[Algal toxins, inhibitors of serine/threonine phosphatases]. / Toxines d'origine algale inhibitrices de sérine/thréonine phosphatases.

Under certain environmental conditions, marine and freshwater phytoplankton may produce phycotoxins inhibitors of serine/thréonine protein phosphatases 1, 2A and 3. In the marine environment, dinoflagellates produce fatty polyethers: okadaic acid and its derivatives, the dinophysistoxins, which accumulate in shellfish and can cause diarrhetic shellfish poisoning (DSP) when ingested. In freshwater, the toxins are microcystins and nodularin, 7 or 5 amino acid cyclic peptides and are hepatotoxic. These toxins have caused massive poisoning of wild animals or domestic livestock and now are a health threat for humans through use of drinking and recreation water. Moreover, all these toxins are potent tumor promoters but belong to a new class, different from the TPA class, because they do not act on Protein Kinase C. Although the mutagenicity Ames test responds negatively, several results show their genotoxic potential, and therefore they are a health hazard through chronic exposition to low doses. Finally, okadaic acid, through its easy penetration in all cellular types can be used as a tool to study mechanisms involved in protein phosphorylation/dephosphorylation processes.

Implication of distinct proteins in cadmium uptake and transport by intestinal cells HT-29.

The mechanisms of intestinal absorption have not been clearly elucidated for cadmium, a toxic metal. In this work, we show the implication of distinct proteins in cadmium transport, and the transport step where these proteins are involved. We first validated the HT-29 model by evaluating nontoxic doses of cadmium (ranging from 1 to 20 micromol/L), and by quantifying metal uptake and transepithelial transport. The time-course of 1 micromol/L cadmium uptake at pH 7.5 showed three steps: a rapid one during the first 4 min, probably due to cadmium binding to the membrane; a slower one, characterized by Km of 1.65+/-0.54 micromol/L and Vmax of 3.9+/-0.3 micromol/min per mg protein; and a third, corresponding to slow accumulation that was not equilibrated even after 48 h of cadmium exposure. Intracellular metallothionein content following 1 or 5 micromol/L cadmium exposure showed a significant increase after 6 h of exposure, and was not equilibrated even after 72 h, allowing cadmium accumulation. After 24 h of exposure, metallothionein content was 5-fold, 14-fold, 26-fold, and 50-fold, respectively, for cells grown in the presence of 1, 5, 10, and 20 micromol/L cadmium, compared to control cells. The second step of uptake, characterized by carrier-mediated transport, was markedly increased at pH 5.5, compared to pH 7.5, and strongly inhibited by the metabolic inhibitor dinitrophenol. Moreover Nramp2 transporter cDNA was present in HT-29 cells. These data suggest the involvement of a proton-coupled transporter, which may be the divalent cation transporter Nramp2 (natural resistance-associated macrophage protein 2). Cadmium uptake was also inhibited by copper, zinc, and para-chloromercuribenzenesulfonate (pCMBS), but not by verapamil or ouabain. Taken together, our results indicate that cadmium could enter HT-29 cell by Nramp2 proton-coupled active transport and by diffusion, and accumulates in the cell as long as it binds to metallothionein. Cadmium toxicity could depend partly on the activity of Nramp2, and partly on metallothionein content.

Characteristics of okadaic acid--induced cytotoxic effects in CHO K1 cells.

This article reports the results of investigations into the process of cell death induced in the Chinese hamster ovary cell K1 subclone (CHO K1) by okadaic acid (OA), a hydrophobic polyether produced by marine dinoflagellates. The IC50 was about 13 nM OA after 24 h of treatment, as determined using neutral red. With the MTT assay, the IC50 was 25 nM, although in this case 25% of the initial staining was still observed at 100 nM. Hoechst staining showed that mitotic figures accumulated at 12 nM OA after a 24- or 48-h treatment. In experiments limited to a 3-day treatment without changing the medium, CHO K1 cells were engaged in the death process at 50 nM OA after about 20 h and at 10 nM OA after 48 h. In many cells nuclear fragmentation that resulted in the apparent appearance of vesicles correlated with increasing cellular volume. But additional cell fragmentation was not observed with any treatment, and the chromatin material seemed to progressively disappear inside the cells. DNA fragmentation was analyzed by electrophoresis and with the TUNEL technique. With both techniques, the DNA was fragmented by 48 h in both 25 and 50 nM OA. Electrophoresis showed that both adherent and nonadherent cells were affected. Annexin-positive/ propidium iodide (PI)-negative cells were rarely observed after OA treatment. Some were seen under the scanning cytometer after 20 h at 50 nM OA or after 48 h at 10 nM OA, but they were never detected by flow cytometry. Most of the time scanning cytometry showed either unstained cells or PI-positive (annexin-positive or -negative) cells (48 h, 50 nM, or 72 h, 10 nM). Flow cytometry cytograms showed two cell subpopulations: one composed of a majority of smaller cells, the other of larger cells. The larger cells markedly decreased with time and OA treatment (50 and 100 nM). Stained-cell counting showed that all cells that stained were both annexin- and PI positive and that most PI-positive cells were smaller. Ki67 antigen labeling showed the proliferative activity of CHO K1 cultures but also demonstrated the loss of this activity in smaller cells treated with 50 nM OA for 48 h. We concluded that in our culture conditions the main OA target within CHO K1 cultures was dividing cells. Our results suggest that cells with disturbed metaphase-anaphase enter apoptosis, leading to necrotic daughter cells.

Stability and biological activity of epoietin beta in parenteral nutrition solutions.

The aim of this in vitro study was to determine stability and biological activity of epoietin (Epo) beta in a parenteral nutrition solution over 24 h. Epo beta was added to the parenteral nutrition solution which was administered through intravenous tubing and a Posidyne Neo filter. Samples were collected after 0, 4, 12, and 24 h. The Epo concentrations were measured before and after filter passage by an ELISA assay. The Epo biological activity was determined in the UT7/Epo cell line. The Epo concentration in the parenteral nutrition solution remained stable for 24 h. However, 35% of the Epo was adsorbed by the filter. The samples collected induced proliferation of UT7/Epo cells. These results suggest that Epo can be administered in parenteral nutrition solutions, but the dosage would need to be increased when a filter is used.