Apolipoprotein CIII Is an Important Piece in the Type-1 Diabetes Jigsaw Puzzle

It is well known that type-2 diabetes mellitus (T2D) is increasing worldwide, but also the autoimmune form, type-1 diabetes (T1D), is affecting more people. The latest estimation from the International Diabetes Federation (IDF) is that 1.1 million children and adolescents below 20 years of age have T1D. At present, we have no primary, secondary or tertiary prevention or treatment available, although many efforts testing different strategies have been made. This review is based on the findings that apolipoprotein CIII (apoCIII) is increased in T1D and that in vitro studies revealed that healthy β-cells exposed to apoCIII became apoptotic, together with the observation that humans with higher levels of the apolipoprotein, due to mutations in the gene, are more susceptible to developing T1D. We have summarized what is known about apoCIII in relation to inflammation and autoimmunity in in vitro and in vivo studies of T1D. The aim is to highlight the need for exploring this field as we still are only seeing the top of the iceberg.

Dyslipidemia in Type 1 Diabetes: AMaskedDanger

Type 1 diabetes (T1D) patients show lipid disorders which are likely to play a role in their increased cardiovascular (CV) disease risk. Quantitative abnormalities of lipoproteins are noted in T1D with poor glycemic control. In T1D with optimal glycemic control, triglycerides and LDL-cholesterol are normal or slightly decreased whereas HDL-cholesterol is normal or slightly increased. T1D patients, even with good glycemic control, show several qualitative and functional abnormalities of lipoproteins that are potentially atherogenic. An association between these abnormalities and CV disease risk has been reported in recent studies. Although the mechanisms underlying T1D dyslipidemia remain unclear, the subcutaneous route of insulin administration, that is responsible for peripheral hyperinsulinemia, is likely to be an important factor.

Relative quantitation of glycoisoforms of intact apolipoprotein C3 in human plasma by liquid chromatography-high-resolution mass spectrometry

Glycosylation is one of the most important post-translational modifications to mammalian proteins. Distribution of different glycoisoforms of certain proteins may reflect disease conditions and, therefore, can potentially be utilized as biomarkers. Apolipoprotein C3 (ApoC3) is one of the many plasma glycoproteins extensively studied for association with disease states. ApoC3 exists in three main glycoisoforms, including ApoC3-1 and ApoC3-2, which contain an O-linked carbohydrate moiety consisting of three and four monosaccharide residues, respectively, and ApoC3-0 that lacks the entire glycosylation chain. Changes in the ratio of different glycoisoforms of ApoC3 have been observed in pathological conditions such as kidney disease, liver disease, and diabetes. They may provide important information for diagnosis, prognosis, and evaluation of therapeutic response for metabolic conditions. In this current work, a liquid chromatography (LC)-high-resolution (HR) time-of-flight (TOF) mass spectrometry (MS) method was developed for relative quantitation of different glycoisoforms of intact ApoC3 in human plasma. The samples were processed using a solid-phase extraction (SPE) method and then subjected to LC-full scan HRMS analysis. Isotope peaks for each targeted glycoisoform at two charge states were extracted using a window of 50 mDa and integrated into a chromatographic peak. The peak area ratios of ApoC3-1/ApoC3-0 and ApoC3-2/ApoC3-0 were calculated and evaluated for assay performance. The results indicated that the ratio can be determined with excellent reproducibility in multiple subjects. It has also been observed that the ratios remained constant in plasma exposed to room temperature, freeze-thaw cycles, and long-term frozen storage. The method was applied in preliminary biomarker research of diabetes by analyzing plasma samples collected from normal, prediabetic, and diabetic subjects. Significant differences were revealed in the ApoC3-1/ApoC3-0 ratio and in the ApoC3-2/ApoC3-0 ratio among the three groups. The workflow of intact protein analysis using full scan HRMS established in this current work can be potentially extended to relative quantitation of other glycosylated proteins. To our best knowledge, this is the first time that a systematic approach of relative quantitation of targeted intact protein glycoisoforms using LC-MS has been established and utilized in biomarker research.

Evidence for low-density lipoprotein–induced expression of connective tissue growth factor in mesangial cells

BACKGROUND

Although hyperlipidemia is a risk factor for the progression of renal damage, the relationship between increased plasma lipoproteins and glomerular injury is poorly defined. Connective tissue growth factor (CTGF) is emerging as a key determinant of progressive fibrotic diseases and its expression is up-regulated by diabetes. To define the mechanisms through which low-density lipoproteins (LDLs) promote glomerular injury, we evaluated whether LDL can modulate the expression of CTGF and collagen I.

METHODS

The effects of LDL on CTGF and collagen I expression were carried out in rat mesangial cells.

