NADH-dependent microsomal interaction with ferric complexes and production of reactive oxygen intermediates

Genetic 3'UTR variations and clinical factors significantly contribute to survival prediction and clinical response in breast cancer patients

The study describes a relationship between the 3′UTR variants, clinicopathological parameters and response to chemotherapy. We analyzed 33 germline polymorphisms in 3′UTRs of ADME genes in 305 breast cancer women treated with FAC regime. Clinical endpoints of this study were: overall survival (OS), progression-free survival (PFS), recurrence-free survival (RFS) and overall response defined as treatment failure-free survival (TFFS). The shortened OS was connected with the presence of NR1/2 rs3732359 AA, SLC22A16 rs7756222 CC, as well as SLC22A16 rs9487402 allele G and clinical factors belonging to TNM classification: tumor size >1 cm, nodal involvement and presence of metastases. PFS was related to two polymorphisms PGR rs1824125 GG, PGR rs12224560 CC and SLC22A16 rs7756222 CC as well as preexisting metastases. The RFS was shortened due to the DPYD rs291593 CC, AKR1C3 rs3209896 AG and negative expression of PGR. The presence of ALDH5A1 rs1054899 allele A, lack of pre-chemotherapy surgery and negative status of PGR correlated with worse treatment response. The germline variants commonly present in the population are important factors determining the response to treatment. We observed the effect of the accumulation of genetic and clinical factors on poor survival prognosis and overall treatment response.

Synergistic Interaction of Light Alcohol Administration in the Presence of Mild Iron Overload in a Mouse Model of Liver Injury: Involvement of Triosephosphate Isomerase Nitration and Inactivation

It is well known that iron overload promotes alcoholic liver injury, but the doses of iron or alcohol used in studies are usually able to induce liver injury independently. Little attention has been paid to the coexistence of low alcohol consumption and mild iron overload when either of them is insufficient to cause obvious liver damage, although this situation is very common among some people. We studied the interactive effects and the underlining mechanism of mild doses of iron and alcohol on liver injury in a mouse model. Forty eight male Kunming mice were randomly divided into four groups: control, iron (300 mg/kg iron dextran, i.p.), alcohol (2 g/kg/day ethanol for four weeks i.g.), and iron plus alcohol group. After 4 weeks of treatment, mice were sacrificed and blood and livers were collected for biochemical analysis. Protein nitration level in liver tissue was determined by immunoprecipitation and Western blot analysis. Although neither iron overload nor alcohol consumption at our tested doses can cause severe liver injury, it was found that co-administration of the same doses of alcohol and iron resulted in liver injury and hepatic dysfunction, accompanied with elevated ratio of NADH/NAD⁺, reduced antioxidant ability, increased oxidative stress, and subsequent elevated protein nitration level. Further study revealed that triosephosphate isomerase, an important glycolytic enzyme, was one of the targets to be oxidized and nitrated, which was responsible for its inactivation. These data indicate that even under low alcohol intake, a certain amount of iron overload can cause significant liver oxidative damage, and the modification of triosephosphate isomerasemight be the important underlining mechanism of hepatic dysfunction.

NAD+ as the Link Between Oxidative Stress, Inflammation, Caloric Restriction, Exercise, DNA Repair, Longevity, and Health Span

Oxidative stress and decreased DNA damage repair in vertebrates increase with age also due to lowered cellular NAD+. NAD+ depletion may play a major role in the aging process at the cellular level by limiting (1) energy production, (2) DNA repair, and (3) genomic signaling. In this study, we hypothesize that it is not NAD+ as a cofactor in redox reactions and coenzyme in metabolic processes that has the ultimate role in aging, but rather the role of NAD+ in cellular signaling when used as substrate for sirtuins (SIRT1-7 in mammals) and PARPs [Poly(ADP-ribose) polymerases]. Both sirtuins and PARPs influence many transcription factors and can affect gene expression. As a signaling molecule, NAD+ is consumed in the reaction donating ADP-ribose and releasing nicotinamide (NAM) as a by-product. It seems that aging at the cellular level is associated with a decline of NAD+ and that NAD+ restoration can reverse phenotypes of aging by inducing cellular repair and stress resistance. Adequate intracellular NAD+ concentrations may be an important longevity assurance factor, while lowered cellular NAD+ concentration may negatively influence the life span.

Nicotinamide adenine dinucleotide: An essential factor in preserving hearing in cisplatin-induced ototoxicity

Ototoxicity is an important issue in patients receiving cisplatin chemotherapy. Numerous studies have demonstrated that several mechanisms, including oxidative stress, DNA damage, and inflammatory responses, are closely associated with cisplatin-induced ototoxicity. Although much attention has been directed at identifying ways to protect the inner ear from cisplatin-induced damage, the precise underlying mechanisms have not yet been elucidated. The cofactor nicotinamide adenine dinucleotide (NAD(+)) has emerged as an important regulator of cellular energy metabolism and homeostasis. NAD(+) acts as a cofactor for various enzymes including sirtuins (SIRTs) and poly(ADP-ribose) polymerases (PARPs), and therefore, maintaining adequate NAD(+) levels has therapeutic benefits because of its effect on NAD(+)-dependent enzymes. Recent studies demonstrated that disturbance in intracellular NAD(+) levels is critically involved in cisplatin-induced cochlear damage associated with oxidative stress, DNA damage, and inflammatory responses. In this review, we describe the importance of NAD(+) in cisplatin-induced ototoxicity and discuss potential strategies for the prevention or treatment of cisplatin-induced ototoxicity with a particular focus on NAD(+)-dependent cellular pathways.

