Increased hepatic secretion of very-low-density lipoprotein apolipoprotein B-100 in NIDDM

Summary We measured the hepatic secretion of very-low-density lipoprotein apolipoprotein B-100 (VLDL apoB) using a stable isotope gas-chromatography mass-spectrometry method in six patients with non-insulin-dependent diabetes mellitus (NIDDM) (four males, two females, age 57.5±2.2 years (mean±SEM), weight 88.2±5.5 kg, glycated haemoglobin (HbA₁) 8.5±0.5%, plasma total cholesterol concentration 5.7±0.5 mmol/l, triglyceride 3.8±0.9 mmol/l, high-density lipoprotein (HDL) cholesterol 1.0±0.1 mmol/l) and six non-diabetic subjects matched for age, sex and weight (four males, two females, age 55.7±2.8 years, weight 85.8±5.6 kg, HbA₁ 6.5±0.1%, plasma total cholesterol concentration 5.7±0.5 mmol/l, triglyceride 1.2±0.1 mmol/l, HDL cholesterol 1.4±0.1 mmol/l). HbA₁, plasma triglyceride and mevalpnic acid (an index of cholesterol synthesis in vivo) concentrations were significantly higher in the diabetic patients than in the non-diabetic subjects (p=0.006, p=0.02 and p=0.004, respectively). VLDL apoB absolute secretion rate was significantly higher in the diabetic patients compared with the non-diabetic subjects (2297±491 vs 921±115 mg/day, p<0.05), but there was no significant difference in the fractional catabolic rate of VLDL apoB. There was a positive correlation between VLDL apoB secretion rate and (i) fasting C-peptide (r=0.84, p=0.04) and (ii) mevalonic acid concentration (r=0.83, p<0.05) in the diabetic patients but not in the non-diabetic subjects. There was also a significant positive association between plasma mevalonic acid and plasma C-peptide (r=0.82, p<0.05) concentrations in the diabetic patients. We conclude that in NIDDM, there is increased hepatic secretion of VLDL apoB which may partly explain the dyslipoproteinaemia seen in this condition. We suggest that increased secretion of this apolipoprotein may be a consequence of resistance to the inhibitory effect of insulin on VLDL apoB secretion. Insulin resistance may also be the mechanism by which cholesterol synthesis, a regulator of apoB secretion, is increased in NIDDM.Abbreviations ApoB Apolipoprotein B-100 - VLDL very-low-density lipoprotein - GCMS gas-chromatography mass-spectrometry - MVA mevalonic acid - Hep G2 hepatoma G2 - -KIC -ketoisocaproic acid - TC total cholesterol - TG triglyceride - NEFA non-esterified fatty acids - FSR fractional secretion rate - ASR absolute secretion rate - m/z mass to charge ratio - CV coefficient of variation     

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

Summary 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 [S_f]>400, B: S_f, 175–400, C: S_f 100–175, D: S_f 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 (HbA_1c 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). VLDL of smaller size were also the only particles with an abnormal composition consisting of a significant increase in esterified cholesterol (12.2±0.8 vs 8.7±1.2%, p <0.01). Post-heparin hepatic lipase activity was significantly reduced in diabetic patients as compared to control subjects (232.9±27.9 vs 332±42.3 mU/ml; p <0.05) while post-heparin lipoprotein lipase activity was similar in the two groups. Furthermore, hepatic lipase activity was inversely related to the percentage of smaller VLDL (D)(r=–0.72; p <0.01) in diabetic patients and this relationship was independent of changes in intermediate VLDL (VLDL C). In conclusion the data suggest that Type 1 diabetic patients, although normolipidaemic and in good blood glucose control, show a shift in the distribution of VLDL subclasses toward VLDL of a smaller size which also have an abnormal composition. The different distribution of VLDL subfractions seems to be related to a reduced hepatic lipase activity.     

Normal metabolism of apolipoprotein B100-containing lipoproteins despite qualitative abnormalities in type 1 diabetic men

