A model of wound healing in chronically radiation-damaged rat skin

Senescent fibroblast facilitates re-epithelization and collagen deposition in radiation-induced skin injury through IL-33-mediated macrophage polarization

BACKGROUND

The need for radiotherapy among the elderly rises with increasing life expectancy and a corresponding increase of elderly cancer patients. Radiation-induced skin injury is one of the most frequent adverse effects in radiotherapy patients, severely limiting their life quality. Re-epithelialization and collagen deposition have essential roles in the recovery of skin injuries induced by high doses of ionizing radiation. At the same time, radiation-induced senescent cells accumulate in irradiated tissues. However, the effects and mechanisms of senescent cells on re-epithelialization and collagen deposition in radiation-induced skin injury have not been fully elucidated.

RESULTS

Here, we identified a role for a population of senescent cells expressing p16 in promoting re-epithelialization and collagen deposition in radiation-induced skin injury. Targeted ablation of p16+ senescent cells or treatment with Senolytics resulted in the disruption of collagen structure and the retardation of epidermal coverage. By analyzing a publicly available single-cell sequencing dataset, we identified fibroblasts as a major contributor to the promotion of re-epithelialization and collagen deposition in senescent cells. Notably, our analysis of publicly available transcriptome sequencing data highlighted IL-33 as a key senescence-associated secretory phenotype produced by senescent fibroblasts. Neutralizing IL-33 significantly impedes the healing process. Finally, we found that the effect of IL-33 was partly due to the modulation of macrophage polarization.

CONCLUSIONS

In conclusion, our data suggested that senescent fibroblasts accumulated in radiation-induced skin injury sites participated in wound healing mainly by secreting IL-33. This secretion regulated the local immune microenvironment and macrophage polarization, thus emphasizing the importance of precise regulation of senescent cells in a phased manner.

Effects of hyperbaric oxygen therapy on rat facial skin

INTRODUCTION

We used immunohistochemistry to investigate the histopathologic effects of hyperbaric oxygen (HBO) on the facial skin of rats.

MATERIAL AND METHODS

Rats in the HBO group (n = 6) were placed in a 20 L HBO chamber at 2.5 atmospheres absolute at 25-26°C with 100% oxygen for 90 min/day for 7 days. Following euthanasia, sections of facial skin were removed for examination.

RESULTS

Epidermal hyperplasia and degeneration, basal-cell hypertrophy, subepithelial fibrosis, and increased connective tissue were observed in the HBO group. E-cadherin expression was reduced in the epidermis, hair follicles, and sebaceous glands in HBO-treated rats relative to control animals. HBO treatment was associated with vimentin immunoreactivity in fibroblasts, endothelial cells, and the bulbus pilorum of a subset of hair follicles. It also resulted in increased type IV collagen expression within the connective tissue in the hair follicles and sebaceous glands.

CONCLUSION

The HBO group demonstrated epidermal hyperplasia and degeneration, basal-cell hypertrophy, and subepithelial fibrosis. In addition, HBO decreased E-cadherin expression, which suggests that HBO may impair intracellular adhesion. Expression of vimentin and type IV collagen was also observed in the dermis. Increased connective tissue, hemorrhage, and mononuclear cell infiltration were observed in the dermis of HBO-treated animals. Thus, HBO has effects on the structures of the epidermis and dermis.

A synthetic superoxide dismutase/catalase mimetic EUK-207 mitigates radiation dermatitis and promotes wound healing in irradiated rat skin

