Prostacyclin and vascular disease

We hypothesize that prostacyclin (PGI2) is an anti-atherosclerotic hormone and that atherosclerosis develops when endothelial PGI2 synthetase is inhibited by lipid peroxides. Serum lipid peroxides occur in low-density lipoproteins (LDL). LDL lipid peroxides are elevated in common types of hyperlipoproteinaemias, PGI2 generation is impaired in atherosclerosis, and infusion of synthetic PGI2 into patients alleviates symptoms resulting from arteriosclerosis obliterans, central retinal vein occlusion or spontaneous angina.     

Increased oxidazability of plasma low density lipoprotein from patients with coronary artery disease

Oxidative modification of lipoproteins may play a crucial role in the pathogenesis of atherosclerosis. This study was designed to examine whether increased lipid peroxides and/or oxidative susceptibility of plasma lipoproteins occur in patients with coronary artery disease. The levels of lipid peroxides, estimated as thiobarbituric acid-reactive substances (TBARS), were significantly greater in the plasma and very low density lipoprotein (VLDL) of symptomatic patients with coronary artery disease than in those of healthy persons, but the TBARS levels of low density lipoprotein (LDL) and high density lipoprotein (HDL) showed insignificant difference between patients and normals. To evaluate the oxidative susceptibility of lipoproteins, we employed in vitro Cu²⁺ oxidation of lipoproteins monitored by changes in fluorescenece, TBARS level, trinitrobenzene sulfonic acid (TNBS) reactivity, apolipoprotein immunoreactivity and agarose gel electrophoretic mobility. While VLDL and LDL of normal controls were oxidazed at 5–10 μM Cu²⁺, pooled VLDL and LDL of patients with coronary artery disease were oxidized at 1–2.5 μM Cu²⁺, i.e., at relatively lowver oxidative stress. At 5 μM Cu²⁺, VLDL and LDL of patients with coronary artery disease still showed at faster oxidation rate, judged by the rate of fluorescence increase, higher TBARS level, less TNBS reactivity, greater change in apo B immunoreactivity and higher electrophoretic mobility than those of normal controls. However, the difference on the oxidizability of HDL was insignificant for patients vs. normals. In conclusion, we have shown that plasm VLDL and LDL of patients with coronary artery disease are more susceptible to in vitro oxidative modification than those of health persons. The data suggest that enhanced oxidizability of plasma lipoproteins may be important factor influencing the development of coronary artery disease.     

Inhibition of prostaglandin I2 (PGI2) formation by LDL-cholesterol or LDL-peroxides?

A hypothesis of Gryglewski et al. explains the correlation between increased level of LDL and development of atherosclerosis by inhibition of PGI₂ synthesis by increased peroxide content of LDL. The aim of the present paper was to examine this hypothesis. The major results are: 1) Preparation of LDL in the presence of .02 % butylated hydroxytoluene did not reduce the lipid peroxide content of LDL from men and women and not change the inhibition or stimulation of the in vitro biosynthesis of PGI₂ by LDL isolated from blood of men or women, respectively. 2) In the LDL and HDL, respectively, of healthy men we found nearly the same lipid peroxide levels (nmole malondialdehyde (MDA)/mg lipoprotein-cholesterol) as in the lipoproteins of male patients with hyperlipidemia type IIa or IV, but the peroxide concentration is three times higher in HDL as in LDL. 3) LDL isolated from healthy men inhibited in dose dependent fashion the generation of PGI₂ from PGH₂ by aortic microsomes whereas LDL from premopausal women stimulated PGI₂ formation even calculated as LDL lipid peroxides (in nM MDA/ml). The results call into question the hypothesis that diminished PGI₂ formation by atherosclerotic vessels is related to inhibition of PGI₂ synthetase by lipid peroxides present in LDL in the lesions. A new working hypothesis is presented that also the fatty acid pattern and the lipid class composition in the LDL are important for their influence on the PGI₂ formation.     

