Distinct response of lactating and nonlactating rats exposed to inorganic mercury on hepatic δ-aminolevulinic acid dehydratase activity

Mercury toxicity in pregnant and lactating rats: zinc and N-acetylcysteine as alternative of prevention

This study evaluated the toxic effects of inorganic mercury (Hg) in pregnant and lactating rats, as well as the possible protective effect of zinc (Zn) and N-acetylcysteine (NAC). Pregnant and lactating rats were pre-treated with ZnCl₂ (27 mg/kg) and/or NAC (5 mg/kg) and after 24 h, they were exposed to HgCl₂ (10 mg/kg). Animals were sacrificed 24 h after Hg exposure, and biochemical tests and metal determination were performed. Regarding pregnant rats, Hg exposure caused kidney, blood, and placenta δ-aminolevulinic acid dehydratase (δ-ALA-D) activity inhibition, and the pre-treatments showed a tendency of protection. Moreover, all the animals exposed to Hg presented high Hg levels in the kidney, liver, and placenta when compared with control group. Pregnant rats pre-exposed to Zn (Zn-Hg and Zn/NAC-Hg groups) presented an increase in hepatic metallothionein levels. Therefore, lactating rats exposed to Hg presented renal and blood δ-ALA-D inhibition; the pre-treatments showed a tendency to prevent the renal δ-ALA-D inhibition and prevented the blood δ-ALA-D inhibition caused by Hg. Lactating rats exposed to Hg presented high Hg levels in the kidney and liver. These results showed that 10 mg/kg of HgCl₂ causes biochemistry alterations in pregnant and lactating rats, and Zn and NAC present promising results against these damages.

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.

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.

Effects of zinc against mercury toxicity in female rats 12 and 48 hours after HgCl2 exposure

This work investigated the toxicity of inorganic mercury and zinc preventive effects in female rats sacrificed 12 or 48 h after HgCl₂ exposure. Female Wistar rats were subcutaneously injected with ZnCl₂ (27 mg/kg) or saline (0.9 %), and 24 h later they were exposed to HgCl₂ (5 mg/kg) or saline (0.9 %). Rats sacrificed 12 hours after Hg administration presented an increase in kidney weight and a decrease in renal ascorbic acid levels. Zinc pretreatment prevented the renal weight increase. Rats sacrificed 48 h after Hg exposure presented a decrease in body weight gain, an increase in renal weight, a decrease in renal δ-aminolevulinic acid dehydratase activity, an increase in serum creatinine and urea levels, and a decrease in kidney total thiol levels. Zinc pretreatment partly prevented the decrease in body weight gain and increase in creatinine levels, in addition to totally preventing renal δ-aminolevulinic acid dehydratase inhibition. Mercury accumulation in the kidney and liver in both periods was observed after Hg administration. These results show the different Hg effects along the time of intoxication, and a considerably preventive effect of zinc against Hg toxicity.

Zinc and N-acetylcysteine modify mercury distribution and promote increase in hepatic metallothionein levels

This study investigated the ability of zinc (Zn) and N-acetylcysteine (NAC) in preventing the biochemical alterations caused by mercury (Hg) and the retention of this metal in different organs. Adult female rats received ZnCl2 (27mg/kg) and/or NAC (5mg/kg) or saline (0.9%) subcutaneously and after 24h they received HgCl2 (5mg/kg) or saline (0.9%). Twenty-four hours after, they were sacrificed and analyses were performed. Hg inhibited hepatic, renal, and blood δ-aminolevulinic acid dehydratase (δ-ALA-D) activity, decreased renal total thiol levels, as well as increased serum creatinine and urea levels and aspartate aminotransferase activity. HgCl2-exposed groups presented an important retention of Hg in all the tissues analyzed. All pre-treatments demonstrated tendency in preventing hepatic δ-ALA-D inhibition, whereas only ZnCl2 showed this effect on blood enzyme. Moreover, the combination of these compounds completely prevented liver and blood Hg retention. The exposure to Zn and Hg increased hepatic metallothionein levels. These results show that Zn and NAC presented promising effects against the toxicity caused by HgCl2.