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==What is Vitamin B₆ (Pyridoxine)?==

==What is Vitamin B₆ (Pyridoxine)?==

Vitamin B₆, also commonly called '''pyridoxine''', is an '''essential water-soluble vitamin''' used as a [[Nutrition Glossary#Cofactor|cofactor]] in a number of enzymatic reactions. Vitamin B₆ in the diet is found as pyridoxine, pyridoxal, and pyridoxamine all of which are hydrolysed by a phosphatase before absorption across the intestinal mucosa by [[Diffusion - Physiology|passive diffusion]]. Once within the enterocyte the hydrolysed vitamin B₆ derivative is phosphorylated by pyridoxine kinase and transported to the [[Liver - Anatomy & Physiology|liver]] for continued metabolism to its '''active form, pyridoxal-5-phosphate (PLP)'''. In the liver PLP is bound to [[albumin]] and then transported to target tissues. Large concentrations of pyridoxine are found in [[Muscle Development - Anatomy & Physiology|muscle]], but this depot is not available during periods of Vitamin B₆ deficiency and is only released during muscle catabolism. Vitamin B₆ derivatives are freely filtered by the [[Nephron Microscopic Anatomy#Proximal Tubule|renal tubules]].  

Vitamin B₆, also commonly called '''pyridoxine''', is an '''[[Nutrition Glossary#Essential Nutrients|essential]] water-soluble vitamin''' used as a [[Nutrition Glossary#Cofactor|cofactor]] in a number of enzymatic reactions. Vitamin B₆ in the diet is found as pyridoxine, pyridoxal, and pyridoxamine all of which are hydrolysed by a phosphatase before absorption across the intestinal mucosa by [[Diffusion - Physiology|passive diffusion]]. Once within the enterocyte the hydrolysed vitamin B₆ derivative is phosphorylated by pyridoxine kinase and transported to the [[Liver - Anatomy & Physiology|liver]] for continued metabolism to its '''active form, pyridoxal-5-phosphate (PLP)'''. In the liver PLP is bound to [[albumin]] and then transported to target tissues. Large concentrations of pyridoxine are found in [[Muscle Development - Anatomy & Physiology|muscle]], but this depot is not available during periods of Vitamin B₆ deficiency and is only released during muscle catabolism. Vitamin B₆ derivatives are freely filtered by the [[Nephron Microscopic Anatomy#Proximal Tubule|renal tubules]].

==Why is it Important?==

==Why is it Important?==

The active form of Vitamin B₆, PLP, participates in a number of reactions involving amino acid metabolism (e.g., aminotransferases, decarboxylases, racemizations) as well as various synthetic pathways and gluconeogenesis.  

The active form of Vitamin B₆, PLP, participates in a number of reactions involving amino acid metabolism (e.g. aminotransferases, decarboxylases, racemizations) as well as various synthetic pathways and gluconeogenesis.

==Roles in the Body==

==Roles in the Body==

Vitamin B₆ as PLP is an essential cofactor for glycogen phosphorylase during gluconeogenesis. It is also a cofactor in serine palmitoyl transferase used sphingolipid synthesis, a cofactor in γ-aminolevulinic acid synthentase, the first and rate-limiting step in heme synthesis. PLP is also required for synthesis of [[Taurine - Nutrition|taurine]], dopamine, histamine, and norepinephrine, and is involved in multiple steps in the conversion of [[Tryptophan - Nutrition|tryptophan]] to [[Vitamin B3 (Niacin) - Nutrition|niacin]]<ref>Shane B. Folic Acid, Vitamin B12, and Vitamin B6. In Biochemical and physiological aspects of human nutrition. 2000 Philadelphia, PA: WB Saunders Company p. 511-518.</ref>.  

Vitamin B₆ as PLP is an essential cofactor for glycogen phosphorylase during gluconeogenesis. It is also a cofactor in serine palmitoyl transferase used sphingolipid synthesis, a cofactor in γ-aminolevulinic acid synthentase, the first and rate-limiting step in [[Erythrocytes#Function|heme]] synthesis. PLP is also required for synthesis of [[Taurine - Nutrition|taurine]], dopamine, histamine, and norepinephrine, and is involved in multiple steps in the conversion of [[Tryptophan - Nutrition|tryptophan]] to [[Vitamin B3 (Niacin) - Nutrition|niacin]]<ref>Shane B. Folic Acid, Vitamin B12, and Vitamin B6. In Biochemical and physiological aspects of human nutrition. 2000 Philadelphia, PA: WB Saunders Company p. 511-518.</ref>.

