Heat-killed salmonella typhimurium (HKST) protects mice against radiation in TLR4-dependent manner

Insights Into Antioxidant Strategies to Counteract Radiation-Induced Male Infertility

Significance: Radiotherapy, which employs ionizing radiation to destroy or prevent the multiplication of tumor cells, has been increasingly used in the treatment of neoplastic diseases, especially cancers. However, radiation collaterally leads to prolonged periods of sperm count suppression, presumably due to impaired spermatogenesis by depleting the germ cell pool, which has long-term side effects for male reproduction. Recent Advances: Studies of antioxidant compounds as a potential strategy for male fertility preservation have been performed mainly from animal models, aiming to prevent and restore the male germinal tissue and its function, particularly against the oxidative stress effects of radiation. Evidence in preclinical and clinical trials has shown that inhibitors of the renin-angiotensin system and other drugs, such as statins and metformin, are candidates for ameliorating radiation-induced damage to several tissues, including the testis and prostate. Critical Issues: Research for developing an ideal radioprotective agent is challenging due to toxicity in the normal tissue, tumor radioresistance, cellular response to radiation, costs, regulation, and timeline development. Moreover, male radioprotection experiments in humans, mainly clinical trials, are scarce and use few individuals. This scenario is reflected in the slow progress of innovation in the radioprotection field. Future Directions: Expanding human studies to provide clues on the efficacy and safety of radioprotective compounds in the human reproductive system is necessary. Drug repurposing, frequently used in clinical practice, can be a way to shorten the development pipeline for innovative approaches for radioprotection or radiomitigation of the repercussions of radiotherapy in the male reproductive system.

TLR4 Agonist MPLA Ameliorates Heavy-Ion Radiation Damage via Regulating DNA Damage Repair and Apoptosis

Heavy-ion radiation received during radiotherapy as well as the heavy-ion radiation received during space flight are equally considered harmful. Our previous study showed that TLR4 low toxic agonist, monophosphoryl lipid A (MPLA), alleviated radiation injury resulting from exposure to low-LET radiation. However, the role and mechanism of MPLA in heavy-ion-radiation injury are unclear. This study aimed to investigate the role of MPLA on radiation damage. Our data showed that MPLA treatment alleviated the heavy-ion-induced damage to microstructure and the spleen and testis indexes. The number of karyocytes in the bone marrow from the MPLA-treated group was higher than that in the irradiated group. Meanwhile, western blotting analysis of intestine proteins showed that pro-apoptotic proteins (cleaved-caspase3 and Bax) were downregulated while anti-apoptotic proteins (Bcl-2) were upregulated in the MPLA-treated group. Our in vitro study demonstrated that MPLA significantly improved cell proliferation and inhibited cell apoptosis after irradiation. Moreover, immunofluorescence staining and quantification of nucleic γ-H2AX and 53BP1 foci also suggested that MPLA significantly attenuated cellular DNA damage repair. Collectively, the above evidence supports the potential ability of MPLA to protect against heavy-ion-radiation injury by inhibiting apoptosis and alleviating DNA damage in vivo and vitro, which could be a promising medical countermeasure for the prevention of heavy-ion-radiation injury.

TLR4-A Pertinent Player in Radiation-Induced Heart Disease?

The heart is one of the organs that is sensitive to developing delayed adverse effects of ionizing radiation (IR) exposure. Radiation-induced heart disease (RIHD) occurs in cancer patients and cancer survivors, as a side effect of radiation therapy of the chest, with manifestation several years post-radiotherapy. Moreover, the continued threat of nuclear bombs or terrorist attacks puts deployed military service members at risk of exposure to total or partial body irradiation. Individuals who survive acute injury from IR will experience delayed adverse effects that include fibrosis and chronic dysfunction of organ systems such as the heart within months to years after radiation exposure. Toll-like receptor 4 (TLR4) is an innate immune receptor that is implicated in several cardiovascular diseases. Studies in preclinical models have established the role of TLR4 as a driver of inflammation and associated cardiac fibrosis and dysfunction using transgenic models. This review explores the relevance of the TLR4 signaling pathway in radiation-induced inflammation and oxidative stress in acute as well as late effects on the heart tissue and the potential for the development of TLR4 inhibitors as a therapeutic target to treat or alleviate RIHD.

