Vildagliptin therapy reduces postprandial intestinal triglyceride-rich lipoprotein particles in patients with type 2 diabetes

Aims/hypothesis We assessed the effects of vildagliptin, a novel dipeptidyl peptidase IV inhibitor, on postprandial lipid and lipoprotein metabolism in patients with type 2 diabetes.Subjects, materials and methods This was a single-centre, randomised, double-blind study in drug-naive patients with type 2 diabetes. Patients received vildagliptin (50 mg twice daily, n=15) or placebo (n=16) for 4 weeks. Triglyceride, cholesterol, lipoprotein, glucose, insulin, glucagon and glucagon-like peptide-1 (GLP-1) responses to a fat-rich mixed meal were determined for 8 h postprandially before and after 4 weeks of treatment.Results Relative to placebo, 4 weeks of treatment with vildagliptin decreased the AUC_0–8h for total trigyceride by 22±11% (p=0.037), the incremental AUC_0–8h (IAUC_0–8h) for total triglyceride by 85±47% (p=0.065), the AUC_0–8h for chylomicron triglyceride by 65±19% (p=0.001) and the IAUC_0–8h for chylomicron triglyceride by 91±28% (p=0.002). This was associated with a decrease in chylomicron apolipoprotein B-48 (AUC_0–8h, −1.0±0.5 mg l⁻¹ h, p=0.037) and chylomicron cholesterol (AUC_0–8h, −0.14±0.07 mmol l⁻¹ h, p=0.046). Consistent with previous studies, 4 weeks of treatment with vildagliptin also increased intact GLP-1, suppressed inappropriate glucagon secretion, decreased fasting and postprandial glucose, and decreased HbA_1c from a baseline of 6.7% (change, −0.4±0.1%, p<0.001), all relative to placebo.Conclusions/interpretation Treatment with vildagliptin for 4 weeks improves postprandial plasma triglyceride and apolipoprotein B-48-containing triglyceride-rich lipoprotein particle metabolism after a fat-rich meal. The mechanisms underlying the effects of this dipeptidyl peptidase IV inhibitor on postprandial lipid metabolism remain to be explored.     

Plasma lipoprotein distribution and lipid transfer activities in patients with type IIb hyperlipidemia treated with simvastatin

The aim of the present study was to search in type IIb hyperlipidemic patients for putative concomitant effects of simvastatin on the physicochemical characteristics of low density lipoproteins (LDL) and high density lipoproteins (HDL), as well as on the activities of the cholesteryl ester transfer protein (CETP) and the phospholipid transfer protein (PLTP) that were determined in both endogenous lipoprotein-dependent and endogenous lipoprotein-independent assays. In a double-blind, randomized trial, patients received either placebo (one tablet/day; n = 12) or simvastatin (20 mg/day; n = 12) for a period of 8 weeks after a 5-week run-in period. Simvastatin, unlike placebo, reduced the lipid and apolipoprotein B contents of the most abundant LDL-1, LDL-2, and LDL-3 subfractions without inducing significant changes in the overall size distribution of LDL and HDL. Whereas simvastatin significantly increased PLTP activity in an endogenous lipoprotein-dependent assay (P < 0.01), no variation was observed in a lipoprotein-independent assay. Simvastatin significantly decreased plasma CETP activity in an endogenous lipoprotein-dependent assay (P < 0.01), and the reduction in plasma cholesteryl ester transfer rates was explained by a 16% drop in CETP mass concentration (P < 0.01). In contrast, the specific activity of CETP was unaffected by the simvastatin treatment reflecting at least in part the lack of significant alteration in plasma triglyceride-rich lipoprotein acceptors. The simvastatin-induced changes in plasma CETP mass levels correlated positively with changes in plasma CETP activity (r = 0.483, P = 0.0561), in total cholesterol levels (r = 0.769; P < 0.01), and in LDL-cholesterol levels (r = 0.736; P < 0.01). Whereas the observations suggest that simvastatin might exert concomitant beneficial effects on plasma CETP and LDL levels, neither plasma cholesteryl ester transfer activity nor plasma phospholipid transfer activity appeared as the main determinants of the LDL and HDL distribution profiles in type IIb hyperlipidemic patients.     