The MnSOD Ala16Val SNP: relevance to human diseases and interaction with environmental factors

The relevance of reactive oxygen species (ROS) production relies on the dual role shown by these molecules in aerobes. ROS are known to modulate several physiological phenomena, such as immune response and cell growth and differentiation; on the other hand, uncontrolled ROS production may cause important tissue and cell damage, such as deoxyribonucleic acid oxidation, lipid peroxidation, and protein carbonylation. The manganese superoxide dismutase (MnSOD) antioxidant enzyme affords the major defense against ROS within the mitochondria, which is considered the main ROS production locus in aerobes. Structural and/or functional single nucleotide polymorphisms (SNP) within the MnSOD encoding gene may be relevant for ROS detoxification. Specifically, the MnSOD Ala16Val SNP has been shown to alter the enzyme localization and mitochondrial transportation, affecting the redox status balance. Oxidative stress may contribute to the development of type 2 diabetes, cardiovascular diseases, various inflammatory conditions, or cancer. The Ala16Val MnSOD SNP has been associated with these and other chronic diseases; however, inconsistent findings between studies have made difficult drawing definitive conclusions. Environmental factors, such as dietary antioxidant intake and exercise have been shown to affect ROS metabolism through antioxidant enzyme regulation and may contribute to explain inconsistencies in the literature. Nevertheless, whether environmental factors may be associated to the Ala16Val genotypes in human diseases still needs to be clarified.

Central role of mitochondria in drug-induced liver injury

A frequent mechanism for drug-induced liver injury (DILI) is the formation of reactive metabolites that trigger hepatitis through direct toxicity or immune reactions. Both events cause mitochondrial membrane disruption. Genetic or acquired factors predispose to metabolite-mediated hepatitis by increasing the formation of the reactive metabolite, decreasing its detoxification, or by the presence of critical human leukocyte antigen molecule(s). In other instances, the parent drug itself triggers mitochondrial membrane disruption or inhibits mitochondrial function through different mechanisms. Drugs can sequester coenzyme A or can inhibit mitochondrial β-oxidation enzymes, the transfer of electrons along the respiratory chain, or adenosine triphosphate (ATP) synthase. Drugs can also destroy mitochondrial DNA, inhibit its replication, decrease mitochondrial transcripts, or hamper mitochondrial protein synthesis. Quite often, a single drug has many different effects on mitochondrial function. A severe impairment of oxidative phosphorylation decreases hepatic ATP, leading to cell dysfunction or necrosis; it can also secondarily inhibit ß-oxidation, thus causing steatosis, and can also inhibit pyruvate catabolism, leading to lactic acidosis. A severe impairment of β-oxidation can cause a fatty liver; further, decreased gluconeogenesis and increased utilization of glucose to compensate for the inability to oxidize fatty acids, together with the mitochondrial toxicity of accumulated free fatty acids and lipid peroxidation products, may impair energy production, possibly leading to coma and death. Susceptibility to parent drug-mediated mitochondrial dysfunction can be increased by factors impairing the removal of the toxic parent compound or by the presence of other medical condition(s) impairing mitochondrial function. New drug molecules should be screened for possible mitochondrial effects.

Age related changes in NAD+ metabolism oxidative stress and Sirt1 activity in wistar rats

The cofactor nicotinamide adenine dinucleotide (NAD+) has emerged as a key regulator of metabolism, stress resistance and longevity. Apart from its role as an important redox carrier, NAD+ also serves as the sole substrate for NAD-dependent enzymes, including poly(ADP-ribose) polymerase (PARP), an important DNA nick sensor, and NAD-dependent histone deacetylases, Sirtuins which play an important role in a wide variety of processes, including senescence, apoptosis, differentiation, and aging. We examined the effect of aging on intracellular NAD+ metabolism in the whole heart, lung, liver and kidney of female wistar rats. Our results are the first to show a significant decline in intracellular NAD+ levels and NAD:NADH ratio in all organs by middle age (i.e.12 months) compared to young (i.e. 3 month old) rats. These changes in [NAD(H)] occurred in parallel with an increase in lipid peroxidation and protein carbonyls (o- and m- tyrosine) formation and decline in total antioxidant capacity in these organs. An age dependent increase in DNA damage (phosphorylated H2AX) was also observed in these same organs. Decreased Sirt1 activity and increased acetylated p53 were observed in organ tissues in parallel with the drop in NAD+ and moderate over-expression of Sirt1 protein. Reduced mitochondrial activity of complex I-IV was also observed in aging animals, impacting both redox status and ATP production. The strong positive correlation observed between DNA damage associated NAD+ depletion and Sirt1 activity suggests that adequate NAD+ concentrations may be an important longevity assurance factor.

