Acid sphingomyelinase (Asm) deficiency patients in The Netherlands and Belgium: disease spectrum and natural course in attenuated patients

Niemann-Pick disease (NPD) is a neurovisceral lysosomal storage disorder caused by acid sphingomyelinase (ASM) deficiency, which can be categorized as either Niemann-Pick disease type A [NPD-A], with progressive neurological disease and death in early childhood, or as Niemann-Pick disease type B [NPD-B], with a more variable spectrum of manifestations. Enzyme replacement therapy (ERT) with recombinant sphingomyelinase is currently studied as potential treatment for NPD-B patients. The objective of this study is to characterize the clinical features of patients with ASM deficiency in the Netherlands and Belgium with focus on the natural disease course of NPD-B patients. Prospective and retrospective data on ASM deficient patients were collected in The Netherlands and part of Belgium. Patients with NPD-B that could be followed prospectively were evaluated every 6-12 months for pulmonary function tests, 6 minute walk test (6 MWT), imaging (bone marrow infiltration measured by QCSI, organ volumes by MRI and CT scan of the lungs) and biochemical markers. Twenty-five patients with ASM deficiency were identified (13 males, 12 females, median age 13years, range 1-59 years). Nine patients had died at the time of the study, including four NPD-A patients at the age of 1,1, 2, 3 and five NPDB patents at the age of 5, 6, 43, 56 and 60 years. There was a high prevalence of homozygosity and compound heterozygosity for the common p.Arg608del mutation in 43% and 19% of NPD-B patients, respectively. In NPD-B patients, thrombocytopenia was present in most, while anemia and leucopenia were less common (33% and 6 % respectively). HDL cholesterol was reduced in most patients. Pulmonary disease was severe in several patients. Follow-up up to 11 years revealed a gradual decrease in platelet count. Detailed investigations in 6 NPD-B patients with follow-up in 4 patients revealed remarkable stable disease parameters up to 6 years, with some decline in pulmonary function and 6 MWT. Bone marrow fat fractions were decreased, indicating the presence of storage macrophages. Lung involvement was not related to the extent of visceromegaly, cytopenia or bone marrow involvement. In conclusion, in NPD-B patients pulmonary disease is the most debilitating feature. Disease manifestations are mostly stable in attenuated patients. Bone marrow infiltration is a less prominent feature of the disease.

Short-term manipulation of plasma free fatty acids does not change skeletal muscle concentrations of ceramide and glucosylceramide in lean and overweight subjects

CONTEXT

Increased plasma free fatty acid (FFA) concentrations may be in part responsible for the increased levels of ceramide in skeletal muscle of obese subjects.

OBJECTIVE

We studied the effect of lowering and increasing plasma FFA levels on muscle ceramide and glucosylceramide concentrations in lean and obese subjects.

DESIGN

Plasma FFAs were either increased or decreased for 6 h by infusing a lipid emulsion or using Acipimox, respectively. Muscle biopsies were performed before and after the intervention for measurements of ceramide and glucosylceramide.

STUDY SUBJECTS

Eight lean [body mass index 21.9 (range, 19.6-24.6) kg/m2] and six overweight/obese [body mass index 34.4 (27.8-42.5) kg/m2] subjects without type 2 diabetes mellitus participated in the study.

MAIN OUTCOME MEASURE

Differences in muscle ceramide and glucosylceramide upon manipulation of plasma FFAs were measured.

RESULTS

There were no differences in muscle ceramide and glucosylceramide between lean and obese subjects, respectively. Increasing or decreasing plasma FFAs for 6 h had no effect on ceramide [high FFAs: 24 (19-25) vs. 24 (22-27) pmol/mg muscle, P=0.46; and 22 (20-28) vs. 24 (18-26) pmol/mg muscle, P=0.89 in lean and obese, respectively; low FFAs: 26 (24-35) vs. 23 (18-27) pmol/mg muscle, P=0.17 and 24 (15-44) vs. 24 (19-42) pmol/mg muscle, P=0.6 in lean and obese, respectively] and glucosylceramide [high FFAs: 2.0 (1.7-4.3) vs. 3.4 (2.1-4.6) pmol/mg muscle, P=0.17; and 3.0 (1.3-6.7) vs. 2.6 (1.2-3.9) pmol/mg muscle, P=0.89 in lean and obese, respectively; low FFAs: 2.2 (1.0-4.4) vs. 1.7 (1.4-3.0) pmol/mg muscle, P=0.92; and 6.6 (1.0-25.0) vs. 4.3 (1.3-7.6) pmol/mg muscle, P=0.7 in lean and obese, respectively] concentrations in skeletal muscle.

CONCLUSION

Short-term manipulation of plasma FFAs has no effect on ceramide and glucosylceramide concentrations in skeletal muscle from lean and obese subjects.

Plasma chitotriosidase and CCL18: early biochemical surrogate markers in type B Niemann-Pick disease

Type B Niemann-Pick disease (NPD) is a nonneuronopathic lysosomal storage disorder which is characterized by accumulation of sphingomyelin-laden macrophages. The availability of plasma markers for storage cells may be of great value in facilitating therapeutic decisions. Given the similarity of the storage cells in NPD and Gaucher disease, we studied Gaucher plasma markers (chitotriosidase and CCL18) in two siblings homozygous for the R228C mutation in acid sphingomyelinase (ASM) and a type B course of NPD. The older sibling, first examined at the age of 9 months, showed marked hepatosplenomegaly and pulmonary involvement. The younger sibling has mild asymptomatic hepatosplenomgaly at the age of 5 months. Analysis of plasma specimens revealed markedly increased levels of chitotriosidase and CCL18 in the older sibling. In the younger child also, plasma chitotriosidase and CCL18 were clearly elevated above normal values almost immediately after birth and rapidly increased further. Histochemistry confirmed production of CCL18 by foam cells. In conclusion, plasma chitotriosidase and CCL18 may also serve as markers for the formation of pathological lipid-laden macrophages in type B NPD, in analogy to Gaucher disease. The availability of sensitive plasma surrogate markers may be of great value for monitoring the efficacy of enzyme supplementation therapy that is currently being developed.

Delayed lysosomal metabolism of lipids in mucolipidosis type IV fibroblasts after LDL-receptor-mediated endocytosis

We specifically probed the low-density lipoprotein-receptor-dependent endosomal/lysosomal pathway of lipid degradation in control and mucolipidosis type IV fibroblasts using either [choline-methyl-14C]sphingomyelin in complex with apolipoprotein E, or cholesteryl [14C]oleate-labelled low-density lipoprotein as a substrate. Mucolipidosis type IV fibroblasts metabolized [14C]sphingomyelin and cholesteryl [14C]oleate significantly more slowly than controls and fibroblasts from patients with Hurler disease or Niemann-Pick disease type C. So far, no lysosomal enzyme deficiency has been reported for mucolipidosis type IV. Rather, the defect in mucolipidosis type IV cells has recently been suggested to be related to intracellular trafficking. Our results suggest that the defect in mucolipidosis type IV also affects the low-density lipoprotein-receptor-mediated endocytosis pathway.

Biosynthesis of phosphatidylcholine from a phosphocholine precursor pool derived from the late endosomal/lysosomal degradation of sphingomyelin

Previous studies suggest that the steps of the CDP- choline pathway of phosphatidylcholine synthesis are tightly linked in a so-called metabolon. Evidence has been presented that only choline that enters cells through the choline transporter, and not phosphocholine administered to cells by membrane permeabilization, is incorporated into phosphatidylcholine. Here, we show that [(14)C]phosphocholine derived from the lysosomal degradation of [(14)C]choline-labeled sphingomyelin is incorporated as such into phosphatidylcholine in human and mouse fibroblasts. Low density lipoprotein receptor-mediated endocytosis was used to specifically direct [(14)C]sphingomyelin to the lysosomal degradation pathway. Free labeled choline was not found either intracellularly or in the medium, not even when the cells were energy-depleted. Deficiency of lysosomal acid phosphatases in mouse or alkaline phosphatase in human fibroblasts did not affect the incorporation of lysosomal [(14)C]sphingomyelin-derived [(14)C]phosphocholine into phosphatidylcholine, supporting our finding that phosphocholine is not degraded to choline prior to its incorporation into phosphatidylcholine. Inhibition studies and analysis of molecular species showed that exogenous [(3)H]choline and sphingomyelin-derived [(14)C]phosphocholine are incorporated into phosphatidylcholine via a common pathway of synthesis. Our findings provide evidence that, in fibroblasts, phosphocholine derived from sphingomyelin is transported out of the lysosome and subsequently incorporated into phosphatidylcholine without prior hydrolysis of phosphocholine to choline. The findings do not support the existence of a phosphatidylcholine synthesis metabolon in fibroblasts.

