POSSIBLE INHIBITORY EFFECT OF LIPID PEROXIDES ON ACID LIPASE ACTIVITY VIA LOW-DENSITY-LIPOPROTEIN IN HUMAN MONONUCLEAR LEUKOCYTES

Acid lipase (AL) activity was measured in mononuclear leukocytes (MNL) isolated from 214 subjects. An inverse relation was observed between the AL activity and serum cholesterol (CHO) with age variation: The age groups above 30, which showed low AL activities in their MNL, exhibited high serum CHO; whereas the 20-to-29 age group, which had the highest AL activity among the age groups, showed the lowest CHO value. Moreover, the hypercholesterolemic group with high apo-B levels showed significantly low AL activity in both sexes when compared with the normolipidemic group. Significant negative correlations were also observed in the hypercholesterolemic group between the AL activity and both CHO and apo-B, and between the AL activity and lipid peroxides (LPO). On the other hand, while the addition of low-density lipoprotein (LDL) from patients with type II hypercholesterolemia to the AL assay system and the culture medium of MNL resulted in the inhibition of the AL activity, the inhibitory effect was prevented by preincubation of LDL with anti apo-B serum. These data suggest a certain regulatory mechanism of LDL, the physiological substrate of AL, on the AL activity; this action possibly occurs through lipid peroxides in LDL.