Hydroxyproline assay

Since hydroxyproline is a basic constituent of collagen structure, its content can serve as indicator of collagen synthesis (23). Hydroxyproline analysis was performed to assess the amount of collagen in liver tissues (24). In brief, the samples were hydrolyzed with 6 M HCl at 130°C for 12 h. Then, 1 ml hydroxyproline developer (β-dimethylaminobenzaldehyde solution) was added to the samples and standards. The optical densities were measured at 558 nm using a spectrophotometer (Bio-Rad Laboratories, Inc.). Finally, the hydroxyproline/mg liver tissue was calculated according to the standard curve constructed with serial concentrations of commercial hydroxyproline.