Mitochondrial involvement in drug-induced liver injury

Mitochondrial dysfunction is a major mechanism of liver injury. A parent drug or its reactive metabolite can trigger outer mitochondrial membrane permeabilization or rupture due to mitochondrial permeability transition. The latter can severely deplete ATP and cause liver cell necrosis, or it can instead lead to apoptosis by releasing cytochrome c, which activates caspases in the cytosol. Necrosis and apoptosis can trigger cytolytic hepatitis resulting in lethal fulminant hepatitis in some patients. Other drugs severely inhibit mitochondrial function and trigger extensive microvesicular steatosis, hypoglycaemia, coma, and death. Milder and more prolonged forms of drug-induced mitochondrial dysfunction can also cause macrovacuolar steatosis. Although this is a benign liver lesion in the short-term, it can progress to steatohepatitis and then to cirrhosis. Patient susceptibility to drug-induced mitochondrial dysfunction and liver injury can sometimes be explained by genetic or acquired variations in drug metabolism and/or elimination that increase the concentration of the toxic species (parent drug or metabolite). Susceptibility may also be increased by the presence of another condition, which also impairs mitochondrial function, such as an inborn mitochondrial cytopathy, beta-oxidation defect, certain viral infections, pregnancy, or the obesity-associated metabolic syndrome. Liver injury due to mitochondrial dysfunction can have important consequences for pharmaceutical companies. It has led to the interruption of clinical trials, the recall of several drugs after marketing, or the introduction of severe black box warnings by drug agencies. Pharmaceutical companies should systematically investigate mitochondrial effects during lead selection or preclinical safety studies.

Genetic Polymorphisms in Antioxidant Enzymes Modulate Hepatic Iron Accumulation and Hepatocellular Carcinoma Development in Patients with Alcohol-Induced Cirrhosis

Manganese superoxide dismutase (MnSOD) converts the superoxide anion into H(2)O(2), which, unless it is detoxified by glutathione peroxidase 1 (GPx1), can increase hepatic iron and can react with iron to form genotoxic compounds. We investigated the role of Ala/Val-MnSOD and Pro/Leu-GPx1 polymorphisms on hepatic iron accumulation and hepatocellular carcinoma development in patients with alcoholic cirrhosis. Genotypes were determined in 162 alcoholic patients with cirrhosis but without hepatocellular carcinoma initially, who were prospectively followed up for hepatocellular carcinoma development. We found that patients with two Val-MnSOD alleles (slow H(2)O(2) production) and two Pro-GPx1 alleles (presumably quick H(2)O(2) detoxification) had a lower risk of hepatocellular carcinoma development than other patients (chi(2) trend test, P = 0.001; log-rank, P = 0.0009). Indeed, hepatocellular carcinoma percentage was 0% in subjects with this "2Val-MnSOD/2Pro-GPx1" genotype versus 16%, 27%, and 32% in "2Val-MnSOD/1or2Leu-GPx1," "1or2Ala-MnSOD/2Pro-GPx1," and "1or2Ala-MnSOD/1or2Leu-GPx1" patients, respectively. The percentage of patients with stainable hepatic iron increased progressively with these genotypic associations: 22%, 28%, 50%, and 53%, respectively (chi(2) trend test, P = 0.005). Stainable iron was a risk factor for hepatocellular carcinoma (log-rank, P = 0.0002; relative risk, 3.40). In conclusion, polymorphisms in antioxidant enzymes modulate hepatic iron accumulation and hepatocellular carcinoma development in French alcoholic patients with cirrhosis.

Iron and CYP2E1-dependent oxidative stress and toxicity

Iron plays a critical role in catalyzing the formation of potent oxidants. Increases in iron content enhance oxidative stress, whereas removal of iron deceases such stress. An association between iron and alcoholic liver injury has been proposed. The ability of iron to modulate the biochemical and toxicologic actions of cytochrome P450 2E1 (CYP2E1) has been evaluated by using isolated microsomes and intact liver cells. The ability of different iron complexes to stimulate microsomal lipid peroxidation and hydroxyl radical production during reduced form of nicotinamide adenine dinucleotide phosphate (NADPH)- and reduced form of nicotinamide adenine dinucleotide (NADH)-dependent electron transfer has been characterized. Certain iron complexes have been shown to be effective in promoting lipid peroxidation; others are better catalysts of hydroxyl radical production as a complex pattern has been found. Reactive oxygen production, lipid peroxidation, and interaction with iron chelates have been shown to be enhanced with microsomes isolated from ethanol-treated rats with elevated levels of CYP2E1. This increase was prevented by anti-CYP2E1 immunoglobulin (Ig)G or chemical inhibitors of CYP2E1. Thus, in the presence of iron complexes, microsomes enriched in CYP2E1 are especially reactive in generation of reactive oxygen species. To assess the toxicologic significance of this iron-CYP2E1 interaction, iron (ferric-nitrilotriacetate) was added to HepG2 cells, which were engineered to express the human CYP2E1. Ferric-nitrilotriacetate produced a greater toxicity in the CYP2E1-expressing HepG2 cells than that in control HepG2 cells. This enhanced, synergistic toxicity was blocked by antioxidants and inhibitors of CYP2E1. Mitochondrial membrane potential and ATP levels were decreased, and damage to the mitochondria played a critical role in the CYP2E1-plus-iron-dependent toxicity. These results support the suggestion that low concentrations of iron and polyunsaturated fatty acids can act as priming or sensitizing factors for CYP2E1-induced injury in HepG2 cells and hepatocytes. Such interactions may play a role in alcohol-induced liver injury.

Homozygosity for alanine in the mitochondrial targeting sequence of superoxide dismutase and risk for severe alcoholic liver disease

BACKGROUND & AIMS

For similar ethanol consumption, some subjects only develop macrovacuolar steatosis whereas others develop severe liver lesions. A genetic dimorphism encodes for either alanine or valine in the mitochondrial targeting sequence of manganese superoxide dismutase and could modulate its mitochondrial import.

METHODS

The DNA of 71 white patients with alcoholic liver disease and 79 white blood donors was amplified and genotyped.

