Table 2.
Preclinical studies establishing the cause-and-effect role of gut microbiota in radiation injury
| References | Animal model | Key techniques | Major endpoints | Conclusions and highlights |
|---|---|---|---|---|
| Onoue, Japan, [16] | ICR mice, M, n = 10–42/group |
TBI: 20 Gy Oral administration of single strain |
Survival; histopathology of multiple organs | The first study distinguishing beneficial microorganisms from harmful ones based on the observation of radio-resistance in germ-free mice |
| Crawford And Gordon, US, [4] | FVB/N, B6 mice, M/F, n = 3–27/group |
TBI: 10–22 Gy Bacteria culture |
Survival; histopathology of intestine | The radio-protective fasting-induced adipose factor is suppressed by the gut microbiota although the specific microbe(s) responsible were not identified |
| Lam, US, [19] | Wistar rats, M, n = 5/group |
TBI: 10, 18 Gy/6Fx Feaces for 16S rRNA sequencing |
NA | The first study establishing microbiota-based acute and chronic ratios as effective biomarkers of prior radiation exposure |
| Fan, China, [7] | B6 mice, M, n = 3–10/group |
TAI: 5 Gy Feaces for 16S rRNA sequencing |
Survival | Circadian rhythm disorder interacts with gut microbiota to augment radiation injury |
| Fan, China, [5] | B6 mice, M/F, n = 4–18/group |
TBI: 6.5 Gy Feaces for 16S rRNA sequencing + intestine for RNA sequencing |
Survival; histopathology of intestine + circulating blood cell counting + spleen weight | Faecal microbiota transplantation is radio-protective without accelerating tumor growth |
| Fan, China, [13] | B6 mice, M, n = 4–20/group |
TAI: 15 Gy Feaces for 16S rRNA sequencing + intestine for microRNA assay |
Survival; histopathology of intestine + circulating blood cell counting | Radio-protective hydrogen-water restores radiation-induced gut dysbiosis |
| Gerassy, Israel, [17] |
B6 mice, F, n = 8–33/group Germ-free Swiss Webster mice† for faecal MT assay |
Rectum brachytherapy: 22 Gy/4Fx Feaces and colonic tissues for 16S rRNA sequencing + cytokine analysis |
Survival; histopathology of intestine | The pro-inflammatory dysbiosis induced by radiation is transmissible via faecal microbiota transplantation and renders radio-sensitivity to intestine |
| Tian, China, [22] |
SD ratsa, n = 30/group |
TBI: 0,4,8,12 Gy Feaces for 16S rRNA sequencing |
Survival; histopathology of intestine |
The first study showing the dose-dependent microbiota features in association with radiation injury in rodent models |
| Carbonero, US, [21] |
Gottingen minipig, M, n = 7–13/group Chinese rhesus macaques, M, n = 12–16/group |
TBI: 1.65–2.25 Gy for minipig; 5.9–7.7 Gy for macaque Feaces for 16S rRNA sequencing |
Survival | The first study showing the dose-dependent microbiota features in association with post-radiation survival in large primate models |
| Kweon, Korea, [55] | B6, ICR mice, M/F, n = 3–5/group |
TBI: 10 Gy or 12 Gy Gavage with lactate-producing microbes or conditioned medium or lactate + intestine for lactate measurement |
Survival; histopathology of intestine + organoid measurement |
Probiotics-derived lactate imposes intestinal radio-protection by activating Wnt/β-catenin in intestinal stem cells to accelerate epithelial repairment |
| MA Ciorba, US, [53], [54] | B6b, BALB/ca, n = 4–10/group |
TBI: 12 Gy, TAI: 28-32 Gy/7-8Fx Gavage with live or heat-killed Lactobacillus or Lactobacillus-conditioned medium Luminal microbial analysis using qPCR |
Survival; histopathology of intestine + circulating lymphocyte & hematopoietic stem cell counting |
Lactobacillus-derived lipoteichoic acid imposes intestinal radio-protection without compromising anticancer efficacy by activating EGF pathway in intestinal stem cells |
| Fan, China, [11] | B6 mice, M, n = 3–10/group |
TAI: 15 Gy Feaces for 16S rRNA sequencing |
Survival; histopathology of intestine + circulating blood cell & bone marrow cell counting | Radio-protective 3,3’-diindolylmethane restores radiation-induced gut dysbiosis |
| Li, China, [12] | B6 mice, M, n = 3–15/group |
TBI: 9 Gy Feaces for 16S rRNA sequencing + intestine for RNA sequencing |
Survival; histopathology of intestine + organoid culture | Radio-protective VND3207 restores radiation-induced gut dysbiosis |
| Fan, China, [9] | B6 mice M/F, n = 5–24/group |
TBI: 7 Gy for survival; 4 Gy for hematopoietic toxicity; TAI: 12 Gy for gastrointestinal toxicity; Feaces for 16S rRNA sequencing + intestine for RNA sequencing |
