Vitamin B-6 exists in different forms; one of those forms, pyridoxal 5'-phosphate (PLP), serves a cofactor in many enzyme reactions, including the transsulfuration pathway, in which homocysteine is converted to cystathionine and then to cysteine.

Is supplementation with Pyridoxal 5 Phosphate necessary? Based on my initial review of the medical literature, it appears that P5P supplements may not be needed by most individuals since regular vitamin B6 supplementation raises levels of P5P. However, there may be rare individuals who have a deficiency in enzymes that convert pyridoxine into pyridoxal 5 phosphate, and hence may benefit from P5P supplementation. For the role of B vitamins in mind enhancement, see memory.

Benefit of Pyridoxine
Pyridoxine (vitamin B6) is a co-factor in many enzymatic pathways involved in amino acid metabolism: the main biologically active form is pyridoxal 5-phosphate. Pyridoxine has been used as an antidote in acute intoxications, including isoniazid overdose, Gyromitra mushroom or false morrel (monomethylhydrazine) poisoning and hydrazine exposure. It is also recommended as a co-factor to improve the conversion of glyoxylic acid into glycine in ethylene glycol poisoning. Other indications are recommended by some sources (for example crimidine poisoning, zipeprol and theophylline-induced seizures, adjunct to d-penicillamine chelation), without significant supporting data.

Pyridoxal 5 Phosphate Research Update
Inherited disorders of neurotransmitters in children and adults.
Clin Biochem. 2005 Nov 17; Pearl PL, Capp PK, Novotny EJ, Gibson KM.
Department of Neurology, Children's National Medical Center, George Washington University School of Medicine and Health Sciences, Washington, DC
Inherited disorders of neurotransmitters are a group of neurometabolic syndromes attributable to a primary disturbance of neurotransmitter metabolism or transport. This is an enlarging group of recognized disorders requiring specialized diagnostic procedures for detection. This review considers clinical disorders of biopterin, catecholamines, serotonin, glycine, pyridoxine, and GABA metabolism. Newly described syndromes such as cerebral folic acid deficiency and pyridoxal-5-phosphate dependency are included. The disorders of the metabolic pathways of biopterin, catecholamines, and serotonin are linked due to their common synthetic components. Glycine encephalopathy represents an enlarging phenotype related to abnormalities of the glycine degradative cleavage system. Both pyridoxine and pyridoxal-5-phosphate dependency need to be considered in refractory neonatal seizures. The most common disorder of GABA metabolism is SSADH deficiency, which has a broad phenotype of mental retardation, epilepsy, ataxia, and hyporeflexia and which invokes the combined problems of elevated brain GABA and GHB.

Pyridoxine supplementation corrects vitamin B6 deficiency but does not improve inflammation in patients with rheumatoid arthritis.
Arthritis Res Ther. 2005;7(6):R1404-11. Epub 2005 Oct 14.
Patients with rheumatoid arthritis have subnormal vitamin pyridoxine B6 status, both quantitatively and functionally. Abnormal vitamin B6 status in rheumatoid arthritis has been associated with spontaneous tumor necrosis factor (TNF)-alpha production and markers of inflammation, including C-reactive protein and erythrocyte sedimentation rate. Impaired vitamin B6 status could be a result of inflammation, and these patients may have higher demand for vitamin B6. The aim of this study was to determine if daily supplementation with 50 mg of pyridoxine for 30 days can correct the static and/or the functional abnormalities of vitamin B6 status seen in patients with rheumatoid arthritis, and further investigate if pyridoxine supplementation has any effects on the pro-inflammatory cytokine TNF-alpha or IL-6 production of arthritis. This was a double-blinded, placebo-controlled study involving patients with rheumatoid arthritis with plasma pyridoxal 5 phosphate below the 25th percentile of the Framingham Heart Cohort Study. Vitamin B6 status was assessed via plasma and erythrocyte pyridoxal 5 phosphate concentrations, the erythrocyte aspartate aminotransferase activity coefficient (alphaEAST), net homocysteine increase in response to a methionine load test (DeltatHcy), and 24 h urinary xanthurenic acid (XA) excretion in response to a tryptophan load test. Urinary 4-pyridoxic acid (4-PA) was measured to examine the impact of pyridoxine treatment on vitamin B6 excretion in these patients. Pro-inflammatory cytokine (TNF-alpha and IL-6) production, C-reactive protein levels and the erythrocyte sedimentation rate before and after supplementation were also examined. Pyridoxine supplementation significantly improved plasma and erythrocyte pyridoxal 5 phosphate concentrations, erythrocyte alphaEAST, urinary 4-PA, and XA excretion. These improvements were apparent regardless of baseline B6 levels. Pyridoxine supplementation also showed a trend towards a reduction in post-methionine load DeltatHcy. Supplementation did not affect pro-inflammatory cytokine production. Although pyridoxine supplementation did not suppress pro-inflammatory cytokine production in patients with rheumatoid arthritis, the suboptimal vitamin B6 status seen in rheumatoid arthritis can be corrected by 50 mg pyridoxine supplementation for 30 days. Data from the present study suggest that patients with rheumatoid arthritis may have higher requirements for vitamin B6 than those in a normal healthy population.

