Localized intestinal radiation and liquid diet enhance survival and permit evaluation of long-term intestinal responses to high dose radiation in mice

Feasibility and guidelines for the use of an injectable fiducial marker (BioXmark ®) to improve target delineation in preclinical radiotherapy studies using mouse models

BACKGROUND

Preclinical models of radiotherapy (RT) response are vital for the continued success and evolution of RT in the treatment of cancer. The irradiation of tissues in mouse models necessitates high levels of precision and accuracy to recapitulate clinical exposures and limit adverse effects on animal welfare. This requirement has been met by technological advances in preclinical RT platforms established over the past decade. Small animal RT systems use onboard computed tomography (CT) imaging to delineate target volumes and have significantly refined radiobiology experiments with major 3Rs impacts. However, the CT imaging is limited by the differential attenuation of tissues resulting in poor contrast in soft tissues. Clinically, radio-opaque fiducial markers (FMs) are used to establish anatomical reference points during treatment planning to ensure accuracy beam targeting, this approach is yet to translate back preclinical models.

METHODS

We report on the use of a novel liquid FM BioXmark ® developed by Nanovi A/S (Kongens Lyngby, Denmark) that can be used to improve the visualisation of soft tissue targets during beam targeting and minimise dose to surrounding organs at risk. We present descriptive protocols and methods for the use of BioXmark ® in experimental male and female C57BL/6J mouse models.

RESULTS

These guidelines outline the optimum needle size for uptake (18-gauge) and injection (25- or 26-gauge) of BioXmark ® for use in mouse models along with recommended injection volumes (10-20 µl) for visualisation on preclinical cone beam CT (CBCT) scans. Injection techniques include subcutaneous, intraperitoneal, intra-tumoral and prostate injections.

CONCLUSIONS

The use of BioXmark ® can help to standardise targeting methods, improve alignment in preclinical image-guided RT and significantly improve the welfare of experimental animals with the reduction of normal tissue exposure to RT.

Precision targeting of the vagal anti-inflammatory pathway attenuates the systemic inflammatory response to burn injury

BACKGROUND

The systemic inflammatory response (SIRS) drives late morbidity and mortality after injury. The α7 nicotinic acetylcholine receptor (α7nAchR) expressed on immune cells regulates the vagal anti-inflammatory pathway that prevents an overwhelming SIRS response to injury. Nonspecific pharmacologic stimulation of the vagus nerve has been evaluated as a potential therapeutic to limit SIRS. Unfortunately, the results of clinical trials have been underwhelming. We hypothesized that directly targeting the α7nAchR would more precisely stimulate the vagal anti-inflammatory pathway on immune cells and decrease gut and lung injury after severe burn.

METHODS

C57BL/6 mice underwent 30% total body surface area steam burn. Mice were treated with an intraperitoneal injection of a selective agonist of the α7nAchR (AR-R17779) at 30 minutes postburn. Intestinal permeability to 4 kDa FITC-dextran was measured at multiple time points postinjury. Lung vascular permeability was measured 6 hours after burn injury. Serial behavioral assessments were performed to quantify activity levels.

RESULTS

Intestinal permeability peaked at 6 hours postburn. AR-R17779 decreased burn-induced intestinal permeability in a dose-dependent fashion (p < 0.001). There was no difference in gut permeability to 4 kDa FITC-dextran between sham and burn-injured animals treated with 5 mg/kg of AR-R17779. While burn injury increased lung permeability 10-fold, AR-R17779 prevented burn-induced lung permeability with no difference compared with sham (p < 0.01). Postinjury activity levels were significantly improved in burned animals treated with AR-R17779.

CONCLUSION

Directly stimulating the α7nAchR prevents burn-induced gut and lung injury. Directly targeting the α7nAChR that mediates the cholinergic anti-inflammatory response may be an improved strategy compared with nonspecific vagal agonists.

