SRM-based measurements of proprotein convertase subtilisin/kexin type 9 and lipoprotein(a) kinetics in nonhuman primate serum

Elevated levels of lipoprotein(a) (Lp(a)) have been identified as an independent and causal risk factor for coronary heart disease. Lp(a) consists of an LDL-like moiety covalently linked to the unique glycoprotein apolipoprotein(a) (apo(a)). The mechanism by which Lp(a) is catabolized is currently unknown, but may form the basis for the development of drug therapy to reduce high levels of plasma Lp(a). Although the role of the LDL receptor (LDLR) in Lp(a) catabolism is controversial, recent evidence has shown that Lp(a) levels are significantly reduced with an antibody against proprotein convertase subtilisin kexin type 9 (PCSK9) in patients with hypercholesterolemia receiving statin therapy. Therefore, we explored the role of PCSK9 in Lp(a)/apo(a) internalization by hepatic cells. Lp(a) or apo(a) internalization is significantly reduced in HepG2 (human hepatoma) cells either by overexpressing PCSK9 or by treatment with purified PCSK9. The ability of Lp(a) and apo(a) to be internalized was significantly reduced in the presence of the lysine analogue, ε-ACA, indicating lysine-dependent interactions with cellular receptors. Mutation of the strong lysine binding site in a recombinant apo(a) variant resulted in a reduced ability to be internalized. While LDL can bind to PCSK9 and inhibit its ability to degrade the LDLR, we found that Lp(a) lacked these properties. Interestingly, overexpressing the LDLR on HepG2 cells significantly increased the ability of Lp(a) to be internalized, an effect that was partially reduced by the addition of PCSK9. This indicates a potential key role for the LDLR in regulating Lp(a) catabolism. Furthermore, knockdown of clathrin heavy chain resulted in a significant decrease in apo(a) internalization and apo(a) internalization was not further reduced by pre-treatment of PCSK9 in the context of clathrin heavy chain knockdown. Treatment of HepG2 cells with a lysosomal inhibitor, but not a proteosomal inhibitor, resulted in accumulation of Lp(a) in HepG2 cells indicating that Lp(a) is potentially targeted for degradation through lysosomes. Taken together, these results indicate that Lp(a)/apo(a) uptake can be regulated in HepG2 cells by PCSK9 and the LDLR through clathrin-mediated endocytosis and lysosomal degradation.

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Abstract 14556: Is There a Relationship Between Lipoprotein (a) and Proprotein Convertase Subtilisin /keksin Type 9 and Cardiovascular Events After Acute Myocardial Infarction?

Circulation ◽

10.1161/circ.142.suppl_3.14556 ◽

2020 ◽

Vol 142 (Suppl_3) ◽

Author(s):

Albert GALYAVICH ◽

Alsu Gimadeeva

Keyword(s):

Myocardial Infarction ◽

Acute Myocardial Infarction ◽

Unstable Angina ◽

Blood Level ◽

Cardiovascular Events ◽

Cardiovascular Death ◽

Blood Levels ◽

Proprotein Convertase ◽

Pcsk9 Inhibitors ◽

Lipoprotein A

Introduction: Lipoprotein (a) (Lp(a)) has atherogenic effects. Proprotein convertase subtilisin /keksin type 9 (PCSK9) involved in the degradation of LDL-C receptors, increasing LDL-C blood level. Hypothesis: Identify the relationship between Lp(a) and PCSK9 blood levels and major cardiovascular events (unstable angina, myocardial infarction, cardiovascular death) after acute myocardial infarction. Methods: The study included 119 patients with acute myocardial infarction (97 men and 22 women aged 50-70 years). Blood samples were taken on the 2nd day of myocardial infarction. The Lp(a) blood level was determined by immunoturbidimetry (RANDOX), the PCSK9 blood level was determined by ELISA (BioVendor). Primary combined endpoint included hospitalization due to myocardial infarction and unstable angina and cardiovascular death. Patient follow-up was 52 weeks. Statistical analysis methods included Mann-Whitney test and non-parametric correlation by Spearman. Results: In 36 (30.2%) patients with acute myocardial infarction the Lp(a) blood levels were higher than 30 mg/dL. In 83 (69.7%) patients the Lp(a) blood level were below 30 mg/dL. Mean values of Lp(a) blood level was 29.26 ± 2.79 (men 27.71 ± 2.82 mg/dL, women 36.07 ± 8.54 mg/dL, p = 0.797). Mean PCSK9 blood level was 479.7 ± 15.4 ng/ml (males 465.6 ± 16.2ng/ml, females 534.9 ± 38.9 ng/ml, p = 0.122). There was no significant correlation of Lp(a) blood level with total cholesterol, LDL-C, triglycerids and PCSK9 blood levels. No significant correlation was found between Lp(a) and PCSK9 blood levels and cardiovascular events within 12 months. In the group of smoking patients (n = 22) there was found negative correlation between PCSK9 and HDL-C blood levels (-0.45, p = 0.039). Conclusions: Due to the fact that there is no relationship between Lp(a) and PCSK9 blood levels and subsequent cardiovascular events within 52 weeks, the effectiveness of the use of PCSK9 inhibitors after acute myocardial infarction is doubtful.

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