Uptake of N-(4'-pyridoxyl)amines and release of amines by renal cells: a model for transporter-enhanced delivery of bioactive compounds.
The importing of vitamin B6 by renal proximal tubular cells from the rat is facilitated and Na(+)-dependent and reflects specificity for the meta-phenolate pyridinium structure with a 5-hydroxymethyl function. This transporter can, however, accept competitively each of the natural nonphosphorylated vitamers (pyridoxine, pyridoxamine, and pyridoxal) and other B6 analogues differing only in the groups at position 4. A series of N-(4'-pyridoxyl)amines was synthesized by sodium borohydride or boro[3H]hydride reduction of aldimines formed by condensing the amines with pyridoxal. The unlabeled B6-secondary amine compounds were found to competitively inhibit the uptake of [4'-3H]pyridoxine by the renal cells. Moreover, the 3H-labeled N-(4'-pyridoxyl)amines were shown to enter the cells by the process facilitated by the B6 transporter. Upon entry the labeled compounds were converted to N-(5'-phospho-4'-pyridoxyl)amines in a reaction catalyzed by pyridoxal kinase, an enzyme that tolerates considerable functional variation in position 4 of the B6 structure. The 5'-phosphates were subsequently converted within the cell to pyridoxal 5'-phosphate with liberation of the original amine in a reaction catalyzed by pyridoxamine (pyridoxine) 5'-phosphate oxidase, an enzyme with broad specificity for 4'-substituted amines on the 5'-phospho-B6 structure. This system illustrates how knowledge of transporter specificity can permit design of a compound with potential biologic activity. A drug or other intracellular effector may be piggybacked onto a transported solute (e.g., vitamin or other nutrient) that gains facilitated entry to a cell and is, thereafter, metabolized to release the active compound.
Zhang
Z M
ZM
Department of Biochemistry, Emory University, Atlanta, GA 30322.
McCormick
D B
DB
D000588:Amines / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D001711:Biotransformation; D002352:Carrier Proteins / Q000378:metabolism*; D066298:In Vitro Techniques; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D015394:Molecular Structure; D011733:Pyridoxamine / Q000494:pharmacology; D011736:Pyridoxine / Q000031:analogs & derivatives* / Q000378:metabolism* / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
D000588:Amines; D002352:Carrier Proteins; D011733:Pyridoxamine; D011736:Pyridoxine