Relationship between plasma insulin concentration and plasma remnant lipoprotein response to an oral fat load in patients with type 2 diabetes

Postprandial Hyperlipidemia: Its Pathophysiology, Diagnosis, Atherogenesis, and Treatments

Postprandial hyperlipidemia showing postprandial increases in serum triglyceride (TG) is associated with the development of atherosclerotic cardiovascular disease (ASCVD). To diagnose postprandial hyperlipidemia, the oral fat loading test (OFLT) should be performed; however, this test is very time-consuming and is difficult to perform. Elevated serum TG levels reflect an increase in TG-rich lipoproteins (TRLs), such as chylomicrons (CM), very low-density lipoproteins (VLDL), and their remnants (CM remnants [CMRs] and VLDL remnants [VLDLRs]). Understanding of elevation in CMR and/or VLDLR can lead us to understand the existence of postprandial hyperlipidemia. The measurement of apo B48, which is a constituent of CM and CMR; non-fasting TG, which includes TG content in all lipoproteins including CM and CMR; non-high-density lipoprotein cholesterol (non-HDL-C), which includes TRLs and low-density lipoprotein; and remnant cholesterol are useful to reveal the existence of postprandial hyperlipidemia. Postprandial hyperlipidemia is observed in patients with familial type III hyperlipoproteinemia, familial combined hyperlipidemia, chronic kidney disease, metabolic syndrome and type 2 diabetes. Postprandial hyperlipidemia is closely related to postprandial hyperglycemia, and insulin resistance may be an inducing and enhancing factor for both postprandial hyperlipidemia and postprandial hyperglycemia. Remnant lipoproteins and metabolic disorders associated with postprandial hyperlipidemia have various atherogenic properties such as induction of inflammation and endothelial dysfunction. A healthy diet, calorie restriction, weight loss, and exercise positively impact postprandial hyperlipidemia. Anti-hyperlipidemic drugs such pemafibrate, fenofibrate, bezafibrate, ezetimibe, and eicosapentaenoic acid have been shown to improve postprandial hyperlipidemia. Anti-diabetic drugs including metformin, alpha-glucosidase inhibitors, pioglitazone, dipeptidyl-peptidase-4 inhibitors and glucagon-like peptide 1 analogues have been shown to ameliorate postprandial hyperlipidemia. Although sodium glucose cotransporter-2 inhibitors have not been proven to reduce postprandial hyperlipidemia, they reduced fasting apo B48 and remnant lipoprotein cholesterol. In conclusion, it is important to appropriately understand the existence of postprandial hyperlipidemia and to connect it to optimal treatments. However, there are some problems with the diagnosis for postprandial hyperlipidemia. Postprandial hyperlipidemia cannot be specifically defined by measures such as TG levels 2 h after a meal. To study interventions for postprandial hyperlipidemia with the outcome of preventing the onset of ASCVD, it is necessary to define postprandial hyperlipidemia using reference values such as IGT.

Postprandial triglyceride levels rather than fat distribution may reflect early signs of disturbed fat metabolism in Iraqi immigrants

PURPOSE

Previous studies have shown that at a similar body mass index, Middle Eastern immigrants are more insulin resistant and at higher risk for type 2 diabetes (T2D) than native Europeans. Insulin resistance is strongly associated with disturbed fat metabolism and cardiovascular disease (CVD). However, fat metabolism is poorly investigated comparing Middle Eastern and European ethnicities.

METHODS

This observational study included 26 Iraqi and 16 Swedish-born men without T2D or clinical risk factors for CVD. An oral fat tolerance test (OFTT) was performed, where plasma triglycerides (p-TG) were measured for 6 h. mRNA expression and adipocyte size were measured in subcutaneous adipose tissue biopsies collected prior to OFTT, and magnetic resonance imaging was conducted to assess body fat distribution.

RESULTS

The median p-TG accumulation was higher and the clearance slower among Iraqis than Swedes. None of the groups reached their fasting p-TG (Iraqis 1.55 mmol/l; Swedes 0.95 mmol/l) after 6 h (Iraqis p-TG 3.10 mmol/l; Swedes p-TG 1.50 mmol/l). Adipocyte size, mRNA expression, and fat accumulation in the liver, muscle and abdomen were similar in both groups.

CONCLUSION

Postprandial p-TG levels rather than fat distribution may reflect early signs of disturbed fat metabolism in Iraqi immigrants without CVD risk factors.

Identification of the Chinese Population That Can Benefit Most From Postprandial Lipid Testing: Validation of the Use of Oral Fat Tolerance Testing in Clinical Practice

BACKGROUND

Dyslipidemia has become increasingly prevalent in recent decades. Blood lipid concentrations are significantly influenced by diet; however, postprandial triglyceride concentration (PTG) is not often measured. PTG can reflect the risks of diabetes and cardiovascular disease, but not all individuals would benefit from PTG testing.

OBJECTIVE

The aim of the present study was to determine the PTG response in a Chinese cohort and identify who would benefit from diagnostic PTG measurement.

METHODS

A total of 400 Chinese adults were enrolled and underwent oral fat tolerance test (OFTT), which was well tolerated. The participants were assigned to groups according to their fasting triglyceride concentration to evaluate the usefulness of PTG testing. A PTG concentration > 2.5 mmol/L was defined as high (HPTG).

RESULTS

Of the 400 participants, 78.9% showed an undesirable PTG response. Those with FTG ≥1.0 mmol/L had a delayed PTG peak and higher peak values. Seventy-five percent of those with 1.0 mmol/L ≤FTG <1.7 mmol/L had HPTG, of whom 18.6% had impaired glucose tolerance.

CONCLUSIONS

The present data confirm the previously reported predictive value of PTG testing. Moreover, the findings indicate that Chinese people with FTGs of 1.0 -1.7 mmol/L may benefit most from the identification of postprandial hyperlipidemia through OFTT because more than half of them have occult HPTG, which may require treatment. Thus, the detection of HPTG using an OFTT represents a useful means of identifying dyslipidemia and abnormal glucose metabolism early.

CLINICAL TRIAL REGISTRATION

[http://www.chictr.org.cn/index.aspx], identifier ChiCTR1800019514.

Thresholds for postprandial hyperglycemia and hypertriglyceridemia associated with increased mortality risk in type 2 diabetes patients: A real-world longitudinal study

AIMS/INTRODUCTION

To identify thresholds for postprandial hyperglycemia and hypertriglyceridemia predictive of all-cause mortality in patients with type 2 diabetes.

MATERIALS AND METHODS

A total of 1,928 patients with type 2 diabetes visited our clinic for the first time from 1995 to 1999 and were followed up for ≥1 year. During the first year, 2-h post-breakfast blood glucose (2h-BG) levels were measured in 1,122 patients (BG cohort) and postprandial serum triglyceride (ppTG) levels were measured in 1,826 patients (TG cohort). Patients were retrospectively followed until 2017 and administered questionnaires. Associations between 2h-BG and ppTG levels and mortality risk were assessed by the multivariate Cox regression analysis.

RESULTS

Over of 17,429 person-years, 162 deaths occurred in the BG cohort, and over 28,026 person-years, 253 deaths occurred in the TG cohort. Hazard ratios (HRs) with 95% confidence intervals for all-cause mortality per 1-standard deviation increases in 2h-BG and ppTG were 1.34 (1.08-1.67) and 1.24 (1.06-1.45), respectively. HRs showed increasing trends across quintiles of 2h-BG (P = 0.034) and ppTG (P = 0.007). The HR was significantly elevated (2.37, 1.26-4.47) in the fifth quintile of 2h-BG (≥13.8 mmol/L) compared with the first quintile (<7.0 mmol/L; P = 0.008). The HR was also significantly elevated (1.63, 1.03-2.60) in the fifth quintile of ppTG (≥2.30 mmol/L) compared with the first quintile (<0.91 mmol/L; P = 0.038).

CONCLUSIONS

Postprandial hyperglycemia and hypertriglyceridemia were associated with all-cause mortality in patients with type 2 diabetes. We propose thresholds of 13.8 mmol/L 2h-BG and 2.30 mmol/L ppTG to identify patients at increased risk of mortality.

