Natural-history Characterization of a Murine Partial-body Irradiation Model System: Establishment of a Multiple-Parameter Based GI-ARS Severity-Scoring System

The purpose of this investigation was to characterize the natural history of a murine total-abdominal-irradiation exposure model to measure gastrointestinal acute radiation injury. Male CD2F1 mice at 12 to 15 weeks old received total-abdominal irradiation using 4-MV linear accelerator X-rays doses of 0, 11, 13.5, 15, 15.75 and 16.5 Gy (2.75 Gy/min). Daily cage-side (i.e., in the animal housing room) observations of clinical signs and symptoms including body weights on all animals were measured up to 10 days after exposure. Jejunum tissues from cohorts of mice were collected at 1, 3, 7 and 10 days after exposure and radiation injury was assessed by histopathological analyses. Results showed time- and dose-dependent loss of body weight [for example at 7 days: 0.66 (±0.80) % loss for 0 Gy, 6.40 (±0.76) % loss at 11 Gy, 9.43 (±2.06) % loss at 13.5 Gy, 23.53 (± 1.91) % loss at 15 Gy, 29.97 (±1.16) % loss at 15.75 Gy, and 31.79 (±0.76) % loss at 16.5 Gy]. Negligible clinical signs and symptoms, except body weight changes, of radiation injury were observed up to 10 days after irradiation with doses of 11 to 15 Gy. Progressive increases in the severity of clinical signs and symptoms were found after irradiation with doses >15 Gy. Jejunum histology showed a progressive dose-dependent increase in injury. For example, at 7 days postirradiation, the percent of crypts, compared to controls, decreased to 82.3 (±9.5), 69.2 (±12.3), 45.4 (±11.9), 18.0 (±3.4), and 11.5 (± 1.8) with increases in doses from 11 to 16.5 Gy. A mucosal injury scoring system was used that mainly focused on changes in villus morphology damage (i.e., subepithelial spaces near the tips of the villi with capillary congestion, significant epithelial lifting along the length of the villi with a few denuded villus tips). Peak levels of total-abdominal irradiation induced effects on the mucosal injury score were seen 7 days after irradiation for doses ≥15 Gy, with a trend to show a decline after 7 days. A murine multiple-parameter gastrointestinal acute-radiation syndrome severity-scoring system was established based on clinical signs and symptoms that included measures of appearance (i.e., hunched and/or fluffed fur), respiratory rate, general (i.e., decreased mobility) and provoked behavior (i.e., subdued response to stimulation), weight loss, and feces/diarrhea score combined with jejunum mucosal-injury grade score. In summary, the natural-history radio-response for murine partial-body irradiation exposures is important for establishing a well-characterized radiation model system; here we established a multiple-parameter gastrointestinal acute-radiation syndrome severity-scoring system that provides a radiation injury gastrointestinal tissue-based assessment utility.

Effect of antioxidant supplementation on digestive enzymes in radiation induced intestinal damage in rats

PURPOSE

Intestinal mucosa, a rapidly proliferating tissue, is highly sensitive to radiation and undergoes apoptosis as a consequence of over generation of oxidative free radicals and the lack of the antioxidants. Thus the present study was designed to investigate the intestinal damage induced by radiation and to study if supplementation of the diet with antioxidant vitamins could ameliorate the intestinal damage and its digestive activity, as determined by the expression of various border enzymes.

MATERIALS AND METHODS

Swiss Albino rats (150-200 g body weight) were divided into six groups. Group I: Control untreated; Group II: Irradiated; Group III: Irradiated + vitamin A; Group IV: Irradiated + vitamin C; Group V: Irradiated + vitamin E; and Group VI: Irradiated + lycopene. Animals were exposed to whole body γ-radiation from (60)Co at the rate of 8 Gy for 15 min/rat. Intestinal morphology and changes in various digestive enzymes together with, DNA damage was studied in six groups and each group consisted of 18 animals.

RESULTS

The gastrointestinal toxicity resulted in malabsorption, diarrhoea, weight loss, loss of appetite, abdominal haemorrhage and hair loss. The activities of sucrase and alkaline phosphatase were elevated and those of lactase, leucine aminopeptidase (LAP) and gamma-glutamyl transpeptidase or tranferase (γ-GTP) were markedly reduced. Antioxidant vitamin A, C or E supplementations prevented changes in brush border enzyme activities as compared to lycopene administration in rat intestine by radiation exposure. Intestinal histology showed that the vitamin supplementation to irradiated rats minimized the intestinal damage in rats.

CONCLUSION

These findings suggest that the epithelial lining of the intestine is highly sensitive to radiation exposure and supplementation of antioxidant vitamins is helpful in minimizing the intestinal damage and supplementation by vitamin E was most potent in ameliorating the intestinal aberrations.

Efficacy of glutamine in the prevention of acute radiation enteritis: a randomized controlled trial

BACKGROUND

Acute radiation enteritis is a common adverse effect related to radiotherapy (RT). Glutamine is an immune modulator and antioxidant amino acid that can exert a protective role in patients receiving abdominal or pelvic radiation. The aim of this study was to test if glutamine prevents radiation enteritis during RT.

