Rho/ROCK pathway as a molecular target for modulation of intestinal radiation-induced toxicity

Protective effects of tauroursodeoxycholate against radiation-induced intestinal injury in a mouse model

In patients with high-level radiation exposure, gastrointestinal injury is the main cause of death. Despite the severity of damage to the gastrointestinal tract, no specific therapeutic option is available. Tauroursodeoxycholic acid (TUDCA) is a conjugated form of ursodeoxycholic acid that suppresses endoplasmic reticulum (ER) stress and regulates various cell-signaling pathways. We investigated the effect of TUDCA premedication in alleviating intestinal damage and enhancing the survival of C57BL/6 mice administered a lethal dose (15Gy) of focal abdominal irradiation. TUDCA was administered to mice 1 h before radiation exposure, and reduced apoptosis of the jejunal crypts 12 h after irradiation. At later timepoint (3.5 days), irradiated mice manifested intestinal morphological changes that were detected via histological examination. TUDCA decreased the inflammatory cytokine levels and attenuated the decrease in serum citrulline levels after radiation exposure. Although radiation induced ER stress, TUDCA pretreatment decreased ER stress in the irradiated intestinal cells. The effect of TUDCA indicates the possibility of radiation therapy for cancer in tumor cells. TUDCA did not affect cell proliferation and apoptosis in the intestinal epithelium. TUDCA decreased the invasive ability of the CT26 metastatic colon cancer cell line. Reduced invasion after TUDCA treatment was associated with decreased matrix metalloproteinase (MMP)-7 and MMP-13 expression, which play important roles in invasion and metastasis. This study shows a potential role of TUDCA in protecting against radiation-induced intestinal damage and inhibiting tumor cell migration without any radiation and radiation therapy effect.

Epigenetic regulation of TGF-β pathway and its role in radiation response

PURPOSE

Transforming growth factor (TGF-β) plays a dual role in tumor progression as well as a pivotal role in radiation response. TGF-β-related epigenetic regulations, including DNA methylation, histone modifications (including methylation, acetylation, phosphorylation, ubiquitination), chromatin remodeling and non-coding RNA regulation, have been found to affect the occurrence and development of tumors as well as their radiation response in multiple dimensions. Due to the significance of radiotherapy in tumor treatment and the essential roles of TGF-β signaling in radiation response, it is important to better understand the role of epigenetic regulation mechanisms mediated by TGF-β signaling pathways in radiation-induced targeted and non-targeted effects.

CONCLUSIONS

By revealing the epigenetic mechanism related to TGF-β-mediated radiation response, summarizing the existing relevant adjuvant strategies for radiotherapy based on TGF-β signaling, and discovering potential therapeutic targets, we hope to provide a new perspective for improving clinical treatment.

Inhibition of ROCK ameliorates pulmonary fibrosis by suppressing M2 macrophage polarisation through phosphorylation of STAT3

BACKGROUND

Emerging evidence provides mechanistic insights into the pathogenesis of pulmonary fibrosis (PF), and rare anti-PF therapeutic method has promising effect in its treatment. Rho-associated coiled-coil kinases (ROCK) inhibition significantly ameliorates bleomycin-induced PF and decreases macrophage infiltration, but the mechanism remains unclear. We established bleomycin and radiation-induced PF to identify the activity of WXWH0265, a newly designed unselective ROCK inhibitor in regulating macrophages.

METHODS

Bleomycin-induced PF was induced by intratracheal instillation and radiation-induced PF was induced by bilateral thoracic irradiation. Histopathological techniques (haematoxylin and eosin, Masson's trichrome and immunohistochemistry) and hydroxyproline were used to evaluate PF severity. Western blot, quantitative real-time reverse transcription-polymerase chain reaction and flow cytometry were performed to explore the underlying mechanisms. Bone marrow-derived macrophages (BMDMs) were used to verify their therapeutic effect. Clodronate liposomes were applied to deplete macrophages and to identify the therapeutic effect of WXWH0265.

RESULTS

Therapeutic administration of ROCK inhibitor ameliorates bleomycin-induced PF by inhibiting M2 macrophages polarisation. ROCK inhibitor showed no significant anti-fibrotic effect in macrophages-depleted mice. Treatment with WXWH0265 demonstrated superior protection effect in bleomycin-induced PF compared with positive drugs. In radiation-induced PF, ROCK inhibitor effectively ameliorated PF. Fibroblasts co-cultured with supernatant from various M2 macrophages phenotypes revealed that M2 macrophages stimulated by interleukin-4 promoted extracellular matrix production. Polarisation of M2 macrophages was inhibited by ROCK inhibitor treatment in vitro. The p-signal transducer and activator of transcription 3 (STAT3) in lung tissue and BMDMs was significantly decreased in PF in vivo and vitro after treated with ROCK inhibitors.

CONCLUSION

Inhibiting ROCK could significantly attenuate bleomycin- and radiation-induced PF by regulating the macrophages polarisation via phosphorylation of STAT3. WXWH0265 is a kind of efficient unselective ROCK inhibitor in ameliorating PF. Furthermore, the results provide empirical evidence that ROCK inhibitor, WXWH0265 is a potential drug to prevent the development of PF.

Herb-Partitioned Moxibustion Improves Crohn's Disease-Associated Intestinal Fibrosis by Suppressing the RhoA/ROCK1/MLC Pathway

Background and Aims

Intestinal fibrosis is one of the severe and common complications of Crohn's disease (CD), but the etiology and pathogenesis remain uncertain. The study intended to examine whether the effect of herb-partitioned moxibustion on rats with CD-associated intestinal fibrosis is associated with the RhoA/ROCK1/MLC pathway.

