Hannu U. Saarni

Unusual patterns of benzo[a]pyrene metabolites and DNA-benzo[a]pyrene adducts produced by human placental microsomes in vitro☆

Human placental microsomes were incubated with [3H]benzo[a]pyrene (BP) and Salmon sperm DNA and the resulting metabolite-nucleoside complexes resolved by Sephadex LH-20 chromatography. The metabolite pattern was analyzed by high-pressure liquid chromatography (HPLC). The incubates were also co-chromatographed with extracts obtained from incubates with rat liver microsomes and [14C] BP. Phenols, quinones and 7,8-dihydrodiol were detected in the placental incubates. Both 9,10- and 4,5-dihydrodiols were very low as compared with control rat liver samples. Placental microsomes catalyzed the binding of BP metabolites to DNA in vitro, giving rise to two main complexes which co-chromatographed with rat liver-produced peaks attributable to 7,8-diol-9,10-epoxide and 7,8-oxide and/or quinones when metabolized further. The nucleoside metabolite peaks attributable to 4,5-oxide and 9-phenol-4,5-oxide were lacking when compared with the binding pattern catalyzed by rat liver. Both the total binding and specific metabolite-nucleoside adducts in the placenta correlated with fluorometrically measured aryl hydrocarbon hydroxylase (AHH) activity and with the amount of dihydrodiol formed. The results demonstrate that both the metabolite pattern and the nucleoside-metabolite complexes formed by the placental microsomes in vitro differed greatly from thos produced by rat liver microsomes. These sstudies also suggest that it is not possible to predict specific patterns of DNA binding from AHH measurements or even from BP metabolite patterns, especially when comparing different tissues and species.

Dose-dependent effects of medroxyprogesterone acetate on the hepatic drug-metabolizing enzyme system in rats

Abstract The activity of the hepatic microsomal drug metabolism was examined in vitro in rats pretreated with 10–600 mg/kg medroxyprogesterone acetate intraperitoneally daily for seven days. In both sexes there was a significant increase in the liver weight, amount of cytochrome P-450, activity of NADPH-cytochrome c reductase, benzo[ a ]pyrene hydroxylase and 2,5-diphenyloxazole hydroxylase. The increase in 7-ethoxycoumarin- O -deethylase activity was also significant in female rats, but not in male rats. In the female rats pretreated with medroxyprogesterone acetate, the ability of α-naphtho-flavone and SKF 525A to inhibit benzo[ a ]pyrene hydroxylase was decreased and slightly increased, respectively. The results show that medroxyprogesterone acetate has a dose-dependent inducing effect on the hepatic drug metabolism in rats. Female rats seem to be more sensitive to the inducing effect of medroxyprogesterone acetate than the males. The characteristics of medroxyprogesterone acetate induction resemble mostly those caused by phenobarbital and pregnenolone-16α-carbonitrile.

Effects of Medroxyprogesterone Acetate on Hepatic Glucose Metabolism and Microsomal Enzyme Activity in Rats with Normal and Altered Liver

Effects of medroxyprogesterone acetate (MPA) on hepatic glucose handling and drug metabolism were investigated in female rats with intact and damaged liver. Hepatic glucose-6-phosphatase activity, glycogen content and fasting blood glucose were assessed as indices of glucose metabolism. Cytochrome P-450 content and NADPH-cytochrome P-450 reductase activity were assayed to reflect liver drug metabolism. Liver injury was induced by dimethylnitrosamine and carbon tetrachloride. The results demonstrate that hepatic glucose handling and drug metabolism were changed in a parallel fashion in intact, damaged and induced liver. The MPA-induced changes in glucose metabolism were slight in intact animals, whereas the compound has an increasing effect on glucose and drug metabolism in rats with damaged liver. The findings demonstrate the MPA enhances the normallization of hepatic glucose and drug metabolism in damaged liver.

Medroxyprogesterone acetate improvement of the hepatic drug-metabolizing enzyme system in rats after chemical liver injury

Medroxyprogesterone acetate (MPA) has an inducing effect on the hepatic drug-metabolizing enzyme system in the rat. The effect of MPA on the liver metabolism was further evaluated here by investigating the restoration of hepatic function after chemical liver injury in female rats. The hepatic injury was induced by pretreating the animals with CCl4 and dimethylnitrosamine for 4 weeks, after which rats treated with MPA for a week were compared with rats showing spontaneous regeneration upon treatment with the MPA vehicle only. Changes in various parameters of the drug-metabolizing enzyme system were used as indices of hepatic function together with liver protein content. The results showed that MPA therapy increased the cytochrome P-450 content and the activity of NADPH-cytochrome c reductase, the monooxygenase enzymes benzo[a]pyrene hydroxylase and aminopyrine N-demethylase, epoxide hydrolase and glutathione S-transferase. MPA increased the relative values in the rats with liver injury almost equally to, or even more than, that seen in the intact animals in comparison to the corresponding vehicle-treated rats. MPA seemed to enhance protein synthesis during liver regeneration, as indicated by changes in total liver protein and in the gel electrophoresis pattern of the microsomal proteins. The hepatic enzyme induction and enhancement of protein synthesis achieved by MPA after liver injury may be of value in the treatment of liver diseases.

