We determined the insulin response to an oral glucose ingestion and levels of serum lipoproteins in 25 untreated patients with type 2 diabetes mellitus, in 26 subjects with impaired glucose tolerance (IGT), and in 35 non-diabetic control subjects. The three groups had similar compositions with respect to age and sex distribution. The levels of VLDL triglyceride in the subjects with type 2 diabetes or IGT were higher than those in controls. Serum HDL- and HDL2 cholesterol were significantly decreased in type 2 diabetics, and the subjects with IGT showed a similar tendency. Serum apolipoprotein A-II levels were lower in the male subjects with type 2 diabetes or IGT than in controls. Insulin response, i.e., sum of immunoreactive insulin (IRI) levels at basal, 30, 60, 90 and 120 min after a 75-g oral glucose load, negatively correlated to HDL- and HDL2 cholesterol levels (r = -0.396, P less than 0.05; r = -0.482, P less than 0.001, respectively), and positively correlated to VLDL triglyceride values (r = 0.485, P less than 0.001) in the male subjects with type 2 diabetes or IGT. In the female subjects, fasting plasma IRI values significantly correlated to HDL cholesterol (r = -0.496, P less than 0.05). There was a significant negative correlation between the concentrations of HDL2 cholesterol and VLDL triglyceride. These data show that lipoprotein metabolism, not only in type 2 diabetics, but also in IGT tends to show changes such as decreased HDL2 cholesterol and increased VLDL triglyceride levels, and which might be related to the hypersecretion of endogenous insulin.

To investigate whether there were associations between the free fatty acid (FFA) response during a fat tolerance test and changes in concentrations of triglyceride-rich lipoproteins 57 healthy Caucasian men between 57 and 70 years of age underwent a fat tolerance test lasting 8 h. FFA concentrations initially decreased from 0.75 +/- 0.03 to 0.64 +/- 0.03 mmol/l at 2 h and thereafter increased to 1.2 +/- 0.04 mmol/l at 8 h. Maximum FFA concentration was the only significant determinant of 8 h triglyceride-rich lipoprotein (TGRLP) concentrations (pooled chylomicron and VLDL fractions d < 1.006) (TGRLP-TG r = 0.33, P = 0.012; TGRLP apo B r = 0.37, P = 0.004; TGRLP cholesterol r = 0.38, P = 0.004). The strength of the association between FFA and TGRLP was affected by the apo B signal peptide genotype. Only in individuals who were homozygous for the 27 amino acid (SP27 or I) allele of the apo B signal peptide were there significant associations between maximum FFA concentration quartile and 8 h TGRLP concentration (P value for linear trend = 0.025). In this genotype group there were lower HDL cholesterol concentrations (1.16 mmol/l compared to 1.38 mmol/l in subjects either heterozygous or homozygous for the SP24 [D] allele; P = 0.005) and there was a trend toward increased 8 h TGRLP concentrations. We propose that the association between post-prandial FFA concentrations and post-prandial TGRLP concentrations in individuals who are homozygous for the SP27 allele may be linked to the increased prevalence of ischemic heart disease (IHD) in this genotypic group.

Moderate hypertriglyceridemia is associated with several abnormalities of the plasma lipoprotein particles and it may be a risk factor for atherosclerotic vascular diseases. Plasma lipid, lipoprotein and apolipoprotein levels, as well as lipoprotein composition and physical properties, were examined by ultracentrifugation in a zonal rotor and by gradient gel electrophoresis in 14 patients with moderate hypertriglyceridemia (plasma triglycerides 4.00 +/- 0.32 mmol/l, mean +/- S.D.) and in 14 control subjects. Based on zonal ultracentrifugation hypertriglyceridemic patients have higher levels of cholesterol in all VLDL subclasses (Sf>> 200, 100-200, 60-100 and 20-60), in IDL and in small and dense LDL. Both HDL2 and HDL3 cholesterol levels are reduced. The LDL flotation rate is inversely related to plasma triglyceride levels, thus indicating that the higher the plasma triglycerides the smaller and/or denser the LDL are. The triglyceride percent content of LDL2 and HDL3 is increased, while that of esterified cholesterol is reduced in hypertriglyceridemic patients. Gradient gel electrophoresis shows that the LDL peak size is lower (25.2 +/- 0.5 nm, mean +/- S.D.) in hypertriglyceridemic than in control subjects (27.1 +/- 0.4 nm; P < 0.0001). Considering both hypertriglyceridemic and control subjects the LDL peak effluent volume from the zonal rotor (which reflects the LDL flotation rate) is inversely related to the LDL peak size determined by gradient gel electrophoresis (r = -0.71; P = 0.0006) and the plasma triglyceride levels are related to LDL peak effluent volume (r = 0.74; P = 0.0002) and to LDL peak size (r = -0.95; P < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

