Accelerated cholesteryl ester transfer in patients with insulin-dependent diabetes mellitus

High prevalence of small LDL particles in non-insulin-dependent diabetic patients with nephropathy

To determine whether small-sized low density lipoprotein (LDL) is associated with a high incidence of coronary heart disease in diabetic nephropathy, we measured the LDL particle size in non-insulin-dependent diabetes mellitus (NIDDM) patients with various degrees of albuminuria (n = 95) and age-, weight-matched non-diabetic control subjects (n = 31). The diabetic subjects were divided into three groups, normoalbuminuric, microalbuminuric and macroalbuminuric NIDDM, based on the amount of albuminuria. The average diameter of LDL particles was determined by non-denaturing polyacrylamide gradient (2-16%) gel electrophoresis. The plasma lipid and lipoprotein concentrations were comparable between the non-diabetic controls and normoalbuminuric NIDDM, whereas the plasma triglyceride, very-low-density lipoprotein (VLDL) or LDL concentration was significantly increased in diabetic nephropathy. The mean LDL particle size was significantly smaller in microalbuminuric NIDDM compared with the controls or normoalbuminuric NIDDM, and the LDL size was further decreased in macroalbuminuric NIDDM. The incidence of small LDL (diameter < 255 A) was remarkably increased in microalbuminuric (58%) and macroalbuminuric NIDDM (67%) compared to the control (13%) and normoalbuminuric NIDDM (27%). Corresponding to the decreased LDL size, the cholesterol content of the LDL was significantly depleted in NIDDM with nephropathy. The high prevalence of small LDL in diabetic nephropathy was also observed even when hypertriglyceridemic or hypertensive subjects were excluded from each group. The increment in triglyceride-rich lipoprotein (d < 1.006) after oral fat-loading was increased, and postheparin lipoprotein lipase activity was decreased significantly in diabetic nephropathy. These abnormalities were significantly associated with LDL particle size. Multivariate regression analysis revealed that the amount of albuminuria was closely associated with the average LDL particle size, and this association was independent of the plasma triglyceride level. Neither insulin resistance nor glycemic control was directly associated with LDL particle diameter. The present study indicates that LDL particles become smaller in diabetic nephropathy, and this may be associated primarily with abnormal triglyceride metabolism. However, in addition to hypertriglyceridemia, other metabolic abnormalities caused by diabetic nephropathy may also be involved in the pathogenesis of small LDL particles.

Alterations in composition and concentration of lipoproteins and elevated cholesteryl ester transfer in non-insulin-dependent diabetes mellitus (NIDDM)

Cholesteryl esters (CE) exchange between lipoproteins through the action of cholesteryl ester transfer protein (CETP). Situations at high risk for atherosclerosis are often accompanied by an accelerated net mass CE transfer (CET) from high density lipoproteins (HDL) to very low (VLDL) and low density lipoproteins (LDL). However, the question as to whether the net mass CET is increased or decreased in non-insulin-dependent diabetes mellitus (NIDDM) has led to controversial data. To clarify this point, we have undertaken a detailed study of CET in 105 NIDDM patients by comparison with 17 control subjects. Net mass CET was approximately doubled in NIDDM. Plasma CETP activity and unidirectional CET from HDL to VLDL + LDL (CETHDL-->VLDL + LDL) or from VLDL + LDL to HDL (CETVLDL + LDL-->HDL) were measured under controlled lipoprotein concentrations using radioisotopic assays. No difference was observed in plasma CETP activity between NIDDM and controls. In NIDDM, CETHDL-->VLDL + LDL and CETVLDL + LDL-->HDL were decreased by 25% and 20%, respectively, as a consequence of alterations in lipoprotein compositions. Net mass CET was highly correlated with plasma triglyceride (TG) concentration (r = 0.66, P < 0.001) but not with that of LDL-cholesterol (r = 0.06, P > 0.6). When TG levels were decreased following dietetic recommendations or insulinotherapy, the net mass CET was lowered accordingly. We conclude that net mass CET is accelerated in NIDDM in spite of a decreased unidirectional CETHDL-->VLDL + LDL. This results from a lowered CETVLDL + LDL-->HDL and from elevated TG concentration, and the latter probably reflects a concentration effect of VLDL.

