Effects of hyperprolactinemia on toxicological parameters and proliferation of islet cells in male rats.

Prolactin has a wide variety of biological effects. Consequences of hyperprolactinemia on islet B cell proliferation as well as general toxicological parameters were here examined using anterior pituitary-grafted rats. Three or six anterior pituitary glands were implanted under single renal capsules of F344 male rats and left there for 13 weeks afterward. Clinical observation along with measurement of body weight and food consumption was conducted during the observation period, and subsequently hematology, blood biochemistry, gross pathology, organ weights and histopathology were examined. In addition, the proliferation rate of islet B cells was measured by a 5-bromo-2'-deoxy-uridine (BrdU) labeling technique. Serum prolactin concentrations at week 13 were 36, 70, 75 and 105 ng/ml in the sham-operated, 3-pituitary-grafted groups from male or female donors, and 6-pituitary-grafted group from male donors, respectively. Higher cholinesterase and total cholesterol values, lower trigriceride and leutenizing hormones (LH) values, and higher adrenal weights compared to those in the sham-operated group were apparent in the 3- and/or 6-pituitary-grafted groups. Also, the study revealed that mammary gland structure was transformed with change of differentiation from a male to a female acinar pattern. Furthermore a specific increase of islet cell proliferation rate was found, positively correlated with serum prolactin concentration. These findings suggest that elevation of serum prolactin level over 13 weeks induces islet cell proliferation and changes in toxicological parameters, including cholinesterase activity, elements of lipid metabolism and histopathology/morphology of the adrenals and mammary glands in male rats.

Comparison of the effects of the synthetic pyrethroid Metofluthrin and phenobarbital on CYP2B form induction and replicative DNA synthesis in cultured rat and human hepatocytes.

High doses of Metofluthrin (MTF) have been shown to produce liver tumours in rats by a mode of action (MOA) involving activation of the constitutive androstane receptor leading to liver hypertrophy, induction of cytochrome P450 (CYP) forms and increased cell proliferation. The aim of this study was to compare the effects of MTF with those of the known rodent liver tumour promoter phenobarbital (PB) on the induction CYP2B forms and replicative DNA synthesis in cultured rat and human hepatocytes. Treatment with 50 microM MTF and 50 microM PB for 72 h increased CYP2B1 mRNA levels in male Wistar rat hepatocytes and CYP2B6 mRNA levels in human hepatocytes. Replicative DNA synthesis was determined by incorporation of 5-bromo-2'-deoxyuridine over the last 24 h of a 48 h treatment period. Treatment with 10-1000 microM MTF and 100-500 microM PB resulted in significant increases in replicative DNA synthesis in rat hepatocytes. While replicative DNA synthesis was increased in human hepatocytes treated with 5-50 ng/ml epidermal growth factor or 5-100 ng/ml hepatocyte growth factor, treatment with MTF and PB had no effect. These results demonstrate that while both MTF and PB induce CYP2B forms in both species, MTF and PB only induced replicative DNA synthesis in rat and not in human hepatocytes. These results provide further evidence that the MOA for MTF-induced rat liver tumour formation is similar to that of PB and some other non-genotoxic CYP2B form inducers and that the key event of increased cell proliferation would not occur in human liver.

Mode of action analysis for the synthetic pyrethroid metofluthrin-induced rat liver tumors: evidence for hepatic CYP2B induction and hepatocyte proliferation.

