Lp(a) lipoprotein in patients with arterial insufficiency of the lower extremities

Lipoprotein (a) as a cause of cardiovascular disease: insights from epidemiology, genetics, and biology

Human epidemiologic and genetic evidence using the Mendelian randomization approach in large-scale studies now strongly supports that elevated lipoprotein (a) [Lp(a)] is a causal risk factor for cardiovascular disease, that is, for myocardial infarction, atherosclerotic stenosis, and aortic valve stenosis. The Mendelian randomization approach used to infer causality is generally not affected by confounding and reverse causation, the major problems of observational epidemiology. This approach is particularly valuable to study causality of Lp(a), as single genetic variants exist that explain 27-28% of all variation in plasma Lp(a). The most important genetic variant likely is the kringle IV type 2 (KIV-2) copy number variant, as the apo(a) product of this variant influences fibrinolysis and thereby thrombosis, as opposed to the Lp(a) particle per se. We speculate that the physiological role of KIV-2 in Lp(a) could be through wound healing during childbirth, infections, and injury, a role that, in addition, could lead to more blood clots promoting stenosis of arteries and the aortic valve, and myocardial infarction. Randomized placebo-controlled trials of Lp(a) reduction in individuals with very high concentrations to reduce cardiovascular disease are awaited. Recent genetic evidence documents elevated Lp(a) as a cause of myocardial infarction, atherosclerotic stenosis, and aortic valve stenosis.

Correlation of serum lipoprotein(a) with the angiographic and clinical presentation of coronary artery disease

This study reports the association of elevated serum lipoprotein(a) levels with angiographically extensive coronary disease and the presence of totally occluded coronary arteries, as well as the association of elevated lipoprotein(a) with unstable angina. These results support the role of lipoprotein(a) in the human atherothrombotic process.

Lipoprotein(a) and inflammation in human coronary atheroma: association with the severity of clinical presentation

OBJECTIVES

The purpose of this study was the investigation of the in vivo role of lipoprotein(a) [Lp(a)] and inflammatory infiltrates in the human coronary atherosclerotic plaque and their correlation with the clinical syndrome of presentation.

BACKGROUND

Lipoprotein(a) is an atherogenic and thrombogenic lipoprotein, and has been implicated in the pathogenesis of acute coronary syndromes. Lipoprotein(a) induces monocyte chemoattraction and smooth muscle cell activation in vitro. Macrophage infiltration is considered one of the mechanisms of plaque rupture.

METHODS

This study of atherectomy specimens investigated the in vivo role of Lp(a) at different stages of the atherogenic process, and its relationship with macrophage infiltration. We examined coronary atheroma removed from 72 patients with stable or unstable angina. Specimens were stained with antibodies specific for Lp(a), macrophages (KP-1), and smooth muscle cells (alpha-actin). Morphometric analysis was used to quantify the plaque areas occupied by each of the three antigens, and their colocalization.

RESULTS

All specimens had localized Lp(a) staining; the mean fractional area was 58.2%. Ninety percent of the macrophage areas colocalized with Lp(a) positive areas, whereas 31.3% of the smooth muscle cell areas colocalized with Lp(a) positive areas. Patients with unstable angina (n = 46) had specimens with larger mean plaque Lp(a) areas than specimens from stable angina patients (n = 26): 64.4% versus 47.7% (p = 0.004). Unstable angina patients with rest pain (n = 28) had greater mean plaque Lp(a) area than unstable angina patients with crescendo exertional pain (n = 18): 71.1% versus 52.4% (p < 0.001). Mean KP-1 area was 31.2% in unstable rest angina versus 18.3% in stable angina (p = 0.05); alpha-actin area was greater in stable (48.5%) and crescendo exertional angina (48.8%) than in rest angina (30.4%). The strongest correlation between plaque KP-1 and Lp(a) area was in unstable rest angina (r = 0.88, p < 0.001), and between alpha-actin and Lp(a) areas in the crescendo exertional angina (r = 0.62, p < 0.01).

CONCLUSIONS

Lipoprotein(a) is ubiquitous in human coronary atheroma. It is detected in larger amounts in tissue from culprit lesions in patients with unstable compared to stable syndromes, and has significant colocalization with plaque macrophages. A correlation of plaque alpha-actin and Lp(a) area suggests a role of Lp(a) in plaque growth.

