Low Density Lipoprotein Phospholipids Research Articles

HDL and the inflammatory response induced by LDL-derived oxidized phospholipids.

Oxidation of low density lipoprotein (LDL) phospholipids containing arachidonic acid at the sn-2 position occurs when a critical concentration of "seeding molecules" derived from the lipoxygenase pathway is reached in LDL. When this critical concentration is reached, the nonenzymatic oxidation of LDL phospholipids produces a series of biologically active, oxidized phospholipids that mediate the cellular events seen in the developing fatty streak. Normal high density lipoprotein (HDL) contains at least 4 enzymes as well as apolipoproteins that can prevent the formation of the LDL-derived oxidized phospholipids or inactivate them after they are formed. In the sense that normal HDL can prevent the formation of or inactivate these inflammatory LDL-derived oxidized phospholipids, normal HDL is anti-inflammatory. HDL from mice that are genetically predisposed to diet-induced atherosclerosis became proinflammatory when the mice are fed an atherogenic diet, injected with LDL-derived oxidized phospholipids, or infected with influenza A virus. Mice that were genetically engineered to be hyperlipidemic on a chow diet and patients with coronary atherosclerosis, despite normal lipid levels, also had proinflammatory HDL. It is proposed that LDL-derived oxidized phospholipids and HDL may be part of a system of nonspecific innate immunity and that the detection of proinflammatory HDL may be a useful marker of susceptibility to atherosclerosis.

Supplementation of postmenopausal women with fish oil does not increase overall oxidation of LDL ex vivo compared to dietary oils rich in oleate and linoleate

Although replacement of dietary saturated fat with monounsaturated and polyunsaturated fatty acids (MUFA and PUFA) has been advocated for the reduction of cardiovascular disease risk, diets high in PUFA could increase low density lipoprotein (LDL) susceptibility to oxidation, potentially contributing to the pathology of atherosclerosis. To investigate this possibility, 15 postmenopausal women in a blinded crossover trial consumed 15 g of sunflower oil (SU) providing 12.3 g/day of oleate, safflower oil (SA) providing 10.5 g/day of linoleate, and fish oil (FO) providing 2.0 g/day of eicosapentaenoate (EPA) and 1.4 g/day of docosahexaenoate (DHA). During CuSO4-mediated oxidation, LDL was depleted of α-tocopherol more rapidly after FO supplementation than after supplementation with SU (P = 0.0001) and SA (P = 0.05). In LDL phospholipid and cholesteryl ester fractions, loss of n-3 PUFA was greater and loss of n-6 PUFA less after FO supplementation than after SU and SA supplementation (P < 0.05 for all), but loss of total PUFA did not differ. The lag phase for phosphatidylcholine hydroperoxide (PCOOH) formation was shorter after FO supplementation than after supplementation with SU (P = 0.0001) and SA (P = 0.006), whereas the lag phase for cholesteryl linoleate hydroperoxide (CE18:2OOH) formation was shorter after FO supplementation than after SU (P = 0.03) but not SA. In contrast, maximal rates of PCOOH and CE18:2OOH formation were lower after FO supplementation than after SA (P = 0.02 and 0.0001, respectively) and maximal concentrations of PCOOH and CE18:2OOH were lower after FO supplementation than after SA (P = 0.03 and 0.0006, respectively). Taken together, our results suggest that FO supplementation does not increase the overall oxidation of LDL ex vivo, especially when compared with SA supplementation. Consequently, health benefits related to increased fish consumption may not be offset by increased LDL oxidative susceptibility. —Higdon, J. V., S. H. Du, Y. S. Lee, T. Wu, and R. C. Wander. Supplementation of postmenopausal women with fish oil does not increase overall oxidation of LDL ex vivo compared to dietary oils rich in oleate and linoleate.

