Formation of DNA adducts by cyproterone acetate and some structural analogues in primary cultures of human hepatocytes

Genotoxic effects of drospirenone and ethinylestradiol in human breast cells (in vitro) and bone marrow cells of female mice (in vivo)

Estrogen and progesterone congeners as found in various oral contraceptive formulations have been implicated as the cause of cancer in sex and tissue-specific targets. The mechanism of carcinogenesis by sex steroids is still debatable. In this study, we evaluated the genotoxicity induced by two components of one of the commonly used oral contraceptive formulation; drospirenone and ethinylestradiol in human breast cells (MCF-7) in vitro and in bone marrow cells of female mice in vivo. DNA damage was assessed by alkaline comet assay. Both of the drugs produced DNA damage in human breast cells at exposure concentrations which are about 100-fold and above than normally found in human blood after their lowest recommended doses. The DNA damage was produced only after metabolic activation by mice liver S-9 fraction in both cases. The co-exposure with both the compounds at median exposure levels resulted in potentiation of DNA damage. In bone marrow cells of adult female mice, both the compounds produced DNA damage at human equivalent doses after exposure was carried out repeatedly for approximately one estrus cycle (5 days). The co-administration with the compounds resulted in potentiation of DNA damage as indicated by percent tail DNA in comet assay. Thus it is concluded that drospirenone and ethinylestradiol cause DNA damage in certain target specific tissue (mammary epithelial cells) and in female bone marrow cells. The co-exposure with drospirenone and ethinylestradiol results in potentiation of genotoxicity which may pose a threat of cancer development in women taking these drugs for long periods.

Progesterone and Breast Cancer

Synthetic progestogens (progestins) have been linked to increased breast cancer risk; however, the role of endogenous progesterone in breast physiology and carcinogenesis is less clearly defined. Mechanistic studies using cell culture, tissue culture, and preclinical models implicate progesterone in breast carcinogenesis. In contrast, limited epidemiologic data generally do not show an association of circulating progesterone levels with risk, and it is unclear whether this reflects methodologic limitations or a truly null relationship. Challenges related to defining the role of progesterone in breast physiology and neoplasia include: complex interactions with estrogens and other hormones (eg, androgens, prolactin, etc.), accounting for timing of blood collections for hormone measurements among cycling women, and limitations of assays to measure progesterone metabolites in blood and progesterone receptor isotypes (PRs) in tissues. Separating the individual effects of estrogens and progesterone is further complicated by the partial dependence of PR transcription on estrogen receptor (ER)α-mediated transcriptional events; indeed, interpreting the integrated interaction of the hormones may be more essential than isolating independent effects. Further, many of the actions of both estrogens and progesterone, particularly in "normal" breast tissues, are driven by paracrine mechanisms in which ligand binding to receptor-positive cells evokes secretion of factors that influence cell division of neighboring receptor-negative cells. Accordingly, blood and tissue levels may differ, and the latter are challenging to measure. Given conflicting data related to the potential role of progesterone in breast cancer etiology and interest in blocking progesterone action to prevent or treat breast cancer, we provide a review of the evidence that links progesterone to breast cancer risk and suggest future directions for filling current gaps in our knowledge.

Genotoxic and mutagenic studies of teratogens in developing rat and mouse

In this review, genotoxic and mutagenic effects of teratogenic chemical agents in both rat and mouse have been reviewed. Of these chemicals, 97 are drugs and 33 are pesticides or belong to other groups. Large literature searches were conducted to determine the effects of chemicals on chromosome abnormalities, sister chromatid exchanges, and micronucleus formation in experimental animals such as rats and mice. In addition, studies that include unscheduled DNA synthesis, DNA adduct formations, and gene mutations, which help to determine the genotoxicity or mutagenicity of chemicals, have been reviewed. It has been estimated that 46.87% of teratogenic drugs and 48.48% of teratogenic pesticides are positive in all tests. So, all of the teratogens involved in this group have genotoxic and mutagenic effects. On the other hand, 36.45% of the drugs and 21.21% of the pesticides have been found to give negative results in at least one test, with the majority of the tests giving positive results. However, only 4.16% of the drugs and 18.18% of the pesticides were determined to give negative results in the majority of the tests. Among tests with major negative results, 12.50% of the teratogenic drugs and 12.12% of the teratogenic pesticides were negative in all conducted tests.

