Background and Aims

Background and Aims: Evolocumab and alirocumab (mAbs anti-PCSK9) block the function of PCSK9 but determine a significant increase of its plasma levels, an effect that can be determined by 1) an increased synthesis or 2) reduced clearance by the liver.

Methods

Methods: We have measured total PCSK9 plasma levels, by ELISA assay, in hypercholesterolemic patients at baseline and under treatment with mAbs anti-PCSK9. In vitro human hepatocarcinoma cell line (Huh7) was incubated with evolocumab or alirocumab and total PCSK9 and LDLR were determined.

Results

Results: Baseline plasma levels of PCSK9 (n=26 patients) was 458.8±297.4 ng/ml and increased to 1533.3±333.5 ng/ml in response to mAbs anti-PCSK9. In a second cohort of patients (n=30) we observed levels of PCSK9 equal to 1702.0±164.9 ng/ml which declined to 1360.0±344.8 ng/ml after 2 weeks post-injection.

Huh7 were incubated with simvastatin (5 µM), evolocumab (10 µg/ml) and alirocumab (10 µg/ml) for 4, 24 and 48 h. Simvastatin induced both the LDLR and PCSK9 in a time-dependent manner with maximal effect at 48 h (2.15 and 10.8-fold for LDLR and PCSK9, respectively). mAbs anti-PCSK9 induced the LDLR already after 4 h incubation (+46% and +43% for evolocumab and alirocumab, respectively). On the contrary, evolocumab and alirocumab strongly reduced both intracellular and extracellular PCSK9 at 48 h, as determined by western blot and ELISA assays (0.29 and 0.16 vs basal).

Conclusions

Conclusions: Our in vitro results suggest that alirocumab and evolocumab increase PCSK9 plasma levels by reducing its hepatic clearance.