Josefina Naya-Vigne

Apolipoprotein L, a New Human High Density Lipoprotein Apolipoprotein Expressed by the Pancreas IDENTIFICATION, CLONING, CHARACTERIZATION, AND PLASMA DISTRIBUTION OF APOLIPOPROTEIN L

In this study, we have identified and characterized a new protein present in human high density lipoprotein that we have designated apolipoprotein L. Using a combination of liquid-phase isoelectrophoresis and high resolution two-dimensional gel electrophoresis, apolipoprotein L was identified and partially sequenced from immunoisolated high density lipoprotein (Lp(A-I)). Expression was only detected in the pancreas. The cDNA sequence encoding the full-length protein was cloned using reverse transcription-polymerase chain reaction. The deduced amino acid sequence contains 383 residues, including a typical signal peptide of 12 amino acids. No significant homology was found with known sequences. The plasma protein is a single chain polypeptide with an apparent molecular mass of 42 kDa. Antibodies raised against this protein detected a truncated form with a molecular mass of 39 kDa. Both forms were predominantly associated with immunoaffinity-isolated apoA-I-containing lipoproteins and detected mainly in the density range 1.123 < d < 1.21 g/ml. Free apoL was not detected in plasma. Anti-apoL immunoaffinity chromatography was used to purify apoL-containing lipoproteins (Lp(L)) directly from plasma. Nondenaturing gel electrophoresis of Lp(L) showed two major molecular species with apparent diameters of 12.2–17 and 10.4–12.2 nm. Moreover, Lp(L) exhibited both pre-β and α electromobility. Apolipoproteins A-I, A-II, A-IV, and C-III were also detected in the apoL-containing lipoprotein particles.

Relation of Increased Prebeta-1 High-Density Lipoprotein Levels to Risk of Coronary Heart Disease

Preβ-1 high-density lipoprotein (HDL) plays a key role in reverse cholesterol transport by promoting cholesterol efflux. Our aims were (1) to test previous associations between preβ-1 HDL and coronary heart disease (CHD) and (2) to investigate whether preβ-1 HDL levels also are associated with risk of myocardial infarction (MI). Plasma preβ-1 HDL was measured by an ultrafiltration-isotope dilution technique in 1,255 subjects recruited from the University of California-San Francisco Lipid and Cardiovascular Clinics and collaborating cardiologists. Preβ-1 HDL was significantly and positively associated with CHD and MI even after adjustment for established risk factors. Inclusion of preβ-1 HDL in a multivariable model for CHD led to a modest improvement in reclassification of subjects (net reclassification index 0.15, p = 0.01; integrated discrimination improvement 0.003, p = 0.2). In contrast, incorporation of preβ-1 HDL into a risk model of MI alone significantly improved reclassification of subjects (net reclassification index 0.21, p = 0.008; integrated discrimination improvement 0.01, p = 0.02), suggesting that preβ-1 HDL has more discriminatory power for MI than for CHD in our study population. In conclusion, these results confirm previous associations between preβ-1 HDL and CHD in a large well-characterized clinical cohort. Also, this is the first study in which preβ-1 HDL was identified as a novel and independent predictor of MI above and beyond traditional CHD risk factors.

Lack of association of lipoprotein(a) levels with coronary calcium deposits in asymptomatic postmenopausal women

OBJECTIVES This study sought to determine the relationship of lipoprotein(a) (Lp(a)) and other cardiac risk factors to coronary atherosclerosis as measured by calcification of coronary arteries in asymptomatic postmenopausal women. BACKGROUND Lipoprotein(a) is considered a risk factor for coronary heart disease. Coronary calcium deposition is believed to be a useful noninvasive marker of coronary atherosclerosis in women. However, to our knowledge, there are no reports of the relationship of Lp(a) to coronary calcium in postmenopausal women. METHODS In 178 asymptomatic postmenopausal women (64 +/- 8 years), we measured Lp(a) and other cardiac risk factors: age, hypertension, diabetes, low-density lipoprotein cholesterol, smoking status, body mass index, physical activity level and duration of hormone replacement therapy. Electron-beam computed tomography was done to measure coronary calcium (calcium score). We analyzed the relationship between calcium score and cardiac risk factors using multivariate analysis. RESULTS Although calcium score correlated with traditional risk factors of age, diabetes, hypertension and smoking, it did not correlate with Lp(a) in the asymptomatic postmenopausal women. Similar multivariate analyses were done in the subjects age >60 years and in the subjects with significant coronary calcium deposit (calcium score > or =50). These analyses also have failed to show an association of levels of Lp(a) with coronary calcium deposits. CONCLUSIONS We conclude that in asymptomatic postmenopausal women, Lp(a) levels do not correlate with coronary atherosclerosis as measured by coronary calcium deposits.

Heterogeneity of high-density lipoproteins and apolipoprotein A-I as related to quantification of apolipoprotein A-I.

Publisher Summary Apolipoprotein (apo) A-I is the major protein constituent of the human plasma high-density lipoproteins (HDL). It is present on the bulk of the HDL particles, isolated from the fasting plasma of normolipidemic individuals. Accurate measurement of apoA-I is central to the study of HDL. Plasma levels of apoA-I correlate well with plasma HDL cholesterol levels and it has been suggested that apoA-I may actually be a more accurate predictor of cardiovascular risk than HDL cholesterol. In addition, HDL complexes are heterogeneous, with respect to protein constituents and, therefore, an accurate determination of the apoA-I will aid in the elucidation of the apolipoprotein stoichiometry of the various complexes and the distribution of apoA-I among them. Direct quantitation of apoA-I, by immunoassay, is complicated, by variability in the epitopes of apoA-I. This variability may arise either from the structural differences in the apoA-I protein itself or from the conformational differences, owing to the association of apoA-I with distinct HDL species.