Chemosensitizers of the multixenobiotic resistance in amorphous aggregates(marine snow): etiology of mass killing on the benthos in the Northern Adriatic?

Periodically appearing amorphous aggregates, 'marine snow', are formed in t he sea and if settled as mars on the sea bottom cause death of benthic meta zoans. Especially those animals are killed which are sessile filter feeders , e.g, sponges, mussels, or Anthozoa. The etiology of the toxic principle(s ) is not yet well understood. Gel-like marine snow aggregates occurred in t he Northern Adriatic during summer 1997. Samples of these aggregates were c ollected during the period July to September and the outer as well as the i nner zones were analyzed for (i) cell toxicity, and (ii) chemosensitizing a ctivity of the multixenobiotic resistance (MXR) mechanism. Organic extracts were prepared and cell toxicity was determined using mouse lymphoma cells. The experiments revealed that the major activity is seen in the center of the mats of the gel-like aggregates; a growth inhibitory activity of up to 54% (correlated to 5 mi of snow sample) was determined. The same extracts w ere used to determine the inhibition of the P-glycoprotein (Pgp) extrusion pump which confers the multixenobiotic resistance. The analyses were perfor med with cells from the sponge Suberites domuncula and with gills from the clam Corbicula fluminea in situ. Both systems have been shown to express th e Pgp extrusion pump. The data show that extracts from the outer zone of th e gel-like aggregate samples display pronounced inhibitory activity on the MXR extrusion pump and hence act as chemosensitizers by reversing the MXP p roperty. These findings indicate that gel-like aggregates contain compounds in the outer zone; chemosensitizer of the Pgp extrusion pump, which lower the level of protection of metazoan animals towards dissolved compounds in their surrounding milieu, and in the center toxic compounds which are-very likely-even in the absence of chemosensitizers hazardous for the invertebra tes. (C) 1998 Elsevier Science B.V. All rights reserved.