Aims/hypothesis Type 1 diabetic subjects are at increased risk of cardiovascular disease and exhibit multiple qualitative abnormalities of apolipoprotein (apo) B100-containing lipoproteins. This stable isotope kinetic experiment was designed to study whether these abnormalities are associated with changes in the synthesis and fractional catabolic rates of VLDL-, IDL- and LDL-apoB100.Methods Using a bolus followed by a 16-h constant infusion of ¹³C-leucine, we performed a kinetic study in eight men with type 1 diabetes treated with a continuous subcutaneous insulin infusion administered by an external pump and in seven healthy men, in the fed state.Results The mean HbA₁c level in the type 1 diabetic patients was 8.00±1.48%. Plasma triglyceride, and total, LDL and HDL cholesterol levels were similar in patients and control subjects. VLDL were less triglyceride rich in type 1 diabetic patients than in control subjects (VLDL triglyceride : apoB 6.91±0.81 vs 8.29±1.24 mmol/g, p=0.05). Conversely, the IDL and LDL of the type 1 diabetic patients contained relatively higher levels of triglycerides (IDL triglycerides : apoB 2.16±0.36 vs 1.57±0.30 mmol/g, p<0.01; LDL triglycerides : apoB 0.27±0.06 vs 0.16±0.04 mmol/g, p<0.05). The apoB100 pool size, production and fractional catabolic rates in the two groups of subjects were similar for all lipoprotein fractions.Conclusions/interpretation Despite qualitative abnormalities, especially abnormalities of triglyceride content, the metabolism of apoB100-containing lipoproteins is not altered in type 1 diabetic men with fair glycaemic control with continuous subcutaneous insulin infusion. The high risk of atherosclerosis in these patients cannot be explained by kinetic abnormalities of apoB100-containing lipoproteins.     

Changes of lipolytic enzymes cluster with insulin resistance syndrome

Summary The activities of hepatic and lipoprotein lipase and the levels of lipo- and apoproteins were compared in two groups of normoglycaemic men representing the highest (n=18) and lowest (n=15) fasting insulin quintiles of first degree male relatives of non-insulin-dependent diabetic patients. The high insulin group representing insulin-resistant individuals had significantly lower post-heparin plasma lipoprotein lipase activity than the low insulin group (14.2±4.0 vs 20±5.8 mol NEFA·ml^–1·h^–1, p<0.001); hepatic lipase activity did not differ between the two groups (24.2±11 vs 18.0±5.3 mol NEFA·ml^–1·h^–1, NS). The lipoprotein lipase/hepatic lipase ratio in the high insulin group was decreased by 66% as compared to the low insulin group (0.75±0.57 vs 1.25±0.65, p<0.01). In the high insulin group both total and VLDL triglycerides were higher than in the low insulin group (1.61±0.57 vs 0.86±0.26 mmol/l, p< 0.001 and 1.00±0.47 vs 0.36±0.16 mmol/l, p<0.001, respectively) whereas HDL cholesterol and HDL₂ cholesterol were lower (1.20±0.30 vs 1.43±0.22 mmol/l, p<0.05 and 0.49±0.21 vs 0.71±0.17 mmol/l, p<0.05, respectively). Total cholesterol, LDL cholesterol or HDL₃ cholesterol did not differ between the two groups. The mean particle size of LDL was smaller in the high insulin group than in the low insulin group (258±7 vs 265±6 å, p<0.05). We propose that the changes of lipoprotein lipase and lipoprotein lipase/hepatic lipase ratio cluster with insulin resistance and provide a possible mechanism to explain the lowering of HDL cholesterol and elevation of triglyceride concentrations observed in insulin-resistant subjects.Abbreviations LPL Lipoprotein lipase - HL hepatic lipase - VLDL very low density lipoprotein - IDL intermediate density lipoprotein - LDL low density lipoprotein - HDL high density lipoprotein - chol cholesterol - TG triglycerides - NEFA non-esterified fatty acids     

Low density lipoprotein cholesterol: An association with the severity of diabetic retinopathy

Summary Diurnal profiles of total and lipoprotein cholesterol and triglycerides were measured in 11 insulin-dependent diabetic subjects without retinopathy, 10 with background and 10 with proliferative retinopathy. The groups were closely matched for age and duration of diabetes. Total cholesterol levels were higher in patients with proliferative (5.6±0.5 mmol/l) than background (5.1±0.7 mmol/l) or no retinopathy (4.6±0.8 mmol/l, trend test; p < 0.003), due to raised levels of low density lipoprotein (LDL) cholesterol (3.8±0.9, 3.2±0.6 and 2.8±0.8 mmol/l respectively; p < 0.02). High density lipoprotein (HDL) levels were similar in patients with and without retinopathy and HDL/ LDL ratios were lower with more severe retinopathy (p < 0.025). Cholesterol levels were similar in diabetic subjects without retinopathy and in 12 normal subjects. Triglyceride levels were not related to retinopathy and no measure of plasma lipids correlated with HbA₁ or 24-h mean plasma glucose. Total and LDL cholesterol were weakly inversely correlated with creatinine clearance but the association with retinopathy was independent of this effect.     

