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A I Cederbaum

Publications and source records attributed to A I Cederbaum.

At least 145 records · Page 8Linked to original sources
PubMed1987

Production of 4-hydroxypyrazole from the interaction of the alcohol dehydrogenase inhibitor pyrazole with hydroxyl radical.

Pyrazole, an effective inhibitor of alcohol dehydrogenase, was previously shown to be a scavenger of the hydroxyl radical. 4-Hydroxypyrazole is a major metabolite in the urine of animals administered pyrazole in vivo. Experiments were conducted to show that 4-hydroxypyrazole was a product of the interaction of pyrazole with hydroxyl radical generated from three different systems. The systems utilized were the iron-catalyzed oxidation of ascorbate, the coupled oxidation of hypoxanthine by xanthine oxidase, and NADPH-dependent microsomal electron transfer. Ferric-EDTA was added to all the systems to catalyze the production of hydroxyl radicals. A HPLC procedure employing either uv detection or electrochemical detection was utilized to assay for the production of 4-hydroxypyrazole. The three systems all supported the oxidation of pyrazole to 4-hydroxypyrazole by a reaction which was sensitive to inhibition by competitive hydroxyl radical scavengers such as ethanol, mannitol, or dimethyl sulfoxide and to catalase. The sensitivity to catalase implicates H2O2 as the precursor of the hydroxyl radical by all three systems. Superoxide dismutase inhibited production of 4-hydroxypyrazole only in the xanthine oxidase reaction system. In the absence of ferric-EDTA (and azide), microsomes catalyzed the oxidation of pyrazole to 4-hydroxypyrazole by a cytochrome P-450-dependent reaction which was independent of hydroxyl radicals. This latter pathway may be primarily responsible for the in vivo metabolism of pyrazole to 4-hydroxypyrazole. The production of 4-hydroxypyrazole from the interaction of pyrazole with hydroxyl radicals may be a sensitive, rapid technique for the detection of these radicals in certain tissues or under certain conditions, e.g., increasing oxidative stress.

Alcohol Dehydrogenase↗
PubMed1987

Hydroxyl radical generation by microsomes after chronic ethanol consumption.

The effect of iron and other compounds known to be toxic because of the production of oxygen radicals, e.g., paraquat and menadione on the generation of hydroxyl radicals (.OH) by microsomes from chronic ethanol-fed rats and their pair-fed controls was determined. In the absence of any additions, or in the presence of ferric-chloride, -ADP or -EDTA, microsomes from the ethanol-fed rats showed a 2-fold increase in the production of .OH. Paraquat and menadione increased the generation of .OH by microsomes from the ethanol-fed and the pair-fed controls to an identical extent and thus these promoters of oxidative stress were not any more effective in interacting with microsomes after ethanol treatment. Under all conditions, .OH generation was sensitive to inhibition by catalase, implicating H2O2 as the precursor of .OH, whereas superoxide dismutase was without any significant effect. A working scheme to accommodate aspects of the interaction of iron, menadione and paraquat with microsomes with the subsequent production of .OH is described. The fact that .OH generation by microsomes in the presence of several sources of iron such as unchelated iron or ferric-ADP is elevated after chronic ethanol consumption could contribute to the hepatotoxic effects of ethanol. Studies on iron metabolism by liver cells and the effect of ethanol on the disposition of this critical trace metal are needed to further evaluate the role of oxygen radicals in the actions of ethanol.

Alcoholism↗
PubMed1986

Inhibition of the low-Km mitochondrial aldehyde dehydrogenase by diethyl maleate and phorone in vivo and in vitro. Implications for formaldehyde metabolism.

