Variability and Heritability of Thiamine Pharmacokinetics With Focus on OCT1 Effects on Membrane Transport and Pharmacokinetics in Humans.

Thiamine is substrate of the hepatic uptake transporter organic cation transporter 1 (OCT1), and pathological lipid metabolism was associated with OCT1-dependent thiamine transport. However, it is unknown whether clinical pharmacokinetics of thiamine is modulated by OCT1 genotype. We analyzed thiamine transport in vitro, thiamine blood concentrations after high-dose and low-dose (nutritional) intake, and heritability of thiamine and thiamine-phosphate blood concentrations. The variant OCT1*2 had reduced and OCT1*3 to OCT1*6 had deficient thiamine uptake activity. However, pharmacokinetics of thiamine did not differ depending on OCT1 genotype. Further studies in primary human hepatocytes indicated that several cation transporters, including OCT1, OCT3, and THTR-2, contribute to hepatic uptake of thiamine. As much as 54% of the variation in thiamine and 75% in variation of thiamine monophosphate plasma concentrations was determined by heritable factors. Apparently, thiamine is not useful as a probe drug for OCT1 activity, but the high heritability, particularly of thiamine monophosphate, may stimulate further genomic research.