Sitagliptin improves plasma apolipoprotein profile in type 2 diabetes: A randomized clinical trial of sitagliptin effect on lipid and glucose metabolism (SLIM) study

AIM

This study aims to evaluate the effect of dipeptidyl peptidase-4 inhibitors on lipid metabolism in patients with type 2 diabetes mellitus (T2D).

METHODS

This is a multicenter, open-labeled, randomized controlled study. T2D patients with HbA1c 6.9-8.9% (52-74 mmol/mol) who were under treatment with sulfonylurea were randomly allocated to either the sitagliptin group or the non-sitagliptin group. Glucose and lipid metabolism parameters including apolipoproteins (apo), sterols, and urinary albumin were assessed at baseline, 3, and 6 months of the treatment.

RESULTS

A total of 164 patients completed the 6-month observation (n = 81 for sitagliptin and n = 83 for non-sitagliptin). HbA1c decreased in the sitagliptin group but not in the non-sitagliptin group. Serum TG and total, LDL and HDL cholesterol levels did not change in either group. Apo B-48, apo CII, and apo CIII levels decreased in the sitagliptin group, but not in the non-sitagliptin group. The change in urinary albumin was significantly different between the groups with a preferable change in the sitagliptin group. There were no changes in serum sterols levels in the two groups.

CONCLUSIONS

The treatment of sitagliptin for 6 months improves the metabolism of glucose and chylomicron and reduces plasma levels of atherogenic lipoproteins in patients with T2D.

Comparison of nonfasting and fasting lipoprotein subfractions and size in 15,397 apparently healthy individuals: An analysis from the VITamin D and OmegA-3 TriaL

BACKGROUND

Elevated postprandial triglycerides reflect a proatherogenic milieu, but underlying mechanisms are unclear.

OBJECTIVE

We examined differences between fasting and nonfasting profiles of directly measured lipoprotein size and subfractions to assess if postprandial triglycerides reflected increases in very low density lipoprotein (VLDL), intermediate density lipoprotein (IDL) and remnants, or small dense lipid depleted LDL (sdLDL) particles.

METHODS

We conducted a cross-sectional analysis of 15,397 participants (10,135 fasting; 5262 nonfasting [<8 hours since last meal]) from the VITamin D and OmegA-3 TriaL. Baseline cholesterol subfractions were measured by the vertical auto profile method and particle subfractions by ion mobility. We performed multivariable linear regression adjusting for cardiovascular and lipoprotein-modifying risk factors.

RESULTS

Mean age (SD) was 68.0 years (±7.0), with 50.9% women. Adjusted mean triglyceride concentrations were higher nonfasting by 17.8 ± 1.3%, with higher nonfasting levels of directly measured VLDL cholesterol (by 3.5 ± 0.6%) and total VLDL particles (by 2.0 ± 0.7%), specifically large VLDL (by 12.3 ± 1.3%) and medium VLDL particles (by 5.3 ± 0.8%), all P < .001. By contrast, lower concentrations of low density lipoprotein (LDL) and IDL cholesterol and particles were noted for nonfasting participants. sdLDL cholesterol levels and particle concentrations showed no statistically significant difference by fasting status (-1.3 ± 2.1% and 0.07 ± 0.6%, respectively, P > .05).

CONCLUSIONS

Directly measured particle and cholesterol concentrations of VLDL, not sdLDL, were higher nonfasting and may partly contribute to the proatherogenicity of postprandial hypertriglyceridemia. These differences, although statistically significant, were small and may not fully explain the increased risk of postprandial hypertriglyceridemia.

Lipoprotein Subfractions and Glucose Homeostasis in Prediabetes and Diabetes in Taiwan

AIMS

Prediabetes and diabetes are associated with increased insulin resistance and decreased insulin production, dyslipidemia, and increased cardiovascular disease (CVD) risk. Our goals were to assess lipoprotein subfractions using novel assays in such subjects.

METHODS

Fasting normal, prediabetic, and diabetic Taiwanese men and women (n=2,049) had their serum glucose, glycosylated hemoglobin, insulin, total cholesterol (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), HDL3-C, apolipoprotein E-HDL-C, direct low-density lipoprotein cholesterol (LDL-C), small dense LDL-C (sdLDL-C), LDL-TG, and remnant lipoprotein cholesterol (RLP-C) levels measured using novel assays. HDL2-C, LDL-C, and large-buoyant LDL-C (lbLDL-C) were calculated.

RESULTS

Prediabetic male and female subjects had significantly higher levels of TG, RLP-C, sdLDL-C, the sdLDL-C/LDL-C ratio, and LDL-TG than normal subjects, and statin treatment abolished this effect in men, but not in women. Diabetic male and female subjects had significantly higher TG and sdLDL-C/LDL-C ratios, and significantly lower levels of HDL-C, HDL2-C, HDL3-C, and apoE HDL-C than normal subjects, as did prediabetic women. Median direct LDL-C levels were ＞100 mg/dL in all groups, even in those receiving statin therapy. Calculated LDL-C significantly underestimated direct LDL-C by ＞10% in diabetic subjects.

CONCLUSIONS

Our data indicate that prediabetic subjects were more likely to have significantly elevated RLP-C, sdLDL-C, and LDL-TG, while diabetic subjects were more likely to have significantly decreased HDL-C, HDL2-C, HDL3-C, and apoE HDL-C than normal subjects, and calculated LDL-C significantly underestimated their direct LDL-C. In our view, direct LDL-C and sdLDL-C should be measured and optimized in both diabetic and prediabetic subjects to reduce CVD risk.

The microRNA-29/PGC1α regulatory axis is critical for metabolic control of cardiac function

Different microRNAs (miRNAs), including miR-29 family, may play a role in the development of heart failure (HF), but the underlying molecular mechanisms in HF pathogenesis remain unclear. We aimed at characterizing mice deficient in miR-29 in order to address the functional relevance of this family of miRNAs in the cardiovascular system and its contribution to heart disease. In this work, we show that mice deficient in miR-29a/b1 develop vascular remodeling and systemic hypertension, as well as HF with preserved ejection fraction (HFpEF) characterized by myocardial fibrosis, diastolic dysfunction, and pulmonary congestion, and die prematurely. We also found evidence that the absence of miR-29 triggers the up-regulation of its target, the master metabolic regulator PGC1α, which in turn generates profound alterations in mitochondrial biogenesis, leading to a pathological accumulation of small mitochondria in mutant animals that contribute to cardiac disease. Notably, we demonstrate that systemic hypertension and HFpEF caused by miR-29 deficiency can be rescued by PGC1α haploinsufficiency, which reduces cardiac mitochondrial accumulation and extends longevity of miR-29–mutant mice. In addition, PGC1α is overexpressed in hearts from patients with HF. Collectively, our findings demonstrate the in vivo role of miR-29 in cardiovascular homeostasis and unveil a novel miR-29/PGC1α regulatory circuitry of functional relevance for cell metabolism under normal and pathological conditions.

To combat diseases, we first need to gain knowledge on how cells function at the molecular level to maintain normal physiology. One great scientific achievement of the last decade was the identification of thousands of small regulatory RNA molecules, called microRNAs. Strikingly, each microRNA has the potential to fine-tune the expression of hundreds of target genes depending on the spatiotemporal context. Therefore, defects in key microRNAs can contribute to the development of diseases. In the present work, we characterize the role for miR-29 in cardiac function in a mouse model. We found that mice deficient for miR-29 develop life-threatening cardiometabolic alterations that subsequently cause heart failure with diastolic dysfunction and systemic hypertension. We also demonstrate that these pathological phenotypes originate in part by the anomalous up-regulation of the transcriptional coactivator PGC1α, which can lead to mitochondrial hyperplasia in the heart. Genetic removal of one copy of PGC1α significantly attenuated the severity of the cardiovascular phenotype observed in miR-29–deficient mice. In addition, we show that PGC1α expression is misregulated in heart failure patients, suggesting that the implementation of miR-29 replacement therapy could potentially be used to treat these fatal pathologies.

