Lipid peroxidation in liver of rats administrated with methyl mercuric chloride

Parenteral administration of methyl mercuric chloride (MMC, CH₃HgCl) to rats enhanced lipid peroxidation in liver of rats, as measured by the thiobarbituric acid reaction for malondialdehyde (MDA) in fresh tissue homogenates. After sc injection of CH₃HgCl (5 mg/kg body wt), MDA concentration in liver became significantly increased at 24 h and further increased at 48 h. Dose-response studies were carried out with male albino rats of the Fisher-344 strain (body wt 170–280 g) injected with 3 or 5 mg Hg/kg as CH₃HgCl and sacrificed after 24 h. In time-response studies, animals were administered 5 mg Hg/kg as CH₃HgCl and sacrificed after 24 and 48 h. Studies in the authors’ laboratory have shown that (1) mercury is accumulated in liver; (2) concentration of MDA is increased in liver of CH₃HgCl-treated rats; (3) severity of hepatotoxicity is generally proportional to the elevation of MDA concentration, based upon the dose-effect relationships observed after administration of CH₃HgCl to rats. The results of this study implicate that the lipid peroxidation is one of the molecular mechanisms for cell injury in acute CH₃HgCl poisoning.     

Lipid peroxidation in rats administrated with mercuric chloride

Parenteral administration of mercuric chloride (HgCl₂) to rats enhanced lipid peroxidation in liver, kidney, lung, testis, and serum (but not in heart, spleen, or muscle), as measured by the thiobarbituric acid reaction for malondialdehyde (MDA) in fresh tissue homogenates and body fluids. After sc injection of HgCl₂ (5 mg/kg body wt), MDA concentrations in liver and kidney became significantly increased by 9 h and reached peak values at 24 h. Dose-response studies were carried out with male albino rats of the Fisher-344 strain (body wt 170–280 g) injected with 1, 3, 5 mg Hg/kg as HgCl₂ and sacrificed after 24 h. In time-response studies, animals were administered 5 mg Hg/kg as HgCl₂ and sacrificed after 3, 9, 18, 24, and 48 h. Studies in the authors' laboratory have shown that (1) concentrations of MDA are increased in targets (liver, kidney, lung, and testis) of HgCl₂-treated rats; (2) severity of hepatotoxicity and nephrotoxicity is generally consistent with the elevation of Hg and MDA concentrations, based upon the time-course and dose-effect relationships observed after administration of HgCl₂ to rats; and (3) concentrations of MDA are reduced in target tissues after pretreatment with antioxidants and chelators to HgCl₂-treated rats. The results of this study implicate that the lipid peroxidation is one of the molecular mechanisms for cell injury in acute HgCl₂ poisoning.     

Inhibition by methyl mercury chloride and mercuric chloride of the in vitro polymerization of microtubules

Mercury was tested at the same concentration but under two different forms, organic CH3HgCl and inorganic HgCl2, in order to compare its relative inhibitory effect on in vitro microtubules polymerization. Induced by GTP and glycerol 8 M, tubulin polymerization was completely inhibited by HgCl2 10(-3) M while a 75.8% inhibition was measured for CH3HgCl2 10(-3) M.     

Suppression of experimental allergic encephalomyelitis in rats by mercuric chloride

Brown-Norway (BN) rats are uniquely susceptible to development of autoimmune phenomena and enlargement of lymph nodes and spleen after repeated injections of mercuric chloride. Despite its ability to produce autoimmunity, HgCl2 inhibited the development in BN rats of experimental allergic encephalomyelitis (EAE), another autoimmune process. The inhibition by mercury was probably due to lack of the normal absorption and granulomatous reaction to the EAE inoculum in the enlarged lymph nodes draining the inoculation site. Lewis rats did not develop enlarged nodes from HgCl2 treatment. Lewis lymph nodes absorbed the EAE inoculum abundantly and developed an extensive granulomatous reaction despite the mercury treatment, and there was only a slight inhibition of EAE. Therefore, the ability of HgCl2 to produce lymphadenopathy in BN rats may be responsible for the inability of these rats to absorb the inoculated antigen. The mercury-induced failure of absorption was manifested as an inhibition of EAE in BN rats.     

