[The 4 Provinces Study: its principal objectives and design. The Researchers of the 4 Provinces Study]

INTRODUCTION AND OBJECTIVES

Spain shows an important variation in the geographical distribution of ischaemic heart disease and cerebrovascular disease mortality. In this article, the primary objectives and design of the Four Provinces study are described. In this study we analyzed the contribution of environmental factors (diet, lipid profile and plasma antioxidants), acting in childhood, to explain differences in cardiovascular mortality rates between different provinces in Spain.

METHODS

An ecological design was projected in which the units to study were four Spanish provinces with a wide variation in cardiovascular mortality in adulthood. The design compares diet, anthropometric variables and biological markers (particularly plasma lipids and antioxidant levels) in 6-7-year-old children, between the two provinces with the highest cardiovascular mortality rates and the two provinces with the lowest. The information for each province is collected in a cross-sectional manner in a representative sample of children from each province.

DISCUSSION

Evidence from the literature concerning Northern European countries suggest the contribution of environmental factors during early age in the development of cardiovascular disease in adulthood. The "Four Provinces" study will provide, for the first time, information about the influence of factors in early childhood of cardiovascular risk in a Mediterranean country. The study will also offer interesting data about food intake during school age in four provinces and it will allow us to estimate values of population of the variables of interest in those provinces.

Induction of apoptosis in p53-null HL-60 cells by inhibition of lanosterol 14-alpha demethylase

To determine the role of cholesterol deprivation in cell proliferation and, eventually, in apoptosis, HL-60 promyelocytic cells were incubated in a cholesterol-depleted medium in the presence of SKF 104976, a specific inhibitor of lanosterol 14-alpha demethylase. As expected, SKF 104976 efficiently blocked the [14C]-acetate incorporation into cholesterol, whereas it induced the accumulation of both lanosterol and, especially, dihydrolanosterol. As a consequence, cell proliferation was greatly depressed at 24 h of treatment with the drug, and clear signs of apoptosis--annexin V binding, condensed and fragmented nuclei and DNA ladder--were observed thereafter. Provided that the HL-60 cell line does not express p53, it may be concluded that apoptosis induced by cholesterol deprivation is not dependent on this tumor suppressor protein. Supplementing the incubation medium with LDL-cholesterol or pure free cholesterol, fully prevented cell growth inhibition and apoptosis induction, whereas mevalonate was ineffective. These results indicate that cholesterol plays a specific role in cell proliferation, a function that is not shared by its precursors lanosterol and dihydrolanosterol.

Relationship between serum parathyroid hormone levels and lipid profile in hemodialysis patients. Evolution of lipid parameters after parathyroidectomy

To determine the influence of parathyroid hormone (PTH) on lipid disturbances of uremia, the lipid profile was determined in 34 hemodialysis (HD) patients, comparing lipid parameters among subjects classified according to their intact PTH level. Furthermore, the effect of correction of severe secondary hyperparathyroidism on serum lipids was evaluated in 7 patients after parathyroidectomy. Total cholesterol, high-density lipoproteins (HDL), triglycerides, apolipoproteins A-I and B-100 (Apo B and Apo B), lipoprotein(a) and the ratios of cholesterol/HDL and Apo A/Apo B were analyzed. There was no correlation between serum lipids and PTH levels in the total group. Lipid profile was similar among patients classified according to their PTH level. No correlations were observed in either group between lipids and PTH. Lipid profile did not change in the seven patients with severe secondary hyperparathyroidism after parathyroidectomy. In conclusion, there was no relationship between PTH and lipids and risk ratios in HD patients. Lipid profile did not change in patients with severe secondary hyperparathyroidism after parathyroidectomy. These findings suggest that PTH does not play a significant role in the dyslipidemia of renal failure.

Human CD36 is a high affinity receptor for the native lipoproteins HDL, LDL, and VLDL

Mouse and hamster SR-BI glycoproteins and their putative human counterpart CLA-I are so far the only scavenger receptors known to bind both native and modified lipoproteins. CD36, a multigland glycoprotein structurally related to SR-BI and CLA-1, has been reported to bind oxidized low density lipoprotein (OxLDL) and acetylated LDL (AcLDL). In this report, we have studied the ability of CD36 to bind native lipoproteins. By transient expression of human CD36 in mammalian and insect cells, we demonstrate that CD36 is a high affinity receptor for the native lipoproteins HDL, LDL, VLDL, and, as previously reported, for OxLDL and AcLDL. The specificity of these interactions is supported by the dose-dependent inhibiton, effect of a monoclonal antibody against CD36. Furthermore, at least for HDL, binding to CD36 does not require the presence of apoE. These findings, together with preferential expression of CD36 in tissues performing very active fatty acid metabolism (skeletal muscle, heart, mammary epithelium, and adipose tissue) and its involvement in foam cell formation (macrophages), suggest that binding of lipoproteins to CD36 might contribute to the regulation of lipid metabolism, and to the pathogenesis of atherosclerosis.

