Collagen structure and nonlinear susceptibility: effects of heat, glycation, and enzymatic cleavage on second harmonic signal intensity.
OBJECTIVE
Helical macromolecules such as collagen and DNA are characterized by nonlinear optical properties, including nonlinear susceptibility. 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 attributed to structural changes in collagen. The purpose of this study is to determine whether various modifications of collagen structure affect second harmonic intensity.


METHODS
SHG was measured in tissues from cows, humans, and chickens. The effects of beam polarization, thermal denaturation, glyco-oxidative damage, and enzymatic cleavage of tissues on second harmonic intensity was studied.


RESULTS
The second harmonic intensity differed considerably among different tissues, as did the effect of the incident beam polarization. In structurally modified collagen, SHG was significantly degraded from SHG in intact collagen.


CONCLUSIONS
These structural modifications are representative of changes that occur in pathophysiologic conditions such as thermal injury, diabetes, tumor invasion, and abnormal wound healing. The ability to assess these changes rapidly and noninvasively has considerable clinical applicability. SHG analysis might provide a unique tool for monitoring these structural changes of collagen.
Kim
B M
BM
Medical Technology Program, Lawrence Livermore National Laboratory, Livermore, California 94550, USA. kim12@llnl.gov
Eichler
J
J
Reiser
K M
KM
Rubenchik
A M
AM
Da Silva
L B
LB
D000818:Animals; D002417:Cattle; D002645:Chickens; D003094:Collagen / Q000737:chemistry*; D006358:Hot Temperature; D006801:Humans; D007834:Lasers; D055095:Optics and Photonics; D012867:Skin / Q000737:chemistry; D013710:Tendons / Q000737:chemistry
D003094:Collagen