Nuclear magnetic resonance-determined lipoprotein subclass profile in the DCCT/EDIC cohort: associations with carotid intima-media thickness

AIMS

To relate nuclear magnetic resonance lipoprotein subclass profiles (NMR-LSP) and other lipoprotein-related factors with carotid intima-media thickness (IMT) in Type 1 diabetes.

METHODS

Lipoprotein-related factors were determined in sera (obtained in 1997-1999) from 428 female [age 39 +/- 7 years (mean +/- SD)] and 540 male (age 40 +/- 7 years) Diabetes Control and Complications Trial (DCCT)/Epidemiology of Diabetes Interventions and Complications (EDIC) participants. NMR quantifies chylomicrons, three very low-density lipoprotein (VLDL) subclasses, intermediate density lipoprotein (IDL), three low-density lipoprotein (LDL) subclasses, two high-density lipoprotein (HDL) subclasses, mean VLDL, LDL and HDL size, and LDL particle concentration. Conventional lipids, ApoA1, ApoB and Lp(a) and in vitro LDL oxidizibility were also measured. IMT was determined (in 1994-1995) using high-resolution B-mode ultrasound. Relationships between IMT and lipoproteins were analysed by multiple linear regression, controlling for age, diabetes-related factors, and cardiovascular disease (CVD) risk factors.

RESULTS

IMT associations with lipoproteins were stronger for the internal than the common carotid artery, predominantly involving LDL. Internal carotid IMT was positively (P < 0.05) associated with NMR-based LDL subclasses and particle concentration, and with conventional LDL-cholesterol and ApoB in both genders. Common carotid IMT was associated, in men only, with large VLDL, IDL, conventional LDL cholesterol and ApoB.

CONCLUSIONS

NMR-LSP reveals significant associations with carotid IMT in Type 1 diabetic patients, even 4 years after IMT measurement. NMR-LSP may aid early identification of high-risk diabetic patients and facilitate monitoring of interventions. Longer DCCT/EDIC cohort follow-up will yield CVD events and IMT progression, permitting more accurate assessment of pre-morbid lipoprotein profiles as determinants of cardiovascular risk in Type 1 diabetes.

Immunochemical characterization of purified human oxidized low-density lipoprotein antibodies

The goal of this study was to characterize the isotypes and reactivity of human autoantibodies to copper oxidized LDL (oxLDL). Forty-six purified oxLDL antibodies contained immunoglobulins of the three major isotypes, with a predominance of IgG, subclasses 1 and 3. These IgG isotypes are known to interact with FcRgammaI and to activate the complement system and thus are potentially able to activate macrophages and cause foam cell formation. The same purified antibodies were tested for cross-reactivity with malondialdehyde (MDA)-, glycated (Glyc)-, and native (n)LDL and cardiolipin. Absorption with oxLDL resulted in a decrease of reactivity of 77.2 +/- 4.7%. Absorption with MDA-LDL resulted in a wider range of reduction of reactivity values, ranging from 50 to 87%, possibly reflecting differences in the degree of MDA modification. Absorption with Glyc- and nLDL caused a minor decrease in the reactivity of antibodies to oxLDL (5.9 +/- 7.1 and 6.8 +/- 6. 4%, respectively), comparable to the reduction of reactivity (2.1 +/- 4.0%) measured after absorption with transferrin, an irrelevant protein used as a negative control. These results suggest that oxLDL antibodies recognize primarily MDA epitopes. To determine whether purified oxLDL antibodies also recognize other epitopes known to be generated during copper oxidation of LDL, such as 4-hydroxynonenal (HNE)- and N(epsilon)(carboxymethyl)-lysine (CML), two additional sets of experiments were carried out. First, we monitored the formation of CML-, MDA-lysine, and HNE-lysine at different times during copper oxidation of two LDL pools. Both pools showed simultaneous increases in protein modification, as indicated by increasing fluorescence emission at 430 nm, and in immunoreactivity with oxLDL antibodies, coinciding closely with MDA modification of lysine groups. Second, we assessed whether the reactivity of oxLDL antibodies could be blocked by absorption with CML- or HNE-LDL. HNE-LDL did not react with isolated oxLDL antibodies. Highly modified CML-LDL (>90% of lysine residues modified) reduced the reactivity of oxLDL antibodies, but only by 25.5%. Finally, we investigated the possible cross-reactivity of oxLDL antibodies with cardiolipin. Seventeen purified oxLDL antibodies were used in this study, which showed that absorption with oxLDL or nLDL did not affect their reactivity with immobilized cardiolipin.

