Intralipid alters macrophage membrane fatty acid composition and inhibits complement (C2) synthesis.

Abstract

AbstractIntralipid (IL) is a soybean oil emulsion commonly used as a parenteral nutrient. IL is taken up by macrophages. These cells are a site of synthesis of several of the proteins in the complement system, a major mediator of the humoral system. These studies were undertaken to determine whether IL has an effect on the production of the second (C2) and the fourth (C4) components of complement by guinea pig and human macrophages in vitro. Guinea pig macrophages incubated with IL, in concentrations from 5 to 40 mg/dl, produced significantly decreased amounts of C2 and C4 when compared with controls (decreases from 40% at 5 mg/dl to 60% at 40 mg/dl). Human macrophages incubated in IL, 19 or 38 mg/dl, also produced significantly decreased amounts of C2 when compared to controls (decreases were 45 and 50% at 19 and 38 mg/dl, respectively). The maximum concentration of IL used in these studies did not significantly affect cell viability, or the production of lysozyme or β‐glucosaminidase. For human macrophages, which were studied more thoroughly, the inhibition of C2 production was reversible. C2 levels returned to normal after removal of IL. Cells stimulated with opsonized zymosan produced levels of C2 comparable to stimulated control cells, despite the continued presence of IL within the cells. Human macrophages incubated with arachidonic acid, in addition to IL, produced C2 as well as control cells did. Thus, IL appears to have a selective, reversible effect on C2 production. It is possible that a general increase in fat metabolism, in response to the ingestion of IL, nonspecifically consumed arachidonic acid, decreasing its availability as a substrate for a cell product important in production of C2. Since the effects on C2 production were seen with concentrations of IL commonly seen in plasma of infants receiving IL intravenously, these studies have implications for the clinical use of oil emulsions in parenteral nutrition.