Table 1.

Overview of the main characteristics of human thyroid hormone transporters.

Transporter	Gene Name	Substrates Uptake	Substrates Efflux	Expression and Tissue Distribution	Relevance for Thyroid Hormone Physiology	Reference
MCT8	SLC16A2	T3, T4 > rT3 > 3, 3′-T2	T3, T4	Ubiquitously (including brain, eye, liver, kidney, muscle)	MCT8 deficiency (Allan-Herndon-Dudley syndrome)	[9,13,14,15]
MCT10	SLC16A10	T3 >> T4	T3	Ubiquitously (including liver, kidney, pancreas, placenta, heart, lung, stomach, brain)	Unknown	[9,14,16,17,18]
LAT1	SLC7A5	3, 3′-T2 > rT3 > T3 > T4	3, 3′-T2	Brain, liver, placenta, spleen	Unknown	[9,16,19]
LAT2	SLC7A8	3, 3′-T2 > T3	No	Ubiquitously (including eye, kidney, lung, pancreas, placenta, skin, spleen, stomach)	Unknown	[9,20,21,22,23]
NTCP	SLC10A1	T3S, T4S > T3, T4	No	Liver	Unknown	[9,24,25,26]
SLC17A4	SLC17A4	T3, T4 > rT3	T3, T4	Intestine, liver	SNP associated with serum FT4 concentrations	[9,27,28]
OATP1A2	SLCO1A2	T3 > rT3, T4, T3S, rT3S, T4S	Unknown	Brain, gonad	SNPs associated with higher T3 or T4S concentration	[9,29,30]
OATP1B1	SLCO1B1	T3, T4	Unknown	Liver	SNP associated with serum FT4 concentrations	[9,31]
OATP1B3	SLCO1B3	T3, T4	Unknown	Liver	SNP associated with serum FT4 concentrations	[9,31]
OATP1C1	SLCO1C1	T4, T4S, rT3	Unknown	Brain	OATP1C1 deficiency	[9,32,33]
OATP2B1	SLCO2B1	T4	Unknown	Liver, brain, intestine, lung, placenta, spleen	Unknown	[9,29,30]
OATP3A1	SLCO3A1	T4	Unknown	Brain, heart, skin, spleen	Unknown	[9,34,35]
OATP4A1	SLCO4A1	T3 > T4, rT3	Unknown	Amnion, placenta	Unknown	[9,29]
OATP4C1	SLCO4C1	T3, T4	Unknown	Kidney, liver	Unknown	[9,35,36]
ABCB1	ABCB1	Unknown	T3	Heart, liver, placenta	SNP associated with serum FT4 concentrations	[9,37,38]

The (sulfated) iodothyronine substrates of the transporters are listed and > indicates substrate preference. Expression and tissue distribution in human fetal tissues were summarized from Supplementary Figure S1. SNP: single nucleotide polymorphism; FT4: free T4.