Prognostic value of serum albumin and undeproteinized plasma pyridoxal 5'-phosphate

Relation between pyridoxal and pyridoxal phosphate concentrations in plasma, red cells, and white cells in patients with critical illness

BACKGROUND

Evidence suggests that the relation between plasma and red cell vitamin B-6 concentrations is perturbed as part of the systemic inflammatory response in critically ill patients.

OBJECTIVE

The aim was to examine the cross-sectional and longitudinal interrelations between pyridoxal (PL) and pyridoxal phosphate (PLP) concentrations in plasma and red and white cells in patients with critical illness.

DESIGN

PLP and PL concentrations were measured by HPLC in plasma and red and white cells in normal subjects (n = 126) and critically ill patients (n = 96) on admission and on follow-up.

RESULTS

On admission, compared with the controls, median plasma PLP and PL (P < 0.001 and < 0.01, respectively) and red cell PLP and PL (P < 0.001 and < 0.05, respectively) and their ratio (PLP:PL) in plasma and red cells (P < 0.001 and < 0.01, respectively) were significantly lower in the critically ill. In critically ill patients, plasma PLP:PL was significantly lower than red cell PLP:PL (P = 0.001) and white cell PLP:PL (P = 0.008). Plasma PL concentration was directly associated with both red cell PL (r(s) = 0.73, P < 0.001) and white cell PL (r(s) = 0.68, P < 0.001). Red cell PL and white cell PL were directly associated with red cell PLP (r(s) = 0.82, P < 0.001) and white cell PLP (r(s) = 0.68, P < 0.001), respectively. Longitudinal measurements (n = 48) were similar.

CONCLUSIONS

The relation between plasma PLP and PL was significantly perturbed in critical illness. This effect was less pronounced in red and white cells. Therefore, these results confirm the hypothesis that intracellular PLP concentrations are more likely to be a reliable measure of status than are plasma measurements in the critically ill patient.

Prenatal high-dose pyridoxine may prevent hypertension and syndrome X in-utero by protecting the fetus from excess glucocorticoid activity

The increased risk for hypertension, insulin resistance syndrome, and coronary events associated with small-for-gestational-age birth, has plausibly been attributed to excessive prenatal exposure to glucocorticoids; this may up-regulate glucocorticoid activity throughout life by permanently decreasing expression of hippocampal glucocorticoid receptors crucial for feedback control of cortisol secretion. Since pyridoxal phosphate is a safe physiological antagonist of glucocorticoid activity, it is proposed that prenatal supplementation with high-dose pyridoxine may counteract the adverse impact of glucocorticoids on fetal growth, as well as on subsequent cardiovascular risk.

High-dose pyridoxine as an 'anti-stress' strategy

Pyridoxine nutritional status has a significant and selective modulatory impact on central production of both serotonin and GABA - neurotransmitters which control depression, pain perception, and anxiety - owing to the fact that the decarboxylases which produce these neurotransmitters have a relatively low affinity for pyridoxal phosphate (PLP). Pyridoxine deficiency leads to increased sympathetic outflow and hypertension in rodents, possibly reflecting decreased central production of these neurotransmitters; conversely, supplemental pyridoxine lowers blood pressure in many animal models of hypertension, and there is preliminary evidence for antihypertensive activity in humans as well. Additionally, physiological levels of PLP interact with glucocorticoid receptors to down-regulate their activity. Thus, high-dose pyridoxine, by amplifying tissue levels of PLP, may be expected to have a favorable impact on certain dysphoric mental states, while diminishing sympathetic output and acting peripherally to blunt the physiological impact of corticosteroids. In light of growing evidence that chronic dysphoria, particularly when accompanied by hopelessness or cynicism, has a major negative impact on morbidity and mortality from a wide range of disorders, high intakes of pyridoxine may have the potential to improve prognosis in many individuals. With respect to cardiovascular health, reduction of homocysteine levels should contribute to this benefit. These predictions are consistent with recent epidemiology correlating plasma PLP levels with risk for vascular events and overall survival.