Formaldehyde can be oxidized primarily by two different enzymes, the low-Km mitochondrial aldehyde dehydrogenase and the cytosolic GSH-dependent formaldehyde dehydrogenase. Experiments were carried out to evaluate the effects of diethyl maleate or phorone, agents that deplete GSH from the liver, on the oxidation of formaldehyde. The addition of diethyl maleate or phorone to intact mitochondria or to disrupted mitochondrial fractions produced inhibition of formaldehyde oxidation. The kinetics of inhibition of the low-Km mitochondrial aldehyde dehydrogenase were mixed. Mitochondria isolated from rats treated in vivo with diethyl maleate or phorone had a decreased capacity to oxidize either formaldehyde or acetaldehyde. The activity of the low-Km, but not the high-Km, mitochondrial aldehyde dehydrogenase was also inhibited. The production of CO2 plus formate from 0.2 mM-[14C]formaldehyde by isolated hepatocytes was only slightly inhibited (15-30%) by incubation with diethyl maleate or addition of cyanamide, suggesting oxidation primarily via formaldehyde dehydrogenase. However, the production of CO2 plus formate was increased 2.5-fold when the concentration of [14C]formaldehyde was raised to 1 mM. This increase in product formation at higher formaldehyde concentrations was much more sensitive to inhibition by diethyl maleate or cyanamide, suggesting an important contribution by mitochondrial aldehyde dehydrogenase. Thus diethyl maleate and phorone, besides depleting GSH, can also serve as effective inhibitors in vivo or in vitro of the low-Km mitochondrial aldehyde dehydrogenase. Inhibition of formaldehyde oxidation by these agents could be due to impairment of both enzyme systems known to be capable of oxidizing formaldehyde. It would appear that a critical amount of GSH, e.g. 90%, must be depleted before the activity of formaldehyde dehydrogenase becomes impaired.

Acetaldehyde↗
PubMed1986

Effect of chronic ethanol consumption on microsomal lipid peroxidation. Role of iron and comparison between controls.

Microsomes isolated from chronic ethanol-fed rats displayed elevated rats of malondialdehyde production when compared to pair-fed controls, but lower rates when compared to chow-fed controls. These differences did not correlate with total content of cytochrome P-450 or activity of NADPH-cytochrome c reductase. Titration curves with the potent iron-chelating agent desferrioxamine revealed that the content of iron was greater in microsomes from the chow-fed and lowest in microsomes from the pair-fed control. However, other variables must also exist since even when excess iron was added to the microsomes, the order of malondialdehyde production remained chow-fed greater than chronic ethanol greater than pair-fed control. The variabilities associated with the different controls and the role and content of transition metals such as iron probably contribute towards the divergent effects of ethanol on lipid peroxidation.

Alcoholism↗
PubMed1986

Differential effects of the cytochrome P-450/reductase ratio on the oxidation of ethanol and the hydroxyl radical scavenging agent 2-keto-4-thiomethylbutyric acid (KMBA).

NADPH-cytochrome P-450 reductase catalyzes a low rate of oxidation of hydroxyl radical scavenging agents such as ethanol and 2-keto-4-thiomethylbutyric acid (KMBA), in a reaction markedly stimulated by the addition of ferric-EDTA. The effect of various ratios of cytochrome P-450 (phenobarbital-inducible isozyme)/reductase on the oxidation of ethanol and KMBA was determined: There was essentially no increase in KMBA oxidation over the range of ratios from 0.5 to 5 as compared to the reductase-catalyzed rate. High ratios actually caused some decrease in KMBA oxidation, which was especially notable under conditions of increased rates of hydroxyl radical generation (presence of increasing amounts of ferric-EDTA). This decrease at high P-450/reductase ratios could reflect tight coupling of reductase to P-450-PB, therefore decreasing electron transfer from reductase to ferric-EDTA, or could involve non-specific scavenging of .OH by P-450-PB. Indeed, native, but not boiled, P-450 inhibited KMBA oxidation by the xanthine oxidase system. By contrast, the oxidation of ethanol was stimulated at all concentrations of P-450-PB, and this increase was not sensitive to desferrioxamine. However, under conditions of high rates of .OH production, the ethanol oxidation profile tended to resemble the KMBA oxidation profile with respect to the effect of P-450-PB, whereas the two profiles were different under conditions of low rates of .OH production. These results suggest that P-450-PB does not catalyze the oxidation of .OH scavengers or promote the production of .OH, even at ratios of P-450/reductase approaching those found with intact microsomes and even in the presence of excess iron-EDTA, whereas ethanol is directly oxidized by P-450-PB, as are typical drug substrates. However, the P-450-PB-dependent oxidation of ethanol can be masked under conditions in which .OH production is increased.