Human alpha-N-acetylgalactosaminidase (alpha-NAGA) deficiency: no association with neuroaxonal dystrophy?

Two new individuals with alpha-NAGA deficiency are presented. The index patient, 3 years old, has congenital cataract, slight motor retardation and secondary demyelinisation. Screening of his sibs revealed an alpha-NAGA deficiency in his 7-year-old healthy brother who had no clinical or neurological symptoms. Both sibs are homozygous for the E325K mutation, the same genotype that was found in the most severe form of alpha-NAGA deficiency presenting as infantile neuroaxonal dystrophy. Thus, at the age of 7 years the same genotype of alpha-NAGA may present as a 'non-disease' (present healthy case) and can be associated with the vegetative state (the first two patients described with alpha-NAGA deficiency). The clinical heterogeneity among the 11 known individuals with alpha-NAGA deficiency is extreme, with a 'non-disease' (two cases) and infantile neuroaxonal dystrophy (two cases) at the opposite sides of the clinical spectrum. The broad spectrum is completed by a very heterogeneous group of patients with various degrees of epilepsy/behavioural difficulties/psychomotor retardation (four patients) and a mild phenotype in adults without overt neurological manifestations who have angiokeratoma and clear vacuolisation in various cell types (three cases). These observations are difficult to reconcile with a straightforward genotype-phenotype correlation and suggest that factors or genes other than alpha-NAGA contribute to the clinical heterogeneity of the 11 patients with alpha-NAGA deficiency.

Intrauterine fetal death due to Farber disease: case report

We report a case of Farber disease in a fetus who died in utero at a gestational age of 29 weeks. Macroscopic examination showed moderate postmortem changes in a microcephalic female fetus (46,XX) with mild internal hydrops, two vessels in the umbilical cord, and a moderately enlarged, relatively well-preserved spleen. Microscopic examination showed foamy cells in the spleen. Electron microscopic examination revealed the presence of Farber bodies within these foamy cells. Enzyme studies of the fetus were not possible because all tissues were formalin fixed. Lipids were extracted from formalin-fixed tissues and increased levels of ceramide and the presence of hydroxyceramide in tissue of the spleen, liver, and lung were found. Glucosylceramide was not increased excluding saposin-precursor-deficiency. Because of these findings, both parents were tested for acid ceramidase activity in their leukocytes. They both had markedly reduced enzyme activity consistent with heterozygosity for Farber disease. To the best of our knowledge, this is the first published case of Farber disease in Dutch nonconsanguineous parents.

Difference in substrate specificity between human and mouse lysosomal acid lipase: low affinity for cholesteryl ester in mouse lysosomal acid lipase

Lysosomal acid lipase (LAL) is essential for the intracellular degradation of cholesteryl esters (CE) and triacylglycerols (TG) that are delivered to lysosomes by low density lipoprotein (LDL) receptor mediated endocytosis. We have analysed the difference in the catalytic properties and substrate specificity of human and mouse LALs. LAL activities were measured in human and mouse fibroblasts and in HeLa cells transiently expressing wild-type or site-directed mutant LALs of the two species using the T7 vaccinia system. Cholesteryl esterase and triacylglycerol lipase activities were determined in cellular homogenates with a phospholipid/detergent vesicle assay, an assay frequently used to diagnose human LAL deficiency syndromes, and with LDL particles, a more physiological substrate. Characterisation of human and mouse LAL using these two assays demonstrated marked differences in their TG and CE hydrolysing activities. Compared to human LAL mouse LAL showed a much lower cholesteryl esterase activity in both assays used. The difference was more pronounced in the vesicle assay. The lower cholesteryl esterase activity of mouse LAL did not affect the LDL-CE degradation in intact fibroblasts. The analysis of site-directed mutants suggests a role of the non-conserved cysteine residue at position 240 in cholesteryl esterase activity in human LAL. Our results show a significant difference between human and mouse LAL in their specificity toward cholesteryl esters. The low cholesteryl esterase activity does not result in reduced LDL-cholesterol ester degradation in mouse fibroblasts in situ. In addition, this work emphasises the importance of the physical state of substrates in studies of the specificity and properties of lipolytic enzymes.

Oxidized VLDL induces less triglyceride accumulation in J774 macrophages than native VLDL due to an impaired extracellular lipolysis

The present study examined the relative contributions of the different pathways by which oxidatively modified VLDL (oxVLDL) promotes the uptake and intracellular accumulation of lipids in J774 macrophages. VLDL was oxidized for a maximum of 4 hours, resulting in an increase in thiobarbituric acid-reactive substances and an increased electrophoretic mobility on agarose gel. The lipid composition of the relatively moderately oxidized VLDL samples did not differ significantly from that of nonoxidized VLDL samples. The uptake of (125)I-labeled VLDL by the J774 cells increased with oxidation time and was completely blocked on coincubation with polyinosinic acid (PolyI), indicating that oxVLDL is taken up by the cells via the scavenger receptor only. Despite the 2-fold increased uptake of oxVLDL protein, the cell association of triglyceride (TG)-derived fatty acids by the J774 macrophages after incubation with oxVLDL was only 50% of that with native VLDL. In line with these observations, the induction of de novo synthesis of TG by J774 cells was approximately 3-fold less efficient after incubation with oxVLDL than after incubation with native VLDL. The induction of de novo synthesis of TG with oxVLDL was even further decreased on simultaneous incubation with PolyI, whereas PolyI did not affect the native VLDL-induced TG synthesis. These results indicate that oxVLDL induces endogenous TG synthesis predominantly through particle uptake via the scavenger receptor and much less via the extracellular lipoprotein lipase (LPL)-mediated hydrolysis of TG, as is the case for native VLDL. In line with these observations, we showed that the suitability of VLDL as a substrate for LPL decreases with oxidation time. Addition of oxVLDL to the LPL assay did not interfere with the lipolysis of native VLDL. However, enrichment of the oxidized lipoprotein particle with native apoC2 was able to fully restore the impaired lipolysis. Thus, from these studies it can be concluded that on oxidation, VLDL becomes less efficient in inducing TG accumulation in J774 cells as a consequence of a defect in apoC2 as an activator for the LPL-mediated extracellular lipolysis.

Prenatal diagnosis of lysosomal storage diseases using fetal blood

Lysosomal storage diseases are a rare but significant cause of non-immune hydrops fetalis (NIHF). In 17 cases of NIHF detected by ultrasound, the activity of five lysosomal enzymes was measured in leukocytes or plasma of 1 ml of fetal blood obtained by cordocentesis. By this approach seven lysosomal storage diseases known to present with hydrops fetalis can be diagnosed. In this series one case of mucopolysaccharidosis VII (M. Sly) was diagnosed at 20 weeks' gestation. The other samples allowed the establishment of reference ranges for lysosomal enzymes associated with NIHF in fetal blood. We conclude that, also in view of the poor prognosis of lysosomal storage diseases presenting with hydrops fetalis, the use of fetal blood for the early and fast biochemical diagnosis of these diseases is a valuable supplement in the diagnostic work-up and the management of NIHF.

