Increased incidence of coronary disease in people with impaired glucose tolerance: link with increased lipoprotein(a) concentrations?

Correlation between lipoprotein(a) and other risk factors for cardiovascular disease and diabetes in Cherokee Indians: the Cherokee Diabetes Study

PURPOSE

To study the age and gender effects on the distribution of lipoprotein (a) [Lp(a)] and its relationship with other cardiovascular disease (CVD) and diabetes risk factors in the participants of the Cherokee Diabetes Study (CDS) (1995-2000).

METHODS

The CDS is a population based cross-sectional study of diabetes and its risk factors in Cherokee Indians aged 5 to 40 years of Oklahoma. Lp(a) levels were measured in 2205 participants.

RESULTS

The median Lp(a) (mg/dL) levels in the females were not significantly different among four age groups (5-9, 10-19, 20-29, and 30-40 years). However, the 20- to 29-year-old males had significantly lower Lp(a) levels than the males 10 to 19 and 30 to 40 years old. Females had significantly higher Lp(a) levels than males in the 20- to 29-year-old age group only. In the 5- to 19-year-old children/adolescents, Lp(a) levels were significantly negatively correlated with the degree of Indian heritage (DIH) and positively correlated with total cholesterol (TC), low-density lipoproteins (LDL), and apolipoprotein B (apoB) in girls, but not in boys. In the young adults aged 20 to 29 years, Lp(a) levels were significantly correlated with DIH, body mass index (BMI), waist-hip ratio (WHR), percentage of body fat (PBF), systolic blood pressure (SBP), triglycerides (TG), 2-hour plasma glucose (2hPG), and insulin in males, and DIH, PBF, TC, LDL, TG, and insulin in females. In adults aged 30 to 40 years, Lp(a) levels were significantly correlated with DIH, TG, and LDL in females, and DIH and insulin in males.

CONCLUSION

In the girls, Lp(a) levels appear to be associated with several CVD and diabetes risk factors at an early age (5-19 years), while in the boys, the association occurs at older ages (> 19 years). There are significant age and gender differences regarding the distribution of Lp(a) and its correlates in the 5 to 9, 10 to 19, and 20 to 29-year-old age groups, but the differences tend to be weaker in the 30- to 40-year-old age group. For the same age and gender groups, Lp(a) concentrations in Cherokee Indians were much lower than those reported in blacks and slightly lower than those in whites. In Cherokee Indians, the Lp(a) levels were consistently and positively correlated with LDL, and negatively correlated with DIH, TG, and insulin.

Correlates of lipoprotein(a) levels in a biracial cohort of young girls: the NHLBI Growth and Health Study

Elevated levels of lipoprotein(a) [Lp(a)] are associated with increased risk for coronary heart disease (CHD). However, racial differences in both Lp(a) levels and their associated CHD risk are observed, with African Americans having, on average, higher Lp(a) levels than US whites but not the expected increase in CHD risk. We determined Lp(a) levels and their correlates in a large cohort (n = 2379) of black and white girls, ages 9 to 10 years, at the baseline visit of a longitudinal study of obesity development, the National Heart, Lung, and Blood Institute Growth and Health Study. Lp(a) levels were available for 1269 girls. The median Lp(a) level in black girls was over 3-fold higher than that in white girls. Associations were examined between Lp(a) levels and low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol, apolipoprotein B, triglycerides, adiposity, pubertal maturation stage, body fat patterning (triceps/truncal skinfold ratio), and dietary fat (Keys' score). In black girls multiple regression analysis identified LDL-C (P <.001) and adiposity (P =. 08) as predictors of Lp(a) levels. In white girls only LDL-C (P =. 02) was associated with Lp(a). In conclusion, the level of Lp(a) was significantly higher in black girls. Our study also revealed a racial difference in correlates of Lp(a), such as LDL-C and adiposity. Whether this racial difference is due to an underlying biologic difference or is merely a reflection of a greater statistical power to detect a relationship with the level, which was 2.5-fold higher in black girls than in white girls, needs further investigation.

Elevated glycated haemoglobin in non-diabetic patients is associated with an increased mortality in myocardial infarction

Diabetes is associated with increased mortality following acute myocardial infarction compared to the general population. Elevated glycated haemoglobin (HbA1c) in diabetic patients is also associated with increased mortality following acute myocardial infarction, while mild elevation in HbA1c are associated with impaired glucose tolerance. The aim of this study was to determine the influence of HbA1c on outcome of acute myocardial infarction in 253 non-diabetic patients, 46 of whom died in one year. In univariate analysis, risk factors for death included smoking, glucose, cholesterol and HbA1c. In logistic regression analysis HbA1c was an independent risk factor for death. Over one-third of the fatality group had an HbA1c in the highest quartile, compared to one-fifth of the surviving group (p = 0.02). Elevated HbA1c is a risk marker for short-term mortality following acute myocardial infarction in non-diabetic subjects.

