title: Elevated plasma 4-pyridoxic acid in renal insufficiency.
abstract: BACKGROUND
  Renal insufficiency is associated with altered vitamin B-6 metabolism. We have observed high concentrations of 4-pyridoxic acid, the major catabolite of vitamin B-6 metabolism, in plasma during renal insufficiency.
  
  
  OBJECTIVE
  The objective was to evaluate the renal handling of 4-pyridoxic acid and the effects of renal dysfunction on vitamin B-6 metabolism.
  
  
  METHODS
  We measured the renal clearance of 4-pyridoxic acid and creatinine in 17 nonpregnant, 17 pregnant, and 16 lactating women. We then examined the influence of vitamin B-6 or alkaline phosphatase activity on the ratio of 4-pyridoxic acid to pyridoxal (PA:PL) in plasma in 10 men receiving a low (0.4 mg pyridoxine.HCl/d) or high (200 mg pyridoxine.HCl/d) vitamin B-6 intake for 6 wk, in 10 healthy subjects during a 21-d fast, in 1235 plasma samples from 799 people screened for hypophosphatasia, and in 67 subjects with a range of serum creatinine concentrations.
  
  
  RESULTS
  Renal clearance of 4-pyridoxic acid was 232 +/- 94 mL/min in nonpregnant women, 337 +/- 140 mL/min in pregnant women, and 215 +/- 103 mL/min in lactating healthy women. These values were approximately twice the creatinine clearance, indicating that 4-pyridoxic acid is at least partially eliminated by tubular secretion. Elevated plasma creatinine concentrations were associated with marked elevations in 4-pyridoxic acid and PA:PL. PA:PL was not affected by wide variations in vitamin B-6 intake or by the wide range of pyridoxal-P concentrations encountered while screening for hypophosphatasia.
  
  
  CONCLUSIONS
  Plasma 4-pyridoxic acid concentrations are markedly elevated in renal insufficiency. Plasma PA:PL can distinguish between increases in 4-pyridoxic acid concentrations due to increased dietary intake and those due to renal insufficiency.
authors.affiliation: Department of Biochemistry, Fort Wayne State Developmental Center, Fort Wayne, IN 46835, USA. coburn@ipfw.edu
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Coburn
authors.forename: Robert D
authors.initials: RD
authors.lastname: Reynolds
authors.forename: J Dennis
authors.initials: JD
authors.lastname: Mahuren
authors.forename: Wayne E
authors.initials: WE
authors.lastname: Schaltenbrand
authors.forename: Yao
authors.initials: Y
authors.lastname: Wang
authors.forename: Karen L
authors.initials: KL
authors.lastname: Ericson
authors.forename: Michael P
authors.initials: MP
authors.lastname: Whyte
authors.forename: Yvonne M
authors.initials: YM
authors.lastname: Zubovic
authors.forename: Paula J
authors.initials: PJ
authors.lastname: Ziegler
authors.forename: David L
authors.initials: DL
authors.lastname: Costill
authors.forename: William J
authors.initials: WJ
authors.lastname: Fink
authors.forename: David R
authors.initials: DR
authors.lastname: Pearson
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Pauly
authors.forename: K George
authors.initials: KG
authors.lastname: Thampy
authors.forename: Jacobo
authors.initials: J
authors.lastname: Wortsman
mesh_terms: D000328:Adult; D000469:Alkaline Phosphatase / Q000378:metabolism; D003404:Creatinine / Q000378:metabolism; D005260:Female; D006801:Humans; D007774:Lactation / Q000378:metabolism*; D008297:Male; D011247:Pregnancy; D011735:Pyridoxic Acid / Q000097:blood*; D051437:Renal Insufficiency / Q000378:metabolism*; D025101:Vitamin B 6 / Q000378:metabolism*
chemical_list: D011735:Pyridoxic Acid; D025101:Vitamin B 6; D003404:Creatinine; D000469:Alkaline Phosphatase