Lipoprotein(a) concentration and molecular weight of apolipoprotein(a) in patients with cerebrovascular disease and diabetes mellitus

Lipoprotein (a) level as a risk factor for stroke and its subtype: A systematic review and meta-analysis

The role of lipoprotein-A [Lp (a)] as a risk factor for stroke is less well documented than for coronary heart disease. Hence, we conducted a systematic review and meta-analysis for the published observational studies in order to investigate the association of Lp (a) levels with the risk of stroke and its subtypes. In our meta-analysis, 41 studies involving 7874 ischemic stroke (IS) patients and 32,138 controls; 13 studies for the IS subtypes based on TOAST classification and 7 studies with 871 Intracerebral hemorrhage (ICH) cases and 2865 control subjects were included. A significant association between increased levels of Lp (a) and risk of IS as compared to control subjects was observed (standardized mean difference (SMD) 0.76; 95% confidence interval (CIs) 0.53-0.99). Lp (a) levels were also found to be significantly associated with the risk of large artery atherosclerosis (LAA) subtype of IS (SMD 0.68; 95% CI 0.01-1.34) as well as significantly associated with the risk of ICH (SMD 0.65; 95% CI 0.13-1.17) as compared to controls. Increased Lp (a) levels could be considered as a predictive marker for identifying individuals who are at risk of developing IS, LAA and ICH.

Lipoprotein (a) and Stroke

Background and Purpose— The relationship between elevated lipoprotein (a) levels[Lp(a)] and stroke is controversial. We systematically reviewed the literature to determine whether Lp(a) is a risk factor for stroke.

Methods— We searched MEDLINE (1966 to 2006), EMBASE (1974 to 2006), and Google scholar for articles on Lp(a) and cerebrovascular disease. From potentially relevant references retrieved, we excluded uncontrolled studies, studies of children with stroke, studies investigating carotid atherosclerosis, and studies lacking adequate data.

Results— Thirty-one studies comprising 56 010 subjects with >4609 stroke events met all inclusion criteria and were included in the meta-analysis. In case-control studies (n=23 with 2600 strokes) unadjusted mean Lp(a) was higher in stroke patients (standardized mean difference, 0.39; 95% CI, 0.23 to 0.54) and was more frequently abnormally elevated (OR, 2.39; 95% CI, 1.57 to 3.63). Sensitivity analysis and meta-regression did not find any influence of study design, measurement period of Lp(a) in relationship to stroke episode, subtype, age, and sex to explain the substantial heterogeneity between studies (I 2 =83.7%; P <0.001). There was no evidence of publication bias. In nested case-control studies (n=3 with 364 strokes) Lp(a) was not a risk factor for incident stroke (OR, 1.04; 95% CI, 0.6 to 1.8). In prospective cohort studies (n=5 with >1645 strokes), incident stroke was more frequent in patients in the highest tertile of Lp(a) distribution compared with the lowest tertile of Lp(a) (RR, 1.22; 95% CI, 1.04 to 1.43). There was no publication bias or heterogeneity in the prospective studies (I 2 =0.00%; P =0.67).

Conclusion— This meta-analysis suggests that elevated Lp(a) is a risk factor for incident stroke.

Increased lipoprotein (a) levels as an independent risk factor for venous thromboembolism

Elevation of serum lipoprotein (a) (Lp[a]) is a known risk factor predisposing to cardiovascular and cerebrovascular disease. However, little is known about the role of increased Lp(a) in venous thromboembolism (VTE). This study evaluated the role of Lp(a) among a panel of established hereditary thrombogenic defects in patients with VTE. A total of 685 consecutive patients with at least one episode of VTE and 266 sex- and age-matched healthy controls were screened with regard to activated protein C resistance, protein C, protein S, and antithrombin deficiency, elevated serum levels of Lp(a), and the factor V G1691A, MTHFR C677T, and prothrombin G20210A mutations. Elevated Lp(a) levels above 30 mg/dL were found in 20% of all patients, as compared to 7% among healthy controls (P < .001, odds ratio [OR] 3.2, 95% confidence interval [CI], 1.9-5.3). The coexistence of FV G1691A and elevated Lp(a) was significantly more prevalent among patients with VTE than in the control group (7% versus 0.8%; P < .001, OR 9.8, 95% CI, 2.4-40.7). No other established prothrombotic risk factor was found to be significantly combined with increased Lp(a). These data suggest that Lp(a) concentrations greater than 30 mg/dL are a frequent and independent risk factor for VTE. Furthermore, elevated Lp(a) levels might contribute to the penetrance of thromboembolic disease in subjects being affected by other prothrombotic defects, such as FV G1691A mutation.