Methods

All experimental rats were randomly allocated into the normal control group (NC), model control group (MC), and herb-partitioned moxibustion group (HPM). Intestinal fibrosis was established in rats with CD by repeated rectal administrations of 2,4,6-trinitrobenzenesulfonic acid (TNBS). Herb-partitioned moxibustion was applied at the Qihai (CV6) and Tianshu (ST25) acupoints once daily for 10 days in the HPM group. In this study, histological changes were examined by hematoxylin and eosin (HE) staining; then, Masson's trichrome staining was used to assess the degree of fibrosis in each group. Experimental methods of immunohistochemistry, western blotting, and real-time PCR were applied to detect the levels of α-SMA, collagen III, RhoA, ROCK1, and p-MLC. Moreover, the double immunofluorescent staining for the colocalization of both α-SMA and ROCK1 was performed.

Results

Contrasted with the normal controls, the collagen deposition and fibrosis scores were increased in colonic tissue of model rats, and HPM decreased the collagen deposition and fibrosis scores. The protein of α-SMA and collagen III in the MC group exceeds that of the NC group; HPM decreased the expression of α-SMA and collagen III in rats with intestinal fibrosis. Similarly, the expression of RhoA, ROCK1, and p-MLC in model rats was obviously increased compared with normal controls; the expression of RhoA, ROCK1, and p-MLC was decreased after HPM. The coexpression of α-SMA and ROCK1 in rats with intestinal fibrosis was higher than normal rats.

Conclusion

HPM improves CD-associated intestinal fibrosis by suppressing the RhoA/ROCK1/MLC pathway.

Rho-Proteins and Downstream Pathways as Potential Targets in Sepsis and Septic Shock: What Have We Learned from Basic Research

Sepsis and septic shock are associated with acute and sustained impairment in the function of the cardiovascular system, kidneys, lungs, liver, and brain, among others. Despite the significant advances in prevention and treatment, sepsis and septic shock sepsis remain global health problems with elevated mortality rates. Rho proteins can interact with a considerable number of targets, directly affecting cellular contractility, actin filament assembly and growing, cell motility and migration, cytoskeleton rearrangement, and actin polymerization, physiological functions that are intensively impaired during inflammatory conditions, such as the one that occurs in sepsis. In the last few decades, Rho proteins and their downstream pathways have been investigated in sepsis-associated experimental models. The most frequently used experimental design included the exposure to bacterial lipopolysaccharide (LPS), in both in vitro and in vivo approaches, but experiments using the cecal ligation and puncture (CLP) model of sepsis have also been performed. The findings described in this review indicate that Rho proteins, mainly RhoA and Rac1, are associated with the development of crucial sepsis-associated dysfunction in different systems and cells, including the endothelium, vessels, and heart. Notably, the data found in the literature suggest that either the inhibition or activation of Rho proteins and associated pathways might be desirable in sepsis and septic shock, accordingly with the cellular system evaluated. This review included the main findings, relevance, and limitations of the current knowledge connecting Rho proteins and sepsis-associated experimental models.

Distinct contribution of Rac1 expression in cardiomyocytes to anthracycline-induced cardiac injury

Cardiotoxicity is the dose limiting adverse effect of anthracycline-based anticancer therapy. Inhibitor studies point to Rac1 as therapeutic target to prevent anthracycline-induced cardiotoxicity. Yet, supporting genetic evidence is still missing and the pathophysiological relevance of different cardiac cell types is unclear. Here, we employed a tamoxifen-inducible cardiomyocyte-specific rac1 knock-out mouse model (Rac1^{flox/flox/MHC-MerCreMer}) to investigate the impact of Rac1 expression in cardiomyocytes on cardiac injury following doxorubicin treatment. Distinctive stress responses resulting from doxorubicin treatment were observed, including upregulation of systemic markers of inflammation (IL-6, IL-1α, MCP-1), cardiac damage (ANP, BNP), DNA damage (i.e. DNA double-strand breaks (DSB)), DNA damage response (DDR) and cell death. Measuring the acute doxorubicin response, the serum level of MCP-1 was elevated, cardiac mRNA expression of Hsp70 was reduced and cardiac DDR was specifically enhanced in Rac1 deficient mice. The frequency of apoptotic heart cells remained unaffected by Rac1. Employing a subactue model, the number of doxorubicin-induced DSB was significantly reduced if Rac1 is absent. Yet, the doxorubicin-triggered increase in serum ANP and BNP levels remained unaffected by Rac1. Overall, knock-out of rac1 in cardiomyocytes confers partial protection against doxorubicin-induced cardiac injury. Hence, the data provide first genetic evidence supporting the view that pharmacological targeting of Rac1 is useful to widen the therapeutic window of anthracycline-based anticancer therapy by alleviating acute/subacute cardiomyocyte damage. Furthermore, considering published data obtained from the use of pharmacological Rac1 inhibitors, the results of our study indicate that Rac1-regulated functions of cardiac cell types others than cardiomyocytes additionally influence the adverse outcomes of anthracycline treatment on the heart.

