Altered activation/detoxication enzymology following neonatal diethylstilbestrol treatment

Imprinting and Reproductive Health: A Toxicological Perspective

This overview discusses the role of imprinting in the development of an organism, and how exposure to environmental chemicals during fetal development leads to the physiological and biochemical changes that can have adverse lifelong effects on the health of the offspring. There has been a recent upsurge in the use of chemical products in everyday life. These chemicals include industrial byproducts, pesticides, dietary supplements, and pharmaceutical products. They mimic the natural estrogens and bind to estradiol receptors. Consequently, they reduce the number of receptors available for ligand binding. This leads to a faulty signaling in the neuroendocrine system during the critical developmental process of 'imprinting'. Imprinting causes structural and organizational differentiation in male and female reproductive organs, sexual behavior, bone mineral density, and the metabolism of exogenous and endogenous chemical substances. Several studies conducted on animal models and epidemiological studies provide profound evidence that altered imprinting causes various developmental and reproductive abnormalities and other diseases in humans. Altered metabolism can be measured by various endpoints such as the profile of cytochrome P-450 enzymes (CYP450's), xenobiotic metabolite levels, and DNA adducts. The importance of imprinting in the potentiation or attenuation of toxic chemicals is discussed.

Responsiveness of cerebral and hepatic cytochrome P450s in rat offspring prenatally exposed to lindane

Prenatal exposure to low doses of lindane has been shown to affect the ontogeny of xenobiotic metabolizing cytochrome P450s (CYPs), involved in the metabolism and neurobehavioral toxicity of lindane. Attempts were made in the present study to investigate the responsiveness of CYPs in offspring prenatally exposed to lindane (0.25 mg/kg b. wt.; 1/350th of LD(50); p. o. to mother) when challenged with 3-methylcholanthrene (MC) or phenobarbital (PB), inducers of CYP1A and 2B families or a sub-convulsant dose of lindane (30 mg/kg b. wt., p. o.) later in life. Prenatal exposure to lindane was found to produce an increase in the mRNA and protein expression of CYP1A1, 1A2, 2B1, 2B2 isoforms in brain and liver of the offspring at postnatal day 50. The increased expression of the CYPs in the offspring suggests the sensitivity of the CYPs during postnatal development, possibly, to low levels of lindane, which may partition into mother's milk. A higher increase in expression of CYP1A and 2B isoenzymes and their catalytic activity was observed in animals pretreated prenatally with lindane and challenged with MC (30 mg/kg, i. p. x 5 days) or PB (80 mg/kg, i. p. x 5 days) when young at age (approx. 7 weeks) compared to animals exposed to MC or PB alone. Further, challenge of the control and prenatally exposed offspring with a single sub-convulsant dose of lindane resulted in an earlier onset and increased incidence of convulsions in the offspring prenatally exposed to lindane have demonstrated sensitivity of the CYPs in the prenatally exposed offspring. Our data assume significance as the subtle changes in the expression profiles of hepatic and cerebral CYPs in rat offspring during postnatal development could modify the adult response to a later exposure to xenobiotics.

Modulation of adult rat benzo(a)pyrene (BaP) metabolism and DNA adduct formation by neonatal diethylstilbestrol (DES) exposure

This study seeks to elucidate the role of diethylstilbestrol (DES), a synthetic estrogen on benzo(a)pyrene (BaP) metabolism in the male rat reproductive tissues. Offspring of timed-pregnant Sprague-Dawley rats were neonatally treated on days 2, 4, and 6 post-partum with 1.45 micromol/kg of DES. Ten weeks after birth, the adult rats were challenged with radiolabeled benzo(a)pyrene (3H BaP) (10 micromol/kg) and the rats were sacrificed 2 h after BaP exposure. Prostrate, testis, lung, liver, urine and feces samples were collected and extracted using a mixture of H2O, MeOH and CHCl3. The extracts were analyzed by reverse phase HPLC. The concentrations of BaP organic metabolites in DES rats were lower compared to controls (vehicle-treated rats). On the other hand, concentrations of aqueous metabolites were significantly increased in DES treated animals. The toxication to detoxication ratios were significantly decreased in DES rats compared to controls. This trend is also reflected in the decreased concentrations of BaP-DNA adducts in DES rats. Collectively these results suggest that DES is capable of modulating the metabolic pathway of BaP towards detoxification thereby preventing the manifestation of toxicity.

