Effects of diethyldithiocarbamate (DDTC) on the plasma biotransformations of tetrachloro(d,l-trans)-1,2-diaminocyclohexaneplatinum(IV) (tetraplatin) in Fischer 344 rats.

We have studied the effects of diethyldithiocarbamate (DDTC) on the biotransformations of toxic doses of tetrachloro (d,l-trans)1,2-diaminocyclohexaneplatinum(IV) (tetraplatin) in Fischer 344 rats. In animals not treated with DDTC, tetraplatin was rapidly converted to dichloro(d,l-trans)1,2-diaminocyclohexaneplatinum(II) [PtCl2(dach)]. Subsequent biotransformations included the transient formation of the (d,l-trans)1,2-diaminocyclohexane-aquachloroplatinum(II) [Pt(H2O)(Cl)(dach)]+ complex, followed by formation of the platinum (Pt)-methionine and either Pt-cysteine or Pt-ornithine complexes. Significant amounts of free (d,l-trans) 1,2-diaminocyclohexane (dach) were observed in plasma as a result of intracellular trans-labilization reactions. DDTC caused a marked decrease in both total and protein-bound platinum in the circulation. A significant increase in the plasma concentration of free dach was also observed as a result of formation of the Pt(DDTC)2 complex. Some of the free dach could have arisen from intracellular reactions with DDTC, but the displacement of platinum from plasma proteins was more than sufficient to account for the increase in free dach in the circulation. DDTC treatment also decreased plasma concentrations of tetraplatin, PtCl2(dach), [Pt(H2O)(Cl) (dach)]+, the Pt-methionine complex, and one unidentified biotransformation product, but had no effect on the Pt-cysteine (or Pt-ornithine) complex. These effects of DDTC on protein-bound platinum and low-molecular-weight biotransformation products in plasma may contribute to the decrease in tetraplatin toxicity seen in DDTC-treated rats.     

N-terminal globin adducts as biomarkers for formation of butadiene derived epoxides

The aim of this review is to summarize our recent data on butadiene (BD) derived hemoglobin adducts as biomarkers for the internal formation of the individual epoxides formed by butadiene (BD). It is well known that BD is oxidized by cytochrome P450s to several epoxides that form DNA and protein adducts. 1,2-Epoxy-3-butene (EB), 1,2;3,4-diepoxybutane (DEB) and 1,2-epoxy-3,4-butanediol (EB-diol) form N-(2-hydroxy-3-butenyl)-valine (HB-Val), N,N-(2,3-dihydroxy-1,4-butadiyl)-valine (pyr-Val) and N-(2,3,4-trihydroxybutyl)-valine (THB-Val) adducts, respectively. The analysis of HB-Val and THB-Val by the modified Edman degradation and GC-MS/MS has generated valuable insights into BD metabolism across species. In addition, a recently established method for the analysis of pyr-Val has been proven to be suitable for detection of pyr-Val in rodents exposed to BD as low as 1 ppm. These technologies have been applied to study a wide range of exposures to BD, EB, DEB, and 3-butene-1,2-diol as a precursor of EB-diol in male and female mice and rats. Altogether the data have shown that BD metabolism is species and concentration dependent, consistent with metabolism and carcinogenesis data. Mice form much more HB-Val and pyr-Val than rats, especially at low exposures. After 10 days of inhalation exposure to 3 ppm BD, mice formed 12.5-fold more pyr-Val than rats. In contrast, the amounts of THB-Val were similar in mice and rats exposed to 3 or 62.5 ppm BD. Furthermore, it appears that the formation of THB-Val is supralinear in mice and rats due to saturation of metabolic activation pathways. Gender differences in metabolism are less well established. One study with male and female rats exposed to 1000 ppm BD for 90 days demonstrated a 1.6-, 3.5- and 2.0-fold gender difference in formation of HB-Val, pyr-Val and THB-Val, respectively, with females being more efficient in epoxide formation. The analyses of BD derived protein adducts correlate well with the observed species and gender differences in BD-carcinogenesis and suggest that DEB may indeed be the most important metabolite.     