Marine lipids normalize cholesteryl ester transfer in IDDM

Patients with insulin-dependent diabetes mellitus (IDDM) have a pathological increase in cholesteryl ester transfer (CET) that enriches the apolipoprotein B-containing lipoproteins with cholesteryl ester and increases their atherogenicity. Since we have shown earlier that omega-3 (n-3) fatty acids present in marine lipids normalize both CET and lipoprotein composition in non-diabetic patients with hypercholesterolaemia, we sought to determine whether the same beneficial effects could be achieved in nine normolipidaemic (triglycerides 1.10; cholesterol 4.94, high density lipoprotein 1.10 mmol/l) IDDM patients (fructosamine 424 +/- 156; normal 174-286 mumol/l) treated for 2 months with n-3 fatty acids (4.6 g/day). Before treatment, CET measured by both mass and isotopic assays was abnormally accelerated (p < 0.001). While marine lipids modestly decreased triglyceride levels (-14%; p < 0.05 ), CET fell dramatically in all subjects (mass assay: -97% at 1 h; isotopic assay: -58%; p < 0.001) to below control levels with no change in glycaemic control (fructosamine 408 +/- 103 mumol/l). The mass of cholesteryl ester transfer protein paradoxically increased significantly (pre-treatment: 2.04 +/- 0.86 vs post-treatment 2.48 +/- 0.97 micrograms/ml; p < 0.05). Since it is believed that accelerated CET promotes the formation of atherogenic cholesteryl ester-enriched apo B-containing lipoproteins, the capacity of marine lipids to reverse this functional abnormality without altering glycaemic control suggests that these agents may have an adjunctive role to play in the nutritional therapy of IDDM.

Postprandial cholesteryl ester transfer and high density lipoprotein composition in normotriglyceridemic non-insulin-dependent diabetic patients

Altered postprandial HDL metabolism is a possible cause of defective reverse cholesterol transport and increased cardiovascular risk in diabetic patients with a normal fasting lipoprotein profile. Ten normolipidemic, normoponderal non-insulin dependent diabetes mellitus (NIDDM) patients and seven controls received a 980 kcal meal containing 78 g lipids with 100 000 IU vitamin A. Chylomicron clearance was not different, but area under the curve (AUC) for retinyl palmitate in chylimicron-free serum (remnant clearance) was greater in patients (P < 0.02). LCAT activity increased postprandially to the same extent in both groups. In control subjects, cholesteryl ester transfer protein (CETP) activity (CETA) also increased by 20% (P < 0.01 at 6 h) in parallel with a 20% decrease in HDL2-CE (r = -0.55, P = 0.009). In NIDDM patients, on the contrary, CETA which was 35% higher in the fasting state (P < 0.005), decreased postprandially yet HDL2-CE remained unchanged. Postprandial HDL3 of controls were enriched with phospholipid (PL) (30.3 +/- 2.6% at 6 h) with respect to fasting (25.6 +/- 2.5%, P < 0.01) and to NIDDM-HDL3 (25.8 +/- 1.7% at 6 h, P < 0.01). These results show that variation in plasma CETA has little impact on HDL2-CE in NIDDH subjects. They support the concept that, in controls, the combined enrichment of HDL3 with PL, increased LCAT and CETA create the conditions for stimulation of cell cholesterol efflux and CE transfer to apo B lipoproteins. In NIDDM, because of the lesser HDL3 enrichment with PL and of the inverse trend of CETA, these conditions fail to occur, depriving the patients of a potentially efficient mechanism of unesterified cholesterol (UC) clearance, despite their strictly normal preprandial profile.

Ethanol-induced redistribution of cholesteryl ester transfer protein (CETP) between lipoproteins

Since alcohol drinking reduces the concentration and activity of plasma cholesteryl ester transfer protein (CETP), we investigated the effects of alcohol on its synthesis and secretion by perfusing rabbit livers for 4 hours in the absence or presence of ethanol. The quantity of CETP mRNA in the perfused livers did not differ between the control and ethanol (25 mmol/L or 50 mmol/L) perfusions. CETP activity was determined by incubating [3H]cholesteryl ester-labeled human LDL and unlabeled human HDL with the perfusion medium after removing the endogenous VLDL (secreted by the perfused liver) by ultracentrifugation. CETP activity in the perfusion medium increased at a linear rate that was not affected by ethanol. When the VLDL was removed by precipitation with polyethylene glycol or a heparin-Sepharose column instead of ultracentrifugation, practically no CETP activity was detected in the ethanol perfusions, whereas these procedures did not affect CETP activity in the control perfusions. Inhibition of ethanol oxidation by 4-methylpyrazole resulted in CETP activity similar to that of the controls. We conclude that ethanol does not affect the synthesis or secretion of CETP, but its oxidation may alter the distribution of CETP in lipoproteins. CETP seems to be present in VLDL as well as in HDL, and since VLDL is more rapidly catabolized with HDL, this may explain the low plasma CETP concentration associated with alcohol consumption.