Lipid peroxidation--the factor promoting cholesterol accumulation in cells in atherogenesis

The cholesterol transfer between human erythrocytes and main classes of serum lipoproteins (LP) from healthy donors and artery-coronary disease patients was studied (artery-coronary disease is the main manifestation of atherosclerosis). It is shown that low-density lipoproteins (LDL) are capable of transporting cholesterol to erythrocytes, which lack the specific receptors for LDL. The cell cholesterol content in comparison with erythrocytes incubated without LDL was increased by 11.4%. The effect was even higher in case of LDL, isolated from serum of artery-coronary subjects (the cell cholesterol content was increased by 33.8%). High-density lipoproteins (HDL) accept cholesterol from cell membranes. However, cholesterol-accepting properties of HDL from artery-coronary disease patients were suppressed as compared with normal HDL. Both discovered events must promote the cholesterol accumulation in cell membranes in atherosclerosis. As it is shown by the spin probe method, lipid peroxidation (LPO) causes the disturbance of the structural organization of LP and as the consequence of that--the increase of LDL cholesterol-donating ability and the decrease of HDL cholesterol-accepting ability. The greater LDL are oxidized, the more cholesterol they transport to erythrocytes during incubation. The greater is the level of HDL peroxidation, the stronger their cholesterol-accepting function is suppressed. These results suggest that LPO can play an important role in LP modification, the disturbance of their interaction with cell surface and the cholesterol accumulation in cells in atherosclerosis.     

Isolation of desialylated low density lipoproteins from the blood of patients with ischemic heart disease by affinity chromatography

The attempt was performed to isolate desialylated low density lipoproteins (LDL) from the blood of healthy subjects and patients with coronary heart disease by affinity chromatography with immobilized agglutinin of Ricinus communis, a lectin that interacts specifically with galactose residues. A part of LDL was bound to sorbent and could be replaced by galactose but not other saccharide constituents of the LDL molecule. Bound LDL subfraction had a 2-3-fold lower content of desialylated LDL in CAD patients was about 3-fold higher than in healthy subjects. Desialylated LDL induced a 2- to 4-fold increase of total cholesterol content in cultured human aortic intimal cells, whereas unbound LDL had no effect on intracellular cholesterol level. It is assumed that the subfraction of desialylated LDL may be responsible for the atherogenic properties of LDL in CAD patients.     

Does paraoxonase play a role in susceptibility to cardiovascular disease?

Human serum paraoxonase (PON1) is an esterase that is bound to high-density lipoproteins (HDLs). It can hydrolyze organophosphates and its activity is inversely related to atherosclerosis. Some studies also suggest that a relationship exists between polymorphisms of the gene that encodes paraoxonase and coronary heart disease (CHD), whereas other studies, in different populations, have not found such an association. One mechanism by which certain PON1 allozymes might protect against atherosclerosis is by inhibition of the oxidation of HDL and low-density lipoprotein (LDL). Experimental studies suggest that this protection is associated with the ability of PON1 to hydrolyze specific lipid peroxides in oxidized lipoproteins. Interventions that preserve or enhance PON1 activity, as well as manipulations of PON1 polymorphisms, might help delay the onset of CHD.     

Low density lipoproteins isolated from the blood of patients with ischemic heart disease induce accumulation of lipids in human aortic intima cells

Very low density lipoproteins (VLDL), low density lipoproteins (LDL) and high density lipoproteins (HDL) were isolated from the blood of healthy subjects and CHD patients. LDL from the blood of healthy individuals did not raise the intracellular lipid values within 24 h of cultivation. During intracellular lipid values within 24 h of cultivation. During the same incubation period. LDL obtained from the blood of CHD patients caused a 2- to 5-fold rise in cholesterol esters as well as a 1.5- to 3-fold rise in free cholesterol and triglycerides, while the intracellular phospholipid levels remained unchanged. In one of the three cases, the ability to raise the intracellular level of cholesterol esters was demonstrated by VLDL (500 micrograms/ml) derived from CHD patients blood. HDL did not affect the lipid levels in smooth muscle cells cultured from unaffected intima. The obtained data suggests that circulating LDL and, possibly, VLDL in the blood of CHD patients are capable of inducing the accumulation of fat in vascular wall cells.     