Genetically modified lentiviruses that preserve microvascular function protect against late radiation damage in normal tissues

Improvements in cancer survival mean that long-term toxicities, which contribute to the morbidity of cancer survivorship, are being increasingly recognized. Late adverse effects (LAEs) in normal tissues after radiotherapy (RT) are characterized by vascular dysfunction and fibrosis causing volume loss and tissue contracture, for example, in the free flaps used for immediate breast reconstruction after mastectomy. We evaluated the efficacy of lentivirally delivered superoxide dismutase 2 (SOD2) overexpression and connective tissue growth factor (CTGF) knockdown by short hairpin RNA in reducing the severity of LAEs in an animal model of free flap LAEs. Vectors were delivered by intra-arterial injection, ex vivo, to target the vascular compartment. LVSOD2 and LVshCTGF monotherapy before irradiation resulted in preservation of flap volume or reduction in skin contracture, respectively. Flaps transduced with combination therapy experienced improvements in both volume loss and skin contracture. Both therapies reduced the fibrotic burden after irradiation. LAEs were associated with impaired vascular perfusion, loss of endothelial permeability, and stromal hypoxia, which were all reversed in the treatment model. Using a tumor recurrence model, we showed that SOD2 overexpression in normal tissues did not compromise the efficacy of RT against tumor cells but appeared to enhance it. LVSOD2 and LVshCTGF combination therapy by targeted, intravascular delivery reduced LAE severities in normal tissues without compromising the efficacy of RT and warrants translational evaluation as a free flap-targeted gene therapy.

Rho inhibition by lovastatin affects apoptosis and DSB repair of primary human lung cells in vitro and lung tissue in vivo following fractionated irradiation

Thoracic radiotherapy causes damage of normal lung tissue, which limits the cumulative radiation dose and, hence, confines the anticancer efficacy of radiotherapy and impacts the quality of life of tumor patients. Ras-homologous (Rho) small GTPases regulate multiple stress responses and cell death. Therefore, we investigated whether pharmacological targeting of Rho signaling by the HMG-CoA-reductase inhibitor lovastatin influences ionizing radiation (IR)-induced toxicity in primary human lung fibroblasts, lung epithelial and lung microvascular endothelial cells in vitro and subchronic mouse lung tissue damage following hypo-fractionated irradiation (4x4 Gy). The statin improved the repair of radiation-induced DNA double-strand breaks (DSBs) in all cell types and, moreover, protected lung endothelial cells from IR-induced caspase-dependent apoptosis, likely involving p53-regulated mechanisms. Under the in vivo situation, treatment with lovastatin or the Rac1-specific small molecule inhibitor EHT1864 attenuated the IR-induced increase in breathing frequency and reduced the percentage of γH2AX and 53BP1-positive cells. This indicates that inhibition of Rac1 signaling lowers IR-induced residual DNA damage by promoting DNA repair. Moreover, lovastatin and EHT1864 protected lung tissue from IR-triggered apoptosis and mitigated the IR-stimulated increase in regenerative proliferation. Our data document beneficial anti-apoptotic and genoprotective effects of pharmacological targeting of Rho signaling following hypo-fractionated irradiation of lung cells in vitro and in vivo. Rac1-targeting drugs might be particular useful for supportive care in radiation oncology and, moreover, applicable to improve the anticancer efficacy of radiotherapy by widening the therapeutic window of thoracic radiation exposure.

Rebamipide ameliorates radiation-induced intestinal injury in a mouse model

Radiation-induced enteritis is a major side effect in cancer patients undergoing abdominopelvic radiotherapy. Radiation exposure produces an uncontrolled inflammatory cascade and epithelial cell loss leading to impaired epithelial barrier function. The goal of this study was to determine the effect of rebamipide on regeneration of the intestinal epithelia after radiation injury. The abdomens of C57BL/6 mice were exposed to 13Gy of irradiation (IR) and then the mice were treated with rebamipide. Upon IR, intestinal epithelia were destroyed structurally at the microscopic level and bacterial translocation was increased. The intestinal damage reached a maximum level on day 6 post-IR and intestinal regeneration occurred thereafter. We found that rebamipide significantly ameliorated radiation-induced intestinal injury. In mice treated with rebamipide after IR, intestinal barrier function recovered and expression of the tight junction components of the intestinal barrier were upregulated. Rebamipide administration reduced radiation-induced intestinal mucosal injury. The levels of proinflammatory cytokines and matrix metallopeptidase 9 (MMP9) were significantly reduced upon rebamipide administration. Intestinal cell proliferation and β-catenin expression also increased upon rebamipide administration. These data demonstrate that rebamipide reverses impairment of the intestinal barrier by increasing intestinal cell proliferation and attenuating the inflammatory response by inhibiting MMP9 and proinflammatory cytokine expression in a murine model of radiation-induced enteritis.

Current Status of Targeted Radioprotection and Radiation Injury Mitigation and Treatment Agents: A Critical Review of the Literature

As more cancer patients survive their disease, concerns about radiation therapy-induced side effects have increased. The concept of radioprotection and radiation injury mitigation and treatment offers the possibility to enhance the therapeutic ratio of radiation therapy by limiting radiation therapy-induced normal tissue injury without compromising its antitumor effect. Advances in the understanding of the underlying mechanisms of radiation toxicity have stimulated radiation oncologists to target these pathways across different organ systems. These generalized radiation injury mechanisms include production of free radicals such as superoxides, activation of inflammatory pathways, and vascular endothelial dysfunction leading to tissue hypoxia. There is a significant body of literature evaluating the effectiveness of various treatments in preventing, mitigating, or treating radiation-induced normal tissue injury. Whereas some reviews have focused on a specific disease site or agent, this critical review focuses on a mechanistic classification of activity and assesses multiple agents across different disease sites. The classification of agents used herein further offers a useful framework to organize the multitude of treatments that have been studied. Many commonly available treatments have demonstrated benefit in prevention, mitigation, and/or treatment of radiation toxicity and warrant further investigation. These drug-based approaches to radioprotection and radiation injury mitigation and treatment represent an important method of making radiation therapy safer.

