Additionally, this ratio at periosteal cortical surfaces correlated with maximum energy to failure (inversely). Structural properties TriSmi and Tb.Th correlated only with maximum force to failure. In contrast, μFE analysis did not show any effect of treatment on stiffness,

potentially due to the fact that the alteration of collagen cross-links was combined with preservation of the mineralization parameters as described by qBEI analysis. To determine the anatomical locations of compromised mechanical performance bone, nanoindentation tests (corrected for amount of mineral present based on qBEI analysis) were performed. The results indicated that the mechanical performance differences between control and β-APN treated animals are limited to areas of lower Pirfenidone mw Selleckchem Inhibitor Library mineralization, a logical outcome given the fact that the β-APN effect on bone was necessarily restricted to bone that was formed during the period of treatment. It is also in the same anatomical areas that the spectroscopically determined collagen cross-link ratio (Pyd/divalent) was altered. The fact that there were no differences in these bone areas between the animals either in mineral content or in maturity/crystallinity suggests that the observed differences in mechanical properties were due to alterations of collagen. In

this context it may be worth remarking that small local confined changes in mechanical properties of a composite material are not likely to affect the overall modulus of the bone material, which is always an average (though not necessarily an arithmetic average) of the local properties. However, it may have a profound effect on its strength, because strength depends essentially on the strength

of the weakest link in the chain. This seems to fit well also to the observation in the present study that the overall modulus of whole bone is essentially not affected, while the strength is reduced. It should be kept in mind when considering the results of the present study that not all of the expected changes in collagen due to β-APN administration were monitored. For example, we did not Niclosamide analyze for pyrroles (important trivalent cross-links), as no microspectroscopic parameters have been developed to date describing them, thus the anatomical spatial distribution could not be established. In summary, the results of the present study show the good correspondence between biochemically and spectroscopically determined pyd/divalent collagen cross-link ratio. They suggest that normalization for tissue age is critical as it excludes interference in the results from specimen age induced variability. They also indicate that collagen cross-link alterations, even when limited to certain anatomical areas (as in the case of the present study where they were confined to bone forming areas only), coupled with structural properties alterations are capable of affecting the mechanical performance of the whole bone.