Cholesteryl linoleate

An update on lipid oxidation and inflammation in cardiovascular diseases

Cardiovascular diseases (CVD), including ischemic heart diseases and cerebrovascular diseases, are the leading causes of morbidity and mortality worldwide. Atherosclerosis is the major underlying factor for most CVD. It is well-established that oxidative stress and inflammation are two major mechanisms leading to atherosclerosis. Under oxidative stress, polyunsaturated fatty acids (PUFA)-containing phospholipids and cholesterol esters in cellular membrane and lipoproteins can be readily oxidized through a free radical-induced lipid peroxidation (LPO) process to form a complex mixture of oxidation products. Overwhelming evidence demonstrates that these oxidized lipids are actively involved in the inflammatory responses in atherosclerosis by interacting with immune cells (such as macrophages) and endothelial cells. In addition to lipid lowering in the prevention and treatment of atherosclerotic CVD, targeting chronic inflammation has been entering the medical realm. Clinical trials are under way to lower the lipoprotein (a) (Lp(a)) and its associated oxidized phospholipids, which will provide clinical evidence that targeting inflammation caused by oxidized lipids is a viable approach for CVD. In this review, we aim to give an update on our understanding of the free radical oxidation of LPO, analytical technique to analyze the oxidation products, especially the oxidized phospholipids and cholesterol esters in low density lipoproteins (LDL), and focusing on the experimental and clinical evidence on the role of lipid oxidation in the inflammatory responses associated with CVD, including myocardial infarction and calcific aortic valve stenosis. The challenges and future directions in understanding the role of LPO in CVD will also be discussed.

Lipids including cholesteryl linoleate and cholesteryl arachidonate contribute to the inherent antibacterial activity of human nasal fluid

Mucosal surfaces provide first-line defense against microbial invasion through their complex secretions. The antimicrobial activities of proteins in these secretions have been well delineated, but the contributions of lipids to mucosal defense have not been defined. We found that normal human nasal fluid contains all major lipid classes (in micrograms per milliliter), as well as lipoproteins and apolipoprotein A-I. The predominant less polar lipids were myristic, palmitic, palmitoleic, stearic, oleic, and linoleic acid, cholesterol, and cholesteryl palmitate, cholesteryl linoleate, and cholesteryl arachidonate. Normal human bronchioepithelial cell secretions exhibited a similar lipid composition. Removal of less-polar lipids significantly decreased the inherent antibacterial activity of nasal fluid against Pseudomonas aeruginosa, which was in part restored after replenishing the lipids. Furthermore, lipids extracted from nasal fluid exerted direct antibacterial activity in synergism with the antimicrobial human neutrophil peptide HNP-2 and liposomal formulations of cholesteryl linoleate and cholesteryl arachidonate were active against P. aeruginosa at physiological concentrations as found in nasal fluid and exerted inhibitory activity against other Gram-negative and Gram-positive bacteria. These data suggest that host-derived lipids contribute to mucosal defense. The emerging concept of host-derived antimicrobial lipids unveils novel roads to a better understanding of the immunology of infectious diseases.

The reduction of cholesteryl linoleate in lipoproteins: an index of clinical severity in beta-thalassemia/Hb E

Background: Oxidative modification of lipoproteins has been reported in beta-thalassemia and has been suggested to relate to atherogenesis-risk. This study focused on the change in cholesteryl esters in plasma lipoproteins under oxidative stress resulting from iron overload in beta-thalassemia/hemoglobin E (beta-thal/Hb E) patients.
Methods: Markers of oxidative damage and cholesteryl esters (CEs) were measured in plasma and lipo-proteins from 30 beta-thal/Hb E patients and compared to those from 10 healthy volunteers. CEs in plasma, low-density lipoprotein (LDL) and high-density lipoprotein (HDL) were separated and identified using HPLC.
Results: beta-Thal/Hb E patients presented iron overload, a precipitous decrease in alpha-tocopherol and increased lipid peroxidation (thiobarbituric acid-reactive substances; TBARs) in both plasma and lipoproteins. Cholesteryl linoleate, the most abundant CE in lipoproteins, showed a reduction of 70% in LDL, while other CEs showed a lower reduction (50%). An inverse relationship between the cholesteryl linoleate/cholesteryl oleate ratio (CL/CO) and the degree of clinical severity suggested that the CL/CO ratio is an index of damaged lipoproteins and could be used as a pathologic marker of underlying iron overload. Good correlation of non-transferrin-bound iron (NTBI) and TBARs (r=0.8, p<0.01) in LDL strongly supported the contention that iron overload is responsible for initiating the lipid peroxidation in beta-thal/Hb E.
Conclusions: This study suggests that cholesteryl linoleate is the primary target of oxidative modification induced by NTBI in beta-thal/Hb E patients and that reduction in cholesteryl linoleate in lipoproteins could be used as a severity index for beta-thal/Hb E.