In the event of a radionuclear attack or nuclear accident, the skin would be the first barrier exposed to radiation, though skin injury can progress over days to years following exposure. Chronic oxidative stress has been implicated as being a potential contributor to the progression of delayed radiation-induced injury to skin and other organs. To examine the causative role of oxidative stress in delayed radiation-induced skin injury, including impaired wound healing, we tested a synthetic superoxide dismutase (SOD)/catalase mimetic, EUK-207, in a rat model of combined skin irradiation and wound injury. Administered systemically, beginning 48 hours after irradiation, EUK-207 mitigated radiation dermatitis, suppressed indicators of tissue oxidative stress, and enhanced wound healing. Evaluation of gene expression in irradiated skin at 30 days after exposure revealed a significant upregulation of several key genes involved in detoxication of reactive oxygen and nitrogen species. This gene expression pattern was primarily reversed by EUK-207 therapy. These results demonstrate that oxidative stress has a critical role in the progression of radiation-induced skin injury, and that the injury can be mitigated by appropriate antioxidant compounds administered 48 hours after exposure.

Does hyperbaric oxygen administration before or after irradiation decrease side effects of irradiation on implant sites?

BACKGROUND

One of the main limitations of implant-based breast reconstruction is the high rate of complications such as capsular contracture and poor aesthetic outcome, due to adjuvant radiotherapy. Hyperbaric oxygen treatment (HBOT) has been used to assist wound healing in the prevention and treatment of the side effects of irradiation. We aimed to investigate this effect of HBOT on the capsule reaction and skin, applied before and after irradiation, following the placement of an implant under the dorsal skin of the rat.

METHODS

Fifteen Wistar rats were randomly divided into 3 groups. A 18-mL smooth testicular implant was introduced into a subcutaneous pocket located on the dorsum of each rat. A single dose of 17-Gy irradiation was given to the implanted area of each rat at the third week. HBOT which lasted 3 weeks was administered to group I before irradiation, group II after irradiation. The control group did not receive HBOT. All of the rats were killed at the ninth week (6 weeks after irradiation). The dorsal skin with the capsule overlying the implant were excised for histopathological processing. The thickness of the capsule reaction of each group was evaluated statistically.

RESULTS

Our histopathological examination revealed changes due to radiation in the control group. Many of these findings were found to be more subtle in group I and nearly absent in the group II. There was not any statistical difference between the thickness of the capsule reactions of the control group and group I, or group I and group II, but the capsular thickness of the control group was statistically higher than group II.

CONCLUSION

It can be predicted that the use of HBOT following irradiation is an effective tool to reduce the capsule reaction of the implanted area and the tissue damage seen in radiodermatitis.

Modifying normal tissue damage postirradiation. Report of a workshop sponsored by the Radiation Research Program, National Cancer Institute, Bethesda, Maryland, September 6-8, 2000

Late effects that develop in normal tissues adjacent to the tumor site in the months to years after radiotherapy can reduce the quality of life of cancer survivors. They can be dose-limiting and debilitating or life-threatening. There is now evidence that some late effects may be preventable or partially reversible. A workshop, "Modifying Normal Tissue Damage Postirradiation", was sponsored by the Radiation Research Program of the National Cancer Institute to identify the current status of and research needs and opportunities in this area. Mechanistic, genetic and physiological studies of the development of late effects are needed and will provide a rational basis for development of treatments. Interdisciplinary teams will be needed to carry out this research, including pathologists, physiologists, geneticists, molecular biologists, experts in functional imaging, wound healing, burn injury, molecular biology, and medical oncology, in addition to radiation biologists, physicists and oncologists. The participants emphasized the need for developing and choosing appropriate models, and for radiation dose-response studies to determine whether interventions remain effective at the radiation doses used clinically. Both preclinical and clinical studies require long-term follow-up, and easier-to-use, more objective clinical scoring systems must be developed and standardized. New developments in biomedical imaging should provide useful tools in all these endeavors. The ultimate goals are to improve the quality of life and efficacy of treatment for cancer patients treated with radiotherapy.

Therapeutic ultrasound and wound closure: lack of healing effect on x-ray irradiated wounds in murine skin

OBJECTIVE

To evaluate the efficacy of ultrasonography as a therapeutic agent in wound healing.

DESIGN

Randomized, controlled trial.

SETTING

University animal laboratory.

