Steroidogenic impairment after lindane treatment in male rats

Inhibitors of testosterone biosynthetic and metabolic activation enzymes

The Leydig cells of the testis have the capacity to biosynthesize testosterone from cholesterol. Testosterone and its metabolically activated product dihydrotestosterone are critical for the development of male reproductive system and spermatogenesis. At least four steroidogenic enzymes are involved in testosterone biosynthesis: Cholesterol side chain cleavage enzyme (CYP11A1) for the conversion of cholesterol into pregnenolone within the mitochondria, 3β-hydroxysteroid dehydrogenase (HSD3B), for the conversion of pregnenolone into progesterone, 17α-hydroxylase/17,20-lyase (CYP17A1) for the conversion of progesterone into androstenedione and 17β-hydroxysteroid dehydrogenase (HSD17B3) for the formation of testosterone from androstenedione. Testosterone is also metabolically activated into more potent androgen dihydrotestosterone by two isoforms 5α-reductase 1 (SRD5A1) and 2 (SRD5A2) in Leydig cells and peripheral tissues. Many endocrine disruptors act as antiandrogens via directly inhibiting one or more enzymes for testosterone biosynthesis and metabolic activation. These chemicals include industrial materials (perfluoroalkyl compounds, phthalates, bisphenol A and benzophenone) and pesticides/biocides (methoxychlor, organotins, 1,2-dibromo-3-chloropropane and prochloraz) and plant constituents (genistein and gossypol). This paper reviews these endocrine disruptors targeting steroidogenic enzymes.

Biochemical effects induced by the hexachlorocyclohexanes

The hexachlorocyclohexanes (HCHs) are synthetic compounds that have been widely used for the control of pests. The most common HCH isomers are the α-, β-, δ-, and γ-HCH. Although the have the same chlorine substitution pattern, the spatial orientation of chlorine atoms is different on each one of them, resulting in unique structures that have distinct molecular properties. Humans are exposed to individual HCH isomers through various routes, including ingestion of contaminated water or food, absorbed through the skin or by inhalation, and because of their liposolubility, these chemicals are mostly stored in fat-containing tissues. The isomer-specific spectrum of biochemical actions for these compounds has been wee characterized for different endpoints such as enzyme activation, calcium homeostasis, gap junctional intercellular communication, endocrine disruption, and cancer, among others. The interaction with the GABA reception has been one of the most extensively studied properties of the HCHs. For instance, γ-HCH acts as a GABAA channel blocker, whereas α- and δ-HCH potentiate currents , all working as allosteric modulators of the receptor. The changes in calcium homeostasis elicited by HCHs are both isomer and cell type specific. For example, in neurons, both the δ- and γ-isomers of HCH stimulate Ca²+ influx through different voltage-gated Ca²+ channels. In human neutrophils, α-,δ-, and γ-HCH, but not β-HCH, increase intracellular Ca²+ concentrations. This isomer-dependent behavior is also similar to that observed for phospholipase A2 activation and also correlates with oxidative stress generation. On the other hand, there are several lines of evidence suggesting that HCHs alter genomic integrity, and, therefore, these compounds have been classified as possibly carcinogenic to humans . Finally, HCHs have been reported to be endocrine disrupters. In fact, γ- and β-HCH have been shown to have weak estrogenic activity, and together with the α- and the δ-isomer, also interfere with steroidogenesis. In short, the HCH isomers are good examples of structurally related chemicals, for which the geometrical patterns present in each one of the different conformers create structures that possess specific mechanisms of action and toxicological properties.

Proapoptotic effects of lindane on mouse primordial germ cells

Lindane (gamma-HCH) was examined for its effect on primordial germ cell (PGC) development in the mouse embryo. We found that exposure by gavage of pregnant mice to 15 or 30 mg/kg/bw lindane during the period of PGC migration and gonad colonization (from 8.5 to 11.5 days post coitum, dpc) resulted in a significant reduction of the number of germ cells within 12.5 dpc testis and ovaries (a maximum of about 25 and 40%, respectively). Similarly, lindane caused a dose-dependent decrease of the PGC number in an in vitro culture model. Further experiments showed that in such model, lindane induced features of apoptotic cell death in PGCs such as increase in caspase-3 activity, poly-ADP-ribose polymerase cleavage, and terminal dUTP nick-end labeling (TUNEL) positivity. A marked increase of the number of PGCs positive for TUNEL staining was also observed in 12.5 dpc gonads of embryos from pregnant mice subjected one day before to acute lindane treatment (60 mg/kg/bw). Finally, we show that a brief incubation of isolated PGCs with 10(-5)M lindane resulted in a marked decrease of the basal and kit-ligand-induced phosphorylation level of the AKT kinase, known to be crucial for PGC survival. Taken together these results demonstrate that embryo exposure to lindane during early stages of gametogenesis can severely impair the number of germ cells in the fetal gonads; the compound appears to affect PGC survival through a direct proapoptotic action likely resulting from its adverse effect on AKT activity in such cells.