Flavonoid-induced ability of minimally modified low-density lipoproteins to support lymphocyte proliferation

Low-density lipoprotein (LDL) peroxidation appears to be involved in atherogenesis. We studied the ability of minimally modified LDL (MM-LDL) to be used by proliferating lymphocytes and the effects of antioxidant flavonoids on this lipoprotein. MM-LDL were obtained by storing LDL at 4 degrees for 1 month, which resulted in a decrease in lipophilic antioxidants and an increased susceptibility to oxidation when incubated with cells. MM-LDL were not cytotoxic; however, in cells treated with lovastatin that require cholesterol for cell growth, they were much less efficient than fresh LDL in sustaining proliferation as determined by [3H]thymidine incorporation into DNA. Pure quercetin and grape-derived beverages restored proliferation in the presence of MM-LDL and prevented the apoptosis otherwise induced by lovastatin. These effects of flavonoids correlated with their activity in inhibiting LDL peroxidation. The results demonstrate that potent antioxidants, such as flavonoids, protect MM-LDL from lipoperoxidation and preserve their ability to efficiently deliver cholesterol to cells.

[Familial hypercholesterolemia: molecular identification and characterization of the first compound homozygote in Spain]

Homozygous familial hypercholestrolemia (FH) is a rare genetic disorder (one in 1 million persons) due to two different mutations in the LDL receptor gene (compound homozygous) or, rarely, to the presence of the same mutation in the two aleles. In these patients the absence of a functional LDL receptor produces extreme elevations of plasma cholesterol levels that need an aggressive and expensive treatment with LDL apheresis or hepatic transplantation. The clinical evolution is poor with early coronary heart disease. Molecular biology techniques allow a genetic diagnosis and a genetic counseling in the affected subjects. We have identified and characterized the first compound homozygous of FH in Spain using the single strand conformational polymorphism (SSCP) analysis. The patient is a 30 years old female, who carried two different mutations in the LDL receptor gene: the G528V and the D280G (a new mutation). These mutations produce significant changes in the aminoacid sequence and could be classified as class 2.

CLA-1 is an 85-kD plasma membrane glycoprotein that acts as a high-affinity receptor for both native (HDL, LDL, and VLDL) and modified (OxLDL and AcLDL) lipoproteins

Lipoprotein metabolism is regulated by the functional interplay between lipoprotein components and the receptors and enzymes with which they interact. Recent evidence indicates that the structurally related glycoproteins CD36 and SR-BI act as cell surface receptors for some lipoproteins. Thus, CD36 has been reported to bind oxidized LDL (OxLDL) and acetylated LDL (AcLDL), while SR-BI also binds native LDL and HDL. The cDNA of human CLA-1 predicts a protein 509 amino acids long that displays a 30% and an 80% amino acid identity with CD36 and mouse or hamster SR-BI, respectively. In this report, we describe the structural characterization of CLA-1 as an 85-kD plasma membrane protein enriched in N-linked carbohydrates. The expression of CLA-1 on mammalian and insect cells has been used to demonstrate that CLA-1 is a high-affinity specific receptor for the lipoproteins HDL, LDL, VLDL, OxLDL, and AcLDL. Northern blot analysis of the tissue distribution of CLA-1 in humans indicated that its expression is mostly restricted to tissues performing very active cholesterol metabolism (liver and steroidogenic tissues). This finding, in the context of the capability of this receptor to bind to both native and modified lipoproteins, strongly suggests that the CLA-1 receptor contributes to lipid metabolism and atherogenesis.

