Multiple effects of mercuric chloride on hexose transport in Xenopus oocytes.

HgCl(2) had both stimulatory and inhibitory effects on [(3)H]2-deoxyglucose (DG) uptake in Xenopus laevis oocytes. The Hg dose response was complex, with 0.1-10 microM Hg increasing total DG uptake, 30-50 microM Hg inhibiting, and concentrations >100 microM increasing uptake. Analyses of the effects of Hg on DG transport kinetics and cell membrane permeability indicated that low concentrations of Hg stimulated mediated uptake, intermediate concentrations inhibited mediated uptake, but high Hg concentrations increased non-mediated uptake. 10 microM Hg increased the apparent V(max) for DG uptake, but caused little or no change in apparent K(m). Phenylarsine oxide prevented the increase in DG uptake by 10 microM Hg, suggesting that the increase was due to transporter recruitment. Microinjecting low doses of HgCl(2) into the cell increased mediated DG uptake. Higher intracellular doses of Hg increased both mediated and non-mediated DG uptake. Both insulin and Hg cause cell swelling in isotonic media and, for insulin, this swelling has been linked to the mechanism of hormone action. Osmotically swelling Xenopus oocytes stimulated DG transport 2-5-fold and this increase was due to an increased apparent V(max). Exposing cells to 10 microM Hg or 140 nM insulin both increased cellular water content by 18% and increased hexose transport 2-4-fold. These data indicate that low concentrations of Hg and insulin affect hexose transport in a similar manner and that for both an increase cellular water content could be an early event in signaling the increase in hexose transport.     

Inorganic mercury in mammary cells: viability,metal uptake but efflux?

The viability, cellular uptake and subcellular distribution of heavy metal Hg, were determined in human mammary cell lines (MCF-7, MDA-MB-231 and MCF-10A). It was observed that Hg had the capacity of being excluded from the cells with a different type of possible transporters. MCF-7 cells showed the lowest viability, while the other two cell lines were much more resistant to Hg treatments. The intracellular concentration of Hg was higher at lower exposure times in MCF-10A cells and MCF-7 cells; but as the time was increased only MDA-MB-231 showed the capacity to continue introducing the metal. In MCF-7 and MCF-10A cells the subcellular distribution of Hg was higher in cytosolic fraction than nucleus and membrane, but MDA-MB-231 showed membrane and nucleus fraction as the enriched one. The analysis of RNA-seq about the genes or family of genes that encode proteins which are related to cytotoxicity of Hg evidenced that MCF-10A cells and MCF-7 cells could have an active transport to efflux the metal. On the contrary, in MDA-MB-231 no genes that could encode active transporters have been found.     

Characterization of DNA lesions produced by HgCl2 in cell culture systems

HgCl2 is extremely cytotoxic to Chinese hamster ovary (CHO) cells in culture since a 1-h exposure to a 75- microM concentration of this compound reduced cell plating efficiency to 0 and cell growth was completely inhibited at 7.5 microM . The level of HgCl2 toxicity depended upon the culture incubation medium and has previously been shown to be inversely proportional to the extracellular concentration of metal chelating amino acids such as cysteine. Thus, HgCl2 toxicity in a minimal salts/glucose maintenance medium was about 10-fold greater than the toxicity in McCoy's culture medium. The HgCl2 toxicity in the latter medium was 3-fold greater than that in alpha-MEM which contains more of the metal chelating amino acids. When cells were exposed to HgCl2 there was a rapid and pronounced induction of single strand breaks in the DNA at time intervals and concentrations that paralleled the cellular toxicity. The DNA damage was shown to be true single strand breaks and not alkaline sensitive sites or double strand breaks by a variety of techniques. Consistent with the toxicity of HgCl2, the DNA damage under an equivalent exposure situation was more pronounced in the salts/glucose than in the McCoy's medium and more striking in the latter medium than in alpha-MEM. Most of the single strand breaks occurred within 1 h of exposure to the metal. We believe that the DNA damage caused by HgCl2 leads to cell death because the DNA single strand breaks are not readily repaired. DNA repair activity measured by CsCl density gradient techniques was elevated above the untreated levels at HgCl2 concentrations that produced little measurable binding of the metal to DNA or few single strand breaks assessed by the alkaline elution procedure. DNA repair activity decreased at HgCl2 concentrations that produced measurable DNA binding and single strand breaks. These irreversible interactions of HgCl2 with DNA may be responsible for its cytotoxic action in cells.     