Intensive insulin therapy reduces small dense low-density lipoprotein particles in patients with type 2 diabetes mellitus: relationship to triglyceride-rich lipoprotein subspecies

It remains unclear whether insulin improves dyslipidemia in patients with type 2 diabetes mellitus. Small dense low-density lipoprotein (sd-LDL) particles are recognized as a powerful risk factor for coronary heart disease and are often elevated in type 2 diabetes mellitus. We examined the effect of intensive insulin therapy on sd-LDL particles and triglyceride (TG)-rich lipoprotein subspecies. Intensive insulin therapy (insulin aspart [NovoRapid, Tokyo, Japan] before each meal and isophane insulin suspension at bedtime) was given to poorly controlled type 2 diabetic patients (n = 46) who were on high doses of sulfonylureas. Fasting serum samples were collected before and 14 days after the commencement of insulin therapy. Low-density lipoprotein size was measured by gradient gel electrophoresis, and the small dense LDL cholesterol (sd-LDL-C) concentration was measured by a new precipitation method. Chylomicrons (Svedberg flotation unit >400), very low-density lipoprotein 1 (VLDL1) (Sf, 60-400), and VLDL2 (Sf, 20-60) were separated by ultracentrifugation. Serum apolipoprotein B-48 and lipoprotein lipase levels were measured by the enzyme immunoassay method. Serum glucose and glycoalbumin levels were substantially decreased by insulin treatment. The LDL size increased (25.8-26.0 nm, P < .05) and the sd-LDL-C level was significantly reduced (44-34 mg/dL, P < .005). Apolipoproteins B-48 and C-III were decreased, whereas lipoprotein lipase was increased. Triglyceride levels in chylomicrons, VLDL1, and VLDL2 all showed a decrease. Changes of sd-LDL-C or LDL size were associated with changes of the TG levels in the major TG-rich lipoprotein subspecies. These results suggest that intensive insulin therapy decreases atherogenic sd-LDL particles by reducing TG in TG-rich lipoproteins. We did not find any specific relationship between VLDL1 and sd-LDL during insulin treatment.     

Phospholipid and cholesteryl ester transfer are increased in lipoprotein lipase deficiency

OBJECTIVES: Phospholipid transfer protein (PLTP) and cholesteryl ester transfer protein (CETP) are key enzymes in lipoprotein metabolism by mediating the transfer and exchange of phospholipids (PL) and neutral lipids between lipoproteins. Lipoprotein lipase (LPL) deficiency is associated with low HDL-cholesterol (HDL-C) levels in both, the homozygous and heterozygous state. In the present study we set out to investigate the role of lipid transfer proteins, which are known to strongly determine HDL-C levels, in LPL deficiency. DESIGN/SUBJECTS: Phospholipid acceptor and donor properties of lipoproteins, PLTP activity, CETP mass, activity and cholesteryl ester (CE) transfer were determined in two homozygous and six heterozygous LPL-deficient subjects and in 10 healthy, normolipidaemic controls, respectively. RESULTS: The HDL isolated from LPL-deficient subjects showed strongly increased PL-acceptance when compared with controls (homozygotes versus heterozygotes versus control: 26.46 +/- 15.26 vs. 3.41 +/- 1.61 vs. 1.89 +/- 0.33 micromol mL-1 h-1/micromol mL-1 PL; all P < 0.05). Phospholipid transfer from apolipoprotein B containing lipoproteins was increased in heterozygotes when compared with controls (46.66 +/- 23.3 vs. 28.91 +/- 18.05 micromol mL-1 h-1/micromol mL-1 PL, P = 0.05). PLTP activity, however, was similar in LPL-deficient subjects and controls. CETP mass was highest in homozygotes, whilst enzyme activity was similar in LPL-deficient subjects and controls. CE transfer was highest in homozygotes (72.5 +/- 8.8%) and lowest in controls (28.7 +/- 5.2%, P < 0.01). CONCLUSIONS: In conclusion, PL and CE transfer are increased in LPL deficiency and thus, partly explain low HDL-levels in LPL-deficient subjects. Enhanced transfer seems rather to be the result of altered lipoprotein composition and concentration than altered enzyme activity. Our findings on mechanisms leading to low HDL-C levels might show another aspect in atherogenesis in LPL deficiency.     