Two-year treatment with high doses of Metofluthrin produced hepatocellular tumors in both sexes of Wistar rats. To understand the mode of action (MOA) by which the tumors are produced, a series of studies examined the effects of Metofluthrin on hepatic microsomal cytochrome P450 (CYP) content, hepatocellular proliferation, hepatic gap junctional intercellular communication (GJIC), oxidative stress and apoptosis was conducted after one or two weeks of treatment. The global gene expression profile indicated that most genes with upregulated expression with Metofluthrin were metabolic enzymes that were also upregulated with phenobarbital. Metofluthrin induced CYP2B and increased liver weights associated with centrilobular hepatocyte hypertrophy (increased smooth endoplasmic reticulum [SER]), and induction of increased hepatocellular DNA replication. CYP2B1 mRNA induction by Metofluthrin was not observed in CAR knockdown rat hepatocytes using the RNA interference technique, demonstrating that Metofluthrin induces CYP2B1 through CAR activation. Metofluthrin also suppressed hepatic GJIC and induced oxidative stress and increased antioxidant enzymes, but showed no alteration in apoptosis. The above parameters related to the key events in Metofluthrin-induced liver tumors were observed at or below tumorigenic dose levels. All of these effects were reversible upon cessation of treatment. Metofluthrin did not cause cytotoxicity or peroxisome proliferation. Thus, it is highly likely that the MOA for Metofluthrin-induced liver tumors in rats is through CYP induction and increased hepatocyte proliferation, similar to that seen for phenobarbital. Based on analysis with the International Life Sciences Institute/Risk Science Institute MOA framework, it is reasonable to conclude that Metofluthrin will not have any hepatocarcinogenic activity in humans, at least at expected levels of exposure.

Case study: an evaluation of the human relevance of the synthetic pyrethroid metofluthrin-induced liver tumors in rats based on mode of action.

In recent years, mode of action (MOA) frameworks have been developed through the International Life Sciences Institute Risk Science Institute and the International Programme on Chemical Safety, including an evaluation of the human relevance of the animal MOA data. In the present paper, the MOA for rat liver tumors induced by Metofluthrin is first analyzed through this framework based on data from studies on Metofluthrin and information on related chemicals from the literature. The human relevance of the rat liver carcinogenic response is then discussed based upon the human relevance framework. Two-year treatment with high dose of Metofluthrin produced hepatocellular tumors in both sexes of the Wistar rats. Metofluthrin induced CYP2B (increased smooth endoplasmic reticulum), resulted in increased liver weights which were associated with centrilobular hepatocyte hypertrophy, and induction of increased hepatocellular DNA replications. The above parameters related to the key events in Metofluthrin-induced liver tumors were observed at or below tumorigenic dose levels. Furthermore, CYP2B induction by Metofluthrin was shown to involve activation of the constitutive androstane receptor in rat hepatocytes. Based on the evidence, including a comparison with the results with another chemical, phenobarbital, acting by a similar MOA, it is reasonable to conclude that Metofluthrin will not have any hepatocarcinogenic activity in humans.

Functional genomics may allow accurate categorization of the benzimidazole fungicide benomyl: lack of ability to act via steroid-receptor-mediated mechanisms.

Although benomyl and its metabolite carbendazim have been shown to adversely affect male reproduction, the mechanisms of action do not appear to involve the endocrine system. However, few studies have been conducted using currently proposed tests specifically focused on endocrine disruption. Here, potential estrogen- and androgen-mediated activity of benomyl was therefore investigated in vitro and in vivo. Benomyl and carbendazim proved negative for agonistic and antagonistic activity in reporter gene assays for the human estrogen receptor alpha and androgen receptor. In uterotrophic and Hershberger assays using Crj:CD(SD)IGS rats, benomyl (100, 300 or 1000 mg/kg/day, p.o., N = 6) did not exert agonistic effects. However, the highest dose decreased uterine weights in the uterotrophic assay, and decreased weights of some androgen-related tissues of castrated rats receiving a testosterone propionate (TP, 0.2 mg/kg) injection in the Hershberger assay; the effects were less severe than those with p,p'-DDE (100 mg/kg/day). When 4 mg/kg/day of TP was injected, decrease of organ weights due to benomyl was attenuated but still observed. Thus, its influence in some tissues was more potent than that of p,p'-DDE. Benomyl had no apparent effects on serum androgen levels. Microarray analysis of the gene expression profile in the ventral prostate of TP-injected castrated rats treated with benomyl indicated clear differences from the patterns observed with p,p'-DDE and flutamide. Taken together, these findings suggest the decreased organ weights observed in vivo to be caused by mechanisms that are not steroid-receptor-mediated, such as interfering with assembly of microtubules by benomyl. The study furthermore suggests that functional genomics may provide a reliable evidence for accurate categorization of test chemicals.

