High-density lipoprotein metabolism

Dietary soybean lecithin promoted growth performance and feeding in juvenile Chinese perch (Siniperca chuatsi) could be by optimizing glucolipid metabolism

To explore the potential benefits of dietary phospholipids (PLs) in fish glucose metabolism and to promote feed culture of Chinese perch (Siniperca chuatsi), we set up six diets to feed Chinese perch (initial mean body weight 37.01 ± 0.20 g) for 86 days, including: Control diet (CT), 1% (SL1), 2% (SL2), 3% (SL3), 4% (SL4) soybean lecithin (SL) and 2% (KO2) krill oil (KO) supplemental diets (in triplicate, 20 fish each). Our study found that the SL2 significantly improved the weight gain rate and special growth rate, but the KO2 did not. In addition, the SL2 diet significantly improved feed intake, which is consistent with the mRNA levels of appetite-related genes (npy, agrp, leptin A). Additionally, in the CT and SL-added groups, leptin A expression levels were nearly synchronized with serum glucose levels. Besides, the SL2 significantly upregulated expression levels of glut2, gk, cs, fas and downregulated g6pase in the liver, suggesting that it may enhance glucose uptake, aerobic oxidation, and conversion to fatty acids. The SL2 also maintained the hepatic crude lipid content unchanged compared to the CT, possibly by significantly down-regulating the mRNA level of hepatic lipase gene (hl), and by elevating serum low-density lipoprotein (LDL) level and intraperitoneal fat ratio in significance. Moreover, the serum high-density lipoprotein levels were significantly increased by PL supplementation, and the SL2 further significantly increased serum total cholesterol and LDL levels, suggesting that dietary PLs promote lipid absorption and transport. Furthermore, dietary SL at 1% level could enhance non-specific immune capacity, with serum total protein level being markedly higher than that in the CT group. In conclusion, it is speculated that the promotion of glucose utilization and appetite by 2% dietary SL could be linked. We suggest a 1.91% supplementation of SL in the diet for the best growth performance in juvenile Chinese perch.

Effect of Hanwoo Crust on the Physicochemical Properties of Emulsion-Type Sausages

This study aimed to investigate the effects of Hanwoo crust, inedible surface layer formed during dry aging, on the physicochemical properties of emulsion-type sausages. Sausage samples were prepared with various amounts of Hanwoo crust—0% (i.e., control), 1%, 2%, and 3%. The physicochemical properties studied included the proximate composition, pH, color, water holding capacity (WHC), cooking yield (CY), and viscosity. Texture profile analysis (TPA) and sensory evaluation were also carried out. Protein, fat, and ash contents of the Hanwoo crust-treated samples were found to be significantly higher than those of the control (p<0.05). Moreover, the CIE b* value of cooked sausage with Hanwoo crust treatments was significantly lower than that of the control (p<0.05). The CIE L* value of uncooked and cooked samples with 3% Hanwoo crust was significantly lower than that of the control (p<0.05). In contrast, the CIE a* value of uncooked and cooked samples with 3% Hanwoo crust was significantly higher than that of the control (p<0.05). The viscosity of the uncooked samples increased with increasing Hanwoo crust content. Samples containing 3% Hanwoo crust exhibited significantly higher WHC and CY than the control (p<0.05). In the TPA, samples containing 2% and 3% Hanwoo crust showed significantly higher hardness, gumminess, and chewiness than the control (p<0.05). Overall, the sensory properties of Hanwoo crust treatments were significantly better than those of the control (p<0.05). In conclusion, adding 3% Hanwoo crust to emulsion-type sausage leads to optimal physicochemical properties.

Reverse cholesterol transport: From classical view to new insights

Cholesterol is of vital importance for the human body. It is a constituent for most biological membranes, it is needed for the formation of bile salts, and it is the precursor for steroid hormones and vitamin D. However, the presence of excess cholesterol in cells, and in particular in macrophages in the arterial vessel wall, might be harmful. The accumulation of cholesterol in arteries can lead to atherosclerosis, and in turn, to other cardiovascular diseases. The route that is primarily thought to be responsible for the disposal of cholesterol is called reverse cholesterol transport (RCT). Therefore, RCT is seen as an interesting target for the development of drugs aimed at the prevention of atherosclerosis. Research on RCT has taken off in recent years. In this review, the classical concepts about RCT are discussed, together with new insights about this topic.

Apolipoprotein A-I gene expression is upregulated by polychlorinated biphenyls in rat liver

Xenobiotics such as polychlorinated biphenyls (PCB) increase serum cholesterol level (especially high density lipoprotein cholesterol) and apolipoprotein A-I (apo A-I) level in rats. The effect of PCB on serum apo A-I and hepatic apo A-I gene expression and the relationship between apo A-I and drug-metabolizing enzymes in rats were investigated. Serum levels of cholesterol and apo A-I were increased by dietary addition of PCB in a dose-dependent manner (0-500 mg/kg diet). Hepatic apo A-I mRNA level was also elevated by PCB in a similar fashion. Serum level of cholesterol gradually increased during feeding period of PCB (200 mg/kg diet, 105 days) and reached a two-fold higher level in PCB group than in controls. The levels of serum apo A-I and hepatic apo A-I mRNA linearly elevated during feeding period of PCB and were increased 3- or 4-fold, respectively, compared to controls. Although acute administration (16 hr) of PCB, 3-methylcholanthrene, and phenobarbital induced cytochrome P-450 gene expression in the liver, hepatic apo A-I gene expression was not increased by these xenobiotics. These results indicated that the serum levels of cholesterol and apo A-I had positive correlation with hepatic level of apo A-I mRNA in rats fed PCB, and that hepatic apo A-I gene expression was dependent upon intake of PCB but was not directly related to the induction of drug-metabolizing enzymes. This study demonstrated that xenobiotic-induced hyper-alpha-cholesterolemia would be caused by the increased apo A-I gene expression and cholesterol synthesis in the liver, coordinately.

Clinical significance of plasma HDL subfractions (HDL2, HDL3) in patients with peripheral arterial disease (PAD) in the Greek population

OBJECTIVE

In this study the major high density lipoprotein (HDL) subfractions (HDL2, HDL3) were examined, in angiographically selected patients with peripheral arterial disease (PAD).

RESULTS

Patients with PAD have significantly high triglyceride levels. HDL2 and HDL3 levels were found significantly reduced in patients with PAD. Also, the ratio HDL2-C/HDL3-C was significantly reduced in patients with PAD.

CONCLUSIONS

The aim of the present study is to provide additional support to the hypothesis that the determination of HDL subfractions could be useful to elucidate possible mechanism(s) for a better assessment of the risk profile for PAD.