Reversibility of Rat Liver Cirrhosis by Medroxyprogesterone Acetate

The possible effects of a synthetic progesterone, medroxyprogesterone acetate (MPA), on carbon tetrachloride/phenobarbital (CCl4/PB)-induced rat liver injury were studied by morphological methods. CCl4/PB-treated rats showed extensive liver fibrosis consisting of procollagen type III aminoterminal propeptide-positive strands and fibres with concomitant extensive basement membrane deposits and fibronectin synthesis. MPA treatment after CCl4/PB-induced liver damage reduced alterations in cytoplasmic organelles, inflammation and hemorrhages and reversed the fibrosis, mostly around individual liver cells, possibly due to the normalization of cellular structure and function with a decrease in fibronectin deposits.

Time course of hepatic changes produced by medroxyprogesterone acetate in the rat

Abstract 1. 1. The time course of the effects of medroxyprogesterone acetate (MPA) treatment (100 mg/kg, i.p.) on hepatic drug metabolism was investigated in female rats. 2. 2. The findings demonstrate that the maximum effects of MPA on the microsomal enzyme systems, liver weight and protein content were attained within 3–7 days depending on the measured parameter. 3. 3. The blood concentration of MPA reached a constant level of about 120 ng/ml in 3 days. 4. 4. After cessation of MPA administration the induced values decreased to the control level within about 11 days.The time course of the effects of medroxyprogesterone acetate (MPA) treatment (100 mg/kg, i.p.) on hepatic drug metabolism was investigated in female rats. The findings demonstrate that the maximum effects of MPA on the microsomal enzyme systems, liver weight and protein content were attained within 3-7 days depending on the measured parameter. The blood concentration of MPA reached a constant level of about 120 ng/ml in 3 days. After cessation of MPA administration the induced values decreased to the control level within about 11 days.

Treatment of liver cirrhosis with microsomal enzyme-inducing compound in the rat

The effect of therapy with a microsomal enzyme-inducing drug on the cirrhotic liver in male Wistar rats was investigated by morphological and biochemical means. The cirrhotic animals were treated with medroxyprogesterone acetate (MPA) 100 mg/kg body wt, i.p. daily for a week. In the cirrhotic rats liver weight was enhanced, liver protein content was increased while total liver DNA content remained unchanged upon MPA treatment. The hepatic regenerative nodule size increased, as determined by morphological means. Hepatic microsomal metabolic activity was improved, as seen by increases in NADPH-cytochrome P-450 reductase and aminopyrine N-demethylase activities and cytochrome P-450 content. Since the increases in liver protein content and metabolic activity were relatively greater in the cirrhotic than intact animals upon MPA treatment, it was suggested that the spontaneous regeneration associated with liver cirrhosis may affect the induction phenomenon. The results demonstrate that an enzyme inducer may have beneficial effects on the cirrhotic liver by elevating metabolic activity and parenchymal mass.

Medroxyprogesterone acetate (MPA) enhances liver NADPH-generating enzyme activities in normal rats

The aim of the present study was to evaluate the effects of medroxyprogesterone acetate (MPA), an inducer of liver drug metabolism, on the ability of liver to generate NADPH, a reducing cofactor for drug oxidation reactions in normal rats and to compare these results with those obtained in rats receiving phenobarbital (PB), a well known inducer of liver drug metabolism. The results showed that: 1. Administration of MPA (100 mg/kg body wt) for a week increased liver wt and NADPH cytochrome P-450 reductase activity, suggesting that the compound induced liver drug metabolism. 2. The regimen also increased the activities of two NADPH generating enzymes, isocitrate dehydrogenase and malic enzyme, suggesting that MPA enhanced the capacity of normal liver tissue to produce NADPH. 3. Phenobarbital treatment increased the activities of three NADPH generating enzymes, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and malic enzyme, suggesting that MPA and PB differ in their effects on the liver NADPH-producing system.