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
Authors: Carney Bonnie C. , Oliver Mary A. , Kurup Sanjana , Collins Monica , Keyloun John W. , Moffatt Lauren T. , Shupp Jeffrey W. , Travis Taryn E. 
Published: April 2023

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.