engleski

Pumping-out: The first-line defence to water pollution in aquatic organisms

Aquatic organisms are inherently equipped with a mechanism that rescues organisms by pumping potentially toxic xenobiotics out of the cells before they express their toxic potential. The presence of this multixenobiotic resistance (MXR) mechanism in water organisms may explain, at least partly, the simultaneous resistance of many aquatic organisms to different chemicals presents in polluted water. The presence of this ATP-dependent membrane P-glycoprotein (Pgp) pump, identical to Pgp in a mechanism of multidrug resistance (MDR) in tumor cells, was confirmed in water organisms by biochemical ("binding"), molecular (immunohistochemical, Western, Northern), physiological (verapamil-sensitivity) and toxicological (modulation of toxicity) methods. The inducibility of MXR in the presence of xenobiotics and its wide taxonomic distribution suggests its role as a general biological first-line defence mechanism. Thus, the discovery of the presence and operation of MXR in aquatic organisms should play a central role among parameters most often used for characterisation of exposure in the assessment of impact of pollution, like uptake, bioavailability, bioaccumulation, internal dose, synergism, and toxicity. However, this defence mechanism is fragile: Some xenobiotics, the chemosensitizers, can inhibit this defence mechanism. Such MXR-inhibitors, for example, enhance the accumulation of carcinogenic aromatic amines in mussel, with subsequent enhancement in production of their mutagenic metabolites, induction of single strand breaks in DNA, and induction of DNA-adducts. The property to inhibit defence mechanism of organisms classifies MXR-inhibitors among top-hazardous environmental chemicals. The concentration of such MXR-inhibitors is significantly higher in polluted than in unpolluted waters. These concentrations were able to enhance the accumulation of xenobiotics in exposed aquatic organisms, demonstrating the ecotoxicological significance of this new class of hazardous chemical.

aquatic organisms; multixenobiotic resistance; P170 glycoprotein; induction; inhibition; chemosensitizers; determination

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