The impact of D-Trp6 LH-RH on plasma lipid levels

BACKGROUND

There is increasing evidence regarding the correlation between the risk of death from cardiovascular disease and low levels of HDL-cholesterol or high plasma concentrations of LDL-cholesterol, total cholesterol, and triglycerides. Gonadotropin releasing hormone (GhRH) analogues are widely used in assisted reproduction programs. Therefore, it seems important to evaluate possible changes in serum lipoprotein levels following treatment with these compounds.

PURPOSE

Our purpose was to assess possible lipoprotein changes following administration of the long-acting GnRH analogue, D-Trp6 luteinizing hormone-releasing hormone (LH-RH).

DESIGN

Serum levels of cholesterol, HDL-cholesterol, LDL-cholesterol, and triglicerydes were determined before and after 6 weeks of treatment.

RESULTS

No significant changes in either cholesterol or HDL-cholesterol, LDL-cholesterol, or triglicerydes following treatment with D-Trp6 LH-RH were demonstrated in the group of 25 patients investigated.

CONCLUSIONS

Short-term use of D-Trp6 LH-RH is not associated with any significant change in plasma lipid levels. Further studies are still required with patients undergoing repeated treatment cycles, especially those who exhibit elevated pretreatment plasma lipid levels, to confirm the long-term safety of GnRH analogues with respect to lipid metabolism.

Lipoprotein metabolism and its relationship to atherosclerosis

Lipoproteins are macromolecular complexes that transport cholesterol and triglycerides through the blood stream. The assembly and secretion of lipoproteins occurs in the liver and small intestine, but many modifications and transformations occur in the plasma. Plasma levels of cholesterol and triglycerides are regulated by both environmental effects on lipid metabolism and by genetic factors affecting both apoproteins on the surface of the lipoproteins and enzymes in plasma. Abnormalities of the lipoprotein transport system can increase an individual's risk for developing atherosclerosis.

Increased production rates of LDL are common in individuals with low plasma levels of HDL cholesterol, independent of plasma triglyceride concentrations

Reduced plasma levels of high density lipoprotein (HDL) cholesterol are associated with increased risk for coronary heart disease. Although plasma HDL levels are, in general, inversely related to plasma triglyceride (TG) concentrations, a small proportion of individuals with low HDL cholesterol concentrations have normal plasma TG levels. We wished to determine whether subjects with low plasma levels of HDL cholesterol could be characterized by common abnormalities of lipoprotein metabolism independent of plasma TGs. Therefore, we studied the metabolism of low density lipoprotein (LDL) apolipoprotein B (apo B) and HDL apolipoprotein A-I (apo A-I) in subjects with low plasma HDL cholesterol concentrations with or without hypertriglyceridemia. Nine subjects with low plasma HDL cholesterol levels and normal levels of plasma TGs and LDL cholesterol were studied. Autologous 131I-LDL and 125I-HDL were injected intravenously, and blood samples were collected for 2 weeks. LDL apo B and HDL apo A-I levels were measured by specific radioimmunoassays. Fractional catabolic rates (FCRs, pools per day) and production rates (PRs, milligrams/kilogram.day) for each apolipoprotein were determined. The results were compared with those obtained previously in nine subjects with low plasma HDL cholesterol levels and hypertriglyceridemia and in seven normal subjects. The normal subjects had an HDL apo A-I FCR (mean +/- SD) of 0.21 +/- 0.04. Despite large differences in plasma TG levels, the HDL apo A-I FCRs were similar in the low-HDL, normal-TG group (0.30 +/- 0.09) and the low-HDL, high-TG group (0.33 +/- 0.10), although only the latter value was significantly increased versus control subjects (p < 0.03). Increased apo A-I FCRs were associated with reduced HDL apo A-I levels in both groups of patients. Apo A-I PRs were similar in all groups. In contrast, LDL apo B PR was increased approximately 50% in the low-HDL, normal-TG group (19.3 +/- 6.6; p < 0.01) compared with normal subjects (12.5 +/- 2.6). There was a strong trend toward a greater LDL apo B PR in the low-HDL, high-TG group (17.6 +/- 4.5; p = 0.06 versus normal subjects) as well. LDL apo B FCRs were similar in all three groups. LDL apo B concentrations were also increased in the group with low HDL cholesterol and normal TG levels. Both groups with low HDL cholesterol levels had cholesterol-depleted LDL and HDL particles.(ABSTRACT TRUNCATED AT 400 WORDS)

Increased plasma and renal clearance of an exchangeable pool of apolipoprotein A-I in subjects with low levels of high density lipoprotein cholesterol

Plasma levels of HDL apo A-I are reduced in individuals with low HDL cholesterol (HDL-C) concentrations as a result of increased fractional catabolic rates (FCRs). To determine the basis for the high apo A-I FCRs, seven subjects with low HDL-C levels (31.0 +/- 4.3 mg/dl) were compared with three subjects with high HDL-C levels (72.0 +/- 4.5 mg/dl). Each subject received autologous HDL that was labeled directly by the iodine-monochloride method (whole-labeled) and autologous HDL that was labeled by exchange with homologous radiolabeled apo A-I (exchange-labeled). Blood was obtained for 2 wk, specific activities determined, and FCRs (d-1 +/- SD) estimated. In every subject, whether in the low or high HDL-C group, the exchange-labeled FCR was greater than the whole-labeled FCR. The exchange-labeled FCR was higher in the low HDL-C group (0.339 +/- 0.043) versus the high HDL-C group (0.234 +/- 0.047; P < 0.009). The whole-labeled FCR was also greater in the low HDL-C group (0.239 +/- 0.023) versus the high HDL-C group (0.161 +/- 0.064; P < 0.02). In addition, in both low and high HDL groups ultracentrifugation resulted in more radioactivity in d > 1.210 (as percentage of total plasma counts per minute) with the exchange-labeled tracer than with the whole-labeled tracer (12.55 +/- 4.95% vs. 1.02 +/- 0.38%; P < 0.003). With both HDL tracers, more radioactivity was found in d > 1.210 in the low versus the high HDL-C groups. When apo A-I catabolism was studied by perfusing isolated rabbit kidneys with whole-labeled HDL, there was twice as much accumulation (cpm/g cortex) of HDL apo A-I isolated from subjects with low HDL-C than from subjects with high HDL-C (P < 0.0025). Finally, HDL that had been isolated from subjects with high levels of HDL-C was triglyceride enriched and exposed to partially purified lipases before perfusion through kidneys. Threefold more apo A-I from modified HDL accumulated in the cortex compared with the unmodified preparation (P < 0.007). The results of these in vivo and ex vivo studies indicate that individuals with low HDL-C levels have more loosely bound, easily exchanged apo A-I and that this exchangeable apo A-I is more readily cleared by the kidney.

