Protein binding of salicylic and salicyluric acid in serum from malnourished children: the influence of albumin, competitive binding and non-esterified fatty acids.

The serum protein binding of salicylic and salicyluric acid has been determined by ultrafiltration in 60 children after administration of oral salicylate. The children were classified according to nutritional status: well-nourished (n = 12), underweight (n = 12), marasmic (n = 17) marasmic-kwashiorkor (n = 7) and kwashiorkor (n = 12). Salicylic acid free fractions were 0.106 +/- 0.026, 0.114 +/- 0.069, 0.141 +/- 0.037, 0.285 +/- 0.279 and 0.438 +/- 0.190 in the five groups, respectively. Salicyluric acid free fractions were 0.184 +/- 0.057, 0.280 +/- 0.282, 0.236 +/- 0.114, 0.484 +/- 0.497 and 0.646 +/- 0.261, respectively. The degree of binding was dependent on serum albumin levels, ligand concentrations and non-esterified fatty acids (NEFA). The NEFA/albumin ratio ranged from 0.05 to 6.6. The fitting of a one-site Scatchard binding model to the collective data was improved when a decrease was allowed for in the number of binding sites in proportion to NEFA concentrations. Salicyluric acid binding could be fitted only when inhibition of the parent compound was included. Binding was not affected by age or sex. The major determinants of salicylate binding in sera from malnourished children have thus been identified.