title: Toxicity and uptake mechanism of cylindrospermopsin and lophyrotomin in primary rat hepatocytes.
abstract: The toxicities and uptake mechanisms of two hepatotoxins, namely cylindrospermopsin and lophyrotomin, were investigated on primary rat hepatocytes by using microcystin-LR (a well-known hepatotoxin produced by cyanobacteria) as a comparison. Isolated rat hepatocytes were incubated with different concentrations of hepatotoxins for 0, 24, 48 and 72 h. The cell viability was assayed by the tetrazolium-based (MTT) assay. Microcystin-LR, cylindrospermopsin and lophyrotomin all exhibited toxic effects on the primary rat hepatocytes with 72-h LC(50) of 8, 40 and 560 ng/ml, respectively. The involvement of the bile acid transport system in the hepatotoxin-induced toxicities was tested in the presence of two bile acids, cholate and taurocholate. Results showed that the bile acid transport system was responsible for the uptake, and facilitated the subsequent toxicities of lophyrotomin on hepatocytes. This occurred to a much lesser extent with cylindrospermopsin. With its smaller molecular weight, passive diffusion might be one of the possible mechanisms for cylindrospermopsin uptake into hepatocytes. This was supported by incubating a permanent cell line, KB (devoid of bile acid transport system), with cylindrospermopsin which showed cytotoxic effects. No inhibition of protein phosphatase 2A by cylindrospermopsin or lophyrotomin was found. This indicated that other toxic mechanisms besides protein phosphatase inhibition were producing the toxicities of cylindrospermopsin and lophyrotomin, and that they were unlikely to be potential tumor promoters.
authors.affiliation: Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong, People's Republic of China.
authors.forename: M W K
authors.initials: MW
authors.lastname: Chong
authors.forename: B S F
authors.initials: BS
authors.lastname: Wong
authors.forename: P K S
authors.initials: PK
authors.lastname: Lam
authors.forename: G R
authors.initials: GR
authors.lastname: Shaw
authors.forename: A A
authors.initials: AA
authors.lastname: Seawright
mesh_terms: D000470:Alkaloids; D000818:Animals; D001427:Bacterial Toxins; D001647:Bile Acids and Salts / Q000494:pharmacology; D002470:Cell Survival / Q000187:drug effects; D000087522:Cyanobacteria Toxins; D004791:Enzyme Inhibitors / Q000633:toxicity; D022781:Hepatocytes / Q000187:drug effects / Q000473:pathology*; D006801:Humans; D066298:In Vitro Techniques; D007624:KB Cells; D008297:Male; D008387:Marine Toxins / Q000633:toxicity; D052998:Microcystins; D009842:Oligopeptides / Q000378:metabolism / Q000633:toxicity*; D010456:Peptides, Cyclic / Q000633:toxicity; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D054648:Protein Phosphatase 2; D051381:Rats; D017208:Rats, Wistar; D014498:Uracil / Q000031:analogs & derivatives* / Q000378:metabolism / Q000633:toxicity*
chemical_list: D000470:Alkaloids; D001427:Bacterial Toxins; D001647:Bile Acids and Salts; D000087522:Cyanobacteria Toxins; D004791:Enzyme Inhibitors; D008387:Marine Toxins; D052998:Microcystins; D009842:Oligopeptides; D010456:Peptides, Cyclic; C089595:cylindrospermopsin; D014498:Uracil; C055573:lophyrotomin; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; C057862:cyanoginosin LR