RESULTS

Treatment of mesangial cells with LDL for 24 hours produced a significant increase in the protein levels of CTGF and collagen I compared to unstimulated controls. To explore if CTGF and collagen I are downstream targets for regulation by transforming growth factor-beta (TGF-beta), mesangial cells were treated with various concentration of TGF-beta for 24 hours. TGF-beta produced a concentration-dependent increase in the protein levels of CTGF and collagen I. The increase in CTGF and collagen I induced by LDL was significantly inhibited by neutralizing anti-TGF-beta antibodies. Inhibition of p38(mapk) or p42/44(mapk) activities did not affect LDL-induced TGF-beta1, CTGF, and collagen I expression, whereas inhibition of c-Jun NH2-terminal kinase (JNK) suppressed LDL-induced TGF-beta, CTGF, and collagen I expression.

CONCLUSION

These findings implicate JNK pathway and TGF-beta1 as key players in LDL signaling leading to CTGF and collagen I expression in mesangial cells. The data also point to a potential mechanistic pathway through which lipoproteins may promote glomerular injury.

The effect of improved post-prandial blood glucose control on post-prandial metabolism and markers of vascular risk in people with Type 2 diabetes

A variety of abnormalities of metabolic, haemostatic and endothelial markers are associated with Type 2 diabetes. Evidence suggests that poor post-prandial blood glucose control may contribute to vascular risk. We aimed to examine whether the restoration of a more physiological insulin profile post-prandially would improve these abnormalities. Twenty-one patients with insulin-treated Type 2 diabetes were recruited into a single centre, crossover, double-blind study. Patients were randomized to unmodified human insulin or insulin aspart before main meals for 6-week study periods, both together with NPH insulin. At the end of each study period, pre-breakfast levels of markers of vascular risk were assessed and a test meal performed. There was no significant difference in HbA(1c) (7.04 +/- 0.13% (+/-S.E.) versus 7.15 +/- 0.11%, P = 0.060) with insulin aspart compared to human insulin at the end of each study period. The mean post-prandial blood glucose concentration at 90 min from self-monitored results was lower with insulin aspart than with human insulin (7.9 +/- 0.4 mmol/l versus 9.3 +/- 0.4 mmol/l, P = 0.011) as was study day post-prandial blood glucose at 90 min (8.4 +/- 0.5 mmol/l versus 9.2 +/- 0.6 mmol/l, P = 0.046). No significant differences were found in fasting lipid profile, apolipoproteins, fibrinogen, plasminogen activator inhibitor-1, E-selectin, or homocysteine between the two study periods. Insulin aspart resulted in improved post-prandial glycaemic control when compared to human insulin in Type 2 diabetic patients, but this was not associated with changes in markers of vascular risk.

Apolipoprotein CIII promotes Ca2+-dependent beta cell death in type 1 diabetes

In type 1 diabetes (T1D), there is a specific destruction of the insulin secreting pancreatic beta cell. Although the exact molecular mechanisms underlying beta cell destruction are not known, sera from T1D patients have been shown to promote Ca(2+)-induced apoptosis. We now demonstrate that apolipoprotein CIII (apoCIII) is increased in serum from T1D patients and that this serum factor both induces increased cytoplasmic free intracellular Ca(2+) concentration ([Ca(2+)](i)) and beta cell death. The apoCIII-induced increase in [Ca(2+)](i) reflects an activation of the voltage-gated L-type Ca(2+) channel. Both the effects of T1D sera and apoCIII on the beta cell are abolished in the presence of antibody against apoCIII. Increased serum levels of apoCIII can thus account for the increase in beta cell [Ca(2+)](i) and thereby beta cell apoptosis associated with T1D.

Serum lipid metabolism abnormalities and change in lipoprotein contents in patients with advanced-stage renal disease

BACKGROUND

Arteriosclerosis is the major cause of death in patients with chronic renal failure. There is much interest in the lipid metabolism of patients treated with hemodialysis.

METHODS

We analyzed low-density lipoproteins (LDL) and high-density lipoproteins (HDL) in chronic renal failure (CRF) patients according to patients on hemodialysis (HD), patients with diabetic nephropathy before initiation of dialysis (DN), and patients with chronic glomerulonephritis in the conservative stage (CGN); and compared the lipid metabolic abnormalities in patients on hemodialysis and those not yet on hemodialysis. We also analyzed the qualitative abnormalities of LDL and HDL and their relationship with the pathological stages.

RESULTS

Electrophoretic patterns identified small LDL particles and small HDL particles in the three groups, and the degree of denaturation was more enhanced in CRF patients in the conservative stage than in HD patients. For LDL susceptibility to oxidation LDL (oxLDL) by addition of Cu(2+), the lag time was approximately 57 min in healthy controls and CGN patients, but was prolonged to approximately 75 min in HD and DN patients. For HDL susceptibility to oxidation HDL (oxHDL), HD, DN and CGN patients showed lag times shorter than those found in healthy control subjects. These results showed that LDL and HDL in the serum of CRF patients were in a state of enhanced susceptibility to oxidative modification. In Western blot analysis using anti-human-denatured LDL and anti-human-oxidized HDL monoclonal antibodies, bands of low molecular oxLDL at 150-197 kDa were detected in all CRF patients, with marked tailing in CGN patients. Similarly, bands of small oxHDL particles at 110 and 120 kDa were found in HD, DN and CGN patients.

