Drug-induced lipid peroxidation in mice—I Modulation by monooxegenase activity,glutathione and selenium status

Feeding male mice for 2 days with sucrose leads to a decrease of total liver glutathione by more than 50 per cent when compared to controls. Such animals were intoxicated with 300 mg/kg paracetamol and upon administration of inducers of the drug-metabolizing system, in vivo and vitro lipid peroxidation in these animals was largely increased as well as the susceptibility to the drug. Pretreatment of the mice with methylcholanthrene led to a 28-fold, with benzo(α)pyrene to a 22-fold, and with phenobarbital to a tenfold increase in ethane exhalation. In vivo administration of various monooxygenase inhibitors showed that all agents effectively inhibit paracetamol-induced lipid peroxidation. It is concluded that phase I metabolism of paracetamol is a prerequisite for the manifestation of drug-induced lipid peroxidation.Selenium deficiency in mice neither affected hepatic levels of glutathione nor its decrease following sucrose feeding, nor glutathione transferase, superoxide dismutase, catalase and glutathione reductase activity. Selenium-dependent glutathione peroxidase activity of selenium-deficient mice, reactive with H₂O₂ as well as with t-butylhydroperoxide, decreased to 5 per cent of the supplemented controls. A glutathione peroxidase activity, which utilized cumenehydroperoxide as a substrate but insensitive to selenium deficiency, was found. Selenium-deficient diethylmaleate-pretreated animals were much more susceptible to paracetamol-induced lipid peroxidation than controls. Supplemented diethylmaleate-pretreated animals showed no signs of lipid peroxidation if treated with 100 mg/kg aminopyrine or ethylmorphine. However, deficient animals exhibited high ethane exhalation rates, drastically increased serum transaminases, loss of hepatic glutathione and mortality upon administration of these drugs. Qualitatively similar results with lower ethane exhalation rates were observed when 125 mg/kg furosemide was administered to diethylmaleate-pretreated selenium-deficient or -adequate mice. Even administration of 200 mg/kg ethoxycoumarin in combination with diethylmaleate lead to significant lipid peroxidation in phenobarbital-induced mice.The results demonstrate that in vivo selenium-dependent glutathione peroxidase plays a predominant role within the glutathione redox couple system. The enzyme protects the liver from peroxidative damage evoked by phase I metabolism of various drug types, as long as sufficient glutathione is available. It is suggested that activated oxygen released from the microsomal monooxygenase is the species responsible for the observed lipid peroxidation accompanied by severe acute liver lesions.     

Sex differences in biochemical manifestations of selenium deficiency in rat liver with special reference to heme metabolism

In addition to its well-known effect on glutathione peroxidase, selenium deficiency causes: (1) a defect in hepatic heme metabolism characterized by a phenobarbital-mediated increase in microsomal heme oxygenase activity, and (2) an increase in hepatic glutathione S-transferase activity. Since these effects were reported in selenium-deficient male rats, and since female rats have a lower selenium requirement than males, we examined whether these effects were sex-dependent. Weanling male rats, female rats, castrated male rats, and testosterone-treated female rats were fed either a selenium-deficient or a control diet. After 8 weeks, selenium-dependent hepatic glutathione peroxidase activity was 1 per cent of respective control values in each of the selenium-deficient groups. Hepatic glutathione,S-transferase activity was doubled by selenium deficiency in normal, unoperated males but was unaffected in the other groups. In control diet fed rats phenobarbital given as a single injection caused either no significant change or a decrease in the activity of hepatic microsomal heme oxygenase, the rate-limiting enzyme in heme degradation. In contrast, microsomal heme oxygenase activity was stimulated by phenobarbital in all selenium-deficient rats. The stimulation was greatest in males and least in females with intermediate values in castrated males and testosterone-treated females. These results demonstrate a marked effect of sex, castration of males, and testosterone treatment of females on the response of hepatic heme metabolism to phenobarbital and on glutathione S-transferase activity in selenium deficiency even though glutathione peroxidase was reduced to the same extent by selenium deficiency in all groups.     

