Firefighters' Burn and Surgical Research Laboratory, MedStar Health Research Institute, Washington, DC, USA.
The Burn Center, Department of Surgery, MedStar Washington Hospital Center, Washington, DC, USA.
J Burn Care Res. 2023 Jul 5;44(4):758-768. doi: 10.1093/jbcr/irad010.
Mechanisms and timing of hypertrophic scar (HTS) improvement with laser therapy are incompletely understood. Epidermal keratinocytes influence HTS through paracrine signaling, yet they are understudied compared to fibroblasts. It was hypothesized that fractional ablative CO2 laser scar revision (FLSR) would change the fibrotic histoarchitecture of the epidermis in HTS. Duroc pigs (n = 4 FLSR and n = 4 controls) were injured and allowed to form HTS. HTS and normal skin (NS) were assessed weekly by noninvasive skin probes measuring trans-epidermal water loss (TEWL) and biopsy collection. There were 4 weekly FLSR treatments. Immediate laser treatment began on day 49 postinjury (just after re-epithelialization), and early treatment began on day 77 postinjury. Punch biopsies from NS and HTS were processed and stained with H&E. Epidermal thickness and rete ridge ratios (RRR) were measured. Gene and protein expression of involucrin (IVL) and filaggrin (FIL) were examined through qRT-PCR and immunofluorescent (IF) staining. After treatment, peeling sheets of stratum corneum were apparent which were not present in the controls. TEWL was increased in HTS vs NS at day 49, indicating decreased barrier function (P = .05). In the immediate group, TEWL was significantly decreased at week 4 (P < .05). The early group was not significantly different from NS at the prelaser timepoint. After four sessions, the epidermal thickness was significantly increased in treated scars in both FLSR groups (immediate: P < .01 and early: P < .001, n = 8 scars). Early intervention significantly increased RRR (P < .05), and immediate treatment trended toward an increase. There was no increase in either epidermal thickness or RRR in the controls. In the immediate intervention group, there was increased IVL gene expression in HTS vs NS that decreased after FLSR. Eight scars had upregulated gene expression of IVL vs NS levels pretreatment (fold change [FC] > 1.5) compared to four scars at week 4. This was confirmed by IF where IVL staining decreased after FLSR. FIL gene expression trended towards a decrease in both interventions after treatment. Changes in epidermal HTS histoarchitecture and expression levels of epidermal differentiation markers were induced by FLSR. The timing of laser intervention contributed to differences in TEWL, epidermal thickness, and RRR. These data shed light on the putative mechanisms of improvement seen after FLSR treatment. Resolution of timing must be further explored to enhance efficacy. An increased understanding of the difference between the natural history of HTS improvement over time and interventional-induced changes will be critical to justifying the continued approved usage of this treatment.
激光治疗增生性瘢痕（HTS）改善的机制和时机尚不完全清楚。表皮角质形成细胞通过旁分泌信号影响 HTS，但与成纤维细胞相比，它们的研究较少。假设分数性消融 CO2 激光瘢痕修正（FLSR）将改变 HTS 表皮的纤维化组织形态。杜洛克猪（FLSR 组 n=4，对照组 n=4）受伤并形成 HTS。每周通过非侵入性皮肤探头测量经表皮水分流失（TEWL）和活检采集来评估 HTS 和正常皮肤（NS）。每周进行 4 次 FLSR 治疗。在受伤后 49 天（刚好在再上皮化后）开始即刻激光治疗，在受伤后 77 天开始早期治疗。取自 NS 和 HTS 的活检进行处理和 H&E 染色。测量表皮厚度和嵴状突起比（RRR）。通过 qRT-PCR 和免疫荧光（IF）染色检查 involucrin（IVL）和 filaggrin（FIL）的基因和蛋白表达。治疗后，在对照组中未发现的剥落的角质层明显存在。与 NS 相比，HTS 在第 49 天 TEWL 增加，表明屏障功能降低（P=.05）。在即刻组中，第 4 周 TEWL 显著降低（P<.05）。早期组在激光前时间点与 NS 无显著差异。经过 4 次治疗，在即刻和早期治疗组中，治疗性瘢痕的表皮厚度均显著增加（即刻：P<.01 和早期：P<.001，n=8 个瘢痕）。早期干预显著增加 RRR（P<.05），即刻治疗则呈增加趋势。对照组的表皮厚度或 RRR 均无增加。在即刻干预组中，与 NS 相比，HTS 的 IVL 基因表达增加，经 FLSR 后降低。与第 4 周的 4 个瘢痕相比，8 个瘢痕的 IVL 基因表达预处理时（FC>1.5）上调，与 NS 相比。这通过 FLSR 后 IVL 染色减少得到确认。FIL 基因表达在治疗后两种干预下均呈下降趋势。FLSR 诱导 HTS 表皮组织形态学和表皮分化标志物表达水平的改变。激光干预的时机导致 TEWL、表皮厚度和 RRR 的差异。这些数据阐明了 FLSR 治疗后观察到的改善的潜在机制。解决时间问题必须进一步探讨，以提高疗效。深入了解 HTS 随时间改善的自然史与干预诱导的变化之间的差异，对于证明这种治疗方法的持续批准使用至关重要。
