Disposition of inorganic mercury in pregnant rats and their offspring

A methionine biomolecule-modified chromenylium-cyanine fluorescent probe for the analysis of Hg2+ in the environment and living cells

The objective of the study is, for the first time, to construct a new near infrared (NIR) fluorophore, spectrophotometric, colorimetric, ratiometric, and turn-on probe (CSME) based on chromenylium cyanine platform decorated with methionine biomolecule to provide an efficient solution for critical shortcoming to be encountered for analysis of hazardous Hg²⁺ in environment and living cell. The CSME structure and its interaction with Hg²⁺ ion were evaluated by NMR, FTIR, MS, UV-Vis and fluorescence methods as well as Density Functional Theory (DFT) calculations. The none fluorescence CSME having spirolactam ring only interacted with Hg²⁺ in aqueous solution including competing ions. This interaction caused the fluorescence CSME with opened spirolactam form which exhibited spectral and colorimetric changes in the NIR region. The probe based on UV-Vis and fluorescence techniques respond in 90 s, has wide linear ranges (for UV-Vis: 6.29 × 10^-8 - 1.86 × 10^-4 M; for fluorescence: 9.49 × 10^-9 - 1.13 × 10^-5 M), and has a lower Limit of Detection (LOD) value (for fluorescence: 4.93 × 10^-9 M, 0.99 ng/mL) than the value predicted by the US Environmental Protection Agency (EPA) organization. Hg²⁺ analysis was performed in drinking and tap water with low Relative Standard Deviation (RSD) values and high recovery. Smartphone and living cell applications were successfully performed for colorimetric sensing Hg²⁺ in real samples and 3T3 cells, respectively.

Gestational cadmium exposure disrupts fetal liver development via repressing estrogen biosynthesis in placental trophoblasts

Cadmium (Cd), commonly found in diet and drinking water, is known to be harmful to the human liver. Nevertheless, the effects and mechanisms of gestational Cd exposure on fetal liver development remain unclear. Here, we reported that gestational Cd (150 mg/L) exposure obviously downregulated the expression of critical proteins including PCNA, Ki67 and VEGF-A in proliferation and angiogenesis in fetal livers, and lowered the estradiol concentration in fetal livers and placentae. Maternal estradiol supplement alleviated aforesaid impairments in fetal livers. Our data showed that the levels of pivotal estrogen synthases, such as CYP17A1 and 17β-HSD, was markedly decreased in Cd-stimulated placentae but not fetal livers. Ground on ovariectomy (OVX), we found that maternal ovarian-derived estradiol had no major effects on Cd-impaired development in fetal liver. In addition, Cd exposure activated placental PERK signaling, and inhibited PERK activity could up-regulated the expressions of CYP17A1 and 17β-HSD in placental trophoblasts. Collectively, gestational Cd exposure inhibited placenta-derived estrogen synthesis via activating PERK signaling, and therefore impaired fetal liver development. This study suggests a protective role for placenta-derived estradiol in fetal liver dysplasia shaped by toxicants, and provides a theoretical basis for toxicants to impede fetal liver development by disrupting the placenta-fetal-liver axis.

Selenium Status: Its Interactions with Dietary Mercury Exposure and Implications in Human Health

Selenium is an essential trace element in humans and animals and its role in selenoprotein and enzyme antioxidant activity is well documented. Food is the principal source of selenium, and it is important that selenium status in the body is adequately maintained for physiological functions. There has been increasing attention on the role of selenium in mitigating the toxic effects of mercury exposure from dietary intake in humans. In contrast, mercury is a neurotoxin, and its continuous exposure can cause adverse health effects in humans. The interactions of selenium and mercury are multi-factorial and involve complex binding mechanisms between these elements at a molecular level. Further insights and understanding in this area may help to evaluate the health implications of dietary mercury exposure and selenium status. This review aims to summarise current information on the interplay of the interactions between selenium and mercury in the body and the protective effect of selenium on at-risk groups in a population who may experience long-term mercury exposure.

