In vivo characterization of early-stage radiation skin injury in a mouse model by two-photon microscopy

Establishing an animal model for post-inflammatory hyperpigmentation following fractional CO2 laser application

BACKGROUND

Post-inflammatory hyperpigmentation (PIH) is a common cosmetic concern, often leading to significant psychological distress for the patients. With the widespread application of lasers including ablative fractional resurfacing (AFR) with a 10,600 nm CO2 laser, PIH caused by lasers is becoming increasingly common. But due to the absence of an appropriate animal research model, our understanding of pathophysiological mechanisms and preventive strategies for PIH remains limited.

METHODS

This study aimed to establish an animal model to investigate PIH following AFR CO2 laser application, focusing on the dynamic changes in melanin, inflammatory cytokines, growth factors, and skin structures as PIH developed. We employed pigmented guinea pigs as our experimental subjects and conducted our research in two phases. In the first phase, we utilized three modes of AFR CO2 laser to identify which laser mode could induce PIH by monitoring dynamic melanin changes. In the second phase, the laser mode that most reliably induced PIH was applied to re-establish the PIH model. Pathophysiological changes during PIH progression were investigated through histopathological observations, real-time quantitative polymerase chain reaction, and two-photon microscopy.

RESULTS

We successfully established a replicable animal model for PIH following AFR CO2 laser application. We observed a significant increase in inflammatory cytokines and growth factors within the skin tissue by the second week, with stable pigmentation becoming apparent by the third week.

CONCLUSIONS

Our research provides a promising animal model for understanding and further investigating the mechanisms of PIH after laser procedures.

EBM LEVEL

V (animal study).

Sea Buckthorn Oil Promotes the PI3K-Akt-ERK Signaling Pathway and Macrophage M2 Polarization to Reduce Radiation-induced Skin Injury

In this work, we explored the role and mechanism of sea buckthorn oil in reducing radiation-induced skin damage. The radiation-induced rat skin injury model was established using strontium-90. Rats were treated with sea buckthorn oil twice a day postirradiation, and skin damage was observed at different times and evaluated using an injury score. Skin pathological changes were observed using hematoxylin and eosin (H&E) staining. Western blotting and immunohistochemistry were used to detect the expression of vascular growth and pathway proteins. ELISA was used to detect the secretion level of inflammatory factors. Immunohistochemistry was used to detect macrophage polarization marker proteins. We found that sea buckthorn oil can alleviate radiation-induced skin damage, accelerate skin vascular regeneration, and promote the up-regulation of vascular endothelial growth factor (VEGF) and its receptor (VEGFR). These results demonstrate the beneficial effects of sea buckthorn oil on radiation-induced skin damage. Furthermore, the levels of IL-1β and TNF-α in the sea buckthorn oil treatment group were significantly lower than those in the control group, while the levels of IL-4 and IL10 were significantly higher (P < 0.05). CD206 expression also increased in the sea buckthorn oil treatment group, while CD16 expression decreased compared to the control group (P < 0.05). Western blotting showed that PI3K, Akt and ERK expression increased in the sea buckthorn oil treatment group (P < 0.05). The beneficial effect of sea buckthorn oil in reducing the inflammatory response in irradiated rats was diminished when they were treated with PI3K inhibitor. We conclude that sea buckthorn oil may regulate macrophage M2 polarization by increasing the PI3K-Akt-ERK signaling pathway, thereby inhibiting the inflammatory response and promoting skin vascular regeneration to prevent and treat radiation-induced skin damage.

