Dyspigmented hypertrophic scars: Beyond skin color

Treatment of hypopigmented burn hypertrophic scars with short-term topical tacrolimus does not lead to repigmentation

OBJECTIVES

Dyschromia is an understudied aspect of hypertrophic scar (HTS). The use of topical tacrolimus has successfully shown repigmentation in vitiligo patients through promotion of melanogenesis and melanocyte proliferation. It was hypothesized that HTSs treated with topical tacrolimus would have increased repigmentation compared to controls.

METHODOLOGY

Full-thickness burns in red Duroc pigs were either treated with excision and meshed split-thickness skin grafting or excision and no grafting, and these wounds formed hypopigmented HTSs (n = 8). Half of the scars had 0.1% tacrolimus ointment applied to the scar twice a day for 21 days, while controls had no treatment. Further, each scar was bisected with half incurring fractional ablative CO2 laser treatment before topical tacrolimus application to induce laser-assisted drug delivery (LADD). Pigmentation was evaluated using a noninvasive probe to measure melanin index (MI) at Days 0 (pretreatment), 7, 14, and 21. At each timepoint, punch biopsies were obtained and fixed in formalin or were incubated in dispase. The formalin-fixed biopsies were used to evaluate melanin levels by H&E staining. The biopsies incubated in dispase were used to obtain epidermal sheets. The ESs were then flash frozen and RNA was isolated from them and used in quantitative reverse transcription polymerase chain reaction for melanogenesis-related genes: Tyrosinase (TYR), TYR-related protein-1 (TYRP1), and dopachrome tautomerase (DCT). Analysis of variance test with Šídák's multiple comparisons test was used to compare groups.

RESULTS

Over time, within the grafted HTS and the NS group, there were no significant changes in MI, except for Week 3 in the -Tacro group. (+Tacro HTS= pre = 685.1 ± 42.0, w1 = 741.0 ± 54.16, w2 = 750.8 ± 59.0, w3 = 760.9 ± 49.8) (-Tacro HTS= pre = 700.4 ± 54.3, w1 = 722.3 ± 50.7, w2 = 739.6 ± 53.2, w3 = 722.7 ± 50.5). Over time, within the ungrafted HTS and the NS group, there were no significant changes in MI. (+Tacro HTS= pre = 644.9 ± 6.9, w1 = 661.6 ± 3.3, w2 = 650.3 ± 6.2, w3 = 636.3 ± 7.4) (-Tacro HTS= pre = 696.8 ± 8.0, w1 = 695.8 ± 12.3, w2 = 678.9 ± 14.0, w3 = 731.2 ± 50.3). LADD did not lead to any differential change in pigmentation compared to the non-LADD group. There was no evidence of increased melanogenesis within the tissue punch biopsies at any timepoint. There were no changes in TYR, TYRP1, or DCT gene expression after treatment.

CONCLUSION

Hypopigmented HTSs treated with 0.1% tacrolimus ointment with or without LADD did not show significantly increased repigmentation. This study was limited by a shorter treatment interval than what is known to be required in vitiligo patients for repigmentation. The use of noninvasive, topical treatments to promote repigmentation are an appealing strategy to relieve morbidity associated with dyschromic burn scars and requires further investigation.

Rete ridges are decreased in dyschromic burn hypertrophic scar: A histological study

Dyschromic hypertrophic scar (HTS) is a common sequelae of burn injury, however, its mechanism has not been elucidated. This work is a histological study of these scars with a focus on rete ridges. Rete ridges are important for normal skin physiology, and their absence or presence may hold mechanistic significance in post-burn HTS dyschromia. It was posited that hyper-, and hypo-pigmented areas of scars have different numbers of rete ridges. Subjects with dyschromic burn hypertrophic scar were prospectively enrolled (n = 44). Punch biopsies of hyper-, hypo-, and normally pigmented scar and skin were collected. Biopsies were paraffin embedded, sectioned, stained with H&E, and imaged. The number of rete ridges were investigated. Burn hypertrophic scars that healed without autografts were first investigated. The number of rete ridges was higher in normal skin compared to HTS that was either hypo- (p < 0.01) or hyper-pigmented (p < 0.001). This difference was similar despite scar pigmentation phenotype (p = 0.8687). Autografted hyper-pigmented scars had higher rete ridge ratio compared to non-autografted hyper-pigmented HTS (p < 0.0001). Burn hypertrophihc scars have fewer rete ridges than normal skin. This finding may explain the decreased epidermal adherence to underlying dermis associated with hypertrophic scars. Though, contrary to our hypothesis, no direct link between the extent of dyschromia and rete ridge quantity was observed, the differences in normal skin and hypertrophic scar may lead to further understanding of dyschromic scars.

