The effect of two intravenous fat emulsions and their components on bilirubin binding to albumin

The effect of two intravenous lipid emulsions on the binding of bilirubin to albumin was investigated in vitro. Various concentrations of a soybean (Intralipid) or a safflower (Liposyn) oil emulsion in 0.48 mM albumin were assayed for changes in bilirubin displacement using Sephadex G-25 gel filtration and for alterations of albumin reserve binding capacity by a novel difference spectroscopy technique. Two major components of the emulsions, glycerol and egg phosphatides, were also assayed by difference spectroscopy. A significant enhancement of the total reserve bilirubin binding capacity of albumin was noted with concentrations of 200 to 500 mg/100 ml lipid emulsion using difference spectroscopy. Using salicylate to block secondary albumin binding sites for bilirubin, reserve bilirubin binding capacity at nonsalicylate competitive sites was shown to have increased (maximum 61%) over the range of 50 to 1000 mg/100 ml lipid emulsion. Only changes in nonsalicylate competitive binding sites could be detected at concentrations normally achieved in vivo. Egg phosphatides had little effect and glycerol decreased reserve bilirubin binding capacity. Sephadex studies were unable to detect any significant change in bilirubin retained on the column with 50 or 500 mg/100 ml lipid emulsion at any bilirubin/albumin ratio. The enhancement of reserve bilirubin binding capacity caused by lipid emulsions is mediated through changes in nonsalicylate competitive albumin binding sites. Product differences demonstrated in vitro point out the complexity of their effects on bilirubin/albumin binding and the necessity for in vivo investigations with structurally different nutritional products designed for use in newborns.