Vitamin B6 Dependence of One-Carbon Metabolism - Full Text View

Purpose

Marginal vitamin B6 deficiency, which occurs commonly worldwide, leads to a cellular deficiency of the coenzyme pyridoxal phosphate (PLP). PLP is a coenzyme in several phases of one carbon (1C) metabolism, which is the array of reactions in which one carbon units are acquired and used in reactions including nucleotide synthesis, regeneration of methionine (Met) from homocysteine (Hcy), and methylation of many biological compounds. 1C metabolism is linked to the transsulfuration pathway in which Hcy undergoes PLP-dependent catabolism leading to cysteine, whose availability governs the formation of the antioxidant glutathione. Nutritional or genetic conditions that impair 1C metabolism are associated with elevation in plasma Hcy concentration and increased risk of vascular disease. It is believed that the metabolic effects of vitamin B6 deficiency will be most pronounced following protein intake when the vitamin B6-dependent pathways of amino acid metabolism experience the greatest substrate load. The human subjects protocols of this study consist of two distinct phases intended to extend our understanding of basic human 1C metabolism and the effects of marginal vitamin B6 deficiency under postprandial conditions. Phase 1 will investigate the effects of vitamin B6 nutrition on the PLP-dependent generation of 1C units by the glycine cleavage system and on the synthesis of glutathione. Phase 2 will investigate the dependence of methionine metabolism on vitamin B6 nutritional status, with particular emphasis on the recycling of Hcy to Met. Each phase of this study will involve 14 healthy, nutritionally adequate, young adults (7 male, 7 female) who will undergo metabolite profiling and kinetic analysis using intravenously infused stable isotopic tracers performed both before and after a ~4-week period of dietary vitamin B6 restriction. Subjects will be assigned to either Phase 1 or Phase 2, which will be identical in design except for the tracers and analytical methods used. We hypothesize that vitamin B6 deficiency will yield reduction in postprandial rates of homocysteine remethylation, generation of 1C units from glycine, and synthesis of glutathione. The results of this study will aid in assessing the consequences of nutritional and genetic variables affecting human metabolism and will further our understanding of the relationships between vitamin B6 nutrition and disease.

Condition	Intervention
Vitamin B6 Deficiency	Dietary Supplement: Arm 1 glycine and leucine Dietary Supplement: Arm 2 Intervention of Serine and methionine infusion

Study Type:	Interventional
Study Design:	Allocation: Non-Randomized Endpoint Classification: Pharmacokinetics Study Intervention Model: Single Group Assignment Masking: Open Label Primary Purpose: Diagnostic
Official Title:	Vitamin B6 Dependence of One-Carbon Metabolism

Resource links provided by NLM:

MedlinePlus related topics: B Vitamins

Drug Information available for: Glycine Serine Pyridoxine hydrochloride Racemethionine Leucine Methionine Pyridoxine Vitamin B Complex Amino acids

U.S. FDA Resources

Further study details as provided by University of Florida:

Primary Outcome Measures:

Hypothesis Aim 1 [ Time Frame: One year ] [ Designated as safety issue: No ]
(a) Vitamin B6 deficiency will reduce the rate of glycine turnover and interconversion with serine and will reduce the generation of 1C units by the glycine cleavage system. (b) Vitamin B6 deficiency will yield a reduced in vivo rate of erythrocyte glutathione synthesis.
Hypotheses Aim 2 [ Time Frame: 30 days ] [ Designated as safety issue: No ]
(a) Vitamin B6 deficiency will reduce the in vivo rate of generation of one-carbon units from serine and, thus, overall homocysteine remethylation. (b) In vivo rates of cysteine synthesis will be reduced in vitamin B6 deficiency. (c) Thymidylate synthesis from serine-derived one-carbon units will be reduced during vitamin B6 deficiency

Secondary Outcome Measures:

Hypotheses Aim 3 [ Time Frame: 30 days ] [ Designated as safety issue: No ]
(a) Vitamin B6 deficiency will yield increased plasma glycine, cystathionine and glutathione but decreased erythrocyte glutathione concentration. (b) Vitamin B6 deficiency will cause reduced activity of lymphocyte SHMT and the glycine cleavage system and reduced cellular (lymphocyte) glycine concentration..

