Alterations of lipoprotein(a) in patients with diabetic nephropathy

Lp(a) is not Related to Retinopathy in Diabetic Subjects

PURPOSE

To examine the association between Lp(a) concentrations and the severity of retinopathy in 22 younger-onset and 48 older-onset diabetic subjects from the Wisconsin Epidemiologic Study of Diabetic Retinopathy (WESDR), a population-based study of diabetic retinopathy.

METHODS

We used a subset of the WESDR population with standardized protocols and stereoscopic color fundus photography to determine the severity of diabetic retinopathy in relation to Lp(a) concentrations. Lp(a) concentrations were measured by a monoclonal anti-Lp(a) antibody.

RESULTS

Lp(a) levels were not significantly different between younger-onset or older-onset subjects with and without retinopathy.

CONCLUSION

Our results do not support a link between higher levels of Lp(a) and severe retinopathy in either younger-onset or older-onset diabetic subjects but this needs confirmation in larger prospective studies.

Elevated Plasma Lipoprotein(a) Levels and Hypoalbuminemia in Peritoneal Dialysis Patients

Plasma lipoprotein(a), Lp(a), is strongly and independently associated with atherosclerosis, and levels are elevated in hemodialysis (HD) patients and in some studies of those on peritoneal dialysis (PD). We hypothesized that protein losses and hypoalbuminemia could stimulate hepatic Lp(a) synthesis, and this effect would be accentuated in PD patients with malnutrition. The PD subjects (n=24) had higher plasma Lp(a) levels than those (n=10) on HD (median 34.4 vs 21.0 mg/dl, p<0.05), and values exceed normal in 62.5% vs 20% of the subjects (p<0.03), respectively. The serum albumin levels inversely correlated with concentrations of Lp(a) and apolipoprotein B, as well as the apolipoprotein B/AI ratio. In conclusion, plasma Lp(a) concentrations are frequently elevated in PD as well as HD patients. Measuring Lp(a) levels is useful in identifying patients at increased atherogenic risk, which may not be reflected in routine lipid profiles. The negative correlation between plasma Lp(a) and albumin levels suggests that the latter may be linked pathophysiologically to hepatic Lp(a) production. The association of hypoalbuminemia with higher Lp(a) values is of particular concern because malnutrition frequently occurs in PD patients.

Serum lipoprotein(a) levels and diabetic nephropathy among Japanese patients with type 2 diabetes mellitus

AIMS

We aimed to evaluate the association between serum lipoprotein(a) [Lp(a)] levels and diabetic nephropathy among Japanese patients with type 2 diabetes mellitus.

METHODS

This study included 581 patients with type 2 diabetes mellitus. Serum Lp(a) levels were divided into four groups; the cut-off points were at the 30th, 60th, and 90th percentile values on the basis of the distribution for all subjects. Diabetic nephropathy was defined as present when the urinary albumin-creatinine ratio was ≥33.9mg/mmol creatinine and/or the estimated glomerular filtration rate was <30ml/min/1.72m(2). Adjustment was made for age, sex, body mass index, hemoglobin A1c, duration of diabetes mellitus, current drinking, current smoking, hypertension, dyslipidemia, coronary heart disease, and stroke.

RESULTS

Higher serum Lp(a) levels were significantly associated with a higher prevalence of diabetic nephropathy: the adjusted odds ratios (95% confidence intervals) for diabetic nephropathy in relation to serum Lp(a) levels of ≤6, 7-15, 16-38, and ≥39mg/dl were 1.00 (reference), 2.74 (1.08-7.00), 3.31 (1.28-8.54), and 4.80 (1.57-14.60), respectively (P for trend=0.004).

CONCLUSIONS

The results suggest that serum Lp(a) levels may be positively associated with diabetic nephropathy among Japanese patients with type 2 diabetes mellitus.

Lipoprotein (a) in chronic renal failure: effect of maintenance hemodialysis

BACKGROUND

Coronary artery disease accounts for significant morbidity and mortality in patients with chronic kidney disease (CKD). Besides the higher prevalence of traditional risk factors, several uremia-related factors may play a role in accelerated atherosclerosis, such as elevated levels of lipoprotein (a) (Lp(a)). The effect of maintenance hemodialysis (MHD) on Lp(a) levels is not well understood. The present work was carried out to study the Lp(a) levels in Stage 4 and Stage 5 CKD patients as well as the effect of MHD on Lp(a) levels in patients with Stage 5 CKD.

METHODS

The study subjects included 15 patients with Stage 4 CKD, 15 patients with Stage 5 CKD, and 15 age- and sex-matched healthy controls. Plasma Lp(a) was measured by ELISA in all the subjects at the time of entry into the study and after 4 weeks of MHD in patients with Stage 5 CKD. Patients on MHD were dialyzed two to three times weekly for 4 hr during each session.

RESULTS

Mean Lp(a) levels were significantly higher in patients with CKD than in control patients. In patients with Stage 4 CKD, the Lp(a) level was 34.0 +/- 19.5 mg/dL, whereas in Stage 5 CKD the level was 49.0 +/- 30.9 and in healthy controls it was 22.2 +/- 16.4. In patients with Stage 5 CKD, 4 weeks of MHD led to a significant fall in Lp(a) levels by 23.6% (P < 0.001).

CONCLUSIONS

The results of this study show that increases in Lp(a) levels start early during the course of CKD and become more pronounced with increased severity of disease. Initiation of MHD lowers Lp(a) levels and may have a long-term beneficial effect on cardiovascular morbidity and mortality.

Antiproteinuric effect of niceritrol, a nicotinic acid derivative, in chronic renal disease with hyperlipidemia: a randomized trial

PURPOSE

Lipoprotein (a) [Lp(a)] levels increase in patients with renal disease. We administered niceritrol, a nicotinic acid derivative, to patients with chronic renal disease and a high serum Lp(a) level, and studied its effects on lipid metabolism, proteinuria, and renal function.

