engleski

Multixenobiotic resistance mechanism in aquatic organisms

Background and purpose: Recently we described a new type of environmentally hazardous chemicals -- the chemosensitizers of multixenobiotic resistance (MXR) mechanism. This was the result of capitalisation on the discovery of MXR in aquatic organisms, a mechanism that, similarly to the mechanism of multidrug resistance (MDR) in resistant tumor cells, pumps out of the cell xenobiotics using an ATP-dependent P-glycoprotein 170 (Pgp)-pump. In this review we present additional recent evidence for the presence of Pgp and function of MXR in aquatic organisms. Methods: The presence of Pgp in a marine mussel was determined by indirect "binding" and direct immunochemical (Western) methods. The function and the induction of Pgp were measured by the level of modulation in accumulation of vincristine (VCR), rhodamine B (RB), 2-acetylaminofluorene (AAF), or 2-aminofluorene (AF) in organisms exposed under physiological conditions. The concentration of chemosensitizers in water concentrates and sediment extracts was measured by the level of modulation in accumulation of VCR in a culture of S180 cells, or of calcein AM in NIH 3T3 cells. Function of MXR, as well as concentration of chemosensitizers in natural waters was measured by the efflux-version of the RB-method. Toxicological effects of chemosensitizers were measured by the increase in number of single strand breaks in the DNA, using a filter alkaline elution method, or by the increased formation of ultimate mutagens, as detected by Ames-test, after exposure of mussels to AAF or AF, respectively. Results: Membrane vesicles from gills of Mytilus galloprovincialis bind VCR in a verapamil-sensitive manner and cross-react with polyclonal antibodies raised against Pgp. Accumulation of AAF, VCR, or RB in gills of M. galloprovincialis, Corbicula fluminea or Dresissena polymorpha is enhanced in the presence of verapamil, staurosporine and cyclosporin A (CA), respectively. C. fluminea exposed to no observable effect level of AAF induces in the presence of staurosporine high number of single strand breaks. D. polymorpha exposed to water spiked AF produces 7 times more mutagens in the presence than in the absence of CA. Concentrate of Sava River water and extract of its sediment contain more chemosensitizers, as measured by cell-culture technique, than water or sediment from Dobra River. Natural Sava River water, or natural seawater from a polluted Factory Site contains more chemosensitizers, as measured by the efflux-version of RB-method with D. polymorpha or M. galloprovincialis, than Dobra River waters or seawater from Limski Kanal, respectively. Conclusions: Multixenobiotic resistance phenotype expressed in aquatic organisms serves as a defence mechanism that protects organisms by the mechanism that pumps out of the cell many structurally diverse lipophilic xenobiotics. The exposure to polluted water induces the expression of MXR. Many classes of chemicals are capable to inhibit the MXR-mechanism. This new class of compounds, referred to as chemosensitizers, deserves a top rank among environmentally hazardous chemicals, since they may block the basic biologic defence mechanism and revert natural resistance to pathobiologic sensitivity. Therefore the detection and control of MXR-inhibitors deserve the highest priority in ecological risk assessment studies.

multixenobiotic resistance ; P-glycoprotein ; aquatic organisms ; induction ; biomarker ; toxicity ; chemosensitizers

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