Scar Management and Dyschromia: A Summary Report from the 2021 American Burn Association State of the Science Meeting

Burn scars, and in particular, hypertrophic scars, are a challenging yet common outcome for survivors of burn injuries. In 2021, the American Burn Association brought together experts in burn care and research to discuss critical topics related to burns, including burn scars, at its State of the Science conference. Clinicians and researchers with burn scar expertise, as well as burn patients, industry representatives, and other interested stakeholders met to discuss issues related to burn scars and discuss priorities for future burn scar research. The various preventative strategies and treatment modalities currently utilized for burn scars were discussed, including relatively noninvasive therapies such as massage, compression, and silicone sheeting, as well as medical interventions such as corticosteroid injection and laser therapies. A common theme that emerged is that the efficacy of current therapies for specific patient populations is not clear, and further research is needed to improve upon these treatments and develop more effective strategies to suppress scar formation. This will necessitate quantitative analyses of outcomes and would benefit from creation of scar biobanks and shared data resources. In addition, outcomes of importance to patients, such as scar dyschromia, must be given greater attention by clinicians and researchers to improve overall quality of life in burn survivors. Herein we summarize the main topics of discussion from this meeting and offer recommendations for areas where further research and development are needed.

Laser-assisted drug delivery of synthetic alpha melanocyte stimulating hormone and L-tyrosine leads to increased pigmentation area and expression of melanogenesis genes in a porcine hypertrophic scar model

OBJECTIVES

One symptom of hypertrophic scar (HTS) that can develop after burn injury is dyschromia with hyper- and hypopigmentation. There are limited treatments for these conditions. Previously, we showed there is no expression of alpha melanocyte stimulating hormone (α-MSH) in hypopigmented scars, and if these melanocytes are treated with synthetic α-MSH in vitro, they respond by repigmenting. The current study tested the same hypothesis in the in vivo environment using laser-assisted drug delivery (LADD).

METHODS

HTSs were created in red Duroc pigs. At Day 77 (pre), they were treated with CO₂ fractional ablative laser (FLSR). Synthetic α-MSH was delivered as a topical solution dissolved in  l-tyrosine (n = 6, treated). Control scars received LADD of  l-tyrosine only (n = 2, control). Scars were treated and examined weekly through Week 4. Digital images and punch biopsies of hyper, hypo-, and normally pigmented scar and skin were collected. Digital pictures were analyzed with ImageJ by tracing the area of hyperpigmentation. Epidermal sheets were obtained from punch biopsies through dispase separation and RNA was isolated. qRT-PCR was run for melanogenesis-related genes: tyrosinase (TYR), tyrosinase-related protein-1 (TYRP1), and dopachrome tautomerase (DCT). Two-way ANOVA with multiple comparisons and Dunnett's correction compared the groups.

RESULTS

The areas of hyperpigmentation were variable before treatment. Therefore, data is represented as fold-change where each scar was normalized to its own pre value. Within the LADD of NDP α-MSH + l-tyrosine group, hyperpigmented areas gradually increased each week, reaching 1.3-fold over pre by Week 4. At each timepoint, area of hyperpigmentation was greater in the treated versus the control (1.04 ± 0.05 vs. 0.89 ± 0.08, 1.21 ± 0.07 vs. 0.98 ± 0.24, 1.21 ± 0.08 vs. 1.04 ± 0.11, 1.28 ± 0.11 vs. 0.94 ± 0.25; fold-change from pre-). Within the treatment group, pretreatment, levels of TYR were decreased -17.76 ± 4.52 below the level of normal skin in hypopigmented scars. After 1 treatment, potentially due to laser fractionation, the levels decreased to -43.49 ± 5.52. After 2, 3, and 4 treatments, there was ever increasing levels of TYR to almost the level of normally pigmented skin (-35.74 ± 15.72, -23.25 ± 6.80, -5.52 ± 2.22 [p < 0.01, Week 4]). This pattern was also observed for TYRP1 (pre = -12.94 ± 1.82, Week 1 = -48.85 ± 13.25 [p < 0.01], Weeks 2, 3, and 4 = -34.45 ± 14.64, -28.19 ± 4.98, -6.93 ± 3.05 [p < 0.01, Week 4]) and DCT (pre = -214.95 ± 89.42, Week 1 = -487.93 ± 126.32 [p < 0.05], Weeks 2, 3, and 4 = -219.06 ± 79.33, -72.91 ± 20.45 [p < 0.001], -76.00 ± 24.26 [p < 0.001]). Similar patterns were observed for scars treated with LADD of  l-tyrosine alone without NDP α-MSH. For each gene, in hyperpigmented scar, levels increased at Week 4 of treatment compared to Week 1 (p < 0.01).