METHODS

Thirty-three patients with chronic renal disease whose serum Lp(a) levels were > or = 15 mg/dL were randomly (but not blindly) assigned to treatment with niceritrol (n = 16) or to an untreated control group (n = 17). Parameters of lipid metabolism, excretion of urinary protein, and renal function were examined for 12 months.

RESULTS

Changes in urinary protein excretion, as well as Lp(a) levels, differed significantly between the two groups. The mean (+/- SD) change from baseline in excretion of urinary protein was 0.77 +/- 1.23 g/d in the control group compared with -1.41 +/- 2.26 g/d in the niceritrol group at 12 months (P =0.003). Mean Lp(a) levels increased by 3 +/- 10 mg/dL in the control group compared with a decrease of 10 +/- 13 mg/dL in the niceritrol group at 12 months (P =0.004). The mean creatinine clearance declined by 10 +/- 12 mL/min in the control group, compared with 1 +/- 13 mL/min in the niceritrol group at 12 months (P =0.06).

CONCLUSION

Lipid levels improved with niceritrol treatment, whereas the excretion of urinary protein decreased, perhaps slowing the rate of loss of renal function in chronic renal disease.

Pathogenesis of vascular disease

Only recently are we beginning to understand the complex interplay of factors involved in vascular disease and diabetes. Insulin resistance provides a starting point to explain the many factors that lead to the more severe vascular disease characteristic of diabetes. Insulin resistance syndrome comprises insulin resistance and compensatory hyperinsulinaemia as well as hypertension, dyslipidaemia, macrovascular disease, and increased plasminogen activator inhibitor-1 activity. The development of type 2 diabetes may be viewed as the inability of the pancreas to continue to overcome insulin resistance, even with excessive insulin production.

Pathogenesis of atherosclerosis in diabetes and hypertension

Prevalence of atherosclerotic vascular disease is markedly increased among individuals with diabetes-mellitus and hypertension. Its major clinical manifestations are consequences of atherosclerosis of coronary arteries, cerebral arteries and large arteries of lower extremities. Thus, atherosclerotic vascular disease is the major cause of mortality and significant morbidity in diabetes and hypertension. Dyslipidemia, hyperinsulinemia, and central obesity seem to be associated with increased risk of atherosclerosis, along with the development of hypertension and diabetes (NIDDM). Insulin resistance is the fundamental factor in this situation which has strong genetic predisposition. Accelerated atherosclerosis in diabetes due to mechanism unique to diabetes like non-enzymatic glycation of proteins, oxidative modification of lipoproteins, formation of lipoproteins immune complexes, lipoproteins aggregation, disturbances of cell replication and growth factors and propensity to thrombosis are clearly established. Therapeutic implication for the prevention of atherosclerosis in diabetes and hypertension clearly emphasizes the need to achieve tight control of hyperglycemia, hypertension, and hyperlipidemia in addition to avoiding cigarette smoking and developing obesity.

Microalbuminuria predicts cardiovascular events and renal insufficiency in patients with essential hypertension

BACKGROUND

Some patients with essential hypertension manifest greater than normal urinary excretion of albumin (UAE). Authors of a few retrospective studies have suggested that there is an association between microalbuminuria and cardiovascular risk.

OBJECTIVE

To evaluate whether microalbuminuria is associated with a greater than normal risk of cardiovascular and renal events.

METHODS

We performed a retrospective cohort analysis of 141 hypertensive individuals followed up for approximately 7 years. Hypertensive patients were defined as having microalbuminuria if the baseline average UAE of three urine collections was in the range 30-300 mg/24 h.

RESULTS

Fifty-four patients had microalbuminuria and 87 had normal UAE. At baseline, the two groups were similar for age, weight, blood pressure, and rate of clearance of creatinine. Serum levels of cholesterol, triglycerides, and uric acid in patients with microalbuminuria were higher than levels in those with normal UAE, whereas levels of high-density lipoprotein cholesterol in patients with microalbuminuria were lower than levels in patient with normal UAE. During follow-up, 12 cardiovascular events occurred among the 54 (21.3%) patients with microalbuminuria and only two such events among the 87 patients with normal UAE (P < 0.0002). Stepwise logistic regression analysis showed that UAE (P = 0.003), cholesterol level (P = 0.047) and diastolic blood pressure (P = 0.03) were independent predictors of the cardiovascular outcome. Rate of clearance of creatinine from patients with microalbuminuria decreased more than did that from those with normal UAE (decrease of 12.1 +/- 2.77 versus 7.1 +/- 0.88 ml/min, P < 0.03).

CONCLUSIONS

This study suggests that hypertensive individuals with microalbuminuria manifest a greater incidence of cardiovascular events and a greater decline in renal function than do patients with normal UAE.

Glycated proteins modulate tissue-plasminogen activator-catalyzed plasminogen activation

Plasminogen activation by tissue-plasminogen activator (t-PA) is accelerated by the presence of a macromolecular surface, which acts as a template that brings enzyme and substrate in close proximity. Modification of lysine residues, which are important for this template function, occurs in diabetic patients as a consequence of glycation of proteins. In this study, we investigated the effects of glycation of fibrin and other proteins in t-PA-catalyzed plasmin formation. Plasminogen activation on glycated fibrin(ogen) was increased compared to non-glycated fibrin(ogen), which could fully be attributed to an increased affinity of t-PA for glycated fibrin(ogen). Binding of plasminogen to glycated fibrin was increased, but did not contribute to increased plasminogen activation. Both plasminogen activator inhibitor-1 (PAI-1) binding and activity were increased on glycated fibrin. Induction of template function in plasminogen activation was also observed on immobilized glycated bovine serum albumin (BSA) and human gamma-globulins (IgG). Increased plasmin generation at sites of deposition of glycated proteins may lead to increased extracellular matrix breakdown and thereby affect the integrity of the endothelial monolayer. Moreover, soluble glycated BSA and glycated IgG can inhibit t-PA binding to immobilized glycated fibrin and interfere with fibrinolysis in diabetic patients.

