Significance of plasma copper and caeruloplasmin concentrations in rheumatoid arthritis

Abstract

To understand the role of copper in initiating protein alterations in rheumatoid arthritis (RA) as reported previously, concentrations of copper anc caeruloplasmin were determined in RA patients. The mean copper concentration of the RA population examined was 24.8 mumol/l (157.5 mug/100 ml), and the mean caeruloplasmin concentration in this RA population was 45.52 mg/100 ml. These values are not different from those reported by previous workers. However, when the RA population was divided into three groups according to sex and oestrogen therapy it was found that caeruloplasmin and copper concentrations in the group of female RA patients on oestrogens was significantly different from other groups (P less than 0.001). A highly significant (P less than 0.01) positive correlation was obtained between copper and caeruloplasmin concentrations (r = 0.91). Concentrations of copper and caeruloplasmin failed to explain the low sulphydryl content of plasma which was observed to be independent of these two parameters. Increased alpha2-globulin concentration, which was refractory to chrysotherapy but 'finger-printed' with a pure preparation of caeruloplasmin in electrophoresis, along with the absence of Kayser-Fleischer rings, supports the contention that copper is not present in a free ionic state in RA patients. This study shows that only a concurrent oestrogen therapy raises copper and caeruloplasmin concentration significantly in a female RA population. Past investigators appear to have overlooked this fact, and it could be that a disproportionate sex distribution (more female rheumatoid arthritics) could cause misleading results in RA studies. The role of oestrogens, copper, and caeruloplasmin in causing exacerbation of RA symptoms is discussed.