Physico-chemical properties of low density lipoproteins isolated in an equilibrium density gradient

The tryptophanyls of total low density lipoproteins (LDL) (1.006-1.063 g/ml) from coronary heart disease (CHD) patients and subjects without CHD signs had different accessibility to fluorescence quenchers (I-and acrylamide). LDL were separated into subfractions in equilibrium density gradient. The coefficient of extinction , quantum yield and other spectral characteristics of LDL intrinsic fluorescence, rotational mobility of maleimide spin labels and fatty acid spin probe were different in LDL subfractions from healthy subjects. LDL subfractions with hydrated density 1.045-1.05 g/ml bound to B,E-receptors of cultured fibroblasts more effectively than did subfractions with density 1.01-1.03 g/ml. Structural differences of apo-B in the particles with different lipid to protein ratio are supposed.     

Oxidized lipoproteins in blood plasma: possible marker of atherosclerosis progression

Oxidized lipoproteins and antioxidants were detected during the course of hypercholesterolemia development in cholesterol-fed rabbits. Lipid peroxides in blood plasma and very-low-, low-, and high-density lipoproteins (beta-VLDL, LDL, and HDL) were increased during the course of hypercholesterolemia. The content of phospholipid peroxides increased in beta-VLDL and LDL in parallel to that of cholesterol, whereas the amount of alpha-tocopherol was decreased either in lipoproteins or blood plasma. Ascorbate and urate concentrations were also decreased. Lipid peroxides were positively correlated with volume and area of atherosclerotic lesions, suggesting a relation between the concentrations of lipid peroxides in blood plasma and the progression of atheromatous lesions.     

Changes in the surface potential of plasma lipoproteins in ischemic heart disease. Studied with spin probes

Changes in lipoprotein surface potentials were studied by a positively charged analog as a spin probe. Low density lipoproteins (LDL) and high density lipoproteins (subfractions HDL2 and HDL3) of patients with coronary heart disease (CHD) were studied. CHD patients have revealed a significant decrease (by 14.4 +/- 0.3 mV) in LDL and an increase (by 6.3 +/- 2.0 mV) in HDL3 negative surface potential, as compared to the control. The increase in HDL2 surface potential in CHD patients was insignificant (1.9 +/- +/- 2.5 mV). The possible role of LDL and HDL3 surface potential changes in the mechanism of interaction of these types of lipoproteins with vascular wall and blood cellular membranes and in pathogenesis of CHD and atherosclerosis is discussed.     

Enrichment of endothelial cell arachidonate by lipid transfer from high density lipoproteins: relationship to prostaglandin I2 synthesis

We have previously shown that plasma high density lipoproteins (HDL) stimulate release of prostacyclin, measured as its stable metabolite, 6-keto-PGF1 alpha, by cultured porcine aortic endothelial cells. The present experiments were designed to elucidate the contribution of HDL lipids to endothelial cellular phospholipid pools and to prostacyclin synthesis. In experiments with reconstituted HDL, both the lipid and protein moieties were required to stimulate prostacyclin release in amounts equivalent to the native HDL particle. Endothelial cells incorporated label from reconstituted HDL containing cholesteryl [1-14C]arachidonate into the cellular neutral and phospholipid pools as well as into 6-keto-PGF1 alpha and PGE2. Labeled arachidonate incorporated into endothelial cell lipids from reconstituted HDL containing cholesteryl [1-14C]arachidonate was also metabolized to prostaglandins after the cells were exposed to the calcium ionophore, A-23187. Both rat and human HDL which stimulated 6-keto-PGF1 alpha release (rat greater than human) increased the weight percentage of arachidonate in endothelial cell phospholipids; phospholipid arachidonate in the enriched cells fell after exposure to the phospholipase activator, A-23187, with release of 6-keto-PGF1 alpha which was greater than in control cells. Rat HDL that was depleted of cholesteryl arachidonate (achieved by incubation with human low density lipoproteins (LDL) in the presence of cholesteryl ester transfer protein) stimulated 6-keto-PGF1 alpha release less than native rat HDL. LDL enriched in cholesteryl arachidonate stimulated 6-keto-PGF1 alpha release more than native LDL. ApoE-depleted HDL also stimulated 6-keto-PGF1 alpha release more than apoE-rich HDL suggesting the apoE receptor was not involved in the response.(ABSTRACT TRUNCATED AT 250 WORDS)     