Modification of Chemical Toxicity by Selenium Deficiency

Modification of Chemical Toxicity by Selenium Deficiency. Burk,R.F. and Lane, J.M. (1983). Fundam. Appl. Toxicol. 3: 218–221.Selenium deficiency causes a number of hepatic metabolic alterationsin the rat which could lead to changes in chemical toxicity.It causes a decrease in glutathione peroxidase activity, anincrease in glutathione S-transferase activity, and an increasein the rate of glutathione synthesis. The hepatotoxicities ofthree compounds which bind to glutathione S-transferase; iodipamide,acetaminophen, and aflatoxin B₁, are decreased by selenium deficiency.The toxicity of redox cycling compounds is generally increasedby selenium deficiency and is accompanied by evidence of lipidperoxidation. Thus, nitrofurantoin (100 mg/kg) causes renaltubular necrosis in selenium-deficient rats but not in controls.Selenium-deficient rats are much more sensitive to diquat toxicitythan are controls. Lethality of diquat in selenium-deficientrats appears to be causally linked to lipid peroxidation. Lethalityof diquat in control rats is not linked to lipid peroxidation.The effect of selenium does not appear to be mediated by glutathioneperoxidase, however, indicating that selenium has another oxidantdefense function. Another interesting observation made was thatincreases in inspired O₂ tension decreased ethane production(lipid peroxidation) in selenium-deficient and in control ratsgiven diquat. Thus, O₂ appears to prevent diquat-induced lipidperoxidation.     

Maternal selenium deficiency enhances the fetolethal toxicity of methyl mercury

The effect of maternal selenium deficiency on methyl mercury fetotoxicity was examined in the ICR strain of mice. Pregnant mice were fed either selenium-deficient diets based on torula yeast or selenium-supplemented diets which were identical to the former except that 0.1, 0.2, or 0.4 mg of selenium per kilogram of diet was added as sodium selenite. Fetolethality of methyl mercury was exacerbated by maternal selenium deficiency when mothers were administered sc 15, 25, or 35 mumol/kg/day of methylmercuric chloride (MMC) on the 13, 14, and 15th days of pregnancy. One-tenth part per million of selenium in the diet was sufficient to protect the fetuses against MMC fetolethality when dams were administered 25 mumol/kg/day of MMC. Mercury concentrations in maternal and fetal tissues were independent of the dietary selenium level. Selenium concentration and glutathione peroxidase (GSH-Px) activity in maternal tissues were unaffected by MMC administration. In fetal liver, on the other hand, selenium concentration was increased and GSH-Px activity was decreased concurrently by maternal MMC administration in the selenium-supplemented groups. Therefore, as far as GSH-Px activity was concerned, the bioavailability of selenium was markedly decreased in fetal liver by maternal injection of MMC. The increase in selenium content in fetal liver, which was observed only in the selenium-supplemented groups, may play an important role in protection against fetolethal toxicity of MMC.     

Fenvalerate induced hepatic oxidative stress in selenium- and/or iodine-deficient rats

Considering the potential adverse effects of selenium and iodine deficiencies, and frequency of intensive but improper use of insecticides, this study was designed to evaluate the effects of a pyrethroid insecticide, fenvalerate, on the oxidant/antioxidant status of liver using a rat model of iodine and/or selenium deficiency. The study was conducted on eight groups of 3-week old Wistar rats. Iodine and/or selenium deficiency was introduced by feeding the animals with a diet containing <0.005 mg selenium/kg and/or supplying with 1% sodium perchlorate containing drinking water for a period of 7 weeks. Fenvalerate exposure (100 mg/kg/d, i.p., for the last 7 days) in normal rats increased hepatic glutathione peroxidase activity and lipid peroxidation, decreased glutathione content, but did not change the activities of catalase or any of the superoxide dismutase forms; in iodine-deficient animals caused only the elevation of lipid peroxidation; in selenium-deficient animals and in combined iodine/selenium deficiency decreased glutathione peroxidase, increased catalase activities and lipid peroxidation, and decreased all the forms of superoxide dismutase activity only in combined deficiency. These results suggested that fenvalerate is an oxidant stress inducer in rat liver, and its potential effects on pro-oxidant/antioxidant balance may also be important for human populations, particularly with iodine and/or selenium deficiencies.     

