Detoxification reactions in isolated hepatocytes. Role of glutathione peroxidase, catalase, and formaldehyde dehydrogenase in reactions relating to N-demethylation by the cytochrome P-450 system

Outcome of early emergency intubation and early emergency dialysis in deliberate self-harm with formic acid in a tertiary care center in South India: A retrospective cohort study

OBJECTIVE

The objective is to evaluate the outcome of early emergency intubation and early dialysis in formic acid (FA) poisoning and to determine the clinical features associated with its mortality.

METHODS

It is a retrospective cohort study of 78 patients who presented to the emergency medicine department from July 2008 to June 2015 with alleged history and clinical features of FA poisoning. The outcome of early intubation and early dialysis was studied in terms of 7-day and 30-day mortality. The outcome was compared in severe and not severe groups separately. Severity was graded according to Med-Tu chart used for corrosive poisoning.

RESULTS

In the severe group (n = 53), early dialysis was done in 15 patients. There was 53% (n = 8) 30-day mortality. In the group where early dialysis was not done there was a significant increase in mortality 92.1% (n = 35). This was statistically significant with a P = 0.003. In a similar fashion 7-day mortality was analyzed in the severe group where mortality was higher when early dialysis was not done. In not severe group early dialysis has minimally decreased the mortality. Early intubation in severe group did not demonstrate any mortality benefit. Patients who were intubated early and not intubated early had equally high mortality. In not severe group, intubation could not make any significant difference in mortality.

CONCLUSION

In this retrospective study, we observed that early dialysis in the severe group has a better outcome in terms of 7-day and 30-day mortality.

Findings in redox biology: From H2O2 to oxidative stress

My interest in biological chemistry proceeded from enzymology in vitro to the study of physiological chemistry in vivo Investigating biological redox reactions, I identified hydrogen peroxide (H2O2) as a normal constituent of aerobic life in eukaryotic cells. This finding led to developments that recognized the essential role of H2O2 in metabolic redox control. Further research included studies on GSH, toxicological aspects (the concept of "redox cycling"), biochemical pharmacology (ebselen), nutritional biochemistry and micronutrients (selenium, carotenoids, flavonoids), and the concept of "oxidative stress." Today, we recognize that oxidative stress is two-sided. It has its positive side in physiology and health in redox signaling, "oxidative eustress," whereas at higher intensity, there is damage to biomolecules with potentially deleterious outcome in pathophysiology and disease, "oxidative distress." Reflecting on these developments, it is gratifying to witness the enormous progress in redox biology brought about by the science community in recent years.

Redox Equivalents and Mitochondrial Bioenergetics

Mitochondrial energy metabolism depends upon high-flux and low-flux electron transfer pathways. The former provide the energy to support chemiosmotic coupling for oxidative phosphorylation. The latter provide mechanisms for signaling and control of mitochondrial functions. Few practical methods are available to measure rates of individual mitochondrial electron transfer reactions; however, a number of approaches are available to measure steady-state redox potentials (E _h) of donor/acceptor couples, and these can be used to gain insight into rate controlling reactions as well as mitochondrial bioenergetics. Redox changes within the respiratory electron transfer pathway are quantified by optical spectroscopy and measurement of changes in autofluorescence. Low-flux pathways involving thiol/disulfide redox couples are measured by redox Western blot and mass spectrometry-based redox proteomics. Together, the approaches provide the opportunity to develop integrated systems biology descriptions of mitochondrial redox signaling and control mechanisms.

Role of Cell Death in Toxicology: Does It Matter How Cells Die?

My research activity started with studies on drug metabolism in rat liver microsomes in the early 1960s. The CO-binding pigment (cytochrome P450) had been discovered a few years earlier and was subsequently found to be involved in steroid hydroxylation in adrenal cortex microsomes. Our early studies suggested that it also participated in the oxidative demethylation of drugs catalyzed by liver microsomes, and that prior treatment of the animals with phenobarbital caused increased levels of the hemoprotein in the liver, and similarly enhanced rates of drug metabolism. Subsequent studies of cytochrome P450-mediated metabolism of toxic drugs in freshly isolated rat hepatocytes characterized critical cellular defense systems and identified mechanisms by which accumulating toxic metabolites could damage and kill the cells. These studies revealed that multiple types of cell death could result from the toxic injury, and that it is important to know which type of cell death results from the toxic injury.

Hydrogen peroxide as a central redox signaling molecule in physiological oxidative stress: Oxidative eustress

Hydrogen peroxide emerged as major redox metabolite operative in redox sensing, signaling and redox regulation. Generation, transport and capture of H2O2 in biological settings as well as their biological consequences can now be addressed. The present overview focuses on recent progress on metabolic sources and sinks of H2O2 and on the role of H2O2 in redox signaling under physiological conditions (1-10nM), denoted as oxidative eustress. Higher concentrations lead to adaptive stress responses via master switches such as Nrf2/Keap1 or NF-κB. Supraphysiological concentrations of H2O2 (>100nM) lead to damage of biomolecules, denoted as oxidative distress. Three questions are addressed: How can H2O2 be assayed in the biological setting? What are the metabolic sources and sinks of H2O2? What is the role of H2O2 in redox signaling and oxidative stress?

Hydrogen peroxide and central redox theory for aerobic life: A tribute to Helmut Sies: Scout, trailblazer, and redox pioneer

When Rafael Radi and I wrote about Helmut Sies for the Redox Pioneer series, I was disappointed that the Editor restricted us to the use of "Pioneer" in the title. My view is that Helmut was always ahead of the pioneers: He was a scout discovering paths for exploration and a trailblazer developing strategies and methods for discovery. I have known him for nearly 40 years and greatly enjoyed his collegiality as well as brilliance in scientific scholarship. He made monumental contributions to 20th century physiological chemistry beginning with his first measurement of H2O2 in rat liver. While continuous H2O2 production is dogma today, the concept of H2O2 production in mammalian tissues was largely buried for half a century. He continued this leadership in research on oxidative stress, GSH, selenium, and singlet oxygen, during the timeframe when physiological chemistry and biochemistry transitioned to contemporary 21st century systems biology. His impact has been extensive in medical and health sciences, especially in nutrition, aging, toxicology and cancer. I briefly summarize my interactions with Helmut, stressing our work together on the redox code, a set of principles to link mitochondrial respiration, bioenergetics, H2O2 metabolism, redox signaling and redox proteomics into central redox theory.

Modulation of nitrosative stress via glutathione-dependent formaldehyde dehydrogenase and S-nitrosoglutathione reductase

Glutathione-dependent formaldehyde dehydrogenase (GFD) from Taiwanofungus camphorata plays important roles in formaldehyde detoxification and antioxidation. The enzyme is bifunctional. In addition to the GFD activity, it also functions as an effective S-nitrosoglutathione reductase (GSNOR) against nitrosative stress. We investigated the modulation of HEK (human embryonic kidney) 293T cells under nitrosative stress by transfecting a codon optimized GFD cDNA from Taiwanofungus camphorata (Tc-GFD-O) to these cells. The parental and transfected HEK 293T cells were then subjected to S-nitrosoglutathione treatment to induce nitrosative stress. The results showed that in Tc-GFD-O-transfected 293T cells, the expression and activity of GFD increased. Additionally, these cells under the nitrosative stress induced by S-nitrosoglutathione showed both higher viability and less apoptosis than the parental 293T cells. This finding suggests that the Tc-GFD-O in HEK 293T cells may provide a protective function under nitrosative stress.

