[Cytotoxicity of Malondialdehyde and Cytoprotective Effects of Taurine via Oxidative Stress and PGC-1α Signal Pathway in C2C12 Cells].

One of the end-products of ROS-induced peroxidation, malondialdehyde (MDA), induces the cross-links in proteins, which leads to perturbation of the physiological functions of cells and contributes to abnormal biological regulation and various disorders. Taurine (2-aminoethanesulfonic acid, Tau) aids in adjusting normal physiological functions to confer stress resistance. The protective effects of Tau against MDA stress in vitro or in vivo were reported previously. In this study, we had investigated the protective effects of taurine on viability, oxidative stress levels and mitochondrial biogenesis in mouse muscle C2C12 cells undergoing MDA induced stress. We show that the treatment with 100 µM MDA leads to increase in cell oxidative stress levels, inhibition of mitochondrial biogenesis and the reduction of the cell survival rates. The pretreatment with 0.1 µM taurine reduced MDA-induced death rate via inhibition of oxidative stress, restoration of mitochondrial functions of the mitochondrial membrane potential (MMP) and ATP production. In MDA stress, the pre-treatment with 0.1 µM taurine leads to upregulation of the factors of mitochondrial biogenesis. These observations suggest that the cytoprotective effects of taurine may be due to an induction of mitochondrial biogenesis.

Profenofos induced modulation in physiological indices, genomic template stability and protein banding patterns of Anabaena sp. PCC 7120.

To understand the mechanism underlying organophosphate pesticide toxicity, cyanobacterium Anabaena PCC 7120 was subjected to varied concentrations (0, 5, 10, 20 and 30 mg L(-1)) of profenofos and the effects were investigated in terms of changes in cellular physiology, genomic template stability and protein expression pattern. The supplementation of profenofos reduced the growth, total pigment content and photosynthetic efficiency of the test organism in a dose dependent manner with maximum toxic effect at 30 mg L(-1). The high fluorescence intensity of 2', 7' -dichlorofluorescin diacetate and increased production of malondialdehyde confirmed the prevalence of acute oxidative stress condition inside the cells of the cyanobacterium. Rapid amplified polymorphic DNA (RAPD) fingerprinting and SDS-PAGE analyses showed a significant alteration in the banding patterns of DNA and proteins respectively. A marked increase in superoxide dismutase, catalase, peroxidase activity and a concomitant reduction in glutathione content indicated their possible role in supporting the growth of Anabaena 7120 up to 20 mg L(-1). These findings suggest that the uncontrolled use of profenofos in the agricultural fields may not only lead to the destruction of the cyanobacterial population, but it would also disturb the nutrient dynamics and energy flow.

Mechanisms of Thymoquinone Hepatorenal Protection in Methotrexate-Induced Toxicity in Rats.

To investigate mechanisms by which thymoquinone (TQ) can prevent methotrexate- (MTX-) induced hepatorenal toxicity, TQ (10 mg/kg) was administered orally for 10 days. In independent rat groups, MTX hepatorenal toxicity was induced via 20 mg/kg i.p. at the end of day 3 of experiment, with or without TQ. MTX caused deterioration in kidney and liver function, namely, blood urea nitrogen, creatinine, alanine aminotransferase, and aspartate aminotransferase. MTX also caused distortion in renal and hepatic histology, with significant oxidative stress, manifested by decrease in reduced glutathione and catalase, as well as increase in malondialdehyde levels. In addition, MTX caused nitrosative stress manifested by increased nitric oxide, with upregulation of inducible nitric oxide synthase. Furthermore, MTX caused hepatorenal inflammatory effects as shown by increased tumor necrosis factor-α, besides upregulation of necrosis factor-κB and cyclooxygenase-2 expressions. MTX also caused apoptotic effect, as it upregulated caspase 3 in liver and kidney. Using TQ concurrently with MTX restored kidney and liver functions, as well as their normal histology. TQ also reversed oxidative and nitrosative stress, as well as inflammatory and apoptotic signs caused by MTX alone. Thus, TQ may be beneficial adjuvant that confers hepatorenal protection to MTX toxicity via antioxidant, antinitrosative, anti-inflammatory, and antiapoptotic mechanisms.

