Enhancement of Lindane-induced Liver Oxidative Stress and Hepatotoxicity by Thyroid Hormone is Reduced by Gadolinium Chloride

The role of Kupffer cells in the hepatocellular injury and oxidative stress induced by lindane (20 mg/kg; 24 h) in hyperthyroid rats (daily doses of 0.1 mg l -3,3',5-triiodothyronine (T 3 )/kg for three consecutive days) was assessed by the simultaneous administration of gadolinium chloride (GdCl 3 ; 2 doses of 10 mg/kg on alternate days). Hyperthyroid animals treated with lindane exhibit enhanced liver microsomal superoxide radical ( O₂^.-) production and NADPH cytochrome c reductase activity, with lower levels of cytochrome P450, superoxide dismutase (SOD) and catalase activity, and glutathione (GSH) content over control values. These changes are paralleled by a substantial increase in the lipid peroxidation potential of the liver and in the O₂^.-09 generation/SOD activity ratio, thus evidencing a higher oxidative stress status that correlates with the development of liver injury characterized by neutrophil infiltration and necrosis. Kupffer cell inactivation by GdCl₃ suppresses liver injury in lindane/T₃ -treated rats with normalization of altered oxidative stress-related parameters, excepting the reduction in the content of GSH and in catalase activity. It is concluded that lindane hepatotoxicity in hyperthyroid state, that comprises an enhancement in the oxidative stress status of the liver, is largely dependent on Kupffer cell function, which may involve generation of mediators leading to pro-oxidant and inflammatory processes.     

Increases in tumor necrosis factor-alpha in response to thyroid hormone-induced liver oxidative stress in the rat

Thyroid hormone-induced calorigenesis contributes to liver oxidative stress and promotes an increased respiratory burst activity in Kupffer cells, which could conceivably increase the expression of redox-sensitive genes, including those coding for cytokines. Our aim was to test the hypothesis that L-3,3',5-triiodothyronine (T3)-induced liver oxidative stress would markedly increase the production of TNF-alpha by Kupffer cells and its release into the circulation. Sprague-Dawley rats receive a single dose of 0.1 mg T3/kg or vehicle (controls) and determinations of liver O2 consumption, serum TNF-alpha, rectal temperature, and serum T3 levels, were carried out at different times after treatment. Hepatic content of total reduced glutathione (GSH) and biliary glutathione disulfide (GSSG) efflux were measured as indices of oxidative stress. In some studies, prior to T3 injection animals were administered either (i) the Kupffer cell inactivator gadolinium chloride (GdCl3), (ii) the antioxidants alpha-tocopherol and N-acetyl-L-cysteine (NAC), or (iii) an antisense oligonucleotide against TNF-alpha (ASO TJU-2755). T3 elicited an 80-fold increase in the serum levels of TNF-alpha at 22h after treatment, which coincided with the onset of thyroid calorigenesis. Pretreatment with GdCl3, alpha-tocopherol, NAC, and ASO TJU-2755 virtually abolished this effect and markedly reduced T3-induced liver GSH depletion and the increases in biliary GSSG efflux. It is concluded that the hyperthyroid state in the rat increases the circulating levels of TNF-alpha by actions exerted at the Kupffer cell level and these are related to the oxidative stress status established in the liver by thyroid calorigenesis.     

Liver microsomal parameters related to oxidative stress and antioxidant systems in hyperthyroid rats subjected to acute lindane treatment

Liver microsomal functions related to xenobiotic biotransformation and free radical production were studied in control rats and in animals subjected to L-3,3′,5-triiodothyronine (T₃) and/or lindane administration as possible mechanisms contributing to oxidative stress, in relation to the activity of enzymes (superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx), and glucose-6-phosphate dehydrogenase (G-6PDH)) and content of lipid-soluble vitamins (α-tocopherol, β-carotene, and lycopene) affording antioxidant protection. Lindane treatment in euthyroid rats at a dosage of 20 mg/kg did not modify the content of liver microsomal cytochromes P450 and b₅, the activity of NADPH-cytochrome P450 reductase and NADH-cytochrome b₅ reductase, and the production of superoxide radical (O^·-₂), as well as antioxidant systems, except for the reduction in lycopene levels. Hyperthyroidism elicited a calorigenic response and increased specific and molecular activities of NADPH-cytochrome P450 reductase, O^·-₂ generation, and G-6PDH activity, concomitantly with diminution in liver SOD and catalase activities and in α-tocopherol, β-carotene, and lycopene levels. The administration of lindane to hyperthyroid animals led to a further increase in the molecular activity of NADPH-cytochrome P450 reductase and in the O^·-₂ production/SOD activity ratio, and decrease of hepatic α-tocopherol content, in a magnitude exceeding the sum of effects elicited by the separate treatments, as previously reported for reduced glutathione depletion. Collectively, these data support the contention that the increased susceptibility of the liver to the toxic effects of acute lindane treatment in hyperthyroid state is conditioned by potentiation of the hepatic oxidative stress status.     