A solution hybridization/RNase protection assay with riboprobes to determine absolute levels of apoB, A-I, and E mRNA in human hepatoma cell lines

A solution hybridization/RNase protection assay with riboprobes was developed to quantitate apolipoprotein mRNA concentrations. Previously, radiolabeled DNA probes have been used in solution hybridization/S1 nuclease protection assays for this purpose. The new assay requires less time for probe preparation and hybridization compared to previous assays. In addition, the vector used for riboprobe preparation can also be used to conveniently produce cRNA required to generate the standard curve to quantitate absolute apolipoprotein mRNA levels. The solution hybridization RNase protection assay was used to quantitate apoB, A-I, and E mRNA levels in four human hepatoma cell lines, HepG2, Hep3B, WRL-68, SK-Hep2. HepG2 and Hep3B, but not WRL-68 and SK-Hep2 cells had concentrations of all three apolipoprotein mRNAs comparable to liver in vivo. These data suggest that HepG2 and Hep3B are suitable models to study liver specific apolipoprotein gene expression.     

DNA damage produced by cadmium in a human fetal hepatic cell line

Cadmium (Cd) is one of the most important heavy metal environmental toxicants. It alters a wide variety of cellular and biochemical processes. The objective of this work was to study DNA damage and recovery after acute and chronic CdCl2 treatment in a human fetal hepatic cell line (WRL-68 cells). Using the alkaline microgel electrophoresis assay that detects DNA single-strand breaks and/or alkali-labile sites in individual cells, we evaluated for levels of DNA damage. The mean migration length in control cells was 35.37+/-1. 43 microm (8% damaged cells), whereas the mean migration in cells treated with 0.005 microM CdCl2 for 3 h (acute low dose) was 65. 87+/-2.07 microm (88% damaged cells). Treatment with 0.01 microM CdCl2 for the same time (acute high dose) increased the mean migration length to 125.79+/-2.91 microm (92% damaged cells). However, a 0.005 microM CdCl2 treatment for 7 days (chronic treatment) only increased 65% DNA migration to 58.38+/-2.59 microm (88% damaged nucleus). Lipoperoxidative damage expressed as malondialdehyde (MDA) production per milligram of protein was 15. 7+/-2.6 for control cells, whereas in Cd-treated cells the values were 20.2+/-2.4 (acute low dose), 22.9+/-2.2 (acute high dose), and 22.6+/-2.1 (chronic treatment). To study the repair of DNA damage, cells were washed with 0.01 microM meso-2,3-dimercaptosuccinic acid (DMSA), and fresh Dulbecco's modified essential medium (DMEM) added. The percentage of damaged cells diminished after 90 min, with DNA migration returning to control values by 120 min. Cd treatment produced DNA single-strand breaks and the damage was greater in acute high dose treated cells. Lipid peroxidation values did not correlate with DNA single-strand breaks.     

