Studies on lipid peroxidation in normal and tumour tissues. The Yoshida rat liver tumour

Consumption of thermally-oxidized sunflower oil by chicks reduces alpha-tocopherol status and increases susceptibility of tissues to lipid oxidation

The effect of heated sunflower oil consumption on alpha-tocopherol status, fatty acid composition and oxidative stability of chicken tissues was investigated. Chicks were fed on diets containing (g/kg): fresh sunflower oil (FSO) 40, heated sunflower oil (HSO) 40 or heated sunflower oil (40) supplemented with alpha-tocopheryl acetate (HSE) to a similar alpha-tocopherol concentration as the FSO diet. Concentrations of alpha-tocopherol in tissues of chicks fed on HSO and HSE were significantly lower than those of chicks fed on FSO. Significant correlations were observed between plasma alpha-tocopherol concentration and the alpha-tocopherol concentrations of other tissues (r > or = 0.67, P < 0.005) and between log plasma alpha-tocopherol and plasma thiobarbituric acid-reacting substances (TBARS) concentrations (r -0.851, P < 0.001). The concentrations of TBARS in tissues of chicks fed on the various diets were generally very similar before stimulation of peroxidation with Fe-ascorbate. Susceptibility of tissues to Fe-ascorbate-induced lipid peroxidation was increased by feeding HSO. Supplementation with alpha-tocopheryl acetate reduced susceptibility to lipid oxidation to varying degrees, depending on the tissue. The results suggest that chronic ingestion of oxidized lipids may compromise free-radical-scavenging activity in vivo by depleting alpha-tocopherol in the gastrointestinal tract, or possibly in plasma and other tissues.

DNA lesions, inducible DNA repair, and cell division: three key factors in mutagenesis and carcinogenesis

DNA lesions that escape repair have a certain probability of giving rise to mutations when the cell divides. Endogenous DNA damage is high: 10(6) oxidative lesions are present per rat cell. An exogenous mutagen produces an increment in lesions over the background rate of endogenous lesions. The effectiveness of a particular lesion depends on whether it is excised by a DNA repair system and the probability that it gives rise to a mutation when the cell divides. When the cell divides, an unrepaired DNA lesion has a certain probability of giving rise to a mutation. Thus, an important factor in the mutagenic effect of an exogenous agent whether it is genotoxic or non-genotoxic, is the increment it causes over the background cell division rate (mitogenesis) in cells that appear to matter most in cancer, the stem cells, which are not on their way to being discarded. Increasing their cell division rate increases mutation and therefore cancer. There is little cancer from nondividing cells. Endogenous cell division rates can be influenced by hormone levels, decreased by calorie restriction, or increased by high doses of chemicals. If both the rate of DNA lesions and cell division are increased, then there will be a multiplicative effect on mutagenesis (and carcinogenesis), for example, by high doses of a mutagen that also increases mitogenesis through cell killing. The defense system against reactive electrophilic mutagens, such as the glutathione transferases, are also almost all inducible and buffer cells against increments in active forms of chemicals that can cause DNA lesions. A variety of DNA repair defense systems, almost all inducible, buffer the cell against any increment in DNA lesions. Therefore, the effect of a particular chemical insult depends on the level of each defense, which in turn depends on the past history of exposure. Exogenous agents can influence the induction and effectiveness of these defenses. Defenses can be partially disabled by lack of particular micronutrients in the diet (e.g., antioxidants).

Lipid peroxidation and disintegration of the cell membrane structure in cultures of rat lung fibroblasts treated with asbestos

Rat lung fibroblasts were cultured for 24 and 48 h with UICC standard reference asbestos samples of amosite, crocidolite or Canadian chrysotile at various concentrations, and thiobarbituric acid-reactive substances (TBARS) in the media and the cells were measured. Tests by the trypan blue dye-exclusion method showed that cell viability was 80 +/- 5% (mean +/- SD) and 71 +/- 6% when cultured for 48 h in the presence of 500 micrograms ml-1 of amosite and crocidolite, respectively, but was not affected by chrysotile. In cultures for 24 and 48 h, both chrysotile and crocidolite at > 250 micrograms ml-1 significantly increased TBARS in the medium, whereas amosite did so at > 500 micrograms ml-1. TBARS in the cells was not increased significantly by chrysotile at any concentration in the cultures for 24 and 48 h, but crocidolite at > 250 micrograms ml-1 significantly increased TBARS in the cells when cultured for 24 or 48 h. Although amosite at all concentrations tested did not increase significantly TBARS in the cells of the 24-h culture, it did increase TBARS significantly in the cells when cultured for 48 h at a concentration of 500 micrograms ml-1 amosite. The increases of TBARS in media of the cultures with asbestos were accompanied by increases of lactate dehydrogenase (LDH) activity in the media, indicating the leakage of the enzyme from the cell into the media. The activity of LDH and the amount of TBARS showed a good correlation with each other, with a significant correlation coefficient value of 0.655.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhancement by tamoxifen of the membrane antioxidant action of the yeast membrane sterol ergosterol: relevance to the antiyeast and anticancer action of tamoxifen