Oxidized cholesterol in the diet is a source of oxidized lipoproteins in human serum

The aim of this study was to determine in humans whether oxidized cholesterol in the diet is absorbed and contributes to the pool of oxidized lipids in circulating lipoproteins. When a meal containing 400 mg cholestan-5alpha,6alpha-epoxy-3beta-ol (alpha-epoxy cholesterol) was fed to six controls and three subjects with Type III hyperlipoproteinemia, alpha-epoxy cholesterol in serum was found in chylomicron/chylomicron remnants (CM/RM) and endogenous (VLDL, LDL, and HDL) lipoproteins. In controls, alpha-epoxy cholesterol in CM/RM was decreased by 10 h, whereas in endogenous lipoproteins it remained in the circulation for 72 h. In subjects with Type III hyperlipoproteinemia, alpha-epoxy cholesterol was mainly in CM/RM. In vitro incubation of the CM/RM fraction containing alpha-epoxy cholesterol with human LDL and HDL that did not contain alpha-epoxy cholesterol resulted in a rapid transfer of oxidized cholesterol from CM/RM to both LDL and HDL. In contrast, no transfer was observed when human serum was substituted with rat serum, suggesting that cholesteryl ester transfer protein is mediating the transfer. Thus, alpha-epoxy cholesterol in the diet is incorporated into the CM/RM fraction and then transferred to LDL and HDL, contributing to lipoprotein oxidation. Moreover, LDL containing alpha-epoxy cholesterol displayed increased susceptibility to further copper oxidation in vitro. It is possible that oxidized cholesterol in the diet accelerates atherosclerosis by increasing oxidized cholesterol levels in circulating LDL and chylomicron remnants.     

阻塞性睡眠呼吸暂停低通气综合征患者血脂水平的变化

探讨阻塞性睡眠呼吸暂停低通气综合征(OSAHS)与血脂水平的关系。方法:选取32例OSAHS患者(OSAHS组)为试验组和30例健康体检者为对照组,均经多导睡眠监测仪(PSG)检查,测定空腹血清总胆固醇(TC)、甘油三酯(TG)、高密度脂蛋白(HDL)、低密度脂蛋白(LDL)的含量,比较两组间的差异。结果:OSAHS组空腹时TC、TG、LDL显著高于对照组,而HDL显著低于对照组。结论:OSAHS可引起脂质代谢异常,从而促进心血管疾病的发生。     

Severity of coronary atherosclerosis related to lipoprotein concentration.

The influence of individual lipoproteins on the severity of coronary atherosclerosis was studied in 41 patients undergoing coronary angiography. The extent of athero-sclerosis was quantified by a coronary atherosclerosis score (CAS) based on the number and severity of lesions in eight proximal segments of the coronary circulation. The concentration of high-density lipoprotein (HDL) showed a strong inverse association with CAS, which was independent of the effects of age and other lipoproteins. On multivariate analysis concentrations of other lipids--namely, total plasma cholesterol, low-density lipoprotein (LDL) cholesterol, and the combined effect of LDL cholesterol plus very-low-density lipoprotein triglyceride--showed direct, significant correlations with CAS, but these were weaker than that of HDL. This study shows that concentrations of several circulating lipoproteins are related to the severity of coronary atherosclerosis, HDL having an apparent retarding effect. These findings may partly explain the influence of lipoproteins on the development of clinical coronary heart disease.     