Plasma lipoprotein(a) distribution in the Framingham Offspring Study as determined with a commercially available immunoturbidimetric assay

The purpose of our research was to evaluate a commercially available, automated, immunoturbidimetric assay for lipoprotein(a) (Lp(a)), to determine the distribution of Lp(a) in the Framingham Offspring Study population, and to determine Lp(a) levels that may be useful for assessing coronary heart disease risk. The mean between-run coefficient of variation for this assay was 5.65%. Lp(a) concentration was slightly, but significantly, higher in 1949 white women (mean +/- S.D. 214 +/- 195 mg/l, median 150 mg/l) than in 1884 white men (mean +/- S.D. 200 +/- 193 mg/l, median 130 mg/l) participating in Cycle 4 of the Framingham Offspring Study (P = 0.0015). Lp(a) values of 300 mg/l and 500 mg/l corresponded to approximately the 75th and 90th percentiles, respectively, for both men and women, and subjects with concentrations greater than or equal to 500 mg/l were more likely to have coronary heart disease than subjects with an Lp(a) concentration less than 300 mg/l (P < 0.05 for men).

Lipoprotein(a) in renal disease

Lipoprotein(a) [Lp(a)] is a genetically determined risk factor for atherosclerotic vascular disease. Several studies have described a correlation between high Lp(a) plasma levels and coronary heart disease, stroke, and peripheral atherosclerosis. In healthy individuals Lp(a) plasma concentrations are almost exclusively controlled by the apolipoprotein(a) [apo(a)] gene locus on chromosome 6q2.6-q2.7. More than 30 alleles at this highly polymorphic gene locus determine a size polymorphism of apo(a). There exists an inverse correlation between the size (molecular weight) of apo(a) isoforms and Lp(a) plasma concentrations. Average Lp(a) levels are high in individuals with low molecular weight isoforms and low in those with high molecular weight isoforms. Mean Lp(a) plasma levels are elevated over controls in patients with renal disease. Patients with nephrotic syndrome exhibit excessively high Lp(a) plasma concentrations, which can be reduced with antiproteinuric treatment. The mechanism underlying this elevation is unclear, but the general increase in protein synthesis caused by the liver due to high urinary protein loss is a likely explanation. Patients with end-stage renal disease (ESRD) also have elevated Lp(a) levels. These are even higher in patients treated by continuous ambulatory peritoneal dialysis than in those receiving hemodialysis. Lipoprotein(a) concentrations decrease to values observed in controls matched for apo(a) type following renal transplantation. This clearly demonstrates the nongenetic origin of Lp(a) elevation in ESRD. Both the increase in ESRD and the decrease following renal transplantation are apo(a) phenotype dependent. Only patients with high molecular weight phenotypes show the described changes in Lp(a) levels. In patients with low molecular weight types the Lp(a) concentrations remain unchanged during both phases of renal disease. As in the general population, Lp(a) is a risk factor for cardiovascular events in ESRD patients. In this patient group the apo(a) phenotype seems to be equally or better predictive of the degree of atherosclerosis than is Lp(a) concentration. Further prospective studies will be necessary to confirm these observations. Whether Lp(a) also plays a key role in the pathogenesis and progression of renal diseases needs further study. Controversial data on the role of the kidney in Lp(a) metabolism result from insufficient sample sizes of several studies. Due to the broad range and skewed distribution of Lp(a) plasma concentrations, large study groups must be investigated to obtain reliable results.

Serum lipoprotein(a) concentrations and apolipoprotein(a) phenotypes in the families of NIDDM patients

We studied the quantitative and qualitative characteristics of lipoprotein(a) [Lp(a)] as a function of apolipoprotein(a) [apo(a)] phenotype in 87 members (42 males, 45 females) of 20 diabetic families, 26 of whom were diagnosed with non-insulin-dependent diabetes mellitus (NIDDM) with moderate glycaemic control (HbA1c 7.1 +/- 1.2%). Apo(a) phenotyping was performed by a sensitive, high-resolution technique using SDS-agarose/gradient PAGE (3-6%). To date, 26 different apo(a) phenotypes, including a null type, have been identified. Serum Lp(a) levels of NIDDM patients and non-diabetic members of the same family who had the same apo(a) phenotypes were compared, while case control subjects were chosen from high-Lp(a) non-diabetic and low-Lp(a) nondiabetic groups with the same apo(a) phenotypes in the same family. Serum Lp(a) levels were significantly higher in NIDDM patients than in non-diabetic subjects (39.8 +/- 33.3 vs 22.3 +/- 19.5 mg/dl, p < 0.05). The difference in the mean Lp(a) level between the diabetic and non-diabetic groups was significantly (p < 0.05) greater than that between the high-Lp(a) non-diabetic and low-Lp(a) non-diabetic groups. An analysis of covariance and a least square means comparison indicated that the regression line between serum Lp(a) levels [log Lp(a)] and apo(a) phenotypes in the diabetic patient group was significantly (p < 0.01) elevated for each apo(a) phenotype, compared to the regression line of the control group. These data together with our previous findings that serum Lp(a) levels are genetically controlled by apo(a) phenotypes, suggest that Lp(a) levels in diabetic patients are not regulated by smaller apo(a) isoforms, and that serum Lp(a) levels are greater in diabetic patients than in non-diabetic family members, even when they share the same apo(a) phenotypes.