Hypertriglyceridemia in Diabetes Mellitus: Implications for Pediatric Care

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality in type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM). It is estimated that the risk of CVD in diabetes mellitus (DM) is 2 to 10 times higher than in the general population. Much of this increased risk is thought to be related to the development of an atherogenic lipid profile, in which hypertriglyceridemia is an essential component. Recent studies suggest that dyslipidemia may be present in children and adolescents with DM, particularly in T2DM and in association with poor control in T1DM. However, the role of hypertriglyceridemia in the development of future CVD in youth with DM is unclear, as data are scarce. In this review, we will evaluate the pathophysiology of atherogenic hypertriglyceridemia in DM, the evidence regarding an independent role of triglycerides in the development of CVD, and the treatment of hypertriglyceridemia in patients with DM, highlighting the potential relevance to children and the need for more data in children and adolescents to guide clinical practice.

Atherogenic postprandial remnant lipoproteins; VLDL remnants as a causal factor in atherosclerosis

Oxidized LDL (Ox-LDL) and chylomicron (CM) remnants have been suggested to be the most atherogenic lipoproteins that initiate and exacerbate coronary atherosclerosis. In this review, we propose a hypothesis of the causal lipoproteins in atherosclerosis based on our recent findings on postprandial remnant lipoproteins (RLP). Plasma RLP-C and RLP-TG increased significantly after food intake, especially a fat load. More than 80% of the TG increase after the fat load consisted of the TG in RLP, which contained significantly greater apoB100 than apoB48 particles as VLDL remnants. The majority of the LPL in non-heparin plasma was found in RLP as an RLP-LPL complex and released into the circulation after hydrolysis. Plasma LPL did not increase after food intake, which may have caused the partial hydrolysis of CM and VLDL as well as the significant increase of RLP-TG in the postprandial plasma. LPL was inversely correlated with the RLP particle size after food intake. We showed that VLDL remnants are the major atherogenic lipoproteins in the postprandial plasma associated with insufficient LPL activity and a causal factor in the initiation and progression of atherosclerosis. We also propose "LPL bound TG-rich lipoproteins" as a new definition of remnant lipoproteins based on the findings of the RLP-LPL complex in the non-heparin plasma.

Effects of a Dipeptidyl Peptidase 4 Inhibitor Sitagliptin on Glycemic Control and Lipoprotein Metabolism in Patients with Type 2 Diabetes Mellitus (GLORIA Trial)

Aim: The morbidity of cardiovascular disease in patients with type 2 diabetes mellitus (DM) deteriorates in combination with dyslipidemia. The accumulation of remnant lipoproteins in patients with fasting and postprandial hypertriglyceridemia is highly atherogenic. The current study investigated whether the dipeptidyl peptidase-4 inhibitor sitagliptin ameliorates dyslipidemia and hyperglycemia.

Methods: We enrolled 38 patients with type 2 DM (20 males and 18 females, 65.7 ± 9.9 years old, HbA1c levels < 8.4%), and all patients gave written informed consent. Sitagliptin (50 mg/day) was added to current antidiabetic treatments and increased to 100 mg/day to achieve low HbA1c levels (< 7.4%). Glucose and lipoprotein metabolism profiles were analyzed at 0, 4, and 12 weeks after sitagliptin administration.

Results: Sitagliptin significantly decreased fasting levels of triglyceride (TG) (161 ± 90 vs. 130 ± 66 mg/dl, p < 0.01) and non-HDL-C (129 ± 29 vs. 116 ± 20 mg/dl, p < 0.01) in combination with glucose (150 ± 47 vs. 129 ± 27 mg/dl, p < 0.01) and HbA1c (7.1 ± 0.6 vs. 6.6 ± 0.7 mg/dl, p < 0.001). Sitagliptin also significantly decreased the fasting levels of apolipoprotein (apo) B-48 (7.8 ± 6.7 vs. 5.6 ± 4.0 µg/ml, p < 0.01), remnant lipoprotein cholesterol (15.3 ± 9.5 vs. 12.0 ± 7.9 mg/dl, p < 0.05) and other apolipoproteins, such as apoB, apoC-II, apoC-III, and apoE. Analyses of the lipoprotein profiles of fasting sera revealed that sitagliptin significantly decreased cholesterol and TG levels of lipoprotein fractions in the size of very low density lipoprotein and low density lipoprotein.

Conclusions: These findings indicated that sitagliptin administration ameliorated the lipid and lipoprotein profiles in patients with diabetes, which may be due to the decrease in atherogenic remnant lipoproteins (UMIN#000013218).

Abbreviations:apo

apolipoprotein

ASCVD

atherosclerotic cardiovascular disease

CHD

coronary heart disease

CLEIA

chemiluminescence enzyme immunoassay

CM

Chylomicron

DPP-4

dipeptidyl peptidase-4

FFAs

free fatty acids

HPLC

high-performance liquid chromatography

IMT

intima-media thickness

LDL

low-density lipoprotein

LPL

lipoprotein lipase

PHTG

postprandial hypertriglyceridemia

RemL-C

remnant lipoprotein cholesterol

RLP-C

remnant-like particle cholesterol

TG

triglyceride

TRL

triglyceride-rich lipoprotein

VLDL

very low density lipoprotein

The Combination Therapy of Fenofibrate and Ezetimibe Improved Lipid Profile and Vascular Function Compared with Statins in Patients with Type 2 Diabetes

AIM

Elevated level of serum triglyceride (TG) is a characteristic of type 2 diabetes. We evaluated the clinical significance of intervention for the serum TG levels in the fasting and postprandial states in patients with type 2 diabetes.

METHODS

Fifty patients with type 2 diabetes, treated with statins, were selected and divided into two groups. One group was treated with a combination of fenofibrate and ezetimibe (F/E group) and the other group with statins (statin group) for 12 weeks. The lipoprotein profile of both groups was compared using high-performance liquid chromatography, and the vascular function was assessed using flow-mediated dilation (FMD) at the forearm.

RESULTS

The levels of very low-density lipoprotein (VLDL) cholesterol, malondialdehyde low-density lipoprotein (MDA-LDL), total TG, chylomicron-TG, VLDL-TG, and HDL-TG decreased in the F/E group, whereas those of HDL cholesterol increased. Furthermore, the peak particle size of LDL increased, but that of HDL decreased in the F/E group. The combination treatment significantly improved the FMD. The change in the cholesterol level in a very small fraction of HDL was a significant independent predictor for determining the improvement of FMD (p＜0.01).

CONCLUSIONS

Compared with the treatment with statins, the treatment with the combination of fenofibrate and ezetimibe effectively controlled the LDL cholesterol and TG levels, increased the HDL cholesterol level, especially in its small fraction, and improved vascular function of patients with type 2 diabetes.

Reduced first-phase insulin secretion increases postprandial lipidemia in subjects with impaired glucose tolerance

OBJECTIVE

It is not clear which phase of insulin secretion is more important to regulate lipoprotein lipase (LPL) activity. After a meal, insulin is released and acts as a major regulator of LPL activity. Postprandial hyperlipidemia is a common comorbidity in subjects with insulin resistance (IR). Therefore this study aimed to evaluate the role of the first-phase insulin secretion (FPIS) on postprandial lipidemia in subjects with IR and impaired glucose tolerance (IGT).

RESEARCH DESIGN AND METHODS

This is a cross-sectional, observational and comparative study. We included male and female subjects between 40 and 60 years with a body mass index (BMI) between 23 and 30 kg/m². Then, patients were divided into three groups. Group 1 consisted of control subjects with normal glucose tolerance and preserved FPIS. Group 2 included patients with IGT and a reduced FPIS. Group 3 consisted of subjects with IGT but normal FPIS. Both groups were paired by age and BMI with subjects in the control group. Subjects underwent an intravenous glucose tolerance test to classify each case, and then a load with a mixed meal load to measure postprandial lipidemia.

RESULTS

A total of 32 subjects were evaluated: 10 were control subjects, 8 subjects with IGT with a reduced FPIS and 14 subjects with IGT and preserved FPIS. After administration of a standardized meal, group 2 showed a greater glucose area under the curve (AUC) at 30 and 120 min (p=0.001, for both). This group also showed a statistically significant increase (p<0.001) in triglyceride AUC.

CONCLUSIONS

A reduced FPIS is significantly and independently associated with a larger postprandial hyperlipidemia in subjects with IGT.