Biochemical Parameters of Female Wistar Rats and Their Offspring Exposed to Inorganic Mercury in Drinking Water during the Gestational and Lactational Periods

The aim of this study was to investigate the effects of inorganic mercury (Hg²⁺) exposure on biochemical parameters of dams and their offspring exposed to metal in drinking water. Female Wistar rats were exposed to 0, 10, and 50 µg Hg²⁺/mL (as HgCl₂) for 42 days corresponding to gestational (21 days) and lactational (21 days) periods. The offspring were sacrificed on postnatal days 10, 20, 30, and 40. Dams exposed to Hg²⁺ presented a decrease in water intake in gestation [total: F(2,19) = 15.84; p ≤ 0.0001; daily: F(2,21) = 12.71; p = 0.0002] and lactation [total: F(2,19) = 4.619; p = 0.024; daily: F(2,21) = 5.309; p = 0.0136] without alteration in food intake. Dams exposed to 50 µg Hg²⁺/mL had an increase in kidney total [F(2,21) = 8.081; p = 0.0025] and relative [F(2,21) = 14.11; p = 0.0001] weight without changes in biochemical markers of nephrotoxicity. Moreover, dams had an increase in hepatic [F(2,10) = 3.847; p = 0.0577] and renal [F(2,11) = 6.267; p = 0.0152] metallothionein content concomitantly with an increase in renal Hg levels after Hg²⁺ exposure. Regarding offspring, the exposure to Hg²⁺in utero and breast milk increased the relative liver [F(2,18) = 5.33; p = 0.0152] and kidney [F(2,18) = 3.819; p = 0.0415] weight only on the postnatal day 40. In conclusion, dams were able to handle the Hg²⁺ avoiding the classic Hg²⁺ toxic effects as well as protecting the offspring. We suggest that this protection is related to the hepatic and renal metallothionein content increase.

Leaf ethanolic extract of Etlingera hemesphaerica Blume mitigates defects in fetal anatomy and endochondral ossification due to mercuric chloride during the post-implantation period in Mus musculus

This study aimed to investigate the effectiveness of leaf ethanolic extract of Etlingera hemisphaerica (LE3H) in reducing defects in fetal anatomy and endochondral ossification in mice induced by HgCl₂ during the post-implantation period. Pregnant mice were divided into four groups, each consisting of 10 dams, and received drink and food ad libitum. The first group was administered LE3H (E1), the second one HgCl₂ (E2), the third one HgCl₂+LE3H (E3), and the fourth was control (E0), administered double-distilled water only. HgCl₂ (5 mg/kg bw) was administrated by injection intraperitoneally on gestation day (GD)9 and LE3H (0.39 mg/g bw) was administered by gavage on GD10. The treated and control animals were killed by cervical dislocation on GD18, dissected, and the morphologically normal living fetuses (MNLF) were collected. The MNLF of E0, E1, E2, and E3 from 5 dams were fixed with Bouin solution, and observed using the free hand razor blade technique for soft tissue examination. The remaining MNLF were fixed with 96% ethanol, and then stained with Alizarin Red S and Alcian Blue for ossification examination. Index of length of ossified part (ILOP) of humerus, index of width of ossified part (IWOP) of humerus, ILOP of femur, and IWOP of femur were calculated. E2 had higher cases of anatomical defects (74,6%) than E3 (48.9%), E1 (15.0%), and E0 (0%). E2 had humerus IWOP of 0.82±0.03, which was significantly lower than that of E0 (0.89±0.04) and E1 (0.89±0.03), while that of E1 and E0 was not significantly different from each other. Meanwhile, IWOP in E3 (0.88±0.03) was significantly higher than that in E2, but not different from that in E1 and E0. Thus, LE3H mitigated defects in fetal anatomy and endochondral ossification induced by HgCl₂ in mice.