RESULTS

The frequency of the alanine-encoding allele and the percentage of alanine homozygotes were higher in all patients than in controls and increased with the severity of liver lesions. The percentage of alanine homozygotes was 19% in controls, 17% in alcoholic patients with macrovacuolar steatosis, 43% in patients with microvesicular steatosis, 58% in patients with alcoholic hepatitis, and 69% in patients with cirrhosis. Alcohol consumption in alcoholics was similar whatever the genotype. Alanine homozygosity did not change the risk of developing macrovacuolar steatosis in alcoholics, but increased by 3-fold that of microvesicular steatosis, and 6- and 10-fold that of alcoholic hepatitis and cirrhosis.

CONCLUSIONS

Homozygosity for alanine in the mitochondrial targeting sequence of manganese superoxide does not modify alcohol consumption and the risk of macrovacuolar steatosis in alcoholics but is a major risk factor for severe alcoholic liver disease.

Acute and chronic hepatic steatosis lead to in vivo lipid peroxidation in mice

BACKGROUND/AIMS

Several liver diseases that are characterized by chronic steatosis lead to steatohepatitis lesions in some susceptible subjects. We tested the hypothesis that acute or chronic steatosis may lead to lipid peroxidation.

METHODS

Diverse steatogenic treatments were administered to mice, and lipid peroxidation was assessed by measuring thiobarbituric acid reactants in the liver and the exhalation of ethane in breath.

RESULTS

Administration of ethanol (5 g/kg), tetracycline, chlortetracycline, demeclocycline (0.25 mmol/kg each), amineptine (1 mmol/kg), amiodarone (1 mmol/kg), pirprofen (2 mmol/kg), or valproate (2 mmol/kg) led to microvesicular steatosis of the liver and lipid peroxidation. After tetracycline administration, hepatic triglycerides reached a maximum at 24 h and then declined; ethane exhalation followed a similar time course. Microvesicular steatosis and lipid peroxidation were also observed after 4 days of treatment with either ethionine (0.02 mmol/kg daily) or dexamethasone (0.25 mmol/kg daily) or after 7 days of tetracycline (0.25 mmol/kg daily) administration. Administration of ethanol in the drinking water for 5.5 months led to macrovacuolar and microvesicular steatosis, lipid peroxidation, and a few necrotic hepatocytes.

CONCLUSIONS

We conclude that acute or chronic fat deposition due to a variety of compounds was associated with lipid peroxidation in mice. We suggest that the presence of oxidizable fat in the liver leads to peroxidation, and that chronic lipid peroxidation might represent the common (but not exclusive) mechanism for the possible development of steatohepatitis lesions in conditions characterized by chronic steatosis.

Nuclear DNA damage during NAD(P)H oxidation by membrane redox chains

Nuclear DNA damage, as the result of active oxygen formation by NAD(P)H-dependent redox chains, was studied. Isolated rat liver nuclei were incubated in the presence of NAD(P)H and iron chelators. Nuclear DNA damage was analyzed by electrophoresis in alkaline agarose. DNA damage after the addition of electron donors alone or with FeCl3 or DFO-Fe3+ was not visualized. Dramatic decay of high molecular weight DNA was observed with EDTA-Fe3+ or DTPA-Fe3+ in the presence of NAD(P)H. SOD did not prevent DNA damage, whereas catalase was protective. DNA damage was revealed after the addition of cumene hydroperoxide with EDTA-Fe3+, and it was sharply increased in the presence of NADPH. It is suggested that alkoxyl radicals in addition to hydroxyl radicals are involved in DNA damage during NAD(P)H oxidation in the presence of iron chelators, which can be reduced by membrane redox chains.

Increased cytotoxicity of 3-morpholinosydnonimine to HepG2 cells in the presence of superoxide dismutase. Role of hydrogen peroxide and iron

3-Morpholinosydnonimine (SIN-1) is widely used to generate nitric oxide (NO(x).) and superoxide radical (O2-.). The effect of SOD on the toxicity of SIN-1 is complex, depending on what is the ultimate species responsible for toxicity. SIN-1 (< 1 mM) was only slightly toxic to HepG2 cells. Copper, zinc superoxide dismutase (Cu,Zn-SOD) or manganese superoxide dismutase (Mn-SOD) increased the toxicity of SIN-1. Catalase abolished, while sodium azide potentiated, this toxicity, suggesting a key role for H2O2 in the overall mechanism. Depletion of GSH from the HepG2 cells also potentiated the toxicity of SIN-1 plus SOD. Although Me2SO, sodium formate, and mannitol had no protective effect, iron chelators, thiourea and urate protected the cells against the SIN-1 plus Cu,Zn-SOD-mediated cytotoxicity. The cytotoxic effect of Cu,Zn-SOD but not Mn-SOD, showed a biphasic dose response being most pronounced at lower concentrations (10-100 units/ml). In the presence of SIN-1, Mn-SOD increased accumulation of H2O2 in a concentration-dependent manner. In contrast, Cu,Zn-SOD increased H2O2 accumulation from SIN-1 at low but not high concentrations of the enzyme, suggesting that high concentrations of the Cu,Zn-SOD interacted with the H2O2. EPR spin trapping studies demonstrated the formation of hydroxyl radical from the decomposition of H2O2 by high concentrations of the Cu,Zn-SOD. The cytotoxic effect of the NO donors SNAP and DEA/NO was only slightly enhanced by SOD; catalase had no effect. Thus, the oxidants responsible for the toxicity of SIN-1 and SNAP or DEA/NO to HepG2 cells under these conditions are different, with H2O2 derived from O2-. dismutation playing a major role with SIN-1. These results suggest that the potentiation of SIN-1 toxicity by SOD is due to enhanced production of H2O2, followed by site-specific damage of critical cellular sites by a transition metal-catalyzed reaction. These results also emphasize that the role of SOD as a protectant against oxidant damage is complex and dependent, in part, on the subsequent fate and reactivity of the generated H2O2.