Changes in the amount of reduced glutathione and activity of antioxidant enzymes in chosen mouse organs influenced by zymosan and melatonin administration

Reduced glutathione (GSH), superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSHPx) are vital components of the antioxidative barrier in animal cells. It is suggested more often now that the effectiveness of the protection of cells against the oxidative stress caused by the inflammation process depends on the amount of GSH and the activity of SOD, CAT and GSHPx. That is why the effect of zymosan A (40 mg/kg body mass) and the combined treatment with zymosan A (at the same dose) and melatonin (50 mg/kg body mass) on the amount of GSH in the blood and the amount of GSH and activity of SOD, CAT and GSHPx in the brain, liver and kidneys of male mice was estimated. Animals (n = 108) were decapitated after 3, 6 and 24 hours since the moment of the administration of only zymosan A, and combined zymosan A and after one hour melatonin. After the injection of zymosan A it was found that the amount of GSH is significantly lower after 3 and 6 hours in the blood and studied organs. The administration of zymosan A, followed by the administration of melatonin limited the decrease in the amount of this tripeptide in the same time. Simultaneously, the decrease in the amount of GSH in the studied organs was accompanied by a similar decrease in the activity of SOD, CAT and GSHPx after the injection of only zymosan A and a limited decrease in the activity after the administration of both zymosan A and melatonin. It is suggested that a decreased content of GSH and a decrease in the activity of the studied antioxidative enzymes is caused by the oxidative stress accompanying the inflammation process.     

Tinospora cordifolia induces enzymes of carcinogen/drug metabolism and antioxidant system, and inhibits lipid peroxidation in mice

The present study is an effort to identify a potent chemopreventive agent against various diseases (including cancer) in which oxidative stress plays an important causative role. Here, we investigated the effect of a hydroalcoholic (80% ethanol: 20% distilled water) extract of aerial roots of Tinospora cordifolia (50 and 100mg/kg body wt./day for 2 weeks) on carcinogen/drug metabolizing phase-I and phase-II enzymes, antioxidant enzymes, glutathione (GSH) content, lactate dehydrogenase and lipid peroxidation in liver of 8-week-old Swiss albino mice. The modulatory effect of the extract was also examined on extrahepatic organs, i.e., lung, kidney and forestomach, for the activities of GSH S-transferase (GST), DT-diaphorase (DTD), superoxide dismutase (SOD) and catalase. Significant increases in the levels of acid-soluble sulfhydryl (-SH) and cytochrome P(450) contents, and enzyme activities of cytochrome P(450) reductase, cytochrome b(5) reductase, GST, DTD, SOD, catalase, GSH peroxidase (GPX) and GSH reductase (GR) were observed in the liver. Both treated groups showed decreased malondialdehyde (MDA) formation. In lung SOD, catalase and GST; in kidney SOD and catalase; and in forestomach SOD, DTD and GST showed significant increase at both dose levels of treatment. BHA (0.75%, w/w in diet), a pure antioxidant compound, was used as a positive control. This group showed increase in hepatic levels of GSH content, cytochrome b(5), DTD, GST, GR and catalase, whereas MDA formation was inhibited significantly. In the BHA-treated group, the lung and kidney showed increased levels of catalase, DTD and GST, whereas SOD was significantly increased in the kidney and forestomach; the latter also showed an increase in the activities of DTD and GST. The enhanced GSH level and enzyme activities involved in xenobiotic metabolism and maintaining antioxidant status of cells are suggestive of a chemopreventive efficacy of T. cordifolia against chemotoxicity, including carcinogenicity, which warrants further investigation of active principle (s) present in the extract responsible for the observed effects employing various carcinogenesis models.     