LDL from aerobically-trained subjects shows higher resistance to oxidative modification than LDL from sedentary subjects

We studied the effect of regular intense aerobic exercise on the LDL susceptibility to oxidation and the electronegative LDL-proportion (LDL(-)). A group of 38 well-trained athletes was compared to a group of 38 age-BMI-matched sedentary individuals. Athletes showed higher concentration of total cholesterol (athletes 5.08 +/- 0.70 versus controls 4.65 +/- 0.75 mmol/l, P = 0.0229) and HDL cholesterol (athletes 1.72 +/- 0.47 versus controls 1.46 +/- 0.39 mmol/l, P = 0.0068); total plasma triglyceride, LDL cholesterol and VLDL cholesterol did not differ between trained and untrained subjects. The susceptibility of LDL to oxidation, determined by conjugated dienes formation and expressed as lag phase, was lower in athletes than in sedentaries (trained subjects 47.0 +/- 5.6 versus sedentary subjects 41.9 +/- 5.0 min, P = 0.0002). LDL(-) was similar in both groups (athletes 10.32 +/- 4.70 versus controls 10.26 +/- 3.71%). The antioxidant content in total plasma and isolated LDL (alpha-tocopherol, retinol, lycopene, alpha-carotene and beta-carotene) was quantitated by HPLC in a subgroup of 32 athletes and 32 control subjects. Athletes showed higher amounts of alpha-tocopherol and retinol in plasma, but not in LDL. However, none of these antioxidants correlated with the lag phase time. Trained subjects showed lower prevalence of smoking. However, no differences were observed between smokers and non-smokers concerning lag phase. No significant difference between athletes and sedentaries concerning LDL density, or composition was observed. We conclude that LDL from trained subjects is more resistant to oxidative modification than LDL from sedentary subjects. This observation could not be attributed to conventional antioxidants as alpha-tocopherol and carotene content of LDL was unchanged in trained subjects. Thus, although none of the variables studied appear as a single predictor of the LDL susceptibility to oxidation, an additive effect of the antioxidant content, the presence of some undetermined co-antioxidant, HDL and/or smoking habits cannot be discarded as responsible for the increased resistance to oxidation of LDL in trained subjects.

Fatty acid composition of lipoprotein lipids in hepatobiliary diseases

Liver damage and alterations in the exocrine function of the gland lead to a profound alteration of the plasma lipoprotein profile. To determine whether hepatic disease results in changes in the lipoprotein fatty acid composition, i.e. to determine whether liver function influences the homeostasis of complex lipids in plasma, we studied the fatty acid profile of lipids from VLDL, LDL and HDL, as well as from total plasma, in thirty-one patients of both sexes with hepatobiliary pathology (compensated liver cirrhosis, uncompensated liver cirrhosis, primary biliary cirrhosis, other intrahepatic cholestasis, and acute viral hepatitis). We also studied a group of healthy adults as controls. We present the lipoprotein profile and the fatty acid composition (myristic C14, palmitic C16, palmitoleic C16: 1, stearic C18, oleic C18: 1, linoleic C18: 2, eicosatrienoic C20: 3 omega 6 and arachidonic C20: 4) of lipoprotein and total plasma triacylglycerols, cholesteryl esters and phospholipids. The main observation of this study is that, despite the profound changes in the lipoprotein profile and the lower abundance of polyunsaturated fatty acids in complex lipids, the composition of all triacylglycerols, cholesteryl esters and phospholipids is very similar for the corresponding lipoproteins of patients with hepatobiliary disease and of control subjects. This indicates that in the controls as in the studied patients, the exchange of lipids between plasmatic lipoproteins is very rapid and demonstrates the possible importance of the extrahepatic synthesis of cholesteryl ester transfer protein.

Cholesteryl ester transfer activity in liver disease and cholestasis, and its relation with fatty acid composition of lipoprotein lipids

