P gps expressed in cells and

P-gps, expressed in (R)-(+)-Etomoxir sodium salt sale and tissues of human and animals, play an active role in cellular protection against multiple toxicants by transporting them out of a cell. Thus, improving transport activity of P-gp may contribute to removing Cd from living oysters. Cd accumulation in the cultured cells is increased in the presence of P-gp inhibitors or UIC2, a P-gp monoclonal antibody during pretreatment. Lower rate of Cd efflux might be explained by inhibition of P-gp, a possible Cd efflux pump (Endo et al., 2002). Notably, the expression and transport activity of P-gps in the American oyster Crassostrea virginica Gmelin significantly increase after Cd exposure (Ivanina and Sokolova, 2008). Influenced by P-gp inhibitors, more accumulation of heavy metals and less heavy metal tolerance was found in the intertidal copepod Tigriopus japonicas (Jeong et al., 2014). However, there are rare researches investigating the role of P-gp in Cd decontamination instead of accumulation of oysters. Among biological changes in organisms exposed to metal stress, the increase of metallothioneins (MTs) and antioxidant defenses are considered to be important cellular responses to metal toxicity (G.Y. Wang et al., 2018, W.X. Wang et al., 2018). MTs, metal-binding proteins with low relative molecular mass (6000–7000), function in homeostasis and detoxification of metals in oysters. They provide α and β-domains to bind multiple metal ions including Cd, both of which contain cysteines (Jenny et al., 2004). MTs in many aquatic organisms can be induced by metal exposure or intracellular metal accumulation. It has been reported that Cd exposure led to apparent increase of MT protein in Crassostrea gigas (Amiard et al., 2006; Marie et al., 2006). Metal toxicity induces the production of reactive oxygen species (ROS), which is responsible for oxidative stress. Peroxidase (POD) and superoxide dismutase (SOD) are typical components of antioxidant enzymes in cellular antioxidant system. Thus, changed activity of POD and SOD may reflect the changes in the bioaccumulation level of Cd. Malondialdehyde (MDA), the end product of ROS-mediated lipid peroxidation, is also proposed as an indicator of oxidative stress brought from Cd toxicity. The aim of this study was to explore the relationship between P-gp activity and Cd level in the oyster Crassostrea gigas by adding rifampicin and verapamil, which are an inducer and inhibitor respectively for P-gp, to natural seawater. We also tested MT concentration, the activity of POD and SOD, and MDA concentration in Crassostrea gigas to indirectly reveal the remaining Cd toxicity after Cd removal experiments. The effect of this removal method on the nutritive value of oyster was analyzed by comparing the content of beneficial metal elements, proteins and fats with the control.
Materials and methods
Results
Discussion Our study tentatively exploring the potential of Cd removal by P-gp showed that Cd level in Crassostrea gigas was influenced under the treatment with an inhibitor or inducer for P-gp. The oysters were collected at 1, 2, 3, 4 and 5 days of depuration in natural seawater in our preliminary experiments, and the maximum removal rate occurred after 3 days of depuration. Therefore, all the 5 experiment groups were depurated in a period of 3 days to observe the effect of the inducer and inhibitor on Cd removal. In our study, a Cd decrease of samples in natural seawater was found in line with the earlier researches about reduction of heavy metals in marine species using clean sterilized seawater (Hiraoka, 1991; Han et al., 1993). However, this method reduced the content of Cd only to a limited extent. Since living aquatic products are required to be processed in a short period in seafood circulation, it is hoped that a more efficient method is applied to obtain an edible Crassostrea gigas with low level of Cd. Verapamil was extensively chosen in pharmacological study as an inhibitor for P-gp, which was responsible for drug exhaustion while rifampicin can act as an inducer or inhibitor depending on the species of the drug (Fei et al., 2017; G.Y. Wang et al., 2018, W.X. Wang et al., 2018; Kosa et al., 2018; Yang et al., 2018). These studies have not involved the role of rifampicin and verapamil in heavy metals transport by mediating P-gp. Our research suggests rifampicin and verapamil might serve as an inducer and an inhibitor respectively for P-gp in Crassostrea gigas, which explains the change of Cd concentration in Crassostrea gigas from seawater with rifampicin and verapamil.