solution samples, taken at different photo-treatment times, were tested in cultured human lymphocytes applying the cytokinesis block micronucleus (CBMN) assay. The genotoxicity of the solution was reduced near to the control level after prolonged UV irradiation.

3-aminobenzanthrone, a human metabolite of the carcinogenic environmental pollutant 3-nitrobenzanthrone, induces biotransformation enzymes in rat kidney and lung

3-aminobenzanthrone (3-ABA) is the metabolite of the carcinogenic air pollutant 3-nitrobenzanthrone (3-NBA). 3-ABA was investigated for its ability to induce cytochrome P450 1A1 (CYP1A1) and NAD(P)H:quinone oxidoreductase (NQO1) in kidney and lung of rats, and for the influence of such induction on DNA adduct formation by 3-ABA and 3-NBA. NQO1 is the enzyme that reduces 3-NBA to N-hydroxy-3-aminobenzanthrone (N-OH-3-ABA) and CYP1A enzymes oxidize 3-ABA to the same intermediate. When activated by cytosolic and and/or microsomal fractions isolated from rat lung, the target organ for 3-NBA carcinogenicity, and kidney, both compounds generated the same DNA-adduct pattern, consisting of five adducts. When pulmonary cytosols isolated from rats that had been treated i.p. with 40 mg/kg bw of 3-ABA were incubated with 3-NBA, DNA adduct formation was up to 1.7-fold higher than in incubations with cytosols from control animals. This increase corresponded to an increase in protein level and enzymatic activity of NQO1. In contrast, no induction of NQO1 expression by 3-ABA treatment was found in the kidney. Incubations of 3-ABA with renal and pulmonary microsomes of 3-ABA-treated rats led to an increase of up to a 4.5-fold in DNA-adduct formation relative to controls. The stimulation of DNA-adduct formation correlated with a higher protein expression and activity of CYP1A1 induced by 3-ABA. These results show that by inducing lung and kidney CYP1A1 and NQO1, 3-ABA increases its own enzymatic activation as well as that of the environmental pollutant, 3-NBA, thereby enhancing the genotoxic and carcinogenic potential of both compounds.

Effect of sulfur dioxide inhalation on CYP1A1 and CYP1A2 in rat liver and lung

Sulfur dioxide (SO2) is a ubiquitous air pollutant, presents in low concentrations in the urban air, and in higher concentrations in the working environment. In the present study, male Wistar rats were housed in exposure chambers and treated with 14.00+/-1.53, 28.00+/-2.12 and 56.00+/-4.28 mg/m3 SO2 for 6 h/day for 7 days, while control rats were exposed to filtered air in the same condition. Highly specific substrates were used as probes of cytochrome P4501A1 (CYP1A1) and cytochrome P4501A2 (CYP1A2). The mRNA levels of CYP1A1 and 1A2 were analyzed in livers and lungs by using a real-time reverse transcription-polymerase chain reaction (real-time RT-PCR) assay. Our results showed that the activities and mRNA levels of P450 were decreased in livers and lungs of rats exposed to SO2. In the liver, a decrease down to 0.68- and 0.64-fold in the CYP1A1 activity, probed by the O-deethylation of ethoxyresorufin (EROD), was observed at higher dose of SO2 (28 and 56 mg/m3); Similarly, CYP1A1 mRNA levels were reduced in livers of rats exposed to SO2 at 28 and 56 mg/m3. For livers, CYP1A2-mediated methoxyresorufin O-demethylase activity (MROD) was unaltered by SO2 at low concentrations, except for a significant decrease in the rats exposed to SO2 at 56 mg/m3 (0.79-fold); however, SO2 at higher concentrations significantly decreased levels of CYP1A2 (28 and 56 mg/m3) (p<0.05). Significant inhibition of both EROD and MROD was observed in lungs of rats exposed to SO2 at 28 and 56mg/m3. CYP1A1 activity was repressed 0.62- and 0.53-fold, while CYP1A2 activity was reduced to 0.74- and 0.55-fold in lungs, respectively. SO2 at higher concentrations (28 and 56 mg/m3) decreased significantly pulmonary CYP1A1 and 1A2 mRNA levels relative to control animals. Furthermore, the decreases of activities and mRNA levels of these P450 enzymes caused by SO2 at different concentrations in lungs and livers of rats followed linear dose-response curves. These results lead to the conclusion that SO2 exposure can reduce CYP1A1 and 1A2 in lungs and livers of rats and ROS and/or cytokines might act as mediators of this effect according to previous studies performed in mice. Reduction of hepatic and pulmonary CYPlAl and lA2 expression during SO2 exposure may be part of an adaptive response by the liver and lung to minimize cell damage.

CYP1A1 induction by pyridine and its metabolites in HepG2 cells

Pyridine and its metabolites have been shown in previous studies to induce cytochrome P4501A1 (CYP1A1) expression in vivo in the rat and in vitro in cultured human lung explants. In this study, we assessed the role of the metabolites in CYP1A1 induction by the parent compound. This was accomplished by comparing pyridine, 2-hydroxypyridine, 3-hydroxypyridine, pyridine N-oxide, and N-methylpyridinium in terms of the induction of CYP1A1 mRNA, CYP1A1 catalytic activity, and a xenobiotic response element-directed chloramphenicol acetyltransferase reporter gene, using HepG2 cells as the experimental system. We also assessed the effect of expression of the pyridine-metabolizing enzyme cytochrome P4502E1 on CYP1A1 induction by the parent pyridine. Only 2-hydroxypyridine significantly induced the CYP1A1 mRNA expression and CYP1A1-preferential activity ethoxyresorufin O-deethylase in wild-type HepG2 cells. Similarly, only 2-hydroxypyridine induced the expression of a xenobiotic response element-directed reporter gene in transfected HepG2 cells. Pyridine elevated CYP1A1 mRNA abundance 4.6-fold in HepG2 cells transfected with a human CYP2E1 expression vector relative to the abundance of the transcript in empty vector-transfected (control) HepG2 cells; the elevation was inhibited by the CYP2E1 inhibitor dimethyl sulfoxide. The results indicate that CYP1A1 induction by pyridine is mediated largely by metabolites, the formation of which may be catalyzed by CYP2E1.

Induction of CYP1A1 and CYP1A2 expressions by prototypic and atypical inducers in the human lung

The inducibility of cytochrome P4501A1 gene (CYP1A1) expression was examined in human lung samples from 27 subjects, using an explant culture system and semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. CYP1A1 transcripts were present in all of the lung specimens and were induced by the prototypic inducers 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and benzo[a]pyrene (B[a]P), and by the atypical inducers pyridine, nicotine, and omeprazole. 2-Hydroxypyridine was a better inducer than pyridine, implicating metabolites in CYP1A1 induction by the parent compound. The prototypical inducers were the most effective inducers in many samples but were ineffective in some samples in which the atypical compounds were effective inducers. Cytochrome P4501A2 (CYP1A2) transcripts were also detected in most of the lung specimens and were inducible in some specimens. The results show the suitability of the explant culture system for examining the inducibility of human pulmonary CYP1A1 and CYP1A2, indicate the heterogeneity in individual sensitivity to the induction, and underscore the need to include atypical inducers in studies of CYP1A inducibility in humans.