Evaluation of estrogenicity of major heavy metals

Gender differences in the disposition and toxicity of metals

There is increasing evidence that health effects of toxic metals differ in prevalence or are manifested differently in men and women. However, the database is small. The present work aims at evaluating gender differences in the health effects of cadmium, nickel, lead, mercury and arsenic. There is a markedly higher prevalence of nickel-induced allergy and hand eczema in women compared to men, mainly due to differences in exposure. Cadmium retention is generally higher in women than in men, and the severe cadmium-induced Itai-itai disease was mainly a woman's disease. Gender differences in susceptibility at lower exposure are uncertain, but recent data indicate that cadmium has estrogenic effects and affect female offspring. Men generally have higher blood lead levels than women. Lead accumulates in bone and increased endogenous lead exposure has been demonstrated during periods of increased bone turnover, particularly in women in pregnancy and menopause. Lead and mercury, in the form of mercury vapor and methylmercury, are easily transferred from the pregnant women to the fetus. Recent data indicate that boys are more susceptible to neurotoxic effects of lead and methylmercury following exposure early in life, while experimental data suggest that females are more susceptible to immunotoxic effects of lead. Certain gender differences in the biotransformation of arsenic by methylation have been reported, and men seem to be more affected by arsenic-related skin effect than women. Experimental studies indicate major gender differences in arsenic-induced cancer. Obviously, research on gender-related differences in health effects caused by metals needs considerable more focus in the future.

Sperm quality, birth rates and the environment in Flanders (Belgium)

The relationship between fertility and pollution is unclear. We evaluated sperm quality of 562 candidate donors (years 1977-2004), births rates (births), pollutants, and the number of females in reproductive age (NFRA, 20-39 years) in Flanders. Total sperm count did not change significantly with time. Births correlated with sperm morphology (r=0.60, P=0.0027). Continuing decline in sperm morphology with time is confirmed, statistically unrelated to pollutants. Grade A sperm motility declined (1977-1992) with gradual incomplete recovery thereafter. Multiple regression analysis (1995-2002) indicated dioxin (negative association) as the only independent variable for grade A motility (r-adjusted co-efficient of determination "r-adjusted"=0.76, P=0.008). Births and pollution were positively associated but births were only dependent on NFRA (r-adjusted=0.91, P<0.001). Our results suggest a relation between dioxin and sperm motility, partially reversible upon reduction of environmental dioxin. Though significantly correlated with sperm morphology, births are primarily associated with demographic factors.

Metalloestrogens: an emerging class of inorganic xenoestrogens with potential to add to the oestrogenic burden of the human breast

Many compounds in the environment have been shown capable of binding to cellular oestrogen receptors and then mimicking the actions of physiological oestrogens. The widespread origin and diversity in chemical structure of these environmental oestrogens is extensive but to date such compounds have been organic and in particular phenolic or carbon ring structures of varying structural complexity. Recent reports of the ability of certain metal ions to also bind to oestrogen receptors and to give rise to oestrogen agonist responses in vitro and in vivo has resulted in the realisation that environmental oestrogens can also be inorganic and such xenoestrogens have been termed metalloestrogens. This report highlights studies which show metalloestrogens to include aluminium, antimony, arsenite, barium, cadmium, chromium (Cr(II)), cobalt, copper, lead, mercury, nickel, selenite, tin and vanadate. The potential for these metal ions to add to the burden of aberrant oestrogen signalling within the human breast is discussed.

Cadmium exposure and breast cancer risk

Cadmium, a highly persistent heavy metal, has been categorized as a probable human carcinogen by the U.S. Environmental Protection Agency. Primary exposure sources include food and tobacco smoke. We carried out a population-based case-control study of 246 women, aged 20-69 years, with breast cancer and 254 age-matched control subjects. We measured cadmium levels in urine samples by inductively coupled plasma mass spectrometry and conducted interviews by telephone to obtain information on known breast cancer risk factors. Odds ratios (ORs) and 95% confidence intervals (CIs) for breast cancer by creatinine-adjusted cadmium levels were calculated by multivariable analysis. Statistical tests were two-sided. Women in the highest quartile of creatinine-adjusted cadmium level (> or = 0.58 microg/g) had twice the breast cancer risk of those in the lowest quartile (<0.26 microg/g; OR = 2.29, 95% CI = 1.3 to 4.2) after adjustment for established risk factors, and there was a statistically significant increase in risk with increasing cadmium level (P(trend) = .01). Based on this study, the absolute risk difference is 45 (95% CI = 0 to 77) per 100,000 given an overall breast cancer rate of 124 per 100,000. Whether increased cadmium is a causal factor for breast cancer or reflects the effects of treatment or disease remains to be determined.