CONCLUSIONS

A clinically-relevant FLSR treatment method can be combined with topical delivery of synthetic α-MSH and l-tyrosine to increase the area of pigmentation and expression of melanogenesis genes in hypopigmented HTS. LADD of  l-tyrosine alone leads to increased expression of melanogenesis genes. Future studies will aim to optimize drug delivery, timing, and dosing.

Epigenetic Influences on Wound Healing and Hypertrophic-Keloid Scarring: A Review for Basic Scientists and Clinicians

Primary care physicians and dermatologists are challenged by patients affected by keloid or hypertrophic scarring resulting from accidental wounding, surgical incisions, tattooing, or “branding” procedures to demonstrate their association with a specific culture, fraternity, or cult. The dysregulated wound healing associated with keloids and hypertrophic scarring adversely affects genetically susceptible individuals, especially persons of color with Fitzpatrick Skin types IV-VI. Although the specific mechanisms of bulky hypertrophic/keloid scarring and its association with oxidative stress and inflammation remain unclear, the current knowledge base is sufficient to provide some guidance to health practitioners who must serve, treat, and counsel affected individuals. This review focuses on providing insight to healthcare professionals about the role of epigenetics, oxidative stress, poor local oxygenation, and its relationship to impaired wound healing. The goal is to promote further research on bulky hypertrophic and keloid scarring for its prevention and to develop evidence-based clinical guidelines for optimal treatment.

In-depth examination of hyperproliferative healing in two breeds of Sus scrofa domesticus commonly used for research

Background

Wound healing can result in various outcomes, including hypertrophic scar (HTS). Pigs serve as models to study wound healing as their skin shares physiologic similarity with humans. Yorkshire (Yk) and Duroc (Dc) pigs have been used to mimic normal and abnormal wound healing, respectively. The reason behind this differential healing phenotype was explored here.

Methods

Excisional wounds were made on Dc and Yk pigs and were sampled and imaged for 98 days. PCR arrays were used to determine differential gene expression. Vancouver Scar Scale (VSS) scores were given. Re-epithelialization was analyzed. H&E, Mason's trichrome, and immunostains were used to determine cellularity, collagen content, and blood vessel density, respectively.

Results

Yk wounds heal to a "port wine" HTS, resembling scarring in Fitzpatrick skin types (FST) I-III. Dc wounds heal to a dyspigmented, non-pliable HTS, resembling scarring in FST IV-VI. Gene expression during wound healing was differentially regulated versus uninjured skin in 40/80 genes, 15 of which differed between breeds. Yk scars had a higher VSS score at all time points. Yk and Dc wounds had equivalent re-epithelialization, collagen disorganization, and blood vessel density.

Conclusions

Our findings demonstrate that Dc and Yk pigs can produce HTS. Wound creation and healing were consistent among breeds, and differences in gene expression were not sufficient to explain differences in resulting scar phenotype. Both pig breeds should be used in animal models to investigate novel therapeutics to provide insight into a treatment's effectiveness on various skin types.