The TLR4-associated phospholipase D1 activation is crucial for Der f 2-induced IL-13 production

BACKGROUND

House dust mites (HDMs) are the most important source of indoor aeroallergens that contribute to the rising incidence of allergic diseases such as allergic asthma. The major HDM, Der f 2, induces inflammatory cytokine expression. Little is known about the signaling pathway involved.

OBJECTIVE

We wanted to define the Der f 2 signaling pathway from its receptor to the transcription factor responsible for IL-13 expression and production.

METHODS

Human bronchial epithelial cells were stimulated with Der f 2. The release and gene expression of IL-13 were measured by means of ELISA and RT-PCR, respectively. In the airway inflammation mouse model, airway responses were assessed using ELISA, histology, BAL fluid, and methacholine responsiveness.

RESULTS

Here, we show that Der f 2 binds to TLR4 and induces IL-13 expression and production. In the airway inflammation mouse model, Der f 2-induced IL-13 production significantly decreased with treatment of TAK-242, a novel TLR4 inhibitor. Activation of TLR4 by Der f 2 requires the recruitment and activation of Syk, which leads to phosphorylation of PLCγ and membrane translocation of PKCα. p38 MAPK is then activated by PKCα and stimulates PLD1 activity by phosphorylating the Thr147 residue of PLD1. PLD1 activation enhanced binding of ROCK1 to ATF-2 and leads to increased expression of IL-13.

CONCLUSION

Our data extend the knowledge for a variety of possible roles of PLD1 in allergic disorders including asthma pathogenesis and suggest possible candidacy of PLD1 as a molecular target for novel therapeutic approaches.

Rho Kinase (ROCK) Inhibitors and Their Therapeutic Potential

Rho kinases (ROCKs) belong to the serine-threonine family, the inhibition of which affects the function of many downstream substrates. As such, ROCK inhibitors have potential therapeutic applicability in a wide variety of pathological conditions including asthma, cancer, erectile dysfunction, glaucoma, insulin resistance, kidney failure, neuronal degeneration, and osteoporosis. To date, two ROCK inhibitors have been approved for clinical use in Japan (fasudil and ripasudil) and one in China (fasudil). In 1995 fasudil was approved for the treatment of cerebral vasospasm, and more recently, ripasudil was approved for the treatment of glaucoma in 2014. In this Perspective, we present a comprehensive review of the physiological and biological functions for ROCK, the properties and development of over 170 ROCK inhibitors as well as their therapeutic potential, the current status, and future considerations.

A Novel In Vivo Protocol for Molecular Study of Radiation-Induced Fibrosis in Head and Neck Cancer Patients

OBJECTIVES

Radiation-induced fibrosis is a common complication for patients following head and neck cancer treatment. This study presents a novel minimally invasive protocol for molecular study of fibrosis in the stromal tissues.

METHODS

Subjects with radiation-induced fibrosis in the head and neck who were at least 6 months post treatment received submental core needle biopsies, followed by molecular processing and quantification of gene expression for 14 select pro-inflammatory and pro-fibrotic genes. Control biopsies from the upper arm were obtained from the same subjects. Patients were followed up at 1 and 2 weeks to monitor for safety and adverse outcomes.

RESULTS

Six subjects were enrolled and completed the study. No subjects experienced adverse outcomes or complication. An 18 gauge core biopsy needle with a 10 mm notch inserted for up to 60 seconds was needed. Subcutaneous tissue yielded 3 ng of RNA, amplified to 6 µg of cDNA, allowing for adequately sensitive quantitative polymerase chain reaction (qPCR) analysis of approximately 28 genes.

CONCLUSIONS

This study demonstrates the safety and utility of a novel technique for the molecular study of fibrosis in head and neck cancer patients. Longitudinal studies of patients undergoing radiation therapy will allow for identification of molecular targets that contribute to the process of fibrosis in the head and neck.

Rho GTPases: Novel Players in the Regulation of the DNA Damage Response?

The Ras-related C3 botulinum toxin substrate 1 (Rac1) belongs to the family of Ras-homologous small GTPases. It is well characterized as a membrane-bound signal transducing molecule that is involved in the regulation of cell motility and adhesion as well as cell cycle progression, mitosis, cell death and gene expression. Rac1 also adjusts cellular responses to genotoxic stress by regulating the activity of stress kinases, including c-Jun-N-terminal kinase/stress-activated protein kinase (JNK/SAPK) and p38 kinases as well as related transcription factors. Apart from being found on the inner side of the outer cell membrane and in the cytosol, Rac1 has also been detected inside the nucleus. Different lines of evidence indicate that genotoxin-induced DNA damage is able to activate nuclear Rac1. The exact mechanisms involved and the biological consequences, however, are unclear. The data available so far indicate that Rac1 might integrate DNA damage independent and DNA damage dependent cellular stress responses following genotoxin treatment, thereby coordinating mechanisms of the DNA damage response (DDR) that are related to DNA repair, survival and cell death.