Selenium in water enhances antioxidant defenses and protects against copper-induced DNA damage in the blue mussel Mytilus edulis

Selenium and copper are naturally occurring elements in the environment that have important roles in cellular function. Selenium is known for its role in antioxidant defense, whereas copper is a redox-active metal capable of acting as a pro-oxidant. We investigated the effects of short term selenium (Na₂SeO₃) supplementation (4 μg/L for 3 days) on antioxidant parameters of the blue mussel, Mytilus edulis, and its possible protective effects against a subsequent copper (CuSO₄) exposure (56 μg/L for 3 days). Selenium supplementation caused a 4-fold increase in glutathione levels in gills. The activity of selenium-dependent glutathione peroxidase was modulated by selenium in gills (2-fold increase) and also in cell-free haemolymph (40% increase). Copper exposure produced decreases in protein thiol levels (35%) and in thioredoxin reductase activity (60%) in gills and induced an increase in DNA damage in haemocytes (70% increase in % tail DNA observed using the comet assay). The decrease in thioredoxin reductase activity may constitute a mechanism of copper toxicity in bivalves, warranting further investigation. Pre-treatment with selenium largely prevented these deleterious effects of copper on protein thiols, thioredoxin reductase activity and DNA damage. The results suggest that induction of key antioxidant defenses such as glutathione and selenium-dependent glutathione peroxidase, as a result of selenium supplementation, may play an important role in protection of aquatic organisms against oxidative stress.     

Ethane production and liver necrosis in rats after administration of drugs and other chemicals

Lipid peroxidation and liver necrosis due to a number of drugs and chemicals were studied. The agents were administered to control, vitamin E-deficient, and selenium-deficient rats. Vitamin E deficiency was documented by a low serum tocopherol level (0.34 mg/100 ml) and selenium deficiency by a specific activity of the selenoenzyme glutathione peroxidase in 105,000g liver supernatant which was approximately 1% of the control value. Glutathione S-transferase specific activity, measured with 1-chloro-2,4-dinitrobenzene as substrate, was doubled by selenium deficiency. Ethane production was measured as the index of in vivo lipid peroxidation. Hepatic necrosis was assessed histologically and by measuring serum glutamic-pyruvic transaminase. When no agents were administered, vitamin E-deficient rats produced more ethane than did control or selenium-deficient rats. Phenobarbital did not cause an increase in ethane production. CCl₄ (60 μl/100 g) and BrCCl₃ (5 μl/100 g) caused large ethane production and moderately severe liver necrosis. The vitamin E-deficient and selenium-deficient groups given BrCCl₃ produced more ethane than the controls but had no more severe hepatic necrosis than the controls. Thioacetamide (5 mmol/kg) and acetaminophen (3 g/kg) caused moderate to severe liver necrosis but only small ethane production. Vitamin E deficiency potentiated acetaminophen hepatotoxicity and selenium deficiency inhibited it. Iodipamide (1.5 mmol/kg) caused very large ethane production and death within hours in vitamin E-deficient rats. At a dose of 2 mmol/kg it caused severe liver necrosis in control rats but only small ethane production. This dose caused no liver necrosis in selenium-deficient rats. Acetylhydrazine (30 mg/kg) caused moderate ethane production in all groups but no liver necrosis. A single dose of ethanol (0.68 ml/100 g) led to small production of ethane in all groups. This study shows that many agents are capable of causing in vivo lipid peroxidation, but that lipid peroxidation does not always correlate with liver necrosis. Selenium deficiency is not a simple glutathione peroxidase deficiency state, as hepatic glutathione S-transferase is increased by it and it protects against acetaminophen and iodipamide hepatotoxicity.     

