Difficulties in applying the Scatchard model of ligand binding to proteins--proposal of new mathematical tools--application to salicylates.

Ill-considered use of the Scatchard model often leads to unjustified deductions. Since the main difficulty of this model is its number of parameters, new models are proposed that have only two parameters. After checking the models on simulated data, they were applied to real data on the binding of salicylates to albumin.

Decrease of in vitro serum protein binding of salicylate in rheumatoid arthritis.

Free and bound fractions of salicylates were separated by equilibrium dialysis and measured by spectrofluorimetry in 27 patients with rheumatoid arthritis and in 16 controls. The results showed that in patients with rheumatoid arthritis, the binding of salicylate to proteins decreased in an overproportional manner with the decrease of serum albumin concentrations. This phenomenon was linked with the severity of the inflammatory syndrome. The saturation binding capacity per unit of protein concentration was lower in the patients suffering from active forms of the condition, a finding which suggests that the changes observed are not due only to quantitative changes in the serum albumins. This study confirms the importance of determining free salicylate concentrations in the treatment of patients with inflammatory diseases.

[Protein binding of salicylates in rheumatoid arthritis]. / Fixation protéique des salicylés au cours de la polyarthrite rhumatoïde.

Protein binding of salicylates was determined in 16 control subjects and 27 patients suffering from rheumatoid arthritis. Results obtained after separation of the free and bound fractions by dialysis to equilibrium and measured by spectrofluorometry were analyzed using a new mathematical model. In correlation with the decrease in plasma albumin concentrations, a decrease was found in the protein binding of salicylates in patients with rheumatoid arthritis. This phenomenon was less marked in therapeutic zones and was related to the degree of severity of the inflammatory syndrome. The binding capacity per albumin molecule at saturation was decreased in patients suffering from advanced forms, suggesting that the changes seen were not due solely to quantitative variations in serum albumin levels. This study confirms the value of the determination of free salicylate levels in patients suffering from inflammatory rheumatic disorders.