Large area fractional laser treatment of mouse skin increases energy expenditure

Abstract

Fractional laser (FL) treatment is a common dermatologic procedure that generates arrays of microscopic treatment zones separated by intact tissue, promoting fast wound healing. Using a mouse model, we introduced a large area fractional laser treatment (LAFLT) method to study metabolic effects. Using two laser modalities, ablative FL (AFL) and non-ablative FL (NAFL), and exposing different percentages of mice's total body surface area (TBSA), we followed changes in metabolic parameters in real time using metabolic cages. Additionally, body composition, markers of inflammation, neurohormonal signaling, and browning of adipocytes were investigated. LAFLT, especially in high TBSA groups, had specific metabolic effects such as significantly increased average daily energy expenditure, increased fat mass loss, systemic browning of adipocytes, and inflammatory states, without compromising other organs. The ability of LAFLT to stimulate metabolism in a controlled way could develop into a promising therapeutic treatment to induce positive metabolic changes that replace or augment systemic drugs.

Keywords: Biological sciences; Dermatology; Immunology; Photomedicine.

Graphical abstract

Figure 1

Metabolic cage data and treatment timeline After a 2-day acclimation period, baseline metabolic data were collected for 1 day. On the treatment day, mice were anesthetized, shaved, depilated, treated with an AFL or NAFL, and returned to the metabolic cages. 6 days after the treatment, mice were euthanized for tissue and organ collection. See also Table S1.

Figure 2

Metabolic cage analysis pre- and post-LAFLT (A–E) Average daily (A) energy expenditure, (B) respiratory exchange rate, (C) food consumption, (D) water consumption, and (E) Locomotor activity. All data are presented as means ± standard deviation. Differences were calculated using a non-parametric repeated measures ANOVA. p∗<0.05, p∗∗<0.001.

Figure 3

Body Composition changes after LAFLT (A–H) Body composition analysis pre and 6 days post-LAFLT showing the change in (A) body mass, (B) lean mass, and (C) fat mass. The (D) body, (E) lean, and (F) fat mass change pre and 6 days post-FL treatment. The (G) lean mass and (H) fat mass is expressed as % of the body weight. The control group received the same pretreatments (shaving, depilation, buprenorphine and ketamine/xylazine anesthesia) as the fractional laser treatment groups. Data are represented as mean ± SEM. Differences were calculated using t-test. p∗<0.05, p∗∗<0.001.

Figure 4

Skin changes after LAFLT Photographs of mice showing the surface healing response following LAFLT. The top row of photographs shows representative mice before FL treatment, the center row shows the same mice immediately after laser exposure, and the bottom row shows them 6 days post exposure. Immediately after laser treatment, a skin tightening effect could be observed. On day 6 post treatment, all laser thermal injuries healed scar-free, however, the AFL-High mice showed scabbing (∗), which was easily removed (∗∗), and presented an underneath intact, healthy skin with light erythema.

Figure 5

Histological changes of skin immediately and after 6 days of LAFLT The NBTC stain was used to highlight thermally injured tissue (loss of blue stain) immediately after laser exposure for: (A) Vertical and horizontal sections of a mouse skin treated with an AFL with energies of 17 mJ/pulse and 25% density as determined by the segmentation of thermally injured tissue. (B) Vertical and horizontal sections of mouse skin treated with a NAFL with energies of 8 mJ/pulse, 7 passes at 2.2% fractional density resulting in 15% fractional density as confirmed by the segmentation of the thermally injured tissue. (C) H&E histology 6 days post-LAFLT. Laser-induced lesions are outlined, and immune cell infiltrate is presented in higher magnification. Black arrows show fibroblasts, blue arrows show neutrophils, green arrows show histiocytes, yellow arrows show lymphocytes, and red arrows show foaming macrophages.

Figure 6

Cytokine and catecholamine response after LAFLT IL-6 and NA levels in FL-treated mice vs. control were determined on day 6. (A) IL-6 levels from AFL-High were statistically significant compared to sham groups (p = 0.003, one-way ANOVA). (B) The NA concentrations in all FL groups were not statistically significant compared to the sham group (p = 0.0784, one-way ANOVA). Data are represented as mean ± SEM. See also Figure S1.

Figure 7

Histological evaluation of livers on day 6 after LAFLT (A) H&E, (B) Oil red O, and (C) periodic acid Schiff stains. (D) Quantitative analysis of TG content of livers. (E) Quantitative analysis of ALT activity. See also Figures S2 and S3.