Effects of diethyldithiocarbamate (ddtc) on the plasma biotransformations of tetrachloro(d,i-trans)-1,2-diaminocyclohexaneplatinum(iv) (tetraplatin) in fischer 344 rats

We have studied the effects of diethyldithiocarbamate (DDTC) on the biotransformations of toxic doses of tetrachloro (d,l-trans)1,2-diaminocyclohexaneplatinum(IV) (tetraplatin) in Fischer 344 rats. In animals not treated with DDTC, tetraplatin was rapidly converted to dichloro(d,I-trans)1,2-diaminocyclohexaneplatinum(II) [PtCl₂(dach]. Subsequent biotransformations included the transient formation of the (d,I-trans)1,2-diaminocyclohexane-aquachloroplatinum(II) [Pt(H₂O)(Cl)(dach)]+ complex, followed by formation of the platinum (Pt)-methionine and either Pt-cysteine or Pt-ornithine complexes. Significant amounts of free (d,I-trans) 1,2-diaminocyclohexane (dach) were observed in plasma as a result of intracellular trans-labilization reactions. DDTC caused a marked decrease in both total and protein-bound platinum in the circulation. A significant increase in the plasma concentration of free dach was also observed as a result of formation of the Pt(DDTC)₂ complex. Some of the free dach could have arisen from intracellular reactions with DDTC, but the displacement of platinum from plasma proteins was more than sufficient to account for the increase in free dach in the circulation. DDTC treatment also decreased plasma concentrations of tetraplatin, PtCl₂(dach), [Pt(H₂O)(Cl)(dach)]⁺, the Pt-methionine complex, and one unidentified biotransformation product, but had no effect on the Pt-cysteine (or Pt-ornithine) complex. These effects of DDTC on protein-bound platinum and low-molecular-weight biotransformation products in plasma may contribute to the decrease in tetraplatin toxicity seen in DDTC-treated rats.     

The role of glutathione conjugate metabolism and cysteine conjugate beta-lyase in the mechanism of S-cysteine conjugate toxicity in LLC-PK1 cells

A cell line derived from pig kidney, LLC-PK1, was grown in a culture system in which the cells express morphological and biochemical characteristics of the proximal tubule. This model was used to investigate the mechanism of S-cysteine conjugate toxicity and the role of glutathione conjugate metabolism. LLC-PK1 cells have the degradative enzymes of the mercapturate pathway, and S-(1,2-dichlorovinyl)-L-cysteine and S-(1,2-dichlorovinyl)-L-glutathione are toxic. S-(1,2-Dichlorovinyl)-L-glutathione is not toxic when the cells are pretreated with AT-125, an inhibitor of gamma-glutamyl transpeptidase. The cells respond to a variety of toxic cysteine conjugates. Cysteine conjugate beta-lyase activity is not detectable by standard assays, but can be measured using radiolabeled S-(1,2-dichlorovinyl)-L-cysteine. Pyruvate stimulates the beta-elimination reaction with S-(1,2-dichlorovinyl)-L-cysteine as substrate 2-3-fold. The data suggest that a side transamination reaction regulates the flux of substrate through the beta-elimination pathway; therefore, cysteine conjugate beta-lyase in LLC-PK1 cells may be regulated by transamination, and measurement of lyase activity in some systems may require the presence of alpha-ketoacids. Aminoxyacetic acid blocks both the metabolism of S-(1,2-dichlorovinyl)-L-cysteine to a reactive species which covalently binds to cellular macromolecules and toxicity. Glutathione inhibits the binding of the sulfur containing cleavage fragment to acid insoluble material in vitro. The data provide direct evidence that S-(1,2-dichlorovinyl)-L-cysteine is metabolized to a reactive species which covalently binds to cellular macromolecules, and the binding is proportional to toxicity.     

