Differential low density lipoprotein receptor-dependent formation of eicosanoids in human blood-derived monocytes.

Abstract

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_-4C] 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.We and others have observed stimulatory effects of native plasma lipoproteins on the formation of prostacyclin and prostaglandin (PG) E2 in cultured endothelial cells, smooth muscle cells, and fibroblasts (1-3). Furthermore, we have shown (4) that the stimulatory effect of low density lipoprotein (LDL) on prostacyclin and PGE2 production by plateletderived growth factor-stimulated fibroblasts was a consequence of the LDL receptor-dependent delivery of arachidonic acid (AA) to the PGH synthase (EC 1.14.99.1) reaction and that it was followed by a profound inhibition of PGH synthase. This raised the possibility that the LDL pathway might have a role in the regulation of eicosanoid synthesis in fibroblasts in addition to its known role in the maintenance of cellular cholesterol homeostasis. Furthermore, since all animal cells can express the LDL receptor and also can convert AA into one or more eicosanoids (of which more than 40 with very different biological activities have been identified to date; for review, see refs. 5 and 6), it seemed possible that the LDL pathway might play a similar role in other cell types. To investigate the latter possibility, we turned our attention to human blood-derived monocytes. Unlike most mammalian cells, monocytes express both the PGH synthase pathway that leads to the formation of prostacyclin, thromboxane (TX) A2, and PGE2 (7) and the 5-lipoxygenase (EC 1.13.11.12) pathway that leads to the formation of leukotriene (LT) B4 and LTC4 (8). Furthermore, the products ofthe two pathways play distinct, and in some instances even opposing, biological roles (5). Our results demonstrate that human monocytes use the classical LDL receptor pathway (for review, see refs. 9 and 10) to deliver AA for the production of prostacyclin, TXA2, and PGE2, and that N-formylmethionylleucylphenylalanine (fMet-Leu-Phe) induces formation of LTB4 and LTC4 from AA that originates in LDL cholesteryl esters (CEs). MATERIALS AND METHODSMaterials. fMet-Leu-Phe, AA, Ca2+ ionophore A 23187, and all other materials were from Sigma; [14C]AA and [14C]AA-CE (specific activity, 54.9 mCi/mmol; 1 Ci = 37 GBq) were from NEN.Cell Preparation and Cell Culture. Human blood-derived mononuclear cells were isolated by leukapheresis from fasting volunteers, and monocytes were purified as described (11,12). Cells were maintained in minimum essential medium supplemented with undialyzed 20%

Suppression of Macrophage Eicosanoid Synthesis by Atherogenic Lipoproteins Is Profoundly Affected by Cholesterol-Fatty Acyl Esterification and the Niemann-Pick C Pathway of Lipid Trafficking

“…1-4) provide direct evidence for the hypothesis that incorporation of lipoprotein-derived NAAFAs into cellular phospholipids directly causes the suppression of cPLA 2 -mediated AA release, leading to decreased production of both PGE 2 and LT-C 4 /D 4 /E 4 . Of interest, previous work has shown that incubation of other cell types with lipoproteins that are enriched in AA can actually enhance eicosanoid biosynthesis (44,45). These data are consistent with the overall model outlined in this paper (Fig.…”

Involvement of 15-lipoxygenase in early stages of atherogenesis.

“…In this case, the oxidative modification of LDL would depend on the expression of the classical LDL receptor at the cell membrane. It has been shown before that arachidonic acid which is taken up by cells with the native LDL may be metabolized via 5-1i-poxygenase and the cyclooxygenase pathway after being released from the LDL ester lipids in the lysosomes (38,39). The second is extracelhlar localization of the 15-1ipoxygenase.…”

Periodontal Diseases: Pathogenesis

“…This terminal signal, such as endotoxin, induces the green state or final active metabolic burst with rapid cytokine secretion. Both AGEs and elevated unsaturated fatty acids (often associated with diabetes) are capable of inducing an amber monocytic state.330 332 Thus, metabolic dysregulation may be a possible explanation for the up-regulated monocyte response seen in diabetics. The critical point of these examples, is that various host-based risk factors can now be placed into a model which accommodates the site-specificity of the disease process and the association of periodontal pathogen overgrowth.…”