Relationship between plasma lipoprotein (a), apolipoprotein (a) phenotypes, and other coronary heart disease risk factors in a Melbourne South Asian population

BACKGROUND

High plasma lipoprotein(a) [Lp(a)] level is a strong and important risk factor for cardiovascular disease (CVD). Small-sized apolipoprotein(a) [apo(a)] isoforms (F, B, S1, and S2) are inversely correlated with the high levels of Lp(a) in plasma and significantly associated with CVD. Although the effects of apo(a) phenotypes and various risk factors on Lp(a) status in South Asian population may have been studied in other countries, there are no reports involving these risk factors in Australia.

METHODS AND RESULTS

Factors contributing to variation in Lp(a) were surveyed in 402 (216 males and 186 females) South Asian Melburnians. There was a negative relationship between low alcohol beer per day and Lp(a) in men (P < 0.05). Approximately 21% of the variance of Lp(a) concentration in men and 6% in women were explained by age. Age was positively associated with Lp(a) concentrations in men but negatively in women. The most commonly occurring phenotype was apo(a) S3. In this phenotype, Lp(a) concentrations ranged from non-detectable to 811 mg/l. After adjusting for age, an inverse correlation was observed between Lp(a) concentration and apo(a) phenotypes (P < 0.01).

CONCLUSIONS

Although Lp(a) has been reported to be genetically determined, there are clearly other factors contributing to variations in Lp(a) concentrations in a South Asian population.

Factors contributing to variation in lipoprotein (a) in Melbourne Anglo-Celtic population

AIM

The purpose of this report is to survey the factors contributing to variation in lipoprotein(a) (Lp(a)) in a population-based sample of Anglo-Celtic Melburnians.

RESULTS

The plasma Lp(a) levels were highly skewed towards low levels in this population, with a median of 156 mg/l and a mean of 262 mg/l. Approximately 33% had plasma Lp(a) above the threshold value of 300 mg/l, while 35% had Lp(a) levels below 100 mg/l. The most commonly occurring phenotype was apo(a) S3. In this phenotype, Lp(a) concentrations ranged from 10 to 596 mg/l. Lp(a) was consistently associated with diastolic blood pressure, systolic blood pressure, total protein, albumin and nitrogen excretion in the 40-60 y age group. Multiple stepwise regression analyses, in non-dietary factors, were used to explain about 13% of the variance in Lp(a) (19% in men and 23% in women). Remarkably, in the <40 y age group, non-dietary factors may account for 86% of the variance in Lp(a) and dietary factors, analysed separately, 46%. Thus, although Lp(a) is mainly genetically determined, there are clearly other factors which contribute to variations in Lp(a) concentrations.

High allele frequency of apolipoprotein(a) phenotype LpS4 is associated with low serum Lp(a) concentrations in Koreans

We determined apo(a) phenotypes using SDS-PAGE followed by immunoblotting in samples from a control group of 179 and from 68 Korean patients with coronary artery disease (CAD). The CAD group showed significantly higher Lp(a) levels than the control group, which might be partially attributable to the differences in apo(a) phenotype frequencies although it was not statistically significant, and was partially attributable to the significant difference in Lp(a) levels of S2 or null phenotypes between the two groups. The apo(a) allele frequencies between ethnic groups already reported (Austrians, American blacks, Japanese, and Koreans), were compared by the Chi-square test. In the Korean population, the apo(a) allele frequencies demonstrated a high frequency of the LpS4 allele associated with a low Lp(a) concentration. This result suggests that the concentration and allele frequency of Lp(a) might be one of the factors in explaining the low incidence of CAD in the Korean population.

Apolipoprotein(a) phenotypes in cardio-cerebrovascular diseases

We report apolipoprotein(a) (apo(a)) phenotypes of 69 myocardial infarction survivors and 56 stroke patients, and compare them with those of 190 healthy Chinese. The results indicate that the distribution of apo(a) phenotype frequency in cardio-cerebrovascular disease patients is different from those of controls. The frequency of the phenotypes B, S1 and S2 in patients is remarkably higher than those in controls within the same single-band apo(a) phenotype. Moreover, the Lp(a) serum concentrations in CCVD patients are significantly higher than those in controls within the same single-band apo(a) phenotype. The apo(a) phenotype analyses of two pedigrees are shown as a typical autosomal dominant inheritance.

Characterization of apo(a) polymorphism by a modified immunoblotting technique in an Italian population sample

Apo(a), the specific lipoprotein(a) (Lp(a)) apolipoprotein, is characterized by different isoforms (from 6 to 11 on SDS-PAGE) encoded by a system of autosomal codominant alleles. Electrophoresis on agarose gel displays a better resolving power than SDS-PAGE (a larger number of apo(a) isoforms is detected). The aim of this work was to set up a simple technique that uses a capillary blotting apparatus and a polyvinylidene difluoride membrane for protein transfer. We tested an Italian population sample of 202 healthy subjects (123 men and 79 women) and we detected 22 apo(a) isoforms varying from 280 to 775 kDa. In our sample, 135 subjects (66.5%) had a single-band phenotype, 64 (31.7%) had a double-band phenotype and 3 subjects (1.5%) had no detectable bands ('null' phenotype). This simple and reproducible technique could be applied in the genetic screening of apo(a) polymorphisms and for clinical investigations of the risk of developing cardiovascular diseases.

A simple, sensitive technique for classification of apolipoprotein(a) isoforms by sodium dodecyl sulphate-polyacrylamide gel electrophoresis

Lipoprotein(a) (Lp(a)) is a lipoprotein containing a unique glycoprotein, apolipoprotein(a) (apo(a)), which shows considerable heterogeneity of apparent molecular mass on sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). A unifying classification of isoform has been lacking. A simple sensitive procedure for classifying apo(a) isoforms was developed in which the relative mobility of apo(a) on SDS-PAGE was related to that of apolipoprotein (apo) B-100 (Rf vs B). After Western blotting apo(a) bands were visualised by a sensitive double antibody technique employing commercial polyclonal antibodies (sheep antihuman Lp(a) antibody, alkaline phosphatase-linked donkey antisheep antibody). The technique was sensitive (lower limit of detection 0.02 micrograms apo(a)) and had good reproducibility (coefficient of variation 0.9-6.4%). Ten isoform mobilities are described (less than 0.35, 0.40, 0.50, 0.60, 0.70, 0.80, 1.0, 1.10, greater than 1.15). Individuals may have single or double band phenotypes. This classification is compatible with those previously described and the method is suitable for many laboratories, as it employs standard equipment and commercially available materials.