Redox equivalents and mitochondrial bioenergetics

Mitochondrial energy metabolism depends upon high-flux and low-flux electron transfer pathways. The former provide the energy to support chemiosmotic coupling for oxidative phosphorylation. The latter provide mechanisms for signaling and control of mitochondrial functions. Few practical methods are available to measure rates of individual mitochondrial electron transfer reactions; however, a number of approaches are available to measure steady-state redox potentials (E (h)) of donor/acceptor couples, and these can be used to gain insight into rate-controlling reactions as well as mitochondrial bioenergetics. Redox changes within the respiratory electron transfer pathway are quantified by optical spectroscopy and measurement of changes in autofluorescence. Low-flux pathways involving thiol/disulfide redox couples are measured by redox western blot and mass spectrometry-based redox proteomics. Together, the approaches provide the opportunity to develop integrated systems biology descriptions of mitochondrial redox signaling and control mechanisms.

One carbon metabolism in SAR11 pelagic marine bacteria

The SAR11 Alphaproteobacteria are the most abundant heterotrophs in the oceans and are believed to play a major role in mineralizing marine dissolved organic carbon. Their genomes are among the smallest known for free-living heterotrophic cells, raising questions about how they successfully utilize complex organic matter with a limited metabolic repertoire. Here we show that conserved genes in SAR11 subgroup Ia (Candidatus Pelagibacter ubique) genomes encode pathways for the oxidation of a variety of one-carbon compounds and methyl functional groups from methylated compounds. These pathways were predicted to produce energy by tetrahydrofolate (THF)-mediated oxidation, but not to support the net assimilation of biomass from C1 compounds. Measurements of cellular ATP content and the oxidation of ¹⁴C-labeled compounds to ¹⁴CO₂ indicated that methanol, formaldehyde, methylamine, and methyl groups from glycine betaine (GBT), trimethylamine (TMA), trimethylamine N-oxide (TMAO), and dimethylsulfoniopropionate (DMSP) were oxidized by axenic cultures of the SAR11 strain Ca. P. ubique HTCC1062. Analyses of metagenomic data showed that genes for C1 metabolism occur at a high frequency in natural SAR11 populations. In short term incubations, natural communities of Sargasso Sea microbial plankton expressed a potential for the oxidation of ¹⁴C-labeled formate, formaldehyde, methanol and TMAO that was similar to cultured SAR11 cells and, like cultured SAR11 cells, incorporated a much larger percentage of pyruvate and glucose (27–35%) than of C1 compounds (2–6%) into biomass. Collectively, these genomic, cellular and environmental data show a surprising capacity for demethylation and C1 oxidation in SAR11 cultures and in natural microbial communities dominated by SAR11, and support the conclusion that C1 oxidation might be a significant conduit by which dissolved organic carbon is recycled to CO₂ in the upper ocean.

CARDIAC-SPECIFIC OVEREXPRESSION OF CATALASE PROLONGS LIFESPAN AND ATTENUATES AGEING-INDUCED CARDIOMYOCYTE CONTRACTILE DYSFUNCTION AND PROTEIN DAMAGE

1. Oxidative stress plays a role in senescence-associated organ deterioration. This is supported by the beneficial effects of anti-oxidants against ageing-related organ damage, although their role in cardiac ageing has not been elucidated. 2. The aim of the present study was to examine the impact of cardiac-specific overexpression of catalase, an enzyme for H(2)O(2) detoxification, on cardiac contractile function and protein damage in young (3-4 months) and old (26-28 months) male mice. Lifespan was analysed using the Kaplan-Meier survival curve. Cardiomyocyte contractile indices at various stimulus frequencies (0.1-5.0 Hz) were analysed, including peak shortening (PS), time to 90% PS, time to 90% relengthening (TR(90)) and maximal velocity of shortening/relengthening (+/-dL/dt). Protein damage was assessed using protein carbonyl formation. Catalase transgenic mice showed longer lifespan than wild-type FVB mice. The catalase transgene itself did not alter bodyweight or organ weight, or myocyte function. Ageing depressed +/-dL/dt and prolonged TR(90), but had no effect on other indices in FVB mice. Increased frequency triggered decreases in PS amplitude were exaggerated in aged FVB myocytes. Interestingly, ageing-induced mechanical defects were significantly attenuated in myocytes from catalase mice. Protein carbonyl formation was elevated in aged FVB compared with young FVB mice, which was significantly diminished in catalase mice. The proteomes of the myocardium of young or old FVB and catalase mice were compared using two-dimensional gel electrophoresis and mass spectrometry. Six proteins with differential expression between young and old FVB groups were tentatively identified, some of which were reversed by catalase. 3. In summary, the present data suggest that catalase protects cardiomyocytes from ageing-induced contractile defects and protein damage.

Positive and negative transcriptional regulators of glutathione-dependent formaldehyde metabolism

A glutathione (GSH)-dependent pathway is used for formaldehyde metabolism by a wide variety of prokaryotes and eukaryotes. In this pathway, S-hydroxymethylglutathione, produced by the reaction of formaldehyde with the thiolate moiety of glutathione, is the substrate for a GSH-dependent formaldehyde dehydrogenase (GSH-FDH). While expression of GSH-FDH often increases in the presence of metabolic or exogenous sources of formaldehyde, little is known about the factors that regulate this response. Here, we identify two signal transduction pathways that regulate expression of adhI, the gene encoding GSH-FDH, in Rhodobacter sphaeroides. The loss of the histidine kinase response regulator pair RfdRS or the histidine kinase RfdS increases adhI transcription in the absence of metabolic sources of formaldehyde. Cells lacking RfdRS further increase adhI expression in the presence of metabolic sources of formaldehyde (methanol), suggesting that this negative regulator of GSH-FDH expression does not respond to this compound. In contrast, mutants lacking the histidine kinase response regulator pair AfdRS or the histidine kinase AfdS cannot induce adhI expression in the presence of either formaldehyde or metabolic sources of this compound. AfdR stimulates activity of the adhI promoter in vitro, indicating that this protein is a direct activator of GSH-FDH expression. Activation by AfdR is detectable only after incubation of the protein with acetyl phosphate, suggesting that phosphorylation is necessary for transcription activation. Activation of adhI transcription by acetyl-phosphate-treated AfdR in vitro is inhibited by a truncated RfdR protein, suggesting that this protein is a direct repressor of GSH-FDH expression. Together, the data indicate that AfdRS and RfdRS positively and negatively regulate adhI transcription in response to different signals.

