Molecular aspects of catechol and pyrogallol inhibition of liver microsomal lipid peroxidation stimulated by ferrous ion-ADP-complexes or by carbon tetrachloride

Biochemical studies of transient intermediates in relation to chemical carcinogenesis

Many chemical carcinogens must be metabolized to chemically reactive transient species before they can exert their full toxic action on mammalian cells. In general, this metabolic activation is performed by NADPH-dependent enzymes in the endoplasmic reticulum; the NADPH-cytochrome P-450 electron-transport chain is very important in this respect. Biochemical studies on the chemical reactivities of such transient intermediates require the application of various fast-reaction and free-radical techniques: the use of such techniques is illustrated by reference to the metabolism of carbon tetrachloride. CCl4 is metabolized by liver endoplasmic reticulum in the presence of NADPH to a highly reactive product, probably CCl3; this activation of CCl4 results in covalent binding of CCl3 and lipid peroxidation. The steady-state concentration of CCl3 is too low to be measured directly by e.s.r. spectroscopy but radical species can be accumulated with spin-trap techniques. The CCl3 radical can be generated by pulse radiolysis and the ensuing reactions with biologically important neighbouring species can be followed in the microsecond range by kinetic spectroscopy. The results point to the high reactivity of CCl3 and its restriction to a microenvironment within the endoplasmic reticulum. Highly reactive electrophilic radicals (e.g. CCl3) can initiate lipid peroxidation in biomembranes and this is associated with changes in polyunsaturated fatty acids and in membrane fluidity. The results are discussed in relation to carcinogen activation, to free-radical-mediated reactions in biomembranes, and to the general thesis that the production of reactive aldehydes by lipid peroxidation may act as a 'coarse control' of cell division.

Different roles of Fpg and Endo III on catechol-induced DNA damage in extended-term cultures of human lymphocytes and L5178Y mouse lymphoma cells

Catechol is a genotoxic agent assumed to induce DNA damage via the oxidative pathway. Using the comet assay and the repair-specific enzymes formamido pyrimidine glycosylase (Fpg) and endonuclease III (Endo III), we examined the ability of catechol to induce DNA damage in extended-term cultures of human lymphocytes and mouse lymphoma cells. Our results suggest that mouse lymphoma cells are somewhat more sensitive towards catechol-induced DNA damage than the extended-term cultures of human lymphocytes. At high concentrations, the catechol-induced damage seemed to be independent of both Fpg and Endo III, possibly indicating a non-oxidative pathway for the DNA damage (involving, for example, a bulky adduct). The fact that Endo III, but not Fpg, enhanced the DNA damaging effect of catechol, suggests that this metabolite of benzene either mediates oxidation of pyrimidines rather than purines, or that oxidised purines are repaired more efficiently, at least in human lymphocytes. In the latter cells, low concentrations of catechol were found to reduce the DNA migration. Considering the role of Fpg and it's adduct specific detection of 8-oxoguanine, this suggests that a low concentration of catechol has an antioxidative effect reducing the background levels of oxidized purines.

Review of the career of Professor Dr. Herbert Remmer

This article is a laudatio summarizing the scientific career and accomplishments of Herbert Remmer as observed by one of his first students. The article traces over fifty years of multiple contributions of Herbert Remmer to pharmacology and toxicology and clearly identifies the leadership characteristics of this memorable man.

Phenol and catechol induce prehemolytic and hemolytic changes in human erythrocytes

