Abstract
High fat diets (HFD) are common in Western countries, especially among the elderly (65+). Both aging and HFD increase fracture risk and reduce bone quality. Our data show that aging and HFD both reduce fracture toughness in C57BL/6 mice (Fig. A), suggesting that matrix properties are compromised by both. We hypothesized that aging and HFD differently impact bone matrix. Female and male C57BL/6 mice were fed low fat diet (LFD, 10% fat) or HFD (45% fat) for 8 weeks and euthanized at 5 or 22 months of age (n = 7-11/group). A fluorometric assay quantified advanced glycation end products (fAGEs) from the flushed cortical bone of humeri. Hydrated Raman spectroscopy was performed at the periosteal surface and the area near the endocortical surface of the femur diaphysis (0-30% cortical thickness, 7 µm spacing between rows). At both sites, medians were measured for matrix structure (I1670/I1640, I1670/I1610), mineral:matrix ratio (v1phos:amideIII), and mineral maturity (carbonate:phosphate, crystallinity). For endocortical measures, the gradient (slope of data linear fit) and heterogeneity (data root mean square deviation) were also calculated. 3-way ANOVA was used to analyze all measures. Clustering by absolute correlation identified matrix properties most strongly correlated with fracture toughness for males. At the periosteal surface, sex and age differences were found. Males had lower median mineral:matrix than females (-12%, p < 0.001) and aging increased mineral maturity (median carbonate:phosphate ratio, +12%, p < 0.001). At the endocortical region, sex and diet effects were pronounced. HFD impacted several matrix measures for females and less for males. Compared to LFD, HFD females had a lower median mineral crystallinity (-15%, p = 0.017) and matrix structure heterogeneity (I1670/I1610, -85%, p < 0.001). Males did not have significant differences with HFD. Nonetheless, for males, fracture toughness strongly correlated with median matrix structure (I1670/I1610), matrix structure heterogeneity (I1670/I1610), and median mineral:matrix ratio. fAGEs were not significantly different between groups or strongly correlated with fracture toughness (Fig. B). We show that age and diet both contribute to the loss of fracture toughness and matrix quality. HFD and aging both decrease fracture toughness, but the contributing changes to bone matrix properties differ. Our data advances understanding of how matrix properties vary with different causes of bone fragility and could lead to the development of improved therapies.