A glutathione-dependent formaldehyde-activating enzyme (Gfa) from Paracoccus denitrificans detected and purified via two-dimensional proton exchange NMR spectroscopy

The formation of S-hydroxymethylglutathione from formaldehyde and glutathione is a central reaction in the consumption of the cytotoxin formaldehyde in some methylotrophic bacteria as well as in many other organisms. We describe here the discovery of an enzyme from Paracoccus denitrificans that accelerates this spontaneous condensation reaction. The rates of S-hydroxymethylglutathione formation and cleavage were determined under equilibrium conditions via two-dimensional proton exchange NMR spectroscopy. The pseudo first order rate constants k(1)* were estimated from the temperature dependence of the reaction and the signal to noise ratio of the uncatalyzed reaction. At 303 K and pH 6.0 k(1)* was found to be 0.02 s(-1) for the spontaneous reaction. A 10-fold increase of the rate constant was observed upon addition of cell extract from P. denitrificans grown in the presence of methanol corresponding to a specific activity of 35 units mg(-1). Extracts of cells grown in the presence of succinate revealed a lower specific activity of 11 units mg(-1). The enzyme catalyzing the conversion of formaldehyde and glutathione was purified and named glutathione-dependent formaldehyde-activating enzyme (Gfa). The gene gfa is located directly upstream of the gene for glutathione-dependent formaldehyde dehydrogenase, which catalyzes the subsequent oxidation of S-hydroxymethylglutathione. Putative proteins with sequence identity to Gfa from P. denitrificans are present also in Rhodobacter sphaeroides, Sinorhizobium meliloti, and Mesorhizobium loti.

Link between the membrane-bound pyridine nucleotide transhydrogenase and glutathione-dependent processes in Rhodobacter sphaeroides

The presence of a glutathione-dependent pathway for formaldehyde oxidation in the facultative phototroph Rhodobacter sphaeroides has allowed the identification of gene products that contribute to formaldehyde metabolism. Mutants lacking the glutathione-dependent formaldehyde dehydrogenase (GSH-FDH) are sensitive to metabolic sources of formaldehyde, like methanol. This growth phenotype is correlated with a defect in formaldehyde oxidation. Additional methanol-sensitive mutants were isolated that contained Tn5 insertions in pntA, which encodes the alpha subunit of the membrane-bound pyridine nucleotide transhydrogenase. Mutants lacking transhydrogenase activity have phenotypic and physiological characteristics that are different from those that lack GSH-FDH activity. For example, cells lacking transhydrogenase activity can utilize methanol as a sole carbon source in the absence of oxygen and do not display a formaldehyde oxidation defect, as determined by whole-cell (13)C-nuclear magnetic resonance. Since transhydrogenase can be a major source of NADPH, loss of this enzyme could result in a requirement for another source for this compound. Evidence supporting this hypothesis includes increased specific activities of other NADPH-producing enzymes and the finding that glucose utilization by the Entner-Doudoroff pathway restores aerobic methanol resistance to cells lacking transhydrogenase activity. Mutants lacking transhydrogenase activity also have higher levels of glutathione disulfide under aerobic conditions, so it is consistent that this strain has increased sensitivity to oxidative stress agents like diamide, which are known to alter the oxidation reduction state of the glutathione pool. A model will be presented to explain the role of transhydrogenase under aerobic conditions when cells need glutathione both for GSH-FDH activity and to repair oxidatively damaged proteins.

Platelet dopamine receptors and oxidative stress parameters as markers of manganese toxicity

The present study has been undertaken to investigate whether neurotoxic effects of manganese (Mn) are reflected in platelets in rats to monitor the usefulness of platelet as peripheral model. Exposure of rats to Mn (10 or 15 mg/kg bw, i.p.) for 45 days caused a significant increase in membrane fluidity as evidenced by decrease in fluorescence polarisation in platelets (11% and 14%) and striatum (9% and 13%). These rats exhibited a significant increase in superoxide dismutase activity both in platelets (24% and 37%) and striatum (31% and 42%), respectively, in comparison to controls. Exposure of rats to Mn for 45 days (15 mg/kg bw, i.p.) caused a significant decrease in reduced glutathione content (platelets 20%, striatum 24%) and catalase activity (platelets 35%, striatum 44%) compared to control rats. Rats exposed to Mn (10 or 15 mg/ kg bw, i.p.) for 15 days exhibited a significant increase in dopamine receptors both in platelets (55% and 40%) and striatum (38% and 31%). The results suggest that exposure to Mn may alter the membrane functions and impair the anti-oxidant defense mechanism both in platelets and brain. The study also suggests that dopaminergic mechanisms are impaired following Mn exposure and such changes are reflected in platelets. Interestingly, parallel changes both in striatum and platelets, as observed in the present study, strengthen the usefulness of platelets as a peripheral neuronal model.

In vitro toxicity assessment of a new series of high energy compounds

Hydrazine is an aircraft fuel and propellant used by the US Air Force. Due to its toxicity the Propulsion Directorate of the Air Force Research Laboratory (AFRL/PR) has investigated alternative chemicals to replace hydrazine. AFRL/PR has synthesized a series of high energy chemicals (HECs), primarily hydrazine derivatives and amino containing compounds such as hydrazinium nitrate (HZN), 2-hydroxyethyl-hydrazine nitrate (HEHN), diethyl hydrazine nitrate (DEHN), ethanolamine nitrate (EAN), histamine dinitrate (HDN) and methoxylamine nitrate (MAN) to study as alternative chemical candidates. Although HECs are reliable constituents of powered propellant systems, they constitute an important class of toxic agents to which military and civilian personnel can be exposed. The current study was undertaken to examine the toxicity of HECs in primary hepatocytes in vitro. The effects of short-term exposure (4 h) of hepatocytes to HECs were investigated with reference to viability, mitochondrial function and oxidative stress markers. The results showed a decrease in mitochondrial activity, increase in lactate dehydrogenase (LDH) leakage and depletion of reduced glutathione (GSH) levels. The levels of reactive oxygen species (ROS) increased dose dependently in HZN, MAN and HDN exposed cells. However, there was no induction of ROS generation in EAN, DEHN and HEHN exposed cells. Depletion of GSH in hepatocytes by buthionine sulfoximine (BSO) prior to exposure to HZN increased its toxicity. The results suggest that at least one mechanism of HEC toxicity is mediated through oxidative stress.

Effects of 2(RS)-n-propylthiazolidine-4(R)-carboxylic acid on extrahepatic sulfhydryl levels in mice treated with acetaminophen

The cysteine (Cys) precursor 2(RS)-n-propylthiazolidine-4(R)-carboxylic acid (PTCA) has been shown to protect against acetaminophen (APAP)-induced hepatic GSH, GSSG, and Cys depletion and hepatic necrosis. The aim of this study was to determine the effects of PTCA on the concentrations of sulfhydryl compounds in extrahepatic tissues, including renal cortex, whole blood, and brain, in C57BL/6 mice treated with hepatotoxic doses of APAP. PTCA (1-5 mmol/kg, i.p.) was administered 30 min after the administration of APAP at a dose (800 mg/kg; 5.29 mmol/kg, i.p.) that depleted hepatic GSH and Cys at 4 hr by 95 and 86%, respectively. Tissue concentrations of GSH and Cys were determined by HPLC. At 4 hr following APAP administration, renal cortical GSH and Cys concentrations were decreased to 64 and 39%, respectively, of vehicle-treated control values, and blood concentrations were decreased to 87 and 30%, respectively, of vehicle controls. Brain GSH and Cys were not depleted by APAP. PTCA at 5 mmol/kg (i) attenuated the APAP-induced depletion of GSH and Cys at 4 hr in renal cortex (78 and 65%, respectively, of vehicle controls), (ii) prevented APAP-induced Cys depletion in blood (670% of vehicle controls) with no effect on GSH concentration (94% of vehicle controls), and (iii) increased GSH and Cys concentrations in brain (119 and 411%, respectively, of vehicle controls). The results demonstrate a high degree of tissue selectivity in the APAP-induced depletion of GSH and Cys, and in the effectiveness of PTCA in maintaining and even elevating sulfhydryl levels in extrahepatic tissues of APAP-treated mice.