The toxic potency of two industrially used compounds (phenol and catechol) was studied in human blood cells in vitro. Catechol was found to be a more harmful toxin than phenol, since it provokes statistically significant changes in the function of erythrocytes even at low doses. Most of the changes was statistically significant for the doses of 50 ppm of catechol and 250 ppm of phenol. Both compounds induced methaemoglobin formation, glutathione depletion and conversion of oxyhaemoglobin to methaemoglobin, which is associated with superoxide anion production and lead to formation of ferryl hemoglobin, hydrogen peroxide or hydroxyl radicals. It is known that oxidation of catechol leads to formation of semiquinone radicals. Semiquinones are able to bind to nucleophilic residues like -SH or -NH2 of proteins and these macromolecules may undergo inactivation. We observed among especially susceptible to action of catechol are catalase (CAT) (100 ppm) and superoxide dismutase (SOD) (250 ppm). Decrease of the activity of catalase and SOD by catechol induced radical species formation. This lead to inhibition of another protective enzymes such as glutathione-S-transferase (500 ppm), glutathione reductase (1000 ppm), glucose-6-phosphate dehydrogenase activity (1000 ppm). Cytotoxicity of phenol or catechol was noted as hemolysis. Haemoglobin liberated from erythrocytes in this process may further generate oxygen free radicals and subsequently initiate enzymes damage. It seems to be essential that in phenol and catechol toxicity special role play damages of heme proteins and other proteins molecule, and damages of lipids are not so important.

Chemical properties of catechols and their molecular modes of toxic action in cells, from microorganisms to mammals

Catechols can undergo a variety of chemical reactions. In this review, we particularly focus on complex formations and the redox chemistry of catechols, which play an inportant role in the toxicity of catechols. In the presence of heavy metals, such as iron or copper, stable complexes can be formed. In the presence of oxidizing agents, catechols can be oxidized to semiquinone radicals and in a next step to o-benzoquinones. Heavy metals may catalyse redox reactions in which catechols are involved. Further chemical properties like the acidity constant and the lipophilicity of different catechols are shortly described as well. As a consequence of the chemical properties and the chemical reactions of catechols, many different reactions can occur with biomolecules such as DNA, proteins and membranes, ultimately leading to non-repairable damage. Reactions with nucleic acids such as adduct formation and strand breaks are discussed among others. Interactions with proteins causing protein and enzyme inactivation are described. The membrane-catechol interactions discussed here are lipid peroxidation and uncoupling. The deleterious effect of the interactions between catechols and the different biomolecules is discussed in the context of the observed toxicities, caused by catechols.

Mechanisms for regulating oxygen toxicity in phytophagous insects

The antioxidant enzymatic defense of insects for the regulation of oxygen toxicity was investigated. Insect species examined were lepidopterous larvae of the cabbage looper (Trichoplusia ni), southern armyworm (Spodoptera eridania), and black swallowtail (Papilio polyxenes). These phytophagous species are subject to both endogenous and exogenous sources of oxidative stress from toxic oxygen radicals, hydrogen peroxide (H2O2) and lipid peroxides (LOOH). In general, the constitutive levels of the enzymes superoxide dismutase (SOD), catalase (CAT), glutathione transferase (GT), and its peroxidase activity (GTpx), and glutathione reductase (GR), correlate well with natural feeding habits of these insects and their relative susceptibility to prooxidant plant allelochemicals, quercetin (a flavonoid), and xanthotoxin (a photoactive furanocoumarin). Induction of SOD activity which rapidly destroys superoxide radicals, appears to be the main response to dietary prooxidant exposure. A unique observation includes high constitutive activity of CAT and a broader subcellular distribution in all three insects than observed in most mammalian species. These attributes of CAT appear to be important in the prevention of excessive accumulation of cytotoxic H2O2. Unlike mammalian species, insects possess very low levels of a GPOX-like activity toward H2O2. Irrefutable proof that this activity is due to a selenium-dependent GPOX found in mammals, is lacking at this time. However, the activity of selenium-independent GTpx is unusually high in insects, suggesting that GTpx and not GPOX plays a prominent role in scavenging deleterious LOOHs. The GSSG generated from the GPOX and GTpx reactions may be reduced to GSH by GR activity. A key role of SOD in protecting insects from prooxidant toxicity was evident when its inhibition resulted in enhanced toxicity towards prooxidants. The role of antioxidant compounds in protecting these insects from toxic forms of oxygen has not been explored in depth. A major finding, however, is that these insects are lutein accumulators. Lutein is a dihydroxy (diol) derivative of beta-carotene, and it is a good quencher of activated forms of oxygen and free radicals. Levels of lutein are highest in P. polyxenes which specializes in feeding on prooxidant-containing plants.

