Appearance of multidisperse low density lipoprotein and altered lipoprotein composition in non-insulin-dependent diabetes with type IIa hyperlipoproteinemia

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.

Decreased affinity of low density lipoprotein (LDL) particles for LDL receptors in patients with cholesteryl ester transfer protein deficiency

We have reported that the disorder of lipoprotein metabolism in hyperalphalipoproteinaemic patients with a deficiency of cholesteryl ester transfer protein (CETP) is characterized by the polydisperse low density lipoprotein (LDL) particles and the accumulation of cholesteryl ester (CE) in high density lipoprotein (HDL) particles, forming cholesterol-induced HDL (HDLc)-like particles. In the present study we have investigated the interaction of these abnormal LDL with LDL receptors of normal human fibroblasts. Since the ultracentrifugally separated LDL fraction (1.019 < d < 1.063 g mL-1) from the CETP-deficient patients contained HDLc-like particles, these particles were removed by anti-apolipoprotein (apo) A-I immunoaffinity column chromatography. The lipoproteins eluted in the unbound fraction of this column did not contain apo A-I, so this fraction was considered to be authentic LDL. The authentic LDL of the patients were deficient in CE and rich in triglycerides and apo B. The authentic LDL itself showed polydispersity, ranging in size from 23 nm to 30 nm. The affinity of these abnormal LDL particles for LDL receptors was analysed by a competitive assay in which cold LDL from the patients or control compete with 125I-labelled LDL for fibroblast LDL receptors. The concentration of LDL particles at which 50% of 125I-labelled normal LDL was replaced was two to three times higher for the patients than for the normal control. Therefore, the affinity of patient LDL was thought to be reduced compared to that of control LDL. These results demonstrate that CETP may play an important role in making LDL particles homogeneous and rich in CE.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of glipizide treatment on postprandial lipaemia in patients with NIDDM

The primary goal of the present study was to examine the effects of improved glycaemic control associated with glipizide treatment on postprandial lipaemia in non-insulin-dependent diabetic patients. The metabolism of triglyceride-rich lipoproteins of intestinal origin was assessed by measuring the retinyl palmitate content in plasma and the Svedberg flotation index (Sf) > 400 and Sf 20-400 lipoprotein fractions. Fasting plasma glucose concentrations (14.5 +/- 0.5 vs 9.0 +/- 0.5 mmol/l), glycated haemoglobin levels (13.1 +/- 0.6 vs. 9.7 +/- 0.6%), and daylong plasma glucose concentrations were all significantly lower after glipizide treatment (p < 0.001). The improvement in glycaemic control was associated with increases in insulin-mediated glucose uptake (p < 0.001) and plasma post-heparin lipoprotein and hepatic lipolytic activities (p < 0.02). Both fasting plasma triglyceride (3.09 +/- 0.51 vs 2.37 +/- 0.34 mmol/l), and postprandial triglyceride concentrations (p < 0.05-0.001) were lower following glipizide treatment, associated with a significant fall in retinyl palmitate content in all three lipoprotein fractions (p < 0.02-0.001), with the most substantial decrease seen in the Sf20-400 fraction. These data indicate that glipizide-induced improvement in glycaemic control was associated with changes in the metabolism of triglyceride-rich lipoproteins of intestinal origin that would be anticipated to reduce risk of coronary heart disease in non-insulin-dependent diabetic patients.

Diabetic dyslipidemia

Diabetes is associated with increased morbidity and mortality from cardiovascular disease in the absence of the major risk factors: cigarette smoking, hypertension, and serum cholesterol concentration. When these risk factors are present, the attributable risk to each factor alone and to the combination of risk factors is higher in diabetics than in nondiabetics. Thus, stringent measures to correct risk factors for cardiovascular disease have been advocated in diabetic patients. In addition to hypercholesterolemia, other lipid and lipoprotein abnormalities collectively referred to as diabetic dyslipidemia are likely to contribute to vascular risk. Hypertriglyceridemia often associated with low high-density lipoprotein cholesterol is common in non-insulin-dependent diabetes mellitus patients and is associated with insulin resistance. Recent information in diabetic patients pointing to the association of hypertriglyceridemia with accumulation of remnant particles and alterations in low-density lipoprotein subfractions helps to explain the strong relationship between hypertriglyceridemia and vascular risk in these individuals. Although there are as yet no intervention trials with lipid-lowering diets or drugs in diabetic patients to judge the impact on vascular disease, national and international bodies have furnished guidelines for the identification and treatment of lipid disorders in diabetes in the hope of reducing the huge toll of vascular disease in these patients.

