Thiamine uptake in human intestinal biopsy specimens, including observations from a patient with acute thiamine deficiency

Mucosal biopsy specimens obtained by routine endoscopy from 108 human subjects, including one patient with thiamine deficiency, were incubated at 37 °C in oxygenated calcium-free Krebs-Ringer solution (pH 7.5) containing tritiated thiamine and [¹⁴C]dextran as a marker of adherent mucosal water. The amount of labeled thiamine taken up was measured radiometrically. In subjects with no clinical evidence of thiamine deficiency, 1) thiamine uptake by duodenal mucosa had a hyperbolic time course, reaching equilibrium at 10 min; 2) thiamine concentrations <2.5 μmol/L were taken up predominantly by a saturable mechanism displaying Michaelis-Menten kinetics (K(m) 4.4 μmol/L and J(max) 2.3 pmol · mg wet tissue^-1 · 6 min^-1), whereas higher concentrations were taken up by passive diffusion; 3) thiamine transport had different capacities along the gastrointestinal tract (duodenum >> colon > stomach); and 4) thiamine uptake was competitively inhibited in the duodenum by thiamine analogs, albeit with a different order of potency compared with rats, and was blocked by 2,4-dinitrophenol. In the thiamine-deficient patient, the duodenal saturable uptake was increased, with higher K(m) and J(max) values. In conclusion, physiologic concentrations of thiamine were transported in human small intestine by a specific mechanism dependent on cellular metabolism, whose transporters appear to be down-regulated.