Hydroxyl radical scavenging and antipsoriatic activity of benzoic acid derivatives

The hydroxyl radical scavenging and antipsoriatic activity of a number of lipophilic and hydrophilic benzoic acid derivatives was investigated. To quantify antioxidative effects, a newly introduced test system based on the diminution of the ESR signal of DMPO-OH (generated by Fenton's reagent) by the tested compounds was applied. It was found that the in vitro antioxidative (toward hydroxyl radical) activity of benzoic acid esters decreases with increasing chain length whereas the antipsoriatic activity increases. This effect is discussed in terms of a larger lipophilicity of long-chain esters. Propyl gallate was found to be the most active OH scavenger since it is some orders of magnitude more efficient than "model" antioxidants like alpha-tocopherol or mannitol. The highest antipsoriatic activity was exhibited by hydroxy benzoic acid decyl ester.

Immunomodulating properties of cianidanol on responsiveness and function of human peripheral blood T-cells and K-cells

Cianidanol (Ci) [(+)-catechin] is a lipophilic compound which interacts with membrane lipids and affects responsiveness and function of immunocompetent cells. We therefore studied the immunomodulating properties of Ci on the proliferative response of human peripheral T-cells in one-way mixed lymphocyte reaction (1-MLR) and autologous mixed lymphocyte reaction (AMLR); on the generation of cytotoxic T-cells (Tc-cells), suppressor T-cells (Ts-cells, comprising radiosensitive as well as radioresistant suppressor T-cells) and radioresistant suppressor T-cells (rrTs) in 1-MLC; and on the cytolytic activity of Tc-cells and K-cells. In 1-MLR we observed a small stimulation of cell proliferation at Ci concentrations up to 108 microM whereas higher concentrations led to a marked suppression (100% at 435 microM). The generation of Ts-cells and rrTs-cells in 1-MLR was clearly suppressed at Ci-concentrations above 435 microM and 108 microM, respectively. The timing of Ts-cell formation was not influenced. The Tc-cell generation in 1-MLR was inhibited at high doses, and at 870 microM 59% suppression was observed. A similar dose-dependent suppressive effect of Ci was seen by testing for the cytolytic activity of ADCC-reactive K-cells and of CML-reactive Tc-cells generated in 1-MLR in the absence of Ci. At the highest concentration used (870 microM) the CML was suppressed by 45% and the ADCC by 46%. Our investigation on Ci's influence on the efferent and afferent part of immune responses in vitro demonstrated both stimulatory and inhibitory effects usually occurring at low and high concentrations, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the protective effect of various flavonoids against lipid peroxidation of erythrocyte membranes (induced by cumene hydroperoxide)

An experimental model system was designed to test the antioxidant effects of various pharmacologic compounds. Cumene hydroperoxide induces in vitro the peroxidation of erythrocyte membrane and the subsequent formation of malonaldehyde and fluorescent lipid-soluble products. The protective effect of various flavonoids was compared to that of butylated hydroxytoluene (BHT). Protective effect was evaluated by the inhibition of peroxidation product formation. In this experimental system, quercetin and catechin showed a protective effect against lipid peroxidation as high as that of BHT. Morin, rutin, trihydroxyethylrutin, and naringin were active but to a lesser degree, whereas flavone was devoid of antioxidant activity.

Oxygen radical formation and DNA damage due to enzymatic reduction of bleomycin-Fe(III)

Aerobic incubations of bleomycin, FeCl3, DNA, NADPH, and isolated liver microsomal NADPH-cytochrome P-450 reductase resulted in NADPH and oxygen consumption and malondialdehyde formation, indicating that the deoxyribose moiety of DNA was split. All parameters measured depended on the active enzyme, bleomycin and FeCl3. In the absence of oxygen malondialdehyde formation was very low. When bleomycin, FeCl3 and the reductase were incubated with methional ethene (ethylene) was formed, suggesting that during the enzyme-catalyzed redox cycle of bleomycin-Fe(III/II) hydroxyl radicals were formed. Ethene formation also depended on oxygen, NADPH, the enzyme, bleomycin, and FeCl3. During aerobic incubations of bleomycin, FeCl3, NADPH, and isolated liver nuclei oxygen and NADPH were consumed and malondialdehyde was formed. Oxygen and NADPH consumption and malondialdehyde formation depended on bleomycin and FeCl3. In the absence of oxygen malondialdehyde was not formed. These results indicate that nuclear NADPH-cytochrome P-450 reductase redox cycles the bleomycin-Fe(III/II) complex and that the reduced complex activates oxygen, whereby hydroxyl radicals are formed which damage the deoxyribose of nuclear DNA.

