James D. Eisenbart

Rhesus monkey lipoprotein(a) binds to lysine Sepharose and U937 monocytoid cells less efficiently than human lipoprotein(a). Evidence for the dominant role of kringle 4(37).

Rhesus lipoprotein(a) (Lp[a]) binds less efficiently than human Lp(a) to lysine-Sepharose and to cultured U937 cells. Studies using elastase-derived plasminogen fragments indicated that neither kringle 5 nor the protease domain of Lp(a) are required in these interactions pointing at an involvement of the K4 region. Comparative structural analyses of both the human and simian apo(a) K4 domain, together with molecular modeling studies, supported the conclusion that K4(37) plays a dominant role in the lysine binding function of apo(a) and that the presence of arginine 72 rather than tryptophan in this kringle can account for the functional deficiency observed with rhesus Lp(a). These in vitro results suggest that rhesus Lp(a) may be less thrombogenic than human Lp(a).

Plasma lipoprotein (a) protein concentration and coronary artery disease in black patients compared with white patients

PURPOSE This study examines the relation between lipoprotein (a) protein levels and other lipid parameters and coronary artery disease in white and black patients. PATIENTS AND METHODS Plasma lipoprotein (a) protein levels were measured prior to coronary angiography in a population of 127 white and 111 black patients. Each angiogram was given a total coronary artery disease score based on the number and severity of atherosclerotic coronary lesions. RESULTS White and black patients exhibited no differences in total plasma cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and triglycerides. Black patients had higher lipoprotein (a) protein levels than white patients (8.6 versus 4.0 mg/dL; p < 0.0001). The extent and severity of coronary artery disease was the same in white and black patients. White and black patients with coronary artery disease had higher lipoprotein (a) levels than patients without coronary lesions (4.37 versus 1.99 mg/dL, p = 0.027 for white; 9.23 versus 6.87 mg/dL, p = 0.072 for black). In both groups of patients, there was a weak but significant positive correlation between lipoprotein (a) protein levels and coronary artery disease score. CONCLUSION Lipoprotein (a) is higher in patients with coronary artery disease. Black patients have higher plasma lipoprotein (a) protein levels than white patients and a comparable degree of coronary artery disease. It follows that the cardiovascular pathogenicity of lipoprotein (a) is not significantly greater in black patients despite higher lipoprotein (a) levels.

Attenuation of immunologic reactivity of lipoprotein(a) by thiols and cysteine-containing compounds. Structural implications.

Samples of human plasma having lipoprotein(a) (Lp[a]) protein levels between 5 and 15 mg/dl and a single apolipoprotein(a) (apo[a]) isoform were incubated in vitro at pH 7.7 with various concentrations (1-20 mM) of N-acetylcysteine, homocysteine, 2-mercaptoethanol (2ME), and dithiothreitol (DTT) for 1 hour at 37 degrees C under a nitrogen atmosphere. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by immunoblot analyses using a polyclonal antibody specific for apo(a) showed a progressive decrease in apo(a) immunoreactivity as a function of reductant concentration. This decrease of apo(a) immunoreactivity was corroborated by enzyme-linked immunosorbent assay (ELISA) using anti-apo(a) as the capture antibody and either anti-apo B or anti-apo(a) as the developing antibody. In turn, there was no significant decrease in the immunoreactivity of apo B-100, as assessed by ELISA using anti-apo B as both the capture and the detecting antibody. In the case of high concentrations of DTT the plasma samples had to be diluted to prevent gel formation on addition of the reductant. A progressive drop in immunoreactivity as a function of reagent concentration was also observed in pure preparations of Lp(a) incubated with the reducing agents at pH 7.7. At equivalent stoichiometries the changes were more marked than those observed with whole plasma, suggesting a quenching effect by the plasma proteins on the activity of the reductants. The changes in immunoreactivity were attended by dissociation of apo(a) from Lp(a) as assessed by Western blotting. This dissociation, which we interpret as the result of cleavage of the interchain disulfide bond(s), was complete at 5 mM DTT and 100 mM 2ME.(ABSTRACT TRUNCATED AT 250 WORDS)

Postprandial lipoprotein (a) response to a single meal containing either saturated or ω-3 polyunsaturated fatty acids in subjects with hypoalphalipoproteinemia

We have recently reported that the apolipoprotein (apo) B-100-apo(a) complex, the protein moiety of lipoprotein(a) [Lp(a)], has a high affinity for triglyceride(TG)-rich particles (TRP) and that this complex can affiliate with endogenous TG-rich lipoproteins. To shed more light on the apo B-100-apo(a) complex associated with plasma TRP during postprandial lipidemia, we fed five male subjects presenting with primary hypoalphalipoproteinemia (HP) and four male controls a single fat meal (60 g/m2) containing saturated fatty acids (SFA) and, 6 weeks later, an isocaloric meal containing omega-3 polyunsaturated fatty acids. The subjects were phenotyped for plasma Lp(a) and apo C-III levels, apo(a) and apo E isoforms, and lipoprotein lipase and hepatic lipase activities. Vitamin A was included in the meal as a marker of intestinally derived TRP. Following the SFA meal, three of the HP subjects showed a decrease in plasma levels of Lp(a) that lasted 10 to 12 hours in the presence of an increased hypertriglyceridemic response. Two HP subjects who had low preprandial lipoprotein lipase activity and elevated plasma apo C-III levels showed an increase in plasma Lp(a) levels along with the hypertriglyceridemic excursion. However, in all cases, inclusive of the controls, there was an elevation in plasma levels of TRP of Sf greater than 1,000 that contained apo B-100-apo(a) 6 to 8 hours after the meal. This TRP excursion appeared not to be related to the basal levels of plasma Lp(a), high-density lipoprotein (HDL) cholesterol, TGs, or apo(a) and apo E isoforms, and it did not coincide with the retinyl ester peak.(ABSTRACT TRUNCATED AT 250 WORDS)