Enrollment:	45
Study Start Date:	January 2008
Study Completion Date:	September 2010
Primary Completion Date:	September 2010 (Final data collection date for primary outcome measure)

Arms	Assigned Interventions
Experimental: Arm 1 glycine and leucine infusion Determine in healthy, adequately pyridoxine nourished humans using a protocol based on amino acid glycine tracer methods: (a) the postprandial rates of in vivo glycine turnover, glycine-based generation of one-carbon units, thymidylate and purine synthesis, and the impact of vitamin B6 deficiency on the rates of these processes and (b) the effect of vitamin B6 deficiency on the postprandial rate of glutathione synthesis. 14 subjects will be chosen after screening is complete and will begin a B6 deficient diet for 30 days. At the beginning and end of the 30 days they will receive an infusion of leucine and glycine then they will begin the four week diet. At the end of four weeks the infusion will be repeated.	Dietary Supplement: Arm 1 glycine and leucine Arm 1 glycine and leucine: A subset of 14 participants out of the total enrolled participants with an adequate nutritional status will undergo the tracer infusion of glycine and leucine amino acids protocol while an adequate vitamin pyridoxine, B6 status. After the first infusion each participant will then begin a diet low in vitamin B6 (<0.5 mg/d) for 4 weeks to achieve marginal B6 status followed by a repeat of fasting blood sampling and tracer infusion protocol. Other Names: Arm 1 glycine and leucine amino acids B6 leucine methionine deficieny
Experimental: Arm 2 Intervention of Serine and methionine infusion This arm will allow investigation of total Hcy remethylation and remethylation from serine-derived 1C units, kinetics of serine and the methionine cycle and kinetics of transsulfuration reactions. 14 healthy subjects will be selected and screened. Prior to starting a B6 deficient diet for four weeks an infusion of serine and methionine will commence. Following the first infusion the diet will begin and after four weeks another infusion will be done.	Dietary Supplement: Arm 2 Intervention of Serine and methionine infusion Arm 2 Intervention of Serine and methionine infusion: A subset of 14 participants out of the total enrolled participants. Received an adequate nutritional status will undergo the tracer infusion of methionine and serine amino acids protocol while in adequate vitamin pyridoxine, B6 status. After the first infusion each subject will then begin a diet low in vitamin B6 (<0.5 mg/d) for 4 weeks to achieve marginal B6 status followed by repeat of fasting blood sampling and tracer infusion protocol. Other Names: Arm 2 Intervention of Serine and methionine infusion B6 deficiency methionine serine

Arms

Assigned Interventions

Experimental: Arm 1 glycine and leucine infusion

Determine in healthy, adequately pyridoxine nourished humans using a protocol based on amino acid glycine tracer methods: (a) the postprandial rates of in vivo glycine turnover, glycine-based generation of one-carbon units, thymidylate and purine synthesis, and the impact of vitamin B6 deficiency on the rates of these processes and (b) the effect of vitamin B6 deficiency on the postprandial rate of glutathione synthesis. 14 subjects will be chosen after screening is complete and will begin a B6 deficient diet for 30 days. At the beginning and end of the 30 days they will receive an infusion of leucine and glycine then they will begin the four week diet. At the end of four weeks the infusion will be repeated.

Dietary Supplement: Arm 1 glycine and leucine

Arm 1 glycine and leucine: A subset of 14 participants out of the total enrolled participants with an adequate nutritional status will undergo the tracer infusion of glycine and leucine amino acids protocol while an adequate vitamin pyridoxine, B6 status. After the first infusion each participant will then begin a diet low in vitamin B6 (<0.5 mg/d) for 4 weeks to achieve marginal B6 status followed by a repeat of fasting blood sampling and tracer infusion protocol.