The anticancer drug tamoxifen inhibits lipid peroxidation in ox-brain phospholipid liposomes, and is a good antiyeast agent, with clinical potential. We now report that the ergosterol-containing lipid fraction derived from yeast microsomal membranes (and the ergosterol separated from it) inhibited lipid peroxidation when introduced into ox-brain phospholipid liposomes. Inhibition of lipid peroxidation by the lipid fraction was greatly enhanced when yeast cell growth was inhibited with tamoxifen prior to lipid extraction. The ability of tamoxifen to enhance the membrane antioxidant ability of ergosterol is expressed in terms of a tamoxifen enhancement coefficient. Enhancement by tamoxifen of the membrane antioxidant action of ergosterol is discussed in relation to the antifungal and anticancer actions of tamoxifen.

Radical production from peroxide and peracid tumour promoters: EPR spin trapping studies

EPR spin trapping using the spin traps 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and 3,5-dibromo-4-nitrosobenzene sulphonic acid (DBNBS) has been employed to examine the generation of radicals from a number of organic peroxides and peracids which are known or suspected tumour promoters. All of the compounds when incubated with rat liver microsomal fractions in the presence of NADPH or NADH are metabolised to radical species which can be detected, and in most cases identified definitively, as the corresponding spin adducts; the assignment of particular signals to certain spin adducts has been confirmed by photolytic experiments. In the majority of cases, the predominant species are the arenecarbonyloxyl [RC(O)O.] and hydroxyl radical adducts. The mechanism of formation of the former species is shown to be enzymatic and cytochrome P-450 dependent and requires the presence of reducing equivalents. This type of radical is shown to undergo ready decarboxylation to give aryl radicals in agreement with previous chemical studies. The detection of these radical species, which are known to cause DNA strand breaks and be cytotoxic, with all the compounds tested, provides strong supportive evidence for the theory that it is the generation of radical species from these compounds which is the cause of their tumour-promoting activity.

Doxorubicin-induced lipid peroxidation and glutathione peroxidase activity in tumor cell lines selected for resistance to doxorubicin

Doxorubicin-induced lipid peroxidation was evaluated in four human or murine cell strains in culture and in their doxorubicin-resistant variants, by the quantification of malondialdehyde produced after a 2-h incubation of cells with the drug. Significantly increased malondialdehyde levels were obtained 24 h after doxorubicin treatment in three of the wild-type cell lines with doses as low as 0.05-0.1 micrograms/ml, which is within an order of magnitude of the concentration of the drug which inhibits cell growth by 50%. This production of malondialdehyde was abolished in two doxorubicin-resistant strains, even with high doses of drug (100-300 micrograms/ml), but was maintained in the third resistant line. No malondialdehyde production was observed in the fourth cell line, sensitive or resistant. It is remarkable that an enhancement of selenium-dependent and non-selenium-dependent glutathione peroxidase activities was exhibited during the acquisition of resistance to doxorubicin in the two first lines, but not in the third, whereas a constitutively high non-selenium-dependent glutathione peroxidase activity existed in the doxorubicin-sensitive and doxorubicin-resistant variants of the fourth cell line. Gene expression of selenium-dependent glutathione peroxidase and of glutathione S-transferase pi, which is known partially to bear a non-selenium-dependent glutathione peroxidase activity, were correlated with the corresponding enzyme activities. It appears, therefore, that the already known enhancement of glutathione peroxidase activity and expression in doxorubicin-resistant cell lines has a quantifiable consequence upon doxorubicin-induced lipid peroxidation and may have consequences in the mechanism of resistance to this drug.

Mechanisms and effects of lipid peroxidation

Lipid peroxidation is an important mechanism in free radical mediated cell injury. It can damage cell membranes directly and the reactive carbonyl products may spread the damage far from the original site of radical production. It has long been considered to be involved in various toxic tissue injuries and in certain disease processes, including cancer. Paradoxically, cancer cells are very resistant to lipid peroxidation. Recently, it has been suggested that lipid peroxidation may exert more subtle effects than was previously thought possible, by influencing gene expression.