Effect of simvastatin on Lp(a) concentrations

The effect of HMG-CoA reductase inhibitors on Lp(a) concentrations is controversial, with some studies showing an increase and others showing no effect on Lp(a) concentrations. Many of these studies have been limited by small sample size and the lack of a prospective design. We evaluated the effect of four treatments: (1) placebo, (2) simvastatin 10 mg PO QPM, (3) simvastatin 20 mg PO QAM, and (4) simvastatin 20 mg PO QPM on Lp(a) concentrations in a prospective, randomized, controlled clinical trial of 24 weeks in 343 subjects in 28 clinical sites in the United States. Simvastatin was not associated with a change in Lp(a) concentrations relative to placebo. These results were not affected by controlling for race, initial Lp(a) level, or urinary albumin excretion. Simvastatin significantly reduced low-density lipoprotein (LDL) cholesterol levels (10 mg PO QPM: -27.6%; 20 mg PO QAM: -28.1%; and 20 mg PO QPM: -34.3%, all p < 0.001). It was concluded that in a large, randomized, controlled trial, simvastatin does not affect Lp(a) levels but markedly lowers LDL cholesterol levels.

The role of lipoprotein(a) in the vascular complications of diabetes mellitus

Lipoprotein(a) has been identified as an independent risk factor for atherosclerotic vascular disease in non-diabetic populations. Because of its potential role in the pathogenesis of both microvascular and macrovascular complications in diabetes, there have recently been many reports on lipoprotein(a) in diabetic populations. Some studies indicate an association between elevated lipoprotein(a) and macrovascular disease in non-insulin-dependent diabetes mellitus (NIDDM), but this link has not been found with insulin-dependent diabetes mellitus (IDDM). In IDDM, elevated lipoprotein(a) has been found in groups with diabetic nephropathy and retinopathy, raising the possibility that it plays a causative role. The relationship between glycaemic control and the lipoprotein(a) level has not been fully resolved. Most studies have not found any connection in NIDDM, but some found higher lipoprotein(a) levels in hyperglycaemic IDDM patients. Potentially, lipoprotein(a) is an important factor linking the microvascular and macrovascular complications of diabetes.

Effect of glycation on the properties of lipoprotein(a)

Lipoprotein(a) [Lp(a)] was glycated by incubation in vitro with glucose (0 to 200 mmol/L), and its properties were compared with native Lp(a) and native and glycated LDL. Glucose was incorporated into Lp(a) in proportions that mirrored the distribution of lysines between apolipoprotein (apo) B-100 and apo(a). Because the kringle IV domains of apo(a) are lysine poor, only 10% of glucose bound to apo(a), whereas 90% was attached to the apoB-100 of Lp(a). Approximately 3% of the lysines of both Lp(a) and LDL were modified, which is a level comparable with that observed in LDL isolated from diabetic individuals. Glucose uptake by Lp(a) and LDL was almost identical and was linear as a function of concentration and time. Glycation increased the negative charge of Lp(a) and LDL as monitored by electrophoresis and ion-exchange chromatography and also reduced the affinity of Lp(a) and LDL for heparin-Sepharose. Glycation did not affect the lysine-binding property of Lp(a) or generate measurable malondialdehyde oxidation adducts. The catabolism of glycated Lp(a) by human monocyte-derived macrophages (HMDMs), like that of native Lp(a), was largely LDL receptor independent. Both glycated Lp(a) and LDL were degraded at a comparatively faster rate and stimulated greater cholesteryl ester formation than their unmodified counterparts. However, the degradation rate of glycated Lp(a) was approximately four- to fivefold slower and its stimulation of cholesteryl ester formation was ninefold lower than that of either form of LDL. These results show that Lp(a) can be glycated nonenzymatically in vitro, that the incorporation of glucose is dependent on the distribution of lysines between apo(a) and apoB-100, and that glycation does not affect the lysine-binding properties of Lp(a). Furthermore, glycation produced modest increases in the degradation rate of Lp(a) and associated cholesteryl ester synthesis by HMDMs. Based on these data, glycation does not appear to significantly enhanced the atherogenic potential of unmodified Lp(a).

Effect of gemfibrozil versus lovastatin on increased serum lipoprotein(a) levels of patients with hypercholesterolemia

The aim of this study was to determine the effect of gemfibrozil, compared with lovastatin, in patients with high levels of lipoprotein(a) and on plasma lipid profile. Twenty-seven nondiabetic patients with high levels of plasma lipids and lipoprotein(a), 19 male and eight female, aged 37-68 (mean +/- S.D. 54.2 +/- 7.5) years, were randomly assigned to 2 weeks of treatment with gemfibrozil 600 mg twice daily (14 pts.) or lovastatin 40-80 mg once daily (13 pts.). Patients had fasting plasma total cholesterol levels > or = 6.2 mmol/l, low-density lipoprotein > 4.14 mmol/l and lipoprotein(a) > 0.62 mmol/l. All patients but one had triglycerides > 2.82 mmol/l. There were no statistical differences between both groups in terms of age, sex, clinical diagnosis and previous medication. After 3 months of treatment, gemfibrozil reduced triglycerides (47.9% vs. 24.5%; P < 0.001), very low density lipoprotein (43.9% vs. 24.6%; P < 0.05), lipoprotein(a) (25.3% vs. 4.9%; P < 0.05) and increased high-density lipoprotein (34.4% vs. 11%; P < 0.01) more than lovastatin. Gemfibrozil and lovastatin reduced comparably total cholesterol (21.4% vs. 29.0%; P = NS) and low-density lipoprotein (26.5% vs. 37.3%; P = NS). The plasma levels of high-density lipoprotein and lipoprotein(a) were unchanged significantly by lovastatin. In conclusion, besides well-known efficacy in hyperlipidemia treatment, gemfibrozil also increased high-density lipoprotein and reduced lipoprotein(a), which may have important epidemiologic implications.

