Abstract
Macrophages may play an important role in the atherogenic process because they appear to be precursors of some arterial wall foam cells. Recently, it has been reported that human peripheral monocytes in culture synthesize and secrete lipoprotein lipase (LPL). LPL catalyzes the hydrolysis of triglycerides which are transported in plasma by chylomicrons and very low density lipoprotein (VLDL). Consequently, it is possible that LPL secretion by human monocytes is related to atherogenesis. As shown below, human monocytes and guinea pig alveolar macrophages in culture synthesize and secrete LPL. The purpose of this research is to study the significance of this macrophage LPL.
Therefore I investigated the effect of lipoprotein on LPL activity of guinea pig alveolar macrophages.
Monocytes were obtained from a normal healthy donor and were separated from whole blood by Ficoll-Hypaque. The lungs of guinea pig were washed 10-12 times with 0.9% NaCl and the washings were cultured. The enzyme activity was determined by a modification of the method of Schotz et al. The separation of the lipoprotein fractions was performed in a type RP-40 rotor by ultracentrifugation by the method of Havel et al.
The rate of LPL secretion from human monocytes was low initially but increased with time in culture. During 14 days in culture, maximal activity was attained on the 12th day.
On the other hand, guinea pig alveolar macrophages increased from the beginning. During 8 days in culture, maximal activity was attained on the 4th day. Next, we investigated the effect of lipoprotein on LPL activity of guinea pig alveolar macrophages. Alveolar macrophages were cultured for 2 days with either RPMI-1640 medium containing 10% lipoprotein deficient serum (LPDS) or that medium with the addition of VLDL, LDL, and HDL respectively in the concentrations of 300μg protein/ml. When VLDL was added to LPDS after one day, LPL activity was significantly reduced to 48.3% within 2 days of exposure when compared with LPDS controls. (p<0.02). A possible explanation for this phenomenon, is that LPL activity may be inhibited by apoprotein CIII of VLDL.
