Serum proteasome levels were measured using a 20S/26S Proteasome ELISA Kit (Enzo Life Sciences, Farmingdale, NY, USA). Serum levels of NEDD8 were measured using a Human NEDD8 ELISA Kit (MyBioSource, San Diego, CA, USA). Statistical analysis of the ELISA data was performed using JMP Pro® 15.2.1 software. The Mann–Whitney U test was used to compare groups (two-sided), with p < 0.05 considered significant.