No evidence for lysophospholipid formation during peroxidation of phospholipids by NADPH-cytochrome P-450 reductase and iron ions

Liposomes comprised of liver microsomal phospholipids and radioactive phosphatidylcholine or phosphatidylethanolamine as tracers were incubated with isolated liver microsomal NADPH-cytochrome P-450 reductase, NADPH and ADP-EDTA-chelated iron ions, a system which stimulates peroxidation of unsaturated fatty acids of phospholipids. Phospholipids and their reaction products were extracted and chromatographed on HPLC. Phosphatidylcholine and phosphatidylethanolamine considerably decreased after 30 min incubation, depending on the enzyme and NADPH as measured by UV absorbance and radioactivity. However, neither a lysophospholipid peak nor a lysophospholipid-like peak were detectable. We suggest that lysophospholipid formation during microsomal lipid peroxidation is exclusively due to phospholipase A2 and not due to peroxidative breakdown of the unsaturated fatty acid in the beta-position of glycerol.

On the mechanism of antithrombotic action of flavonoids

Flavonols (quercetin and rutin) and flavanes (cyanidol and meciadonol) were studied for their effect on non-enzymatic lipid peroxidation, lipoxygenase and cyclo-oxygenase activities, binding to albumin and platelet membranes. These biochemical properties of four flavonoids were compared with respect to their antithrombotic action in vivo and their efficacy at influencing the platelet-endothelium interaction in vitro. All four flavonoids inhibited the ascorbate-stimulated formation of malondialdehyde by boiled rat liver microsomes (quercetin greater than rutin approximately cyanidol approximately meciadonol) and inhibited platelet lipoxygenase activity (quercetin greater than cyanidol greater than meciadonol greater than rutin) whereas only flavonols, but not flavanes, stimulated cyclo-oxygenase and were bound to platelet membranes. The same two flavonols dispersed platelet thrombi which were adhering to the rabbit aortic endothelium in vitro (EC50 for quercetin was 80 nM and for rutin 500 nM) and prevented platelets from aggregation over blood-superfused collagen strip in vivo (ED50 for quercetin was 5 nmol/kg and for rutin 33 nmol/kg i.v.). Cyanidol and meciadonol were not effective as anti-thrombotic agents. It is concluded that activated platelets adhering to vascular endothelium generate lipid peroxides and oxygen-free radicals which inhibit endothelial biosynthesis of prostacyclin and destroy endothelium-derived relaxing factor (EDRF). Flavonols are anti-thrombotic because they are selectively bound to mural platelet thrombi and owing to their free radical scavenging properties resuscitate biosynthesis and action of endothelial prostacyclin and EDRF. Thus, flavonols release the thrombolytic and vasoprotective endothelial mediators only in these vascular segments which are covered by a carpet of aggregating platelets.

Liver nuclear NADPH-cytochrome P-450 reductase may be involved in redox cycling of bleomycin-Fe(III), oxy radical formation and DNA damage

When NADPH-cytochrome P-450 reductase isolated from rat liver microsomes was aerobically incubated with bleomycin, FeCl3, NADPH and DNA parallel NADPH and oxygen were consumed and malondialdehyde was formed. A similar parallelism of NADPH- and oxygen-consumption and malondialdehyde formation was observed when cell nuclei isolated from rat liver were incubated under the same conditions. The formation of malondialdehyde which was identified by HPLC and which was most likely released from oxidative cleavage of deoxyribose of nuclear DNA required oxygen, bleomycin, FeCl3 and NADPH. This indicates that a nuclear NADPH-enzyme, presumably NADPH-cytochrome P-450 reductase, is able to redox cycle a bleomycin-iron-complex which in the reduced form can activate oxygen to a DNA-damaging reactive species. The data suggest that the activity of this enzyme in the cell nucleus could play an important role in the cytotoxicity of bleomycin in tumor cells.