Radiation dermatitis in the hairless mouse model mimics human radiation dermatitis

Over half of all people diagnosed with cancer receive radiation therapy. Moderate to severe radiation dermatitis occurs in most human radiation patients, causing pain, aesthetic distress, and a negative impact on tumor control. No effective prevention or treatment for radiation dermatitis exists. The lack of well-characterized, clinically relevant animal models of human radiation dermatitis contributes to the absence of strategies to mitigate radiation dermatitis. Here, we establish and characterize a hairless SKH-1 mouse model of human radiation dermatitis by correlating temporal stages of clinical and pathological skin injury. We demonstrate that a single ionizing radiation treatment of 30 Gy using 6 MeV electrons induces severe clinical grade 3 peak toxicity at 12 days, defined by marked erythema, desquamation and partial ulceration, with resolution occurring by 25 days. Histopathology reveals that radiation-induced skin injury features temporally unique inflammatory changes. Upregulation of epidermal and dermal TGF-ß1 and COX-2 protein expression occurs at peak dermatitis, with sustained epidermal TGF-ß1 expression beyond resolution. Specific histopathological variables that remain substantially high at peak toxicity and early clinical resolution, including epidermal thickening, hyperkeratosis and dermal fibroplasia/fibrosis, serve as specific measurable parameters for in vivo interventional preclinical studies that seek to mitigate radiation-induced skin injury.

Longitudinal Neuropathological Consequences of Extracranial Radiation Therapy in Mice

Cancer-related cognitive impairment (CRCI) is a consequence of chemotherapy and extracranial radiation therapy (ECRT). Our prior work demonstrated gliosis in the brain following ECRT in SKH1 mice. The signals that induce gliosis were unclear. Right hindlimb skin from SKH1 mice was treated with 20 Gy or 30 Gy to induce subclinical or clinical dermatitis, respectively. Mice were euthanized at 6 h, 24 h, 5 days, 12 days, and 25 days post irradiation, and the brain, thoracic spinal cord, and skin were collected. The brains were harvested for spatial proteomics, immunohistochemistry, Nanostring nCounter® glial profiling, and neuroinflammation gene panels. The thoracic spinal cords were evaluated by immunohistochemistry. Radiation injury to the skin was evaluated by histology. The genes associated with neurotransmission, glial cell activation, innate immune signaling, cell signal transduction, and cancer were differentially expressed in the brains from mice treated with ECRT compared to the controls. Dose-dependent increases in neuroinflammatory-associated and neurodegenerative-disease-associated proteins were measured in the brains from ECRT-treated mice. Histologic changes in the ECRT-treated mice included acute dermatitis within the irradiated skin of the hindlimb and astrocyte activation within the thoracic spinal cord. Collectively, these findings highlight indirect neuronal transmission and glial cell activation in the pathogenesis of ECRT-related CRCI, providing possible signaling pathways for mitigation strategies.

An Experimental Model of Proton-Beam-Induced Radiation Dermatitis In Vivo

Radiation dermatitis (RD) is one of the most common side effects of radiation therapy. However, to date, there is a lack of both specific treatments for RD and validated experimental animal models with the use of various sources of ionizing radiation (IR) applied in clinical practice. The aim of this study was to develop and validate a model of acute RD induced using proton radiation in mice. Acute RD (Grade 2-4) was obtained with doses of 30, 40, and 50 Gy, either with or without depilation. The developed model of RD was characterized by typical histological changes in the skin after irradiation. Moreover, the depilation contributed to a skin histology alteration of the irradiated mice. The assessment of animal vital signs indicated that there was no effect of proton irradiation on the well-being or general condition of the animals. This model can be used to develop effective therapeutic agents and study the pathogenesis of radiation-induced skin toxicity, including that caused by proton irradiation.

Effects of Radiation-Induced Skin Injury on Hyaluronan Degradation and Its Underlying Mechanisms

Radiation-induced skin injury (RISI) is a frequent and severe complication with a complex pathogenesis that often occurs during radiation therapy, nuclear incidents, and nuclear war, for which there is no effective treatment. Hyaluronan (HA) plays an overwhelming role in the skin, and it has been shown that UVB irradiation induces increased HA expression. Nevertheless, to the best of our knowledge, there has been no study regarding the biological correlation between RISI and HA degradation and its underlying mechanisms. Therefore, in our study, we investigated low-molecular-weight HA content using an enzyme-linked immunosorbent assay and changes in the expression of HA-related metabolic enzymes using real-time quantitative polymerase chain reaction and a Western blotting assay. The oxidative stress level of the RISI model was assessed using sodium dismutase, malondialdehyde, and reactive oxygen species assays. We demonstrated that low-molecular-weight HA content was significantly upregulated in skin tissues during the late phase of irradiation exposure in the RISI model and that HA-related metabolic enzymes, oxidative stress levels, the MEK5/ERK5 pathway, and inflammatory factors were consistent with changes in low-molecular-weight HA content. These findings prove that HA degradation is biologically relevant to RISI development and that the HA degradation mechanisms are related to HA-related metabolic enzymes, oxidative stress, and inflammatory factors. The MEK5/ERK5 pathway represents a potential mechanism of HA degradation. In conclusion, we aimed to investigate changes in HA content and preliminarily investigate the HA degradation mechanism in a RISI model under γ-ray irradiation, to consider HA as a new target for RISI and provide ideas for novel drug development.