PLP and PMP radicals: a new paradigm in coenzyme B6 chemistry.
Bioorg Chem. 2001 Aug;29(4):234-57. Agnihotri G, Liu HW.
Division of Medicinal Chemistry, College of Pharmacy, University of Texas, Austin, Texas 78712
Enzymes frequently rely on a broad repertoire of cofactors to perform chemically challenging transformations. The B6 coenzymes, composed of pyridoxal 5 phosphate ( PLP ) and pyridoxamine 5'-phosphate (PMP), are used by many transaminases, racemases, decarboxylases, and enzymes catalyzing alpha,beta and beta,gamma-eliminations. Despite the variety of reactions catalyzed by B6-dependent enzymes, the mechanism of almost all such enzymes is based on their ability to stabilize high-energy anionic intermediates in their reaction pathways by the pyridinium moiety of PLP/PMP. However, there are two notable exceptions to this model, which are discussed in this article. The first enzyme, lysine 2,3-aminomutase, is a PLP-dependent enzyme that catalyzes the interconversion of L-lysine to L-beta-lysine using a one-electron-based mechanism utilizing a [4Fe-4S] cluster and S-adenosylmethionine. The second enzyme, CDP-6-deoxy-L-threo-D-glycero-4-hexulose-3-dehydrase, is a PMP-dependent enzyme involved in the formation of 3,6-dideoxysugars in bacteria. This enzyme also contains an iron-sulfur cluster and uses a one-electron based mechanism to catalyze removal of a C-3 hydroxy group from a 4-hexulose. In both cases, the participation of free radicals in the reaction pathway has been established, placing these two B6-dependent enzymes in an exclusive class by themselves.

Inhibition of acetyl-CoA carboxylase isoforms by pyridoxal phosphate.
J Biol Chem. 2005 Oct 25; Lee WM, Elliott JE, Brownsey RW.
Biochemistry & Molecular Biology, University of British Columbia, Vancouver, B.C. V6T 1Z3.
Mammalian isoforms of acetyl-CoA carboxylase (ACC-1 and ACC-2) play important roles in synthesis, elongation and oxidation of long-chain fatty acids; the possible significance of ACC in the development of obesity having led to interest in development of inhibitors. Here, we demonstrate that pyridoxal phosphate (PLP) is a linear and reversible inhibitor of ACC-1 and ACC-2. ACC from rat liver and white adipose tissue (largely ACC-1) exhibited an IC(50) of ~200muM while ACC-2 from heart or skeletal muscle exhibited an IC(50) exceeding 500muM.

Clinical vitamin B6 analysis: an interlaboratory comparison of pyridoxal 5'-phosphate measurements in serum.
Clin Chem. 2005 Jul;51(7):1223-31. Rybak ME, Jain RB, Pfeiffer CM.
Inorganic Toxicology and Nutrition Branch, Division of Laboratory Sciences, National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, GA 30341, USA.
Recent investigations into the role vitamin B(6) plays in reducing risk of stroke and cardiovascular disease have heightened interest in vitamin B(6) intake and its relationship to clinical status indicators. Because a true reference method and certified reference materials are lacking, little is known about the relative analytical performance of clinical vitamin B(6) assays. METHODS: Ten laboratories experienced in clinical vitamin B(6) analysis participated in a 3-day analysis of 69 serum and 3 aqueous specimens for pyridoxal 5'-phosphate (PLP). Laboratories used either HPLC-based or enzymatic assays. CONCLUSION: Agreement among vitamin B(6) methods is good, but large differences in laboratory proficiency exist, pointing to the need for vitamin B(6) reference materials and external quality assurance programs.