Postprandial Hyperlipidemia and Remnant Lipoproteins

Fasting hypertriglyceridemia is positively associated with the morbidity of coronary heart disease (CHD), and postprandial (non-fasting) hypertriglyceridemia is also correlated with the risk status for CHD, which is related to the increase in chylomicron (CM) remnant lipoproteins produced from the intestine. CM remnant particles, as well as oxidized low density lipoprotein (LDL) or very low density lipoprotein (VLDL) remnants, are highly atherogenic and act by enhancing systemic inflammation, platelet activation, coagulation, thrombus formation, and macrophage foam cell formation. The cholesterol levels of remnant lipoproteins significantly correlate with small, dense LDL; impaired glucose tolerance (IGT) and CHD prevalence. We have developed an assay of apolipoprotein (apo)B-48 levels to evaluate the accumulation of CM remnants. Fasting apoB-48 levels correlate with the morbidity of postprandial hypertriglyceridemia, obesity, type III hyperlipoproteinemia, the metabolic syndrome, hypothyroidism, chronic kidney disease, and IGT. Fasting apoB-48 levels also correlate with carotid intima-media thickening and CHD prevalence, and a high apoB-48 level is a significant predictor of CHD risk, independent of the fasting TG level. Diet interventions, such as dietary fibers, polyphenols, medium-chain fatty acids, diacylglycerol, and long-chain n-3 polyunsaturated fatty acids (PUFA), ameliorate postprandial hypertriglyceridemia, moreover, drugs for dyslipidemia (n-3 PUFA, statins, fibrates or ezetimibe) and diabetes concerning incretins (dipeptidyl-peptidase IV inhibitor or glucagon like peptide-1 analogue) may improve postprandial hypertriglyceridemia. Since the accumulation of CM remnants correlates to impaired lipid and glucose metabolism and atherosclerotic cardiovascular events, further studies are required to investigate the characteristics, physiological activities, and functions of CM remnants for the development of new interventions to reduce atherogenicity.

Postprandial hyperlipidemia as a potential residual risk factor

Statin therapy targeting reduction of low-density lipoprotein cholesterol (LDL-C) decreases the risk of coronary heart disease (CHD) and all-cause mortality. However, a substantial number of cases of CHD are not prevented and residual risk factors remain unsettled. A high triglyceride (TG) level is considered to be an important and residual risk factor. Postprandial hyperlipidemia is a condition in which TG-rich chylomicron remnants are increased during the postprandial period and hypertriglycedemia is protracted. Postprandial hyperlipidemia evokes atherogenesis during the postprandial period. Several prospective studies have revealed that nonfasting serum TG levels predict the incidence of CHD. Values of TG, remnant lipoprotein cholesterol, and remnant lipoprotein TG after fat loading were significantly higher in diabetes patients with insulin resistance than in diabetes patients without insulin resistance. Endothelial dysfunction is an initial process of atherogenesis and it contributes to the pathogenesis of CHD. Postprandial hyperlipidemia (postprandial hypertriglyceridemia) is involved in the production of proinflammatory cytokines, recruitment of neutrophils, and generation of oxidative stress, resulting in endothelial dysfunction in healthy subjects, hypertriglyceridemic patients, or type 2 diabetic patients. Effective treatment has not been established till date. Ezetimibe or omega-3 fatty acids significantly decrease postprandial TG elevation and postprandial endothelial dysfunction. Ezetimibe or omega-3 fatty acids added to statin therapy reduce serum TG levels and result in good outcomes in patients with CHD. In conclusion, postprandial hyperlipidemia is an important and residual risk factor especially in patients with insulin resistance syndrome (metabolic syndrome) and diabetes mellitus. Further studies are needed to establish effective treatment.

Fasting remnant lipoproteins can predict postprandial hyperlipidemia

BACKGROUND

Hypertriglyceridemia and postprandial hyperlipidemia is thought to play an important role in atherosclerosis, but to select patients at high-risk for cardiovascular diseases is difficult with triglycerides (TG) alone in these patients.

METHODS

To predict postprandial hyperlipidemia without inconvenient test meal loading, we examined lipid concentrations before and after test meal loading and fasting adiponectin, and investigated which of these other than TG were significant during the fasting period in 45 healthy individuals (men: women, 26:19).

RESULTS

TG, remnant-like particle-cholesterol and -triglyceride (RemL-C, RLP-C, and RLP-TG), and TG/apolipoprotein(apo)B were significantly elevated after loading and fasting values significantly and positively correlated with incremental area under the curve (iAUC) (r=0.80, r=0.79, r=0.63, r=0.58, r=0.54; p<0.0001). Fasting adiponectin positively correlated with fasting high-density lipoprotein-cholesterol (r=0.43, p<0.005) and apoA-I (r=0.34, p<0.05), and negatively correlated with iAUC of TG, RemL-C, RLP-C, RLP-TG, and TG/apoB (r=-0.37, r=-0.41, r=-0.37, r=-0.36, r=-0.37; p<0.05). We constructed the model of multivariable linear regression analysis without fasting TG. In the sex-, BMI-, age-, and waist circumference-adjusted analysis of postprandial TG elevation 2 h after test meal loading in all participants, RemL-C, RLP-C, RLP-TG, and TG/apoB were significant factors, but adiponectin was not.

CONCLUSION

Fasting triglyceride-rich lipoprotein-related values, especially RemL-C, RLP-C, RLP-TG, and TG/apoB are useful predictors of postprandial hyperlipidemia in young healthy individuals. Although fasting adiponectin concentration correlated with the iAUCs for TG, RemL-C, RLP-C, RLP-TG, and TG/apoB, it was not a significant predictor of postprandial hyperlipidemia in multivariable linear regression analysis.

Postprandial lipoprotein metabolism: VLDL vs chylomicrons

Since Zilversmit first proposed postprandial lipemia as the most common risk of cardiovascular disease, chylomicrons (CM) and CM remnants have been thought to be the major lipoproteins which are increased in the postprandial hyperlipidemia. However, it has been shown over the last two decades that the major increase in the postprandial lipoproteins after food intake occurs in the very low density lipoprotein (VLDL) remnants (apoB-100 particles), not CM or CM remnants (apoB-48 particles). This finding was obtained using the following three analytical methods; isolation of remnant-like lipoprotein particles (RLP) with specific antibodies, separation and detection of lipoprotein subclasses by gel permeation HPLC and determination of apoB-48 in fractionated lipoproteins by a specific ELISA. The amount of the apoB-48 particles in the postprandial RLP is significantly less than the apoB-100 particles, and the particle sizes of apoB-48 and apoB-100 in RLP are very similar when analyzed by HPLC. Moreover, CM or CM remnants having a large amount of TG were not found in the postprandial RLP. Therefore, the major portion of the TG which is increased in the postprandial state is composed of VLDL remnants, which have been recognized as a significant risk for cardiovascular disease.

Pitavastatin prevents postprandial endothelial dysfunction via reduction of the serum triglyceride level in obese male subjects

Obesity is a well-established risk factor for the development and progression of coronary heart disease. Moreover, endothelial dysfunction is an early event in atherosclerosis and is known to be associated with postprandial hypertriglyceridemia. The purpose of this study was to determine whether a statin might have an effect on postprandial hypertriglyceridemia, and thereby on endothelial function in obese subjects. Twenty-four obese male subjects were recruited for this study. They were randomly assigned to receive pitavastatin (2 mg/day) or placebo for 2 weeks. The oral fat loading test using OFTT cream was performed pre- and post-treatment, in which the lipid profile and flow-mediated dilation (FMD) were assessed before and 4 h after an oral fat load. In the oral fat loading test conducted pretreatment, the oral fat load induced a marked increase of the serum triglyceride (TG) level and decrease in FMD in the pitavastatin and placebo group. In the test conducted post-treatment, the increase in postprandial TG was attenuated (+183 vs. +81 mg/dL, P < 0.001) and decrease in postprandial FMD was completely abolished (-1.1 vs. +0.1%, P < 0.01) by pitavastatin treatment. Moreover, there was a good correlation between the change in postprandial TG and the change in postprandial FMD after the 2 weeks of treatment (r = -0.737, P < 0.001). Pitavastatin might prevent endothelial dysfunction caused by postprandial hypertriglyceridemia within 2 weeks of therapy in obese subjects.

