Alterations of high density lipoprotein subclasses in obese subjects

The object of this study was to investigate the characteristics of lipid metabolism in obese subjects, with particular emphasis on the alteration of HDL subclass contents and distributions. A population of 581 Chinese individuals was divided into four groups (25 underweight subjects, 288 of desirable weight, 187 overweight, and 45 obese) according to body mass index (BMI). Apoprotein A-I (apoA-I) contents of plasma HDL subclasses were determined by 2-D gel electrophoresis associated with an immunodetection method. The concentrations of TG and the apoA-I content of pre-α₁-HDL were significantly higher (P<0.01 and P<0.01, respectively), but the levels of HDL cholesterol, and the apoA-I contents of HDL_2a and HDL_2b were significantly lower (P<0.01, P<0.05, and P<0.01, respectively) in obese subjects than in subjects having a desirable weight. Moreover, with the elevation of BMI, small-sized pre-α₁-HDL increased gradually and significantly, whereas large-sized HDL_2b decreased gradually and significantly. Meanwhile, the variations in HDL subclass distribution were more obvious with the elevation of TG levels in obese as well as overweight subjects. In addition, Pearson correlation analysis revealed that BMI and TG levels were positively correlated with pre-α₁-HDL but negatively correlated with HDL_2b. Multiple regression analysis also showed that TG concentrations were associated independently and positively with high pre-α₁-HDL and independently and negatively with low HDL_2b in obese and overweight subjects. The HDL particle size was smaller in obese and overweight subjects. The shift to smaller size was more obvious with the elevation of BMI and TG, especially TG levels. These observations, in turn, indicated that HDL maturation might be abnormal, and reverse cholesterol transport might be impaired. The first two authors contributed equally to this study.     

Oxidative Modification and Poor Protective Activity of HDL on LDL Oxidation in Thalassemia

Oxidative modification of low-density lipoprotein (LDL) has been reported in thalassemia, which is a consequence of oxidative stress. However, the levels of oxidized high-density lipoprotein (HDL) in thalassemia have not been evaluated and it is unclear whether HDL oxidation may be linked to LDL oxidation. In this study, the levels of total cholesterol, iron, protein, conjugated diene (CD), lipid hydroperoxide (LOOH), and thiobarbituric acid reactive substances (TBARs) were determined in HDL from healthy volunteers and patients with β-thalassemia intermedia with hemoglobin E (β-thal/Hb E). The protective activity of thalassemic HDL on LDL oxidation was also investigated. The iron content of HDL₂ and HDL₃ from β-thal/HbE patients was higher while the cholesterol content was lower than those in healthy volunteers. Thalassemic HDL₂ and HDL₃ had increased levels of lipid peroxidation markers i.e., conjugated diene, LOOH, and TBARs. Thalassemic HDL had lower peroxidase activity than control HDL and was unable to protect LDL from oxidation induced by CuSO₄. Our findings highlight the oxidative modification and poor protective activity of thalassemic HDL on LDL oxidation which may contribute to cardiovascular complications in thalassemia.     

Interaction of plasma high density lipoprotein HDL2b (d 1.063–1.100 g/ml) with single-bilayer liposomes of dimyristoylphosphatidylcholine

Incubation of a major subfraction, HDL_2b (d 1.063–1.100 g/ml), of human plasma high density lipoproteins, HDL (d 1.063–1.21 g/ml), with single-bilayer liposomes of dimyristoylphosphatidylcholine (DMPC) resulted in uptake of DMPC by the HDL_2b and dissociation of lipid-free apolipoprotein A-I (apoA-I). In the presence of excess DMPC, the dissociated apoA-I was also incorporated with DMPC into discoidal complexes. Preliminary studies with model apoA-I-DMPC complexes indicated that they also can interact with native HDL_2b with the resultant transfer of their DMPC to HDL_2b and the concomitant release of their apoA-I. After interaction of HDL_2b with DMPC liposomes, the DMPC-enriched HDL_2b product showed a lower hydrated density and a larger particle size than the control HDL_2b. The molecular properties of the lipoprotein product suggest that stabilization of the apoA-I-depleted HDL_2b probably occurred via substitution of DMPC for the apoA-I at the HDL_2b surface rather than by fusion of the apoA-I-depleted HDL_2b. The above interactions of HDL_2b with single-bilayer liposomes and discoidal complexes indicate pathways of phospholipid transfer relevant to the possible role of HDL in the metabolism of lipoprotein surface components in vivo.     