CONCLUSIONS

Oxidative modification of both LDL and HDL occurs in patients with advanced CRF resulting in small lipoproteins. Increased production of oxLDL and oxHDL is the main cause of lipid metabolic abnormality in CRF patients.

High plasma insulin and lipids profile in older individuals: the Italian longitudinal study on aging

BACKGROUND

The inverse relationship of insulin level to high-density lipoprotein (HDL)-cholesterol and its positive association with hypertriglyceridemia has been demonstrated in several studies; however, the relationship of insulin to low-density lipoprotein (LDL)-cholesterol in elderly persons is not clear. This study investigates the relationships of fasting plasma insulin and selected metabolic and biological risk factors in an aged population.

METHODS

The present study is based on a cross-sectional analysis of the data collected at baseline of the Italian Longitudinal Study on Aging in 1992 on a random sample of 5632 Italians aged 65-84 years. Analyses were performed to compare the distribution of risk factors, such as blood level of lipids, creatinine, albumin, fibrinogen, apolipoprotein A-1 and B, blood pressure, and body mass index (BMI), by quartiles of insulin, in both diabetic and nondiabetic participants.

RESULTS

Significantly higher levels of triglycerides and BMI and lower levels of HDL-cholesterol were found in the upper quartile of insulin among nondiabetic individuals. In men, we also found significantly higher levels of systolic and diastolic blood pressure. The same trend for these variables, although not significant for HDL-cholesterol and blood pressure, was seen in diabetic men. In diabetic women, total and LDL-cholesterol were significantly lower in the highest insulin quartile (p <.001), while no significant differences were seen in nondiabetic women or in men. We also found higher levels of white blood cells in the highest insulin quartile of diabetic women.

CONCLUSIONS

These results, apparently in disagreement with earlier reports on the clustering of cardiovascular disease risk factors in hyperinsulinemic individuals, could be due to the high frequency of chronic inflammation and the high prevalence of urinary infections in older diabetic women.

Lipoprotein composition and serum apolipoproteins in normoglycaemic first-degree relatives of non-insulin dependent diabetic patients

Cardiovascular disease is the leading cause of death in non-insulin dependent diabetes mellitus and first degree relatives of such patients are at increased risk of developing diabetes and cardiovascular disease. The aim of the present study was to determine whether lipid abnormalities occur in normoglycaemic relatives of non-insulin dependent diabetic patients. Cholesterol, triglycerides, apolipoprotein A-I and apolipoprotein B concentrations were measured in serum; the lipoprotein fractions very low density, intermediate density, low density and high density lipoprotein were prepared by sequential flotation ultracentrifugation and their composition investigated. The groups were matched for age, sex and blood glucose concentrations although the relatives (n = 126) were more insulin resistant as determined using the homeostasis model assessment method [1.9 (0.8-9.0) vs 1.6 (0.4-4.9) mmol/mU per l (mean [95% confidence intervals]); p < 0.001] and had greater body mass indices [26.6 (4.1) vs 24.8 (3.9) (mean [S.D.]); p = 0.001] than control subjects (n = 126). Relatives had higher serum apolipoprotein B concentrations than control subjects [0.9 (0.3) vs 0.8 (0.3) g/l, p = 0.02) and lower serum apolipoprotein A-I concentrations (1.4 (0.3) vs 1.5 (0.3), p = 0.02). In multivariate linear regression analysis of all subjects log insulin resistance (p = 0.0001), age (p = 0.002) and waist:hip ratio (p = 0.01) were independent predicators of apolipoprotein B concentrations while waist:hip ratio (p < 0.001) and smoking status (p = 0.002) were independent predictors of apolipoprotein A-I concentrations. Lipoprotein composition (measured in a subgroup of 76 control subjects and 88 relatives), serum cholesterol and serum triglyceride concentrations did not differ between the groups. We conclude that atherogenic apolipoprotein abnormalities occur in normoglycaemic relatives of non-insulin dependent diabetic patients.

Thrombomodulin and induced tissue factor expression on monocytes as markers of diabetic microangiopathy: a prospective study on hemostasis and lipoproteins in insulin-dependent diabetes mellitus