Acute toxicity and responses of antioxidant systems to 1-methyl-3-octylimidazolium bromide at different developmental stages of goldfish.

Acute toxicity of 1-methyl-3-octylimidazolium bromide ([C(8)mim]Br) to goldfish at different developmental stages and responses of the antioxidant system in adult goldfish were evaluated in the present study. The results indicate that post-embryonic developmental toxicity of [C(8)mim]Br on goldfish is developmental-stage dependent. The juvenile and larva goldfish are more sensitive to [C(8)mim]Br-toxicity than the adult fish. Histological observations in adult goldfish reveal that acute [C(8)mim]Br exposure damages the hepatopancreas, intestines, and kidneys, indicating that these are possible target organs of [C(8)mim]Br toxicity in goldfish. Subsequent biochemical assays in adult goldfish show that [C(8)mim]Br also induces changes in the activities of the superoxide dismutase, catalase, glutathione peroxidase, and glutathione content of fish hepatopancreas. These results suggest that [C(8)mim]Br exposure may induce oxidant stress and lipid peroxidation in hepatopancreas of adult goldfish. In addition, we also find that [C(8)mim]Br causes a remarkable increase in malondialdehyde (MDA) levels in the hepatopancreas of adult goldfish, and thus we think that the MDA level change can be a biomarker of [C(8)mim]Br toxicity in goldfish. The present study indicates that ionic liquids can be a threat to the survival, growth, and development of the fish population once they are accidentally leaked into aquatic ecosystems.

Exposure to benzene induces oxidative stress, alters the immune response and expression of p53 in gasoline filling workers.

BACKGROUND: Chronic exposure to benzene can lead to deleterious effects on many biological systems including blood and blood-forming organs. We investigated the adverse effects of benzene among workers occupationally exposed to benzene in India. METHODS: Four hundred twenty-eight gasoline filling workers occupationally exposed to benzene and 78 unexposed individuals were recruited for this study. Benzene concentration was determined by gas chromatography, reactive oxygen species (ROS) by dichlorofluorescin diacetate (DCFH-DA) method, malondialdehyde (MDA) by thiobarbituric acid reactive substances assay (TBARS), total superoxide dismutase (T-SOD) by RANSOD kit and glutathione (GSH) by 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) reaction, respectively. CD4, CD8, IgG were carried out by using fluorescence activated cell sorter (FACS Calibur) and mRNA expression of p53 by reverse transcriptase PCR (RT-PCR). RESULTS: A significant increase in the concentration of benzene and its byproducts in both blood and urine were found in the workers compared with the controls. The levels of ROS and MDA were significantly elevated, and GSH and total T-SOD were decreased in the workers compared with the controls. A statistically significant decrease in the immunoglobulin levels, CD4T cells, CD4/CD8 ratio was observed in workers (vs. controls), whereas no significant difference was observed in CD8T cells. p53 gene expression was markedly higher in workers than in controls. CONCLUSION: Occupational exposure to benzene causes oxidative stress, immune suppression and increases the expression of tumor-suppressing gene p53 in gasoline filling workers. These bio-functional markers might be useful in screening and surveillance for occupational hazard.

The effects of pollution on the vitamins A, E, C, beta-carotene contents and oxidative stress of the freshwater crayfish, Astacus leptodactylus.

In this study, we determined the effects of pollution on levels of antioxidant vitamins (A, E, C), beta-carotene and malondialdehyde (MDA), in the hepatopancreas and muscle tissues of freshwater crayfish (Astacus leptodactylus). The crayfish samples were collected from Aydincik (unpolluted control site) and Agin (polluted site) in the Keban Dam Lake (Elazig-Turkey) in August 2007. The results showed that the concentrations of vitamins E, C and beta-carotene in both tissues were significantly lower, and MDA levels were higher than in controls. There were no significant alterations in vitamin A levels. In comparison among the sex groups, some values were different significantly between the localities. The comparison of same-sex groups of the different localities also showed that concentrations of the vitamins E, C, beta-carotene and MDA changed statistically according to the tissues between the localities.