Animals↗
PubMed1986

Inhibition of microsomal oxidation of ethanol by pyrazole and 4-methylpyrazole in vitro. Increased effectiveness after induction by pyrazole and 4-methylpyrazole.

Pyrazole and 4-methylpyrazole, which are inhibitors of alcohol dehydrogenase, were also found to be effective inhibitors of the oxidation of ethanol by liver microsomes (microsomal fractions) in vitro. Ethanol oxidation by microsomes from rats previously treated for 2 or 3 days with either pyrazole or 4-methylpyrazole appeared to be especially sensitive to inhibition in vitro by pyrazole or 4-methylpyrazole. The kinetics of inhibition by pyrazole or 4-methylpyrazole in all microsomal preparations were mixed, as the Km for ethanol was elevated while Vmax was lowered. However, Ki values for pyrazole (about 0.35 mM) and especially 4-methylpyrazole (about 0.03-0.10 mM) were much lower than those found with the saline controls (about 0.7-1.1 mM). In contrast, Ki values for dimethyl sulphoxide as an inhibitor of microsomal ethanol oxidation were similar in all microsomal preparations. Pyrazole and 4-methylpyrazole reacted with microsomes to produce type II spectral changes whose magnitude increased after treatment with either pyrazole or 4-methylpyrazole. Thus the increased inhibitory effectiveness of pyrazole and 4-methylpyrazole appears to be associated with increased interactions with the cytochrome P-450 isoenzyme(s) induced by these compounds. These isoenzymes have properties similar to those of the isoenzyme induced by chronic ethanol treatment. Therefore, caution is needed in the use of pyrazole or 4-methylpyrazole to assess pathways of ethanol metabolism, especially after chronic ethanol treatment, since these agents, besides inhibiting alcohol dehydrogenase, are also effective inhibitors of microsomal ethanol oxidation.

Animals↗
PubMed1986

Prevention of microsomal production of hydroxyl radicals, but not lipid peroxidation, by the glutathione-glutathione peroxidase system.

The glutathione-glutathione peroxidase system is an important defense against oxidative stress. The ability of this system to protect against iron-catalyzed microsomal production of hydroxyl radicals [oxidation of 4-methylmercapto-2-oxo-butyrate (KMBA)] and lipid peroxidation was evaluated. When rat liver cytosol was added to microsomes, strong inhibition against KMBA oxidation was observed. No protection was found when the cytosol was boiled or dialyzed. In the latter case, the addition of 0.5 mM glutathione restored almost complete protection, whereas in the former case protection could be restored by the addition of both glutathione and glutathione peroxidase. Cysteine could not replace glutathione, nor could glutathione S-transferase replace glutathione peroxidase. The glutathione-glutathione peroxidase system was also very effective in decreasing production of hydroxyl radicals stimulated by the addition of menadione or paraquat to microsomes. In the absence of cytosol, the addition of glutathione plus glutathione peroxidase was also effective; however, 5 mM glutathione was necessary to protect against KMBA oxidation. The effective concentration of glutathione required for protection was lowered when glutathione reductase was added to the system, to regenerate reduced glutathione. These results indicate that low concentrations of glutathione in conjunction with glutathione peroxidase plus reductase can be very effective in preventing microsomal formation of hydroxyl radicals catalyzed by iron and other toxic compounds. Microsomal lipid peroxidation was decreased 40% by glutathione alone, and this decrease was potentiated in the presence of glutathione reductase. In contrast to KMBA oxidation, the combination of glutathione plus glutathione peroxidase was not any more effective than glutathione alone in preventing lipid peroxidation. The differences in sensitivities of microsomal lipid peroxidation and KMBA oxidation to glutathione peroxidase suggest that these two processes can be distinguished from each other, and that free H2O2 and hydroxyl radicals are involved in KMBA oxidation, but not lipid peroxidation.