The frequency of lysosomal storage diseases in The Netherlands

We have calculated the relative frequency and the birth prevalence of lysosomal storage diseases (LSDs) in The Netherlands based on all 963 enzymatically confirmed cases diagnosed during the period 1970-1996. The combined birth prevalence for all LSDs is 14 per 100,000 live births. Glycogenosis type II is the most frequent LSD with a birth prevalence of 2.0 per 100,000 live births, representing 17% of all diagnosed cases. Within the group of lipidoses, metachromatic leukodystrophy (MLD) is the most frequent LSD. MLD was diagnosed in 24% of lipidoses and the calculated birth prevalence was 1.42 per 100,000 for all types combined. Krabbe disease, diagnosed in 17% of cases, also belongs to the more frequent lipid storage diseases in The Netherlands with a birth prevalence of 1.35 per 100,000. The birth prevalence of Gaucher disease, commonly regarded as the most frequent lipid storage disease is 1.16 per 100,000 for all types combined. The combined birth prevalence for all lipid storage diseases is 6.2 per 100,000 live births. Within the group of mucopolysaccharidoses (MPSs), MPS I has the highest calculated birth prevalence of 1.19 per 100,000 (25% of all cases of MPS diagnosed), which is slightly more frequent than MPS IIIA with an estimated birth prevalence of 1.16 per 100,000. As a group, MPS III comprises 47% of all MPS cases diagnosed and the combined birth prevalence is 1.89 per 100,000 live births. The birth prevalence of MPS II is 0.67 per 100,000 (1.30 per 100,000 male live births). All other MPSs are rare. The combined birth prevalence for all MPSs is 4.5 per 100,000 live births. Mucolipidoses and oligosaccharidoses are very rare with birth prevalences between 0.04 and 0.20 for individual diseases. Only 49 cases were diagnosed between 1970 and 1996. Their combined birth prevalence is 1.0 per 100,000 live births.

Lysosomal phospholipase activity is decreased in mucolipidosis II and III fibroblasts

Mucolipidosis (ML) II and III are rare autosomal recessively inherited diseases characterized by deficiency of multiple lysosomal enzymes and, as a result, a generalized storage of macromolecules in lysosomes of cells of mesenchymal origin. In ML II and ML III fibroblasts, most, but not all, newly synthesized lysosomal enzymes are secreted into the medium instead of being targeted correctly to lysosomes. Defects in the enzyme UDP-N-acetylglucosamine:lysosomal enzyme N-acetylglucosamine-1-phosphotransferase underlie this effect. It is unknown how lysosomal phospholipases are targeted to the lysosomes of fibroblasts. In the present study lysosomal phospholipase activity was determined in delipidated fibroblast homogenates and plasma from ML II and ML III patients and controls using a [3H]choline-labeled phosphatidylcholine. After incubation, residual phosphatidylcholine and its labeled degradation products (lysophosphatidylcholine, glycerophosphorylcholine and choline phosphate) were quantified. We found that ML II and ML III fibroblasts are deficient in lysosomal phospholipase A and C activity. These enzymes were present in elevated amounts in plasma of ML II and ML III patients. These data indicate that phospholipases, like most other lysosomal enzymes in these diseases, are secreted into the blood instead of being targeted specifically to lysosomes. Thus, the mannose-6-phosphate receptor pathway is needed for proper delivery of lysosomal phospholipases to lysosomes. We also found that production of labeled choline phosphate was mainly due to the activity of acid sphingomyelinase instead of phospholipase C under the assay conditions used. Other active lipolytic enzymes were phospholipase A and lysophospholipase. No evidence for phospholipase D activity was found.

Moderate doses of alcoholic beverages with dinner and postprandial high density lipoprotein composition

Moderate alcohol consumption is associated with a reduced risk of coronary heart disease. In this study, postprandial changes in plasma lipids, high-density lipoprotein (HDL) composition and cholesteryl ester transfer protein (CETP) and lecithin: cholesterol acyltransferase (LCAT) activity levels were investigated in response to moderate alcohol consumption. A dose of 40 g of alcohol was consumed as beer, wine or spirits by eight healthy middle-aged men before and during dinner thus simulating social drinking. Lipid parameters were studied before, and at 1, 3, 5, 9, and 13 h after dinner. An alcohol-induced elevation of plasma triglycerides was observed at 3 and 5 h after dinner, but total plasma cholesterol and apolipoprotein B were hardly affected. HDL lipids changed during the postprandial phase after alcohol consumption, HDL triglycerides were elevated at 5 and 9 h, HDL phospholipids were elevated at 9 and 13 h, and HDL cholesterol was elevated at 13 h. A 6% increase in the concentration of apolipoprotein A-II was observed at 13 h. Plasma LCAT activity was slightly increased 9 h after dinner, but CETP activity levels were not affected. The LCAT changes appeared similar for all three alcoholic beverages. It is concluded that moderate alcohol consumption with dinner affects plasma triglyceride concentration as well as HDL composition.

Delayed increase in high density lipoprotein-phospholipids after ingestion of a fat load in normolipidemic patients with coronary artery disease

We studied the effect of a single oral fat load, supplemented with retinyl palmitate (RP), on high density lipoprotein (HDL) lipids in six normolipidemic men with coronary artery disease (CAD) and in six age- and lipid-matched controls. All subjects were selected from a study group which underwent the same protocol 2 years earlier. Post-prandial total plasma lipids, plasma RP levels, and HDL lipids were evaluated at 2-h intervals up till 10 h after the meal. In most subjects the post-prandial response of plasma triglyceride (TG) and plasma RP was identical in the first and second tests. Following the fat load, control subjects showed no change in HDL total cholesterol (TC) or HDL cholesteryl ester (CE) and showed an increase in HDL-TG. CAD subjects however showed a decrease in HDL-TC and HDL-CE and an increase in HDL-TG, similar to the increase in control subjects. In control subjects an increase in HDL phospholipid (PL) was apparent between 0 and 8 h after the fat load. By contrast, in CAD subjects the increase in HDL-PL was only found after as long as 6 h. The magnitude of the post-prandial response of HDL-PL measured during the test was significantly lower in the CAD group. The effects of the fat load on HDL free cholesterol (FC) were similar to the changes in HDL-PL. These data support the hypothesis that PL and FC released during the degradation of chylomicrons as surface remnants are taken up by HDL. This process is clearly delayed in normolipidemic CAD subjects compared with controls. The data suggest that differences in the post-prandial response to an oral fat load in normolipidemic CAD patients and control subjects are not confined to the clearance of TG-rich lipoproteins, but also involve a difference in the uptake of chylomicron surface material by HDL.

Lowering of serum cholesteryl ester transfer protein--but not lecithin:cholesterol acyltransferase--activity levels by hypocholesterolemic drugs in the rabbit

Cholesteryl ester transfer protein (CETP) and lecithin:cholesterol acyltransferase (LCAT) are important factors in the regulation of serum lipoprotein metabolism. Rabbits were fed hypocholesterolemic drugs to investigate the effect on serum CETP and LCAT activity levels. The activities were assayed using exogenous substrate assays and are an estimate of CETP and LCAT mass. Groups of eight rabbits were fed a cholesterol-free diet containing either 0.03% simvastatin or 1% cholestyramine for 6 weeks. For comparison eight rabbits were fed a cholesterol-free control diet without drugs or a diet containing 0.1% cholesterol for 6 weeks. Total serum and lipoprotein triglyceride concentrations were not different after intervention with the hypocholesterolemic drugs or the cholesterol diet. Dietary cholesterol induced higher VLDL, IDL, and LDL cholesterol, as well as serum CETP activity, as expected. Serum LCAT activity showed little change with intervention. Both simvastatin and cholestyramine tended to lead to decreased cholesterol in all lipoprotein fractions and caused a significant decrease in serum CETP activity when compared with the control diet. Both drugs also caused a significant lower LDL particle concentration, as judged from differences in LDL protein levels. Intervention with simvastatin or cholestyramine led to relatively cholesterol-poor LDL. These effects on LDL concentration and composition were opposite from the effects of cholesterol feeding. Differences in the cholesterol contents of VLDL and IDL were comparable with those in LDL. The results suggest that decreasing serum CETP activity levels by treatment with simvastatin or cholestyramine may contribute to lowering of cholesterol apo B-containing lipoproteins. The effects are additional to the well-known increase in hepatic LDL receptor activity, which is likely to be the most important factor in LDL cholesterol lowering by these drugs.