Connexin26 Modulates Radiation-Induced Skin Damage by Regulating Chemokine CCL27 through MAPK Signaling

Connexin26 (Cx26) plays an important role in ionizing radiation-induced damage, and CC chemokine ligand 27 (CCL27) regulates the skin immune response. However, the relationship between Cx26 and CCL27 in radiation-induced skin damage is unclear. After X-ray irradiation, clonogenic survival and micronucleus formation were assessed in immortalized human keratinocytes (HaCaT). Proteins in the mitogen activated protein kinase (MAPK) signaling pathway and CCL27-related proteins were detected by immunoblotting. HaCaTCx26-/- cells were constructed to verify the effects of Cx26 on CCL27 secretion. A mouse model was established to examine the expression of CCL27 and skin inflammation in vivo. The degree of skin injury induced by 6 MV of X rays was closely related to CCL27. The phosphorylation of ERK, p38 and NF-κB was significantly increased in irradiated cells. The secretion of CCL27 was significantly decreased in HaCaT wild-type cells relative to HaCaTCx26-/- cells. Whereas cell survival fractions decreased, and the micronuclei formation rate increased as a function of increasing X-ray dose in HaCaT cells, the opposite trend occurred in HaCaTCx26-/- cells. Our findings show that Cx26 likely plays a role in the activation of the MAPK and NF-κB/COX-2 signaling pathways and regulates the secretion of CCL27 in keratinocytes after X-ray radiation-induced skin damage.

Preclinical modeling of low energy X-rays radiological burn: Dosimetry study by monte carlo simulations and EPR spectroscopy

Interventional radiology has grown considerably over the last decades and become an essential tool for treatment or diagnosis. This technique is mostly beneficial and mastered but accidental overexposure can occur and lead to the appearance of deterministic effects. The lack of knowledge about the radiobiological consequences for the low-energy X-rays used for these practices makes the prognosis very uncertain for the different tissues. In order to improve the radiation protection of patients and better predict the risk of complications, we implemented a new preclinical mouse model to mimic radiological burn in interventional radiology and performed a complete characterization of the dose deposition. A new setup and collimator were designed to irradiate the hind legs of 15 mice at 30 Gy in air kerma at 80 kV. After irradiation, mice tibias were collected to evaluate bone dose by Electron Paramagnetic Resonance (EPR) spectroscopy measurements. Monte Carlo simulations with Geant4 were performed in simplified and voxelized phantoms to characterize the dose deposition in different tissues and evaluate the characteristics of secondary electrons (energy, path, momentum). 30 mice tibias were collected for EPR analysis. An average absorbed dose of 194.0 ± 27.0 Gy was measured in bone initially irradiated at 30 Gy in air kerma. A bone to air conversion factor of 6.5 ± 0.9 was determined. Inter sample and inter mice variability has been estimated to 13.9%. Monte Carlo simulations shown the heterogeneity of the dose deposition for these low X-rays energies and the dose enhancement in dense tissue. The specificities of the secondary electrons were studied and showed the influence of the tissue density on energies and paths. A good agreement between the experimental and calculated bone to air conversion factor was obtained. A new preclinical model allowing to perform radiological burn in interventional radiology-like conditions was implemented. For the development of new preclinical radiobiological model where the exact knowledge of the dose deposited in the different tissues is essential, the complementarity of Monte Carlo simulations and experimental measurements for the dosimetric characterization has proven to be a considerable asset.