Animals↗
PubMed1986

Inhibition of CO2 production from aminopyrine or methanol by cyanamide or crotonaldehyde and the role of mitochondrial aldehyde dehydrogenase in formaldehyde oxidation.

Previous results have shown that cyanamide or crotonaldehyde are effective inhibitors of the oxidation of formaldehyde by the low-Km mitochondrial aldehyde dehydrogenase, but do not affect the activity of the glutathione-dependent formaldehyde dehydrogenase. These compounds were used to evaluate the enzyme pathways responsible for the oxidation of formaldehyde generated during the metabolism of aminopyrine or methanol by isolated hepatocytes. Both cyanamide and crotonaldehyde inhibited the production of 14CO2 from 14C-labeled aminopyrine by 30-40%. These agents caused an accumulation of formaldehyde which was identical to the loss in CO2 production, indicating that the inhibition of CO2 production reflected an inhibition of formaldehyde oxidation. The oxidation of methanol was stimulated by the addition of glyoxylic acid, which increases the rate of H2O2 generation. Crotonaldehyde inhibited CO2 production from methanol, but caused a corresponding increase in formaldehyde accumulation. The partial sensitivity of CO2 production to inhibition by cyanamide or crotonaldehyde suggests that both the mitochondrial aldehyde dehydrogenase and formaldehyde dehydrogenase contribute towards the metabolism of formaldehyde which is generated from mixed-function oxidase activity or from methanol, just as both enzyme systems contribute towards the metabolism of exogenously added formaldehyde.

Aldehyde Dehydrogenase↗
PubMed1986

Complex-formation and reduction of ferric iron by 2-oxo-4-thiomethylbutyric acid, and the production of hydroxyl radicals.

2-Oxo-4-thiomethylbutyric acid (OMBA) is a widely used oxygen-radical-scavenging agent and has been used for the detection of .OH-like species in a variety of systems. This scavenger reacts with other radicals and is therefore not specific for .OH. Since iron is required in most systems for the generation of OH-like species, studies were carried out to investigate the possible interaction of OMBA with iron. Fe3+ reacted with OMBA to produce complexes that gave rise to discrete spectra. Intense purple complexes, with broad absorbance maxima of 525-550 nm, were found at OMBA/Fe3+ ratios of up to 1:1, whereas red complexes with a prominent shoulder between 440 and 480 nm were found at higher OMBA/Fe3+ ratios. OMBA caused reduction of ferric iron to the ferrous state, as detected with 2,2'-bipyridyl as the indicator. This reduction occurs in the dark, can be photo-accelerated especially by light with wavelengths near the absorbance maximum of the respective complexes, and is increased as the OMBA/Fe3+ ratio is elevated. The presence of phosphate buffer quenches the purple and red ferric-ion-OMBA complexes and lowers the rate of reduction of Fe3+ by OMBA about 10-fold. The resulting ferrous-ion-OMBA-phosphate complex is very stable against autoxidation. Both the ferrous-ion-OMBA and ferric-ion-OMBA complexes reacted with H2O2, with the subsequent production of ethylene gas from OMBA. The interaction with H2O2 resulted in discrete spectral changes of both the ferrous-ion-OMBA and ferric-ion-OMBA complexes. The ferrous-ion-OMBA/H2O2 or ferric-ion-OMBA/H2O2 system appeared to produce .OH free radicals via a Fenton-type of reaction since ethylene production was inhibited by competitive OH scavengers. Ferrous-ion-OMBA complex reacted with H2O2 not only to produce ethylene from the OMBA, but also to promote the oxidation of another scavenger, ethanol. The ability of OMBA to chelate iron, to promote reduction of ferric iron and to react with H2O2 to produce potent oxidizing radicals may play a role in the lack of specificity of OMBA as a scavenger of oxygen radicals.