Changes in high density lipoprotein subfraction lipids during neutral lipid transfer in healthy subjects and in patients with insulin-dependent diabetes mellitus

While it is known that the transfer of cholesteryl ester (CE) from high density lipoprotein (HDL) to the apo B-containing lipoproteins is increased in patients with diabetes, the extent to which the various lipoprotein fractions engage in neutral lipid exchange and the magnitude to which triglyceride (TG) is translocated is not known. To examine in greater detail neutral lipid net mass transfer in diabetes, the HDL subfractions and the apo B-containing lipoproteins were separated, and the net mass transfer of CE and TG was compared to that of control subjects. In both groups, bidirectional transfer of CE from HDL3 to very low density lipoprotein (VLDL) + low density lipoprotein (LDL) and of TG from VLDL + LDL to HDL3, took place, but this process was significantly greater (P < .01) in insulin-dependent diabetes mellitus (IDDM). In contrast, CE and TG accumulated in HDL2 to a similar degree in normal and IDDM subjects. In recombination experiments with each of the apo B-containing lipoproteins, IDDM VLDL had a greater capacity to facilitate the exchange of core lipids from both IDDM and control HDL3: on the other hand, LDL from IDDM and control subjects both donated TG and CE to HDL2 and affected little change in HDL3. These findings indicate that all the major plasma fractions normally participate in the trafficking of CE and TG among the lipoproteins during neutral lipid transfer and show that the principal perturbation in cholesteryl ester transfer in IDDM involves altered interaction between VLDL and the HDL3 subfraction.

Intraperitoneal insulin therapy corrects abnormalities in cholesteryl ester transfer and lipoprotein lipase activities in insulin-dependent diabetes mellitus

Patients with insulin-dependent diabetes mellitus (IDDM) have proatherogenic disturbances in cholesteryl ester transfer (CET) despite intensive subcutaneous insulin therapy (ISC). Since CET is activated by insulin-sensitive lipoprotein lipase (LPL), which normally increases postprandially, we queried whether iatrogenic hyperinsulinism from ISC stimulated LPL and CET by studying well-controlled IDDM patients after ISC and then 6 months after lowering systemic insulin levels by intraperitoneal (IP) insulin delivery. Although glycemic control (HbA1c IDDM, 6.9 +/- 1.7%; control, 4.5% to 8%) was excellent during ISC, CET was accelerated (P < .001) and both systemic insulin levels and LPL specific activity were increased (P < .05). Following IP, basal systemic insulin levels declined by more than one half (ISC, 8.22 +/- 6.5 versus IP, 2.77 +/- 2.4 microU/mL; mean +/- SD; P < .025), and both LPL and CET activities returned to normal. Plasma triglyceride, cholesterol, high-density lipoprotein-2 (HDL2) cholesterol, HDL3 cholesterol, cholesteryl ester transfer protein mass, and glycemic control (HbA1c, 6.3 +/- 0.8%) were unchanged and remained normal. These findings indicate that ISC is associated with high levels of basal CET and LPL. These alterations both appear to be closely linked to iatrogenic hyperinsulinemia resulting from ISC. The fact that they are both reversed when systemic insulin levels are reduced by IP suggests that insulin, acting through LPL, influences the nature of the interaction of the lipoproteins engaged in CET.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma cholesteryl ester transfer in patients with non-insulin dependent diabetes mellitus

