[Effects of pol beta on biological characteristics and DNA damage in mouse embryonic fibroblast]

OBJECTIVE

To explore the effect of DNA polymerase beta (pol beta) expression level on biological characteristics of mouse embryonic fibroblast (MEF) and the cellular response to DNA damage induced by potassium dichromate.

METHODS

pol beta wild-type cells (pol beta +/+), pol beta null cells (pol beta -/-) and pol beta overexpressed cells (pol beta oe) were applied as a model system. The growth curve of cells was plotted by MTT assay; the doubling time of cells was detected by double time experiment; the spontaneous mutation frequency was determined by HGPRT gene mutation method and single cell gel electrophoresis assay (SCGE) was employed to observe the DNA damage either happened spontaneously or induced by potassium dichromate.

RESULTS

Growth characteristic and doubling time of the three kinds of cells were similar and no obvious differences were found on spontaneous DNA damage and mutations frequency among them (P > 0.05). Potassium dichromate increased comet rate and tail length in the three kinds of cells in a concentration dependent way. DNA damage of pol beta -/- cells at the same dosage were more serious than the other cells both in comet rate and tail length (P < 0.05). pol beta oe cells demonstrated more resistant to DNA damage obviously than the others.

CONCLUSION

The expression level of pol beta has no significant effect on the biological characteristic and spontaneous mutation frequency of MEF. pol beta knock out cells is more sensitive to DNA damage induced by potassium dichromate, whereas, pol beta over expression can help cells response to DNA damage and protect cells from death in a certain degree.

Protective effects of Selenium (Se) on Chromium (VI) induced nephrotoxicity in adult rats

Chromium is a toxic metal implicated in human diseases. This study was focused on investigating the possible protective effect of Se against K(2)Cr(2)O(7). Female Wistar rats, used in this study, were divided into four groups of six animals each: group I served as control which received standard diet; group II received orally only K(2)Cr(2)O(7) (700 ppm equivalent to 67 mg/kgbw); group III received both K(2)Cr(2)O(7) and Se (0.5 mg/kg of diet); group IV received Se (0.5mg Na(2)SeO(3)/kg of diet). The exposure of rats to K(2)Cr(2)O(7) for 21 days provoked renal damages with a significant increase in kidney malondialdehyde, superoxide dismutase, plasma creatinine, and uric acid levels, while catalase, glutathione peroxidase, non-protein thiol, Metallothionein and plasma urea levels decreased. Coadministration of Se in the diet of chromium-treated group improved malondialdehyde, renal biomarkers levels and antioxidant enzyme activities. Kidney histological studies confirmed biochemical parameters and the beneficial role of selenium.

Assessment of the potential toxicity of a linear alkylbenzene sulfonate (LAS) to freshwater animal life by means of cladoceran bioassays

The acute and chronic toxic effects of LAS on the cladocerans Daphnia similis, Ceriodaphnia dubia and Ceriodaphnia silvestrii were tested. Both types of toxicity bioassays and the methods of culture and stock maintenance of the test organisms conformed to the recommendations of ABNT (Brazilian Society of Technical Standards), which closely follow the standard methods of USEPA. The results obtained for EC(50) (48 h) were: 14.17 mg L(-1) for D. similis, 11.84 mg L(-1) for C. dubia and 13.52 mg L(-1) for C. silvestrii. In the chronic toxicity tests performed on C. dubia and C. silvestrii, there was a significant decrease in the fecundity of the exposed animals; the value of NOEC for C. dubia and C. silvestrii were 1.00 mg L(-1) and 2.50 mg L(-1), respectively. Cladoceran bioassays provided evidence that LAS concentration as low as 1.00 mg L(-1) can damage invertebrate animal life in freshwaters, concentrations that can be found in many eutrophic rivers and reservoirs.