辐射所致小鼠肾脏氧化损伤及川芎嗪的保护作用

目的:研究川芎嗪对辐射所致小鼠肾脏氧化损伤的预防和治疗作用。方法:采用60Co-γ射线5 Gy全身单次照射小鼠造模,在照射前和照射后分别于每天腹腔注射川芎嗪130 mg/kg,连续给药10 d,进行预防和治疗,并设对照组,观察肾组织中丙二醛(MDA)、超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、还原型谷胱甘肽(GSH)、谷胱甘肽过氧化物酶(GSH-Px)及总抗氧化力(T-AOC)的变化。结果:与阴性对照组比较,照射可显著增加肾组织中MDA的含量(P<0.05),降低SOD、CAT的活性(P<0.05),升高GSH-Px活性(P<0.05),降低GSH含量(P<0.05),使肾组织T-AOC下降(P<0.05),。与照射组比较,给予川芎嗪预防和治疗后,均可降低肾组织MDA含量(P<0.05),升高肾组织T-AOC(P<0.05),且治疗组优于预防组,与阴性对照组无显著性差异。同时,预防组可使SOD活性和GSH含量升高(P<0.05),治疗组可使SOD和CAT活性增高(P<0.05),但均对GSH-Px活性无显著影响(P>0.05)。结论:川芎嗪具有很好的抗氧化作用,无论预防和治疗均可降低辐射所致小鼠肾脏的氧化应激损伤,并且治疗效果优于预防效果。     

Derangement of Kupffer cell functioning and hepatotoxicity in hyperthyroid rats subjected to acute iron overload

Liver oxidative stress, Kupffer cell functioning, and cell injury were studied in control rats and in animals subjected to L-3,3',5-tri-iodothyronine (T3) and/or acute iron overload. Thyroid calorigenesis with increased rates of hepatic O2 uptake was not altered by iron treatment, whereas iron enhanced serum and liver iron levels independently of T3. Liver thiobarbituric acid reactants formation increased by 5.8-, 5.7-, or 11.0-fold by T3, iron, or their combined treatment, respectively. Iron enhanced the content of protein carbonyls independently of T3 administration, whereas glutathione levels decreased in T3- and iron-treated rats (54%) and in T3Fe-treated animals (71%). Colloidal carbon infusion into perfused livers elicited a 109% and 68% increase in O2 uptake in T3 and iron-treated rats over controls. This parameter was decreased (78%) by the joint T3Fe administration and abolished by gadolinium chloride (GdCl3) pretreatment in all experimental groups. Hyperthyroidism and iron overload did not modify the sinusoidal efflux of lactate dehydrogenase, whereas T3Fe-treated rats exhibited a 35-fold increase over control values, with a 54% reduction by GdCl3 pretreatment. Histological studies showed a slight increase in the number or size of Kupffer cells in hyperthyroid rats or in iron overloaded animals, respectively. Kupffer cell hypertrophy and hyperplasia with presence of inflammatory cells and increased hepatic myeloperoxidase activity were found in T3Fe-treated rats. It is concluded that hyperthyroidism increases the susceptibility of the liver to the toxic effects of iron, which seems to be related to the development of a severe oxidative stress status in the tissue, thus contributing to the concomitant liver injury and impairment of Kupffer cell phagocytosis and particle-induced respiratory burst activity.     

Cardioprotective effect of the alcoholic extract of Terminalia arjuna bark in an in vivo model of myocardial ischemic reperfusion injury

The present study was designed to investigate the effects of chronic administration of the alcoholic extract of Terminalia arjuna (TAAE) bark on isoproterenol induced myocardial injury. The TAAE was administered orally to Wistar albino rats (150-200 g) in three different doses, by gastric gavage [3.4 mg/kg: (T1), 6.75 mg/kg: (T2) and 9.75 mg/kg: (T3)] 6 days/week for 4 weeks. At the end of this period, all the animals, except the normal untreated rats that served as the control group, were administered isoproterenol (ISO) 85 mg/kg, S.C., for two consecutive days to induce in vivo myocardial injury. After 48 hours rats were anaesthetized with anaesthetic ether, then sacrificed and the hearts were harvested for biochemical and histological studies. A significant rise in myocardial thiobarbituric acid reactive substances (TBARS) and loss of reduced glutathione (GSH), superoxide dismutase (SOD) and catalase (suggestive of increased oxidative stress) occurred in the hearts subjected to in vivo myocardial ischemic reperfusion injury. The 6.75 mg/kg TAAE treatment group (baseline) shows a significant increase in myocardial TBARS as well as endogenous antioxidants (GSH, SOD, and catalase), but not in the other treatment groups. In in vivo ischemic reperfusion injury of the TAAE treated rats there was a significant decrease in TBARS in all the groups. In 6.75 mg/kg treatment group, a significant rise in the levels of GSH, SOD and catalase were observed, and it shows better recovery profile than the other groups subjected to in vivo ischemic reperfusion injury. In histological studies, all the groups, except the isoproterenol treated group, showed preserved myocardium. The present study demonstrates that the 6.75 mg/kg TAAE augments endogenous antioxidant compounds of the rat heart and also prevents the myocardium from isoproterenol induced myocardial ischemic reperfusion injury.     

