Heterozygosity for ABCA1 gene mutations: effects on enzymes, apolipoproteins and lipoprotein particle size

A cohort of 13 female and 14 male heterozygotes for ATP binding cassette A1 (ABCA1) gene defects was directly compared with 13 and 14 unaffected female and male family members of almost exact same age. The activities of three proteins that play key roles in HDL metabolism were measured in addition to extensive lipid and (apo) lipoprotein subfraction analysis. Compared to controls, LCAT activity was reduced by 15% in affected subjects (P < 0.001) while PLTP activity was unaffected. Interestingly, CETP activity was elevated by 50% in the heterozygote siblings of one kindred but was unaffected in heterozygotes of the three other families. With respect to lipids, the heterozygotes had normal total cholesterol (TC), and LDL-cholesterol concentrations but presented with a trend towards increased triglyceride levels (13%; P = 0.08). HDL metabolism, by contrast, was severely affected as illustrated by 40% reductions in HDL-cholesterol (P < 0.001) with concomitant reductions in apoAI (25%; P < 0.001) levels and in lipoprotein subfraction LpAI (28%; P < 0.001), LpAI:AII (24%; P=0.014), and LpCIII:nonB (34%; P < 0.001) concentrations. We furthermore observed reduced average HDL particle size (5%; P = 0.004; 16% in female and 3.6% in male) and reduced plasma apoCIII concentration (15%; P = 0.006) while apoAII, apoAIV, apoE and apoB levels were unchanged. In conclusion, heterozygosity for ABCA1 defects was associated with reduced LCAT activity in absence of effects on PLTP activity. Of special interest was our finding that the effects of compromised ABCA1 function on HDL were more pronounced in women than in men.

Analysis of apolipoprotein A-I, lecithin:cholesterol acyltransferase and glucocerebrosidase genes in hypoalphalipoproteinemia

Hypoalphalipoproteinemia (HALP) is a dyslipidemia characterized by low HDL-cholesterol (HDL-C) levels with important genetic contribution. However, no common genetic mutations have been found to be associated with this disorder. We screened the promoter and coding sequence of apolipoprotein (apo) A-I and lecithin:cholesterol acyltransferase (LCAT) genes and the 5' apo C-III region by SSCP and heteroduplex analysis, and DNA sequencing in 66 unrelated subjects with recurrent low HDL-C levels. We also analyzed the N370S and L444P variants, in the glucocerebrosidase (GBA) gene by restriction fragment analysis. Three mutations in the apo A-I gene (L144R, W108R, g.1833C>T) and 3 mutations in the LCAT gene (S208T, I178T, IVS3-23C>A) were detected, in six heterozygous subjects. In addition, a novel polymorphic site in LCAT gene (g.4886C>T) has been identified. Allelic frequencies of polymorphisms g.(-636)C>A, g.(-625)G>A, g.(-620)T>del, g.(-479C>T and g.(-452)T>C, located upstream of the apo C-III gene, were in normal range, and no other mutation was found in this region. Two HALP subjects were found to carry the N370S mutation at GBA locus. In conclusion, 12% of HALP subjects were found to carry mutations in apo A-I, LCAT, or GBA genes, which could explain this phenotype. Our results confirm the molecular, genetic and phenotypic heterogeneity of HALP.

Impaired serum lipids and lipoproteins in fetal macrosomia related to maternal obesity

The aim of this work was to determine lipoprotein metabolism alterations in macrosomic newborns and to see whether these lipoprotein abnormalities are parallel or not to those found in their obese or nonobese mothers. Serum lipids, apo A-I, apo B100, lipoproteins (VLDL, LDL, HDL2, and HDL3), and LCAT activity were investigated in obese and nonobese mothers and cord blood of their macrosomic or appropriate-for-gestational-age (AGA) newborns. Serum and VLDL triglyceride concentrations were higher in obese mothers of AGA newborns than in nonobese mothers. Serum triglyceride, VLDL, and apo B100 levels were higher, while serum apo A-I and HDL2 cholesterol concentrations were lower in obese mothers of macrosomic newborns than in the other groups. In their macrosomic newborns, serum lipid, lipoprotein, apo B100, and apo A-I levels were higher as compared with those of other newborns. Macrosomic newborns of nonobese mothers had lipoprotein profiles similar to those in AGA newborns. LCAT activity was similar in both mother groups and in both newborn groups. In conclusion, maternal obesity and fetal macrosomia were associated with lipoprotein abnormalities consistent with high atherogenic risk.