Statin Treatment Improves Plasma Lipid Levels but not HDL Subclass Distribution in Patients Undergoing Percutaneous Coronary Intervention

Despite the established efficacy of statin therapy, the risk of cardiovascular events remains high in many patients. We examined high-density lipoprotein (HDL) subclass distribution profiles among statin-treated coronary heart disease (CHD) patients undergoing percutaneous coronary intervention (PCI). Plasma HDL subclasses were measured in 85 patients with established CHD and quantified by two-dimensional gel electrophoresis and immunoblotting. In CHD patients with statin treatment, the mean value of total cholesterol (TC) reached the desirable level and the triacylglycerol level (TAG) was borderline high. Moreover, low density lipoprotein cholesterol (LDL-C), high density lipoprotein cholesterol (HDL-C), apolipoproteinA-I, and apolipoproteinB-100 levels in these patients resembled those in normolipidemic healthy subjects. The HDL subclass did not show a normal distribution and was characterized by the lower large-sized HDL_2b contents and higher contents of small-sized preβ₁-HDL in CHD patients, compared to those in normolipidemic control subjects. Multiple stepwise regression analysis revealed that the severity of coronary stenosis, determined by the Gensini Score, was significantly and independently predicted by HDL_2b and HDL_3b. Statin therapy was effective in modifying plasma lipids levels, but not adequate as a monotherapy to normalize the HDL subclass distribution phenotype of patients with CHD undergoing PCI. The HDL subclass distribution may aid in risk stratification, especially in patients with CHD and therapeutic LDL-C and HDL-C levels.     

The influence of plasma apolipoprotein A‐II concentrations on HDL subclass distribution

Background and aims: To investigate the impact of plasma apoA‐II concentrations on the alteration of HDL subclass distribution, and the cooperative effect of apoA‐I and apoA‐II on it. Methods and results: The apoA‐I contents of plasma HDL subclasses were quantified by two‐dimensional gel electrophoresis associated with immunodetection for 292 Chinese people. These subjects were divided according to the mean ± 1 SD of apoA‐II and apoA‐I levels as two cut‐points, respectively. Compared with the low‐apoA‐II group, the apoA‐I contents of HDL_3a (in the high group), HDL_3b, and HDL_2b increased strikingly, both in the middle‐ and high‐apoA‐II group. The apoA‐I contents of all HDL subclasses increased progressively when the apoA‐I and apoA‐II levels simultaneously or the apoA‐I/apoA‐II ratio increased, and in comparison to the low‐apoA‐I–A‐II levels group, the apoA‐I contents of HDL_2b (115%) increased more significantly than those of preβ₁‐HDL (39%) in the high‐apoA‐I–A‐II levels group. Multiple analyses also indicated that the three HDL subclasses, HDL_3a, HDL_3b and HDL_2b, were independently predicted by apoA‐II. Conclusion: Excess apoA‐II can cause the accumulation of both large‐sized HDL_2b and small‐sized HDL₃, which implies that apoA‐II plays a double role in the HDL maturation metabolism. Meanwhile, the degree of HDL_2b increased significantly relative to that of preβ₁‐HDL when apoA‐I and apoA‐II levels were elevated simultaneously, suggesting that the maturation and metabolism of HDL might be promoted and reverse cholesterol transport might be enhanced.     