Reduced levels of catalase activity potentiate MPP+-induced toxicity: comparison between MN9D cells and CHO cells

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) has been shown to be toxic by inducing oxygen free radicals in the mammalian nervous system, especially in the nigrostriatal dopaminergic system. The present study was designed to compare the toxic effects of MPP+, the active metabolite of MPTP, in MN9D neuronal cells that exhibit relatively low levels of catalase activity, as compared to CHO cells, which exhibit high levels of catalase activity. The survival of the MN9D cells in the presence of 250 microM MPP+ was less than 10%, whereas CHO cells exhibited 70% survival at the same concentration of MPP+. The ED50 values of MPP+ in MN9D and CHO cell lines were 60-600 microM, respectively. MN9D cells contain less catalase, an enzyme believed to be involved in the detoxification of free radicals compared to CHO cells. The catalase activity was 2 Units/mg protein in MN9D cells and 30 U/mg protein in CHO cells. The catalase activity in CHO cells increased with increasing MPP+ concentrations from 100-500 microM, however, it decreased at 1 mM MPP+. In contrast, catalase activity in MN9D remained the same at all MPP+ concentrations. When the CHO cells were pre-treated with 10-25 mM 3-aminotriazole (3-AT), which inhibits catalase activity, and exposed to MPP+ at various concentrations, they became susceptible to MPP+. It is evident from these data that the differential susceptibility to MPP+ in these two cell lines are due to differences in catalase activity. In addition, the inhibition of constituentive catalase activity in CHO cells by 3-AT treatment enhances their susceptibility. In conclusion, the study demonstrates that catalase activity represents an important defence mechanism in MPTP-induced toxicity.

Pathways for transcriptional activation of a glutathione-dependent formaldehyde dehydrogenase gene

The widespread occurrence of glutathione-dependent formaldehyde dehydrogenases (GSH-FDH) suggests that this enzyme serves a conserved function in preventing the cytogenetic and potentially lethal interaction of formaldehyde with nucleic acids, proteins and other cell constituents. Despite this potential role of GSH-FDH, little is known about how its expression is regulated. Here, we identify metabolic and genetic signals that activate transcription of a GSH-FDH gene (adhI) in the bacterium Rhodobacter sphaeroides. Activity of the adhI promoter is increased by both exogenous formaldehyde and metabolic sources of this toxin. Elevated adhI promoter activity in DeltaGSH-FDH mutants implicates formaldehyde or the glutathione adduct that serves as a GSH-FDH substrate, S-hydroxymethylglutathione, as a transcriptional effector. From studying adhI expression in different host mutants, we find that the photosynthetic response regulator PrrA and the trans-acting spd-7 mutation increase function of this promoter. The behavior of a nested set of adhI::lacZ fusions indicates that activation by formaldehyde, PrrA and spd-7 requires only sequences 55 bp upstream of the start of transcription. A working model is presented to explain how GSH-FDH expression responds to formaldehyde and global signals generated from the reduced pyridine nucleotide produced by the activity of this enzyme.

Suppression of doxorubicin cardiotoxicity by overexpression of catalase in the heart of transgenic mice

Weak antioxidant capacity, particularly low catalase activity in the heart, may be a factor responsible for the high sensitivity of this organ to doxorubicin-induced oxidative damage. To test this hypothesis, a heart-specific promoter was used to drive the expression of murine catalase cDNA in transgenic mice. Fifteen healthy transgenic mouse lines were produced. Cardiac catalase activity was constitutively overexpressed in both atrium and ventricule, ranging from 2- to 630-fold higher than normal. This enzyme activity was not altered in liver, kidneys, lungs, and skeletal muscles. Other antioxidant components, including glutathione, glutathione peroxidase, glutathione reductase, metallothionein, and superoxide dismutase, were not altered in the catalase-overexpressing heart. Mice (7 weeks old) from several transgenic lines and from nontransgenic controls were treated intraperitoneally with doxorubicin at a single dose of 20 mg/kg and sacrificed on the 4th day after treatment. As compared to normal controls, transgenic lines expressing catalase activity 60- or 100-fold higher than normal exhibited a significant resistance to doxorubicin-induced cardiac lipid peroxidation, elevation of serum creatine phosphokinase, and functional changes in the isolated atrium. Interestingly, 200-fold or greater elevation of catalase activity did not provide protection. The results provide direct evidence for the role of catalase in doxorubicin cardiotoxic responses.

Inhibition of the Ca pump of intact red blood cells by t-butyl hydroperoxide: importance of glutathione peroxidase

Incubation of human red blood cells (RBCs) with t-butyl hydroperoxide (tBHP) resulted in inhibition of the Ca-pump ATPase. This was demonstrated using an assay of the Ca-pump ATPase activity in intact RBCs. In this assay, activity of the Ca-pump ATPase is expressed as the rate constant of the initial loss of ATP in RBCs exposed to Ca and A23187. Pseudo-first-order rate constants (Ca-pump ATPase rate constants) were lower in the presence of tBHP versus controls. Incubation of RBCs with tBHP resulted in both a time- and concentration-dependent inhibition of the Ca-pump ATPase (IC50 approximately 1 mM). Incubation of RBCs with tBHP also resulted in decreased oxyhemoglobin, increased methemoglobin and increased thiobarbituric acid reactive substances (TBARS). GSH levels were significantly lower in the presence of tBHP. GSH fell from a control value of 2.2 mmol/l RBC to 0.46 mmol/l RBC after incubation with 0.25 mM tBHP for 15 min. Both butylated hydroxytoluene and stobadine prevented the formation of TBARS and were partially effective in protecting the Ca-pump ATPase from tBHP-induced inhibition. Dithiothreitol was completely effective in preventing the tBHP-induced formation of TBARS as well as inhibition of the Ca-pump ATPase. However, when added after exposure to tBHP, dithiothreitol was unable to restore Ca-pump ATPase activity completely. An activity of dithiothreitol independent of enzymic thiol group reduction was apparent. In the presence of mercaptosuccinate, a potent inhibitor of glutathione peroxidase, the ability of dithiothreitol to protect the Ca-pump ATPase from tBHP-induced inhibition was abolished. Therefore, protection by dithiothreitol may be afforded by its ability to replenish GSH from oxidized glutathione, thus allowing glutathione peroxidase to metabolize tBHP. These results may be interpreted to suggest that inhibition of the Ca-pump ATPase in intact RBCs occurs as a result of tBHP-induced oxidant stress and subsequent lipid peroxidation which can be prevented by certain antioxidants including butylated hydroxytoluene, stobadine, and thiol-containing compounds such as dithiothreitol. These findings provide further insight into the mode of action of hydroperoxides and certain reactive oxygen species that have been implicated in oxidative stress associated with various pathological conditions. The importance of the GSH/glutathione peroxidase system in metabolizing organic hydroperoxides is also demonstrated.