Vascular complications are the main cause of morbidity in diabetes mellitus. To evaluate lipoprotein and hemostatic parameters and their relationship with clinically detectable microangiopathy, we studied 58 insulin-dependent diabetes mellitus patients and 60 controls matched for age, sex, and body mass index. Thirteen patients presented clinically detectable microangiopathy (8 retinopathy and 5 both retinopathy and microalbuminuria). A cross-sectional study of lipid profile, coagulation parameters, and a flow-cytometric evaluation of tissue factor expression in normal monocytes induced by patient plasma were performed. Patients were re-evaluated for microangiopathy in a 3-year median follow-up. Patients showed triglyceride enrichment in low (P = 0.00002) and high density lipoproteins (P = 0.004) and increased levels of D-dimer (P < 0.00001), prothrombin fragment 1 + 2 (P < 0.00001), and thrombin-antithrombin III complex (P = 0.0001). Patients with clinically detectable microangiopathy had increased type 1 plasminogen activator inhibitor (P = 0.00001), thrombomodulin (P = 0.02), and induced monocyte tissue factor expression (P < 0.00001). Nine patients developed clinically detectable microangiopathy in the follow-up and the only predictive variable was increased induced tissue factor expression. In conclusion, in these patients elevated thrombin and fibrin generation reflects a hypercoagulable state but clinically detectable microangiopathy seems related to endothelial cell injury markers and to increased induced tissue factor expression on monocytes.

Plasma protein abnormalities in nephrotic syndrome: effect on plasma colloid osmotic pressure and viscosity

The concentrations of 25 plasma proteins were measured in 22 patients with membranous nephropathy. For some large proteins, the plasma concentrations were increased; there were also large proteins with low plasma concentrations, but small or medium-sized proteins showed uniformly lower plasma concentration than the controls. Plasma colloid osmotic pressure (π) and viscosity (η) were not interrelated but showed positive and significant correlations with plasma concentrations of small and medium-sized proteins (π) and plasma concentrations of large proteins (η), respectively. Nephrotic plasma is not efficient in maintaining plasma π but highly efficient in maintaining plasma η. High plasma fibrinogen concentrations and low antithrombin III concentrations may predispose to thrombosis, and low IgG concentrations may account for the higher predisposition to bacterial infection. The relative composition of nephrotic plasma is heavily dependent on the size of the different proteins. Plasma π and η are also maintained by the relative preponderance of different plasma proteins.

The influence of hypoalbuminemia in the generation of nephrotic hyperlipidemia

Lipoprotein measurements in a group of 29 patients with massive proteinuria and without hypoalbuminemia, were compared with those observed in matched controls and patients with overt nephrotic syndrome to assess the influence of plasma albumin concentration and proteinuria in modulating blood lipid levels. Plasma apoprotein B and apo B containing lipoproteins were not increased in proteinuric normoalbuminemic patients. There was a good correlation between plasma albumin and oncotic pressure (r = 0.937; P < 0.001). Plasma oncotic pressure was inversely correlated with plasma apoprotein B in nephrotic patients (r = -0.44, P = 0.017) but not in normoalbuminemics (r = 0.17, P = 0.369), suggesting that plasma albumin affects apoprotein B secretion. Other findings, however, indicate that multiple processes are ocurring simultaneously in these patients. There was an accumulation of very low- and intermediate density lipoproteins in normoalbuminemics, suggesting a residual defect in the lipoprotein removal. Also, raised (P < 0.05) lipoprotein(a) levels respect to controls (median, 0.15 g/l) were noted in both, normoalbuminemics (median, 0.72 g/l) and hypoalbuminemics (median, 0.84 g/l) with similar degree of proteinuria (6.4 vs. 6.6 g/24 h), suggesting that other mechanisms may be operative in lipoprotein(a) derangements. Our findings suggest that there is no unique mechanism in the pathogenesis of nephrotic hyperlipidemia but that both hypoalbuminemia and proteinuria can have a distinct contribution, individually or in combination.

Effect of diabetes on lipoprotein size

The effects of diabetes on lipoprotein particle sizes were assessed using samples from 94 subjects with non-insulin-dependent diabetes mellitus. From a larger population of nondiabetic subjects who showed normal glucose tolerance, we selected an exact match in terms of age, sex, and menopausal status. We designed a protocol to make nondenaturing gradient gels for the resolution of LDL subfractions and generated two measures of LDL size: diameter of the predominant LDL species and proportion of LDL cholesterol (LDL-C) in particles larger than 25.5 nm (large LDL-C). Similarly, we made two measures of HDL size, large HDL cholesterol (HDL-C) and large HDL-apoAI, which represents the proportion of HDL-C and apoAI, respectively, occurring on particles larger than HDL-3. In pairwise comparisons, diabetes was associated with significantly (P < .004) smaller lipoprotein particles for all measures except large HDL-C. Each of the size measures was significantly and positively correlated with each of the others, suggesting that common metabolic mechanisms influence lipoprotein particle sizes across classes of lipoproteins. In addition, each of the size measures was correlated with a variety of measures of HDL and beta-lipoprotein concentrations, which included HDL-C, LDL-C, triglycerides, and apoAI, apoB, and apoE. We used stepwise regression analyses to select from the measures of lipoprotein concentrations those independently correlated with each of the lipoprotein size measures. After adjusting for these metabolic correlates of lipoprotein size measures, we found the effect of diabetes on lipoprotein size measures was no longer significant except for a modest effect (P = .027) on large HDL-apoAI.