The response of adult rat sertoli cells,immortalized by a temperature-sensitive mutant of SV40, to 1,2-dinitrobenzene, 1,3-dinitrobenzene, 2,4-dinitrotoluene, 3,4-dinitrotoluene,and cadmium

In this study we test the hypothesis that immortalized adult rat Sertoli cells respond to known testicular toxins in a similar manner to Sertoli cells tested in vivo and in primary culture. This cell line was developed by immortalizing adult rat Sertoli cells with the temperature-sensitive mutant of SV40, ts255, such that the cells proliferate at the permissive temperature of 33 degrees C but express differentiated characteristics at the nonpermissive temperature of 40 degrees C. Confluent monolayers, grown at 33 degrees C or 40 degrees C, were exposed to a range of concentrations of dinitrobenzene (DNB) or dinitrotoluene (DNT) isomers or to cadmium chloride. Cellular response was assessed by neutral-red cell viability assay and ultrastructural changes. Cells grown at 40 degrees C were sensitive to lower concentrations of each toxicant than were cells grown at 33 degrees C. 1,2-DNB was more toxic than 1,3-DNB, and 3,4-DNT was more toxic than 2,4-DNT, as judged by the neutral-red cell viability assay. Ultrastructurally, cells treated with 1,2-DNB or 2,4-DNT showed increased numbers of autophagic vesicles compared to controls. Intercellular penetration of ruthenium red demonstrated breached tight junctions in 1,2-DNB and cadmium-treated cells. From these observations, we conclude that this cell line can serve as a model for studying toxic mechanisms in adult Sertoli cells.     

Pharmacology and immune modulating properties of 5-androstene-3β,7β,17β-triol, a DHEA metabolite in the human metabolome

Androst-5-ene-3β,7β,17β-triol (βAET) is an anti-inflammatory metabolite of DHEA that is found naturally in humans, but in rodents only after exogenous DHEA administration. Unlike DHEA, C-7-oxidized DHEA metabolites cannot be metabolized into potent androgens or estrogens, and are not peroxisome proliferators in rodents. The objective of our current studies was to characterize the pharmacology of βAET to enable clinical trials in humans. The pharmacology of βAET was characterized by pharmacokinetics, drug metabolism, nuclear hormone receptor interactions, androgenicity, estrogenicity, and systemic toxicity studies. βAET's acute anti-inflammatory activity and immune modulating characteristics were measured in vitro in RAW264.7 cells and in vivo in murine models with parenteral administration. βAET was rapidly metabolized and cleared from circulation in mice and monkeys. βAET was weakly androgenic and estrogenic in immature rodents, but not bound by androgen, estrogen, progesterone, or glucocorticoid nuclear hormone receptors. βAET did not induce peroxisome proliferation, nor was it systemically toxic or trophic for sex hormone responsive tissues in mature rats and monkeys. βAET significantly attenuated acute inflammation both in vitro and in vivo, augmented immune responses in adult mice, and reversed immune senescence in aged mice. βAET may contribute to the anti-inflammatory activity in rodents attributed to DHEA. Unlike DHEA, βAET's anti-inflammatory activity cannot be ascribed to activation of PPARs, androgen, or estrogen nuclear hormone receptors. Exogenous βAET is unlikely to produce untoward toxicity or hormonal perturbations in humans.     

Synthesis of derivatives of C-nucleoside analogues using 'push-pull' functionalized monosaccharides.

7-Deoxy-1,2:3,4-di-O-isopropylidene-alpha-D-galacto-heptopyranos-6-ulose (1) reacted with carbon disulphide and methyl iodide in the presence of a base to furnish 7,8-dideoxy-1,2:3,4-di-O-isopropylidene-8,8-[bis(methylthio)]-alpha-D-galacto-oct-7-enopyranos-6-ulose (2). This 'push-pull' activated unsaturated monosaccharide underwent a ring closure reaction with hydrazine hydrate to give the 'inversed' C-nucleoside analogue 3. Compound 1 and malononitrile yielded the 7-cyano-6,7-dideoxy-1,2:3,4-di-O-isopropylidene-6-methyl-alpha-D-galacto-oct-6-enopyranurononitrile (4). Treatment of 4 with carbon disulphide and methyl iodide in the presence of a base afforded the sugar 'push-pull' butadiene 5 which was transformed into the pyridine nucleoside analogue 6.     

