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Browsing by Subject "ABCB1"

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  • Hurmalainen, Virpi (2021)
    P-glycoprotein is an efflux transporter of the ABC family. It is expressed mainly in tissues that have a role in limiting the absorption and distribution of xenobiotics in the body or their elimination. P-glycoprotein is known to have an important role for example in the blood-brain barrier and in protecting the fetus from xenobiotics in the mother’s blood stream. Genetic polymorphisms in transporter proteins can cause individual differences in the pharmacokinetics of drug substances, which can lead to differences in drug efficacy or side effects. In the ABCB1 gene, which codes for p-glycoprotein, several polymorphisms have been discovered. The frequencies of these polymorphisms vary in different ethnic populations. Previous studies have shown that the effects of these polymorphisms are often substrate-dependent. Since there are several confounding factors usually present in clinical association studies, in vitro studies are needed to clarify the effects of individual polymorphisms. Polymorphisms can be studied in vitro by making intentional mutations to the gene sequence and expressing the variant gene in a suitable cell line. In this study four variant p-glycoprotein genes (c.781A>G, c.1199G>T, c.2005C>T and c.3421T>A) were created by site-directed mutagenesis, and expressed in HEK293 cells using a baculovirus recombinant protein expression method. The effects of the polymorphisms were studied by determining the expression level and the transport acitivity of the variant proteins compared to the wild-type. Western blot was used to determine the expression level and a calcein accumulation assay in HEK293 cells was used to compare the transport activities. Also a membrane vesicle transport assay with n-methyl quinidine was set up and optimized, but the variants were not yet studied with this method during this study. In this study no statistically significant differences were found in the transport activities of any of the four variants compared to the wild-type p-glycoprotein. Also the differences in protein expression level between wild-type and variant proteins were small. However, because of the previously reported substrate dependency of polymorphism effects, it would be beneficial to study the variants with at least one other substrate and one other assay method, and thus the membrane vesicle transport assay would be useful to further compare the transport activities of variant proteins to the wild-type p-glycoprotein.