ANIMALS

Male BALB/c mice randomly allocated to 5 groups.

INTERVENTIONS

In group 1, mice were left untreated; in groups 2 through 5, a well-defined area on the dorsum was exposed to 20Gy x-ray irradiation. Seventy-two hours postirradiation, all mice were anesthetized by inhalation (isoflurane anesthetic) and a 7 x 7mm area wound made on the dorsum. All wounds were videotaped alongside a marker scale 3 times weekly until closure was complete. Mice in groups 4 and 5 were treated with pulsed therapeutic ultrasound for 5 minutes, 3 times weekly at 1 and 3MHz, respectively (intensity, 0.5W/cm(2)); mice in group 3 received placebo ultrasound. Subsequently, the area of each wound was measured from video by using an image analysis system.

MAIN OUTCOME MEASURE

Wound closure as a fraction of day zero.

RESULTS

Irradiation caused a significant (p < .01) delay in the rate of wound closure by day 11. However, neither placebo ultrasound nor treatment at 1 or 3MHz affected the closure rate.

CONCLUSION

These findings provide little evidence that 1 or 3MHz ultrasound applied to a radiation-impaired wound stimulates wound closure in mice.

Effects of External Beam Irradiation on the TRAM Flap: An Experimental Model

The rat model of the transverse rectus abdominis musculocutaneous (TRAM) flap was used in the present study to determine the effects of external beam radiation on myocutaneous flap histology and pathophysiology. A total of 57 adult Sprague-Dawley rats underwent a TRAM procedure. A pilot study with 17 animals was first performed to determine proper radiation dosages, and the remaining 40 rats were then used in the definitive study. In half of the definitive study group, the flaps were subjected to fractionated doses of external beam radiation, whereas the other half served as controls. Six weeks after the last radiation dose, all animals were killed and the flaps were harvested for mechanical assessment and histopathologic evaluation. All TRAM flaps survived in both groups. The irradiated and nonirradiated flaps were minimally distinguishable in viscoelastic properties, as well as by histopathologic examination. Growth of the flap in the irradiated animals was significantly diminished (48 percent average surface area increase in irradiated flaps, versus 92 percent increase in nonirradiated flaps, p < 0.05). These findings suggest that the myocutaneous flap is relatively resistant to some of the known adverse affects of radiation on living tissues.

Allograft dermal implant (AlloDerm) in a previously irradiated field

OBJECTIVE

To evaluate the integration of AlloDerm (LifeCell Corp., The Woodlands, TX) in a field exposed to external-beam radiation (EBR) by analyzing graft thickness, fibroblast recellularization, and neovascularization.

STUDY DESIGN

Randomized control.

METHODS

Thirty-six male Sprague-Dawley rats (n = 36) were randomly assigned to four groups. One hind leg of each rat was exposed to 20 Gy of EBR; the other limb served as the nonirradiated control. Two weeks after irradiation, AlloDerm was implanted into both hind legs. Grafts were harvested at 3, 4, 6, and 14 weeks after implantation and underwent histological analyses.

RESULTS

There was no statistically significant difference in graft thickness, fibroblast count, or neovascularization between the grafts placed in the irradiated bed and the controls (n = 33, P = .332, P = .336, and P = .057, respectively). However, at week 3, fibroblast counts in the graft placed in the field exposed to EBR were significantly lower than those of controls (P = .019), although at week 14 the counts in the experimental limb were higher than those of the controls (P = .002). Graft thickness (P = .001) and fibroblast count (P < .004) were lower at week 14 than at earlier time periods for both the experimental and control grafts.

CONCLUSIONS

In the rat model, graft thickness and neovascularization of the AlloDerm dermal implant do not appear to be adversely affected by a field that has received EBR. Fibroblast ingrowth may be hindered in the early postimplantation period but appears to normalize in the long term. Furthermore, overall graft thickness and fibroblast counts decrease over time, regardless of irradiation status.