Products of oxidative stress inhibit aldehyde oxidation and reduction pathways in dopamine catabolism yielding elevated levels of a reactive intermediate.

Dopamine (DA) has been implicated as an endogenous neurotoxin to explain the selective neurodegeneration as observed for Parkinson's disease (PD). In addition, oxidative stress and lipid peroxidation are hypothesized culprits in PD pathogenesis. DA undergoes catabolism by monoamine oxidase (MAO) to 3,4-dihydroxyphenylacetaldehyde (DOPAL), which is further oxidized to 3,4-dihydroxyphenylacetic acid (DOPAC) via aldehyde dehydrogenase (ALDH). As a minor and compensatory metabolic pathway, DOPAL can be reduced to 3,4-dihydroxyphenylethanol (DOPET) via cytosolic aldehyde or aldose reductase (AR). Previous studies have found DOPAL to be significantly more toxic to DA cells than DA and that the major lipid peroxidation products, that is, 4-hydroxynonenal (4HNE) and malondialdehyde (MDA), potently inhibit DOPAL oxidation via ALDH. The hypothesis of this work is that lipid peroxidation products inhibit DOPAL oxidation, yielding aberrant levels of the toxic aldehyde intermediate. To test this hypothesis, nerve growth factor-differentiated PC6-3 cells were used as a model for DA neurons. Cell viability in the presence of 4HNE and MDA (2-100 microM) was measured by MTT assay, and it was found that only 100 microM 4HNE exhibited significant cytotoxicity. Treatment of cells with varying concentrations of 4HNE and MDA resulted in reduced DOPAC production and significant elevation of DOPAL levels, suggesting inhibition of ALDH. In cells treated with 4HNE that exhibited elevated DOPAL, there was a significant increase in DOPET. However, elevated DOPET was not observed for the cells treated with MDA, suggesting MDA to be an inhibitor of AR. Using isolated cytosolic AR, it was found that MDA but not 4HNE inhibited reductase activity toward DOPAL, surprisingly. These data demonstrate that the oxidative stress products 4HNE and MDA inhibit the aldehyde biotransformation step of DA catabolism yielding elevated levels of the endogenous neurotoxin DOPAL, which may link oxidative stress to selective neurodegeneration as seen in PD.

Carbonyl stress: malondialdehyde induces damage on rat hippocampal neurons by disturbance of Ca(2+) homeostasis.

The objective of this study was to investigate the influences of carbonyl stress induced by malondialdehyde (MDA), a typical intermediate of lipid peroxidation, on intracellular free Ca(2+) concentration ([Ca(2+)](i)) alterations in cultured hippocampal neurons of rat. The microphotographic study clearly demonstrated that the hippocampal neurons became gradually damaged following exposure to different concentrations of MDA. Further study indicated that the plasma membrane Ca(2+)-ATPase (PMCA) activity was inhibited by MDA in a concentration- and time-dependent manner. The supplementation of 100 microM MDA was found to cause a notable early phase increase of [Ca(2+)](i) in hippocampal neuron cultures followed by a more pronounced late-phase elevation of [Ca(2+)](i). Such effect of MDA was prevented by the addition of nimodipine, an inhibitor of L-type calcium channel or by an extracellular Ca(2+) chelator EGTA. The identification of the calcium signalling pathways were studied by applying U73122, an inhibitor of PL-C, and H-89, an inhibitor of protein kinase A (PKA), showing the involvement of PL-C/IP3 pathway but not the PKA/cAMP pathway. These results suggested that MDA-related carbonyl stress caused damages of rat hippocampal neurons by triggering Ca(2+) influx and influencing Ca(2+) homeostasis in cultured neurons, and also MDA may act as a signalling molecule regulating Ca(2+) release from intracellular stores.

Contamination versus preservation of cosmetics: a review on legislation, usage, infections, and contact allergy.