Time-course of changes in hepatic lipid peroxidation and glutathione metabolism in rats with carbon tetrachloride-induced cirrhosis

1. The aims of the present study were to assess: (i) the temporal relationships between hepatic lipid peroxidation, changes in the glutathione detoxification system and the onset/development of cirrhosis in CCl4-treated rats; and (ii) the effects of oral zinc administration on these parameters. 2. Cirrhosis was induced in 120 rats by intraperitoneal injections of CCl4 twice a week over 9 weeks. One hundred and twenty additional animals were used as controls. Both groups were further subdivided to receive either a standard diet or one supplemented with zinc. Subsets of 10 animals each were killed at weeks 1, 2, 3, 5, 7 and 9 from the start of the study. 3. Induction of cirrhosis produced a decrease in the components of the hepatic glutathione anti-oxidant system: glutathione transferase activity decreased from week 1, the concentration of reduced glutathione (GSH) decreased from week 5 and glutathione peroxidase (GPx) activity decreased from week 7. This impairment was chronologically related to an increase in free radical generation. Hepatic lipid peroxidation was significantly correlated with GPx activity (r = -0.47; P < 0.001) in CCl4-treated rats. Zinc administration did not produce any significant improvement of the hepatic glutathione system. 4. In conclusion, cirrhosis induction in rats by CCl4 administration produced a decrease in the hepatic glutathione antioxidant system that was related to an increase in free radical production. Furthermore, zinc supplementation produced a reduction in the degree of hepatic injury and a normalization of lipid peroxidation, but not an improvement of the hepatic GSH anti-oxidant system.     

Dietary selenium and aniline-induced methemoglobinemia in rats

Depletion of selenium from rats for 8 weeks decreased blood glutathione peroxidase activity to 5.7% of that in selenium-supplemented (0.5 ppm selenium as Na2SeO3) rats. Aniline (60 mg/kg, i.p.) resulted in no significant difference in methemoglobin and blood reduced glutathione (GSH) levels between Se-deficient and Se-supplemented rats. A lowered aniline dose (36 mg/kg, i.p.) also resulted in no difference in methemoglobin levels. The selenium-deficient rat was able to reduce methemoglobin induced by aniline as efficiently as the selenium-sufficient rat.     

Differential changes of glutathione S-transferase activity by dietary selenium

Dietary selenium deficiency produced increased activity of the glutathione S-transferases in the liver, kidney and duodenal mucosa. In these tissues, the residual activity of total glutathione peroxidase that included selenium-independent activity was considerably higher than that of selenium-dependent glutathione peroxidase. The enhanced activity of glutathione S-transferases was restored to control level 48 hr after an injection of selenite equivalent to the amount of daily selenium intake. Under the same conditions, selenium-dependent glutathione peroxidase activity increased with time and reached 11.9, 11.6 and 46.2% of the activity in the liver, kidney and duodenal mucosa of selenium-supplemented rats, respectively, 48 hr after selenite injection, whereas total glutathione peroxidase activity was not altered except in the kidney. These differential changes of glutathione S-transferase activity were intimately related to those of selenium-dependent glutathione peroxidase activity produced by selenium depletion and repletion, suggesting that the glutathione S-transferase activity was regulated by dietary selenium. Present findings support the idea that glutathione S-transferases having selenium-independent glutathione peroxidase activity function as a substitute for selenium-dependent glutathione peroxidase in selenium-deficient rats.     

Testing the hypothesis that selenium deficiency is a risk factor for clozapine-induced agranulocytosis in rats

Clozapine is an effective atypical antipsychotic associated with a relatively high incidence of drug-induced agranulocytosis. It forms a reactive nitrenium ion metabolite upon oxidation by peripheral neutrophils and their precursors in the bone marrow. Although the mechanism of this idiosyncratic drug reaction is still unknown, the observation that it does not occur rapidly on rechallenge of patients with a history of clozapine-induced agranulocytosis suggests that it is not immune-mediated. Previous studies by other research groups had found that patients on clozapine had lower plasma and red blood cell levels of selenium. The reactive metabolite of clozapine reacts with glutathione, and therefore, it is likely that it also binds to selenocysteine-containing proteins, such as glutathione peroxidase, thioredoxin reductase, and protein disulfide isomerase. We set out to test the hypothesis that clozapine-induced agranulocytosis is associated with selenium deficiency with rats on a selenium-deficient diet. We studied the effects of clozapine on selenium levels and the effect of selenium deficiency on leukocyte and neutrophil counts and clozapine covalent binding. We did not observe any significant difference between clozapine-treated rats given a selenium-adequate or deficient diet. Therefore, it is unlikely that selenium deficiency is a major risk factor for clozapine-induced agranulocytosis.     