Treatment of non-insulin-dependent diabetes mellitus and its complications. A state of the art review

Non-insulin-dependent diabetes mellitus (NIDDM) is a major health problem which occurs predominantly in the older population; 16.8% of persons over age 65 years have NIDDM. The total health costs of NIDDM are in excess of $US20 billion annually. The primary objective in the treatment of NIDDM is to achieve normoglycaemia, without aggravating coexisting abnormalities. Common abnormalities include obesity, hypertension, retinopathy, nephropathy and neuropathies. Diet, and consequent bodyweight reduction, is the cornerstone of therapy for NIDDM. Total calorie intake should be limited, while the percentage of calories from carbohydrates should be increased and that from fats and cholesterol should be decreased. Exercise may also help to reduce bodyweight. Sulphonylurea drugs stimulate insulin secretion from beta-cells, and may be a useful adjunct to nonpharmacological therapy. Failure to respond to sulphonylurea drugs may be primary (25 to 30% of initially treated patients) or secondary (5 to 10% per year). It is not clear which is the most effective pharmacological intervention in such cases. Options include switching to or combining therapy with insulin, a biguanide, or other insulin-sparing antihyperglycaemic agents, e.g. alpha-glucosidase inhibitors, thiazolidinediones, chloroquine or hydroxychloroquine, or fibric acid derivatives such as clofibrate. Other experimental agents include the fatty acid oxidation inhibitors and dichloroacetate. Specific agents, such as antihypertensives, lipid lowering agents and sorbitol inhibitors, may be needed to prevent the complications arising from the spectrum of clinical and metabolic abnormalities which arise from insulin resistance.

Abnormal distribution of VLDL subfractions in type 1 (insulin-dependent) diabetic patients: could plasma lipase activities play a role?

Very low density lipoproteins (VLDL) have an abnormal lipid composition in Type 1 (insulin-dependent) diabetic patients. Since VLDL represent a heterogeneous lipoprotein class, this might be due either to a shift in the distribution or to an abnormal composition of VLDL subclasses or both. In order to investigate these possibilities and to evaluate possible pathogenetic mechanisms, lipid composition (non-esterified and esterified cholesterol, triglycerides, phospholipids) of four VLDL subfractions of decreasing size (A: Svedberg flotation unit [Sf] > 400, B: Sf > 400, B: Sf 175-400, C: Sf 100-175, D: Sf 20-100), isolated by density gradient preparative ultracentrifugation, and plasma post-heparin lipolytic activity (lipoprotein lipase and hepatic lipase) were evaluated in 13 male normolipidaemic insulin-dependent diabetic patients in good glycaemic control (HbAlc 6.9 +/- 0.5%) (mean +/- SEM) and 9 male control subjects matched for age, body mass index and plasma lipid values. Compared to control subjects, diabetic patients showed a reduced total lipid concentration of VLDL of intermediate size (B and C) reaching statistical significance only for VLDL C (0.16 +/- 0.02 vs 0.24 +/- 0.03 mmol/l; p < 0.05). Expressing each VLDL subfraction as percent of the total VLDL lipid concentration, a significant decrease in particles of intermediate size (C) (20.5 +/- 1.6 vs 27.9 +/- 1.5%; p < 0.005) was present, which was compensated by an increase in the smallest ones (D) (50.5 +/- 2.7 vs 37.4 +/- 3.1%; p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Lipoprotein compositional abnormalities in type 1 (insulin-dependent) diabetic patients

