Radiation-induced changes in intestinal and tissue-nonspecific alkaline phosphatase: implications for recovery after radiation therapy

The Effects of Ionizing Radiation on Gut Microbiota: What Can Animal Models Tell Us?-A Systematic Review

BACKGROUND

The gut microbiota is relatively stable; however, various factors can precipitate an imbalance that is known to be associated with various diseases. We aimed to conduct a systematic literature review of studies reporting the effects of ionizing radiation on the composition, richness, and diversity of the gut microbiota of animals.

METHODS

A systematic literature search was performed in PubMed, EMBASE, and Cochrane library databases. The standard methodologies expected by Cochrane were utilized.

RESULTS

We identified 3531 non-duplicated records and selected twenty-nine studies after considering the defined inclusion criteria. The studies were found to be heterogeneous, with significant differences in the chosen populations, methodologies, and outcomes. Overall, we found evidence of an association between ionizing radiation exposure and dysbiosis, with a reduction of microbiota diversity and richness and alterations in the taxonomic composition. Although differences in taxonomic composition varied across studies, Proteobacteria, Verrucomicrobia, Alistipes, and Akkermancia most consistently reported to be relatively more abundant after ionizing radiation exposure, whereas Bacteroidetes, Firmicutes, and Lactobacillus were relatively reduced.

CONCLUSIONS

This review highlights the effect of ionizing exposure on gut microbiota diversity, richness, and composition. It paves the way for further studies on human subjects regarding gastrointestinal side effects in patients submitted to treatments with ionizing radiation and the development of potential preventive, therapeutic approaches.

Potential role of gut microbiota and its metabolites in radiation-induced intestinal damage

Radiation-induced intestinal damage (RIID) is a serious disease with limited effective treatment. Nuclear explosion, nuclear release, nuclear application and especially radiation therapy are all highly likely to cause radioactive intestinal damage. The intestinal microecology is an organic whole with a symbiotic relationship formed by the interaction between a relatively stable microbial community living in the intestinal tract and the host. Imbalance and disorders of intestinal microecology are related to the occurrence and development of multiple systemic diseases, especially intestinal diseases. Increasing evidence indicates that the gut microbiota and its metabolites play an important role in the pathogenesis and prevention of RIID. Radiation leads to gut microbiota imbalance, including a decrease in the number of beneficial bacteria and an increase in the number of harmful bacteria that cause RIID. In this review, we describe the pathological mechanisms of RIID, the changes in intestinal microbiota, the metabolites induced by radiation, and their mechanism in RIID. Finally, the mechanisms of various methods for regulating the microbiota in the treatment of RIID are summarized.

Comparative metabolic profiles of total and partial body radiation exposure in mice using an untargeted metabolomics approach

INTRODUCTION

A large scale population exposure to ionizing radiation during intentional or unintentional nuclear accidents undoubtedly generates a complex scenario with partial-body as well as total-body irradiated victims. A high throughput technique based rapid assessment method is an urgent necessity for stratification of exposed subjects independent of whether exposure is uniform total-body or non-homogenous partial-body.

OBJECTIVE

Here, we used Nuclear Magnetic Resonance (NMR) based metabolomics approach to compare and identify candidate metabolites differentially expressed in total and partially irradiated mice model.

METHODS

C57BL/6 male mice (8-10 weeks) were irradiated total-body or locally to thoracic, hind limb or abdominal regions with 10 Gy of gamma radiation. Urine samples collected at 24 h post irradiation were examined using high resolution NMR spectroscopy and the datasets were analysed using multivariate analysis.

RESULTS

Multivariate and metabolic pathway analysis in urine samples collected at 24 h post-radiation exhibited segregation of all irradiated groups from controls. Metabolites associated with energy metabolism, gut flora metabolism and taurine were common to partial and total-body irradiation, thus making them potential candidates for radiation exposure. Nevertheless, a distinct metabolic pattern was observed in partial-body exposed groups with maximum changes observed in the hind limb region indicating differential tissue associated radiation sensitivity. The organ-specific changes may provide an early warning regarding the physiological system at risk after radiation injury.

CONCLUSION

The study affirms potentiality of metabolite markers and comparative analysis could be an important piece of information for an integrated solution to a complex research question in terms of radiation biomarkers.

Radiotherapy Induces Intestinal Barrier Dysfunction by Inhibiting Autophagy

Radiation enteritis is a common complication of abdominal irradiation (IR) therapy. However, the molecular mechanism of radiation enteritis accompanied by impaired intestinal barrier function is not clear. The aim of this study was to investigate the important role of autophagy in radiation-induced intestinal barrier function impairment. IR increased the abundance of autophagy-related genes in the colonic mucosa of mice. An autophagy activator (rapamycin) inhibited the oxidative stress (reactive oxygen species, reactive nitrogen species, malondialdehyde, and hydrogen peroxide) and inflammatory response (interleukin-1β, -6, -8, and tumor necrosis factor-α) in the colon samples. Antioxidant indices (superoxide dismutase, glutathione peroxidase, catalase, and total antioxidant capacity) in serum and colonic mucosa were significantly increased in the rapamycin group. Rapamycin can improve the activity of mitochondrial respiratory chain complexes I-V in colon mucosa. In addition, rapamycin reduced the gene expression and enzyme activity of caspase in the colonic mucosa. Levels of endotoxin, diamine peroxidase, d-lactic acid, and zonulin in serum and colonic mucosa were significantly reduced in the rapamycin group. Moreover, rapamycin significantly elevated the gene abundance of zonula occludens-1, occludin, claudin-1, and claudin-4. In contrast, completely opposite results were obtained for the autophagy inhibitor 3-methyladenine as compared to those of rapamycin. These results revealed that inhibition of autophagy is an important mechanism of intestinal barrier function damage caused by radiation. Collectively, these findings increase our understanding of the pathogenesis of radiation-induced intestinal barrier dysfunction.