Dietary safflower phospholipid reduces liver lipids in laying hens

This experiment was conducted to determine the effects of dietary safflower phospholipids (crude safflower phospholipid and purified safflower phospholipid) on performance and lipid metabolism of laying hens. Sixty-week-old Single Comb White Leghorn laying hens were divided into four groups of seven birds each, and were given one of four experimental diets containing 5% beef tallow (served as a control, tallow), a mixture of safflower oil and palm oil (SP-oil), crude safflower phospholipid (Saf-PLcrude), or purified safflower phospholipid (Saf-PL) for 7 wk. Egg production ratio and daily egg mass were significantly higher in hens fed Saf-PLcrude diets than in hens of the other diet groups. There were no significant differences in egg weight among groups. Liver cholesterol and triglyceride contents were significantly decreased in all treated groups as compared with the control. The activity of hepatic 3-hydroxy-3 methylglutaryl coenzyme A reductase was the highest in hens fed the Saf-PLcrude diet. Serum esterified cholesterol concentration was decreased by feeding of SP-oil, Saf-PLcrude, or Saf-PL diets. Serum lecithin-cholesterol acyltransferase activity was highest in hens fed the tallow diet. Excreta neutral steroid excretion was significantly increased in the Saf-PLcrude or Saf-PL diet groups, although acidic steroid excretion was not affected by dietary treatments. Total cholesterol, triglyceride, and phospholipid contents in egg yolks were not different for any dietary treatments. The fatty acid compositions of egg yolks from hens fed Saf-PLcrude diets were not different with those fed the SP-oil diet, although eggs of hens fed the Saf-PL diet showed lower total polyunsaturated fatty acids. These results suggest that dietary safflower phospholipids may be a valuable ingredient to layers for reducing liver triglycerides and serum cholesterol without any adverse effects.

Determinants of plasma HDL-cholesterol in hypertriglyceridemic patients. Role of cholesterol-ester transfer protein and lecithin cholesteryl acyl transferase

Hypertriglyceridemic patients commonly have low levels of HDL cholesterol. Elevated triglycerides per se may be one cause of low HDL levels, but other factors also may be involved. The current study was designed to define the role of cholesterol-ester transfer protein (CETP) in causation of a low HDL cholesterol in hypertriglyceridemic patients; in addition other factors-lecithin cholesterol acyl transferase (LCAT), hepatic triglyceride lipase (HTGL), and lipoprotein lipase (LPL)-were examined. Plasma activities of CETP and LCAT were measured in 137 male patients with moderate hypertriglyceridemia (plasma triglycerides [TGs] 200 to 500 mg/dL and LDL cholesterol < 160 mg/dL). Results were compared with those from 50 normolipidemic men of similar age and body habitus. In addition, lipase activities in postheparin plasma were measured in 118 of the subjects with hypertriglyceridemia. The activities of CETP and LCAT were 17% (P < .01) and 7% (P < .05), respectively, higher in the hypertriglyceridemic group than in control subjects. By stepwise regression analysis CETP appeared to contribute 15.2% and LCAT 9.8% to variation in HDL-cholesterol levels. Activities of LPL and HTGL together contributed an additional 14.1% to HDL-cholesterol variation. In contrast, levels of plasma TG accounted for only 5.4% of the variation. There were no differences in relative contributions of these parameters in patients with and those without coronary heart disease. This study indicates that several factors contribute to the variation in HDL-cholesterol levels in hypertriglyceridemic patients, and five factors-CETP, LCAT, HTGL, LPL, and triglyceride levels-account for almost half of this variation.

Apolipoprotein AIV of human interstitial fluid is associated with apolipoprotein AI-containing but not with AII-containing particles

Apolipoproteins and lipoprotein particles from human interstitial fluid and plasma were analyzed. The interstitial fluid was enriched in apolipoproteins AI, AII, and AIV compared with apo B, apo CIII, and apo E, LpAI was found to contain apo AIV which was absent from LpAI: AII. Moreover, the bulk of lecithin-cholesterol acyl-transferase was present in LpAI. The concentration range of these particles was in agreement with those required in vitro for cholesterol efflux. Thus the interstitial fluid contains particles in which two agonists but no antagonists of cholesterol efflux are associated with lecithin-cholesterol acyltransferase activity. This supports apolipoprotein AI- and/or AIV-containing particles playing a critical role in the first step of reverse cholesterol transport.

Two different allelic mutations in a Finnish family with lecithin:cholesterol acyltransferase deficiency

Lecithin:cholesterol acyltransferase (LCAT) deficiency is a genetic disorder associated with low levels of serum HDL cholesterol. The proband of the Finnish LCAT-deficient family had corneal opacities, proteinuria, anemia with stomatocytosis, low serum HDL cholesterol (0.27 mmol/L), and low LCAT activity. Sequence analysis of his LCAT gene revealed compound heterozygosity for two different mutations: a C insertion in exon 1 between nucleotides 932 and 937 and a C-to-T point mutation in exon 6 at position 4976. The C insertion in exon 1 is predicted to result in premature termination and a truncated polypeptide containing only 16 amino acids. The C-to-T point mutation in exon 6 substitutes cysteine for arginine at residue 399. The functional significance of the Arg399-->Cys mutation was examined by expressing the mutated and wild-type LCAT cDNAs in COS cells. COS cells transfected with mutated and wild-type cDNAs showed comparable levels of mature LCAT mRNA. However, LCAT activity in the cell media of COS cells transfected with the mutant LCAT cDNA was significantly lower than that of COS cells transfected with the wild-type cDNA (1.4% versus 12.0% cholesterol esterified, respectively). A polymerase chain reaction-based duplex assay, in which both mutations can be detected simultaneously, was used for preliminary screening of Finnish subjects with serum HDL levels below 0.9 mmol/L; two additional individuals heterozygous for the Arg399-->Cys mutation were identified.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipoprotein composition in insulin-dependent diabetes mellitus with chronic renal failure: effect of kidney and pancreas transplantation

