Chronic CCl₄ intoxication causes liver and bone damage similar to the human pathology of hepatic osteodystrophy: A mouse model to analyse the liver-bone axis

Patients with chronic liver diseases frequently exhibit decreased bone mineral densities (BMD), which is defined as hepatic osteodystrophy (HOD). HOD is a multifactorial disease whose regulatory mechanisms are barely understood. Thus, an early diagnosis and therapy is hardly possible. Therefore, the aim of our study consisted in characterizing a mouse model reflecting the human pathomechanism. Serum samples were collected from patients with chronic liver diseases and 12-week old C57Bl6/N mice after 6-week treatment with carbon tetrachloride (CCl₄). Repetitive injections of CCl₄ induced liver damage in mice, resembling liver fibrosis in patients, as assessed by serum analysis and histological staining. Although CCl₄ did not affect primary osteoblast cultures, μCT analysis revealed significantly decreased BMD, bone volume, trabecular number and thickness in CCl ₄-treated mice. In both HOD patients and CCl₄-treated mice, an altered vitamin D metabolism with decreased CYP27A1, CYP2R1, vitamin D-binding protein GC and increased 7-dehydrocholesterol reductase hepatic gene expression, results in decreased 25-OH vitamin D serum levels. Moreover, both groups exhibit excessively high active transforming growth factor-beta (TGF-β) serum levels, inhibiting osteoblast function in vitro. Summarizing, our mouse model presents possible mediators of HOD, e.g. altered vitamin D metabolism and increased active TGF-β. Liver damage and significant changes in bone structure and mineralization are already visible by μCT analysis after 6 weeks of CCl₄ treatment. This fast response and easy transferability makes it an ideal model to investigate specific gene functions in HOD.