Analysis of metal-induced DNA lesions and DNA-repair replication in mammalian cells

The potency of several metal compounds in causing lesions in DNA either directly or by exposure of intact cultured cells has been examined using the neutral conditions of nucleoid gradient sedimentation. HgCl2 was clearly the most potent inducer of single-strand breakage when added to isolated nucleoids or when nucleoids were prepared from cells treated with this compound. CaCrO4 , however, caused DNA-strand breaks in nucleoids isolated from cells treated with this agent but did not induce DNA strand breaks when added directly to nucleoids. Although less potent than HgCl2, NiCl2 also caused significant single strand breakage in isolated nucleoids or in nucleoids prepared from cells treated with this metal. Since strand breakage of DNA in intact cells may occur secondary to activation of DNA-dependent nucleases during repair replication, CsCl gradient density sedimentation was utilized to examine whether repair processes were induced by exposure of cells to NiCl2, HgCl2 and CaCrO4 . CaCrO4 and NiCl2 induced substantial DNA-repair activity at concentrations and exposure times where DNA lesions could not be detected whereas HgCl2 induced a 10-fold lower level of DNA-repair activity compared to CaCrO4 at optimal concentrations which again were below the concentrations of this metal that produced measurable DNA lesions. Both the induction of DNA-repair activity and DNA-strand breakage by these metals was concentration- and time-dependent. These results demonstrate some unique aspects of the interaction of HgCl2, NiCl2 and CaCrO4 with the DNA of intact cells and point to the possible important correlation of induction of DNA repair to carcinogenesis since nickel and chromate have clearly been implicated as carcinogens and induce considerable repair whereas HgCl2 is not considered a carcinogen and induces the least DNA repair despite its potency in producing DNA lesions.     

Zinc transport by respiratory epithelial cells and interaction with iron homeostasis

Despite recurrent exposure to zinc through inhalation of ambient air pollution particles, relatively little information is known about the homeostasis of this metal in respiratory epithelial cells. We describe zinc uptake and release by respiratory epithelial cells and test the postulate that Zn²⁺ transport interacts with iron homeostasis in these same cells. Zn²⁺ uptake after 4 and 8 h of exposure to zinc sulfate was concentration- and time-dependent. A majority of Zn²⁺ release occurred in the 4 h immediately following cell exposure to ZnSO₄. Regarding metal importers, mRNA for Zip1 and Zip2 showed no change after respiratory epithelial cell exposure to zinc while mRNA for divalent metal transporter (DMT)1 increased. Western blot assay for DMT1 protein supported an elevated expression of this transport protein following zinc exposure. RT-PCR confirmed mRNA for the metal exporters ZnT1 and ZnT4 with the former increasing after ZnSO₄. Cell concentrations of ferritin increased with zinc exposure while oxidative stress, measured as lipid peroxides, was decreased supporting an anti-oxidant function for Zn²⁺. Increased DMT1 expression, following pre-incubations of respiratory epithelial cells with TNF-α, IFN-γ, and endotoxin, was associated with significantly decreased intracellular zinc transport. Finally, incubations of respiratory epithelial cells with both zinc sulfate and ferric ammonium citrate resulted in elevated intracellular concentrations of both metals. We conclude that exposure to zinc increases iron uptake by respiratory epithelial cells. Elevations in cell iron can possibly affect an increased expression of DMT1 and ferritin which function to diminish oxidative stress. Comparable to other metal exposures, changes in iron homeostasis may contribute to the biological effects of zinc in specific cells and tissues.     

Effect of mercury and organomercurials on cellular glucose utilization: a study using resting mercury-resistant yeast cells

AIMS: Mercury compounds are highly toxic to all types of living cells. Isolated yeast strains of Rhodotorula rubra showed high and low resistance pattern towards mercury and organomercurial compounds. To investigate the basis of differential sensitivity of these two types of strains, glucose utilization was measured in the presence of mercury compounds. METHODS AND RESULTS: Glucose utilization process remained unaffected in resting cells of highly Hg(2+)-resistant strain in the presence of HgCl(2) but not in the presence of phenylmercuric acetate and thimerosal. However, HgCl(2) significantly affected glucose utilization in the case of low-resistant cells. The Hg-retaining ability of the cell wall of highly Hg(2+)-resistant yeast strain was greater than that of the weakly Hg(2+)-resistant strain. The spheroplast-bound Hg(2+) was also significantly less in the highly Hg(2+)-resistant strain than in the weakly Hg(2+)-resistant strain. CONCLUSIONS: Glucose uptake machinery was not affected in the presence of toxic metal ions in the case of high-resistant strains. But in the case of low Hg(2+)-resistant strain, glucose transport system may be affected either by inactivation of sensor proteins containing -SH group associated with glucose uptake. SIGNIFICANCE AND IMPACT OF THE STUDY: Cell wall of mercury-resistant yeast cells may play an important role in heavy metal bioremediation process.     

