Chloramphenicol: magic bullet or double-edge sword?

Daphnia stress response to environmental concentrations of chloramphenicol-multi-omics approach

Commonly used medicines, when discarded or improperly disposed of, are known to contaminate freshwater ecosystems. Pharmaceuticals can be toxic and mutagenic, and can modify freshwater organisms, even at environmentally relevant concentrations. Chloramphenicol (CAP) is an antibiotic banned in Europe. However, it is still found in surface waters around the world. The aim of this study was to evaluate the impact of chloramphenicol contamination in freshwater on the model organism Daphnia magna. Specific life history parameters, proteome, and host-associated microbiome of four D. magna clones were analyzed during a three-generation exposure to CAP at environmental concentrations (32 ng L-1). In the first generation, no statistically significant CAP effect at the individual level was detected. After three generations, exposed animals were smaller at first reproduction and on average produced fewer offspring. The differences in D. magna's life history after CAP treatment were in accordance with proteome changes. D. magna's response to CAP presence indicates the high stress that the tested organisms are under, e.g., male production, upregulation of ubiquitin-conjugating enzyme E2 and calcium-binding protein, and downregulation of glutathione transferase. The CAP-exposed D. magna proteome profile confirms that CAP, being reactive oxygen species (ROS)-inducing compounds, contributes to structural changes in mitochondria. Microbiome analysis showed a significant difference in the Shannon index between control and CAP-exposed animals, the latter having a more diverse microbiome. Multilevel analyses, together with long exposure in the laboratory imitating conditions in a polluted environment, allow us to obtain a more complete picture of the impact of CAP on D. magna.

Microbial genotoxicity bioreporters based on sulA activation

A bacterial genotoxicity reporter strain was constructed in which the tightly controlled strong promoter of the Escherichia coli SOS response gene sulA was fused to the alkaline phosphatase-coding phoA reporter gene. The bioreporter responded in a dose-dependent manner to three model DNA-damaging agents-hydrogen peroxide, nalidixic acid (NA), and mitomycin C (MMC)-detected 30-60 min after exposure. Detection thresholds were 0.15 μM for MMC, 7.5 μM for nalidixic acid, and approximately 50 μM for hydrogen peroxide. A similar response to NA was observed when the bioreporter was integrated into a specially designed, portable electrochemical detection platform. Reporter sensitivity was further enhanced by single and double knockout mutations that enhanced cell membrane permeability (rfaE) and inhibited DNA damage repair mechanisms (umuD, uvrA). The rfaE mutants displayed a five- and tenfold increase in sensitivity to MMC and NA, respectively, while the uvrA mutation was advantageous in the detection of hydrogen peroxide. A similar sensitivity was displayed by the double rfaE/uvrA mutant when challenged with the pre-genotoxic agents 2-amino-3-methylimidazo[4,5-f]quinoline and 2-aminoanthracene following metabolic activation with an S9 mammalian liver fraction.

Cytotoxicity and DNA damaging potency of chloramphenicol and six metabolites: a new evaluation in human lymphocytes and Raji cells

Chloramphenicol (CAP) is an antibiotic which has been implicated in the etiology of aplastic anemia in man. This product is also used in veterinary medicine. The medical use of chloramphenicol has been limited to cases where the drug is indispensible but veterinary use may lead to the presence of residues in the meat of treated animals and it is essential to establish acceptable levels of intake of such residues in order to protect human health. CAP is metabolized into at least 6 metabolites: nitroso-CAP (NO-CAP), formed in the liver, 3 excretion products: the glucuronide (CAP-G), the CAP base (NAPD), and an alcoholic derivative, HAP. Dehydro-CAP (DH-CAP) and the dehydro-CAP base (NPAP) are formed by enterobacteria in the large bowel. The objective of the present study was to investigate (1) the cytotoxicity of CAP and its metabolites and (2) their ability to induce DNA damage in human cells. This work was performed with human peripheral blood lymphocytes (PBL) and with a lymphoma cell line (Raji).

Sister-chromatid exchanges induced by chloramphenicol on bovine lymphocytes

The induction of sister-chromatid exchanges (SCE) was studied in bovine lymphocyte cultures treated with chloramphenicol (CAP), an antibiotic agent in wide use in human and animal therapy. A total of six individuals, matched for sex, race, age and environmental conditions, were used for the analysis. Chloramphenicol was tested at four different concentrations (5, 10, 20 and 40 micrograms/ml) and acted for the last 24 h of the culture. Each experiment included two animals, each of which was exposed to all chloramphenicol doses, for a total of three repetitions. The results of the corresponding analysis of variance showed that this chemical had a small but statistically significant effect on the SCE frequency. In addition, the lymphocyte cultures responded strangely to this chemical: the highest SCE induction was produced by the lowest dose. However, the study of high frequency cells did not show the presence of this kind of cell which could explain this chloramphenicol response. In addition, chloramphenicol induced a high delay in the cell cycle.

Genotoxicity testing of chloramphenicol in rodent and human cells

The results of this work, carried out to extend the limited information at present available on the genotoxic potential of chloramphenicol (CAP), indicate that in millimolar concentrations this antibacterial agent produced a minimal amount of DNA fragmentation in both V79 cells and metabolically competent rat hepatocytes. Moreover, a level of DNA-repair synthesis indicative of a weak but positive response was detected in primary cultures of liver cells obtained from 2 of 3 human donors, and a borderline degree of repair was present in those prepared from rats. The promutagenic character of CAP-induced DNA lesions was confirmed by a low but significant increase in the frequency of 6-thioguanine-resistant clones of V79 cells, which, however, was absent when the exposure was done in the presence of co-cultured rat hepatocytes. Finally, oral administration to rats of 1/2 LD50 CAP did not increase the incidence of either micronucleated polychromatic erythrocytes or micronucleated hepatocytes. Taken as a whole these findings suggest that CAP should be considered a compound intrinsically capable of producing a very weak genotoxic effect, but only at concentrations about 25 times higher than those occurring in patients treated with maximal therapeutic dosages.