Metabolism of phosphatidylglycerol by alveolar macrophages in vitro

In whole animal studies, it has been shown that turnover of surfactant dipa lmitoylphosphatidylglycerol (DPPG) is faster than that of dipalmitoylphosph atidylcholine (DPPC). The goal of this investigation was to characterize th e metabolism of DPPG by alveolar macrophages and to determine whether they contribute to the faster alveolar clearance of DPPG. Isolated rat alveolar macrophages were incubated with liposomes colabeled with [H-3]DPPG and [C-1 4]DPPC. Macrophages internalized both lipids in a time- and temperature-dep endent manner. The uptake of both lipids was increased by surfactant protei n (SP) A and by adherence of the macrophages to plastic slides. The isotope ratio of DPPC to DPPG internalized by macrophages in suspension in the abs ence of SP-A was significantly lower than the isotope ratio in liposomes, s uggesting that macrophages preferentially internalize DPPG when SP-A is abs ent. Phospholipase activity in macrophage homogenate was higher toward sn-2 -labeled DPPG than toward sn-2-labeled DPPC. These studies show that alveol ar macrophages play an important role in catabolizing surfactant lipids and may be partially responsible for the relatively faster clearance of DPPG f rom the lung.