Cholesteryl ester transfer protein gene polymorphism is a determinant of HDL cholesterol and of the lipoprotein response to a lipid-lowering diet in type 1 diabetes

The TaqIB cholesteryl ester transfer protein (CETP) gene polymorphism (B1B2) is a determinant of HDL cholesterol in nondiabetic populations. Remarkably, this gene effect appears to be modified by environmental factors. We evaluated the effect of this polymorphism on HDL cholesterol levels and on the lipoprotein response to a linoleic acid-enriched, low-cholesterol diet in patients with type 1 diabetes. In 44 consecutive type 1 diabetic patients (35 men), CETP polymorphism, apolipoprotein (apo) E genotype, serum lipoproteins, serum CETP activity (measured with an exogenous substrate assay, n = 30), clinical variables, and a diet history were documented. The 1-year response to diet was assessed in 14 type 1 diabetic patients, including 6 B1B1 and 6 B1B2 individuals. HDL cholesterol was higher in 10 B2B2 than in 14 B1B1 homozygotes (1.63 +/- 0.38 vs. 1.24 +/- 0.23 mmol/l, P < 0.01). HDL cholesterol, adjusted for triglycerides and smoking, was 0.19 mmol/l higher for each B2 allele present. CETP activity levels were not significantly different between CETP genotypes. Multiple regression analysis showed that VLDL + LDL cholesterol was associated with dietary polyunsaturated:saturated fatty acids ratio (P < 0.02) and total fat intake (P < 0.05) in the B1B1 homozygotes only and tended to be related to the presence of the apo E4 allele (P < 0.10). In response to diet, VLDL + LDL cholesterol fell (P < 0.05) and HDL cholesterol remained unchanged in 6 B1B1 homozygotes. In contrast, VLDL + LDL cholesterol was unaltered and HDL cholesterol decreased (P < 0.05) in 6 B1B2 heterozygotes (P < 0.05 for difference in change in VLDL + LDL/HDL cholesterol ratio). This difference in response was unrelated to the apo E genotype. Thus, the TaqIB CETP gene polymorphism is a strong determinant of HDL cholesterol in type 1 diabetes. This gene effect is unlikely to be explained by a major influence on the serum level of CETP activity, as an indirect measure of CETP mass. Our preliminary data suggest that this polymorphism may be a marker of the lipoprotein response to dietary intervention.

Metabolic fate of oleic acid derived from lysosomal degradation of cholesteryl oleate in human fibroblasts

Low density lipoprotein cholesteryl [14C]oleate (LDL-[14C]CO) was used as a tool to label lysosomes with cholesteryl [14C]oleate (CO) and to follow subsequently the metabolic processing of oleic acid released by acid lipase. Liberated [14C]oleate was incorporated into glycerolipids, mainly into phosphatidylcholine. Incubations in the presence of various concentrations of exogenously added oleic acid and double label experiments showed that oleic acid derived from lysosomal degradation of CO and exogenously added oleic acid distributed in a similar fashion among triacylglycerol and various phospholipids. To further study the metabolism of LDL-derived oleic acid, experiments were performed in which fibroblasts were prelabeled with LDL-[14C]CO. The subsequent processing of lysosome-derived oleic acid was followed with time without LDL-[14C]CO in the medium. From these experiments it became clear that apart from the esterification into glycerolipids a substantial part of lysosome-derived oleic acid was released into the medium. The efflux of oleic acid into the medium preceded the incorporation into glycerolipids, was dependent on the composition of the extracellular medium, and was energy-independent. Our data are compatible with a mechanism in which lysosome-derived fatty acids are transported to the plasma membrane prior to transport to endoplasmic reticulum for esterification. Intra- and extra-cellular factors influence the distribution of lysosome-derived oleic acid among cells and medium.

CETP activity in liver perfusates and plasma from rabbits hypo- or hyperresponsive to dietary cholesterol

We investigated the relationship between the development of hypercholesterolemia in rabbits and cholesteryl ester transfer protein (CETP) activity secretion by their perfused livers. Two inbred strains of rabbits were compared which differ markedly in their hypercholesterolemic response to dietary cholesterol. Feeding a high-cholesterol (0.3%) diet, increased plasma and liver cholesterol level in the two strains, the increments being 15 mM and 30 mumol/g greater in the hyperresponders, respectively. The high-cholesterol diet caused an about 2-fold increased hepatic secretion of CETP activity, but there was no difference between the two rabbit strains. Feeding a lower amount of dietary cholesterol (0.08%) also caused higher cholesterolemic (2 mM) and hepatocholesterolic (28 mumol/g) responses in hyper- than in hyporesponsive rabbits. The activity of hepatic CETP secretion was not increased by the low-cholesterol diet, and there was no difference between hypo- and hyperresponsive rabbits. Cholesterol feeding increased plasma CETP activity by 90% in both rabbit strains, but there was no difference between the strains. Our combined data suggest that with increasing plasma cholesterol levels hepatic CETP secretion may be increased in a parabolic manner, reaching its maximum rate for before plasma cholesterol concentrations are maximal. There were no differences in hepatic CETP activity secretion of plasma CETP activity levels between the genetically different strains of hypo- and hyperresponsive rabbits.

Prenatal diagnosis of glycogen storage disease type II: enzyme assay or mutation analysis?

Two mutations in the lysosomal alpha-glucosidase gene, a single base pair deletion (delta T525) and a deletion of exon 18, have recently been identified with a relatively high incidence in Caucasian patients with glycogen storage disease type II (GSD II). Prenatal diagnosis was made in a pregnancy of consanguineous parents of a child with GSD II. The delta T525 deletion was demonstrated in this family but unexpectedly in only one of the parents. The absence of the delta T525 deletion in DNA isolated from the chorionic villi and a normal alpha-glucosidase activity indicated that the fetus was not affected. The possible role of mutation analysis in the prenatal diagnosis of GSD II is discussed in the light of our previous experience from a series of 100 prenatal diagnoses for this disorder by enzyme analysis.

Induction of net mass lipid transfer reactions in plasma by wine consumption with dinner

Moderate alcohol consumption is associated with a reduced risk of coronary heart disease. Alcohol may exert protection through its effects on the metabolism of plasma lipoproteins. In the present study we investigated the effects of moderate wine consumption with an evening dinner on lipoprotein composition and parameters of reverse cholesterol transport (plasma lipid transfer reactions and cholesterol esterification) in eight healthy middle-aged men. Wine consumption, if compared with mineral water, resulted in increased postprandial plasma levels of triglyceride-(TG)-rich lipoproteins (P < 0.005 or < 0.002 at two different time points) and in increased net mass transfer of cholesterylesters (CE) from high-density lipoprotein (HDL) to apolipoprotein B-containing lipoproteins during in vitro incubation of plasma (P < 0.001). Net mass transfer of TG (in the opposite direction) was also significantly increased by wine (P = 0.014). The concentrations of total plasma cholesterol, HDL-cholesterol and apolipoproteins A-I, A-II and B did not change postprandially and were not affected significantly by wine, but the CE TG-1 in HDL was affected postprandially and decreased by wine consumption. It is concluded that moderate wine consumption with evening dinner induces transfer reactions of CE and TG between HDL and TG-rich lipoproteins. Due to the fact that wine raises plasma TG, it also causes changes in plasma cholesterol metabolism and lipoprotein composition, without major effects on total plasma cholesterol concentration.