Inverse relationship of ethane or n-pentane and malondialdehyde formed during lipid peroxidation in rat liver microsomes with different oxygen concentrations

When we incubated rat liver microsomes with ferrous ions and an NADPH-regenerating system, ethane and n-pentane formation increased correspondingly with decreasing concentrations of oxygen in the atmosphere above the incubation, whereas malondialdehyde increased with increasing oxygen concentrations up to a plateau. At very low oxygen concentrations - 100% helium as atmosphere, but presumably traces of oxygen were present in the microsomes - ethane and n-pentane formation were maximal and dependent on the concentrations of ferrous ions, in the case of ethane, a peak being reached at about 20 microM Fe2+, whereas n-pentane continuously increased with increasing concentrations of Fe2+. It is suggested that the inverse relationship of ethane or n-pentane and malondialdehyde is due to two different reaction sequences of microsomal lipid peroxidation with different oxygen sensitivities.

Inhibition of microsomal lipid peroxidation by naphthoquinones: structure-activity relationships and possible mechanisms of action

Menadione (2-methyl-1,4-naphthoquinone) is a remarkably potent inhibitor of microsomal lipid peroxidation, effective at submicromolar concentrations. Its possible mechanism of action and the relationship between naphthoquinone structure and antioxidant activity were the topics of this investigation. In the microsomal lipid-peroxidizing system dependent on NADPH and ferric pyrophosphate, menadione, at concentrations of 50 microM or higher virtually eliminated the accumulation of malondialdehyde and lipid hydroperoxides. In the NADPH-independent, cumene hydroperoxide-dependent system, menadione was also an effective antioxidant, but only in the presence of reducing equivalents. These and other observations indicate that a reduced form of menadione, either the hydroquinone or semiquinone, is the active antioxidant, and suggest that it may trap hydroperoxy radicals, alkoxy radicals, or other free radicals involved in propagating lipid peroxidation. Moreover, these results show that electron diversion per se cannot account for the antioxidant effects of menadione. A comparison of the antioxidant activities of eight 1,4-naphthoquinones indicated that methyl substitution of C-2, lack of steric hindrance at C-3 or C-5, and (in the case of weak acids) a relatively high pKa are favorable structural features associated with strong antioxidant activity.

Inhibition of in vitro microsomal lipid peroxidation by isoflavonoids

In a comparative study the inhibition of microsomal lipid peroxidation induced by an Fe2+-ADP-complex and NADPH by naturally occurring isoflavones and their reduced derivatives (isoflavanones and isoflavans) has been examined. It is found that the isoflavanones are more active than the parent isoflavones and the isoflavans are by far the most potent inhibitors. In our in vitro test system 6,7,4'-trihydroxy- and 6,7-dihydroxy-4'-methoxyisoflavans (IC50 values 1.3 X 10(-6) and 1.1 X 10(-6) mol/l respectively) surpass the inhibitory effect of alpha-tocopherol, (+)-cyanidanol-3 and BHA (butylated hydroxyanisole). In order to establish a structure-activity relationship, a few more isoflavans have been included in the investigation.

Influence of paracetamol (acetaminophen) on cadmium-induced lipid peroxidation in hepatocytes from starved rats

Isolated hepatocytes form thiobarbituric acid (TBA)-reactants, a parameter of lipid peroxidation (LPO), when exposed to cadmium (Cd). Paracetamol (Para) inhibits this response, dependent on time and concentration. Cd-induced SH-group decline, however, and enhanced plasma membrane permeability to Trypan Blue (TB) were not inhibited by Para. This indicates that Cd-induced cell damage and Cd-induced LPO are independent events. Experiments using cells with enhanced and lowered metabolism of Para after phenobarbital- and acetone- or heat-and metyrapone treatment, respectively, suggest a potentially inhibitory effect of both Para and its metabolite(s) on LPO. The antioxidative potency of Para turned out to be small compared to that of the radical scavenger (+)-cyanidanol-3.