Cosmetics with high water content are at a risk of being contaminated by micro-organisms that can alter the composition of the product or pose a health risk to the consumer. Pathogenic micro-organisms such as Staphylococcus aureus and Pseudomonas aeruginosa are frequently found in contaminated cosmetics. In order to avoid contamination of cosmetics, the manufacturers add preservatives to their products. In the EU and the USA, cosmetics are under legislation and all preservatives must be safety evaluated by committees. There are several different preservatives available but the cosmetic market is dominated by a few preservatives: parabens, formaldehyde, formaldehyde releasers, and methylchloroisothiazolinone/methylisothiazolinone. Allergy to preservatives is one of the main reasons for contact eczema caused by cosmetics. Concentration of the same preservative in similar products varies greatly, and this may indicate that some cosmetic products are over preserved. As development and elicitation of contact allergy is dose dependent, over preservation of cosmetics potentially leads to increased incidences of contact allergy. Very few studies have investigated the antimicrobial efficiency of preservatives in cosmetics, but the results indicate that efficient preservation is obtainable with concentrations well below the maximum allowed.

The effect of malondialdehyde is modified by simian virus 40 transformation in human lung fibroblast cells.

The effects of malondialdehyde (MDA), a product of oxidative stress, on normal lung fibroblast cells (MRC5) and transformed cells (MRC5 SV2) showed differing responses between the two cell lines. MRC5 cells showed lower viability at low MDA concentrations (<250 µM) but had better viability at higher concentrations than the transformed cells. Both cell lines showed an increase in the number of micronuclei, nuclear size and a relocation of p53 to the nucleus with increasing MDA. The expression of p53 was higher in the MRC5 cells at 24 h; 2-8 fold induction vs 1-2.5 fold in the MRC5 SV2 cells, but reduced to almost zero at 48 h in the MRC5 cells. Mutation sequencing of the PCR products of a 689 bp region (residues 4640-5328) of the TP53 gene revealed MRC5 had more mutations than MRC5 SV2 cells (n = 21 and 11 respectively) and that they were predominantly insertions (MRC5 81%, MRC5 SV2 100%). A common mutation was observed in both cell lines; a G insertion at residue 4724 (n = 7) which could prove to be a mutational hotspot. These results indicate that the transformed cells are slower to respond to oxidative stress and/or mutagenic compounds. The mutation spectrum of predominantly frameshift mutations (insertions) suggests that oxidative stress plays a minimal role in smoking related lung cancer, but could be of greater importance to other lung diseases and cancer caused by exposures such as passive smokers, passive vapers and atmospheric pollutants.

Temporal variations in physiological responses of Kandelia obovata seedlings exposed to multiple heavy metals.

A study was conducted to quantify temporal variations in physiological responses of Kandelia obovata under multiple heavy metal stress. The results showed that plant growth was not significantly affected by multiple heavy metal stress during the 120-days experiment. At the start, levels of net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) showed effects of "low-promotion, high-inhibition", but Pn and Gs reduced with increasing heavy metal stress at the end. Temporary lipid oxidation was shown by high levels of malondialdehyde (MDA) under high heavy metal stress at the start but was unaffected at the end of the experiment. MDA negatively correlated with biomass and photosynthetic parameters and acted as a sensitive indicator. Proline also shared similar trend and indicated its temporary role in osmotic adjustment. Negative correlations between osmotic adjustment matter and photosynthetic parameters further confirmed the significant role of osmotic adjustment under heavy metal stress.

Malonaldehyde acts as a mitochondrial toxin: Inhibitory effects on respiratory function and enzyme activities in isolated rat liver mitochondria.