Physical exercise conditioning in the absence of weight loss reduces fasting and postprandial triglyceride-rich lipoprotein levels

The effect of physical exercise conditioning on fasting and postprandial lipoprotein levels was studied in six normolipidemic subjects. The study consisted of two phases: a baseline stabilization phase in which subjects maintained their regular physical activity and an exercise conditioning phase in which subjects had 29 exercise sessions during a 7-week period. Each of these sessions consisted of jogging on a treadmill for 30 minutes. The subjects averaged 15.2 miles/wk. To control for possible confounding factors, such as changes in diet composition and weight loss, we placed the subjects on a metabolic diet and increased their daily caloric intake during the exercise phase. At the end of each phase of the study, a vitamin A-fat loading test was done to specifically label and follow postprandial lipoprotein levels, and a maximum oxygen consumption test was done to evaluate the subjects' physical fitness. The exercise conditioning phase significantly increased the subjects' aerobic capacity and postheparin lipoprotein lipase activity, and the phase decreased fasting triglyceride levels. Physical exercise also significantly decreased chylomicron (Sf greater than 1,000) levels by 37%. In summary, this study suggests that physical exercise conditioning reduces fasting and postprandial lipoprotein levels by increasing the catabolism of triglyceride-rich particles. Because these particles may have a role in atherogenesis, this could be a major mechanism by which exercise prevents coronary heart disease.     

Changes in high-density lipoprotein subfraction distribution and increased cholesteryl ester transfer after probucol

The effects of probucol (500 mg twice daily) on high-density lipoprotein (HDL) subfractions and cholesteryl ester transfer from HDL to lower density lipoproteins were tested in a series of patients with Type II hypercholesterolemia. In this placebo-controlled crossover trial, patients received probucol or placebo for 8 weeks, then switched to the other agent for another 8 weeks. Probucol significantly lowered total, low-density lipoprotein and HDL cholesterol levels. HDL subfractions, separated by rate zonal ultracentrifugation, showed a dramatic reduction in HDL2, whereas changes in HDL3 were not significant. Both subfractions eluted at a characteristically lower volume, indicating a reduced flotation rate. These findings were confirmed by gradient gel electrophoretic separation, which showed a typical reduction or disappearance of HDL2b particles and the prevalence of particles in the HDL3a-HDL3b electrophoretic range in almost all patients. After treatment, cholesteryl ester transfer from HDL to lower density lipoproteins was significantly increased in all patients. These data suggest that probucol may accelerate HDL particle conversion, leading to improvement in reverse cholesterol transport from the periphery to the liver, through HDL and very low density lipoprotein.     

Unmodified low density lipoprotein causes cholesteryl ester accumulation in J774 macrophages.

Cholesteryl ester (CE)-loaded macrophages (foam cells) are a prominent feature of atherosclerotic plaques. Previous studies have shown that human monocytes or resident mouse peritoneal macrophages accumulate CE in response to low density lipoprotein (LDL) only when the LDL has been appropriately chemically modified. By contrast, we report here that J774 macrophages accumulate large amounts of CE when incubated with unmodified LDL. The CE is stored in oil red O-positive droplets, which have the typical appearance of foam cell inclusions by electron microscopy. The fatty acid moieties of the cellular CE are enriched in oleate unlike those of LDL-CE, which are enriched in linoleate, indicating that the LDL-CE undergoes hydrolysis and reesterification by acyl CoA:cholesterol acyltransferase. Studies with 125I-labeled LDL at both 4 degrees C and 37 degrees C indicate that the LDL is internalized by a specific receptor that has several characteristics in common with the apolipoprotein B/E (apo B/E) receptor. However, in comparison with fibroblasts, the LDL receptor and 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase activity in J774 cells are relatively resistant to down-regulation by LDL or 25-hydroxycholesterol, leading to receptor-mediated CE storage. In addition, J774 cells appear to accumulate CE from LDL internalized by nonspecific means. Thus, macrophage-like cells can accumulate CE in response to unmodified LDL by both nonspecific and receptor-mediated processes.     