Lindane-induced liver oxidative stress.

The development of an oxidative stress condition in the liver by lindane intoxication is discussed as a possible hepatotoxic mechanism of the insecticide. Lindane is metabolized by liver microsomal enzymes to a variety of metabolites, which are susceptible of conjugation for proper elimination. In addition, the interaction of lindane with the liver tissue results in the induction of the microsomal cytochrome P-450 system, together with enhanced rates of superoxide radical generation and a significant increase in indicators of lipid peroxidation. Concomitantly, lindane intoxication induces a derangement of some antioxidant mechanisms of the liver cell, including decreased superoxide dismutase and catalase activities and alterations in reduced glutathione content leading to depressed GSH/GSSG ratios. The time course study of the changes in hepatic lipid peroxidation and antioxidant parameters are closely interrelated and coincide with the onset and progression of morphological lesions.     

Quercetin attenuates lindane induced oxidative stress in wistar rats

A wide number of pesticides, including highly persistent organochlorine compounds, such as lindane (γ-Hexachlorocyclohexane), have deteriorative effect on fauna and flora by inducing oxidative stress. Lindane induces cell damage by producing free radicals and reactive oxygen species. Quercetin, a dietary flavonoid, is ubiquitous in fruits and vegetables and plays an important role in human health by virtue of its antioxidant function. In this study the flavonoid quercetin was used to investigate its antioxidative effect against lindane induced oxidative stress in rats. The level of lipid peroxidation, reduced glutathione (GSH) were analysed in addition to the antioxidant enzymes such as catalase (CAT), glutathione peroxidase (GPx), superoxide dismutase (SOD) and glutathione-s-transferase (GST) activities in the liver and kidney tissue. Levels of hepatic marker enzymes in serum like Aspartate transaminase (AST), Alanine transaminase (ALT), Alkaline phosphatase (ALP) and Lactate dehydrogenase (LDH) and renal markers like serum creatinine and serum urea were estimated. Administration of Lindane induced histopathological alterations and increased levels of serum hepatic and renal markers and malondialdehyde (MDA) with a significant decrease in GSH content and CAT, SOD, GPx and GST activities. Cotreatment of quercetin along with lindane significantly decreased the lindane induced alteration in histology, serum hepatic and renal markers and MDA and also improved the cellular antioxidant status. The results show that Quercetin ameliorates Lindane induced oxidative stress in liver and kidney. The quercetin exhibited chemopreventive effect when administered along with lindane.     

Melatonin and vitamin C administration ameliorate diazepam-induced oxidative stress and cell proliferation in the liver of rats

Abstract.  Objective : Oxidative stress is a likely molecular mechanism in long-term diazepam administration. The benefits of antioxidants (melatonin and vitamin C) against diazepam-induced cell proliferation, DNA synthesis and oxidative damage were investigated in this study. Materials & methods : Four equal-sized groups of male rats [control, diazepam (3 mg/kg), diazepam plus melatonin (5 mg/kg) and diazepam plus vitamin C (50 mg/kg)] were used. Levels of lipid peroxides (LPO), superoxide dismutase (SOD) activity and glutathione (GSH) concentration were measured in tissue homogenates. Cell proliferation and rate of DNA synthesis were detected by autoradiography. Results : Results documented increased labelling index, ³H-thymidine incorporation (DNA synthesis), LPO plus decrease in GSH levels and SOD activity in livers of diazepam-administered rats versus those of controls. When melatonin and vitamin C were given to diazepam-administered rats, they almost attenuated the increase of labelling index, DNA synthesis and LPO, and restored the levels of GSH and SOD activity. Conclusion : These results suggest long-term hazard in use of drugs such as diazepam; they may be toxic and damage terminates in complex liver damage. Furthermore, melatonin and vitamin C may be useful in combating free radical-induced liver injury resulting from hazard and/or repeated diazepam administration.     

