A Fiber-Rich Diet and Radiation-Induced Injury in the Murine Intestinal Mucosa.

Dietary fiber is considered a strong intestinal protector, but we do not know whether dietary fiber protects against the long-lasting mucosal damage caused by ionizing radiation. To evaluate whether a fiber-rich diet can ameliorate the long-lasting pathophysiological hallmarks of the irradiated mucosa, C57BL/6J mice on a fiber-rich bioprocessed oat bran diet or a fiber-free diet received 32 Gray in four fractions to the distal colorectum using a linear accelerator and continued on the diets for one, six or 18 weeks. We quantified degenerating crypts, crypt fission, cell proliferation, crypt survival, macrophage density and bacterial infiltration. Crypt loss through crypt degeneration only occurred in the irradiated mice. Initially, it was most frequent in the fiber-deprived group but declined to levels similar to the fiber-consuming group by 18 weeks. The fiber-consuming group had a fast response to irradiation, with crypt fission for growth or healing peaking already at one week post-irradiation, while crypt fission in the fiber-deprived group peaked at six weeks. A fiber-rich diet allowed for a more intense crypt cell proliferation, but the recovery of crypts was eventually lost by 18 weeks. Bacterial infiltration was a late phenomenon, evident in the fiber-deprived animals and intensified manyfold after irradiation. Bacterial infiltration also coincided with a specific pro-inflammatory serum cytokine profile. In contrast, mice on a fiber-rich diet were completely protected from irradiation-induced bacterial infiltration and exhibited a similar serum cytokine profile as sham-irradiated mice on a fiber-rich diet. Our findings provide ample evidence that dietary fiber consumption modifies the onset, timing and intensity of radiation-induced pathophysiological processes in the intestinal mucosa. However, we need more knowledge, not least from clinical studies, before this finding can be introduced to a new and refined clinical practice.

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.

Dietary Fiber and the Hippocampal Neurogenic Niche in a Model of Pelvic Radiotherapy.

We sought to determine whether radiation to the colorectum had an impact on parameters of hippocampal neurogenesis and, if so, whether it could be modulated by a fiber-rich diet. Male C57BL/6J mice were fed a diet containing bioprocessed oat bran or a fiber-free diet, starting two weeks before colorectal irradiation with 4 fractions of 8 Gray or sham-irradiation. Diets were then continued for 1, 6 or 18 weeks, whereafter parameters of hippocampal neurogenesis were analyzed and correlated to serum cytokine levels. No statistically significant changes in neuronal markers or cell proliferation were found at one week post-irradiation. Six weeks post-irradiation there was a decreased cell proliferation in the subgranular zone that appeared slightly more pronounced in irradiated animals on a fiber-free diet and increased numbers of immature neurons per mm2 dentate gyrus in the irradiated mice, with a statistically significant increase in mice on a fiber-rich diet. Microglial abundancy was similar between all groups. 18 weeks post-irradiation, a fiber-free diet had reduced the number of immature neurons, whereas irradiation resulted in an increase. Despite this, the population of mature neurons was stable. Analysis of serum cytokines revealed a negative correlation between MIP1-α and the number of immature neurons one week after irradiation, regardless of diet. Our findings show that pelvic radiotherapy has the potential to cause a long-lasting impact on hippocampal neurogenesis, and dietary interventions may modulate this impact. More in-depth studies on the relationship between irradiation-induced intestinal injury and brain health are warranted.

Nuclear translocation and calpain-dependent reduction of Bcl-2 after neonatal cerebral hypoxia-ischemia.

Apoptosis-related mechanisms are important in the pathophysiology of hypoxic-ischemic injury in the neonatal brain. Caspases are the major executioners of apoptosis, but there are a number of upstream players that influence the cell death pathways. The Bcl-2 family proteins are important modulators of mitochondrial permeability, working either to promote or prevent apoptosis. In this study we focused on the anti-apoptotic Bcl-2 protein after neonatal cerebral hypoxia-ischemia (HI) in 8-day-old rats. Bcl-2 translocated to nuclei and accumulated there over the first 24h of reperfusion after HI, as judged by immunohistochemistry and immuno-electron microscopy. We also found that the total level of Bcl-2 decreased after HI in vivo and after ionophore challenge in cultured human neuroblastoma (IMR-32) cells in vitro. Furthermore, the Bcl-2 reduction was calpain-dependent, because it could be prevented by the calpain inhibitor CX295 both in vivo and in vitro, suggesting cross-talk between excitotoxic and apoptotic mechanisms.

Long-term mucosal injury and repair in a murine model of pelvic radiotherapy.