Low dose DDT inhibition of hepatocarcinogenesis initiated by diethylnitrosamine in male rats: possible mechanisms.

Previously we reported a tendency for reduction of the development of glutathione-S-transferase placental form (GST-P) positive foci, recognized as preneoplastic changes in rat liver, by a low dose of 1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT), which belongs to the same group of hepatic cytochrome P-450 inducers as phenobarbital and is itself a non-genotoxic hepatocarcinogen. In order to clarify the biological significance of this phenomenon, we investigated the reproducibility and changes in other parameters using an initiation-promotion model in which male F344 rats were treated with DDT at doses of 0, 0.005, 0.5, 500 ppm in the diet for 11 or 43 weeks after initiation of hepatocarcinogenesis with N-diethylnitrosamine (DEN). When 500 ppm DDT was applied, the formation of GST-P positive foci and tumor were markedly elevated. In contrast, induction of GST-P positive foci and liver tumors tended to be inhibited at a dose of 0.005 ppm, correlating with protein levels of cytochrome P450 2B1 and 3A2 (CYP2B1 and 3A2) and generation of 8-hydroxy-2'-deoxyguanosine (8-OHdG), a marker of oxidative DNA damage. mRNA levels for 8-oxoguanine glycosylase 1 (OGG1), an 8-OHdG repair enzyme, connexin 32 (Cx32), a major component of Gap junctions, and hepatic nuclear factor 1alpha (HNF-1alpha), a Cx32 regulator, were inversely correlated with GST-P positive foci and tumor formation. These results indicate that low dose DDT may indeed exhibit inhibitory effects on chemically initiated-rat hepatocarcinogenicity, in contrast to the promotion observed with high doses, and that this is related to changes in metabolizing enzymes, cell communication, and DNA damage and its repair.

Susceptibilities of p53 knockout and rasH2 transgenic mice to urethane-induced lung carcinogenesis are inherited from their original strains.

In the present study, susceptibility of CB6F1 mice carrying the human prototype c-Ha-ras gene (rasH2 mice) and p53 gene knockout mice (p53 (+/-) mice) to urethane-induced lung carcinogenesis was compared under the same experimental conditions. Both strains were administered 500 ppm urethane in their drinking water for 3 weeks. At week 26, lung adenocarcinomas and adenomas were observed in 53% and 100% of rasH2 mice, respectively, and lung adenomas were observed in 67% of rasH2 littermate (non-Tg) mice. However, lung tumors were not observed in either p53 (+/-) or p53 (+/+) mice. Peliosis hepatis and hepatic hemangiomas were observed in 27% and 67% of p53 (+/-) mice, but only in 6.7% and 6.7% of the rasH2 animals, respectively. Under the same experimental conditions, BALB/c mice, the strain of origin of the rasH2 mice, developed lung adenomas at an incidence of 93%, whereas none of the C57BL/6 original strain for p53 (+/-) mice developed lung tumors. Peliosis hepatis was observed in 40% of the C57BL/6 mice, but not in BALB/c mice; hepatic and splenic hemangiomas were not observed in these animals. These results indicate that organ susceptibility of rasH2 and p53 (+/-) mice is inherited from their strains of origin, the rasH2 and BALB/c lines being much more sensitive to the induction of pulmonary carcinogenesis.

alpha(2)-Macroglobulin: a novel cytochemical marker characterizing preneoplastic and neoplastic rat liver lesions negative for hitherto established cytochemical markers.