Chronic renal failure (CRF) in nondiabetics is associated with a number of lipoprotein abnormalities that place these patients at high risk for atherosclerosis. This study compared the lipoprotein composition of nondiabetic controls (n = 68) with that of patients with insulin-dependent diabetes mellitus ([IDDM] n = 13) and of patients with IDDM and CRF ([IDDM + CRF] n = 74). Six lipoprotein subfractions (very-low-density lipoprotein [VLDL], intermediate-density lipoprotein [IDL], low-density lipoprotein [LDL], high-density lipoprotein-light [HDL-L], HDL-medium [HDL-M], and HDL-dense [HDL-D]) were isolated by rapid gradient ultracentrifugation using a fixed-angle rotor. The apolipoprotein (by reverse-phase high-performance liquid chromatography [HPLC]) and lipid (by enzymatic assays) composition of each subfraction was determined. The only abnormalities found in IDDM patients were increases in IDL and HDL-L triglyceride (TG) levels and an increase in the HDL-L free cholesterol (FC) level. The IDDM + CRF group had multiple abnormalities including (1) elevated TG, apolipoprotein (apo) C-II, and apo C-III levels in all lipid subfractions; (2) elevated VLDL and IDL apo B, TG, FC, cholesterol ester (CE), and phospholipid (PL) levels (with an increased CE/TG ratio in VLDL only); (3) decreased HDL-M apo A-I, apo A-II, CE, and PL levels, but an increased HDL-D apo A-I level; and (4) decreased lecithin:cholesterol acyltransferase (LCAT) activity. Twenty-five of the IDDM + CRF patients underwent combined pancreas and kidney (P + K) transplantation, and 12 patients received only a kidney transplant. Lipoprotein composition was determined at 3, 6, and 12 months posttransplant. Both types of transplantation resulted in similar alterations in lipoprotein composition, even though there was essential normalization of blood glucose levels in most of the patients who received a pancreas transplant (hemoglobin A1C [HbA1C], 9.1% +/- 1.1% v 5.7% +/- 0.3% at 12 months, P < .01). These posttransplant changes included (1) no improvement in the elevated TG level in any lipid subfraction even though there was some reduction in apo C-III levels in VLDL; (2) reductions in levels of VLDL and IDL apo B but increases in LDL apo B; (3) increases in HDL apo C-III and FC concentrations despite an increase in LCAT activity; and (4) increases in apo A-I levels in HDL-L and HDL-M. The addition of a pancreas to a kidney transplant had no obvious impact on the lipoproteins.(ABSTRACT TRUNCATED AT 400 WORDS)

Lipoproteins containing apolipoprotein A-IV: composition and relation to cholesterol esterification

In order to investigate the relationship of lipid and apolipoprotein composition to cholesterol esterification in lipoproteins containing apolipoprotein (apo) A-IV, apo A-containing lipoprotein particles were isolated from fresh human plasma using a system of sequential immunoaffinity chromatography. Plasma was first depleted of apo B- and apo E-containing lipoproteins. Four major subpopulations of apo A-containing lipoprotein particles were separated: Lp A-I, Lp A-I: A-II, Lp A-IV and Lp A-I: A-IV: A-II. Lp A-IV and Lp A-I: A-IV: A-II contained less total lipid, less cholesterol and more triacylglycerol than Lp A-I and Lp A-I: A-II. Lp A-IV and Lp A-I: A-IV: A-II contained more sphingomyelin and less phosphatidylcholine than Lp A-I and Lp A-I: A-II and were richer in (16:0 + 18:0) saturated fatty acids. Among these isolated lipoprotein particles, Lp A-IV contained the highest lecithin: cholesterol acyltransferase (LCAT) activity per micrograms of protein. Cholesterol esterification rates were 2.6 +/- 0.5, 5.3 +/- 0.4 and 0.8 +/- 0.2 mumol of cholesterol per hour per mg of lipoproteins for Lp A-IV, Lp A-I and Lp A-I: A-II, respectively. The apolipoprotein and lipid composition and LCAT activity of Lp A-IV suggest that this lipoprotein may be a source of cholesterol esterification in plasma.

Follicular fluid lipoproteins in the mare: evaluation of HDL transfer from plasma to follicular fluid

Using a density gradient ultracentrifugal procedure, we have separated equine plasma and follicular fluid high-density lipoproteins (HDL). The density distribution of the follicular fluid HDL was clearly displaced towards the highest densities in comparison with that of plasma HDL. Similarly, an analysis of size distributions showed a decrease in follicular fluid HDL diameters (4.2 to 9.2 nm) compared to plasma HDL (5.5 to 9.5 nm). HDL were isolated into three subfractions on the basis of the disposition of the Sudan Black stained bands in the centrifuge tubes. Concentrations of each subfraction were clearly lower in the follicular fluid, and the relative percentages with regard to the plasma equivalents were inversely proportional to the molecular weights (23.8% for HDL-1, 49.9% for HDL-2 and 63.7% for HDL-3). The cholesterol/phospholipid molar ratio and the esterified/free cholesterol molar ratio were clearly increased in the follicular HDL-2 and HDL-3 subfractions. The apolipoprotein distribution in follicular fluid HDL was very close to that in plasma HDL. LCAT activity measured in human as well as equine samples was weaker in follicular fluid compared to plasma in both species (4.0 nmol of free cholesterol esterified per h per ml vs. 24 nmol per h per ml). Theoretical concentrations of follicular fluid HDL were calculated assuming that the HDL particles would be merely a filtration product undergoing no detectable metabolic modifications. Biochemical measurements showed that the lightest particles (HDL-1) were less numerous than suggested by the theoretical calculation. Thus, although follicular fluid HDL appear to be a filtration product of plasma HDL, they undergo metabolic transformations that we suggest may be linked to hormonal synthesis and reverse cholesterol transport.