Malonaldehyde (MDA) is a product of oxidative damage to lipids, amino acids and DNA, and accumulates with aging and diseases. MDA can possibly react with amines to modify proteins to inactivity enzymes and also modify nucleosides to cause mutagenicity. Mitochondrial dysfunction is a major contributor to aging and age-associated diseases. We hypothesize that accumulated MDA due to mitochondrial dysfunction during aging targets mitochondrial enzymes to cause further mitochondrial dysfunction and contribute to aging and age-associated diseases. We investigated the effects of MDA on mitochondrial respiration and enzymes (membrane complexes I, II, III and IV, and dehydrogenases, including alpha-ketoglutaric dehydrogenase (KGDH), pyruvate dehydrogenase (PDH), malate dehydrogenase (MDH)) in isolated rat liver mitochondria. MDA showed a dose-dependent inhibition on mitochondrial NADH-linked respiratory control ratio (RCR) and ADP/O ratio declined from the concentrations of 0.2 and 0.8 micromol/mg protein, respectively, and succinate-linked mitochondrial RCR and ADP/O ratio declined from 1.6 and 0.8 micromol/mg protein. MDA also showed dose-dependent inhibition on the activity of PDH, KGDH and MDH significantly from 0.1, 0.2 and 2 micromol/mg protein, respectively. Activity of the complexes I and II was depressed by MDA at 0.8 and 1.6 micromol/mg protein. However, MDA did not affect activity of complexes III and IV in the concentration range studied (0-6.4 micromol/mg protein). These results suggest that MDA can cause mitochondrial dysfunction by inhibiting mitochondrial respiration and enzyme activity, and the sensitivity of the enzymes examined to MDA is in the order of PDH>KGDH>complexes I and II>MDH>complexes III and IV.

Molecular requirements for the mutagenicity of malondialdehyde and related acroleins.

Malondialdehyde, a product of lipid peroxidation and prostaglandin biosynthesis, is mutagenic in Salmonella. To determine the molecular requirements for its mutagenicity, we tested a series of beta-substituted acroleins in Salmonella typhimurium hisD3052 . Mutagenicity is dependent on the steric bulk of the substituent (revertants/mumol) at the beta position: beta- methoxyacrolein , 220; beta- ethoxyacrolein , 110; and beta- isobutoxyacrolein , 40. A good leaving group at the beta position substantially increases the mutagenic activity (revertants/mumol): beta-(p-nitrophenoxy)acrolein, 620; beta- benzoyloxyacrolein , 320; beta- chloroacrolein , 890; and di-gamma- oxopropenyl ether, 870. These data suggest that nucleophilic attack on the beta-carbon followed by elimination of the beta substituent is important for mutagenicity. Substitution of a methyl group at the alpha-carbon abolishes mutagenicity of these compounds. This effect can be explained by the lack of chemical reactivity of the alpha-methyl analogues toward oxygen or nitrogen nucleophiles. Propynal , which can add nucleophiles to generate a substituted acrolein, exhibits the highest mutagenicity (1370 revertants/mumol) in this series. The importance of the aldehyde functionality is suggested by the nonmutagenicity of propiolonitrile , ethyl propiolate , 4-benzoyloxy-3- buten -2-one, and 4-methoxy-3- buten -2-one. Aldehyde addition subsequent to the formation of the Michael adduct is, therefore, important for mutagenesis. An investigation of the toxicity of the present series indicates that toxicity and mutagenicity are independent events based on different chemical reactions.

Lens opacity induced by lipid peroxidation products as a model of cataract associated with retinal disease.

The cataractous lenses of patients with retinitis pigmentosa have been studied by electron microscopy. The posterior subcapsular opacities showed common ultrastructural features. Large areas of disruption of the lens fibre pattern were observed which showed an increase in the number of fibre membranes per unit area. In many regions an elaborate and regular folding of membranes was noted which produced complex 'figure-of-eight' and 'tramline' patterns, as well as membranous lamellar bodies. Masses of various size globules were also identified. It has been established that injection into the vitreous body of the rabbit eye of a suspension of liposomes prepared from phospholipids containing lipid peroxidation products induces the development of posterior subcapsular cataract. Such modelling of cataract is based on a type of clouding of the crystalline lens similar to that observed in cataract resulting from diffusion of toxic lipid peroxidation products from the retina to the lens through the vitreous body on degeneration of the photoreceptors. Saturated liposomes (prepared from beta-oleoyl-gamma-palmitoyl-L-alpha-phosphatidylcholine) do not cause clouding of the lens, which demonstrates the peroxide mechanism of the genesis of this form of cataract. Clouding of the lens is accompanied by accumulation of fluorescing lipid peroxidation products in the vitreous body, aqueous humor and the lens and also by a fall in the concentration of reduced glutathione in the lens. From the results it is concluded that lipid peroxidation may initiate the development of cataract.

