Investigation of the cortical bone metabolome of C57BL/6J mice with adenine-induced kidney disease

Abstract The loss of bone fracture resistance in Chronic Kidney Disease (CKD) results from both a loss of bone mass and decreased bone material properties, which together result from changes to the health and activities of bone cells. Determining changes to bone tissue metabolism with CKD may reveal insights important to monitoring and mitigating the decrease in bone fracture resistance with this disease. In this study, untargeted metabolomics was conducted on marrow-flushed cortical tibiae from female and male C57BL/6J mice fed either control or 0.2% w/w adenine diets for 3.5 or 7 weeks. Liquid chromatography mass spectrometry assessed metabolites from tibia extracts. Group comparisons (adenine vs control, 7 weeks vs 3.5 weeks, female vs male) were conducted using principal components analysis (PCA) and partial least squares discriminant analysis (PLS-DA). Clusters of metabolites were also assessed using ensemble clustering with cluster optimization analysis (ECCO). Volcano plots and VIP scores identified metabolites that differed between groups, and pathway analyses were conducted using these features. Adenine-induced CKD produced few differences in cortical bone tissue metabolism, based on the comparison of pooled adenine vs control groups. However, pantothenate and CoA biosynthesis, along with essential and nonessential amino acid pathways, registered notably high VIP scores for adenine vs control comparisons. There were many significant differences between 3.5- and 7-week treatment groups (adenine and control). The pathways different between diet lengths for control mice reveal potential effects of skeletal aging. However, there were significant changes in the pentose phosphate pathway and cysteine metabolism between 3.5- and 7-week adenine diets, indicating an effect of CKD severity. While sex differences in this study were modest, there was greater separation between female adenine vs control groups compared to male adenine vs control groups, indicating potential sex differences in the impacts of CKD on bone tissue metabolism.