Elevated plasma chitotriosidase activity in various lysosomal storage disorders

Recently a striking elevation of the activity of chitotriosidase, an endo beta-glucosaminidase distinct from lysozyme, was found in plasma from patients with Gaucher type I disease (McKusick 230800). Plasma chitotriosidase originates from activated macrophages and this elevation is secondary to the basic defect in Gaucher disease. To investigate the specificity of this phenomenon, we have investigated 24 different lysosomal storage diseases. In 11 different diseases increased chitotriosidase activity in plasma was found (in 28% of the patients). None of these diseases showed elevations as high as in Gaucher disease. Chitotriosidase was not significantly elevated in plasma from 20 different non-lysosomal enzymopathies or in plasma from patients with infectious diseases associated with hepatomegaly. The results show that marked elevation of chitotriosidase activity in plasma appears to be specific for Gaucher disease. The data further suggest that elevated levels of chitotriosidase activity in plasma from patients with unexplained diseases may be indicative for a lysosomal disorder.

Plasma activities of lecithin:cholesterol acyltransferase, lipid transfer proteins and post-heparin lipases in inbred strains of rabbits hypo- or hyper-responsive to dietary cholesterol

Plasma lipoproteins, plasma activities of lecithin:cholesterol acyltransferase (LCAT), phospholipid transfer protein (PLTP), cholesteryl ester transfer protein (CETP) and post-heparin lipases were measured before and after cholesterol challenge in two inbred strains of rabbits with either a high (hyper-responders) or a low (hyporesponders) response of plasma cholesterol to dietary cholesterol. The purpose of this study was to provide clues about the mechanisms underlying the effect of dietary cholesterol on lipoprotein levels and composition, and particularly those underlying the strain difference of this effect. Cholesterol feeding (0.15 g of cholesterol/100 g of diet) caused increased plasma total cholesterol concentrations and an increased ratio of cholesteryl esters:triacylglycerol in all lipoprotein particles in both strains; these effects were significantly greater in hyper- than hypo-responsive rabbits. Feeding on the high-cholesterol diet lowered plasma triacylglycerols in hyper-responders, but caused increased plasma triacylglycerol levels in hyporesponders. This was accompanied by significantly greater increases in the activities of hepatic triacylglycerol lipase and lipoprotein lipase in hyper- than in hypo-responders. Both strains showed a dietary-cholesterol-induced rise in plasma CETP as well as in PLTP activity. The increase in PLTP activity was greater in the hyper-responders, but that of CETP was less. There was no effect of dietary cholesterol on LCAT activity. It is hypothesized that the lipases are involved in the removal of cholesterol-rich lipoproteins.

Different locations of cholesteryl ester transfer protein and phospholipid transfer protein activities in plasma

Activities of cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP) were measured in plasma of four vertebrate species: man, rabbit, pig, and rat. The activities were measured in the absence and presence of antibodies raised against purified human CETP. PLTP activities were present in all four species with highest values in pig (11.7 +/- 1.2 U/ml) and human plasma (9.2 +/- 1.6 U/ml). Considerable lower activities were found in rabbit (3.5 +/- 0.6 U/ml) and rat plasma (1.6 +/- 0.7 U/ml). These activities were not affected significantly by antibody against human CETP. CETP activities could be measured in human (0.23 +/- 0.05 U/ml) and in rabbit plasma (0.19 +/- 0.03 U/ml). CETP activity in human plasma was inhibited over 97% by antibody against human CETP. Plasma was chromatographed on a Superose 6 gel filtration column. Average HDL particle sizes in the four species differed notably and decreased in the order: rat HDL greater than rabbit HDL greater than human HDL greater than pig HDL. A separation of the two lipid transfer activities was evident after gel filtration chromatography. The peak of the PLTP activity coeluted with a fraction of HDL particles with the size of human HDL2 (particle weights 300-375 kDa). CETP activity in human and rabbit plasma coeluted largely with relatively small HDL particles (particle weights 140-180 kDa). These results show that CETP and PLTP activities are located in different macromolecular complexes.

Diet-induced alteration in the activity of plasma lipid transfer protein in normolipidemic human subjects

Studies were performed to investigate the effect of diets rich in oleic or linoleic acids on the activity of plasma cholesteryl ester transfer protein (CETP) in normolipidemic subjects. Previous to the test diets, all subjects consumed a baseline diet rich in saturated fatty acids ("sat-diet") for 17 days. The test diets, rich in either monounsaturated fatty acids ("mono-diet") or rich in polyunsaturated fatty acids ("poly-diet"), were given for 5 weeks to 52 normolipidemic healthy volunteers. The activity of CETP was measured, using a method independent of endogenous plasma lipoproteins, as the rate of exchange of radioactive cholesteryl oleate between labelled LDL and unlabelled HDL. The "mono-diet" induced a statistically significant decrease in CETP activity (from 115 +/- 20 to 102 +/- 19 units/ml plasma, P less than 0.01), while the small decrease on the "poly-diet" (from 111 +/- 23 to 107 +/- 22 units/ml plasma) did not reach significancy. The percentual decrease in CETP activity induced by the "mono-diet" was higher than that induced by the "poly-diet" as was also found for the decrease in LDL cholesterol. In both diet groups a positive correlation was found between changes in CETP activity and changes in plasma total or (VLDL + LDL) cholesterol. The results suggest that high levels of dietary monounsaturated fatty acids may result in decreased plasma CETP activity, as well as LDL cholesterol levels. The mechanisms of these effects, and their possible interrelations, remain to be established.

Elevated cholesteryl ester transfer protein activity in IDDM men who smoke. Possible factor for unfavorable lipoprotein profile

OBJECTIVES

To determine the effect of cigarette smoking on the activity of cholesteryl ester transfer protein (CETP) and high-density (HDL), low-density (LDL), and very-low-density (VLDL) lipoproteins in insulin-dependent diabetic (IDDM) men with microvascular complications.

RESEARCH DESIGN AND METHODS

We performed a case-control study in a referral-based diabetes clinic on a sequential sample of 9 cigarette-smoking and 12 nonsmoking IDDM men with microvascular complications and 12 nonsmoking control men. CETP activity was determined in each serum with an isotope assay with exogenous cholesteryl ester-labeled LDL and HDL. The method is independent of the endogenous lipoprotein present in serum.

RESULTS

The HDL-cholesterol (VLDL and LDL) ratio was lower in the smoking diabetic men than in the other groups (P less than 0.05 vs. the nonsmoking diabetic men and P less than 0.01 vs. the control subjects). CETP activity was 70% higher in the smoking diabetic men than in the control subjects (P less than 0.01) and 30% higher than in the nonsmoking diabetic men (P less than 0.05). The HDL-cholesterol (VLDL and LDL) ratio and the apolipoprotein A-I-B ratio were inversely correlated to CETP activity in the diabetic patients (r = -0.52, P less than 0.02 and r = -0.45, P less than 0.05, respectively).

CONCLUSIONS

CETP activity is increased in cigarette-smoking IDDM men with microvascular complications. High CETP activity may contribute to the unfavorable lipoprotein profile in these patients.

Net mass transfer of cholesteryl esters from low density lipoproteins to high density lipoproteins in plasma from normolipidemic subjects

Net mass transfer of lipids was measured in plasma from fasted, normolipidemic subjects. The plasma was incubated, and lipoproteins were subsequently separated by polyanion precipitation or density gradient ultracentrifugation. Total cholesterol, unesterified cholesterol, and triglycerides were measured in the isolated lipoprotein fractions. The rate of cholesterol esterification was measured simultaneously. All plasma samples showed an increase in high density lipoprotein (HDL) cholesteryl esters during 1-hour incubations. In most cases, this increase was higher than the cholesteryl ester formation in total plasma due to cholesterol esterification. Therefore, we concluded that a net mass transfer of cholesteryl esters occurred from the very low plus low density lipoprotein (VLDL + LDL) fractions to HDL in plasma from most of the subjects studied. Transfer of triglycerides occurred from VLDL + LDL to HDL in plasma from all subjects. The cholesteryl ester transfer (measured after 1 hour) is not related to the activity of cholesteryl ester transfer protein. Inhibition of cholesterol esterification did not change the direction of cholesteryl ester or triglyceride transfer. Ultracentrifugal separation of plasma lipoproteins revealed that both HDL and VLDL are acceptors of cholesteryl esters and that VLDL donates triglycerides to both LDL and HDL. Removal of VLDL from plasma by ultracentrifugation did not affect the cholesteryl ester transfer from LDL to HDL. We conclude that LDL may act as a donor of cholesteryl esters during incubation of normolipidemic plasma.