High-density lipoprotein cholesterol esterification and transfer rates to lighter density lipoproteins mediated by cholesteryl ester transfer protein in the fasting and postprandial periods are not altered in type 1 diabetes mellitus

Background: Diabetes mellitus is associated with atherosclerosis that has, in part, been ascribed to abnormalities in the reverse cholesterol transport system. Methods: We determined, in the fasting and post-alimentary periods, rates of HDL cholesterol esterification and transfer to apoB-containing lipoproteins, cholesteryl ester transfer protein (CETP) concentration, and apoB lipoprotein size in 10 type 1 diabetics and 10 well-matched controls. Autologous HDL was labeled with [14C]cholesterol and incubated at 37 degrees C during a period of 30 min for measurement of the cholesterol esterification rate (CER), as well as for 24 h for measurement of the endogenous HDL [14C]cholesteryl ester ([14C]CE) transfer rate to apoB-containing lipoproteins after 2- and 4-h incubations with the subject's own plasma. Exogenous cholesteryl ester transfer activity (CETA) was estimated by incubation of the participant's plasma (CETP source) with [14C]CE-HDL and VLDL from a pool of plasma donors. ApoB lipoprotein size was determined using non-denaturing polyacrylamide gradient gel electrophoresis of whole plasma. Results: Contrary to previous studies, we showed that even not well-controlled type 1 diabetics did not differ from lipid-matched, non-diabetic subjects in HDL-[14C]cholesterol esterification rate, transfer rates, or CETP concentration. CETP concentration correlates with the exogenous method of [14C]CE transfer and with the endogenous method only when the latter is corrected for plasma triacylglycerol (TG) concentration. In addition, during the postprandial phase, diabetic patients' VLDL are smaller and IDL size increases less than in controls. Conclusion: In type 1 diabetes mellitus, CETA is not altered when the plasma levels of donor and/or acceptor lipoproteins are within the normal range.     

Relationship between cholesteryl ester transfer activity and high density lipoprotein composition in hyperlipidemic patients

Cholesteryl ester transfer from solid-phase bound HDL to endogenous plasma HDL or VLDL/LDL was determined in 50 patients with primary disorders of lipid metabolism and 27 normolipidemic subjects. Transfer to the plasma HDL pool was significantly reduced in familial hypercholesterolemia, familial combined hyperlipidemia, hypoalphalipoproteinemia and dysbetalipoproteinemia. Subfractionation of HDL revealed that the lipid transfer to HDL3 was significantly reduced in all patient groups while transfer to HDL2 was increased in those with dysbetalipoproteinemia and familial hypertriglyceridemia. Transfer to LDL and VLDL was increased only in patients with dysbetalipoproteinemia and hypoalphalipoproteinemia. Reduced transfer to HDL occurred in samples with altered HDL composition; particularly where HDL-triglyceride was significantly increased and HDL-cholesteryl esters were reduced. Transfer of cholesteryl ester to HDL3 was significantly decreased in patients with vascular disease. These findings indicate that impaired interaction of cholesteryl ester transfer protein with the HDL3 pool may contribute to the risk of coronary heart disease in patients with specific plasma lipid abnormalities.     

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 100000 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.     

The role of cholesteryl ester transfer protein and phospholipid transfer protein in the remodeling of plasma high-density lipoproteins

Recent studies demonstrated that alterations in the size distribution of high-density lipoproteins (HDLs) constitute reliable markers for the risk of coronary artery disease. These observations suggested that the determination of the size distribution of HDL subpopulations by using polyacrylamide gradient gel electrophoresis might constitute an effective tool in clinical practice for the detection of patients with elevated risk. During the last decade, concordant observations revealed that all the HDL subpopulations are metabolically interrelated, and their relative abundances are dependent on the activity of several plasma factors, among them the cholesteryl ester transfer protein (CETP) and the phospholipid transfer protein (PLTP). As reviewed in the present article, although both CETP and PLTP can promote the size redistribution or conversion of HDL, the two plasma lipid transfer proteins can alter differently the plasma HDL distribution profile through distinct mechanisms. (Trends Cardiovasc Med 1997;7:218-224). ? 1997, Elsevier Science Inc.     

Association between small dense low-density lipoprotein and postprandial accumulation of triglyceride-rich remnant-like particles in normotriglyceridemic patients with myocardial infarction.