Stimulation of NADH-dependent microsomal DNA strand cleavage by rifamycin SV

Rifamycin SV is an antibiotic anti-bacterial agent used in the treatment of tuberculosis. This drug can autoxidize, especially in the presence of metals, and generate reactive oxygen species. A previous study indicated that rifamycin SV can increase NADH-dependent microsomal production of reactive oxygen species. The current study evaluated the ability of rifamycin SV to interact with iron and increase microsomal production of hydroxyl radical, as detected by conversion of supercoiled plasmid DNA into the relaxed open circular state. The plasmid used was pBluescript II KS(-), and the forms of DNA were separated by agarose-gel electrophoresis. Incubation of rat liver microsomes with plasmid plus NADH plus ferric-ATP caused DNA strand cleavage. The addition of rifamycin SV produced a time- and concentration-dependent increase in DNA-strand cleavage. No stimulation by rifamycin SV occurred in the absence of microsomes, NADH or ferric-ATP. Stimulation occurred with other ferric complexes besides ferric-ATP, e.g. ferric-histidine, ferric-citrate, ferric-EDTA, and ferric-(NH4)2SO4. Rifamycin SV did not significantly increase the high rates of DNA strand cleavage found with NADPH as the microsomal reductant. The stimulation of NADH-dependent microsomal DNA strand cleavage was completely blocked by catalase, superoxide dismutase, GSH and a variety of hydroxyl-radical-scavenging agents, but not by anti-oxidants that prevent microsomal lipid peroxidation. Redox cycling agents, such as menadione and paraquat, in contrast with rifamycin SV, stimulated the NADPH-dependent reaction; menadione and rifamycin SV were superior to paraquat in stimulating the NADH-dependent reaction. These results indicate that rifamycin SV can, in the presence of an iron catalyst, increase microsomal production of reactive oxygen species which can cause DNA-strand cleavage. In contrast with other redox cycling agents, the stimulation by rifamycin SV is more pronounced with NADH than with NADPH as the microsomal reductant. Interactions between rifamycin SV, iron and NADH generating hydroxyl-radical-like species may play a role in some of the hepatotoxic effects associated with the use of this antibacterial antibiotic.

Boldine prevents human liver microsomal lipid peroxidation and inactivation of cytochrome P4502E1

Boldine, an alkaloid found in the leaves and bark of boldo, prevented the ferric-ATP catalyzed peroxidation of human liver microsomes. Lipid peroxidation, dependent upon electron transfer from NADPH or NADH, was comparably inhibited by boldine, with a K(I) value of about 5 microM. Inactivation and decreased content of human cytochrome P4502E1 as a consequence of incubating microsomes with ferric-ATP and reductant was completely prevented by boldine. However, inactivation of cytochrome P4502E1 by CCl4 was not prevented by boldine, although the alkaloid prevented CCl4-catalyzed lipid peroxidation. This suggests that the CCl4 inactivation of P4502E1 may be independent of CCl4-mediated lipid peroxidation. In view of its low toxicity, lack of effect on P450 activity, and strong inhibition of peroxidation of human liver microsomes, boldine may be valuable as an antioxidant and hepatoprotective agent.

DNA strand cleavage as a sensitive assay for the production of hydroxyl radicals by microsomes: role of cytochrome P4502E1 in the increased activity after ethanol treatment

There is increasing interest in the role of reactive oxygen radicals in the hepatotoxicity associated with ethanol consumption. Reactive oxygen intermediates interact with DNA and can cause single-strand breaks of supercoiled DNA. Experiments were carried out to evaluate the utility of this system as a sensitive assay for the detection of potent oxidants generated by rat liver microsomes isolated from pair-fed control rats and rats treated chronically with ethanol. DNA strand cleavage was assayed by monitoring the migration of the supercoiled and open circular forms in agarose. Microsomes catalysed DNA strand breakage with either NADPH or NADH as cofactors; iron was required to catalyse the reaction and various ferric complexes were effective in promoting the reaction. DNA strand cleavage was prevented by catalase, superoxide dismutase, GSH and hydroxyl-radical-scavenging agents, suggesting that a hydroxyl-radical-like species was the oxidant responsible for the breakage. This assay system proved to be much more sensitive in detecting hydroxyl radicals than are other methods, such as e.s.r. spectroscopy or oxidation of chemical scavenging agents with respect to the amount of microsomal protein and the nature and concentration of the iron catalyst required. Microsomes from ethanol-treated rats were more reactive than control microsomes in catalysing the DNA strand cleavage with either NADPH or NADH; increased catalytic activity was observed with various ferric complexes and was sensitive to the above antioxidants. Compared with preimmune IgG, anti-(cytochrome P4502E1) IgG had no effect on DNA strand cleavage by the control microsomes, but completely prevented the NADPH- and the NADH-dependent increased activity found with microsomes from the ethanol-treated rats. Inhibitors of cytochrome P4502E1, such as diethyl dithiocarbamate and tryptamine, also lowered the extent of increase of DNA strand cleavage produced by microsomes from the ethanol-treated rats. These results indicate that DNA strand cleavage is a very sensitive assay for detecting the production of hydroxyl radicals by microsomes and to demonstrate increased activity by microsomes after chronic ethanol treatment. This increased activity with NADPH and NADH is due, at least in part, to induction of cytochrome P4502E1.