Metabolism of HDL apolipoprotein A-I and A-II in Type 1 (insulin-dependent) diabetes mellitus

Summary Concentrations of HDL cholesterol and apolipoprotein A-I are commonly increased in Type 1 (insul-independent) diabetes mellitus but the mechanisms whereby diabetes influences HDL metabolism have not been studied. We investigated the metabolism of HDL apoproteins A-I and II in normolipidaemic Type 1 diabetic men (n=17, HbA₁ 6.4–11.9%) without microalbuminuria but with a wide range of HDL cholesterol (0.85–2.10 mmol/l) and in nondiabetic men (n=18) matched for body mass index and the range of HDL cholesterol. Input rates and fractional catabolic rates for apolipoproteins A-I and II were determined following injection of ¹²⁵I-apolipoprotein A-I and ¹³¹I-apolipoprotein A-II tracers. Additional multicompartmental analysis was performed using a model to describe the kinetics of HDL particles containing only apolipoprotein A-I (Lp A-I) and apolipoprotein A-I and apolipoprotein A-II (Lp A-I/ A-II). No gross differences from normal subjects were observed in the mean levels of lipids, lipoproteins, apoproteins and the lipolytic enzymes in the diabetic men as a result of the selection process. Furthermore, the relationship between apolipoprotein A kinetics and plasma HDL cholesterol levels appeared to be preserved in the diabetic group. However, some normal interrelationships were disrupted in the diabetic men. Firstly, the rate of apolipoprotein A-II synthesis was 22% lower than in control subjects (p<0.05). Modelling indicated that this was due to decreased input of Lp A-I/A-II particles whereas the input of Lp A-I particles was similar in the two groups. Secondly, there was no correlation between VLDL triglyceride and HDL cholesterol or VLDL triglyceride and the fractional catabolic rate of apolipoproteins A-I and A-II in diabetic men in contrast to that seen in control subjects. We conclude that there is a disruption in the normal association between VLDL and HDL metabolism in Type 1 diabetic men and postulate that the observed differences may be due to the therapeutic use of exogenous insulin.     

Inability of HDL from type 2 diabetic patients to counteract the inhibitory effect of oxidised LDL on endothelium-dependent vasorelaxation

Aims/hypothesis In healthy normolipidaemic and normoglycaemic control subjects, HDL are able to reverse the inhibition of vasodilation that is induced by oxidised LDL. In type 2 diabetic patients, HDL are glycated and more triglyceride-rich than in control subjects. These alterations are likely to modify the capacity of HDL to reverse the inhibition of vasodilation induced by oxidised LDL.Subjects and methods Using rabbit aorta rings, we compared the ability of HDL from 16 type 2 diabetic patients and 13 control subjects to suppress the inhibition of vasodilation that is induced by oxidised LDL.Results Oxidised LDL inhibited endothelium-dependent vasodilation (maximal relaxation [Emax]=58.2±14.6 vs 99.3±5.2% for incubation without any lipoprotein, p<0.0001). HDL from control subjects significantly reduced the inhibitory effect of oxidised LDL on vasodilatation (Emax=77.6±12.9 vs 59.5±7.7%, p<0.001), whereas HDL from type 2 diabetic patients had no effect (Emax=52.4±20.4 vs 57.2±18.7%, NS). HDL triglyceride content was significantly higher in type 2 diabetic patients than in control subjects (5.3±2.2 vs 3.1±1.4%, p<0.01) and was highly inversely correlated to Emax for oxidised LDL+HDL in type 2 diabetic patients (r=−0.71, p<0.005).Conclusions/interpretation In type 2 diabetes mellitus, the ability of HDL to counteract the inhibition of endothelium-dependent vasorelaxation induced by oxidised LDL is impaired and is inversely correlated with HDL triglyceride content. These findings suggest that HDL are less atheroprotective in type 2 diabetic patients than in control subjects.     

Very low density lipoprotein metabolism in non-ketotic diabetes mellitus: Effect of dietary restriction

