COMPARATIVE CHARACTERISTICS OF SKIN RECOVERY IN RATS AFTER ULTRAVIOLET IRRADIATION WITH AND WITHOUT ERBIUM LASER
Authors: Sulym Hryhorii , Lyndin Mykola , Shamrai Alevtyna , Lyndina Yuliia , Romaniuk Anatolii 
Published: October 2024

Introduction. Ultraviolet radiation, which has a significant biological impact among the spectrum of sunlight, can cause skin aging and tumors, but in controlled use it also has therapeutic effects on the skin. Ultraviolet radiation with a wavelength of 311 nm is used for phototherapy of skin diseases. Melanin, contained in melanosomes (MS), is produced in melanocytes (MC) during melanogenesis. Phototherapy can cause clinical hyperpigmentation by provoking an increase in the number of MCs. Ablative lasers, such as Er:YAG, are used to manage hyperpigmentation, but at the same time have the risk of causing hyperpigmentation. The frequency of such side effects varies from 10 to 46%.
The aim of the study was to determine changes in the number of MCs in the epidermis relative to the length of the basement membrane and the density of MSs in the epidermis in two groups of animals: after UV irradiation without and with an ablative laser.
Materials and methods. The study began with an imitation of phototherapy of dermatoses with narrow-band UV radiation. The animals were divided into 2 experimental groups: free readaptation, using laser and a separate control group (intact rats). Skin samples were taken from 54 rats: 12 animals per checkpoint (6 for each group) on days 31, 45, 61, and 121, and 6 animals in the control group. The melanocytic and melanosomal components of the epidermis were evaluated, and comparisons were made between groups and with intact animals.
Results. In the group of free readaptation on day 45, the density of MCs reached 0.78±0.16 cells per 100 mkm of basal membrane (units), which exceeded the normal value, but did not show statistical significance (p=0.37). On days 61 and 121, the density was 0.72±0.13 units and 0.70±0.17 units, respectively, which indicated a correlation with the elapsed time, r = -0.732, but at once was not significantly different from the control group.
In the laser hypopigmentation group, the density of MCs on the basement membrane was 0.68±0.26, 0.70±0.26 and 0.69±0.23 units on days 45, 61 and 121, respectively, demonstrating stability. The correlation between MCs density and time after UV irradiation was not taken into account (r = ‑0.485).
As for the analysis of MSs, in the control group, the area of MSs was 0.77±0.24% of the epidermis square. On day 31, the density of MSs reached a peak and amounted to 1.21±0.32%, statistically different from the control group (p=0.04).
Subsequently, in the group of free readaptation, the area of MSs decreased to 1.03±0.16% on day 45, 0.91±0.13% on day 61, and 0.91±0.25% on day 121. An inverse correlation was observed between the density of MSs and the elapsed time, r = -0.735.
Similar patterns were observed in the laser ablation group. On days 45, 61, and 121, the area of MSs was 1.07±0.28%, 0.92±0.22%, and 0.84±0.19%, respectively. The correlation between MSs density and time after UV irradiation was significant, r = -0.881.
Comparison of the density of MSs in the epidermis between the experimental groups did not reveal statistical differences at any stage of the experiment.
Conclusions. The described ultraviolet impact on the skin did not lead to a statistically significant increase in the number of MCs on the basal membrane (p=0.37), but significantly increased the area of MSs in the epidermis (p=0.04). Comparison of the density of MCs in the groups of laser hypopigmentation and free readaptation did not reveal statistically significant differences between each other and the control group. Laser ablation did not lead to either an increase or decrease in the average concentration of MSs in the epidermis compared to the free readaptation group.