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Collagen Cross-linking (collagen + cross-linking)
Selected AbstractsLysyl Hydroxylase-2b Directs Collagen Cross-Linking Pathways in MC3T3-E1 Cells,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 8 2004Suchaya Pornprasertsuk Abstract To elucidate the roles of LH2b in collagen cross-linking, MC3T3-E1 cell clones expressing higher (S) or lower (AS) levels of LH2b were established. Compared with controls, the collagen cross-linking pattern was shifted toward hydroxylysine-aldehyde (S clones)- or lysine-aldehyde (AS clones)-derived pathways. The data indicate that LH2b directs collagen cross-linking pathways through its action on telopeptidyl lysine residues. Introduction: Lysine (Lys) hydroxylation is a post-translational modification of collagen critical for cross-linking and glycosylation. Currently, three isoforms of lysyl hydroxylase (LH) have been identified, but their specific functions are still not well defined. Recently, we proposed that LH2 might modulate collagen cross-linking pattern through its action on Lys residues located in the telopeptide domains of collagen. Materials and Methods: To directly test this hypothesis, several MC3T3-E1 cell-derived clones expressing higher (sense [S]) or lower (antisense [AS]) levels of LH2b, the predominant form of LH2 in this cell line, were established and cultured for 2 weeks, and collagen cross-links and precursor aldehydes in the matrices were analyzed. Results: In S clones tested, the ratio of dihydroxylysinonorleucine (DHLNL) to hydroxylysinonorleucine (HLNL) was significantly higher than the average of controls (76% and 140% increase, respectively), and the level of pyridinoline (Pyr) was elevated (100% and 150% increase, respectively). In contrast, when MC3T3-E1 cells were transfected with a LH2b antisense construct (AS clones), the DHLNL/HLNL ratios were significantly lower than that of controls (56% and 73% decrease, respectively), and Pyr was not detected. Furthermore, significant amounts of an aldol-derived cross-link, dehydrohistidinohydroxymerodesmosine, were produced (,0.3 mol/mol of collagen) in AS clones. Conclusions: The data clearly show a critical role of LH2b in determining collagen cross-linking pathways, most likely through its action on telopeptidyl Lys residues. [source] Effect of UV irradiation on type I collagen fibril formation in neutral collagen solutionsPHOTODERMATOLOGY, PHOTOIMMUNOLOGY & PHOTOMEDICINE, Issue 3 2001Julian M. Menter Background: Collagens have the well-known ability to spontaneously self-associate to form fibrils at physiological temperature and neutral pH in vitro and in vivo. Because solar UV may photochemically alter collagen, the kinetics of fibril formation may be modified. Thus, we have begun a systematic study of the effect of various UV wavebands on fibril formation. Methods: Citrate-soluble calf skin collagen (Elastin Products) was dissolved at 0.05% in 0.5 M HOAc, dialyzed over 2 days into two changes of 0.0327 M phosphate buffer, pH 7.0 at 4 °C, and centrifuged at 48 000×g. Photolysis was carried out at 4 °C with either (a) UVC (UVG,11 lamp), (b) filtered solar-simulating radiation (SSR) or UVA (SSR or UVL,21 lamp filtered with a 2.0 mm Schott WG 345 filter). Gelation was commenced by rapidly raising the temperature from 8 °C to 33 °C. Nucleation and growth were followed by turbidimetric measurements at 400 nm. Results: UVC radiation (0,17.3 J/cm2) resulted in a dose-dependent decrease in the rate of fibril growth. Under these conditions, concomitant collagen cross-linking and degradation occurred. Fibril nucleation, a prerequisite for growth, was rapid (threshold , 2 min) and was not affected by UVC, UVA or SSR. SSR (0,1320 J/cm2) caused a small decrease in growth rate and in the degree of fibril formation. UVA radiation (0,1080 J/cm2) had a similar effect. "Direct" photochemical damage thus paralleled absorption via various collagen chromophores, with UVC>SSR,UVA. The presence of riboflavin (RF) resulted in ground-state interactions that markedly altered both nucleation and growth kinetics. Irradiation with 29.6 J/cm2 UVA in the presence of RF photosensitizer caused relatively minor additional changes in fibrillation kinetics. Conclusions: These results collectively indicate that fibril formation is markedly dependent on specific ground state interactions and relatively insensitive to nonspecific UV damage. On the other hand, fibrils thus formed from photochemically altered collagen may have altered structural properties that could have subtle but unfavorable effects on the local dermal milieu in vivo. Notwithstanding, the relative insensitivity of fibrillogenesis to non-specific photochemical damage probably represents a favorable adaptation, overall, which tends to conserve the mechanical integrity of the skin. [source] 3231: The effect of riboflavin mediated corneal crosslinking on corneal hydrationACTA OPHTHALMOLOGICA, Issue 2010G KONTADAKIS Purpose To evaluate the primary effect of corneal collagen crosslinking on corneal hydration. Methods Twenty corneal buttons from freshly enucleated porcine eyes where immersed in riboflavin 0.1% in dextran 20% dilution for three hours in order for their hydration to reach an equilibrium. Corneal buttons where divided in two groups; the first group was stored in dark conditions while the other group was irradiated with UV radiation (390nm) for 30 minutes to stimulate collagen cross-linking according to the clinically applied protocol. After irradiation all corneas were immersed in dextran 20% solution for 30 additional minutes and subsequently weighted. Finally all corneal buttons were dehydrated for 48 hours in a desiccating oven set at 62Co and weighted again to obtain their dry mass. Hydration (%) of each button was calculated. Results were analyzed with non parametric tests. Results Irradiated group of corneas had statistically significant lower hydration than the non irradiated group. (p<0.05, Mann-Whitney Test). Mean hydration in the irradiated group was 71% and in the non-irradiated 75%. Conclusion Collagen crosslinking causes corneal dehydration that can be detected immediately after the procedure. This phenomenon may contribute to increased mechanical stiffness of the cornea. [source] Long-term biomechanical properties of rabbit cornea after photodynamic collagen crosslinkingACTA OPHTHALMOLOGICA, Issue 1 2009Gregor Wollensak Abstract. Purpose:, Photodynamic riboflavin/ultraviolet-A (UVA)-induced collagen cross-linking, which increases the biomechanical stiffness of the human cornea by about 300%, has been introduced recently as a possible treatment for progressive keratoconus. The present study was undertaken to evaluate the longterm biomechanical effects of this new cross-linking treatment as a necessary prerequisite to its clinical success. Methods:, The corneas of the left eyes of nine male rabbits were cross-linked. The contralateral eyes served as controls. After removal of the central 7 mm of the epithelium, the corneas were treated with the photosensitizer riboflavin and UVA irradiation for 30 mins with an irradiance of 3 mW/cm2 using a 370-nm UVA double diode. Groups of three animals were killed immediately after treatment and at 3 and 8 months, respectively. Biomechanical stress,strain measurements were performed using a microcomputer-controlled biomaterial tester on 4 × 10-mm corneal strips. Results:, Corneal thickness in the treated rabbit cornea was 408 ± 20 ,m. A constant and significant increase in ultimate stress (of 69.7,106.0%), Young's modulus of elasticity (of 78.4,87.4%) and a decrease in ultimate strain (of 0.57,78.4%) were found over a time period of up to 8 months after cross-linking treatment. Conclusions:, Riboflavin/UVA-induced collagen cross-linking leads to a longterm increase in biomechanical rigidity which remains stable over time. These data support our previous longterm clinical observations and give hope that this new treatment will halt progressive keratoconus definitively. [source] | ||||||||||