Post-transcriptional control of increased hepatic catalase gene expression in response to oxidative stress

Alteration of hepatocellular antioxidant gene expression pattern and biomarkers of oxidative damage in diazinon-induced acute toxicity in Wistar rat: A time-course mechanistic study

In the present survey, the plasma level of diazinon after acute exposure was measured by HPLC method at a time-course manner. In addition, the impact of diazinon on the expression of the key genes responsible for hepatocellular antioxidative defense, including PON1, GPx and CAT were investigated. The increase in oxidative damages in treated rats was determined by measuring LPO, protein carbonyl content and total antioxidant power in plasma. After administration of 85 mg/kg diazinon in ten groups of male Wistar rats at different time points between 0-24 hours, the activity of AChE enzyme was inhibited to about 77.94 %. Significant increases in carbonyl groups and LPO after 0.75 and 1 hours were also observed while the plasma antioxidant power was significantly decreased. Despite the dramatic reduction of GP_X and PON1 gene expression, CAT gene was significantly upregulated in mRNA level by 1.1 fold after 4 hours and 1.5-fold after 24 hours due to diazinon exposure, compared to control group. Furthermore, no significant changes in diazinon plasma levels were found after 4 hours in the treated rats. The limits of detection and quantification were 137.42 and 416.52 ng/mL, respectively. The average percentage recoveries from plasma were between 90.62 % and 95.72 %. In conclusion, acute exposure to diazinon increased oxidative stress markers in a time-dependent manner and the changes were consistent with effects on hepatic antioxidant gene expression pattern. The effect of diazinon even as a non-lethal dose was induced on the gene expression of antioxidant enzymes. The change in antioxidant defense system occurs prior to diazinon plasma peak time. These results provide biochemical and molecular evidence supporting potential acute toxicity of diazinon and is beneficial in the evaluation of acute toxicity of other organophosphorus pesticides as well.

Is Ozone Really a “Wonder Drug”?

Even if the reader has only browsed through the previous chapters, he ought to have received my feeling that ozone has an enormous therapeutic potential that, so far, has been either disregarded, if not obstructed by world medical authorities. Reasons for delaying the use of ozone are multiple: while quacks and inexpert ozonetherapists are at fault for poor work, other aspects such as commercial and pharmaceutical interests, prejudice, lack of knowledge and a myopic medical vision have done their best to block a substantial and rapid progress.

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.

Doxorubicin Paradoxically Protects Cardiomyocytes against Iron-mediated Toxicity

The cardiotoxicity induced by the anticancer anthracycline doxorubicin (DOX) is attributed to reactions between iron and reactive oxygen species (ROS) that lead to oxidative damage. We found that DOX forms ROS in H9c2 cardiomyocytes, as shown by dichlorodihydrofluorescein oxidation and the expression of stress-responsive genes such as catalase or aldose reductase. DOX also increased ferritin levels in these cells, particularly the H subunit. A considerable increase in ferritin mRNA levels showed that DOX acted at transcriptional level, but an additional potential mechanism was identified as the down-regulation of iron regulatory protein-2, post-transcriptional inhibitor of ferritin synthesis. Pretreatment with DOX protected H9c2 cells against the damage induced by subsequent exposure to ferric ammonium citrate, and experiments with (55)Fe revealed that the protection was due to the deposition of iron in ferritin. Cytoprotection was also observed when DOX was replaced by glucose/glucose oxidase, a source of H(2)O(2), thus suggesting that DOX increases ferritin synthesis through the action of ROS. This concept was supported by three more lines of evidence. (i) DOX-induced ferritin synthesis was blocked by N-acetylcysteine, a scavenger of ROS. (ii) Mitoxantrone, a ROS-forming analogue, similarly induced ferritin expression and protected the cells against iron toxicity. (iii) 5-Iminodaunorubicin, an analogue lacking ROS-forming activity, did not induce ferritin synthesis or protect the cells against iron toxicity. These results characterize a paradoxically beneficial link between anthracycline-derived ROS, increased ferritin synthesis, and resistance to iron-mediated damage. The role of iron and ROS in anthracycline-induced cardiotoxicity may, therefore, be more complex than previously believed.