Inhibition of acetaminophen oxidation by cimetidine and the effects on glutathione and activated sulphate synthesis rates

The aim of the present study was to examine the effects of the hepatotoxic drug, acetaminophen, on the synthesis rates of glutathione, activated sulphate (PAPS, adenosine 3'-phosphate 5'-phosphosulphate) and the acetaminophen metabolites, acetaminophen-glutathione and acetaminophen-sulphate after inhibition of cytochrome P-450 drug oxidation by cimetidine in isolated rat hepatocytes. The synthesis rates of glutathione and PAPS were determined simultaneously by an established method based on trapping of radioactivity (35S) in the prelabelled glutathione and PAPS pools. Preincubation of the hepatocytes with 60 micrograms/ml cimetidine for 30 min. did not affect PAPS (1.71 versus 1.78 nmol/10(6) cells) nor glutathione concentration (16.0 versus 16.4 nmol/10(6) cells). The subsequent incubation with 5 mM acetaminophen resulted in decreased PAPS synthesis in the cimetidine treated cells [0.79 x 10(3) versus 0.92 x 10(3) nmol/(10(6) cells.hr)] (P < 0.05). There was no difference in PAPS concentration or acetaminophen-sulphate synthesis [1.73 versus 1.79 nmol/10(6) cells and 13.0 versus 12.9 nmol/(10(6) cells.hr), respectively]. Decreased PAPS synthesis may be related to decreased ATP supply or may be the result of a feed-back regulation due to diversion of sulphur from glutathione synthesis to sulfoxidation. The glutathione synthesis was not significantly affected by cimetidine treatment [57 x 10(3) versus 27 x 10(3) nmol/(10(6) cells.hr)]. As expected acetaminophen-glutathione synthesis decreased by 38% [1.66 versus 2.68 nmol/(10(6) cells.hr)] (P < 0.01). Also the glutathione concentration was lower in cimetidine treated cells [15.2 versus 15.9 nmol/10(6) cells] (P < 0.05). We have previously shown that glutathione synthesis was reduced if substrate availability decreased (acetaminophen concentration lowered).(ABSTRACT TRUNCATED AT 250 WORDS)

Spectral analysis of cytochromes in rat heart myocytes: transient and steady-state photodiode array spectrophotometry measurements

Myocytes prepared from rat heart have been studied by optical spectroscopy using a photodiode array spectrophotometer adapted to a stopped flow apparatus (PASF). The isolated cells were viable for 3-4 h (i.e., over the total time of the experiments), as tested employing morphological parameters of cell damage, reactivity toward trypan blue, and the ability to use succinate in the absence and presence of digitonin. Respiration was activated by addition of sodium ascorbate and tetramethyl-para-phenylenediamine (TMPD) as exogenous reductants, in order to single out the contributions of cytochrome c and cytochrome c oxidase among the complexes of the mitochondrial respiratory chain. TMPD was shown to be freely permeable across cytoplasmic and mitochondrial membranes, with a measured KD = 0.9 mM. The use of singular value decomposition analysis coupled to PASF acquisition proved very powerful in resolving statically and kinetically, in the millisecond time region, the spectral contributions of the cytochromes. Spectral analysis was improved by adding carbon monoxide at concentrations which did not affect cytochrome c oxidase activity, but kept myoglobin fully saturated (and thus uninfluential to absorbance changes).

Effects of cysteine and acetaminophen on the syntheses of glutathione and adenosine 3'-phosphate 5'-phosphosulfate in isolated rat hepatocytes

The aim of the present study was to introduce and validate a radioactive tracer method in which adenosine 3'-phosphate 5'-phosphosulfate (PAPS) and glutathione (GSH) are measured simultaneously in isolated hepatocytes. PAPS and GSH are co-substrates in sulphation and GSH conjugation, and both are dependent on sulphur deriving from cysteine. The effect of cysteine on the syntheses was investigated at non-toxic and toxic concentrations of the hepatotoxic drug acetaminophen (AA). Administration of AA trapped radioactivity (35S) in the pre-labelled PAPS and GSH pools by formation of the metabolites, AA-sulphate and AA-GSH. Turnover rates were determined from the decline of AA-sulphate and AA-GSH specific activity. Syntheses of PAPS and GSH were calculated by multiplying the rates with the concentrations of the respective co-substrates. Increasing AA concentration from non-toxic to toxic levels resulted in increased median PAPS and GSH syntheses (8 to 11 and 311 to 2218 nmol/10(6) cells/min, respectively) (P less than 0.05). Addition of cysteine did not alter median PAPS synthesis (5 to 3 nmol/10(6) cells/min) but decreased median GSH synthesis (666 to 261 nmol/10(6) cells/min) (P less than 0.05) in experiments with non-toxic AA concentrations. In experiments with toxic AA concentrations opposite effects of cysteine were seen, i.e. median PAPS synthesis was reduced (3 to 2 nmol/10(6) cells/min) (P less than 0.05) while median GSH synthesis was unchanged (23 to 16 nmol/10(6) cells/min). The present method provides a tool in which two important detoxification pathways can be measured simultaneously and the data suggest that the two pathways are regulated by substrate availability.

Dichloromethane (methylene chloride): metabolism to formaldehyde and formation of DNA-protein cross-links in B6C3F1 mice and Syrian golden hamsters

Dichloromethane (DCM) is metabolized via a glutathione transferase (GST)-dependent pathway to formaldehyde (HCHO), a mutagenic compound that could play an important role in the carcinogenic effects of DCM observed in the liver and lungs of B6C3F1 mice at 2000 and 4000 ppm. Syrian hamsters metabolize DCM more slowly than mice via this pathway, and hamsters exposed to 3500 ppm showed no apparent carcinogenic response. The possible formation of DNA-protein cross-links (DPX) from DCM in both species was examined. Male mice and hamsters were pre-exposed for 2 days (6 hr/day) to 4000 ppm of DCM and on the third day were exposed (6 hr) to a decaying concentration (4500 to 2500 ppm) of [14C]DCM. DPX were detected in mouse liver, but not in mouse lung, hamster liver, or hamster lung. The failure to detect DPX in mouse lung does not exclude their possible formation in a subpopulation of lung cells. Metabolic incorporation of 14C derived from [14C]DCM into DNA suggested a higher rate of turnover of some mouse lung cells than of hamster lung cells, but no large difference in the turnover rates of liver cells in the two species under these conditions. These results demonstrate that HCHO derived from DCM can form DNA-protein cross-links in the liver of the B6C3F1 mouse. The formation of DPX is dependent on the activity of the GST pathway, and species such as hamsters and humans having much lower rates of DCM metabolism via this pathway may not generate toxicologically significant concentrations of HCHO and DPX.