Particle size of apoB-48 carrying lipoproteins in remnant lipoproteins isolated from postprandial plasma

BACKGROUND

Particle size of apoB-48 carrying lipoproteins in remnant-like lipoprotein particles (RLP) in postprandial plasma has not been well characterized.

METHODS

Plasma lipids, lipoproteins and apolipoproteins in 12 healthy subjects were analysed after an oral fat load. RLP isolated by immunoaffinity gel from plasma of a normolipidaemic and a hyperlipidaemic subject in four hours after an oral fat load was fractionated by high-performance liquid chromatography (HPLC) and monitored by total cholesterol (TC), triglycerides (TG), apoB-48 and apoB-100.

RESULTS

TC, low-density lipoprotein (LDL)-C and apoB did not change after an oral fat load, while TG, RLP-C, RLP-TG and apoB-48 increased significantly in postprandial plasma. HPLC profiles monitored by TC and TG revealed that major lipoproteins increased in RLP after an oral fat load was VLDL size particles. The percentage of RLP-TG in total TG and the ratio of RLP-TG/RLP-C were significantly increased in four hours after an oral fat load compared with the fasting state (P < 0.01). RLP in four hours after an oral fat load fractionated by HPLC and monitored by TC, TG, apoB-48 and apoB-100 revealed that VLDL size or smaller particles were the major lipoproteins.

CONCLUSIONS

ApoB-48 carrying lipoproteins in RLP isolated from a normolipidaemic and a hyperlipidaemic subject after an oral fat load showed a similar particle size with apoB-100 carrying VLDL remnants. Therefore, the most apoB-48 carrying particles found in postprandial RLP can be classified as CM remnants. The majority of remnants in the postprandial state were not CM remnants, but VLDL remnants.

APOB-516 T allele homozygous subjects are unresponsive to dietary changes in a three-month primary intervention study targeted to reduce fat intake

Dietary guidelines aim to control fat intake and reduce cardiovascular risk but an important interindividual variability occurs among subjects. The objective was to investigate whether the response of lipid and glucose homeostasis parameters after a three-month diet aimed at reducing cardiovascular risk could be modulated by the -516C/T polymorphism in the apolipoprotein B gene (APOB). Middle-aged men (n = 69) and women (n = 100) with moderate cardiovascular disease risk were advised to reduce total energy and fat intakes and replace saturated dietary fat by monounsaturated and polyunsaturated fat. Subjects were genotyped for APOB-516C/T polymorphism. At the entry and at the end of the three-month period, fasting and postprandial plasma lipid analyses were performed. At entry, subjects homozygous for the APOB-516 T allele exhibited significantly lower fasting plasma concentrations of apolipoprotein B 48, triglycerides and triglyceride-rich lipoproteins-triglycerides compared to C carrier subjects. After the diet period, while C carrier subjects presented a clear improvement of most biological parameters, paradoxically T/T subjects did not modify them. In addition, the apoB 48 postprandial response after a standardized mixed test meal was not improved in T/T subjects after the three-month diet, contrary to C allele carriers. Even though their phenotype at entry does not show any significant increase of risk factors when compared to other groups, subjects homozygous for the APOB-516 T allele are unresponsive to a healthy diet that improves cardiovascular risk status in the whole population.

Methods to assess impaired post-prandial metabolism and the impact for early detection of cardiovascular disease risk

Post-prandial lipaemia has emerged as a key contributor to cardiovascular disease (CVD) risk and progression. Specifically, delayed clearance of chylomicrons (CM) and their remnants increase the delivery of triglyceride and cholesteryl ester to the vessel wall and can accelerate the progression of atherosclerosis, which may be particularly pertinent to individuals with insulin resistance and/or obesity. As the number of studies linking post-prandial metabolism and chronic disease increases, interest has grown in the use of parameters reflecting CM metabolism as a possible indicator of early CVD risk. This, in turn has raised the question of what method might be most appropriate to detect CM and their remnants in plasma accurately. However, the handful of techniques able to measure CM metabolism (triglyceride-rich lipoprotein fractions; remnant-lipoprotein cholesterol; retinyl esters, CM-like emulsion; sodium dodecyl sulphate-polyacrylamide gel electrophoresis; immunoblotting, enzyme-linked immunoabsorbent assays; C(13) breath test; capillary finger prick) differ in their specificity, cost and applicability in research and in the clinical setting. In this review, we explore the scientific and clinical implications of CM methodology to better understand early risk assessment of CVD. We raise ongoing issues of the need to appreciate differential separation of very low-density lipoprotein and CM fractions, as well as to identify the technical basis for imprecision between assays for apolipoprotein B48. We also highlight emerging issues with respect to the practicality of measuring post-prandial metabolism in large clinical studies and offer opinions on the appropriateness of existing techniques in this field.

A deficiency of cholesteryl ester transfer protein whose serum remnant-like particle-triglyceride significantly increased, but serum remnant-like particle-cholesterol did not after an oral fat load

Background

We found a unique cholesteryl ester transfer protein (CETP) deficient case with markedly elevated serum triglyceride (TG) as well as high-density lipoprotein cholesterol (HDL-C) levels. Most of the CETP deficiency cases were reported to have normal or reduced serum TG with elevated HDL-C.

Methods

The case subject was a 40-year-old male with a compound heterozygous CETP deficiency. Two heterozygous CETP deficient cases and 10 normal volunteers were also recruited as controls. They underwent an oral fat tolerance test (OFTT) and their blood was taken at fasting and during the OFTT to be used for laboratory tests.

Results

The case subject had apolipoprotein E (apo-E) phenotype 4/2 with fatty liver but without any cardiovascular disease. His serum TG, HDL-C, apo-AI and apo-B48 levels were significantly higher, but the low-density lipoprotein cholesterol level was lower than controls. Although post-heparin plasma lipoprotein lipase and hepatic lipase (both mass and activity) were nearly normal, the serum level of angiopoietin-like-protein-3 was extremely elevated. While his serum remnant-like particles-TG (RLP-TG) and total TG levels significantly increased after a fat load, the RLP-cholesterol (RLP-C) level did not increase during OFTT.

Conclusions

The case subject was different from the common CETP deficient cases reported previously. Also, the results indicated that the metabolic pathways of RLP-C and RLP-TG formation in the postprandial state are controlled independently in CETP deficient cases. CETP deficiency itself may not be atherogenic, while one with elevated RLPs may be atherogenic. These cases may have raised the controversy of whether CETP deficiency is atherogenic or not.

Fasting and postprandial remnant-like particle cholesterol concentrations in obese participants are associated with plasma triglycerides, insulin resistance, and body fat distribution

Elevated plasma concentrations of remnant-like particle cholesterol (RLP-C) are atherogenic. However, factors that determine RLP-C are not fully understood. This study evaluates which factors affect RLP-C in the fasting and postprandial state, using multiple regression analyses in a large cohort of lean and obese participants. All participants (n = 740) underwent a test meal challenge containing 95 energy % (en%) fat (energy content 50% of predicted daily resting metabolic rate). Fasting and postprandial concentrations of circulating metabolites were measured over a 3-h period. Obese participants (n = 613) also participated in a 10-wk weight loss program (-2510 kJ/d), being randomized to either a low-fat or a high-fat diet (20-25 vs. 40-45en% fat). Postprandial RLP-C was associated with fasting RLP-C, waist:hip ratio (WHR), HOMA(IR) (homeostasis model assessment index for insulin resistance) (P < 0.001), and age, independently of BMI and gender [adjusted R(2) (adj. R(2)) = 0.70). These factors were also related to fasting RLP-C (P < 0.010), along with gender and physical activity (adj. R(2) = 0.23). The dietary intervention resulted in significantly lower fasting RLP-C concentrations, independently mediated by weight loss, improvements in HOMA(IR), and the fat content of the prescribed diet. However, after inclusion of plasma triglyceride (TG), HDL-cholesterol, and FFA concentrations in the models, HOMA(IR) and WHR no longer significantly predicted fasting RLP-C, although WHR remained a predictor of postprandial RLP-C (P = 0.002). Plasma TG was strongly associated with both fasting and postprandial RLP-C (P < 0.001). In conclusion, plasma RLP-C concentrations are mainly associated with plasma TG concentrations. Interestingly, the high-fat diet was more effective at decreasing fasting RLP-C concentrations in obese participants than the low-fat diet.