Plasma newly synthesised cholesteryl ester transfer (NCET) rates from high density lipoproteins (HDL) to very low density lipoproteins (VLDL) and low density lipoproteins lipoproteins (LDL) were measured in 26 patients with non-insulin dependent diabetes mellitus (NIDDM), 26 healthy subjects with closely matching plasma triglyceride (TG) levels and 10 normolipidaemic healthy individuals. In addition, insulin mediated glucose uptake was measured in the NIDDM patients and the normolipidaemic subjects. Rates of NCET were significantly (P < 0.05) elevated in NIDDM patients compared with healthy normolipidaemic individuals but were similar to rates in healthy subjects with closely matching TG levels. In all groups of subjects plasma NCET was significantly (P < 0.001) correlated with plasma TG concentration. In NIDDM patients correlations between NCET and plasma glucose (r = 0.489, P = 0.011) independently of plasma TG levels, and glycated haemoglobin levels (r = 0.430, P = 0.028) were also recorded. Insulin mediated glucose uptake was unrelated to plasma NCET rates in the study. These data suggest that in NIDDM patients under good diabetic control elevated plasma NCET rates are mainly due to hypertriglyceridaemia and a specific and possibly stimulatory effect of diabetes on these rates may be seen only in patients with poorly controlled diabetes.

Abnormal acyltransferase activities and accelerated cholesteryl ester transfer in patients with nephrotic syndrome

To determine the effects of the nephrotic syndrome (NS) on atherogenic risk, we studied the lipoprotein composition and the activities of lecithin-cholesterol acyltransferase (LCAT), lysolecithin acyltransferase (LAT), and cholesteryl ester transfer (CET) in the plasma of 11 NS patients and 10 control subjects. NS plasma had lower ratios of high-density lipoprotein (HDL) to low-density lipoprotein (LDL) and HDL2/HDL3 and an elevated free cholesterol (FC) to phosphatidyl choline (PC) ratio (1.09 +/- 0.27 in NS and 0.72 +/- 0.21 in controls, P < .02), all of which indicate an increased atherogenic potential. LCAT activity was normal in NS plasma when assayed with an exogenous substrate, but was 40% lower than in control plasma when assayed with the endogenous substrates. However, in vitro addition of serum albumin to NS plasma failed to normalize the LCAT activity. The LAT reaction, which is catalyzed by LCAT protein in the presence of LDL, was 60% to 80% higher in NS plasma, and consequently the ratio of LAT/LCAT activities was increased twofold. CET activity was significantly increased (+160% of control), and this abnormality was attributable to changes in both the acceptor (very-low-density lipoprotein [VLDL] + LDL) and donor (HDL) lipoproteins and possibly in CET protein. These results suggest that the NS may increase the risk of atherosclerosis not only by adversely affecting the concentrations of lipoproteins, but also by altering their composition and function.

DNA polymorphisms at the locus for human cholesteryl ester transfer protein (CETP) are associated with macro- and microangiopathy in non-insulin-dependent diabetes mellitus

The effect of variation at the cholesteryl ester transfer protein (CETP) gene locus and in the apolipoprotein (apo) AI-CIII-AIV gene cluster on the susceptibility of individuals with non-insulin-dependent diabetes mellitus (NIDDM) to atherosclerotic vascular disease was studied in 136 male and 122 female patients with NIDDM. The prevalence of myocardial infarction was high (38%) in patients with the EcoNI genotype 2-2 of the CETP gene locus (= 2-2; subjects homozygous for the absence of the restriction site) compared with patients with the genotype 1-1 (= 1-1; subjects homozygous for the presence of the restriction site) (18%, p < 0.02). The prevalence of any evidence of coronary heart disease (CHD) (presence of ischaemic ECG changes or definite myocardial infarction) was high in 2-2 (73%) compared with the genotype 1-2 (= 1-2; heterozygous for the presence of the restriction site) (52%, p < 0.02) and genotype 1-1 (p = 0.06). CHD was more prevalent in men with 2-2 (70%) than in those with 1-1 (42%, p < 0.05), but in women no significant differences were found in the prevalences of CHD between the EcoNI genotypes. Neuropathy was more often present in the patients with 2-2 (31%) than in those with 1-1 (12%, p < 0.02) or 1-2 (14%, p < 0.01). Plasma total cholesterol and total- and VLDL-triglycerides were higher in women with the EcoNI genotype 1-1 than in those with the genotype 1-2. In men no significant differences in plasma lipids were found. In addition, the prevalence of cerebrovascular disease was high (21%) in the patients with the genotype 1-1 of the TaqIB polymorphism compared with the genotype 2-2 (6%, p < 0.02). None of the alleles defined by four polymorphisms in the apo AI-CIII-AIV gene region were associated with an increased risk for macroangiopathy. The PstI polymorphism had an effect on plasma triglyceride levels. At the CETP locus one pair of loci (TaqIB and EcoNI) and three pairs of loci at the apo AI-CIII-AIV gene cluster (SacI and MspI, SacI and PvuII and MspI and PvuII) showed significant allelic association. In conclusion, the variation of CETP locus modulates the risk for diabetic complications in patients with NIDDM and the effect seems to be different between men and women. In contrast, the AI-CIII-AIV gene cluster polymorphisms seem not to be related to the risk of CHD in NIDDM.(ABSTRACT TRUNCATED AT 400 WORDS)

