The immunogenic potential of PCSK9 peptide vaccine in mice

Abstract Background Proprotein convertase subtilisin/Kexin 9 (PCSK9) is a serum protein expressed by liver cells that regulates plasma low-density lipoprotein cholesterol (LDL-C) levels by modulating LDL receptors (LDLR). Recent studies of our group indicated the efficient immunogenicity of the nanoliposomal PCSK9 peptide vaccine in different animal models. Purpose Herein, we sought to evaluate the immunogenic potential of the non-liposomal form of the vaccine due to its simplicity of processing and lower production cost. Methods PCSK9 immunogenic peptide was prepared by linking a short PCSK9 peptide to a tetanus peptide as B and T cell epitopes, respectively. The immunogenic peptide and 0.4% alum adjuvant, in a 1:1 ratio, were mixed thoroughly and homogeneously prior to administration as vaccine formulation. In order to assess the humoral immune response, mice were inoculated subcutaneously four times at bi-week intervals. Immunized animals' blood was sampled two weeks after the last injection. The titers of the anti-PCSK9 antibodies in the serum of vaccinated mice were evaluated using the ELISA method. ELISA was also used to investigate the effects of anti-PCSK9 vaccination on PCSK9 serum concentrations and its interaction with LDL receptor (LDLR). Results ELISA analysis showed significant induction of IgG antibody titers by PCSK9 peptide vaccine in vaccinated mice compared to the control group (586±12000 and 642±11566 in male and female vaccinated mice, respectively, p<0.001). No significant difference was found between the male and female vaccine groups (p>0.05). Mechanistic analyses showed that vaccine-induced antibodies decreased serum PCSK9 concentration in vaccine groups compared to the control group (in male mice by 26±5 ng/mL, p<0.01 and female mice by 29±5 ng/mL, p<0.01). Serum concentrations of PCSK9 in control and vaccine groups were found to be 131±8.6 ng/mL and 102±8.1 ng/ml in male mice, and 124±6 ng/ml and 98±10 ng/ml in female mice, respectively. Moreover, vaccine-induced antibodies inhibited the PCSK9/LDLR interaction in the presence of serum from vaccinated mice compared to control mice serum (in male and female groups by 34% and 26%, respectively). The PCSK9 peptide vaccine significantly reduced LDL-C in immunized mice in both male (16.93±2.5 mg/dL, p=0.001) and female groups (22±2.7 mg/dL, p=0.001) compared with the control group. Conclusions According to our results, the PCSK9 peptide vaccine stimulates the humoral immune response in albino mice to produce active antibodies that inhibit plasma PCSK9 resulting in plasma LDL-C reduction. Funding Acknowledgement Type of funding sources: None.