Stimulation of luteal cell progesterone production by lipoproteins from cows fed control or fat-supplemented diets

Plasma lipoproteins from lactating dairy cows fed 0 or 7% supplemental fat were examined for their composition and ability to stimulate luteal cell progesterone production in vitro. Ultracentrifugation was utilized to isolate blood lipoproteins, and heparin affinity chromatography allowed separation of lipoprotein fractions based on the presence (low density lipoproteins) or absence of apolipoprotein B (high density lipoproteins). A portion of high density lipoproteins was fractionated by size, utilizing gel filtration chromatography. Slaughterhouse corpora lutea were dissociated, and plasma lipoproteins were added to the luteal cells on d 3 of culture and incubated for 48 h. In Experiment 1, blood was collected from heifers fed a diet that was not supplemented with fat. The addition of cholesterol from large, high density lipoproteins with a high cholesterol to protein ratio to luteal cultures increased progesterone production by an average of 17% compared with the addition of cholesterol from small, high density lipoproteins with a low cholesterol to protein ratio. In Experiment 2, electrophoretic mobility, apolipoprotein composition, and size of lipoproteins from control and fat-supplemented cows were similar. Lipoproteins from cows assigned to either a control or fat-supplemented diet showed no difference in their ability to stimulate progesterone production. Increased plasma progesterone concentration in lactating dairy cows fed supplemental fat does not appear to be mediated by alterations in lipoprotein composition.

Plasma lecithin-cholesterol acyltransferase activity and cholesterol and phospholipid levels in premature newborn infants

Lecithin-cholesterol acyltransferase (LCAT) activity has been suggested to play an important role in the regulation of lipid metabolism. The present study was undertaken to examine any relationship between LCAT activity and altered cholesterol levels in plasma of full-term and preterm newborn infants. Plasma total, free and esterified cholesterol, total phospholipid and LCAT activity (cholesterol esterified, nmol/ml per h) were determined in placental cord blood. There was a significant negative relationship between total cholesterol levels and gestational age. The increased cholesterol with prematurity was due to both free and esterified cholesterol. There was also a significant negative relationship between LCAT activity and free cholesterol levels but not between LCAT activity and total cholesterol and esterified cholesterol levels. There was no relationship between esterified-to-free cholesterol ratio and LCAT activity. Total phospholipid was not significantly related to either gestational age or LCAT activity. This study suggests that reduced LCAT activity may be one of the factors that result in the accumulation of cholesterol in premature infants.

Age and dietary polyunsaturated fat alter high density lipoprotein subfraction cholesterol concentrations in a pediatric population of African green monkeys

African green monkeys were raised from birth to 60 months of age on diets containing cholesterol (0.8 mg/kcal) and enriched in polyunsaturated (polyunsaturated to saturated fat ratio [P:S] = 2.5) or saturated (P:S = 0.3) fat. Lipoproteins were isolated from plasma of a group of animals (N = 123) and were separated by gel filtration chromatography at 9, 14, 26, 38, and 50 months of age, which covered a period through adolescence into young adulthood. Total plasma cholesterol (TPC) concentrations were 16% lower (p = 0.01) in the polyunsaturated fat-fed group, and high density lipoprotein (HDL) cholesterol concentrations averaged 20% lower (p = 0.008) in this group between 14 and 50 months of age, while plasma apolipoprotein A-I (apo A-I) averaged 7% lower (p = 0.06) over this age interval in the animals. The HDL cholesterol to apo A-I ratio was found to be significantly lower (p = 0.006) in the animals fed the polyunsaturated fat diet. This suggested that the HDL subfraction distribution might differ between groups. In a subset of animals (n = 105, 64 male and 41 female), HDL was subfractionated by density gradient ultracentrifugation into six subfractions, HDL-I to HDL-VI, from lowest to highest density. The saturated fat-fed animals had significantly higher cholesterol concentrations in HDL-I and significantly lower cholesterol concentrations in HDL-III, HDL-IV, and HDL-V. These effects held across all ages studied; therefore, these diet effects were not age dependent. In both diet groups, the HDL subfraction pattern changed with age such that the HDL-I and HDL-II cholesterol concentrations decreased, and those of HDL-IV, HDL-V, and HDL-VI increased as the animals matured. The decrease in HDL-I with age appeared to result primarily from a decrease in HDL-I in males, while the HDL-I cholesterol concentration in females did not change with age. We conclude that diet, age, and gender all affect HDL subfraction distribution and therefore can potentially modify the relative atherogenicity of the plasma HDL populations. It remains for future studies to demonstrate the effectiveness of each subfraction in promoting or preventing the cholesterol deposition of atherosclerosis.

Effect of smoking cessation on serum apolipoprotein A-I and A-II concentrations

This study investigated the effects of 6 weeks' smoking cessation on serum levels of total-cholesterol, triglyceride, high-density lipoprotein cholesterol (HDL-C) and apolipoproteins A-I and A-II (apo A-I and apo A-II) in 64 subjects of both sexes. Smoking cessation was associated with an increase in levels of apo A-II. Concurrent changes in weight and alcohol consumption during attempted smoking cessation, together with change in thiocyanate level, were entered as predictor variables into a multiple regression analysis. The change in apo A-II was found to be best accounted for by change in plasma thiocyanate level, and, in women, change in HDL-C and apo A-I by change in weight. The changes induced by smoking cessation may be due, at least in part, to associated changes in alcohol consumption and/or dietary intake, but in the case of apo A-II there is evidence of a more direct effect.

Cholesterol efflux from and high-density-lipoproteins binding to cultured bovine vascular endothelial cells are higher than with vascular smooth muscle cells

Cholesterol metabolism was studied and compared in confluent cultures of adult bovine aortic endothelial and bovine aortic smooth muscle cells which were grown under similar conditions. The total cholesterol content/mg protein was only slightly higher in smooth muscle cells than in endothelial cells and upon exposure to [3H]cholesterol the maximal specific activity/mg protein obtained was similar in both cell types. Most (98%) of the incorporated [3H]cholesterol remained in the form of free cholesterol in both cell types, and provided a system for the study of cholesterol efflux. The role of high-density lipoproteins (HDL) and human serum in cholesterol influx and efflux, in both endothelial and smooth muscle cells, was studied. Net cholesterol transport in the cultures was calculated and net efflux was observed in both cell types. This was higher in endothelial than in smooth muscle cells and HDL was more efficient than human serum in promoting net cholesterol efflux. During the influx experiments, no conversion of [3H]cholesterol to [3H]cholesteryl ester was observed either in the cell layer or in the incubation medium. On the other hand, during efflux experiments when HDL but not human serum was the acceptor, some (about 6%) conversion of [3H]cholesterol to [3H]cholesteryl ester occurred in the incubation medium. 125I-HDL3 binding to endothelial and smooth muscle cells was studied and demonstrated saturation at a concentration of about 100 micrograms protein/ml for both cell types. However, endothelial cells bound about six times more 125I-HDL3 than smooth muscle cells. These studies indicate that vascular endothelial cells are more protected against cholesterol accumulation than vascular smooth muscle cells. The greater ability of endothelial cells to bind HDL complexes when compared with smooth muscle cells, and thereby to be more susceptible to HDL induced cholesterol efflux, may add a new mechanism through which endothelial cells protect the blood vessel from cholesterol accumulation.