The triglyceride content of the plasma very-low-density lipoprotein (VLDL) fraction is the most important factor affecting the size of low-density lipoprotein (LDL) in humans. Because cholesteryl ester transfer protein (CETP) can influence the size distribution of LDL particles in human plasma, the implication of lipid transfers in the formation of small-sized LDL patterns, which have been associated with elevated plasma triglyceride levels, was investigated. The size distribution of LDL particles in 15 plasma samples was determined by electrophoresis of the plasma LDL fraction on 20 to 160 g/L polyacrylamide gradient gels. The apparent diameter of the major LDL subfraction was shown to correlate negatively with triglyceride concentrations (r = -.706, P < .005) and positively with both high-density lipoprotein cholesterol levels (r = .637, P < .02) and the high-density lipoprotein/VLDL + LDL cholesterol ratio (r = .768, P < .001). In addition, LDL size correlated negatively with both the ability of plasma LDL to donate cholesteryl esters (r = -.79, P < .001) and its ability to acquire triglycerides (r = -.72, P < .005). Whereas these observations indicated that CETP-mediated alterations of the triglyceride/cholesteryl ester ratio of the LDL core would contribute to changes in LDL diameter, they suggested that the formation of small-sized gradient gel LDL patterns would require another biochemical event, such as lipolysis, in addition to neutral lipid transfers. To test this hypothesis, total plasma samples with or without added VLDL (added triglyceride concentration, 2.0 g/L) were preincubated for 24 hours at 37 degrees C. Preincubation mainly induced the replacement of cholesteryl esters by triglycerides in the LDL core, and changes in LDL composition were greater when total plasma was supplemented with VLDL. Subsequently, isolated LDL was incubated in the presence of bovine milk lipoprotein lipase as a source of triglyceride hydrolysis activity. Lipolysis tended to reduce the size of the major LDL subpopulation, and the mean change in LDL diameter was significantly greater when plasma was preincubated with VLDL supplementation than when it was not (-0.6 +/- 0.3 versus -0.2 +/- 0.2 nm, respectively; (P < .01). Moreover, sequential effects of lipid transfer and lipolysis activities induced dramatic changes in the general shape of gradient gel LDL patterns. The largest plasma LDL subpopulations tended to disappear, and the formation of new, small LDL particles could be observed. The combined effects of neutral lipid transfers and triglyceride hydrolysis could account for variations of gradient gel LDL profiles in human plasma.(ABSTRACT TRUNCATED AT 400 WORDS)

Previously we reported that human blood-borne and THP-1 monocyte-macrophages have an apolipoprotein E- and lipoprotein lipase-independent, high affinity, specific binding site for the uptake and degradation of hypertriglyceridemic VLDL and plasma chylomicrons distinct from the LDL receptor gene family and the acetyl LDL receptor (Gianturco et al., J. Lipid Res. 35:1674-1687, 1994). Ligand blot analyses identified two cell-surface, structurally related membrane binding proteins as receptor candidates of M(r) approximately 200 kDa and M(r) approximately 235 kDa which are converted into a single ligand binding species of intermediate mobility upon reduction. We now report a approximately 1200-fold purification of the reduced candidate receptor protein from cultured THP-1 monocytes.

OBJECTIVE

To study size heterogeneity of triglyceride rich lipoproteins (TRL) in metabolic syndrome (MS).

METHODS

Thirty MS patients and 14 healthy subjects were included. In fasting serum we measured: lipid profile, free fatty acids (FFA) and adiponectin; TRL were isolated (d<1.006 g/mL) and analysis by size exclusion HPLC followed by UV detection was performed; each subfraction was expressed as percentage of total TRL.

RESULTS

MS patients, even those with normal triglycerides, presented higher proportion of very large VLDL (90 nm diameter) and large VLDL (60 nm) and slightly lower of typical VLDL (37 nm) (p<0.04); increased FFA (p=0.04) and lower adiponectin (p=0.001). FFA correlated with large VLDL% (r=0.58; p=0.003), independently of insulin-resistance and waist. Furthermore, the lower the adiponectin, the greater the predominance of large VLDL (r=-0.40; p=0.04).

