To measure collagen deposition, measurements of skin thickness in the irradiated area were performed. Each tissue section was divided into 10 equal sections and measurements of the four central sections were obtained to exclude edge artifacts from histologic processing. Raw data were analyzed by nSolver software NanoString Technologies using standard settings and were normalized against the housekeeping genes Abcf1, Hprt, and Oaz1 and fold changes of selected genes involved in inflammation and fibrosis were calculated. The association between treatment groups and the probability of chronic wound formation was analyzed using Fisher's exact test.
For the wound area analysis, the mean wound area for the mice at each time point was normalized by log2 transformation of the data. For the skin thickness measurements, the mean thickness based on the four central measured sections was obtained for each treatment group as well as the control area for each mouse. Representative images from the control and experimental groups over time are shown in Figure 2. Maximum injury was observed around 3—4 weeks postirradiation with erythema, moist desquamation, and ulceration present in both groups with a similar wound size observed in the PBM Initial resolution of the injury in both groups was apparent at 6 weeks postirradiation including substantial hair regrowth.
At 12 weeks postirradiation, recurrent ulceration was observed more often in the vehicle group. In the PBM group, either a decrease in size of the wound area or complete resolution of the wound was observed. However, there were mice in the PBM group that developed nonhealing wounds as well, as observed in the second row of the figure.
Therefore, week 1 on the graph represents either week 4 or 5 after irradiation. As seen in the graph, the wound area closure over time between the two groups was similar until 10 weeks postmaximum wound area at which point a separation between the two groups was observed.
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The difference between the groups became subsequently larger over time and at weeks 12, 13, and 14, a statistically significant difference between the two groups was observed. At 12 weeks postmaximum wound area, the PBM group wound area was At 13 weeks postmaximum wound area, the PBM group wound area was Finally, at 14 weeks postmaximum wound area, the PBM group wound area was 5.
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Mice were sacrificed at weeks 9 and 17 postirradiation and the irradiated and control skin from the abdomen was harvested for histologic analysis. When comparing the PBM to vehicle alone group, epidermal hyperplasia, hyperkeratosis, and inflammatory cell infiltrate was present and apparent in both groups when compared with the control skin which was not irradiated or treated. However, as reflected in the wound healing measurements, the area of skin where these histological changes were present was generally smaller in the PBM compared to the vehicle alone group.
Representative images from the 17 week postirradiation time point are shown in Figure 5. In the representative example shown, a continued degree of epidermal hyperplasia was present in the skin treated with PBM Figure 5 A and D , which was less severe than that observed in the vehicle alone group Figure 5 B and E. In addition, hyperkeratosis persisted in the vehicle alone group. As there was no statistically significant difference in skin thickness observed histologically between the PBM and vehicle groups at the 17 week postirradiation time point, gene expression analysis was performed to evaluate for differential expression of fibrosis and chronic inflammatory genes.
This analysis revealed no statistically significant difference between the vehicle and PBM groups in expression of inflammatory genes including Il1a, Il1b, and Il1rn as shown in Figure 7 A—C. Similarly, there was no statistically significant difference observed in fibrosis gene expression in the irradiated skin between the vehicle and PBM groups including Tgfb1, Spp1, and Stat3 as shown in Figure 7 D—F.
Skin is a relatively radiosensitive organ due to the presence of rapidly proliferating and maturing cells.
While a standardized approach for the treatment of severe CRI does not exist, 21 the mainstay is surgical excision and either skin grafting or flap placement. New lesions can appear weeks, months, or even years later, requiring excision with additional reconstruction, with many extremity cases ultimately ending in amputation. Francois et al. Horton et al.
Growth factors have also been shown to have wound healing activity in irradiated tissue. Osteoradionecrosis of the mandible is a serious complication of head and neck radiation therapy resulting in pain, possible infection, and even pathologic fracture. One study showed a benefit of PRP to aid in mucosal healing and postextraction socket closure following radiation therapy, 35 while a second study showed no benefit with the use of fresh PRP in decreasing pain or prevention of osteoradionecrosis.
Iervolino et al. In the remaining 3 patients, 2 developed progressive or metastatic disease and 1 patient had a partial response to treatment. PRP has also been used topically to treat mucosal ulcerations. Biologic therapies are expensive to produce.
PBM materials can be manufactured at a relatively low cost compared to other biologic products. In this study, the use of topical PBMs for the treatment of CRI was investigated using a commercially available ointment, Aquaphor, as a delivery vehicle. The dorsal surface of mice was exposed to a single high dose of 35 Gy to simulate an acute radiation exposure. Topical treatment was initiated at and after 24 hours of radiation exposure for a duration of 5 weeks. More complete healing and fewer recurrent ulcerations were observed in the PBM group compared to the vehicle group, representing an improvement in acute toxicity with PBM treatment.
Further, an evaluation of fibrosis and chronic inflammatory genes did not show a significant difference in gene expression between the PBM and vehicle groups at the 17 week postirradiation time point. An optimal formulation with the correct balance of factors may reduce both acute and late toxicity by promoting healing and preventing the formation of fibrosis. Potential issues have been suggested with the use of PBMs in the treatment of radiation related injuries. The application of PBMs for the treatment of radiation dermatitis in patients with malignancies treated with radiation therapy is of particular concern.
For many of the cancers where cutaneous radiation injury is a major issue, tumorigenesis has been associated with growth factor receptor signaling pathways including in head and neck cancer and soft tissue sarcoma. We note several limitations in this study. First, for this initial study, only one concentration of PBM was investigated using a single treatment schedule. It is possible that a different response would be observed by altering either the concentration of the product or by applying the material for a shorter or longer duration after radiation exposure which is the subject of future studies.
Second, this study was performed using a simple cutaneous wound healing model. Depending on the nature of the radiation exposure and in the event of an accompanying detonation, additional tissues are likely to be damaged including underlying bone and soft tissue with potential thermal burns. The goal of future studies is to investigate the use of PBMs for treatment of more complex tissue damage including combined thermal and radiation injuries.
Finally, it is difficult to compare the results of this study with those of other studies due to variation in irradiation technique. For this study, the skin received 35 Gy in a single exposure using kV beam energy which was verified with dosimetry.
Preventing and Treating Radiation Injuries and Illness
In this study, we demonstrated that PBMs may be used to help stimulate wound healing of cutaneous tissue following an acute exposure to a high dose of radiation. While PBMs were able to effectively mitigate acute toxicity following cutaneous radiation exposure, they were less effective at mitigating late toxicity including fibrosis. While this is a promising first study for the use of PBMs to treat cutaneous radiation injury, additional work is needed to fully realize the potential of these materials for the treatment of these challenging wounds.
The authors would like to thank James Sommerfield for fabrication of the mouse holder for radiation delivery as well as fabrication of the imaging device. Conflicts of Interest : Jason Smith, PhD, was an employee of Carmell Therapeutics while this study was being conducted, but did not perform the experiments or perform primary analysis of the data. This study was not funded by Carmell Therapeutics. Volume 27 , Issue 2. The full text of this article hosted at iucr.
If you do not receive an email within 10 minutes, your email address may not be registered, and you may need to create a new Wiley Online Library account. If the address matches an existing account you will receive an email with instructions to retrieve your username. Wound Repair and Regeneration Volume 27, Issue 2. Eric D. Jason D. Ahmet S. Phil G. Aashish D. Naduparambil K.