Apoptotic-related protein changes induced by hexavalent chromium in mice liver

Although it has been reported that hexavalent chromium (Cr(VI)) could induce apoptosis in a variety of cell types, the molecular mechanisms underlying this process is still largely unknown. This study was undertaken to determine effects of single oral 0, 25, 50, and 100 mg/kg body weight doses of potassium dichromate on the expression level of p53, Bcl-2, Bax, cytochrome c, and caspase-3, which are vital regulators of apoptosis, in mice liver. The results showed that Cr(VI) could upregulate the protein expression of p53, Bax, cytochrome c, and caspase-3 and downregulate the expression of Bcl-2 in mice liver. All these results suggested that p53, Bcl-2, Bax, cytochrome c, and caspase-3 may be involved in the regulation of Cr(VI) induced apoptosis in vivo.

Land use, genetic diversity and toxicant tolerance in natural populations of Daphnia magna

Provided that gene flow is not too high, selection by local environmental conditions in heterogeneous landscapes can lead to genetic adaptation of natural populations to their local habitat. Pollution with anthropogenic toxicants may create pronounced environmental gradients that impose strong local selection pressures. Toxic contaminants may also directly impact genetic structure in natural populations by exhibiting genotoxicity or by causing population declines resulting in genetic bottlenecks. Using populations of Daphnia magna established from the dormant egg banks of ponds located in a landscape dominated by anthropogenic impact, we aimed at detecting evidence for local adaptation to environmental contamination. We explored the relationship between land use around the 10 investigated ponds, population genetic diversity as measured by neutral genetic markers (polymorphic allozymes) and the tolerance of the populations originating from these ponds to acute lethal effects of two model toxicants, the pesticide carbaryl and the metal potassium dichromate. Genetic diversity of the populations as observed by neutral markers tended to be negatively impacted by agricultural land use intensity (Spearman rank correlation, R=-0.614, P=0.059), indicating that genetic bottlenecks may have resulted from anthropogenic impact. We experimentally observed differences in susceptibility to both carbaryl and potassium dichromate among the studied pond populations of D. magna (analysis of deviance, P<0.001). Because the experimental design excluded the possibility of physiological adaptation of the test animals to the toxicants, we conclude that the differences in susceptibility must have a genetic basis. Moreover, carbaryl tolerance levels of the populations tended to increase with increasing agricultural land use intensity as described by ranked percentage of land coverage with cereal and corn crop in the proximity of the ponds (Spearman rank correlation, R=0.602, P=0.066). Together, these two findings provide evidence for local adaptation of D. magna populations to pesticide contamination. Overall, the results demonstrate the potential selection pressure imposed by anthropogenic pollution and provide evidence that genetic erosion in natural Daphnia populations is related to anthropogenic impact.

Antigenotoxic effects of Citrus aurentium L. fruit peel oil on mutagenicity of two alkylating agents and two metals in the Drosophila wing spot test

Antigenotoxic effects of Citrus aurentium L. (Rutaceae) fruit peel oil (CPO) in combination with mutagenic metals and alkylating agents were studied using the wing spot test of D. melanogaster. The four reference mutagens, potassium dichromate (K2Cr2O7), cobalt chloride (CoCl2), ethylmethanesulfonate (EMS), and N-ethyl-N-nitrosourea (ENU) were clearly genotoxic. CPO alone at doses from 0.1 to 0.5% in Tween 80 was not mutagenic and did not enhance the mutagenic effect of the reference mutagens. However, antigenotoxic effects of CPO were clearly demonstrated in chronic cotreatments with mutagens and oil, by a significant decrease in wing spots induced by all four mutagens. The D. melanogaster wing spot test was found to be a suitable assay for detecting antigenotoxic effects in vivo.

[Humoral immune response in experimental animals exposed to organic and inorganic compounds]

A humoral immune response was studied in the Wistar rats and (CBAxC57B16)F1 mice orally given potassium bichromate, benzene, and their mixture with drinking water. The test substances were found to have an immunosuppressive effect on both the parameters of an immune response and the level of lysozyme in the experimental animals, which appeared as reductions in the number of splenocytes in the rats, the relative count of antibody-forming cells in the mice, the absolute count of AFC on the spleen in the rats and mice, the level of hemagglutinins in the rats, and that of lysozyme in the rats and mice. Benzene and a mixture of benzene and potassium bichromate showed the most marked immunosuppressive effect on these animals.