Association of apolipoprotein A phenotypes and oxidized low-density lipoprotein immune complexes in children

BACKGROUND

Small apolipoprotein A (apo [A]) phenotypes and oxidized low-density lipoprotein immune complexes (oxLDL-ICs) are known to be associated with the development of atherosclerosis in adults. Presence of these factors in children and their relationships with other known cardiovascular risk factors have not been well documented.

OBJECTIVE

To examine the relationship of oxLDL-ICs with apo(A) phenotypes and other known cardiovascular risk factors in children.

DESIGN

A survey of asymptomatic 9- to 11-year-old children, randomly selected from a cohort of children stratified based on family history of premature coronary artery disease.

SETTING

A preventive medicine research institute.

PARTICIPANTS

Thirty-five children with or without a family history of premature coronary artery disease who are participating in a longitudinal cardiovascular health study.

MAIN OUTCOME MEASURES

The influence of apo(A) phenotypes on plasma levels of oxLDL-ICs after controlling for lipid/lipoprotein levels, percentage of body fat, and physical fitness.

RESULTS

Oxidized low-density lipoprotein immune complexes were significantly correlated with the levels of total cholesterol (r = 0.56, P< or =.05), low-density lipoprotein cholesterol (r = 0.64, P< or =.01), and low-density lipoprotein cholesterol/high-density lipoprotein cholesterol (r = 0.54, P<.05). Oxidized low-density lipoprotein immune complexes were also correlated with total cholesterol high-density lipoprotein cholesterol (r = 0.49, P< or =.06) and percentage of body fat (r = 0.48, P< or =.06). However, they achieved only a borderline level of statistical significance after adjustment for multiple comparisons. Multiple regression analysis demonstrated that small apo(A) phenotypes, levels of low-density lipoprotein cholesterol, and family history of premature coronary artery disease explained 54% of the variation of oxLDL-ICs using a parsimonious model (P = .001).

CONCLUSIONS

Significant correlations exist between oxLDL-ICs and known cardiovascular risk factors in children. The association of oxLDL-ICs with the genetically controlled small apo(A) phenotype suggests that the genetic predisposition to immune complex formation may be an important determinant of future coronary artery disease.

Diabetes research in South Carolina: past, present, and future

Medical investigators in South Carolina have been on the "cutting edge" of diabetes research for a number of decades. Despite this fact, our state ranks second in the nation in diabetes prevalence, and diabetes complications are more severe here than anywhere else. It is from the efforts of these investigators that our hope for a brighter future comes. Through a concerted effort toward prevention, improvements in care, and investigation of the pathophysiology of diabetes and its complications, researchers may reduce the substantial burden of diabetes in our state and throughout the world.

Immunosuppressive effects of fish oil in normal human volunteers: correlation with the in vitro effects of eicosapentanoic acid on human lymphocytes

We have studied the effects of dietary supplementation with fish oil on immunological parameters in a group of six normal volunteers, four of whom received a fish oil extract (total EPA dose of 2.4 g/day, which is on the lower range of clinically effective doses) for 6 weeks and two of which received a placebo (olive oil) for an identical period of time. Each volunteer was followed up for a period of 23 weeks after the dietary intervention was ended. All volunteers were boosted with tetanus toxoid (TT) at the onset of the trial. Several immune parameters were followed longitudinally, including NBT reduction and lysozyme release to test neutrophil function; lymphocyte subpopulations; mitogenic responses to phytohemagglutinin (PHA), concanavalin A (Con A) and anti-CD3; IL-2 release after PHA and pokeweed mitogen (PWM) stimulation; immunoglobulin and anti-TT antibody (ATT) synthesis by stimulated lymphocytes; and serum levels of immunoglobulins and of ATT. No consistent changes were observed in neutrophil function tests, mitogenic responses to PHA and Con A, and lymphocyte subsets. The mitogenic response to anti-CD3 and the release of IL-2 after stimulation with PHA and PWM appeared reduced as a consequence of fish oil ingestion, and levels of serum immunoglobulins decreased in three of the volunteers receiving fish oil supplementation. The systemic humoral response after the TT booster appeared not to be influenced by the ingestion of fish oil. However, in those subjects who were given fish oil supplementation, the specific in vitro response of their peripheral blood lymphocytes to TT appeared to be compromised at Week 3. This could reflect the need for progressive accumulation of EPA in lymphocyte membranes for the suppressive effect to be detectable, but it could also reflect a differential sensitivity to the effects of fish oil of circulating B lymphocytes vs. bone marrow B lymphocytes. All the parameters apparently affected by fish oil ingestion were also affected by the incubation of normal lymphocytes with EPA in vitro. In conclusion, low doses of fish oil may have a mild immunosuppressive effect affecting both T and B cell functions. These observations stress the need for more extensive trials designed to determine whether immunosuppressive effects can be consistently elicited and for studies aimed at determining the mechanisms by which omega-3 fatty acids affect the immune system.