Study of the components of reverse cholesterol transport in lecithin:cholesterol acyltransferase deficiency

Enzymatic and lipid transfer reactions involved in reverse cholesterol transport were studied in healthy and lecithin:cholesterol acyltransferase (LCAT), deficient subjects. Fasting plasma samples obtained from each individual were labeled with [3H]cholesterol and subsequently fractionated by gel chromatography. The radioactivity patterns obtained corresponded to the elution volumes of the three major ultracentrifugally isolated lipoprotein classes (very low density lipoproteins (VLDL), low density lipoproteins (LDL), and high density lipoproteins (HDL)). In healthy subjects, the LCAT activity was consistently found in association with the higher molecular weight portion of HDL. Similar observations were made when exogenous purified LCAT was added to the LCAT-deficient plasma prior to chromatography. Incubation of the plasma samples at 37 degrees C resulted in significant reduction of unesterified cholesterol (FC) and an increase in esterified cholesterol (CE). Comparison of the data of FC and CE mass measurements of the lipoprotein fractions from normal and LCAT-deficient plasma indicates that: (i) In normal plasma, most of the FC for the LCAT reaction originates from LDL even when large amounts of FC are available from VLDL. (ii) The LCAT reaction takes place on the surface of HDL. (iii) The product of the LCAT reaction (CE) may be transferred to either VLDL or LDL although VLDL appears to be the preferred acceptor when present in sufficient amounts. (iv) CE transfer from HDL to lower density lipoproteins is at least partially impaired in LCAT-deficient patients. Additional studies using triglyceride-rich lipoproteins indicated that neither the capacity to accept CE from HDL nor the lower CE transfer activity were responsible for the decreased amount of CE transferred to VLDL and chylomicrons in LCAT-deficient plasma.     

Modulation of TXA2 generation of platelets by human lipoproteins

The lipoprotein (LP) fractions VLDL, LDL, HDL2 and HDL3 were prepared by ultracentrifugation of plasma from healthy volunteers and from patients with coronary heart disease (CHD). We investigated the capacity of platelets from healthy volunteers and patients with atherosclerosis to generate thromboxane A2 (TXA2) during spontaneous clotting of whole blood under the influence of the lipoprotein fractions. In our experiments the serum concentration of TXB2, reflecting the capacity of platelets to generate TXA2 during clotting, depends on several factors: the type of LP fraction used, the blood used for generation of TXA2, and for the same LP fraction whether it was taken from plasma of healthy volunteers or patients with CHD. VLDL prepared from plasma of healthy volunteers inhibited but VLDL prepared from plasma of patients with CHD enhanced the TXA2 formation of platelets from healthy volunteers (p less than 0.05, resp.). LDL from CHD patients inhibited the TXA2 formation of platelets from atherosclerotic patients (p less than 0.01). The HDL subfractions HDL2 and HDL3 from healthy volunteers inhibited TXA2 formation by platelets from healthy volunteers as well as those from atherosclerotic patients (p less than 0.05; p less than 0.01, respectively). HDL2 from patients with CHD inhibited only the TXA2 formation of platelets from healthy volunteers (p less than 0.01), whereas HDL3 from CHD patients inhibited only the TXA2 formation of platelets from atherosclerotic patients (p less than 0.01).     

Separation and selective detection of lipoprotein particles of patients with coronary artery disease by frit-inlet asymmetrical flow field-flow fractionation