Pesticide exposure and timing of menopause: the Agricultural Health Study

Age at menopause has implications for fertility and risk of hormonally related chronic diseases. Some pesticides disrupt reproductive hormones or are toxic to the ovary, but little is known about the association between pesticide exposure and timing of menopause. Cox proportional hazards modeling was used to examine the association between use of pesticides and age at menopause among 8,038 women living and working on farms in Iowa and North Carolina. Premenopausal women aged 35-55 years were followed from enrollment (1993-1997) to the date of their last menstrual period, or their follow-up interview (1999-2003) if still premenopausal. Women who experienced surgical menopause were censored at the date of surgery. Approximately 62% of the women reported ever mixing or applying pesticides; women who had never used pesticides were the comparison group for all analyses. After control for age, smoking status, and past use of oral contraceptives, the median time to menopause increased by approximately 3 months for women who used pesticides (hazard ratio = 0.87, 95% confidence interval: 0.78, 0.97) and by approximately 5 months for women who used hormonally active pesticides (hazard ratio = 0.77, 95% confidence interval: 0.65, 0.92). Pesticide use may be associated with a later age at menopause.

Pesticide use and menstrual cycle characteristics among premenopausal women in the Agricultural Health Study

Menstrual cycle characteristics may have implications for women's fecundability and risk of hormonally related diseases. Certain pesticides disrupt the estrous cycle in animals. The authors investigated the cross-sectional association between pesticide use and menstrual function among 3,103 women living on farms in Iowa and North Carolina. Women were aged 21-40 years, premenopausal, not pregnant or breastfeeding, and not taking oral contraceptives. At study enrollment (1993-1997), women completed two self-administered questionnaires on pesticide use and reproductive health. Exposures of interest were lifetime use of any pesticide and hormonally active pesticides. Menstrual cycle characteristics of interest included cycle length, missed periods, and intermenstrual bleeding. The authors used generalized estimating equations to assess the association between pesticide use and menstrual cycle characteristics, controlling for age, body mass index, and current smoking status. Women who used pesticides experienced longer menstrual cycles and increased odds of missed periods (odds ratio = 1.5, 95% confidence interval: 1.2, 1.9) compared with women who never used pesticides. Women who used probable hormonally active pesticides had a 60-100% increased odds of experiencing long cycles, missed periods, and intermenstrual bleeding compared with women who had never used pesticides. Associations remained after control for occupational physical activity.

Effect of dibromochloropropane (DBCP) on the hormone receptors of the male rat reproductive system

The effects of dibromochloropropane (DBCP), a pesticide, on the male rat reproductive system were examined at morphological and hormonal expression levels. Changes of Leydig cells and seminiferous tubules were examined in rats treated with one subcutaneous (s.c.) injection of DBCP at doses of 10, 50, 75 and 100 mg/kg of body weight. The Leydig cells degenerated and decreased in number in those rats with an s.c. injection of DBCP at a dose of 50 mg/kg of body weight. However, these morphological changes were not significant in those rats that were treated with four separate s.c. injections of DBCP at 10 mg/kg of body weight. The expression of luteinizing hormone receptor mRNA, which is specifically expressed in Leydig cells, was decreased significantly in the DBCP-treated rats as compared with the normal-control rats. The expression of follicle-stimulating hormone receptor mRNA was decreased to a mild degree in DBCP-treated rats. At a dose of 75 mg/kg of body weight, seminiferous tubules as well as Leydig cells were severely damaged morphologically and at hormonal receptor expression levels. Multinucleated giant cells appeared at a dose of 75 mg/kg of body weight. All the rats died at a dose of 100 mg/kg of body weight. Our data indicate that DBCP had a cytotoxic effect on the male rat reproductive system in a dose-dependent manner.