Liver disease is accompanied by major qualitative and quantitative disturbances in plasma lipoprotein metabolism, the extent and intensity of which depend on the degree of parenchymal damage, cholestasis, or both. The main objective of this study was to determine the cholesteryl ester transfer CETP activity and its association with the lipoprotein neutral lipid composition in patients with either liver cirrhosis or cholestasis, as compared to normal controls. Lipoproteins were isolated by ultracentrifugation, lipids and apolipoproteins were measured by conventional methods, and the fatty acid composition was established by gas chromatography; CETP activity in lipoprotein-deficient plasma was measured by determining the transfer of [3H]cholesteryl esters from HDL to VLDL. Lipoprotein lipase and hepatic lipase activities were measured in post-heparin plasma by radiochemical methods. In patients with liver cirrhosis, low levels of VLDL, HDL, apo B, and Lp(a) were observed, as well as a change in the composition of HDL particles, with increases in the relative proportion of triglyceride and free cholesterol. Respectively, the last two changes could be attributed in part to the low hepatic lipase activity observed in this study, and to the low lecithin:cholesterol acyltransferase activity previously observed by others. In patients with cholestasis, a moderate hyperlipidemia due to the elevation of LDL was found. In contrast, HDL and apo A-I levels were very low reflecting a low number of HDL particles, which also had altered compositions with increases in the triglyceride and free cholesterol contents relative to apo A-I and esterified cholesterol, respectively. As regards the fatty acid composition of lipoprotein lipids, the two groups of patients showed, in general, a lower proportion of linoleic acid and a compensating higher proportion of oleic acid as compared to the controls, changes that were observed in both cholesteryl esters and triglycerides. In contrast, the proportions of oleic and palmitoleic acids in phospholipids were increased, whereas that of stearic acid was decreased in patients as compared to controls. In patients with liver cirrhosis, as well as in controls, no changes were observed in the fatty acid compositions of cholesteryl ester, triglycerides, or phospholipids among the different lipoproteins, which probably reflects the equilibration reached by the action of CETP. In patients with cholestasis, no differences were observed in fatty acid composition among the lipoprotein phospholipids but, interestingly, cholesteryl esters from VLDL had a significantly lower linoleic acid content than those from HDL, whereas triglycerides from VLDL had significantly higher oleic acid and lower linoleic acid contents than those from HDL. This distinct fatty acid composition of the neutral lipids between lipoproteins was associated with a significant decrease (25%) in the cholesteryl ester transfer activity in patients with cholestasis. We suggest that fat malabsorption due to the biliary defect may induce a decrease in cholesteryl ester transfer protein synthesis or section, which in turn would slow the equilibration of the neutral lipids among plasma lipoproteins.

Longitudinal study on lipoprotein profile, high density lipoprotein subclass, and postheparin lipases during gestation in women

To understand the mechanism responsible for maternal hyperlipidemia, 25 healthy pregnant women were studied longitudinally during the three trimesters of gestation and at post-partum, and 11 were studied again at post-lactation. Triglyceride and cholesterol levels increased with gestation in all the lipoprotein fractions. However, the greatest change appeared in low density (LDL) and high density (HDL) lipoproteins, both of which showed an increase in their triglyceride/cholesterol ratio. The proportional distribution of HDL subfractions showed that the HDL2b fraction was the only one that increased with gestation, whereas both HDL3a and HDL3b had the greatest decrease. Cholesteryl ester transfer protein activity increased during the second trimester of gestation. While postheparin lipoprotein lipase activity decreased during the third trimester, postheparin hepatic lipase activity progressively decreased from the first trimester. The 17 beta-estradiol, progesterone, and prolactin hormones progressively increased from the first trimester of gestation. The lipoprotein-triglyceride values correlated linearly and negatively with the logarithm of either postheparin lipase activities, HDL-triglycerides showing the highest correlation coefficient when plotted against the hepatic lipase values (r = -0.757). It appeared that the highest correlation between any of the HDL subclasses and the activity of the enzymes was for hepatic lipase activity versus HDL2b (r = 0.456) or HDL3a (r = 0.519). A significant lineal correlation also appeared between the postheparin hepatic lipase activity and the logarithm of any of the sex hormones studied, the highest value corresponding to estradiol (r = -0.783). Therefore, during gestation, the effect of estrogen in enhancing very low density lipoprotein (VLDL) production and decreasing hepatic lipase activity plays a key role in the accumulation of triglycerides in lipoproteins of density higher than VLDL.

Binding of lipoprotein lipase to apolipoprotein B-containing lipoproteins

The binding of lipoprotein lipase (LPL) to different lipoproteins and to a lipid emulsion was studied. After incubating the same amount of 125I-labelled LPL with VLDL, LDL or a lipid emulsion containing no apolipoproteins, we separated the free enzyme from the lipoprotein-bound LPL by gel filtration and by lipoprotein precipitation with phosphotungstic acid. By the former method we observed that all these types of lipid particles bound LPL indicating that the lipid moiety accounts for the LPL-lipoprotein interaction. This binding of LPL to lipoproteins was disrupted by high salt concentrations. When balanced by the apolipoprotein B content, it was observed that a significantly higher amount of 125I-labelled LPL co-eluted with VLDL than with LDL in gel permeation. The Kd values for binding of LPL to lipoproteins were estimated by use of lipoprotein precipitation. The obtained Kd values, both in the absence and in the presence of human lipoprotein deficient serum, were lower for VLDL than for LDL indicating a higher affinity of LPL for VLDL than for LDL. We finally compared binding capacity of LPL to VLDL subfractions with different apo E content. For this, we used apo E-poor (VLDL-B) and apo E-rich (VLDL-D) subfractions separated by heparin-Sepharose chromatography. We found that 125I-labelled LPL co-eluted to a similar extent with both subfractions on gel filtration, and the estimated Kd values from lipoprotein precipitation were not statistically different. Taken together, our results indicate that the lipid moiety, probably the phospholipids, accounts for the LPL-lipoprotein interaction; differences in size, the presence of C apolipoproteins or the conformation of apo B may be responsible for the higher affinity of LPL for VLDL than for LDL herein observed.