Summary We have measured the turnover of very low density lipoprotein (VLDL) triglyceride as well as plasma glucose, insulin and non-esterified fatty acid levels in nine mildly obese non-ketotic, insulinopenic diabetic subjects before and during an energy restricted diet. During the baseline period, subjects were hypertriglyceridaemic, hyperglycaemic and insulinopenic. During dietary restriction (mean weight loss: 2.3±0.4 kg) plasma triglyceride fell from 8.4±3.0 to 3.4±0.89 mmol/l (mean±SEM; p<0.05), and plasma glucose fell from 13.9 ±1.7 to 9.8±1.4 mmol/l (p<0.01). Neither fasting plasma insulin nor the insulin response to an oral glucose load changed. Plasma non-esterified fatty acid concentrations remained constant as well. During the baseline period, the transport rate of VLDL-triglyceride in the diabetic subjects was more than twice that in an age-weighted matched control group (27.4±2.9 versus 12.1±0.8 mg/kg ideal body weight per h). The fractional catabolic rates were similar in the two groups (0.20±0.05 versus 0.21±0.02/h). During energy restriction of the diabetic subjects, the VLDL-triglyceride transport rate fell to 17.4±2.9 mg/kg ideal body weight per h (p<0.05 versus baseline) while the fractional catabolic rate remained constant at 0.21±0.06/h (NS versus baseline). These data indicate that the major abnormality in triglyceride metabolism in these non-ketotic, insulinopenic diabetic patients was over-production of VLDL-triglyceride.     

Very low density lipoprotein subfraction abnormalities in IDDM patients: any effect of blood glucose control?

Summary Normolipidaemic insulin-dependent diabetic (IDDM) patients are characterized by an increase in the smaller VLDL particles, considered to be the most atherogenic. Since blood glucose control is one of the main regulators of lipid metabolism in diabetic patients, it could influence the shift in the distribution of VLDL subfractions towards smaller particles. To evaluate this possibility, VLDL subfractions, post-heparin lipoprotein lipase and hepatic lipase activities have been evaluated in male IDDM patients with either unsatisfactory blood glucose control (group 1, HbA_1c>8%, n=18) or good blood glucose control (group 2, HbA_1c<8%, n=16) and in 16 normoglycaemic individuals. The three groups were comparable for sex, age, body mass index, and plasma lipid levels. Three VLDL subfractions (large, Svedberg flotation unit (Sf) 175–400; intermediate, Sf 100–175; small, Sf 20–100) were separated by density gradient ultracentrifugation and analysed for cholesterol, triglyceride, and phospholipid levels. When compared to control subjects both groups of IDDM patients showed a clear shift in VLDL subfraction distribution with a significant increase in the proportion of small VLDL (group 1; 49±2%; p<0.005; group 2: 51±3%, p<0.01; control subjects 40±2%) (mean ± SEM) in relation to total VLDL. By contrast, the absolute lipid concentration of small VLDL was higher only in group 1, compared to control subjects (35±4 vs 27±3 mg/dl, p=0.05). Post-heparin hepatic lipase activity was significantly reduced in both IDDM groups (group 1: 254±19 mU/ ml, p<0.05; group 2: 202±19 mU/ml, p<0.005; control subjects 317±31 mU/ml). In conclusion, normolipidaemic IDDM patients show an increase in the smallest VLDL, whatever their degree of blood glucose control. However, this abnormality may be clinically relevant only in patients with unsatisfactory blood glucose control, since absolute lipid concentration of these potentially atherogenic particles is only increased in this group.Abbreviations IDDM Insulin-dependent diabetes mellitus - VLDL very low density lipoprotein - LPL lipoprotein lipase - HL hepatic lipase     

Effect of glipizide treatment on postprandial lipaemia in patients with NIDDM

Summary 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 Sf 20–400 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.Abbreviations RP Retinyl palmitate - Sf Sverdberg flotation index - CHD coronary heart disease - SSPI steady-state plasma insulin concentration - SSPG steady-state plasma glucose concentration - IDL intermediate density lipoprotein - NEFA non-esterified fatty acid; non-insulin-dependent diabetes mellitus     

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 (HbA_1c) 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 (0.34±0.05 vs 0.85±0.14; p<0.05). The flotation rate of 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. Diabetic patients had lower apoprotein AII and higher CII and E levels than control subjects. the plasma lipoproteins in type 1 diabetes mellitus are characterized by increased intermediate density lipoprotein and LDL₃ concentrations and by abnormal LDL₂ flotation properties. These lipoprotein abnormalities might have a role in atherogenesis in type 1 diabetic patients since similar alterations were associated in some recent epidemiological studies with an increased incidence of cardiovascular disease in non-diabetic patients.     

