Two-Photon Microscopy for the Investigation of Morphological and Quantitative Changes in Skin Chrono- and Photo-Aging

Introduction: Skin aging is influenced both by intrinsic factors and environmental exposures, such as UV radiation, which accelerate structural changes within the skin’s extracellular matrix (ECM). Understanding these changes is crucial for developing effective anti-aging treatments. Materials and Methods: This pilot cross-sectional study examined skin biopsy samples from three Caucasian male subjects with different levels of UV exposure, aiming to evaluate the effectiveness of two-photon microscopy (2PM) and Second Harmonic Generation (SHG) in visualizing and quantifying structural changes associated with skin aging. The samples were analyzed using 2PM to assess the structure and density of collagen and elastin fibers within the ECM. Integrated optical density (IOD) and the SHG-to-Autofluorescence Aging Index of the Dermis (SAAID) were used for quantitative analysis. Results: This study revealed a significant decrease in collagen density and increased disorganization in the ECM with age. Photo-exposed skin showed a more pronounced degradation of collagen and a higher increase in elastin content compared to non-photo-exposed skin. The average IOD for collagen was notably lower in elderly subjects compared to younger subjects, with a marked decrease in chronically photo-exposed skin. Discussion: The SAAID values indicated a substantial impact of photoaging, with lower scores in photo-exposed elderly skin compared to non-exposed skin. Conclusions: In conclusion, 2PM and SHG microscopy were effective in visualizing and quantifying age- and UV-induced skin remodeling, providing valuable insights into the distinct mechanisms driving intrinsic and extrinsic aging.