Glucagon-like peptide-1 protects against cardiac microvascular endothelial cells injured by high glucose

OBJECTIVE

To investigate the protective effect of glucagon-like peptid-1 (GLP-1) against cardiac microvascular endothelial cell (CMECs) injured by high glucose.

METHODS

CMECs were isolated and cultured. Superoxide assay kit and dihydroethidine (DHE) staining were used to assess oxidative stress. TUNEL staining and caspase 3 expression were used to assess the apoptosis of CMECs. H89 was used to inhibit cAMP/PKA pathway; fasudil was used to inhibit Rho/ROCK pathway. The protein expressions of Rho, ROCK were examined by Western blot analysis.

RESULTS

High glucose increased the production of ROS, the activity of NADPH, the apoptosis rate and the expression level of Rho/ROCK in CMECs, while GLP-1 decreased high glucose-induced ROS production, the NADPH activity and the apoptosis rate and the expression level of Rho/ROCK in CMECs, the difference were statistically significant (P<0.05).

CONCLUSIONS

GLP-1 could protect the cardiac microvessels against oxidative stress and apoptosis. The protective effects of GLP-1 are dependent on downstream inhibition of Rho through a cAMP/PKA-dependent manner, resulting in a subsequent decrease in the expression of NADPH oxidase.

Chronic heart damage following doxorubicin treatment is alleviated by lovastatin

The anticancer efficacy of anthracyclines is limited by cumulative dose-dependent early and delayed cardiotoxicity resulting in congestive heart failure. Mechanisms responsible for anthracycline-induced heart damage are controversially discussed and effective preventive measures are preferable. Here, we analyzed the influence of the lipid lowering drug lovastatin on anthracycline-induced late cardiotoxicity three month after treatment of C57BL/6 mice with five low doses of doxorubicin (5×3mg/kg BW; i.p.). Doxorubicin increased the cardiac mRNA levels of BNP, IL-6 and CTGF, while the expression of ANP remained unchanged. Lovastatin counteracted these persisting cardiac stress responses evoked by the anthracycline. Doxorubicin-induced fibrotic alterations were neither detected by histochemical collagen staining of heart sections nor by analysis of the mRNA expression of collagens. Extensive qRT-PCR-array based analyses revealed a large increase in the mRNA level of heat shock protein Hspa1b in doxorubicin-treated mice, which was mitigated by lovastatin co-treatment. Electron microscopy together with qPCR-based analysis of mitochondrial DNA content indicate that lovastatin attenuates doxorubicin-stimulated hyperproliferation of mitochondria. This was not paralleled by increased expression of oxidative stress responsive genes or senescence-associated proteins. Echocardiographic analyses disclosed that lovastatin protects from the doxorubicin-induced decrease in the left ventricular posterior wall diameter (LVPWD), while constrictions in fractional shortening (FS) and ejection fraction (EF) evoked by doxorubicin were not amended by the statin. Taken together, the data suggest beneficial effects of lovastatin against doxorubicin-induced delayed cardiotoxicity. Clinical studies are preferable to scrutinize the usefulness of statins for the prevention of anthracycline-induced late cardiotoxicity.

Epac contributes to cardiac hypertrophy and amyloidosis induced by radiotherapy but not fibrosis

BACKGROUND

Cardiac toxicity is a side-effect of anti-cancer treatment including radiotherapy and this translational study was initiated to characterize radiation-induced cardiac side effects in a population of breast cancer patients and in experimental models in order to identify novel therapeutic target.

METHODS

The size of the heart was evaluated in CO-HO-RT patients by measuring the Cardiac-Contact-Distance before and after radiotherapy (48months of follow-up). In parallel, fibrogenic signals were studied in a severe case of human radiation-induced pericarditis. Lastly, radiation-induced cardiac damage was studied in mice and in rat neonatal cardiac cardiomyocytes.

RESULTS

In patients, time dependent enhancement of the CCD was measured suggesting occurrence of cardiac hypertrophy. In the case of human radiation-induced pericarditis, we measured the activation of fibrogenic (CTGF, RhoA) and remodeling (MMP2) signals. In irradiated mice, we documented decreased contractile function, enlargement of the ventricular cavity and long-term modification of the time constant of decay of Ca(2+) transients. Both hypertrophy and amyloid deposition were correlated with the induction of Epac-1; whereas radiation-induced fibrosis correlated with Rho/CTGF activation. Transactivation studies support Epac contribution in hypertrophy stimulation and showed that radiotherapy and Epac displayed specific and synergistic signals.

CONCLUSION

Epac-1 has been identified as a novel regulator of radiation-induced hypertrophy and amyloidosis but not fibrosis in the heart.

Rac1 modulates acute and subacute genotoxin-induced hepatic stress responses, fibrosis and liver aging