CONCLUSIONS

MS was associated with large VLDL, described as more atherogenic beyond triglyceride levels. Size exclusion HPLC would represent a useful tool for assessing subfractions' lipoprotein profile.

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

A micromethod is described for isolating and quantifying human very-low-density lipoprotein (VLDL) from 0.1 mL of human serum, by which more than 100 samples can be processed in half a day with a standard ultracentrifuge. Replicate analysis of 10 normal and hyperlipemic samples gave median coefficients of variation of 11.7% for VLDL cholesterol, 5.1% for VLDL triglycerides. Results obtained by micro-ultracentrifugation and enzymic cholesterol measurement agreed closely with those measured with an electrophoretic method (Pearson's r = 0.98). Compared with the established method, on the other hand, lower values were found for both VLDL cholesterol (r = 0.89) and triglycerides (r = 0.97).

Thirty postmenopausal women were randomly treated with desogestrel (DG) or levonorgestrel (LN) 125 micrograms/day for 3 weeks. Desogestrel reduced the serum total and free (non-protein bound) testosterone concentrations. It caused a small decrease in the sex hormone binding globulin capacity (SHBG) but did not influence the free testosterone index (testosterone/SHBG ratio). Levonorgestrel, on the other hand, did not influence the free testosterone concentration, but caused a significant increase in the free testosterone index. Levonorgestrel reduced the HDL and particularly the HDL2 cholesterol concentrations (mean change from 1.75 to 1.45 mmol/l for HDL and from 0.73 to 0.50 mmol/l for HDL2, P less than 0.001). It also caused a reduction in the VLDL triglyceride (P less than 0.05) but not the total serum triglyceride concentration. Desogestrel did not cause any significant changes in HDL or HDL2 cholesterol concentrations, but it reduced the VLDL triglyceride (P less than 0.01) and total serum (P less than 0.05) triglyceride concentrations. Neither of the two progestins influenced the postheparin plasma lipoprotein lipase (LPL) activity or the serum cholesterol esterification rate by lecithin:cholesterol acyltransferase (LCAT). It is therefore possible that both steroids decreased the hepatic output of triglycerides, which may be clinically important since both progestins are used in combination with ethinylestradiol (EE) which increases the hepatic TG synthesis. The failure of desogestrel to change HDL levels is consistent with earlier data on the lack of effects on HDL by non-androgenic progestins. Levonorgestrel increased the mean activity of postheparin plasma hepatic lipase (HL) from 23.3 to 28.0 mumol X h-1 X ml-1 (P less than 0.05). In contrast, this activity was not influenced by desogestrel. The magnitude of the changes in postheparin plasma HL activity and the free testosterone index (testosterone/SHBG ratio) showed significant positive correlation (+ 0.41, P less than 0.05). On the other hand, the changes in the HDL2 cholesterol and the postheparin plasma HL activity were inversely interrelated (r = 0.52, P less than 0.01). These relationships are consistent with the idea that the effects of different progestins on the HDL cholesterol are mediated by the sex steroid sensitive hepatic endothelial lipase.

Data from cellular systems and transgenic animal models suggest a role of apolipoprotein (apo) A-II in the regulation of very low-density lipoprotein (VLDL) metabolism. However, the precise mechanism whereby apoA-II regulates VLDL metabolism remains to be elucidated in humans. In this study, we examined the associations between the kinetics of high-density lipoprotein (HDL)-apoA-II and VLDL-apoB-100 kinetics, and plasma adiponectin concentrations. The kinetics of HDL-apoA-II and VLDL-apoB-100 were measured in 37 nonobese men using stable isotope techniques. Plasma adiponectin concentration was measured using immunoassays. Total plasma apoA-II concentration was positively associated with HDL-apoA-II production rate (PR) (r = 0.734, P < .01); both were positively associated with plasma triglyceride concentration (r = 0.360 and 0.369, respectively) and VLDL-apoB-100 PR (r = 0.406 and 0.427, respectively), and inversely associated with plasma adiponectin concentration (r = -0.449 and -0.375, respectively). Plasma adiponectin was inversely associated with plasma triglyceride concentration (r = -0.327), VLDL-apoB-100 concentration (r = -0.337), and VLDL-apoB-100 PR (r = -0.373). In multiple regression models including waist circumference and plasma insulin, plasma adiponectin concentration was an independent determinant of total plasma apoA-II concentration (β-coefficient = -0.508, P = .001) and HDL-apoA-II PR (β-coefficient = -0.374, P = .03). Conversely, total plasma apoA-II concentration (β-coefficient = 0.348, P = .047) and HDL-apoA-II PR (β-coefficient = -0.350, P = .035) were both independent determinants of VLDL-apoB-100 PR. However, these associations were not independent of plasma adiponectin. Variation in HDL apoA-II production, and hence total plasma apoA-II concentration, may exert a major effect on VLDL-apoB-100 production. Plasma adiponectin may also contribute to the variation in VLDL-apoB-100 production partly by regulating apoA-II transport.

