Effect of heat shock on the mutagenicity of mutagens and carcinogens in Euglena gracilis

Euglena gracilis as an eukaryotic test organism for detecting mutagens and antimutagens

The unicellular flagellate Euglena gracilis was used in order to assess the inhibition of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and N-methyl-N-nitrosourea (MNU) mutagenicities, which induce white mutants due to the irreversible loss of chloroplasts. All tested compounds, including o-aminobenzoic acid and p-aminobenzoic acid, salicylic acid, acetylsalicylic acid, sodium salicylate and p-aminosalicylic acid, were not mutagenic per se and inhibited MNNG mutagenicity by at least 50%. The last two compounds inhibited by at least 50% also MNU mutagenicity.

Euglena gracilis as a supplementary test organism for detecting biologically active compounds

The mutagenic activity of more than 120 antimicrobial agents and protective components was investigated. Only Kathon showed a consistent increase in revertant counts in the Ames test on Salmonella typhimurium. The hereditary bleaching test on Euglena gracilis used for detecting extranuclear mutations, showed positive results for Kathon, triethanolamine and diamine silver tetraborate.

Different effect of hyperthermia and heat shock on the action of quinolone drugs versus some mutagens against chloroplasts of Euglena gracilis

Hyperthermia (37 degrees C permanently) and heat shock (42 degrees C for 10 min, and then 27 degrees C) retarded the elimination of chloroplasts from the flagellate Euglena gracilis induced by quinolone antibacterial chemotherapeutics (OA, NA, Cnx, Ofx, Cpfx, Enx, Nfx) in comparison with their action at 27 degrees C. In the case of OA, NA, and Cnx those hyperthermic conditions completely blocked their action against chloroplasts. On the other hand, both temperature regimes accelerated the antichloroplast activity of the mutagens/carcinogens nitrosoguanidine and furylfuramide.

Interaction of drugs with extranuclear genetic elements and its consequences

Bacterial ancestry of mitochondria and plastids is now generally accepted. Both organelles contain their own DNA and transcription-translation apparatus of a prokaryotic type. Due to this fact these systems carry bacteria-like properties. Thus organellar DNA and ribosomes are essentially different from nuclear DNA and cytoplasmic ribosomes in physical as well as in functional respects. Due to the bacterial character of both types of organelles they are susceptible to various antibacterial chemicals. Inhibitors of bacterial protein synthesis inhibit mitochondrial (plastidial) biogenesis. Therefore the cellular content of mitochondria (plastids)-made proteins decreases during cytoplasmic turnover or cell division in the presence of these drugs. Such drug activity consequently leads to a reduced capacity for oxidative phosphorylation or photosynthesis. Organellar genomes are less stable and more sensitive to mutagenesis as compared to nuclear genome. It means also that genotoxic agents induce various disorders of mitochondrial (plastidial) functions. Impairments in the respiratory chain are associated with structural as well as functional abnormalities of mitochondria. These are clinically expressed mostly in tissues with a high demand for ATP: brain, heart, skeletal muscle, and retina. On the other hand, some antibacterial inhibitors of mitochondrial biogenesis (e.g., tetracyclines) inhibit selectively tumor cell proliferation. Therefore they may be considered for use in anticancer therapy. The article summarizes the response of mitochondria and plastids in various organisms to drugs and environmental xenobiotics. Various model organisms suitable for detection of xenobiotic effect on mitochondria (plastids) are presented as well as the possible consequences of such interaction.

Quinolones and coumarins eliminate chloroplasts from Euglena gracilis

Quinolones and coumarins were potent eliminators of chloroplasts from Euglena gracilis. There was a remarkable similarity between antichloroplastic and antibacterial activities of DNA gyrase inhibitors. Quinolones produced 100% chloroplast-free cells in concentrations which do not affect cell viability. Optimal conditions were exponential growth, continuous illumination, and neutral or slightly alkaline pH. Coumarins were more toxic than quinolones. Among the quinolones, ofloxacin was the most potent in eliminating chloroplasts. Among the coumarins, coumermycin A1 was the most potent. New quinolones and coumermycin A1 were able to induce the complete inability of originally green cells to form green colonies after 24 h of drug exposure, while clorobiocin and novobiocin required several days of exposure. Darkness, heat shock (42 degrees C, 10 min), or simultaneous treatment with chloramphenicol or rifampin decreased the potency of DNA gyrase inhibitors for producing chloroplast-free cells. Remarkably, in cells in which division was blocked by three different methods (resting medium, hyperthermic conditions [37 degrees C], or addition of cycloheximide), new quinolones and coumermycin A1 nevertheless eliminated chloroplasts. The antichloroplastic activity of DNA gyrase inhibitors is additional data suggesting an evolutionary relationship between chloroplasts and eubacteria.