Antigenotoxic effects of ascorbic acid against megestrol acetate-induced genotoxicity in mice

The genotoxicity of megestrol acetate was studied in mouse bone marrow cells using sister chromatid exchanges (SCEs) and chromosomal aberrations (CAs) as parameters. Megestrol acetate (8.12, 16.25 and 32.50 mg/ kg of body weight) was injected intraperitoneally separately in different groups of animals. Both CAs and SCEs were statistically increased at 16.25 and 32.50 mg/kg of body weight. Our earlier in vitro studies show the generation of free oxygen radicals, by synthetic progestins responsible for the genotoxic damage. As the genotoxic effects of steroids can be reduced by natural products having antioxidant properties, and ascorbic acid possesses antioxidant activity, ascorbic acid (20, 40 or 60 mg/kg of body weight) administered together with megestrol acetate (32.50 mg/kg of body weight) significantly decreased CAs and SCEs, suggesting an antigenotoxic role of ascorbic acid against megestrol acetate induced genotoxic damage in mice bone marrow cells. The antigenotoxic effect was clearly dose dependent. The highest protective effect was observed at 60 mg/kg body weight of ascorbic acid treated with 32.50 mg/kg body weight of megestrol acetate.

Antigenotoxic effect of nordihydroguaiaretic acid against chlormadinone acetate-induced genotoxicity in mice bone-marrow cells

Nordihydroguaiaretic acid (NDGA), a phenolic lignan, was tested for its antigenotoxic potential against chlormadinone acetate (CMA)-induced genotoxic damage in mice bone-marrow cells. Doses of about 22.50 mg/kg body weight of CMA were given along with 1, 5 and 10 mg/kg body weight of NDGA intraperitoneally. The treatment resulted in the reduction of sister chromatid exchanges and chromosomal aberrations induced by CMA, suggesting an antigenotoxic potential of NDGA. Earlier studies show that CMA generates reactive oxygen species, responsible for genotoxic damage. The free radical-scavenging property of NDGA is responsible for the reduction of genotoxic damage induced by CMA in mice bone-marrow cells.

Anti-genotoxic effect of Ocimum sanctum L. extract against cyproterone acetate induced genotoxic damage in cultured mammalian cells

The anti-genotoxic effect of Ocimum sanctum L. extract was studied against the genotoxic effect induced by a synthetic progestin cyproterone acetate, on human lymphocytes using chromosomal aberrations, mitotic index, sister chromatid exchanges and replication index as a parameters. About 30 microM of cyproterone acetate was treated with O. sanctum L. infusion, at dosages of 1.075 x 10(-4), 2.125 x 10(-4) and 3.15 x 10(-4) g/ml of culture medium. A clear dose-dependent decrease in the genotoxic damage of cyproterone acetate was observed, suggesting a possible modulating role of the plant infusion. The results of the present study suggest that the plant infusion per se does not have genotoxic potential, but can modulate the genotoxicity of cyproterone acetate on human lymphocytes in vitro.

Genotoxic potential of medroxyprogesterone acetate in cultured human peripheral blood lymphocytes

Medroxyprogesterone acetate was studied at three different concentrations (1, 5 and 10 microM), for its genotoxic effects in human peripheral blood lymphocyte culture using chromosomal aberrations and sister chromatid exchanges as parameters. Duplicate peripheral blood cultures were treated with three different concentrations (1, 5 and 10 microM) of medroxyprogesterone acetate. The study was carried out both in the absence as well as in the presence of metabolic activation (S9 mix) with and without NADP. Medroxyprogesterone acetate was found genotoxic at 5 and 10 microM in the presence of S9 mix with NADP. To study the possible mechanism of the genotoxicity of medroxyprogesterone acetate, superoxide dismutase and catalase at different doses were used separately and in combination with 10 microM of medroxyprogesterone at different doses in the presence of S9 mix with NADP. Superoxide dismutase treatment results in an increase of the genotoxic damage but catalase treatment reduce the genotoxic damage of medroxyprogesterone acetate. Catalase treatment in combination with superoxide dismutase also results in the further reduction of the genotoxic damage. The results of the present study reveal that medroxyprogesterone acetate is genotoxic only in the presence of metabolic activation (S9 mix) with NADP. Treatments with superoxide dismutase and catalase suggests the possible generation of reactive oxygen species by redox cycling of various forms of quinones, similar to estrogens, that are the results of aromatic hydroxylation by cytochrome P450s.

Genotoxic potential of cyproterone acetate: a possible role of reactive oxygen species

The genotoxicity of cyproterone acetate was studied in human lymphocytes using chromosomal aberrations (CAs), mitotic index (MI) and sister chromatid exchanges (SCEs) as a parameter. Cyproterone acetate was found to be genotoxic at 20 and 30 microM. To study the possible mechanism of the genotoxicity of cyproterone acetate, superoxide dismutase (SOD) and catalase (CAT) were used separately and in combination along with the 30 microM of cyproterone acetate at different doses. SOD treatment increases CAs, SCEs and decreases MI as compared to treatment with 30 microM CPA alone, at both of the tested doses. CAT treatment decreases the frequencies of CAs and SCEs and increases MI in both, as compared to treatment with 30 microM CPA alone, separately and in combination with SOD, suggesting a possible role of reactive oxygen species for the genotoxic damage.

