TABLE 1

Comparison of absolute protein quantification of OATP1B1, OATP1B3, OATP2B1, and P-gp in human livers by different studies

StudyNumber of Livers QuantifiedLiver Tissue Weight per Extraction (mg)Membrane Protein ExtractionMembrane Protein SolubilizerProtein Amount per DigestionProtein:Trypsin RatioDigestion TimeOATP1B1aOATP1B3aOATP2B1aP-gpaSignature Peptide
OATP1B1OATP1B3OATP2B1P-gp
Balogh et al. (2013)4NDProteoExtract (M-PEK)10% DOC80 μg20:144 hours10.6 ± 5.35.9 ± 4.42.9 ± 1.5NDNVTGFFQSFKNVTGFFQSLKSSPAVEQQLLVSGPGK
Kimoto et al. (2012)9NDProteoExtract (M-PEK)10% DOC80 μg20:1Overnight9.7 ± 4.36.3 ± 2.83.7 ± 1.4NDNVTGFFQSFKNVTGFFQSLKSSPAVEQQLLVSGPGK
Karlgren et al. (2012)1bNDCrude membrane fractionSDSNANDND7.2 ± 0.36.3 ± 0.44.0 ± 0.4NDNVTGFFQSFKNVTGFFQSLKSSPAVEQQLLVSGPGK
Ohtsuki et al. (2012)5–17NDDifferential centrifugation for microsomal fractionNone (resuspended in 10 mM Tris–HCl, pH 8.0)NA100:116 hours2.7 ± 3.7 (n = 8)1.7 ± 0.5 (n = 17)0.5 ± 0.9 (n = 5)1.5 ± 0.4 (n = 17)LNTVGIAKIYNSVFFGRVLLQTLRNTTGALTTR
Prasad et al. (2014)64100 mgProteoExtract (M-PEK)None40 μg25:124 hours2.0 ± 0.91.1 ± 0.51.7 ± 0.60.4 ± 0.2NVTGFFQSFKNVTGFFQSLKVLAVTDSPARNTTGALTTR
ND0.9 ± 0.51.5 ± 0.60.3 ± 0.2YVEQQYGQPSSKIYNSVFFGRSSPAVEQQLLVSGPGKIATEAIENFR
This study14140–60 mgProteoExtract (M-PEK)10% Na-DOC50 μg20:118 hours15.0 ± 6.016.1 ± 8.14.1 ± 1.30.6 ± 0.2NVTGFFQSFK (OATP1B1_pep1)IYNSVFFGR (OATP1B3_pep2)SSPAVEQQLLVSGPGK (OATP2B1_pep1)NTTGALTTR (P-gp_pep1)
9.7 ± 3.810.5 ± 4.02.8 ± 0.9NDTYNSTSFSR (OATP1B1_pep3)NVTGFFQSLK (OATP1B3_pep1)YYNNDLLR (OATP2B1_pep2)
3.1 ± 1.2NDNDNDSSIIHIER (OATP1B1_pep9)

  • M-PEK, Native Membrane Protein Extraction Kit; NA, not applicable; ND, not described or not determined.

  • ↵a fmol protein per microgram of total membrane protein ± S.D.

  • ↵b One human liver that represented the average OATP protein expression of 12 livers was selected for targeted protein quantification.