Differential Low Density Lipoprotein Receptor-Dependent Formation of Eicosanoids in Human Blood-Derived Monocytes

We studied the ability of low density lipoproteins (LDLs) to provide arachidonic acid (AA) for eicosanoid biosynthesis in human blood-derived monocytes. When incubated in the presence of reconstituted LDL that contained cholesteryl[1-14C] arachidonate (recLDL-[14C]AA-CE), resting monocytes formed three labeled products of the prostaglandin (PG) H synthase pathway: 6-keto-PGF1α, thromboxane B2, and PGE2. The amounts of these eicosanoids in response to recLDL-[14C]AA-CE were comparable to or exceeded those that were produced in response to the addition of 10 μM unesterified[1-14C]AA. By contrast, resting monocytes formed only small amounts of products of the 5-lipoxygenase pathway, leukotriene (LT) B4and LTC4from either recLDL-[14C]AA-CE or[14C]AA, indicating preferential utilization of AA in the PGH synthase reaction. However, they converted LDL-derived [14C]AA efficiently into LTB4and LTC4, when they were first incubated with recLDL-[14C]AA-CE and subsequently stimulated with the chemotactic peptide N-formylmethionylleucylphenylalanine or the Ca2+ionophore A23187. The classical LDL receptor pathway mediated the synthesis of all of the above eicosanoids from LDL but not from unesterified AA. These results demonstrate that the LDL receptor pathway preferentially promotes the synthesis of PGH synthase products in resting human blood-derived monocytes and that an additional mechanism is required to promote effective synthesis of 5-lipoxygenase pathway products from AA that originates in LDL cholesteryl esters.