Aspirin Reduces Apolipoprotein(a) (Apo(a)) Production in Human Hepatocytes by Suppression of Apo(a) Gene Transcription

Therapeutic antibodies targeting proprotein convertase subtilisin kexin type 9 (PCSK9) (e.g. alirocumab) lower low-density lipoprotein cholesterol (LDL-C) and lipoprotein (a) [Lp(a)] levels in clinical trials. We recently showed that PCSK9 enhances apolipoprotein(a) [apo(a)] secretion from primary human hepatocytes but does not affect Lp(a) cellular uptake. Here, we aimed to determine how PCSK9 neutralization modulates Lp(a) levels in vivo. Six nonhuman primates (NHP) were treated with alirocumab or a control antibody (IgG1) in a crossover protocol. After the lowering of lipids reached steady state, NHP received an intravenous injection of [2H3]-leucine, and blood samples were collected sequentially over 48 h. Enrichment of apolipoproteins in [2H3]-leucine was assessed by liquid chromatography–tandem mass spectrometry (LC–MS/MS). Kinetic parameters were calculated using numerical models with the SAAMII software. Compared with IgG1, alirocumab significantly reduced total cholesterol (TC) (−28%), LDL-C (−67%), Lp(a) (−56%), apolipoprotein B100 (apoB100) (−53%), and apo(a) (−53%). Alirocumab significantly increased the fractional catabolic rate of apoB100 (+29%) but not that of apo(a). Conversely, alirocumab sharply and significantly reduced the production rate (PR) of apo(a) (−42%), but not significantly that of apoB100, compared with IgG1, respectively. In line with the observations made in human hepatocytes, the present kinetic study establishes that PCSK9 neutralization with alirocumab efficiently reduces circulating apoB100 and apo(a) levels by distinct mechanisms: apoB primarily by enhancing its catabolism and apo(a) primarily by lowering its production.

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No Effect of Fibrates on Synthesis of Apolipoprotein(a) in Primary Cultures of Cynomolgus Monkey and Human Hepatocytes: Apolipoprotein A-I Synthesis Increased

Biochemical and Biophysical Research Communications ◽

10.1006/bbrc.1998.8279 ◽

1998 ◽

Vol 244 (2) ◽

pp. 374-378 ◽

Cited By ~ 8

Author(s):

Diana M. Neele ◽

Allard Kaptein ◽

Holger Huisman ◽

Elly C.M. de Wit ◽

Hans M.G. Princen

Keyword(s):

Cynomolgus Monkey ◽

Primary Cultures ◽

Human Hepatocytes ◽

Apolipoprotein A

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A proximal tissue-specific module and a distal negative regulatory module control apolipoprotein(a) gene transcription

Biochemical Journal ◽

10.1042/bj20030985 ◽

2004 ◽

Vol 379 (1) ◽

pp. 151-159 ◽

Cited By ~ 9

Author(s):

Sarita NEGI ◽

Saurabh K. SINGH ◽

Nirupma PATI ◽

Vikas HANDA ◽

Ruchi CHAUHAN ◽

...

Keyword(s):

Transcription Factors ◽

Gene Transcription ◽

Hela Cells ◽

Hepg2 Cells ◽

Regulatory Element ◽

Regulatory Elements ◽

Tissue Specific ◽

Apolipoprotein A ◽

Regulatory Module ◽

Specific Manner

The apo(a) [apolipoprotein(a)] gene is responsible for variations in plasma lipoprotein(a), high levels of which are a risk factor for atherosclerosis and myocardial infarction. The apo(a) promoter stimulates the expression of reporter genes in HepG2 cells, but not in HeLa cells. In the present study, we demonstrate that the 1.4 kb apo(a) promoter comprises two composite regulatory regions: a distal negative regulatory module (positions −1432 to −716) and a proximal tissue-specific module (−716 to −616). The distal negative regulatory module contains two strong negative regulatory regions [polymorphic PNR (pentanucleotide repeat region) and NREβ (negative regulatory element β)], which sandwich the postive regulatory region PREβ (positive regulatory element β). The PNR was shown to bind to transcription factors in a tissue-specific manner, whereas the ubiquitous transcription factors hepatocyte nuclear factor 3α and GATA binding protein 4 bound to NREβ to repress gene transcription. The proximal tissue-specific module contains two regulatory elements: an activating region (PREα) that activates transcription in HepG2 cells, and NREα, which is responsible for repressing the apo(a) gene in HeLa cells. NREα binds to a HeLa-specific repressor. These multiple regulatory elements might work co-operatively to finely regulate apo(a) gene expression. Although the tissue-specific module is required for apo(a) gene activation and repression in a tissue-specific manner, the combinatorial interplay of the distal and proximal regulators might define the complex pathway(s) of apo(a) gene regulation.

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