Apolipoprotein A-I and A-II levels in an Australian population

Values for apolipoproteins A-I and A-II (apo A-I and apo A-II) are reported for 389 women and 390 men in the town of Busselton, Western Australia. Apo A-I levels were found to be relatively constant with age in men but to rise with age in women. Apo A-II levels remained constant with age in men until older age, when they declined, but rose with age in women, showing a fall in the oldest age group. Apo A-I levels were greater in women than in men, but apo A-II levels were lower in younger women than in younger men, and higher in older women than in older men. On stepwise multiple regression analysis, neither apo A-I nor apo A-II levels showed an independent relationship with age in women; the same was true for apo A-I in men. Alcohol consumption was directly associated with apo A-I and A-II levels in both sexes; adiposity was inversely associated with apo A-I levels in both sexes but with apo A-II only in women. Triglyceride levels showed an inverse association with apo A-II in women. Frequency of exercise was independently and directly associated with apo A-I and A-II levels in women only.

The secondary structure of apolipoproteins in human HDL3 particles after chemical modification of their tyrosine, lysine, cysteine or arginine residues. A Fourier transform infrared spectroscopy study

Fourier transform infrared spectra of apolipoprotein E-depleted human HDL3 have been obtained in H2O and 2H2O buffers. The absorption bands in the protein amide I and amide II regions (1700-1500 cm-1) were assigned to alpha-helical, disordered and beta-strand/beta-turn structures of apolipoproteins A-I and A-II (apoA-I and apoA-II), the apolipoprotein constituents of HDL3. Modification of HDL3 by tetranitromethane (TNM) treatment, acetylation, reduction plus alkylation and 1,2-cyclohexanedione treatment derivatised tyrosine, lysine, cysteine and arginine residues, respectively, and caused alteration of the secondary structure of the HDL3 apolipoproteins to different extents. Each of the chemical modifications caused changes in the frequency of bands associated with beta-strands/beta-turns, but only TNM treatment of HDL3, as judged by the second- and fourth-derivative spectra, resulted in a shift of the band assigned to the alpha-helical structure of the proteins. In agreement with other workers, only TNM treatment of HDL3 particles was found to inhibit their binding by high-affinity cell membrane receptors. It is proposed, therefore, that receptor recognition of HDL3 particles is dependent on conservation of the alpha-helix structures within apoA-I and apoA-II, and that beta-strand/beta-turn structures are not involved. This conclusion is consistent with the predominance of amphipathic alpha-helical structures in both apolipoproteins and with the relaxed specificity of the receptors which are thought to recognise both apoA-I and apoA-II.

Heterogeneity of apolipoprotein A-I turnover in subjects with reduced concentrations of plasma high density lipoprotein cholesterol

Reduced plasma levels of high density lipoprotein cholesterol (HDLC) and apolipoprotein A-I (apoA-I) are both indicators of increased risk of developing coronary artery disease. We have used autologous 125-I-HDL to determine the rates of production (PR) and fractional catabolism (FCR) of apoA-I, the major, structural apolipoprotein in HDL, in three groups of men that included the following: four normal subjects (triglyceride [TG] = 61.0 +/- 5.0 mg/dL, HDLC = 51.5 +/- 7.0 mg/dL), four subjects with both hypertriglyceridemia and reduced HDLC (TG = 360.3 +/- 111.1 mg/dL, HDLC = 23.8 +/- 6.1 mg/dL), and seven subjects with only reduced HDLC (TG = 103.7 +/- 49.5 mg/dL, HDLC = 25.6 +/- 6.1 mg/dL). In the group with both the high TG and low HDL, apoA-I PR was significantly greater than the apoA-I PR in the normal group (14.2 +/- 2.3 v 10.6 +/- 1.9 mg/kg.d, P less than .05). ApoA-I FCR was also significantly greater in the former group v normals (0.38 +/- 0.08 v 0.21 +/- 0.04 d-1, P less than .02). In contrast, the group of subjects with only low HDLC had a significantly lower apoA-I PR v the normal subjects (7.1 +/- 2.0 v 10.6 +/- 1.9 mg/kg.d; P less than .05). ApoA-I FCR was variable in the group with isolated low HDLC, but the mean FCR was not different from normal (0.26 +/- 0.09 v 0.21 +/- 0.04 d-1).(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of the effects of Buserelin versus danazol on plasma lipoproteins during treatment of pelvic endometriosis

Twelve patients receiving Buserelin and seven patients receiving danazol for treatment of endometriosis were studied to assess the effect of medication on plasma lipoproteins. Danazol significantly lowered plasma HDL-C levels at 6 months of treatment. Total plasma cholesterol was elevated at 6 months of therapy in the Buserelin group. No effect by either drug on plasma triglycerides was seen.

Serum lipids and apolipoproteins in children with type 1 (insulin-dependent) diabetes during the first two years of the disease

Serum lipoproteins and apolipoproteins were studied at diagnosis and 6, 12 and 24 months later in 30 consecutive children aged 3-15 years with newly detected Type 1 (insulin-dependent) diabetes mellitus (December 1982-October 1984) and in 44 healthy control children. Serum triglycerides at diagnosis were significantly higher than after 6-24 months and also higher than in the control group (p less than 0.001). At follow-up, triglycerides in the very low density lipoproteins and low density lipoproteins were restored to normal, while high density lipoprotein triglycerides remained high. Serum cholesterol at onset of diabetes was significantly higher than in the control children (p less than 0.01), mainly because of increased very low density lipoprotein cholesterol (p less than 0.001). Cholesterol in serum and in the serum lipoprotein fractions was similar to that in the control children at follow-up, except that high density lipoprotein cholesterol was higher in the diabetic children after 6 months. The concentrations of the serum apolipoproteins A-I, A-II and B were higher at onset of diabetes than in the control children (p less than 0.001, p less than 0.01, p less than 0.05 respectively), with a significantly increased ratio of apolipoprotein A-I to A-II in the diabetic children (p less than 0.001). The serum apolipoprotein concentrations were normalised during treatment. The ratio of apolipoprotein A-I to B did not differ from that in control children. On admission, there were strong positive correlations between HbA1c and the concentrations of the very low density lipoproteins and the low density and high density lipoprotein triglycerides.(ABSTRACT TRUNCATED AT 250 WORDS)