Heat Killed Salmonella typhimurium Protects Intestine Against Radiation Injury Through Wnt Signaling Pathway

Gastrointestinal (GI) toxicity caused by ionizing radiation (IR) is a dose limiting factor in radiotherapy and a great threat for individual nuclear-related military missions. However, there are currently no available strategies to effectively prevent the damage on the intestine induced by IR. In the present study, the protective activity of Heat Killed Salmonella typhimurium (HKST) on intestine against IR was investigated. Through mouse intestinal organoids and whole body irradiation of mice, we found that the pretreatment with HKST significantly preserved the structure of small intestine upon IR exposure and promoted the proliferation of intestinal cells post-IR. Further study revealed that the radioprotective effects of HKST were involved in DNA damage response (DDR) signaling. Moreover, the stimulation of DDR signaling by HKST upon radiation damage was mediated by Wnt signaling, in which the inhibition of Wnt signaling diminished the radioprotective effects of HKST. To sum up, our study suggested HKST as a potential radioprotectant used for prevention of IR-induced GI toxicity.

Ionizing radiation and toll like receptors: A systematic review article

Ionizing radiation, including X and gamma rays, are used for various purposes such as; medicine, nuclear power, research, manufacturing, food preservation and construction. Furthermore, people are also exposed to ionizing radiation from their workplace or the environment. Apart from DNA fragmentation resulting in apoptosis, several additional mechanisms have been proposed to describe how radiation can alter human cell functions. Ionizing radiation may alter immune responses, which are the main cause of human disorders. Toll like receptors (TLRs) are important human innate immunity receptors which participate in several immune and non-immune cell functions including, induction of appropriate immune responses and immune related disorders. Based on the role played by ionizing radiation on human cell systems, it has been hypothesized that radiation may affect immune responses. Therefore, the main aim of this review article is to discuss recent information regarding the effects of ionizing radiation on TLRs and their related disorders.

Novel chimeric TLR2/NOD2 agonist CL429 exhibited significant radioprotective effects in mice

Severe ionizing radiation causes the acute lethal damage of haematopoietic system and gastrointestinal tract. Here, we found CL429, the novel chimeric TLR2/NOD2 agonist, exhibited significant radioprotective effects in mice. CL429 increased mice survival, protected mice against the lethal damage of haematopoietic system and gastrointestinal tract. CL429 was more effective than equivalent amounts of monospecific (TLR2 or NOD2) and combination (TLR2 + NOD2) of molecules in preventing radiation‐induced death. The radioprotection of CL429 was mainly mediated by activating TLR2 and partially activating NOD2. CL429‐induced radioprotection was largely dependent on the activation of TLR2‐MyD88‐NF‐κB signalling pathway. In conclusion, the data suggested that the co‐activation of TLR2 and NOD2 could induce significant synergistic radioprotective effects and CL429 might be a potential high‐efficiency selective agent.

Heat-killed Salmonella Typhimurium protects mice against carbon ion radiation

OBJECTIVE

Patients receiving carbon-ion radiation therapy and astronauts exploring outer space are inevitably exposed to heavy ion radiation. The aim of this study was to develop radioprotectors to minimize the injuries induced by carbon ion radiation.

METHODS

Heat-killed Salmonella Typhimurium (HKST) was administered to mice by gavage prior to irradiation with a ¹²C⁶⁺ heavy ion accelerator. Hematoxylin and eosin staining and immunofluorescence TdT-mediated dUTP Nick-End Labeling staining were used to assess the radioprotective effect of HKST on organ damage and levels of apoptosis, respectively, in mice. To investigate the mechanism underlying the radioprotective effect of HKST, levels of the pro-apoptotic proteins BAX and caspase 3 as well as interferon-regulatory factor (IRF) 3/7 in the femur, testis and intestine were assessed using immunofluorescence.

RESULTS

Injuries induced by carbon ion radiation were significantly eased by pretreatment with HKST. Both apoptosis and high expression levels of pro-apoptotic proteins induced by heavy ion radiation were inhibited by HKST pretreatment. The radioprotective effect of HKST was associated with stimulation of Toll-like receptor signaling mediated by enhanced IRF3 and IRF7 signaling.