The composition and metabolism of high density lipoprotein subfractions

The composition and metabolism of high density lipoprotein (HDL) subfractions were investigated in seven nomal individuals. Mean HDL₂ (d, 1.063–1.125 g/ml) composition (by weight) was 43% protein, 28% phospholipid, 23% cholesterol, and 6% triglyceride, and mean HDL₃ (d, 1.125–1.21 g/ml) composition was 58% protein, 22% phospholipid, 14% cholesterol, and 5% triglyceride. The mean apoA-I; apoA-II weight ratio was 4.75 for HDL₂ and 3.65 for HDL₃.HDL₂ protein was proportionally slightly richer in C apolipoproteins and higher molecular weight constituents (including apoE) than HDL₃. Kinetic studies utilizing radiolabeled HDL_A (d, 1.09–1.21 g/ml), HDL₂, and HDL₃ demonstrated rapid exchange of apoA-I and apoA-II radioactivity among HDL subfractions, similar fractional rates of catabolism of apoA-I and apoA-II within HDL, and similar radioactivity decay within HDL subfractions. Mean plasma residence time was 5.74 days for radiolabeled HDL₂ and 5.70 days for radiolabeled HDL₃. Differences in HDL protein mass among individuals were largely due to alterations in catabolism, and in general both HDL₂ and HDL₃ were catabolized via a plasma and a nonplasma pathway. Data from simultaneous radiolabeled very low density lipoprotein and HDL studies in 2 individuals are consistent with the concept that apoC-II and apoC-III are catabolized at a different rate than are apoA-I and apoA-II within the HDL density range.     

Changes in high density lipoprotein subfraction lipids during neutral lipid transfer in healthy subjects and in patients with insulin-dependent diabetes mellitus

While it is known that the transfer of cholesteryl ester (CE) from high density lipoprotein (HDL) to the apo B-containing lipoproteins is increased in patients with diabetes, the extent to which the various lipoprotein fractions engage in neutral lipid exchange and the magnitude to which triglyceride (TG) is translocated is not known. To examine in greater detail neutral lipid net mass transfer in diabetes, the HDL subfractions and the apo B-containing lipoproteins were separated, and the net mass transfer of CE and TG was compared to that of control subjects. In both groups, bidirectional transfer of CE from HDL₃ to very low density lipoprotein (VLDL) + low density lipoprotein (LDL) and of TG from VLDL+LDL to HDL₃, took place, but this process was significantly greater (P<.01) in insulin-dependent diabetes mellitus (IDDM). In contrast, CE and TG accumulated in HDL₂ to a similar degree in normal and IDDM subjects. In recombination experiments with each of the apo B-containing lipoproteins, IDDM VLDL had a greater capacity to facilitate the exchange of core lipids from both IDDM and control HDL₃: on the other hand, LDL from IDDM and control subjects both donated TG and CE to HDL₂ and affected little change in HDL₃. These findings indicate that all the major plasma fractions normally participate in the trafficking of CE and TG among the lipoproteins during neutral lipid transfer and show that the principal perturbation in cholesteryl ester transfer in IDDM involves altered interaction between VLDL and the HDL₃ subfraction.     

Gender and age differences in the distribution of the HDL subclasses among the Chinese population

Background and aims: to analyze the gender and age differences in the distribution of the high‐density lipoprotein (HDL) subclasses among the Chinese population, and to clarify the mechanism of these changes. Methods and results: the apoA‐I contents of the plasma HDL subclasses were determined by 2‐DE coupled with immunodetection in 324 men (including 186 normolipidemic subjects) and 186 women (including 114 normolipidemic subjects). The contents of preβ₁‐HDL and HDL₃ (HDL_3c, HDL_3b, HDL_3a) were significantly lower, whereas the contents of HDL_2a and HDL_2b were higher for women than for men in the <50 years age group. Moreover, the contents of preβ₁‐HDL and HDL₃ were higher for female subjects; the HDL_2a and HDL_2b contents were lower for both female and male subjects in the 50–59, 60–69, and ≥70 years age groups versus the subjects of the same gender in the <50 years age group. When compared to the normolipidemic premenopausal women, preβ₁‐HDL, HDL_3b, and HDL_3a increased while HDL_2b decreased significantly in normolipidemic men and postmenopausal women. Conclusions: the contents of the large‐sized HDL particles HDL_2b were higher, but the contents of the small‐sized HDL particles (preβ₁‐HDL, HDL_3b, HDL_3a) were lower for women versus men in the <50 years age group. Meanwhile, the gender difference in distribution of the HDL subclass narrowed obviously with advancing age. Moreover, the characteristics of the HDL subclass distribution profile for the normolipidemic postmenopausal women resembled those for the normolipidemic men.     