The activity of cholesteryl ester transfer protein is decreased in hypothyroidism: a possible contribution to alterations in high-density lipoproteins

The activity of cholesteryl ester transfer protein is instrumental in the distribution of cholesteryl ester between lipoproteins in plasma. We measured the activity of cholesteryl ester transfer protein in plasma, designated cholesteryl ester transfer activity, as the rate of cholesteryl ester transfer between exogenous radiolabelled low-density and high-density lipoproteins. The effect of hypothyroidism on cholesteryl ester transfer activity was investigated in 13 athyreotic patients who were studied in the hypothyroid condition and in the euthyroid state, after they had received triiodothyronine supplementation for 33 to 67 days. During hypothyroidism plasma total cholesterol, very-low- plus low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, plasma triacylglycerol, apolipoprotein A1 and B were significantly higher than in the euthyroid state. Cholesteryl ester transfer activity was 15% lower during hypothyroidism (P less than 0.02), and an effect of treatment duration was observed. The changes in high-density lipoprotein total cholesterol (P less than 0.02), free cholesterol (P less than 0.001), triacylglycerol (P less than 0.05) and the free cholesterol/cholesteryl ester molar ratio in high-density lipoproteins (P less than 0.01) were inversely-related to the changes in cholesteryl ester transfer activity. We concluded that thyroid hormone is involved in the regulation of cholesteryl ester transfer protein activity, and that cholesteryl ester transfer protein activity may play a role in the alterations in high-density lipoprotein lipids observed in hypothyroidism.

Alimentary lipemia-induced redistribution of cholesteryl ester between lipoproteins. Studies in normolipidemic, combined hyperlipidemic, and hypercholesterolemic men

Alimentary lipemia stimulates the transfer of cholesteryl ester between lipoproteins in vitro and may alter lipoprotein cholesteryl ester distribution in vivo. The effect of a single, large oral fat load on lipoprotein cholesteryl ester redistribution and the activity of cholesteryl ester transfer protein was investigated in six normolipidemic men (Group A), six combined hyperlipidemic men (Group B), and six hypercholesterolemic men (Group C). Fasting triglyceride-rich lipoprotein cholesteryl ester was high in Group B, low in Group A, and intermediate in Group C (A less than C less than B, p less than 0.05). After an oral fat load, total plasma cholesteryl ester was unchanged in all groups. In Group A, cholesteryl ester increased in smaller triglyceride-rich lipoproteins and remained so at 24 hours. Conversely, low density and high density lipoprotein cholesteryl ester decreased and returned to fasting values at 24 hours. In Group B, cholesteryl ester increased in large triglyceride-rich lipoproteins. Low density and high density lipoprotein cholesteryl ester (expressed as percentage of plasma cholesteryl ester) decreased. By contrast, in Group C, triglyceride-rich lipoprotein and low density lipoprotein cholesteryl ester remained unaltered, and only high density lipoprotein cholesteryl ester decreased. The activity of cholesteryl ester transfer protein increased in all groups and returned to fasting values at 24 hours. No differences in response were observed among the three groups. It is concluded that an oral fat load can induce a shift in lipoprotein cholesteryl ester distribution from high and low density lipoproteins to triglyceride-rich lipoproteins without affecting total plasma cholesteryl ester.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of lipid transfer protein on plasma lipids, apolipoproteins and metabolism of high-density lipoprotein cholesteryl ester in the rat

The role of human plasma lipid transfer protein (LTP) in lipoprotein metabolism was studied in the rat, a species without endogenous cholesteryl ester and triacylglycerol transfer activity. Partially purified human LTP was injected intravenously into rats. The plasma activity was between 1.5- and 4-fold that of human plasma during the experiments. 6 h after the injection of LTP, a significant increase in serum apoB, and no significant changes in serum total cholesterol, free cholesterol, triacylglycerols, apoA-I, apoE, or apoA-IV were noted. Cholesterol was increased in very-low density and low-density lipoproteins (VLDL and LDL) and decreased in large-sized apoE-rich HDL. ApoA-I-containing particles with a size smaller than in normal rats were present in serum of LTP-treated rats. The mean diameter of HDL particles decreased and apoE, normally present on large-sized HDL, was present on smaller sized particles. The metabolic fate of cholesteryl ester, originally associated with HDL, was studied by injection of [3H]cholesteryl linoleyl ether-labelled apoA-I-rich HDL in the absence and in the presence of LTP. The disappearance of [3H]cholesteryl linoleyl ether, injected as part of apoA-I-rich HDL, from serum was increased in the LTP-treated rats; the t1/2 changed from 3.9 to 2.2 h, resulting in an increased accumulation of [3H]cholesteryl linoleyl ether in the liver. This can be explained by the redistribution of HDL [3H]cholesteryl linoleyl ether to VLDL and LDL in the presence of LTP, leading to the combined contribution of VLDL, LDL and HDL to the hepatic uptake. The present findings show profound effects of LTP on the chemical composition of HDL subspecies, the size of HDL and on the plasma turnover and hepatic uptake of cholesteryl esters originally present in apo A-I-rich HDL.

Increased cholesterylester transfer activity in complicated type 1 (insulin-dependent) diabetes mellitus--its relationship with serum lipids

In Type 1 (insulin-dependent) diabetes mellitus, macrovascular complications and the increased risk for cardiovascular disease in patients with microvascular complications may be related to alterations in plasma cholesterylester transfer. The activity of cholesterylester transfer protein, which mediates cholesterylester transfer between lipoproteins and lipoprotein lipid levels, was assessed in 7 normolipidaemic control subjects, 7 Type 1 diabetic control subjects without complications, 11 Type 1 diabetic patients with microvascular complications (retinopathy, incipient nephropathy) and in 7 Type 1 diabetic patients with macrovascular atherosclerotic lesions. The cholesterylester transfer activity was 30% higher in the diabetic groups with macrovascular and microvascular lesions than in the 2 control groups. Very low + low density lipoprotein cholesterol was higher in the 3 diabetic groups than in the non-diabetic control group. High density lipoprotein cholesterol was not different. The cholesterylester transfer activity was correlated positively with HbA1, urinary albumin excretion rate, serum cholesterol, very low + low density lipoprotein cholesterol and apolipoprotein B. The high density lipoprotein over very low + low density lipoprotein cholesterylester molar ratio was lower in the diabetic groups with micro- and macrovascular complications. A role for cholesterylester transfer activity in the lipoprotein abnormalities found in complicated Type 1 diabetes is suggested. A high cholesterylester transfer activity might be indicative of mechanisms which promote atherogenesis.

Lipid transfer protein-catalyzed exchange of cholesteryl ester between high density lipoproteins and apoB-containing lipoproteins

Low density lipoproteins (LDL), lipoprotein (a)(Lp(a)), and lipoprotein(a) after removal of the a-protein (Lp(a-)) were compared with respect to their ability to accept cholesteryl ester from high density lipoproteins (HDL). The incubations were performed at constant concentrations of HDL and various concentrations of either LDL, Lp(a), or Lp(a-). Lp(a) exchanged cholesteryl ester with HDL, but at a rate that was only 48.5 +/- 3.8% of the exchange rate found in the presence of autologous LDL. Cleavage of the apo(a) from Lp(a) resulted in Lp(a-), an LDL-like particle, with characteristics of cholesteryl ester exchange very similar to LDL.