A new developmental toxicity test for pelagic fish using anchoveta (Engraulis ringens J.)

A series of six 96-h static bioassays were performed to validate the use of anchoveta (Engraulis ringens) embryos as test organisms for ecotoxicological studies. The standardization protocol utilized potassium dichromate (K(2)Cr(2)O(7)) as a reference toxicant and egg mortality as the endpoint. The results indicated that the mean sensitivity of anchoveta embryos to potassium dichromate was 156.1 mg L(-1) (range: 131-185 mg L(-1)). The statistical data analysis showed high homogeneity in LC50 values among bioassays (variation coefficient = 11.02%). These results demonstrated that the protocol and handling procedures implemented for the anchoveta embryo bioassays comply with international standards for intra-laboratory precision. After secondary treatment, an effluent from a modern Kraft pulp mill was tested for E. ringens embryo toxicity, finding no significant differences from the controls.

A comparative study of Saccharomyces cerevisiae sensitivity against eight yeast species sensitivities to a range of toxicants

Fungi are widespread and very important in many ecosystems but the extensive use of pesticides can adversely affect beneficial fungi. The yeast, Saccharomyces cerevisiae has been proposed for the toxicological assessment of the effects of environmental pollutants on non-target fungi. To assess whether S. cerevisiae is a good representative of the immense ecological and phylogenetic diversity of yeasts, we compare the sensitivity of eight other yeasts from diverse phylogenetic taxa to a range of toxicants and environmental samples. Sensitivity was assessed using both the growth inhibition and alamar blue (resorufin fluorescence inhibition) bioassays. The growth inhibition bioassay showed that all yeast species had similar dose-response curves for the five organic fungicides and two environmental samples used. However, two yeast species, Trichosporon dulcitum and Pseudozyma fusiformata, were a great deal more sensitive than all others to CuSO4 and K2Cr2O7 while S. cerevisiae was the most tolerant to these chemicals. S. cerevisiae, however, showed similar sensitivity as other species to all toxicants in the resorufin fluorescence inhibition bioassay. It can therefore be used as a representative yeast species for assessing effects of environmental contaminants to non-target fungi and in the screening of chemical libraries for fungicidal activity.

Chromium (VI) induced changes in growth and root plasma membrane redox activities in pea plants

The effect of chromium (Cr) on growth as well as root plasma membrane redox reactions and superoxide radical production was studied in pea (Pisum sativum L. cv. Azad) plants exposed for 7 days to 20 and 200 microM Cr (VI), respectively, supplied as potassium dichromate. The growth of pea plants declined significantly at 200 microM Cr, as indicated by reduced leaf area and biomass. Relative to the control plants (no Cr exposure), the Cr content of roots increased significantly, both at 20 and 200 microM Cr. Following exposure to 200 microM Cr, there was a significant increase in root lipid peroxidation and hydrogen peroxide (H(2)O(2)) content, while both the Fv/Fm ratio and chlorophyll content were reduced. Exposure to Cr increased NADPH-dependent superoxide production in pea root plasma membrane vesicles, with the effect being more significant at 200 microM Cr than at 20 microM Cr. Treatment with Cr rapidly increased the activities of NADPH oxidase: relative to the controls, plants exposed to 20 microM Cr showed approximately a 67% increase in activity while there was a threefold increase in those plants exposed to 200 microM Cr. NADH-ferricyanide oxido-reductase activity was found to be inhibited by 16 and 51% at 20 and 200 microM Cr, respectively. The results of this study suggest that exposure to excess Cr damages pea root plasma membrane structure and function, resulting in decreased photosynthesis and poor plant growth.