The Current Status of Research on High-Density Lipoproteins (HDL): A Paradigm Shift from HDL Quantity to HDL Quality and HDL Functionality

The quantity of high-density lipoproteins (HDL) is represented as the serum HDL-C concentration (mg/dL), while the HDL quality manifests as the diverse features of protein and lipid content, extent of oxidation, and extent of glycation. The HDL functionality represents several performance metrics of HDL, such as antioxidant, anti-inflammatory, and cholesterol efflux activities. The quantity and quality of HDL can change during one’s lifetime, depending on infection, disease, and lifestyle, such as dietary habits, exercise, and smoking. The quantity of HDL can change according to age and gender, such as puberty, middle-aged symptoms, climacteric, and the menopause. HDL-C can decrease during disease states, such as acute infection, chronic inflammation, and autoimmune disease, while it can be increased by regular aerobic exercise and healthy food consumption. Generally, high HDL-C at the normal level is associated with good HDL quality and functionality. Nevertheless, high HDL quantity is not always accompanied by good HDL quality or functionality. The HDL quality concerns the morphology of the HDL, such as particle size, shape, and number. The HDL quality also depends on the composition of the HDL, such as apolipoproteins (apoA-I, apoA-II, apoC-III, serum amyloid A, and α-synuclein), cholesterol, and triglyceride. The HDL quality is also associated with the extent of HDL modification, such as glycation and oxidation, resulting in the multimerization of apoA-I, and the aggregation leads to amyloidogenesis. The HDL quality frequently determines the HDL functionality, which depends on the attached antioxidant enzyme activity, such as the paraoxonase and cholesterol efflux activity. Conventional HDL functionality is regression, the removal of cholesterol from atherosclerotic lesions, and the removal of oxidized species in low-density lipoproteins (LDL). Recently, HDL functionality was reported to expand the removal of β-amyloid plaque and inhibit α-synuclein aggregation in the brain to attenuate Alzheimer’s disease and Parkinson’s disease, respectively. More recently, HDL functionality has been associated with the susceptibility and recovery ability of coronavirus disease 2019 (COVID-19) by inhibiting the activity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The appearance of dysfunctional HDL is frequently associated with many acute infectious diseases and chronic aging-related diseases. An HDL can be a suitable biomarker to diagnose many diseases and their progression by monitoring the changes in its quantity and quality in terms of the antioxidant and anti-inflammatory abilities. An HDL can be a protein drug used for the removal of plaque and as a delivery vehicle for non-soluble drugs and genes. A dysfunctional HDL has poor HDL quality, such as a lower apoA-I content, lower antioxidant ability, smaller size, and ambiguous shape. The current review analyzes the recent advances in HDL quantity, quality, and functionality, depending on the health and disease state during one’s lifetime.     

Interaction of discoidal complexes of dimyristoyl phosphatidylcholine-cholesterol-apolipoprotein A-I with human plasma high density lipoprotein HDL3

The interaction of human plasma high density lipoproteins (HDL₃) with discoidal complexes of apolipoprotein A-I (apoA-I) and dimyristoyl phosphatidylcholine (DMPC) containing 0, 10, 20 or 30 mol % cholesterol was investigated. Discoidal complexes containing various amounts of cholesterol were prepared by incubating apoA-I and DMPC-cholesterol liposomes for 12 hr at 25 C; the protein-lipid complexes were isolated by gel filtration chromatography on Bio-Gel A15m. Increasing the cholesterol content from 0 to 30 mol % caused a decrease in the fluidity of the discoidal complexes as determined by fluorescence polarization with 1,6-diphenyl-1,3,5-hexatriene; a reduced phase-transition amplitude; a decrease in the ratio of apoA-I to DMPC; and an increase in the width of the discoidal complexes as determined by electron microscopy after negative staining. Incubation of the apoA-I-lipid complexes with HDL₃ resulted in a complete breakdown of the discoidal structures and a transfer of DMPC and cholesterol to HDL₃. As a result of lipid transfer, there was an increase in the size of HDL₃. These in vitro results may be of significance as they relate to the interconversion of HDL subfractions during lipoprotein-lipase-induced lipolysis of triglyceride-rich lipoproteins.     