Separation and aquatic toxicity of enantiomers of the organophosphorus insecticide trichloronate

Many of the organophosphorus pesticides (OPs) currently used are chiral and therefore consist of mixture of enantiomers. Despite the fact that the biological processes of chiral pesticides are enantioselective, the acute aquatic toxicity of chiral OPs with respect to enantioselectivity has so far received limited research. In this study, the enantiomeric separation and acute aquatic toxicity of trichloronate were investigated. Baseline enantioseparation of trichloronate was successfully achieved using high-performance liquid chromatography on a Chiralcel OJ column, with a mobile phase of n-hexane/n-heptane/ethanol (90/5/5, v/v/v) at the flow rate of 1.0 ml min(-1) and room temperature. The resolved enantiomers were characterized for their optical rotation and by gas chromatography coupled with mass spectrometry. Significant differences were found between the enantiomers in acute aquatic toxicity to Ceriodaphnia dubia and Daphnia magna. The (-)-trichloronate was 8-11 times more toxic to the test organisms than its (+)-form, while the racemate showed intermediate toxicity. These results suggest that assessment of the environmental safety of chiral OPs should take stereospecificity into consideration.     

Ethanol induction of acetaminophen toxicity and metabolism

Chronic consumption of moderate amounts of ethanol (10% solution in the drinking water) dramatically enhances the toxicity of acetaminophen in CF-1 mice as demonstrated by a significant decrease in the LD₅₀. The increased toxicity appears to result from an acceleration in the microsomal biotransformation of acetaminophen to a reactive intermediate. Accelerated acetaminophen metabolism in ethanol-treated animals, in turn, causes more rapid depletion of glutathione. These studies suggest a mechanism to account for the toxic synergism between chronic alcohol consumption and acute acetaminophen intake.     

From PCBs to highly toxic metabolites by the biphenyl pathway

The degradation of polychlorobiphenyls (PCBs) by diverse bacteria, including Burkholderia sp. LB400, is incomplete with a concomitant accumulation of metabolic intermediates. In this study, the toxicity of diverse (chloro)biphenyls and of their biotransformation into the first two metabolic intermediates of the biphenyl pathway, were determined for the model bacterium Escherichia coli. Recombinant E. coli strains expressing different subsets of bph genes of strain LB400 accumulated metabolic intermediates from (chloro)biphenyls. During biotransformation of these compounds into metabolic intermediates, the viability and metabolic kinetics were determined. The toxicity of biotransformation of (chloro)biphenyls into different metabolic intermediates of (chloro)biphenyls varied. Dihydrodiols and dihydroxybiphenyls are very toxic metabolites for bacteria even after short incubation times, affecting the cell viability much more than (chloro)biphenyls. When bacteria transformed 2-CB into dihydrodiol or dihydroxybiphenyl, a great decrease of intact cells and abundant cell lysis was observed by transmission electronic microscopy. Cell viability of Burkholderia sp. LB400 and of E. coli exposed directly to 2,3-dihydroxybiphenyl decreased also drastically. The toxicity of metabolites generated during oxidation of PCBs may partly explain the recalcitrance to biodegradation of these pollutants. Conversion of less toxic compounds into products with increased toxicity resembles the bioactivation of xenobiotics in higher organisms.     

Liquid chromatographic determination of the glutathione conjugate and ring-opened metabolites formed from coumarin epoxidation

Species differences in the biotransformation of coumarin are thought to play an important role in its toxicity. Since the putative toxic metabolite is coumarin 3,4-epoxide (CE), methods to measure the metabolites of CE were developed. The glutathione (GSH) conjugate of CE (CE-SG) at the 3-position was purified by reversed-phase (RP)-high performance liquid chromatography (HPLC), and characterized by mass spectrometry (MS) and nuclear magnetic resonance spectroscopy (NMR). An RP-HPLC method was developed to quantify CE-SG in hepatic microsomal mixtures and a separate RP-HPLC method was also developed to quantify the three ring-opened coumarin metabolites; o-hydroxyphenylacetic acid (o-HPAA), o-hydroxyphenylethanol (o-HPE) and o-hydroxyphenylacetaldehyde (o-HPA) in hepatic microsomal mixtures. Detection limits for all four products of coumarin epoxidation exceeded 3.5 ng/ml and recovery from hepatic microsomal mixtures was essentially quantitative with RSD values less than 8%. Species differences in o-HPA detoxification were consistent with sensitivity to coumarin, thereby demonstrating that these methods have utility in addressing the fate of CE and its contribution to toxicity.     