The Potential of Photoacoustic Imaging in Radiation Oncology

Radiotherapy is recognized globally as a mainstay of treatment in most solid tumors and is essential in both curative and palliative settings. Ionizing radiation is frequently combined with surgery, either preoperatively or postoperatively, and with systemic chemotherapy. Recent advances in imaging have enabled precise targeting of solid lesions yet substantial intratumoral heterogeneity means that treatment planning and monitoring remains a clinical challenge as therapy response can take weeks to manifest on conventional imaging and early indications of progression can be misleading. Photoacoustic imaging (PAI) is an emerging modality for molecular imaging of cancer, enabling non-invasive assessment of endogenous tissue chromophores with optical contrast at unprecedented spatio-temporal resolution. Preclinical studies in mouse models have shown that PAI could be used to assess response to radiotherapy and chemoradiotherapy based on changes in the tumor vascular architecture and blood oxygen saturation, which are closely linked to tumor hypoxia. Given the strong relationship between hypoxia and radio-resistance, PAI assessment of the tumor microenvironment has the potential to be applied longitudinally during radiotherapy to detect resistance at much earlier time-points than currently achieved by size measurements and tailor treatments based on tumor oxygen availability and vascular heterogeneity. Here, we review the current state-of-the-art in PAI in the context of radiotherapy research. Based on these studies, we identify promising applications of PAI in radiation oncology and discuss the future potential and outstanding challenges in the development of translational PAI biomarkers of early response to radiotherapy.

Acute Radiation Dermatitis Evaluation with Reflectance Confocal Microscopy: A Prospective Study

Background: During radiotherapy (RT), most breast cancer patients experience ionizing radiation (IR)-induced skin injury—acute radiation dermatitis (ARD). The severity of ARD is determined by a physician according to CTCAE or RTOG scales, which are subjective. Reflectance confocal microscopy (RCM) is a noninvasive skin imaging technique offering cellular resolution. Digital dermoscopy (DD) performed in conjugation with RCM can provide more information regarding skin toxicity. The purpose of this study is to create an RCM and DD features-based ARD assessment scale, to assess the association with CTCAE scale and possible predictive value. Methods: One hundred and three breast cancer patients during RT were recruited; every week, clinical symptoms of ARD (CTCAE scale) were evaluated and RCM, together with digital dermoscopy (DD), was performed. Results: According to RCM; after 2 RT weeks, exocytosis and/or spongiosis were present in 94% of patients; after 3 weeks, mild contrast cells (MMCs) were detected in 45%; disarrayed epidermis (DE) was present in 66% of patients after 4 weeks and in 93% after 5 weeks; abnormal dermal papillae (ADP) were present in 68% of patients after 5 weeks. The coefficients of RCM features (RCM_coef) alone and together with dermoscopically determined erythema (RCM-ERY_coef) were significantly associated with ARD severity grade. RCM_coef is a significant predictive factor for the clinical manifestation of ARD. Conclusions: RCM features of irradiated skin appear earlier than clinical symptoms, have a characteristic course, and allow the severity of ARD to be predicted.

Animal and Human Models of Tissue Repair and Fibrosis: An Introduction

Reductionist cell culture systems are not only convenient but essential to understand molecular mechanisms of myofibroblast activation and action in carefully controlled conditions. However, tissue myofibroblasts do not act in isolation and the complexity of tissue repair and fibrosis in humans cannot be captured even by the most elaborate culture models. Over the past five decades, numerous animal models have been developed to study different aspects of myofibroblast biology and interactions with other cells and extracellular matrix. The underlying principles can be broadly classified into: (1) organ injury by trauma such as prototypical full thickness skin wounds or burns; (2) mechanical challenges, such as pressure overload of the heart by ligature of the aorta or the pulmonary vein; (3) toxic injury, such as administration of bleomycin to lungs and carbon tetrachloride to the liver; (4) organ infection with viruses, bacteria, and parasites, such as nematode infections of liver; (5) cytokine and inflammatory models, including local delivery or viral overexpression of active transforming growth factor beta; (6) "lifestyle" and metabolic models such as high-fat diet; and (7) various genetic models. We will briefly summarize the most widely used mouse models used to study myofibroblasts in tissue repair and fibrosis as well as genetic tools for manipulating myofibroblast repair functions in vivo.