To investigate the importance of the Ras-homologous GTPase Rac1 for the hepatic response to genotoxic insults and liver aging, rac1 was deleted in liver of mice by Mx1-Cre-based recombination. Knockout of rac1 caused complex changes in basal as well as doxorubicin and ionizing radiation-induced mRNA expression of various genotoxic stress response-related genes, including hspa1b, rad51, wrn and xpc. Rac1 deletion protected the liver from acute toxicity following doxorubicin treatment. Moreover, the level of S139 phosphorylated histone H2AX (γH2AX), which is indicative of DNA damage, and mRNA expression of pro-inflammatory (IL-6) and pro-fibrotic (CTGF, TGFβ, αSMA) factors were mitigated in rac1 knockout animals. By contrast, lack of rac1 promoted subacute hepatotoxicity, which was determined 3 weeks after injection of multiple low doses of doxorubicin by assaying the γH2AX level, mitotic index and pro-fibrotic gene expression. Regarding ionizing radiation, rac1 deficiency had no major effects on DNA damage induction or acute pro-inflammatory and pro-fibrotic stress responses. Mice lacking hepatic rac1 for extended period of time (15 months) revealed increased mRNA expression of fibrosis-related factors (CTGF, TGFβ, collagen, MMP1) and fibrotic tissue remodeling. In addition, protein expression of the senescence marker p16 was enhanced in the absence of rac1. Taken together, the data provide evidence that Rac1 is required for doxorubicin-induced DNA damage induction. It is also involved in both the acute and delayed inflammatory and fibrotic stress response in the liver following doxorubicin, but not ionizing radiation, treatment and, furthermore, protects against endogenous liver aging.

Evidence of delayed gastrointestinal syndrome in high-dose irradiated mice

The acute effects of irradiation on the gastrointestinal (GI) system are well documented, but the longer-term effects are less well known. Increased incidence of adenocarcinoma has been noted, but apart from descriptions of fibrosis, the development of other pathologies specific to survivors of acute radiation is poorly understood. Samples were taken from C57BL/6 mice irradiated with partial-body irradiation where the thorax, head, and forelimbs were shielded (i.e., sparing 40% of the bone marrow). Tissue from age-matched controls was also collected. There were clear pathological changes in the intestine associated with DEARE (Delayed Effects of Acute Radiation Exposure) at doses greater than 12 Gy, with a dose-related increase in observed pathologies. Mice maintained on the synthetic antibiotic ciprofloxacin during the acute phase (days 4 to 20), however, had a lower or delayed incidence of symptoms. After 20 d, mice developed structures similar to early adenomas. Abnormally high levels of apoptotic and mitotic cells were present in some crypts, along with the early adenomas, suggesting tissue regeneration and areas of deregulated cell turnover. Over time, there was inhibited crypt cell proliferation in animals with advanced symptoms, a blunting of the crypts and villi, and an enlargement of villus girth, with an increasingly acellular and fibrotic extracellular matrix (a characteristic that has been demonstrated previously in aging mice). Together these changes may lead to a reduced functional surface area and less motile intestine. These observations are similar to those seen in geriatric animals, suggesting a premature aging of the GI tract.

Therapeutic management of intestinal fibrosis induced by radiation therapy: from molecular profiling to new intervention strategies et vice et versa

Chronic toxicities of locoregional and systemic oncological treatments commonly develop in long-term cancer survivors. Amongst these toxicities, post-radiotherapeutic complications alter patient's quality of life. Reduction of exposure of normal tissues can be achieved by optimization of radiotherapy. Furthermore, understanding of the fibrogenic mechanisms has provided targets to prevent, mitigate, and reverse late radiation-induced damages. This mini-review shows how (i) global molecular studies using gene profiling can provide tools to develop new intervention strategies and (ii) how successful clinical trials, conducted in particular with combined pentoxifylline-vitamin E, can take benefice of biological and molecular evidences to improve our understanding of fibrogenic mechanisms, enhance the robustness of proposed treatments, and lead ultimately to better treatments for patient's benefice.

Fibroproliferative disorders and their mechanobiology

Benign and malignant fibroproliferative disorders (FPDs) include idiopathic pulmonary fibrosis, hepatic cirrhosis, myelofibrosis, systemic sclerosis, Dupuytren's contracture, hypertrophic scars, and keloids. They are characterized by excessive connective tissue accumulation and slow but continuous tissue contraction that lead to progressive deterioration in the normal structure and function of affected organs. In recent years, research in diverse fields has increasingly highlighted the potential role of mechanobiology in the molecular mechanisms of fibroproliferation. Mechanobiology, the heart of which is mechanotransduction, is the process whereby cells sense mechanical forces and transduce them, thereby changing the intracellular biochemistry and gene expression. Understanding mechanosignaling may provide new insights into the convergent roles played by interrelated molecules and overlapping signaling pathways during the inflammatory, proliferative, and fibrotic cellular activities that are the hallmarks of fibroproliferation. The main cellular players in FPDs are fibroblasts and myofibroblasts. Consequently, this article discusses integrins and the roles they play in cellular-extracellular matrix interactions. Also described are the signaling pathways that are known to participate in mechanosignaling: these include the transforming growth factor-β/Smad, mitogen-activated protein kinase, RhoA/ROCK, Wnt/β-catenin, and tumor necrosis factor-α/nuclear factor kappa-light-chain-enhancer of activated B cells pathways. Also outlined is the progress in our understanding of the cellular-extracellular matrix interactions that are associated with fibroproliferative mechanosignaling through matricellular proteins. The tensegrity and tensional homeostasis models are also discussed. A better understanding of the mechanosignaling pathways in the FPD microenvironment will almost certainly lead to the development of novel interventions that can prevent, reduce, or even reverse FPD formation and/or progression.

