Effects of DMSO on Vacuole Formation, Contractile Vacuole Function, and Nuclear Division in Tetrahymena Pyriformis GL

Formation and ingression of division furrow can progress under the inhibitory condition of actin polymerization in ciliate Tetrahymena pyriformis

In eukaryotic cells that multiply by binary fission, the interaction of actin filaments with myosin II in the contractile ring is widely recognized to generate force for membrane ingression into the cleavage furrow; however, the expression of myosin II is restricted in animals, yeast, fungi, and amoeba (collectively, unikonts). No corresponding motor protein capable of forming mini-filaments that could exert sufficient tension to cleave the cell body is found in bikonts, consisting of planta, algae, and most protozoa; however, cells in some bikont lineages multiply by binary fission, as do animal cells. Of these, the ciliate Tetrahymena is known to form an actin ring beneath the division furrow in cytokinesis. Here, we investigated the role of filamentous actin in the cytokinesis of Tetrahymena pyriformis by treating synchronized dividing cells with an actin-inhibiting drug, Latrunculin-A. Video microscopic observation of live cells undergoing cytokinesis was performed, and contrary to expectation, we found that initiation of furrow ingression and its progress are not suppressed under the inhibitory condition of actin polymerization in Tetrahymena cells. We suggest that an actin filament-independent mechanism of binary fission may have been acquired during the evolution in this organism.

Assessment of anthracene toxicity toward environmental eukaryotic microorganisms: Tetrahymena pyriformis and selected micromycetes

The toxicity of anthracene, a nonmutagenic, noncarcinogenic, low-molecular-weight polycyclic aromatic hydrocarbon present in the environment, was assessed using a ciliated protozoan, Tetrahymena pyriformis, and a selection of 10 micromycetes from different taxonomic groups living in two environmental compartments, namely aquatic and soil ecosystems. With T. pyriformis, a concentration-dependent inhibitory effect was shown on the cell proliferation rate, IC(50) = 33.40+/-4.84 mg/L (kinetic method). Phagocytosis of nonsoluble anthracene was confirmed by the presence of digestive vacuoles with photon microscopy. In fungi, anthracene did not exhibit a fungicide effect but showed a fungistatic action. Except for Absidia fusca and Cladosporium herbarum, the micromycetes showed a concentration-dependent decrease in growth. From IC(50) values determined by endpoint or kinetic methods, Rhodotorula glutinis and all of the Ascomycotina (except for Penicillium chrysogenum) were the most sensitive species, while Phanerochaete chrysosporium, P. chrysogenum, and the two Deuteromycotina were more resistant to anthracene. Our discussion focuses on the evaluation of toxicity by the two methods used for the calculation of the IC(50) values (endpoint and kinetic), the advantages of studying growth by a kinetic method (the dynamic aspect), and a comparison of toxicity to T. pyriformis and the different micromycetes.

Morphological and physiological changes in Tetrahymena pyriformis for the in vitro cytotoxicity assessment of Triton X-100

Non-ionic surfactants such as Triton X-100 have been widely used in industrial processing and in cleaning products for almost 50 years, being effective and economic emulsifying, wetting agents, dispersants and solubilizers. Cleaning products containing these surfactants are disposed of mainly by discharge into wastewater, which receives biological treatment in wastewater treatment systems. However, surface-active agents interact with eukaryotic cell membranes leading to biological damage at high concentrations. Tetrahymena pyriformis was used here as model organism to assess the effects of Triton X-100 through a series of in vitro cytotoxicity tests. Growth rates and morphological changes were, by their simplicity and reproducibility, the simplest toxicological assays. Cytoskeleton analysis seemed to be related with phagocytosis rate. Viability was evaluated by two different tests. Calcein AM/EthD-1 was used to assess T. pyriformis membrane damage during the 48-h experiment. The colorimetric MTT assay proved to be highly sensitive even at very short periods of Triton X-100 exposure. Tests performed in this study included simple and fast bioassays that provide overall information on the morphological and physiological state of cells exposed to different non-lytic and lytic concentrations of Triton X-100.

Cytotoxicity assessment of three therapeutic agents, cyclosporin-A, cisplatin and doxorubicin, with the ciliated protozoan Tetrahymena pyriformis

Cyclosporin-A, a drug possessing potent immunosuppressive properties, is used to prevent allograft rejection. Cisplatin and doxorubicin are two of the pharmaceutical drugs most widely used in cancer chemotherapy. In this study, the cytotoxicological impact of these three therapeutic agents was determined using bioassays performed with a unicellular eukaryote, the ciliated protozoan Tetrahymena pyriformis. For this purpose we used the population growth impairment test and the non-specific esterase activities test. We also examined some morphological effects. The results show that these three agents are toxic towards T. pyriformis. A concentration-dependent inhibitory effect on the cell proliferation rate of T. pyriformis populations was found for the three drugs. The IC(50) values were, respectively, 42.03+/-4.64, 124.37+/-7.47 and 74.62+/-6.12 microM for cyclosporin-A, cisplatin and doxorubicin. Non-specific esterase activities were also modified compared with untreated cells. The IC(50) values were, respectively, 88.32+/-8.35 and 44.61+/-3.33 microM for cisplatin and doxorubicin. Exposure of T. pyriformis to these drugs caused the prompt appearance of digestive vacuoles concentrating particulate elements. This phenomenon was more pronounced at higher concentrations. We also observed deformed cells with cisplatin. T. pyriformis bioassays can offer an alternative in vitro method to cell cultures for the risk assessment of potentially toxic drugs.