Interplay among p21Waf1/Cip1, MUSASHI-1 and Krüppel-like factor 4 in activation of Bmi1-CreER reserve intestinal stem cells after gamma radiation-induced injury

Gamma radiation is a commonly used adjuvant treatment for abdominally localized cancer. Since its therapeutic potential is limited due to gastrointestinal (GI) syndrome, elucidation of the regenerative response following radiation-induced gut injury is needed to develop a preventive treatment. Previously, we showed that Krüppel-like factor 4 (KLF4) activates certain quiescent intestinal stem cells (ISCs) marked by Bmi1-Cre^ER to give rise to regenerating crypts following γ irradiation. In the current study, we showed that γ radiation-induced expression of p21^Waf1/Cip1 in Bmi1-Cre^ER cells is likely mitigated by MUSASHI-1 (MSI1) acting as a negative regulator of p21^Waf1/Cip1 mRNA translation, which promotes exit of the Bmi1-Cre^ER cells from a quiescent state. Additionally, Bmi1-specific Klf4 deletion resulted in decreased numbers of MSI1⁺ cells in regenerating crypts compared to those of control mice. We showed that KLF4 binds to the Msi1 promoter and activates its expression in vitro. Since MSI1 has been shown to be crucial for crypt regeneration, this finding elucidates a pro-proliferative role of KLF4 during the postirradiation regenerative response. Taken together, our data suggest that the interplay among p21^Waf1/Cip1, MSI1 and KLF4 regulates Bmi1-Cre^ER cell survival, exit from quiescence and regenerative potential upon γ radiation-induced injury.

Elucidation of gastrointestinal dysfunction in response to irradiation using metabolomics

Gastrointestinal toxicity is frequently observed secondary to accidental or therapeutic radiation exposure. However, the variation in the intestinal metabolites after abdominal radiation exposure remains ambiguous. In the present study, C57BL/6 mice were exposed to 0, 2, and 20 Gy irradiation dose. The Head and chest of each mouse were covered with a lead shield before x-ray irradiation. 24 h post-irradiation treatment, intestinal tissue of each mouse was excised and prepared for metabolites measurement using gas chromatography-mass spectrometry (GC-MS). Our comprehensive analysis of metabolites in the intestinal tissues detected 44 metabolites after irradiation, including amino acids, carbohydrates, organic acids, and sugars. Amino acid levels in the intestinal tissue gradually rose, dependent on the radiation dose, perhaps as an indication of oxidative stress. Our findings raise the possibility that amino acid metabolism may be a potential target for the development of treatments to alleviate or mitigate the harmful effects of oxidative stress-related gastrointestinal toxicity due to radiation exposure.

•

Gastrointestinal damage frequently results from radiation exposure.

•

We analyzed the metabolic profile after local irradiation to the intestine.

•

Amino acid levels in the intestinal tissue rose dependent on the radiation dose.

•

Amino acid metabolism may be a good target for future therapies.

Fasting-Mimicking Diet Modulates Microbiota and Promotes Intestinal Regeneration to Reduce Inflammatory Bowel Disease Pathology

Dietary interventions are potentially effective therapies for inflammatory bowel diseases (IBDs). We tested the effect of 4-day fasting-mimicking diet (FMD) cycles on a chronic dextran sodium sulfate (DSS)-induced murine model resulting in symptoms and pathology associated with IBD. These FMD cycles reduced intestinal inflammation, increased stem cell number, stimulated protective gut microbiota, and reversed intestinal pathology caused by DSS, whereas water-only fasting increased regenerative and reduced inflammatory markers without reversing pathology. Transplants of Lactobacillus or fecal microbiota from DSS- and FMD-treated mice reversed DSS-induced colon shortening, reduced inflammation, and increased colonic stem cells. In a clinical trial, three FMD cycles reduced markers associated with systemic inflammation. The effect of FMD cycles on microbiota composition, immune cell profile, intestinal stem cell levels and the reversal of pathology associated with IBD in mice, and the anti-inflammatory effects demonstrated in a clinical trial show promise for FMD cycles to ameliorate IBD-associated inflammation in humans.

