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Okadaic acid (OA) is a marine toxin, a tumour promoter and an inducer of apoptosis. It mainly inhibits protein-phosphatases, protein synthesis and enhances lipid peroxidation. Cadmium (Cd) is known to be carcinogenic in animals and humans (group 1 according to the International Agency for Research on Cancer (IARC) classification). Cd also induces oxidative stress in living organisms. Since they are sometimes found simultaneously in mussels, we have evaluated in the present investigation, the lipid peroxidation, as malondialdehyde (MDA) production, in the variation of the ratios of 8-(OH)-dG/10(5)dG and m5dC/(dC + m5dC) induced by OA and/or Cd in Caco-2 cells. When cells were treated exclusively by OA (15 ng/ml) or Cd (0.625 and 5 microg/ml) for 24 h, protein synthesis was inhibited (by 42 +/- 5%, 18 +/- 13%, and 90 +/- 4% respectively) while MDA production was 2,235 +/- 129, 1710 +/- 20, and 11,496 +/-1,624 pmol/mg protein respectively. In addition, each toxicant induced modified bases in DNA; increases in oxidised bases and methylated dC. The combination of OA and cadmium was more cytotoxic and caused more DNA base modifications; the ratio m(5)dC/(m(5)dC + dC) was increased from 3 +/- 0.15 to 9 +/- 0.15 and the ratio 8-(OH)-dG/10(5) dG also (from 36 +/- 2 to 76 +/- 6). The combination of OA and Cd also increased the level of MDA (1,6874 +/- 2,189 pmole/mg protein). The present results strongly suggest that DNA damage resulting from the oxidative stress induced by these two toxicants may significantly contribute to increasing their carcinogenicity via epigenetic processes.

Capsaicin, a natural product of Capsicum species, induces excitation of pain perception at nociceptive terminals. Our previous studies have shown that capsaicin inhibits protein synthesis in cultured monkey kidneys cells (Vero cells) and in primoculture of rat astrocytes. We have now investigated the effect of capsaicin on human neuroblastoma cells SHSY-5Y. The cytotoxicity has been assessed by incorporation of [(3)H]L-leucine into cellular protein in the presence of capsaicin and the genotoxicity has been evaluated using the comet assay and the fragmentation assay after incubation of neuroblastoma cells with 25-100 microM capsaicin. The concentration required to inhibit 50% of the protein synthesis (IC(50)) was found to be 60 microM after incubation with the toxin during one cellular cycle (5 days) of SHSY-5Y. The results of the comet test and DNA fragmentation assay clearly suggest that capsaicin is able to induce DNA strand breaks already with concentrations in the range of 50 microM, corresponding to 29.3 microM of capsaicin not bound to alpha-1 acid glycoprotein. Several daily topical applications of preparations containing 0.075% of capsaicin could lead to blood capsaicin concentration of this order of magnitude following transdermal passage (5% of the total quantity applied). Because DNA strand breaks or DNA lesions may affect cellular functions, lead to cell death and/or mutagenesis, our data in case of inappropriate DNA repair may have important implications for the possible health threats of capsaicin, specially in the case of misuse of capsaicin preparations in pathological situations.

The effects of fumonisin B1 (FB1) from Fusarium moniliforme on lipid peroxidation and protein and DNA syntheses were studied in monkey kidney cells (Vero cells). FB1 was found to be a potent inducer of malondialdehyde (MDA), one of the secondary products formed during lipid peroxidation. At 0.14 microM (0.1 microg/ml), FB1 induced 0.496 +/- 0.1 nmoles of MDA/ mg protein, compared to the control level 0.134 +/- 0.01 nmoles of MDA/mg protein (P < 0.005). No inhibition of protein or DNA synthesis was observed at this concentration of FB1. Inhibition of protein and DNA syntheses was observed at FB1 concentrations > 14 microM (10 microg/ml) with an IC50 of 33 microM for both protein synthesis and DNA synthesis. These results indicate that lipid peroxidation is a very sensitive cellular response to the mycotoxin fumonisin B1 observed at concentrations lower than that required to inhibit cellular synthesis of macromolecules, protein and DNA. This oxidative damage induced by FB1 concentrations encountered in naturally contaminated foodstuffs and feed might lead to mutagenicity and genotoxicity.