A comparative study using a fluorescence-based and a direct-count assay to determine cytotoxicity in Tetrahymena pyriformis

A novel cellular cytotoxicity assay using two fluorescent dyes was developed as an alternative method to the standard direct count of viable protozoa under light microscopy. The compound calcein AM is a non-fluorescent substance that diffuses passively across intact cell membranes and is converted by intracellular esterases to the green fluorescent calcein, which is retained in viable cells. The addition of EthD-1 that binds to DNA stained nuclei of dead cells red. The experiments were carried out in order to assess viability in the freshwater ciliate Tetrahymena pyriformis after exposure to eight surfactants, two of each representing one of four ionic class (non-ionic, anionic, cationic and amphoteric), and two heavy metals, copper and zinc, at several concentrations. In earlier time exposure, less than one hour of contact with surfactants at sublethal concentrations, the fluorescent method is more sensitive and provides more accurate results than direct counting under light microscopy. In contrast, with increasing time exposure, the results obtained by the two methods were similar. Calcein was shown to be a poor viability marker in the presence of zinc and copper since the fluorescence intensity was affected by the metal presence. However, the fluorescent method offers new opportunities to use advanced techniques, such as flow cytometry, to assess cytotoxicity in protozoa.

Trends in the use of protozoa in the assessment of wastewater treatment

Increasing environmental pollution and the continuous development of new chemicals and drugs has led to ever growing concern about the potential effects of these compounds directly or indirectly on human health. As concerns water pollution, protozoa seem to be an excellent tool to assess both toxicity and pollution: they are regarded as biological indicators of pollution when their presence or absence can be related to particular environmental conditions, and they are considered test organisms when a species or population is used to evaluate the toxicity of relevant toxic compounds. Thus, an integrated approach is being developed to assess how toxic compounds affect the different biological levels of organisation--from the community level to the species level--of ciliated protozoa. The present paper reports and discusses the current state of the art of this approach.

Vanadate affects nuclear division and induces aberrantly-shaped cells during subsequent cytokinesis in Tetrahymena

Sodium orthovanadate at 0.1-5.0 mM affected cell proliferation of Tetrahymena in a dose-dependent manner. At 1 h the cell increment was 76-12% of the control (100%), but after lag periods in 1-5 mM the growth rate remained at 76% of control in 0.1 mM vanadate and at 64-61% of control in 0.2-5.0 mM vanadate. Endocytosis was affected in both a time- and dose-dependent manner; an increasing number of cells did not form vacuoles. Cell motility increased initially in 0.1 mM vanadate but decreased later as it did in 0.5-2.0 mM vanadate where the proportion of immobile cells increased with time. Cell divisions occurred at all concentrations but macronuclear elongation was disturbed and subsequent cytokinesis resulted in daughter cells containing the entire G2 macronucleus, a large or small portion of it, or no nucleus at all. Moreover, odd cell shapes appeared with time. The size of the cell and nucleus increased but there was great variation with disturbed cytoplasm/nucleus ratios. Treated cells had dilated rough endoplasmic reticulum that included dense material, presumed to be vanadate, which was not seen in control cells. Scant amounts of dense material were found in dense granules, small vacuoles, and abundantly in contractile vacuoles. It is argued that interference with proper microtubular function is the main effect of vanadate.

Effects of dimethyl sulfoxide on Tetrahymena pyriformis GL. Fine structural changes and their reversibility

Fine-structural changes are induced in Tetrahymena by exposure to 7.5% dimethyl sulfoxide (DMSO) in the presence of growth medium. Some of these changes (nucleolar, mitochondrial, peroxisomal) resemble those seen during starvation, in agreement with the previously reported inhibitory effect of DMSO on food-vacuole formation; however, changes such as helical formations of polyribosomes indicate additional internal actions of the reagent. The effects vary to some extent within the same group of cells, suggesting that sensitivity to the reagent may differ with the stage in the cell cycle. The structural changes induced by a 1-hr exposure to DMSO are reversible, but recovery of the cells after removal of the reagent is slower than that seen after starvation. The observations suggest that the recovery is associated with renewed synthesis.

The in vivo effect of dimethyl sulphoxide (DMSO) on protein synthesis and the polyribosome profile in Paramecium

When Paramecium tetraurelia in log phase growth is treated with 4% dimethyl sulphoxide (DMSO) for five minutes the amount of polyribosomes is reduced 3- to 4-fold while there is a corresponding increase in 80s ribosomal material. Reducing the concentration of DMSO to 1% allows immediate reversal of the condition. Paramecium polyribosomes subjected to 4% DMSO either in whole cell homogenates or during purification through sucrose density gradients appear unaffected while cycloheximide at concentrations up to 100 mug/ml did not prevent DMSO from exerting its effect in vivo. Analyses of 14C amino acid incorporation experiments indicated a strict correspondence between the effect of DMSO on polyribosomes and overall protein synthesis. The reduction of acid precipitable radioactivity in the polyribosomal region after DMSO treatment was associated with a corresponding increase in radioactivity in the 80s region. There was no comparable increase in the acid precipitable radioactivity in the soluble fraction. The overall results of the study suggest that DMSO acts on polyribosommes indirectly through some unknown primary reaction with cell constitutents, and that the mode of action is such as to cause the release of ribosomes from messenger RNA (mRNA) rather than to prevent initiation of the ribosome-mRNA complex. Our data suggest that the effect may be selective. Finally, it is of interest that high concentrations of DMSO (above 8%) appear to have the opposite effect of lower concentrations of DMSO, i.e., they appear to "freeze" the ribosomes to mRNA.