Oxidative stress-mediated down-regulation of rat hydroxyacid oxidase 1, a liver-specific peroxisomal enzyme

Hydroxyacid oxidase 1 (Hao1) is a liver-specific peroxisomal enzyme that oxidizes glycolate to glyoxylate with concomitant production of H2O2. In Hao1 messenger RNA (mRNA), an iron-responsive element (IRE) homologous to the sequence recognized by iron regulatory proteins (IRP), key regulators of iron homeostasis, is present, but the involvement of iron in Hao1 regulation remains unclear. In this study, we found a reduction of Hao1 mRNA content in livers of rats with chronic dietary iron overload, which showed decreased IRP activity and higher ferritin expression as expected, but also induction of heme oxygenase (HO-1), a marker of oxidative damage, and lipid peroxidation. Hao1 mRNA levels were not altered significantly in livers of rats administered doses of iron sufficient to induce ferritin expression and to repress IRP activity, but not to activate HO-1 and to promote lipid peroxidation, as well as in the liver of iron-deficient rats. These observations were not consistent with a post-transcriptional down-regulation of Hao1 by iron through the IRE/IRP pathway and suggested an effect of reactive oxygen species (ROS). Indeed, a marked decrease of Hao1 mRNA was observed in the liver of rats subjected to oxidative stress induced by either glutathione depletion or postischemic reperfusion. Nuclear run-on analysis showed an effect of ROS at the transcriptional level. In conclusion, down-regulation of Hao1 expression during oxidative stress may provide a mechanism to prevent excessive H2O2 formation in liver peroxisomes and may represent the prototype of a poorly recognized but potentially relevant response to oxidative injury involving down-regulation of ROS-producing enzymes.

Post-transcriptional control of catalase expression in garlic-treated rats

Regulation of catalase (CAT) expression, a major antioxidant enzyme that detoxifies H2O2, is very complex. Garlic is effective to prevent or ameliorate oxidative stress probably through its intrinsic antioxidant properties and/or to its ability to modify antioxidant enzyme expression. In this paper we studied the effect of a 2% garlic diet on the renal and hepatic CAT expression (mRNA levels, and enzyme activity, content, synthesis, and degradation). The study was made 2 weeks after feeding rats with a 2% garlic diet. CAT activity and content were measured by a spectrophotometric method and Western blot, respectively. CAT mRNA levels and CAT synthesis (k(s)) and degradation (kD) in vivo were measured by Northern blot and kinetic of reappearance of CAT activity after aminotriazole injection, respectively. Garlic-treatment decreased CAT activity and content, and CAT mRNA levels were unchanged in both tissues. k(s) decreased and kD remained unchanged in kidney and liver. The decrease in k(s) without changes in kD and CAT mRNA levels could explain the low CAT expression in garlic-fed rats. In vivo H2O2 generation in kidney and liver was markedly decreased in garlic-fed rats which could be due to a direct antioxidant effect of garlic. This may be the initial event in the garlic-fed rats that leads to the decreased CAT expression. Our data strongly suggest that the diminished renal and hepatic CAT expression in garlic-fed rats is mediated by post-transcriptional changes (mainly low translational efficiency) which could be an adaptation to the low H2O2.

Changes in antioxidant defence systems induced by cyclosporine A in cultures of hepatocytes from 2- and 12-month-old rats

The in vitro effect of cyclosporine A (CsA) was studied in reference to the production of reactive oxygen species (peroxides and superoxide anion) and to cell enzyme-mediated antioxidant defence in hepatocytes isolated from rats aged 2 and 12 months. Primary cultures of hepatocytes were incubated in the presence of concentrations of cyclosporine in the range of 0 to 50 microM for 24 hr, and the release of lactate dehydrogenase into the culture medium was evaluated as a parameter of cytotoxicity and membrane lysis. Peroxides were quantified by using 2',7'-dichlorodihydrofluorescein diacetate, and superoxide anion levels were evaluated by the fluorescence of dihydroethidium. Enzyme activity and gene expression of catalase and Mn- and Cu,Zn-superoxide dismutase were also assayed. CsA cytotoxicity was significantly higher in hepatocytes from rats aged 12 months when compared to those aged 2 months. Intracellular peroxide content resulted in a dose-dependent increase, while the anion superoxide intracellular level slightly decreased as CsA increased from 0-50 microM. The progressive increase in intracellular peroxides in cell cultures in the range from 0-50 microM CsA was associated with the loss of cell viability and accompanied by significantly higher levels of Mn- and Cu, Zn-superoxide dismutase enzyme activities and mRNAs, and slight increases in catalase activity and mRNA. We conclude that, in primary hepatocyte cultures, the cytotoxicity of CsA was dose-dependent in both age groups and significantly higher in cultures from 12-month-old rats when compared to those from 2-month-old animals. The non-coordinated regulation of the gene expression of antioxidant enzyme systems, i.e. catalase and Mn- and Cu,Zn-superoxide dismutases, evidenced to a greater extent in hepatocytes from the older group of rats, could be one of the mechanisms involved in CsA toxicity.