Ethanol-mediated promotion of oral carcinogenesis in hamsters: association with lipid peroxidation

Pouches of male Syrian Golden hamsters were painted with 1% 7,12-dimethylbenz[a]anthracene (DMBA) three times for one week. One week after DMBA treatment, hamsters were fed an ethanolic diet and continued on this diet until they were killed 22 and 35 weeks after the start of the experiment. Phospholipids, cholesterol, indexes of lipid peroxidation (malondialdehyde, diene and triene conjugates, lipid fluorescence), and the antioxidants glutathione and vitamin E were determined in the buccal mucosa, as was the incidence of tumors. At 22 weeks, the relative proportion of cholesterol to phospholipids in ethanol-consuming hamsters was significantly increased. At 35 weeks, most of the treatments showed a return of cholesterol vs. phospholipids toward that of untreated mucosa at 22 weeks. Ethanol consumption also increased the indexes of lipid peroxidation at 22 weeks; the largest increases occurred when ethanol use was combined with DMBA treatment. However, at 35 weeks such increases in lipid peroxidation had either returned to intermediate levels or were not different from the untreated controls at 22 weeks. Glutathione decreased in pouches of hamsters fed ethanol diets at 22 weeks, but at 35 weeks there was no appreciable difference. However, vitamin E increased significantly with ethanol consumption at 22 weeks, which increased further when combined with DMBA treatment, but at 35 weeks these values were intermediate. No tumors were seen at 22 weeks. At 35 weeks, DMBA-treated ethanol-fed hamsters had a significantly higher incidence of tumors, more multiple tumors per hamster with tumors, and more of the larger tumors than DMBA-treated control-fed hamsters. The results suggest that an increase in lipid peroxidation occurs with ethanol-related tumor promotion processes, but this lipid peroxidation declines when tumors appear to be preceded by increases in cholesterol relative to phospholipids and increases in vitamin E.

Measurement of doxorubicin-induced lipid peroxidation under the conditions that determine cytotoxicity in cultured tumor cells

We have investigated doxorubicin-induced lipid peroxidation by the measure of malondialdehyde (MDA) formation in rat glioblastoma cells and human breast carcinoma cells in culture. There was a significant production of MDA when the cells were incubated with pharmacologically relevant doxorubicin concentrations, i.e., concentrations that produce a significant cytotoxicity (0.1 micrograms/ml). At equitoxic doses, vincristine provided no lipid peroxidation, indicating that MDA formation is not a consequence of cell death. Doxorubicin-induced lipid peroxidation was maximal 24 h after incubation of the cells with doxorubicin, indicating that a delay was necessary for the free radical-mediated membrane damage induced by doxorubicin. In the presence of alpha-tocopherol in the culture medium, the doxorubicin-induced MDA formation was inhibited. The development of this method will help in defining the role of free radicals and lipid peroxidation in the cytotoxicity of doxorubicin.

UV induces oxy- and chromanoxyl free radicals in microsomes by a new photosensitive organic hydroperoxide, N,N'-bis(2-hydroperoxy-2-methoxyethyl)- 1,4,5,8-naphtalene-tetra-carboxylic-diimide

Low oxygen tension, a high content of reducing equivalents and endogenous vitamin E are responsible for the resistance of cancer cells to oxidative stress-based therapy. N,N'-bis(2-hydroperoxy-2-methoxyethyl)-1,4,5,8-naphthalene-tetra- carboxylic-diimide (NP-III), capable to release radicals both in the absence and in the presence of oxygen upon UV-illumination, is a new potential anticancer agent. UV-induced reactions of NP-III in rat liver microsomes were studied under aerobic and anaerobic conditions with (i) vitamin E homologue, chromanol-alpha-C-6 having a shorter (6-carbon) hydrocarbon side chain and higher antioxidant activity, and (ii) the spin-trap 5,5-dimethyl-1-pyrroline-1-oxide, DMPO. UV-induced generation of chromanoxyl radicals was observed in the presence of NP-III under aerobic conditions, which was SOD+catalase sensitive. Hydroxyl-, superoxide- and alkoxyl-radical DMPO adducts were found upon UV-illumination of NP-III under aerobic conditions and only hydroxyl-radical adducts under anaerobic conditions. The light-dependent generation of oxy- and chromanoxyl free radicals and depletion of endogenous antioxidants suggests to be a promising strategy to overcome the inherent resistance of tumor cells to oxidative stress.