MATERIALS AND METHODS

Double-blind, randomized, controlled trial including 69 patients who needed RT because of pelvic or abdominal malignancies and received glutamine (30 g/d) or placebo (casein, 30 g/d). Enteritis was evaluated according to the Radiation Therapy Oncology Group scale, intestinal inflammation using fecal calprotectin, and gut integrity with citrulline. The incidence of enteritis was analyzed by Kaplan-Meier curves, and the hazard ratio (HR) was calculated using Cox regression.

RESULTS

Patients were predominantly male (65.2%), with an average (SD) age of 66.6 (9.9) years, with urologic (44.9%), rectal (24.6%), or gynecological cancer (23.1%). More patients developed enteritis with glutamine than with the placebo (55.9% vs 22.0%; P = .002), with an HR OF 1.59 (95% confidence interval, 0.624.05). There were no differences in final calprotectin levels (glutamine, 57.9 [85.8] mg/kg vs placebo, 54.0 [57.7] mg/kg; p = .182) or the number of patients with values 50 mg/kg (glutamine, 58.1% vs placebo, 54.6%; p = .777). Final citrulline levels were similar between groups (glutamine, 26.31 [10.29] mmol/l vs placebo, 27.69 [12.31] mmol/l; p = .639), without differences in the number of patients with 20 mmol/l (glutamine, 24.1% vs placebo, 25.0%; P = .938). Citrulline concentration was reduced during rt with placebo but remained unchanged with glutamine.

CONCLUSION

Glutamine does not prevent the development of enteritis during RT.

The age-related decline in intestinal lipid uptake is associated with a reduced abundance of fatty acid-binding protein

Aging is associated with changes in the absorptive capacity of the small intestine. We tested the hypotheses that (i) aging is associated with a decline in lipid absorption, and that (ii) this decreased lipid absorption is due to a decline in the abundance of mRNA and/or the enterocyte cytosolic intestinal FA-binding protein (I-FABP), the liver FA-binding protein (L-FABP), and the ileal lipid-binding protein (ILBP). In vitro uptake studies were performed on Fischer 344 rats at ages 1, 9, and 24 mon. Northern blotting (L-FABP, ILBP) and immunohistochemistry (I-FABP, ILBP) were performed. Aging was associated with decreased animal weights, but the surface area of the intestine was not significantly altered with age. The rates of ileal uptake of 16:0, 18:0, 18:1, and 18:2 were reduced by greater than 50% with aging when expressed on the basis of mucosal weight. This decline was not associated with reduced expression of mRNA for L-FABP or ILBP but was associated with a 50% decrease in the abundance of I-FABP and a 40% decrease in the abundance of ILBP. Thus, the decrease with aging in the ileal uptake of some FA when rates were expressed on the basis of mucosal weight was associated with a reduced abundance of I-FABP and ILBP.

An isocaloric PUFA diet enhances lipid uptake and weight gain in aging rats

Aging is associated with a change in the morphology and absorptive capacity of the small intestine. In young rats, feeding a semisynthetic diet containing saturated FA (SFA) increases nutrient uptake, as compared with an isocaloric diet containing polyunsaturated FA (PUFA). We tested the hypotheses that (i) aging is associated with a decline in lipid absorption in the Fischer 344 rat; (ii) this decline can be corrected by manipulating the fat composition of the diet; and (iii) the age- and diet-associated variations in lipid uptake are associated with changes in the ileal lipid-binding protein (ILBP) or the intestinal or liver FA-binding proteins (I- or L-FABP, respectively) in the cytosol of the enterocyte. In rats fed SFA or PUFA, aging was associated with a decline in the in vitro uptake of stearic acid (18:0) when expressed on the basis of intestinal or mucosal weight. In contrast, age had no effect on lipid uptake when expressed on the basis of serosal surface area, whereas lipid uptake increased with age when expressed on the basis of mucosal surface area. The age-associated variations in lipid uptake were not associated with changes in protein abundance and/or expression of ILBP, I-FABP, or L-FABP. In 24-mon-old rats, when uptake of lipids was expressed on the basis of mucosal surface area, feeding PUFA enhanced lipid uptake and body weight gain as compared with rats fed SFA. Future studies must determine whether the enhanced lipid uptake and body weight gain observed in older animals fed PUFA have any therapeutic benefit.

Dietary lipids alter the effect of steroids on the transport of glucose after intestinal resection: Part I. Phenotypic changes and expression of transporters

BACKGROUND/PURPOSE

Glucocorticosteroids alter the function of the intestine. This study was undertaken to assess the effect on D-glucose uptake of budesonide (Bud), prednisone (Pred), or dexamethasone (Dex) in animals with a 50% intestinal resection and fed chow or a diet enriched with saturated (SFA) or polyunsaturated fatty acids (PUFA).

