Differential expression of double-band apolipoprotein(a) phenotypes in healthy Spanish subjects detected by SDS-agarose immunoblotting.
A sodium dodecyl sulphate-agarose apolipoprotein(a) [apo(a)] phenotyping method was set up to attain accurate scanning densitometry of proteins. Serum samples from 99 healthy Spanish men were analysed and twenty-five different apo(a) isoforms (12 to 37 kringle 4 repeats) were detected. Double-band phenotypes accounted for 39.4% (n = 39) and three different patterns of protein expression were identified: pattern A (20.5% of double-band phenotyped samples) predominantly expressed the highest molecular weight isoform; pattern B (53.9%) mainly the lowest molecular weight isoform, and pattern AB (25.6%), expressed both isoforms equally. A significant linear association between expression pattern and lipoprotein(a) [Lp(a)] concentration > or = 0.30 g/l was observed. Single-band phenotyped samples (n = 60) were stratified according to apo(a) kringle 4 repeat categories and showed that 90% of isoforms < 20 K4 repeats had high Lp(a) concentrations (> or = 0.30 g/l), whereas isoforms with 20 to 24 or more than 24 kringle 4 repeats had Lp(a) concentrations > or = 0.30 g/l in 47% and 14%, respectively. A logistic regression model was fitted to test the association between apo(a) size, expression pattern and Lp(a) concentration. In this model, apo(a) isoform < 25 kringle 4 repeats was significantly associated with serum Lp(a) concentration > or = 0.30 g/l in both single and double-band phenotyped samples (odds ratio = 8.9, p < 0.001). In the latter, a differential expression pattern with respect to smaller size isoforms (pattern AB vs A) was significantly associated with Lp(a) concentration > or = 0.30 g/l (odds ratio = 17.97, P = 0.045). Heterogeneity in protein apo(a) size expressed according to kringle 4 repeat number could be categorized in heterozygous phenotypes as three patterns. When small-sized isoform was expressed (pattern B) or both isoforms were equally expressed (pattern AB), the probability of having Lp(a) > or = 0.30 g/l is higher.
Martín
S
S
Unitat de Lipids i Epidemiologia Cardiovascular, IMIM, Universidad Autónoma de Barcelona, Spain.
Ladona
M G
MG
Pedro-Botet
J
J
Covas
M I
MI
Rubiés-Prat
J
J
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001053:Apolipoproteins / Q000097:blood*; D053241:Apoprotein(a); D006801:Humans; D015151:Immunoblotting / Q000379:methods*; D017270:Lipoprotein(a); D008297:Male; D008875:Middle Aged; D010641:Phenotype; D012016:Reference Values; D015203:Reproducibility of Results; D012685:Sepharose; D012967:Sodium Dodecyl Sulfate; D013030:Spain / Q000208:ethnology
D001053:Apolipoproteins; D017270:Lipoprotein(a); D012967:Sodium Dodecyl Sulfate; D012685:Sepharose; D053241:Apoprotein(a)