Determinants of Bioactivity of Oxidized Phospholipids

Abstract

Abstract-We previously described 3 bioactive oxidation products of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (PAPC) containing oxovaleroyl (POVPC), glutaroyl (PGPC), and epoxyisoprostane (PEIPC) groups at the sn-2 position that were increased in minimally modified/oxidized low density lipoprotein (MM-LDL) and rabbit atherosclerotic lesions. We demonstrated specific and contrasting effects of POVPC and PGPC on leukocyte-endothelial interactions and described an effect of PEIPC on monocyte binding. The major purpose of the present study was to determine the effects of structural changes on the bioactivities of these 3 lipids. We demonstrate herein that the group at the sn-2 position determines the specific bioactivity and that the substitution of stearoyl for palmitoyl at the sn-1 position or ethanolamine for choline at the sn-3 position of the phospholipid did not alter bioactivity. Oxidized PAPC, oxidized 1-stearoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine, and oxidized 1-stearoyl-2-arachidonoyl-snglycero-3-phosphorylethanolamine stimulated monocyte binding and inhibited lipopolysaccharide-induced expression of the neutrophil-binding molecule E-selectin. Furthermore, all oxovaleroyl phospholipids but not the glutaroyl phospholipids induced monocyte binding without an increase in vascular cell adhesion molecule-1 (VCAM-1) expression and inhibited lipopolysaccharide-induced E-selectin expression. In contrast, glutaroyl phospholipids but not oxovaleroyl phospholipids stimulated E-selectin and VCAM-1 expression. We further demonstrate that all parts of the phospholipid molecules are required for these bioactivities. Hydrolysis with phospholipase (PL) A 1 , PLA 2 , and PLC strongly reduced the bioactivities of POVPC, PGPC, and mixed isomers of PEIPC. PLD had a smaller but still significant effect. The effects of POVPC and PEIPC could be abolished by sodium borohydride treatment, indicating the importance of the reducible groups (carbonyl and epoxide) in these molecules. In summary, these studies identify 6 new bioactive, oxidized phospholipids that are increased in MM-LDL and, where measured, in atherosclerotic lesions. They thus suggest that a family of phospholipid oxidation products containing oxovaleroyl, glutaroyl, and epoxyisoprostane at the sn-2 position play an important role in the regulation of leukocyte-endothelial interactions, bioactivity being in part controlled by several types of phospholipid hydrolases. Key Words: atherosclerosis Ⅲ oxidized phospholipids Ⅲ monocyte-endothelial interactions Ⅲ E-selectin Ⅲ phospholipases M inimally oxidized LDL (MM-LDL), in contrast to native LDL, has been shown to stimulate endothelial cells to increase monocyte-endothelial interactions. 1 Monocytes are the major inflammatory cells in the atherosclerotic lesion and have been shown to be important mediators of lesion initiation and progression. 2,3 An important characteristic of atherosclerotic lesions and other chronic, inflammatory lesions is that they contain essentially no neutrophils. 4 Our gr...

Apolipoprotein A-I Promotes the Formation of Phosphatidylcholine Core Aldehydes That Are Hydrolyzed by Paraoxonase (PON-1) during High Density Lipoprotein Oxidation with a Peroxynitrite Donor

“…Remarkably, the present study has shown that apoA-I increases the yield of a class of oxidized phospholipids, the core aldehydes, that have been identified as a major bioactive component of minimally modified LDL (59). We propose that, in vivo, this function of apoA-I is coupled with the activity of PAF-AH and PON-1 to effectively divert phosphatidylcholine hydroperoxides to biologically inactive products.…”

The Aldo-Keto Reductase Superfamily and its Role in Drug Metabolism and Detoxification

“…Reduction by AKR1B may also be important for inactivating POVPC. Chemical reduction of POVPC by sodium borohydride abolishes its ability to activate endothelial cells to bind monocytes, suggesting that its reductive product PHVPC is inactive (Subbanagounder et al, 2000). In comparison, hydrolysis by phospholipase A2 could generate more reactive metabolites such as lysoPC, which impairs arterial relaxation, induces growth factor gene expression, superoxide production and arachidonic acid release (Kita et al, 2000;Tselepis and John, 2002).…”

Oxidized Phospholipid Inhibition of Toll-like Receptor (TLR) Signaling Is Restricted to TLR2 and TLR4

“…Activated polymorphonuclear cells in particular express enzymes such as NADPH oxidase and myeloperoxidase, which together generate a range of oxidants, including superoxide, hydrogen peroxide, and hypochlorous acid, each of which may be released from these cells to cause oxidative damage not only to invading microorganisms but also to host molecules in surrounding tissues (1). Phospholipids containing polyunsaturated fatty acid chains, such as the abundant phospholipid 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphorylcholine (PAPC), 2 are particularly susceptible to oxidation by such mediators (2,3), and products of PAPC oxidation have been shown to accumulate at sites of inflammation (3)(4)(5)(6) and in cells treated with stimulants such as IL-1␤, TNF-␣, or long wave ultraviolet radiation (7)(8)(9). Oxidation of PAPC leads to the formation of a mixture of products, ranging from epoxyisoprostanes to truncated chain derivatives that are collectively termed OxPAPC, which is a widely used model for the investigation of oxidized phospholipid (OxPL) function (10 -12).…”