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

Abstract

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.