We tried to identify a novel marker characteristic for rat hepatocellular preneoplastic and neoplastic lesions, undetectable by well established cytochemical markers. Glutathione S-transferase placental (GST-P)-negative hepatocellular altered foci (HAF), hepatocellular adenoma (HCA), and hepatocellular carcinoma (HCC) were generated by two initiation-promotion models with N-nitrosodiethylamine (NDEN) and peroxisome proliferators, Wy-14,643 and clofibrate. Total RNAs isolated from laser-microdissected GST-P-negative HAF (amphophilic cell foci) and adjacent normal tissues were applied to microarray analysis. As a result, five up-regulated genes were identified, and further detailed examinations of the gene demonstrating most fluctuation, ie, that for alpha(2)-macroglobulin (alpha(2)M) were performed. In reverse transcriptase-polymerase chain reaction, alpha(2)M mRNA was overexpressed not only in amphophilic GST-P-negative HAF but also in amphophilic GST-P-negative HCA and HCC. In situ hybridization showed accumulation of alpha(2)M mRNA to be evenly distributed within GST-P-negative HAF (predominantly amphophilic cell foci). Distinctive immunohistochemical staining for alpha(2)M could be consistently demonstrated in GST-P-negative HAF, HCA, and HCC induced not only by peroxisome proliferators but also N-nitrosodiethylamine alone. Thus our findings suggest that alpha(2)M is an important novel cytochemical marker to identify hepatocellular preneoplastic and neoplastic lesions, particularly amphophilic cell foci, undetectable by established cytochemical markers and is tightly linked to rat hepatocarcinogenesis.

Evaluation for reliability and feasibility of the draft protocol for the enhanced rat 28-day subacute study (OECD Guideline 407) using androgen antagonist flutamide.

As part of an international validation project to establish a test protocol for the 'Enhanced OECD Test Guideline no. 407', a 28-day repeated dose study of flutamide was performed (1) to examine which of the current and/or additional parameters can detect endocrine effects of test chemicals most reliably and sensitively, (2) to investigate whether it is actually feasible to routinely include all additional parameters into the testing routine, and (3) to assess intra-laboratory variability by performing two identical studies (experiments A and B) in parallel using groups of five animals each per dose and sex. Groups of five male and five female CD(SD)IGS rats were treated by oral gavage with 0, 1, 10 and 100 mg flutamide/kg body weight for at least 28 days. The dose level considered to be around the MTD (100 mg/kg) exerted the expected antiandrogenic effects on androgen related tissues: significant decrease of the weights of androgen dependent organs and the sperm count and increase in histopathological lesions. At the middle dose (10 mg/kg), significant decrease of prostate weight (ventral and dorso-lateral parts combined) was observed and it was suggested that weight measurement of androgen dependent organs provides the most reliable and sensitive endpoint with this protocol. As for the feasibility, because of many items in this protocol, selection should be based on the sensitivity. From our data, addition of weight measurement of androgen dependent organs to the items of the existing OECD 407 guideline might allow accurate screening for endocrine disruptors. At the dose level considered to be around the MTD, the findings achieving statistical significance in one experiment with five animals/dose/sex could be reproduced in the second experiment, and evaluation with the small groups was consistent with findings using the combined groups of 10 animals/dose/sex. The results demonstrate that the protocol can reliably detect antiandrogenic effects of flutamide.

Enhanced rat Hershberger assay appears reliable for detection of not only (anti-)androgenic chemicals but also thyroid hormone modulators.