We examined 18 Type 2 diabetic and 19 non-diabetic subjects in order to determine the association between insulin resistance and LDL particle size distribution in mildly hypertriglyceridemic and hyperinsulinemic subjects with and without Type 2 diabetes. Insulin sensitivity of the patients was characterized by their insulin-stimulated glucose uptake rate determined by euglycemic clamp technique. LDL particle size distribution was determined by nondenaturing polyacrylamide gradient gel electrophoresis. Type 2 diabetic and non-diabetic subjects had closely similar serum lipid and lipoprotein concentrations as well as the mean particle diameters of the major LDL peak (246 +/- 6 A and 244 +/- 6 A, respectively). To evaluate the effect of insulin resistance on LDL particle size the participants were categorized into two subgroups using the median of their insulin-stimulated glucose uptake rate (14.67 mumol/kg/min) as a cut-off point. Neither lipid and lipoprotein concentrations nor the LDL particle size distributions differed between the more insulin resistant group (nine diabetic and nine non-diabetic subjects) and less insulin resistant group (nine diabetic and ten non-diabetic subjects). LDL particle size was not associated with the insulin-stimulated glucose uptake rate or with the mean 24-h concentration of serum insulin. Mean 24-h concentration of serum triglycerides was the strongest discriminator for LDL particle size (r = -0.44, P < 0.01). In conclusion, neither Type 2 diabetes nor insulin resistance seem to have any direct effect on LDL particle size in mildly hypertriglyceridemic subjects. The fact that LDL particle size was associated with serum triglycerides indicates that the effect of diabetes and insulin resistance on LDL particle size could be explained by the effects of insulin resistance and/or hyperinsulinism on VLDL metabolism.

A new method was used for selective measurement of lipoprotein lipase and hepatic lipase in human postheparin plasma. Hepatic lipase was assayed in 1.0 M NaCl withour addition of serum, and the activity of lipoprotein lipase was determined in 0.1 M NaCl after immunoprecipitation of hepatic lipase with specific antiserum. The activity of both these enzymes and the total lipolytic activity were measured in plasma samples taken during a 4-h infusion of heparin. Each of the activities was related to basal serum triglyceride concentration and to the fractional removal constant (K) of Intralipid in 13 obese subjects before and after prolonged fasting. During a normal isocaloric diet the lipolytic activities showed a biphasic response to heparin infusion in all subjects. A peak activity was reached within 30 minutes ("early response") and thereafter the lipase activities decreased to a constant level maintained during the rest of the heparin infusion ("late response"). The early response of lipoprotein lipase showed a significant inverse correlation with the basal serum triglyceride level (r = -0.85) and a significant positive correlation with the fractional removal rate of Intralipid (r = 0.84). The late response of lipoprotein lipase was not related to either of these parameters. The early response of hepatic lipase was not correlated with basal triglyceride concentration or Intralipid removal, whereas the late response of this enzyme showed a significant negative correlation with the removal rate of Intralipid (r = -0.82). After fasting for several days the acute response of all lipolytic activities to heparin was markedly decreased or totally abolished, but the magnitude of the late response was similar to that seen in the fed state. The fractional removal rate of Intralipid was slightly increased by starvation. All correlations between postheparin plasma lipases and serum triglyceride concentration and removal disappeared in fasting subjects. It is concluded that the rapidly releasable lipoprotein lipase probably reflects the activity of the tissue enzyme(s) which is responsible for the primary removal of very low density lipoprotein (VLDL) triglycerides and chylomicrons. It is probable that this component of the postheparin plasma lipolytic activity is derived from the endothelial lipoprotein lipase pool. This enzyme plays a key role in the efflux of plasma triglycerides under normal conditions, and it is thus one determinant of plasma triglyceride level. Prolonged fasting obviously changes the triglyceride removal sites and mechanism but does not impair the removal efficiency.