Arterial Damage, Triglycerides, Apolipoprotein, and Lp-(a) Values in PVD Patients

The aim of the study was to provide a detailed apolipoproteic profile in stage II peripheral vascular disease (PVD) patients and to ascertain whether lower ankle/ arm pressure index (API) values were associated with a worse profile.

Apolipoproteins of 83 stage II PVD patients (average age 64.7 ± 9.3 years) were selected and compared with those of a group of 44 normal control subjects, similar in terms of age, sex, and smoking and eating habits. Neither PVD patients nor controls had ever received lipid-lowering agents or defined dietary treatment. A diagnosis of PVD was confirmed by an API of <0.85. Arteriopathic patients were also split into two groups, depending on their API values, similar in terms of age, sex and smoking habits: API values of one group (n = 38) were ≥0.6, those of the other group (n = 45) were <0.6. The following biohumoral parameters were considered: fasting glycemia, total cholesterol, triglycerides (TGs); high-density lipoprotein cholesterol (HDL-C); low density lipoprotein cholesterol (LDL-C), very low density lipoprotein cholesterol (VLDL-C), total cholesterol (TC)/HDL-C (TC/ HDL-C), Apoproteins (Apos) AI, AII, B, CII, CIII, and E; and lipoprotein a [Lp(a)].

HDL-C and Apo AI were lower ( p < 0.01), while TC/ HDL-C ratios, Apo B, and Apo CII were higher ( p < 0.01) in PVD patients compared with controls. The comparison between the two PVD groups with different API values showed higher blood TG and VLDL-C values for the patients with lower API values (p < 0.05), indicating a relationship between hypertriglyceridemia and greater arterial damage. Key Words: Peripheral arterial occlusive disease-Triglyceride-Lipoprotein a.

Lipoprotein (a), homocysteine, and hypercoagulable states in young men with premature peripheral atherosclerosis: a prospective, controlled analysis

PURPOSE

Elevated lipoprotein (a) (Lp[a]) lipoprotein, total homocysteine, and hypercoagulable states (HCS) have all been implicated as risk factors for premature-onset atherosclerosis. This study was performed to determine the prevalence of these abnormalities in young men with chronic lower extremity ischemia (peripheral vascular disease [PVD]) and to determine their relative strengths as risk factors for premature peripheral atherosclerosis.

METHODS

We analyzed 50 young white men (aged 45 years or younger at onset of symptoms) and compared them with 45 age-matched white male control subjects.

RESULTS

Atherosclerotic risk factors were similar in both groups. The mean (+/- SEM) Lp(a) lipoprotein level was 36 +/- 6 mg/dl among the study patients, compared with 14 +/- 2 mg/dl among control subjects (p = 0.02, Mann-Whitney). Twenty (40%) study patients and seven (16%) control subjects had Lp(a) lipoprotein levels of 30 mg/dl or greater (atherosclerotic risk threshold) (p = 0.01, odds ratio = 3.62, confidence interval (CI) 1.4 to 9.5). Positive HCS panels (antiphospholipid antibodies or deficiencies in antithrombin III, protein C, or protein S) were nearly twice as prevalent in study patients (n = 15, 30%) as in controls (n = 8, 18%), but this difference did not achieve statistical significance. The mean total plasma homocysteine level among the study patients was 15.9 +/- 0.9 mumol/L, which was not significantly different from the mean control value of 14.7 +/- 0.7 mumol/L. Lp(a) lipoprotein was related to risk of premature PVD through a linear logistic relationship (p = 0.003, odds ratio per each 1 mg/dl Lp(a) change was 1.03, CI 1.0 to 1.1). Multivariate analysis with stepwise logistic regression selected two variables: Lp(a) lipoprotein > or = 30 mg/dl (p = 0.01, odds ratio = 3.6, CI 1.3 to 9.9) and family history (p = 0.07, odds ratio = 2.2, CI 0.9 to 5.3). Tests of interaction demonstrated no effect between Lp(a) lipoprotein, HCS, and homocysteine.

CONCLUSIONS

Lp(a) lipoprotein of 30 mg/dl or greater is an independent risk factor for premature peripheral atherosclerosis in men. None of the other examined variables exhibited a significant association with premature PVD.

