**6. Lp(a) and stroke**

number of control individuals, plasma Lp(a) concentrations were measured by latex-enhanced immune-turbidimetry (see below) and apo(a) isoforms were assayed by SDS-polyacrylamide gel electrophoresis followed by immune blotting, using the isoform-standard from Immuno A.G., Vienna. Unfortunately, Immuno A.G. does not exist anymore and isoform standards are nowadays hard to obtain. The authors of PROCARDIS calculated the odds ratio (OR) of patients and controls between the first and last quintile before and after adjusting for the number of K-IV repeats. In both calculations, an OR of 2.05 (*p* < 0.001) was found, i.e. no difference could be observed whether the apo(a) size polymorphism was taken into consid‐ eration or not. This report appears to quite definitely conclude this debate and is proof that Lp(a) exerts its atherogenicity through its plasma concentration and not through possible structural differences in K-IV repeats. In an editorial to this report, F. Kronenberg (Innsbruck) pointed out that the analysis of SNPs—in particular rs41272114, rs10455872 and rs3798220, which exhibit the strongest association to plasma Lp(a) concentrations can neither be taken as surrogates nor as substitutions for the number of K-IV repeats. He further pointed out that more than half the number of individuals with isoforms containing less than 22 K-IV repeats

In a further publication by the PROCARDIS Consortium published in ATVB [21], the question was asked as to what extent the LPA "null allele" (rs41272114) might influence the plasma concentration of Lp(a) in heterozygous individuals and if it might be a determinant for atherogenic risk. In this study comprising some 8000 CAD patients, an allele frequency for rs41272114 of approximately 3% was found. Patients containing the null allele exhibited significantly lower plasma Lp(a) levels as compared to control individuals without the rs41272114 allele (OR 0.79; *p* = 0.023). According to findings from the group of G. Utermann [22], the rs41272114 SNP represents a donor-splice site mutation leading to the biosynthesis of a truncated apo(a) with only 7 K-IVs (K-IV 1–7) in total and no K-V or protease domain. As a consequence of the absence of K-IV type 9, which contains the only free –SH group in apo(a) and is responsible for the covalent binding to apoB-100, the truncated apo(a) fragments are well secreted from the liver into the blood but do not assemble with LDL and thus are rapidly degraded and removed from the circulation. The PROCARDIS study also proved that individuals with only one apo(a) isoform exhibit a large variation in their plasma Lp(a) concentrations and that there exists a sigmoid correlation between the number of K-IV repeats and plasma Lp(a) levels. The question of the mechanism that causes this variation, however, could not be answered by this study. The authors of the PROCARDIS Consortium claimed, on the basis of their results, that in future epidemiological studies by SNP analysis for the assessment of the CAD risk, the rs41272114 polymorphism must be taken into consideration

Further support of the hypothesis published in 1981 by our group [15] indicating that Lp(a) might be a significant risk factor for MI comes from the "Bruneck Study" comprising 826 male and female probands [23]. In a recall survey after 15 years, it was found that the inclusion of Lp(a) in the Framingham algorithm for the risk assessment of CHD, an improvement of 0.016 in the C-index was reached. Consideration of Lp(a) plasma levels improved the hit rate in the

are not recorded by this SNP analysis mentioned above.

142 Lipoproteins - From Bench to Bedside

as a matter of state-of-the-art experiments.

prediction of CHD by 40%.

The question as to what extent Lp(a) might also be causally related to stroke was addressed in numerous publications (reviewed in ref. [24]). Sultan et al. [25] recently published the results of his meta-analysis, where he included 10 published papers dealing with ischemic stroke in children. Setting the cutoff level for Lp(a) at 30 mg/dl, a positive association between Lp(a) and stroke was found with a Mantel-Haenszel OR of 4.24 (*p* < 0.00001).

As mentioned above, the physiological function of Lp(a) is in the dark. Concerning the pathophysiology, the work of Tsimikas et al. from San Diego is noteworthy because they believe that the high affinity of Lp(a) for oxidized phospholipids might be responsible for its atherogenicity [26]. Oxidized phospholipids are known to promote the synthesis of inflam‐ matory cytokines that recruit monocytes and T-lymphocytes. Monocytes differentiate to macrophages that phagocytose oxLDL and are transformed to foam cells, hallmarks in atherogenesis. Negatively charged phospholipids such as Ox-Phos are key components in oxLDL and also bind a specific protein, β-2-glykoprotein-I (β2-GPI). The latter also forms a complex with Lp(a). In a recently published paper, it was reported that the plasma levels of Lp(a), Ox-Lp(a) and β2GP-I-Lp(a) in stroke patients were significantly higher than in controls (124 patients vs. 64 controls). In addition, a positive correlation of these plasma parameters with the severity of stroke was established [27]. These findings point towards the assumption that Lp(a) might not neutralize ox-PL but in contrast boosts its atherogenic properties.
