Dexamethasone induces hepatic cytochrome P-450 content and increases certain monooxygenase activities in rhesus monkey fetuses

MarmosetCYP3A21, a model for humanCYP3A4: Protein expression and functional characterization of the promoter

Due to its small size and the relative evolutionary proximity, the marmoset has been proposed as a model for studies of human drug interactions and metabolism. The current study investigated the expression and regulation of marmoset CYP3A using mass spectrometry and reporter gene techniques. Expression levels of hepatic marmoset CYP3A protein range from 51 to 123 pmol mg-1 total protein (mean 85.2 pmol mg-1, n = 10) and CYP3A21 is the dominant hepatic CYP3A protein in marmosets. The sequence similarity between human CYP3A4 and CYP3A21 across the first 7.5 kb of the cloned CYP3A21 promoter is 88% within the xenobiotic-responsive enhancer module (XREM) and the proximal promoter. Both regulatory modules confer transcriptional activation of CYP3A21-luciferase reporter gene constructs cotransfected with hPXR in intestinal LS174T cells. The pronounced response to rifampin and the moderate response to dexamethasone were similar to those observed with CYP3A4. Taken collectively, these data establish substantial similarities in expression and gene regulation between marmoset CYP3A21 and human CYP3A4. CYP3A21 may be an equivalent of CYP3A4 in New World monkeys, consistent with the phylogenetic relationship between these genes. The marmoset, therefore, appears to be a suitable in vivo model to study CYP3A4 function and regulation.

Developmental consequences of antenatal dexamethasone treatment in nonhuman primates

Research assessing fetal exposure to dexamethasone and betamethasone in animals has raised concerns about the potential for adverse side effects following antenatal treatments, not withstanding the beneficial and desired improvement in lung function. Some of the inhibitory effects on physical growth and the long-term alterations in endocrine, immune and neural physiology may reflect species differences in the fetal sensitivity of rodents and monkeys to corticosteroids or perhaps could be attributed to the higher drug doses often used in animal studies. However, since steroidal drugs can be administered for extended periods in clinical practice, and also are occasionally given in the range found to cause significant effects on the brain and immune responses of infant monkeys, the simian studies have important cautionary implications for obstetrical and pediatric practice.

The influence of age and some inducers on UDP-glucuronyltransferase activity

UDP-glucuronyltransferase (UDP-GT) activity was examined in male Wistar rats aged 0.5, 1, 2, 4, 8, 12, 20, and 28 months. The rats were treated with phenobarbital (75 mg/kg, 72 and 48 h before death), beta-naphthoflavone or dexamethasone (40 mg/kg and 20 mg/kg, respectively, for three days before death). Prior to decapitation the rats were fasted for 12 h. Hepatic microsomes were prepared according to the method of Dallner. UDP-GT activity was determined by the method of Burchell and Weatherill. p-Nitrophenol was used as an aglucone. UDP-GT activity decreased rapidly in the control rats aged from two weeks to four months. In the older control rats the activity tended to increase. Two-week-old rats treated with phenobarbital showed a slightly increased UDP-GT activity. In the older animals (up to one year) UDP-GT activity increased to 150% of the control value and stayed at this level in the remaining age groups. beta-Naphthoflavone was a more potent inducer of UDP-GT than phenobarbital. The activity of beta-naphthoflavone-induced UDP-GT was low in the youngest rats. It was about 180% in two-month-old rats and reached 260% of the control value in eight-month-old rats. Although the activity decreased in the older rats, it still exceeded 200%. Dexamethasone did not affect UDP-GT activity. Only in two-week-old and two-month-old rats did we observe a slight increase in the activity of UDP-GT.

Effects of age, phenobarbital, β-naphthoflavone and dexamethasone on rat hepatic δ-aminolevulinic acid synthase

delta-Aminolevulinic acid synthase is a key enzyme leading to the synthesis of cytochrome P-450, a compound of the mixed function oxidase system. Because of this, we have studied the effects of both age and three typical mixed function oxidase system induces on this enzyme activity in male Wistar rats. Our results suggest that delta-aninolevulinic acid synthase activity in intact rats increases up to maturity and then decreases being, however, higher in the oldest animals than in the youngest. Phenobarbital affects delta-aminolevulinic acid synthase activity very characteristically. This activity is high in 4-week-old animals and then increases slightly until the twelfth month of life. Phenobarbital enzymic inducibility tends to decrease with age. In the beta-naphthoflavone groups, the profile of delta-aminolevulinic acid synthase activity looks like that in the control ones. Generally, beta-naphthoflavone is a weaker delta-aminolevulinic acid synthase inducer than phenobarbital, but it seems to induce delta-aminolevulinic acid synthase like dexamethasone, which, being a physiological inducer of the mixed function oxidase system, is also an inducer of delta-aminolevulinic acid synthase and this inducibility is closely connected with age.

Altered activity of hepatic mixed function oxidase, cytochrome P-450 and glutathione-S-transferase by styrene in rat fetal liver

The effect of in utero exposure to styrene 200 or 400 mg/kg/day orally was studied on mixed function oxidase activities, cytochrome P-450 and glutathione contents and on the glutathione-S-transferase activity in rat fetal liver. Activities of aminopyrene-N-demethylase, aniline hydroxylase, aryl hydrocarbon hydroxylase and the cytochrome P-450 contents were significantly decreased in the fetal liver. A significant decrease in the glutathione contents and the glutathione-S-transferase activity was also observed in the liver of the fetuses of styrene exposed animals. The current data show that prenatal exposure to styrene could adversely affect the developing biotransformation process.

The role of metabolism in the testing of developmental toxicants

The delivery of potential developmental toxicants to the conceptus is dependent on several metabolic and pharmacokinetic factors. Within the maternal-embryo/fetal unit, maternal, placental, and embryo/fetal factors must be considered. These factors include blood flow, permeability, biotransformation, and elimination. Pharmacokinetic models based on data gathered from appropriate in vivo and in vitro studies may be used to describe the effect of these factors on toxicant delivery to the conceptus. Several known human developmental toxicants are discussed in terms of the metabolic and pharmacokinetic factors controlling their delivery to the conceptus. Metabolic events, including activation and/or detoxification, have been reported for the majority of the toxicants examined. Thus it would appear that the role of metabolism should be considered during the testing of potential developmental toxicants.