Pregnancy in a patient with homozygous familial hypercholesterolemia undergoing low-density lipoprotein apheresis by dextran sulfate adsorption

Pregnancy and delivery in homozygous familial hypercholesterolemic (HFH) patients is extremely rare. We describe the case of a woman with HFH treated with low-density lipoprotein (LDL) apheresis by dextran sulfate adsorption who became pregnant and reached delivery uneventfully. LDL apheresis was performed biweekly, and lipoprotein analyses in pre-apheresis samples showed progressive increases in triglyceride, total cholesterol, and apolipoprotein (apo) B plasma concentrations. The fractional catabolic rate (FCR) for LDL cholesterol, as estimated by the first-order disappearance constants (k values) of the recovery of LDL cholesterol concentration to basal values after each apheresis session, increased more than threefold from week-24 to week-4 (labor is considered as time 0). After delivery basal values were recovered, but normalization was slower for LDL cholesterol than for the other lipidic parameters. High-density lipoprotein (HDL) showed a different pattern: HDL3 remained stable throughout gestation, whereas HDL2 cholesterol and apo A-I had a maximum at midgestation, then declined, and finally increased again at late gestation. With the exception of this latter increase of HDL2, all the other changes in lipoprotein concentrations during pregnancy and postpartum were similar to those found in healthy women. Thus, LDL apheresis does not interfere with physiologic adaptations of lipoprotein metabolism during pregnancy in HFH patients.

Long-term thyroid replacement therapy and levels of lipoprotein(a) and other lipoproteins

There is a general interest to know whether lipoprotein(a) [Lp(a)] is under hormonal control. Hypothyroidism is a well known cause of secondary hyperlipidemia, which mainly affects low density lipoprotein (LDL) cholesterol levels, but the result on the effects of L-T4 replacement therapy on the Lp(a) concentration is controversial. We studied 12 severely hypothyroid, hypercholesterolemic patients under basal conditions and during L-T4 treatment. We found a rapid decrease in both LDL cholesterol (5.71 +/- 0.62 vs. 4.37 +/- 0.44 mmol/L basally and after 1 month of thyroid replacement, respectively) and apolipoprotein-B (Apo-B) levels (1.89 +/- 0.02 vs. 1.52 +/- 0.17 g/L, respectively); these changes persisted for up 1 yr of analytical euthyroidism and paralleled the improvement in the thyroid status of the patients. In contrast, the plasma Lp(a) concentration did not change at any time (496 +/- 123, 464 +/- 128, and 441 +/- 110 mg/L under basal conditions and after 1 and 14-15 months of thyroid replacement, respectively), and the small fluctuations observed in some patients did not correlate with those in LDL cholesterol or Apo-B, and were not associated with any particular Apo(a) phenotype. In relation to HDL fractions, high density lipoprotein3 (HDL3) remained stable, but HDL2 cholesterol and phospholipid levels decreased during treatment, changes that were the inverse of those in postheparin plasma hepatic lipase activity. Patients in the present study were normotriglyceridemic, except one who was hypertriglyceridemic at diagnosis, but even in this patient, triglyceride levels were unaffected by T4 substitution therapy, as was postheparin plasma lipoprotein lipase activity. The changes observed in LDL, HDL2, and hepatic lipase activity delineate the lipoprotein-related response to T4 replacement therapy, whereas potential individual fluctuations in Lp(a) levels are probably more dependent on other factors, such as the production rate, which are not affected by thyroid hormones.