The Farnesoid X-activated Receptor Mediates Bile Acid Activation of Phospholipid Transfer Protein Gene Expression

Bile acids facilitate the absorption of dietary lipids and fat-soluble vitamins and are physiological ligands for the farnesoid X-activated receptor (FXR), a member of the nuclear hormone receptor superfamily. FXR functions as a heterodimer with the retinoid X receptor and in the presence of ligand, the heterodimer binds to specific DNA sequences in the promoters of target genes to regulate gene transcription. Phospholipid transfer protein (PLTP) has been identified as a possible target gene for FXR because the human promoter contains a potential FXR response element, an inverted repeat in which consensus receptor-binding hexamers are separated by one nucleotide (inverted repeat-1). PLTP is essential in the transfer of very low density lipoprotein phospholipids into high density lipoprotein (Jiang, X. C., Bruce, C., Mar, J., Lin, M., Ji, Y., Francone, O. L., and Tall, A. R. (1999) J. Clin. Invest. 103, 907-914). Here we report the regulation of PLTP gene expression by FXR and bile acids. In CV-1 cells, cotransfection of FXR and the retinoid X receptor resulted in bile acid-dependent transactivation of a luciferase reporter construct containing the human PLTP promoter. Mutation analysis demonstrated that the inverted repeat-1 (IR-1) in the PLTP promoter is required for this transactivation. Finally, we demonstrate that bile acids are able to regulate PLTP gene expression in vivo. Mice fed a chow diet supplemented with bile acid showed increased hepatic PLTP mRNA levels. These results suggest that FXR may play a role in high density lipoprotein metabolism via the regulation of PLTP gene expression.

Detection of plasmalogen from plasma low density lipoprotein and high density lipoprotein in carp, Cyprinus carpio, and rainbow trout, Oncorhynchus mykiss

The study revealed the presence of plasmalogens in the low density lipoprotein (LDL) and high density lipoprotein (HDL) of the fish. The composition of the plasmalogen in the carp plasma LDL phospholipids was 0.94 and 0.23% in the HDL; the LDL phospholipids in the rainbow trout were 0.44% and the HDL was 0.18%. Aldehydes from the plasmalogen were derivatized with dansylhydrazides and separated by high performance liquid chromatography (HPLC). Their presence was detected using a fluorescence detector. Hexadecanal (C16: 0), octadecanal (C18: 0) and octadecenal (C18: 1) were determined to be the major components in the carp and rainbow trout.

P-Hydroxyphenylacetaldehyde, an Aldehyde Generated by Myeloperoxidase, Modifies Phospholipid Amino Groups of Low Density Lipoprotein in Human Atherosclerotic Intima

Oxidation of low density lipoprotein (LDL) may be of critical importance in the pathogenesis of atherosclerosis. Recent studies suggest that oxidized phospholipids render LDL atherogenic. However, both the structures and the physiologically relevant pathways for the formation of modified phospholipids in oxidized LDL remain poorly understood. We previously showed that p-hydroxyphenylacetaldehyde (pHA) is the major product of L-tyrosine oxidation by the myeloperoxidase/hydrogen peroxide/chloride system of phagocytes. In the current studies, we demonstrate that this reactive aldehyde targets the aminophospholipids of LDL in vitro and in vivo. Activated human neutrophils generated pHA-ethanolamine, the reduced adduct of pHA with the amino group of phosphatidylethanolamine, on LDL phospholipids by a reaction that required myeloperoxidase, H(2)O(2), and L-tyrosine. The cellular system could be replaced by HOCl and L-tyrosine but not by a wide variety of other oxidation systems, indicating that pHA-ethanolamine is a specific marker for covalent modification of aminophospholipids by myeloperoxidase. To determine whether aldehydes modify aminophospholipids in vivo, we quantified levels of pHA-ethanolamine in acid hydrolysates of reduced lipid extracts through isotope dilution gas chromatography/mass spectrometry. Circulating LDL contained undetectable levels of pHA-modified phospholipid (<0.1 mmol/mol). In contrast, the concentration of pHA-ethanolamine in LDL isolated from human atherosclerotic lesions was strikingly elevated (4.5 mmol/mol). Collectively, these results demonstrate a novel, myeloperoxidase-based mechanism for modifying the amino group of LDL phospholipids. They also offer the first evidence that myeloperoxidase may damage LDL lipids in vivo, raising the possibility that aldehyde-modified aminophospholipids play a role in inflammation and vascular disease.