An analytical method to improve the characterization of lipoprotein fractions is presented. Human plasma samples were treated with Sudan Black B to stain the lipid component in lipoproteins, then the stained lipoproteins were separated by frit inlet asymmetrical flow field-flow fractionation (FI-AFlFFF), according to the lipoprotein particle sizes, with the selective detection of eluting lipoprotein fractions, high-density lipoproteins (HDL), low-density lipoproteins (LDL) and very-low-density lipoproteins (VLDL), at 610 nm. The capability of this technique has been evaluated with plasma samples obtained from patients with coronary artery disease (CAD), and it showed that the retention profile of patients' lipoprotein samples was clearly distinct from those of healthy persons. The potential of this technique comes with the direct injection of a stained lipoprotein sample without a prior procedure such as ultracentrifugation for sample preparation, and the size calculation of lipoprotein particles from the experimental retention time by theory. Since sample relaxation was achieved hydrodynamically in an FI-AFlFFF channel, sample injection and separation processes were continuously made without stopping the separation flow. This study demonstrated the potential of the FI-AFlFFF technique to be utilized as a powerful tool for the determination of the LDL profiles of patients with CAD.     

Profil lipidoprotéinique,isotopique et risque athérogène dans la drépanocytose en Côte d’Ivoire

The principal goal of this study was to assess the possible disturbances of lipids and lipoproteins in sickle cell disease and establish a relationship between painful crisis and atherogenic risks by the atherogenicity index in Ivoirian adults. We analysed serum plasma lipid and lipoprotein profiles of 126 subjects with sickle cell anemia, and 55 “Hb AA” healthy individuals. The lipid and lipoprotein parameters studied were total cholesterol, triglycerids, HDL, LDL, apoproteins A1 and B, electrophoresis of lipoproteins and haemoglobin. In painful crisis, levels of total cholesterol, HDL-cholesterol, LDL-cholesterol, apoproteins A1 (apo A1) in sickle cell anemia patients were shown to be significantly lower and levels of triglycerides higher than that of control group and steady state. The electrophoresis profile showed a significant fall of α lipoproteins while β lipoproteins were significantly high in period of crisis. The atherogenicity index (total cholesterol/HDL ratio) was also significantly high, just as LDL/HDL ratio in period of crisis. The overview of these results might hypothesize a high relatively atherogenic risk during the sickle-cell anemia crisis. A special monitoring of the patients in crisis is also necessary in order to prevent the risk of cardiovascular diseases.     

Comparative biochemical analysis of blood serum lipoproteins from human and various animal species

Lipid composition of blood serum and total lipids of low density lipoproteins (LDL) and high density lipoproteins (HDL2 and HDL3) were studied in human (donors, patients with ischemic heart disease, bronchial asthma, chronic obstructive bronchitis, as well as with a combined pathology), in mammals predisposed to atherosclerosis (pig, rabbit) and resistant to atherosclerosis (rat, mink, Arctic fox), in birds (hen, pigeon), in teleost fish (white fish, pikeperch, pike, bream, burbot) and cartilaginous fish (sturgeon, housen). It has been established that the most enriched in lipids is the blood serum of animals, particularly of cartilaginous fish. Twice lower is the lipid content in blood serum of donors than of animals. However, in the vascular, bronchial-pulmonary, and combined human pathologies the lipid level rises statistically significantly. In human and in animals predisposed to atherosclerosis the main mass of lipid is located in LDL, whereas in animals resistant to this disease--in HDL. The ratio of the human lipid content in LDL/HDL increases from 1.4 (in donors) to 2.7 in pathological states--in ischemic heart disease and its combination with chronic obstructive disease. In animals, a decrease of this ratio is noted from 1.0 to 0.2 in cartilaginous fish. By the example of one taxon (fish) there is established a regularity that indicates that evolution of lipoproteins occurred with an increase of the lipid amount in the "younger" LDL and with a decrease of concentration of the "colder" HDL.     

Changes in the surface charge of plasma lipoproteins during their auto-oxidation

Low density lipoproteins (LDL) and high density lipoproteins (HDL) surface potential (charge) changes were studied upon autooxidation, using positively charged spin probes. Lipid peroxidation product accumulation in LDL and HDL suspensions was found to be accompanied by a significant reduction in their surface area associated with a decreased negative surface charge, and probably, deposition of lipid peroxidation polar products and/or surface charge redistribution as a result of lipoprotein autooxidative modification.