PHOSPHOLIPASE D-MODIFIED LOW-DENSITY-LIPOPROTEIN IS TAKEN UP BY MACROPHAGES AT INCREASED RATE - A POSSIBLE ROLE FOR PHOSPHATIDIC-ACID

Macrophage uptake of modified forms of LDL leads to cellular cholester ol accumulation. Upon incubation of LDL with phospholipase D (PLase D) , a time- and enzyme dose-dependent production of phosphatidic acid (P A), paralleled by a rapid reduction in LDL phosphatidyl choline conten t (up to 65% within 15 min of incubation) was noted. No lipid peroxida tion could be found in PLase D-modified LDL. Upon in vitro incubation of PLase D-LDL with copper ions, however, this modified LDL was substa ntially oxidized. The addition of 100 mug PA/ml to native LDL for the period of its in vitro oxidation resulted in a 63% elevation in the li poprotein peroxides content. Incubation of PLase D-LDL with J-774A.1 m acrophage-like cell line resulted in an increase in its cellular bindi ng and degradation (up to 91 and 110%, respectively) in comparison wit h native LDL (via the LDL receptor). When PA was added to LDL before i ts incubation with the macrophages, a PA dose-dependent elevation in t he cellular uptake of LDL (by up to twofold) was noted in comparison w ith LDL that was incubated without PA, suggesting that PA production i n PLase D-LDL may be involved in the increased cellular uptake of PLas e D-LDL. PLase D activity towards LDI, was demonstrated in J-774A.1 ma crophages. Human plasma was also shown to possess PLase D activity. Th us, PLase D modification of LDL may take place under certain pathologi cal conditions and PLase D-LDL interaction with arterial wall macropha ges can potentially lead to foam cell formation.