We observed the appearance of two intermediate density lipoprotein (IDL) subfractions on gradient gel electrophoresis of lipoproteins in the density range 1.006-1.030 g/ml and estimated their approximate concentrations in plasma in subjects with a wide range of lipid levels, from 0.55 to 28.0 mmol/l plasma triglyceride and 3.75-10.0 mmol/l cholesterol. The larger species, IDL-I (31.7 +/- 0.7 nm, mean +/- SD), showed little variation in size in normal and moderate hyperlipidaemic individuals. The estimated concentration of IDL-I was positively related to plasma triglyceride (r = 0.63, P = 0.0004) and low density lipoprotein (LDL) cholesterol (r = 0.68, P = 0.0003). These findings are consistent with the view that IDL-I is a metabolic intermediate between very low density lipoprotein (VLDL) and LDL. The smaller subfraction, IDL-II (25.7 +/- 2.4 nm) was virtually the only true species observed in subjects with plasma triglyceride < 1.0 mmol/l and its estimated concentration fell as plasma triglyceride increased (r = -0.58, P = 0.0002). IDL-II particle size changed in concert with LDL particle size (r = 0.61, P < 0.0001), suggesting that they were influenced by common metabolic factors. These observations provide further support for the hypothesis outlined by Musliner et al. [1] that IDL-I was part of the delipidation chain from VLDL to LDL, whereas IDL-II arose from a separate source, possibly directly released from the liver. Hence the two subpopulations of IDL differ in their relationship to plasma triglyceride and cholesterol levels.

A method is described for the selective precipitation of VLDL in blood serum using phosphotungstic acid/MgCl2. The method allows for the calculation of LDL apolipoprotein B as well as for the calculation of LDL cholesterol (following the additional determination of HDL cholesterol). Dependent on the triglyceride and the cholesterol content of the serum, three different procedures were developed using phosphotungstic acid and MgCl2 in different concentrations in the precipitation assay. Within the tested range of 3-10 mmol/l total cholesterol and 1-4 mmol/l triglyceride in blood serum the VLDL were nearly completely precipitated with negligible coprecipitation of LDL and HDL, but 40-50% coprecipitation of Lp(a). Regression analysis of the cholesterol values obtained by precipitation with phosphotungstic acid/MgCl2 (= serum cholesterol - LDL cholesterol), and the cholesterol values obtained by ultracentrifugation (d greater than 1.006 kg/l) revealed a good measure of agreement (r = 0.97, y = 0.93 X + 0.35, n = 76). An equally good measure of agreement was found for the corresponding apolipoprotein B values (r = 0.96, y = 1.03 X - 0.2, n = 61). In the determination of LDL cholesterol a variation coefficient of 4.3% (n = 20) was found in relation to the precision in the series, and a variation coefficient of 4.8% (n = 25) in relation to day to day precision.

As compared to 7 normolipidemic donors, the maximal velocity of sodium-lithium countertransport was accelerated by nearly 70% in 10 patients with elevated levels of triglyceride-rich lipoproteins and tended to be stimulated also in 5 patients with hypercholesterolemia. No significant differences were observed between normolipidemia and both hyperlipidemic groups for the apparent affinities of the transport system for intracellular sodium and extracellular lithium. Strong positive relations of the maximal activity of sodium-lithium countertransport to the percentages of red cell membrane phosphatidylcholine (r = 0.85, 2P < 0.001), the phosphatidylcholine/sphingomyelin (r = 0.82, 2P < 0.001) and the phosphatidylcholine/phosphatidylethanolamine ratio (r = 0.81, 2P < 0.001) were seen in all donors. A negative correlation was found to membrane sphingomyelin (r = -0.72, 2P < 0.001). Also plasma phosphatidylcholine and sphingomyelin exhibited positive and negative associations, respectively, to the maximal activity of sodium-lithium countertransport (r = 0.66, 2P < 0.01 and r = -0.78, 2P < 0.001). Among several plasma lipoprotein parameters investigated, total triglycerides or VLDL cholesterol levels showed independent relations to both the plasma and the membrane phosphatidylcholine/sphingomyelin ratio as well as to the maximal velocity of sodium-lithium countertransport. The results indicate that an increase in red cell membrane phosphatidylcholine and a concomitant fall in sphingomyelin are closely associated with the acceleration of sodium-lithium countertransport in hyperlipidemia.

OBJECTIVE

Insulin resistance plays a crucial role in the pathogenesis of type 2 diabetes and cardiovascular diseases. Recently, paraoxonase-1(PON1) is reported to have an ability to reduce insulin resistance by promoting glucose transporter-4 (GLUT-4) expression in vitro. Single nucleotide polymorphism (SNP) in PON1 is associated with variability in enzyme activity and concentration. Based on this we aimed to investigate the association of PON1 (Q192R and L55M) polymorphisms with the risk of developing insulin resistance in adult South Indian population.