Ferritin-dependent inactivation of microsomal glucose-6-phosphatase

Glucose-6-phosphatase (G6Pase) is a microsomal enzyme which is very sensitive to inactivation by lipid peroxidation. Experiments were carried out to evaluate whether ferritin, which is the major storage form of iron within cells, could catalyze inactivation of G6Pase and to determine the mechanism responsible for this effect of ferritin. Incubation of microsomes with NADPH in the absence of ferritin led to decreased activity of G6Pase. Ferritin stimulated this inactivation of G6Pase in a time- and concentration-dependent manner. Ferritin did not stimulate G6Pase inactivation when NADH replaced NADPH as the microsomal reductant. Superoxide dismutase but not catalase or DMSO prevented the ferritin-stimulated inactivation of G6Pase suggesting a role for superoxide, but not H2O2 or hydroxyl radical, in the overall mechanism. Trolox, at concentrations which prevent lipid peroxidation, also prevented the ferritin-catalyzed inactivation of G6Pase. Inhibition of G6Pase by ferritin was further enhanced in the presence of ATP but was inhibited in the presence of EDTA or desferrioxamine; ferric-ATP stimulates, whereas ferric-EDTA inhibits microsomal lipid peroxidation. The redox cycling agent paraquat increased the ability of ferritin to inactivate G6Pase by a reaction prevented by superoxide dismutase, trolox, EDTA, and desferrioxamine, but not by catalase or DMSO. Ferritin stimulated microsomal light emission, a reaction reflecting lipid peroxidation, with time and concentration dependence, and sensitivity to scavengers (trolox, superoxide dismutase), iron chelators and paraquat, identical to the inactivation of G6Pase. These results indicate that one possible toxicological consequence of ferritin-catalyzed lipid peroxidation is inhibition of microsomal enzymes such as G6Pase.

Oxygen free radical induced damage during intestinal ischemia/reperfusion in normal and xanthine oxidase deficient rats

This study looks at the role of xanthine oxidase (XO) in ischemia/reperfusion (I/R) induced intestinal mucosal damage using normal and xanthine oxidase deficient rats. Tungstate feeding for 3 days depleted the intestinal mucosal XO by 80%. A ligated loop of the rat small intestine (both normal and XO-deficient) was subjected to 1 h of total ischemia followed by 5 min revascularisation. The ensuing mucosal damage was assessed by biochemical and histological studies. Ischemia or I/R increased the XO levels in normal rats without any change in XO-deficient rats. Myeloperoxidase (a neutrophil marker) level was increased in both group of rats but it was comparatively higher in the XO-deficient rats. Accumulation of peroxidation products such as malondialdehyde, conjugated diene and increased production of hydroxyl radicals by microsomes were seen after ischemia and I/R and were similar in normal and XO-deficient rats. Studies on other parameters of peroxidation showed a decrease in polyunsaturated fatty acids and alpha-tocopherol, an increase in cysteine and cystine levels after I/R and were similar in both normal and XO-deficient rats. Histological results indicated gross morphological changes in the intestinal mucosa due to ischemia and I/R, and the damage was more severe in XO-deficient rats. These observations suggest that oxygen-derived free radicals are involved in the intestinal mucosal damage during I/R and infiltrated neutrophils rather than XO may be the primary source of free radicals under these conditions.

Stimulation of microsomal chemiluminescence by ferritin

The ability of ferritin to catalyze rat liver microsomal chemiluminescence was determined in the absence and presence of the redox cycling agent paraquat, and with either NADPH or NADH as reductant. Microsomal chemiluminescence was used as a index of lipid peroxidation. In the absence of added ferritin, NADPH-dependent microsomal light emission was 4-fold greater than the NADH-dependent reaction, and was not sensitive to superoxide dismutase, catalase or DMSO. Ferritin stimulated NADPH-, but not NADH-dependent chemiluminescence in a time- and concentration-dependent manner. The stimulation by ferritin was completely sensitive to superoxide dismutase, but not to catalase or DMSO, suggesting the requirement for superoxide to mobilize iron from ferritin. An iron ligand was not required for the stimulation by ferritin; the addition of certain ligands such as EDTA, DETAPAC or desferrioxamine resulted in inhibition of the stimulation by ferritin. Paraquat potentiated the effect of ferritin on microsomal chemiluminescence with NADPH as cofactor and was weakly stimulatory with NADH. The potentiation by paraquat plus ferritin was prevented by superoxide dismutase and was further elevated by ligands such as ATP. Chemiluminescence proved to be a more sensitive parameter than production of thiobarbituric acid-reactive components to evaluate the stimulation of oxygen radical production by iron released from ferritin, in the absence or in the presence of paraquat.