Interactions between Environmental Exposures and the Microbiome: Implications for Fetal Programming

Decades of population-based health outcomes data highlight the importance of understanding how environmental exposures in pregnancy affect maternal and neonatal outcomes. Animal model research and epidemiological studies have revealed that such exposures are able to alter fetal programming through stable changes in the epigenome, including altered DNA methylation patterns and histone modifications in the developing fetus and infant. It is similarly known that while microbes can biotransform environmental chemicals via conjugation and de-conjugation, specific exposures can also alter the community profile and function of the human microbiome. In this review, we consider how alterations to the maternal and or fetal/infant microbiome through environmental exposures could directly and indirectly alter fetal programming. We highlight two specific environmental exposures, cadmium (Cd) and polycyclic aromatic hydrocarbons (PAHs), and outline their effects on the developing fetus and the perinatal (maternal and fetal/infant) microbiome. We further consider how chemical exposures in the setting of natural disasters may be of particular importance to environmental health.

Sex differences in renal handling of inorganic mercury in aged rats

The sex of an individual/animal has been shown to play an important role in many biological processes. Furthermore, sex may also be a factor in the way environmental toxicants, such as heavy metals, are handled by organisms. However, the effect of sex on the handling and disposition of heavy metals, such as mercury (Hg), has not been shown. Aging has also been shown to be a factor in the accumulation of heavy metals in that older individuals tend to have higher burdens of these metals. Therefore, the purpose of the current study was to evaluate the effect of sex on the accumulation of mercury in aged animals. Aged male and female rats were injected intravenously with 0.5 μmol or 2.0 μmol·kg⁻¹ HgCl₂ (containing radioactive Hg) and organs were harvested after 24 h. In general, the renal accumulation of Hg was significantly greater in males than in females. Similarly, urinary excretion of Hg was greater in males than in females. There were no significant differences between males and females in the burden of Hg in other organs. Sex differences in the renal accumulation of Hg may be related to differences in the expression of membrane transporters involved in the uptake of mercuric species into tubular epithelial cells. The results of the current study illustrate the need to evaluate both sexes when assessing the renal effects of environmental toxicants.

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Renal accumulation of mercury is greater in aged male rats than aged female rats.

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Mercury accumulation differed among zones of the kidney.

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Sex did not appear to alter accumulation of mercury in other organs studied.

Chronic kidney disease in pregnant mothers affects maternal and fetal disposition of mercury

Chronic kidney disease (CKD) affects over 15 % of the adults in the United States. Pregnant women with CKD present an additional challenge in that they are at increased risk for adverse events such as preterm birth. Exposure to environmental toxicants, such as methylmercury, may exacerbate maternal disease and increase the risk of adverse fetal outcomes. We hypothesized that fetuses of mothers with CKD are more susceptible to accumulation of methylmercury than fetuses of healthy mothers. The current data show that when mothers are in a state of renal insufficiency, uptake of mercury in fetal kidneys is enhanced significantly. Accumulation of Hg in fetal kidneys may be related to the flow of amniotic fluid, maternal handling of Hg, and/or underdeveloped mechanisms for cellular export and urinary excretion. The results of this study indicate that renal insufficiency in mothers leads to significant alterations in the way toxicants such as mercury are handled by maternal and fetal organs.