DNA-protein cross-links in erythrocytes of freshwater fish exposed to hexavalent chromium or divalent nickel

DNA-protein cross-links (DPXs) in fish erythrocytes represent a potential biomarker for exposure to metal cations, such as hexavalent chromium (Cr[VI]) and divalent nickel (Ni[II]). Species-specific sensitivities to DPX formation were studied by coexposure of juvenile specimens of rainbow trout, hybrid bluegill, and channel catfish to waterborne metals, such as Cr(VI) and Ni(II). In a species comparison, 4 days of exposure to 2 ppm Cr(VI) induced highest DPXs in bluegill erythrocytes, followed by trout and catfish, at 186%, 97%, and 48% above controls, respectively. A similar pattern of species sensitivity was observed following co-exposure of the fish to 15 ppm Ni(II) for 4 days, with 237%, 124%, and 82% increased DPXs above control bluegill, trout, and catfish, respectively. Biological stability of Cr(VI)-induced DPXs was demonstrated in Cr(VI)-exposed bluegill, as DPX levels remained elevated for up to 20 days after discontinuation of exposure. Similar results were found following exposure of catfish to Ni(II), with detectable DPXs found 10 days after acute exposure. In both bluegill and catfish, a continued increase in DPX formation in erythrocytes was seen for 5-10 days after Cr(VI) was removed from tank water, suggesting that residual Cr(VI) may be involved in DPX formation following acute exposure of fish.

Acute toxicity of atrazine, endosulfan sulphate and chlorpyrifos to Vibrio fischeri, Thamnocephalus platyurus and Daphnia magna, relative to their concentrations in surface waters from the Alentejo region of Portugal

Ecotoxicological effects of the herbicide atrazine and the insecticides endosulfan sulphate and chlorpyrifos were evaluated using a test battery comprising aquatic organisms from different trophic levels. According to the categories established in the EU legislation, atrazine can be considered non-harmful for the species tested, while the insecticides can be considered very toxic for the crustaceans. The results of acute toxicity tests showed that the sensitivity of organisms were as follows: Thamnocephalus platyurus > Daphnia magna > Vibrio fischeri. Chlorpyrifos may act as a toxic compound in the aquatic environment of Guadiana River, as it may be detected in water at levels that promote toxic effects.

Difference in the sensitivity to chemical compounds between female and male neonates of Daphnia magna

Daphnia magna usually produce female offspring by parthenogenesis, and thus only female neonates are used to evaluate the environmental toxicity to chemicals. Additionally, it is known that male daphnids are induced by exposure to a juvenile hormone, methyl farnesoate, during late ovarian development. In this study, we investigated the concentration of methyl farnesoate in a 24-h exposure producing 100% males, and the difference in sensitivity to chemical compounds, potassium dichromate, pentachlorophenol, and paraquat, between females and males, referring to OECD Test Guideline 202. The results show that the minimum concentration for 100%-male induction of methyl farnesoate in adult females was 50 microg/L. In addition, acute toxicity tests (immobility test) with the other chemicals showed that male neonates have higher tolerance to potassium dichromate and pentachlorophenol than females for at least 24 h after birth, while no sex difference was observed in the sensitivity to paraquat. The differences in the median effective concentrations in these compounds between female and male neonates suggest two different overall modes of action. Using female daphnids for environmentally toxicity testing seems reasonable, since the females are more sensitive to chemicals than males. Furthermore, the method of male induction established in this study could be used for screening of endocrine disruptors.

Regucalcin down-regulation in rat kidney tissue after treatment with nephrotoxicants