Increased ethane exhalation, an in vivo index of lipid peroxidation, in alcohol-abusers

Ethane exhalation was measured in 42 control subjects, 52 patients with various non-alcoholic liver diseases, and 89 alcohol abusers who had been admitted to hospital for alcohol withdrawal and assessment of liver disease (six with normal liver tests, 10 with steatosis with or without fibrosis, six with alcoholic hepatitis, 29 with cirrhosis, 34 with both cirrhosis and alcoholic hepatitis, and four with both cirrhosis and a hepatocellular carcinoma). Ethane exhalation was similar in control subjects and in patients with non-alcoholic liver diseases, but was five times higher in alcohol abusers. Ethane exhalation in alcohol abusers was significantly, but very weakly, correlated with the daily ethanol intake before hospital admission, and the histological score for steatosis, but not with the inflammation or alcoholic hepatitis scores. Ethane exhalation was inversely correlated with the duration of abstinence before the test. In nine alcoholic patients, the exhalation of ethane was measured repeatedly, and showed slow improvement during abstinence. Ethane exhalation was significantly but weakly correlated with the Pugh's score in patients with alcoholic cirrhosis. It is concluded that the mean ethane exhalation is increased in alcohol abusers. One of the possible mechanisms may be the presence of oxidizable fat in the liver. The weak correlation with the Pugh's score is consistent with the contribution of many other factors in the progression to severe liver disease.

Inhibition of rat liver microsomal lipid peroxidation by boldine

The alkaloid boldine, found in the leaves and bark of boldo, was an effective inhibitor of rat liver microsomal lipid peroxidation under a variety of conditions. The following systems all displayed a similar sensitivity to boldine: non-enzymatic peroxidation initiated by ferrous ammonium sulfate; iron-dependent peroxidation produced by ferric-ATP with either NADPH or NADH as cofactor; organic hydroperoxide-catalyzed peroxidation; and carbon tetrachloride plus NADPH-dependent peroxidation. Boldine inhibited the excess oxygen uptake associated with microsomal lipid peroxidation. Thus, boldine was effective in inhibiting iron-dependent and iron-independent microsomal lipid peroxidation, with 50% inhibition occurring at a concentration of about 0.015 mM. Boldine did not appear to react efficiently with superoxide radical or hydrogen peroxide, but was effective in competing for hydroxyl radicals with chemical scavengers. Concentrations of boldine which produced nearly total inhibition of lipid peroxidation had no effect on microsomal mixed-function oxidase activity nor did boldine appear to direct electrons from NADPH-cytochrome P450 reductase away from cytochrome P450. Boldine completely protected microsomal mixed-function oxidase activity against inactivation produced by lipid peroxidation. The effectiveness of boldine as an anti-oxidant under various conditions, and its low toxicity, suggest that this alkaloid may be an attractive agent for further evaluation as a clinically useful anti-oxidant.

Stimulation of microsomal production of reactive oxygen intermediates by rifamycin SV: effect of ferric complexes and comparisons between NADPH and NADH

Rifamycins are antibacterial antibiotics which are especially useful for the treatment of tuberculosis. Reactive oxygen intermediates are produced in the presence of rifamycin SV and metals such as copper or manganese. Experiments were carried out to evaluate the interaction of rifamycin SV with rat liver microsomes to catalyze the production of reactive oxygen species. At a concentration of 1 mM, rifamycin SV increased microsomal production of superoxide with NADPH as cofactor 3-fold, and with NADH as reductant by more than 5-fold. Rifamycin SV increased rates of H2O2 production by the microsomes twofold with NADPH, and 4- to 8-fold with NADH. In the presence of various iron complexes, microsomes generated hydroxyl radical-like (.OH) species. Rifamycin SV had no effect on NADPH-dependent microsomal .OH production, irrespective of the iron chelate. A striking stimulation of .OH production was found with NADH as the reductant, ranging from 2- to 4-fold with catalyst such as ferric-EDTA and ferric-DTPA to more than 10-fold with ferric-ATP, -citrate, or -histidine. Catalase and competitive .OH scavengers lowered rates of .OH production (chemical scavenger oxidation) and prevented the stimulation by rifamycin. Superoxide dismutase had no effect on the NADH-dependent rifamycin stimulation of .OH production with ferric-EDTA or -DTPA, but was inhibitory with the other ferric complexes. In contrast to the stimulatory effects on production of O2-., H2O2, and .OH, rifamycin SV was a potent inhibitor of microsomal lipid peroxidation. These results show that rifamycin SV stimulates microsomal production of reactive oxygen intermediates, and in contrast to results with other redox cycling agents, is especially effective with NADH as the microsomal reductant. These interactions may contribute to the hepatotoxicity associated with use of rifamycin, and, since alcohol metabolism increases NADH availability, play a role in the elevated toxic actions of rifamycin plus alcohol.

Increased NADH-dependent production of reactive oxygen intermediates by microsomes after chronic ethanol consumption: comparisons with NADPH

Microsomes from chronic ethanol-fed rats were previously shown to catalyze the NADPH-dependent production of reactive oxygen intermediates at elevated rates compared to controls. Recent studies have shown that NADH can also serve as a reductant and promote the production of oxygen radicals by microsomes. The current study evaluated the influence of chronic ethanol consumption on NADH-dependent microsomal production of reactive oxygen intermediates, and compared the results with NADH to those of NADPH. Microsomal oxidation of chemical scavengers, taken as a reflection of the production of hydroxyl radical (.OH)-like species was increased about 50% with NADH as cofactor and about 100% with NADPH after chronic ethanol consumption. The potent inhibition of the production of .OH-like species by catalase suggests a precursor role for H2O2 in .OH production. Rates of NADH- and NADPH-dependent H2O2 production were increased by about 50 and 70%, respectively, after chronic ethanol consumption. A close correlation between rates of H2O2 production and generation of .OH-like species was observed for both NADH and NADPH, and increased rates of H2O2 production appear to play an important role in the elevated generation of .OH-like species after chronic ethanol treatment. Microsomal lipid peroxidation was elevated about 60% with NADH, and 120% with NADPH, after ethanol feeding. With both types of microsomal preparations, the characteristics of the NADH-dependent reactions were similar to the NADPH-dependent reactions, e.g., sensitivity to antioxidants and free radical scavengers and catalytic effectiveness of ferric complexes. However, rates with NADPH exceeded the NADH-dependent rates by 50 to 100%, and the increased production of reactive oxygen intermediates by microsomes after ethanol treatment was greater with NADPH (about twofold) than with NADH (about 50%). Oxidation of ethanol results in an increase in hepatic NADH levels and interaction of NADH, iron, and microsomes can produce potent oxidants capable of initiating lipid peroxidation and oxidizing .OH scavengers. These acute metabolic interactions produced by ethanol-derived NADH are increased, not attenuated, in microsomes from chronic ethanol-fed rats, and it is possible that such increases in NADH (and NADPH)-dependent production of reactive oxygen species play a role in the development of oxidative stress in the liver as a consequence of ethanol treatment.