Pathways of phospholipid oxidation by HOCl in human LDL detected by LC-MS

A wealth of evidence now indicates that low-density lipoprotein (LDL) must be modified to promote atherosclerosis, and that this may involve oxidants released by phagocytes. Many studies of oxidative damage in atherosclerosis previously have concentrated on damage by nonhalogenated oxidants, but HOCl is a highly toxic oxidant produced by myeloperoxidase in phagocytes, which is also likely to be important in the disease pathogenesis. Currently some controversy exists over the products resulting from reaction of HOCl with LDL lipids, in particular regarding whether predominantly chlorohydrins or lipid peroxides are formed. In this study LC-MS of phosphatidylcholines in human LDL treated either with HOCl or the myeloperoxidase system was used as a specific method to detect chlorohydrin and peroxide formation simultaneously, and with comparable sensitivity. Chlorohydrin products from lipids containing oleic, linoleic and arachidonic acids were detected, but no hydroperoxides of linoleoyl or arachidonoyl lipids could be observed. This study provides the first direct evidence that lipid chlorohydrins rather than peroxides are the major products of HOCl- or myeloperoxidase-treated LDL phospholipids. This in turn provides important information required for the study of oxidative damage in vivo which will allow the type and source of oxidants involved in the pathology of atherosclerosis to be investigated.

Inflammatory Platelet-activating Factor-like Phospholipids in Oxidized Low Density Lipoproteins Are Fragmented Alkyl Phosphatidylcholines

Oxidation of human low density lipoprotein (LDL) generates proinflammatory mediators and underlies early events in atherogenesis. We identified mediators in oxidized LDL that induced an inflammatory reaction in vivo, and activated polymorphonuclear leukocytes and cells ectopically expressing human platelet-activating factor (PAF) receptors. Oxidation of a synthetic phosphatidylcholine showed that an sn-1 ether bond confers an 800-fold increase in potency. This suggests that rare ether-linked phospholipids in LDL are the likely source of PAF-like activity in oxidized LDL. Accordingly, treatment of oxidized LDL with phospholipase A(1) greatly reduced phospholipid mass, but did not decrease its PAF-like activity. Tandem mass spectrometry identified traces of PAF, and more abundant levels of 1-O-hexadecyl-2-(butanoyl or butenoyl)-sn-glycero-3-phosphocholines (C(4)-PAF analogs) in oxidized LDL that comigrated with PAF-like activity. Synthesis showed that either C(4)-PAF was just 10-fold less potent than PAF as a PAF receptor ligand and agonist. Quantitation by gas chromatography-mass spectrometry of pentafluorobenzoyl derivatives shows the C(4)-PAF analogs were 100-fold more abundant in oxidized LDL than PAF. Oxidation of synthetic alkyl arachidonoyl phosphatidylcholine generated these C(4)-PAFs in abundance. These results show that quite minor constituents of the LDL phosphatidylcholine pool are the exclusive precursors for PAF-like bioactivity in oxidized LDL.

Modification of the lipid-protein interaction in human low-density lipoprotein destabilizes ApoB-100 and decreases oxidizability.

The interactions of the lipid and protein moiety of human low-density lipoprotein (LDL) and their influence on the oxidation behavior of LDL were modified using an amphipathic peptide, melittin, as a probe. The interaction of melittin with the LDL phospholipid surface resulted in a destabilization of apolipoprotein B-100 (apoB-100) as monitored by differential scanning calorimetry, while the characteristics of lipid core melting remained nearly unchanged. Binding of melittin caused a restriction of lipid chain mobility near the glycerol backbone, but not in the middle or near the methyl terminus of the fatty acyl chains as observed by electron paramagnetic resonance. Also, upon melittin addition, the level of copper binding to apoB-100 and the oxidizability of LDL by Cu2+ ions were greatly reduced, as indicated by abolished tryptophan fluorescence quenching upon Cu2+ binding and, during oxidation, prolongation of the lag phase of oxidation, attenuated consumption of alpha-tocopherol, and a lowered maximal rate of conjugated diene formation. This reduction of oxidizability could not be reversed by increasing the Cu2+ concentration. It is deduced that interaction of Cu2+ and alpha-tocopherol is required for reductive activation of the metal. It can be abolished by interfering with the interactions between apoB-100 and the lipid moiety of LDL which modifies the conformation of LDL and, as a consequence, hinders copper binding to apoB-100.