High density-lipoprotein subfractions of patients using cardio-selective beta-blockers

Treatment of hypertension with beta-adrenergic blockers (BB) slightly increases plasma triglycerides and decreases high density lipoprotein (HDL) cholesterol levels. However, only little is known about BB-related lipid changes in patients with coronary artery disease (CAD), who usually a priori have decreased HDL cholesterol levels; and even less data exist on HDL subfraction cholesterol in these patients. We therefore quantified levels of lipids, lipoprotein lipids including HDL2 and HDL3 cholesterol, and apolipoproteins in 107 consecutive men undergoing elective coronary angiography. Of the 107 patients, 84 had angiographically established coronary atherosclerosis (1 lesion with 50% narrowing, CAD+), and 23 had no major lesion (CAD–); 67 were taking ß1-selective BB (metoprolol or atenolol) for treatment of angina and/or hypertension and 40 were not. Patients using BB had significantly higher cholesterol levels than patients not using BB (5.99 ± 0.93 vs. 5.63 ± 1.07 mmol/l, mean ± SD, p = 0.029). Their HDL cholesterol and HDL2 cholesterol levels were significantly lower (1.19 ± 0.27 vs. 1.28 ± 0.33 mmol/l, p = 0.048, and 0.22 ± 0.12 vs. 0.27 ± 0.18 mmol/l, p = 0.038, respectively). Accordingly, the total cholesterol/HDL cholesterol ratio was significantly higher in patients taking BB than in those not taking BB (5.23 ± 1.27 vs. 4.68 ± 1.63, p = 0.010). Considering CAD+ and CAD– patients separately, there was a trend towards lower HDL cholesterol and its subfractions with significantly lower HDL2 cholesterol in patients with BB in the CAD– group, suggesting a stronger dyslipidemic effect of BB in these patients with a priori normal or near normal baseline lipid levels.     

Low HDL‐cholesterol is common in European Type 2 diabetic patients receiving treatment for dyslipidaemia: data from a pan‐European survey

Aims To measure the prevalence of low high‐density lipoprotein (HDL)‐cholesterol (men < 1.03 mmol/l; women < 1.29 mmol/l) in European Type 2 diabetic patients receiving treatment for dyslipidaemia. Methods The pan‐European Survey of HDL‐cholesterol measured lipids and other cardiovascular risk factors in 3866 patients with Type 2 diabetes and 4436 non‐diabetic patients undergoing treatment for dyslipidaemia in 11 European countries. Results Diabetic patients were more likely to be obese or hypertensive than non‐diabetic patients. Most patients received lifestyle interventions (87%) and/or a statin (89%); treatment patterns were similar between groups. Diabetic patients had [means (SD)] lower HDL‐cholesterol [1.22 (0.37) vs. 1.35 mmol/l (0.44) vs. non‐diabetic patients, P < 0.001] and higher triglycerides [2.32 (2.10) vs. 1.85 mmol/l (1.60), P < 0.001]. More diabetic vs. non‐diabetic patients had low HDL‐cholesterol (45% vs. 30%), high triglycerides (≥ 1.7 mmol/l; 57% vs. 42%) or both (32% vs. 19%). HDL‐cholesterol < 0.9 mmol/l was observed in 18% of diabetic and 12% of non‐diabetic subjects. Differences between diabetic and non‐diabetic groups were slightly greater for women. LDL‐ and total cholesterol were lower in the diabetic group [3.02 (1.05) vs. 3.30 mmol/l (1.14) and 5.12 (1.32) vs. 5.38 mmol/l (1.34), respectively, P < 0.001 for each]. Conclusions Low HDL‐cholesterol is common in diabetes: one in two diabetic women has low HDL‐cholesterol and one diabetic man in four has very low HDL‐cholesterol. Management strategies should include correction of low HDL‐cholesterol to optimize cardiovascular risk in diabetes.     

Effects of the combination of insulin and glibenclamide in Type 2 (non-insulin-dependent) diabetic patients with secondary failure to oral hypoglycaemic agents

