title: Pollutant-specific and general lysosomal responses in digestive cells of mussels exposed to model organic chemicals.
abstract: The present study was carried out to elucidate whether lysosomal size reduction in digestive cells of mussels Mytilus galloprovincialis constitutes a selective response against a particular group of organic chemical compounds, in contrast to the lysosomal enlargement characteristic of general stress response. Mussels were treated with di(2-ethylhexyl) phthalate (DEHP), benzo(a)pyrene (B[a]P), and the water accommodated fraction (WAF) of a lubricant oil, which were daily applied by either injection through the adductor muscle for 7 days or water-exposure for 21 days. Control mussels were either kept untreated in clean sea water, or treated with acetone (injection and water-exposure), vehicle used for DEHP and B[a]P. A third set of controls consisted of mussels with pierced shell kept in clean seawater. Digestive glands were excised at various treatment days and beta-glucuronidase activity was demonstrated in 8-microm cryotome sections. Lysosomal volume, surface and numerical densities, and surface-to-volume ratio were quantified by image analysis. Other sections were stained with oil red 0 to demonstrate neutral lipids and changes in lipid levels were quantified by image analysis. Neutral lipid accumulation in digestive cells was used as a complementary indication of exposure to organic chemicals. It resulted to be a very prompt and all-or-nothing response, which reached a plateau before 1 day of treatment with WAF, DEHP and B[a]P after both injection and water-exposure. DEHP-treatment induced a general stress response characterised by lysosomal enlargement in digestive cells, which was already induced after 1 day. Treatment with either WAF or B[a]P elicited a comparable biphasic response. A transient lysosomal enlargement, shorter with WAF than with B[a]P treatment, was evidenced after both injection and water-exposure. Further, under water-exposure conditions, WAF reduced the endo-lysosomal system in size more markedly than B[a]P. Such lysosomal size reduction constitutes a transient response after exposure to diverse organic xenobiotics (acetone, WAF and B[a]P). In addition, this lysosomal size reduction might be followed by a further lysosomal enlargement, which later might yet again give rise to an apparent lysosomal size reduction under chronic exposure conditions. As a whole, the lysosomal response is intricate and cannot be simply interpreted in environmental pollution monitoring programmes. Nevertheless, it still constitutes a powerful and sensitive biomarker extremely useful as early-warning signal.
authors.affiliation: Cell Biology and Histology Laboratory, Zoology and Animal Cell Dynamics Department, University of the Basque Country, P.O. Box 644, E-48080 Bilbo, Basque Country, Spain. zopmaali@lg.ehu.es
authors.forename: Ionan
authors.initials: I
authors.lastname: Marigómez
authors.forename: Lurraine
authors.initials: L
authors.lastname: Baybay-Villacorta
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001564:Benzo(a)pyrene / Q000633:toxicity; D049872:Bivalvia / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D004051:Diethylhexyl Phthalate / Q000633:toxicity; D004064:Digestive System / Q000166:cytology / Q000187:drug effects* / Q000473:pathology; D050356:Lipid Metabolism; D008153:Lubrication; D008247:Lysosomes / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D008954:Models, Biological; D009930:Organic Chemicals / Q000633:toxicity*; D010578:Petroleum / Q000633:toxicity; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D009930:Organic Chemicals; D010578:Petroleum; D014874:Water Pollutants, Chemical; D001564:Benzo(a)pyrene; D004051:Diethylhexyl Phthalate