The effects of lipid lowering drugs on metabolic control and lipoprotein composition in type 2 diabetic patients with mild hyperlipidaemia

Patients with Type 2 diabetes are at increased risk from macrovascular disease whether or not they are hyperlipidaemic. Several factors may contribute to this increased risk including abnormalities of lipoprotein composition. The aim of our study was to determine the effects of lipid lowering drugs on lipoprotein composition (lipoprotein fractions were separated by sequential flotation ultracentrifugation) and insulin sensitivity (measured by a modified Harano technique) in 44 patients with mild hyperlipidaemia. All patients had total cholesterol concentrations between 5.2 and 6.5 mmol l-1 and total triglyceride concentrations < 3.0 mmol l-1, and were randomized by minimization to receive treatment for 12 weeks with bezafibrate, acipimox, simvastatin or placebo. Total cholesterol concentrations were decreased by simvastatin, 5.7 +/- 0.4 to 3.7 +/- 0.6 mmol l-1 (p < 0.05), due mainly to reduced LDL-cholesterol levels (-1.25 mmol l-1; p < 0.05), and bezafibrate 5.7 +/- 0.6 to 4.6 +/- 0.4 mmol l-1 (p < 0.05). The LDL:HDL-cholesterol ratio was reduced in the simvastatin group 2.0 +/- 0.5 to 1.2 +/- 0.3 (p < 0.005). There was no effect of the drugs on glycated haemoglobin or insulin sensitivity. In conclusion bezafibrate and simvastatin improve the lipid profile in Type 2 diabetic patients without adversely affecting diabetic control.

Serum lipids, lipoproteins and apolipoproteins in pregnant non-diabetic patients

AIMS

To investigate the effect of pregnancy on serum concentrations of lipids, lipoproteins, and apolipoproteins.

METHODS

Fasting serum concentrations of total cholesterol, triglyceride, low density lipoprotein cholesterol (LDL), high density lipoprotein cholesterol (HDL), apolipoproteins AI, AII, and B, and lipoprotein (a) were measured in 178 women with normal glucose tolerance in the second and third trimesters of pregnancy and in a control group of 58 non-pregnant women of similar age. Data were analysed using the unpaired t test and by one-way analysis of variance.

RESULTS

The pregnant women had significantly higher concentrations of total cholesterol, triglyceride, LDL cholesterol, HDL cholesterol, and apolipoproteins AI and B (p < 0.001) and apolipoprotein AII (p = 0.003) than the control women. The ratio of apolipoprotein B:apolipoprotein AI was significantly higher in the pregnant women than in the controls (p < 0.001), but the total cholesterol:HDL cholesterol ratio was not significantly different. No significant difference was found in the concentration of lipoprotein (a).

CONCLUSIONS

Hyperlipidaemia is common in the second half of pregnancy. This may be a purely physiological response to pregnancy or it may be indicative of pathology in some women. These results warrant a follow up study to investigate whether the hyperlipidaemic response to pregnancy is variable and if so, whether it can predict future hyperlipidaemia in a manner analogous to that of impaired glucose tolerance during pregnancy, predicting non-insulin dependent diabetes in later life.

Response to repeated phlebotomies in patients with non-insulin-dependent diabetes mellitus

Regardless of type, uncontrolled diabetes represents a serious disruption of fuel homeostasis with consequences throughout the body. This may hamper the applicability of predeposited autologous blood transfusion in diabetic patients because metabolic changes are expected as a consequence of repeated bleeding. We undertook this study to determine whether the presence of non-insulin-dependent diabetes mellitus (NIDDM) influences the erythropoietin (EPO) response to repeated phlebotomies with respect to normal subjects. We included 22 consecutive patients scheduled for major surgery during a 2-year period in which clinical and metabolic complications were excluded and renal and liver function was considered unaffected. Selected biochemical and hematologic variables were serially measured during donation of several units of blood in a 12- to 29-day period. Bleeding produced a significant decrease in serum glucose, cholesterol, triglyceride, and apoprotein B concentration in diabetic patients. Except for glucose, this effect was not observed in controls. Both groups were comparable with respect to initial hemoglobin concentrations and all hematologic variables measured. The decrease in hemoglobin concentration did not produce clinical symptoms in these patients, and recovery was regarded as normal in both groups. Serum EPO levels in diabetic patients were negatively influenced by the initial hemoglobin A1c (HbA1c) proportion. Moreover, three nonrespondent diabetic patients with poor glycemic control responded normally 6 to 13 months later, in a second operation, when glycemic control had improved significantly. In conclusion, NIDDM may limit the donation of requested units for major surgery only if poor glycemic control is present. When possible, phlebotomies should be delayed and metabolic control reinforced.