Other Names:

Arm 1 glycine and leucine
amino acids
B6
leucine
methionine
deficieny

Experimental: Arm 2 Intervention of Serine and methionine infusion

This arm will allow investigation of total Hcy remethylation and remethylation from serine-derived 1C units, kinetics of serine and the methionine cycle and kinetics of transsulfuration reactions. 14 healthy subjects will be selected and screened. Prior to starting a B6 deficient diet for four weeks an infusion of serine and methionine will commence. Following the first infusion the diet will begin and after four weeks another infusion will be done.

Dietary Supplement: Arm 2 Intervention of Serine and methionine infusion

Arm 2 Intervention of Serine and methionine infusion: A subset of 14 participants out of the total enrolled participants. Received an adequate nutritional status will undergo the tracer infusion of methionine and serine amino acids protocol while in adequate vitamin pyridoxine, B6 status. After the first infusion each subject will then begin a diet low in vitamin B6 (<0.5 mg/d) for 4 weeks to achieve marginal B6 status followed by repeat of fasting blood sampling and tracer infusion protocol.

Other Names:

Arm 2 Intervention of Serine and methionine infusion
B6 deficiency
methionine
serine

Show Detailed Description

Eligibility

Ages Eligible for Study:	20 Years to 40 Years
Genders Eligible for Study:	Both
Accepts Healthy Volunteers:	Yes

Criteria

Inclusion Criteria:

20-40 years of age
adequate vitamin B6 levels
not pregnant

Exclusion Criteria:

abnormal labs
pregnancy
on medications

Contacts and Locations

Please refer to this study by its ClinicalTrials.gov identifier: NCT00877812

Locations

United States, Florida
University of Florida
Gainesville, Florida, United States, 32611

Sponsors and Collaborators

University of Florida

National Institutes of Health (NIH)

Investigators

Principal Investigator:

Jesse F Gregory, PhD

University of Florida

More Information

Publications:

Lamers Y, Williamson J, Gilbert LR, Stacpoole PW, Gregory JF 3rd. Glycine turnover and decarboxylation rate quantified in healthy men and women using primed, constant infusions of [1,2-(13)C2]glycine and [(2)H3]leucine. J Nutr. 2007 Dec;137(12):2647-52.

Lamers Y, O'Rourke B, Gilbert LR, Keeling C, Matthews DE, Stacpoole PW, Gregory JF 3rd. Vitamin B-6 restriction tends to reduce the red blood cell glutathione synthesis rate without affecting red blood cell or plasma glutathione concentrations in healthy men and women. Am J Clin Nutr. 2009 Aug;90(2):336-43. doi: 10.3945/ajcn.2009.27747. Epub 2009 Jun 10.

Lamers Y, Williamson J, Ralat M, Quinlivan EP, Gilbert LR, Keeling C, Stevens RD, Newgard CB, Ueland PM, Meyer K, Fredriksen A, Stacpoole PW, Gregory JF 3rd. Moderate dietary vitamin B-6 restriction raises plasma glycine and cystathionine concentrations while minimally affecting the rates of glycine turnover and glycine cleavage in healthy men and women. J Nutr. 2009 Mar;139(3):452-60. doi: 10.3945/jn.108.099184. Epub 2009 Jan 21.

Responsible Party:	University of Florida
ClinicalTrials.gov Identifier:	NCT00877812 History of Changes
Other Study ID Numbers:	R01 D072398
Study First Received:	April 1, 2009
Last Updated:	March 25, 2013
Health Authority:	United States: Institutional Review Board

Keywords provided by University of Florida:

Vitamin B6
Vitamin B6 deficiency
Amino acids
pyridoxine

Additional relevant MeSH terms:

Vitamin B 6 Deficiency
Vitamin B Deficiency
Avitaminosis
Deficiency Diseases
Malnutrition
Nutrition Disorders
Glycine
Pyridoxine
Vitamin B 6
Pyridoxal

Vitamin B Complex
Vitamins
Glycine Agents
Neurotransmitter Agents
Molecular Mechanisms of Pharmacological Action
Pharmacologic Actions
Physiological Effects of Drugs
Micronutrients
Growth Substances

ClinicalTrials.gov processed this record on May 21, 2013