Further studies on adriamycin induced in vitro lipid peroxidation

Adriamycin (AM)-induced lipid peroxidation was studied in rat liver microsomal system, measuring colour produced by thiobarbituric acid (TBA) reactive material and the development of volatile hydrocarbons. The onset of this degradative process is closely related to the AM content. This phenomenon appears to be highly influenced by the buffer used for the microsomal preparation. The effect of AM on FE--ADP-induced lipid peroxidation in liver microsomes has also been studied.

Comparison of methods of assessment of metal-induced lipid peroxidation in isolated rat hepatocytes

There is some controversy about which method of assessment of lipid peroxidation in isolated hepatocytes is most appropriate. The present study was undertaken primarily to compare measurement of concentrations of thiobarbituric acid (TBA) reacting substances with measurement of ethane concentrations in the gas phase of the incubation flask as indicators of lipid peroxidation. Four metal salts, FeCl2, NaVO3, CdCl2, and MnCl2, were selected as agents that interact with the lipid peroxidation process. Furthermore, reduced glutathione (GSH) concentrations and enzyme leakage were assayed to determine whether there was a consistent pattern of interaction between lipid peroxidation and change in GSH concentrations and enzyme leakage. The effects of the metal ions on the concentration of TBA reactants estimated in the whole cell suspension and on the gaseous ethane concentration were similar. However, the assessment of TBA reactants was a little more sensitive, and ethane concentrations continued to climb with incubation time rather than leveling off as observed for TBA reactants. In general, the results of both assays were in good agreement. No consistent pattern of interaction between lipid peroxidation, GSH, and enzyme leakage was discernible in the results of the present study. It is suggested that perhaps the best approach to an experimental situation where lipid peroxidation is thought to be of central importance is measurement of both parameters, TBA reactants and ethane concentrations.

Post-translational carboxylation of preprothrombin

In summary, in this review on the function of vitamin K in post-translational modification of precursor proteins by carboxylation of certain glutamyl residues, I have tried to cover in particular the recent work on the reaction, the enzymes involved and the mechanisms being considered. In doing this I have also considered vitamin K, its discovery, its functional form and the possible relation of its metabolism to the carboxylation reaction. Equally the various vitamin K-dependent gla-containing proteins currently known have been described. The carboxylation of synthetic small molecule exogenous substrates and the synthesis and metabolism of the products of carboxylation are of great help in studying the reaction. Structural specificity of vitamin K analogs in vivo and in vitro has been compared and the use of various antagonists in vivo and in vitro considered in attempts to gain an understanding of the overall reaction. The reactions subsequent to carboxylation, e.g., the activation of prothrombin to thrombin via serine proteases and the related activation of the other vitamin K-dependent proteins have not been considered in this review. The review has not covered prothrombin or other vitamin K-dependent protein isolation, nor the determination of these proteins. As the vitamin K-dependent protein carboxylation story has developed over the past six years, a number of reviews have been written which help in keeping up with the various aspects of the field as it has expanded. These reviews refer to many of the papers I have had to eliminate due to space limitations. They are referenced as 469-489. The review is in no sense comprehensive and many papers have been missed or only mentioned. I have tried to concentrate on the more recent work and, thus, much of the very fine work of the 1940's on vitamin K chemistry is hardly mentioned. Some redundancy has been built into the organization of the review so that a reader can obtain a reasonable view of any one section without having to search the whole review for all possible relevant information on any particular part of the field.

