Differential expression of double-band apolipoprotein(a) phenotypes in healthy Spanish subjects detected by SDS-agarose immunoblotting

Effect of Nandrolone Decanoate on serum lipoprotein (a) and its isoforms in hemodialysis patients

Malnutrition, anemia and increased atherosclerosis are the main causes of mortality in hemodialysis patients. Therapies designed to improve the disorders might therefore be expected to improve outcome. The effects of Nandrolone Decanoate (ND), in 64 stable hemodialysis patients, were studied with respect to the following parameters: nutritional status, hematological indexes, lipid profiles including serum levels of lipoprotein(a) [Lp(a)] in terms of differences in apolipoprotein(a) [apo(a)]. The patients were treated with ND at dose of 100 mg/I.M./week for 4 months. After 2 and 4 months of treatment the elevations in the serum levels of albumin (p < 0.0001), creatinine (p < 0.009), hemoglobin (p < 0.03), hematocrit (p < 0.03), cholesterol (p = 0.007) and triglyceride (p < 0.04) were noticed. Marked decrease in the concentration of high-density lipoprotein cholesterol (p = 0.007) and Lp(a) (p < 0.0001) were also found. These effects after 2 months of treatment withdrawal were relatively constant. By dividing patients according to the baseline Lp(a) levels and molecular weight of apo(a) isoform, it was noticed that the decrease in serum Lp(a) was significant in patients with high Lp(a) (>30 mg/dl) than those of with low Lp(a) (<30 mg/dl), irrespective of apo(a) molecular weight. It may be suggested that, ND has beneficial effect on nutritional status and treatment of anemia in hemodialysis patients. In spite the adverse effect of ND on lipid profile, it decreases Lp(a) mostly in patients with high serum Lp(a) preferently by the effect on apo(a) gene transcriptional activity.

Study of apo(a) length polymorphism and lipoprotein(a) concentrations in subjects with single or double apo(a) isoforms

Cardiovascular risk is associated with high lipoprotein(a) (Lp(a)) concentrations and low molecular weight apolipoprotein(a) (apo(a)) isoforms. We studied the relationship between these two biological parameters, particularly in subjects expressing two apo(a) isoforms. Plasma Lp(a) was measured by immunonephelometry in 530 unrelated Caucasian patients at high cardiovascular risk, and apo(a) size determined by immunoblotting using a recombinant standard. Two, one, or no apo(a) isoforms were detected in 258, 270, and 2 subjects, respectively. Lp(a) concentrations showed a non-Gaussian distribution, being higher in the 'double band' than in the 'single band' group (median 0.42 vs. 0.11 g/l, p < 0.0005). Apo(a) size distribution was bimodal, with two frequency peaks at 18 kringles (K) and 27 K. Small size apo(a) isoforms were more frequently found in the 'double band' group, where major isoforms were of lower size than minor isoforms (median 20 vs. 27 K). Regression analysis showed that apo(a) gene length accounted for 33% of Lp(a) variation, with a threshold effect at 20 K, no correlation being found over this value. The minor apo(a) isoform did not significantly influence Lp(a) concentration. These data confirm the relationship between apo(a) size and Lp(a) concentration and suggest that the assessment of cardiovascular risk should take into account the threshold effect at 20 K and the absence of influence of the minor apo(a) isoform.

Differential apolipoprotein(a) isoform expression in heterozygosity is an independent contributor to lipoprotein(a) levels variability

BACKGROUND AND METHODS

Lipoprotein(a) [Lp(a)] levels represent an independent risk factor for cardio- and cerebrovascular diseases. Since lipoprotein(a) levels show a wide variability even in subjects with similar apolipoprotein(a) isoforms, we investigated the contribution of apolipoprotein(a) heterozygosity to lipoprotein(a) variance. Lipoprotein(a) levels, apolipoprotein(a) isoforms identification and expression, and the correlation with other lipo-apolipoprotein parameters have been investigated in 628 subjects >18 years of age.