CONCLUSION

HKST was an effective radioprotector alleviating damage to multiple organs caused by heavy ion radiation.

Heat-killed Salmonella typhimurium mitigated radiation-induced lung injury

Radiation-induced lung injury (RILI) is a serious complication in thoracic tumour radiotherapy. It often occurs in clinical chest radiotherapy and acute whole-body irradiation (WBI) caused by nuclear accidents or nuclear weapon attack. Some radioprotective agents have been reported to exert protective effects when given prior to radiation exposure, however, there is no treatment strategy available for preventing RILI. In this study, we demonstrated that heat-killed Salmonella typhimurium (HKST), a co-agonist of Toll-like receptors 2 (TLR2), Toll-like receptors 4 (TLR4) and Toll-like receptors 5 (TLR5), mitigated radiation-induced lung injury through the transforming growth factor-β (TGF-β) signalling pathway. We found that HKST alleviated lung hyperaemia and pathological damage after irradiation, indicated that HKST inhibits the early inflammatory reaction of radiation-induced lung injury. Then, for the first time, we observed HKST reduced collagen deposit induced by irradiation in the later phase (7-14 week) of RILI, and we found that HKST inhibited radiation-induced cell apoptosis in lung tissues. We found that HKST reduced the level of TGF-β and regulated its downstream signalling pathway. Finally, it was found that HKST inhibited radiation-induced epithelial-mesenchymal transition (EMT) in lung tissues. In conclusion, our data showed that HKST effectively mitigated RILI through regulating TGF-β, provide novel treatment strategy for RILI in whole-body irradiation and radiotherapy.

Mechanisms for Radioprotection by Melatonin; Can it be Used as a Radiation Countermeasure?

BACKGROUND

Melatonin is a natural body product that has shown potent antioxidant property against various toxic agents. For more than two decades, the abilities of melatonin as a potent radioprotector against toxic effects of ionizing radiation (IR) have been proved. However, in the recent years, several studies have been conducted to illustrate how melatonin protects normal cells against IR. Studies proposed that melatonin is able to directly neutralize free radicals produced by IR, leading to the production of some low toxic products.

DISCUSSION

Moreover, melatonin affects several signaling pathways, such as inflammatory responses, antioxidant defense, DNA repair response enzymes, pro-oxidant enzymes etc. Animal studies have confirmed that melatonin is able to alleviate radiation-induced cell death via inhibiting pro-apoptosis and upregulation of anti-apoptosis genes. These properties are very interesting for clinical radiotherapy applications, as well as mitigation of radiation injury in a possible radiation disaster. An interesting property of melatonin is mitochondrial ROS targeting that has been proposed as a strategy for mitigating effects in radiosensitive organs, such as bone marrow, gastrointestinal system and lungs. However, there is a need to prove the mitigatory effects of melatonin in experimental studies.

CONCLUSION

In this review, we aim to clarify the molecular mechanisms of radioprotective effects of melatonin, as well as possible applications as a radiation countermeasure in accidental exposure or nuclear/radiological disasters.

Monophosphoryl lipid a attenuates radiation injury through TLR4 activation

Ionizing radiation causes severe damage to human body, and normal tissue toxicity in cancer radiotherapy also limits its further application. It is urgently required to develop safe and effective radioprotector. Our previous study has shown that toll like receptor 4 (TLR4) was dispensable for basal radiation resistance. However, severe toxicity of its traditional agonist lipopolysaccharide limits the clinical application. In present study, we demonstrated that monophosphoryl lipid A (MPLA), a potent TLR4 agonist with low toxicity, effectively attenuated radiation injury on in vitro and in vivo. MPLA increased cell survival and inhibited cell apoptosis after irradiation, and cell cycle arrest was also inhibited. Radiosensitive tissues including spleen, intestine, bone marrow and testis were protected from radiation damages in a TLR4 dependent manner. We also found that myeloid differentiation factor 88 (MyD88) accounted more than Toll/IL-1R domain-containing adaptor inducing IFN-β (TRIF) for the radioprotective effects of MPLA. In conclusion, our finding suggests TLR4 agonist MPLA as a safe and effective radioprotector for clinical application.