Free apolipoproteins A-I and A-IV present in human plasma displace high-density lipoprotein on cultured bovine aortic endothelial cells

Adult bovine aortic endothelial (ABAE) cells, exposed to serum-free medium, specifically bind 125I-labeled human high-density lipoprotein (125I-HDL). Addition of human lipoprotein-deficient serum (LPDS) reduces the specific binding of 125I-HDL in a concentration-dependent manner, such that LPDS at a concentration of 6 mg protein/ml almost completely inhibits the specific binding of 125I-HDL. ABAE cultures exposed to 125I-labeled LPDS (125I-LPDS) specifically bind two peptides, which appear as minor iodinated components in 125I-LPDS. The binding of these two components is abolished in the presence of excess amounts of unlabeled LPDS or HDL. Preincubation of ABAE cells with 25-hydroxycholesterol (25-HC) results in an increase in the binding of the two 125I-LPDS components, similar to the increase observed in 125I-HDL binding in the presence of 25-HC. These two LPDS components comigrate on sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS-PAGE) with apolipoproteins A-I and A-IV of molecular masses 28 kDa and 43 kDa respectively. Furthermore, these two proteins were transferred from the SDS gel to nitrocellulose paper and interacted specifically with anti-(A-I) and anti-(A-IV) sera respectively. When ABAE cultures, pretreated with 25-HC in the presence of LPDS, are subjected to cell-surface iodination, the A-IV appears as one of the major proteins on the cell surface accessible to iodination. The interaction of A-IV with the cell surface of 25-HC-treated cells is not specific to ABAE cells and appears also in human skin fibroblasts. Analysis of the relative amounts of various apolipoproteins in the 125I-HDL bound to ABAE cells demonstrates a decrease in the relative amount of iodinated A-II concomitant with increase in the relative amounts of the other iodinated apolipoproteins, when compared to the composition of the native 125I-HDL. These changes are similar whether the binding is done in the presence or absence of LPDS. It indicates that the decrease in 125I-HDL binding in the presence of LPDS is not due to displacement of the iodinated apolipoproteins A-I and A-IV in the 125I-HDL by unlabeled A-I and A-IV present in LPDS. The results indicate that free apolipoproteins A-I and A-IV, present in LPDS, can displace HDL on the cell surface of ABAE cells. Thus, free A-I and A-IV, present in plasma, control the binding of HDL to endothelial cells and may regulate the process of cholesterol removal from the cells performed by HDL.

Altered high density lipoprotein metabolism in patients with myeloproliferative disorders and hypocholesterolemia

Patients with the myeloproliferative disorders (MPD), myeloid metaplasia and polycythemia vera, have significantly reduced concentrations of plasma low density (LDL) and high density (HDL) lipoprotein cholesterol (C). We have previously demonstrated that increased catabolism of LDL was associated with the low LDL-C levels. In the present study we have determined the rates of synthesis and removal of apolipoprotein A-1 (apoA-1) in five subjects with MPD who had markedly reduced HDL-C concentrations (18.2 +/- 4.1 mg/dL). Their results were compared to those obtained in six subjects with hypertriglyceridemia (HTG) with similar levels of HDL-C (19.7 +/- 3.9 mg/dL) and five subjects with normal (N) HDL-C concentrations (49.6 +/- 7.4 mg/dL). The results demonstrated that the fractional catabolic rate (FCR) for apoA-1 was significantly increased in the MPD group v N (0.38 +/- 0.15 v 0.21 +/- 0.03 day-1, P less than 0.05) while the synthetic rates for apoA-1 were similar in the two groups. The FCR for apoA-1 in the HTG group (0.36 +/- 0.07 day-1) was nearly identical to that in the MPD group, in spite of the large differences in their plasma triglyceride concentrations (406.2 +/- 217.9 v 117.0 +/- 29.8 mg/dL, P less than 0.05). Compositional studies indicated that the HTG group had very cholesterol depleted HDL while the HDL particles in the MPD group appeared to have a normal cholesterol content. These studies indicate that subjects with MPD have striking increases in HDL catabolism that can account fully for their markedly reduced levels of HDL cholesterol. The pathophysiologic mechanisms that are the basis of this alteration remain to be determined.

Effects of alcohol consumption on serum lipoprotein-lipid and apolipoprotein concentrations. Results from an intervention study in healthy subjects

Serum levels of cholesterol, triglyceride, cholesterol in low density lipoprotein (LDL) and in high density lipoprotein (HDL) and its major subfractions, and of apolipoproteins A-I, A-II and B were measured in 48 healthy men at the end of two 6-week periods in which they consumed normal alcohol (5.0%, v/v) or low alcohol (0.9%, v/v) beer, respectively. Other dietary and behavioural variables were kept constant. Mean levels of triglyceride, HDL cholesterol, HDL2- and HDL3 cholesterol, and apolipoproteins A-I and A-II were higher at the end of the normal compared with the low alcohol periods, and levels of LDL cholesterol were lower. Body weight was greater at the end of the normal alcohol period than at the end of the period of low alcohol but multiple regression analysis suggested that the changes in lipoprotein-lipid and apolipoprotein levels were due primarily to the change in alcohol consumption rather than concomitant changes in body weight. This study confirms an effect of alcohol on both major subfractions of HDL and on its major apolipoproteins.