Marked changes in endogenous antioxidant expression precede vitamin A-, C-, and E-protectable, radiation-induced reductions in small intestinal nutrient transport

Rapidly proliferating epithelial crypt cells of the small intestine are susceptible to radiation-induced oxidative stress, yet there is a dearth of data linking this stress to expression of antioxidant enzymes and to alterations in intestinal nutrient absorption. We previously showed that 5-14 days after acute γ-irradiation, intestinal sugar absorption decreased without change in antioxidant enzyme expression. In the present study, we measured antioxidant mRNA and protein expression in mouse intestines taken at early times postirradiation. Observed changes in antioxidant expression are characterized by a rapid decrease within 1h postirradiation, followed by dramatic upregulation within 4h and then downregulation a few days later. The cell type and location expressing the greatest changes in levels of the oxidative stress marker 4HNE and of antioxidant enzymes are, respectively, epithelial cells responsible for nutrient absorption and the crypt region comprising mainly undifferentiated cells. Consumption of a cocktail of antioxidant vitamins A, C, and E, before irradiation, prevents reductions in transport of intestinal sugars, amino acids, bile acids, and peptides. Ingestion of antioxidants may blunt radiation-induced decreases in nutrient transport, perhaps by reducing acute oxidative stress in crypt cells, thereby allowing the small intestine to retain its absorptive function when those cells migrate to the villus days after the insult.

[Reirradiation of normal tissues: preclinical radiobiological data]

Reirradiation represent an unfrequent particular clinical situation. The risk/benefit ratio assessment must be taken into account, considering both clinical and dosimetric aspects. There is a relatively limited amount of preclinical data available to date and clinicians should cautiously perform reirradiations in selected indications. This review summarizes the experimental data available on reirradiation of normal tissues, the consequences on early and late toxicities as well as the intrinsic limitations of these models.

Radiation-induced reductions in transporter mRNA levels parallel reductions in intestinal sugar transport

More than a century ago, ionizing radiation was observed to damage the radiosensitive small intestine. Although a large number of studies has since shown that radiation reduces rates of intestinal digestion and absorption of nutrients, no study has determined whether radiation affects mRNA expression and dietary regulation of nutrient transporters. Since radiation generates free radicals and disrupts DNA replication, we tested the hypotheses that at doses known to reduce sugar absorption, radiation decreases the mRNA abundance of sugar transporters SGLT1 and GLUT5, prevents substrate regulation of sugar transporter expression, and causes reductions in sugar absorption that can be prevented by consumption of the antioxidant vitamin A, previously shown by us to radioprotect the testes. Mice were acutely irradiated with (137)Cs gamma rays at doses of 0, 7, 8.5, or 10 Gy over the whole body. Mice were fed with vitamin A-supplemented diet (100x the control diet) for 5 days prior to irradiation after which the diet was continued until death. Intestinal sugar transport was studied at days 2, 5, 8, and 14 postirradiation. By day 8, d-glucose uptake decreased by approximately 10-20% and d-fructose uptake by 25-85%. With increasing radiation dose, the quantity of heterogeneous nuclear RNA increased for both transporters, whereas mRNA levels decreased, paralleling reductions in transport. Enterocytes of mice fed the vitamin A supplement had > or = 6-fold retinol concentrations than those of mice fed control diets, confirming considerable intestinal vitamin A uptake. However, vitamin A supplementation had no effect on clinical or transport parameters and afforded no protection against radiation-induced changes in intestinal sugar transport. Radiation markedly reduced GLUT5 activity and mRNA abundance, but high-d-fructose diets enhanced GLUT5 activity and mRNA expression in both unirradiated and irradiated mice. In conclusion, the effect of radiation may be posttranscriptional, and radiation-damaged intestines can still respond to dietary stimuli.

Lovastatin attenuates ionizing radiation-induced normal tissue damage in vivo

BACKGROUND AND PURPOSE

HMG-CoA-reductase inhibitors (statins) are widely used lipid-lowering drugs. Moreover, they have pleiotropic effects on cellular stress responses, proliferation and apoptosis in vitro. Here, we investigated whether lovastatin attenuates acute and subchronic ionizing radiation-induced normal tissue toxicity in vivo.

MATERIALS AND METHODS

Four hours to 24h after total body irradiation (6Gy) of Balb/c mice, acute pro-inflammatory and pro-fibrotic responses were analyzed. To comprise subchronic radiation toxicity, mice were irradiated twice with 2.5Gy and analyses were performed 3weeks after the first radiation treatment. Molecular markers of inflammation and fibrosis as well as organ toxicities were measured.

RESULTS

Lovastatin attenuated IR-induced activation of NF-kappaB, mRNA expression of cell adhesion molecules and mRNA expression of pro-inflammatory and pro-fibrotic marker genes (i.e. TNFalpha, IL-6, TGFbeta, CTGF, and type I and type III collagen) in a tissue- and time-dependent manner. gammaH2AX phosphorylation stimulated by IR was not affected by lovastatin, indicating that the statin has no major impact on the induction of DNA damage in vivo. Radiation-induced thrombopenia was significantly alleviated by lovastatin.

CONCLUSIONS

Lovastatin inhibits both acute and subchronic IR-induced pro-inflammatory and pro-fibrotic responses and cell death in normal tissue in vivo. Therefore, lovastatin might be useful for selectively attenuating acute and subchronic normal tissue damage caused by radiotherapy.

Predictive markers for normal tissue reactions: fantasy or reality?