Platelet function during continuous insulin infusion treatment in insulin-dependent diabetic patients

Patients with diabetes mellitus manifest increased in vitro platelet aggregation and increased synthesis of the proaggregant and vasoconstrictor, thromboxane A2 (TXA2). We studied the effects of continuous insulin infusion treatment on platelet aggregation and arachidonic acid (AA)-stimulated platelet TXA2 synthesis (15 and 30 s post-AA, 1 mM) in 16 type I diabetic patients. Strict glycemic control was induced with the Biostator for 2 days and maintained for 12-14 days with continuous subcutaneous insulin infusion (CSII). The average premeal plasma glucose level (4/day) fell from 184 +/- 15, before treatment, to 107 +/- 6 mg/dl on the final day (P less than 0.001). After control, platelet synthesis of TXA2, measured by radioimmunoassay of its stable metabolite, immunoreactive TXB2 (iTXB2), decreased in all patients (30 s: 276 +/- 31 versus 199 +/- 28 ng iTXB2/ml/5 X 10(5) platelets; P less than 0.05). The reduction in platelet iTXB2 synthesis (15 and 30 s) was greater in poorly controlled patients (HbA1c greater than 12%; N = 8), and for all patients the decrease in iTXB2 (15 and 30 s) was correlated with the prestudy HbA1c level (15 s: r = 0.6; P less than 0.01). In contrast, platelet aggregation responses did not improve during intensive insulin treatment. The ED50 for AA (dose producing 50% maximum aggregation at 1 min) was unchanged after 2 wk of treatment and the ED50 for aggregation induced by ADP fell significantly in patients with HbA1c greater than 12% (2.8 +/- 1.3 versus 1.2 +/- 0.6 microM; P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of insulin treatment in streptozocin-induced diabetic rats on in vitro platelet function and plasma von Willebrand factor activity and factor VIII-related antigen

Diabetes mellitus is associated with altered platelet function and endothelial damage, but their relationship remains unclear. We examined the effect of short-term metabolic control with insulin in 14- and 28-day streptozocin-induced diabetic rats on alterations in in vitro platelet aggregation and serotonin release. Endothelial damage was assessed by plasma concentrations of von Willebrand factor activity (VIIIR:WF) and factor VIII-related antigen (VIIIR:Ag). Insulin was administered for 5 or 7 days at 9 or 21 days, respectively, after streptozocin. Enhanced platelet aggregation responses to adenosine diphosphate (ADP) and thrombin occurred after both durations of diabetes. Insulin therapy returned ADP-induced, but not thrombin-induced, responses to normal. Enhanced thrombin-induced platelet release of serotonin occurred at both times. Collagen-induced platelet release was enhanced in 28-day diabetic rats. Insulin therapy returned these responses to normal. Plasma concentrations of VIIIR:WF and VIIIR:Ag were elevated in 28-day, but only VIIIR:WF was elevated in 14-day diabetic rats. Insulin therapy reduced the elevated levels of VIIIR:Ag in 28-day diabetic rats, but had little effect on either parameter after the shorter duration of diabetes. In summary, Enhanced platelet aggregation and increased release of serotonin occur shortly after the induction of diabetes by streptozocin in adult rats. These platelet changes precede alterations of endothelial function, as determined by plasma VIIIR:WF and VIIIR:Ag levels. Platelet changes respond more rapidly to insulin therapy than do endothelial changes in diabetic rats. The duration of diabetes before insulin therapy does not affect these relationships.(ABSTRACT TRUNCATED AT 250 WORDS)

New concepts about the pathogenesis of atherosclerosis in diabetes mellitus

New concepts about the pathogenesis of atherosclerosis in diabetes mellitus are presented. Emphasis is given to alterations of endothelial function, as indicated by von Willebrand factor activity, prostacyclin release, and fibrinolytic activity in diabetes mellitus. Previous work on platelet aggregation and arachidonic acid metabolism is updated and recent findings are emphasized. The atherogenic mix of elevated low-density lipoprotein cholesterol and low high-density lipoprotein cholesterol levels in uncontrolled diabetes mellitus is noted. The lipid hypothesis is extended by consideration of very low-density lipoprotein and intermediate-density lipoprotein metabolism in diabetes. Lipoprotein-cell interactions that may contribute to atherosclerosis are reviewed and suggestions are made for future research in order to clarify the pathogenesis of atherosclerosis in diabetes mellitus.