Alterations in microRNA expression linked to microcystin-LR-induced tumorigenicity in human WRL-68 Cells

Microcystin-LR (MC-LR) is a cyclic heptapeptide that acts as a potent hepatotoxin and carcinogen. However, the mechanism of its carcinogenic action remains undetermined. In this study, MC-LR was used to induce the malignant transformation of the WRL-68 cell line. Alterations in microRNA (miRNA) expression in the transformed cell were analyzed to determine the role of miRNAs in MC-LR-induced carcinogenesis. Cultured WRL-68 cells (labeled 25MC10) were continuously exposed to a low concentration (10 μg/L) of MC-LR for 25 passages. Compared with the mock-treated parental cells, the induced 25MC10 cells exhibited a higher growth rate, resistance to serum-induced terminal differentiation, and tumorigenicity in a nude mouse xenograft test. A pilot miRNA expression array analysis was conducted on the 25MC10 cells, followed by validation of select miRNAs by RT-PCR. We found that the onco-miRNAs miR-21 and miR-221 displayed upregulated expression while the liver-specific miR-122 was downregulated. These results suggest that chronic MC-LR exposure alters the miRNA expression profile of WRL-68 cells and causes phenotypic transformation. We propose that characteristic miRNA alterations could be used as molecular targets for the development of environmental water monitoring methods.     

Specificity and Reversibility of the Inhibition by HgCl2 of Glutamate Transport in Astrocyte Cultures

Inhibition of glutamate transport is a potential indirect cause of excitotoxic damage by glutamate in the CNS. The mercuric ion, the form in which metallic mercury vapor is believed to exert its neurotoxic action, is a known inhibitor of amino acid transport. This study examines the specificity with which HgCl2 inhibits glutamate transport in mouse cerebral astrocytes by means of comparative measurements of 2-deoxyglucose uptake. Uptake of 2-deoxyglucose is an index of glucose utilization that reflects the function of Na+,K+-ATPase and hexokinase, and is sensitive to Na+ entry. The kinetic parameters, ionic dependence, and substrate specificity of glutamate transport in these astrocyte cultures were consistent with the commonly occurring system designated X-AG. Acute exposure to 0.5 microM HgCl2 inhibited by 50% the initial rate of glutamate transport but did not affect 2-deoxyglucose uptake. Glutamate transport was not detectably inhibited by Al2+, Pb2+, Co2+, Sr2+, Cd2+, or Zn2+ (10 microM as chlorides). The inhibitory action of 0.5 microM HgCl2 on glutamate transport was rapidly reversible. The action of 1-2 microM HgCl2 was progressive when exposures were extended to 1-3 h, and was more slowly reversible. These results suggest that Hg2+ can impair glial glutamate transport reversibly at exposure levels that do not compromise some other vital cell functions.     

Metal accumulation,filtration and O(2) uptake rates in the mussel Perna perna (Mollusca: Bivalvia) exposed to Hg(2+), Cu(2+) and Zn(2+)