Effect of the composition of very low and low density lipoproteins on the rate of cholesterylester transfer from high density lipoproteins in man, studied in vitro

The process of cholesterylester (CE) transfer is supposed to be a regulatory factor in the distribution of CE between lipoproteins. In addition to the activity of CE transfer protein, this process may be affected by acceptor lipoprotein characteristics. In this study the effect of the composition of different very low density lipoproteins (VLDL) and low density lipoproteins (LDL) on the ability to accept CE from HDL in vitro was investigated. [3H]-CE high density lipoprotein (HDL) (100 nmol CE) from one batch was incubated with VLDL (75 nmol CE), isolated from fifteen subjects for 4 h and separately with LDL (250 nmol CE), isolated from thirteen subjects for 16 h, both in the presence of lipoprotein-free plasma providing a source of cholesterylester transfer protein. The CE transfer rate of VLDL (range 1.34-2.84% [3H]-CE transferred h-1) was correlated to the triacylglycerol (TG):CE molar ratio (r: 0.63, P less than 0.05), to the phospholipid (PL):CE molar ratio (r: 0.75, P less than 0.01), to the protein (Pr):CE ratio (expressed in g nmol-1) (r: 0.72, P less than 0.01) and to the free cholesterol (FC):CE molar ratio (r: 0.69, P less than 0.01), but not to the FC:PL molar ratio (r: -0.08, NS). The CE transfer rate to LDL (range 1.18-3.59 nmol CE h-1) was correlated to the Pr:CE ratio (r: 0.72, P less than 0.01) and inversely to the FRC:PL molar ratio (r: -0.88, P less than 0.001), but not to the TG:CE molar ratio (r: 0.40, NS), nor to the FC:CE molar ratio (r: -0.37, NS).(ABSTRACT TRUNCATED AT 250 WORDS)

A hyperalphalipoproteinaemic family with normal cholesteryl ester transfer/exchange activity

Reports of two independent studies suggest that familial hyperalphalipoproteinaemia (FHALP) may be caused by a deficiency of cholesteryl ester transfer/exchange activity (CETP). We also have studied CETP in the plasma of an Italian FHALP kindred. The study group was divided into blood relatives with greater than 1.70 mM high-density-lipoprotein cholesterol (HDL-C) (group I, n = 9), with less than 1.70 mM-HDL-C (group II, n = 12) and in spouses (group III, n = 6). Two different assays were performed to measure CETP activity. In method A the interfering endogenous lipoproteins in the plasma samples were removed by poly(ethylene glycol) precipitation or by ultracentrifugation at a relative density (d) of 1.180. The CETP-activity of these samples was measured in a system consisting of fixed amounts of HDL and cholesteryl [1-14C]oleate-labelled low-density lipoproteins (LDL). In method B, trace amounts of HDL (radiolabelled with cholesteryl [1-14C]oleate) were incubated with plasma for 3 h at 37 degrees C and the distribution of the label among lipoproteins was measured (CET activity). The results can be summarized as follows. The mean CETP activities measured by method A were 187, 213 and 243 nmol/h per ml in groups I, II and III respectively. The proband with the highest HDL-C (4.98 mM) had a CETP activity of 231 nmol/h per ml. The corresponding CET activities measured by method B and expressed as percentage transfer/h were 4.3, 8.0 and 11.2 in groups I-III. The proband with HDL-C = 4.98 mM had a value of only 1.7%/h. There was a strong negative correlation between percentage CE transfer and HDL-C concentration. Calculating these data in terms of CE exchange (nmol/h per ml), groups I, II and III exhibited mean activities of 86, 124 and 110 nmol/h per ml respectively; for the proband this value was 80 nmol/h per ml. Only a slight correlation was found between these values and the HDL-C value. Thus by both methods, (A), measuring the CETP activity per se and (B), measuring the activity in whole plasma (reflecting the activity of the protein and the concentration and composition of lipoproteins), no major differences could be found between the three groups. In our family, therefore, no connection between FHALP and CETP deficiency could be found. It is concluded that, for hyper- and dys-lipoproteinaemic samples, a careful selection of the assay procedure as well as the mode of calculating results is essential. Since this may not hold the previous studies, the supposed connection between FHALP and CETP deficiency is challenged.

The role of LCAT and cholesteryl ester transfer proteins for the HDL and LDL structure and metabolism

Since the early detection of LCAT by Glomset, a great deal of research has been conducted for establishing the role of this enzyme in the Lp metabolism. It became apparent that LCAT produces more than 3/4 of the CE found in plasma. LCAT acts primarily on Lp with high PC/FC contents and high PC/FC ratios. For expression of the full activity, apo-Lp cofactors such as apo-AI, -CI, -AIV and -E are necessary. Although it was believed for a long time that HDL are the only substrate for LCAT we could demonstrate that LDL and even apoA/C/E free LpB is utilized by LCAT. The CE formed in PC/FC rich Lp are transferred to VLDL and LDL by specific proteins, which also promote the exchange of CE against TG. TG in these particles are hydrolyzed by liver lipase providing new space in the core for further cholesterol esterification. Thus LCAT exerts its physiological role in concert with other enzymes e.g. LPL, hepatic lipase and possibly phospho-lipases as well as with exchange and transfer processes partly catalyzed by specific exchange/transfer proteins. The main function of LCAT without doubt is the reverse cholesterol transport from periphery to liver counteracting the accumulation of CE in reticulo endothelial cells by the scavenger pathway. Metabolic studies revealed that the cholesterol clearance from the circulation proceeds in the same order of magnitude as the esterification by LCAT takes place. This possibly implies that LCAT might be the rate limiting enzyme for cholesterol catabolism from blood.

Improved estimation of cholesteryl ester transfer/exchange activity in serum or plasma

This simple, routine assay for measuring cholesteryl ester transfer/exchange activity in human plasma is based on the removal of interfering lipoproteins--very-low-density (VLDL) and low-density lipoproteins (LDL)--by precipitation with polyethylene glycol. High-density lipoproteins (HDL) in the samples do not affect the results. The supernate after precipitation is mixed with [14C]cholesteryl ester-labeled LDL as donor and with HDL as the acceptor for the cholesteryl ester. After incubation for 16 h at 37 degrees C, LDL is separated from HDL by precipitation with dextran sulfate and the radioactivity measured in the supernate, which contains the HDL. The assay is applicable to samples containing as much as 10 mmol of triglycerides per liter. The within-assay CV was 2.7%, the day-to-day CV 6.8%. Results compared well with those by conventional procedures.

Improved estimation of cholesteryl ester transfer/exchange activity in serum or plasma

This simple, routine assay for measuring cholesteryl ester transfer/exchange activity in human plasma is based on the removal of interfering lipoproteins--very-low-density (VLDL) and low-density lipoproteins (LDL)--by precipitation with polyethylene glycol. High-density lipoproteins (HDL) in the samples do not affect the results. The supernate after precipitation is mixed with [14C]cholesteryl ester-labeled LDL as donor and with HDL as the acceptor for the cholesteryl ester. After incubation for 16 h at 37 degrees C, LDL is separated from HDL by precipitation with dextran sulfate and the radioactivity measured in the supernate, which contains the HDL. The assay is applicable to samples containing as much as 10 mmol of triglycerides per liter. The within-assay CV was 2.7%, the day-to-day CV 6.8%. Results compared well with those by conventional procedures.

Diet, lipoproteins and cholesteryl ester transfer activity in hyperlipidaemic subjects

In order to study the response of cholesteryl ester transfer activity (CETA) to alteration in diet in humans we carried out a longitudinal study in hyperlipidaemic patients. Five subjects, all hyperlipidaemic, were first given a low fat diet for 7 to 15 days and then a diet high in fat for 7 to 21 days. In four out of five patients both diets were low in energy. The plasma lipoprotein levels and CETA were measured daily. All patients responded on the low fat diet by a decrease in total cholesterol and total triglycerides. No response on the high fat diet was noticed except in the patient for whom the high fat diet was also high in energy. In all patients the changes in CETA ran parallel to changes in (VLDL + LDL) cholesterol. It is concluded that diet induced changes in (VLDL + LDL) cholesterol are accompanied by similar changes in CETA in hyperlipidaemic subjects.