Stage-dependency of apoptosis and the blood-testis barrier in the dogfish shark (Squalus acanthias): cadmium-induced changes as assessed by vital fluorescence techniques

Naturally occurring heavy metals and synthetic compounds are potentially harmful for testicular function but evidence linking heavy metal exposure to reduced semen parameters is inconclusive. Elucidation of the exact stage at which the toxicant interferes with spermatogenesis is difficult because the various germ cell stages may have different sensitivities to any given toxicant, germ cell development is influenced by supporting testicular somatic cells and the presence of inter-Sertoli cell tight junctions create a blood-testis barrier, sequestering meiotic and postmeiotic germ cells in a special microenvironment. Sharks such as Squalus acanthias provide a suitable model for studying aspects of vertebrate spermatogenosis because of their unique features: spermatogenesis takes place within spermatocysts and relies mainly on Sertoli cells for somatic cell support; spermatocysts are linearly arranged in a maturational order across the diameter of the elongated testis; spermatocysts containing germ cells at different stages of development are topographically separated, resulting in visible zonation in testicular cross sections. We have used the vital dye acridine orange and a novel fluorescence staining technique to study this model to determine (1) the efficacy of these methods in assays of apoptosis and blood-testis barrier function, (2) the sensitivity of the various spermatogonial generations in Squalus to cadmium (as an illustrative spermatotoxicant) and (3) the way that cadmium might affect more mature spermatogenic stages and other physiological processes in the testis. Our results show that cadmium targets early spermatogenic stages, where it specifically activates a cell death program in susceptible (mature) spermatogonial clones, and negatively affects blood-testis barrier function. Since other parameters are relatively unaffected by cadmium, the effects of this toxicant on apoptosis are presumably process-specific and not attributable to general toxicity.

Investigations on cellular proliferation induced by zearalenone and its derivatives in relation to the estrogenic parameters

Many man-made chemicals (pesticides) and naturally occurring compounds (mycotoxins and phytoestrogens) can enter the food chain and bind to estrogen receptors (ERs). Mycotoxins, including zearalenone (ZEA) and its derivatives, can occur worldwide in cereals and cause several health disorders. In order to characterize the estrogenic activity of zearalenone and its derivatives (alpha-zearalenol (alpha-ZEA), beta-zearalenol (beta-ZEA), alpha-zearalanol (alpha-ZAL) and beta-zearalanol (beta-ZAL)), the proliferation of ER-positive (MCF-7) and ER-negative (MDA-MB-231) human breast cancer cell lines was measured. After exposure at levels ranging from 0.1 pM to 0.1microM, cell proliferation (E-screen assay) was evaluated by MTT test through estrogenic parameters. On the MCF-7 cell line, estrogenic concentration that induced 50% cellular proliferation (EC(50)) of beta-zearalenol was statistically higher (5.2 x 10(-3)microM) than those of other zearalenone-related compounds, in agreement with other authors. All mycotoxins showed similar estrogenic parameters, with the exception of alpha-zearalenol that induced a higher proliferative effect (PE=2.6) and relative proliferative potency (RPP=7). Since MCF-7 contains both ERalpha and ERbeta-positive cells, at the mRNA and protein level, the estrogenic activity induced by mycotoxins may be ER-mediated, particularly through ERalpha that was the predominant ER subtype in these cells. A partial antagonism of mycotoxin-related estrogenic proliferation was seen when tamoxifen was used, confirming a receptor-dependent estrogenic response. MDA-MB-231 cells did not show ERs and after exposure to mycotoxins or 17beta-estradiol marginal PE values related to growth variability of MDA-MB-231 were found. Further studies are needed to understand in human tissues the mechanisms of action of ZEA and its derivatives that may be found as contaminants in the human diet.

Urinary cadmium and serum levels of estrogens and androgens in postmenopausal Japanese women

BACKGROUND

Recent laboratory studies have suggested that cadmium is an estrogenic compound and may be a potential risk factor for breast cancer.

METHODS

We investigated the relationship between urinary cadmium concentrations and serum concentrations of estrone, testosterone, and dehydroepiandrosterone sulfate in 164 postmenopausal Japanese women.

RESULTS

There was a significant positive association between the urinary cadmium and serum testosterone levels after controlling for age and body mass index. The mean testosterone level was 28% higher in women with high urinary cadmium (> or = 3.00 microg/g creatinine) than in those with low urinary cadmium (< 2.00 microg/g creatinine). Urinary cadmium was not significantly associated with serum estrone and dehydroepiandrosterone sulfate levels. Additional adjustment for smoking, alcohol and reproductive factors including known risk factors for breast cancer did not substantially alter the results.

CONCLUSION

Data suggested that cadmium exposure is associated with increased testosterone levels. As high testosterone levels have been associated with the risk of breast cancer, the involvement of cadmium exposure in breast cancer risk should be evaluated in future studies.