Tissue metal concentrations, filtration and oxygen uptake rates were investigated for Perna perna (Bivalvia: Mollusca) during exposure to Hg(2+), Cu(2+) and Zn(2+) (50 microg/l for 24 days, and 24 days recovery with no metal). Hg and Cu tissue levels increased with exposure time, reaching maximum levels after 24 days (87.5 microg Hg/g dry mass and 45 microg Cu/g dry mass, respectively). Zn levels peaked after 4 days exposure (to 233 microg Zn/g dry mass) and stabilized thereafter. Accumulated metal was rapidly lost from tissues when mussels were returned to uncontaminated seawater, suggesting that tissue concentration data may be of limited use in biomonitoring situations where environmental metals fluctuate to low levels. Filtration rates fell below control rates during Hg(2+) exposure, and became elevated again during the recovery period. Cu(2+) and Zn(2+) exposure had little effect on filtration, but suppressed oxygen uptake. During recovery, oxygen uptake of Cu(2+) and Zn(2+) exposed mussels was elevated above the controls. Filtration and oxygen uptake rates were not correlated, but rather responded in different ways to metal pollution. While these physiological responses of P. perna may be of limited use in biomonitoring, they could indicate how populations may respond to marine pollution.     

水曲柳幼苗根系在不同浓度NH4NO3溶液中水流导度的变化

水分吸收过程是根系重要的生理过程。水孔蛋白在根系水分径向运输中起着重要的作用,根系水流导度(L_p)的测定是研究水孔蛋白的重要途径。该研究采用压力流的方法,对相同生长条件下的水曲柳(Fraxinus mandshurica)幼苗根系进行研究,测定了根系在去离子水和不同浓度NH₄NO₃溶液中的L_p。结果表明:未经处理的水曲柳幼苗根系,L_p随NH₄NO₃浓度的增加而上升,而且NH₄NO₃溶液中的L_p比去离子水中的L_p平均高77%;经HgCl₂处理后,水曲柳幼苗根系的L_p仍然随NH₄NO₃浓度的增加而增大,但是根系L_p在去离子水下降了22%,而在NH₄NO₃溶液中下降了68%,与以前的研究相比发现,经HgCl₂处理后,以营养液为吸水基质的根系L_p的降低值普遍高于以去离子水为基质的试验。因此,基质中养分离子的存在对根系中水孔蛋白活性产生了重要的影响,进而影响根系水分的吸收过程。     

Stimulation of bumetanide-sensitive K+ transport in Swiss 3T3 fibroblasts by serum and mitogenic hormones

Rapidly growing Swiss 3T3 fibroblasts possess a bumetanide-sensitive K+ transport system that is dependent on both Na+ and Cl- ions; a smaller bumetanide-insensitive component of K+ transport is also present. In cells brought to the quiescent state by 8-11 days of incubation without a medium change, the bumetanide-sensitive rate of transport was reduced by 63%; the bumetanide-insensitive rate did not change. Removal of dialyzed fetal calf serum from the uptake medium resulted in a substantial reduction in bumetanide-sensitive uptake in both rapidly growing cells (33% reduction) and quiescent cells (68% reduction) but had no effect on bumetanide-insensitive uptake. Insulin was almost as effective as dialyzed fetal calf serum in stimulating bumetanide-sensitive uptake; insulin was maximally stimulatory at 2.5 micrograms/ml. The combination of insulin, epidermal growth factor, and arginine-vasopressin was maximally effective in stimulating both bumetanide-sensitive K+ uptake and 3H-thymidine incorporation in quiescent cells; bumetanide, however, did not interfere with the hormonal stimulation of DNA synthesis. Thus, the bumetanide-sensitive K+ transport system is not necessary for such stimulation to occur. Furthermore, concentrations of hormones which stimulated significant levels of DNA synthesis produced no elevation in the intracellular concentration of K+. We conclude that the bumetanide-sensitive pathway of K+ transport is modulated by serum and by mitogenic hormones, but does not play a role in the stimulation of DNA synthesis by these factors.     

