CTSB and age-related macular degeneration: In addition, western blot assay and immunohistochemistry were used to determine the protein expression of cathepsin B. The data showed that the protein abundance of this enzyme was significantly elevated in the AMD mice without treatment, but treatment with Fructus lycii ethanol extract dose-dependently downregulated its expression in the eye tissues (Figures 2(b) and 2(c)).