Serum LP(a) levels in African aboriginal Pygmies and Bantus, compared with Caucasian and Asian population samples

Serum lipoprotein(a) (Lp(a)) and its correlates were studied in African Aboriginal Pygmies (n = 146) and Bantus (n = 208) from Cameroon. Geometric mean Lp(a) levels were 274 and 289 mg/l in Bantu males and females, respectively, and 220 and 299 mg/l in Pygmy males and females, the gender difference being significant in Pygmies (p = 0.024). In Pygmies 41% and 52% of the males and females, respectively, had Lp(a) levels above 300 mg/l, compared with 47% and 55% in Bantus. Overall, Lp(a) levels did not significantly differ between Pygmies and Bantus, and did not correlate with age, body mass index (BMI), systolic and diastolic blood pressure. Compared with healthy Asian and Caucasian population samples, age- and BMI-adjusted geometric Lp(a) means were 2.3- to 5.0-fold higher in Pygmy and Bantu males, and 2.9- to 3.6-fold higher in Pygmy and Bantu females (p < or = 0.05). Across the population samples studied ethnicity predicted 12% and 17% of serum Lp(a) variance in males and females, respectively.

Monthly intra-individual variation in lipoprotein(a) in 22 normal subjects over 12 months

OBJECTIVES

It is generally believe that lipoprotein(a) (Lp(a)) levels remain relatively constant in the same individual, but there is a paucity of data to substantiate this belief. This study was undertaken to determine the extent of intra-individual variation in Lp(a) over a 12-month period.

DESIGN AND METHODS

Lp(a) was measured monthly in duplicate over a 12-month period in 11 females and 11 males who were healthy, free-living, normal subjects by the Incstar Immunoprecipitin method using a goat antibody which was monospecific for Lp(a).

RESULTS

Some subjects showed considerable month-to-month variations which were not correlated with changes in other lipid parameters or with weight. Others showed fairly constant Lp(a) levels, with a few values which were quite different from the rest. This was not attributable to methodological factors; low and high controls gave mean (mg/L), SD and CV values of 181, 8.6, 4.7 and 431, 14, 3.3, respectively. The difference between the minimum and maximum values in the same individuals ranged from a low of 14 mg/L in one subject to a high of 229 mg/L in another over the one-year period.

CONCLUSIONS

Lp(a) showed greater intra-individual variations in normal subjects than is commonly believed. It is therefore recommended that Lp(a) should be measured sequentially over a few weeks to arrive at a mean value for assessing risk of coronary heart disease.

Lipoprotein(a) concentrations in non-insulin-dependent diabetes mellitus and borderline hyperglycemia: a population-based study

The objective of the study was to compare lipoprotein(a) [Lp(a)] concentrations in population-based samples of individuals with non-insulin-dependent diabetes mellitus (NIDDM), borderline hyperglycemia, and normoglycemia. From 2,740 male Italian Telephone Company employees aged 40 to 59 years participating in a health screening, we selected all those with NIDDM (n = 100) plus a random sample of 950 nondiabetic individuals. Diabetes was defined as fasting plasma glucose (FPG) of at least 140 mg/dL or current use of hypoglycemic drugs. Among nondiabetic individuals, 854 were defined as normoglycemic (FPG < 115 mg/dL) and 95 were defined as borderline hyperglycemic (115 < FPG < 140 mg/dL). Lp(a) level was measured on frozen plasma by enzyme-linked immunosorbent assay. Lp(a) concentrations were similar in people with NIDDM, borderline hyperglycemia, and normoglycemia: 11.2 +/- 14, 14.1 +/- 20, and 13.9 +/- 18 mg/dL, respectively (F = 1.03). Accordingly, the proportion of subjects with Lp(a) levels of at least 30 mg/dL was comparable in the three groups (12%, 15%, and 14%; chi 2 = 3.95, P = .41). Results were not confounded by differences in age, body mass index (BMI), waist to hip ratio, plasma lipids, alcohol consumption, physical activity, and use of drugs. Furthermore, within the diabetic group Lp(a) levels were not significantly different for those on diet only versus those on oral agents (10.8 +/- 14.1 v 11.7 +/- 14.7, P = .7) or for people with FPG of at least 180 as compared with people with FPG less than 180 mg/dL (9.9 +/- 12.8 v 11.5 +/- 14.8, P = .5).(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison between the effects of gemfibrozil and simvastatin on insulin sensitivity in patients with non-insulin-dependent diabetes mellitus and hyperlipoproteinemia