Tangier disease: isolation and characterization of LpA-I, LpA-II, LpA-I: A-II and LpA-IV particles from plasma

Tangier disease (TD) is characterized by extremely low plasma levels of HDL, apoA-I and apoA-II due to very rapid catabolism. However, the risk of premature coronary heart disease (CHD) is not markedly increased in TD. In order to gain insight into reverse cholesterol transport in TD, we isolated LpA-I, LpA-I:A-II, LpA-II and LpA-IV particles from fasting plasma of 5 TD patients. LpA-I composition was similar to control LpA-I, but TD LpA-I had more LCAT and CETP activity (respectively, 0.35 +/- 0.14 and 0.14 +/- 0.04 mumol of cholesterol esterified/h/micrograms of protein, and 7 +/- 2.5 and 1.4 +/- 0.3 mumol of cholesteryl ester transferred/h/micrograms of protein). In contrast, TD LpA-I:A-II had abnormal composition, with a low molar ratio of apoA-I to apoA-II (0.2-1.33). In addition, LpA-I:A-II in TD contained a substantial amount of apoA-IV compared with control, making this particle an LpA-I:A-II:A-IV complex. LpA-I:A-II from normal plasma do not promote cholesterol efflux from adipocytes cells, whereas TD LpA-I:A-II:A-IV complexes promoted cholesterol efflux from these cells. Moreover LpA-I:A-II:A-IV complexes have more LCAT and CETP activity than control (respectively 1.2 +/- 0.16 and 0.05 +/- 0.01 mumol of cholesterol esterified/h/micrograms of protein and, 41 +/- 3.7 and 1 +/- 0.4 mumol of cholesteryl ester transferred/h/micrograms of protein). The LpA-II particle in TD represented in fact an LpA-II:A-IV complex (75% mol apoA-II and 22% mol apoA-IV).(ABSTRACT TRUNCATED AT 250 WORDS)

Expression and characterization of recombinant human lecithin:cholesterol acyltransferase

We have established a baby hamster kidney (BHK) cell line that constitutively expresses significant quantities of human recombinant lecithin:cholesterol acyltransferase (rLCAT). LCAT cDNA was cloned into a mammalian expression vector containing the metallothionein promoter and the dihydrofolate reductase gene. After transfection, the BHK cells were treated with 500 microM methotrexate for 2 weeks to select the successfully transfected cells. Surviving colonies were subcloned and high level secretors were identified by measurement of LCAT activity and mass in the culture medium. The attachment of transfected cells to microcarrier beads enabled the efficient production of large quantities of rLCAT in a serum-free medium. After a single-step chromatography procedure, the rLCAT was purified to homogeneity with yields exceeding 1 mg of rLCAT per 100 ml of culture medium. The molecular weight of rLCAT (approximately 66,000) was identical to that of purified human plasma LCAT on SDS polyacrylamide electrophoresis. The rLCAT was activated by apolipoprotein A-I and had an average specific activity that was similar to purified plasma LCAT. After selective deglycosylation with either neuraminidase or N-glycanase, rLCAT and plasma LCAT had identical molecular weights. The simplification of the production and purification of rLCAT reported here will enable a more in depth analysis of the structure and function of this enzyme.

Short-term changes in lipid and protein metabolism in liver transplants from living-related donors

The effects of liver transplantation involving living-related donors were investigated in 20 pediatric cases in terms of protein and lipid metabolism using the extent of cholesterol esterification and the levels of total cholesterol, lecithine-cholesterol acyltransferase, apolipoprotein A-I, cholinesterase, and rapid turnover proteins as parameters. Cholesterol esterification increased from preoperative values of 39% +/- 4% to 67% +/- 1% (mean +/- SEM, n = 17) at 3 weeks after liver transplantation in successful cases but decreased from the preoperative value of 45% +/- 10% to 26% +/- 6% (n = 3) at 3 weeks in unsuccessful cases. Cholinesterase, transferrin, and prealbumin levels remained low after 3 weeks even in successful cases. Patients who had partial liver transplantations from living-related donors showed rapid recovery of cholesterol esterification. However, patients with graft livers required an extensive period before normalization of protein metabolism occurred, indicating the necessity for long-term follow-up of recipient development.

Continuous fluorescence assay for lecithin:cholesterol acyltransferase using a water-soluble phosphatidylcholine

A water-soluble fluorescent phosphatidylcholine, 1,2-bis[4-(1-pyreno-butanoyl]-sn-glycero-3-phosphocholine (DPybPC) has been used to develop a sensitive, continuous assay for pure lecithin:cholesterol acyltransferase (LCAT) in solution. The monomeric substrate allowed us to examine the reaction of LCAT in the absence of a lipid/water interface in terms of the sensitivity of the enzymatic reaction to anions, ionic strength, apolipoproteins A-I and A-II, and a series of lysophosphatidylcholines and fatty acids. In contrast to the reaction of LCAT with aggregated phosphatidylcholines, the reaction of DPybPC with LCAT was not significantly affected by anions, ionic strength, nor apolipoproteins, indicating that these are only effectors of the interfacial reaction. Lysophosphatidylcholines and fatty acids inhibited LCAT in a chain-length-dependent manner below the critical micellar concentrations of these amphiphiles, indicating that the products of the LCAT reaction can bind to the enzyme and affect its kinetics even in the absence of an interface.

