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64 S.Y. Lee et al. / Journal of Photochemistry and Photobiology B: Biology 88 (2007) 51–67 synthesized collagen from proteolytic degradation by MMPs. Future studies involving serial quantification of MMPs and TIMPs are merited to understand their roles in dermal matrix remodeling after LED therapy. There are some limitations in interpreting the changes in IL-6 and ICAM-1 because of the lack of consistency. IL-6 is known to increase in the acute inflammatory phase and to be induced by IL-1ß and TNF-a [51,52]. This does not correspond with our results, as the level of IL-6 decreased despite the increase of IL-1ß and TNF-a. On the other hand, ICAM-1 is known to mediate the antigen recognition process of T cells and leukocyte-endothelial cell interac- tion, and to elevate the inflammatory response through helping the extravasation of immune cells to recruit them to the target sites [53–56]. This adhesion molecule is also induced by IL-1ß and TNF-a [56]. Our results showed increases of ICAM-1 in group 1 and 3, but a decrease in group 2, in spite of the increase of the primary cytokines. More data from a study using a larger sample size are needed to investigate changes in IL-6 and ICAM-1 after LED phototherapy. Gap junctional intercellular communication (GJIC) by connexin channels is known to be vital for maintaining tis- sue homeostasis, growth control, development and synchro- nized response of cells to stimuli [57–60]. Cx43 is the main protein of which gap junctions are composed [57,59]. In human skin, Cx43 is primarily located in the interfollicular epidermis, throughout the spinous and granular cell layers and focally in the basal cell layer, and is also expressed in dermal fibroblasts, hair follicles, smooth muscle cells and endothelial cells [57]. Various kinds of skin tumors, includ- ing melanoma, are known to express decreased levels of Cx43 than normal skin [57,61–63]. During the early wound healing process, up-regulation of Cx43 is observed in smooth muscle cells and endothelial cells in the dermis, which is considered to mediate transendothelial migration of leukocytes through GJIC [57,64,65]. An in vitro study using normal human dermal fibroblast suggested that the increase of Cx43 expression may enhance GJIC, which results in improvement of the tissue strength [66]. In our study, the elevation of Cx43 mRNA was found in all treatment groups. Because light at 633 nm and 830 nm penetrates the epidermis and largely affects the dermis, it can be postulated that the increased Cx43 might be expressed by dermal components such as fibroblasts, hair follicle cells, or endothelial cells. It is our assumption that the increased expression of Cx43 might enhance cell-cell communication between these dermal components, espe- cially the fibroblasts, and make them synchronize the cellu- lar responses to the photobiostimulation effects from LED treatment to produce new collagen throughout a more extensive area, even in those areas not irradiated directly. We consider that this hypothesis may explain one of the reasons for the extensive increase of collagen in the entire dermis shown in our histological findings, where the dermal matrix remodeling appeared to have occurred in sites other than the directly stimulated region. Our hypothesis mentioned above can be understood in a similar context with the bystander effect theory. The bystander effect refers to a phenomenon where biological changes as a result of ionizing radiation occur also in cells that are not directly irradiated by the incident radiation [67]. So far this phenomenon has been mainly investigated in radiotherapy for cancers. In addition, there was an in vivo study which demonstrated that low-energy laser radiation-mediated enhanced wound healing had been observed in regions other than the directly irradiated sites, suggesting that the bystander effect may also occur in ben- eficial biological events [40]. The current understanding of the bystander effect is that irradiated cells may secret inter- cellular signaling molecules or that the gap junctional com- munication between irradiated cells and non-irradiated cells may play an important role in causing this phenome- non [67]. In the present study, we have demonstrated an induction of biologic signaling molecules such as pro- inflammatory cytokines and that of a major gap junction protein, which may suggest an enhanced gap junctional communication, after LED phototherapy. Therefore, it can be postulated that these changes might be a reflection of the LED therapy-mediated bystander effect, which might propagate the photobiomodulation effect between cells, even into the deeper dermis, and bring about the his- tological alterations of collagen and elastic fiber production to the dramatically large extent as illustrated by the histol- ogy in the present study. Further studies are necessary to verify our hypothesis and to investigate the exact mecha- nisms of action of LED photobiomodulation effects. Comparison of clinical efficacy between the three differ- ent treatment protocols showed some characteristics in each measured property. In terms of wrinkle severity, the percentage reduction was greatest after a combination of 830 and 633 nm LED treatment (group 3), while skin elas- ticity increased most remarkably after 830 nm alone treat- ment (group 1). On the other hand, the reduction of the amount of melanin was observed only after treatment with 633nm alone (group 2), and the patients’ satisfaction about skin brightening was also reported largely in group 2 (data not shown). In terms of the subjective global assess- ment, the proportion of highly satisfied patients with this therapy was highest in groups 1 and 3 in both of which the infrared LED head was used. Considering that skin rejuvenation aims at both wrinkle reduction and improve- ment of skin tone, we consider that the combination of 830 and 633 nm LED treatment would offer the best clinical effectiveness by combining the different bioadvantages pro- duced by these two wavelengths of light. Further studies will be merited to optimize the treatment protocols for LED phototherapy for skin rejuvenation. 5. Conclusions Our study results showed that LED phototherapy is an effective treatment for skin rejuvenation through objec- tively measured data and histological and ultrastructuralPDF Image | LED phototherapy for skin rejuvenation
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