Lipids and Lp(a) lipoprotein levels and coronary artery disease in subjects with non-insulin-dependent diabetes mellitus

OBJECTIVE

To determine whether increased Lp(a) lipoprotein levels are associated with either non-insulin-dependent diabetes mellitus (NIDDM) or coronary artery disease (CAD) in patients with NIDDM and to examine the relationship between Lp(a) levels and glycemic control.

DESIGN

We conducted a cross-sectional study of subjects with NIDDM who were participants in the Rochester Diabetic Neuropathy Study and healthy control subjects from the population of Rochester, Minnesota.

MATERIAL AND METHODS

Lipids and Lp(a) lipoprotein levels were compared in 227 subjects with NIDDM and 163 control subjects and, among the subjects with NIDDM, in those with (N = 96) and without (N = 131) CAD. The correlation between Lp(a) levels and glycosylated hemoglobin was investigated.

RESULTS

Subjects with NIDDM had higher triglyceride and lower high-density lipoprotein cholesterol levels than did control subjects. Subjects with NIDDM and CAD had higher total cholesterol, triglyceride, and low-density lipoprotein cholesterol levels and lower high-density lipoprotein cholesterol levels than did subjects with NIDDM without CAD. Subjects with NIDDM had significantly higher Lp(a) levels than did control subjects, but subjects with NIDDM and CAD did not have significantly higher Lp(a) levels than did those without CAD. Among subjects with NIDDM, the level of Lp(a) was not significantly correlated with glycosylated hemoglobin.

CONCLUSION

Although subjects with NIDDM have higher Lp(a) levels than do control subjects, Lp(a) does not seem to be associated with CAD in subjects with NIDDM. In this study, no association was found between Lp(a) level and glycemic control.

Lp(a) concentrations and phenotypes in children with insulin-dependent diabetes mellitus

Subjects with insulin-dependent diabetes mellitus (IDDM) have an increased incidence of coronary heart disease. Several studies have suggested that Lp(a) levels may be increased in IDDM subjects, although these studies have been limited by the lack of information on apo(a) phenotype and urinary albumin excretion. We compared Lp(a) concentrations in 66 children with IDDM and 18 non-diabetic children; all were non-Hispanic whites and none had detectable albuminuria. Lp(a) concentrations (mg/dl) were lower in subjects with IDDM than in non-diabetic subjects (12.0 +/- 2.2 vs. 20.0 +/- 6.1, respectively), although these means were not significantly different (P = 0.276). Postpubertal subjects, particularly males, had increased Lp(a) concentrations relative to prepubertal subjects (P = 0.041). Higher apo(a) molecular weight was associated with decreased Lp(a) concentrations in both diabetic and non-diabetic subjects. However, apo(a) size was not different in diabetic and non-diabetic subjects. Lp(a) concentrations were not significantly correlated with glycosylated hemoglobin levels in diabetic subjects (r = 0.11, P = NS). We also found similar Lp(a) concentrations in postpubertal IDDM subjects compared with adult non-Hispanic white non-diabetic subjects (n = 208) from the San Antonio Heart Study, a population-based study. These observations do not support increased Lp(a) concentrations in young normoalbuminuric IDDM subjects.

Elevated lipoprotein (a) levels in primary nephrotic syndrome

Elevated plasma levels of total cholesterol and increase in the hepatic synthesis of some apo B-containing lipoproteins have been noted in the nephrotic syndrome. Apoprotein (a), the apolipoprotein distinguishing lipoprotein (a) [Lp(a)] from low-density lipoprotein, is equally of hepatic origin, and Lp(a) recently has been shown to possess both atherogenic and thrombogenic activities. However, little is known of Lp(a) levels in nephrotic patients. We measured plasma Lp(a) concentrations in 11 patients with primary nephrotic syndrome in the absence of hematuria, hypertension, and renal insufficiency. Histologic lesions were minimal-change disease in five cases, membranous glomerulopathy in four cases, and focal and segmental glomerulosclerosis in two cases. Mean levels of Lp(a) (98 +/- 92 mg/dL [mean +/- SD]) were markedly elevated in the nephrotic patients as compared with the controls (14 +/- 13 mg/dL). No correlation was noted between plasma Lp(a) and proteinuria, albuminemia, total cholesterolemia, low-density lipoprotein cholesterol, apoprotein B100, or plasminogen. Furthermore, there was no correlation between Lp(a) levels and apoprotein (a) isoform size. In four patients, the level of Lp(a) decreased approximately fourfold after remission of the nephrotic syndrome under corticosteroid treatment. Our observation that Lp(a) levels are elevated in the nephrotic syndrome is consistent with the hypothesis that these patients may be at an increased risk of cardiovascular and thrombotic complications.

Apolipoprotein(a) phenotypes and serum lipoprotein(a) levels in maintenance hemodialysis patients with/without diabetes mellitus