Platelet high affinity low density lipoprotein binding and import of lipoprotein derived phospholipids

The binding of low density lipoprotein (LDL) to the platelet cell membrane could facilitate the transfer of phospholipids from LDL to the platelets. A polyclonal antibody against the platelet glycoproteins IIb/IIIa inhibited the high affinity binding of 125I-LDL by up to 80%. The transfer of pyrene (py)-labeled sphingomyelin (SM), phosphatidylcholine and phosphatidylethanolamine from LDL to the platelets was unaffected by the antibody. The lectin wheat germ agglutinin (WGA) reduced the binding of 125I-LDL to the platelets by approximately 80%. In contrast, the lectin stimulated the transfer of SM from LDL into the platelets by about three-fold. WGA also specifically augmented the transfer of py-SM between lipid vesicles and the platelets, the stimulation being abolished in the presence of N-acetylglucosamine. Dextran sulfate (DS) increased the specific binding of 125I-LDL to the platelets by up to 2.8-fold. On the other hand, the import of LDL-derived py-phospholipids was unaffected by DS. Together, the results indicate that the phospholipid transfer from LDL to the platelets is independent of the high affinity LDL binding to the platelets and is specifically stimulated by WGA. Thus, the interactions of platelets with LDL phospholipids differ markedly from those with the apoprotein components of the lipoproteins.

Low-Density Lipoprotein Fatty Acids in Patients with Acute Myocardial Infarction

Dietary and plasma fatty acid composition is strongly related to the development of coronary heart disease (CHD). Since low-density lipoprotein (LDL) is the main vehicle for the uptake of lipids into the artery wall, it is important to know whether the fatty acid composition of this lipoprotein fraction differs in patients with CHD and healthy control subjects. The study comprised 59 newly presenting male patients with myocardial infarction (MI) and 94 healthy male control subjects. The cholesteryl esters (CE) of LDL of the MI group contained less 14:0 (p<0.0000001) and 16:0 (p<0.0001) but more 18:0 (p<0.0001) than those of the control group. For LDL phospholipids (PL), 14:0 (p<0.02) and 16:0 (p<0.0001) were higher in the MI group while 18:0 was lower (p<0.003). In addition, polyunsaturated acids 18:3n-3, 20:2n-6 and 20:4n-6 were all significantly lower in PL in the patient group. Triglyceride fatty acids showed little differences between the two groups. The most striking feature was the difference in the distribution of saturated fatty acids between the LDL CE and PL in the two subject groups (the ratio of PL saturates to CE saturates was 3.41 +/- 1.21 for the control group and 5.39 +/- 3.08 for the MI group (p<0.0000001). This study therefore demonstrates for the first time that highly significant differences occur in the relative proportions of LDL fatty acids in MI patients and control subjects and suggests the importance of dietary lipid intake and of lipid exchange during lipoprotein metabolism in producing LDL particles of low atherogenicity.

Phospholipase A2 type II binds to extracellular matrix biglycan: modulation of its activity on LDL by colocalization in glycosaminoglycan matrixes.

We recently reported the presence of secretory, nonpancreatic phospholipase A2 type II (snpPLA2; EC 3.1.1.4) in human atherosclerotic arteries (Hurt-Camejo et al, Arterioscler Thromb Vasc Biol. 1997;17:300-309). SnpPLA2 may generate the proinflammatory products lysophospholipids and free fatty acids, thus contributing to atherogenesis when acting on low density lipoproteins (LDLs) retained in the arterial wall. Immunohistochemical studies showed that smooth muscle cells (SMCs) in human arterial tissue are the main sources of snpPLA2. In cultures of human arterial SMCs, snpPLA2 interacts with versican and smaller heparan/chondroitin sulfate proteoglycans (PGs) secreted as soluble components into the medium. In the present study, we investigated the binding of snpPLA2 to extracellular matrix (ECM) PGs produced by SMCs. The results show that snpPLA2 can bind to the ECM at physiological salt concentrations. ECM-bound snpPLA2 was active, hydrolyzing phosphatidylcholine-containing micelles. Soluble chondroitin-6-sulfate at concentrations >1 micromol/L, but not heparin or heparan sulfate, was able to release ECM-bound snpPLA2. The PG mainly involved in the binding of snpPLA2 was identified as biglycan. Perlecan was also present in the ECM synthesized by SMCs, but it contributed less to the binding of snpPLA2. Experiments with immobilized glycosaminoglycans indicated that snpPLA2 hydrolyzed 7-fold more LDL phospholipids when the lipoprotein and the enzyme were colocalized in a matrix with chondroitin-6-sulfate compared with one with heparin. These data suggest that retention of snpPLA2 in ECMs of different composition may modulate the enzymatic activity of snpPLA2 toward LDL. The results presented in this work support the hypothesis of the potential contribution of snpPLA2 to atherosclerosis.