Interpatient heterogeneity in normal tissue reactions varies considerably, yet the genetic determinants and the molecular mechanisms of therapeutic radiation sensitivity remain poorly understood. Predictive assays and markers for normal tissue reactions are still in their infancy, although some progress has been made, particularly, for predicting late toxicity. For instance the T-lymphocyte radiation-induced apoptosis assay was shown to significantly predict differences in late toxicity between individuals and an 18 gene classifier based on radiation-induced expression in subcutaneous fibroblasts has also been identified that differentiated between patients with a high and low risk of radiation-induced fibrosis. However, the technical set-up for gene expression measurements means that this latter assay is unlikely to be introduced soon into a routine clinical setting but has importantly allowed the identification of genes that are involved in the fibrotic process. Serum markers have also been identified that show potential for the prediction of patients who will develop acute and late pulmonary toxicity. Few genetic predictive markers for normal tissue reaction have been identified and validated. Many of the single nucleotide polymorphism association studies have been limited by size and the inclusion of subjects with different kinds of radiation morbidity. International collaboration to assemble well-defined cohorts and technological progress should mean that the identification and validation of such markers using candidate gene approaches and whole genome association studies, which have been successful in other research areas, will make rapid progress.

Specific signals involved in the long-term maintenance of radiation-induced fibrogenic differentiation: a role for CCN2 and low concentration of TGF-beta1

The fibrogenic differentiation of resident mesenchymal cells is a key parameter in the pathogenesis of radiation fibrosis and is triggered by the profibrotic growth factors transforming growth factor (TGF)-beta1 and CCN2. TGF-beta1 is considered the primary inducer of fibrogenic differentiation and is thought to control its long-term maintenance, whereas CCN2 is considered secondary effector of TGF-beta1. Yet, in long-term established fibrosis like that associated with delayed radiation enteropathy, in situ TGF-beta1 deposition is low, whereas CCN2 expression is high. To explore this apparent paradox, cell response to increasing doses of TGF-beta1 was investigated in cells modeling initiation and maintenance of fibrosis, i.e., normal and fibrosis-derived smooth muscle cells, respectively. Activation of cell-specific signaling pathways by low TGF-beta1 doses was demonstrated with a main activation of the Rho/ROCK pathway in fibrosis-derived cells, whereas the Smad pathway was mainly activated in normal cells. This leads to subsequent and cell-specific regulation of the CCN2 gene. These results suggested a specific profibrotic role of CCN2 in fibrosis-initiated cells. Furthermore, the modulation of CCN2 expression by itself and the combination of TGF-beta1 and CCN2 was investigated in fibrosis-derived cells. In fibrosis-initiated cells CCN2 triggered its autoinduction; furthermore, low concentration of TGF-beta1-potentiated CCN2 autoinduction. Our findings showed a differential requirement and action of TGF-beta1 in the fibrogenic response of normal vs. fibrosis-derived cells. This study defines a novel Rho/ROCK but Smad3-independent mode of TGF-beta signaling that may operate during the chronic stages of fibrosis and provides evidence of both specific and combinatorial roles of low TGF-beta1 dose and CCN2.

Pravastatin Inhibits the Rho/CCN2/extracellular matrix cascade in human fibrosis explants and improves radiation-induced intestinal fibrosis in rats

PURPOSES

Intestinal complications after radiotherapy are caused by transmural fibrosis and impair the quality of life of cancer survivors. Radiation fibrosis was considered permanent and irreversible, but recently, its dynamic nature was shown, providing new opportunities for the development of antifibrotic therapies. Among these new targets, we identified the Rho/ROCK pathway and thought to investigate whether pravastatin treatment inhibits Rho pathway activation and elicits an antifibrotic action.

EXPERIMENTAL DESIGN

Rho and ROCK activities were monitored in human explants presenting radiation fibrosis remodeling after incubation with pravastatin. Subsequent modulation of CCN2, type I collagen, and fibronectin expression were assessed ex vivo and in intestinal smooth muscle cells derived from radiation enteropathy. Then, the therapeutic relevance of the antifibrotic action of pravastatin was explored in vivo in a rat model of chronic radiation fibrosis (19 Gy X-rays) treated with 30 mg/kg/d pravastatin in the drinking water.

RESULTS

The results obtained with human explants show that pravastatin specifically inhibits Rho activity in submucosal mesenchymal cells. Pravastatin also elicits ROCK inhibition, and subsequent CCN2 production in human explants and smooth muscle cells isolated from radiation enteropathy. Inhibition of type I collagen and fibronectin does occur, showing that pravastatin modulates the secretory phenotype of mesenchymal cells. Lastly, curative pravastatin administration improves radiation enteropathy in rats. This structural improvement is associated with decreased deposition of CCN2 and subsequent decreased extracellular matrix deposition.

CONCLUSION

Targeting established fibrosis with pravastatin is an efficient and safe antifibrotic strategy in radiation-induced enteropathy, and is easily transferable into the clinic.

Maintenance of radiation-induced intestinal fibrosis: cellular and molecular features

Recent advances in cell and molecular radiobiology clearly showed that tissue response to radiation injury cannot be restricted to a simple cell-killing process, but depends upon continuous and integrated pathogenic processes, involving cell differentiation and crosstalk between the various cellular components of the tissue within the extracellular matrix. Thus, the prior concept of primary cell target in which a single-cell type (whatever it's epithelial or endothelial cells) dictates the whole tissue response to radiation injury has to be replaced by the occurrence of coordinated multicellular response that may either lead to tissue recovery or to sequel development. In this context, the present review will focus on the maintenance of the radiation-induced wound healing and fibrogenic signals triggered by and through the microenvironment toward the mesenchymal cell compartment, and will highlight how sequential and sustained modifications in cell phenotypes will in cascade modify cell-to-cell interactions and tissue composition.