Interaction of human plasma high density lipoprotein HDL2 with synthetic saturated phosphatidylcholines

The interaction of human plasma high density lipoprotein HDL₂ (d 1.063–1.125 g/ml) with sonicated dispersions of synthetic saturated phosphatidylcholines, dipalmitoyl- (diC₁₆PC), dimyristoyl- (diC₁₄PC), didodecanoyl- (diC₁₂PC), didecanoyl- (diC₁₀PC), and dioctanoyl- (diC₈PC) L-alpha phosphatidylcholine, was investigated. Incubation (4.5 hr, 37 C) of HDL₂ with diC₁₄PC, diC₁₂PC, diC₁₀PC and diC₈PC followed by gradient gel electrophoresis or preparative ultracentrifugation resulted in a redistribution of apolipoprotein A-I (apoA-I). The extent of redistribution depended on the molar ratio of the phospholipid to HDL₂ in the incubation mixture. Redistributed apoA-I occurred as lipid-free apoA-I and/or as complexes of apoA-I with phosphatidylcholine. Increasing the length of time of ultracentrifugation of the interaction mixtures did not increase the extent of redistribution. No redistribution of apoA-I was detected following incubation and gradient gel electrophoresis or preparative ultracentrifugation of mixtures of HDL₂ with dispersions of diC₁₆PC. Presented in part at the Joint Meeting of the American Oil Chemists' Society and the Japan Oil Chemists' Society, 1979.     

Lipid-Modulating Treatments for Mixed Dyslipidemia Increase HDL-Associated Phospholipase A2 Activity with Differential Effects on HDL Subfractions

The effect of lipid-modulating treatments on modification of high density lipoprotein (HDL) subfractions remains unknown. In this study, mixed dyslipidemia patients (n = 100) inadequately controlled with a standard statin dose were randomized to switch to 40 mg of rosuvastatin or add-on extended release nicotinic acid/laropiprant (ER-NA/LRPT) or add-on fenofibrate. The cholesterol concentrations of HDL (HDL-C) subfractions and HDL-associated lipoprotein-associated phospholipase A₂ (HDL-Lp-PLA₂) activity were assessed at baseline and 3 months later. We observed that large HDL-C increased by 50 and 6 % in the add-on-ER-NA/LRPT and rosuvastatin groups, respectively, while it decreased by 20 % in the add-on-fenofibrate group (p < 0.01 vs baseline for all groups and p < 0.01 for all comparisons among groups). On the other hand, small HDL-C decreased by 17 % in the add-on-ER-NA/LRPT group (p < 0.01 vs baseline), while it increased by 25 % in the add-on-fenofibrate group (p < 0.01 vs baseline) without any change in the rosuvastatin group (p < 0.01 for all comparisons among groups). HDL-Lp-PLA₂ activity increased by 55, 33 and 18 % in add-on-ER-NA/LRPT, add-on-fenofibrate and rosuvastatin groups, respectively (p < 0.01 for all comparisons vs baseline and for all comparisons among groups). In conclusion, add-on-ER-NA/LRPT was associated with an increase in large HDL-C and a decrease in small HDL-C, while opposite effects were noticed in the add-on-fenofibrate group. Add-on-ER-NA/LRPT was associated with the most pronounced increase in HDL-Lp-PLA₂ activity.     

ApoA-I secretion by rabbit intestinal mucosa cell cultures

Lipid and apolipoprotein (apo) A-I concentrations in different density fractions of New Zealand White (NZW) and Watanabe (WHHL) rabbit plasma were studied. Aside from the low plasma apoA-I and high density lipoprotein (HDL) cholesterol levels in WHHL rabbits, the distribution of apoA-I was also different between the two rabbits. ApoA-I was concentrated in both the HDL₂ and HDL₃ fractions of NZW rabbits but was found primarily in the HDL₃ fraction of WHHL rabbits. ApoA-I secretion in these two rabbits was further studiedin vitro by using intestinal and hepatocyte cell cultures. ApoA-I secretion was highest from cultures of the duodenum and the proximal end of the jejunum; whereas, cell cultures of the distal end of the small intestine secreted very little apoA-I into the medium. Intestinal cell cultures from WHHL rabbits secreted less, but significant amounts of, apoA-I compared to that of NZW rabbits. ApoA-I was most concentrated in the density range of 1.12–1.21 (HDL₃) fraction in medium containing 10% fetal calf serum (FCS). Serum-free medium promoted apoA-I secretion by intestinal cell cultures that was mostly found in the d>1.21 (lipoprotein-deficient) fraction. Hepatocytes isolated from the same rabbits by collagenase perfusion secreted little apoA-I, and it was found only in the d>1.21 fraction. The addition of oleic acid into the culture medium with 10% FCS decreased the secretion of total apoA-I and HDL by intestinal cell cultures and increased the secretion of very low density lipoprotein (VLDL) and intermediate density lipoproteins (IDL). The results indicate that intestinal cells, not hepatocytes, are responsible for the secretion of apoA-I and HDL₃ in rabbits, and that the secretion may be regulated under different nutritional conditions.     