Essential differences in cholesteryl ester metabolism between human monocyte-derived and J774 macrophages. Evidence against the presence of hormone-sensitive lipase in human macrophages

Cholesteryl ester-laden macrophages are the hallmark of the fatty streaks that precede arteriosclerotic plaques in humans and experimental animals. This article studies several aspects of cytoplasmic cholesteryl ester metabolism in cultured human monocyte-derived macrophages. Adenosine 3',5'-cyclic monophosphate (cAMP) consistently inhibited cholesteryl ester mobilization from cells that had been loaded with cholesteryl esters by preincubation with acetylated low-density lipoprotein. This effect was observed in both the absence and presence of extracellular cholesterol acceptors as well as with acyl coenzyme A: cholesterol acyltransferase inhibitors. In contrast, dibutyryl cAMP activated cholesteryl ester hydrolysis in J774 macrophages. Since hormone-sensitive lipase is thought to be responsible for the neutral cholesteryl ester hydrolytic activity in several cell types, we looked for the presence of its mRNA in our macrophages by means of reverse transcription coupled to the polymerase chain reaction technique. Hormone-sensitive lipase mRNA was detected in J774 macrophages but not in human monocytes or in human monocyte-derived macrophages. These results demonstrated great differences in cholesteryl ester metabolism between macrophages of different origin. While hormone-sensitive lipase may be responsible for neutral cholesteryl ester hydrolytic activity in J774 macrophages, in human monocyte-derived macrophages it is not; thus, a different and as yet unidentified enzyme must be present.

Changes in cholesteryl ester transfer protein activity during normal gestation and postpartum

Cholesteryl ester transfer protein (CETP) activity was measured in a d > 1.21 kg/L plasma fraction collected from healthy women at different times during gestation, postpartum, and in control women. CETP activity was highest in the second trimester of gestation, declined at the third trimester, and was lowest at postpartum. Only the value at the second trimester was significantly different from that of control women. This trend differed from that of circulating lipoproteins: very low-density lipoprotein (VLDL)-lipids, including triglycerides and cholesterol, increased progressively from the first to the third trimester, and then declined at postpartum. Low-density lipoprotein (LDL)-cholesterol levels, like VLDL levels, rose during gestation but then remained elevated at postpartum. High-density lipoprotein (HDL)-cholesterol as well as HDL-phospholipids and apolipoprotein A-I, peaked in the second trimester, remaining elevated in the third trimester and then fell at postpartum. Finally, HDL-triglyceride increased markedly from the first to the second trimester, rose somewhat higher during the third trimester, and declined at postpartum. When all the samples from pregnant women were considered together, CETP activity correlated significantly with HDL-triglyceride levels and the changes in CETP activity during gestation and postpartum paralleled those of the HDL-triglyceride/VLDL-triglyceride ratio. These results suggest that CETP contributes to the exaggerated accumulation of triglycerides in HDL that begins in the second trimester of human gestation.

Changes in lipoprotein(a), LDL-cholesterol and apolipoprotein B in homozygous familial hypercholesterolaemic patients treated with dextran sulfate LDL-apheresis

We evaluated the effect of periodical treatment with LDL-apheresis by adsorption to dextran sulfate (Liposorber LA-15) on several aspects related to LDL and Lipoprotein(a) metabolisms, in three homozygous familial hypercholesterolaemic patients with LDL receptor deficiency. The dextran sulfate columns retained apolipoprotein B-containing particles with high affinity and capacity, in such a way that the treatment of a volume of plasma equivalent to three times the patient plasma volume resulted in an 85% decrease of circulating LDL-cholesterol and Lipoprotein(a). The continuous treatment with LDL-apheresis was highly beneficial for these patients since an average plasma concentration lower than 200 mg dl-1 for LDL-cholesterol, and lower than 25 mg dl-1 for Lipoprotein(a) could be achieved by treating the patients once a week. After each apheresis treatment, plasma concentrations of these metabolites progressively returned to the pretreatment, steady-state, levels. The analysis of the rates of return allowed us to estimate the fractional catabolic rates. FCRs of LDL-cholesterol were 0.052, 0.049 and 0.047 pools day-1, and those of apolipoprotein B, 0.065, 0.045 and 0.050 pools day-1 in the three subjects, respectively. These values are much lower than those in normolipidaemic individuals as observed by others, and are in accordance with the LDL-receptor deficiency condition of our patients. Two of them had highly elevated Lipoprotein(a) plasma concentrations, and their FCRs of Lipoprotein(a) were calculated to be 0.112 and 0.066 pools day-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholesteryl ester transfer activity in lipoprotein lipase deficiency and other primary hypertriglyceridemias

