Effect of pretreatment with hydroxylated xenobiotics on the activities of rat liver UDP-glucuronosyl-transferases

Contributions of Nrf2 to Puerarin Prevention of Cardiac Hypertrophy and its Metabolic Enzymes Expression in Rats

Previous evidence has suggested that puerarin may attenuate cardiac hypertrophy; however, the potential mechanisms have not been determined. Moreover, the use of puerarin is limited by severe adverse events, including intravascular hemolysis. This study used a rat model of abdominal aortic constriction (AAC)-induced cardiac hypertrophy to evaluate the potential mechanisms underlying the attenuating efficacy of puerarin on cardiac hypertrophy, as well as the metabolic mechanisms of puerarin involved. We confirmed that puerarin (50 mg/kg per day) significantly attenuated cardiac hypertrophy, upregulated Nrf2, and decreased Keap1 in the myocardium. Moreover, puerarin significantly promoted Nrf2 nuclear accumulation in parallel with the upregulated downstream proteins, including heme oxygenase 1, glutathione transferase P1, and NAD(P)H:quinone oxidoreductase 1. Similar results were obtained in neonatal rat cardiomyocytes (NRCMs) treated with angiotensin II (Ang II; 1 μM) and puerarin (100 μM), whereas the silencing of Nrf2 abolished the antihypertrophic effects of puerarin. The mRNA and protein levels of UGT1A1 and UGT1A9, enzymes for puerarin metabolism, were significantly increased in the liver and heart tissues of AAC rats and Ang II-treated NRCMs. Interestingly, the silencing of Nrf2 attenuated the puerarin-induced upregulation of UGT1A1 and UGT1A9. The results of chromatin immunoprecipitation-quantitative polymerase chain reaction indicated that the binding of Nrf2 to the promoter region of Ugt1a1 or Ugt1a9 was significantly enhanced in puerarin-treated cardiomyocytes. These results suggest that Nrf2 is the key regulator of antihypertrophic effects and upregulation of the metabolic enzymes UGT1A1 and UGT1A9 of puerarin. The autoregulatory circuits between puerarin and Nrf2-induced UGT1A1/1A9 are beneficial to attenuate adverse effects and maintain the pharmacologic effects of puerarin.

Drug metabolizing enzyme induction by simple diaryl pyridines; 2-substituted isomers selectively increase only conjugation enzyme activities, 4-substituted isomers also induce cytochrome P450

Pyridine derivatives bearing aryl containing substitutions at the 2- and 4-position were administered to male rats, daily, for 3 days at 75 mg/kg. All five 2-substituted pyridines investigated increased rat hepatic UDP-glucuronosyltransferase activities toward three aglycones (morphine, p-nitrophenol, and 1-naphthol) without inducing cytochrome P450. Two of the 4-substituted pyridines investigated (4,4'-dipyridyl, 4-benzylpyridine) significantly induced cytochrome P450. UDP-glucuronosyl-transferase activity by the 4-substituted pyridines was increased to a much lesser extent than seen for the equivalent 2-isomers. The two 4-substituted pyridines eliciting induction of cytochrome P450 were also the only 4-isomers which increased cytosolic glutathione-S-transferase activity, but three 2-substituted pyridines (2-benzoylpyridine, 2-benzylpyridine, and trans-1,2-bis(2-pyridyl)ethylene) increased this activity in the absence of cytochrome P450 induction. No compound investigated induced cytosolic sulfotransferase activity. Diaryl compounds lacking a heterocyclic ring did not increase any of the investigated drug metabolizing enzyme activities. For simple diarylpyridines, the position of substitution on the pyridine ring rather than the nature of the substituent appears to be a major determinant for selective induction of UDP-glucuronosyltransferases without concurrent increases in cytochrome P450. The 2-substituted pyridines were consistently selective inducers of only Phase II or conjugation enzymes. The 4-substituted pyridines included derivatives that could selectively induce Phase II and nonselectively induce both Phase I and Phase II and one derivative that induced neither.