A novel mouse model of radiation-induced cancer survivorship diseases of the gut

A deeper understanding of the radiation-induced pathophysiological processes that develop in the gut is imperative to prevent, alleviate, or eliminate cancer survivorship diseases after radiotherapy to the pelvic area. Most rodent models of high-dose gastrointestinal radiation injury are limited by high mortality. We therefore established a model that allows for the delivering of radiation in fractions at high doses while maintaining long-term survival. Adult male C57/BL6 mice were exposed to small-field irradiation, restricted to 1.5 cm of the colorectum using a linear accelerator. Each mouse received 6 or 8 Gy, two times daily in 12-h intervals in two, three, or four fractions. Acute cell death was examined at 4.5 h postirradiation and histological changes at 6 wk postirradiation. Another group was given four fractions of 8 Gy and followed over time for development of visible symptoms. Irradiation caused immediate cell death, mainly limited to the colorectum. At 6 wk postirradiation, several crypts displayed signs of radiation-induced degeneration. The degenerating crypts were seen alongside crypts that appeared perfectly healthy. Crypt survival was reduced after the fourth fraction regardless of dose, whereas the number of macrophages increased. Angiogenesis was induced, likely as a compensatory mechanism for hypoxia. Four months postirradiation, mice began to show radiation-induced symptoms, and histological examination revealed an extensive crypt loss and fibrosis. Our model is uniquely suitable for studying the long-term trajectory and underlying mechanisms of radiation-induced gastrointestinal injury.NEW & NOTEWORTHY A novel mouse model for studying the long-term trajectory of radiation-induced gut injury. The method allows for the use of high doses and multiple fractions, with minor impact on animal health for at least 3 mo. Crypt loss and a slow progression of fibrosis is observed. Crypt degeneration is a process restricted to isolated crypts. Crypt degeneration is presented as a convenient proxy endpoint for long-term radiation-induced gut injury.

Association between expression of inflammatory factors and gastric and duodenal mucosa injury induced by radiotherapy in patients with pancreatic cancer

AIM: To investigate the relationship between the expression of interleukin-6 (IL-6), tumor necrosis factor α (TNF-α), interleukin-22 (IL-22) and radiation induced gastric and duodenal injury in pancreatic cancer patients.

METHODS: Twenty healthy adults and 30 pancreatic cancer patients were enrolled in the study. Peripheral blood samples were collected from these subjects before, in the middle of and after radiotherapy. Real-time quantitative PCR (QPCR) and enzyme linked immunosorbent assay (ELISA) were used to detect the mRNA and protein levels of IL-6, TNF-α and IL-22, respectively.

RESULTS: Expression of IL-6, TNF-α, and IL-22 mRNAs was significantly higher in the experimental group than in the normal control group (t = 4.404, P = 0.000; t = 2.250, P = 0.030; t = 2.178, P = 0.038). At the protein level, the expression of IL-6 was significantly higher in the experimental group than in the control group (t = 3.766, P = 0.001). The expression of IL-6 and TNF-α mRNAs showed a descending trend along with the accumulation of radiation dose. The expression level of IL-6 mRNA had a significant difference between before and after radiotherapy (t = 2.800, P = 0.007). The expression level of IL-22 was slightly higher in the experimental group than in the control group, though the difference was not statistically significant (P > 0.05). The incidence of mucosal injury was 40% (12 cases) in the study. The expression of IL-6 and TNF-α mRNAs in patients without mucosal injury group showed a gradually declining trend. The expression of IL-6 in patients differed between after and before radiotherapy (t = 2.439, P = 0.021). The expression of IL-6 in patients with mucosal injury was maintained at a relatively high level after radiotherapy. The mRNA expression of IL-22 in patients without mucosal injury decreased in the middle of radiotherapy. The expression of inflammatory factors in patients with mucosa injury was significantly lower than that in patients without mucosa injury (P > 0.05). Similarly, although protein expression of IL-6 in patients without mucosa injury seemed lower than that in patients with mucosa injury groups, and the expression of IL-22 seemed higher than that in the injury group, the differences were not statistically significant (P > 0.05).

CONCLUSION: IL-6, TNF-α and IL-22 are associated with the pathogenesis of radiation induced gastric and duodenal injury in patients with pancreatic cancer. These inflammatory factors may be used as predictors of radiation induced gastric and duodenal injury in pancreatic cancer patients.