We studied the quantitative and qualitative characteristics of lipoprotein(a) [Lp(a)] as a function of apolipoprotein(a) [apo(a)] phenotypes in 152 patients (123 males, 29 females) undergoing maintenance hemodialysis (HD) with or without diabetes mellitus (DM), in 101 patients with diabetes mellitus without hemodialysis (58 males, 43 females), and in 421 normal controls (333 males, 88 females). Serum Lp(a) levels were significantly (P < 0.01) higher in patients than in controls (26.2 +/- 18.3 mg/dl in HD with DM, 26.4 +/- 22.0 mg/dl in HD without DM, 27.1 +/- 27.3 mg/dl in DM without HD, and 14.9 +/- 13.7 mg/dl in controls, respectively). Apo(a) phenotyping was performed by a sensitive, high resolution technique using SDS-agarose/gradient (3 to 6%) PAGE. In normal controls, the molecular weights of apo(a) isoforms were inversely correlated with plasma Lp(a) levels, and the same tendency was found in patients who were undergoing hemodialysis and/or who had diabetes mellitus. We assumed the differences in apo(a) phenotypes detectable with our method reflected consecutive differences in molecular weights of apo(a). The results of an analysis of covariance and a least square means comparison indicated that the regression lines between serum Lp(a) levels [log Lp(a)] and apo(a) phenotypes in patient groups were significantly (P < 0.01) elevated for every apo(a) phenotype, as compared to the regression line of the control group. Even after the low molecular weight apo(a) phenotypes (A1-A8) were omitted, the same tendency was observed. However, no differences were observed between the patient groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Alteration of lipoprotein(a) concentration with glycemic control in non-insulin-dependent diabetic subjects without diabetic complications

Recently, a high plasma level of lipoprotein(a) [LP(a)] has been considered an independent risk factor for atherosclerosis and its sequelae, particularly myocardial infarction. Patients with non-insulin-dependent diabetes mellitus (NIDDM) have an increased mortality rate from cardiovascular and cerebrovascular disease. Therefore, plasma concentrations of Lp(a) were determined and the relationship between fasting plasma Lp(a) level and diabetic control was investigated in NIDDM patients without any diabetic complications. Fasting plasma Lp(a) levels were measured using enzyme-linked immunosorbent assay kits [Terumo Medical Corp, Elkton, MD, Lp(a)] in 61 NIDDM subjects (30 men aged 56 +/- 2.0 years, 31 women aged 53 +/- 2.1 years [mean +/- SEM]) who were without any diabetic macroangiopathy and microangiopathy such as retinopathy, nephropathy, and neuropathy and in 56 healthy age- and sex-matched controls. Plasma Lp(a) levels were significantly higher in the diabetic group than in the control group (23.5 +/- 2.5 v 11.7 +/- 1.4 mg/dL [mean +/- SEM], P < .001). There was no significant correlation between log-transformed plasma Lp(a) levels and other factors such as age, sex, body mass index (BMI), blood pressure, duration of diabetes, fasting plasma glucose (FPG) level, glycosylated hemoglobin (HbA1C) level, and plasma lipid levels except for low-density lipoprotein cholesterol (LDL-C) levels in diabetic patients. A significant positive correlation was noted in diabetic patients between the changes of log Lp(a) and HbA1C levels after a 3-month follow-up period (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Lipoprotein(a) in patients treated by continuous ambulatory peritoneal dialysis

Lipoprotein(a) [Lp(a)] has been identified as an independent, inherited risk factor for atherosclerotic vascular disease. An elevation of Lp(a) plasma levels has been documented in several series of uremic patients submitted to maintenance dialysis treatment methods or after renal transplantation. We have measured the plasma levels of Lp(a) using an enzyme-linked immunosorbent enzyme method in 19 patients treated with continuous ambulatory peritoneal dialysis (CAPD). Mean (+/- SD) concentration of Lp(a) was significantly higher in the patients than in the 19 healthy controls (51 +/- 48 mg/dL v 16 +/- 15 mg/dL, P < 0.005). No significant differences in Lp(a) levels were found between diabetic patients (n = 5) and nondiabetic patients (n = 14) or between patients who had (n = 6) or had not (n = 13) suffered a previous major cardiovascular complication. No correlation was evident between Lp(a) levels and the patients' ages, period of time on CAPD treatment, or any other lipid-lipoprotein investigated parameter. The mechanisms accounting for the elevation of Lp(a) levels in CAPD patients as well as the specific value of increased Lp(a) concentration as a cardiovascular risk predictor in uremic patients remain thus far speculative. Additional experimental and clinical studies are warranted before the administration of drugs to attempt to lower Lp(a) levels in CAPD patients can be recommended.

Elevated plasma concentrations of lipoprotein(a) in patients with end-stage renal disease are not related to the size polymorphism of apolipoprotein(a)

Patients with terminal renal insufficiency suffer from an increased incidence of atherosclerotic diseases. Elevated plasma concentrations of lipoprotein(a) [Lp(a)] have been established as a genetically controlled risk factor for these diseases. Variable alleles at the apo(a) gene locus determine to a large extent the Lp(a) concentration in the general population. In addition, other genetic and nongenetic factors also contribute to the plasma concentrations of Lp(a). We therefore investigated Apo(a) phenotypes and Lp(a) plasma concentrations in a large group of patients with end-stage renal disease (ESRD) and in a control group. Lp(a) concentrations were significantly elevated in ESRD patients (20.1 +/- 20.3 mg/dl) as compared with the controls (12.1 +/- 15.5 mg/dl, P < 0.001). However, no difference was found in apo(a) isoform frequency between the ESRD group and the controls. Interestingly, only patients with large size apo(a) isoforms exhibited two- to fourfold elevated levels of Lp(a), whereas the small-size isoforms had similar concentrations in ESRD patients and controls. Beside elevated Lp(a) concentrations, ESRD patients had lower levels of plasma cholesterol and apolipoprotein B. These results show that elevated Lp(a) plasma levels might significantly contribute to the risk for atherosclerotic diseases in ESRD. They further indicate that nongenetic factors related to renal insufficiency or other genes beside the apo(a) structural gene locus must be responsible for the high Lp(a) levels.

