Mechanism and regulation of human intestinal niacin uptake
Open Access
- 1 July 2005
- journal article
- Published by American Physiological Society in American Journal of Physiology-Cell Physiology
- Vol. 289 (1), C97-C103
- https://doi.org/10.1152/ajpcell.00009.2005
Abstract
The mechanism of uptake of dietary niacin (nicotinic acid) by intestinal epithelial cells is not well understood, and nothing is known about regulation of the uptake process. In this investigation, we used human-derived intestinal epithelial Caco-2 cells and purified intestinal brush-border membrane vesicles (BBMVs) isolated from human organ donors to assess niacin uptake. Our findings show niacin uptake by Caco-2 cells to be 1) temperature and energy dependent; 2) Na+independent, but highly dependent on extracellular acidic pH; 3) saturable as a function of concentration, with an apparent Kmof 0.53 ± 0.08 μM; 4) severely inhibited by the membrane-impermeable sulfhydryl group of reagents; and 5) highly specific for niacin but not affected by monocarboxylic acids. A marked trans stimulation in [3H]niacin efflux from preloaded Caco-2 cells by unlabeled niacin in the incubation buffer was also observed. These findings suggest the involvement of a specialized, pH-dependent, carrier-mediated mechanism for human intestinal niacin uptake. This suggestion was confirmed in studies with native human intestinal BBMVs. We also examined possible regulation of niacin uptake by Caco-2 cells via specific intracellular regulatory pathways. The results show that while the PKA-, PKC-, and Ca2+/calmodulin-mediated regulatory pathways play no role in regulating niacin uptake, a role for a protein tyrosine kinase (PTK)-mediated pathway is apparent. The results of these studies show for the first time the existence of a specialized, acidic pH-dependent, carrier-mediated system of niacin uptake by human intestinal epithelial cells that operates at the micromolar (physiological) range of niacin. The results also suggest the possible involvement of a PTK-mediated pathway in the regulation of niacin uptake.Keywords
This publication has 20 references indexed in Scilit:
- Management of the metabolic syndrome—nicotinic acidEndocrinology and Metabolism Clinics of North America, 2004
- Mechanism and regulation of folate uptake by human pancreatic epithelial MIA PaCa-2 cellsAmerican Journal of Physiology-Cell Physiology, 2004
- Expression and functional contribution of hTHTR-2 in thiamin absorption in human intestineAmerican Journal of Physiology-Gastrointestinal and Liver Physiology, 2004
- Molecular Identification of High and Low Affinity Receptors for Nicotinic AcidPublished by Elsevier BV ,2003
- Nicotinic Acid Transport Mediated by pH-dependent Anion Antiporter and Proton Cotransporter in Rabbit Intestinal Brush-border MembraneJournal of Pharmacy and Pharmacology, 1996
- Carrier-mediated uptake of nicotinic acid by rat intestinal brush-border membrane vesicles and relation to monocarboxylic acid transport.Journal of Pharmacobio-Dynamics, 1990
- Absorption of nicotinic acid and nicotinamide from rat small intestine in vitroBiochimica et Biophysica Acta (BBA) - Biomembranes, 1980
- NIACIN AND NIACINAMIDE TRANSPORT IN THE CENTRAL NERVOUS SYSTEM. IN VIVO STUDIESJournal of Neurochemistry, 1979
- GI Absorption of Niacin in HumansJournal of Pharmaceutical Sciences, 1977
- Nicotinic acid active transport by in vitro bullfrog small intestineBiochimica et Biophysica Acta (BBA) - Biomembranes, 1974