Protective effects of carnosine against protein modification mediated by malondialdehyde and hypochlorite.

Malondialdehyde (MDA) and hypochlorite anions are deleterious products of oxygen free-radical metabolism. The effects of carnosine, a naturally occurring dipeptide (beta-alanyl-L-histidine), on protein modification mediated by MDA and hypochlorite have been studied. MDA and hypochlorite induced formation of carbonyl groups and high molecular weight and cross-linked forms of crystallin, ovalbumin and bovine serum albumin. The presence of carnosine effectively inhibited these modifications in a concentration-dependent manner. It is proposed that relatively non-toxic carnosine and related peptides might be explored as potential therapeutic agents for pathologies that involve protein modification mediated by MDA or hypochlorite.

Cytotoxicity and genotoxicity of lipid-oxidation products.

The autoxidation of unsaturated lipids contained in oils, fats, and food and the endogenous oxidative degradation of membrane lipids by lipid peroxidation result in the formation of a very complex mixture of lipid hydroperoxides, chain-cleavage products, and polymeric material. Experimental animal studies and biochemical investigations lend support to the hypothesis that lipid-oxidation products, ingested with food or produced endogenously, represent a health risk. The oral toxicity of oxidized lipids is unexpectedly low. Chronic uptake of large amounts of such materials increases tumor frequency and incidence of atherosclerosis in animals. 4-Hydroxynonenal, a chain-cleavage product resulting from omega 6 fatty acids, disturbs gap-junction communications in cultured endothelial cells and induces several genotoxic effects in hepatocytes and lymphocytes. Although the concentrations of the aldehyde needed to produce these effects are in the range expected to occur in vivo, their pathological significance is far from clear. Recent findings strongly suggest that in vivo modification of low-density lipoprotein by certain lipid-peroxidation products (eg, 4-hydroxynonenal and malonaldehyde) renders this lipoprotein more atherogenic and causes foam-cell formation. Proteins modified by 4-hydroxynonenal and malonaldehyde were detected by immunological techniques in atherosclerotic lesions.

Ageing of Neurospora crassa. VIII. Lethality and mutagenicity of ferrous ions, ascorbic acid, and malondialdehyde.

Ferrous ions were highly lethal and mutagenic to germinated conidia of Neurospora crassa. At comparable survival, treatment with 0.2 mM ferrous ions was 14- and 50-fold more mutagenic than ultra-violet irradiation or X-rays, respectively, in the reversion of an inositol auxotroph. Ascorbic acid alone (2 mM) was not reproducibly lethal and inhibited both the lethality and mutagenicity of ferrous ions. Bovine superoxide dismutase (SOD) completely inhibited the residual lethality of ferrous ascorbate. Protection by ascorbic acid and SOD indicates that superoxide radicals, generated by oxidation of Fe(II), are directly or indirectly mutagenic and lethal. Malondialdehyde (MDA) was lethal and appeared to be mutagenic; however, its action is probably different from that of superoxide. Therefore, superoxide-mediated production of endogenous MDA by way of peroxidation of polyunsaturated fatty acids is probably not an alternate mutagenic pathway, at least in the reversion of the allele of the inl locus examined. These results and the demonstration of superoxide-mediated decrease in the synthetic fidelity of DNA polymerase in vitro (Rana and Munkres, in preparation) warrant additional exploration of the hypothesis that endogenous cellular free radicals, generated by pre- and post-senescent metabolism, may enter into lethal and mutagenic reactions.