Suppressive effects of diacylglycerol oil on postprandial hyperlipidemia in insulin resistance and glucose intolerance

The diacylglycerol (DAG), a commonly used as a cooking oil in Japan, results in a lower elevation of serum triglyceride (TG) after ingestion compared to triacylglycerol (TAG). Postprandial hyperlipidemia (PPHL) and an increase in remnant lipoproteins (RLP) levels are risk factors for CAD, and a close relationship between PPHL and type 2 diabetes and/or insulin resistance has been reported. To evaluate the effect of DAG on PPHL in insulin resistance and glucose intolerance, 11 subjects with a normal glucose tolerance (NGT) and 14 subjects with IGT received oral fat tolerance test (OFTT) twice. They ingested emulsified test oils prepared with either DAG or TAG. In the IGT subjects, after the DAG and TAG load, the serum concentrations of TG, RLP-TG, and RLP-cholesterol increased throughout the 4-h study. The responses of these variables above baseline after the DAG load were significantly smaller than those after the TAG load (p<0.05). In contrast, in the NGT subjects, changes in these parameters were much smaller than those observed for IGT subjects. The difference in the integrated responses for serum RLP-cholesterol concentration during OFTT between DAG and TAG in all subjects can be easily explained by the integrated response of insulin rather than glucose during oral glucose tolerance test (r=0.7, p<0.01). DAG was more effective in insulin resistant and hyperinsulinemic participants regardless of glucose intolerance, and may be beneficial in reducing the extent of CAD risk in such individuals.

Serum concentration of small dense low-density lipoprotein-cholesterol during oral glucose tolerance test and oral fat tolerance test

BACKGROUND

Small dense low-density lipoprotein (sdLDL) is well known as an atherogenic lipoprotein. We developed a new assay to measure serum concentration of sdLDL-cholesterol (sdLDLC). Using this assay, we reported a unique circadian rhythm of sdLDLC. We determined whether a glucose intake and/or a fat intake affects on serum sdLDLC concentration and determined the modulators of serum sdLDLC concentration.

METHODS

Ten healthy volunteers were recruited to perform both a 75 g oral glucose tolerance test (OGTT) and an oral fat tolerance test (OFTT) to determine the effects of glucose and fat ingestion separately. Blood was measured for sdLDLC concentration and other valuables.

RESULTS

Serum concentrations of total cholesterol, LDLC, remnant-like particles-cholesterol (RLPC), and apolipoprotein B significantly decreased during OGTT (p<0.05). SdLDLC also decreased and was a minimum at 2 h after glucose ingestion and increased to the baseline by 3 h. The sdLDLC decrease was seen while serum insulin level was high. The change of sdLDLC during OGTT had greater inverse correlationship with that of serum insulin level (r=-0.74, p<0.01) than that of plasma glucose level (r=-0.69, p=0.04). After fat ingestion, triglyceride and RLPC increased remarkably (p<0.01) but sdLDLC, LDLC, apolipoprotein B, and insulin did not change significantly.

CONCLUSIONS

Serum concentration of sdLDLC was not affected by a fat intake but by a glucose intake. The change of sdLDLC was associated by that of serum insulin level, suggesting that insulin can be one of the key modulator of serum sdLDLC level as well as LDL metabolism.

Effect of pioglitazone on atherogenic outcomes in type 2 diabetic patients: a comparison of responders and non-responders

The aim of this study was to evaluate the anti-atherogenic efficacy of pioglitazone, a thiazolidinedione derivative, on the change in atherogenic outcomes by comparing responder and non-responder groups in type 2 diabetic patients. Twenty-three patients with poor diabetic control were treated with 15 mg of pioglitazone for 12 months. The levels of fasting plasma glucose (FPG), HbA1c, triglycerides (TG), total cholesterol (T-Cho), low-density lipoprotein-cholesterol (LDL-C), and high-density lipoprotein-cholesterol (HDL-C) were measured monthly, and those of remnant-like particle-cholesterol (RLP-C) and lipoprotein (a) [Lp (a)] were measured every 3 months. In Month 6, the patients were divided into two groups according to the decrease in HbA1c level: the responder group showed a decrease of > or =1%; the non-responder group, a decrease of <1%. In the responder group, the levels of FPG and HbA1c decreased significantly after Month 3. The values of the body mass index (BMI), homeostasis model assessment of insulin resistance (HOMA-IR) index, LDL-C, and RLP-C were significantly higher in the responder group than in the non-responder group. Although the levels of T-Cho and HDL-C were unchanged in both groups, those of TG and RLP-C were drastically reduced in the responder group. Interestingly, the relative change in Lp (a) was significantly decreased in both groups. These results strongly suggest that pioglitazone is beneficial for type 2 diabetic patients with high levels of BMI, HOMA-IR, LDL-C, and RLP-C, as it helps to prevent the progression of atherosclerosis, including coronary heart diseases.

Postprandial lipemia is modified by the presence of the APOB-516C/T polymorphism in a healthy Caucasian population

Apolipoprotein (apoB) plays a fundamental role in the transport and metabolism of plasma triacylglycerols (TAGs) and cholesterol. Several apoB polymorphic sites have been studied for their potential use as markers for coronary heart disease in the population. In view of the importance of apoB in postprandial metabolism, our objective was to determine whether the presence of the -516C/T polymorphism in the APOB gene promoter could influence postprandial lipoprotein metabolism in healthy subjects. Forty-seven volunteers who were homozygous for the E3 allele at the APOE gene were selected (30 homozygous for the common genotype (C/C) and 17 heterozygotes for the -516T allele (C/T). They were given a fat-rich meal containing 1 g fat and 7 mg cholesterol per kg body weight and vitamin A 60,000 IU/m(2) body surface. Fat accounted for 60% of calories, and protein and carbohydrates for 15 and 25% of energy, respectively. Blood samples were taken at time 0, every 1 h until 6 h, and every 2.5 h until 11 h. Total cholesterol and TAGs in plasma, and cholesterol, TAGs and retinyl palmitate in triacylglycerol-rich lipoproteins (large and small triacylglycerol-rich lipoproteins) were determined by ultracentrifugation. Individuals carrying the C/T genotype presented greater postprandial concentrations of TAGs in small triacylglycerol-rich lipoproteins than did carriers of the C/C genotype (P = 0.022). Moreover, C/T individuals presented higher concentrations of plasma TAGs during the postprandial period than did C/C subjects (P = 0.039). No other statistically significant genotype-related differences for other parameters were observed. These results suggest that the presence of the genotype C/T is associated with a higher postprandial response. Thus, the allele variability in the -516C/T polymorphism in the APOB gene promoter may partly explain the interindividual differences in postprandial lipemic response in healthy subjects.

Circadian rhythm of serum concentration of small dense low-density lipoprotein cholesterol

BACKGROUND

The atherogenicity of small dense low-density lipoprotein (sdLDL) has been reported and recently a new easy-handling method for measuring serum concentration of sdLDL cholesterol (sdLDLC) has been developed. Using this method, we observed the circadian rhythm of sdLDLC to determine the adequacy of fasting measurement of it and to seek the modulator of the atherogenic lipoprotein.

METHODS

Study population was consisted of 20 healthy volunteers (10 women and 10 men, mean age 28 y). They had 3 meals per day and blood samples were taken before and 2 h after every meal and next morning. Serum concentrations of sdLDLC and other valuables including triglyceride (TG) and remnant-like particles cholesterol (RLPC) were determined.

RESULTS

Serum concentration of sdLDLC had a unique circadian rhythm that was highest before breakfast (fasting status), decreased after each meal, hit the bottom after dinner and then increased during at night. Fasting sdLDLC was highly correlated with TG levels. The sum of the 6 TG values during a day (i.e., average TG level) had higher correlation coefficient with sdLDLC than fasting TG or fasting RLPC.

CONCLUSIONS

From the observation of the unique circadian rhythm, measuring sdLDLC at fasting status is exactly reasonable because it never underestimate the risk of atherosclerotic diseases. Measuring sdLDLC can also be used as a marker for average TG levels regardless of the existence of postprandial hyperlipidemia.