Increased synthetic capacity for metallothionein in cultured liver cells following dimethyl sulfoxide pretreatment

Cultured TRL 1215 cells in log phase of growth were exposed to dimethyl sulfoxide (DMSO; 14-280 mM) followed 48 h later by cadmium (10 micron). Intracellular concentrations of metallothionein (MT) were measured 24 h after cadmium addition. Cadmium alone caused a 10-fold increase in the levels of MT, while DMSO alone had no effect on cellular MT levels. DMSO pretreatment followed by cadmium exposure, however, resulted in MT levels that were elevated by a factor of as much as 25-fold those observed in control cells. Concurrent treatment with the DNA synthesis inhibitor hydroxyurea (HU) eliminated the enhancing effect of DMSO pretreatment on cadmium induction of MT, indicating the requirement of DNA synthesis. An enhancement of the cellular accumulation of the metal ion did not account for the increased cadmium-induced MT synthesis in DMSO-pretreated cells as these cells did not show significantly increased uptake of cadmium during the initial period of exposure. DMSO pretreatment enhances cadmium induction of MT synthesis through a mechanism that appears to be dependent on the synthesis of DNA.     

Dissociation by cytochalasin B of movement, DNA synthesis and transport in 3T3 cells.

Cytochalasin B was used as a tool to study the inter-relationships between cell movement, the reinitiated DNA synthesis and the enhanced transport of specific small molecules stimulated by serum in quiescent 3T3 cells. Cytochalasin at concentrations of less than 1 mug/ml inhibits serum-stimulated movement within the monolayer and migration into a wound. Even at ten times this concentration there is little effect on the increase in DNA in the culture, indicating that movement away from neighboring cells is not required for the initiation of DNA synthesis. While DNA synthesis is not inhibited by concentrations of cytochalasin up to 10 mug/ml, the increased thymidine transport which is associated with the onset of the S phase of the cell cycle is inhibited and DNA synthesis cannot be measured by the labelling of nuclei with radioactive thymidine. Cytochalasin has a differential effect on the early transport changes produced by serum addition. Glucose transport is inhibited by low concentrations of the drug (less than 1 mug/ml) while the enhanced uptake of phosphate and uridine is unaffected by a 10-fold increase in concentration. Although the doses of cytochalasin required for 50% inhibition of hexose uptake and of cell movement are the same, no causal relationship between sugar transport and locomotion can be demonstrated. Cytochalasin affects membrane functions in at least two different ways. The drug inhibits the uptake of glucose directly but affects only the S-phase associated increase in thymidine transport.     

Scavenger receptor class B,type I on non-malignant and malignant human epithelial cells mediates cholesteryl ester-uptake from high density lipoproteins

Hepatoma cell lines serve as a suitable model to study hepatic clearance of lipoprotein-associated cholesteryl esters (CEs). The present study aimed at investigating holoparticle-association of and selective CE-uptake from human high density lipoprotein subclass 3 (HDL3) by non-malignant adult (Chang-liver) and non-malignant fetal (WRL-68) epithelial cell lines as well as a hepatocellular carcinoma (HUH-7) cell line. Binding properties of 125I-HDL3 at 4 and 37 degrees C were similar for all three cell lines while degradation rates were highest for Chang-liver cells. Calculating the selective uptake of HDL3-associated CEs as the difference between [3H]CE- and 125I-HDL3 cell-association revealed that the selective lipid uptake and holoparticle-association was similar in Chang-liver while in WRL-68 and HUH-7 cells pronounced capacity for lipid tracer uptake in excess of holoparticle uptake was measured. Using RT-PCR, Northern and Western blot analysis, as well as immunocytochemical technique pronounced expression of scavenger receptor class B, type I (SR-BI) but not SR-BII (a splice variant of SR-BI less efficient for selective CE-uptake than SR-BI) could be identified in HUH-7 and WRL-68 cells. A polyclonal antiserum raised against SR-BI significantly decreased cell-association of [3H]CE-HDL3 in HUH-7 and WRL-68. The present findings suggest that the capacity for selective cholesteryl ester-uptake from high density lipoprotein by malignant and normal epithelial cells from the liver depends on expression of the scavenger receptor class B, type I.     

