Plasma vitamin B12 binding proteins correlate with disease activity in patients with rheumatoid arthritis

The unsaturated vitamin B12 (cobalamin) binding capacity (UB12BC), transcobalamin (TC) I, II and III were measured in plasma and synovial fluid of 55 patients (10 men and 45 women, 25-60 years of age) with rheumatoid arthritis. The vitamin B12 binding proteins in 55 clinically and haematologically normal subjects of similar age group and sex were also studied as controls. The mean plasma concentrations of UB12BC, TCI, II and III were all significantly raised in patients with rheumatoid arthritis (RA) as compared to the normal controls. The increase of all vitamin B12 binding proteins in these patients showed a positive correlation with the increase of total proteins and globulin concentrations, and a negative (inverse) correlation with the albumin concentrations in the plasma, suggesting that these biochemical changes may be systemic consequences of the inflammatory and immunological processes characteristic of rheumatoid arthritis. The UB12BC, TC I and TC III concentrations in the synovial fluid were significantly higher than the corresponding plasma concentrations of these vitamin B12 binding proteins in patients with RA. Vitamin B12 binding proteins in the synovial fluid in these patients were probably at least partly produced locally by inflammatory cells. The mean levels of plasma transcobalamins in patients with severe disease activity were significantly higher than in patients with median or least disease activity. Therefore these proteins may be further studied as possible additional markers of disease activity in patients with RA.