Effects of estrogen on susceptibility to oxidation of low-density and high-density lipoprotein in postmenopausal women

Objective: To investigate the effects of estrogen on the susceptibility to oxidation of low-density lipoprotein (LDL) and high-density lipoprotein (HDL) in postmenopausal women. Methods: A total of 23 postmenopausal women were treated with 0.625 mg of conjugated equine estrogen daily for 3 months. Blood samples were obtained before and after therapy. Plasma levels of total cholesterol and triglyceride and the concentrations of cholesterol, triglyceride, phospholipid in LDL and HDL were determined enzymatically and the levels of apolipoprotein A-I, A-II in HDL and apolipoprotein B in LDL were measured by turbidimetric immunoassay. The isolated LDL and HDL were incubated at 37°C for 24 h with CuSO 4 5 μmol/l and the lipid peroxide concentration of LDL and HDL was measured. Results: Estrogen significantly reduced the plasma level of total cholesterol and significantly increased the plasma level of triglyceride. The LDL concentrations of cholesterol, phospholipid and apolipoprotein B were significantly decreased following estrogen therapy. The triglyceride level of LDL did not change significantly. The HDL concentrations of cholesterol, triglyceride, phospholipid and apolipoprotein A-I and A-II were all significantly elevated after estrogen therapy. Estrogen significantly inhibited the peroxidation of LDL at 50–2000 μg of LDL protein (14.17±4.17–11.49±1.42 nmol/200 μg of LDL protein, P<0.001) and of HDL (4.49±1.74–3.37±1.24 nmol/200 μg of HDL protein, P<0.03) induced by their incubation in the presence of CuSO 4. Conclusions: Estrogen inhibited the susceptibility of LDL and HDL to oxidative modification and favorably affected lipid metabolism by reducing the number of LDL particles and increasing the number of HDL particles in plasma that were resistant to oxidation.

Structural and Functional Changes of Hen's Egg Yolk Low-Density Lipoproteins with Phospholipase A2

Structural and functional changes of hen's egg yolk low-density lipoproteins (LDL) as a result of modifying its phospholipids (PLs) using phospholipase A2 were examined. The 31P NMR spectrum and enzyme hydrolysis profiles revealed that the PLs are more susceptible in LDL complex than in small unilamellar vesicles (SUV) or PLs emulsions, suggesting higher membrane fluidity of LDL and that the interactions of proteins with PLs are not strong. Although the modification of PLs in LDL did not affect the secondary structure of proteins or immunological property of LDL, the emulsions stabilized with the modified LDL showed considerable heat stability. The differences in thermal behavior of modified LDL by DSC analysis suggested the formation of a structurally heat-stable complex of LysoPLs/polypeptides in LDL during heat treatment. The enhancement of PLs−protein interactions in LDL by phospholipase A2 could be responsible for the heat stability of emulsions made from the modified LDL. Keywords: Egg yolk; low-den...

Oxidation of Free Fatty Acids in Low Density Lipoprotein by 15-Lipoxygenase Stimulates Nonenzymic, α-Tocopherol-mediated Peroxidation of Cholesteryl Esters

15-Lipoxygenase has been implicated in the in vivo oxidation of low density lipoprotein (LDL) a process thought to be important in the origin and/or progression of human atherogenesis. We have suggested previously that oxidation of LDL's cholesteryl esters (CE) and phospholipids by soybean (SLO) or human recombinant 15-lipoxygenase (rhLO) can be ascribed largely to alpha-tocopherol (alpha-TOH)-mediated peroxidation (TMP). In this study we demonstrate that addition to LDL of unesterified linoleate (18:2), other free fatty acid (FFA) substrates, or phospholipase A2 (PLA2) significantly enhanced the accumulation of CE hydro(pero)xides (CE-O(O)H) induced by rhLO, whereas the corresponding CE and nonsubstrate FFA were without effect. The enhanced CE-O(O)H accumulation showed a dependence on the concentration of free 18:2 in LDL. In contrast, addition of 18:2 had little effect on LDL oxidation induced by aqueous peroxyl radicals or Cu2+ ions. Analyses of the regio- and stereoisomers of oxidized 18:2 in SLO-treated native LDL demonstrated that the small amounts of 18:2 associated with the lipoprotein were oxidized enzymically and within minutes, whereas cholesteryl linoleate (Ch18:2) was oxidized nonenzymically and continuously over hours. alpha-Tocopheroxyl radical (alpha-TO.) formed in LDL exposed to SLO was enhanced by addition of 18:2 or PLA2. With rhLO and 18:2-supplemented LDL, oxidation of 18:2 was entirely enzymic, whereas that of Ch18:2 was largely, though not completely, nonenzymic. The small extent of enzymic Ch18:2 oxidation increased with increasing enzyme to LDL ratios. Ascorbate and the reduced form of coenzyme Q, ubiquinol-10, which are both capable of reducing alpha-TO. and thereby preventing TMP, inhibited nonenzymic Ch18:2 oxidation induced by rhLO. Trolox and ascorbyl palmitate, which also inhibit TMP, ameliorated both enzymic and nonenzymic oxidation of LDL's lipids, whereas probucol, a radical scavenger not capable of preventing TMP, was ineffective. These results demonstrate that rhLO-induced oxidation of CE is largely nonenzymic and increases with LDL's content of FFA substrates. We propose that conditions which increase LDL's FFA content, such as the presence of lipases, increase 15-LO-induced LDL lipid peroxidation and that this process requires only an initial, transient enzymic activity.