Lipoprotein compositional abnormalities and insulin resistance in type II diabetic patients with mild hyperlipidemia

Lipoprotein composition was determined using ultracentrifugation in 20 non-insulin-dependent (NIDDM) diabetic patients on diet only (D), 20 NIDDM patients on diet and sulfonylurea therapy (T), and 20 nondiabetic control subjects (C), all of whom had total plasma cholesterol concentrations < 6.5 mmol/L and total plasma triglyceride concentrations < 3.0 mmol/L. Although the groups were well matched for age, body mass index, total triglyceride levels, and total cholesterol concentrations, there were significant compositional abnormalities in the low-density lipoprotein (LDL) fractions of diabetic subjects. The LDL total lipid to apolipoprotein B weight ratio (representing the density distributions of LDL particles) was reduced in both diabetic groups: 3.75 +/- 0.3, 3.50 +/- 0.28, and 3.54 +/- 0.22 in C, D, and T groups, respectively (mean +/- SD; P < .05). This was associated with a significant shift in the hydrated density distributions of LDL in the diabetic groups, with the average peak densities being 1.0320 g/mL (in C), 1.0365 g/mL (in D), and 1.0380 g/mL (in T) (P < .05). The LDL particles were also smaller in the NIDDM patients: 21.1 +/- 0.7, 20.4 +/- 0.5, and 20.6 +/- 0.5 nm in C, D, and T groups, respectively (P < .05). When the NIDDM groups were analyzed together, the LDL peak density was found to correlate with both insulin resistance (measured by a modified Harano technique; r = 0.37, P < .015) and total triglyceride concentrations (r = 0.40, P < .01). The results show that diabetic patients have small, dense LDL particles, which may be related to insulin resistance, and that these occur with minimal elevations of total triglyceride concentrations. These potentially atherogenic changes may contribute to the increased coronary heart disease in diabetic patients with mild hyperlipidemia.

Periprandial regulation of lipid metabolism in insulin-treated diabetes mellitus

We have examined the regulation of lipid and glucose metabolism in the postabsorptive and postprandial states in six subjects with insulin-treated diabetes mellitus, and compared them with eight nondiabetic subjects. Blood or plasma concentrations of metabolites and fluxes across forearm and subcutaneous adipose tissue were studied after an overnight fast and for 6 hours after a mixed meal (3.1 MJ, 41% from fat). In the postabsorptive state, regulation of lipid metabolism in the two groups appeared basically similar except that a wider spread of plasma (free) insulin concentrations in the diabetic group led to a wider range of values of plasma nonesterified fatty acid (NEFA) release from adipose tissue, plasma NEFA concentrations, and blood ketone body concentrations. Extraction of ketone bodies across adipose tissue was positively correlated with arterial concentration in both groups (as it was in the forearm), confirming the ability of human adipose tissue to utilize ketone bodies. A single subcutaneous injection of insulin before the meal in the diabetic group produced a plasma free-insulin profile that was blunted and prolonged compared with the postprandial response in the control group. Postprandial forearm glucose uptake followed very closely the plasma (free) insulin concentration. Postprandial suppression of NEFA release from adipose tissue was essentially normal in the diabetic group, and the normal postprandial decrease in plasma NEFA concentrations was reproduced extremely closely. Forearm and adipose tissue blood flow did not differ between the groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipoprotein heterogeneity in end-stage renal disease

Fifteen patients on chronic maintenance hemodialysis without any additional known cause for dyslipidemia were arbitrarily divided into two groups based on fasting plasma triglyceride levels. The hypertriglyceridemic patients (plasma triglyceride levels above 170 mg/dl, N = 7) also had decreased high density lipoprotein (HDL) cholesterol levels and decreased post-heparin plasma lipoprotein lipase activity compared to the normotriglyceridemic patients (N = 8). All lipoprotein fractions collected by density gradient ultracentrifugation were triglyceride-enriched in the hypertriglyceridemic patients. Both groups of patients had elevated intermediate density lipoprotein levels, heterogeneity in the distribution of low density lipoproteins (LDL) and apoprotein-specific HDL subpopulations, and abnormalities in the size and composition of both LDL and HDL. The described alterations tended to be more marked in hypertriglyceridemic patients and are not detected by the usual laboratory evaluation of lipoproteins. These lipoprotein abnormalities have been shown to be atherogenic in patients without renal disease and are likely to contribute to the high prevalence of premature atherosclerosis in end-stage renal disease.

Abnormalities of VLDL, IDL, and LDL characterize insulin-dependent diabetes mellitus