Chronic intestinal injury after pelvic radiotherapy affects countless cancer survivors worldwide. A comprehensive understanding of the long-term injury dynamics is prevented in available animal models. With linear accelerators that are used to treat cancer in patients, we irradiated a small volume encompassing the colorectum in mice with four fractions of 8 Gy per fraction. We then determined the long-term dynamics of mucosal injury, repair, and the duration of inflammation. We show that crypt fission, not cell proliferation, is the main long-term mechanism for rescuing crypt density after irradiation, and provides a potentially wide window for clinical interventions. Persisting macrophage aggregations indicate a chronic mucosal inflammation. A better understanding as to how crypt fission is triggered and why it fails to repair fully the mucosa may help restore bowel health after pelvic radiotherapy. Moreover, anti-inflammatory interventions, even if implemented long after completed radiotherapy, could promote bowel health in pelvic cancer survivors.

Exercise in Adulthood after Irradiation of the Juvenile Brain Ameliorates Long-Term Depletion of Oligodendroglial Cells.

Cranial radiation severely affects brain health and function, including glial cell production and myelination. Recent studies indicate that voluntary exercise has beneficial effects on oligodendrogenesis and myelination. Here, we hypothesized that voluntary running would increase oligodendrocyte numbers in the corpus callosum after irradiation of the juvenile mouse brain. The brains of C57Bl/6J male mice were 6 Gy irradiated on postnatal day 9 during the main gliogenic developmental phase, resulting in a loss of oligodendrocyte precursor cells. Upon adulthood, the mice were injected with bromodeoxyuridine and allowed to exercise on a running wheel for four weeks. Cell proliferation and survival, Ascl1+ oligodendrocyte precursor and Olig2+ oligodendrocyte cell numbers as well as CC1+ mature oligodendrocytes were quantified using immunohistology. Radiation induced a reduction in the number of Olig2+ oligodendrocytes by nearly 50% without affecting production or survival of new Olig2+ cells. Ascl1+ cells earlier in the oligodendroglial cell lineage were also profoundly affected, with numbers reduced by half. By three weeks of age, Olig2+ cell numbers had not recovered, and this was paralleled by a volumetric loss in the corpus callosum. The deficiency of Olig2+ oligodendrocytes persisted into adulthood. Additionally, the depletion of Ascl1+ progenitor cells was irreversible, and was even more pronounced at 12 weeks postirradiation compared to day 2 postirradiation. Furthermore, the overall number of CC1+ mature oligodendrocytes decreased by 28%. The depletion of Olig2+ cells in irradiated animals was reversed by 4 weeks of voluntary exercise. Moreover, voluntary exercise also increased the number of Ascl1+ progenitor cells in irradiated animals. Taken together, these results demonstrate that exercise in adulthood significantly ameliorates the profound and long-lasting effects of moderate exposure to immature oligodendrocytes during postnatal development.

Different reactions to irradiation in the juvenile and adult hippocampus.

PURPOSE: Cranial radiotherapy is an important tool in the cure of primary brain tumors. Unfortunately, it is associated with late-appearing toxicity to the normal brain tissue, including cognitive impairment, particularly in children. The underlying mechanisms are not fully understood but involve changes in hippocampal neurogenesis. Recent studies report essentially different responses in the juvenile and the adult brain after irradiation, but this has never been verified in a comparative study. MATERIALS AND METHODS: We subjected juvenile (9-day-old) and adult (6-month-old) male rats to a single dose of 6 Gray (Gy) whole brain irradiation and euthanized them 6 hours, 7 days or 4 weeks later. Hippocampal lysates were analyzed for caspase-3 activity (apoptosis) and the expression of cytokines, chemokines and growth factors. Four weeks after irradiation, the number of microglia (expressing ionized calcium-binding adapter molecule 1, Iba-1), activated microglia (expressing cluster of differentiation 68 [CD68]), bromodeoxyuridine (BrdU) incorporation and granule cell layer (GCL) volume were assessed. RESULTS: The major findings were (i) higher baseline BrdU incorporation (cell proliferation) in juvenile than in adult controls, which explains the increased susceptibility to irradiation and higher level of acute cell death (caspase activity) in juvenile rats, leading to impaired growth and subsequently a smaller dentate gyrus volume 4 weeks after irradiation, (ii) more activated (CD68-positive) microglia in adult compared to juvenile rats, regardless of irradiation, and (iii) differently expressed cytokines and chemokines after cranial irradiation in the juvenile compared to the adult rat hippocampus, indicating a more pro-inflammatory response in adult brains. CONCLUSION: We found essentially diverse irradiation reactions in the juvenile compared to the adult hippocampus, indicating different mechanisms involved in degeneration and regeneration after injury. Strategies to ameliorate the cognitive deficits after cranial radiotherapy should therefore likely be adapted to the developmental level of the brain.