Corticosteroid regulation of Na+ and K+ transport in the rat distal colon during postnatal development

To study the role of corticosteroids in the regulation of colonic electrogenic amiloride-sensitive Na+ absorption (ISCNa) and barium-sensitive K+ secretion (ISCK) during development, we investigated suckling (10-day old), weanling (25-day old) and adult (90-day old) adrenalectomized rats after they had received aldosterone, dexamethasone or corticosterone. Adrenalectomy reduced markedly ISCNa in suckling rats and completely inhibited ISCNa in weanling animals; the ISCNa was absent in intact adult rats. The doses of aldosterone, corticosterone and dexamethasone estimated to be equivalent to the endogenous production rate of aldosterone and corticosterone restored ISCNa after 1 day in both suckling and weanling rats. Compared with aldosterone, glucocorticoids produced a greater increase in ISCNa. Concurrent spironolactone treatment (a mineralocorticoid antagonist) completely prevented the effect of aldosterone but had no effect in dexamethasone-treated rats. The glucocorticoid antagonist RU 38 486 inhibited the dexamethasone-induction of ISCNa but had no effect on aldosterone. The response to corticosteroids, measured as the increase of ISCNa, declined from suckling to adult rats. In contrast to ISCNa, the same time of treatment and the same doses of corticosteroids did not influence ISCK. ISCK was stimulated only after chronic treatment (4 days). These findings suggest that, in the distal colon of young rats, (1) both corticosteroids may regulate amiloride-sensitive Na+ absorption and barium-sensitive K+ secretion, (2) different receptors mediate the colonic effects of glucocorticoids and mineralocorticoids, (3) immature rats are more sensitive to corticosteroids than adult animals, and (4) the acute effect of corticosteroids is an increase in Na+ absorption which is followed by delayed stimulation of K+ secretion.     

Hemoglobin and albumin adducts of naphthalene-1,2-oxide, 1,2-naphthoquinone and 1,4-naphthoquinone in Swiss Webster mice

The toxicity of naphthalene in rodents has been attributed to the reactive metabolites naphthalene-1,2-oxide (NPO), 1,2-naphthoquinone (1,2-NPQ) and 1,4-naphthoquinone (1,4-NPQ). Differences in the formation of these reactive metabolites in different species can shed light on the mechanism by which naphthalene exerts its toxicity. Protein adducts allow investigators to study the disposition of reactive metabolites that cannot be measured directly. We measured cysteinyl adducts of the above metabolites in hemoglobin (Hb) and albumin (Alb) from the blood of male Swiss Webster mice dosed with 1.56-200mg naphthalene/kg b.w. Levels of NPO adducts (designated as NPO1-Hb, NPO2-Hb, NPO1-Alb and NPO2-Alb) increased nonlinearly with the administered dose; levels of Alb adducts were higher than those of Hb adducts; levels of NPO1 adducts were higher than those of NPO2 adducts. Levels of NPQ adducts (1,2-NPQ-Alb, 1,4-NPQ-Alb, 1,2-NPQ-Hb and 1,4-NPQ-Hb) were lower than those of NPO. Although NPQ-Alb increased with doses above 12.5 mg naphthalene/kg body wt. (b.w.), levels of NPQ-Hb barely increased above the background levels within the dose range examined. The shapes of the dose response curves for total cysteinyl adducts (combined NPO and NPQ) in Hb and Alb were consistent with previous results of radiobinding experiments in naphthalene-dosed mice. Dose-specific levels of NPO-Alb remained essentially constant in mice over the dose range of 25-200 mg/kg b.w. while those of 1,2- and 1,4-NPQ-Alb diminished over this range. Comparing dose-specific levels of NPO-Alb in Swiss Webster mice with those published previously in F344 rats suggests that glutathione depletion in mice occurred at about 1/8th the administered dose previously observed in rats. This suggests that mice could be more susceptible than rats to the toxic effects of naphthalene due to more pronounced depletion of glutathione at a given dose.     