To identify abnormalities of serum lipoprotein composition and concentration that were specific to insulin-dependent diabetes mellitus (IDDM), the procedure of discontinuous gradient ultracentrifugation was employed to isolate lipoprotein fractions in 44 patients with IDDM, 24 nondiabetic subjects with similar lipid and lipoprotein concentrations, and 19 healthy normocholesterolemic (less than 5.2 mmol/l [less than 200 mg/dl]) subjects. The mass concentration of low density lipoprotein (LDL) was greater in IDDM than in both control groups. The free cholesterol to phospholipid ratio in large very low density lipoprotein (VLDL) was greatest in IDDM in comparison with both of the other groups. The contribution of triglyceride to total large VLDL mass was greater, whereas that of phospholipids was lower, in IDDM than in the dyslipidemic nondiabetic group. Protein concentration was reduced and phospholipid increased in small VLDL in IDDM in comparison with both control groups, and the contribution from protein to lipoprotein mass was least in IDDM. Similarly in intermediate density lipoprotein (IDL), the protein concentration and its contribution to overall mass was also lower in IDDM than in either control group, but by contrast, the phospholipid content was increased. The cholesteryl ester to protein ratio was highest in both small VLDL and IDL in IDDM in comparison with both control groups, whereas the free cholesterol to phospholipid ratio in IDL was least in IDDM. In LDL, total cholesterol and triglyceride concentrations were greatest and the contribution from protein to lipoprotein mass was least in IDDM in comparison with both control groups. The LDL free cholesterol to phospholipid ratio was greater in IDDM than in dyslipidemic control subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Atherogenic profiles in insulin-dependent diabetic patients and their treatment

Longitudinal studies have shown a large excess of cardiovascular mortality in insulin-dependent diabetic patients (IDDM) as compared to non-diabetic controls. Although diabetes appears to be an independent cardiovascular risk factor, increases in total and LDL-cholesterol together with a decrease of HDL-cholesterol are more pronounced in diabetics with cardiovascular disease. The general opinion, however, derived from a large number of cross-sectional studies, is that in well-controlled IDDM lipoprotein abnormalities are modest and only slightly different from matched non-diabetic controls. Most of the studies, however, used absolute criteria based on consensus statements and do not take the internal relations of the lipoproteins into account. When atherogenic indices (such as the relationship between total cholesterol and HDL-cholesterol or the Apo A1/apo B quotient) are used, 20 to 30% of an IDDM population considered to be in clinically acceptable control have to be considered pathological. This observation is even more important since the recent Diabetes Control and Complications Trial has shown that, especially in the younger group of patients, significantly higher total cholesterol and triglycerides and lower HDL-cholesterol were observed. Especially in these patients can diet and drug intervention be the most useful in the prevention of cardiovascular disease. These data are consistent with the fact that more sophisticated techniques have previously shown atherogenic changes in the composition of the VLDL-particles and lipoprotein enrichment in apo B. Since these techniques are not easily available in the clinic one has to refer to more classical techniques and the use of above mentioned atherogenic profiles to decide treatment.

The effect of bezafibrate on very low density lipoprotein (VLDL), intermediate density lipoprotein (IDL), and low density lipoprotein (LDL) composition in type 1 diabetes associated with hypercholesterolaemia or combined hyperlipidaemia

Lipoprotein composition was examined in type 1 diabetic subjects with hypercholesterolaemia +/- hypertriglyceridaemia during a 3-month double-blind placebo controlled assessment of bezafibrate therapy. The predominant effect was on lipoprotein lipid content. In those with hypercholesterolaemia alone, bezafibrate significantly reduced the cholesterol (particularly esterified cholesterol) and triglyceride content of large very low density lipoprotein (VLDL) (Svedberg flotation units (Sf) 60-400) in comparison to the placebo group (P less than 0.05), and a trend towards a reduction in free and esterified cholesterol within the intermediate density lipoprotein fraction (IDL) (Sf 12-20) was noted. Low density lipoprotein (LDL) composition was unaltered and in general phospholipid and protein concentrations and cholesteryl ester/protein ratios within the lipoprotein fractions were unaffected. Large VLDL cholesterol and triglyceride concentrations in those with combined hyperlipidaemia were significantly decreased following bezafibrate therapy, both in comparison to placebo-treated subjects and to baseline concentrations (P less than 0.05). An additional significant reduction in small VLDL (Sf 20-60) free cholesterol was recorded (P less than 0.05). Average reductions of large and small VLDL protein of 50-56% were not significant because of wide variation in responses. Bezafibrate had no effect on the abnormal composition of IDL and LDL, characteristic of Type 1 diabetes, regardless of whether or not hypertriglyceridaemia was associated with hypercholesterolaemia. Its major action was to lower VLDL lipid concentrations, but it may also reduce the lipid content of intermediate density lipoprotein in Type 1 diabetes.

Influence of early diabetic nephropathy on very low density lipoprotein (VLDL), intermediate density lipoprotein (IDL), and low density lipoprotein (LDL) composition

