Collagen structure and nonlinear susceptibility: Effects of heat, glycation, and enzymatic cleavage on second harmonic signal intensity

Background and Objective: Helical macromolecules such as collagen and DNA a re characterized by nonlinear optical properties, including nonlinear susce ptibility. Because collagen is the predominant component of most biological tissues, as well as the major source of second harmonic generation (SHG), it is reasonable to assume that changes in harmonic signal can be attribute d to structural changes in collagen. The purpose of this study is to determ ine whether various modifications of collagen structure affect second harmo nic intensity. Study Design/Materials and Methods: SHG was measured in tissues from cows, humans , and chickens. The effects of beam polarization, thermal denaturation, gly co-oxidative damage, and enzymatic cleavage of tissues on second harmonic i ntensity was studied. Results: The second harmonic intensity differed considerably among differen t tissues, as did the effect of the incident beam polarization. In structur ally modified collagen, SHG was significantly degraded from SHG; in intact collagen. Conclusion: These structural modifications are representative of changes th at occur in pathophysiologic conditions such as thermal injury, diabetes, t umor invasion, and abnormal wound healing. The ability to assess these chan ges rapidly and noninvasively has considerable clinical applicability. SHG analysis might provide a unique tool for monitoring these structural change s of collagen. Published 2000 Wiley-Liss, Inc.(dagger)