Decreased Erythrocyte Glutathione Peroxidase Activity in Neuronal Ceroid Lipofuscinosis (NCL) - Corrected with Selenium Supplementation

Abstract A decreased glutathione peroxidase (GPX) activity was demonstrated in erythrocytes from 12 patients with neuronal ceroid lipofuscinosis (NCL). The enzyme activity was corrected to normal levels by selenium (Se) supplementation.     

Role of CYP2E1 in thioacetamide-induced mouse hepatotoxicity

Previous experiments showed that treatment of mice and rats with thioacetamide (TAA) induced liver cell damage, fibrosis and/or cirrhosis, associated with increased oxidative stress and activation of hepatic stellate cells. Some experiments suggest that CYP2E1 may be involved in the metabolic activation of TAA. However, there is no direct evidence on the role of CYP2E1 in TAA-mediated hepatotoxicity. To clarify this, TAA-induced hepatotoxicity was investigated using Cyp2e1-null mice. Male wild-type and Cyp2e1-null mice were treated with TAA (200 mg/kg of body weight, single, i.p.) at 6 weeks of age, and hepatotoxicity examined 24 and 48 h after TAA treatment. Relative liver weights of Cyp2e1-null mice were significantly different at 24 h compared to wild-type mice (p<0.01). Serum levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP) and lactate dehydrogenase (LDH) in Cyp2e1-null mice were significantly different at both time points compared to wild-type mice (p<0.01). Histopathological examination showed Cyp2e1-null mice represented no hepatototoxic lesions, in clear contrast to severe centriobular necrosis, inflammation and hemorrhage at both time points in wild-type mice. Marked lipid peroxidation was also only limited to wild-type mice (p<0.01). Similarly, TNF-alpha, IL-6 and glutathione peroxidase mRNA expression in Cyp2e1-null mice did not significantly differ from the control levels, contrasting with the marked alteration in wild-type mice (p<0.01). Western blot analysis further revealed no increase in iNOS expression in Cyp2e1-null mice. These results reveal that CYP2E1 mediates TAA-induced hepatotoxicity in wild-type mice as a result of increased oxidative stress.     

Selenium-based pharmacological agents: an update

The biochemistry and pharmacology of selenium is a subject of intense current interest, particularly from the viewpoint of public health. Selenium, long recognised as a dietary antioxidant, is now known to be an essential component of the active sites of several enzymes, including glutathione peroxidase and thioredoxin reductase, which catalyse reactions essential to the protection of cellular components against oxidative and free radical damage. A low concentration of selenium in plasma has been identified as a risk factor for several diseases, including cancer, cardiovascular disease, osteoarthritis and AIDS, and several large-scale selenium supplementation human trials are now underway. Evidence is emerging that, at least in the case of cancer, the antitumorigenic effect of selenium supplementation arises at least in part from enhanced production of specific selenium-containing metabolites, not just from maximal expression of selenoenzymes. Therefore a number of novel pharmaceutical agents which are selenium-based or which target specific aspects of selenium metabolism are under development. Among these are orally-active antihypertensive agents, anticancer, antiviral, immunosuppressive and antimicrobial agents, and organoselenium compounds which reduce oxidative tissue damage and edema. It can be anticipated that as our understanding of the basic biology and biochemistry of selenium increases, the coming years will bring further development of new selenium-based pharmaceutical agents with therapeutic potential toward a variety of human diseases.     

