High-Yield Preparation and Characterization of Feline Albumin with Antioxidant Properties and In Vivo Safety

To address the limited supply of serum albumin (SA) and potential pathogen contamination, focus has been concentrated on the heterologous expression of human serum albumin (HSA), particularly in Pichia pastoris. However, there are rare studies on feline serum albumin (FSA), which requires a large amount in pet foods and clinical treatment. In this work, the codon-optimized recombinant feline serum albumin (rFSA) sequence was designed and transferred into P. pastoris GS115 for recombinant expression. The high-level expression strain was selected by a high concentration of G418, followed by plate and shaker screening. At the 5 L fermenter level, the total protein concentration reached 3.89 mg/mL after 113 h of induction. At lower concentrations (1-4 μM), rFSA exhibited a potent free radical scavenging capacity, reaching 99% and 60% for ABTS⁺• and •O^2-, respectively, which surpassed that of natural plasma-derived FSA. The secondary structure and stability of rFSA were found to be consistent with those of FSA. Additionally, an in vivo safety assay in mice showed no significant difference between the rFSA group and the normal saline group in terms of body weight changes, complete blood count, serum biochemistry, inflammatory factors, and tissue sections. These results above indicate that P. pastoris is the optimal host for the high preparation of rFSA. Furthermore, rFSA has been demonstrated to be relatively safe, which paves the way for subsequent industrialized production and its application in pet foods and veterinary clinics.