Summary The effects of combined insulin and sulfonylurea therapy on glycaemic control and B-cell function was studied in 15 Type 2 (non-insulin-dependent) diabetic patients who had failed on treatment with oral hypoglycaemic agents. The patients were first treated with insulin alone for four months. Five patients were given two daily insulin doses and ten patients one dose. During insulin treatment the fasting plasma glucose fell from 14.5±0.8 to 8.8±0.4 mmol/l and the HbA₁ concentration from 12.6±0.4 to 9.2±0.2%. This improvement of glycaemic control was associated with a suppression of basal (from 0.31±0.04 to 0.10±0.02 nmol/l) and glucagon-stimulated (from 0.50±0.08 to 0.19±0.04 nmol/l) C-peptide concentrations. Four months after starting insulin therapy the patients were randomised to a four-month double-blind cross-over treatment with insulin combined with either 15 mg glibenclamide per day or with placebo. Addition of glibenclamide to insulin resulted in a further reduction of the fasting plasma glucose (7.9±0.5 mmol/l) and HbA₁ (8.3±0.2%) concentration whereas the basal (0.21±0.03 nmol/l) and glucagon-stimulated C-peptide concentrations (0.34±0.06 nmol/l) increased again. Addition of placebo to insulin had no effect. The daily insulin dose could be reduced by 25% after addition of glibenclamide to insulin, while it remained unchanged when insulin was combined with placebo. The fasting free insulin concentration did not differ between the glibenclamide and placebo periods (28±6 vs 30±5 mmol/l). The fasting free insulin concentration correlated, however, positively with the insulin dose (r=0.76, p<0.01) indicating that the insulin dose was the main determinant of the free insulin concentration. In contrast, the basal C-peptide concentration was higher during the insulin plus glibenclamide than during the insulin plus placebo period (0.21±0.03 vs 0.16±0.03 nmol/l; p<0.05). Addition of glibenclamide to insulin therapy increased the treatment cost by 30–50%, was associated with increased frequency of mild hypoglycaemic reactions and with a slight, but significant fall in HDL cholesterol concentration (from 1.40±0.07 to 1.29±0.06; p<0.05) compared with insulin plus placebo. We conclude that in Type 2 diabetic patients, who have failed on treatment with oral hypoglycaemic agents, the combination of insulin and glibenclamide resulted in slightly improved glycaemic control and allowed reduction of the insulin dose. The price for this improvement was higher treatment costs, more (mild) hypoglycaemic reactions and a marginal fall in the HDL cholesterol concentration. Whether the same effect could have been achieved with divided insulin doses in all patients is not known.     

Increased hyaluronan production in the glomeruli from diabetic rats: a link between glucose-induced prostaglandin production and reduced sulphated proteoglycan

Summary Exposure in vivo or in vitro to elevated glucose increases production of vasoactive prostaglandins by glomeruli and mesangial cells. This study aimed to determine whether this increased prostaglandin production could provide a link with later structural changes in diabetic nephropathy. Glomerular cores were prepared from control rats and streptozotocin-diabetic rats (3 weeks' duration). Over 24 h in culture hyaluronan production from diabetic glomerular cores was higher than production from control glomerular cores whether maintained in 5.6 mmol/l glucose (105.6±15.5 vs 53.6±8.5 ng hyaluronan per 250 glomerular cores, p<0.001); in 25 mmol/l glucose (149.3±34.8 vs 62.7±7.8 ng hyaluronan per 250 glomerular cores, p<0.01); or in 45 mmol/l glucose (176.8±23.3 vs 102.0±17.9 ng hyaluronan per 250 glomerular cores, p<0.01). At 5.6 mmol/l glucose, exposure in vitro to prostaglandin E₂ caused an increase in hyaluronan production [maximal at 10^–9 mol/l prostaglandin E₂, 237±19 vs 42±4, ng hyaluronan per 250 glomerular cores, p<0.001 (control) and 195±7 vs 103±5, ng hyaluronan per 250 glomerular cores, p<0.001 (diabetic)]. In both control and diabetic glomerular cores hyaluronan production was reduced significantly by the cyclooxygenase inhibitor indomethacin (10^–5 mol/l) [24.7±3.33 vs 40.25±4.11 ng hyaluronan per 250 glomerular cores, p<0.05 (control) and 36.5±6.25 vs 118.0±22.6, p<0.01 (diabetic)]. A direct spectrophotometric microassay was used to determine the concentration of sulphated glycosaminoglycans derived from papain-digested glomerular core proteoglycans. Release of sulphated glycosaminoglycans from diabetic glomerular cores maintained at 5.6 mmol/l glucose was decreased [41.9±1.1 vs 54.0±1.0 g of sulphated glycosaminoglycans (chondroitin sulphate) per 250 glomerular cores p<0.01]. A decrease in sulphated glycosaminoglycans was also shown from control glomerular cores maintained at 25 mmol/l glucose. At this glucose concentration, addition of exogenous hyaluronan or prostaglandin E₂ significantly reduced sulphated glycosaminoglycans from control and diabetic glomerular cores. It is concluded that increased prostaglandin production secondary to high glucose environment can lead to an increased glomerular hyaluronan synthesis. This can substantially affect the levels of sulphated glycosaminoglycans in the extracellular matrix. We propose that these effects provide a possible link between the initial biochemical consequences of hyperglycaemia and later structural changes seen in the glomerulus in diabetes.Abbreviations PG Prostaglandins - GC glomerular cores - STZ-D streptozotocin diabetes - GAG sulphated glycosaminoglycans - PDGF platelet derived growth factor - PGE₂ prostaglandin E₂ - STZ streptozotocin - HSPG heparan sulphate proteoglycan - HA hyaluronan     