Hypopigmented burn hypertrophic scar contains melanocytes that can be signaled to re-pigment by synthetic alpha-melanocyte stimulating hormone in vitro

There are limited treatments for dyschromia in burn hypertrophic scars (HTSs). Initial work in Duroc pig models showed that regions of scar that are light or dark have equal numbers of melanocytes. This study aims to confirm melanocyte presence in regions of hypo- and hyper-pigmentation in an animal model and patient samples. In a Duroc pig model, melanocyte presence was confirmed using en face staining. Patients with dyschromic HTSs had demographic, injury details, and melanin indices collected. Punch biopsies were taken of regions of hyper-, hypo-, or normally pigmented scar and skin. Biopsies were processed to obtain epidermal sheets (ESs). A subset of ESs were en face stained with melanocyte marker, S100β. Melanocytes were isolated from a different subset. Melanocytes were treated with NDP α-MSH, a pigmentation stimulator. mRNA was isolated from cells, and was used to evaluate gene expression of melanin-synthetic genes. In patient and pig scars, regions of hyper-, hypo-, and normal pigmentation had significantly different melanin indices. S100β en face staining showed that regions of hyper- and hypo-pigmentation contained the same number of melanocytes, but these cells had different dendricity/activity. Treatment of hypo-pigmented melanocytes with NDP α-MSH produced melanin by microscopy. Melanin-synthetic genes were upregulated in treated cells over controls. While traditionally it may be thought that hypopigmented regions of burn HTS display this phenotype because of the absence of pigment-producing cells, these data show that inactive melanocytes are present in these scar regions. By treating with a pigment stimulator, cells can be induced to re-pigment.

Galectin-1 production is elevated in hypertrophic scar

Upon healing, burn wounds often leave hypertrophic scars (HTSs) marked by excess collagen deposition, dermal and epidermal thickening, hypervascularity, and an increased density of fibroblasts. The Galectins, a family of lectins with a conserved carbohydrate recognition domain, function intracellularly and extracellularly to mediate a multitude of biological processes including inflammatory responses, angiogenesis, cell migration and differentiation, and cell-ECM adhesion. Galectin-1 (Gal-1) has been associated with several fibrotic diseases and can induce keratinocyte and fibroblast proliferation, migration, and differentiation into fibroproliferative myofibroblasts. In this study, Gal-1 expression was assessed in human and porcine HTS. In a microarray, galectins 1, 4, and 12 were upregulated in pig HTS compared to normal skin (fold change = +3.58, +6.11, and +3.03, FDR <0.01). Confirmatory qRT-PCR demonstrated significant upregulation of Galectin-1 (LGALS1) transcription in HTS in both human and porcine tissues (fold change = +7.78 and +7.90, P <.05). In pig HTS, this upregulation was maintained throughout scar development and remodeling. Immunofluorescent staining of Gal-1 in human and porcine HTS showed significantly increased fluorescence (202.5 ± 58.2 vs 35.2 ± 21.0, P <.05 and 276.1 ± 12.7 vs 69.7 ± 25.9, P <.01) compared to normal skin and co-localization with smooth muscle actin-expressing myofibroblasts. A strong positive correlation (R = .948) was observed between LGALS1 and Collagen type 1 alpha 1 mRNA expression. Gal-1 is overexpressed in HTS at the mRNA and protein levels and may have a role in the development of scar phenotypes due to fibroblast over-proliferation, collagen secretion, and dermal thickening. The role of galectins shows promise for future study and may lead to the development of a pharmacotherapy for treatment of HTS.

Outcome of Repeated Use of Donor Site for Noncultured Epidermal Cellular Grafting in Stable Vitiligo: A Retrospective Study

Background

Noncultured epidermal suspension (NCES) is a surgical technique which employs cellular grafting onto depigmented lesions. However, scarring and dyschromia at the donor site often occurs.

Objective

To assess the outcome of reusing the same donor site in subsequent sessions of NCES procedures.

Methods

Electronic records of vitiligo patients who had undergone two sessions of NCES procedures were retrospectively reviewed. Information on the first and second NCES was retrieved for analyses.

Results

A total of 30 patients (female 19 and male 11) were included. The majority of patients had nonsegmental vitiligo (66.7%). The median donor-to-recipient ratios were 1 : 3 (1 : 1–1 : 20) for the first session and 1 : 3 (1 : 1–1 : 13.5) for the second session (p=0.661). The mean melanocyte count was 220.7 ± 65.5 cells/mm² vs. 242.4 ± 55.3 cells/mm² on the first and second sessions, respectively (p=0.440). The mean repigmentation rate was 84.2% (±21.1%) and 82.3 (±22.1%) for the first and second NCESs, respectively (p=0.645). The frequency of color mismatch and pigment loss were similar between both sessions (p=0.706 and p=1.000).

Conclusions

Repeated use of donor sites in subsequent NCES sessions gave comparable repigmentation.