Age-dependent effects on redox status, oxidative stress, mitochondrial activity and toxicity induced by fluoroquinolones on primary cultures of rabbit tendon cells

The age-related difference in fluoroquinolone-induced tendon toxicity was investigated. In vitro tendon cells from juvenile and young adult rabbits, respectively, were incubated with quinolone (nalidixic acid, NA) or fluoroquinolone (ofloxacin, OFX or pefloxacin, PEF) at 0.01 microM to 1 mM for 72 h. Redox status, glutathione (GSH), reactive oxygen species (ROS), and mitochondrial activity were assessed using intracellular fluorescent probes. Fluorescence signal was detected on living adherent tenocytes in microplates using cold-light cytofluorometry. Tendon toxicity differed significantly between the two cell groups and the difference was greatest with highest dose (1 mM). For 72 h, significant (p < 0.001) differences between immature and young adult primary tenocytes were observed for redox status decrease, GSH decrease, and ROS production increase. Mitochondrial activity remained unaltered in immature tenocytes. We confirm two groups of intrinsic tendon toxicity (OFX/NA vs. PEF) associated to oxidative stress (GSH decrease). Our in vitro experimental model confirms the clinical observations of age dependent tenotoxicity. First group (NA, OFX) showed greater intrinsic tenotoxicity for young adult than immature tenocytes, second group (PEF) was highly toxic for immature and young adult cells. The three quinolones do not altered mitochondrial activity in immature tenocytes whereas alteration was observed in young adult tenocytes.     

A review of the genetic and related effects of 1,3-butadiene in rodents and humans

In this paper, the metabolism and genetic toxicity of 1,3-butadiene (BD) and its oxidative metabolites in humans and rodents is reviewed with attention to newer data that have been published since the latest evaluation of BD by the International Agency for Research on Cancer (IARC). The oxidative metabolism of BD in mice, rats and humans is compared with emphasis on the major pathways leading to the reactive intermediates 1,2-epoxy-3-butene (EB), 1,2:3, 4-diepoxybutane (DEB), and 3,4-epoxy-1,2-butanediol (EBdiol). Results from recent studies of DNA and hemoglobin adducts indicate that EBdiol may play a more significant role in the toxicity of BD than previously thought. All three metabolites are capable of reacting with macromolecules, such as DNA and hemoglobin, and have been shown to induce a variety of genotoxic effects in mice and rats as well as in human cells in vitro. DEB is clearly the most potent of these genotoxins followed by EB, which in turn is more potent than EBdiol. Studies of mutations in lacI and lacZ mice and of the Hprt mutational spectrum in rodents and humans show that mutations at G:C base pairs are critical events in the mutagenicity of BD. In-depth analyses of the mutational spectra induced by BD and/or its oxidative metabolites should help to clarify which metabolite(s) are associated with specific mutations in each animal species and which mutational events contribute to BD-induced carcinogenicity. While the quantitative relationship between exposure to BD, its genotoxicity, and the induction of cancer in occupationally exposed humans remains to be fully established, there is sufficient data currently available to demonstrate that 1,3-butadiene is a probable human carcinogen.     

Calcium Dependency and Tetrodotoxin Sensitivity of Neostriatal Dopamine Release in 5-Day-Old and Adult Rats as Measured by In Vivo Microdialysis

Abstract: The calcium dependency and tetrodotoxin sensitivity of extracellular dopamine levels were assessed by microdialysis in the neostriatum of 5-day-old rat pups and were compared with those obtained in adult rats. The removal of calcium from the dialysate reduced spontaneous levels of extracellular dopamine to 20% of normal in the 5-day-old pups and to 10% of normal in the adults. Calcium-free dialysate also decreased potassium-evoked dopamine release to ～20% of baseline in both ages. Furthermore, the addition of tetrodotoxin to the dialysate decreased spontaneous levels of extracellular dopamine to 10% of baseline in both ages. The effects of calcium removal and the addition of tetrodotoxin on extracellular levels of the dopamine metabolite 3,4-dihydroxyphenylacetic acid were less pronounced. The results of this study demonstrate that extracellular levels of dopamine sampled by microdialysis in rats as young as 5 days of age are both calcium dependent and tetrodotoxin sensitive; thus, they are derived from neuronal activity and not from injury caused by acute implantation of the probe. Other age-related differences support the hypothesis that dopamine release and turnover is greater In immature rats and may represent a form of compensation for incomplete dopamine nerve terminal ingrowth.     