Oxidation of low-density lipoprotein in NIDDM: its relationship to fatty acid composition

Summary The increased risk of atherosclerotic disease in diabetic subjects may be due to enhanced foam cell formation following an increased susceptibility of low density lipoprotein to oxidative modification. This study has compared fatty acid content and lipoprotein oxidisability in 10 non-insulin-dependent diabetic subjects with that in 10 control subjects. Both groups were normocholesterolaemic and the diabetic subjects had higher triglyceride levels (2.2±0.4 vs 1.2±0.2 mmol/l, p<0.05). The fatty acid composition was compared in low density lipoprotein following Folch extraction, separation by thin layer chromatography (for the lipid classes) and analysis by gas liquid chromatography. Low density lipoprotein oxidisability was assessed by conjugated diene and thiobarbituric acid reacting substance formation in the presence of copper ions. The esterified/free cholesterol ratio was higher in the low density lipoprotein from patients compared to control subjects (2.9±0.1 vs 1.9±0.3, p<0.05). Linoleic acid in the cholesteryl ester fraction of the lipoprotein was higher in the patients than in the control subjects (48.2±2.2% vs 42.4±3.4%, p<0.05) as was the total quantity of linoleic acid in the cholesteryl ester fraction (317.8±68.0 vs 213.2±28.0 g/mg protein, p<0.05) and in the low-density lipoprotein as a whole (443.2±70.0 vs 340.2±28.2 g/mg protein, p<0.05). Lipoprotein oxidisability was also increased in the diabetic group with increased formation of thiobarbituric acid reacting substances (35.6±7.2 vs 22.3±3.5 nmol/mg protein, p<0.05, increased total diene formation (502±60 vs 400±30 nmol/mg protein, p<0.05) and increased rate of diene formation (7.2±0.6 vs 5.1±0.9 nmol diene · mg protein^–1 · min^–1, p<0.05). This study indicates that low-density lipoprotein from diabetic subjects is more susceptible to oxidation. This could, in vivo, accelerate foam-cell formation thereby increasing atherosclerotic risk in diabetic subjects.Abbreviations BHT Butylated hydroxytoluene - EDTA ethylenediaminetetraacetic acid - TBARS thiobarbituric reacting substances - HPLC high performance liquid chromatography - MDA malondialdehyde - HbA_1c glycated haemoglobin     

LDL-cholesterol/apolipoprotein B ratio is a good predictor of LDL phenotype B in type 2 diabetes

LDL phenotype B is a component of diabetic dyslipidaemia, but its diagnosis is cumbersome. Our aim was to find easily available markers of phenotype B in a group of type 2 diabetic subjects. We studied 123 type 2 diabetic patients (67.5% male, aged 59.3±10.1 years, mean HbA1c 7.4%). Clinical features and fasting total cholesterol, triglyceride, HDL cholesterol, LDL cholesterol (LDLc, using Friedewald's equation and an alternative formula), apolipoprotein B (apoB), lipoprotein (a) and LDL particle size (on gradient polyacrylamide gel electrophoresis) were assessed. Patients with phenotypes A (predominant LDL size ≥25.5 nm) and B (<25.5 nm) were compared, and regression analysis was performed to find the best markers of LDL particle. Cut-off points were obtained and evaluated as predictors of phenotype B (kappa index). Patients with phenotype B (36%) showed higher total cholesterol, triglyceride and apolipoprotein B, and lower HDL cholesterol and LDLc/apoB ratio. Triglyceride was the best predictor of LDL particle size (r=−0.632, p<0.01), but an LDLc/apoB ratio below 1.297 mmol/g detected phenotype B best (sensitivity 65.9%, specificity 92.4%, kappa=0.611). Although triglyceride concentration is the best predictor of LDL size in type 2 diabetes, LDLcholesterol/apolipoproteinB ratio is the best tool to detect phenotype B. Received: 23 August 2001 / Accepted in revised form: 12 July 2002 Correspondence to A. Pérez     

The effect of a new specific α-amylase inhibitor on post-prandial glucose and insulin excursions in normal subjects and Type 2 (non-insulin-dependent) diabetic patients