Contribution of glycaemic control, endogenous lipoproteins and cholesteryl ester transfer protein to accelerated cholesteryl ester transfer in IDDM

In an earlier study we demonstrated that the transfer of cholesteryl ester (CET) estimated as the net mass of CE lost from HDL to the apoB-containing lipoproteins (VLDL + LDL) during incubation of plasma is accelerated in normolipidaemic patients with insulin-dependent diabetes mellitus (IDDM). Recombination experiments with isolated lipoprotein fractions employing this same mass transfer assay indicated that this disturbance resulted from dysfunction of VLDL and not from changes in the activity of CE transfer protein (CETP). In this study, we sought first to determine whether CET estimated with an isotopic method that measures the transfer of radiolabelled CE from exogenous HDL from non-diabetic controls to endogenous VLDL + LDL was also increased in IDDM and, if so, the extent to which this disturbance was affected by glycaemic control, VLDL and CETP. As observed with the mass transfer assay, the rate of transfer of the HDL-CE label to VLDL + LDL was also significantly accelerated in IDDM plasma (IDDM: k = 0.256 +/- 0.07; control: k = 0.092 +/- 0.05; mean +/- SD; P < 0.001). Fasting glucose and fructosamine correlated with both isotopic transfer (k) (r = 0.54, P = 0.009; r = 0.57, P = 0.005, respectively) and the mass of CE transferred at 2 h (r = 0.55, P = 0.006; r = 0.59, P = 0.004, respectively). Recombination experiments revealed that isotopic CET was accelerated when: (a) IDDM VLDL were combined with controls HDL and d > 1.21 fractions; and (b) IDDM d > 1.21 plasma fractions containing CETP were combined with controls VLDL + LDL and HDL.(ABSTRACT TRUNCATED AT 250 WORDS)

LDL subclasses in IDDM patients: relation to diabetic nephropathy

To answer the question whether the elevation of LDL-cholesterol in IDDM patients with incipient and established diabetic nephropathy is accompanied by changes in LDL size or composition, we studied distribution of LDL particles in 57 normoalbuminuric [AER 7 (1-9) micrograms/min, median and range], in 46 microalbuminuric [AER 50 (20-192) micrograms/min] and in 33 proteinuric [AER 422 (233-1756) micrograms/min] IDDM patients as well as in 49 non-diabetic control subjects with normoalbuminuria. The three diabetic groups were matched for duration of diabetes and glycaemic control. The mean particle diameter of the major LDL peak was determined by nondenaturing gradient gel electrophoresis. Composition and density distribution of LDL were determined in the subgroups of each patient group by density gradient ultracentrifugation. Normoalbuminuric IDDM patients had larger LDL particles than non-diabetic control subjects (260 A vs 254 A, p < 0.05). LDL particle diameter was inversely correlated with serum triglycerides in all groups (p < 0.05 for normoalbuminuric and p < 0.001 for other groups). Triglyceride content of LDL was higher in three IDDM groups compared to control group (p < 0.05). The elevation of LDL mass in microalbuminuric and proteinuric IDDM groups compared to normoalbuminuric IDDM group (p < 0.05 for both) was mainly due to the increment of light LDL (density 1.0212-1.0343 g/ml). There were no significant changes in the density distribution or composition of LDL between the three diabetic groups. In conclusion the increase of LDL mass without major compositional changes suggests that the elevation of LDL in incipient and established diabetic nephropathy is primarily due to the increased number of LDL particles.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in reverse cholesterol transport associated with programmable implantable intraperitoneal insulin delivery

