The current study also inferred that MT content in

The current study also inferred that MT content in Crassostrea gigas might be associated with the Cd level, and can be affected by MT turnover. The Ramelteon of MT in cytosol is beneficial for aquatic organisms to adapt the seawater contaminated by heavy metals, and MT is a biomarker for marine invertebrates under Cd exposure (Mao et al., 2012). MT expression, whether at mRNA or protein level, was enhanced during exposure to Cd and weakened during depuration (Bebianno and Langston, 1993; Sun et al., 2018). In addition, transcriptional response of MT gene was positively correlated to Cd content in cockle Cerastoderma glaucum (Karray et al., 2015). Therefore, a higher content of MT in the group under a treatment by 25 μg/L verapamil might be stimulated by its higher content of Cd. Comparison of MT content between the blank and the group exposed to Cd without subsequent depuration testified to the Cd induction of MT. The three groups from natural seawater and seawater containing rifampicin showed variation of MT concentration correlative with their Cd concentration compared with the group kept in Cd exposure without any depuration. Not significant variation of MT level between the two groups with different concentration of rifampicin might be explained by the slow turnover rate of MT in Crassostrea gigas despite lower Cd content in the group treated with 25 μg/L verapamil. A half-life of 25 days for MT in Mytilus edulis has been estimated (Bebianno and Langston, 1993). In fact, it has been accepted that Cd-binding MT prevents Cd from associating with organic matter functioning in biochemical processes such as enzymes, and thus the stable existence of MT is meaningful to detoxification of organisms. As earlier studies showed, MT gene can still express at mRNA or protein level even at the beginning of depuration period (Bebianno and Langston, 1993; Sun et al., 2018). Thereby, a decrease of MT concentration may be not simultaneous with that of Cd concentration.
Conclusions Current study explored the effect of regulating P-gp on Cd removal from Crassostrea gigas. As an inhibitor and inducer of P-gp, verapamil and rifampicin contributed to incremental and diminished Cd level, respectively. There was no significant loss of beneficial metal elements, fats, and proteins in Crassostrea gigas after adding verapamil or rifampicin. With Crassostrea gigas decontaminated by natural seawater as reference, a higher concentration of metallothionein was shown in those treated with verapamil while similar concentration of metallothionein was noticed after rifampicin treatment. Moreover, compared with Crassostrea gigas depurated in natural seawater, antioxidant enzymes including POD and SOD and MDA content showed no decline in gills of Crassostrea gigas treated with rifampicin or verapamil, whereas decrease was measured in the visceral masses. Current study indicated the feasibility to enhance Cd exhaustion and control Cd content in Crassostrea gigas by inducing P-gp. Deeper studies are needed to clarify specific details, for example, the role of P-gp in cellular level during purification of oysters. Besides, considering side effect of rifampicin on human, non-toxic P-gp inducer needs to be found in future.
Introduction Insects cuticle consists of three functionally distinct horizontal layers, including the outer-most waxy coat envelope, the intermediate protein-enriched epicuticle, and the innermost procuticle (a chitin-protein matrix) [1]. The envelope has been described as a cement layer and the lipid bearing epicuticle is an ultrastructural distinct layer underneath the envelope. The epicuticle mainly contains unidentified proteins and lipids, but is devoid of chitin. The procuticle is the innermost cuticle layer under the epicuticle, but is closely attached to the surface of the epidermal cells, and is characterized by a chitin-protein matrix and is subdivided to two sublayers, including upper exocuticle and inner endocuticle. The exocuticle is associated with the epicuticle, and is formed before ecdysis in insects, while endocuticle deposition occurs after ecdysis and ends before the next apolysis [2]. The cuticle contributes to animal survival and protects it from infection, penetration by insecticides, and dehydration. However, the cuticle restricts insect growth, so insect must periodically shed the old cuticle and produce a new one beneath the old one. The cuticle is secreted by the underlying single layer epidermal cells, which release enzymes that digest the base of the old cuticle (much of the endocuticle) and then secrete a new cuticle [3].