Histological and Optical Characteristics of Pigmented Scars in a Swine Model of Human Wound Healing
Taryn E. Travis, MD1,2, Pejhman Ghassemi, PhD3, Nicholas J. Prindeze, BS2, Dereck W. Paul, BS2, Lauren T. Moffatt, PhD2,
Jessica C. Ramella-Roman4, PhD, Jeffrey W. Shupp, MD1,2
1The
Burn Center, Department of Surgery, MedStar Washington Hospital Center, Washington, DC; 2Firefighters' Burn and Surgical
Research Laboratory, MedStar Health Research Institute, Washington, DC; 3Biomedical Engineering Department, The Catholic University
of America, Washington, DC; 4Biomedical Engineering Department, Florida International University, Miami, FL
Introduction: Scarring with abnormal pigmentation is a common problem after thermal and other traumatic skin injury.
Much of the published research pertaining to abnormalities in skin pigmentation relates to topical treatment modalities or
melanocyte involvement in dermatologic neoplasia, rather than the pathophysiology of scar pigmentation. Using a validated
model of human scar formation, we examined hyper- and hypopigmented scar samples for their histological and optical
properties to help elucidate the mechanisms and characteristics of abnormal scar pigmentation.
Methods: Excisional full thickness wounds were created on the flanks of red duroc pigs and allowed to reepithelialize.
Biopsies from areas of hyperpigmentation, hypopigmentation, and uninjured tissue were formalin-fixed and paraffinembedded for histological examination. Histological sections were stained with Azure B to assess melanin content and antiS100 antibody to identify immunofluorescently-labeled melanocytes. Image J software was used to quantify melanin staining
and Zeiss Zen software was used to measure fluorescence intensity of melanocyte staining in histological sections. Spatial
Frequency Domain Imaging (SFDI) was used to examine the optical properties of scars.
Results: Wounds began reepithelialization from their edges and were completely closed between weeks 5 and 6.
Hyperpigmentation was first faintly noticeable in healing wounds around weeks 3-4, becoming darker from weeks 6-8, and
most visible from week 9 on. Immunofluorescently-stained images showed no significant difference in fluorescence intensity
for melanocyte markers. Azure B staining of intra- and extracellular melanin was significantly greater in histological sections
from pigmented areas than sections from both uninjured skin and hypopigmented scar (p<0.00001). Azure B staining was
also significantly greater in histological sections form uninjured skin than in sections from hypopigmented scar (p=0.01) (See
attached image). SFDI at a wavelength of 632 nm resulted in an absorption coefficient map correlating with visibly
hyperpigmented areas of scars.
Conclusions: In a red Duroc model of human scar formation, melanocyte quantity does not appear to influence pigmentation,
while the production of melanin does correlate with the pigmented appearances of skin and scars. These observations open
the door to investigating melanocyte stimulation and the inflammatory environment within a wound that may influence
melanocyte activity. SFDI can be used to identify areas of melanin content in mature, pigmented scars, which may lead to its
usefulness in wounds at earlier time points before markedly apparent pigmentation abnormalities.