Association between postprandial remnant-like particle triglyceride (RLP-TG) levels and carotid intima-media thickness (IMT) in Japanese patients with type 2 diabetes: assessment by meal tolerance tests (MTT)

Our study evaluated the relationship between the pathologic changes associated with atherosclerosis, as primarily represented by postprandial remnant-like lipoproteins and carotid intima-media thickness (IMT), in type 2 diabetic patients. Meal tolerance tests (MTT) were performed in 68 patients with type 2 diabetes. The subjects were divided by pre-meal and 2-h postprandial triglyceride (TG) levels into the normotriglyceridemia (NTG) group; the postprandial hypertriglyceridemia (PHTG) group; and the fasting hypertriglyceridemia (FHTG) group. HOMA-R values were significantly higher in the FHTG group than in the NTG group, with the plasma pre-heparin LPL mass and serum adiponectin levels in the FHTG and PHTG groups significantly lower than in the NTG group. One- and two hour postprandial RLP-TG levels were significantly higher in the PHTG group than in the NTG group, while there was no significant difference in postprandial glucose levels between the two groups. The IMT values were significantly higher in both the FHTG and PHTG groups than in the NTG group. Logistics regression analysis of the 1- and 2-h RLP-TG values using IMT as an induced variable showed the odds ratio for high IMT values to be 5.17 (p < 0.05) for the 1-h RLP-TG values and 3.01 (p = 0.105) for the 2-h RLP-TG values. Our study results suggest that delayed TG metabolism leading to the retention of remnants in type 2 diabetic patients appears to be closely associated with atherosclerosis, and that postprandial hyperlipidemia is an independent risk factor for the early onset of atherosclerosis.

Effects of diacylglycerol ingestion on postprandial hyperlipidemia in diabetes

BACKGROUND

We previously reported that diacylglycerol (DAG) as compared with triacylglycerol (TAG) suppressed increases in postprandial lipids in healthy volunteers. This study was to investigate the effects of DAG on postprandial lipids, particularly remnant lipoproteins in diabetics.

METHODS

Emulsified DAG oil or TAG oil with a fatty acid composition similar to DAG oil was orally administered (30 g fat/m2 of body surface) to moderately controlled six diabetics, with hemoglobin A1c (HbA1c) below 8%, after fasting for at least 12 h in a randomized crossover manner. Serum cholesterol and TAG, lipids in remnant-like particles (RLP), and other lipid parameters including serum ketone bodies were measured prior to and 2, 4, and 6 h after fat loading.

RESULTS

DAG loading significantly suppressed increases in postprandial serum TAG and lipids in RLP as compared with TAG loading. The incremental area under the curve (IAUC) for serum TAG and that for lipids in RLP with DAG loading were also significantly smaller than those with TAG loading. However, changes in serum levels of insulin, free fatty acids, and ketone bodies during fat loading were essentially the same for DAG and TAG.

CONCLUSIONS

This pilot study suggests that substituting DAG intake for TAG may be beneficial to moderately controlled diabetics due to its effect in reducing postprandial hyperlipidemia.

Compensatory hyperinsulinemia and the development of an atherogenic lipoprotein profile: the price paid to maintain glucose homeostasis in insulin-resistant individuals

The ability of insulin to stimulate glucose disposal varies sixfold to eightfold among apparently healthy individuals. The only way that insulin-resistant persons can prevent the development of type 2 diabetes is by secreting the increased amount of insulin that is necessary to compensate for the resistance to insulin action. The greater the magnitude of muscle and adipose tissue insulin resistance, the more insulin must be secreted to maintain normal or near-normal glucose tolerance. Although compensatory hyperinsulinemia may prevent the development of fasting hyperglycemia in insulin-resistant individuals, the price paid is the untoward physiologic effects of increased circulating insulin concentrations on tissues that retain normal insulin sensitivity. This article focused on the interplay between insulin resistance at the level of the muscle and adipose tissue and normal hepatic insulin sensitivity; this leads to the atherogenic lipoprotein profile that is characteristic of insulin-resistant individuals. It would be inappropriate to minimize the importance of differential insulin sensitivity in the genesis of the changes in lipoprotein metabolism that increase CVD risk in insulin-resistant persons. It would be equally remiss not to emphasize that differential tissue insulin resistance also is necessary to explain why insulin-resistant/hyperinsulinemic individuals are more likely to develop the clinical syndromes (with the exception of type 2 diabetes mellitus) that are listed in Box 1.

Remnant lipoproteins and atherosclerosis

A recently developed assay for quantification of remnant-like particle cholesterol has provided considerable evidence that reinforces the concept that elevated levels of plasma remnants are associated with increased cardiovascular disease in different populations and distinct patient groups. In this review, we provide a brief summary of the most recently published studies, emphasizing the clinical relevance of remnant analysis. We discuss recent evidence that sheds light on the mechanisms that may underlie the atherogenicity of remnant lipoproteins. Taken together, these data provide new insight into the significance of remnant lipoproteins in the onset and development of premature atherosclerosis.

Determinants of postprandial triglyceride and remnant-like lipoproteins in type 2 diabetes

BACKGROUND

Postprandial changes in remnant-like lipoprotein particles (RLP) contribute to the severity of coronary heart disease in type 2 diabetes. Since the determinants of postprandial response in RLP are not well understood, this study investigated the roles of fasting triglyceride, apolipoprotein (apo) E polymorphism and insulin resistance in a group of overweight/obese Chinese type 2 diabetic subjects.

METHODS

Postprandial triglyceride (TG) and RLP-cholesterol (RLP-C) were determined after a mixed meal containing 70-g fat at 2-h intervals for 8 h in 32 normotriglyceridemic (NTG) and 31 hypertriglyceridemic (HTG) subjects. RLP-C was measured using an immunoseparation assay and apo E genotypes using polymerase chain reaction and restriction mapping. Insulin resistance was defined as homeostasis model assessment index (HOMA-IR).

RESULTS

The HTG subjects had greater postprandial increase in TG and RLP-C than NTG (p < 0.001), but there were no significant differences in HOMA-IR and apo E allele frequencies. Subjects who were non-E3-carriers had the largest postprandial increment in TG and RLP-C. On stepwise linear regression analysis, log(HOMA-IR) was only an independent determinant of fasting TG but not postprandial TG or RLP-C. The major determinants of fasting and postprandial RLP-C were fasting TG and apo E genotype, accounting for 53 and 6% of the variance of fasting RLP-C (p < 0.01) and 31 and 13% of the variance of postprandial RLP-C respectively (p < 0.01).

CONCLUSIONS

Insulin resistance is mainly a determinant of fasting triglyceride in Chinese type 2 diabetic subjects, whereas apo E genotype is a better predictor of both fasting and postprandial concentrations of RLP.

Effect of diacylglycerol on postprandial lipid metabolism in non-diabetic subjects with and without insulin resistance

The effects of diacylglycerol ingestion on postprandial lipid metabolism in non-diabetic subjects with and without insulin resistance were investigated. This was single dose ingestion study, in a double blind cross over manner and postprandial lipid concentrations were compared between diacylglycerol oil (DAG) and triacylglycerol oil (TAG) ingestion. The subjects were 18 male volunteers and homeostasis model assessment (HOMA-R) was used to classify them into insulin sensitive (IS, n=10, HOMA-R<2.0) and insulin resistant (IR, n=8, HOMA-R> or =2.0) groups. Fasting serum triglycerides (TG) and remnant-like particle cholesterol (RLP-C) correlated with HOMA-R and were significantly higher in the IR as compared to the IS group. Postprandial increments of TG and RLP-C after DAG ingestion were significantly lower as compared to those after TAG ingestion. In a case of TAG ingestion, their increments positively correlated with HOMA-R and were significantly higher in the IR as compared with the IS group. In contrast, their increments remained constant after DAG ingestion in both groups. In the IR group, the postprandial lipidemia were reduced after DAG ingestion to about half of those after TAG ingestion. In conclusion, DAG reduced postprandial lipidemia especially in subjects with insulin resistance and may be beneficial in preventing atherosclerosis and related diseases.