The effects of acute ethanol exposure and ageing on rat brain glutathione metabolism

Abstract

Binge alcohol consumption in adolescents is increasing, and it has been proposed that immature brain deals poorly with oxidative stress. The aim of our work was to study the effect of an acute dose of ethanol on glutathione (GSH) metabolism in frontal cortex, hippocampus and striatum of juvenile and adult rats. We have observed no change in levels of glutathione produced by acute alcohol in the three brain areas studied of juvenile and adult rats. Only in the frontal cortex the ratio of GSH/GSSG was increased in the ethanol-treated adult rats. GSH levels in the hippocampus and striatum were significantly higher in adult animals compared to young ones. Higher glutathione peroxidase (GPx) activity in adult rats was observed in frontal cortex and in striatum. Our data show an increased GSH concentration and GPx activity in different cerebral regions of the adult rat, compared to the young ones, suggesting that age-related variations of total antioxidant defences in brain may predispose young brain structures to ethanol-induced, oxidative stress-mediated tissue damage.     

Lead and Cadmium Co-exposure Mediated Toxic Insults on Hepatic Steroid Metabolism and Antioxidant System of Adult Male Rats

The redox status and steroid metabolism of liver of adult male rat exposed to lead (Pb) and cadmium (Cd) either alone or in co-exposure (0.025 mg/kg body weight intraperitoneally/15 days) was studied. Pb and Cd significantly accumulated in the liver. The activity of steroid metabolizing enzymes 17-βhydroxysteroid oxidoreductase and uridine diphosphate–glucuronyltransferase were decreased in experimental animals. 17-β-Hydroxysteroid dehydrogenase was reduced to 33%, 38%, and 24% on treatment of Pb, Cd, and co-exposure (Pb + Cd). Furthermore, the activity of uridine diphosphate–glucuronosyltransferase was significantly reduced to 27% (Pb exposure), 36% (Cd exposure), and 25% (co-exposure of Pb + Cd). Cd exposure exhibited more toxic effect than Pb, while co-exposure demonstrated the least. The activities of antioxidant enzymes, superoxide dismutase, catalase, glutathione reductase, and glucose-6-phosphate dehydrogenase decreased and glutathione peroxidase increased in mitochondrial and post-mitochondrial fractions. The level of lipid peroxidation increased, and cellular glutathione concentration decreased. Hepatic DNA was decreased, whereas RNA content and the activity of alanine transaminase remained unchanged. Histological studies revealed that only Cd-exposed groups exhibited cytotoxic effect. These results suggest that when Pb and Cd are present together in similar concentrations, they exhibited relatively decreased toxic effect when compared to lead and cadmium in isolation with regard to decreased steroid metabolizing and antioxidant enzyme activities. This seems that the toxic effect of these metals is antagonized by co-exposure due to possible competition amongst Pb and Cd for hepatic accumulation.     

The effects of acute ethanol exposure and ageing on rat brain glutathione metabolism

Binge alcohol consumption in adolescents is increasing, and it has been proposed that immature brain deals poorly with oxidative stress. The aim of our work was to study the effect of an acute dose of ethanol on glutathione (GSH) metabolism in frontal cortex, hippocampus and striatum of juvenile and adult rats. We have observed no change in levels of glutathione produced by acute alcohol in the three brain areas studied of juvenile and adult rats. Only in the frontal cortex the ratio of GSH/GSSG was increased in the ethanol-treated adult rats. GSH levels in the hippocampus and striatum were significantly higher in adult animals compared to young ones. Higher glutathione peroxidase (GPx) activity in adult rats was observed in frontal cortex and in striatum. Our data show an increased GSH concentration and GPx activity in different cerebral regions of the adult rat, compared to the young ones, suggesting that age-related variations of total antioxidant defences in brain may predispose young brain structures to ethanol-induced, oxidative stress-mediated tissue damage.