Prevention of nitrofurantoin-induced cytotoxicity in isolated hepatocytes by fructose

Nitrofurantoin is a widely utilized urinary antimicrobial drug which has been associated with pulmonary fibrosis, neuropathy, and hepatitis as well as hemolytic anemia in glucose-6-phosphate dehydrogenase-deficient individuals. Incubation of freshly isolated rat hepatocytes with nitrofurantoin caused oxygen activation as a result of futile redox cycling. Glutathione disulfide (GSSG) was formed and rapidly exported from the cell resulting in complete glutathione (GSH) depletion followed by cell death. However, fructose prevented the export of GSSG from the cell and GSH levels recovered rapidly without cytotoxicity occurring. Fructose did not affect nitrofurantoin metabolism but rapidly depleted cellular ATP levels by approximately 80% which remained depressed during the incubation period. Fructose, however, did not protect hepatocytes from nitrofurantoin-induced cytotoxicity if GSH was depleted beforehand. Protection by fructose only occurred at concentrations which caused ATP depletion. These results suggest that fructose prevents nitrofurantoin-induced toxicity by depleting ATP and thereby preventing the ATP-dependent GSSG efflux. GSSG is retained enabling NADPH and glutathione-reductase to reduce the GSSG back to GSH, thereby protecting the cell from nitrofurantoin-induced oxidative stress.

Measurement of reduced and oxidized glutathione in cultures of adult rat hepatocytes

A reversed-phase ion-exchange high-performance liquid chromatographic technique, suitable for the separate measurement of reduced (GSH) and oxidized (GSSG) glutathione in cultures of adult rat hepatocytes, is described. A commercially available Nucleosil 120-7NH2 column was used. A complete run took ca. 22 min. The retention times for GSH and GSSG were 10.6 and 12.7 min, respectively, providing a resolution coefficient of 1.4. The coefficients of variation for GSH and GSSG were ca. 5 and 25%, respectively, for freshly isolated hepatocytes, and 16 and 15%, respectively, for 24-h cultured hepatocytes. The detector response was linear as a function of GSH and GSSG concentration and the hepatocytes concentration studied. Addition of up to 1.5 mg/ml bovine serum albumin to the culture medium had no effect on the linearity. The recovery for standards, ranging from 0 to 150 nmol of GSH or GSSG per millilitre in the presence of hepatocytes, was 98% for GSH and 80% for GSSG. The detection limit of the method was between 0.5 and 1.0 nmol of GSH and GSSG per millilitre. In cultured rat hepatocytes, the GSH content increased during the first 24 h of culture, followed by a slow decrease. After six days of culture, the GSH content was less than 50% of the value found for freshly isolated hepatocytes. GSSG was present in cultured rat hepatocytes in only small amounts and becomes unmeasurable after four days of culture.

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.

Oxygen dependence of oxidative stress. Rate of NADPH supply for maintaining the GSH pool during hypoxia

NADPH supply for oxidized glutathione (GSSG) reduction was studied in hepatocytes under different steady-state O2 concentrations with controlled infusions of diamide, a thiol oxidant. When bis-chloro-nitrosourea (BCNU) was used to inhibit GSSG reductase, the rate of GSH depletion approximated the rate of diamide infusion, showing that diamide reacted preferentially with GSH under these experimental conditions. Under aerobic conditions without BCNU treatment, the GSH and NADPH pools were largely unaffected and little diamide accumulation or protein thiol oxidation occurred with diamide infusion rates up to 5.3 nmol/10(6) cells per min. However, at greater infusion rates, GSH and NADPH decreased, diamide and GSSG concentrations increased, and protein thiols were oxidized. This critical infusion rate was easily discernible and provided a convenient means to assess the capacity of cells to reduce GSSG as a function of O2 concentration. As the O2 concentration was decreased below 15 microM, the critical infusion rate decreased from the aerobic value of 5.3 to less than 2 nmol/10(6) cells per min in anoxic cells; half-maximal change occurred at 5 microM O2. Although cells could not maintain normal thiol and NADPH pools at infusion rates above the critical value, analysis of the rates of thiol depletion showed that the maximal NADPH supply rate for GSSG reduction under aerobic conditions was 7-8 nmol/10(6) cells per min and was affected by hypoxia to the same degree as the critical value. Thus, hypoxia and anoxia impair the capability of cells to supply NADPH for the reduction of thiol oxidants. This could be an important factor in the sensitivity of hypoxic and ischemic tissues to oxidative injury.

The hepatic glutathione system--influences of xenobiotics

The hepatic glutathione (GSH) system and the influences of xenobiotics have been reviewed. Key steps in the regulation of hepatic GSH are GSH biosynthesis, the GSH-peroxidase/reductase cycle, the cystathionine pathway, and the carrier-mediated export processes. Influences of xenobiotics on these different pathways are discussed. Xenobiotics may lead to liver injury after biotransformation to highly reactive electrophilic metabolites (mainly cytochrome P-450 mediated), which easily conjugate with GSH, thus producing GSH depletion. This GSH depletion and probably an additional loss of protein sulfhydryl groups cause a disturbance of the intracellular calcium homeostasis which leads to an irreversible cell injury. The different acinar distribution of cytochromes P-450 and of GSH and GSH-related detoxication pathways points to a greater susceptibility of perivenous hepatocytes to xenobiotic-induced damage. Also, the intracellular compartmentation of GSH is important for the understanding of hepatocellular injury induced by several xenobiotics.

A role for the glutathione peroxidase/reductase enzyme system in the protection from paracetamol toxicity in isolated mouse hepatocytes

The role of the glutathione peroxidase/reductase (GSH-Px/GSSG-Rd) enzyme system in protection from paracetamol toxicity was investigated in isolated mouse hepatocytes in primary culture. The effect of inhibitors of these enzymes on the toxicity of paracetamol and on t-butylhydroperoxide (t-BOOH), used as a positive control, was determined. 1,3-Bis(chloroethyl)-1-nitrosourea (BCNU) was used to inhibit GSSG-Rd, and goldthioglucose (GTG) used to inhibit GSH-Px. Both these inhibitors increased cell membrane damage in response to oxidative stress initiated by t-BOOH. However, they also increased the susceptibility of hepatocytes to paracetamol toxicity, indicating that a component of paracetamol's toxic effect involves formation of species that are detoxified by the GSH-Px/GSSG-Rd enzymes. To further examine the role of these enzymes, age-related differences in their activity were exploited. Hepatocytes from two-week-old mice were less susceptible to both t-BOOH and paracetamol toxicity than were those from adult mice. This corresponds to higher activity of cytosolic GSH-Px/GSSG-Rd in this age group. However, after inhibition of GSSG-Rd with BCNU, hepatocytes from these postnatal mice were more susceptible to paracetamol toxicity. This suggests that the higher activity of GSH-Px/GSSG-Rd in hepatocytes from two-week-old mice is responsible for their reduced susceptibility to paracetamol toxicity. The data indicate that the GSH-Px/GSSG-Rd enzymes contribute to protection from paracetamol toxicity and suggest that formation of peroxides contributes to this drug's hepatotoxic effects.