Cocaine cytotoxicity in hepatocyte cultures from phenobarbital-induced rats: involvement of reactive oxygen species and expression of antioxidant defense systems

The present study was designed to investigate whether cocaine modifies the production of reactive oxygen species, affects cellular enzyme-mediated antioxidant defense systems and, subsequently, promotes apoptosis and/or necrosis of hepatocytes. Primary cultures of hepatocytes isolated from phenobarbital-induced rats were exposed to cocaine (0-1000 microM) for 24 hr, and cell death (apoptosis or necrosis), antioxidant enzyme activities and mRNA levels, and peroxide generation were determined. Cocaine cytotoxicity by apoptosis was observed by detecting apoptotic nuclei using optic microscopy and by measurement of the hypodiploid peak (<2C) in DNA histograms obtained by flow cytometry. Necrosis was evidenced by lactate dehydrogenase (LDH) leakage, and peroxide production was quantified with 2',7'-dichlorodihydrofluorescein diacetate. Low concentrations of cocaine (less than 100 microM) resulted in an increase in dichlorofluorescein fluorescence, associated with an enhancement in apoptotic cell death and sharp decreases in the enzyme activities and RNAs of catalase and manganese-superoxide dismutase (Mn-SOD). The progressive decrease in peroxide production in cell cultures detected in the range of 250-1000 microM cocaine was associated with increases in LDH leakage and decreases in the percentage of apoptotic cells, accompanied by low levels in catalase and Mn-SOD enzyme activities and mRNAs, without apparent changes in apoptosis. These data indicate that oxygen radicals may contribute directly or indirectly to cocaine-induced apoptosis in cultured hepatocytes. We conclude that, in primary hepatocyte cultures, cocaine-induced cell death by necrosis was dependent on cocaine concentration, while cell death by apoptosis was parallel to peroxide concentration. The down-regulation of the gene expression of antioxidant enzyme systems should be one of the mechanisms involved in cocaine toxicity.

Effect of the in vivo catalase inhibition on aminonucleoside nephrosis

Reactive oxygen species have been involved in the pathophysiology of puromycin aminonucleoside (PAN)-nephrosis. The role of H2O2 in these rats may be studied modulating the amount or activity of catalase, which breakdowns H2O2 to water and oxygen. To explore the role of H2O2 in this experimental model, we studied the effect of the in vivo catalase inhibiton with 3-amino-1,2,4-triazole (ATZ) on the course of PAN-nephrosis. Four groups of rats were studied: control rats (CT group), PAN-injected rats (PAN group), ATZ-injected rats (ATZ group), and ATZ- and PAN-injected rats (ATZPAN group). Rats were placed in metabolic cages to collect 24 h urine along the study, ATZ (1 g/kg) was given 24 h before PAN injection (75 mg/kg), and the proteinuria was measured on days 0, 2, 4, 6, 8, and 10. Proteinuria started before (day 4) and was significantly higher on days 6, 8, and 10 in the ATZPAN group than in the PAN group. On day 10, hypercholesterolemia was significantly higher in the ATZPAN group than in the PAN group. These data indicate that the in vivo catalase inhibition magnifies PAN-nephrosis, suggesting that H2O2 is produced in vivo and involved in the renal damage in this experimental disease.

Changes in concentration, localization and activity of catalase within the human placenta during early gestation

Using villous tissue from accurately dated gestational age placentae, this study identified significant changes in the protein concentration, enzyme activity and localization of catalase, an enzyme responsible for the intracellular metabolism of hydrogen peroxide, during the first and early second trimester of pregnancy. Enzyme activity was found to increase approximately threefold between weeks 6 and 17, with the greatest increase between 12 and 17 weeks. Immunostaining of tissue sections was supportive of these findings, demonstrating a progressively stronger signal between weeks 6 and 17. Immunostaining also demonstrated that the main cell types expressing catalase were the cytotrophoblast cells as well as a subset of the stromal cells. Between 13-17 weeks gestation, however, it was possible to detect catalase within the syncytiotrophoblast also, although with a much reduced intensity of staining. At the ultrastructural level, immunogold labelling of catalase clearly showed that staining was predominately compartmentalized within peroxisomes, although non-peroxisomal staining was also seen. Immunoreactivity also demonstrated, via morphological identification, that the stromal cells containing detectable levels of catalase were placental macrophages (Hofbauer cells). These results are in agreement with the proposal that the placenta exists in a physiologically low oxygen environment during the early part of gestation. In this environment oxidative activity of the sort resulting in the generation of hydrogen peroxide would presumably be suppressed, thereby limiting the requirement for catalase until oxygen tension begins to rise.

Decrease of immunoreactive catalase protein in specific areas of ageing rat brain

The activity of catalase, the main enzyme responsible for detoxification against hydrogen peroxide, decreases in specific brain areas of aged rats. The reduction of enzyme activity appears to be the consequence of a decreased protein expression rather than an impaired function of the native enzyme. In fact, diminution of the immunoreactive protein parallels enzyme activity decrease. Since the extent of decrease of both activity and protein content was observed to be area dependent, we hypothesise that this phenomenon may underlie, at least in part, the increased susceptibility of specific brain regions to oxidative insults observed in pathological situations related to ageing.