Development of an internationally recognized standard for the Hershberger assay as a screening tool to detect potential (anti-)androgenic chemicals is in progress. In the present preliminary study, we evaluated the reliability of the enhanced Hershberger assay to detect thyroid hormone modulating activity, while concentrating attention on possible confounding influence on evaluation of (anti-)androgenic activity. Castrated or testosterone propionate (TP; 0.2 or 0.25 mg/kg/day)-injected castrated male Crj:CD(SD) IGS rats (seven weeks of age) were dosed for 10 days by oral gavage with vehicle (corn oil) or the following chemicals: propylthiouracil (PTU; 2.5 mg/kg/day), a potent inhibitor of thyroid hormone synthesis, phenobarbital (PB; 125 mg/kg/day) and 2,2-bis(4-chlorophenyl)-1,1-dichloroethylene (p,p'-DDE; 100 mg/kg/day), two hepatic enzyme inducers that enhance the clearance of thyroid hormones. PTU markedly increased thyroid weights, and decreased serum T3 and T4, and increased serum TSH, also causing marked microscopic alteration of the thyroid gland. In comparison, PB and p,p'-DDE only significantly affect serum T4 and revealed some histopathological findings. The alterations appeared to be more robust in the presence of TP. Furthermore, data for p,p'-DDE demonstrated its anti-androgenic effects, whereas PTU and PB had little or no effects on the weights of androgen-related accessory glands/tissues: the ventral prostate, dorso-lateral prostate, seminal vesicles with coagulating glands, glans penis, Cowper's glands, and levator ani plus bulbocavernosus (LABC) muscles. Weight of the LABC muscles was decreased by PB treatment in TP-treated castrated rats. These findings in the present study suggests that the enhanced Hershberger assay, with evaluation of thyroid histopathology and weights, and hormone levels, appears to be reliable for screening for not only (anti-)androgenic chemicals but also thyroid hormone modulators. In order to evaluate whether the sensitivity and specificity of such a thyroid assay is great enough for routine screening purposes, future experiments including dose-response studies using lower dose levels have to be performed.

Effects of perinatal exposure to flutamide on sex hormone responsiveness in F1 male rats.

Pregnant rats were administered flutamide (0 and 10 mg/kg, p.o.) from gestation Day 14 to post-parturition Day 3 and effects on responsiveness to androgens (testosterone propionate, TP; dihydrotestosterone, DHT) in male offspring were examined with a Hershberger assay. Male pups of each group were assigned to 6 subgroups as follows: Group 1, castration and euthanized at postnatal Day 46 (PND 46); Group 2, castration + vehicle; Group 3, castration + TP; Group 4, castration + DHT; Group 5, vehicle; Group 6, DHT. After castrations were conducted at PND 36, animals were treated with TP (2 mg/kg in corn oil, s.c.) or DHT (1.25 mg/kg in corn oil, s.c.) once a day for 10 days, beginning at PND 46. At PND 56, the following organs/tissues were removed and weighed: ventral prostate, dorso-lateral prostate, seminal vesicles with coagulating glands, levator ani muscle plus bulbocavernosus muscle, Cowper's gland, and glands penis. Analysis of serum testosterone, LH and FSH in Groups 2, 3, 4, 5 and 6, and RT-PCR using prostate tissue from Groups 2, 3 and 4 were carried out. Perinatal exposure to flutamide caused decreased weights of androgen-dependent organs. Responses to androgens were recognized in organs of all castrated groups, with increased organ weights, especially in animals administered TP where values were essentially equal to or greater than those of intact animals in both the control and the 10 mg/kg group. On the other hand, the degree of weight increase of the ventral prostate and seminal vesicles with TP or DHT treatment in castrated animals was smaller in the flutamide administration group than in the controls. In hormone assays, castrated + vehicle animals showed higher serum LH than the other groups. Serum FSH was high in the castrated groups (Group 2>Group 4>Group 3), while in the noncastrated group a constant level was noted, with or without flutamide. No effect of flutamide administration was observed regarding sex hormone. RT-PCR using ventral prostate tissue revealed no significant differences in expression of AR, C3, VEGF, TGF-beta1, beta2, KGF and CK8 mRNA after androgen treatment between the control and flutamide treatment groups. C3 mRNA was increased in androgen-treated animals, whereas AR, TGF-beta and KGF mRNAs were decreased. Perinatal exposure to anti-androgen causes irreversible abnormalities in male pups. Concerning the responsiveness to TP and DHT, the degrees of weight changes in ventral prostate and seminal vesicles in castrated animals were decreased. However, the other organ weights, the sex hormone levels and androgen-reactive gene expression in the ventral prostate were not influenced by perinatal flutamide treatment in the present study.

