Table 1.

ABC and SLC transporters possibly involved in neurosteroid transport in the brain.

Transporter	CNS expression (mRNA and protein analysis)	CNS localization (immunohistochemistry)	Steroid substrates (Km value)
ABC Transporters
BCRP (ABCG2)	mRNA: - Total brain1 - Isolated brain microvessels (BMV)2,3 Protein: - BMV (H, M, Mo, R, P)4,5,6,7,8 - Isolated CP9	BBB: apical (luminal) (H, R); CP: apical (H, R)2,10,11	E1-3-S (6.8 μM)12,13 DHEAS12 DHT14
MRP1 (ABCC1)	mRNA: - Total brain1 - BMV3 - Isolated CP15 Protein: - Isolated CP (H, R)9,16	BBB: apical (H, B, M), Basal (abluminal) (R, M); CP: basal (H, R)17,18,19,20	E1-3-S (+GSH)21 DHEAS (+GSH) (5 μM)22 E2-17βG (1.5 μM)23
MRP4 (ABCC4)	mRNA: - Total brain1 - BMV3 - Isolated CP15 Protein: - BMV (H, M, Mo, R)4,5,6,7 - Isolated CP9	BBB: apical (H, M, R), Apical + basal (B); CP: basal (H, R); Astrocytes3,11,19,20,24	DHEAS (2 μM)22 E2-17βG (30 μM)22,25
MRP8 (ABCC11)	mRNA: - Total brain1	Neurons (axonal; cerebellum, cortex)26	E1-3-S (>150 μM)27 DHEAS (13–21 μM)26,27 E2-17βG (63 μM)27
SLC Transporters
OATP1A2 (SLCO1A2)	mRNA: - Total brain1 Protein: - BMV (M, Mo)5,6	BBB: luminal; amacrine neurons28,29,30,31	DHEAS (7 μM)32 E1-3-S (16 μM)31
OATP2B1 (SLCO2B1)	mRNA: - Total brain1 Protein: - Brain capillary cells31 - BMV (M)6	BBB: luminal; CP (ependymal cells) (R); amacrine neurons11,29,30,33	E1-3-S (5–21 μM)34,35 DHEAS (9 μM)35 PregS36
OATP3A1 (SLCO3A1)	mRNA: - Total brain1 Protein: - Isolated CP9 - BMV (P)8	CP; neurons37	E1-3-S38
OAT3 (SLC22A3)	mRNA: - Total brain1 Protein: - Isolated CP9 - BMV (R)7	BBB: basal (R); CP: basal (H, R)39,40,11,41	E1-3-S (8.8 μM)42 DHEAS42
OSTα-OSTβ (SLC51A/B)		Neurons (cerebellum, Hippocampus; Purkinje cells)43	DHEAS (1.5 μM)43 PregS (6.9 μM)43

Unless otherwise specified, the data refer to human tissue and transporter protein. B, bovine; BBB, blood–brain barrier (capillary endothelial cells); BMV, isolated brain microvessels; CP, choroid plexus; DHEAS, dehydroepiandrosterone sulfate; DHT, dihydrotestosterone; E₁-3-S, estrone-3-sulfate; E₂-17βG, estradiol-17 β-glucuronide; H, human; M, mouse; Mo, monkey; P, pig; R, rat; PregS, pregnenolone sulfate. ¹Nishimura and Naito, 2005; ²Cooray et al., 2002; ³Warren et al., 2009; ⁴Shawahna et al., 2011; ⁵Ito et al., 2011; ⁶Uchida et al., 2011; ⁷Hoshi et al., 2013; ⁸Kubo et al., 2015; ⁹Uchida et al., 2015; ¹⁰Aronica et al., 2005; ¹¹Roberts et al., 2008a; ¹²Grube et al., 2007; ¹³Imai et al., 2003; ¹⁴Huss et al., 2005; ¹⁵Niehof and Borlak, 2009; ¹⁶Gazzin et al., 2008; ¹⁷Rao et al., 1999; ¹⁸Wijnholds et al., 2000; ¹⁹Nies et al., 2004; ²⁰Zhang et al., 2004; ²¹Qian et al., 2001; ²²Zelcer et al., 2003; ²³Jedlitschky et al., 1996; ²⁴Leggas et al., 2004; ²⁵Chen et al., 2001; ²⁶Bortfeld et al., 2006; ²⁷Chen et al., 2005; ²⁸Gao et al., 2000; ²⁹Bronger et al., 2005; ³⁰Gao et al., 2015; ³¹Lee et al., 2005; ³²Kullak-Ublick et al., 1998; ³³Ji et al., 2012; ³⁴Pizzagalli et al., 2003; ³⁵Hagenbuch and Stieger, 2013; ³⁶Grube et al., 2006; ³⁷Huber et al., 2007; ³⁸Tamai et al., 2000; ³⁹Alebouyeh et al., 2003; ⁴⁰Kikuchi et al., 2003; ⁴¹Mori et al., 2003; ⁴²Burckhardt, 2012; ⁴³Fang et al., 2010.