Localization of apolipoprotein(a) and B-100 in various renal diseases

Recently it has become clear that abnormalities of lipid metabolism play a large role in the progression of renal diseases. To investigate the relationship between lipids and kidney tissue, we employed an immunofluorescent technique to determine the localization pattern of apolipoprotein(a) [apo(a)], apoB-100, and low-density lipoprotein receptor in the glomeruli, and analyzed the relationship between their presence and the clinical and histological findings of a total 92 patients with glomerular diseases. Immunostaining showed co-localization of apo(a) and apoB-100 in glomeruli. The patients were divided into three groups, as follows: both apo(a) and apoB-100 positive (Group 1; 38 cases), apo(a) positive only (Group 2; 19 cases) and apo(a) negative (Group 3; 35 cases). Group 1 had more severe proteinuria, higher levels of lipoprotein(a) [Lp(a)], and lower total protein levels than Group 3. Group 1 had a higher prevalence of glomerulosclerosis and interstitial changes than Group 3. Group 2 had more severe proteinuria and a higher prevalence of glomerulosclerosis than Group 3. Although apo(a) and apoB-100 are almost absent in normal controls, these apoproteins [and presumably lipoproteins Lp(a)] are present in the glomeruli of patients with glomerular diseases. The data support the view that these apoproteins play a significant role in progressive renal diseases.

Cardiovascular risk factors in non-insulin-dependent diabetic subjects with microalbuminuria

In subjects with insulin-dependent diabetes mellitus, microalbuminuria has been associated with increased triglyceride and lipoprotein (a) (Lp[a]) concentrations and increased blood pressure. However, few studies have examined whether this association is present in subjects with non-insulin-dependent diabetes mellitus (NIDDM). We measured lipids, lipoproteins, Lp(a), blood pressure, and albumin excretion in 234 subjects with NIDDM from the San Antonio Heart Study, a population-based study of diabetes and cardiovascular disease. Seventy-two subjects had microalbuminuria (> or = 30 mg/dl). These subjects had increased systolic and diastolic blood pressures and higher fasting glucose concentrations relative to subjects without microalbuminuria. However, there were no significant differences between subjects with and without microalbuminuria with respect to lipids, lipoproteins, Lp(a), self-reported myocardial infarction, obesity, or body fat distribution. Subjects with diabetic retinopathy had increased microalbuminuria. In multivariate analysis both glycemia and blood pressure continued to be significantly related to the presence of microalbuminuria. We conclude that NIDDM subjects with microalbuminuria have elevated blood pressure and more severe glycemia but do not have a significantly more atherogenic pattern of lipids, lipoproteins, or Lp(a) than subjects without microalbuminuria.

Plasma lipoprotein (a) concentration and phenotypes in diabetes mellitus

Patients with Type 1 (insulin-dependent) and Type 2 (non-insulin-dependent) diabetes mellitus are at increased risk of developing atherosclerotic vascular diseases. A variety of lipoprotein abnormalities have been described as being associated with this increased risk. In this study, apo(a) isoform frequencies and lipoprotein(a) [Lp(a)] concentrations were determined in Type 1 and Type 2 diabetic patients in order to investigate a possible contribution of Lp(a) to the increased risk for atherosclerosis in diabetes. No significant differences in plasma Lp(a) concentrations were found in two ethnically different populations (Austrians from the province of Tyrol and Hungarians from Budapest) in either type of diabetes when compared to respective control groups (91 Type 1 and 112 Type 2 diabetic patients vs 202 control subjects in the Hungarian study and 44 Type 1 diabetic and 44 Type 2 diabetic vs 125 control subjects in the Austrian study). There were also no significant apo(a) isoform frequency differences between both patient groups and control subjects in the two study groups. These data, obtained from two large ethnically different populations, provide no evidence of a contribution of Lp(a) to the increased risk for atherosclerosis in diabetes.

Changes in Lp(a) lipoprotein levels during the treatment of hypercholesterolaemia with simvastatin

Thirty-six patients with total serum cholesterol levels above 6.5 mmol/l and Lipoprotein(a) levels above 100 mg.l-1 were evaluated in a 24 week double-blind, placebo controlled, cross-over study to assess the possible changes in Lp(a) during treatment with the HMG CoA reductase inhibitor simvastatin. The median plasma Lp(a) increased from 359 to 464 mg.l-1 during simvastin treatment as compared to placebo (not significant). Individual changes in Lp(a) varied. In a multivariate linear regression analysis the individual change in Lp(a) was correlated with the baseline Lp(a) (r = 0.64), the change in serum triglycerides (r = 0.48) and the baseline apolipoprotein B (r = 0.36). Differences between the Lp(a) phenotypes may explain some of the varied Lp(a) responses. It appears that the effect of simvastatin on the Lp(a) level in individuals is usually insignificant, but in patients with a high Lp(a) simvastatin may further increase it.

Normal lipoprotein(a) concentrations and apolipoprotein(a) isoforms in patients with insulin-dependent diabetes mellitus

Lipoprotein(a) [Lp(a)] is an LDL particle in which apoliporotein B-100 is attached to a large plasminogen-like protein called apolipoprotein(a) [apo(a)]. Apo(a) has several genetically determined phenotypes differing in molecular weight, to which Lp(a) concentrations in plasma are inversely correlated, and plasma Lp(a) concentrations above 20-30 mg dl-1 are an independant risk factor for ischaemic heart disease (IHD). To investigate whether Lp(a) could be important for the high cardiovascular mortality rate in patients with insulin dependent diabetes mellitus (IDDM), we determined Lp(a) concentrations and phenotypes in a group of 108 men (median age 32 years) with IDDM without nephropathy. A group of 40-year-old men (n = 466) served as controls. The median Lp(a) concentration was 7.4 mg dl-1 [95% CI 4.9 to 11.7] in the diabetic patients and 6.3 mg dl-1 [95% CI 5.2 to 7.0] in controls. The Lp(a) concentration exceeded 30 mg dl-1 in 22% of IDDM patients and in 20% of controls (P = 0.13). Moreover, the distribution of apo(a) phenotypes did not differ between patients and control. Lp(a) levels and apo(a) phenotypes are thus apparently the same in IDDM patients without nephropathy and controls. These findings do not exclude the possibility that Lp(a) may be increased in patients with nephropathy in whom coronary artery disease frequently co-exist or that Lp(a) in a given concentration is more atherogenic in IDDM patients than in persons without IDDM.

