Low levels of PCSK9 are associated with remission in patients with rheumatoid arthritis treated with anti-TNF-α: potential underlying mechanisms

Abstract

Background: Proprotein convertase subtilisin kexin 9 (PCSK9) targets the LDL-receptor (LDLR) which raises LDL-levels. In addition, PCSK9 has proinflammatory immunological effects. Here, we investigate the role of PCSK9 in relation to the inflammatory activity in patients with rheumatoid arthritis (RA).

Methods: PCSK9-levels were determined at baseline by ELISA in 160 patients with RA not previously treated with biologics. The patients started anti-TNF-α (adalimumab, infliximab, or etanercept) treatment and were followed-up for 1 year. Disease activity was determined by DAS28. Effects of PCSK9 on cytokine production from macrophages of healthy individuals and synoviocytes from RA patients and inhibition by anti-PCSK9 antibodies were studied in supernatants by ELISA.

Results: A significantly lower level of PCSK9 at baseline, p = 0.035, was observed in patients who reached remission within 1 year, defined as DAS28 < 2.6, compared to those not in remission. At 12 months of TNF-α antagonist treatment, the mean DAS28 was reduced but was significantly greater in patients with highest quartile PCSK9 (Q4) compared to those at lowest PCSK9 (Q1) in both crude (p = 0.01) and adjusted analysis (p = 0.004). In vitro, PCSK9 induced TNF-alpha and IL-1beta in macrophages and monocyte chemoattractant protein-1 (MCP1) in synoviocytes. These effects were inhibited by anti-PCSK9 antibodies.

Conclusions: Low levels of PCSK9 at baseline are associated with being DAS28-responder to anti-TNF-α treatment in RA. An underlying cause could be that PCSK9 stimulates the production of proinflammatory cytokines from macrophages and synoviocytes, effects inhibited by anti-PCSK9 antibodies. PCSK9 could thus play an immunological role in RA.

Keywords: Disease activity; Macrophages; Proprotein convertase subtilisin kexin 9 (PCSK9); Rheumatoid arthritis; Synoviocytes; Tumor necrosis factor (TNF).

Fig. 1

Results are presented as Scatter dot: median with interquartile range. PCSK9 levels at baseline among TNF–α antagonist-treated patients with remission (DAS < 2.6) vs non-remission (DAS ≥ 2.6) after 1 year. Results are presented as whiskers: min to max. Student’s t test was performed for statistical analysisk

Fig. 2

Macrophages were stimulated with various concentration of PCSK9 in the presence or absence of anti-PCSK9 antibodies for 24 h. a Macrophages induced TNF-alpha and IL-1beta (n = 3) in a concentration-dependent manner. b Macrophages were stimulated with 500 ng/ml of PCSK9 in the presence or absence of 5 μg/ml of anti-PCSK9 antibodies for 24 h. The level of TNF-alpha and IL-1beta was suppressed by anti-PCSK9 antibodies (n = 3). P value ≤ 0.0005 was considered *** and ≤ 0.0001 was condsidered as ****

Fig. 3

Synoviocytes were cultured with or without various concentration of PCSK9 in the presence or absence of anti-PCSK9 antibodies for 24 h. Experiments were performed three times and triplicate in each time. The mean value of 3 independent experiments was presented in the bar diagram. a PCSK9 induced level of MCP1 in the synoviocytes in a concentration-dependent manner (n = 9). b Synoviocytes were stimulated with 500 ng/ml of PCSK9 in the presence or absence of 5 μg/ml of anti-PCSK9 antibodies for 24 h, and the level of MCP1 was inhibited by anti-PCSK9 antibodies (n = 9). P value ≤ 0.0005 was considered *** and ≤ 0.0001 was condsidered as ****