Lipoprotein (a)

Lipoprotein (a) is similar to low-density lipoprotein but is unique in having an additional apolipoprotein called apolipoprotein (a) (apo(a)) covalently linked to it. apo(a), which is a member of the plasminogen gene superfamily, has a protease domain which cannot be activated to cause fibrinolysis. Its sequence of kringles is much longer than that of plasminogen and there is remarkable genetic variation in its length. The consequent inherited differences in apo(a) molecular mass are largely responsible for the wide range of serum Lp(a) concentrations in different individuals with low levels predominating in Europid populations. Physiologically Lp(a) may participate in haemocoagulation or in wound-healing. Epidemiological evidence that it is a risk factor for atherosclerosis, particularly in populations with high serum LDL levels, has led to research to uncover its role in atherogenesis and thrombosis. Diseases such as renal disease, and probably atherogenesis and thrombosis. Diseases such as renal disease, and probably atherosclerosis itself, are associated with an increase in Lp(a) above its genetically determined level and it remains a subject of speculation as to whether such increases are as closely involved in atherothrombosis as are spontaneously high levels resulting from low-molecular-mass apo(a) variants.

Lipoprotein(a) and asymptomatic carotid artery disease. Evidence of a prominent role in the evolution of advanced carotid plaques: the Bruneck Study

BACKGROUND AND PURPOSE

Elevated levels of lipoprotein(a) [Lp(a)] have been reported in association with symptomatic coronary and carotid artery disease. Relevancy of Lp(a) as a risk predictor of presymptomatic atherosclerosis in general populations is not well established.

METHODS

Serum Lp(a) distribution and its relation to sonographically assessed carotid atherosclerosis were examined in a random sample of 885 men and women aged 40 to 79 years (Bruneck Study).

RESULTS

Logistic regression analysis revealed a binary-type association between Lp(a) and carotid artery disease, with the threshold level of Lp(a) for an enhanced atherosclerosis risk defined at 32 mg/dL. The strength of relation increased with advancing severity of carotid atherosclerosis (odds ratios for Lp(a), 1.8 for nonstenotic and 4.7 for stenotic carotid artery disease; P < .001). Lp(a) was unaffected by environmental factors except for a significant decrease in women taking hormone replacement therapy (P < .05). In a multivariate approach, Lp(a) turned out to be an independently significant predictor of carotid atherosclerosis (P < .001). No differential effect of Lp(a) on atherosclerosis (effect modification) was observed for sex, age, low-density lipoprotein cholesterol, apolipoprotein A-I and B, fasting glucose, diabetes, or hypertension. However, the Lp(a)-atherosclerosis relation was significantly modified by fibrinogen (P < .01) and antithrombin III (P < .05).

CONCLUSIONS

The present study demonstrates a strong and independent association between elevated Lp(a) levels and carotid atherosclerosis in a large randomized population and provides evidence of a potential role of Lp(a) in the evolution of carotid stenosis. Apart from atherogenicity of Lp(a) cholesterol, interference with fibrinolysis of atheroma-associated clots and fibrin deposits in the arterial wall may achieve pathophysiological significance.

Elevated levels of lipoprotein (a) in association with cerebrovascular saccular aneurysmal disease

The relationship between cerebrovascular aneurysmal disease and atherosclerosis remains unclear. Elevated serum levels of lipoprotein (a) (Lp[a]), are an independent risk factor for atherosclerosis. We measured serum Lp(a) levels in 50 patients who had angiographically proven saccular aneurysmal disease and who were free of clinically significant atheromatous disease (as judged by their medical histories and the results of physical examination, electrocardiography, and carotid angiography). The Lp(a) serum levels in these patients were compared with the Lp(a) serum levels in a group of 42 normal healthy controls. Serum Lp(a) levels in the patients was 20.1 +/- 0.42 mg/dl (median +/- standard error); however, median serum Lp(a) in the control subjects was 10.8 +/- 0.47 mg/dl (P < 0.01). Among females, the difference in serum Lp(a) levels was significant; the levels were 22.2 +/- 0.6 for female patients (n = 29) and 9.5 +/- 0.53 in female control subjects (n = 26) (P < 0.005). The most significant difference (P < 0.002) was seen in females < 50 years old (14 patients, 10 control subjects). No significant differences were seen in the Lp(a) serum levels between 21 male patients and 16 male control subjects. Lp(a) levels above the threshold level (30 mg/dl) were found in 20 patients and 7 control subjects (chi 2 = 5.99, P < 0.02); 12 female patients and 3 female control subjects (chi 2 = 6.16, P < 0.02; 8 male patients and 4 male control subjects (this difference was not significant). These results indicate either that cerebrovascular aneurysmal disease and subclinical atherosclerosis are related or that Lp(a) is a risk factor for vasculopathies other than atheroma.