The effect of growth hormone replacement therapy for up to 12 months on lipoprotein composition and lipoprotein(a) in growth hormone-deficient adults

The effect of growth hormone replacement therapy in near physiological doses on lipoprotein composition and serum lipoprotein(a) concentrations was investigated in growth hormone-deficient subjects. A randomised, double-blind, placebo-controlled trial of recombinant growth hormone was undertaken for 6 months followed by an open extension for a further 6 months (0.125 IU/kg per week for the first 4 weeks of each 6 month period and thereafter 0.25 IU/kg per week). A total of 18 patients with isolated growth hormone deficiency or hypopituitarism were studied. Lipid concentrations were estimated in lipoprotein fractions and protein concentrations were measured in low density lipoprotein (LDL). Glucose and glycated haemoglobin in blood and insulin, cholesterol, triglyceride, apolipoproteins A-I and B and lipoprotein(a) concentrations were measured in serum. In the placebo-controlled phase fasting blood glucose concentrations increased with growth hormone treatment from 5.0±0.2 to 5.8±0.2 mmol/l ( P=0.02) (mean±S.E.M.), although no significant changes were seen in lipids or lipoproteins. In the group receiving active treatment total serum cholesterol decreased from 6.0±0.4 to 5.2±0.3 mmol/l ( P=0.002) after 6 months, due to reduced LDL cholesterol concentrations. Low density lipoprotein protein concentrations fell (0.8±0.1 versus 0.7±0.1 g/l) ( P=0.005), and LDL phospholipid levels decreased from 0.9±0.1 to 0.7±0.1 mmol/l ( P=0.007). Serum cholesterol and LDL composition reverted to pre-treatment values by 12 months. Fasting blood glucose remained above pre-treatment values ( P=0.036) and fasting insulin was significantly increased ( P=0.044). There was no effect of growth hormone therapy on serum triglyceride, apolipoprotein or lipoprotein(a) concentrations. In conclusion, growth hormone therapy with near physiological doses has no long term effects on serum lipoprotein(a) concentrations or lipoprotein composition.

Ubiquinol-10 and total peroxyl radical trapping capacity of LDL lipoproteins during aging: The effects of Q-10 supplementation

Evidence is rapidly accumulating that oxidative modification of low density lipoprotein (LDL) may play an important role in the pathogenesis of atherosclerosis. In this study we measured the total peroxyl radical trapping capacity of human plasma LDL phospholipids (TRAP LDL) with a luminescent method. The study was carried out with 70 healthy volunteers, aged 28–77. In males an age-related decrease in TRAP LDL was observed. In the age group under 50 years the mean TRAP LDL was 31.36 ± 1.45 pmol peroxyl radicals/nmol Pi; among those over 50 years it was significantly lower at 26.67 0.94 pmol/nmol Pi. As regards the components of TRAp LDL, the concentration of LDL-ubiquinol did not change and a non-significant decrease in the LDL-tocopherol concentration was detected with age. In females, the mean TRAP LDL, LDL-ubiquinol-10 and tocopherol concentrations did not differ between the age groups. When 17 of the participants were given coenzyme Q 10 (Q 10) supplementation, 100 mg/day, a highly significant increase in LDL-ubiquinol concentration was detected. Our results indicate that LDL antioxidant defenses tend to decrease with age in the Finnish male population. The decline is most significant in males under 50 years; in older age groups the values remain stable at a low level. Q 10 supplementation doubles the number of ubiquinol-10-containing LDL molecules and may therefore have an inhibitory effect on LDL oxidation.