Longitudinal MRI study after carbon ion and photon irradiation: shorter latency time for myelopathy is not associated with differential morphological changes

BACKGROUND

Radiation-induced myelopathy is a severe and irreversible complication that occurs after a long symptom-free latency time if the spinal cord was exposed to a significant irradiation dose during tumor treatment. As carbon ions are increasingly investigated for tumor treatment in clinical trials, their effect on normal tissue needs further investigation to assure safety of patient treatments. Magnetic resonance imaging (MRI)-visible morphological alterations could serve as predictive markers for medicinal interventions to avoid severe side effects. Thus, MRI-visible morphological alterations in the rat spinal cord after high dose photon and carbon ion irradiation and their latency times were investigated.

METHODS

Rats whose spinal cords were irradiated with iso-effective high photon (n = 8) or carbon ion (n = 8) doses as well as sham-treated control animals (n = 6) underwent frequent MRI measurements until they developed radiation-induced myelopathy (paresis II). MR images were analyzed for morphological alterations and animals were regularly tested for neurological deficits. In addition, histological analysis was performed of animals suffering from paresis II compared to controls.

RESULTS

For both beam modalities, first morphological alterations occurred outside the spinal cord (bone marrow conversion, contrast agent accumulation in the musculature ventral and dorsal to the spinal cord) followed by morphological alterations inside the spinal cord (edema, syrinx, contrast agent accumulation) and eventually neurological alterations (paresis I and II). Latency times were significantly shorter after carbon ions as compared to photon irradiation.

CONCLUSIONS

Irradiation of the rat spinal cord with photon or carbon ion doses that lead to 100% myelopathy induced a comparable fixed sequence of MRI-visible morphological alterations and neurological distortions. However, at least in the animal model used in this study, the observed MRI-visible morphological alterations in the spinal cord are not suited as predictive markers to identify animals that will develop myelopathy as the time between MRI-visible alterations and the occurrence of myelopathy is too short to intervene with protective or mitigative drugs.

Molecular effects of photon irradiation and subsequent aftercare treatment with dexpanthenol-containing ointment or liquid in 3D models of human skin and non-keratinized oral mucosa

This study aimed to investigate the molecular effects of radiation and subsequent aftercare treatment with dexpanthenol-containing ointment and liquid on established full-thickness 3D skin models depicting acute radiodermatitis and mucositis. To mimic radiomucositis and radiodermatitis, non-keratinized mucous membrane and normal human skin models were irradiated with 5 Gray. Afterwards, models were treated topically every second day with dexpanthenol-containing ointment or liquid in comparison with placebo and untreated controls. On day 7 after irradiation, histological examination showed impairments in irradiated models. In contrast, models treated with dexpanthenol-containing ointment or liquid showed a completely restored epidermal part. While gene expression profiling revealed an induction of genes related to a pro-inflammatory milieu, oxidative stress and an impaired epidermal differentiation after irradiation of the models, aftercare treatment with dexpanthenol-containing ointment or liquid revealed anti-oxidative and anti-inflammatory effects and had a positive effect on epidermal differentiation and structures important for physical and antimicrobial barrier function. Our findings confirm the potential of our established models as in vitro tools for the replacement of pharmacological in vivo studies regarding radiation-induced skin injuries and give indications of the positive effects of dexpanthenol-containing externals after radiation treatments as part of supportive tumor treatment.