Ethanol↗
PubMed1986

Rat liver microsomal induction of the oxidation of drugs and alcohols, and sodium dodecyl sulfate-gel profiles after in vivo treatment with pyrazole or 4-methylpyrazole.

Studies were carried out to characterize and compare the effects of pyrazole and 4-methylpyrazole, potent inhibitors of alcohol dehydrogenase, on microsomal oxidation of a variety of drugs and alcohols. Whereas pyrazole treatment of rats (200 mg/kg b.wt./day for 2 days) resulted in an enrichment of a cytochrome P-450 isozyme with a molecular weight of about 52,000 on sodium dodecyl sulfate gels, 4-methylpyrazole treatment resulted in increased amounts of two or three P-450 isozymes, one of which appeared to be similar to the isozyme increased by pyrazole. The qualitative induction of two or three isozymes of P-450 as shown by sodium dodecyl sulfate-gel electrophoresis correlates with a 2-fold increase in total content of P-450 by 4-methylpyrazole. Microsomes from the pyrazole-treated rats displayed increased activity (expressed per milligram of protein or per nanomole of P-450) with aniline, p-nitroanisole, dimethylnitrosamine (low-Km enzyme) and ethanol as substrates, but not with aminopyrine, ethoxycoumarin or dimethylnitrosamine (high-Km enzyme). A stereochemical preference for the (+)-2-butanol isomer over the (-)-isomer was also observed. Kinetic experiments indicated that the pyrazole treatment increased the Vmax for ethanol, aniline and (+)-2-butanol oxidation. These properties are similar to those found with microsomes from chronic ethanol-fed rats and suggest that, in rats, pyrazole and ethanol may induce similar isozymes of P-450, and that the former may serve as a convenient model for the latter. This comparable induction between ethanol and pyrazole is in contrast to results using imidazole, which has been reported by others not to induce an alcohol-preferring P-450 in rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcohols↗
PubMed1985

Inhibition of mitochondrial aldehyde dehydrogenase and acetaldehyde oxidation by the glutathione-depleting agents diethylmaleate and phorone.

Experiments were carried out to study the effect of two commonly used glutathione-depleting agents, diethylmaleate and phorone, on the oxidation of acetaldehyde and the activity of aldehyde dehydrogenase. The oxidation of acetaldehyde by intact hepatocytes was inhibited when the cells were incubated with diethylmaleate. Washing and resuspending the cells in diethylmaleate-free medium afforded protection against the inhibition of acetaldehyde oxidation. The oxidation of acetaldehyde by isolated rat liver mitochondria as well as by disrupted mitochondria in the presence of excess NAD+ was inhibited by diethylmaleate or phorone, indicating inhibition of the low-Km aldehyde dehydrogenase. In addition, diethylmaleate inhibited oxidation of acetaldehyde by the high-Km cytosolic aldehyde dehydrogenase. Significant accumulation of acetaldehyde occurred when ethanol was oxidized by hepatocytes in the presence, but not in the absence, of diethylmaleate. Thus, diethylmaleate blocks the oxidation of added or metabolically generated acetaldehyde, analogous to results with other inhibitors of the low-Km aldehyde dehydrogenase such as cyanamide. These results suggest that caution should be used in interpreting the effects of diethylmaleate or phorone on metabolic reactions, especially those involving metabolism of aldehydes such as formaldehyde, because, in addition to depleting glutathione, these agents inhibit the low-Km aldehyde dehydrogenase.

Acetaldehyde↗
PubMed1985

Evaluation of microsomal pathways of oxidation of alcohols and hydroxyl radical scavenging agents with carbon monoxide and cobalt protoporphyrin IX.