Our previous studies have suggested that intraperitoneal (IP) insulin delivery may be associated with alterations of reverse cholesterol transport (RCT). We thus studied two parameters of RCT. We performed RCT studies in 10 C-peptide-negative type I diabetic patients who were randomized into two groups. The experimental (A) and control (B) groups were studied at -3 and 0 months before and +3 and +6 months after IP pump subcutaneous (SC) insulin use. The first step in RCT was estimated by measuring patient serum-mediated 3H-cholesterol efflux from cultured fibroblasts. Cholesteryl ester transport protein (CETP) activity was assessed by a solid-phase assay. No changes in glucose control occurred during the study. Total low-density lipoprotein (LDL) and high-density lipoprotein (HDL) cholesterol, apoprotein B, and apoprotein A-I remained unchanged during the study. Cholesterol efflux from group A increased from baseline after 3 months of IP insulin by 9.5% +/- 3.4% (mean +/- SE, P < .05), whereas in group B patients it decreased negligibly by 1.5% +/- 2.9% (P = .045 for changes between groups). CETP activity increased from baseline by 25.3% +/- 7.7% (P < .05) in group A after 3 months of IP insulin, whereas in group B it changed little, -1.5% +/- 7.9%, with modest differences between groups (P = .16). These data indicate that (1) serum from patients treated long-term with IP insulin delivery may enhance cholesterol efflux from fibroblasts and CETP activity, and (2) these effects appear independent from glucose control, implying a direct effect by IP insulin.

A new in vitro method for the simultaneous evaluation of cholesteryl ester exchange and mass transfer between HDL and apoB-containing lipoprotein subspecies. Identification of preferential cholesteryl ester acceptors in human plasma

To date, several methods have been developed to determine the activity of plasma lipid transfer proteins. These methods have largely involved the addition of the transfer protein in question to labeled substrates, followed by prolonged incubation (4 to 18 hours) and subsequent evaluation of the radioactivity transferred to precipitated low-density lipoprotein (LDL). While adequate for determining the activity of cholesteryl ester transfer protein (CETP), these methods generally do not take into account the composition or levels of lipoproteins present within a given individual plasma because pools of high-density lipoprotein (HDL) are labeled and used for the transfer experiments. Both the direction and the extent of lipid transfer are dependent on the composition and relative abundance of both donor and acceptor particles as well as the activity of the lipid transfer protein(s). Here we describe a new method for the determination of the capacity of plasma samples to facilitate cholesteryl ester transfer from HDL to LDL and very-low-density lipoprotein (VLDL), a method that has several advantages. First, the subject's HDL is labeled and used for transfer. Second, the labeled HDL, in a quantity equivalent to 1% of the plasma HDL mass, is added to the subject's plasma, and therefore the relative abundance of both donor and acceptor particles is preserved at their physiological levels. Third, both cholesteryl ester mass and radioactivity are determined, allowing the net mass transfer of cholesteryl ester and cholesteryl ester exchange to be quantified separately.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipoprotein disorders in diabetes mellitus

In IDDM or NIDDM, the total plasma cholesterol and triglycerides are usually within normal limits when the blood glucose is controlled. Marked hypertriglyceridemia can develop with loss of glycemic control and is often due to superimposed genetic abnormalities in lipoprotein metabolism. Tight control in IDDM usually reduces LDL and VLDL to normal levels and may raise HDL above the normal range. Low HDL cholesterol and mild to moderate elevations of VLDL triglyceride are common in NIDDM if obesity or proteinuria is also present. Both HDL and LDL may be smaller and more dense and may be enriched with triglyceride as compared with cholesterol. These abnormalities may require weight loss for control. The increased incidence of cardiovascular disease in diabetes is unexplained but is amplified by the well-defined cardiovascular risk factors. The new American Diabetes Association guidelines call for treatment of high triglycerides and LDL cholesterol to be aggressively reduced. Triglycerides should be under 200 mg/dL, are considered borderline high between 200 and 400 mg/dL, and high when above 400 mg/dL. Low HDL is defined as less than 35 mg/dL. Control of obesity with diet and exercise and reduced intake of saturated fat and cholesterol are important first steps. If needed, drug therapy is appropriate to reduce LDL to levels below 130 mg/dL in all adult diabetics and below 100 mg/dL in those with cardiovascular disease.

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.