Evaluation of proton beam radiation-induced skin injury in a murine model using a clinical SOBP

The purpose of this paper is to characterize the skin deterministic damage due to the effect of proton beam irradiation in mice occurred during a long-term observational experiment. This study was initially defined to evaluate the insurgence of myelopathy irradiating spinal cords with the distal part of a Spread-out Bragg peak (SOBP). To the best of our knowledge, no study has been conducted highlighting high grades of skin injury at the dose used in this paper. Nevertheless these effects occurred. In this regard, the experimental evidence of significant insurgence of skin injury induced by protons using a SOBP configuration will be shown. Skin damages were classified into six scores (from 0 to 5) according to the severity of the injuries and correlated to ED50 (i.e. the radiation dose at which 50% of animals show a specific score) at 40 days post-irradiation (d.p.i.). The effects of radiation on the overall animal wellbeing have been also monitored and the severity of radiation-induced skin injuries was observed and quantified up to 40 d.p.i.

Characterization of early-stage cutaneous radiation injury by using optical coherence tomography angiography

Cutaneous radiation injury (CRI) is a skin injury caused by exposure to high dose ionizing radiation (IR). Diagnosis and treatment of CRI is difficult due to its initial clinically latent period and the following inflammatory bursts. Early detection of CRI before clinical symptoms will be helpful for effective treatment, and various optical methods have been applied with limitations. Here we show that optical coherence tomography angiography (OCTA) could detect changes in the skin during the latent period in CRI mouse models non-invasively. CRI was induced on the mouse hindlimb with exposure to various IR doses and the injured skin regions were imaged longitudinally by OCTA until the onset of clinical symptoms. OCTA detected several changes in the skin including the skin thickening, the dilation of large blood vessels, and the irregularity in vessel boundaries. Some of OCTA findings were confirmed by histology. The study results showed that OCTA could be used for early CRI detection.

Optical coherence tomography-guided dynamic focusing for combined optical and mechanical scanning multimodal photoacoustic microscopy

To achieve fast imaging and large field of view (FOV), we improved our multimodal imaging system, which integrated optical resolution photoacoustic microscopy, optical coherence tomography (OCT), and confocal fluorescence microscopy in one platform, by combining optical scanning with mechanical scanning. To ensure good focusing of the objective lens over all the imaged area, we employed OCT-guided dynamic focusing. Different from our previous point-by-point dynamic focusing, we employed an area-by-area focusing adjustment strategy, in which each fast optical scanning area has a fixed focusing depth. We have demonstrated the performance of the system by imaging biological samples ex vivo (plant leaf) and in vivo (mouse ear). The system has achieved uniform resolution in an FOV of 10  mm  ×  10  mm with an imaging time of about 5 min.

Acute Skin Damage and Late Radiation-Induced Fibrosis and Inflammation in Murine Ears after High-Dose Irradiation

The use of different scoring systems for radiation-induced toxicity limits comparability between studies. We examined dose-dependent tissue alterations following hypofractionated X-ray irradiation and evaluated their use as scoring criteria. Four dose fractions (0, 5, 10, 20, 30 Gy/fraction) were applied daily to ear pinnae. Acute effects (ear thickness, erythema, desquamation) were monitored for 92 days after fraction 1. Late effects (chronic inflammation, fibrosis) and the presence of transforming growth factor beta 1 (TGFβ1)-expressing cells were quantified on day 92. The maximum ear thickness displayed a significant positive correlation with fractional dose. Increased ear thickness and erythema occurred simultaneously, followed by desquamation from day 10 onwards. A significant dose-dependency was observed for the severity of erythema, but not for desquamation. After 4 × 20 and 4 × 30 Gy, inflammation was significantly increased on day 92, whereas fibrosis and the abundance of TGFβ1-expressing cells were only marginally increased after 4 × 30 Gy. Ear thickness significantly correlated with the severity of inflammation and fibrosis on day 92, but not with the number of TGFβ1-expressing cells. Fibrosis correlated significantly with inflammation and fractional dose. In conclusion, the parameter of ear thickness can be used as an objective, numerical and dose-dependent quantification criterion to characterize the severity of acute toxicity and allow for the prediction of late effects.