The effect of dietary n−3 polyunsaturated fatty acids on HDL cholesterol in Chukot residentsvs muscovites

Native Chukot Peninsula residents, in contrast to Muscovites, consume a diet rich in n−3 polyunsaturated fatty acids. This dietary peculiarity is reflected in differences in plasma lipid and apolipoprotein contents. The Chukot residents have lower contents of total cholesterol, triglyceride, LDL (low density lipoprotein) cholesterol and apolipoprotein B, but higher HDL (high density lipoprotein) cholesterol levels than do Muscovites. The apolipoprotein A-I levels were identical in both groups. A higher HDL cholesterol to apolipoprotein A-I ratio was determined in the coastline Chukot residents (0.52±0.01) than in Muscovites (0.43±0.01; p<0.01). In contrast to Muscovites, the coastline Chukot residents also had higher n−3 and lower n−6 polyunsaturated fatty acid percentages in plasma and erythrocyte lipids, and lower phosphatidylcholine and higher sphingomyelin or phosphatidylethanolamine levels in HDL_2b and HDL₃. The higher HDL cholesterol levels in the plasma of the coastline Chukot residents appears to reflect the higher cholesterol-scavenging capacity of their HDL. We conclude from this study that the regular consumption of dietary n−3 polyunsaturated fatty acids by the coastline Chukot residents decreased LDL cholesterol transfer from plasma to peripheral cells, and enhanced cholesterol efflux from cellular membranes toward HDL.     

Small High-Density Lipoprotein (HDL) Subclasses are Increased with Decreased Activity of HDL-Associated Phospholipase A2 in Subjects with Prediabetes

Alterations in high-density lipoprotein (HDL) subclass distribution, as well as in the activities of HDL-associated enzymes, have been associated with increased cardiovascular disease (CVD) risk. HDL subclass distribution and the activities of HDL-associated enzymes remain unknown in prediabetic patients, a condition also associated with increased CVD risk. The aim of the present study was to assess any differences in HDL subclass distribution (using polyacrylamide gel electrophoresis) and in activities of HDL-associated enzymes between prediabetic (impaired fasting glucose, IFG, n = 80) and non-prediabetic subjects (n = 105). Subjects with prediabetes had significantly increased waist circumference, blood pressure and triacylglycerol (TAG) levels compared with subjects with fasting glucose levels <100 mg/dL (all p < 0.05). The proportion of small HDL3 over HDL cholesterol (HDL-C) was significantly increased in prediabetic subjects compared with their controls (p < 0.05). The activity of the anti-atherogenic HDL-associated lipoprotein-associated phospholipase A₂ (HDL-LpPLA₂) was significantly lower in subjects with prediabetes (p < 0.05), whereas the activity of paraoxonase 1 (using both paraoxon and phenyl acetate as substrates) did not significantly differ between subjects with or without prediabetes. In a stepwise linear regression analysis, the proportion of small HDL3 over HDL-C concentration was independently associated with the presence of prediabetes and with total cholesterol and TAG concentration (positively), as well as with HDL-C levels (negatively). We also observed a trend of increased small dense low-density lipoprotein cholesterol levels in prediabetic subjects compared with their controls. Subjects with IFG exhibit increased proportion of small HDL3 particles combined with decreased activity of the anti-atherogenic HDL-LpPLA₂.     