RESULTS

In our study, 246 subjects were found heterozygous for apolipoprotein(a) isoforms. Lipoprotein(a) levels were higher in females. About 40% of the subjects expressed the larger isoform more intensely than the dominant isoform. Lipoprotein(a) was correlated with apolipoprotein(a) dominant isoform size, HDL-cholesterol and smaller apolipoprotein(a) isoform expression rate. Lipoprotein(a) was independently correlated with the smaller apolipoprotein(a) isoform, with its expression rate and with LDL-cholesterol. The inclusion of the smaller apolipoprotein(a) expression rate in a multiple regression model explained at least an additional 4% of the lipoprotein(a) variance after correction for apolipoprotein(a) size.

CONCLUSIONS

The smaller isoforms are not always effectively dominant in heterozygosis since 40% of the subjects expressed more the larger isoform. The individual variability of apolipoprotein(a) isoform expression in heterozygosis could explain part of the lipoprotein(a) levels variability.

Differences between Genotyping and Phenotyping Methods for Assessing Apolipoprotein(a) Size Polymorphisms

The aim of the present study was to analyze, on a double-blind basis, the relationships between the apolipoprotein(a) (apo(a)) gene and protein size polymorphisms in healthy volunteers (n = 99) and patients with premature myocardial infarction (n = 91). Apo(a) genotypes were determined by pulse-field electrophoresis and phenotypes were separated by sodium dodecyl sulfate-agarose gel electrophoresis. Results showed that phenotyping overestimated apo(a) size with respect to genotyping (mean (SD) = 3.7 (3.4) kringle units; p < 0.001) in subjects with a double-band genotype, although both measurements were highly correlated (r = 0.83; p < 0.001). We also observed that the protein band in subjects with a single-band phenotype was related more closely to the smallest allele than to the largest allele band. The correlation of plasma lipoprotein(a) (Lp(a)) concentration was stronger with the phenotype than with the genotype. We hypothesize that post-translational modifications in the apo(a) molecule may be the most plausible explanation for the discrepancies observed. In conclusion, the present study highlights the dissimilarities between phenotyping and genotyping methods for the measurement of apo(a) size and suggests that laboratories should carefully consider these relationships and the transfer of results between such methodologies.

Heterozygous apolipoprotein (a) status and protein expression as a risk factor for premature coronary heart disease

Exactly how apolipoprotein a [APO(a)] isoform size affects the degree of cardiovascular risk associated with high lipoprotein a [LP(a)] levels is not fully understood. Using a sodium dodecyl sulfate-agarose APO(a) & LP(a) phenotyping method, we assessed the role of APO(a) size heterogeneity according to the number of kringle 4 repeats and the differential APO(a) protein expression in 91 male Spanish patients with premature coronary heart disease (CHD) compared with 99 healthy Spanish men. CHD patients had significantly increased median plasma LP(a) levels (0.31 g/L) and a higher percentage of subjects with LP(a) levels of 0.30 g/L or greater (51%) than controls (0.15 g/L and 23%, respectively). Patients with the double-band phenotype had significantly higher plasma LP(a) levels (median 0.37 g/L) compared with those expressing a single-band phenotype (median 0.20 g/L; P =.018) and with their corresponding controls (median 0.15 g/L; P <.001). The double-band phenotype and LP(a) values of 0.30 g/L or greater had a significant association with CHD (odds ratio [OR] 6.47, 95% confidence interval [CI] 2.51-16.7), stronger than that observed for the entire group (OR 4.19, 95% CI 1.97-8.90). The adjusted OR for the APO(a) protein pattern that equally expressed both isoforms indicates an independent association with premature CHD (OR 3.33; 95% CI 1.08-10.3). These results suggest that APO(a) phenotyping might be used in subjects with hyperlipoproteinemia a as a powerful marker to assess the risk of premature CHD because heterozygous status, mainly when both isoforms are equally expressed, is associated with higher cardiovascular risk.