Altered regulation of cholesterol metabolism in type I diabetic women during the menstrual cycle

This study examines the relationship of cellular cholesterol metabolism to oestrogen and progesterone during the menstrual cycle in diabetic and non-diabetic subjects. Nine premenopausal diabetic women were compared to nine non-diabetic women of the same age. Oestrogen, progesterone, lipoproteins, including lipoprotein (a) (Lp(a)) and cholesteryl ester transfer protein (CETP) were determined in serum. Cellular cholesterol content and cellular cholesterol synthesis were measured in mononuclear leucocytes. There was no significant change in serum lipoproteins including Lp(a) during the cycle in either group. CETP activity was significantly higher over the 4 weeks in the diabetic patients compared with non-diabetic subjects (mean 463 +/- 30 mumol l-1 h-1 vs 405 +/- 28 mumol l-1 h-1, p < 0.01). Serum high density lipoprotein (HDL) cholesterol was significantly lower during the 4 weeks in the diabetic patients (1.7 +/- 0.1 mmol l-1 vs 1.8 +/- 0.1 mmol-1, p < 0.05). Cellular cholesterol synthesis decreased steadily up to the third week in cells from the control subjects whereas there was no significant change in cells from diabetic patients whose cellular cholesterol synthesis was higher at week 3 compared with non-diabetic subjects (663 +/- 54 nmol mg-1 cell protein vs 432 +/- 43 nmol mg-1 cell protein, two-way interaction p < 0.05). There was a significant negative correlation between cellular cholesterol synthesis and serum oestrogen in the non-diabetic subjects (p < 0.05) but not in the diabetic patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Decreased ability of high density lipoproteins to transfer cholesterol esters in non-insulin-dependent diabetes mellitus

Esterified cholesterol transfer (ECT) from high density lipoproteins (HDL) to very low (VLDL) and low density lipoproteins (LDL) may be abnormal in situations at high risk for atherosclerosis. It has been shown to increase in insulin-dependent diabetes and to decrease in non-insulin-dependent diabetes (NIDD). Since the net transfer of esterified cholesterol (EC) results from a bidirectional exchange between HDL and VLDL/LDL, we developed a transfer assay specifically designed to measure the unidirectional transfer of EC from HDL to lipid emulsions according to first-order kinetics. Our results show that in NIDD the rate constant of HDL-dependent ECT is decreased by 30% by comparison with control subjects. Analysis of HDL composition revealed that, in both groups, HDL-dependent ECT was positively correlated with the free cholesterol/phospholipid ratio (r = 0.94; P < 0.001) and negatively correlated with the triglyceride/EC ratio (r = -0.85; P < 0.001). It is concluded that, besides the known defect of acceptor lipoproteins, the abnormality of ECT in NIDD is also caused by a decreased ability of HDL to act as an EC donor, presumably because of a change in composition. In addition, our work shows that the amount of EC lost by HDL during the reaction transfer is counterbalanced by a reciprocal equimolar transfer of triglycerides.

Effects of treatment of hypertriglyceridaemia with gemfibrozil on serum lipoproteins and the transfer of cholesteryl ester from high density lipoproteins to low density lipoproteins

Lipoprotein composition and cholesterol esterification, before and after treatment with gemfibrozil, have been examined in the fasting and postprandial state in nine patients with primary hypertriglyceridaemia who participated in a double-blind, placebo controlled study. After 8 weeks of treatment fasting serum triglycerides were reduced significantly from 6.05 mmol/l (range 2.48-10.99 mmol/l) to 1.76 mmol/l (range 1.16-11.90 mmol/l) (P less than 0.001). This was mainly due to a decrease in the triglyceride content of the Sf 12-20, 60-400 and Sf greater than 400 lipoprotein fractions (P less than 0.05). The Sf 0-12 fraction showed an increase in cholesteryl ester, free cholesterol, phospholipids and protein. Consistent with these findings there was a net increase in the mass concentration of the Sf 0-12 fraction (P less than 0.05) and a decrease in that of small very low density lipoproteins (Sf 20-60) (P less than 0.05). In the 8 patients in whom it was measured there was a 40% reduction in the rate at which cholesteryl esters derived from radiolabelled-free cholesterol appeared in very low density lipoprotein (VLDL) and low density lipoprotein (LDL) measured in an in vitro system (P less than 0.02), but serum lecithin:cholesterol acyl transferase (LCAT) activity was unchanged. At the end of each treatment phase (placebo or gemfibrozil) patients were given a mixed meal containing 100 g of fat. Treatment with gemfibrozil resulted in a reduction in serum triglyceride concentrations at all time points for at least 5 h after the meal (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)