Coniferyl aldehyde attenuates radiation enteropathy by inhibiting cell death and promoting endothelial cell function

Radiation enteropathy is a common complication in cancer patients. The aim of this study was to investigate whether radiation-induced intestinal injury could be alleviated by coniferyl aldehyde (CA), an HSF1-inducing agent that increases cellular HSP70 expression. We systemically administered CA to mice with radiation enteropathy following abdominal irradiation (IR) to demonstrate the protective effects of CA against radiation-induced gastrointestinal injury. CA clearly alleviated acute radiation-induced intestinal damage, as reflected by the histopathological data and it also attenuated sub-acute enteritis. CA prevented intestinal crypt cell death and protected the microvasculature in the lamina propria during the acute and sub-acute phases of damage. CA induced HSF1 and HSP70 expression in both intestinal epithelial cells and endothelial cells in vitro. Additionally, CA protected against not only the apoptotic cell death of both endothelial and epithelial cells but also the loss of endothelial cell function following IR, indicating that CA has beneficial effects on the intestine. Our results provide novel insight into the effects of CA and suggest its role as a therapeutic candidate for radiation-induced enteropathy due to its ability to promote rapid re-proliferation of the intestinal epithelium by the synergic effects of the inhibition of cell death and the promotion of endothelial cell function.

IGF1 stimulates crypt expansion via differential activation of 2 intestinal stem cell populations

Insulin-like growth factor 1 (IGF1) has potent trophic effects on normal or injured intestinal epithelium, but specific effects on intestinal stem cells (ISCs) are undefined. We used Sox9-enhanced green fluorescent protein (EGFP) reporter mice that permit analyses of both actively cycling ISCs (Sox9-EGFP(Low)) and reserve/facultative ISCs (Sox9-EGFP(High)) to study IGF1 action on ISCs in normal intestine or during crypt regeneration after high-dose radiation-induced injury. We hypothesized that IGF1 differentially regulates proliferation and gene expression in actively cycling and reserve/facultative ISCs. IGF1 was delivered for 5 days using subcutaneously implanted mini-pumps in uninjured mice or after 14 Gy abdominal radiation. ISC numbers, proliferation, and transcriptome were assessed. IGF1 increased epithelial growth in nonirradiated mice and enhanced crypt regeneration after radiation. In uninjured and regenerating intestines, IGF1 increased total numbers of Sox9-EGFP(Low) ISCs and percentage of these cells in M-phase. IGF1 increased percentages of Sox9-EGFP(High) ISCs in S-phase but did not expand this population. Microarray revealed that IGF1 activated distinct gene expression signatures in the 2 Sox9-EGFP ISC populations. In vitro IGF1 enhanced enteroid formation by Sox9-EGFP(High) facultative ISCs but not Sox9-EGFP(Low) actively cycling ISCs. Our data provide new evidence that IGF1 activates 2 ISC populations via distinct regulatory pathways to promote growth of normal intestinal epithelium and crypt regeneration after irradiation.

An overview of translational (radio)pharmaceutical research related to certain oncological and non-oncological applications

Translational medicine pursues the conversion of scientific discovery into human health improvement. It aims to establish strategies for diagnosis and treatment of diseases. Cancer treatment is difficult. Radio-pharmaceutical research has played an important role in multiple disciplines, particularly in translational oncology. Based on the natural phenomenon of necrosis avidity, OncoCiDia has emerged as a novel generic approach for treating solid malignancies. Under this systemic dual targeting strategy, a vascular disrupting agent first selectively causes massive tumor necrosis that is followed by iodine-131 labeled-hypericin (¹²³I-Hyp), a necrosis-avid compound that kills the residual cancer cells by crossfire effect of beta radiation. In this review, by emphasizing the potential clinical applicability of OncoCiDia, we summarize our research activities including optimization of radioiodinated hypericin Hyp preparations and recent studies on the biodistribution, dosimetry, pharmacokinetic and, chemical and radiochemical toxicities of the preparations. Myocardial infarction is a global health problem. Although cardiac scintigraphy using radioactive perfusion tracers is used in the assessment of myocardial viability, searching for diagnostic imaging agents with authentic necrosis avidity is pursued. Therefore, a comparative study on the biological profiles of the necrosis avid ¹²³I-Hyp and the commercially available ^99mTc-Sestamibi was conducted and the results are demonstrated. Cholelithiasis or gallstone disease may cause gallbladder inflammation, infection and other severe complications. While studying the mechanisms underlying the necrosis avidity of Hyp and derivatives, their naturally occurring fluorophore property was exploited for targeting cholesterol as a main component of gallstones. The usefulness of Hyp as an optical imaging agent for cholelithiasis was studied and the results are presented. Multiple uses of automatic contrast injectors may reduce costs and save resources. However, cross-contaminations with blood-borne pathogens of infectious diseases may occur. We developed a radioactive method for safety evaluation of a new replaceable patient-delivery system. By mimicking pathogens with a radiotracer, we assessed the feasibility of using the system repeatedly without septic risks. This overview is deemed to be interesting to those involved in the related fields for translational research.

