Photodermatol Photoimmunol Photomed 2001; 17: 114–120 Copyright C Munksgaard 2001 Printed in Denmark ¡ All rights reserved Munksgaard ¡ Copenhagen ISSN 0905-4383 Effect of UV irradiation on type I collagen fibril formation in neutral collagen solutions Julian M. Menter 1 , Abrienne M. Patta 1 , Robert M. Sayre 2,3 , John Dowdy 2,4 , Isaac Willis 1 1 Morehouse School of Medicine, Department of Medicine, Atlanta, GA; 2 Rapid Precision Testing Laboratories, Cordova, TN; 3 Department of Medicine, Div. of Dermatology, University of Tennessee Center for the Health Sciences, Memphis, TN; 4 Department of Cellular and Molecular Cell Sciences, University of Memphis, Memphis, TN, USA 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 modi- fied. 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 æC, and centrifuged at 48 000¿g. Photolysis was carried out at 4 æC 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 tem- perature from 8 æC to 33 æC. Nucleation and growth were followed by turbidimetric measurements at 400 nm. Results: UVC radiation (0–17.3 J/cm 2 ) 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– C ollagen fibers are the principal structural element of the extracellular matrix (ECM) in vivo. In addition, they provide a specific milieu for surrounding fibroblasts and other cells. Remodeling of the ECM is a prominent feature in wound healing, tissue development, tumor in- vasion, chronic inflammation and other processes (see (1) and references therein). Depending on the degree of mech- anical stress the ECM is under, the resident fibroblasts may differ markedly in phenotype, morphology, prolifer- ative capacity and collagenase biosynthesis (2). High 114 1320 J/cm 2 ) caused a small decrease in growth rate and in the degree of fibril formation. UVA radiation (0–1080 J/cm 2 ) had a similar effect. ‘‘Direct’’ photo- chemical damage thus paralleled absorption via vari- ous collagen chromophores, with UVCSSR∂UVA. The presence of riboflavin (RF) resulted in ground- state interactions that markedly altered both nu- cleation and growth kinetics. Irradiation with 29.6 J/ cm 2 UVA in the presence of RF photosensitizer caused relatively minor additional changes in fibrillation kin- etics. 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 mi- lieu in vivo. Notwithstanding, the relative insensitivity of fibrillogenesis to non-specific photochemical dam- age probably represents a favorable adaptation, over- all, which tends to conserve the mechanical integrity of the skin. Key words: collagen; fibrillation; ultraviolet radiation. stress (e.g. granulation tissue in wounds) favors cell pro- liferation and biosynthetic activity whereas low stress (in- tact dermis) favors a non-proliferative phenotype and de- creased response to growth factors (2). Perturbations wrought by physical, chemical and/or environmental agents, if severe enough, result in ‘‘wound healing’’ re- sponses by the resident fibroblasts, with attendant changes in ECM structural scaffolding. As a consequence, fibril structure and, by extension, the kinetics of fibril forma- tion could be significantly altered.