Cholesteryl ester transfer protein (CETP) activity was measured in d > 1.21 g/ml plasma from hypertriglyceridemic patients and compared with normolipidemic subjects. The assay consisted in measuring the specific transfer of [3H]cholesteryl oleate from a prelabelled, apo E-poor HDL fraction to VLDL after incubation at 37 degrees C in the presence of the d > 1.21 g/ml plasma sample: the lipoproteins were then separated by precipitation with dextran sulfate/Mg2+ solution. Increasing the volume of d > 1.21 g/ml plasma or purified human CETP in the assay produced linear responses in measured activity, whereas, either during incubation at 4 degrees C or in the presence of rat plasma instead of human plasma, the transfer of [3H]cholesteryl oleate to VLDL was not stimulated. Thus, the assay reflects changes in CETP in the sample and appears to be suitable for measuring CETP activity in d > 1.21 g/ml plasma. CETP activity was very similar in the two groups of normolipidemic subjects considered: adolescents (203 +/- 11 nmol esterified cholesterol transferred per 8 h/ml plasma) and adults (215 +/- 5). Patients were grouped into lipoprotein-lipase (LPL)-deficient and non-LPL-deficient according to their enzyme activity in postheparin plasma. CETP activity was highly increased in LPL-deficient, severe hyperchylomicronemic patients (430 +/- 42) and was directly correlated with VLDL levels in the non-LPL-deficient individuals. Marked differences were observed in the lipid composition of HDL and apolipoprotein A-I levels among patients and controls. In the control group, CETP activity was correlated only with HDL-triglyceride and HDL-triglyceride/apo A-I mass ratio, which is compatible with the physiological role of CETP in transferring triglyceride to HDL from other lipoprotein particles. When all hypertriglyceridemic patients were considered together, CETP activity was inversely correlated with apo A-I and HDL-cholesterol, whereas it was directly correlated with HDL-triglyceride/HDL-cholesterol and HDL-triglyceride/apo A-I mass ratios. The results indicate that the enhanced CETP activity associated with hypertriglyceridemia contributes to the compositional change of HDL, which in turn may be responsible for the reduction of HDL levels in this condition.

Interindividual variation in the partition of lipoprotein(a) into lipoprotein subfractions

In order to evaluate cardiovascular risk, we analyzed the lipid composition of HDL and the presence of lipoprotein(a) [Lp(a)] by both agarose gel electrophoresis and enzyme-linked immunoassay (ELISA). In 681 plasmas we found a close correspondence between the existence of a visible sinking pre-beta lipoprotein band and a concentration of Lp(a) higher than 300 mg/L. In the sinking pre-beta(+) samples, the HDL-cholesterol level obtained by differential ultracentrifugation was significantly higher than that obtained by precipitation with the MgCl2-phosphotungstic acid reagent; and the difference between these HDL-cholesterol values was linearly correlated with plasma Lp(a) concentration. Moreover, the other HDL lipid components and the lipid mass ratios of HDL isolated by ultracentrifugation were significantly different from those of HDL isolated by precipitation, and these changes were also correlated with plasma Lp(a). These differences are attributed to Lp(a) because it was detected in the 1.063-1.21 kg/L plasma fractions, whereas it was absent in the plasma supernates after precipitation with MgCl2-phosphotungstic acid. Although to a lesser extent, Lp(a) was also present in the LDL and VLDL density ranges and it directly depended on both the Lp(a) and the triglyceride plasma concentrations. The proportion of Lp(a) in HDL as related to that in LDL density fractions decreased as Lp(a) plasma levels increased, reflecting an interindividual variation of Lp(a) density species. Since 90% of our study population had detectable Lp(a) in plasma, the results reinforce the concept that the ultracentrifugation method is not equivalent to precipitation in most samples, and the contaminant effect of Lp(a) cannot be predicted because of Lp(a) partition into the different lipoprotein fractions.

Different hydrolytic efficiencies of adipose tissue lipoprotein lipase on very-low-density lipoprotein subfractions separated by heparin-Sepharose chromatography