A prospective investigation of elevated lipoprotein (a) detected by electrophoresis and cardiovascular disease in women. The Framingham Heart Study

BACKGROUND

Sinking prebeta lipoprotein is a putative marker for elevated levels of lipoprotein (a). Although prospective data suggest that increased plasma lipoprotein (a) is an independent risk factor for coronary heart disease in men, no prospective studies are available in women.

METHODS AND RESULTS

From 1968 through 1975, sinking prebeta lipoprotein was determined by paper electrophoresis in 3103 women Framingham Heart Study participants who were free of prevalent cardiovascular disease. A sinking prebeta lipoprotein band was detectable in 434 of the women (14%) studied. The median follow-up interval was approximately 12 years. Incident cardiovascular disease was associated with band presence using a proportional hazards model that included age, smoking, body mass index, systolic blood pressure, glucose intolerance, low- and high-density lipoprotein cholesterol, and ECG left ventricular hypertrophy. Multivariable adjusted relative risk estimates (with 95% confidence intervals) for outcomes in the band present versus absent groups were as follows: myocardial infarction (82 events), 2.37 (1.48 to 3.81); intermittent claudication (62 events), 1.94 (1.07 to 3.50); cerebrovascular disease (83 events), 1.88 (1.12 to 3.15); total coronary heart disease (174 events), 1.61 (1.13 to 2.29); and total cardiovascular disease (305 events), 1.44 (1.09 to 1.91). A subset analysis indicated that band presence was 50.9% sensitive and 95.4% specific for detecting plasma lipoprotein (a) levels of > 30 mg/dL, the threshold value linked to increased cardiovascular disease risk in men.

CONCLUSIONS

Sinking prebeta lipoprotein was a valid surrogate for elevated lipoprotein (a) levels in Framingham Heart Study women. Band presence and, equivalently, elevated plasma lipoprotein (a), was a strong, independent predictor of myocardial infarction, intermittent claudication, and cerebrovascular disease. Confirmation of these findings in other longitudinal studies of women is needed.

Lp(a) lipoprotein in cardiovascular disease

The article summarizes the increased knowledge about the enigmatic Lp(a) lipoprotein and its clinical importance over the past 20 years. The mode of inheritance, the unique features of Lp(a) composition and structure and the unusual distribution of the mainly genetically determined plasma Lp(a) levels are discussed. The main factors that can significantly change the inherited plasma Lp(a) levels are endocrine disorders and hormone treatment. It seems possible that sex hormones protect females to a large extent from the potentially deleterious effects of inherited high Lp(a) levels until menopause. The exceptionally strong independent association found in most studies between Lp(a) lipoprotein levels and atherosclerotic disorders indicates that Lp(a) is a factor of outstanding importance in the pathogenesis of atherosclerosis. Probable pathogenetic mechanisms are reviewed. The associations found between LP(a) and insulin release, rheumatoid arthritis and renal diseases suggest that Lp(a) may be involved in immunological mechanisms. In a new hypothesis it is suggested that an autoimmune process might especially occur in individuals with inherited high Lp(a) levels and certain HLA class II genotypes, triggered by a concurrent infection.

Prevalence of intermittent claudication and risk factors for its development in patients on renal replacement therapy

The prevalence of symptomatic intermittent claudication (IC) was assessed using a standard cardiovascular questionnaire in a cohort of 325 patients on renal replacement therapy (RRT). IC was found in 19% of patients, 77% of whom were smokers and 22% diabetic. It was more common in men than women and in smokers than non-smokers (p < 0.001). Those with IC were significantly older (61 years vs. 50 years p < 0.001), smoked more (23 pack years vs. 12 pack years p = 0.002), had higher median systolic blood pressures (143 mmHg vs. 140 mmHg p = 0.041) and median triglyceride levels (2.07 mmol/l vs. 1.60 mmol/l p = 0.023) than those renal patients without IC. A case control study matching for age, sex and treatment revealed patients with IC to have higher median systolic blood pressure (147 mmHg vs. 140 mmHg p = 0.031), cholesterol (6.70 mmol/l vs. 5.90 mmol/l p = 0.029), LDL cholesterol (4.64 mmol/l vs. 3.86 mmol/l p = 0.011), and contained a greater proportion of smokers (78% vs. 50% p < 0.001). IC is common in patients on RRT. Whilst smoking was prevalent among those with IC it was much less frequent than in the general population with IC. Other factors such as hypertension, lipid abnormalities or the uraemic state itself may also be important in the development of IC in these patients.