Effects of dietary cholesterol on hepatic production of lipids and lipoproteins in isolated hamster liver

The effect of 2-week 2% cholesterol vs. chow feeding on regulation of hepatic lipoprotein, lipids and apoprotein (Apo), and biliary lipids production was evaluated by the isolated perfused hamster liver model. Cholesterol feeding did not change very-low-density lipoprotein (VLDL), low-density lipoprotein (LDL), and high-density lipoprotein (HDL) particle size but significantly increased the hepatic production of VLDL-cholesterol fourfold, VLDL-triglyceride two and one-half-fold but not phospholipid in VLDL. It also increased LDL-cholesterol fourfold but not triglyceride or phospholipid in LDL, whereas lipids in HDL remained unchanged. Gradient sodium dodecyl sulfate-polyacrylamide gel electrophesis (SDS-PAGE) and Western blot analysis (density of apoprotein/density of albumin/g liver) indicated that cholesterol feeding enhanced Apo B tenfold, Apo A-I fivefold but not Apo E in VLDL. Apo E and Apo B did not change in LDL. Apo E but not Apo A-I increased (threefold) in HDL by cholesterol feeding. Cholesterol feeding decreased bile salt secretion 28% but increased cholesterol secretion 118% in bile, whereas phospholipid and bile volume remained unchanged. Increased Apo A-I in VLDL suggested that Apo A-I is involved in enhanced hepatic export of cholesterol and triglyceride. Different patterns of lipid and Apos in VLDL and LDL after cholesterol feeding also suggested separate VLDL and LDL export mechanisms. Elevated Apo E but not lipids in HDL after cholesterol feeding suggests that hepatic HDL may function as a carrier of newly synthesized hepatic Apo E into the circulation for transfer to other lipoproteins (chylomicron [CM], CMr) to facilitate hepatic cholesterol uptake and clearance. (Hepatology 1996 Aug;24(2):424-34)

Effects of Dietary Cholesterol on Hepatic Production of Lipids and Lipoproteins in Isolated Hamster Liver

The effect of 2-week 2% cholesterol vs. chow feeding on regulation of hepatic lipoprotein, lipids and apoprotein (Apo), and biliary lipids production was evaluated by the isolated perfused hamster liver model. Cholesterol feeding did not change very-low-density lipoprotein (VLDL), low-density lipoprotein (LDL), and high-density lipoprotein (HDL) particle size but significantly increased the hepatic production of VLDL-cholesterol fourfold, VLDL-triglyceride two and one-half-fold but not phospholipid in VLDL. It also increased LDL-cholesterol fourfold but not triglyceride or phospholipid in LDL, whereas lipids in HDL remained unchanged. Gradient sodium dodecyl sulfate-polyacrylamide gel electrophesis (SDS-PAGE) and Western blot analysis (density of apoprotein/density of albumin/g liver) indicated that cholesterol feeding enhanced Apo B tenfold, Apo A-I fivefold but not Apo E in VLDL. Apo E and Apo B did not change in LDL. Apo E but not Apo A-I increased (threefold) in HDL by cholesterol feeding. Cholesterol feeding decreased bile salt secretion 28% but increased cholesterol secretion 118% in bile, whereas phospholipid and bile volume remained unchanged. Increased Apo A-I in VLDL suggested that Apo A-I is involved in enhanced hepatic export of cholesterol and triglyceride. Different patterns of lipid and Apos in VLDL and LDL after cholesterol feeding also suggested separate VLDL and LDL export mechanisms. Elevated Apo E but not lipids in HDL after cholesterol feeding suggests that hepatic HDL may function as a carrier of newly synthesized hepatic Apo E into the circulation for transfer to other lipoproteins (chylomicron [CM], CMr) to facilitate hepatic cholesterol uptake and clearance.