Rat liver microsomes catalyze the oxidation of hydroxyl radical scavenging agents by an iron-dependent process, and can oxidize alcohols by pathways dependent on, as well as independent of, .OH. Experiments were carried out to evaluate which microsomal components participate in the production of .OH, and in the two pathways of oxidation of alcohols. Cobalt protoporphyrin IX treatment of rats resulted in a decrease in microsomal oxidation of aminopyrine, .OH scavengers, and alcohols. However, this treatment not only lowered the content of cytochrome P-450, but also decreased the activity of NADPH-cytochrome P-450 reductase. Carbon monoxide, metyrapone and SKF-525A also inhibited the oxidation of aminopyrine but did not affect oxidation of .OH scavengers. Desferrioxamine, a potent iron chelator, inhibited the oxidation of .OH scavengers but not aminopyrine. The oxidation of alcohols was partly sensitive to desferrioxamine and partly sensitive to carbon monoxide, thus showing similarities to the oxidation of .OH scavengers and drugs. These results suggest that the desferrioxamine-sensitive, .OH-dependent pathway of alcohol oxidation is mediated by the reductase, in analogy to results with .OH scavengers, whereas the desferrioxamine-resistant pathway of alcohol oxidation is mediated by cytochrome P-450, in analogy to results with aminopyrine. By the use of desferrioxamine or carbon monoxide, either of the two alcohol-oxidizing pathways can be inhibited independently of each other.

Alcohols↗
PubMed1985

Increased content of cytochrome P-450 and 4-methylpyrazole binding spectrum after 4-methylpyrazole treatment.

4-Methylpyrazole is a potent inhibitor of alcohol dehydrogenase and of ethanol metabolism. In vitro, 4-methylpyrazole was shown to inhibit microsomal oxidation of drugs and alcohols. Treatment of rats with 4-methylpyrazole at doses ranging from 0 to 300 mg per kg body wt per day for three days resulted in a dose-dependent increase in the content of liver microsomal cytochrome P-450. There was no change in the activity of NADPH-cytochrome P-450 reductase. 4-Methylpyrazole interacted with control microsomes to produce a type II binding spectrum, with a peak at 429 nm, and a trough at 392 nm. The magnitude of this spectral change was increased after 4-methylpyrazole treatment. Kinetic experiments indicated that the 4-methylpyrazole treatment lowered the dissociation constant (Ks) for 4-methylpyrazole. The maximal binding (Vs) was increased when expressed per mg microsomal protein, but not per nmol cytochrome P-450. Therefore, 4-methylpyrazole treatment can affect the microsomal mixed-function oxidase system in several ways, including binding to P-450 as well as inducing P-450.

Animals↗
PubMed1985

A long-term study of hemophilic arthropathy of the knee joint on a program of Factor VIII replacement given at time of each hemarthrosis.

Because there is little available data to demonstrate whether demand therapy is adequate to prevent progression of hemophilic arthropathy, a cohort of 64 patients with severe Hemophilia A (Factor VIII level less than 1%) and no inhibitor were studied with respect to the progression of knee arthropathy over a period of 6 years. Both degree of disease in flexion and extension and progression of disease were rated on an arbitrary scale. At the outset of the study, the majority of knees were either not restricted or mildly restricted as to motion. Of those knees that were not restricted at the outset, 96% remained not restricted. Of the knees that were mildly restricted, only 58% remained stable or improved over the 6 years, and of the knees that were moderately to severely restricted, 75% improved or remained stable. It thus appears that a demand therapy program can maintain normal range of motion in a knee joint. However, if the patient's joint has progressed to mild disease, the ability to maintain or improve the joint with demand therapy appears to be decreased.

Adult↗
PubMed1985

Microsomal interactions between iron, paraquat, and menadione: effect on hydroxyl radical production and alcohol oxidation.

