Osteoporosis in murine systemic lupus erythematosus--a laboratory model

The aim of this study was to assess the skeletal metabolism in a murine model of systemic lupus erythematosus (SLE). MRL/n and MRL/l mice (respectively representing a benign and a malignant form of the disease) were observed from 1.5 to 6.5 months of life. The monthly follow-up included: biochemical and histomorphometrical studies of the femoral bone, serum biochemistry, immunoglobulins and osteocalcin, and histological evaluation of the kidney tissue. The results showed a higher femoral weight (+11.5%), calcium (+4.4%) and protein bone content (+11.4%) and a significantly higher (+77%) phosphorus bone content in the MRL/n group; significantly lower (-48.9%) bone alkaline phosphatase enzymatic activity, lower bone alkaline/acid phosphatase enzymatic activities ratio (-40.8%) and lower (-38.4%) serum osteocalcin values in the MRL/l group (which might suggest reduced bone formation in these animals); markedly smaller trabecular bone volume (BV/TV) in the femoral head (-36.2%) and femoral neck (-39.8%), and smaller cortical and femoral areas in the mid-femoral shaft (-38.8% and -38.1% respectively) in the MRL/l group; higher serum immunoglobulins, increased serum blood urea nitrogen (BUN) and creatinine and a higher index of activity in the kidney histology in the MRL/l group, indicating increased activity of the disease in this substrain. The MRL mice, through their two substrains, may serve as a valuable laboratory animal model for study of the skeletal changes in SLE and of the influence of the disease activity on the skeletal metabolism.