The procedure of discontinuous gradient ultracentrifugation (DGU) was used to characterize the influence of early diabetic nephropathy on the composition of very low density lipoprotein (VLDL, flotation density 60-400 Svedberg (Sf) units), low density lipoprotein (LDL, flotation density 0-12 Sf) and subfractions of intermediate density lipoprotein (IDL1 and IDL2, 20-60 and 12-20 Sf, respectively). Forty-six subjects with type 1 (insulin-dependent) diabetes and serum creatinine, less than 140 mumol/l were studied, of whom 23 consistently had normal rates of albumin excretion (AER less than 15 micrograms/min), and 23 had persistent albuminuria (AER 20.0-960.6 micrograms/min). The two groups were similar with respect to total serum lipids, glycaemic control, age and body mass. The composition (lipid, protein and phospholipid) and mass of VLDL, LDL and IDL2 was not appreciably altered by early nephropathy, but free and total cholesterol concentration in IDL1 (Sf 20-60) was increased (total cholesterol 0.68 (0.09) (mean (SE)) vs. 0.47 (0.07) mmol/l, and free cholesterol 0.27 (0.04) vs. 0.17 (0.03) mmol/l, both P less than 0.05). The explanation of these findings was probably an accumulation in the circulation of the remnants of chylomicron metabolism and/or intermediates in the conversion from VLDL to IDL1. In addition, there was a decrease in serum high density lipoprotein (HDL) cholesterol in early nephropathy (1.27 (0.06) vs. 1.38 (0.10) mmol/l, P less than 0.05), due to a decrease in the HDL2 cholesterol subfraction (P less than 0.05). These findings may in part explain the increased risk of premature atherosclerosis associated with the development of albuminuria.

The distribution profiles of very low density and low density lipoproteins in poorly-controlled male, type 2 (non-insulin-dependent) diabetic patients

The distribution and composition of lipoproteins spanning the very low density and low density lipoprotein spectra have been analysed in ten poorly-controlled, male, Type 2 (non-insulin-dependent), diabetic patients pre-disposed to mild, secondary hypertriglyceridaemia. As compared to age-matched control subjects, the diabetic patients displayed grossly modified, distinctly atherogenic lipoprotein profiles. Modifications were not limited to the very low density lipoprotein profile, as would be expected from the pre-treatment hypertriglyceridaemia. There was also an aberrant low density lipoprotein profile, which was not evident from plasma cholesterol measurements, especially as the diabetic patients at entry were well matched to control subjects with respect to plasma levels of this lipid. Compositional abnormalities were also observed in the poorly-controlled diabetic group, although these were less marked than the distributional changes. There were substantial improvements of the abnormalities detailed above, even over a short treatment period (two weeks), with therapy designed primarily to ameliorate metabolic control. The data suggest that, in the presence of poor metabolic control and hypertriglyceridaemia, occult, atherogenic modifications of low density lipoproteins can occur. The results argue in favour of strict control of triglyceride levels even in diabetic patients with apparently acceptable cholesterol levels.

Disparity between apolipoprotein E phenotypes and genotypes (as determined by polymerase chain reaction and oligonucleotide probes) in patients with non-insulin-dependent diabetes mellitus

Apolipoprotein (apo) E phenotype and genotype frequencies, due to allelic variation at amino acids 112 and 158, have been investigated in 95 Caucasian non-insulin dependent diabetic patients (NIDDM). Phenotypes were determined by one-dimensional isoelectric focussing (IEF). In this sample, the frequency of the epsilon 2 allele was higher (0.122) and the frequency of the epsilon 4 allele lower (0.101) than previously reported in Caucasian populations (P less than 0.05). Genotypes were assigned using the technique of polymerase chain reaction and allele specific oligonucleotide probes. By contrast, the frequencies of the alleles determined by genotyping was similar to previously reported in Caucasian populations (apo epsilon 2, 0.095; epsilon 3, 0.758; epsilon 4, 0.147; P greater than 0.1). It is possible that in patients with NIDDM post-translational modification of apo E may lead to disparities, with phenotypes being unrepresentative of allelic variation at this gene locus.

Abnormalities of lipoprotein metabolism in patients with the nephrotic syndrome

BACKGROUND AND METHODS

Patients with the nephrotic syndrome characteristically have multiple abnormalities of lipoprotein metabolism, but the cause and exact nature of these abnormalities are uncertain. In this study, we measured serum lipids and apoproteins in 57 patients with the nephrotic syndrome. We also determined the kinetic indexes of low-density lipoprotein (LDL) metabolism in six patients, and again in three of the six after recovery.

RESULTS

The patients with the nephrotic syndrome had elevated serum concentrations of cholesterol, triglycerides, and phospholipids, which were confined to the lipoproteins containing apoprotein B. The serum concentrations of high-density lipoproteins and the associated A-I and A-II apoproteins were similar in the patients with the nephrotic syndrome and normal subjects. The relative proportions of lipids and their positive association with the increased serum concentrations of apoproteins B, C-II, C-III, and E suggest quantitative rather than qualitative differences in the lipoproteins. All the patients had lipiduria, which probably reflected the excretion of high-density lipoproteins, although no intact immunoreactive apoprotein A-I was found in urine. Serum albumin concentrations were inversely related to serum lipid concentrations in the patients, the severity of the hypoalbuminemia corresponding to the degree of change in serum lipoprotein concentrations. The kinetic studies of lipoprotein metabolism revealed an overproduction of LDL apoprotein B that returned to normal after recovery.

CONCLUSIONS

The elevated serum concentrations of LDL cholesterol, other lipids, and apoprotein B in patients with uncomplicated nephrotic syndrome are due to reversible increases in lipoprotein production.