Tumorigenicity of chloral hydrate, trichloroacetic acid, trichloroethanol, malondialdehyde, 4-hydroxy-2-nonenal, crotonaldehyde, and acrolein in the B6C3F(1) neonatal mouse.

The tumorigenicity of chloral hydrate (CH), trichloroacetic acid (TCA), trichloroethanol (TCE), malondialdehyde (MDA), crotonaldehyde, acrolein, and 4-hydroxy-2-nonenal (HNE) was tested in the B6C3F(1) neonatal mouse. Mice were administered i.p. injections of CH (1000, 2000, 2500, and 5000 nmol per animal), TCA (1000 and 2000 nmol), TCE (1000 and 2000 nmol), MDA (1500 and 3000 nmol), crotonaldehyde (1500 and 3000 nmol), acrolein (75 and 150 nmol), and HNE (750 and 1500 nmol) at 8 and 15 days of age. At 12 months, only male mice treated with the positive control chemicals, 4-aminobiphenyl (500 and 1000 nmol) and benzo[a]pyrene (150 and 300 nmol), had incidences of tumors in the liver significantly higher than the solvent control. Additional male mice were dosed as described above and their livers were excised at 24, 48 h, and 7 days after the final dose. Liver DNA was isolated and analyzed by 32P-postlabeling/high-performance liquid chromatography (HPLC) and HPLC/electrochemical detection for MDA-derived adduct (M(1)G) and 8-oxo-2'-deoxyguanosine (8-OHdG) formation, respectively. At 24 and 48 h after the final dose, CH- and TCA-treated mice exhibited significantly higher M(1)G levels than the controls. 8-OHdG formation was also induced by CH, TCA, and MDA. These results suggest that under these experimental conditions the B6C3F(1) neonatal mouse is not sensitive to carcinogens that induce an increase in endogenous DNA adduct formation through lipid peroxidation or oxidative stress.

Protective effects of carnosine against malondialdehyde-induced toxicity towards cultured rat brain endothelial cells.

Malondialdehyde (MDA) is a deleterious end-product of lipid peroxidation. The naturally-occurring dipeptide carnosine (beta-alanyl-L-histidine) is found in brain and innervated tissues at concentrations up to 20 mM. Recent studies have shown that carnosine can protect proteins against cross-linking mediated by aldehyde-containing sugars and glycolytic intermediates. Here we have investigated whether carnosine is protective against malondialdehyde-induced protein damage and cellular toxicity. The results show that carnosine can (1) protect cultured rat brain endothelial cells against MDA-induced toxicity and (2) inhibit MDA-induced protein modification (formation of cross-links and carbonyl groups).

Exposure to malondialdehyde induces an early redox unbalance preceding membrane toxicity in human erythrocytes.

This work investigated the oxidative injury to human red blood cells (RBCs) by the exposure to exogenous malondialdehyde (MDA), in a physiological environment. When a 10% RBC suspension was incubated in autologous plasma, in the presence of 50 microM MDA, 30% of MDA entered into the cells. A time-course study showed that MDA caused early (30-120 min) and delayed (3-18 h) effects. MDA caused a fast depletion of reduced glutathione, and loss of the glucose-6-phosphate dehydrogenase activity, followed by a decrease of HbO2. Accumulation of methemoglobin, and formation of small amounts of hemichrome were later evident. Also, an HbO2-derived fluorescent product was measured in the membrane. The redox unbalance was followed by structural and functional damage to the membrane, evident as the formation of conjugated diene lipid hydroperoxides, concurrent with a sharp accumulation of MDA, consumption of membrane vitamin E, and egress of K+ ions. SDS--PAGE of membrane proteins showed formation of high molecular weight aggregates. In spite of the marked oxidative alterations, the incubation plasma prevented a substantial hemolysis, even after a 18 h incubation. On the contrary, the exposure of RBCs to 50 microM MDA in glucose-containing phosphate saline buffer, resulted in a 16% hemolysis within 6 h. These results indicate that the exposure to MDA causes a rapid intracellular oxidative stress and potentiates oxidative cascades on RBCs, resulting in their dysfunction.