Patients with type 1 (insulin-dependent) diabetes mellitus in good metabolic control usually have normal plasma lipid levels yet they have an increased incidence of vascular complications. Abnormalities in the distribution and composition of lipoprotein subfractions might in part be responsible for the macroangiopathy seen in type 1 diabetes mellitus. The plasma lipids, lipoproteins and apolipoproteins were studied in 9 type 1 diabetic patients during conventional insulin therapy and in 14 healthy controls. Plasma lipoproteins were analysed by ultracentrifugation in a zonal rotor to evaluate their concentrations and flotation properties and for compositional analysis. In diabetic patients the mean glycosylated haemoglobin (HbA1c) was 9.44 +/- 1.02% and the plasma lipid concentrations were not significantly different from healthy controls. The very low density lipoprotein (VLDL) subclass cholesterol concentrations were no different in diabetic patients and control subjects, but the VLDL cholesterol/triglyceride ratio was significantly lower in diabetic patients than in control subjects (0.43 +/- 0.05 vs 0.85 +/- 0.14; p < 0.05). The flotation rate LDL2, the major component of low density lipoprotein (LDL) was lower in the diabetic patients compared with the control subjects. The cholesterol concentrations of intermediate density lipoprotein and LDL3, the minor component of LDL, were significantly higher (0.17 +/- 0.03 and 0.83 +/- 0.14 mmol/l respectively) in diabetic patients than in control subjects (0.05 +/- 0.02 and 0.24 +/- 0.08 mmol/l). The flotation properties and cholesterol concentrations of the high density lipoprotein (HDL) subclass, and the protein-lipid composition of LDL2, HDL2 and HDL3, were no different in diabetic patients and control subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

LDL subclass phenotypes and triglyceride metabolism in non-insulin-dependent diabetes

Plasma low density lipoprotein (LDL) comprises multiple discrete subclasses differing in size, density, and chemical composition. A common, heritable phenotype characterized by the predominance of small, dense LDL particles (LDL subclass phenotype B) is associated with relatively increased concentrations of plasma triglycerides, reduced levels of high density lipoprotein, and increased risk of coronary artery disease in comparison with subjects with larger LDL (LDL subclass phenotype A). Population studies have indicated that approximately 20-30% of adult men have phenotype B, and another 15-20% have LDL of intermediate size. The lipid changes in phenotype B are similar to those that have been observed in patients with non-insulin-dependent diabetes mellitus (NIDDM). In the present study, we have assessed LDL subclass phenotypes in normolipidemic men with NIDDM and in age-matched control subjects who had similar lipid levels. There was a greater than twofold increase in the percentage of individuals with the LDL B phenotype in the NIDDM subjects. The LDL B phenotype was associated with higher plasma triglyceride levels and a trend toward lower high density lipoprotein cholesterol levels compared with the LDL A phenotype in the NIDDM subjects, as has been previously observed in control groups. Indices of diabetic control, such as fasting and hemoglobin A1 levels, were similar regardless of LDL phenotype pattern, suggesting that glycemic control was not likely to account for the increase in the LDL B phenotype. In both control and NIDDM subjects, the clearance of triglyceride-rich lipoproteins was slowed in the subjects with the LDL phenotype B compared with those with the A phenotype.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypertriglyceridaemia and its influence on low density lipoprotein regulation of cellular cholesterol synthesis: a comparison between hypertriglyceridaemic diabetic and non-diabetic patients

The present investigation was undertaken to examine the relationship between serum triglyceride and composition of lipoprotein. Six groups of patients were examined, three with Type 2 (non-insulin-dependent) diabetes and three without diabetes. The groups were further categorized on the basis of their serum cholesterol and triglyceride levels into normocholesterolaemic (serum cholesterol less than 6.5 mmol l-1) and hypercholesterolaemic (serum cholesterol greater than 6.5 mmol l-1) with and without hypertriglyceridaemia (serum triglyceride greater than or less than 3.5 mmol l-1). Low density lipoprotein (LDL) composition was determined and regulation of cholesterol synthesis by LDL was assessed by measuring its effect on [14C]-acetate incorporation into mononuclear leucocyte cholesterol. LDL from the hypercholesterolaemic diabetic patients had a significantly higher esterified cholesterol content when the patients were normotriglyceridaemic (1.14 +/- 0.04 vs 0.76 +/- 0.04 g g-1; p less than 0.01). The ability of LDL to suppress cholesterol synthesis (percent inhibition) was significantly less using LDL from the normocholesterolaemic diabetic patients or hypercholesterolaemic non-diabetic or diabetic patients compared with LDL from the normocholesterolaemic non-diabetic control subjects (47.4 +/- 3.9%, 39.1 +/- 5.1% and 35.2 +/- 4.1% vs 59.5 +/- 1.2%, p less than 0.01). However, hypertriglyceridaemia had no effect on LDL suppression of cholesterol synthesis. We conclude that hypertriglyceridaemia alters LDL composition but the alteration is not associated with the ability of LDL to regulate cholesterol synthesis.