The inhibitory action of dithiocarbamates and carbon disulphide on malondialdehyde formation resulting from lipid peroxidation in rat liver microsomes

The dithiocarbamates (DTCs) disulfiram, thiram, diethyldithiocarbamate and dimethyldithiocarbamate on the equimolar base inhibited to the same extent both the lipid peroxidation (LPO) induced by ascorbic acid (non-enzymatic) and that stimulated by an NADPH-regenerating system with CCl4 admixture (enzymatic). Lipid peroxidation measurements were made in terms of malondialdehyde (MDA) formation in rat liver microsomes, or in the 9000 X g supernatant. The inhibitory action of tetramethylthiuram monosulphide was considerably weaker. Carbon disulphide (CS2) inhibited the enzymatic and non-enzymatic stimulated microsomal LPO by 4 orders less than the DTCs. In parallel with the inhibition of MDA formation, oxidative destruction of microsomal cytochrome P-450 was delayed with increasing concentrations of the DTCs. A well-correlated, non-linear, semi-logarithmic relation was found for the concentration-activity relationship for all DTCs and CS2. As the DTCs inhibited LPO both in heat-denatured and freshly prepared microsomes, it can be deduced that the DTCs intervene in a non-enzymatic oxidation phase of the LPO. The DTC inhibitory action is attributed to a radical-trap mechanism since LPO that has already been initiated was inhibited with the DTCs. However, more inhibitor is required to trap the radicals the later the DTC administration takes place.

Ethane formation of isolated rat hepatocytes due to carbon tetrachloride

Isolated rat hepatocytes incubated aerobically formed measurable amounts of ethane, a parameter for lipid peroxidation. This ethane formation increased several-fold due to carbon tetrachloride (CCl4) depending on its concentration. Cell damage as measured by trypan blue uptake and lactate dehydrogenase release poorly correlated with ethane formation. Ethane was not metabolized, whereas malondialdehyde (MDA), when added to isolated hepatocytes, decreased very rapidly. The results indicate that rather than MDA is a reliable parameter for lipid peroxidation occurring in isolated hepatocytes, and that a simple relationship between CCl4-induced lipid peroxidation and cell damage is not existing in isolated hepatocytes.

Free radical initiation in proteins and amino acids by ionizing and ultraviolet radiations and lipid oxidation--part III: free radical transfer from oxidizing lipids

Parallels and similarities in chemical and functional damage to proteins by ionizing and uv radiations and oxidizing lipids have been recognized for some time. However, only recently have oxidizing lipids been shown directly by electron spin resonance to be radiomimetic also in their capacity for protein free radical production. Free radicals play a key role in the transformation of energy to molecular and cellular damage. It is thus of critical importance to elucidate the general mechanisms of free radical formation and reactions in proteins in order to understand protein involvement in various pathological conditions and in food deterioration. Accordingly, this review is a detailed comparison of gamma-radiation, UV radiation, and lipid oxidation for what is presently known concerning (1) the specific modes of energy deposition and free radical formation, (2) the free radicals formed in proteins and amino acids, and (3) the typical damage correlating with these radicals.

Oxygen dependence of CCl4-induced lipid peroxidation in vitro and in vivo

Rat liver microsomes showed an atypical oxygen dependence of carbon tetrachloride (CCL4)-induced malondialdehyde formation with a maximum at ca. 7% O2 and a minimum at ca. 15% O2. Rats treated with CCl4 expired less ethane under high oxygen concentrations and more ethane under low oxygen concentrations. The initiation of CCl4-induced lipid peroxidation in the liver would appear to be influenced by the oxygen concentrations present in the hepatocytes.

Mechanisms of protection against the damage produced in biological systems by oxygen-derived radicals

This paper will concentrate on the damage to liver endoplasmic reticulum and plasma membrane fractions that results from exposure to O2- derived radicals and lipid peroxidation. Lipid peroxidation in rat liver endoplasmic reticulum can be produced in various ways involving electron flow out of the NADPH-cytochrome P450 electron-transport chain; analogous reactions occur also in liver plasma membrane suspensions. The subsequent damaging reactions of oxygen-derived radicals and of lipid peroxidation on biological components can be attenuated by various free-radical scavengers and a survey of more than 50 such scavengers in four different systems involving lipid peroxidation has been made. The conditions required for such scavenging reactions to be effective will be outlined, and the difficulties inherent in using such scavengers in vivo will be discussed.