Neonatal exposure to xenobiotics alters adult hepatic protein kinase C alpha levels and testosterone metabolism: differential effects by diethylstilbestrol and phenobarbital

Hepatic enzymes that metabolize endogenous and xenobiotic compounds have been shown to be altered in adult rats that had been exposed to xenobiotics as neonates. Protein kinase C (PKC) is important in intracellular signaling and has been implicated in the regulation of hepatic monooxygenases. Therefore, we examined the effects of neonatal exposure to diethylstilbestrol (DES) and phenobarbital (PB) on hepatic microsomal testosterone metabolism and on the alpha form of protein kinase C (PKC alpha) in adult rats. In adult males, neonatal exposure to DES altered adult testosterone metabolism such that 7 alpha-hydroxylation was increased by 58% but 2 alpha-, 16 alpha-, and 6 beta-hydroxylations and conversion to androstenedione were decreased 31-44%. In contrast, adult males neonatally exposed to PB showed increased (20-27%) testosterone 2 alpha- and 16 alpha-hydroxylations and androstenedione formation, but no effect was observed in the rate of 6 beta- or 7 alpha-hydroxylations. Western blot analyses indicated that cytosolic PKC alpha levels in male rats neonatally exposed to PB were decreased by approximately 63% relative to the vehicle control group but were not significantly altered in the DES males. The PKC alpha levels generally correlated (r = -.75) with 16 alpha-hydroxytestosterone formation in all samples. These results show that neonatal treatment with DES or PB differentially alters hepatic monooxygenase enzyme activities and PKC alpha levels in adult rats.

Protective effect of estrogens and catecholestrogens against peroxidative membrane damage in vitro

The antioxidant effects of natural estrogens (estrone, E1; 17 beta-estradiol), synthetic estrogens (17 alpha-ethynylestradiol, EE2; mestranol, MES; diethylstilbestrol, DES) and catecholestrogens (2-hydroxyestradiol; 4-hydroxyestradiol, 4-OHE2) on lipid peroxidation induced by different means in rat liver microsomes were investigated. The extent of lipid peroxidation was determined by measuring thiobarbituric acid reactive substances. Prooxidants included Fe3+/ADP/reduced NADPH, Fe2+/ascorbate, tert-butyl hydroperoxide (t-BOOH) and 2,2'-azobis(2-amidinopropane) (AAPH). Estrogens and catecholestrogens decreased lipid peroxidation in all four systems tested. In the iron/ascorbate model it was shown that (i) 4-OHE2 and DES had analogous patterns of inhibition, irrespective of the presence of NADPH or the functional integrity of the microsomes, and (ii) the antioxidant activities of E1, EE2 and MES were dependent on the assay conditions with the activity being markedly higher when estrogen metabolism was favored. When peroxidation was initiated by the peroxyl radical generator AAPH, the inhibitory effects observed were least pronounced. Our data also showed that, in each of the systems, all inhibitors displayed the same order of inhibitory potency with DES and catecholestrogens being the most potent antioxidants under all experimental conditions used. The present results confirm earlier findings and point toward a link between estrogen metabolism and estrogen antioxidant activity. The data also indicate that estrogens and catecholestrogens interact with the peroxidative process at different levels with their interactions with iron or the metal-derived species being the most important modes of inhibition.