Biochemical and Histopathological Evaluation of the Radioprotective Effects of Melatonin Against Gamma Ray-Induced Skin Damage

BACKGROUND

Radiotherapy is one of the treatment methods for cancers using ionizing radiations. About 70% of cancer patients undergo radiotherapy. Radiation effect on the skin is one of the main complications of radiotherapy and dose limiting factor. To ameliorate this complication, we used melatonin as a radioprotective agent due to its antioxidant and anti-inflammatory effects, free radical scavenging, improving overall survival after irradiation as well as minimizing the degree of DNA damage and frequency of chromosomal abrasions.

METHODS

Sixty male Wistar rats were randomly assigned to 4 groups: control (C), melatonin (M), radiation (R) and melatonin + radiation (MR). A single dose of 30 Gy gamma radiation was exposed to the right hind legs of the rats while 40 mg/ml of melatonin was administered 30 minutes before irradiation and 2 mg/ml once daily in the afternoon for one month till the date of rat's sacrifice. Five rats from each group were sacrificed 4, 12 and 20 weeks after irradiation. Afterwards, their exposed skin tissues were examined histologically and biochemically.

RESULTS

In biochemical analysis, we found that malondialdehyde (MDA) levels significantly increased in R group and decreased significantly in M and MR groups after 4, 12, and 20 weeks, whereas catalase (CAT) and superoxide dismutase (SOD) activities decreased in the R group and increased in M and MR groups during the same time periods compared with the C group (p<0.05). Histopathological examination found there were statistically significant differences between R group compared with the C and M groups for the three different time periods (p<0.005, p<0.004 and p<0.004) respectively, while R group differed significantly with MR group (p<0.013). No significant differences were observed between C and M compared with MR group (p>0.05) at 4 and 20 weeks except for inflammation and hair follicle atrophy, while there were significant effects at 12 weeks (p<0.05).

CONCLUSION

Melatonin can be successfully used for the prevention and treatment of radiation-induced skin injury. We recommend the use of melatonin in optimal and safe doses. These doses should be administered over a long period of time for effective radioprotection and amelioration of skin damages as well as improving the therapeutic ratio of radiotherapy.

Integrated multimodal photoacoustic microscopy with OCT- guided dynamic focusing

Combining different contrast mechanisms to achieve simultaneous multimodal imaging is always desirable but is challenging due to the various optical and hardware requirements for different imaging systems. We developed a multimodal microscopic optical imaging system with the capability of providing comprehensive structural, functional and molecular information of living tissues. This imaging system integrated photoacoustic microscopy (PAM), optical coherence tomography (OCT), optical Doppler tomography (ODT) and confocal fluorescence microscopy in one platform. By taking advantage of the depth resolving capability of OCT, we developed a novel OCT-guided surface contour scanning methodology for dynamic focusing adjustment. We have conducted phantom, in vivo, and ex vivo tests to demonstrate the capability of the multimodal imaging system for providing comprehensive microscopic information of biological tissues. Integrating all the aforementioned imaging modalities with OCT-guided dynamic focusing for simultaneous multimodal imaging has promising potential for preclinical research and clinical practice in the future.

Monte Carlo GEANT4-based application for in vivo RBE study using small animals at LNS-INFN preclinical hadrontherapy facility

Preclinical studies represent an important step towards a deep understanding of the biological response to ionizing radiations. The effectiveness of proton therapy is higher than photons and, for clinical purposes, a fixed value of 1.1 is used for the relative biological effectiveness (RBE) of protons considered 1.1. Recent in vitro studies have reported that the RBE along the spread-out Bragg peak (SOBP) is not constant and, in particular, the RBE value increases on the distal part of SOBP. The present work has been carried-out in the perspective of a preclinical hadrontherapy facility at LNS-INFN and was focused on the experimental preparation of an in vivo study concerning the RBE variation along the SOBP. The main purpose of this work was to determine, using GEANT4-based Monte Carlo simulations, the best configuration for small animal treatments. The developed GEANT4 application simulates the proton-therapy beam line of LNS-INFN (CATANA facility) and allows to import the DICOM-CT images as targets. The RBE will be evaluated using a deterministic radiation damage like myelopathy as end-point. In fact, the dose at which the 50% of animals will show the myelopathy is supposed to be LET-dependent. In this work, we studied different treatment configurations in order to choose the best two that maximize the LET difference reducing as much as possible the dose released to healthy tissue. The results will be useful to plan hadrontherapy treatments for preclinical in vivo studies and, in particular, for the future in vivo RBE studies.