Biochemical assessment of cholelithiasis

Bile and serum were analysed in 45 cases of cholelithiasis and 25 control subjects for cholesterol, phospholipids, bilirubin, alkaline phosphatase and LCAT activity. Serum phospholipids were found to be elevated in sixty percent of cases, whereas phospholipids in bile were found to be decreased. Serum alkaline phosphatase and alanine aminotransferase were normal. Serum and bile LCAT activity was found to be significantly depressed.

An approach to the functional analysis of lecithin-cholesterol acyltransferase. Activation by recombinant normal and mutagenized apolipoprotein AI

Apolipoprotein AI (apo AI) of human serum high-density lipoprotein functions as an activator of lecithin-cholesterol acyltransferase (LCAT) and therefore plays an important role in reversed cholesterol transport. The mechanism of the acyltransfer, the activating polypeptide domains of apo AI and the active site of LCAT in this transesterification are not yet known. Synthetic peptides of the apo AI sequence have been designed to determine the activating structure, but did not yet lead to conclusive results. This also applies to spontaneous apo AI mutants. We therefore used the method of site-directed mutagenesis of apo AI cDNAs using the overlap extension approach by the polymerase chain reaction. These constructs were cloned into the procaryotic vector pET8c and expressed under the inducible T7 promoter. The engineered apo AI polypeptides were isolated and purified by affinity chromatography and assayed for their activator activity. The essentials of this approach to the structure and function of activators in general have successfully been exemplified for the LCAT activation by engineering apo AI mutant polypeptides a) by the deletion of two adjacent amphipathic helices (amino acid residues 146-186) and b) by introducing a point mutation (Glu111----Gln).

The effects of dietary fiber feeding on cholesterol metabolism in rats

The flux through the sterol biosynthetic pathway was studied in hepatocytes isolated from male Sprague-Dawley rats fed diets containing one of four fiber sources: cellulose, pectin, oat bran and wheat bran. Sterol synthesis measured by the incorporation of tritiated water or [2-14C]mevalonic acid was not inhibited in hepatocytes isolated from animals fed diets containing cellulose, pectin, oat bran or wheat bran when compared to animals fed a fiber-free diet. Based on these results, it is concluded that the intake of fiber has no inhibitory effect on endogenous sterol synthesis. In fact, in comparison to that in fiber-free controls, sterol synthesis was markedly elevated in pectin- and wheat bran-fed animals. In the case of the pectin-treated animals, the higher synthetic rate corresponded to an increase in 3-hydroxy-3-methylglutaryl coenzyme A reductase activity.

A new case of familial lecithin: cholesterol acyltransferase (LCAT) deficiency--paradoxical findings regarding LCAT mass and activity in 23 members of a family

LCAT activity and mass were assayed simultaneously in 23 members of a new family case, revealing two homozygotes with a markedly low HDL--cholesterol level and ester cholesterol ratio. The LCAT mass in these patients was only 0.8 and 0.9 micrograms/ml, respectively (normal range 4.4-8.1) and their LCAT activity was 4 and 6 nM/ml/h 37 degrees C (normal range 60-120). Apolipoprotein (Apo) A-I and II levels were significantly low; however, apolipoprotein E tended to be high. In two-dimensional electrophoresis, apo A-I isoform visualized the increase of immature apo A-I; that is, A-I2. One subject showed the clinical characteristics of classic LCAT deficiency; however, the other, who was a vegetarian, showed corneal opacities and red cell deformity, but not proteinuria. This suggests that a low fat diet which decreases the level of atherogenic large LDL, may lead to a more favourable prognosis with a reduced risk for renal insufficiency. There were two different types of LCAT abnormality in this family series. Among the 10 examined paternal kindred of the proband who was one of two homozygotes, seven had a low LCAT mass but normal LCAT activity with the exception of one kindred who had a low mass and low activity. In contrast, among his seven maternal kindred examined, two had a low LCAT activity but normal mass.

Effect of total parenteral nutrition with intravenous fat on lipids and high density lipoprotein heterogeneity in neonates