The role of thioredoxin reductase activity in selenium-induced cytotoxicity

The selenoprotein thioredoxin reductase is a key enzyme in selenium metabolism, reducing selenium compounds and thereby providing selenide to synthesis of all selenoproteins. We evaluated the importance of active TrxR1 in selenium-induced cytotoxicity using transfected TrxR1 over-expressing stable Human Embryo Kidney (HEK-293) cells and modulation of activity by pretreatment with low concentration of selenite. Treatment with sodium selenite induced cytotoxity in a dose-dependent manner in both TrxR1 over-expressing and control cells. However, TrxR1 over-expressing cells, which were preincubated for 72h with 0.1 microM selenite, were significantly more resistant to selenite cytotoxicity than control cells. To demonstrate the early effects of selenite on behaviour of HEK-293 cells, we also investigated the influence of this compound on cell motility. We observed inhibition of cell motility by 50 microM selenite immediately after administration. Moreover, TrxR1 over-expressing cells preincubated with a low concentration of selenite were more resistant to the inhibitory effect of 50 microM selenite than those not preincubated. It was also observed that the TrxR over-expressing cells showed higher TrxR1 activity than control cells and the preincubation of over-expressing cells with 0.1 microM selenite induced further significant increase in the activity of TrxR1. On the other hand, we demonstrated that TrxR1 over-expressing cells showed decreased glutathione peroxidase activity compared to control cells. These data strongly suggest that TrxR1 may be a crucial enzyme responsible for cell resistance against selenium cytotoxicity.     

Selenite-induced apoptosis in doxorubicin-resistant cells and effects on the thioredoxin system

Selenium treatment of the doxorubicin-resistant cell line, U-1285dox, derived from human small cell carcinoma of the lung, resulted in massive apoptosis. This effect appeared maximal at 2 days after addition of selenite. The apoptosis was caspase-3 independent as revealed by Western blot analysis, activity measurement and by using caspase inhibitors. Induction of apoptosis was significantly more pronounced and occurred after addition of lower concentrations of selenite in the doxorubicin-resistant cells compared to the parental doxorubicin-sensitive cells. High levels of selenite caused necrosis in the doxorubicin-sensitive cells. Analysis of enzymatic activity (insulin reduction) of thioredoxin reductase (TrxR) and TrxR protein concentration, measured by ELISA, revealed increasing activity and protein levels after treatment with increasing concentrations of selenium. Maximum relative increase was induced up to 1 μM in both sublines and at this selenium level the concentrations of TrxR measured as insulin reducing activity or ELISA immunoreactivity were nearly identical. Increasing concentrations of selenite up to 10 μM resulted in increased activity and concentration of TrxR in the sensitive subline but decreasing levels in the resistant subline. The level of truncated Trx (tTrx) was higher in the resistant U-1285dox cells but the level did not change with increasing selenite concentrations. Our results demonstrate pronounced selective selenium-mediated apoptosis in therapy-resistant cells and suggest that redox regulation through the thioredoxin system is an important target for cancer therapy.     

Lung permeability, antioxidant status, and NO2 inhalation: a selenium supplementation study in rats

Little is known about antioxidant status, selenium status in particular, and lung response to NO2, which acts as a proinflammatory air pollutant. The effects of a low selenium diet (1.3 microg Se/d) with or without selenium supplementation were therefore studied in 128 Wistar rats, 2 mo old, male exposed to either acute (50 ppm, 30 min), intermittent subacute (5 ppm, 6 h/d, 5 d), intermittent long-term NO2 (1 ppm, 10 ppm, 6 h/d, 5 d/wk, 28 d), or normal atmospheric air (controls). Following sacrifice, measurements of lipid peroxidation (thiobarbituric acid-reactive substances, chemiluminescence), antioxidative protective enzymes (glutathione peroxidase [GPx], superoxide dismutase [SOD], glutathione S-transferase [GST], ceruloplasmin), lung damage (lactate dehydrogenase, alkaline and acid phosphatases), lung permeability (total protein, albumin), and inflammation (cell populations), along with the determination of new biomarkers such as CC16 (Clara-cell protein), were performed in serum and bronchoalveolar lavage fluid (BALF). While selenium-supplemented animals had increased GPx activity in serum prior to inhalation experiments, they also had decreased BALF CC16, blood SOD, and GST levels. Nevertheless, the protective role of normal selenium status with respect to NO2 lung toxicity was evident both for long-term and acute exposures, as the increase in BALF total proteins and corresponding decrease in serum (indicating increased lung permeability) was significantly more pronounced in selenium-deficient animals. During the various inhalation experiments, serum CC16 demonstrated its key role as an early marker of increased lung permeability. These findings corroborate the important role of selenium status in NO2 oxidative damage modulation, but also indicate, in view of its negative impact on CC16, a natural anti-inflammatory and immunosuppressor, that caution should be used prior to advocating selenium supplementation.     

