## 3 Discussion
Our results indicate that snail mucus leads to decreased immunoexpression of Ki67, which is normal for healthy skin, and indicate the regenerative properties of snail filtrate. Comparing PCNA immunoassayn before and 3 months after the treatment, a 2-fold decrease in the area of positively stained nuclei in the epidermis (8.71% vs. 4.31%) was observed in patients who received snail mucus in combination with micro-needle mesotherapy (group A). PCNA immunoexpression in the epidermis was also significantly reduced in the group of patients who received micro-needle mesotherapy without snail mucus (group B). In the dermis in group A and the needle-free mesotherapy group (group C), 3 months after the treatment, a significant increase in Ki-67 immunoexpression by 95.5% and 37%, respectively, was observed, compared to the results obtained from skin biopsy specimens taken before the treatment. PCNA immunoexpression also increased significantly in these patients by 82.7% and 72.9%, respectively, after treatment with the snail mucus preparation. This may be related to the increased regeneration of the dermis, initiated by the biostatulating properties of the ingredients contained in the snail mucus preparations. Similar results were obtained by [PERSON] et al. (2018) [45], who reported that snail mucus caused an increase in the proliferation index of fibroblasts, which are responsible for the synthesis of ECM components, including elastic fibers and collagen fibers. The effect of the treatments with snail mucus on the expression of metalloproteinase-2 (MMP-2) was also evaluated by immunohistochemistry. Comparing the results on the immunoexpression of MMP-2 before and after the treatment showed its significant increase in patients who received micro-needle and needle-free mesotherapy with snail mucus (groups A and C) by 36% and 39.6%, respectively. Increased activity of metalloproteinases (MMPs) can be observed, among others, during angiogenesis, in the regeneration of damaged tissue and scar formation, as well as in pathological conditions, as an etiological factor in some skin diseases [5; 6]. Increased immunoexpression of MMP-2 in the skin of the patients in the present study may also indicate the regenerative properties of the formulation used in the study. The restorative properties attributed to snail mucus, including participation in the formation of ECM, initiation of granulation, stimulation of angiogenesis, as well as stimulation of skin remodeling, are related to the presence of many biologically active compounds in the mucus, including collagen, allantoin, elastin, glycolic and lactic acid, as well as GAGs [37]. Other findings regarding MMP-2 immunoexpression were reported by [PERSON] et al. (2021) [36]. After applying snail mucus filtrate to a wound in mice, they showed a reduction in the immunoexpression of MMPs. The authors additionally observed that the application of snail mucus filtrate contributed to increased expression of the COL3a1 marker, responsible for the synthesis of type III collagen fibers. However, it should be emphasized again that the study by [PERSON] et al. (2021) involves animal material [36]. Undoubtedly, it is difficult to unequivocally identify a more effective method of mesotherapy in terms of improving the condition of skin with photoaging features. Beneficial changes, indicative of a reduction in photoaging, regarding a decrease in epidermal thickness 3 months after the completion of the series of treatments were noted in each group. A statistically significant increase in the thickness of collagen fiber bundles was also observed in female patients 3 months after a series of micro-needle mesotherapy treatments with snail mucus and with 0.9% NaCl. Skin micro-needling, as a factor that stimulates remodeling processes, had a positive effect on the architecture of collagen fibers, which determines the firmness and mechanical tensile strength of the skin.