In a double-blind, randomized crossover study, 29 patients with non-insulin-dependent diabetes mellitus (NIDDM) and hyperlipoproteinemia were treated with gemfibrozil (1,200 mg/d) or simvastatin (10 mg/d) for 4 months. After gemfibrozil treatment, the insulin concentration was increased during the major part of the intravenous glucose tolerance test (IVGTT) and during the hyperinsulinemic euglycemic clamp. Similar but less pronounced elevations were caused by simvastatin. Insulin sensitivity decreased by 27% and 28% during gemfibrozil and simvastatin treatment, respectively. Low-density lipoprotein (LDL) cholesterol was decreased with simvastatin treatment by 24%. The LDL cholesterol level was not changed by gemfibrozil, but very-low-density lipoprotein (VLDL) cholesterol was reduced by 40%. The VLDL triglyceride concentration was reduced to a significantly greater extent by gemfibrozil. After gemfibrozil treatment, lipoprotein(a) [Lp(a)] was decreased by 24%, and the plasma free fatty acid (FFA) concentration was increased by 20% and skeletal muscle lipoprotein lipase activity (LPLA) by 37%. Although simvastatin more effectively decreased LDL cholesterol levels and the LDL to high-density lipoprotein (HDL) ratio, it cannot be claimed unreservedly that this drug is necessarily preferable in NIDDM patients. Gemfibrozil improved triglyceride removal and decreased VLDL concentrations, with qualitative changes in LDL. The apparent effects on insulin sensitivity are difficult to evaluate and need further study.

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.

Association between impaired glucose tolerance and circulating concentration of Lp(a) lipoprotein in relation to coronary heart disease

OBJECTIVE

To examine whether impaired glucose tolerance and raised Lp(a) lipoprotein concentrations are associated in subjects with coronary artery disease.

DESIGN

Study of two subject populations, one with and one without symptomatic coronary artery disease. Case-control analysis of patients with impaired glucose tolerance and normal glucose tolerance performed in each subject population independently.

SETTING

A general practice and a hospital ward in Newcastle upon Tyne.

SUBJECTS

517 apparently healthy subjects, 13 with impaired glucose tolerance, and 245 patients who had undergone coronary artery bypass graft surgery 12 months before, 51 with impaired glucose tolerance.

MAIN OUTCOME MEASURES

Serum Lp(a) lipoprotein concentration, plasma glucose concentration before and after oral challenge with 75 g glucose monohydrate, and Lp(a) lipoprotein isoforms.

RESULTS

In both the asymptomatic subjects and the subjects with coronary artery disease there was no significant difference between subjects with impaired glucose tolerance and subjects with normal and body mass index in serum Lp(a) lipoprotein concentrations (geometric mean 61 (geometric SD 4) mg/l v 83 (5) mg/l for asymptomatic subjects, 175 (3) v 197 (2) for subjects with heart disease), nor was there any difference in the proportion of subjects who had Lp(a) lipoprotein concentrations > 300 mg/l (31% v 23% for asymptomatic subjects, 37% v 37% for subjects with heart disease). For both subject groups there was no significant correlation between Lp(a) lipoprotein concentration and plasma glucose concentration after a glucose tolerance test, nor did Lp(a) lipoprotein concentration vary by quintile of glucose concentration after the test. Examination of Lp(a) lipoprotein isoforms in the subjects with coronary artery disease revealed an inverse relation between isoform size and plasma Lp(a) lipoprotein concentration, but there was no evidence that impaired glucose tolerance was associated with particular Lp(a) lipoprotein isoforms.

CONCLUSION

Raised Lp(a) lipoprotein concentrations are not responsible for the association between impaired glucose tolerance and coronary artery disease.

Relation between sex hormones and serum lipoprotein and lipoprotein(a) concentrations in premenopausal obese women

Lipoprotein(a) (Lp[a]) is generally considered to be a risk factor for the development of cardiovascular disease, but little is known about the possible influence of obesity on the circulating levels of this lipoprotein. The present study was undertaken to examine this aspect in 136 menstrually active women by comparing the serum concentrations of Lp(a) between 72 obese and 64 age-matched nonobese women. Since an adverse effect of androgens and a protective effect of estrogens have been described for plasma lipoprotein profiles in obese women, the relation between the circulating levels of Lp(a) and those of these other hormones was also investigated in obese patients. In addition, other lipoproteins, anthropometric parameters (body mass index and waist-to-hip ratio), and insulin were evaluated. The levels of Lp(a) were not significantly different (Mann-Whitney U test chi 2, 3.59; p = 0.0582 [NS]) between obese (rank sum, 5,367) and control (rank sum, 3,949) women; in addition, the percentage of patients with high Lp(a) levels (cutoff defined at 30 mg/dL) did not differ between the two groups (obese women, 30%; control, 21.8%; chi 2, 0.90; two-sided p = 0.341 [NS]). Moreover, no correlation was found between Lp(a) and body mass index. Lastly, when the Lp(a) prevalence odds ratio for obesity was examined by adjusting the levels of this lipoprotein for age, triglycerides, total cholesterol, and high density lipoprotein cholesterol, the probability value (0.88) was far from significant. In obese women, no correlation was found between the logarithmically transformed Lp(a) concentrations and all the other variables evaluated in the study. In conclusion, the present study shows that the circulating levels of Lp(a) are not influenced by body weight and cardiovascular risk factors commonly associated with obesity, such as enhanced androgenic activity, hyperinsulinemia, adverse lipoprotein profile, and abdominal fat accumulation.