Elimination half-lives of interleukin-6 and cytokine-induced neutrophil chemoattractant-1 synthesized in response to inflammatory stimulation in rats

The elimination half-lives of in Interleukin-6 (IL-6) and cytokine-induced neutrophil chemoattractant-1 (CINC-1) in rats after inflammatory stimulation were investigated. Five male Sprague-Dawley rats were used (age, 9 weeks; body weight, 235-375 g). Turpentine oil was intramuscularly injected at a dose of 2 mL/kg body weight to induce acute inflammation. Blood was collected pre-injection and 6, 12, 24, 36, 48, 60, 72, 84, and 96 h after the turpentine oil injection. Serum concentrations of IL-6, CINC-1, and α₂-macroglobulin (α2M) were measured by enzyme-linked immunosorbent assay. Half-lives were calculated as 0.693/elimination rate constant. The serum concentration of α2M peaked at 48 h after turpentine oil injection. Serum concentrations of IL-6 and CINC-1 increased and peaked at 12 and 24 h, respectively. The terminal elimination half-lives of IL-6 and CINC-1 were 15.5 and 29.9 h, respectively. The half-life of CINC-1 was significantly longer than that of IL-6 (P=0.006). These results suggested that these cytokines synthesized in response to inflammatory stimulation were rapidly eliminated in rats. The serum concentrations of these cytokines should be measured at an early stage if these cytokines will be used as surrogate inflammatory markers instead of acute-phase proteins.