Time course of changes in in vitro platelet function and plasma von willebrand factor activity (VIIIR:WF) and factor VIII-related antigen (VIIIR:Ag) in the diabetic rat

The relationship between platelet abnormalities and vessel wall changes in diabetes is not known. We have examined the time course of alterations in in vitro platelet function and endothelial damage, as assessed by measurement of plasma levels of von Willebrand factor (VIIIR:WF) and factor VIII-related antigen (VIIIR:Ag), in streptozotocin-induced diabetic rats. Platelet aggregation and the platelet release reaction in response to ADP, thrombin, and collagen were measured in suspensions of washed platelets prepared from rats 3, 7, 14, or 28 days after induction of diabetes and in control animals. Platelets from diabetic animals showed enhanced aggregation response to ADP as early as 3 days after induction of diabetes and became hyperresponsive to thrombin after 7 days, compared to control platelets. Thrombin-induced release of serotonin was greater in platelets from diabetic animals at 14 days. Collagen-induced responses were not different at any time studied. VIIIR:WF was determined by ristocetin-induced platelet agglutination time in gel-filtered platelets, and VIIIR:Ag was determined by immunoelectrophoretic technique. VIIIR:WF and VIIIR:Ag were significantly enhanced in plasma from rats at 28 days after induction of diabetes and VIIIR:Ag was enhanced in plasma from rats at 14 days after induction of diabetes, but at the earlier times studied, neither were different from values in plasma from control-treated rats. Changes in VIIIR:WF and VIIIR:Ag therefore occurred later than the changes in platelet function. Plasma cholesterol concentrations were not significantly different at any of the times studied, but plasma triglyceride concentrations were significantly increased at 3 days and remained increased with further durations of diabetes. This may have contributed to the observed platelet and vessel wall changes. If these in vitro alterations reflect in vivo behavior, then platelet alterations occur before vessel wall changes and therefore do not appear to be a consequence of such changes in experimental diabetes mellitus.

Pathogenesis of atherosclerosis in diabetes mellitus

Numerous studies have shown that patients with diabetes mellitus have accelerated atherosclerotic vascular disease, and major advances in understanding it pathogenesis have been made. Current suggestions are that endothelial injury may be the initial event in the genesis of atherosclerosis, followed by platelet adhesion and aggregation at the site of injury. In diabetes, evidence of endothelial dysfunction is present. Smooth muscle cell proliferation is an important pathologic finding in atherosclerosis. This process is stimulated by a platelet mitogen, which has been partially characterized. The mitogen has not been studied in diabetes. Lipid accumulation in the area of the atherosclerotic lesion is primarily in the form of intracellular and extracellular esterified cholesterol. In uncontrolled diabetes, elevated plasma low density lipoprotein levels and decreased plasma high density lipoprotein levels favor lipid deposition in large vessels. There is evidence of a thrombotic state in certain diabetic patients. Collectively, these abnormalities of endothelial, platelet, smooth muscle, lipoprotein, and coagulation behavior may be viewed as contributing to the problem of accelerated atherosclerosis in diabetes. A thorough understanding of the pathogenesis of this process aids in designing appropriate preventive therapeutic approaches.

Urinary high density lipoprotein in minimal change glomerular disease and chronic glomerulopathies

Serum lipids and lipoproteins and urinary apolipoprotein A (Apo A) were determined in two groups of patients. One group consisted of 11 children (ages ranging from 4 to 14 years) with minimal change glomerular disease. The other group consisted of 13 patients, eight less than 19 years old five adults, with different types of chronic glomerulopathy. Elimination of urinary lysozyme was a feature of chronic glomerulopathies, and creatinine clearances were also significantly lower in this group. Patients with chronic glomerulopathies had significantly lower HDL cholesterol and Apo A concentrations in their sera. In contrast, urinary Apo A concentrations were significantly higher in patients with chronic glomerulopathies, who also showed significantly lower urinary protein selectivities. Lipoprotein electrophoresis of urines containing Apo A showed distinct high-density lipoprotein (HDL) fractions, suggesting that HDL is eliminated in the urine as a result of increased glomerular permeability. This is also supported by a correlation coefficient of 0.77 between the selectivity indices and the ratio of urinary Apo A to total proteinuria. The determination of urinary Apo A appears to give valuable diagnostic information in patients with glomerular disease. According to our results the absence of urinary Apo A is very suggestive of minimal change glomerular disease.