Improved clearance of radioiodinated hypericin as a targeted anticancer agent by using a duodenal drainage catheter in rats

We sought to reduce the radioactive intestinal waste after intravenous injection of necrosis avid iodine-131-labeled hypericin in dual-targeting anticancer radiotherapy and to study its pharmacokinetics in rats using a newly designed catheter. Iodine-123-labeled hypericin was prepared with iodogen as oxidant and characterized by high-performance liquid chromatography and mass spectrometry. After iodine-123-labeled hypericin administration, duodenal juice was collected via a catheter from groups of rats (n = 5) at intervals of 0-4, 4-8 or 20-24 h. The content was assessed by gamma-counting. The biodistribution and pharmacokinetics of iodine-123-labeled hypericin were investigated in rats without (n = 5) and with continuous catheterization (n = 5) for 9 h. After labeling, a high radiochemical yield was obtained with iodine-123-labeled hypericin (>95%), as confirmed by high-performance liquid chromatography and mass spectrometry. In the duodenal aspirate from animals with intermittent catheterization during 24 h, radioactivity accounted for 46% of the total with two peaks at 3 h and 8 h, suggesting enterohepatic circulation. Rats with 9 h of catheterization exhibited one peak representing 20% of the radioactivity. Major metabolites appeared to be conjugated iodine-123-labeled hypericin forms. In rats without and with catheter, iodine-123-labeled hypericin showed exponential elimination from plasma with no significant dehalogenation. Delayed iodine-123-labeled hypericin excretion, a higher maximum concentration (Cmax), larger area under concentration-time curve [AUC(0-∞)] and a longer mean residence time were observed in non-catheterized animals (P < 0.05). The catheterized group exhibited lower urinary excretion than non-catheterized group (P < 0.05). Rats with a catheter showed lower radioactivity (P = 0.01) in the small intestines than those without a catheter (1.82 ± 0.41 versus 18.95 ± 4.32 percentage of the injected dose). After iodine-123-labeled hypericin administration, the radioactivity excreted into bile was efficiently removed from the body via a duodenal catheter. Radiation overexposure due to the prolonged elimination of iodine-131-labeled hypericin can be prevented using this approach.

Development of a mouse model of radiation-induced duodenitis

AIM: To develop a mouse model of radiation-induced duodenitis.

METHODS: Ninety-three female Balb/c mice were randomly divided into seven groups: a control group (n = 13), a 4.5 Gy group (n = 13), a 6.0 Gy group (n = 13), a 9.0 Gy group (n = 13), a 12.0 Gy group (n = 13), a 13.5 Gy group (n = 13) and a 15.0 Gy group (n = 15). Mice were sacrificed 3.5 or 7.0 d after abdominal irradiation with a single dose of Cobalt-60. Duodenal samples were taken for histopathological analysis, and blood, spleen and mesenteric lymph nodes were sampled to detect the levels of inflammatory factors interleukin-6 (IL-6), IL-1β and tumor necrosis factor-α (TNF-α).

RESULTS: The levels of inflammatory factors IL-6, IL-1β and TNF-α increased in all the irradiation groups compared to the control group. The length of villi and the number of crypt were significantly reduced in the 12.0, 13.5 and 15.0 Gy groups compared to the control group on day 3.5, which was consistent with the changes in radiation-induced enteritis. The 13.5 and 15.0 Gy groups had a high mortality, and the 12.0 Gy group was better in simulating clinical radioactive duodenitis.

CONCLUSION: A mouse model of radiation-induced duodenitis can be successfully developed by abdominal irradiation with a single dose (12.0 Gy) of ⁶⁰Co.