Effects of culture duration on hydrogen peroxide-induced hepatocyte toxicity

The effects of culture duration on primary cultured mouse hepatocyte antioxidant levels (superoxide dismutase, catalase, glutathione peroxidase, vitamin E, and glutathione) and susceptibility to glucose oxidase (GO)- and hydrogen peroxide (H2O2)-induced cell killing and lipid peroxidation were examined. Membrane fatty acid composition was also evaluated. Adult male B6C3F1/CrlBR mouse hepatocytes were isolated by collagenase perfusion of the liver and cultured on 60-mm plastic dishes in Leibovitz's L-15 medium supplemented with glucose (1 mg/ml), dexamethasone (1 microM), fetal bovine serum (10%, v/v), and gentamicin sulfate (50 micrograms/ml) for 0 hr (freshly isolated cells) to 96 hr. Hepatocyte toxicity (determined by lactate dehydrogenase release and lipid peroxidation) after a 2-hr exposure to GO (0.8-80 micrograms/ml) or H2O2 (1-5 mM) decreased with increased time in culture. This decreased hepatocyte sensitivity to GO and H2O2 toxicity was not related to antioxidant enzyme activity since superoxide dismutase, catalase, and glutathione peroxidase declined during the 96-hr culture period. In contrast, glutathione and vitamin E levels in the cultured hepatocytes rose to 274.9 +/- 8.3% and 220.6 +/- 18.6% of the levels in freshly isolated cells (129.6 +/- 11.5 nmol and 0.10 +/- 0.01 nmol per 10(6) hepatocytes, respectively). The percentage of polyunsaturated fatty acids in hepatocyte phospholipids and triglycerides decreased with culture duration while the percentage of oleic acid increased in esterified and free fatty acid pools after 2 hr in culture. Total fatty acids were not affected by time in culture. These results suggest that the decreased hepatocyte susceptibility to the toxic effects of hydrogen peroxide may have been due to elevations in cellular GSH and vitamin E levels and decreases in membrane polyunsaturated fatty acids. The data also indicate that hepatocytes in primary culture undergo changes in antioxidant levels and fatty acid composition that may affect free radical toxicity at different times in culture.

Mechanistic study on formaldehyde-induced hepatotoxicity

In isolated, hemoglobin-free perfused livers of fasted rats, formaldehyde at an initial concentration of 10 mmol/l produced toxicity as evidenced by a release of enzymes (GPT, SDH) and of glutathione (mainly GSSG) into the perfusate, an accumulation of calcium in the liver, and a depletion of hepatic glutathione. Formaldehyde also led to an enhanced release of malondialdehyde into the perfusate, indicating peroxidative processes and decreased hepatic oxygen consumption by about 50-70%. The electron microscopic investigation of formaldehyde-exposed livers showed a destruction of the mitochondria (ruptured membranes, loss of the cristae) and some damage of the rough endoplasmic reticulum. Feeding the rats prior to surgery attenuated the hepatotoxic effects of 10 mmol/l formaldehyde. At an initial concentration of 3 mmol/l, formaldehyde did not release enzymes from livers of fed or fasted rats but only from those whose glutathione content had been depleted by treatment with phorone (250 mg/kg ip 2 h earlier). Formaldehyde liberated glucose and lactate from the livers of fed but not from those of fasted rats, indicating anaerobic energy supply in the fed state. The hepatotoxic action of formaldehyde is not due to its metabolism to formate or to the 10% methanol added as a stabilizing agent to the commercially available 37% solution named formalin. In conclusion, by destruction of mitochondria, formaldehyde inhibits aerobic energy supply and thereby presumably produces hepatocellular damage.

Drug-induced hydrogen peroxide production in isolated rat hepatocytes

A method for measuring drug-induced hydrogen peroxide production in freshly isolated rat hepatocytes is described. 3-Amino-1,2,4-triazole, an irreversible inhibitor of the enzyme catalase markedly reduces the capacity of isolated hepatocytes to metabolize hydrogen peroxide, with maximum inhibition (80%) being observed after 40 min of co-incubation. The present method is based on the observation that this inhibition of catalase by 3-amino-1,2,4-triazole is prevented by methanol and that the effect of methanol is reversed in the presence of hydrogen peroxide. Using this assay we could demonstrate increased hydrogen peroxide production during the metabolism of diquat, paraquat, xanthine, benzylamine and glycolate by hepatocytes. Inhibition of the hydrogen peroxide metabolic capacity was greatest with glycolate and diquat, whereas paraquat and benzylamine only had a minor effect.

Comparison of the susceptibility of hepatocytes from postnatal and adult mice to hepatotoxins

Age-related changes of susceptibility to hepatotoxicity induced by four hepatotoxic compounds were investigated using an isolated mouse hepatocyte model. Hepatocytes isolated from 2-week-old mice and adult mice (8-10 weeks old) were exposed to different concentrations (including toxic concentrations) of paracetamol, furosemide, iodoacetic acid and t-butylhydroperoxide for incubation times up to 24 hr. Cell damage was assessed by leakage of lactate dehydrogenase. Analysis of variance indicated that the hepatocytes from the 2-week-old mice were less susceptible to the toxic effects of all four hepatotoxins. The activities of catalase, superoxide dismutase, glutathione peroxidase and glutathione reductase were determined in both hepatocytes and whole liver from the two age groups. While catalase was significantly greater in adults, glutathione peroxidase, glutathione reductase and superoxide dismutase were all higher in the 2-week-old mice. Since these three enzymes are involved with protection against oxidative stress, it is likely that the higher activity in hepatocytes from 2-week-old mice is responsible for the reduced susceptibility to damage induced by the four hepatotoxins.

One-year inhalation toxicity study of formaldehyde in male rats with a damaged or undamaged nasal mucosa

To study the effect of bilateral intranasal electrocoagulation damage on the susceptibility of rats to formaldehyde vapour, male Wistar rats with a damaged or undamaged nasal mucosa were exposed to atmospheres containing 0, 0.1, 1 or 10 ppm formaldehyde vapour during 6 h/day, 5 days/wk for 13 or 52 weeks. Electrocoagulation damage was induced in the anterior third part of the nose. The repair process followed the pattern of wound healing. Loss of turbinates and perforation of the septum were common irreversible findings. After 13 weeks basal cell hyperplasia and squamous metaplasia of the respiratory epithelium, and rhinitis were still visible. After 52 weeks effects attributable to electrocoagulation were slight basal cell hyperplasia and some rhinitis. Major formaldehyde-related adverse effects in the 10 ppm group not subjected to electrocoagulation included growth retardation, reduced urine production, and rhinitis accompanied by squamous metaplasia of the nasal respiratory epithelium. No adverse effects were seen at 0.1 or 1 ppm in rats with an intact nasal mucosa. The principal untoward effects of formaldehyde in electrocoagulation-treated rats seen after 13 and/or 52 weeks comprised increase in basal cell hyperplasia, squamous metaplasia of the nasal respiratory epithelium, damage to the olfactory epithelium at 10 ppm, and focal squamous metaplasia of nasal respiratory epithelium at 0.1 and 1 ppm.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of caffeine on the ultrastructure and mitochondrial function of the embryonic chick heart

Results from this study indicate that caffeine (at an embryotoxic dose equal to the LD40 administered to 3-day chick embryos produced both ultrastructural and functional abnormalities in embryonic cardiac mitochondria. The principal effects of caffeine on the ultrastructure of embryonic myocardial cells were clearly suggestive of cellular injury and included: (1) a marked disruption of mitochondrial cristae with formation of intramitochondrial myelin-like figures and (2) intracellular edema. A biochemical analysis of mitochondrial function revealed that caffeine inhibited the capacity of mitochondria to oxidize succinate. However, when pyruvate and malate were employed as substrates for isolated mitochondria, caffeine did not significantly alter mitochondrial function. Interference with embryonic cardiac mitochondrial succinate oxidation and/or fragmentation of mitochondrial membranes are suggested as possible events in the pathogenesis of caffeine-induced cardiac cell injury which, in turn, may lead to the embryonic death of the chick.

