Plasma pyridoxal 5′-phosphate is not associated with inflammatory and immune responses after adjusting for serum albumin in patients with rheumatoid arthritis

Background/Aims: Plasma pyridoxal 5′-phosphate (PLP) has been shown to be associated with inflammatory and immune responses.Rheumatoid arthritis (RA) is an autoimmune and chronic systemic inflammatory disease and patients with RA have lower plasma PLP levels. We studied the relationship between plasma PLP and inflammatory or immune responses in patients with RA. Methods: This study was designed as an observational cross-sectional study. Forty-three patients with RA were allocated to the adequate (PLP ≥20 nmol/l) (n = 30) or deficient vitamin B 6 (PLP <20 nmol/l) (n = 13) group according to their fasting plasma PLP concentration on the day blood was taken. Plasma PLP, inflammatory parameters [i.e. high-sensitivity CRP (hs-CRP), erythrocyte sedimentation rate, interleukin-6, tumor necrosis factor-α] and immune parameters (i.e. white blood cells, total lymphocytes, neutrophils, T lymphocytes, B lymphocytes, T helper cells and T suppressor cells) were measured. Results: Patients with deficient plasma PLP concentration were mostly considered to have a systemic inflammatory status (hs-CRP >3 mg/l) and apparently had significantly higher mean hs-CRP levels and immune parameters than patients with adequate plasma PLP concentration. There was no significant association between plasma PLP levels and inflammatory parameters. The significantly inverse correlation of plasma PLP with the numbers of white blood cells, neutrophils, total lymphocytes, T lymphocytes and T helper cells remained after adjusting for serum hemoglobin concentration, but the significant correlation disappeared after serum albumin concentration was also considered. Conclusions: RA patients with deficient plasma PLP concentration had more severe inflammatory and immune responses than patients with adequate plasma PLP concentration. However, there was a lack of association of low plasma PLP concentration with inflammatory and immune parameters after serum albumin concentration was considered in patients with RA.