BACKGROUND: Although the small dense low-density lipoprotein (sd-LDL) is associated with hypertriglyceridemia, more than 60% of myocardial infarction (MI) patients are normotriglyceridemic in the fasting state. This study was aimed to investigate the relationship between the low-density lipoprotein (LDL) phenotype and postprandial hyperlipemia (PPL) in MI patients. METHODS AND RESULTS: Oral fat tolerance tests were performed in 71 patients with acute MI and fasting triglyceride concentrations below 200 mg/dl. Postprandial changes in the LDL particle diameter (LDL-PD) and lipids over a 6-h period after a meal were compared among 4 groups of patients classified according to fasting triglyceride levels (A, B as <150, and C, D as > or =150) and postprandial triglyceride levels (A, C as <230 and B, D as > or =230). Although fasting concentrations of triglyceride and remnant-like particle (RLP)-triglyceride were significantly higher in group C than in group B, the areas under the curves of the RLPs were significantly higher in group B. The triglyceride-to-cholesterol ratio in the RLPs was significantly higher in the PPL group than in the nonPPL group postprandially. The prevalence of sd-LDL (LDL-PD < or =25.5 nm) was significantly higher in group D but similar between groups B and C (23%, 42%, 50% and 83% in groups A, B, C and D, respectively). CONCLUSION: These results suggest that postprandial accumulation of triglyceride-rich lipoproteins is strongly associated with sd-LDL in MI patients without hypertriglyceridemia.     

Association of cholesteryl ester transfer protein activity and TaqIB polymorphism with lipoprotein variations in Japanese subjects

Cholesteryl ester transfer protein (CETP) facilitates the transfer of cholesteryl ester from high-density lipoprotein (HDL) to apolipoprotein (apo)B-containing lipoproteins, whereby it potentially regulates steady-state concentrations of HDL-cholesterol (HDL-C), as well as low-density lipoprotein-cholesterol (LDL-C). We performed a multicenter trial to assess the association of CETP activity with plasma lipoprotein levels in 591 Japanese subjects. Women had significantly higher CETP activity (15%) and mass (24%) compared to men. For both genders CETP activity was negatively correlated with HDL-C and HDL(2)-C, but positively correlated with LDL-C. B2 allele frequency in TaqIB polymorphism was 40%, with no gender difference. TaqIB genotypes were significantly associated with CETP activity and HDL-C level (both P <.001). B1B1 had the highest CETP activity and the lowest HDL-C concentrations, whereas B2B2 had the lowest CETP activity and the highest HDL-C concentrations. However, no statistically significant differences in triglycerides (TG) or LDL-C were observed across TaqIB genotypes. Multivariate analysis revealed that determinants of HDL-C were age, gender, body mass index (BMI), smoking, alcohol intake, exercise, CETP activity, and TG, and for LDL-C were BMI, age, and CETP. These data demonstrate that CETP activity is a significant determinant of HDL-C and LDL-C levels and that TaqIB CETP gene polymorphism affects CETP activity and HDL-C level in Japanese population examined.     

Effect of HDL, from Japanese white rabbit administered a new cholesteryl ester transfer protein inhibitor JTT-705, on cholesteryl ester accumulation induced by acetylated low density lipoprotein in J774 macrophage

We have previously reported a potent and specific cholesteryl ester transfer protein (CETP) inhibitor JTT-705 was a potentially anti-atherogenic compound (Nature 406 (2000) 203). In the present study, we investigated in vitro how this compound affects properties of high density lipoprotein (HDL) in Japanese white (JW) rabbits in terms of reverse cholesterol transport in J774 macrophages. Plasma HDL-cholesterol (C) level was significantly higher in the rabbits administered JTT-705 than in control rabbits on days 3 and 7. Both HDL(2) and HDL(3)-C levels were also significantly higher in JTT-705-administered rabbits than in control rabbits. During this period, plasma CETP activity was kept lower in JTT-705-administered rabbits than in controls. To determine how this compound affects the property of HDL particles, we investigated the C efflux induced by HDL from JTT-705-administered and control rabbits in J774 macrophages. Cholesterol ester (CE) concentration in J774 macrophages was reduced in proportion with increasing concentration of the added HDL to the culture media for J774 macrophages in both groups, suggesting that the HDL from JTT-705-administered rabbits was able to reduce CE concentration in J774 macrophages as efficiently as that from control rabbits. This result, together with the finding that the absolute HDL concentration increased in JW rabbits administered this CETP inhibitor, suggests that treatment with this new compound causes a beneficial effect on lipid metabolism in terms of anti-atherogenicity.