Toxicity to alveolar macrophages in rats following parenteral injection of mercuric chloride

Alveolar macrophages collected by pulmonary lavage from male Fisher-344 rats at intervals (24–72 h) after HgCl₂ injection (1–5 mg/kg, sc) were analyzed by several techniques. Within 24–72 h, the macrophages showed morphological signs of activation (hypertrophy and ruffled plasma membrane). Lipid peroxidation (increased malondialdehyde concentration) was not detected until 48 h. Dose- and time-related effects of HgCl₂ on malondialdehyde concentration and time-related effects of HgCl₂ on malondialdehyde concentration and mercury content of alveolar macrophages were observed 24–72 h postinjection. Diminished cell viability occurred only at 72 h after the highest dosage of HgCl₂. This study demonstrates that the alveolar macrophage was a cellular target for mercury toxicity following parenteral exposure to HgCl₂.     

Increased urinary excretion of zinc and copper by mercuric chloride injection in rats

The effects of HgCl₂ on urinary excretion of Zn, Cu and metallothionein at different time intervals were observed in male Wistar rats. The rats were given a daily intraperitoneal injection of²⁰³HgCl₂ (0.5 or 1.0 mg Hg kg^–1) for 2 days.²⁰³Hg, Zn, Cu and metallothionein in urine, kidney and liver were analyzed. Significant increases in urinary Zn and Cu concentrations were found in HgCl₂-dosed groups. Elevated urinary Zn and Cu concentrations were accompanied by an increased metallothionein excretion in urine at different time periods. Zn concentration in urine remained elevated during the entire observation period of 7 days. There were also increased concentrations of Cu and Zn in the renal cortex in one of the two exposed groups. The results indicate that urinary Cu and Zn are related to the manifestation of renal toxicity and/or the synthesis of metallothionein in kidney induced by mercury.     

Persistence and prevention of aluminium- and paraquat-induced adaptive response to methyl mercuric chloride in plant cells in vivo

Induction and persistence of adaptive response by aluminium (Al), 1 or 10 microM, and paraquat (PQ), 5 or 10 microM, against genotoxicity of methyl mercuric chloride (MMCl), 1.26 microM, a standard environmental genotoxin, was investigated in root meristem cells of Allium cepa. Subsequently, three metabolic inhibitors, namely, 3-aminobezamide (3-AB, 10 or 100 microM), an inhibitor of poly(ADP-ribose) polymerase (PARP) implicated in DNA repair and/or apoptosis, cycloheximide (CH, 0.1 or 1 microM), an inhibitor of protein synthesis, and buthionine sulfoximine (BSO, 100 microM or 1mM), an inhibitor of glutathione synthesis were tested for their ability to prevent the adaptive response induced by conditioning doses of Al, 10 or 100 microM; and PQ, 5 or 100 microM, against MMCl-challenge, 1.26 or 100 microM, in root meristems of A. cepa or embryonic shoots of Hordeum vulgare, respectively. The findings demonstrated that once triggered, the Al- or PQ-adaptive response to MMCl could persist for at least 48h in root meristems of A. cepa. Furthermore, the adaptive response could effectively be prevented by 3-AB, to a lesser degree by CH, and the least by BSO, suggesting primarily the involvement of PARP and implicating DNA repair in the underlying mechanisms of adaptive response in plant cells in vivo.     

Distribution of mercury and evaluation of testicular steroidogenesis in mercuric chloride and methylmercury administered rats

Intraperitoneal administration of methylmercury chloride (MMC) and mercuric chloride (MC) to male rats in doses of 5, 10 micrograms MMC/kg or 50, 100 micrograms MC/kg for 90 days induced cellular disintegration of Leydig cells which was conspicuous on day 30 and onwards in the exposed groups. Progressive degeneration of Leydig cells and decrease in their nuclear diameter and population were associated with gradual increase in deposition of mercury. Gradual diminution of 3 beta-hydroxy-delta 5-steroid dehydrogenase activity in Leydig cells after MMC or MC treatment was correlated with different structural deformations of the cells over 90 days. Moreover, a significant decrease in serum testosterone levels by day 90 confirmed steroidogenic impairment after MMC or MC treatment.     

