Adenine-induced kidney disease alters the cortical bone metabolome of C57BL/6J mice in a manner that depends on sex

Chronic kidney disease (CKD) increases the likelihood of bone fracture as well as post-fracture mortality. The loss of bone fracture resistance in 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 that commonly occurs as a result of this disease. In this study, untargeted metabolomics was conducted on marrow-flushed cortical tibiae from female and male C57BL/6J mice fed either a control or 0.2% w/w adenine diet. The diets were continued over 3.5 or 7 weeks to produce different severities of kidney injury. Liquid chromatography mass spectrometry (LC-MS) was used to assess metabolites from tibia extracts. Group comparisons (CKD vs control, 7 weeks vs 3.5 weeks, female vs male) were conducted using principal components analysis (PCA), partial least squares discriminant analysis (PLS-DA), and hierarchical clustering. Clusters of metabolites were also assessed using ensemble clustering and cluster optimization analysis (ECCO).

Volcano plots and VIP scores were used to identify individual metabolites that differed between groups. Pathway analyses were then conducted from these metabolites. The CKD mice, compared with control mice, had dysregulated essential and nonessential amino acid pathways along with altered pathways associated with sugar and fatty acid metabolism. Compared with mice fed an adenine diet for 3.5 weeks, the mice fed an adenine diet over 7 weeks showed dysregulations in the pentose phosphate pathway along with essential and nonessential amino acid metabolism, porphyrin metabolism, steroid hormone biosynthesis, and other pathways relevant to energy production. Sex differences were apparent in the bone tissue metabolomes of females and males. Compared to males, females experienced dysregulations in essential and nonessential amino acid pathways along with other pathways associated with energy derivation, such as pantothenate and CoA biosynthesis. These results demonstrate that CKD alters bone tissue metabolism and reveals novel insights into metabolic dysregulation in disease as well as important sex differences in these metabolic processes.