Effect of various chemicals on the aldehyde dehydrogenase activity of the rat liver cytosol

The cytosolic activity of aldehyde dehydrogenase (ALDH) was studied in the rat liver, after acute administration of various carcinogenic and chemically related compounds. Male Wistar rats were treated with 27 different chemicals, including polycyclic aromatic hydrocarbons, aromatic amines, nitrosamines, azo dyes, as well as with some known direct-acting carcinogens. The cytosolic ALDH activity of the liver was determined either with propionaldehyde and NAD (P/NAD), or with benzaldehyde and NADP (B/NADP). The activity of ALDH remained unaffected after treatment with 1-naphthylamine, nitrosamines and also with the direct-acting chemical carcinogens tested. On the contrary, polycyclic aromatic hydrocarbons, polychlorinated biphenyls (Arochlor 1254) and 2-naphthylamine produced a remarkable increase of ALDH. In general, the response to the effectors was disproportionate between the two types of enzyme activity, being much in favour for the B/NADP activity. This fact resulted to an inversion of the ratio B/NADP vs. P/NAD, which under constitutive conditions is lower than 1. In this respect, the most potent compounds were found to be polychlorinated biphenyls, 3-methylcholanthrene, benzo(a)pyrene and 1,2,5,6-dibenzoanthracene. Our results suggest that the B/NADP activity of the soluble ALDH is greatly induced after treatment with compounds possessing aromatic ring(s) in their molecule. It is not known, if this response of the hepatocytes is related with the process of chemical carcinogenesis.

Formation of glutathione conjugates during oxidation of eugenol by microsomal fractions of rat liver and lung

Rat hepatic and pulmonary microsomes catalyzed the formation of at least three distinct glutathione conjugates with eugenol (4-allyl-2-methoxyphenol). These three conjugates were identical with the products obtained from the chemical reaction of synthetic eugenol quinone methide and glutathione. The microsomal reaction was dependent on NADPH and oxygen and was inhibited by cytochrome P450 inhibitors such as metyrapone, 2-diethylaminoethyl-2,2'-diphenylvalerate (SKF 525-A), alpha-naphthoflavone and piperonyl butoxide. The enzyme responsible for eugenol oxidation was inducible with 3-methylcholanthrene but not phenobarbital pretreatment. The rate of formation of conjugates was not affected by the presence of glutathione-depleted cytosol which contained active glutathione transferase, even at low glutathione concentrations, suggesting that conjugation occurs nonenzymatically with an electrophilic metabolite of eugenol. Covalent binding to microsomal protein was observed using [3H]eugenol. Cumene hydroperoxide catalyzed the formation of these same glutathione conjugates via the formation of a quinone methide-like intermediate which was detected by spectroscopic means. Our results suggest that eugenol is oxidized by cytochrome P450 to a reactive quinone methide intermediate which can then covalently modify protein or conjugate with glutathione.

Heterogeneity of hepatic microsomal UDP-glucuronosyltransferases activities: use and comparison of differential inductions in some mammalian species

1. The co-injection in rats of the inducers 3-methylcholanthrene or phenobarbital and of a protein synthesis inhibitor (cycloheximide) shows that two clusters of hepatic UDP-Glucuronosyltransferases (GT1 and GT2) are under separate genomic expression and differentially regulated. 2. The administration of cycloheximide alone even suggests a distinct turn-over for these two groups of isoenzymes. 3. Indirect evidence for a UDPGT isoform specialized for some structurally-related exogenous substrates, the monoterpenoid alcohols, is brought. Their conjugation exhibits a small deficiency and a marked response to phenobarbital treatment in the Gunn rat and an exclusive inducibility by phenobarbital in the guinea-pig.

Heterogeneity of hepatic microsomal UDP-glucuronosyltransferase(s) activities: comparison between human and mammalian species activities

The first comparative profiles of UDP-glucuronosyltransferase(s) (UDPGT) activities obtained under standard conditions in vitro in mammals (man, rat [Wistar and Gunn], mouse, monkey [Papio papio and Cynomolgus], pig, guinea pig, rabbit, dog) are presented for 16 aglycones. A decreasing scale of these activities was obtained from planar to bulky molecules. The scale was identical for each of the mammals studied, including man. Statistical analysis of the results revealed a division of the aglycones into three groups, one being correlated with the molecular form called GT1 the two others with the GT2 form. The profile of activities in the Gunn rat revealed very weak activity towards planar molecules (GT1). These results provide evidence that under standard conditions, human UDPGT activities are comparable to those from other animals.