Plasma lipid concentrations and high density lipoprotein (HDL) subclass distributions were evaluated in 22 newborn infants nourished with intravenous (iv)-fat. The majority of infants were premature with respiratory distress syndrome. Based on baseline (prior to iv-fat) HDL subclass profiles determined by gradient gel electrophoresis (GGE), infants fell into two classes, one with two or more pronounced peaks within the normal HDL spectrum (group I, 17 subjects) and the other with highly unusual HDL distribution (group II, five subjects). Total plasma cholesterol increased in both groups during low and high fat intravenous feeding. HDL-cholesterol, however, did not change with iv-fat where mean values for groups I and II at baseline, iv-low fat and -high fat were: group I, 31.2 +/- 7.1, 30.0 +/- 8.8, and 36.6 +/- 16.7 mg/dl, respectively; and group II, 20.0 +/- 7.8, 20.2 +/- 7.4, and 19.8 +/- 8.8 mg/dl, respectively. Unlike HDL-cholesterol levels that remained constant with iv-fat, apolipoprotein (apo) AI concentrations increased significantly: group I, 73.0 +/- 11.0, 88.3 +/- 15.9, and 93.1 +/- 21.9 mg/dl, respectively; and group II, 31.8 +/- 10.5, 41.0 +/- 12.8, and 59.3 +/- 18.5 mg/dl, respectively. In group I infants, iv-fat is associated with an increase in larger-sized particles, particularly in the (HDL2b)gge range; in group II there is an increase in (HDL3b)gge and (HDL3c)gge components and a disappearance of particles that fall outside of the size range of normal HDL. In both groups, enteral feeding is associated with a further normalization of HDL subclass distribution. The aberrant GGE profiles and very low apoAI levels of group II infants at baseline were associated with unusual HDL morphology determined by electron microscopy where discoidal structures were prominent. With iv-fat, discoidal particles decline in number while normal spherical structures increase. Prevalence of discoidal HDL at baseline was associated with low concentrations of lecithin:cholesterol acyltransferase (LCAT) (1.12 +/- 0.5 micrograms/ml); with iv-fat this enzyme rose to 1.61 +/- 0.18 micrograms/ml. Increased LCAT is associated with the normalization of HDL morphology. It is likely that iv-fat improves the nutritional status of premature infants, thereby stimulating increased liver synthesis of important proteins, including apoAI and LCAT, associated with HDL metabolism.

Isolation and properties of rat plasma lecithin-cholesterol acyltransferase

Lecithin-cholesterol acyltransferase was purified from rat plasma and the properties of this enzyme during the purification procedures and those of the purified enzyme were investigated in comparison with the human enzyme. The rat enzyme was not adsorbed on hydroxyapatite, which was employed for the purification of the human enzyme. When purified human enzyme was incubated at 37 degrees C in 0.1 mM phosphate buffer (pH 7.4; ionic strength, 0.00025), no alteration of enzyme activity was observed for up to 6 h. In the case of the rat enzyme, however, approximately 40% of the enzyme activity was lost under the same conditions. The human enzyme and rat enzyme were both retained on a Sepharose 4B column to which HDL3 was covalently linked, in 39 mM phosphate buffer, pH 7.4. Although the human enzyme was eluted from the column in 1 mM phosphate buffer, the rat enzyme was dissociated from the column at a lower buffer concentration (0.1 mM phosphate buffer). These findings indicate that the rat enzyme effectively associated with HDL3 in 39 mM phosphate buffer, pH 7.4, but the association was more sensitive to increase of ionic strength compared with that of the human enzyme.

Lecithin cholesterol acyltransferase and possible origin of lysolecithin in rabbit aqueous after a damage of blood-aqueous barrier

Rabbit eye aqueous humor contains lysolecithin (LPC); the LPC concentration markedly increases, if the integrity of the hemato-aqueous barrier is impaired. It is assumed that LPC plays a causal role in the development of cataract because of its detergent action. We have studied the mechanism of LPC cumulation in the aqueous after a mechanical, endotoxic or immunological damage to the hemato-aqueous barrier. We measured in aqueous samples the activity of lecithin cholesterol acyltransferase (LCAT, EC 2.3.1.43), an enzyme which produces LPC and cholesteryl esters in the plasma. The transfer of phospholipids from the plasma into the aqueous was examined in vivo in 32p-prelabeled rabbits. Whereas LCAT was absent in the aqueous humor of intact eyes, an increased transesterification activity could be detected in all cases of impaired hemato-aqueous barrier. The proportion of LPC in aqueous phospholipids was similar to that found in high density lipoproteins, whereas whole plasma and low density lipoproteins contained a much lower proportion of LPC. An increased plasma level of LPC induced by the treatment of rabbits with phospholipase A2 in vivo, did not by itself lead to a preferential passage of plasma LPC through the blood-aqueous barrier. The experimental results rather imply that an impaired blood-aqueous barrier permitted an enhanced transfer from the plasma of intact HDL carrying also LPC and LCAT, and that the enzyme subsequently produced increased amounts of LPC in situ.

An improvement of Barter's method for assaying plasma cholesterol ester transfer activity: experimental and clinical applications

The use of a discontinuous density gradient and of a vertical rotor to separate plasma lipoproteins are modifications of Barter's described method for assaying cholesteryl ester transfer activity (CETA) in plasma. The original feature of our approach is the fast preparation of the labeled substrate by a physiologic-like process, which renders the assay easy and suitable for measurement of this activity in both man and animals.

Identification of the active-site serine in human lecithin: cholesterol acyltransferase

Purified human lecithin:cholesterol acyltransferase (LCAT) was covalently labeled by [3H]diisopropylflourophosphate with concomitant loss of enzymatic activity (M. Jauhiainen and P.J. Dolphin (1986) J. Biol. Chem. 261, 7023-7043). Some 60% of the enzyme was labeled in 1 h. Cyanogen bromide (CNBr) cleavage of the labeled, reduced, and carboxymethylated protein, followed by gel permeation chromatography yielded a 5- to 6-kDa peptide (LCAT CNBr-III) containing at least 60-70% of the incorporated label. Comparison of the amino acid composition of LCAT CNBr-III with that of the CNBr peptides predicted from the LCAT sequence (J. McLean et al. (1986) Proc. Natl. Acad. Sci. USA 83, 2335-2339) indicates that LCAT CNBr-III is peptide 168-220. In 22 cycles of automated Edman degradation of CNBr-III a radioactive derivative was only observed at cycle 14, and of the predicted CNBr fragments only peptide 168-220 contains a serine at position 14 from the amino terminus. Tryptic peptides predicted from the sequence should contain Ser181 at positions 22 and 23 from the N-terminus of fragments 160-199 and 159-199, respectively. On the other hand, Ser216 should be in position 15 from the N-terminus in fragment 202-238. Radiolabel sequencing of the tryptic digest of [3H]diisopropylphosphate-LCAT resulted in recovery of radioactivity in cycles 22 and 23, whereas cycle 15 yielded negligible radioactivity. These results establish that Ser181 is the major active site serine in human LCAT.