Effect of chlorpyrifos on thiobarbituric acid reactive substances, scavenging enzymes and glutathione in rat tissues

The present study showed that exposure of chlorpyrifos, O,O'-diethyl-O-3,5,6-trichloro-2-pyridyl phosphorothionate (CPF), a widely used pesticide in rats caused significant inhibition of acetylcholinesterase (AChE) activity in different tissues viz., liver, kidney and spleen. CPF exposure also generated oxidative stress in the body, as evidenced by increase in thiobarbituric acid reactive substances (TBARS), decrease in the levels of superoxide scavenging enzymes viz., superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) in liver, kidney and spleen at all doses. Malondialdehyde levels were increased by 14%, 31% and 76% in liver, 11%, 31% and 64% in kidney and 32%, 75% and 99.9% in spleen when 50 mg, 100 mg and 200 mg/kg body wt. CPF was administered for three days. SOD and CAT activities were decreased in liver, kidney and spleen, while GPx activity showed slight increase in kidney at 50 mg and 100 mg dose, and decreased on further increase in dose of CPF. Liver and spleen showed dose-dependent decrease in GPx activity. The levels of reduced glutathione (GSH) was decreased, while oxidized glutathione (GSSG) was increased, thus a marked fall in GSH/GSSG ratio was observed in all tissues. A maximum decrease of 83% was observed in liver, followed by kidney and spleen, which showed 78% and 57% decrease, respectively in group given 200 mg/kg CPF. The levels of glucose-6-phosphate dehydrogenase (G6PDH) and glutathione reductase (GR) were also decreased in liver and kidney, while spleen showed increase at lower doses, but decrease at high dose of CPF. The data provide evidence for induction of oxidative stress on CPF exposure.     

Melatonin prevents oxidative stress and hepatocyte cell death induced by experimental cholestasis

The induction of oxidative stress precedes liver injury during experimental obstructive jaundice (OJ). In this sense, different evidences suggest that melatonin (MEL), as antioxidant, may be useful in the protection against apoptosis and necrosis during experimental cholestasis. In addition, we will also assess if MEL-dependent protection is related to a recovery of antioxidant status disturbances induced by OJ. Cholestasis was achieved by double ligature and sectioning of the principal bile duct. MEL was injected intraperitoneally (500 microg/kg/day). Lipid peroxidation was evaluated by the measurement of malondialdehyde (MDA) content in liver. Different parameters related to antioxidant status, such as reduced glutathione (GSH), glutathione peroxidase (GPx), catalase and superoxide dismutase (SOD) were determined in liver. Liver injury was assessed by alanine amino-transferase (ALT) in serum, histological examination, DNA fragmentation and TUNEL assay. The activation of perisinusoidal stellate cells was evaluated by immunohistochemical measurement of alpha-smooth muscle actin in liver sections. The induction of OJ increased all the parameters related to apoptosis and necrosis in liver. The induction of liver injury was associated with stellate cell activation, as well as an increase in MDA (p < 0.0001) and a reduction in GSH, GPx, catalase and SOD content (p < 0.0001) in liver. MEL reduced hepatic apoptosis and necrosis (p < 0.004) with a significant improvement in all oxidative stress markers. In conclusion, our results showed that MEL recovered the antioxidant status and reduced apoptosis and necrosis induced by experimental cholestasis.     

Effects of angiotensin II type 1 receptor blockade on the oxidative stress in spontaneously hypertensive rat tissues

The aim of this work was to investigate the production of oxidative damage in homogenized kidney, liver and brain of spontaneously hypertensive rats (SHR), as well as the involvement of angiotensin (Ang) II in this process. Groups of 12-week-old SHR and Wistar Kyoto rats (WKY) were given 10 mg/kg/day losartan in the drinking water during 14 days. Other groups of WKY and SHR without treatment were used as controls. The production of thiobarbituric acid reactive substances (TBARS), reduced glutathione (GSH) and the activity of the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (Gpx) were determined. No significant difference in TBARS was observed between untreated SHR or WKY rats; GSH content was lower in the liver but higher in the brain of SHR compared to WKY rats. In tissues from the SHR group, SOD and Gpx activities were reduced, whereas CAT activity was slightly increased in kidney. TBARS levels did not change in WKY rats after losartan administration, but were reduced in SHR liver and brain. Losartan treatment decreased GSH content in WKY kidney, but increased GSH in SHR liver. The activity of the antioxidant enzymes was not modified by losartan in WKY rats; however, their activities increased in tissues from treated SHR. The lower activity of antioxidant enzymes in tissues from hypertensive rats compared to those detected in normotensive controls, indicates oxidative stress production. Ang II seems to play no role in this process in normotensive animals, although AT1 receptor blockade in SHR enhances the enzymatic activity indicating that Ang II is implicated in oxidative stress generation in the hypertensive animals.     

