Pyridoxal phosphate decreases in plasma but not erythrocytes during systemic inflammatory response.

Abstract

Vitamin B6 (active 3 hydroxy-2-methylpyridine derivatives) is an essential precursor of pyridoxal (PL) and pyridoxamine phosphate coenzymes of a wide variety of enzymes of intermediary metabolism (1). In plasma, pyridoxal 5′-phosphate (PLP) is the major form, whereas PLP and pyridoxamine 5′-phosphate (PMP) predominate in the cell. The most widely used method to detect vitamin B6 deficiency is the erythrocyte aspartate aminotransferase activation assay (2)(3)(4)(5). As this test is a functional rather than a direct measurement of PLP status, it may be affected by factors other than PLP deficiency (2)(3). The plasma PLP concentration is considered one of the better indicators of vitamin B6 status (1)(6)(7)(8)(9) and is reported to be well correlated with tissue PLP concentrations (8). However, vitamin concentrations in blood cells tend to be a better marker of cellular stores (10). We describe a simple, robust, reversed-phase HPLC method with precolumn derivatization using semicarbazide (11)(12)(13) that is suitable for the simultaneous measurement of PLP, 4-pyridoxic acid (PA), and PL in plasma and red cells and application of the assay in healthy individuals, patients with chronic disease, and critically ill patients requiring intensive care. Venous blood samples (EDTA) and packed red cells for population reference values were obtained from apparently healthy individuals (laboratory staff and those attending a cardiovascular risk clinic). Samples were obtained from a group of chronically ill medical and surgical patients with the potential for vitamin deficiencies (60% with short bowel syndrome and 35% with either chronic liver or renal disease) and from a critically ill group of medical and surgical patients admitted to the intensive care unit (30% with pancreatitis, 30% with trauma, 30% with organ failure). The study was approved by …