云芝多糖对小鼠心、肝、脾、肾和红细胞抗氧化能力的影响

通过测定小鼠心、肝、脾、肾组织和红细胞脂质过氧化物含量和硒谷胱甘肽过氧化物酶活性，观察了云芝多糖对机体各组织及红细胞抗氧化能力的影响。结果表明，云芝多糖能提高机体各组织的硒谷胱甘肽过氧化物酶活性及降低脂质过氧化物含量，提示云芝多糖能有效地提高机体抗氧化能力，为防止或减轻脂质过氧化损伤提供了实验依据。     

硒对硫唑嘌呤引起小鼠肝损伤的保护作用

小鼠灌胃给予Aza 10mg·kg~(-1)·d~(-1)及合用Selmg·kg~(-1)·d~(-1),连续用药1wk和2wk时观察血浆ALT,全血GSH,肝组织匀浆中MDA含量和GSH-Px活力变化.结果1wk和2wk时Aza组小鼠ALT、MDA均明显高于正常对照组,GSH、GSH-Px则明显低于对照组;加Se组则与之相反,ALT、MDA均降到正常,GSH、GSH-Px也明显升高,接近正常.光镜下见Aza组肝细胞明显变性坏死,加Se组则损害很轻微,接近正常.表明Se对Aza的肝损伤有保护作用.     

Protective effects of selenium on acetaminophen-induced hepatotoxicity in the rat

Experiments were undertaken to examine the ability of selenium to protect against acetaminophen-induced hepatotoxicity and to examine possible mechanisms for this protective effect. Pretreatment of male, Sprague-Dawley rats with sodium selenite (12.5 mumol Se/kg, ip) 24 hr prior to acetaminophen administration produced a significant protection against the hepatotoxic effects of acetaminophen as assessed by a decrease in the plasma appearance of alanine aminotransferase and aspartate aminotransferase activities following acetaminophen. This was accompanied by an increase in the hepatic glutathione levels in selenium-treated animals and an inhibition in the decrease in hepatic glutathione content observed in animals receiving hepatotoxic doses of acetaminophen. Selenium pretreatment decreased the in vivo covalent binding of acetaminophen metabolites to hepatic protein, but did not alter hepatic microsomal cytochrome P-450 content or NADPH cytochrome c reductase activity, suggesting that selenium does not significantly alter the metabolism of acetaminophen to reactive electrophilic metabolites by the cytochrome P-450-dependent mixed-function oxidase enzyme system. Selenium produced an increase in the activity of gamma-glutamylcysteine synthetase which may account for the increased glutathione availability in selenium-treated animals and increased the activities of glutathione S-transferase and glucose-6-phosphate dehydrogenase. Examination of the urinary metabolite profile in selenium-treated animals revealed that the urinary excretion of acetaminophen and its metabolites was significantly increased over a 72-hr period. The increase occurred in the AAP-glucuronide metabolite while parent AAP and AAP-sulfate were actually decreased in selenium-treated rats. No change in recovery was observed in the AAP-glutathione or AAP-mercapturate urinary metabolites. While the glutathione conjugating system is enhanced by selenium treatment, amelioration of acetaminophen toxicity is most likely the result of enhanced glucuronidation which effectively diverts the amount of acetaminophen to be converted by the cytochrome P-450 system to the toxic metabolite.