The effects of gut commensal bacteria depletion on mice exposed to acute lethal irradiation

Review: Effect of Gut Microbiota and Its Metabolite SCFAs on Radiation-Induced Intestinal Injury

Gut microbiota is regarded as the second human genome and forgotten organ, which is symbiotic with the human host and cannot live and exist alone. The gut microbiota performs multiple physiological functions and plays a pivotal role in host health and intestinal homeostasis. However, the gut microbiota can always be affected by various factors and among them, it is radiotherapy that results in gut microbiota ¹²dysbiosis and it is often embodied in a decrease in the abundance and diversity of gut microbiota, an increase in harmful bacteria and a decrease in beneficial bacteria, thereby affecting many disease states, especially intestine diseases. Furthermore, gut microbiota can produce a variety of metabolites, among which short-chain fatty acids (SCFAs) are one of the most abundant and important metabolites. More importantly, SCFAs can be identified as second messengers to promote signal transduction and affect the occurrence and development of diseases. Radiotherapy can lead to the alterations of SCFAs-producing bacteria and cause changes in SCFAs, which is associated with a variety of diseases such as radiation-induced intestinal injury. However, the specific mechanism of its occurrence is not yet clear. Therefore, this review intends to emphasize the alterations of gut microbiota after radiotherapy and highlight the alterations of SCFAs-producing bacteria and SCFAs to explore the mechanisms of radiation-induced intestinal injury from the perspective of gut microbiota and its metabolite SCFAs.

Role of Commensal Microbes in the γ-Ray Irradiation-Induced Physiological Changes in Drosophila melanogaster

Ionizing radiation induces biological/physiological changes and affects commensal microbes, but few studies have examined the relationship between the physiological changes induced by irradiation and commensal microbes. This study investigated the role of commensal microbes in the γ-ray irradiation-induced physiological changes in Drosophila melanogaster. The bacterial load was increased in 5 Gy irradiated flies, but irradiation decreased the number of operational taxonomic units. The mean lifespan of conventional flies showed no significant change by irradiation, whereas that of axenic flies was negatively correlated with the radiation dose. γ-Ray irradiation did not change the average number of eggs in both conventional and axenic flies. Locomotion of conventional flies was decreased after 5 Gy radiation exposure, whereas no significant change in locomotion activity was detected in axenic flies after irradiation. γ-Ray irradiation increased the generation of reactive oxygen species in both conventional and axenic flies, but the increase was higher in axenic flies. Similarly, the amounts of mitochondria were increased in irradiated axenic flies but not in conventional flies. These results suggest that axenic flies are more sensitive in their mitochondrial responses to radiation than conventional flies, and increased sensitivity leads to a reduced lifespan and other physiological changes in axenic flies.

Activation of Toll-like receptors by intestinal microflora reduces radiation-induced DNA damage in mice

Activation of Toll-like receptors (TLRs) signaling by intestinal microflora-derived bacterial products plays a key role in injury defence for the host. We investigated the role of TLRs activated by intestinal microflora in radiation-induced DNA damage in mice. We analyzed DNA damage induced by 2Gy γ-ray radiation in an intestinal commensal bacteria-depleted mouse model (CD group), in which TLRs (TLR2/6, TLR4 and TLR5) ligand levels in serum were reduced. Chromosomal aberrations were measured in bone marrow cells and peripheral blood leukocyte comet assays were performed. DNA damage was increased in the CD group compared with the control group. Treatment of mice with TLR agonists (CBLB502, LPS and lipopeptide) 1h before radiation resulted in a significant decrease in DNA damage. Genes induced by TLR5 activation were analyzed; activation of TLRs regulated the expression of Gadd45b, Sod2, and Rad21, which are involved in DNA damage repair. In summary, our data indicate that TLRs activation by intestinal microflora reduces DNA damage induced by radiation and regulates expression of several DNA repair genes.

Animal models for medical countermeasures to radiation exposure

Since September 11, 2001, there has been the recognition of a plausible threat from acts of terrorism, including radiological or nuclear attacks. A network of Centers for Medical Countermeasures against Radiation (CMCRs) has been established across the U.S.; one of the missions of this network is to identify and develop mitigating agents that can be used to treat the civilian population after a radiological event. The development of such agents requires comparison of data from many sources and accumulation of information consistent with the "Animal Rule" from the Food and Drug Administration (FDA). Given the necessity for a consensus on appropriate animal model use across the network to allow for comparative studies to be performed across institutions, and to identify pivotal studies and facilitate FDA approval, in early 2008, investigators from each of the CMCRs organized and met for an Animal Models Workshop. Working groups deliberated and discussed the wide range of animal models available for assessing agent efficacy in a number of relevant tissues and organs, including the immune and hematopoietic systems, gastrointestinal tract, lung, kidney and skin. Discussions covered the most appropriate species and strains available as well as other factors that may affect differential findings between groups and institutions. This report provides the workshop findings.