Quantification of membrane transporter proteins in human lung and immortalized cell lines using targeted quantitative proteomic analysis by isotope dilution nanoLC-MS/MS

Information is needed on the expression of transporters in lung to inform drug development and therapeutic decisions. Much of the information currently available is from semiquantitative gene expression or immunometric densitometry studies reported in the literature. NanoLC-MS/MS (MRM mode) isotope dilution targeted quantitative proteomics was used here to quantify twelve selected transporters in fresh human lung membrane fraction samples and in the membrane fraction of selected immortalized human lung epithelial cell line samples. Fractionation was undertaken by homogenization in crude membrane lysis buffer followed by differential centrifugation of the homogenate. In lung membranes we found OATPs to be the most highly expressed transporters of those measured, followed by PEPT2 and ABCs (P-gp & BCRP). SLC22A transporters (OCTs 2 & 3 and OCTN1) were also found to be expressed. OATP2A1, also known as the prostaglandin transporter, was the most highly expressed transporter, being low in two subjects who were at least occasional smokers. One subject, a non-smoker, had an OATP2A1 concentration that was 8.4 times higher than the next nearest concentration, which itself was higher than the concentration of any other transporter. OATP2A1 is known, from gene expression and animal functional studies, to be present in lung. These results inform the understanding of xenobiotic disposition in the lung and show the distinct profile of transporters in lung compared to other tissues.