X-ray diffraction studies on human tendon show age-related changes in collagen packing.

In this report, X-ray diffraction on native hydrated tendon is established as a monitor of human aging. X-ray diffraction patterns were recorded on toe extensor tendons of persons ranging from 1.6 years to 87 years old. All patterns show a set of 67 nm meridional reflections derived from the collagen fibril axial repeat, and the ratio of the intensities of the 16:17 orders showed a linear increase with age. The spacing of the equatorial maximum, which relates to the lateral packing of molecules in collagen fibrils, was also greater in older tendons. The observed changes in X-ray parameters follow those seen for rat-tail tendons subjected to in vitro non-enzymatic glycosylation. Age-related increases reported for the fluorescence of Maillard products and the concentration of the sugar-derived cross-link pentosidine are similar to the trends in X-ray parameters reported here. Our results support the cumulative nature of non-enzymatic glycosylation in connective tissues during the human lifespan and indicate that structural changes accompany the chemical alterations. The X-ray parameters show a large degree of scatter for ages older than 60 years, suggesting other complicating factors are present. Studies on a small number of diabetic tendons show small, but not significant, increases compared to age-matched controls.