Absorption of the phosphate forms involves their dephosphorylation catalyzed by the enzyme alkaline phosphatase. Most of the vitamin is taken up by the liver. There, the dephosphorylated vitamins are converted to the phosphorylated PLP, PNP and PMP, with the two latter converted to PLP. In the liver, PLP is bound to proteins, primarily albumin. The PLP-albumin complex is what is released by the liver to circulate in plasma. Protein-binding capacity is the limiting factor for vitamin storage. Total body stores, the majority in muscle, with a lesser amount in liver, have been estimated to be in the range of 61 to 167 mg.Enzymatic processes utilize PLP as a phosphate-donating cofactor. PLP is restored via a salvage pathway that requires three key enzymes, pyridoxal kinase, pyridoxine 5-phosphate oxidase, and phosphatases. Inborn errors in the salvage enzymes are known to cause inadequate levels of PLP in the cell, particularly in neuronal cells. The resulting PLP deficiency is known to cause or implicated in several pathologies, most notably infant epileptic seizures.The end-product of vitamin B6 catabolism is 4-pyridoxic acid, which makes up about half of the B6 compounds in urine. 4-Pyridoxic acid is formed by the action of aldehyde oxidase in the liver. Amounts excreted increase within 1–2 weeks with vitamin supplementation and decrease as rapidly after supplementation ceases. Other vitamin forms excreted in the urine include pyridoxal, pyridoxamine and pyridoxine, and their phosphates. When large doses of pyridoxine are given orally, the proportion of these other forms increases.
MMF was judged a consequence of a switch to intramuscular injection and the deltoid muscle being the preferred site of both vaccine injection and biopsy in France (while other sites were preferred for biopsy in other countries) and the commencement of HBV vaccination in French adults. Similar lesions could be detected in babies and children upon biopsy of the quadriceps as this is the site of vaccine administration in this group. MMF could also be experimentally reproduced in animals, with regression over time. It has been proposed that in a small portion of the population, vaccination results in persistence of aluminium-compound particles in macrophages in association with myalgia, fatigue, and cognitive dysfunction. A MMF disorder has been compared to autoimmune/inflammatory syndrome induced by adjuvants. A case-controlled study in France found those with MMF were more likely to have received aluminium-containing vaccines. MMF was also associated with fatigue “and related functional limitations", with fatigue more common in the beginning of the malady that led to the biopsy. However, neither myalgia, arthralgia, nor any other symptoms or risk factors were identified as specific to those with MMF.Many of those with MMF had previously been treated for malaria with chloroquine or hydroxychloroquine.As of 2009, with few exceptions, MMF had only been reported in France. == References ==