A continuous fluorescence assay for lecithin cholesterol acyltransferase

A continuous fluorescence assay was adapted to the measurement of the phospholipase reaction of lecithin cholesterol acyltransferase (LCAT). The fluorescent phospholipid 1-acyl-2-(N-4-nitrobenzo-2-oxa-1,3-diazole)aminocaproyl phosphatidylcholine (C6-NBD-PC) in micelle form reacted with LCAT to yield NBD-caproic acid, resulting in up to 5-fold increases in fluorescence in 30 min. The reaction rates were optimal in mixtures containing 0.1 M NaCl and 4 mM beta-mercaptoethanol at 37 degrees C. Apolipoprotein A-I did not activate the enzyme and bovine serum albumin bound monomeric substrate and interfered with the fluorescence assay. Under similar reaction conditions, bee venom phospholipase A2 was almost 100-fold more reactive than LCAT.

Plasma and lipoprotein fatty acid composition in glycogen storage disease type I

Nocturnal intragastric feeding has been shown to be an effective means to improve clinical and biochemical features in glycogen storage disease type I (GSD-I). In this study, we investigated the fatty acid patterns in a whole plasma and in circulating lipoproteins in patients on this therapy. The results demonstrated massive concentration of total fatty acids coupled with higher levels of triglycerides, free cholesterol, cholesterol ester and phospholipids. This hyperlipidemia involved all fatty acids without distinction of carbon or bond numbers. However, the increase was more pronounced for saturated than polyunsaturated fatty acids, as was demonstrated by the ratios of both oleic acid to linoleic acid (1.91 +/- 0.40 vs 0.80 +/- 0.09 in controls) and of omega 3 + omega 6 to omega 9 fatty acid families (0.92 +/- 0.11 vs 1.66 +/- 0.08 in controls). The fatty acid patterns in very low (VLDL), low (LDL) and high (HDL) density lipoprotein showed substantial differences in composition, reflecting an association between an abnormal lipoprotein pattern and essential fatty acid deficiency. Furthermore, GSD-I patients exhibited a significant increase in VLDL (17 +/- 2 vs 47 +/- 7 mg/dl) and LDL cholesterol (124 +/- 7 vs 206 +/- 24 mg/dl), coupled with a decrease in HDL cholesterol (49 +/- 4 vs 28 +/- 3 mg/dl). These data documenting high LDL cholesterol and low HDL cholesterol associated with an increased concentration and proportion of saturated fatty acids suggest that GSD-I patients on nocturnal intragastric feeding are at high risk for atherosclerosis and its complications.

The apo E/apo CIII molar ratio affects removal of cholesterol ester from modified human lipoproteins injected into cebus monkeys

The removal of postprandial (PP) and postabsorptive (PA) human LDL and HDL cholesterol was examined in cebus monkeys (Cebus albifrons) following in vitro labelling of these lipoproteins by 3H-cholesterol in the presence or absence of DTNB. The removal of LDL cholesteryl ester was 3.5 and 2 times greater than that of HDL in male and female monkeys, respectively. Incubation with DTNB reduced cholesteryl ester removal by 45 and 52% for LDL and HDL, respectively. Cholesteryl ester from PA lipoproteins was removed 80% faster than that PP particles only when plasma was incubated without DTNB. Cholesterol removal from these lipoproteins was positively (r = 0.941) and significantly (P less than 0.001) correlated with the molar apo E/apo CIII ratio. The data suggest that density of lipoproteins was less important than their apoprotein composition in dictating their removal from circulation.

Improvement of the lipid profile during long-term administration of pindolol and hydrochlorothiazide in patients with hypertension

The effect of the combined administration of pindolol (10 or 20 mg daily) and hydrochlorothiazide (50 mg daily) on the serum lipid and lipoprotein levels of 34 hypertensive patients was investigated for 6 to 18.5 months (mean 13.3). Placebo control data were compared with the results obtained during treatment periods in each patient by paired t tests. Mean levels of high-density lipoprotein cholesterol increased by 17% (p less than 0.01), low-density lipoprotein cholesterol decreased by 4% (p less than 0.01) and the high-density lipoprotein: low-density lipoprotein cholesterol ratio increased by 28% (p less than 0.01). Total serum cholesterol, serum triglycerides and very low-density lipoprotein cholesterol showed no statistically significant changes from control values. These findings suggest that the long-term administration of this beta blocker combined with a diuretic results in serum lipid changes considered beneficial in the evaluation of risk factors for coronary artery disease.