Gene expression of regucalcin (Rgn), a calcium-binding protein, was investigated in kidney of male Wistar rats treated with proximal tubule segment-specific nephrotoxicants, namely hexachloro-1:3-butadiene (HCBD), specific for S(3) segment (pars recta) and potassium dichromate (chromate) specific for S(1)-S(2) segments (pars convoluta), according to age of animals and dose of chemicals. In the age-dependent study, male Wistar rats were treated with a single injection of HCBD (100mg/kg b.w. i.p.) or chromate (25 mg/kg b.w. s.c.) at 5 weeks or 12 weeks of age; in dose-response study, rats were treated with a single injection of three doses of HCBD (25, 50, and 100 mg/kg b.w. i.p.) or chromate (8, 12.5, and 25mg/kg b.w. s.c.) at 8 weeks of age. Forty-eight hours after treatment, Rgn and glutamine synthetase (GS) activity in kidney cortex, blood urea nitrogen (BUN) and plasma creatinine were measured; light microscopy was performed also. The results show that young rats are less susceptible to chromate (severe necrosis is evident only in adult rats), whereas age does not influence HCBD nephrotoxicity. Rgn is down regulated by HCBD at both age points, but not by chromate at 5 weeks of age. In addition, HCBD causes down-regulation of Rgn from the low dose in 8-week-old rats, whereas chromate causes the same effect at the high dose only. GS activity in kidney cortex shows a similar behavior, even if sensitive to low doses of chromate also, whereas BUN and creatinine increase after the high dose of both chemicals only. Accordingly, light microscopy shows a segment-specific, dose-dependent increase of severity of damage caused by the chemicals. Rgn gene expression appears a sensitive genomic marker to evaluate the renal impairment caused by chemicals and its down-regulation seems to be related to damage, early or already established, to S(3) segment of the proximal tubule.

Assessment of EDTA in chromium (III-VI) toxicity on marine intertidal crab (Petrolisthes laevigatus)

Chromium poses a potential threat to coastal ecosystems. We used standard toxicity bioassays (semi-static, chronic) to evaluate EDTA as a chelating agent for reducing trivalent and hexavalent chromium toxicity on Petrolisthes laevigatus. Crab survival decreased linearly with increased chromium concentrations and dropped significantly beginning at 40 mg/L Cr (VI) and 80 mg/L Cr (III). No significant differences were observed with Cr (III) + EDTA as compared with untreated controls. Cr (VI) toxicity was greater than that of Cr (III), with low individual survival rates. The protective effect of EDTA in the medium increased crab survival by 41%-48%.

Histopathological effects of hexavalent chromium in the ovary of a fresh water fish, Channa punctatus (Bloch)

The histopathological effects of hexavalent chromium (Cr VI) in the ovary of a fresh water teleost, Channa punctatus were investigated. An exposure-dependent alteration in ovarian histology is reported. For both acute and chronic exposures to Cr (VI), the percentages of atretic oocytes were increased; this increase was more pronounced in the acute exposure group. A decrease in percentage of vitellogenic oocytes was observed in the chronic exposure group indicating impairment of vitellogenesis. The hepatocellular vacuolization and atrophy along with pyknotic nuclei in both acute and chronic chromium exposed fish liver supports the vitellogenic impairment. The observed alterations may be due to both direct cytotoxic effect of Cr (VI) on the ovary as well as mediation by overall systemic toxicity affecting other vital organs.

The effect of potassium dichromate on free radical processes in goldfish: possible protective role of glutathione

The effects of 96 h exposure to Cr(6+) (added as potassium dichromate) on the status of antioxidant defenses and markers of oxidative damage were evaluated in three tissues of goldfish, Carassius auratus. Fish exposure to high dichromate concentrations, 10 and 50mg/l, increased protein carbonyl levels in brain and liver, but not in kidney. Chromium exposure also increased concentrations of lipid peroxides in brain (at 5mg/l) and liver (10mg/l), but not in kidney. The concentrations of reduced glutathione (GSH) were higher in the liver of goldfish treated with 5-50mg/l Cr(6+) than in controls, but in kidney only the 5mg/l-treated group showed increased GSH levels. Dichromate at 1mg/l increased the concentration of oxidized glutathione (GSSG) in liver and kidney by 80% and 60%, respectively, whereas at 10 and 50mg/l the levels of GSSG decreased by 50% in kidney. These results indicate that the dichromate concentrations used induced oxidation of lipids and proteins in goldfish tissues in a concentration- and tissue-specific manner. Also, the redox status of fish tissues was affected in a concentration- and tissue-specific manner. The activities of glutathione reductase increased in all three tissues in response to dichromate treatment, increasing by approximately 2-fold in brain and liver in goldfish treated with 50mg/l Cr(6+). Dichromate treatment did not change the activities of SOD, catalase or GST in brain, but reduced the activities of SOD in liver and kidney, and catalase in liver. The results suggest that the glutathione system may be responsible for protecting against the deleterious effects of dichromate in fish and indicate the possible development of an adaptive response during the 96 h treatment with the toxicant.