Recent advances in intestinal alkaline phosphatase, inflammation, and nutrition

In recent years, much new data on intestinal alkaline phosphatase (IAP) have been published, and major breakthroughs have been disclosed. The aim of the present review is to critically analyze the publications released over the last 5 years. These breakthroughs include, for example, the direct implication of IAP in intestinal tight junction integrity and barrier function maintenance; chronic intestinal challenge with low concentrations of Salmonella generating long-lasting depletion of IAP and increased susceptibility to inflammation; the suggestion that genetic mutations in the IAP gene in humans contribute to some forms of chronic inflammatory diseases and loss of functional IAP along the gut and in stools; stool IAP as an early biomarker of incipient diabetes in humans; and omega-3 fatty acids as direct inducers of IAP in intestinal tissue. Many recent papers have also explored the prophylactic and therapeutic potential of IAP and other alkaline phosphatase (AP) isoforms in various experimental settings and diseases. Remarkably, nearly all data confirm the potent anti-inflammatory properties of (I)AP and the negative consequences of its inhibition on health. A simplified model of the body AP system integrating the IAP compartment is provided. Finally, the list of nutrients and food components stimulating IAP has continued to grow, thus emphasizing nutrition as a potent lever for limiting inflammation.

DETERMINATION OF GUT BACTERIAL METABOLITES IN RADIATION EXPOSED MICE

Gut microflora (GM) impacts human health in various ways, both beneficial and detrimental. Recently, it has attracted attention for its application in treatment, as protective agents, and as biomarkers in radiation exposure. In this study, we focused on organic acids that have not yet been reported to be related to radiation exposure; we measured the pH and organic acid content in the faeces of 0, 2, 4 and 8 Gy-irradiated mice. A common trend of fluctuation of some organic acids was observed in each group, suggesting a correlation between radiation exposure and organic acid fluctuation. Lactate fluctuation was similar between 0 and 2 Gy-, and 4 and 8 Gy-irradiated mice. Based on this finding, we suggest that lactate may also be an organic acid that is greatly affected by irradiation.

Short-term follow-up of intestinal flora in radiation-exposed mice

Some gastrointestinal bacteria, otherwise known as the 'intestinal flora', can cause severe gastrointestinal problems, including sepsis, which are strongly linked to lifestyle-related diseases, including cardiovascular diseases. Several investigations have focused on the long-term changes in the intestinal flora associated with radiation exposure; however, the short-term effects remain unknown. In this study, we tracked the short-term changes in the intestinal flora of mice exposed to different doses of X-ray irradiation (2 Gy and 4 Gy), focusing only on the lactic acid bacteria Bifidobacterium and Lactobacillus. A decrease in the Lactobacillus abundance was detected immediately after irradiation in individuals exposed to both 2 Gy and 4 Gy irradiation. However, mice exposed to 4 Gy of irradiation showed a remarkable increase in Bifidobacterium, indicating a potential role of these bacteria in regeneration of the intestinal epithelial tissue. Studies on changes in intestinal bacteria as a result of radiation exposure are limited. Therefore, continuation of this field of research is expected to provide important fundamental insight into the mechanisms by which radiation causes damage to the intestinal tissues, contributing to the development of sepsis.

Therapeutic role of glutamine in management of radiation enteritis: a meta-analysis of 13 randomized controlled trials

Objective

To systematically evaluate the clinical efficacy of glutamine in treating radiation enteritis in cancer patients treated with radiotherapy.

Methods

Electronic databases including Pubmed, Embase, the Cochrane library, and CNKI were systematically searched, until April 2016. Randomized controlled trials (RCT) of glutamine in the treatment of radiation enteritis in cancer patients were searched, and RevMan 5.3 software was used for Meta-analysis.

Results

A total of 13 RCTs were included, involving 979 patients. The results of meta-analysis showed that the total efficacy of glutamine was higher for patients with radiation enteritis compared with that in control group, however, there was no statistically significant difference(OR = 3.07, 95%CI: 0.79-11.96; P > 0.05). The combined ORs for all 5 grades(from grade 0 to grade 4) of radiation enteritis in patients receiving glutamine were 2.06, 1.35, 0.55, 0.62 and 0.59, respectively(P > 0.05 for all). Glutamine also failed to significantly improve the symptoms of radiation enteritis in terms of tenesmus, abdominal cramping and blood in bowel movement(P > 0.05).

Conclusions

Implementation of glutamine fails to improve the severity and symptoms in patients with radiation enteritis.