Effect of aflatoxin B1 on hepatic drug-metabolizing enzymes in female rats. Interaction with a contraceptive agent

Molecular and Pharmacological Properties of a Potent and Selective Novel Nonsteroidal Progesterone Receptor Agonist Tanaproget

Progesterone receptor (PR) agonists have several important applications in women's health, such as in oral contraception and post-menopausal hormone therapy. Currently, all PR agonists used clinically are steroids. Because of their interactions with other steroid receptors, steroid-metabolizing enzymes, or other steroid-signaling pathways, these drugs can pose significant side effects in some women. Efforts to discover novel nonsteroidal PR agonists with improved biological properties led to the discovery of tanaproget (TNPR). TNPR binds to the PR from various species with a higher relative affinity than reference steroidal progestins. In T47D cells, TNPR induces alkaline phosphatase activity with an EC(50) value of 0.1 nm, comparable with potent steroidal progestins such as medroxyprogesterone acetate (MPA) and trimegestone (TMG), albeit with a reduced efficacy ( approximately 60%). In a mammalian two-hybrid assay to measure PR agonist-induced interaction between steroid receptor co-activator-1 and PR, TNPR showed similar potency (EC(50) value of 0.02 nm) and efficacy to MPA and TMG. Importantly, in key animal models such as the rat ovulation inhibition assay, TNPR demonstrates full efficacy and an enhanced progestational potency (30-fold) when compared with MPA and TMG. Furthermore, TNPR has relatively weak interactions with other steroid receptors and binding proteins and little effect on cytochrome P450 metabolic pathways. Finally, the three-dimensional crystal structure of the PR ligand binding domain with TNPR has been delineated to demonstrate how this nonsteroidal ligand achieves its high binding affinity. Therefore, TNPR is a structurally novel and very selective PR agonist with an improved preclinical pharmacological profile.

Interaction of aflatoxin B1 with the rat monooxygenase system and relationships to its acute toxic effect

The effect of aflatoxin B1 (AFB1) on the liver microsomal and nuclear mixed function oxidase system (MFO) of adult male rats was studied at oral doses of 1 and 3 mg/kg. At first both doses increased the activities and concentrations of all P450 components followed. The maximum values were observed between 24 and 48 h and were dose- and enzyme-dependent. After 72 h the values dropped to 15-55% of the initial values. Inhibition of the MFO system lasted even after 120 h, when a trend to return to the normal values was already noticeable. We assume that AFB1 acts as an inductor of the monooxygenase system and the reactive electrophilic intermediate(s) bind irreversibly to or autocatalytically inactivate P450.

Effect of the leafy vegetable Solanum nigrum on the activities of some liver drug-metabolizing enzymes after aflatoxin B1 treatment in female rats

Wistar albino female rats were maintained for 10 d on diets containing various levels of the vegetable Solanum nigrum. Simultaneously, they received daily intraperitoneal injections of aflatoxin B1 (AFB1) (either 0.2 or 0.4 mg/kg body-weight) diluted in propylene glycol. At the end of the experiment, all animals were killed and their serum and hepatic microsomes were prepared for assay of enzymes. Results showed that aminopyrine N-demethylase activity increased 2.5-fold with 200 (S200) and 600 (S600) g S. nigrum/kg diets. Activity of uridine diphosphate glucuronyltransferase (UDPGT) (EC 2.4.1.17) also increased twofold. Similar results were obtained with glutathione S-transferase (EC 2.5.1.18) activity which increased by 60% with diet S600. After AFB1 treatment, a general increase in the activities of the above enzymes was found, except for UDPGT in the group fed on diet S600. When rats were fed on the diet without S. nigrum, AFB1 induced an increase in alkaline phosphatase (ALP) (EC 3.1.3.1), aspartate aminotransferase (AST) (EC 2.6.1.1) and gamma-glutamyltransferase (gamma-GT) (EC 2.3.2.2) levels in the serum. AFB1 also induced increases in serum ALP and gamma-GT levels when rats were fed on diet S600.

Oral contraceptives stimulate the excretion of clofibric acid glucuronide in women and female rats

1. Glucuronidation of clofibric acid, the pharmacologically active form of the hypolipidemic drug clofibrate was investigated in a human population, either in vitro with liver homogenates from biopsies, or after ingestion of the drug and determination of the urinary metabolite. No difference in the glucuronidation rate according to age of the patients was observed. Bilirubin but not clofibric acid glucuronidation was significantly higher in women (106% increase), when expressed per gram of tissue. 2. The excretion of clofibryl glucuronide in women who took oral contraceptives was significantly enhanced by 25%. 3. In female rats, treatment with the contraceptive agent norethindrone also stimulated by 48% the formation of clofibrylglucuronide in liver microsomes.

Induced hepatotoxicity in female rats by aflatoxin B1 and ethynylestradiol interaction

Female Sprague-Dawley rats were treated with a single ip dose of aflatoxin B1 (AFB1) (3 or 6 mg/kg). Twenty-four hours later and weekly until killed, some of the rats treated with AFB1 were given ethynylestradiol (EE) by gavage at the dose of 13 mg/kg. One, three, six, and nine months following the beginning of the experiment, animals were killed. Light microscopy of liver and histochemical determinations of gamma-glutamyltransferase (GGT) as well as the measurement of hepatic drug-metabolizing enzyme activities were investigated. The results show that AFB1 induced only very weak changes in the levels of different constituents studied. Thus, the mycotoxin did not affect GGT activity and increased epoxide hydrolase activity by a maximum of 42%. In contrast, EE significantly and progressively decreased (20 to 50%) the activity of UDP-glucuronosyltransferase (UDPGT) as well as the concentration of cytochrome P-450 and microsomal proteins. However, the estrogen increased the activity of epoxide hydrolase up to 150% as well as the activity of the hepatic (400%) and plasma (175%) GGT. The results also indicate that AFB1 amplified the EE-induced increase in liver weight and enhanced the depressive effects of the estrogen on microsomal proteins, cytochrome P-450, and UDPGT. Foci of cellular alteration which consisted of clear, acidophilic and basophilic cell lesions were seen in the livers of treated rats examined by light microscopy. These lesions were more prominent in the livers of animals given combinations of AFB1 and EE; they were accompanied by a strong intensity of GGT staining in the periportal area and a marked increase of the enzyme activity in the plasma (324%). From the sixth month, the livers of some animals treated with the combinations of AFB1 and EE showed hyperplastic nodules. This study indicates that the interaction between chronic administration of EE and a single ip injection of AFB1 induces hepatic lesions considered as possible forerunners of liver cell carcinomas. It also shows that GGT is a potential marker of preneoplastic lesions and may be used, therefore, in epidemiologic surveys in humans exposed to liver carcinogens such as the aflatoxins.