Acute effects and bioaccumulation of nodularin in sea trout (Salmo trutta m. trutta L.) exposed orally to Nodularia spumigena under laboratory conditions.

Nodularin (NODLN) is a cyclic pentapeptide hepatotoxin that is regularly produced in high amounts by the cyanobacterium Nodularia spumigena in the Baltic Sea, and can bioaccumulate in Baltic biota. Baltic sea trout (Salmo trutta m. trutta L.) were exposed orally to a single dose of food containing NODLN (125 mg/kg ww) from N. spumigena (strain AV1, from the Baltic Sea). The level of exposure was 210-620 (average 440) microg NODLN per kg bw. Based on an 8-day survey under laboratory conditions, NODLN-like compounds accumulated in trout liver, with increasing liver concentrations (from 19 microg/kg on day 1 up to 1200 microg/kg on day 8 as measured with the EnviroLogix ELISA kit) during the experiment. Thus, accumulation of NODLN-like compounds in liver increased from 0.05% of the total NODLN dose administered on day 1 to 0.53% on day 8. However, the ELISA test kit is also sensitive to metabolites of algal hepatotoxins. In the HPLC chromatograms, no NODLN peak was detected after 24 h that also suggested NODLN absorbed in trout was metabolized or bound rapidly. According to ELISA, NODLN-like compounds also accumulated in trout muscle in lower quantities (from 125 to 34 microg/kg dw). Histopathology revealed complete loss of liver architecture after 1-2 days of the single oral dose. From day 4 to 8, there was partial recovery of liver cells. NODLN did not affect thiamine levels or water content of trout liver. The results showed that NODLN rapidly induces severe but reversible liver damage. Apparently NODLN accumulated in trout liver from cyanobacteria in the intestine, but was detoxified rapidly. On the basis of discrepancies between the histopathology and ELISA, and on the other hand, between the HPLC and ELISA methods, analysis of NODLN and its metabolites in biological tissue needs to be improved.