Ochratoxin A (OTA) is a mycotoxin produced by Aspergillus ochraceus as well as other moulds. This mycotoxin contaminates animal feed and human food and is nephrotoxic for all animal species studied so far. OTA is immunosuppressive, genotoxic, teratogenic and carcinogenic. Recently lipid peroxidation induced by OTA has been reported. OTA, a structural analogue of phenylalanine, inhibits protein synthesis by competition with phenylalanine in the phenylalanine-tRNA aminoacylation reaction, constituting the main mechanism of OTA-induced cytotoxicity. Since it seems impossible to avoid contamination of foodstuffs by toxigenic fungi, investigation is required for preventing the toxicity of OTA. An attempt to prevent its toxic effect, mainly the inhibition of protein synthesis, has been made using aspartame (L-aspartyl-L-phenylalanine methyl ester) a structural analogue of both OTA and phenylalanine. Protein synthesis was assayed in monkey kidney cells (Vero cells) treated by increasing concentrations of OTA (10-100 microM). After 24 h incubation, protein synthesis was inhibited by OTA in a concentration dependent manner (the 50% inhibitory concentration, IC50, was c. 14.5 microM). Aspartame (A19), at tenfold higher concentrations than OTA (100-1000 microM), was found to partially protect against the OTA-induced inhibition of protein synthesis in Vero cells, and more efficiently when added 24 h prior to the toxin (IC50 34 microM) than together (IC50 22 microM). As expected A19(250 microM) prevented the OTA-induced leakage of certain enzymes, including lactate dehydrogenase, gamma-glutamyl transferase, alkaline phosphatase, into the culture medium, and the concomitant decrease of their intracellular activity in OTA (25 microM)-treated cells. In order to investigate the effect of aspartame (A19) on OTA-protein binding as explanation of the above results, the mycotoxin time- and concentration-dependent binding to human samples was studied in static diffusion cells with two compartments separated by a dialysis membrane. When A19 (34 microM) was added to the upper compartment containing plasma before installing OTA (50, 250, 1240 microM) in the lower one. OTA binding was largely prevented (95-98%). When A19 (34 microM) was added to the lower compartment simultaneously with the toxin (50, 250, 1240 microM), for the lowest concentration of OTA, the same efficiency was shown in preventing OTA binding, but at the two high concentrations A19 seemed less efficient.

The mechanism of the grey baby syndrome produced by chloramphenicol overdose is poorly understood. The present study assessed the membrane toxicity of this agent by means of its depressant effect on excitable tissues. The inhibition by drugs of protozoan motility was used as a toxicity endpoint, measured by the swimming speed of Tetrahymena pyriformis using an image analysis system. The n-octanol/water partition coefficient at pH 7.4, 37 degrees C was determined as a measure of the hydrophobicity of the drugs. Chloramphenicol dose-dependently depressed the motility of the test organism with an IC50 value (the concentration reducing the mean swimming speed to 50% of control) of 2.95 +/- 0.25 mM, in contrast to a significantly weaker effect of its succinate salt with an IC50 of 28.2 +/- 1.93 mM. Thiamphenicol, a drug with similar properties to chloramphenicol, produced little effect on protozoan motility. Several other antibiotics either in free or salt forms were also ineffective. A series of agents known to possess membrane stabilising action also tested for comparison showed that chloramphenicol possesses the ability to reduce protozoan motility. Measurement of the n-octanol/water partition coefficient revealed a value for chloramphenicol of 11.9 +/- 0.66. This property was correlated with protozoan immobilising potency among a series of heterogeneous compounds, suggesting that the mechanism involved a hydrophobic interaction with the excitable membrane. These results show that chloramphenicol has a depressant effect on protozoan motility comparable to agents with known toxicity effects on cell membranes. This suggests that chloramphenicol has the potential to cause membrane-mediated toxic effects, a mode of action that may underlie its acute toxicity to excitable tissues.