Stimulation of lecithin:cholesterol acyltransferase activity by apolipoprotein A-II in the presence of apolipoprotein A-I

Various combinations of incorporation and addition of apolipoprotein A-I (apo A-I) and apolipoprotein A-II (apo A-II) individually or together to a defined lecithin-cholesterol (250/12.5 molar ratio) liposome prepared by the cholate dialysis procedure were used to study the effect of apo A-II on lecithin:cholesterol acyltransferase (LCAT, EC 2.3.1.43) activity of both purified enzyme preparations and plasma. When apo A-I (0.1-3.0 nmol/assay) alone was incorporated or added to the liposome, apo A-I effectively activated the enzyme. By contrast, when apo A-II (0.1-3.0 nmol/assay) alone was incorporated into or added to the liposome, apo A-II exhibited minimal activation of LCAT activity, approximately 1% of the activity obtained by an equal amount of apo A-I. Addition of apo A-II (0.1-3.0 nmol/assay) together with apo A-I (0.8 nmol/assay) to the liposome reduced the LCAT activity to approximately 30% of the level obtained with addition of apo A-I alone. On the other hand, addition of apo A-II (0.1-3.0 nmol/assay) or addition of lecithin-cholesterol liposome containing apo A-II (0.1-3.0 nmol/assay) to lecithin-cholesterol liposome containing apo A-I (0.8 nmol/assay) did not significantly alter apo A-I activation of LCAT activity. However, when the same amounts (0.1-3.0 nmol/assay) of apo A-II were incorporated together with apo A-I (0.8 nmol/assay) into the liposome, apo A-II significantly stimulated LCAT activity as compared to activity obtained with incorporation of apo A-I alone. The maximal stimulation was obtained with 0.4 nmol apo A-II/assay for both purified and plasma enzyme. At this apo A-II concentration, approximately 4-fold and 1.8-fold stimulation was observed for purified enzyme and plasma enzyme, respectively. These results indicated that apo A-II must be incorporated together with apo A-I into lecithin-cholesterol liposomes to exert its stimulatory effect on LCAT activity and that apo A-II in high-density lipoprotein may play an important role in the regulation of LCAT activity.

The uptake and metabolism of chylomicron-remnant lipids by rat liver parenchymal and non-parenchymal cells in vitro

The uptake and metabolism of chylomicron-remnant lipids by individual liver cell types was examined by incubating remnants with monolayer cultures of hepatocytes, Kupffer cells, and endothelial cells from rat liver. Remnants were prepared in vitro from radiolabelled mesenteric-lymph chylomicra, utilizing either purified lipoprotein lipase from bovine milk, or plasma isolated from heparinized rats. The resulting particles contained [3H]phosphatidylcholine and cholesterol, and [14C]oleate in the acylglycerol, phospholipid, fatty-acid and cholesterol-ester fractions. The capacities of the three cell types for uptake of both [3H]lipids and [14C]lipids were determined to be, on a per-cell basis, in the order: Kupffer greater than hepatocytes greater than endothelial. The relative proportions of [3H]phospholipid and total [3H]cholesterol taken up by hepatocytes and non-parenchymal cells remained constant with time. The uptake of [14C]oleoyl lipids by all three cell types was slightly greater than that of the total [3H]cholesterol and [3H]phospholipid components. There was evidence of cholesterol-ester hydrolysis and turnover of [14C]oleate in the phospholipid fraction in hepatocytes and Kupffer cells, but not endothelial cells, over the first 2 h. With both remnant preparations, these observations indicate that significant differences exist between the three major liver cell types with respect to the uptake and metabolism of remnant lipid components.

Nonpharmacologic and pharmacologic alteration of high-density lipoprotein cholesterol: therapeutic approaches to prevention of atherosclerosis

High-density lipoprotein (HDL) cholesterol, an independent coronary heart disease (CHD) risk factor, is inversely associated with CHD. Whether interventions to increase concentrations of HDL--particularly the HDL2, HDL3, and apolipoprotein A1 subfractions--will reduce the incidence of CHD in high-risk patients is thus an area of intense speculation. Both nonpharmacologic and pharmacologic regimens will raise HDL concentrations. Nonpharmacologic approaches include habitual high-level aerobic exercise and weight loss--both of these somewhat more effective in men than in women--cessation of cigarette smoking, and changing of dietary habits. A number of drugs have been found to elevate HDL cholesterol. These include the bile acid-binding resin cholestyramine, nicotinic acid, gemfibrozil, phenytoin, exogenous estrogens, and alcohol. Terbutaline has also been reported to raise HDL cholesterol. It is not yet known whether, and to what degree, pharmacologic and nonpharmacologic elevation of HDL cholesterol will retard or reverse the progression of atherosclerosis. Conversely, HDL cholesterol is lowered by a broad variety of drugs, including anabolic--androgenic steroids, exogenous progestins, and probucol, which are used therapeutically to reduce low-density lipoprotein (LDL) cholesterol. Some agents used to treat hypertension also reduce HDL cholesterol, especially thiazide diuretics and the beta blockers, with the possible exception of pindolol. In the antiadrenergic class of antihypertensive agents, reserpine and methyldopa lower HDL cholesterol, but the alpha blocker prazosin does not appear to affect HDL cholesterol. The alpha agonist guanabenz has no effect on HDL cholesterol, and the vasodilator carprazidil has been reported to raise HDL cholesterol. In light of these facts, investigations should be undertaken to determine whether the metabolic effects of antihypertensive agents blunt their beneficial effects on CHD.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipid levels in high density lipoprotein subfractions in smokers with peripheral vascular disease

No significant difference in HDL cholesterol was found between smokers with PVD and corresponding controls. The ratio of HDL cholesterol to the sum of (VLDL + LDL) cholesterol was reduced in patients with PVD. Patients with PVD had significantly highly serum triglyceride levels. A slightly significant difference could be demonstrated for serum cholesterol and serum phospholipids concentrations in smoking patients with PVD.

Activation of lecithin: cholesterol acyltransferase by apolipoproteins E-2, E-3, and A-IV isolated from human plasma

Apolipoprotein A-IV, apolipoprotein E-2 and apolipoprotein E-3 were individually incorporated into defined phosphatidylcholine/cholesterol liposomes for study of lecithin:cholesterol acyltransferase activation. Enzyme activities obtained with these liposomes were compared with that from liposomes containing purified apolipoprotein A-I. Apolipoprotein A-IV, apolipoprotein E-2, and apolipoprotein E-3 all activated lecithin:cholesterol acyltransferase. With purified enzyme and with egg yolk phosphatidylcholine as the acyl donor, maximal activation was obtained at a concentration of approximately 0.5 nmol for apolipoprotein A-IV and 0.4 nmol for the apolipoprotein E isoforms. Apolipoprotein A-IV was approximately 25% as efficient as apolipoprotein A-I for the activation of purified enzyme; apolipoprotein E-2 was 40% as efficient, and apolipoprotein E-3, 30%. Similar activation results were obtained using plasma as the enzyme source. Analysis of the plasma of patients with absence of apolipoprotein A-I or with only trace amounts of apolipoprotein A-I exhibited a reduced rate of cholesterol esterification and lecithin:cholesterol acyltransferase activity that was proportional to the reduced level of the enzyme's mass. These results indicate that apolipoprotein A-IV and apolipoprotein E may serve as physiological cofactors for the enzyme reaction.