Acute and permanent growth effects in the mouse uterus after neonatal treatment with estrogens

Acute and late effects of neonatal estrogen treatment were studied in NMRI mice treated with diethylstilbestrol (DES) or estradiol-17 beta (E2) on days 1 to 5 after birth (estrogenized females). The uterine wet weight (UWW) response in 6-day-old females, after 5 daily treatments with DES, had a peak at a daily dose of 10(-2) micrograms DES and declined with higher doses. Females (26-day-old) treated with DES or E2 neonatally had a reduced UWW response to a challenge with DES; on a dose basis, DES was more effective neonatally than E2. A single injection with DES or E2 in the neonatal period stimulated mitotic activity in the uterine horn epithelium; the UWW response to a 24-h DES pulse increased from day 2 to 6 after birth, but the uterine epithelial mitotic rate response decreased. Epidermal growth factor (EGF) was a more potent stimulator of mitotic activity than DES or E2. DES inhibited mitotic activity in the uterine cervical epithelium; EGF protected from this DES effect. In adult estrogenized females, EGF-induced uterine stimulation of 3H-thymidine incorporation subsided more rapidly than in control females; uterine epithelium did not respond to EGF in vitro. Uterine stroma of adult estrogenized females is postulated to house a population of cells under nonovarian proliferation control while the uterine epithelium may be under influence of an ovary-dependent proliferation inhibiting factor that is gradually lost under culture conditions.

Alterations in cytochrome P-450 levels in adult rats following neonatal exposure to xenobiotics

Neonatal exposure to certain xenobiotics has been shown to alter hepatic metabolism in adult rats in a manner that indicates long-term changes in enzyme regulation. Previously, we have observed changes in adult testosterone metabolism and in cytochrome P-450 (P-450) mRNA levels in animals neonatally exposed to phenobarbital (PB) or diethylstilbestrol (DES). In order to test for other enzyme alterations, we used Western blot procedures for specific P-450s to analyze hepatic microsomes from adult rats (24 wk old) that had been exposed neonatally to DES, PB, 7,12-dimethylbenz[a]anthracene (DMBA), or pregnenolone 16 alpha-carbonitrile (PCN). The most striking effects were observed in the DES-treated males: P-4502C6 and an immunologically similar protein were increased 60 and 90%, respectively, relative to control values, but P-4503A2 was decreased by 44%. No changes were observed in the DES-treated males in levels of P-4502E1, P-4502B, or the male-specific P-4502C13. Adult males neonatally treated with PB had 150% increase in levels of anti-P4502B-reactive protein without significant changes in the other enzymes. The DES- and DMBA-treated females had increased levels of the female-specific P-4502C12 of 38 and 48%, respectively, but no other observed alterations. The results confirm that neonatal exposure to DES or PB can cause alterations in adult hepatic cytochrome P-450 levels but show that these chemicals act on different enzymes. Neonatal DMBA resulted in changes in adult females similar to those produced by the synthetic estrogen DES, but did so at about two-thirds lower dose.

Neonatal diethylstilbestrol treatment alters aflatoxin B1-DNA adduct concentrations in adult rats

Aflatoxin B1-DNA adduct concentrations were measured in the livers of adult Sprague-Dawley CD rats treated on days 2, 4, and 6 postnatally with 1.45 mumols of diethylstilbestrol and in adulthood with phenobarbital, 3-methylcholanthrene, or vehicle prior to treatment with aflatoxin B1. Aflatoxin B1 (1 mg/kg) was injected 5 hr prior to killing the rats. Female rats exposed neonatally to diethylstilbestrol had significantly higher aflatoxin B1-DNA adduct concentrations (three- to sixfold) than adult female rats treated neonatally with propylene glycol. Liver aflatoxin B1-DNA adduct concentrations were slightly higher in control males as compared to adduct concentrations in neonatally diethylstilbestrol-treated males, as compared to adduct concentrations in control females (not significant [NS]). Phenobarbital and 3-methylcholanthrene treatment followed by aflatoxin B1 injection resulted in decreased aflatoxin B1-DNA adduct concentrations in all rats. Our results demonstrate that neonatal exposure to diethylstilbestrol alters the capacity of adult female rats to form and/or dispose of carcinogen-DNA adducts following a single dose of aflatoxin B1 (increased adduct concentration). This alteration may be a consequence of altered imprinting mechanisms with diethylstilbestrol causing developmental modifications early in life. The animals were, however, able to respond to cytochrome P-450 and P-448 inducers as evidenced by decreased aflatoxin B1-DNA adduct concentrations.