Pro-inflammatory activation of monocytes by elevated Lp(a) is reversible by potent Lp(a)-lowering
Potent lipoprotein(a) lowering following apolipoprotein(a) antisense treatment reduces the pro-inflammatory activation of circulating monocytes in patients with elevated lipoprotein(a)
Introduction and methods
An independent and causal relationship between elevated lipoprotein(a) [Lp(a)] levels (>50 mg/dL or ~125 nmol/L) and CVD risk has been suggested by epidemiological and Mendelian randomization studies [1,2]. Healthy individuals with elevated Lp(a) have an activated innate immune system. This is characterized by pro-inflammatory circulating monocytes and coincides with increased white blood cell influx in the arterial wall and increase in arterial wall inflammation . However, mechanistic understanding of monocyte activation in individuals with elevated Lp(a) is missing, as well as whether the inflammatory state can be reversed.
This study assessed the gene expression profile of circulating monocytes in four study groups: healthy subjects with normal Lp(a) (median Lp(a) 7 mg/dL [18 nmol/L], n=13), healthy subjects with elevated Lp(a) (matched for age, sex and BMI, median Lp(a) 87 mg [218 nmol/L], n=12) and CVD patients with elevated Lp(a) from two separate clinical intervention trials: The AKCEA-APO(a)-LRx-trial (n=14) and the ANITSCHKOW study (n=18) [4,5]. In addition, monocyte gene expression and function was assessed before and after treatment with either potent Lp(a) lowering (antisense[AKCEA-APO(a)-LRx]) in the AKCEA-APO(a)-LRx trial or moderate Lp(a) lowering (PCSK9ab [evolocumab, 420 mg once every 4 weeks]) in the ANITSCHKOW trial to evaluate the reversibility of an Lp(a) effect on monocyte activation.
Blood sampling was performed at baseline and after 26 weeks of treatment with AKCEA-APO(a)-LRx or 16 weeks of PCSK9ab treatment. Median Lp(a) at baseline was 82 mg/dL (250 nmol/L) in the AKCEA-APO(a)-LRx-trial. The pooled mean absolute reduction in Lp(a) was 51 (53) mg/dL [128 (132) nmol/L], compared to baseline. The achieved pooled mean percent reduction after a treatment period of 26 weeks was 47(18)%. In ANITSCHKOW study, the median Lp(a) at baseline was 102 mg/dL (255 nmol/L). The mean absolute reduction in Lp(a) was 19 (20) mg/dL [48 (49) nmol/L], compared to baseline. The mean percent reduction was 16 (19)% after 16 weeks of treatment.
- Transcriptome analysis of monocytes from healthy individuals showed 95 significantly differentially expressed genes (DEGs), of which 43 genes were up-regulated and 52 genes were down-regulated in healthy individuals with elevated Lp(a), compared to healthy individuals with normal Lp(a). Among the significantly upregulated pathways, interferon alpha (IFNα) and interferon gamma (IFNγ) were the most pronounced.
- The gene expression profiles of monocytes of CVD patients with elevated Lp(a) was subsequently compared with healthy individuals with normal Lp(a). CVD patients with Lp(a) elevation had 1286 significantly DEGs, of with 769 genes were significantly upregulated, compared to healthy individuals with normal Lp(a). A pronounced up-regulation of multiple immune response-related pathways was revealed, including the TNFA signaling pathway, and IFNα and IFNγ response pathways.
- Next, the gene expression profile in monocytes was assessed after potent Lp(a)-lowering by AKCEA-APO(a)-LRx. 575 Significantly DEGs were found following AKCEA-APO(a)-LRx treatment, compared to baseline. 359 genes were up-regulated and 216 genes were down-regulated. A distinct reduction of multiple immune response-related pathways was observed, including IFNα, IFNγ and Toll-like receptor (TLR) pathways.
- Modest Lp(a)-lowering by PCSK9ab treatment did not alter gene expression in monocytes in CVD patients with elevated Lp(a).
- In line with downregulation of their respective genes, expression of C-C chemokine receptor type 2 (CCR2), CX3C chemokine receptor 1 (CX3CR1) and TLR2 were significantly reduced after potent Lp(a)-lowering in CVD patients treated with AKCEA-APO(a)-LRx, as shown by flow cytometry experiments. Trans-endothelial migration (TEM) activity of monocytes was significantly reduced by 22% (P<0.0001) after potent Lp(a) lowering. Absolute reduction in Lp(a) was positively correlated with percent reduction in TEM (r=0.38, P=0.02).
- No significant differences before vs. after PCSK9ab treatment in CVD patients were found in data from flow cytometry and TEM experiments.
The data from this study imply that elevated Lp(a) contributes to a pro-inflammatory gene expression in both healthy subjects and CVD patients. They also support the hypothesis that pro-inflammatory activation is reversible only by large absolute reductions in Lp(a).