Mercury speciation in meconium and associated factors

Meconium is formed early in gestation and it is normally not excreted until after birth. Thus it may provide a longer and cumulative record of exposure to mercury (Hg). The present study aims to speciate Hg in meconium samples (N = 488) from Slovenian and Croatian new-borns prenatally exposed to low levels of methyl-Hg (MeHg) from maternal seafood intake and to Hg⁰ from maternal dental amalgam fillings. We had complete data of total Hg (THg) and MeHg in meconium and THg in maternal hair (MH), while THg and MeHg in maternal blood (MB) were available only for Croatian mothers. Personal data namely maternal seafood intake, age, pre-pregnancy BMI, parity, smoking, estimated gestational age at birth, sex, and birth weight were available for the majority of participants, except the number of dental amalgams which was in most cases missing for Croatian mothers. The median THg concentration in meconium was 11.1 (range: 0.41-375.2) ng/g and inorganic Hg (Hg(II)) presented 98.8% (range: 82%-100%, CV: 2%) of THg. We observed significant correlation between meconium and MH Hg levels, with the highest correlation between hair THg and meconium MeHg. Correlation analysis including MB (available only for Croatian population) showed a significant positive correlation between THg in meconium and THg in MB (R_s = 0.642). Additionally, MeHg from MB was correlated with MeHg in meconium (R_s = 0.898), while the correlation between Hg(II) in MB and meconium was positive, but not significant. Maternal seafood intake was significantly correlated with meconium MeHg (R_s = 0.498) and Hg(II) (R_s = 0.201). Multiple linear regression (performed on the Slovenian population, N = 143) confirmed a positive association between meconium MeHg and seafood intake. Furthermore, meconium Hg(II) was positively associated with the number of maternal dental amalgam fillings, but linear regression models did not confirm correlation between seafood intake and meconium Hg(II) levels. We assume that Hg⁰ released from maternal dental amalgam fillings and MeHg from seafood intake were both transported through the placental barrier and portioned between different foetal compartments including meconium. Weak correlation between maternal seafood intake and Hg(II) levels in meconium suggests that there is certain evidence of MeHg demethylation. However, because this correlation was not confirmed by the multiple regression, MeHg demethylation during prenatal life cannot be neither confirmed nor excluded. Further investigations at higher level of exposure are needed to confirm this observations. We can conclude that meconium is a suitable biomarker for MeHg and Hg⁰ exposure during pregnancy. However, comparability of the results reported in meconium in different studies is hindered by a lack of standardized sampling protocols, storage, and analysis.

Leaf ethanolic extract of Etlingera hemesphaerica Blume alters mercuric chloride teratogenicity during the post-implantation period in Mus musculus

This study aimed to investigate the effectiveness of leaf ethanolic extract of Etlingera hemisphaerica (LE3H) against the teratogenic effects of mercuric chloride (HgCl₂) in mice (Mus musculus). Pregnant M. musculus were divided into four groups, each consisting of 10 dams, and received drink and food ad libitum. The first, second, and third, and fourth (control) groups were administered with LE3H, HgCl₂, HgCl₂ + LE3H, and double-distilled water alone, respectively. HgCl₂ (5 mg/kg bw) was administered by injection on gestation day (GD) 9, and LE3H (0.39 mg/g bw) was administered by gavage on GD 10. Treated and control animals were killed by cervical dislocation on GD 18, dissected, and the fetuses were collected for evaluation of maternal, embryonic, and fetal toxicity. Eight parameters were measured: (a) embryo resorption or resorbed embryo, (b) dead fetus, (c) living fetus, (d) morphologically normal living fetus, (e) malformed living fetus, (f) number of MLF, (g) length of MNLF, and (h) weight of MNLF. LE3H caused 4 (50.00%), whereas HgCl₂ resulted in 7 (87.50%) parameters that were significantly different from those of the control, indicating that the teratogenicity of HgCl₂ was significantly higher than that of LE3H. HgCl₂ + LE3H showed two effects of LE3H on the teratogenicity of HgCl₂: increased 2 (25.00%), and decreased 6 (75.00%). Thus, LE3H decreased the teratogenic effects of HgCl₂ in M. musculus.

Elevated blood mercury level has a non-linear association with infertility in U.S. women: Data from the NHANES 2013-2016

Mercury is a ubiquitous toxic heavy metal associated with an increased risk of female infertility; however, the evidence supporting this is limited and controversial. We aimed to explore the relationship between the total blood mercury and infertility in 1796 selected participants from the National Health and Nutrition Examination Survey (NHANES) (2013-2016). We found no significant association between mercury and infertility based on a fully-adjusted model (OR 1.04; 95 % CI 0.91, 1.19), and the results remained robust in a series of sensitive analysis. However, a non-linear relationship was detected. By a two-piecewise linear regression model and recursive algorithm, we identified an inflection point of 5.278 μg/L, when blood mercury was >5.278 μg/L, a 1-unit increase in mercury (log2) was associated with 157 % greater adjusted odds of infertility (OR 2.57; 95 % CI 1.12, 5.87). Our findings provide new insights to advance the research of the link between mercury and infertility.