==Consequences of Vitamin B₆ Deficiency==

==Consequences of Vitamin B₆ Deficiency==

====Dogs:====  

====Dogs:====  

Induced vitamin B₆ deficiency has been reported to cause anorexia, weight loss, and microcytic hypo chromic [[Regenerative and Non-Regenerative Anaemias|anaemia]] in puppies, and if left untreated could result in death. Ataxia, hematochezia, seizures, muscle fasciculations, cardiac dilation and hypertrophy of both the left and right auricles and ventricles (with more pronounced changes to the right), and demyelination of peripheral nerves have also been described in adult dogs fed Vitamin B₆ deficient diets<ref>National Research Council (NRC). Vitamins. In Nutrient Requirements for Dogs and Cats. 2006 Washington, DC: National Academies Press p.218-220.</ref><ref>Street HR, et al. Observations on vitamin B6 deficiency in the dog. J Nutr 1941;21:275-290</ref>.

Induced vitamin B₆ deficiency has been reported to cause anorexia, weight loss, and microcytic hypo chromic [[Regenerative and Non-Regenerative Anaemias|anaemia]] in puppies, and if left untreated could result in death. Ataxia, hematochezia, [[seizures]], muscle fasciculations, cardiac dilation and hypertrophy of both the left and right auricles and ventricles (with more pronounced changes to the right), and demyelination of peripheral nerves have also been described in adult dogs fed Vitamin B₆ deficient diets<ref>National Research Council (NRC). Vitamins. In Nutrient Requirements for Dogs and Cats. 2006 Washington, DC: National Academies Press p.218-220.</ref><ref>Street HR, et al. Observations on vitamin B6 deficiency in the dog. J Nutr 1941;21:275-290</ref>.

 

====Cats:====  

====Cats:====  

Induced vitamin B₆ deficiency in kittens was reported to result in poor growth rate, microcytic hypochromic anaemia, and [[Urolithiasis#Calcium oxalate|calcium oxalate]] crystalluria<ref>Bai SC, et al. Vitamin B6 deficiency in kittens. J Nutr 1989;119: 1020-1027.</ref>. Increased dietary intake of [[Protein Overview - Nutrition|protein]] has also been show to increase Vitamin B₆ requirement in cats<ref>Bai SC, et al. The level of dietary protein affects the vitamin B-6 requirement of cats. J Nutr 1991 121;1054-1061.</ref>.

Induced vitamin B₆ deficiency in kittens was reported to result in poor growth rate, microcytic hypochromic anaemia, and [[Urolithiasis#Calcium oxalate|calcium oxalate crystalluria]]<ref>Bai SC, et al. Vitamin B6 deficiency in kittens. J Nutr 1989;119: 1020-1027.</ref>. Increased dietary intake of [[Protein Overview - Nutrition|protein]] has also been show to increase Vitamin B₆ requirement in cats<ref>Bai SC, et al. The level of dietary protein affects the vitamin B-6 requirement of cats. J Nutr 1991 121;1054-1061.</ref>.

Vitamin B₆ is '''light sensitive and prone to degradation with heat processing'''. Conditions associated with diuresis (e.g., chronic disease, such as renal disease or [[Diabetes Insipidus|diabetes]], or therapeutic intervention, such as intravenous fluids or increased water intake with management of [[Cystitis|lower urinary diseases]]) can result in increased loss of Vitamin B₆ and may increase daily requirements. Patients on chronic haemodialysis are at an increased risk for development of deficiency.  

Vitamin B₆ is '''light sensitive and prone to degradation with heat processing'''. Conditions associated with diuresis (e.g. chronic disease, such as [[:Category:Kidney - Pathology|renal disease]] or [[Diabetes Insipidus|diabetes]], or therapeutic intervention, such as [[Fluid therapy|intravenous fluids]] or increased water intake with management of [[Cystitis|lower urinary diseases]]) can result in increased loss of Vitamin B₆ and may increase daily requirements. Patients on chronic haemodialysis are at an increased risk for development of deficiency.

==Toxicity==

==Toxicity==

There are no published toxicity reports in cats, but chronic high intake (i.e., >100x the requirement) of Vitamin B₆ can result in ataxia and tonic convulsions in dogs within 1 week of daily administration<ref>Hoover DM, et al. Ultrastructural Lesions of Pyridoxine Toxicity in Beagle Dogs. Vet Pathol 1981;18: 769-777.</ref><ref>Montpetit VJ, et al. Alteration of neuronal cytoskeletal organization in dorsal root ganglia associated with pyridoxine neurotoxicity. Acta Neuropathol 1988;76:71-81.</ref>.

There are no published toxicity reports in cats, but chronic high intake (i.e. >100x the requirement) of Vitamin B₆ can result in ataxia and tonic convulsions in dogs within 1 week of daily administration<ref>Hoover DM, et al. Ultrastructural Lesions of Pyridoxine Toxicity in Beagle Dogs. Vet Pathol 1981;18: 769-777.</ref><ref>Montpetit VJ, et al. Alteration of neuronal cytoskeletal organization in dorsal root ganglia associated with pyridoxine neurotoxicity. Acta Neuropathol 1988;76:71-81.</ref>.

==Dietary Sources==

==Dietary Sources==

==References==

==References==

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[[Category:Vitamins]]

[[Category:Vitamins]]