Summary Trestatin (Ro 9-0154), a new specific -amylase inhibitor of microbial origin, was tested in six normal subjects and seven Type 2 (non-insulin-dependent) diabetic patients. In normal subjects the maximal increases in blood glucose following a 115-g starch meal were 2.19±0.57 mmol/l (mean±SEM) with placebo, but 1.32±0.39 mmol/l with 10 mg, 1.06±0.26 mmol/l with 20 mg, 0.43±0.07 mmol/l with 50 mg (p<0.05) and 0.26±0.14 mmol/l with 100 mg (p<0.05) Trestatin. The corresponding increases in plasma insulin were 116.5±19.6mU/l; 74.8±17.5 mU/l; 50.7±8.3 mU/l; 28.7±6.9 mU/l (p<0.05) and 16.5±3.2 mU/l (p<0.05). In the diabetic patients the maximal increases in blood glucose following a 50-g starch meal were 6.09±0.02 mmol/l with placebo, but 3.17±0.59 mmol/ (p<0.05) with 10 mg and 1.69±0.41 mmol/l (p<0.05) with 30 mg Trestatin. The corresponding insulin increases were: 58.8±12.7 mU/l, 31.5±9.7mU/l (p<0.05) and 23.4±4.8 mU/l (p<0.05). Trestatin fully retained this pharmacological activity during treatment for 4 weeks in the diabetic patients. Trestatin did not influence glucose and insulin profiles after oral glucose and sucrose. These results are consistent with a specific inhibition of -amylase in man.     

Transfers of esterified cholesterol and triglyceride between high density and very low density lipoproteins: In vitro studies of rabbits and humans

Mixtures of rabbit very low density lipoproteins (VLDL) and high density lipoproteins (HDL), one of which was endogenously labeled with ³H in the free and esterified cholesterol moieties and with ¹⁴C in the triglyceride (TG) moiety, were incubated at 37°C in vitro in the presence of rabbit lipoprotein-free serum. There was a net mass transfer of esterified cholesterol from HDL to VLDL and of TG from VLDL to HDL. Both esterified ³H-cholesterol and ¹⁴C-TG, however, transferred in each direction between the two fractions. In the presence of parachlormercuryphenyl sulfonate (PCMPS), a thiol group blocker that inhibits lecithin:cholesterol acyltransferase (LCAT), the net mass transfers of esterified cholesterol and TG were reduced, as were the bidirectional transfers of ¹⁴C-TG, but the bidirectional transfers of esterified ³H-cholesterol were much less affected. Qualitatively similar results were obtained with incubations of human VLDL and HDL containing tracer amounts of either VLDL or HDL labeled with ³H in the esterified cholesterol moiety. In incubations of unlabeled human VLDL, HDL, and lipoprotein-free plasma, the molar ratio of the net mass transfers of TG:esterified cholesterol was 0.55 ± 0.10 (mean ± SE, n = 8) in the absence of PCMPS, and 0.25 ± 0.04 in the presence of PCMPS. The difference between these ratios was statistically significant (p < 0.02). Therefore, it has been concluded that the net mass transfers of esterified cholesterol and TG between VLDL and HDL may be independent processes.     

Effects of rosiglitazone and pioglitazone on lipoprotein metabolism in patients with Type 2 diabetes and normal lipids

Aims Previous studies have suggested that plasma lipids are affected differently by the peroxisome proliferators‐activated receptor (PPAR)‐γ agonists pioglitazone and rosiglitazone. The aim of this study was to perform a quantitative lipoprotein turnover study to determine the effects of PPAR‐γ agonists on lipoprotein metabolism. Methods Twenty‐four subjects with Type 2 diabetes treated with diet and/or metformin were randomized in a double‐blind study to receive 30 mg pioglitazone, 8 mg rosiglitazone or placebo once daily for 3 months. Before and after treatment, absolute secretion rate (ASR) and fractional catabolic rate (FCR) of very low‐density lipoprotein (VLDL), intermediate‐density lipoprotein (IDL) and low‐density lipoprotein (LDL) apolipoprotein B100 were measured with a 10‐h infusion of 1‐¹³C leucine. Results There was a significant decrease in glycated haemoglobin (HbA_1c) and non‐esterified fatty acids with pioglitazone (P = 0.01; P = 0.02) and rosiglitazone (P = 0.04; P = 0.003), respectively, but no change in plasma triglyceride or high‐density lipoprotein (HDL) cholesterol. Following rosiglitazone, there was a significant reduction in VLDL apolipoprotein B100 (apoB) ASR (P = 0.01) compared with baseline, a decrease in VLDL triglyceride/apoB (P = 0.01), an increase in LDL2 cholesterol (P = 0.02) and a decrease in LDL3 cholesterol (P = 0.02). There was a decrease in VLDL triglyceride/apoB (P = 0.04) in the pioglitazone group. There was no significant difference in change in VLDL ASR or FCR among the three groups. Conclusions In patients with Type 2 diabetes and normal lipids, treatment with rosiglitazone or pioglitazone had no significant effect on lipoprotein metabolism compared with placebo.