Studies on the hyperplasia ('regeneration') of the rat liver following partial hepatectomy. Changes in lipid peroxidation and general biochemical aspects

Using the experimental model of partial hepatectomy in the rat, we have examined the relationship between cell division and lipid peroxidation activity. In rats entrained to a regime of 12 h light/12 h dark and with a fixed 8 h feeding period in the dark phase, partial hepatectomy is followed by a rapid regeneration of liver mass with cycles of synchronized cell division at 24 h intervals. The latter phenomenon is indicated in this study by pulses of thymidine kinase activity having maxima at 24 h, 48 h and 72 h after partial hepatectomy. Microsomes prepared from regenerating livers show changes in lipid peroxidation activity (induced by NADPH/ADP/iron or by ascorbate/iron), which is significantly decreased relative to that in microsomes from sham-operated controls, again at 24 h, 48 h and 72 h after the operation. This phenomenon has been investigated with regard to possible underlying changes in the content of microsomal fatty acids, the microsomal enzymes NADPH:cytochrome c reductase and cytochrome P-450, and the physiological microsomal antioxidant alpha-tocopherol. The cycles of decreased lipid peroxidation activity are apparently due, at least in part, to changes in microsomal alpha-tocopherol content that are closely associated in time with thymidine kinase activity.

Development of mechanisms of protection against oxidative stress in doxorubicin-resistant rat tumoral cells in culture

We have compared some mechanisms involved in the defense against doxorubicin-induced free radical damage in rat hepatoma and glioblastoma cell lines and their doxorubicin-resistant variants presenting an overexpression of the multidrug resistance gene. Immediate in vivo production of malondialdehyde was minor and was not different in sensitive and resistant cells. Alpha-tocopherol was undetectable in all cell lines. Glutathione levels were not different in sensitive and resistant cells and these levels did not vary upon doxorubicin treatment. Resistant cells exhibited either a 50% decrease (hepatoma) or a 25% increase (glioblastoma) of glutathione-S-transferase activity. Glutathione reductase presented no important change upon acquisition of resistance. In contrast, selenium-dependent glutathione peroxidase activity was consistently 2-6-fold increased in the resistant cells, which suggests a magnification of protection mechanisms against hydroxyle radical formation from H2O2 in resistant cells. Depletion of glutathione levels by buthionine sulfoximine sensitized hepatoma resistant cells to doxorubicin, but had no effect on doxorubicin cytotoxicity to glioblastoma cells.

Vitamin E as an in vitro and in vivo antioxidant

alpha-Tocopherol has near optimal activity as a chain-breaking antioxidant. Inherent antioxidant activity plays an important part in determining overall biological activity but the phytyl tail also exerts a very important influence. The new deuterated alpha-tocopherol/GC-MS technique is providing unprecedented insight into the importance of the stereochemistry of the phytyl tail in determining bioavailability, as well as helping to discover how rapidly and effectively absorption, transport, uptake, and loss occur. Measurements of rate of turnover in tissues indicate that differences exist between different types of animals. It is possible that these tissue differences may explain the diverse range of vitamin E deficiency symptoms observed across a wide variety of animals. It is not known what is responsible for the differences in biokinetic behavior.

Quantitative determination of water- and lipid-soluble antioxidants in neoplastic and non-neoplastic human breast tissue

Ascorbic acid, cysteine, glutathione and uric acid were determined by reverse-phase high-pressure liquid chromatography (HPLC) in 46 breast tissue samples [neoplastic (C) and non-neoplastic (N) from the same patient]. Cholesterol, alpha-tocopherol and gamma-tocopherol were quantified in 64 similar samples by extraction into heptane followed by direct-phase HPLC. DNA was measured in all samples and the percentages of epithelium, fat and connective tissue were estimated in sections adjacent to the sample. Results confirm previous findings that ascorbic acid and glutathione, expressed as mumol/g DNA, were greatly increased in the epithelium of neoplastic tissue. Similar increases in cysteine could be accounted for by the presence of inflammatory cells. Although values of alpha- and gamma-tocopherol correlated with the percentage of fat in both types of tissue, these compounds were also present in the epithelium. Because of the varying amounts of fat in the samples, no significant difference could be found between N and C values. Cholesterol correlated with fat in N and epithelium in C. Consideration of 10 cases with equal amounts of fat in C and N tissue suggests that cholesterol is reduced in C in the epithelial cells.

Xenobiotic metabolism in helminths

During its life cycle a parasite, like mammals and other organisms, comes into contact with a variety of toxic molecules. In mammals the main line of defence against such compounds is a group of oxidative enzymes that occur predominantly in the liver. Many of these oxidations are dependent on the haemoprotein cytochrome P-450 which serves as a terminal oxidase accepting electrons from NADPH and cytochrome [Formula: see text] . This review by Wendy Precious and John Barrett illustrates that in contrast to mammals, xenobiotic metabolism in both parasitic and free-living platyhelminths and nematodes is predominantly reductive and hydrolytic as the cytochrome P-450 system is absent. This is surprising since it is present in many groups including bacteria, fungi and protozoa, which suggests an ancient origin. The absence of the cytochrome P-450 system not only severely limits the ability of helminths to detoxify compounds but also limits their ability to activate prodrugs.