Efficiency of propolis extract against mitochondrial stress induced by antineoplasic agents (doxorubicin and vinblastin) in rats

To assess the oxidative stress and mitochondrial dysfunction associated with disease, toxic process and aging, in vivo and in vitro preventive effect of propolis extract against mitochondrial oxidative stress induced by two anticancer drugs (doxorubicin and vinblastin) have been investigated in female wistar rat using liver and heart mitochondria. The results show that doxorubicin and vinblastin altered mitochondrial functions as observed by a decrease in respiratory control value, an activation of swelling and overproduction of superoxide anion. Myocardial tissue from doxorubicin treated rats showed a marked increase in malondialdehyde production, a depletion of reduced glutathione contents and an inhibition of catalase and superoxide dismutase activities. Similar results were also observed in liver tissue. Pretreatment of rats with propolis extract (100 mg/kg/day po) (10(-4) M ip) administered 4 days prior to doxorubicin (20 mg/kg) and/or vinblastin (2 mg/kg) injection, substantially reduced the peroxidative damage in myocardium and hepatic tissues and markedly restored the tissues catalase and SOD activities. The results strongly suggest that propolis extract protects heart and liver tissues from oxidative stress by protecting the mitochondria.     

Acute lindane intoxication: A study on lindane tissue concentration and oxidative stress-related parameters in liver and erythrocytes

Treatment of rats with daily dosis of 20 mg of lindane/kg for 3 consecutive days led to the accumulation of the insecticide in several tissues, including erythrocytes and liver. Lindane did not alter the hematocrit and hemoglobin concentration but reduced methemogiobin levels by 17%. Red blood cells from controls and lindane-treated rats, exposed to t-butyl hydroperoxide, exhibited comparable rates of oxygen uptake and visible chemiluminescence, whereas the induction period that precedes oxygen uptake was significantly enhanced in the latter group. Lindane treatment did not modify the activity of erythrocyte glutathione peroxidase, glucose-6-phosphate dehydrogenase, catalase, and methemoglobin reductase, being the total content of glutathione and superoxide dismutase activity significantly increased. The liver from lindane-treated rats showed an enhanced microsomal pro-oxidant activity, evidenced by higher cytochrome P450 content and NADPH-cytochrome c reductase and NADPH oxidase activities. The higher enzyme activities led to an increased superoxide anion generation (adrenochrome formation) and lipid peroxidation (measured either by the production of thiobarbituric acid reactants and spontaneous visible chemiluminescence). Concomitantly, liver glutathione content and the activity of glutathione peroxidase-glutathione reductase couple were augmented by lindane treatment, without any change in superoxide dismutase activity, together with a reduction in that of catalase. Results suggest that lindane does not alter the prooxidant/antioxidant status of the erythrocyte in conditions of a significant cellular accumulation of the insecticide, which might exert direct action on enzymatic systems leading to enhanced superoxide dismutase activity and glutathione content. In the liver, lindane-induced pro-oxidant condition was not accompanied by cell injury, probably due to the adaptative increase in some antioxidant mechanisms of the hepatocyte.     

Endogenous antioxidant defence system in rat liver following mercury chloride oral intoxication