Direct evidence that reverse cholesterol transport is mediated by high-density lipoprotein in rabbit

Mammalian cells obtain cholesterol for membrane synthesis mostly via the receptor-mediated endocytosis of low-density lipoprotein (LDL). Macrophages and vascular endothelium additionally have receptors that recognize certain modified forms of LDL (for example, acetyl-LDL). The process by which cholesterol returns from peripheral cells to hepatocytes (reverse cholesterol transport) has not been established; although tissue culture studies have favoured high-density lipoprotein (HDL) as the principal vehicle, the in vivo evidence for this is meagre. When cholesterol-loaded macrophages are incubated in medium containing plasma, cholesterol moves from the cells to HDL and is then esterified by lecithin/cholesterol acyltransferase. The accumulation of cholesteryl esters in the particles increases their size and decreases their density; enrichment with apoprotein E (apo E) also occurs, producing a decrease in electrophoretic mobility. We now report that similar changes occur in the circulating HDL of rabbits, when their peripheral tissues are loaded with cholesterol by intravenous (i.v.) injection of acetylated or native human LDL. This result suggests that HDL is involved in reverse cholesterol transport in vivo.

Modifications in plasma cholesterol and apolipoproteins of hypercholesterolaemic rats induced by ethanol-soluble factors of Vicia faba

High-fat-high-cholesterol diets containing casein or a Vicia faba bean (faba bean) protein concentrate as the protein source were given to rats for 5 weeks. When the faba bean protein concentrate or its ethanol extract was present in the diet, a marked decrease was found in the level of circulating cholesterol associated with the lower-density lipoproteins (very-low-, intermediate- and low-density lipoproteins) compared with the level found on the diets containing casein or the faba bean protein concentrate deprived of ethanol-soluble factors. Alterations in apoprotein pattern were detected after the different dietary treatments. In particular, apoA-I appeared in an unusual form with electrophoretic mobility faster than normal in all lipoprotein fractions after feeding the diets that did not lower plasma cholesterol. When the diets contained the faba bean protein concentrate or its ethanol extract, the apoA-I disappeared from the lower-density lipoproteins but its normal form and the unusual one were apparent in the high-density lipoproteins. A moderate increase in faecal excretion of acidic steroids was found after feeding the diets containing the ethanol-soluble factors, irrespective of the protein source. The results are discussed in relation to the presence of saponin and polyunsaturated lecithin in the ethanol extract of the faba bean protein concentrate.

Effects of isotretinoin on serum lipids and lipoproteins, liver and thyroid function

Seven patients with severe rosacea were treated with 1 mg/kg per day isotretinoin for 12 wk. There were significant increases in serum triglyceride (p less than 0.001) and cholesterol (p less than 0.001). Triglyceride associated with very low density lipoprotein (VLDL), low density lipoprotein (LDL) and high density lipoprotein (HDL) increased (p less than 0.01), cholesterol in VLDL and LDL increased (p less than 0.01), and levels of HDL cholesterol decreased (p less than 0.01). There were changes in indices of liver function, with increased levels of gamma-glutamyltransferase (GGT) (p less than 0.01), alkaline phosphatase (ALP) (p less than 0.01) and aspartate aminotransferase (AST) (p less than 0.01), and decreased bilirubin levels (p less than 0.05). Although levels of thyroxine and triiodothyronine were lower after treatment (p less than 0.05), there were no changes in basal levels of thyroid-stimulating hormone (TSH), luteinizing hormone (LH) or follicle-stimulating hormone (FSH), and responses to thyrotrophin releasing hormone (TRH) and luteinizing hormone releasing hormone (LHRH) were unchanged. These changes may partially be explained by induction of hepatic microsomal enzymes by isotretinoin.

Isolation and DNA sequence of full-length cDNA and of the entire gene for human apolipoprotein AI--discovery of a new genetic polymorphism in the apo AI gene

We have isolated full-length cDNA clones for apolipoprotein AI from a human fetal liver cDNA library made in the vector lambda gt10. One such clone, pBL13AI, was 965 nucleotides long and contained the entire preproapolipoprotein AI sequence, in addition to 86 nucleotides of 5' untranslated region and 75 nucleotides of the 3' untranslated region. The complete structure of this clone is presented. Furthermore, we have obtained a 20-kb genomic fragment from a human genomic library, encompassing the entire apo AI gene. Sequence analysis of the gene shows that the coding region is interrupted by three introns of 197, 187, and 588 bp, respectively. Digestion of the DNA of various individuals with the endonuclease Msp I revealed a new restriction site polymorphism in the apo AI gene.

Increased serum high-density lipoprotein cholesterol in hypertensive men treated with the potent vasodilator carprazidil

The effects of the potent arteriolar vasodilator carprazidil on serum lipoproteins and various clinical, biochemical and endocrine parameters were assessed in 15 men with mild to moderate essential hypertension. Following a carprazidil monotherapy (average dose 50 to 60 mg/d) of 8 weeks (N = 15) or 16 weeks (N = 12) duration, blood pressure was decreased significantly (P less than 0.01), while serum high-density lipoprotein cholesterol (+ 26% and + 24%, respectively; P less than 0.01) and the alpha-lipoprotein fraction (+ 26% and + 41%) were increased. Low- and very low-density lipoprotein cholesterol, triglycerides, as well as mean body weight, blood and plasma volume, heart rate, and plasma renin, aldosterone, norepinephrine, and epinephrine were not consistently altered. These results indicate that treatment of hypertensive men with carprazidil in modest dosage may have a favorable influence both on blood pressure and serum lipoproteins.

High-density lipoprotein cholesterol and liver disease

To establish whether there is any significant relationship between high-density lipoprotein cholesterol (HDLC) concentrations and biopsy-documented liver disease, 169 patients had needle biopsies, serum cholesterol, and HDLC evaluated. Twenty-four patients had serial cholesterol, HDLC, prothrombin, and aminotransferase levels and activities examined. In both men and women, HDLC decreased strikingly and significantly in acute alcoholic hepatitis and in acute viral hepatitis, compared to controls (p less than 0.001). Men and women with inactive alcoholic liver disease and chronic active hepatitis showed moderate decreased in HDLC (p less than 0.001). Patients with primary and metastatic hepatic neoplasms also had strikingly decreased HDLC (p less than 0.001). Serial testing showed an excellent direct correlation between HDLC and prothrombin activity, r values ranging from 0.71 to 0.98. Although alcohol intake is known to correlate positively with HDLC concentrations, our data shows that this association is not absolute, and in most cases is reversed once liver disease becomes apparent.

