Academic journal article Environmental Health Perspectives

Hair Mercury Negatively Correlates with Calcium Pump Activity in Human Term Newborns and Their Mothers at Delivery

Academic journal article Environmental Health Perspectives

Hair Mercury Negatively Correlates with Calcium Pump Activity in Human Term Newborns and Their Mothers at Delivery

Article excerpt

BACKGROUND: Calcium homeostasis is a known target of several environmental toxicants including lead and mercury.

OBJECTIVE: Our goal was to determine the relationship between Hg exposure and erythrocyte Ca pump activity in women at delivery and in their newborns.

METHODS: We determined total Hg as well as Pb concentrations in 81 hair and blood samples obtained at delivery. Basal and calmodulin-stimulated Ca pump activity was measured in red blood cells from cord blood and maternal erythrocyte plasma membranes.

RESULTS: Maternal hair Hg negatively correlates with Ca pump activity in maternal and cord blood erythrocytes. Pb and Hg both independently correlate negatively with Ca pump activity without any statistically significant interaction. After adjustment for potential confounders, Pb and Hg explain about 30% and 7% of total variance of Ca pump activity in newborns and mothers, respectively.

CONCLUSION: Our findings confirm results reported in previous experimental studies and support the use of biomarkers in newborns from general population.

KEY WORDS: calcium, cord blood, environmental exposure, lead, mercury, newborn, pregnancy. Environ Health Perspect 116:263--267 (2008). doi:10. 1289/ehp. 10381 available via http://dx.doi.org/[Online 17 November 2007]

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The neurotoxic effects of prenatal exposure to high doses of methylmercury (MeHg) were well established after the serious poisoning epidemics in Japan and Iraq (Harada 1995; Marsh et al. 1987). However, associations between MeHg exposure, developmental milestones, and neurologic tests at exposure levels as low as 10 ppm (estimated in maternal hair) have proven difficult to confirm (Myers and Davidson 2000). Nevertheless, children exposed to mercury levels < 10 ppm have been observed to display subtle neurobehavioral deficits, especially with respect to language, attention, and memory scores (Grandjean et al. 1997; Weihe et al. 2002). In one of three main cohorts, beneficial associations observed between Hg exposure and psychomotor performances (Myers et al. 1995) are believed to be attributable to other nutriments found in fish, such as selenium and/or polyunsaturated fatty acids. Although high-dose MeHg poisoning has been shown to cause developmental disorders, evidence that more subtle low-level developmental exposure contributes to these disorders is limited.

Sensitive biomarkers are needed to assess the effects consequent to low-dose exposures. Calcium homeostasis is a known target of several environmental neurotoxicants including lead and Hg (Habermann et al. 1983; Kirk et al. 2003; Marty and Atchison 1997). Deregulation of Ca homeostasis triggers serious effects on cell functioning because of altered Ca signaling. Normally, cytosolic concentration of free [Ca.sup.2+] (divalent calcium cation) is maintained at low levels ([10.sup.-7] M) by extrusion and compartmentalization systems. A main component of the extrusion process is the plasma membrane Ca--ATPase pump (Carafoli and Brini 2000). Whereas transient elevations of cytosolic [Ca.sup.2+] levels are an important component of cell signaling, sustained [Ca.sup.2+] increases are not tolerated by cells and generally lead to apoptosis or cytotoxicity and necrosis (Orrenius et al. 1989). Intracellular Ca is a sensitive biomarker of pollutant-related stress in amoebic cells exposed to Hg at sublethal doses (Dondero et al. 2006).

Heavy metals are able to inhibit in vitro Ca pump activity in purified plasma membranes obtained from mussel-gill cells. Experimental studies have shown that [Hg.sup.2+] inhibits Ca pump activity by preventing the formation of an essential phosphorylated intermediate of the process of [Ca.sup.2+] transport (Viarengo et al. 1993). One in vitro study reported the compensatory activation of Ca pump protein expression after Hg induced transitory inhibition of Ca pump activity, leading to a net increase in enzyme activity (Burlando et al. …

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