Plasma high density lipoprotein subgroup distribution in rats fed diets with varying amounts of sucrose and sunflower oil

The effect of varying the dietary sunflower oil/sucrose (SO/SU) ratio on rat plasma lipid concentration and lipoprotein distribution was studied. Four groups of 10 rats were fed for 4 weeks diets with varying SO/SU ratios. Lipoprotein components were then estimated in whole plasma and after cumulative density ultracentrifugation. Whole plasma triacylglycerol (TG), total cholesterol (TC) and free cholesterol (FC) decreased with increasing SO/SU ratio; the CE/FC ratio increased, because CE remained virtually unaltered. Plasma TG-lowering was due to a decrease in VLDL and LDL-TG. Protein, CE and FC in d=1.063–1.100 g/ml (HDL_2b) and d=1.100–1.125 g/ml (HDL_2a) lipoproteins decreased upon increasing the SO/SU ratio. In contrast, in d=1.125–1.200 g/ml (HDL₃) lipoproteins, there was a concomitant increase in these components. Although increasing the SO/SU ratio effected more protein and CE transportation in HDL₃ and less in HDL₂, the total amount of these components in high density lipoproteins (d=1.063–1.200 g/ml) remained constant. Apo A-I and apo C-III decreased in HDL₂ but increased in HDL₃ upon increasing the SO/SU ratio. Also, HDL₂ apo E, and the apo C-II/apo C-III and small apo B/large apo B ratios in VLDL and LDL were lowered by increasing the SO/SU ratio. The hepatic VLDL-TG output during isolated liver perfusion was lowest in rats fed the diet with the highest SO/SU ratio. In perfusate, like in plasma, the VLDL and LDL apo C-II/apo C-III ratio, as well as the small apo B/large apo B ratio, decreased upon increasing the dietary SO/SU ratio. The results indicate that there can be appreciable diet-dependent variations in plasma HDL subgroup distribution in spite of unchanged total HDL levels.     

Influence of dietary egg and soybean phospholipids and triacylglycerols on human serum lipoproteins

Human serum lipid and lipoprotein concentrations and compositions were compared in ten healthy middle-aged men consuming phospholipids from egg or from soybean or triacylglycerol mixtures with fatty acid compositions similar to those of the phospholipids. All subjects followed each of the four treatments: egg phospholipids (EP), soybean phospholipids (SP), an oil of fatty acid composition similar to that of EP, and an oil similar in fatty acid composition to SP for six weeks with “wash-out” periods of similar duration between treatment periods. The phospholipids, 15 g/d, and the oils, 12 g/d, which contained approximately equivalent quantities of fatty acids were provided to the subjects in gelatin capsules and were taken before meals. Diet intake was monitored by three-day food records. Serum lipoproteins (L_p) were separated by ultracentrifugation into very low density lipoproteins, low density lipoproteins (LDL), high density lipoproteins (HDL)₂ and HDL₃. L_p fractions and whole serum were analyzed for triacylglycerols, cholesterol (CH), phospholipids (PL), and protein. HDL cholesterol was determined in while serum. Cholesteryl esters were determined in some L_p fractions. Lipid compositions of L_p were expressed in mmol/g protein. Apoprotein B was measured in whole serum and in LDL; apoprotein A-I in whole serum and in HDL₃. In whole serum, CH and PL were significantly lower after the SP compared to EP treatment periods. CH, but not PL, was lower after SPTG compared to EP. CH in HDL₂ was significantly higher after SP compared to SPTG. Also, PL in HDL₂ were significantly higher after SP compared to all other treatments and to baseline. Although human serum lipid responses to dietary phospholipids were generally the same as responses to ingested oils of comparable fatty acid composition, the data suggest the possibility that SP selectively increase HDL₂ cholesterol and phospholipids.     

