Mature enzymatic collagen cross-links, hydroxylysylpyridinoline and lysylpyridinoline, in the aging human vitreous

Purpose. The vitreous body of the human eye undergoes progressive morphologic changes with aging. Since the enzymatic collagen cross-links hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP) are known to be important for the integrity of the collagen matrix, the presence in the vitreous on aging was studied. Methods. Vitreous bodies (VBs; n = 143) from 119 donors (age 4-80 years; mean ± SD, 54.3 ± 17.0 years) were carefully dissected. After weighing and freeze-drying, all samples were analyzed by high performance liquid chromatography. Left and right eyes of 24 donors were compared and, for age-related phenomena, 119 single eyes were used. Results. Within one donor, no significant differences were found between left and right eyes. On aging, VB wet weight (4.42 ± 0.84 g) accumulates until 35 years and decreases thereafter. Collagen content (0.30 ± 0.14 mg), HP per triple helix (TH; 0.55 ± 0.18), and (HP plus LP)/TH (0.61 ± 0.19) increase until 50 years followed by a decrease, whereas LP/TH (0.057 ± 0.018) accumulates until 50 years and remains constant thereafter. The ratio between HP and LP (range, 0.42-31.0; median, 10.0) is constant over time. Conclusions. The accumulation of enzymatic collagen cross-links until 50 years is consistent with collagen maturation and possible collagen synthesis in the human vitreous body. The decline of collagen cross-links after 50 years is consistent with collagen breakdown