Table 1:
Drug transporters expressed in the human placenta
| Name of transporter* | Gene/Alternative name | Technique used for detection/Quantification | Localization in the syncytiotrophoblast | Transporter type | Direction of net transport | Potential effect on fetal drug exposure | Reference | ||
|---|---|---|---|---|---|---|---|---|---|
| First trimester | Second trimester | Third trimester/term | |||||||
| P-gp + | ABCB1, MDR1 | R, P | R, P | R, P, A | Apical membrane | Efflux | Fetal to maternal | Reduced | 21, 22, 37–40, 128–131 |
| BCRP + | ABCG2, MXR | R, P | R, P | R, P, A | Apical membrane | Efflux | Fetal to maternal | Reduced | 21, 22, 37, 38, 41, 128–130, 132 |
| MRP1 # | ABCC1 | R | NA | R, P, A | Basal membrane | Efflux | Maternal to fetal | Enhanced | 37, 46, 132–135 |
| MRP2 ^ | ABCC2, CMRP, CMOAT | R, P | R, P | R, P, A | Apical membrane | Efflux | Fetal to maternal | Reduced | 37, 46, 47, 129–131, 135–137 |
| MRP3 # | ABCC3 | R | NA | R, P, A | Apical membrane | Efflux | Fetal to maternal | Reduced | 37, 46, 135–137 |
| MRP4 | ABCC4 | NA | NA | R, P | Apical membrane | Efflux | Fetal to maternal | Reduced | 137 |
| MRP5 | ABCC5 | R | R | R, P | Basal membrane | Efflux | Maternal to fetal | Enhanced | 46, 138 |
| OATP1A2 + | SLCO1A2, SLC21A3, OATP-A | R, P | NA | R, P, A | Basal membrane | Influx | Fetal to maternal | Reduced | 43, 129, 139, 140 |
| OATP1B1+ | SLCO1B1, OATP-C, LST1 | R | NA | NA | Basal membrane | Influx | Fetal to maternal | Reduced | 43, 140 |
| OATP2B1 + | SLC21A9, OATP-B | P | P | R, P, A | Basal membrane | Influx | Fetal to maternal | Reduced | 22, 42, 141 |
| OATP4A1# | SLC21A12, OATP1, OATP-E | R, P | NA | R, P | Apical membrane | Influx | Maternal to fetal | Enhanced | 43, 139 |
| OCT3 ^ | SLC22A3, EMT | R, P | R, P | R, P, A | Basal membrane | Influx | Fetal to maternal | Reduced | 22, 48, 49, 142–144 |
| OCTN2 + | SLC22A5 | NA | NA | R, P, A | Apical membrane | Influx | Maternal to fetal | Enhanced | 44, 45, 145 |
| OAT4^ | SLC22A9, SLC22A11 | R, P | R, P | R, P | Basal membrane | Influx | Fetal to maternal | Reduced | 22, 141, 146, 147 |
| MATE1# | SLC47A1 | R | NA | R | Apical | Influx | Maternal to fetal | Enhanced | 48, 49 |
R = mRNA; P = protein; A = activity measured using the perfused human placenta; NA = not applicable
*
- bolded transporters are those that are likely to be functionally most important in transplacental transfer of drugs
#
- no change in expression/abundance with gestational age, per mg protein
^
- increase in expression/abundance with gestational age, per mg protein
+
- decrease in expression/abundance with gestational age, per mg protein.
Transporters with no symbol indicate that the data are not available. Reference 22 contains quantitative information for transporters.