Hydrolysis of glycerophosphocholine epoxides by human group IIA,V, and X secretory phospholipases A2

This study was prompted by recent reports that epoxyeicosatrienoic (EET) and epoxyeicosatetraenoic (EEQ) acids accelerate tumor growth and metastasis by stimulation of angiogenesis, while eicosapentaenoic (EPA) and epoxydocosapentaenoic (EDP) acids inhibit angiogenesis, tumor growth, and metastasis. Cytochrome P450 epoxygenases convert arachidonic to EET, eicosapentaenoic acid to EEQ, and docosahexaenoic acid to EDP, which are found both in free form and esterified to glycerophosphocholine (GPC). Both free and esterified epoxy (EP) acids are also formed during lipid autoxidation. For biological activity, the GPC-EP requires hydrolysis, which we presumed could occur by sPLA₂s located in proximity of lipoproteins carrying the lipid epoxides. The plasma lipoproteins were isolated by ultracentrifugation and analyzed by LC/ESI-MS. The GPC-EPs were identified by reference to standards and to retention times of phospholipid masses. The GPC-EP monoepoxides (corrected for isobaric ether overlaps) in stored human LDL, HDL, HDL₃, or APHDL ranged from 0 to 1 nmol/mg protein, but during 4-h incubation at 37°C increased to 1–5 nmol/mg protein. An incubation of autoxidized LDL, HDL, or HDL₃ with 1 μg/ml of group V or X sPLA₂ resulted in complete hydrolysis of diacyl GPC epoxide esters. Group IIA sPLA₂ at 1 μg/ml failed to produce significant hydrolysis in 4 h, but at 2.5 μg/ml in 8 h yielded almost 80% hydrolysis, which represented complete diacyl GPC-EP hydrolysis. The present study shows that group IIA, V, and X sPLA₂s are capable of extensive hydrolysis of PtdCho epoxides of autoxidized plasma lipoproteins. Therefore, all three human sPLA₂s were potentially capable of inducing epoxide biological activity in vivo.     

Human low density lipoprotein structure: Correlations with serum lipoprotein concentrations

Human low density lipoproteins (LDL) were isolated and purified from individuals having widely differing serum lipid concentrations. Very low density lipoproteins (VLDL) and high density lipoproteins (HDL) were also isolated and quantitated. HDL₂ and HDL₃ were separated by flotation velocity in the analytical ultracentrifuge and their relative weight percent determined. The mean density of LDL from 41 individuals was determined by flotation velocity at two different solvent densities. The mean density of LDL was directly proportional to the triglyceride (r=0.65) and VLDL (r=0.50) concentrations and inversely proportional to the HDL (r=−0.55) and HDL₂ (r=−0.74) concentrations (all significant at P<0.001). The mean molecular weight of LDL from 42 individuals was determined by flotation equilibrium centrifugation. The mean molecular weight of LDL was directly proportional to the HDL (r=0.49) and HDL₂ (r=0.48) concentrations and inversely proportional to the serum triglyceride (r=−0.60) and VLDL (r=−0.48) concentrations (all significant at P<0.005 except triglyceride—P<0.001). The molecular weight of LDL was inversely proportional to its density, and thus inversely proportional to its protein/lipid ratio which was confirmed by composition measurements. The density and molecular weight of LDL had no relationship to the concentration of LDL (r=0.04 and 0.03). A preliminary report of this study was given at the American Society for Biological Chemists Meeting in St. Louis, June 1981.     

Effect of essential fatty acid deficiency on the size and distribution of rat plasma HDL

Rat plasma high density lipoproteins (HDL) are comprised of two major particle size subpopulations, HDL₁ (255 Å?140 Å) and HDL₂ (140 Å?84 Å), in which the proportion of arachidonate in fatty acids of cholesteryl esters is greater than 50%. To determine whether decreased availability of arachidonate for cholesterol esterification would alter the distribution and/or amounts of the HDL subpopulations, we compared HDL subpopulations in EFA-deficient and control rats. To separate the effects of EFA deficiency and fat deficiency and to evaluate effects of different saturated fats, we used EFA-deficient diets that were fat-free or that contained 5% saturated fat. The control diets were the EFA-deficient diets plus 1% safflower oil. The saturated fats were hydrogenated coconut oil, hydrogenated cottonseed oil and saturated medium-chain triglycerides. All EFA-deficient diets decreased the proportion of the HDL₁ subpopulation and the peak diameter of the HDL₂ subpopulation. These changes appeared after quite brief EFA depletion in young rats and may be related to the increased liver cholesteryl ester concentrations typical of EFA-deficient rats.