Effects of pancreas transplantation on distribution and composition of plasma lipoproteins

In type I (insulin-dependent) diabetic patients, peripheral hyperinsulinemia due to subcutaneous insulin treatment is associated with increased high-density lipoprotein (HDL) cholesterol, and also with an altered surface composition of HDL. Pancreas grafts also release insulin into the systemic rather than into the portal venous system, giving rise to pronounced peripheral hyperinsulinemia. We hypothesized that if peripheral hyperinsulinemia is responsible for high HDL cholesterol and/or altered surface composition of HDL in diabetic subjects, similar changes in the lipid profile should be present in pancreas-kidney transplant recipients (PKT-R). Using zonal ultracentrifugation, we isolated HDL 2, HDL 3, very-low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), and low-density lipoprotein (LDL) from fasting plasma of 14 type I diabetic PKT-R, eight nondiabetic kidney transplant recipients (KT-R), and 14 healthy control subjects and determined the level and composition of the above lipoproteins. HDL 2 cholesterol was increased in PKT-R as compared with KT-R and healthy controls (both P < .05), whereas HDL 3 cholesterol was unchanged. However, an altered lipoprotein surface composition was evident in PKT-R: HDL 2, HDL 3, and LDL were enriched in unesterified cholesterol ([UC] PKT-R v KT-R, P = .13, P < .005, and P < .05, respectively; PKT-R v controls, all P < .005); HDL 2 was enriched in phospholipids; and LDL was depleted of phospholipid. KT-R, in contrast, showed no changes in lipoprotein surface composition but a substantial triglyceride enrichment of HDL 2 as compared with PKT-R and healthy controls (both P < .05). LDL size as determined by gradient gel electrophoresis was increased in PKT-R compared with controls ( P < .005). The plasma concentration of cholesteryl ester (CE) transfer protein (CETP), involved also in phospholipid transfer, was increased in both transplant groups compared with healthy controls (both P < .05). Insulin concentrations in fasting plasma were directly related to CETP levels and to the weight-percentage of UC in HDL 3, and inversely to the weight-percentage of phospholipids in LDL (all P < .05). We explain the increase in HDL 2 cholesterol and LDL size in PKT-R by their high lipoprotein lipase (LPL) activity conferring an excellent capacity to clear chylomicron triglycerides. Effective handling of postprandial triglycerides, high HDL 2 cholesterol, and predominance of LDL pattern A, respectively, are established indicators of a low risk of atherosclerosis. However, it is presently unclear what effects the compositional changes on the surface of HDL and LDL may have on cardiovascular risk in clinically stable PKT-R.

Plasmalogen phospholipids in plasma lipoproteins of normolipidemic donors and patients with hypercholesterolemia treated by LDL apheresis

Recent evidence indicates that plasmalogen phospholipids are particularly sensitive to oxidation and may possess antioxidative properties. Approximately 4.4%–5.5% of phosphatidylcholine (PC), and 53%–60% of phosphatidylethanolamine (PE) consisted of the plasmalogen phospholipids, plasmenylcholine and plasmenylethanolamine, respectively, in whole plasma, low density lipoprotein (LDL) and high density lipoprotein (HDL) of 11 normolipidemic donors. Of total plasmalogen phospholipids in plasma, slightly more was associated with LDL particles (about 42%) than with HDL (36%). Plasmalogen phospholipid levels were analyzed in 12 patients with familial hypercholesterolemia (FH) regularly treated by LDL apheresis, of whom 6 were supplemented with vitamin E (alpha tocopherol, 400 IU/day), the remaining 6 not receiving the antioxidant. Before apheresis (pre), total plasmalogen phospholipid levels in plasma and LDL (expressed as μmol/mmol cholesterol of compartment) decreased as follows: patients receiving vitamin E > normolipidemia > patients not receiving vitamin E. In both hypercholesterolemic groups, the contents of plasmalogen phospholipids in whole plasma and LDL were 3–5-fold higher than those of vitamin E. Directly after apheresis (post), plasmalogen phospholipid levels in plasma were raised by about 50% in the two hypercholesterolemic groups, mostly due to increases in plasmenylethanolamine levels. Two days after apheresis (48 h post), plasmalogen contents were still elevated in plasma and red blood cell membranes of patients receiving vitamin E, while they had already reached pre-apheresis values in those not supplemented with alpha tocopherol. Molecular species of plasma diacyl phospholipids containing polyunsaturated fatty acids were elevated at pre in patients receiving vitamin E as compared to patients without supplementation. At 48 h post, LDL apheresis induced an increase in these molecular species only in patients receiving vitamin E. In conclusion, the contents of plasmalogen phospholipids in plasma lipoproteins are at least three times higher than those of vitamin E. LDL apheresis raises the level of plasmalogen phospholipids in plasma, the increase persisting longer in patients supplemented with vitamin E. Supplementation with vitamin E appears to protect plasmalogen phospholipids in plasma lipoproteins against oxidative degradation.