NADH-dependent generation of reactive oxygen species by microsomes in the presence of iron and redox cycling agents

NADH was found previously to catalyze the reduction of various ferric complexes and to promote the generation of reactive oxygen species by rat liver microsomes. Experiments were conducted to evaluate the ability of NADH to interact with ferric complexes and redox cycling agents to catalyze microsomal generation of potent oxidizing species. In the presence of iron, the addition of menadione increased NADPH- and NADH-dependent oxidation of hydroxyl radical (.OH) scavenging agents; effective iron complexes included ferric-EDTA, -diethylenetriamine pentaacetic acid, -ATP, -citrate, and ferric ammonium sulfate. The stimulation produced by menadione was sensitive to catalase and to competitive .OH scavengers but not to superoxide dismutase. Paraquat, irrespective of the iron catalyst, did not increase significantly the NADH-dependent oxidation of .OH scavengers under conditions in which the NADPH-dependent reaction was increased. Menadione promoted H2O2 production with either NADH or NADPH; paraquat was stimulatory only with NADPH. Stimulation of H2O2 generation appears to play a major role in the increased production of .OH-like species. Menadione inhibited NADH-dependent microsomal lipid peroxidation, whereas paraquat produced a 2-fold increase. Neither the control nor the paraquat-enhanced rates of lipid peroxidation were sensitive to catalase, superoxide dismutase, or dimethyl sulfoxide. Although the NADPH-dependent microsomal system shows greater reactivity and affinity for interacting with redox cycling agents, the capability of NADH to promote menadione-catalyzed generation of .OH-like species and H2O2 or paraquat-mediated lipid peroxidation may also contribute to the overall toxicity of these agents in biological systems. This may be especially significant under conditions in which the production of NADH is increased, e.g. during ethanol oxidation by the liver.

Role of iron, hydrogen peroxide and reactive oxygen species in microsomal oxidation of glycerol to formaldehyde

Rat liver microsomes can oxidize glycerol to formaldehyde. This oxidation is sensitive to catalase and glutathione plus glutathione peroxidase, suggesting a requirement for H2O2 in the overall pathway of glycerol oxidation. Hydrogen peroxide can not replace NADPH in supporting glycerol oxidation; however, added H2O2 increased the NADPH-dependent rate. Ferric chloride or ferric-ATP had no effect on glycerol oxidation, whereas ferric-EDTA was inhibitory. Certain iron chelators such as desferrioxamine, EDTA or diethylenetriaminepentaacetic acid, but not others such as ADP or citrate, inhibited glycerol oxidation. The inhibition by desferrioxamine could be overcome by added iron. Neither superoxide dismutase nor hydroxyl radical scavengers had any effect on glycerol oxidation. With the exception of propyl gallate, several antioxidants which inhibit lipid peroxidation had no effect on formaldehyde production from glycerol. The inhibition by propyl gallate could be overcome by added iron. In contrast to glycerol, formaldehyde production from dimethylnitrosamine was not sensitive to catalase or iron chelators, thus disassociating the overall pathway of glycerol oxidation from typical mixed-function oxidase activity of cytochrome P450. These studies indicate that H2O2 and nonheme iron are required for glycerol oxidation to formaldehyde. The responsible oxidant is not superoxide, H2O2, or hydroxyl radical. Cytochrome P450 may function to generate the H2O2 and reduce the nonheme iron. There may be additional roles for P450 since rates of formaldehyde production by microsomes exceed rates found with model chemical systems. Elevated rates of H2O2 production by certain P450 isozymes, e.g., P450 IIE1, may contribute to enhanced rates of glycerol oxidation.

Effect of exposure of various oxidants on rat liver and intestinal microsomes--a comparative study

Rat liver and intestinal microsomes were exposed to various free radical generating systems and their effect were assessed by studying different parameters such as formation of malonaldehyde (MDA) and conjugated diene, arachidonic acid depletion and alteration in protein thiol groups and tocopherol levels. These studies revealed that liver being highly vulnerable tissue showed all the effects of free radical attack whereas intestinal microsomes were resistant to most oxidants except iron independent generation of free radicals using 2-2'-azobis (2-amidinopropane) dihydrochloride (ABAP). Intestinal microsomes were found to contain considerable amount of non-esterified fatty acids in total lipid fraction as compared to liver microsomes and iron-fatty acid complex may be incapable of participating in peroxidation. In vitro measurement of hydroxyl radical generation showed that intestinal microsomes were incapable of generating these active species. These results suggest that iron dependent free radical mediated lipid peroxidation might not occur in intestinal epithelial cells.