Cholesteryl ester transfer activity. Localization and role in distribution of cholesteryl ester among lipoproteins in man

The cholesteryl ester exchange/transfer protein is involved in the transport of cholesteryl ester from high density lipoproteins (HDL) to very low density lipoproteins (VLDL) and low density lipoproteins (LDL). Localization of cholesteryl ester transfer activity (CETA) in plasma was studied by measuring CETA in various delipidated fractions from a single step density ultracentrifugation gradient of plasma. CETA was measured in an in vitro system by calculating the exchange of cholesteryl ester in a standard mixture of [3H]CE-HDL and LDL. The method used for the delipidation of plasmas and fractions to be tested was critical. Optimal results were obtained by delipidation with diisopropylether-butanol (60: 40, v/v) at O degrees C. The bulk of CETA was detected in HDL3 (1.125 less than d less than 1.210 g/ml) when the lipoproteins were separated by single-step density gradient ultracentrifugation and in the 'lipoprotein-free' fraction (d greater than 1.250 g/ml) when the lipoproteins were separated by flotation ultracentrifugation including two washes. To determine whether CETA plays a role in the distribution of cholesteryl ester among the various lipoproteins, it was measured in whole plasma from normal and hyperlipidemic subjects. Plasma was delipidated before the assay in order to prevent bias due to variation of cholesterol content. CETA was higher in delipidated plasma of hyperlipidemic subjects (117.3 +/- 36.5 nmol CE/ml/h) than in delipidated plasma of normolipidemic controls (68.7 +/- 17.6 nmol CE/ml/h) (P less than 0.005). A positive correlation (r = 0.80, P less than 0.005) was found between CETA and (VLDL + LDL) cholesterol levels. A negative correlation (r = 0.57, P less than 0.05) existed between CETA and HDL cholesterol. This correlation was found both in the group as a whole and within the normal and the hyperlipidemic groups separately. The activity of the cholesteryl ester transfer appears to be a regulatory factor in the distribution of cholesteryl ester over the various lipoproteins.

Evidence for the existence of only one triacylglycerol lipase of rat liver active at alkaline pH

There have been numerous reports suggesting the existence of two or more lipases in liver capable of hydrolyzing triacylglycerols at neutral to alkaline pH. We set out to determine if rat liver contains an alkaline triacylglycerol lipase, in addition to heparin-releasable lipase, which has an intracellular localization. We report here the results of studies concerning the pH dependence, subcellular localization and kinetic analysis of the alkaline lipase(s) of rat liver. Homogenates and cytosolic, microsomal and plasma membrane-enriched subfractions all exhibited an optimum of lipase activity at approx. pH 8.0. In no case was there evidence of multiple pH optima in the alkaline ranges of conformity to Michaelis-Menten kinetics were calculated for the microsomal (0.91 +/- 0.12 mM), cytosolic (1.55 +/- 0.38 mM) and plasma membrane-enriched (1.02 +/- 0.04 mM) subfractions. To determine if the com- and subfractions prepared from control livers with those prepared from livers perfused with collagenase. The loss (93%) of lipase activity from both the cytosolic and microsomal subfractions after collagenase perfusion was identical to the loss (93%) of activity from the homogenates, suggesting a common origin with the collagenase-sensitive alkaline lipase on plasma membrane. The characteristics of hydrolysis in vitro of triacylglycerol contained in artificial and natural substrate preparations by the alkaline lipase of rat liver were examined. The artificial substrate preparation was emulsified tri[1-14C]oleoylglycerol prepared by sonication and the natural substrate preparation was a triacylglycerol-rich lipid fraction ('liver fat') prepared from rat liver homogenates. Although the curves were complex, apparent Km values (mean +/- S.W., n = 3-6) over the limited concentration ranges of conformity to Michaelis-Menten kinetics were calculated for the microsomal (0.91 +/- 0.12 mM), cytosolic (1.55 +/- 0.38 mM) and plasma membrane-enriched (1.02 +/- 0.04 mM) subfractions. To determine if the complexity of these kinetics was related to changes in the products of lipolysis, we examined the products after incubations of plasma membrane-enriched fractions with lower and higher concentrations of triacylglycerol. In either case, the products of lipolysis were diacylglycerol, fatty acids and glycerol; no monoacylglycerol accumulated under any circumstances. At the lower concentrations of either tri[1-14C]oleoylglycerol or liver fat, most triacylglycerol hydrolyzed was degraded fully to fatty acids and glycerol. At the higher triacylglycerol concentrations, while complete degradation continued, virtually all of the increased lipolysis of triacylglycerol (over the lipolysis at the lower substrate concentrations) yielded diacylglycerol. The data indicated that the hydrolysis of diacylglycerol by the alkaline lipase of rat liver occurred at a rate slower than that of triacylglycerol. If the same enzyme catalyzes the lipolysis of both tri- and diacylglycerols, triacylglycerols would appear to be preferred...

Effect of fasting and feeding a high-sucrose, fat-free diet on the synthesis of hepatic glycerolipids in vivo and in isolated hepatocytes

1. The synthesis of glycerolipids from a number of radioactive precursors, such as [2-3H] glycerol, [32P]phosphate, [Me-14C]choline and [1,2-14C2]ethanolamine proceeds in enzymatically isolated hepatocytes with a specificity that agrees very well with that observed in the liver in vivo. 2. The nutritional state of the rat has a profound influence on the glycerolipid metabolism of isolated hepatocytes. Fasting strongly decreased the incorporation of glycerol via sn-glycerol 3-phosphate into triacylglycerols whereas the formation of phosphatidylcholine and, particularly, phosphatidylethanolamine was much less affected by food deprivation. Refeeding a high-sucrose, fat-free diet caused a tremendous increase in the synthesis of diacylglycerols and triacylglycerols to values exceeding those found in hepatocytes from normally fed animals. The formation of phosphatidylcholine increased more slowly and the synthesis of phosphatidylethanolamine was even depressed by refeeding a high-sucrose, fat-free diet. 3. Alteration of the nutritional state resulted in similar changes in the amounts and metabolism of hepatic glycerolipids in vivo. The formation and, consequently, the amount of diacyglycerol and triacylglycerol were decreased by fasting and increased to values above normal in rats refed a high-sucrose, fat-free diet. The formation and the amounts of phospholipids in the liver decreased slightly by fasting which was mainly due to a decrease in phosphatidylcholine. Refeeding caused a significant increase in the formation and amount of phosphatidylcholine. The amount of phosphatidylethanolamine was even further diminished by feeding a high-sucrose, fat-free diet to 48-h-fasted rats. 4. These results show that the alterations, induced in the in vivo metabolism of hepatic glycerolipids, by changes of the dietary state, are also reflected in the isolated hepatocytes. This finding strengthens the potential significance of isolated hepatocytes in studies on the regulation of hepatic lipid metabolism.

Lipid response to female gonadal hormones of female rats fed a high glucose or a high fructose diet

Sexually mature female rats were given, for 11 weeks, diets high in fructose or glucose and at the same time oestrogen and progestogen were administered both singly and together. Analysis of the lipids in the liver, serum and adipose tissue was carried out after ingestion of 14C-fructose or glucose. Oestrogen lowered the liver triglyceride level but raised the serum triglyceride concentration. Progestogen tended to raise both cholesterol and triglyceride levels in liver and serum and it also caused a greater increase in body weight than in control or in the oestrogen animals. An increased specific activity was seen at first in the adipose tissue of the glucose-fed rats receiving the hormones. Overall, there was a tendency for the female gonadal hormones to exaggerate the changes brought about by the high carbohydrate diets.