Investigations on the role of free radical processes in hexachlorobenzene-induced porphyria in mice

Male C57Bl/10 mice were chronically fed hexachlorobenzene (HCB) (0.02% of the diet) alone or in combination with a single subcutaneous dose of iron (12.5 mg iron per mouse). After eight weeks the group of mice pretreated with the iron overload was highly sensitized to the porphyrogenic effect of HCB, as shown by liver porphyrin accumulation. A synergistic effect of iron was evident on other parameters too, such as HCB-induced hepatic damage, activation of type O of xanthine oxidase, and decreased activity of copper zinc superoxide dismutase and glutathione peroxidase(s). None of these parameters was affected by iron alone. Iron alone and in association with HCB markedly raised the level of lipid peroxides, the increase in the HCB group being smaller. The combined treatment resulted in a significant reduction of HCB's inductive effects on microsomal heme and cytochromes P-450 and b5 and on the activity of aryl hydrocarbon hydroxylase. The content of nonprotein sulfhydryl groups was reduced to the same extent in mice treated with HCB or HCB plus iron. The results suggest that reactive intermediates such as are formed by lipid peroxidation are not sufficient on their own to create the conditions for uroporphyrinogen decarboxylase impairment, as evident in the group of mice receiving iron overload alone. Conversely, HCB administration induced a specific condition of imbalance in the liver between formation and inactivation of reactive intermediates which was associated with hepatic porphyrin accumulation and was potentiated by concomitant administration of iron.

Intact organ spectrophotometry and single-photon counting

In toxicology, it is of interest not only to assess enzyme levels and capacities for potential fluxes, but it is also useful to develop methods for determining actual concentrations and fluxes in the intact cell and organ. To this end, several noninvasive techniques have been developed over the years. Our interest has been largely in photometric techniques. Transmission spectrophotometry through solid organs permits monitoring of the cytochromes of the mitochondrial respiratory chain and cytochrome P-450 as well as other pigments of biological interest. Furthermore, the steady state level of catalase Compound I in liver provides information on rates of H2O2 production. These are in the nM to microM concentration range. More recently, the monitoring of photoemission from intact organs has been useful in toxicological problems. The major photoemissive species, singlet molecular oxygen and excited carbonyls, can now be monitored with good signal/noise ratio. Redox cycling of quinones and the generation of photoemissive species were studied in menadione metabolism. Inhibition of phase II led to a significant increase in the steady state level of singlet oxygen, as did the inhibition of two-electron reduction by using the inhibitor dicoumarol for DT diaphorase. Conversely, the induction of DT diaphorase by pretreatment with BHA protected by decreasing the level of reactive oxygen species.

Suppression of mitochondrial respiratory function after short-term anoxia

Exposure of rat hepatocytes to 30 min anoxia resulted in a substantial decrease in O2 consumption on reoxygenation. Measurement of the sequestered Ca2+ pool of mitochondria by selective release with the protonophore, carbonylcyanide-p-trifluoromethoxyphenylhydrazone (FCCP), and quantitation with the metallochromic indicator, arsenazo III, showed that anoxia caused a marked decrease in mitochondrial Ca2+. This loss could, in part, be due to decreased electrophoretic uptake resulting from a 20% decrease in the magnitude of the mitochondrial transmembranal potential. The decrease was associated with a decrease in ATP synthase activity as expected from the Ca2+ dependence of endogenous inhibitor binding to the ATP synthase. These results show that short-term anoxia suppresses mitochondrial function in hepatocytes and suggest that mitochondrial Ca2+ content may be important in this regulation. Regulation of the ATP synthase and other ion transport systems may provide a means to preserve ion distribution and protonmotive force and thereby prolong the period during which cells can tolerate anoxia.

Oxygen activation during drug metabolism

The peroxidase-H2O2 catalyzed oxidation of certain drugs in the presence of GSH resulted in extensive oxidation to thiyl radicals and GSSG. NADH or arachidonate in place of GSH was also readily oxidized. Extensive oxygen uptake ensued resulting in the formation of superoxide radicals and H2O2. Only catalytic amounts of drugs and low peroxide levels were required, indicating a radox cycling mechanism. Active drugs included morphine, phenothiazines, aminopyrine, p-phenetidine, acetaminophen and 4-N,N-(CH3)2-aminophenol. Other drugs, including dopamine and methyl-alpha-dopa, did not catalyze oxygen uptake, nor was GSH oxidized to GSSG. Instead, GSH was depleted by GSH conjugate formation. Drugs of the former group, e.g. acetaminophen, aminopyrine or N,N-(CH3)2-aniline, have also been found by other investigators to form GSSG and hydrogen peroxide when added to hepatocytes or when perfused through an isolated liver. Although cytochrome P-450 normally catalyzes a two-electron oxidation of drugs, serious consideration should be given to some one-electron oxidation occurring as well and resulting in radical formation, oxygen activation and GSSG formation.

Glutathione oxidation during peroxidase catalysed drug metabolism

The peroxidase catalyzed oxidation of certain drugs in the presence of glutathione (GSH) resulted in extensive oxidation to oxidized glutathione (GSSG). Extensive oxygen uptake ensued and thiyl radicals could be trapped. Only catalytic amounts of drugs were required indicating a redox cycling mechanism. Active drugs included phenothiazines, aminopyrine, p-phenetidine, acetaminophen and 4-N,N-(CH3)2-aminophenol. Other drugs, including dopamine and alpha-methyl dopa, did not catalyse oxygen uptake, nor were GSSG or thiyl radicals formed. Instead, GSH was depleted by GSH conjugate formation. Drugs of the former group, e.g. acetaminophen, aminopyrine or N,N-(CH3)2-aniline have also been found by other investigators to form GSSG and hydrogen peroxide when added to hepatocytes or when perfused through an isolated liver. Although cytochrome P-450 normally catalyses a two-electron oxidation of drugs, serious consideration should be given for some one-electron oxidation resulting in radical formation, oxygen activation and GSSG formation.

On the mechanisms of glutathione depletion in hepatocytes exposed to morphine and ethylmorphine

Incubation of isolated rat hepatocytes with either morphine or ethylmorphine resulted in glutathione (GSH) depletion followed by loss of cell viability. Pretreatment of cells with 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) to inactivate glutathione reductase did not markedly affect the rates of GSH depletion seen in untreated cells. In contrast, hexobarbital stimulated H2O2 production in isolated liver microsomes, incubated aerobically with NADPH, whereas the effects of morphine and ethylmorphine on microsomal H2O2 production were minimal. Finally, incubation of hepatocytes with radioactively labeled morphine resulted in formation of 2 glutathione conjugates, one of which was tentatively identified as formyl glutathione. We conclude that GSH consumption during the metabolism of morphine or ethylmorphine by hepatocytes is due mainly to formation of glutathione conjugates.