IN VIVO EFFECT OF FREE FATTY ACIDS (FFA) ON BILIRUBIN (BR) BINDING

In healthy adults a wide range (0.28 to 5.34mMol/L) of plasma FFA levels were generated by the fat meal-heparin regimen (Schalch DS, Kipnis DM, J.Clin.Invest.44:2010,1965). In each experiment 4-5 blood samples were collected, albumin (Alb) and FFA concentrations were measured and BR binding assessed using: (a) BR titration of sera using Sephadex (S) Column Chromatography (Valaes T, Hyte M, Pediatrics 59:881,1977); (b) the Undiluted Peroxidase (P) method (Ahlfors CE, Clin.Chem.27:692,1981); and (c) the automated Bilirubin Hematofluorometer (HMF) (Wells R et al Clin.Chem.28:432,1982). With S a significant negative correlation was found between the BR/Alb (molar ratio) at the BR titration point ("BR binding capacity") and the FFA/Alb (Y=0.883 -0.088·X, r=-0.90, p<0.001, n=38). Similarly, after "spicing" the sera to BR/Alb of 0.367±0.029(SD) the Apparent Unbound BR (nMol/L) by the P method was significantly related to the FFA/Alb (Y=13.5±41.66.X, r=0.957, p<0.001, n=28). The BR/Alb at BR binding capacity by HMF was only weakly related to FFA/Alb (Y=0.711-0.009·X, r=-0.353, p<0.05, n=34). However, "spicing" of the blood samples to BR/Alb of 0.54±0.054(SD) improved the correlation (Y=0.929-0.041·X, r=-0.835, p<0.001, n=12). The reasons for this effect of "spicing" are not clear. Previous conclusions of no effect up to FFA/Alb of 4, derived from studies with Alb solutions and in vitro additions of FFA, should be revised.