Blood appearance, metabolic transformation and plasma transport proteins of C-14-astaxanthin in Atlantic salmon (Salmo salar L.)

The time of appearance in blood, and transport of astaxanthin, and cataboli c transformation of astaxanthin to idoxanthin were investigated in Atlantic salmon (Salmo salar) that had been force-fed a single dose of C-14-astaxan thin. In addition to the LPs, a major protein, associated with radiolabeled astaxanthin was detected. The maximum level of radiolabeled carotenoids in blood was attained 30 h after administration of C-14-astaxanthin. Radioact ive idoxanthin (combined 3',4'-cis and 3',4'- trans glycolic isomers of ido xanthin) appeared after 6 h and a stable level was obtained after 18 h. LPD P and LP, separated by ultracentrifugation, contained on average 89 and 11% of the total radioactivity in plasma, respectively. During the 168 h exper iment, maximum radioactivity in LP appeared after 22 h. Separation of plasm a by ultracentrifugation on a discontinuous NaCl/KBr-gradient and an iodixa nol-gradient confirmed that most of the radiolabeled carotenoids were prese nt in the HDPF that did not contain LPs (58%), whereas HDL and LDL containe d 36 and 6% of the radioactivity, respectively. Of the recovered radioactiv ity, astaxanthin in the HDPF comprised 82%, idoxanthin 5% and unidentified compounds 12%, whereas HDL contained 78% astaxanthin, 22% idoxanthin and no unidentified compounds. Proteins from the fractions with the high density and high radioactivity (iodixanol-gradient) were separated by PAGE under no n-denaturing conditions and showed a radioactive band with parallel migrati on length to BSA and salmon albumin. These results show that astaxanthin is rapidly converted to idoxanthin and that the majority of astaxanthin in th e plasma is associated with a protein other than LPs, presumably albumin. T he identity of this protein requires verification.