The addition of menadione or paraquat to rat liver microsomes resulted in about a threefold increase in the production of hydroxyl radical (.OH) as reflected by the increased oxidation of 2-keto-4-thiomethylbutyric acid (KMBA) to ethylene. This increase was not sensitive to superoxide dismutase but was blocked by catalase. The increase occurred in the absence of added iron and was not affected by the potent iron chelating agent, desferrioxamine, which suggests the possibility that .OH was produced from an interaction between H2O2 and the paraquat or menadione radical. Menadione and paraquat were especially effective in stimulating the oxidation of KMBA in the presence of certain iron chelates such as ferric-ADP, -ATP, or -EDTA, but not ferric-desferrioxamine, -citrate, or -histidine, or unchelated iron. In fact, ferric-ADP or -ATP only stimulated .OH production in the presence of menadione or paraquat. In the presence of ferric-EDTA, the greater than additive increase of .OH production was sensitive to catalase, but not to superoxide dismutase, suggesting the possibility of reduction of ferric-EDTA by paraquat or menadione radical. The interactions with ferric adenine nucleotides may increase the catalytic effectiveness of menadione or paraquat in producing potent oxidants such as the hydroxyl radical, and thus play a role in the toxicity associated with these agents. Paraquat and menadione had little effect on the overall oxidation of ethanol by microsomes. Microsomal drug metabolism was decreased by menadione or paraquat. As a consequence, the effect of these agents on the microsomal oxidation of ethanol was complex since it appeared that paraquat and menadione stimulated the oxidation of ethanol by a .OH-dependent mechanism, but inhibited the oxidation of ethanol by a cytochrome P-450-dependent oxidation pathway. Experiments with carbon monoxide, ferric-EDTA, and 2-butanol plus catalase tended to verify that microsomal oxidation of alcohols was increased by a .OH-dependent pathway when menadione or paraquat were added to microsomes.

Aminopyrine↗
PubMed1985

Inhibition of the peroxidatic activity of catalase towards alcohols by the aldehyde dehydrogenase inhibitor cyanamide.

Recent results have suggested that catalase is responsible for activating cyanamide to a metabolite which is a potent inhibitor of aldehyde dehydrogenase. In the present report, cyanamide was shown to inhibit the peroxidatic activity of catalase with alcohols such as ethanol or methanol. Inhibition by cyanamide required a brief incubation period with catalase. Ethanol prevented this inhibition of catalase if added before or at the same time as cyanamide, suggesting that ethanol may protect against the activation of cyanamide by catalase.

Alcohols↗
PubMed1985

Ethylene production from alpha-keto-4-thiomethylbutyric acid by isolated rat liver cells, suspension medium, and perfusates in the absence and presence of iron.

Experiments were carried out to evaluate the production of hydroxyl radical-like species by intact rat liver cells by assaying for the production of ethylene from alpha-keto-4-thiomethylbutyric acid in the absence and presence of added iron. In the absence of iron, a low rate of ethylene production, which was not sensitive to superoxide dismutase, catalase, or competitive scavengers was observed. Ethylene was produced when KMBA was incubated with perfusates of rat liver or the suspension medium obtained after incubating liver cells for varying periods of time, followed by removal of the liver cells. Boiling the perfusate or suspension medium had no effect on ethylene production. This ethylene production does not appear to reflect an oxygen radical-mediated event. The addition of ferric-EDTA, but not ferric-desferrioxamine, increased ethylene production by the hepatocyte suspensions in a reaction sensitive to inhibition by catalase, ascorbate oxidase, and competitive scavengers, but not superoxide dismutase. The sensitivity to externally added catalase and ascorbate oxidase suggested that the ethylene production reflected an extracellular oxygen radical generating system. Ferric alone and several ferric chelates, for example, ferric-ATP, ADP, AMP, histidine, and citrate stimulated ethylene production using perfusates of liver or suspension medium after removal of the hepatocytes. The sensitivity of the added iron system to ascorbate oxidase suggested that during perfusion or incubation of liver cells, efflux of ascorbate occurs, followed by reduction of the iron and subsequently, extracellular production of oxygen radicals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