Application of DNA diffusion assay in earthworm coelomocytes

We have applied the DNA diffusion assay proposed by Singh (2000) Exp Cell Res 256:328-337, for quantitative estimation of apoptosis in earthworm coelomocytes, exposed to Chromium (VI) and cypermethrin as model toxicants in vitro. The DNA diffusion assay was originally described for mammalian cells. H2O2, Sodium ascorbate, and hyperthermia were used as positive controls in present study. Apoptosis such as DNA diffusion occurred in dose-dependent manner for Chromium (VI) and cypermethrin at very low concentration (1, 3, and 10 ppm for Chromium (VI) and 4, 8, and 16 ppm for cypermethrin). Three distinct patterns (apoptosis like DNA diffusion, necrosis, and normal) were observed in exposed and nonexposed cells. Present study is probably the first report of application of the DNA diffusion technique in earthworm coelomocytes. Findings of this study indicate that this assay has potential for use in invertebrate cells to differentiate between apoptosis and necrosis.

Physiological responses of Juncus effusus (Rush) to chromium and relevance for wastewater treatment in constructed wetlands

Constructed wetlands are increasingly applied for industrial wastewater treatment. However, current knowledge of the stress responses of helophytes to selected toxicants such as dichromate is limited. The goal of the experiments presented here was to characterize the physiological response of Juncus effusus to different concentrations of dichromate dependent upon the growth and constitution of the plants. The growth parameters, shoot length, and dry weight already were strongly affected at low dichromate concentrations of approximately 34 microM. Concentrations of 340 microM impaired chlorophyll fluorescence and a decrease in chlorophyll a started at concentrations higher than 170 microM dichromate. The concentrations of chlorophyll b and carotenoids also were influenced negatively. Thus, the reduction of the pigment content started before any obvious influence on the chlorophyll fluorescence. The highest concentration of dichromate, which caused no permanent inhibition of growth and photosynthesis, was found to be 17 microM K2Cr2O7. In principle, J. effusus is suitable for constructed wetlands to treat chromium-containing wastewater. Because the stress resistance of J. effusus is limited, the maximum concentration of dichromate in the treated wastewater should not exceed 34 microM. The growth parameters, shoot length, and dry weight were sensitive to much lower dichromate concentrations and did react more quickly than the biochemistry-related parameters chlorophyll fluorescence and pigment concentration. Therefore, the example of Juncus effusus shows that the use of only biochemical parameters to define concentration limits for the treatment of dichromate-containing wastewater can lead to incorrect conclusions and result in disturbed long-term operation of the system.

Biochemical biomarkers in chronically metal-stressed daphnids

Biochemical biomarkers are a popular measure of toxic effects on organisms due to their assumed fast response, and are usually assessed after acute exposure of the organism to the stressor. However, increasing interest in the use of biochemical biomarkers in environmental pollution monitoring calls for more laboratory long-term studies of contaminants' effects on biochemical endpoints. In this study, four biochemical biomarkers (protein content, activity of cholinesterase (ChE), catalase (CAT) and glutathione S-transferase (GST), were correlated with standardised reproductive and survival endpoints of water fleas (Daphnia magna) after chronic exposure to Cr (VI) and Cd. No effect on the reproduction and survival was noticed up to the highest tested concentration of Cr (VI) (52.5 microg/L), while the protein content, and the ChE and CAT activity decreased, and GST activity increased. Cd affected reproduction of daphnids above 0.656 microg/L, but the protein content and ChE activity were changed at 0.328 microg/L and 0.082 microg/L of Cd, respectively. Biochemical biomarkers in some cases proved to be equally or more sensitive than reproduction and mortality. We recommend more frequent use of a battery of biochemical biomarkers in combination with other higher-level biomarkers also in chronic studies and not only in the acute ones.

