A Multimodal Assessment of Melanin and Melanocyte Activity in Abnormally Pigmented Hypertrophic Scar

Abstract

Objective Using a validated swine model of human scar formation, hyper- and hypopigmented scar samples were examined for their histological and optical properties to help elucidate the mechanisms and characteristics of dyspigmentation. Methods Full thickness wounds were created on the flanks of red Duroc pigs and allowed to heal. Biopsies from areas of hyperpigmentation, hypopigmentation, and uninjured tissue were fixed and embedded for histological examination using Azure B and primary antibodies to S100B, HMB45, and α-MSH. Spatial Frequency Domain Imaging (SFDI) was then used to examine the optical properties of scars. Results Hyperpigmentation was first noticeable in healing wounds around weeks 2–3, gradually becoming darker. There was no significant difference in S100B staining for the presence of melanocytes between hyperpigmented and hypopigmented scar samples. Azure B staining of melanin was significantly greater in histological sections from hyperpigmented areas than sections from both uninjured skin and hypopigmented scar (p<0.0001). There was significantly greater staining for α-MSH in hyperpigmented samples compared to hypopigmented samples (p=0.0121) and HMB45 staining was positive for melanocytes in hyperpigmented scar. 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 hypertrophic scar formation, melanocyte number is similar in hyper- and hypopigmented tissues. Hyperpigmented tissues, however, show a greater amount of melanin and α-MSH, along with immunohistochemical evidence of stimulated melanocytes. These observations encourage further investigation of melanocyte stimulation and the inflammatory environment within a wound that may influence melanocyte activity. Additionally, 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.

Dyspigmented hypertrophic scars: Beyond skin color

“…Wounds were created using a Zimmer dermatome (Zimmer, Ltd, Swindon, UK) and excised over the lateral thorax to a full thickness depth of 0.090 inches (3 passes each at 0.030 in). Details related to anesthesia, animal care, wound healing, and scar formation have been previously described (Alkhalil et al, ; Carney et al, ; Ghassemi, Travis, Moffatt, Shupp, & Ramella‐Roman, ; Tejiram et al, ; Travis et al, ; Travis, Mino, et al, ).…”

“…In previous work, dyspigmented hypertrophic scars showing hyper‐ and hypopigmented regions were produced in red Duroc swine (Alkhalil et al, ; Carney et al, ; Tejiram et al, ), and pigmentation phenotypes were shown to be due to increased or absent melanin synthesis (Travis, Ghassemi, et al, ), respectively. Melanocytes were also shown to be present in comparable densities both in dyspigmented and in normal pigmentation phenotypes (Travis, Ghassemi, et al, ). Here, the biological differences between these phenotypes were investigated for differences in transcriptome profiles using microarrays.…”

Spatial frequency domain imaging in 2019: principles, applications, and perspectives

“…Multiple groups have used established preclinical models to show that SFDI can be used to assess burn depth. 18,[94][95][96][97][98] The most unique finding thus far is the correlation of SFDI scattering changes to gold standard measurements of burn depth with histology (H&E, Masson's trichrome, and Vimentin immunostain).…”

Autologe Hautzelltransplantation und Medical Needling zur Repigmentierung von depigmentierten Verbrennungsnarben an UV-exponierter und -geschützter Haut

“…die gleiche Anzahl an Melanozyten in der Haut aufweist. Die individuelle Pigmentierung eines jeden basiert zudem auf der Aktivität der Melanozyten und an der Anzahl und Verteilung der Melanosomen[36,37]. Die vorhandenem Melanozyten produzieren jedoch unter den gleichen Lichtbedingungen immer gleich viel Melanin.…”