METHODS

Two hundred and eighty seven (287) Type 2 diabetes patients and 293 healthy controls were enrolled in this study. All the study subjects were genotyped for PON1 (Q192R and L55M) missense polymorphisms using polymerase chain reaction-restriction fragment length polymorphism (PCRRFLP) method. Fasting serum insulin level was measured by ELISA.

RESULTS

The distribution of QR/RR and LM/MM genotypes were significantly higher in type 2 diabetes patients compared with healthy controls. Moreover, the R and M alleles were significantly associated with type 2 diabetes with an Odds Ratio of 1.68 (P < 0.005) and 2.24 (P < 0.005) respectively. SNP 192 Q>> R genotypes were found to be significantly associated with higher BMI, cholesterol, triglycerides, LDL, fasting serum insulin and HOMA-IR. Further, the mutant allele or genotypes of PON1 L55M were associated with higher BMI, triglycerides, VLDL, fasting serum insulin and HOMA-IR among adult type 2 diabetes patients.

CONCLUSIONS

PON1 (Q192R and L55M) polymorphisms may play a crucial role in pathogenesis and susceptibility of insulin resistance thus leads to the development of type 2 diabetes in South Indian population.

The intravenous fat tolerance test (IVFTT) has been introduced as a measure of the fractional catabolic rate of the endogenous triglyceride of plasma. To assess the validity of this test we have compared this test in 21 normal and hyperlipidaemic subjects with direct measurement of the fractional catabolic rate of autologous radio-iodinated VLDL. There was a strong positive correlation between the rate constant K2 of the IVFTT and the fractional catabolic rate of VLDL-apolipoprotein B (r=+0.87). The two rates were considerably different in magnitude. The IVFTT appears to be a valid index of the fractional catabolic rate of VLDL. Its limitations and uses are discussed.

Cord blood from 73 full term healthy newborns and blood from adults were analysed for the protein content of high density lipoprotein subclasses separated by gradient gel electrophoresis. Cholesterol and triglyceride concentrations of very low (VLDL), low (LDL) and high (HDL) density lipoproteins were also analysed and newborns had lower concentrations of cholesterol and triglycerides in VLDL, LDL and HDL (p less than 0.001) than adults. The HDL3c subclass, comprising the smallest particles of the HDL particle spectrum, was the major component for newborns and the minor one for adults and was the only lipoprotein fraction with a higher concentration in cord than in adult blood. No sex differences were present for any of the lipoprotein levels of the newborns. Serum cholesterol concentrations were positively correlated to HDL2b (r = 0.49, p less than 0.001) and HDL2a levels (0.42, p less than 0.001), correlations confined to the cholesterol contents of HDL (r = 0.72 and r = 0.67 respectively, both p less than 0.001). Serum triglycerides were inversely correlated to HDL2b and HDL2a levels in male newborns only (r = 0.38 and r = 0.34 respectively, both p less than 0.05). Irrespective of sex, gestational age and birthweight the newborns had 2 typical HDL subclass distributions, characterized by high or low levels of HDL2b and HDL2a. The newborns with high HDL2b and HDL2a levels also had low VLDL lipid levels and high HDL cholesterol concentrations.

The regulation of plasma high-density lipoprotein (HDL) cholesterol level by the joint influence of plasma lipoprotein lipids, lipoprotein lipase (LPL), hepatic lipase (HL), cholesteryl ester transfer protein (CETP), oral glucose tolerance, and postload plasma insulin and proinsulin levels was investigated in young postinfarction patients and healthy population-based control subjects. In addition, the association between HDL cholesterol and the number and severity of coronary stenoses previously reported in this cohort of young postinfarction patients was further investigated by analyzing the determinants and angiographic relations of HDL subclasses measured by gradient gel electrophoresis. The following parameters showed significant univariate relations with HDL cholesterol level in the patient group: very-low-density lipoprotein (VLDL) cholesterol and triglyceride, low-density lipoprotein (LDL) triglyceride, and postload plasma insulin concentrations, preheparin plasma LPL mass, and postheparin plasma HL activity. In the control group, significant correlations with HDL cholesterol concentration in addition to those noted among the patients were found for body mass index (BMI), LDL cholesterol level, postload plasma intact proinsulin concentration, and LPL activity in postheparin plasma. In contrast to the patients, no significant relations were noted for postload plasma insulin level and preheparin plasma LPL mass. Multiple stepwise regression analysis showed that 42% of the variability of HDL cholesterol in the patients could be accounted for by VLDL cholesterol concentration (29%), LDL triglyceride level (7%), and postheparin plasma HL activity (8%), whereas the corresponding figure in controls was 35% (VLDL cholesterol concentration [9%] and postheparin plasma HL activity [26%]. The strength of the relationships of HDL cholesterol and HDL subclasses to the coronary stenosis score was similar and statistically significant (r = .25 to .36). When the metabolic parameters that correlated with HDL cholesterol and HDL subclass concentrations in univariate analysis were used as covariates, all relations to the coronary stenosis score disappeared. This clearly indicates that the influence of triglyceride-rich lipoproteins and lipolytic enzymes needs to be considered when assessing the association between HDL cholesterol and coronary artery disease (CAD).