Mercury is a highly toxic metal which induces oxidative stress. Superoxide dismutases, catalase, and glutathion peroxidase are proteins involved in the endogenous antioxidant defence system. In the present study rats were administered orally, by gavage, a single daily dose of HgCl2 for three consecutive days. In order to find a relation between the proteins involved in the antioxidant defence and mercury intoxication, parameters of liver injury, redox state of the cells, as well as intracellular protein levels and enzyme activities of Mn-dependent superoxide dismutase (MnSOD), Cu-Zn-dependent superoxide dismutase (CuZnSOD), catalase, and glutathione peroxidase (GPx) were assayed both in blood and in liver homogenates. HgCl2 at the doses of 0.1 mg/kg produced liver damage which that was detected by a slight increase in serum alanine aminotransferase and gamma glutamyl transferase. Hepatic GSH/GSSG ratio was assayed as a parameter of oxidative stress and a significant decrease was detected, as well as significant increases in enzyme activities and protein levels of hepatic antioxidant defence systems. Changes in both MnSOD and CuZnSOD were parallel to those of liver injury and oxidative stress, while the changes detected in catalase and GPx activities were progressively increased along with the mercury intoxication. Other enzyme activities related to the glutathione redox cycle, such as glutathione reductase (GR) and glucose-6-phosphate dehydrogenase (G6PDH), also increased progressively. We conclude that against low doses of mercury that produce a slight oxidative stress and liver injury, the response of the liver was to induce the synthesis and activity of the enzymes involved in the endogenous antioxidant system. The activities of all the enzymes assayed showed a rapidly induced coordinated response.     

Melatonin Prevents Oxidative Stress and Hepatocyte Cell Death Induced by Experimental Cholestasis

The induction of oxidative stress precedes liver injury during experimental obstructive jaundice (OJ). In this sense, different evidences suggest that melatonin (MEL), as antioxidant, may be useful in the protection against apoptosis and necrosis during experimental cholestasis. In addition, we will also assess if MEL-dependent protection is related to a recovery of antioxidant status disturbances induced by OJ. Cholestasis was achieved by double ligature and sectioning of the principal bile duct. MEL was injected intraperitoneally (500?μg/kg/day). Lipid peroxidation was evaluated by the measurement of malondialdehyde (MDA) content in liver. Different parameters related to antioxidant status, such as reduced glutathione (GSH), glutathione peroxidase (GPx), catalase and superoxide dismutase (SOD) were determined in liver. Liver injury was assessed by alanine aminotransferase (ALT) in serum, histological examination, DNA fragmentation and TUNEL assay. The activation of perisinusoidal stellate cells was evaluated by immunohistochemical measurement of α-smooth muscle actin in liver sections. The induction of OJ increased all the parameters related to apoptosis and necrosis in liver. The induction of liver injury was associated with stellate cell activation, as well as an increase in MDA (p<0.0001) and a reduction in GSH, GPx, catalase and SOD content (p<0.0001) in liver. MEL reduced hepatic apoptosis and necrosis (p<0.004) with a significant improvement in all oxidative stress markers. In conclusion, our results showed that MEL recovered the antioxidant status and reduced apoptosis and necrosis induced by experimental cholestasis.     

Protoporphyrin IX and oxidative stress

The short- and long-term pro-oxidant effect of protoporphyrin IX (PROTO) administration to mice was studied in liver. A peak of liver porphyrin accumulation was found 2 h after the injection of PROTO (3.5 mg/kg, i.p.); then the amount of porphyrins diminished due to biliar excretion. After several doses of PROTO (1 dose every 24 h up to 5 doses) a sustained enhancement of liver porphyrins was observed. The activity of δ-amino-levulinic acid synthetase was induced 70-90% over the control values 4 h after the first injection of PROTO and stayed at these high levels throughout the period of the assay. Administration of PROTO induced rapid liver damage, involving lipid peroxidation. Hepatic GSH content was increased 2 h after the first injection of PROTO, but then decreased below the control values which were maintained after several doses of porphyrin. After a single dose of PROTO, Cu-Zn superoxide dismutase (SOD) was rapidly induced, suggesting that superoxide radicals had been generated. Increased levels of hydrogen peroxide coming from the reaction catalyzed by SOD and lipid peroxides as a consequence of membrane peroxidation, induced the activity of catalase and glutathione peroxidase (GPx), while decreased GSH levels induced glutathione reductase (GRed) activity. However after 5 doses of PROTO, the activity of SOD was reduced reaching control values. GPx and catalase activities slowly went down, while GRed continued increasing as long as the levels of GSH were kept very low. TBARS values, although lower than those observed after a single dose of PROTO, remained above control values; Glutathione S-transferase activity was instead greatly diminished, indicating sustained liver damage.

Our findings would indicate that accumulation of PROTO in liver induces oxidative stress, leading to rapid increase in the activity of the antioxidant enzymes to avoid or revert liver damage. However, constant accumulation of porphyrins provokes a liver damage so severe that the antioxidant system is compromised.