Human very-low-density lipoproteins (VLDL) were subfractionated by heparin-Sepharose chromatography into an unbound (A) and three bound (B, C and D) populations at increasing ionic strengths. Subfractions were characterized regarding their chemical composition and efficiency of triacylglycerol hydrolysis by rat adipose tissue LPL. The triacylglycerol content decreased, whereas the cholesterol and protein contents increased from subfractions A and B to subfraction D. VLDL-D showed the highest apo E/apo C ratio, though all the subfractions contained appreciable apo E. Appearance of VLDL-A resulted from exceeding the binding capacity of the column, since practically all its particles eluted at positions of bound VLDL under re-chromatography. Subfractions B, C and D stimulated LPL activity on emulsified tri[14C]oleoylglycerol to a similar extent, indicating that their apo C-II content was equally effective activating LPL. Incubation of tri[14C]oleoylglycerol labeled VLDL subfractions with fat pad pieces in the presence or absence of heparin resulted in greater hydrolysis and fatty acid uptake for VLDL-B and -C than for VLDL-D, a pattern observed over a wide range of LPL activities in the media. We conclude: (1) any VLDL particle can interact with heparin, which is consistent with the presence of apo E in all the subfractions, and (2) triacylglycerols in apo E-rich VLDL are less efficiently hydrolyzed by LPL than those in apo E-poor particles. We propose that richness in apo E impairs LPL action upon VLDL and decreases the rate of delivery of fatty acids to peripheral tissues.

Longitudinal study of plasma lipoproteins and hormones during pregnancy in normal and diabetic women

Plasma lipoproteins were studied longitudinally at the 1st, 2nd, and 3rd trimester of gestation and at postpartum and postlactation in 12 age-matched PGDM women, 9 GDM women, and 12 healthy control subjects. FPG and HbA1c were higher in every case in PGDM women than in control subjects, whereas in GDM patients, glucose was augmented only after parturition. FFA and beta-hydroxybutyrate levels were higher in both PGDM and GDM patients than in control subjects during gestation but not after parturition. Total TGs and VLDL, LDL, and HDL TGs increased with gestational time in the three groups and declined at postpartum, and although total cholesterol and VLDL, LDL, and HDL cholesterol followed a similar trend, their rise was less pronounced, and the decline after parturition was slower than that of the TGs in the three groups, with no difference among them. The VLDL TG/cholesterol ratio declined in the three groups at the 3rd gestational trimester, whereas in both LDL and HDL, the TG/cholesterol ratio, but not the cholesterol/phospholipid ratio, increased during gestation in the three groups, indicating a specific enrichment of TGs in these particles. The increase in apoA-I and apoB with gestation was parallel to the respective changes in HDL and LDL cholesterol and, again, no difference was observed between the three groups. Plasma levels of beta-estradiol, progesterone, and prolactin increased sharply with gestation and declined at postpartum in the three groups, but absolute values of beta-estradiol and prolactin, at the three trimesters of gestation, were lower in PGDM patients, but progesterone levels were lower than controls in GDM women only at the 3rd trimester. (ABSTRACT TRUNCATED AT 250 WORDS)

[Serum lipoprotein (a) levels during treatment with LDL apheresis for homozygous familial hypercholesterolemia]

BACKGROUND

Due to the double atherogenic and antifibrinolytic action of lipoprotein (a) (Lp [a]) and its predictive value of cardiovascular disease in hypercholesterolemic patients, we document in the present work the changes in Lp (a) levels of a patient with homozygous familial hypercholesterolemia after one year of LDL-apheresis treatment.

METHODS

A child with LDL-receptor deficiency under weekly LDL-apheresis treatment with dextran-sulfate columns. Serum samples were taken in basal conditions (pre-apheresis) and post-apheresis, as well as from the perfusion system to evaluate the lipoprotein retention capacity of the columns. Samples were processed for Lp (a) determination by ELISA with polyclonal antibodies.

RESULTS

When the treatment was initiated, the patient's Lp (a) serum levels were very high (997 mg/l), and they reduced progressively with the apheresis sessions. After one year of treatment, maximum Lp (a) concentration is only slightly higher than 400 mg/l, whereas minimum Lp (a) concentration is lower than 50 mg/l. Dextran-sulfate columns in the apheresis system retain every lipoprotein containing apo B, including LDL and Lp (a), with high affinity and high capacity in such a way that the treatment of three-fold the plasma volume of the patient results in an 85% decrease of Lp (a) levels. After each LDL-apheresis treatment, there is a progressive increase in Lp (a) concentration. The analysis of these data allowed the estimation of the fractional catabolic rate of Lp (a) in the patient, which was 0.08 pools/day. Simultaneous treatment with lovastatin (20 mg/day) did not alter this parameter or Lp (a) serum concentration.

CONCLUSIONS

After one year of weekly LDL-apheresis treatment, the patient's average Lp (a) serum concentration is lower than 300 mg/l, which is below the risk threshold level. Therefore, apheresis with dextran-sulfate columns is a very effective treatment for the reduction of both LDL and Lp (a) serum concentrations in homozygous familial hypercholesterolemia.