Comparative study on in vitro transformation of paralytic shellfish poisoning (PSP) toxins in different shellfish tissues

Dissected tissues of three shellfish species, the Chinese scallop, Chlamys farreri, Manila clam, Ruditapes philippinarum, and Razor shell, Solen strictu were evaluated for in vitro transformation of paralytic shellfish poisoning (PSP) toxins. Tissue homogenates were incubated with extraction from toxic algae Alexandrium minutum to determine toxin conversion. The effects of heating and addition of a natural reductant (glutathione) on toxin conversion were also assessed. The toxin profile was investigated through high performance liquid chromatography with fluorescence detection (HPLC-FLD). The evident variations in the toxin content were observed only in Chinese scallop viscera homogenates. The concentration of GTX4 was reduced by 45% (approximately 0.8 μmol/dm³) and 25% (approximately 1 μmol/dm³) for GTX1, while GTX2 and GTX3 increased by six times (approximately 1 μmol/dm³) and 3 times (approximately 0.3 μmol/dm³) respectively. Simultaneously, the total toxicity decreased by 38% during the 48 h incubation period, the final toxicity was 20.4 nmol STXeq/g. Furthermore, heated Chinese scallop viscera homogenates samples were compared with non-heated samples. The concentration of the GTX4 and GTX1 was clearly 28% (approximately 0.53 μmol/dm³) and 17% (approximately 0.69 μmol/dm³) higher in heated samples, GTX2 and GTX3 were four times (0.66 μmol/dm³) and two times (0.187 μmol/dm³) lower respectively. GSH (+) Chinese scallop viscera homogenates samples were compared with GSH (-) samples, the concentration in the GTX4 and GTX1 was 9% (approximately 0.12 μmol/dm³) and 11% (approximately 0.36 μmol/dm³) lower respectively, GTX2 and GTX3 was 17% (approximately 0.14 μmol/dm³) and 19% (approximately 0.006 μmol/dm³) higher respectively. In contrast,there was a little change in the concentration of PSP toxins of Manila clam and Razor shell tissue homogenates. These observations on three shellfish tissues confirmed that there were species-specific differences in PSP toxins transformation. PSP toxins transformation was more pronounced in viscera tissue than in muscle tissue. PSP toxins was possibly interfered by some carbamoylase enzyme, and the activity in Chinese scallop viscera tissue is more remarkable than in the other two species.