Impaired Skin Barrier Due to Sebaceous Gland Atrophy in the Latent Stage of Radiation-Induced Skin Injury: Application of Non-Invasive Diagnostic Methods

Radiation-induced skin injury can take the form of serious cutaneous damage and have specific characteristics. Asymptomatic periods are classified as the latent stage. The skin barrier plays a critical role in the modulation of skin permeability and hydration and protects the body against a harsh external environment. However, an analysis on skin barrier dysfunction against radiation exposure in the latent stage has not been conducted. Thus, we investigated whether the skin barrier is impaired by irradiation in the latent stage and aimed to identify the molecules involved in skin barrier dysfunction. We analyzed skin barrier function and its components in SKH1 mice that received 20 and 40 Gy local irradiation. Increased transepidermal water loss and skin pH were observed in the latent stage of the irradiated skin. Skin barrier components, such as structural proteins and lipid synthesis enzymes in keratinocyte, increased in the irradiated group. Interestingly, we noted sebaceous gland atrophy and increased serine protease and inflammatory cytokines in the irradiated skin during the latent period. This finding indicates that the main factor of skin barrier dysfunction in the latent stage of radiation-induced skin injury is sebaceous gland deficiency, which could be an intervention target for skin barrier impairment.

Visualization of laser tattoo removal treatment effects in a mouse model by two-photon microscopy

Laser tattoo removal is an effective method of eliminating tattoo particles in the skin. However, laser treatment cannot always remove the unwanted tattoo completely, and there are risks of either temporary or permanent side effects. Studies using preclinical animal models could provide detailed information on the effects of laser treatment in the skin, and might help to minimize side effects in clinical practices. In this study, two-photon microscopy (TPM) was used to visualize the laser treatment effects on tattoo particles in both phantom specimens and in vivo mouse models. Fluorescent tattoo ink was used for particle visualization by TPM, and nanosecond (ns) and picosecond (ps) lasers at 532 nm were used for treatment. In phantom specimens, TPM characterized the fragmentation of individual tattoo particles by tracking them before and after the laser treatment. These changes were confirmed by field emission scanning electron microscopy (FE-SEM). TPM was used to measure the treatment efficiency of the two lasers at different laser fluences. In the mouse model, TPM visualized clusters of tattoo particles in the skin and detected their fragmentation after the laser treatment. Longitudinal TPM imaging observed the migration of cells containing tattoo particles after the laser treatment. These results show that TPM may be useful for the assessment of laser tattoo removal treatment in preclinical studies.

Noninvasive assessment of cutaneous alterations in mice exposed to whole body gamma irradiation using optical imaging techniques

We report the results of a study carried out to investigate the potential of optical techniques such as optical coherence tomography, Mueller matrix spectroscopy, and cross-polarization imaging for noninvasive monitoring of the ionizing radiation exposure-induced alterations in cutaneous tissue of mice. Radiation dose-dependent changes were observed in tissue microvasculature and tissue optical parameters like retardance and depolarization as early as 1 h post radiation exposure. Results suggest that these optical techniques may allow early detection of radiation dose-dependent alterations which could help in screening of population exposed to radiation.

Early biomarker for radiation-induced wounds: day one post-irradiation assessment using hemoglobin concentration measured from diffuse optical reflectance spectroscopy

Normal tissue radiation toxicities are evaluated subjectively and cannot predict the development of severe side-effects. Using a hand-held diffuse reflectance optical spectroscopy probe, we measured optical parameters in mouse skin 1-4 days after irradiation. Using a radiation toxicity model and a therapeutic mitigator described previously [BMC Cancer14, 614 (2014)], we found that hemoglobin (Hb) levels increased sharply 24 h after irradiation only in the irradiated group without the mitigator. This group also had the largest peak wound areas after 14 days. We conclude that increased Hb one day after skin irradiation predicts the severity of the subsequent irradiation-induced wound.