The role of endogenous estrogens and androgens and their potential interaction in atherosclerosis is not well understood. Therefore, we investigated the effects of natural menopause and endogenous sex steroids on triglycerides (TG), a major risk factor for cardiovascular disease in women. Fasting lipid and lipoprotein concentrations, postheparin lipase activities, kinetic indicators of triglyceride lipolysis, and various hormone levels, including dehydroepiandrostenedione-sulfate (DHEA-S), (bioavailable) testosterone, and androstenedione, were determined in 18 premenopausal and 18 postmenopausal women, matched for age and body composition. Fasting plasma TG were 0.69 +/- 0.29 mmol/L in postmenopausal women and 0.73 +/- 0.33 mmol/L in premenopausal women (difference not significant [NS]). Approximately 30% of all plasma TG were present in the very-low-density lipoproteins (VLDLs) in both groups. No differences were found between groups in plasma lipolytic potential of TG-rich lipoproteins. Univariate analysis revealed that VLDL-TG concentrations were strongly related to insulin (r = 0.84, P =.0001) and androstenedione (r = 0.65, P =.004) in postmenopausal women. Multivariate analysis of potential determinants of VLDL-TG showed that insulin, androstenedione, and bioavailable testosterone were independent variables, explaining 87% of the variability (r = 0.93, P =.0001) in postmenopausal women. In contrast, in premenopausal women, the only identified predictor of fasting VLDL-TG in univariate and multivariate analysis was insulin (r = 0.72, P =.001). Our results show that the association of androgens with TG varied depending on androgen concentrations, the relative androgenic potential, and most importantly on hormonal milieu. Endogenous androgens were only related to plasma VLDL-TG in the estrogen-deficient state.

Some hemorheological parameters constitute risk factors for ischemic cardiovascular events. Most of these hemorheological factors are determined by the erythrocyte intrinsic properties and the high molecular weight plasmatic proteins, especially fibrinogen. The contribution of the plasmatic lipids to hemorheological factors is not well established. With this aim we determined hemorheological parameters in 112 healthy volunteers (62 males, 50 females) aged 35+/-10 years, range 19-54 years, members of our hospital staff. A complete set of rheological test was performed. Blood viscosity (BV) 230 sec(-1), plasma viscosity (PV), erythrocyte aggregation index (EAI), erythrocyte elongation index (EEI), hematocrit and fibrinogen. We also determined plasmatic lipids including total cholesterol (T-Ch) and its fractions (HDL-Ch, LDL-Ch, VLDL-Ch), triglycerides, lipoproteins (Apo B, Apo A(1), B/A(1)). Exclusion criteria were concomitant cardiovascular risk factors or any other associated pathology. Our results show a positive correlation between BV 230 sec(-1) and triglycerides (r=0.335) and negative with HDL-Ch (r=-0.451) (p=0.01), respectively; PV shows a positive correlation with T-Ch (r=0.297), LDL-Ch (r=0.298) and Apo B/A (r=0.290) (p=0.01). The EEI was negatively correlated with TG (p=0.05). Of all the rheological parameters evaluated, EAI is the factor which shows the highest significant correlation with plasmatic lipids: T-Ch (r=0.515), TG (r=0.303), LDL-Ch (r=0.507) and Apo B/A ratio (r=0.403); (p=0.01). These results suggest that plasmatic lipids contribute to modulate the blood rheological properties, slowing blood flow, favouring the development of atherothrombotics events, especially in stenotic areas or bifurcations in the vascular tree.