Toxic injury from mercuric chloride in rat hepatocytes

The relationship between cytosolic free Ca2+, mitochondrial membrane potential, ATP depletion, pyridine nucleotide fluorescence, cell surface blebbing, and cell death was evaluated in rat hepatocytes exposed to HgCl2. In cell suspensions, 50 microM HgCl2 oxidized pyridine nucleotides between 1/2 and 2 min, caused ATP depletion between 2 and 5 min, and produced an 89% loss of cell viability after 20 min. Rates of cell killing were identical in high (1.2 mM) and low (2.6 microM) Ca2+ buffers. Cytosolic free Ca2+ was determined in 1-day cultured hepatocytes by ratio imaging of Fura-2 employing multiparameter digitized video microscopy. In high Ca2+ medium, HgCl2 caused a 3-4-fold increase of free Ca2+ beginning after 6-7 min, but free Ca2+ did not change in low Ca2+ medium. Bleb formation occurred after about 4-5 min in both buffers prior to any increase of free Ca2+. Subsequently, in high Ca2+ medium, blebs became hot spots of free Ca2+ (greater than 600 nM). After about 2 min of exposure to HgCl2, rhodamine 123 fluorescence redistributed from mitochondrial to cytosolic compartments signifying collapse of the mitochondrial membrane potential. The results taken together demonstrate that bleb formation, ATP depletion, and the onset of cell death are not dependent on an increase of cytosolic free Ca2+. HgCl2 toxicity appears to be a consequence of inhibition of oxidative phosphorylation leading to ATP depletion and cell death.     

Lactating and nonlactating rats differ to renal toxicity induced by mercuric chloride: the preventive effect of zinc chloride

This study evaluated the effects of HgCl₂ on renal parameters in nonlactating and lactating rats and their pups, as well as the preventive role of ZnCl₂. Rats received 27 mg kg^?1 ZnCl₂ for five consecutive days and 5 mg kg^?1 HgCl₂ for five subsequent days (s.c.). A decrease in δ‐aminolevulinic acid dehydratase (δ‐ALA‐D) activity in the blood and an increase in urine protein content in renal weight as well as in blood and urine Hg levels were observed in lactating and nonlactating rats from Sal―Hg and Zn―Hg groups. ZnCl₂ prevented partially the δ‐ALA‐D inhibition and the proteinuria in nonlactating rats. Renal Hg levels were increased in all HgCl₂ groups, and the ZnCl₂ exposure potentiated this effect in lactating rats. Nonlactating rats exposed to HgCl₂ exhibited an increase in plasma urea and creatinine levels, δ‐ALA‐D activity inhibition and histopathological alterations (necrosis, atrophic tubules and collagen deposition) in the kidneys. ZnCl₂ exposure prevented the biochemical alterations. Hg‐exposed pups showed lower body and renal weight and an increase in the renal Hg levels. In conclusion, mercury‐induced nephrotoxicity differs considerably between lactating and nonlactating rats. Moreover, prior exposure with ZnCl₂ may provide protection to individuals who get exposed to mercury occupationally or accidentally. Copyright © 2014 John Wiley & Sons, Ltd.     

Hemoglobin-catalyzed lipid peroxidation in the presence of mercuric chloride

In order to elucidate the possible mechanism of initiation of peroxidative processes in Hg2+-treated erythrocytes, the effect of HgCl2 on hemoglobin-catalyzed peroxidation of phospholipid liposomes was studied. It was demonstrated that HgCl2 significantly increases the rate of hemoglobin-catalyzed peroxidation. The addition of superoxide dismutase and catalase partially inhibits this effect. Furthermore, it was found that HgCl2 potentiates the hemoglobin oxidation. A suggestion was made that the acceleration of hemoglobin-catalyzed peroxidation by HgCl2 is associated at least in part with the increased production of superoxide anion radicals from hemoglobin.