Evaluation of genotoxic potential of synthetic progestin chlormadinone acetate

The genotoxicity study of a synthetic progestin chlormadinone acetate, was carried out on mouse bone marrow cells using sister chromatid exchanges (SCEs) and chromosomal aberrations (CAs) as parameter, chlormadinone acetate was studied at three different doses, i.e. 5.62, 11.25 and 22.50 mg/kg body weight and was found to be non-genotoxic at 5.62 mg/kg body weight. But at 11.25 and 22.50 mg/kg of body weight chlormadinone acetate increases SCE (P < 0.001) and CA (P < 0.01) at significant level compared to normal control. The results suggests a genotoxic and cytotoxic effect of chlormadinone acetate in mouse bone marrow cells.

Genotoxicity of hormonal steroids

Hormonal steroids have a widespread use in medicine and their side effects are continuously debated. The possible genotoxic activity of steroids has been the subject of many investigations. The natural estrogens estradiol, estrone and estriol are generally negative in the ICH core battery of tests, but several positive results have been obtained when using additional endpoints of genotoxicity. The genotoxic activity of the 4-hydroxy metabolites of estradiol and estrone is well established. The synthetic steroidal estrogens have a comparable profile of negative and positive test results. Cyproterone acetate and some of its analogues have a special position within the group of progestins. Their genotoxic potential has been established. Other progestins are generally negative in the routine tests. Anti-glucocorticoids, anti-progestins, corticosteroids, androgens, anabolics and anti-androgens appear to be devoid of genotoxic activities. The genotoxic potential of estradiol, estrone and cyproterone acetate with its analogues may play no role under normal physiological and therapeutic conditions. The metabolic conditions that are needed for the formation of DNA-reactive metabolites and oxygen radicals may not be present in humans. Epidemiological cancer data seem to support this view. The importance of thresholds in the dose-effect-relationship of genotoxicity data and their use in risk assessment is discussed.

Selection of drugs to test the specificity of the Tg.AC assay by screening for induction of the gadd153 promoter in vitro

Short-term assays for carcinogenicity testing of chemicals that use transgenic mice designed to have altered expression of genes mechanistically relevant to carcinogenesis are attractive alternatives to two-year dosing studies in rodents. The models that have been the received the greatest level of performance evaluation include p53(+/-), rasH2, Xpa/p53(+/-), and Tg.AC mice. For use of these models in a regulatory setting to evaluate the carcinogenic potential of pharmaceuticals, it is important to establish an assurance of assay specificity and positive predictivity based on studies using drugs with a wide spectrum of pharmacologic activity. For this purpose, 99 noncarcinogenic drugs were prioritized based on their activity in an in vitro induction assay correlative with a positive response in the Tg.AC assay (induction of the gadd153 promoter in HepG2 cells). Activities in two assays less predictive of Tg.AC activity (induction of c-fos and zeta-globin gene promoters) were also measured. Nine percent of the screened drugs induced the gadd153 promoter by at least fourfold. Several criteria were used to select candidates for subsequent in vivo testing in the Tg.AC assay: (1) sufficient drug solubility in appropriate skin paint vehicles to elicit systemic toxicity, (2) the level of induction of the gadd153 promoter by the drug, (3) the in vitro potency of the drug, and (4) the cost of the drug required for a 6-month study. Based on these criteria, amiloride, dipyridamole, and pyrimethamine were selected from 99 rodent noncarcinogens in a drug database for testing the specificity of the Tg.AC assay.

Species, sex and inter-individual differences in DNA repair induced by nine sex steroids in primary cultures of rat and human hepatocytes