Remnant Lipoproteins and Atherogenesis

Recent clinical studies have revealed that increased serum triglyceride (TG) levels are closely related to atherosclerosis, independently of serum levels of high-density lipoproteins (HDL) and low-density lipoproteins (LDL). Among triglyceride-rich lipoproteins (TRLs), remnant lipoproteins (RLPs) are considered to be atherogenic and an independent coronary risk factor. We previously reported that monocytes cultured in the presence of RLPs increased their adhesion to vascular endothelial cells. The underlying mechanism involved activation of RhoA, a member of small GTP binding proteins, resulting in activation of focal adhesion kinase (FAK) and s1-integrin. It is also known that RLPs enter vessel walls. In another study, we reported that RLPs induced smooth muscle cell (SMC) proliferation, independently of oxidative stress. Recently, we identified the molecular mechanisms, in which RLPs from hypertriglyceridemic patients stimulated SMC proliferation via epidermal growth factor (EGF) receptor transactivation and heparin-binding EGF-like growth factor (HB-EGF) shedding. More recently, we reported that apoB48 receptor was involved in RLP-induced foam cell formation in macrophages. The current review focused on the molecular mechanisms for the atherogenicity of RLPs.

The effect of acute red wine polyphenol consumption on postprandial lipaemia in postmenopausal women

Postprandial lipoproteins are potentially atherogenic. The aim of this study was to elucidate whether acute consumption of red wine (RW) and dealcoholised red wine (DRW) regulates postprandial lipid and lipoprotein metabolism in 17 dyslipidaemic postmenopausal women. A mixed meal accompanied by either water, RW or DRW was consumed on three separate visits, in random order, 2 weeks apart. One fasting and 6 hourly postprandial blood samples were taken for lipid analysis. Results showed no significant quantitative changes in postprandial apolipoprotein (apo) B48 levels following the consumption of DRW or RW compared to water. However, qualitatively, DRW may reduce arterial exposure to apoB48-containing lipoproteins over the 6-h postprandial period measured. DRW consumption did not significantly change postprandial TG or insulin levels. A 35% (p = 0.02) increase in postprandial triglyceride (TG) levels and a 54% (p = 0.02) increase in insulin levels were observed following RW consumption, compared to water. In conclusion, acute DRW consumption had no effect on postprandial lipid and lipoprotein metabolism in dyslipidaemic postmenopausal women. However, the consumption of full-compliment RW exacerbated the postprandial lipaemic and insulin response over the 6-h period. Collectively, our findings suggest that neither polyphenols nor red wine reduce atherosclerotic risk by acutely modulating postprandial lipaemia over a 6-h period.

A randomized study comparing the effects of a low-carbohydrate diet and a conventional diet on lipoprotein subfractions and C-reactive protein levels in patients with severe obesity

PURPOSE

To compare the effects of a low-carbohydrate diet and a conventional (fat- and calorie-restricted) diet on lipoprotein subfractions and inflammation in severely obese subjects.

METHODS

We compared changes in lipoprotein subfractions and C-reactive protein levels in 78 severely obese subjects, including 86% with either diabetes or metabolic syndrome, who were randomly assigned to either a low-carbohydrate or conventional diet for 6 months.

RESULTS

Subjects on a low-carbohydrate diet experienced a greater decrease in large very low-density lipoprotein (VLDL) levels (difference = -0.26 mg/dL, P = 0.03) but more frequently developed detectable chylomicrons (44% vs. 22%, P = 0.04). Both diet groups experienced similar decreases in the number of low-density lipoprotein (LDL) particles (difference = -30 nmol/L, P = 0.74) and increases in large high-density lipoprotein (HDL) concentrations (difference = 0.70 mg/dL, P = 0.63). Overall, C-reactive protein levels decreased modestly in both diet groups. However, patients with a high-risk baseline level (>3 mg/dL, n = 48) experienced a greater decrease in C-reactive protein levels on a low-carbohydrate diet (adjusted difference = -2.0 mg/dL, P = 0.005), independent of weight loss.

CONCLUSION

In this 6-month study involving severely obese subjects, we found an overall favorable effect of a low-carbohydrate diet on lipoprotein subfractions, and on inflammation in high-risk subjects. Both diets had similar effects on LDL and HDL subfractions.

The close relationship between postprandial remnant metabolism and insulin resistance

The aim of this study was to investigate the relationship between postprandial remnant-like particle (RLP) metabolism and insulin resistance (IR). The study group consisted of 52 randomly selected subjects. To evaluate postprandial hyperlipidemia, serum lipid and lipoprotein concentrations during fasting and 4h after the fat-loading test were measured in each subject. IR was assessed using the index of homeostasis model assessment (HOMA-R). The subjects were divided into two groups according to the value of HOMA-R: an IR group (n=17) with a HOMA-R value >/=1.73, and a normal (NR) group (n=35) with a HOMA-R value <1.73. Both fasting and postprandial RLP-cholesterol (RLP-C) concentrations were higher in the IR group than in the NR group (6.2+/-2.6 versus 4.1+/-1.7mg/dl fasting value, and 9.7+/-4.0 versus 5.8+/-2.9mg/dl postprandial value). The changes in RLP-C concentration during the fat-loading test were twice as high in the IR group compared with the NR group (3.5+/-2.4 versus 1.6+/-1.6mg/dl, P=0.0022). The HOMA-R correlated significantly with both fasting and postprandial triglyceride (r=0.41 and 0.43, respectively) and RLP-C (r=0.36 and 0.50, respectively) in all subjects. Multiple regression analysis indicate that postprandial RLP-C concentration was an independent predictor of HOMA-R regardless of age, BMI, and other lipid profiles. Thus, postprandial RLP metabolism is closely related to IR. Atherosclerotic proliferation in IR syndrome may be caused by the accumulation of postprandial remnant lipoproteins after the daily fat intake.

Postprandial Hyperlipidemia and Atherosclerosis

The development of the remnant like particle (RLP) method for conveniently measuring serum remnant lipoprotein levels in 1993 promoted much research on atherogenic significance and metabolism of remnant lipoproteins. This research brought about many results as the following. A novel apolipoprotein B48 receptor incorporating remnant lipoproteins into macrophages in arterial wall was discovered and the structure of the gene of the receptor was clarified. The expression of apolipoprotein B100 was recognized in the human small intestine, suggesting that dietary very low density lipoproteins (VLDL) might be synthesized in the human small intestine and converted into VLDL remnants and low density lipoproteins (LDL). It is recognized that the atherosclerotic risk of postprandial hyperlipidemia is derived from an increase of remnant lipoproteins and that measurement of serum RLP levels in postprandial state is more sensitive and necessary for evaluating an atherosclerotic risk because serum RLP levels remain high all day in patients with diabetes mellitus or coronary heart disease. The relation between postprandial hyperlipidemia and insulin resistance was clarified.

Clinical Utility and Approach to Estimate Postprandial Hypertriglycemia by A Newly Designed Oral Fat-loading Test

The objective of this study was to estimate postprandial hypertriglycemia by a newly designed oral fat-loading test. Twenty-three healthy normolipidemic volunteers were orally administered a test meal consisting of a mixture of Telmeal 2.0 and 20 g of salt-free butter after fasting for 12 h. To measure the levels of total cholesterol (T-Cho), triglycerides (TG), high-density lipoprotein-cholesterol (HDL-C), remnant-like particle-cholesterol (RLP-C), lipoprotein (a) [Lp (a)], free fatty acid, apolipoproteins (Apos), plasma glucose (PG), immunoreactive insulin (IRI), and high-sensitivity C-reactive protein (hs-CRP), venous blood samples were collected before the meal and at each hour until 9 h after fat-loading. The levels of both TG and RLP-C were drastically elevated at 2 h after fat-loading and these levels remained high until 4 h (p < 0.01). A significant correlation between TG and RLP-C was also observed at 2, 3 and 4 h, and the values of the correlation coefficients (r) were 0.837, 0.838, and 0.908, respectively. In contrast, the levels of T-Cho, HDL-C, Lp (a), Apos, PG, and hs-CRP did not change. Furthermore, there were no gastrointestinal symptoms during or after the study. These results strongly suggested that this newly designed fat-loading test was very useful for evaluating postprandial hypertriglycemia, including remnant concentrations.