Quantitative determinations of HDL2 and HDL3 in patients with liver disease

To elucidate the role of the liver in the metabolism of HDL subfractions, the levels of HDL2 and HDL3 were determined in the sera obtained from patients with liver disease. The determinations were carried out either by zonal ultracentrifugation or by gradient gel electrophoresis combined with HDL cholesterol measurement. Mean HDL3 cholesterol level in patients with liver cirrhosis was about one third of the normal controls whereas no significant changes were observed in HDL2 cholesterol concentration. HDL3 cholesterol levels in patients with chronic hepatitis were about a half of the controls. The levels of HDL3 cholesterol correlated significantly to the levels of serum albumin and to choline esterase activities. The results suggest either that HDL3 is synthesized in the liver or that there is a metabolic defect in the conversion of HDL2 to HDL3 in liver disease.

Organization of unesterified cholesterol in high density lipoproteins probed by filipin

The initial rate of filipin association with unesterified cholesterol in high density lipoproteins (HDL) was measured by stopped-flow spectrophotometry to assess the roles played by apolipoproteins and phospholipids in modulating the surface exposure of cholesterol. The initial rate of filipin-unesterified cholesterol association was enhanced upon hydrolysis of the glycerophospholipids of human HDL3 by phospholipase A2. Rate enhancements were also observed following trypsin-catalyzed hydrolysis of apolipoprotein A-I in canine HDL and of apolipoproteins A-I and A-II in human HDL3. However, the initial rate of filipin-unesterified cholesterol association was not altered upon incubation of HDL3 with polymorphonuclear cells, which causes hydrolysis of apolipoprotein A-II but leaves apolipoprotein A-I intact. These results are consistent with the general structural model of HDL in which unesterified cholesterol, apolipoproteins and glycerophospholipids are presumed to be localized at the surface of the HDL particle. From these studies and from results indicating that the initial rate of filipin-unesterified association was enhanced in canine HDL hybrids in which 50% of the apolipoprotein A-I had been replaced by apolipoprotein A-II, we also conclude that apolipoprotein A-I in HDL is in closer proximity to unesterified cholesterol than apolipoprotein A-II. Thus, it appears that rapid kinetic measurements of filipin-cholesterol association may be useful in assessing the organization of unesterified cholesterol in serum lipoproteins.

The effects of probucol on plasma lipoproteins in polygenic and familial hypercholesterolaemia

During treatment with probucol at the dose of 1 g per day, the mean reduction in low density lipoprotein (LDL) cholesterol concentration was 11.2% in polygenic hypercholesterolaemia (n = 9) and 9.4% in heterozygous familial hypercholesterolaemia (n = 6). However, there was marked heterogeneity of response: in seven of the patients with polygenic hypercholesterolaemia who had in common moderate elevation of LDL cholesterol (5.3-6.4 mmol/1), the reduction ranged from 13 to 40% (mean, 23%). In two of this group the change in LDL concentration was associated with a decrease in LDL apolipoprotein B synthetic rate. Of the patients with familial hypercholesterolaemia one showed a 33% reduction in LDL cholesterol, and one a 13% reduction. Total high density lipoprotein (HDL) cholesterol concentration tended to decrease during treatment. This reflected a reduction of the cholesterol concentration in the HDL3 subclass; HDL2 cholesterol remaining unchanged. Plasma triglyceride and very low density lipoprotein cholesterol were unaffected by probucol. The drug was well tolerated with only one patient complaining of severe diarrhoea, and two of mild and transient diarrhoea. No clinically significant changes occurred in serial resting electrocardiograms. Thus, probucol appears to be a useful drug for the treatment of most patients with polygenic hypercholesterolaemia, and of some patients with heterozygous familial hypercholesterolaemia.

High-density lipoprotein that supports Ureaplasma urealyticum growth

A high-density lipoprotein with growth-promoting activity for Ureaplasma urealyticum was purified in high yield from equine serum by ammonium sulfate fractionation and molecular filtration. Fractions enriched in growth-promoting activity represented 5% of the total serum protein, and 30 micrograms of the purified protein per ml gave an activity equivalent to that from 100 micrograms of whole serum per ml. The serum was totally replaced by purified lipoprotein when tested in a soy peptone-yeast dialysate or when added to a chemically defined synthetic medium. Polyacrylamide gel electrophoresis indicated that one major protein with growth-promoting activity is present. A total of 10 proteins were distinguished by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, with 75% of the total contributed by two proteins with molecular weights of 160,000 and 170,000. A total of 90% of the lipoprotein was an alpha-protein with a mobility of 0.67 in two-dimensional immunoelectrophoresis (albumin = 1.0). The active component was further characterized as high-density lipoprotein by density ultracentrifugation. Two components with S = 6.4 and S = 15.8 were distinguished by velocity sedimentation. The lipid was removed from lipoprotein during its precipitation with acetone. The growth-promoting activity of delipidized protein was dependent upon the addition of exogenous cholesterol, and [14C]cholesterol was transferred to urea-plasmic cells in cultures containing the delipidized protein. A major portion of the [14C]cholesterol remained associated with the protein during filtration on Sepharose 4B columns.

Genetic mediation of lipoprotein cholesterol and apoprotein concentrations in the baboon (Papio sp.)

Genetic effects on serum lipoprotein and apoprotein concentrations were investigated using a paternal half-sib design with 79 progeny of 6 sires. Significant differences (P less than 0.05) were observed among sire progeny groups at 4-6 years of age for serum cholesterol, HDL cholesterol and apoA-I concentrations. A sire effect (P less than 0.10) also was observed for VLDL + LDL cholesterol concentrations, but differences were not observed (P greater than 0.10) among sire progeny groups for apoB concentrations. Estimates of heritability were 0.54 for serum cholesterol, 0.32 for VLDL + LDL cholesterol, 0.78 for HDL cholesterol, 0.56 for apoA-I, and 0.20 for apoB concentration. Genetic (rg) and environmental (re) correlations among serum cholesterol, lipoprotein cholesterol, and apoprotein concentrations were positive except for the negative genetic relationships of apoA-I with apoB (rg = -0.74) and with VLDL + LDL cholesterol (rg = -0.30) concentrations. The phenotypic correlation (rp = 0.31) of VLDL + LDL cholesterol with HDL cholesterol was due entirely to the genetic contribution (0.31) since the environmental contribution was zero. The positive genetic relationship (rg = 0.62) of VLDL + LDL cholesterol and HDL cholesterol may be due to biochemical mechanisms controlling cholesterol turnover since the genetic correlations of VLDL + LDL cholesterol and HDL cholesterol with cholesterol turnover rate were both negative (-0.43 and -0.68, respectively). A strong negative genetic correlation (rg = -0.95) was observed between apoA-I and cholesterol turnover, a finding that suggests a close physiologic relationship between these variables.

Regulation of high density lipoprotein levels

Current concepts of the structure and metabolism of high density lipoproteins are presented and factors that influence their levels in human beings are surveyed.