Copper attenuates early and late biochemical alterations induced by inorganic mercury in young rats

Mercury (Hg), a divalent metal, produces adverse effects predominantly in the renal and central nervous systems. The aim of this study was to determine the effectiveness of copper (Cu) in prevention of mercuric mercury (Hg²⁺)-mediated toxic effects as well as the role metallothioneins (MT) play in this protective mechanism in young rats. Wistar rats were treated subcutaneously with saline (Sal) or CuCl₂.2H₂O (Cu 2.6 mg/kg/day) from 3 to 7 days old and with saline or HgCl₂ (Hg 3.7 mg/kg/day) from 8 to 12 days old. The experimental groups were (1) Sal-Sal, (2) Cu-Sal, (3) Sal-Hg, and (4) Cu-Hg. MTs and metal contents were determined at 13 and 33 days of age. Porphobilinogen synthase (PBG-synthase) activity as well as renal and hepatic parameters were measured at 33 days. At 13 day, Hg²⁺ exposure increased hepatic MT, Hg, zinc (Zn) and iron (Fe) levels, in kidney elevated Cu and Hg and decreased renal Fe concentrations, accompanied by elevated blood Hg levels. At 33 days, Hg²⁺ exposure inhibited renal PBG-synthase activity, increased serum urea levels and lowered Fe and Mg levels. Copper partially prevented the rise in blood Hg and liver Fe noted at 13 days; and completely blocked urea rise and diminished renal PBG-synthase activity inhibition at 33 days. In 13-day-old rats, Cu exposure redistributed the Hg in the body, decreasing hepatic and blood levels while increasing renal levels, accompanied by elevated renal and hepatic MT levels in Hg²⁺-exposed animals. These results suggest that hepatic MT might bind to hepatic and blood Hg for transport to the kidney in order to be excreted.

ABBREVIATIONS

MT: metallothioneins; PBG-synthase: porphobilinogen synthase.

Neurodevelopmental Effects of Mercury

The toxicology of mercury (Hg) is of concern since this metal is ubiquitously distributed in the environment, and living organisms are routinely exposed to Hg at low to high levels. The toxic effects of Hg are well studied and it is known that they may differ depending on the Hg chemical species. In this chapter, we emphasize the neurotoxic effects of Hg during brain development. The immature brain is more susceptible to Hg exposure, since all the Hg chemical forms, not only the organic ones, can harm it. The possible consequences of Hg exposure during the early stages of development, the additive effects with other co-occurring neurotoxicants, and the known mechanisms of action and targets will be addressed in this chapter.

Zuotai and HgS differ from HgCl2 and methyl mercury in Hg accumulation and toxicity in weanling and aged rats

Mercury sulfides are used in Ayurvedic medicines, Tibetan medicines, and Chinese medicines for thousands of years and are still used today. Cinnabar (α-HgS) and metacinnabar (β-HgS) are different from mercury chloride (HgCl₂) and methylmercury (MeHg) in their disposition and toxicity. Whether such scenario applies to weanling and aged animals is not known. To address this question, weanling (21d) and aged (450d) rats were orally given Zuotai (54% β-HgS, 30mg/kg), HgS (α-HgS, 30mg/kg), HgCl₂ (34.6mg/kg), or MeHg (MeHgCl, 3.2mg/kg) for 7days. Accumulation of Hg in kidney and liver, and the toxicity-sensitive gene expressions were examined. Animal body weight gain was decreased by HgCl₂ and to a lesser extent by MeHg, but unaltered after Zuotai and HgS. HgCl₂ and MeHg produced dramatic tissue Hg accumulation, increased kidney (kim-1 and Ngal) and liver (Ho-1) injury-sensitive gene expressions, but such changes are absent or mild after Zuotai and HgS. Aged rats were more susceptible than weanling rats to Hg toxicity. To examine roles of transporters in Hg accumulation, transporter gene expressions were examined. The expression of renal uptake transporters Oat1, Oct2, and Oatp4c1 and hepatic Oatp2 was decreased, while the expression of renal efflux transporter Mrp2, Mrp4 and Mdr1b was increased following HgCl₂ and MeHg, but unaffected by Zuotai and HgS. Thus, Zuotai and HgS differ from HgCl₂ and MeHg in producing tissue Hg accumulation and toxicity, and aged rats are more susceptible than weanling rats. Transporter expression could be adaptive means to reduce tissue Hg burden.