Sex steroids, due to the generally negative responses observed in routinely employed standard genotoxicity assays, are considered epigenetic carcinogens. Some doubts on this conviction are raised by the results of recent studies providing evidence that cyproterone acetate and two structural analogues, chlormadinone acetate and megestrol acetate, are genotoxic in female rats but only for the liver, and in primary human hepatocytes from donors of both genders. The experimental evidence suggests that the metabolic activation of these molecules to reactive species and the consequent formation of DNA adducts occur only in the intact hepatocyte. Since the possibility that other sex steroids cause a liver-specific genotoxic effect cannot be ruled out a priori, we investigated nine drugs of this family for their ability to induce DNA repair synthesis in primary cultures of rat and human hepatocytes. Each steroid was tested in cultures from at least two male and two female donors of each species. Hepatocytes were exposed for 20h to sub-toxic concentrations ranging from 1 to 50 micro M, and DNA repair induction was measured by quantitative autoradiography. In primary rat hepatocytes, induction of DNA repair indicative of a frankly positive response was detected in cultures from: 2/2 males and 3/3 females with drospirenone, 2/2 males and 1/2 females with ethinylestradiol, 1/2 males and 1/2 females with oxymetholone, 1/2 males with norethisterone, 1/4 females with progesterone, and 1/4 males with methyltestosterone. Consistent negative responses were obtained with testosterone and stanozolol. A few inconclusive responses were observed in rat hepatocytes exposed to progesterone, medroxyprogesterone, norethisterone, methyltestosterone and oxymetholone. In contrast, under the same experimental conditions the nine sex steroids provided frankly negative responses in the large majority of cultures of primary hepatocytes from both male and female human donors; the only exceptions being the inconclusive responses obtained in cultures from two of the donors exposed to norethisterone and to ethinylestradiol, and from one of the donors exposed to testosterone, methyltestosterone, and stanozolol. These results and previous findings concerning cyproterone and its structural analogues suggest that sex steroids differ for their ability to induce DNA repair, and that their genotoxicity may be: (i) different in rat and human hepatocytes, (ii) dependent on the sex of the donor, and (iii) affected by inter-individual variability.

Are some progestins genotoxic liver carcinogens?

Progestins (progestogens) are classified by the International Agency for Research on Cancer (IARC) as possibly carcinogenic to humans. In the last decade evidence has shown that a synthetic drug of this family, cyproterone acetate, is activated to a reactive species by the liver, and forms DNA adducts and elicits DNA repair in hepatocytes from both rats and humans. The response is similar in humans of both genders but markedly higher in female than in male rats. The promutagenic character of DNA lesions is indicated by the increase in liver of female rats of the frequency of micronucleated cells, of mutations, and of enzyme-altered preneoplastic foci. Two other synthetic progestins, chlormadinone acetate and megestrol acetate, and an aldosterone antagonist, potassium canrenoate, share with cyproterone acetate the 17-hydroxy-3-oxopregna-4,6-diene structure. While less extensively studied, results so far obtained indicate that they are capable of inducing genotoxic effects qualitatively similar to those of cyproterone acetate. The majority of progestins have not been systematically tested for genotoxicity and the generally negative responses obtained with the standard battery of genotoxicity tests might be the consequence of the use of inappropriate target cells and/or metabolic activation systems. Cyproterone acetate, is activated by the hepatocytes to reactive species of such short half-life that they react only with the DNA of the cell in which are formed. Therefore, it cannot be excluded a priori that other progestins will not display genotoxic effects when tested adequately. This hypothesis is supported by the knowledge that estrogen-progestin combinations used as oral contraceptives are classified by the IARC as carcinogenic to humans due to the increased risk of hepatocellular carcinoma. This risk should probably be ascribed to the progestin component, since estrogens are carcinogenic to humans due to the increased risk of endometrial and possibly of breast cancer but not liver cancer.

Environmental xenobiotics and the antihormones cyproterone acetate and spironolactone use the nuclear hormone pregnenolone X receptor to activate the CYP3A23 hormone response element

The pregnenolone X receptor (PXR), a new member of the nuclear hormone receptor superfamily, was recently demonstrated to mediate glucocorticoid agonist and antagonist activation of a hormone response element spaced by three nucleotides (DR-3) within the rat CYP3A23 promoter. Because many other steroids and xenobiotics can up-regulate CYP3A23 expression, we determined whether some of these other regulators used PXR to activate the CYP3A23 DR-3. Transient co-transfection of LLC-PK1 cells with (CYP3A23)2-tk-CAT and mouse PXR demonstrated that the organochlorine pesticides transnonachlor and chlordane and the nonplanar polychlorinated biphenyls (PCBs) each induced the CYP3A23 DR-3 element, and this activation required PXR. Additionally, this study found that PXR is activated to induce (CYP3A23)2-tk-CAT by antihormones of several steroid classes including the antimineralocorticoid spironolactone and the antiandrogen cyproterone acetate. These studies reveal that PXR is involved in the induction of CYP3A23 by pharmacologically and structurally distinct steroids and xenobiotics. Moreover, PXR-mediated PCB activation of the (CYP3A23)2-tk-CAT may serve as a rapid assay for effects of nonplanar PCBs.