Increased lipoprotein (a) levels as an independent risk factor for venous thromboembolism

Elevation of serum lipoprotein (a) (Lp[a]) is a known risk factor predisposing to cardiovascular and cerebrovascular disease. However, little is known about the role of increased Lp(a) in venous thromboembolism (VTE). This study evaluated the role of Lp(a) among a panel of established hereditary thrombogenic defects in patients with VTE. A total of 685 consecutive patients with at least one episode of VTE and 266 sex- and age-matched healthy controls were screened with regard to activated protein C resistance, protein C, protein S, and antithrombin deficiency, elevated serum levels of Lp(a), and the factor V G1691A, MTHFR C677T, and prothrombin G20210A mutations. Elevated Lp(a) levels above 30 mg/dL were found in 20% of all patients, as compared to 7% among healthy controls (P &lt; .001, odds ratio [OR] 3.2, 95% confidence interval [CI], 1.9-5.3). The coexistence of FV G1691A and elevated Lp(a) was significantly more prevalent among patients with VTE than in the control group (7% versus 0.8%; P &lt; .001, OR 9.8, 95% CI, 2.4-40.7). No other established prothrombotic risk factor was found to be significantly combined with increased Lp(a). These data suggest that Lp(a) concentrations greater than 30 mg/dL are a frequent and independent risk factor for VTE. Furthermore, elevated Lp(a) levels might contribute to the penetrance of thromboembolic disease in subjects being affected by other prothrombotic defects, such as FV G1691A mutation.

Multi-modal expression of apolipoprotein (a) gene in vivo

The apolipoprotein (a) [apo(a)] gene encodes a protein component of lipoprotein (a) [Lp(a)] whose plasma levels vary among individuals. To study the implications of Lp(a), we examined plasma Lp(a) levels and molecular weights of apo(a) in patients with cerebrovascular disease (CVD) or diabetes mellitus (DN). Mean Lp(a) concentrations were higher in the CVD cases with atherothrombotic brain infarction than in those with brain hemorrhage and lacunar infarction. Lp(a) levels were lower in the DM cases on diet therapy alone than in those treated with insulin or oral hypoglycemic agents. These results suggest that Lp(a) is thrombogenic and atherogenic, and that insulin may modulate Lp(a) levels. We subclassified the apo(a) gene into four types (A-D) by polymorphisms in the 5'-flanking region. We also measured plasma Lp(a) concentrations and examined expression of the gene by an in vitro assay. Homozygotes of type C had higher Lp(a) levels than those of type D, and the relative expression of type C was higher than that of type D in vitro. Lp(a) levels, however, varied even within the same 5'-allele having similar apo(a) isoforms. Thus, Lp(a) concentrations are genetically determined and may be modified by some hormones and cytokines. When we examined transcript levels for apo(a) by RT-PCR in various normal tissues, apo(a) was strongly expressed in liver while not in thyroid or leukocytes. Small amounts of apo(a) transcript were observed in all other organs and tissues. Apo(a) in these tissues may also play a role in inframmation, tissue remodeling, cell migration, and other physiological functions.

Plasma lipoprotein(a) levels are high in patients with central retinal artery occlusion

High plasma lipoprotein(a) (Lp[a]) concentration is an independent risk factor for atherosclerosis and thrombosis. To study the implications of Lp(a) in central retinal artery occlusion (CRAO), we examined Lp(a) levels and molecular weights (MWs) of apolipoprotein(a) (apo(a)). Mean Lp(a) concentration was significantly higher in the cases with CRAO than in the controls. Lp(a) levels higher than 30 mg/dl were also more frequent in the CRAO cases than in the controls. Lp(a) concentrations correlated significantly with low-MW isoforms of apo(a). Impaired fibrinolysis and atherogenesis induced by Lp(a) may play a role in the pathophysiology of CRAO. Since high Lp(a) levels were reported in CRVO by other investigators, patients with central retinal vein occlusion (CRVO) were also examined for Lp(a). Although Lp(a) levels were higher in the CRVO cases than in the controls, the difference was not significant. Therefore, high Lp(a) levels may not be associated with venous thrombosis and/or embolism.