Plasma level of lipoprotein Lp(a) is high in predialysis or hemodialysis, but not in CAPD

Plasma Lp(a) lipoprotein level was determined in chronic renal failure (CRF) patients, 24 before initiation of dialysis, 18 undergoing hemodialysis, and 24 on continuous ambulatory peritoneal dialysis (CAPD). Eighteen healthy subjects were studied as controls. Median of Lp(a) level in both predialysis and dialysis patients was significantly increased: 23.5 mg/dl (range: 0 to 109) and 24.0 mg/dl (range: 1.4 to 90), respectively, as compared to healthy controls: 4.7 mg/dl (range: 1.8 to 27; P less than 0.001). By contrast, the median Lp(a) level in CAPD patients, 2.4 mg/dl (range: 0 to 39.5), was similar to the control group. Whether the CAPD procedure reduces the Lp(a) level in CRF patients has to be established in a prospective study.

Lipoprotein(a) and acute-phase proteins in acute myocardial infarction

Lipoprotein(a) (Lp(a)) and the acute-phase proteins, orosomucoid, haptoglobin and alpha 1-antitrypsin, were studied in 32 patients with acute myocardial infarction. Samples were taken at admission and, after fasting overnight, on the following 6 days. In a subgroup of 21 patients total serum cholesterol, high-density lipoprotein (HDL) cholesterol and triglycerides were also estimated. In a linear regression model a significant relation between the relative values of Lp(a) and the time in days was obtained (p = 0.001). Compared with the acute-phase proteins, however, Lp(a) showed a weak increase and the individual responses were very variable. There were no correlations between the individual changes in Lp(a) and the changes in the acute-phase proteins, but Lp(a) changes correlated significantly with the changes in total cholesterol and low-density lipoprotein (LDL) cholesterol. It is suggested that the Lp(a) reaction in myocardial infarction is linked to the reaction of the lipoproteins. There may also be several clinical conditions, including different medications, which influence the Lp(a) level.

Automated measurement of lipoprotein(a) by immunoturbidimetric analysis

Immunoturbidimetric analysis of lipoprotein(a) in plasma or serum was developed for use on the Roche COBAS FARA II and COBAS MIRA clinical chemistry analyzers. The components of the assay are: (1) buffer consisting of 2.25% polyethylene glycol in phosphate-buffered saline, 0.2% gelatin, and a surfactant; (2) fractionated goat anti-human lipoprotein(a) IgG; (3) five standards with lipoprotein(a) concentrations ranging from 0.05 to 1.0 g/l; (4) two controls with concentrations of approximately 0.2 and 0.5 g/l. The analyzer delivers sample and buffer, incubates the reaction mixture at 37 degrees C for 5 min, delivers neat lipoprotein(a) antibody, and incubates for an additional 10 min. The lipoprotein(a) concentration of samples is calculated by the COBAS DENS (Data Evaluation for Non-linear Standard Curves) option by fitting the standard curve values to a four-parameter logit-log curve model. Total imprecision results (CV%) for the FARA II and MIRA were under 11% (NCCLS protocol EP5-T). The assay is linear beyond the highest calibrator to 2.6 g/l. No interference was observed for plasminogen up to 2.3 g/l, apolipoprotein B up to 4.36 g/l, hemoglobin up to 10 g/l, bilirubin up to 4.0 g/l, and triglycerides up to 4.36 g/l. Comparison with a double monoclonal ELISA used at the Northwest Lipid Research Laboratories yielded: R = 0.970, slope = 1.013, and y-intercept = 0.00009 (n = 37). Comparison with a commercially available ELISA kit for lipoprotein(a) yielded: r = 0.987, slope = 1.243, and y-intercept = 0.024 (n = 40). This assay provides rapid, accurate, and precise screening of lipoprotein(a) in serum or plasma.

Apolipoprotein(a) phenotypes, Lp(a) concentration and plasma lipid levels in relation to coronary heart disease in a Chinese population: evidence for the role of the apo(a) gene in coronary heart disease

Elevated lipoprotein(a) (Lp[a]) concentrations are associated with premature coronary heart disease (CHD). In the general population, Lp(a) levels are largely determined by alleles at the hypervariable apolipoprotein(a) (apo[a]) gene locus, but other genetic and environmental factors also affect plasma Lp(a) levels. In addition, Lp(a) has been hypothesized to be an acute phase protein. It is therefore unclear whether the association of Lp(a) concentrations with CHD is primary in nature. We have analyzed apo(a) phenotypes, Lp(a) levels, total cholesterol, and HDL-cholesterol in patients with CHD, and in controls from the general population. Both samples were Chinese individuals residing in Singapore. Lp(a) concentrations were significantly higher in the patients than in the population (mean 20.7 +/- 23.9 mg/dl vs 8.9 +/- 12.9 mg/dl). Apo(a) isoforms associated with high Lp(a) levels (B, S1, S2) were significantly more frequent in the CHD patients than in the population sample (15.9% vs 8.5%, P less than 0.01). Higher Lp(a) concentrations in the patients were in part explained by this difference in apo(a) allele frequencies. Results from stepwise logistic regression analysis indicate that apo(a) type was a significant predictor of CHD, independent of total cholesterol and HDL cholesterol, but not independent of Lp(a) levels. The data demonstrate that alleles at the apo(a) locus determine the risk for CHD through their effects on Lp(a) levels, and firmly establish the role of Lp(a) as a primary genetic risk factor for CHD.