Lack of estrogenic or (anti-)androgenic effects of d-phenothrin in the uterotrophic and Hershberger assays.

Synthetic pyrethroids are among the most common insecticides and pesticides currently in use worldwide. Recently, d-phenothrin, a synthetic pyrethroid, is suspected to have endocrine activities through the estrogen and androgen receptors. However, no study has been conducted to evaluate its potential for hormonal activity using an in vivo test specifically focused on estrogenic and androgenic activities. In this study, we evaluated the interaction of d-phenothrin (0, 100, 300 or 1000 mg/kg per day, p.o.) with estrogen- or androgen-mediated mechanisms using in vivo short-term assays. While internationally standardized protocols for the uterotrophic and Hershberger assays have not yet been fully developed, both are widely used and are being considered by the OECD as short-term screening assays for hormonal activity. The highest dose level tested for d-phenothrin was a limit dose (1000 mg/kg per day) designated in the current draft protocol by the OECD, and in fact there was no excessive systemic toxicity in both assays; slightly increased liver weight but no change of serum androgen levels in accessing anti-androgenicity. Potential estrogenic effect of d-phenothrin was evaluated by means of 3-day uterotrophic assay using immature Crj:CD(SD)IGS rats (20 days of age). No increase in uterine weight (wet or blotted) was observed following oral exposure to d-phenothrin. Reference control ethynyl estradiol (0.001 mg/kg per day) showed a significant effect in this assay protocol. A 10-day Hershberger assay using castrated peripubertal male rats measures the androgenic or anti-androgenic effects of the test chemicals on several accessory glands/tissues (the ventral prostate, dorso-lateral prostate, seminal vesicles with coagulating glands, levator ani plus bulbocavernosus muscles, glans penis and Cowper's glands). d-Phenothrin was administered by oral gavage for 10 days to castrated male Crj:CD(SD)IGS rats (7 weeks of age, rats were castrated at 6 weeks of age) with or without co-administration of 0.2 mg/kg per day testosterone propionate (subcutaneous injection on the dorsal surface). Reference controls of methyltestosterone and p,p'-DDE (100 mg/kg per day) provided significant effects in this assay protocol, whereas d-phenothrin did not show any androgenic or anti-androgenic effects. It is concluded that, based on the results of these two reliable in vivo assays, d-phenothrin exhibits no potential to cause adverse estrogenic or (anti-)androgenic effects even at dose of 1000 mg/kg per day, the limit dose designated in the current draft protocol by the OECD.

Lack of changes in brain muscarinic receptor and motor activity of mice after neonatal inhalation exposure to d-allethrin.

Synthetic pyrethroids are among the most common pesticides and insecticides currently in worldwide use. Eriksson and co-workers postulated that oral exposure of mice to pyrethroids during a neonatal brain growth spurt induces permanent disturbance in the cerebral muscarinic cholinergic receptor (MAChR) and behaviour. However, the scientific basis for these phenomena is now under discussion. The present study was performed to determine whether the experimental findings of Eriksson's study could be reproduced in newborn mice by inhalation. Male and female NMRI mice were exposed to d-allethrin by whole-body inhalation for 6 h per day between postnatal days 10 and 16. Actual concentrations of d-allethrin were 0.43, 1.35, 3.49 and 74.2 mg m(-3) (equivalent to 0.70, 2.2, 5.7 and 120.2 mg kg(-1) day(-1), respectively), and the mass median aerodynamic diameter and geometric log-standard deviation of mist particles ranged from 2.58 to 2.98 micro m and from 1.58 to 2.09 micro m for all groups, respectively. The highest exposure level in the present study (74.2 mg m(-3)) was ca. 13,000 times as high as the concentration used in practice. The MAChR in the three brain areas (cortex, hippocampus and striatum) and motor activity were examined at the ages of 17 days and 4 months. In addition, a water-maze test was performed at the age of 11 months. There was no systemic toxicity interfering with the interpretation of assay results. The neonatal exposure to d-allethrin by inhalation did not induce effects either on the brain MAChR density and motor activity at 17 days and 4 months or on performance in the learning/memory test at the age of 11 months. The effects of allethrins on developmental neurotoxicity that Eriksson and co-workers reported previously were not reproduced in the present study.