Acute mercury exposition of virgin, pregnant, and lactating rats: Histopathological kidney and liver evaluations

This work investigated the effects of mercury chloride (HgCl₂ ) acute exposure on virgin, pregnant and lactating rats by determination of renal and hepatic morphological and ultrastructural parameters and the expression of oxidative stress and stress tolerance markers, due to kidney and liver are the organs that more accumulate inorganic mercury. Adult Wistar rats virgin (90 days old), pregnant (18^th gestation day) and lactating (7^th lactation day) were injected once with HgCl₂ (5 mg/kg) or saline (controls). We observed that HgCl₂ exposure of virgin rats caused significant inflammatory infiltration and severe morphological variations, like glomeruli atrophy, dilatation of Bowman's capsule, tubular degeneration and hepatocytes alteration. Moreover, virgin rats presented mitochondrial modification, important oxidative stress and increase in stress tolerance proteins at both kidney and liver level, compared with virgin controls. In detail, virgin rats exposed to HgCl₂ presented significantly elevated level of inducible nitric oxide synthase, heat shock protein 27 and glucose regulated proteins 75 expressions at both renal tubular and hepatocytes level, respect untreated virgin rats. Interestingly, pregnant and lactating rats exposed to HgCl₂ presented weak renal and liver morphological alterations, showing weak inflammatory infiltration and no significant difference in structural mitochondrial transmembrane protein, oxidative stress markers and stress tolerance proteins expressions respect controls (virgin, pregnant and lactating rats). Although, both control and HgCl₂ -exposed pregnant and lactating rats showed renal glomeruli greater in diameter respect virgin rats. In conclusion, we believe that virgin rats are more sensitive to HgCl₂ toxicity respect pregnant and lactating rats. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1500-1512, 2017.

Chemical Speciation of Selenium and Mercury as Determinant of Their Neurotoxicity

The antagonism of mercury toxicity by selenium has been well documented. Mercury is a toxic metal, widespread in the environment. The main target organs (kidneys, lungs, or brain) of mercury vary depending on its chemical forms (inorganic or organic). Selenium is a semimetal essential to mammalian life as part of the amino acid selenocysteine, which is required to the synthesis of the selenoproteins. This chapter has the aim of disclosing the role of selenide or hydrogen selenide (Se^-2 or HSe^-) as central metabolite of selenium and as an important antidote of the electrophilic mercury forms (particularly, Hg²⁺ and MeHg). Emphasis will be centered on the neurotoxicity of electrophile forms of mercury and selenium. The controversial participation of electrophile mercury and selenium forms in the development of some neurodegenerative disease will be briefly presented. The potential pharmacological use of organoseleno compounds (Ebselen and diphenyl diselenide) in the treatment of mercury poisoning will be considered. The central role of thiol (-SH) and selenol (-SeH) groups as the generic targets of electrophile mercury forms and the need of new in silico tools to guide the future biological researches will be commented.

Zinc protection in fetal rats for maternal mercury exposure-induced growth retardation is probably associated with S100B expression

AIM

The study was conducted to investigate the effects of maternal mercury exposure on fetal rat development and zinc protection in mercury-exposed rats.