Atherosclerosis and lipoprotein metabolism: role of reverse cholesterol transport

To understand the complexity of lipoprotein metabolism and its influence on atherosclerosis, one must be aware of the physiologic characteristics and functions of the different lipoprotein classes, apolipoproteins and enzymes. Understanding of the dynamics of cholesterol and lipoprotein metabolism, especially reverse cholesterol transport, will aid in finding a means of preventing and reversing the atherosclerotic process.

Effect of ethanol on lecithin:cholesterol acyltransferase (LCAT) activity

The effect of variable doses of ethanol on plasma lecithin: cholesterol acyltransferase (LCAT) activity was examined in male, atherosclerosis-susceptible squirrel monkeys over a 12-month period. Primates were divided into three groups: 1) Controls fed isocaloric liquid diet; 2) Low Ethanol monkeys given liquid diet with vodka substituted isocalorically for carbohydrate at 12% of calories; and 3) High Ethanol animals fed diet plus vodka at 24% of calories. There were no significant differences between the treatments in serum glutamate oxaloacetate transaminase (SGOT), a measure of liver function. However, plasma LCAT activity (% esterification/min) measured in vitro was significantly reduced in High Ethanol monkeys while cholesterol esterification was elevated in the Low Ethanol group and intermediate in Controls. Similarly, the in vivo appearance of radiolabeled cholesteryl ester in high density lipoproteins (HDL) following the intravenous injection of 3H mevalonolactone was highest in the Low Ethanol primates, intermediate in Controls and significantly lower in monkeys fed the high alcohol diet. In vitro measurement of LCAT enzyme efficiency was similar for the three groups while substrate efficiency was lower in the High Ethanol treatment. Although LCAT activator (apoprotein A-I) was not markedly altered by dietary ethanol and the concentration of LCAT substrates (HDL free cholesterol and phosphatidyl choline) was significantly elevated in the High Ethanol group, subtle modifications in substrate-product composition may account for the observed reduction in cholesterol esterification. These include potential substrate and/or product LCAT inhibition resulting from increased concentrations of plasma free cholesterol, HDL lysophosphatidyl choline, and higher HDL2/HDL3 subfraction ratios, as well as alterations in HDL phospholipid fatty acid profiles in the High Ethanol group. Results from this study provide the first evidence of an anomalous enhancement in LCAT activity in nonhuman primates fed ethanol at 12% of calories and a marked depression in cholesterol esterification at the 24% dose which may be due to substrate alterations and product inhibition prior to overt biochemical evidence of liver dysfunction.

[Methods for studying the metabolism of lipoproteins]

The present diagnosis and control of dyslipoproteinemia require the analysis, not only of lipids, but also that of their carriers, the lipoproteins, as well as that of the enzymes necessary to their metabolism. Qualitative and quantitative techniques of analysis of lipoproteins have been described. Apolipoprotein quantitation methods have been brought to memory, calling attention to the specific problems related with these determinations, particularly in the case of immunological techniques. The clinical interest of these evaluations has been discussed and the various corresponding pathologies have been mentioned briefly.

Lecithin: cholesterol acyl transferase (LCAT)

Esterification of cholesterol in plasma is mediated by LCAT. The mechanism of the three reactions catalysed by the enzyme is beginning to be understood. LCAT has been purified from human plasma and partially characterized. The enzyme is closely associated with HDL and exists most likely as a complex with its activator apo A-I and apo D. Antibodies were raised against LCAT and the enzyme concentration in plasma has been estimated to range between 4.5 and 8.0 mg/L. In patients with familial LCAT deficiency only trace amounts or no LCAT protein is found. Heterozygotes for this disorder have approximately half the normal amount of the enzyme. LCAT reactivity is essential for normal lipoprotein metabolism and for a proper equilibrium between tissue and plasma cholesterol.

Lecithin: cholesterol acyl transfer rate in hypothyroidism and hyperthyroidism

The initial rate of lecithin: cholesterol acyl transferase and serum concentration of lipids were determined in euthyroid, hypothyroid and hyperthyroid subjects. In hyperthyroid subjects, the serum levels of total and free cholesterol were significantly lower than in normal subjects and the fractional lecithin: cholesterol acyl transfer rate was significantly higher than in normal subjects. The molar lecithin: cholesterol acyl transfer rate was also higher than in normal subjects, but not significantly. The free cholesterol/total cholesterol ratio in hypothyroid females and the serum levels of triglyceride and free fatty acid in hypothyroid male were significantly higher than in normal subjects. The fractional lecithin: cholesterol acyl transfer rates in hypothyroid females were significantly lower than in normal females. After treatment of the thyroid disease the fractional and molar lecithin: cholestorol cholesterol acyl transfer rate approached the normal values. There was a positive correlation between fractional and molar lecithin: cholesterol acyl transfer rate and thyroxine. These results suggest that thyroid hormone influences the cholesterol esterification through the activation of lecithin: cholesterol acyltransferase.

Purification and characterization of lecithin:cholesterol acyltransferase

The purification of lecithin:cholesterol acyltransferase (LCAT] from human plasma is reported. Hydroxylapatite fractions were approximately 16,000 fold purified over the starting plasma and were free of high-density lipoprotein (HDL) and albumin. The enzyme showed one band on polyacrylamide gel electrophoresis, SDS-urea polyacrylamide gel electrophoresis, isoelectric focusing, and one arc in immunodiffusion against a goat antiserum preparation. It was determined to be a glycoprotein with a molecular weight of approximately 70,000 and a pI of 3.7--4.0.