Plasma vitamin B6 vitamers before and after oral vitamin B6 treatment: a randomized placebo-controlled study.
Clin Chem. 2003 Jan;49(1):155-61.
Department of Clinical Biochemistry AKH, Aarhus University Hospital, Norrebrogade 44, DK-8000 Aarhus C, Denmark
Vitamin B(6) has attracted renewed interest because of its role in homocysteine metabolism and its possible relation to cardiovascular risk. We examined the plasma B(6) vitamers, pyridoxal 5'-phosphate (PLP), pyridoxal (PL), pyridoxine (PN), and 4-pyridoxic acid (4-PA) before and after vitamin B(6) supplementation. METHODS: Patients (n = 90; age range, 38-80 years) undergoing coronary angiography (part of the homocysteine-lowering Western Norway B-Vitamin Intervention Trial) were allocated to the following daily oral treatment groups: (A), vitamin B(12) (0.4 mg), folic acid (0.8 mg), and vitamin B(6) (40 mg); (B), vitamin B(12) and folic acid; (C), vitamin B(6); or (D), placebo. EDTA blood was obtained before treatment and 3, 14, 28, and 84 days thereafter. RESULTS: Before treatment, PLP (range, 5-111 nmol/L) and 4-PA (6-93 nmol/L) were the predominant B(6) vitamers identified in plasma. During the 84-day study period, the intraindividual variation (CV) in patients not treated with vitamin B(6) (groups B and D) was 45% for PLP and 67% for 4-PA. Three days after the start of treatment, the increases in concentration were approximately 10-, 50-, and 100-fold for PLP, 4-PA, and PL, respectively. No significant additional increase was observed at the later time points. The PLP concentration correlated to the concentrations of 4-PA and PL before treatment, but not after treatment. The PL concentration correlated with 4-PA before and after treatment. CONCLUSIONS: Vitamin B(6) treatment has an immediate effect on the concentrations and the forms of B(6) vitamers present in plasma, and the changes remain the same during prolonged treatment. Our results suggest that the B(6) vitamers in plasma reflect vitamin B(6) intake.

Pyridoxine deficiency by bariatric surgery
Three months after undergoing Roux-en-Y bariatric surgery, a 32-year-old woman presented with glossitis, angular cheilitis, and an erythematous, desquamative dermatitis with a distribution indicative of photosensitivity causing a burning sensation on her arms and around her neck (Panel A). She reported a 45-kg (100-lb) weight loss during the past four months and no diarrhea or neurologic symptoms. Pellagra was suspected because of the classic appearance of Casal's necklace (i.e., erythema, hyperpigmentation, and scales around the neck) (Panel B). Laboratory studies were notable for a plasma pyridoxine level of 0.6 ng per milliliter (2.4 nmol per liter; normal range, 5 to 10).

P5P information and emails
Q. Can you give me information about P-5-P. I use both your MultiVit Rx and R-Lipoic Acid. I have Type II diabetes. Thanks very much.
     A. As you can see from the pyridoxal 5 phosphate studies above, supplementation with vitamin B6 raises P5P levels, so it is unclear whether P5P supplements need to be taken unless in individuals who do not have the biochemical ability to convert vitamin B6 to P5P, and this is a rare occurrence.

Q. I read your web page on P5P and Vitamin B6 with interest. Are you aware of the research done on pyloruria and Vitamin B6? Here is a web page which discusses it. http://drkaslow.com/html/pyroluria.html. I have not yet had the urine testing done, but I plan to do so (My doctor is skeptical, but then she has been about many things over the years that have turned out to have some basis in reality -- e.g., when I talked to her 15 years ago about homocysteine levels. And some years ago when I thought a low carb diet would allow me to lose weight, she disagreed. She has finally surrendered her "granola" credo as not a one-size-fits-all way to eat. The sweating and low grade fever I experience after a carb heavy meal disappear if I stick to proteins and 5% carb veggies). According to the Pfeiffer Institute, as many as 40% of alcoholics may suffer from this disorder. I think they established this by testing lots of AA members.
Here's a snip from the link above: "Pyroluria is a genetically determined chemical imbalance involving an abnormality in hemoglobin synthesis. Hemoglobin is the protein that holds iron in the red blood cell. Individuals with this disorder produce too much of a byproduct of hemoglobin synthesis called "kryptopyrrole" (KP) or "hemepyrrole." Kryptopyrrole has no known function in the body, and is excreted in urine. Kryptopyrrole has binds to pyridoxine (vitamin B6) and zinc and makes them unavailable for their important roles of co-factors in enzymes and metabolism.
These essential nutrients when bound to kryptopyrrole are removed from the bloodstream and excreted into the urine as pyrroles. Arachidonic acid (an omega-6 fatty acid) is also deficient."
   I suspect this imbalance may worsen with age. But that's just my humble opinion. Anyway, I intuit that the ability to metabolize B6 may be more common than realized. The Irish hospitals did a study on it many years ago. A good
percentage of neonates were found to be deficient in B6 back then, but they weren't sure what that would lead to. For me, being of Celtic origin on both sides of my family as far back as the banshees, it goes a far way in explaining
Ireland's alcohol curse -- i.e., self-medicating.
   A. I have not studied this topic in enough detail to have a strong opinion.