Survival; histopathology of intestine + spleen & thymus weight and blood inflammatory markers | Simvastatin and high-fat diet is radio-protective in male and female mice respectively, which relies on the existence of the sex-specific gut microbiota |
| Fan, China, [8] | B6 mice M, n = 12/group |
TAI: 12-15 Gy Feaces for 16S rRNA sequencing & SCFA quantification (LC) |
Survival; histopathology of intestine | Polysorbate-80 aggravates acute RE by altering the gut microbiota and decreasing butyrate level; post-radiation administration of butyrate reverses the effects of polysorbate-80 |
| Fan, China, [42] | B6 mice, M/F, n = 3–12/group |
TBI: 4-7 Gy; TAI: 12-15 Gy Feaces for 16S rRNA sequencing & SCFA quantification (LC) + intestine for peptide quantification (MS) |
Survival; histopathology of intestine + spleen & thymus weight and blood inflammatory markers | Microbiota-derived valerate alleviates radiation injury by up-regulating AML1/KRT1 which is down-regulated after radiation and is radio-protective |
| Fan, China, [43] | B6 mice & Balb/c nude mice, M/F, n = 6–30/group |
TBI: 7.2 Gy for survival; 4 Gy for hematopoietic toxicity; TAI: 12 Gy for gastrointestinal toxicity; Feaces for 16S rRNA sequencing & untargeted metabolomics (LC/MS) + intestine for peptide quantification (MS) |
Survival; histopathology of intestine + spleen & thymus weight and blood inflammatory markers | Microbiota-derived IPA alleviates radiation injury by re-activating the PXR-ACBP pathway without compromising anticancer efficacy |
| Guo, US, [47] | B6 mice, M/F, n = 4–33/group |
TBI: 8.0–9.2 Gy Feaces for 16S rRNA sequencing & SCFA quantification (GC) & untargeted metabolomics (LC) |
Survival; histopathology of intestines, spleen & bone marrow | Microbiota-derived SCFAs and tryptophan metabolites confer hematopoietic and gastrointestinal radio-protection without compromising anticancer efficacy |
| Tian, China, [20] | B6 mice, M, n = 5–10/group |
TBI: 0,4,8,12 Gy for dose-dependent assay and 9 Gy for probiotic assay; Feaces for 16S rRNA sequencing |
Survival; histopathology of intestine | A longitudinal study demonstrating that microbial quantifications at day3.5 after radiotherapy provide biomarkers for radio-dosimetry and radiation injury |
| Fan, China, [14] | B6 mice, M, n = 5–8/group |
Total chest irradiation: 15 Gy Feaces for 16S rRNA sequencing + LC/MS |
Body weight, histopathology of lung and heart | Radio-protection of L-Histidine relies on the existence of the gut microbiota |
| Fan, China, [10] | B6 mice M/F, n = /group |
TBI: 5 Gy; TAI: 12 Gy Feaces for 16S rRNA sequencing |
Survival; histopathology of intestine + circulating blood cell counting | Radio-protection of caloric-restriction diet relies on the existence of the gut microbiota |
| Kweon, Korea, [63] | B6, F, n = 3–5/group |
TBI: 10 Gy Gavage with Akkermansia or conditioned medium + Cecal contents for SCFA quantification (LC/MS) |
Survival; histopathology of intestine + organoid measurement |
Akkermansia-derived SCFAs impose intestinal radio-protection by activating Wnt/β-catenin in intestinal stem cells to promote proliferation and differentiation |
| Epperly, US, [23] | B6, BALB/c, sv129 mice, M, n = 10–20/group |
TBI: 9.25 Gy Feaces for 16S rRNA sequencing and qPCR validation |
Survival | Akkermansia muciniphila improves post-radiation survival in TBI mice |
| Epperly, US, [24] | B6 mice, F, n = 12/group |
TBI: 9.25 Gy; TAI: 19.75 Gy; Feaces for 16S rRNA sequencing |
Survival; inflammatory protein expression + bone marrow cells counting | Engineered IL-22- producing microbe ameliorates radiation injury |
| Epperly, US, [25] | B6 mice, M, n = 10–15/group |
TBI: 9.25 Gy Feaces for 16S rRNA sequencing |
Survival | Inclusion of microbiota information improves the predictability of survival when controlling for administration of radiation mitigators |
| Dar, US, [52] | B6 mice, F, n = 3–5/group |
TBI: 9.25 Gy Feaces for bacterium counting + intestine for lipidomics (LC/MS) |
Survival; histopathology of intestine | Pseudomonas aeruginosa-derived 15-lipoxygenase increases lipid peroxidation and ferroptosis, thereby exacerbating local inflammation and radiation injury |
M Male, F Female, TBI Total body irradiation, TAI Total abdominal irradiation, NA Not applicable, Fx Fractions, Qpcr Quantitative polymerase chain reaction, EGF Epidermal growth factor, SCFA Short chain fatty acid, LC Liquid chromatography, MS Mass spectrometry, GC Gas chromatography, KRT1 Keratin, type II cytoskeletal 1, IPA Indole 3-propionic acid, PXR Pregnane X receptor, ACBP Acyl-CoA-binding protein
aGender not mentioned
bFemale mice were preferentially used