Lack of (anti-) androgenic or estrogenic effects of three pyrethroids (esfenvalerate, fenvalerate, and permethrin) in the Hershberger and uterotrophic assays.

Synthetic pyrethroids are among the most common pesticides and insecticides currently in use worldwide. Recently, chemicals classified as synthetic pyrethroids are suspected as being endocrine disrupting chemicals. However, no study has been conducted to assess their potential hormonal activities using in vivo test specifically focused on endocrine disruption. In the present study, we evaluated the interaction of three pyrethroids (esfenvalerate, fenvalerate, and permethrin) with androgen receptor (AR)- and estrogen receptor (ER)-mediated mechanisms using in vivo short-term assays. While internationally standardized protocols for the Hershberger and uterotrophic assays have not yet been fully developed, both are widely used and are being considered by OECD as short-term screening assays for hormonal activity. A 5-day Hershberger assay using castrated male rats measures agonistic and androgenic ability of the test chemicals to AR of several accessory glands/tissues (the ventral prostate, dorsolateral prostate, seminal vesicles with coagulating glands, and levator ani plus bulbocavernosus muscles). Esfenvalerate (5, 10, or 20 mg/kg/day), fenvalerate (20, 40, or 80 mg/kg/day), or permethrin (25, 50, or 75 mg/kg/day) was administered by oral gavage for 5 days to castrated male Crj:CD(SD)IGS rats (1 week after the castration, 11 weeks of age) with or without coadministration of 0.25 mg/kg/day testosterone propionate (subcutaneous injection on the dorsal surface). The highest dose levels tested for each chemical were considered the maximum level that could be used without causing excessive systemic toxicity. None of esfenvalerate, fenvalerate, and permethrin showed any androgenic or antiandrogenic effects. Reference control of p,p'-DDE and methyltestosterone (100 mg/kg/day) provided significant effects in this assay protocol. Potential effects of these pyrethroids mediated through the ER were evaluated by means of 3-day uterotrophic assay using ovariectomized Crj:CD(SD)IGS rats (2 weeks after the ovariectomy, 8 weeks of age). No increase in weight of uterus (wet or blotted) was observed following oral exposure to esfenvalerate (5, 10, or 20 mg/kg/day), fenvalerate (20, 40, or 80 mg/kg/day), or permethrin (37.5, 75, or 150 mg/kg/day), respectively. Again, the highest dose levels tested for each chemical were considered the maximum level that could be used without causing excessive systemic toxicity. Reference controls consisting of ethynyl estradiol (0.03 mg/kg/day) and methoxychlor (125 mg/kg/day) both showed a significant effect in this assay protocol. It is concluded that, based on the results of these two reliable in vivo assays, none of esfenvalerate, fenvalerate, or permethrin exhibit any potential to cause adverse (anti-) androgenic or estrogenic effects at dose levels below that of those causing excessive systemic toxicity.

Detailed low-dose study of 1,1-bis(p-chlorophenyl)-2,2,2- trichloroethane carcinogenesis suggests the possibility of a hormetic effect.