Synthesis of (2β,3α,6-?H?cholesteryl linoleate and cholesteryl oleate as internal standards for mass spectrometry

The accurate analysis of trace component in complex biological matrices requires the use of reliable standards. For liquid chromatography/mass spectrometry analysis, the stable isotope-labeled derivatives of the analyte molecules are the most appropriate internal standards. We report here the synthesis of (2β,3α,6-(2)H3)cholesteryl linoleate and oleate containing three non-exchangeable deuterium in the steroid ring. The principal reactions used were: (1) trans diaxial opening of 2α,3α-epoxy-6-oxo-5α-cholestane with LiAlD4 and subsequent oxidation of the resulting (2β,6α-(2)H2)-3α,6β-diol with Jones' reagent, followed by reduction of the resulting (2β-(2)H)-3,6-dione with NaBD4 leading to the (2β,3α,6α-(2)H3)-3β,6β-dihydroxy-5α-cholestane, (2) selective protection of the 3β-hydroxy group as the tert-butyldimethylsilyl ether, (3) dehydration of the 6β-hydroxy group with POCl3 and removal of tert-butyldimethylsilyloxy groups with 5M HCl in acetone, and (4) esterification of the resultant (2β,3α,6-(2)H3)cholesterol with linoleic and oleic acids using 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide. The isotopic purity was found to be satisfactory by mass spectrometry, and nuclear magnetic resonance properties of the new compounds were tabulated. The labeled compounds can be used as internal standards in liquid chromatography/mass spectrometry assays for clinical and biochemical studies.

Exchange of oxidized cholesteryl linoleate between LDL and HDL mediated by cholesteryl ester transfer protein

This study examines the cholesteryl ester transfer protein (CETP)-mediated exchange of cholesteryl linoleate hydroperoxide (Ch18:2-OOH) and cholesteryl linoleate hydroxide (Ch18:2-OH) between low density lipoprotein (LDL) and high density lipoprotein (HDL). When [3H]Ch18:2-OOH- and [3H]18:2-OH-labeled LDL were incubated at 37 degrees C for 0-24 h with unoxidized HDL and purified CETP, Ch18:2-OOH and Ch18:2-OH accumulated in the HDL. Similarly, when incubations were carried out with [3H]Ch18:2-OOH- and [3H]Ch18:2-OH-labeled HDL, unoxidized LDL, and CETP, Ch18:2-OOH and Ch18:2-OH accumulated in the LDL. Comparable results were obtained for the CETP-mediated transfer of [3H]Ch18:2-OH alone from LDL to HDL. Transfer to HDL of oxidized cholesteryl linoleate from [3H]Ch18:2-OOH- and [3H]Ch18:2-OH-labeled LDL was comparable to that of unoxidized cholesteryl linoleate (Ch18:2). However, the rate of transfer of [3H]Ch18:2-OOH and [3H]Ch18:2-OH from LDL to HDL increased linearly as the molar ratio of acceptor (HDL) to donor (oxidized LDL) particles in the incubation increased from 0.5:1 to 10:1. This increased rate of exchange was accompanied by an increased proportion of the oxidized Ch18:2 being present as the hydroxide rather than hydroperoxide. Further increases in the molar ratio of HDL to oxidized LDL particles neither affected the transfer rate nor the extent of reduction of Ch18:2-OOH to Ch18:2-OH. We therefore conclude that i) CETP mediates bidirectional transfers of Ch18:2-OOH and Ch18:2-OH between HDL and LDL; ii) CETP does not distinguish between Ch18:2-OOH, Ch18:2-OH, and Ch18:2 as it mediates their exchange between HDL and LDL; and iii) association with HDL hastens the reduction of Ch18:2-OOH to Ch18:2-OH.