OBJECTIVE

Little is known about the associations of serum fatty acids with lipoprotein profile and the underlying genetic and environmental etiology of these relationships. We aimed to analyze the phenotypic association of serum n-6 and n-3 polyunsaturated (PUFAs), monounsaturated (MUFAs) and saturated (SFAs) fatty acids (relative proportion to total fatty acids) with lipids and lipoproteins, and to quantify common genetic and environmental factors determining their covariation.

METHODS

Two cohorts of healthy Finnish twins were assessed in young adulthood. Data were available for 1269 individual twins including 561 complete pairs. Serum metabolites were measured by nuclear magnetic resonance spectroscopy. Bivariate quantitative genetic models were used to decompose the phenotypic covariance between the pairs of traits into genetic and environmental components.

RESULTS

Among the strongest correlations observed, serum total n-6 PUFAs and linoleic acid were inversely (max. r=-0.65) and MUFAs positively (max. r=0.63) correlated with triglycerides and very low-density lipoprotein (VLDL) particle concentration, particularly with large VLDL (for n-6 PUFAs) and medium VLDL (for MUFAs). Genetic factors significantly contributed to their covariance with bivariate heritability estimates ranging from 44% to 56% for n-6 PUFAs and 58% to 66% for MUFAs. Genetic correlations with lipid traits were moderate to high (max. rA=-0.59 and 0.70 for n-6 PUFAs and MUFAs, respectively). Statistically significant, but substantially weaker phenotypic correlations of total n-3 PUFAs, docosahexaenoic acid (DHA) and SFAs with lipoprotein profile were not decomposed into their genetic and environmental components.

CONCLUSIONS

Shared genetic factors are important in explaining why higher concentrations of serum n-6 PUFAs and lower concentrations of serum MUFAs strongly associate with lower triglyceride and VLDL particle concentrations.

OBJECTIVE

The studies were carried out on 36 growing albino Wistar rats. PARTICIPANTS/MEASUREMENTS: The animals were randomly divided into six equinumerous groups (six rats per group), and were fed six different diets for 42 days. The control group (I) was fed with AIN-93G semi-synthetic diet, whereas groups II-VI were fed with AIN-93G semi-synthetic diet supplemented with: 2, 4, 8, 16 and 32 g of methionine/kg diet, respectively. There were assessed enzymatically, in rats' blood serum, the contents of homocysteine, total cholesterol, HDL fraction and triacyloglicerols. In addition, the LDL+VLDL cholesterol content was calculated.

RESULTS

The methionine content of the diet was found to be highly positively correlated with the homocysteine content (r = 0.981) and negatively correlated with the triacylglycerols content (r = -0.916) of the experimental animals' blood serum.

CONCLUSIONS

In the blood serum of rats fed the highest-methionine diet (32 g methionine/kg diet), the homocysteine content was significantly higher, as were the levels of total cholesterol and its HDL fraction, while the triacylglycerols content was lower as compared to the values obtained for rats fed other diet types.

Dysregulated VLDL-TAG (very-low-density lipoprotein triacylglycerol) metabolism in obesity may account for hypertriacylglycerolaemia and increased cardiovascular disease. ω-3 FAEEs (omega-3 fatty acid ethyl esters) decrease plasma TAG and VLDL concentrations, but the mechanisms are not fully understood. In the present study, we carried out a 6-week randomized, placebo-controlled study to examine the effect of high-dose ω-3 FAEE supplementation (3.2 g/day) on the metabolism of VLDL-TAG in obese men using intravenous administration of d5-glycerol. We also explored the relationship of VLDL-TAG kinetics with the metabolism of VLDL-apo (apolipoprotein) B-100 and HDL (high-density lipoprotein)-apoA-I. VLDL-TAG isotopic enrichment was measured using gas chromatography-mass spectrometry. Kinetic parameters were derived using a multicompartmental model. Compared with placebo, ω-3 FAEE supplementation significantly lowered plasma concentrations of total (-14%, P<0.05) and VLDL-TAG (-32%, P<0.05), as well as hepatic secretion of VLDL-TAG (-32%, P<0.03). The FCR (fractional catabolic rate) of VLDL-TAG was not altered by ω-3 FAEEs. There was a significant association between the change in secretion rates of VLDL-TAG and VLDL-apoB-100 (r=0.706, P<0.05). However, the change in VLDL-TAG secretion rate was not associated with change in HDL-apoA-I FCR (r=0.139, P>0.05). Our results suggest that the TAG-lowering effect of ω-3 FAEEs is associated with the decreased VLDL-TAG secretion rate and hence lower plasma VLDL-TAG concentration in obesity. The changes in VLDL-TAG and apoB-100 kinetics are closely coupled.