To obtain information on the effects of nongenotoxic carcinogens at low doses for human cancer risk assessment, the carcinogenic potential of the organochlorine insecticide, 1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT), in the liver was assessed in F344 rats. In experiment 1, 240 male animals, 21 days old, were administered 0, 0.5, 1.0, 2.0, 5.0, 20, 100 and 500 ppm DDT in the diet for 16 weeks. Experiment 2 was conducted to elucidate the carcinogenic potential of DDT at lower levels using 180 rats given doses of 0, 0.005, 0.01, 0.1, 0.2 and 0.5 ppm. The livers of all animals were immunohistochemically examined for expression of glutathione S-transferase placental form (GST-P), putative preneoplastic lesions. Quantitative values for GST-P-positive foci in the liver were increased dose-dependently in rats given 20 ppm DDT and above with statistical significance as compared with the concurrent control value. In contrast, doses of 0.005 and 0.01 ppm were associated with a tendency for decrease below the control value, although not significantly. Western blotting analysis show that cytochrome P-450 3A2 (CYP3A2) protein expression tended to decrease at 0.005 and 0.01 ppm, a good correlation being observed with the change in the number of GST-P-positive foci. These findings suggest that a DDT hepatocarcinogenicity may show nonlinear response, that is, hormetic response at low doses. Furthermore, since CYP3A2 protein expression appears to be important for the effects of phenobarbital and the alpha-isomer of benzene hexachloride, mRNAs for IL-1 receptor type 1 (IL-1R1) and TNF-alpha receptor type 1 (TNFR1) whose ligands have roles not only in downregulating CYP3A2 expression but also in inducing antiproliferative effect or apoptosis in hepatocyte were examined. Increase was observed at low doses of DDT. Oxidative stress in liver DNA, assessed in terms of 8-hydroxydeoxyguanosine as a marker, was also decreased. These findings suggest that the possible hormetic effect that was observed in our detailed low-dose study of DDT carcinogenesis, although not statistically significant, may be linked to levels of oxidative stress and proinflammatory cytokines.

Effects of perinatal exposure to flutamide on sex hormones and androgen-dependent organs in F1 male rats.

Flutamide, which has antiandrogenic properties, was administered to pregnant rats, and effects on male offspring were examined. Crj: CD (SD) IGS (SPF) females were administered flutamide (0.15, 0.6, 2.5, 10.0, 100 mg/kg, p.o.) from gestation Day 14 to post parturition Day 3. The number of pups, body weights, clinical features, anogenital distance (AGD), nipple retention, testicular descent, and urogenital malformation in F1 males were examined. Hormone measurement, necropsy and histopathological examination were carried out at post-neonatal Day 4 (PND 4) and PND 60. Sperm analysis was also carried out at PND 60. Decrease in body weight was seen in the 100 mg/kg group and the AGD was decreased at 2.5 mg/kg and above. Retention of nipples, hypospadia, vaginal pouches, penis malformation, unilateral ectopic testis, and decrease of organ weights (prostate, seminal vesicles, levator ani muscle plus bulbocavernosus muscle, testis) were observed at 10 mg/kg and above. Testicular testosterone (T) was increased significantly with 100 mg/kg at PND 4 and tendencies for increase were observed in serum T, LH and FSH at 10 mg/kg and more at the same time point. In contrast, elevated levels of LH and FSH were seen with 100 mg/kg at PND 60. Histopathological examination revealed defects or hypoplastic changes of genital organs (> or = 10 mg/kg), squamous metaplasia (10 mg/kg) or mucification (100 mg/kg) of the urethral diverticulum epithelium and inflammation of genital organs (100 mg/kg). Though only undescended testes lacked spermatogenesis at 10 mg/kg, atrophic change of seminiferous tubules and azoospermia were observed in the 100 mg/kg group, despite testicular descent. Perinatal administration of flutamide affected F1 male rats at 2.5 mg/kg and above. In addition to urogenital malformation, 100 mg/kg flutamide caused high LH and FSH levels at PND 60. This study indicates that the most sensitive parameter is AGD, whereby reduction was observed at 2.5 mg/kg. A clear no-effect level (NOEL: 0.6 mg/kg) was obtained in this perinatal study of an antiandrogenic chemical.