title: Okadaic acid: a rapid inducer of lamellar bodies in small intestinal enterocytes.
abstract: Okadaic acid (OA) is a polyether fatty acid produced by marine dinoflagellates and the causative agent of diarrhetic shellfish poisoning. The effect of OA on apical endocytosis in the small intestine was studied in organ cultured porcine mucosal explants. Within 0.5-1 h of culture, the toxin caused hyper protein phosphorylation, but no detectable loss of cell polarity or cytoskeletal integrity of the enterocytes. Using a fluorescent membrane marker, FM dye, endocytosis from the brush border was affected by the toxin. Although constitutive uptake into subapical terminal web-localized early endosomes (TWEEs) occurred unimpeded in the presence of OA, FM condensed in larger subapical structures by 1 h, implying a perturbed endosomal trafficking/maturation. The fluorescent lysosomotropic agent Lysotracker revealed induction of large lysosomal structures by OA. Endocytosis from the brush border was studied at the electron microscopic level using the membrane-impermeable marker Ruthenium Red (RR). Like FM dye, RR was taken up into TWEEs and multivesicular bodies (MVBs). However, OA induced the formation of a large number of lamellar bodies (LBs), a type of lysosome-related organelles. LBs are the hallmark of phospholipidosis, a pathological condition characterized by lysosomal phospholipid accumulation. Phospholipidosis is observed in acquired lysosomal storage diseases and is induced by a large number of cationic amphiphilic drugs. Unlike the latter, however, OA does not act by accumulating in acidic organelles, implying a different toxic mechanism of action. We propose that rapid induction of LBs, an indicator of phospholipidosis, should be included in the future toxicity profile of OA.
authors.affiliation: Department of Cellular and Molecular Medicine, The Panum Institute, Faculty of Health Sciences, University of Copenhagen, Denmark. Electronic address: midan@sund.ku.dk.
authors.forename: E Michael
authors.initials: EM
authors.lastname: Danielsen
authors.affiliation: Department of Cellular and Molecular Medicine, The Panum Institute, Faculty of Health Sciences, University of Copenhagen, Denmark.
authors.forename: Gert H
authors.initials: GH
authors.lastname: Hansen
authors.affiliation: Department of Cellular and Molecular Medicine, The Panum Institute, Faculty of Health Sciences, University of Copenhagen, Denmark.
authors.forename: Mai C K
authors.initials: MC
authors.lastname: Severinsen
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000187:drug effects; D004705:Endocytosis / Q000187:drug effects; D020895:Enterocytes / Q000187:drug effects* / Q000648:ultrastructure; D007413:Intestinal Mucosa / Q000187:drug effects / Q000648:ultrastructure; D007421:Intestine, Small / Q000187:drug effects / Q000648:ultrastructure; D019319:Okadaic Acid / Q000633:toxicity*; D015388:Organelles / Q000187:drug effects*; D010743:Phospholipids / Q000378:metabolism; D013552:Swine
chemical_list: D010743:Phospholipids; D019319:Okadaic Acid
keywords: Enterocyte; Lamellar bodies; Okadaic acid; Phospholipidosis; Shellfish poisoning; Small intestine