Abstract: Environmental cadmium (Cd) is easily enriched in animals and plants, and enter various organisms through the food chain, which in turn, endangers the health of human and animals. The aim of this study is to evaluate the chelation effect of sheep bone collagen peptide (SBCP) with cadmium and determine the protective effects of SBCP against Cd-induced liver injury in chickens. All Hy-line brown chicks were randomly assigned into four groups including control group (basal diet, n=10), Cd group (basal diet with 140 mg·kg^-1 Cd, n=10), SBCP group (basal diet with 3 g·kg^-1 SBCP, n=10) and Cd + SBCP group (basal diet with 140 mg·kg^-1 Cd and 3 g·kg^-1 SBCP, n=10). After 42 days, the cadmium residue level, oxidative stress status, histological changes and mRNA expression levels of mitochondrial apoptosis-related genes in liver were detected. The results showed that no Cd were detected in liver and chest muscle of control group and SBCP group by inductively coupled plasma-mass spectrometry (ICP-MS). Cd in liver and chest muscle of Cd group were 412.57 and 129.47 μg·kg^-1, respectively. Cd in liver and chest muscle of Cd + SBCP group were 216.06 and 49.68 μg·kg^-1, respectively. Meanwhile, compared to control group, the significantly reduced T-SOD and GSH-Px activities, and significantly increased levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and inflammatory cytokines such as IL-2, IL-8, TNF-α, IFN-γ were detected in Cd group. The histopathological results demonstrated that Cd exposure caused disordered arrangement of liver cords, nuclei concentrated necrosis and interstitial lymphocytic infiltration. In addition, Cd exposure significantly increased pro-apoptotic genes bax, cyt C, caspase-3 and caspase-9 expression levels, and significantly reduced the mRNA expression of anti-apoptotic gene bcl-2. However, compared to Cd group, SBCP treatment significantly ameliorated Cd-caused liver injury, reflected by the significantly increased T-SOD and GSH-Px activities, and the significantly decreased levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and inflammatory cytokines. In addition, SBCP treatment improved morphological changes of liver and restored the mRNA expression levels of apoptosis-related genes. Importantly, the results of infrared spectroscopy showed that SBCP chelated with Cd, and produced a new substance, the chelation rate of Cd and SBCP reached 47%. SBCP can reduce cadmium residue by its chelation effect and thus alleviated Cd induced oxidative stress, inflammatory injury and hepatocyte apoptosis. All these results provide theoretical basis that SBCP could be a promising candidate for the prevention of animals poisoning caused by heavy metal.

Key words: sheep bone collagen peptide, liver, cadmium, antioxidant, mitochondrial apoptosis