Chromium induced testicular impairment in relation to adrenocortical activities in adult albino rats

The present study investigates the testicular and adrenocortical activities under different doses and durations of chromium (Cr) exposure and their interactions. Mature male Sprague Dawley rats were injected daily with three different doses (0.2, 0.4, and 0.6 mg/kg bw) of Cr salt (K(2)Cr(2)O(7)) intraperitonealy for 13 and 26 days, respectively. The medium (0.4 mg/kg bw/day) and higher dose (0.6 mg/kg bw/day) of Cr significantly (p<0.05) decrease accessory sex organs weight, testicular Delta(5)3beta-hydroxysteroid dehydrogenase (HSD) and 17beta-HSD activities, epididymal sperm count, effective spermatid degeneration, serum testosterone, LH level, testicular catalase and superoxide dismutase (SOD) activities while testicular lipid peroxidation, serum FSH, corticosterone level, adrenal weight and adrenal Delta(5)3beta-HSD activity increased significantly than that of control and lower dose (0.2 mg/kg bw/day) Cr exposed animals. Testicular histoarchitechture shows deterioration after critical dose (0.4 mg/kg bw/day) and duration (26 days) of Cr exposure. Cr induced alterations on testicular and adrenocortical activities are dose and duration dependent. Adrecortical hyperactivity accompanied by testicular oxidative stress might have a crucial role for Cr induced male reproductive impairment.

Sulfur starvation and chromium tolerance in Scenedesmus acutus: a possible link between metal tolerance and the regulation of sulfur uptake/assimilation processes

In a laboratory-selected Cr-tolerant strain of the unicellular green alga Scenedesmus acutus, the capacity to synthesize higher amounts of cysteine (Cys) and reduced glutathione (GSH) than the wild-type was demonstrated to underlie tolerance to Cd and Cr(VI). In photosynthetic organisms sulfate constitutes the main sulfur source for the biosynthesis of GSH and its precursor Cys, hence it was hypothesized that the sensitivity of the two strains to Cr(VI) could be modified after culturing in sulfate-deprived medium. Both strains were grown in the presence of different concentrations or in the absence of sulfate (sulfur-starved) and then assayed for Cr(VI) tolerance in standard medium. Unstarved, sulfur-starved and sulfur-replete cells (cells maintained in standard medium after S-starvation) were analysed for Cys, GSH and sulfur content. Sulfur-starved cells showed a greater tolerance to Cr(VI) than unstarved ones. The increased tolerance was ascribable to a transient physiological change and can be considered as specifically due to sulfur deprivation, since it was lost after a 3-day culture in standard medium and was not exhibited by nitrogen-starved cells. The comparison between Cys, GSH and sulfur content in sulfur-starved and sulfur-replete cells of the two strains suggests that the higher tolerance to Cr(VI) after S-starvation could depend on the up-regulation of sulfate uptake mechanisms, and that the primary reason for the higher tolerance to chromium in the selected strain could be due to greater sensitivity to the decrease in negative intracellular end-products (free Cys and GSH) leading to an earlier up-regulation of sulfate assimilation processes.

S-allylcysteine scavenges singlet oxygen and hypochlorous acid and protects LLC-PK1 cells of potassium dichromate-induced toxicity