Multiple effects of mercury on cell volume regulation, plasma membrane permeability, and thiol content in the human intestinal cell line Caco-2

In a previous study, we characterized Cd–Hg interactions for uptake in human intestinal Caco-2 cells. We pursued our investigations on metal uptake from metal mixtures, focusing on the effects of Hg on cellular homeostasis. A 4-fold higher equilibrium accumulation value of 0.3 μmol/L ²⁰³Hg was measured in the presence of 100 μmol/L unlabeled Hg in the serum-free exposure medium without modification in the initial uptake rate. This phenomenon was eliminated at 4^∘C. Mercury induced an increase in tritiated water and [³H]mannitol uptakes for exposure times greater than 20 min. Incubations for 20 min and 30 min with 100 μmol/L Hg and 2 mmol/L N-ethylmaleimide (NEM) resulted in a 34% and 50% reductions in cellular thiol staining, respectively, with additive effects. Lactate dehydrogenase leakage and live/dead assays confirmed the maintenance of cell membrane integrity in Hg- or NEM-treated cells. We conclude that Hg may alter membrane permeability and increase cell volume without any loss in cell viability. This phenomenon is sensitive to temperature and could involve Hg interaction with membrane thiols, possibly related to solute transport. During metal uptake from metal mixtures, Hg may thus promote the uptake of other toxic metals by increasing cell volume and consequently cell capacity. Deceased 25 March 2004     

Mangiferin: A xanthone attenuates mercury chloride induced cytotoxicity and genotoxicity in HepG2 cells

Mangiferin (MGN), a dietary C-glucosylxanthone present in Mangifera indica, is known to possess a spectrum of beneficial pharmacological properties. This study demonstrates antigenotoxic potential of MGN against mercuric chloride (HgCl2)-induced genotoxicity in HepG2 cell line. Treatment of HepG2 cells with various concentrations of HgCl2 for 3 h caused a dose-dependent increase in micronuclei frequency and elevation in DNA strand breaks (olive tail moment and tail DNA). Pretreatment with MGN significantly (p < 0.01) inhibited HgCl2 -induced (20 μM for 30 h) DNA damage. An optimal antigenotoxic effect of MGN, both in micronuclei and comet assay, was observed at a concentration of 50 μM. Furthermore, HepG2 cells treated with various concentrations of HgCl2 resulted in a dose-dependent increase in the dichlorofluorescein fluorescence, indicating an increase in the generation of reactive oxygen species (ROS). However, MGN by itself failed to generate ROS at a concentration of 50 μM, whereas it could significantly decrease HgCl2 -induced ROS. Our study clearly demonstrates that MGN pretreatment reduced the HgCl2-induced DNA damage in HepG2 cells, thus demonstrating the genoprotective potential of MGN, which is mediated mainly by the inhibition of oxidative stress.     

急性臭氧暴露对大鼠肺部细胞遗传毒性的影响*

目的: 探讨不同浓度臭氧急性暴露对大鼠肺部细胞的遗传毒性的影响。方法: 36只wistar大鼠随机分为对照组(过滤空气暴露)、臭氧暴露组(0.12 ppm、0.5 ppm、1.0 ppm、2.0 ppm、4.0 ppm)共6组,每组6只。以不同浓度的臭氧对大鼠进行动态染毒4 h后,取肺组织并分离单细胞,采用酶联免疫吸附法检测8-羟基脱氧鸟苷(8-OHdG),利用彗星实验、微核试验和DNA-蛋白质交联实验进行DNA和染色体损伤分析。结果: 与对照组相比,肺组织中8-OHdG含量从臭氧暴露浓度为0.12 ppm起即显著增加,在0.5 ppm时达到最高值。随着臭氧暴露浓度升高,彗星拖尾率逐渐上升,且存在明显的剂量-效应关系;DNA-蛋白质交联率有先升高后下降的趋势,且在2.0 ppm时达到最大值;而肺部细胞微核率尽管呈现出上升趋势,但与对照组相比无显著性差异。结论: 急性臭氧暴露在较低浓度(0.12 ppm)时即可导致大鼠肺部细胞的DNA损伤;而在较高浓度(4 ppm)时却未见显著的染色体损伤。