METHODS

Pregnant rats were subjected to zinc sulfate pre-feeding, mercury exposure and zinc sulfate co-feeding. The control rats were administered distilled water. On day 19, the placental weight, overall weight, size and tail length of fetal rats, mercury content and S100B level in the placenta were determined using Western blot analysis.

RESULTS

Compared with the control, mercury exposure at 2.0 mg/kg.d significantly reduced placental weight and fetal development, resulting in reduced fetal weight, size and tail length, while zinc pre-feeding increased placental weight and other fetal developmental parameters. Compared with mercury exposure, co-feeding with zinc significantly reduced mercury-induced injury in the fetal rats. S100B and mercury content levels were significantly elevated in rats maternally exposed to methylmercury chloride, compared with the unexposed control, while co-feeding with methylmercury chloride and zinc sulfate significantly reduced S100B and mercury levels in the placenta.

CONCLUSION

Maternal exposure to mercury results in increased S100B in the placenta. Zinc sulfate feeding could reduce S100B and mercury levels, thereby protecting the rats from mercury damage. S100B level may be used to measure the antagonism between zinc and mercury during pregnancy.

Protective effects of curcumin against mercury-induced hepatic injuries in rats, involvement of oxidative stress antagonism, and Nrf2-ARE pathway activation

Mercury (Hg) represents a ubiquitous environmental heavy metal that could lead to severe toxic effects in a variety of organs usually at a low level. The present study focused on the liver oxidative stress, one of the most important roles playing in Hg hepatotoxicity, by evaluation of different concentrations of mercuric chloride (HgCl₂) administration. Moreover, the protective potential of curcumin against Hg hepatotoxic effects was also investigated. Eighty-four rats were randomly divided into six groups for a three-days experiment: control, dimethyl sulfoxide control, HgCl₂ treatment (0.6, 1.2, and 2.4 mg kg^-1 day^-1), and curcumin pretreatment (100 mg kg^-1 day^-1) groups. Exposure of HgCl₂ resulted in acute dose-dependent hepatotoxic effects. Administration of 2.4 mg kg^-1 HgCl₂ significantly elevated total Hg, nonprotein sulfhydryl, reactive oxygen species formation, malondialdehyde, apoptosis levels, serum lactate dehydrogenase, and alanine transaminase activities, with an impairment of superoxide dismutase and glutathione peroxidase in the liver. Moreover, HgCl₂ treatment activated nuclear factor-E2-related factor 2-antioxidant response element (Nrf2-ARE) signaling pathway in further investigation, with a significant upregulation of Nrf2, heme oxygenase-1, and γ-glutamylcysteine synthetase heavy subunit expression, relative to control. Pretreatment with curcumin obviously prevented HgCl₂-induced liver oxidative stress, which may be due to its free radical scavenging or Nrf2-ARE pathway-inducing properties. Taking together these data suggest that curcumin counteracts HgCl₂ hepatotoxicity through antagonizing liver oxidative stress.

Mechanisms involved in the transport of mercuric ions in target tissues

Mercury exists in the environment in various forms, all of which pose a risk to human health. Despite guidelines regulating the industrial release of mercury into the environment, humans continue to be exposed regularly to various forms of this metal via inhalation or ingestion. Following exposure, mercuric ions are taken up by and accumulate in numerous organs, including brain, intestine, kidney, liver, and placenta. In order to understand the toxicological effects of exposure to mercury, a thorough understanding of the mechanisms that facilitate entry of mercuric ions into target cells must first be obtained. A number of mechanisms for the transport of mercuric ions into target cells and organs have been proposed in recent years. However, the ability of these mechanisms to transport mercuric ions and the regulatory features of these carriers have not been characterized completely. The purpose of this review is to summarize the current findings related to the mechanisms that may be involved in the transport of inorganic and organic forms of mercury in target tissues and organs. This review will describe mechanisms known to be involved in the transport of mercury and will also propose additional mechanisms that may potentially be involved in the transport of mercuric ions into target cells.