It has been found that S-allylcysteine (SAC), a garlic-derived compound, has in vivo and in vitro antioxidant properties. In addition, it is known that SAC is able to scavenge different reactive oxygen or nitrogen species including superoxide anion (O(2)(-)), hydrogen peroxide (H(2)O(2)), hydroxyl radical (OH()), and peroxynitrite anion (ONOO(-)) although the IC(5O) values for each reactive species has not been calculated and the potential ability of SAC to scavenge singlet oxygen ((1)O(2)) and hypochlorous acid (HOCl) has not been explored. The purposes of this work was (a) to explore the potential ability of SAC to scavenge (1)O(2) and HOCl, (b) to further characterize the O(2)(-), H(2)O(2), OH(), and ONOO(-) scavenging ability of SAC by measuring the IC(50) values using in vitro assays, and (c) to explore the potential ability of SAC to ameliorate the potassium dichromate (K(2)Cr(2)O(7))-induced cytotoxicity in LLC-PK1 cells in which oxidative stress is involved. The scavenging activity was compared against the following reference compounds: N-acetylcysteine for O(2)(-), sodium pyruvate for H(2)O(2), dimethylthiourea for OH(), lipoic acid and glutathione for (1)O(2), lipoic acid for HOCl, and penicillamine for ONOO(-). It was found that SAC was able to scavenge concentration-dependently all the species assayed with the following IC(5O) (mean+/-SEM, mM): O(2)(-) (14.49+/-1.67), H(2)O(2) (68+/-1.92), OH() (0.68+/-0.06), (1)O(2) (1.93+/-0.27), HOCl (2.86+/-0.15), and ONOO(-) (0.80+/-0.05). When the ability of SAC to scavenge these species was compared to those of the reference compounds it was found that the efficacy of SAC (a) to scavenge O(2)(-), H(2)O(2), OH(), and ONOO(-) was lower, (b) to scavenge HOCl was similar, and (c) to scavenge (1)O(2) was higher. In addition, it was found that SAC was able to prevent K(2)Cr(2)O(7)-induced toxicity in LLC-PK1 cells in culture. It was showed for the first time that SAC is able to scavenge (1)O(2) and HOCl and to ameliorate the K(2)Cr(2)O(7)-induced toxicity.

Protective effects of garlic powder against potassium dichromate-induced oxidative stress and nephrotoxicity

Potassium dichromate (K(2)Cr(2)O(7))-induced nephrotoxicity is associated with oxidative stress. In the present work the effect of garlic powder, a recognized antioxidant, on K(2)Cr(2)O(7)-induced nephrotoxicity and oxidative stress was studied. Rats were fed a 2% garlic powder diet for 1 month. A single injection of K(2)Cr(2)O(7) (15 mg/kg) to rats induced tubule interstitial damage and an increase in the following markers of renal injury 2 days later: blood urea nitrogen (4.6-fold), serum creatinine (9.7-fold), proteinuria (35.9-fold), urinary excretion of N-acetyl-beta-d-glucosaminidase (12.9-fold) and glutathione-S-transferase (2.3-fold) and a decrease of 65% in serum glutathione peroxidase activity. In addition, K(2)Cr(2)O(7) injection increased the following nitrosative and oxidative stress markers in kidney: 3-nitrotyrosine (1.9-fold), 4-hydroxy-2-nonenal (2.1-fold), malondialdehyde (1.8-fold) and protein carbonyl content (1.7-fold). It was found that garlic powder feeding was able to prevent by 44-71% the alterations in the markers of renal injury studied, by 55% the histological damage, and by 47-100% the increase in markers of oxidative and nitrosative stress. It is concluded that the ability of garlic powder to ameliorate K(2)Cr(2)O(7)-induced renal injury is associated with its antioxidant properties. Our data support the use of garlic powder as a renoprotective agent.

[Matrix metalloproteinases: new effect biomarkers in the occupational exposure of toxic agents]

Matrix metalloproteinases belong to a growing family of proteases controlled by specific tissue inhibitors, involved in tissutal flogosis, wound healing, cancer invasion and metastasis. We developed an in vitro model to screen for potential toxic compounds in professional exposure. Human keratinocytes (HaCat) were used as target cells while matrix metalloproteinases (MMP) were selected as responders, developing and in vitro model of allergic dermatitis. The chemical agents: potassium dichromate and nickel sulphate as positive teste, because represent the main etiological agents of allergic dermatitis. Nickel contact at very low concentrations (10(-5), 10(-6) M) induced upregulation of MMP-2 and IL-8 mRNA production; chromium contact at very low concentrations killed all cells. Actually, our in vitro research is based on analysis of cytotoxic effects of xenobiotics on human lung fibroblasts; simultaneously we verified serum increasing in vivo of MMP-9, determinated in workers serum, exposed to anesthetic gas (fluorane). In only six exposed workers we observed MMP9 increasing over than normal range. Actually, we are continuing our research on a more representative sample.