METHODS

In vitro ring uptake technique, Western blots, and Northern blots were performed.

RESULTS

Bud increased the jejunal D-glucose uptake, and this effect was prevented by feeding PUFA. SGLT1 and Na+/K+ ATPase protein and mRNA abundance did not correlate with the change in the rate of uptake of glucose.

CONCLUSIONS

(1) Bud increased the jejunal glucose uptake, (2) the activity of the sugar transporter does not correlate with the abundance of protein or their respective mRNAs, (3) th Bud effect on glucose uptake is prevented by feeding PUFA. Thus, the desired intestinal adaptive response after intestinal resection may be enhanced further by the administration of the locally acting steroid budesonide and by feeding a saturated compared with a polyunsaturated fatty acid diet.

Alterations of the VIP-stimulated cAMP pathway in rat distal colon after abdominal irradiation

Ionizing radiation induces hyporesponsiveness of rat colonic mucosa to vasoactive intestinal peptide (VIP). Possible mechanisms responsible for this hyporesponsiveness of the cAMP communication pathway in rat colon were investigated. VIP- and forskolin-stimulated short-circuit current (I(sc)) responses were studied after a 10-Gy abdominal irradiation in Ussing chambers as well as in single, isolated crypts. Adenylyl cyclase (AC) activity and VIP receptor characteristics were determined in mucosal membrane preparations. In addition, alterations in crypt morphology were studied. Impaired secretory responses to VIP and forskolin were observed 4 days after irradiation (decrease of 80%). cAMP analog-stimulated I(sc) responses were unchanged. In isolated crypts, VIP- and forskolin-stimulated cAMP accumulation was markedly reduced by 80 and 50%, respectively. VIP-stimulated AC activity and VIP receptor number were decreased in membrane preparations. No major change of cellularity was associated with these functional alterations. In conclusion, the decreased secretory responses to VIP of rat colon are associated with reduced cAMP accumulation, decreased AC activity, and diminution of VIP receptor numbers without a marked decrease of crypt cell number.

Morphological aspects of ionizing radiation response of small intestine

Knowledge of the acute and late ionizing radiation exposure damage to the gastrointestinal tract, particularly injury of the small intestine, is of great significance in radiotherapy, as is management of accidental radiation exposure. Irradiation (X-ray, neutron, cobalt gamma) induces a series of events in this rapidly renewing tissue resulting in the well-known symptoms of the gastrointestinal (GI) radiation syndrome, such as GI haemorrhage, endotoxemia, bacterial infection, anorexia, nausea, vomiting, diarrhoea, and loss of electrolytes and fluid. In spite of the significant advances that have occurred in research on underlying mechanisms over the last two decades, the overall etiology and pathogenesis of the GI-syndrome still remains unclear. Currently, to our knowledge, these symptoms are probably due to a rapid modification of the intestinal motility and to the structural alteration of the intestinal mucosa (cell loss and altered crypt integrity). Several evidences suggest that radiation-induced dysfunctions and structural changes of this organ (either changes in subcellular, cellular, and histological structure) are mediated by concerted and interrelated changes of a plethora of various extracellular mediators and their intracellular messengers. The aim of this review is to summarize our current knowledge about the pathomorphology and cell biology of the ionizing radiation response of the GI tract with a focus on the small intestine.

Effects of radiation damage on intestinal morphology

The current flow of papers on intestinal structure, radiation science, and intestinal radiation response is reflected in the contents of this review. Multiparameter findings and changes in compartments, cells, or subcellular structure all contribute to the overall profile of the response. The well-recognized changes in proliferation, vessels, and fibrogenesis are accompanied by alterations in other compartments, such as neuroendocrine or immune components of the intestinal wall. The responses at the molecular level, such as in levels of hormones, cytokines, or neurotransmitters, are of fundamental importance. The intestine responds to localized radiation, or to changes in other organs that influence its structure or function: some structural parameters respond differently to different radiation schedules. Apart from radiation conditions, factors affecting the outcome include the pathophysiology of the irradiated subject and accompanying treatment or intervention. More progress in understanding the overall responses is expected in the next few years.

Ionizing radiation stimulates muscarinic regulation of rat intestinal mucosal function

The aim of this study was to determine whether ionizing radiation modifies muscarinic regulation of intestinal mucosal function. Rats exposed to total body 8-Gy gamma-irradiation or sham irradiated were studied up to 21 days after irradiation. Basal and carbachol-stimulated short-circuit current (Isc) and transepithelial conductance (Gt) of stripped ileum were determined in Ussing chambers. Muscarinic receptor characteristics using the muscarinic antagonist [3H]quinuclidinyl benzilate and three unlabeled antagonists were measured in small intestinal plasma membranes together with two marker enzyme activities (sucrase, Na+-K+-ATPase). Enzyme activities were decreased 4 days after irradiation (day 4). Basal electrical parameters were unchanged. Maximal carbachol-induced changes in Isc and Gt were increased at day 4 (maximal DeltaIsc = 195.8 +/- 14.7 microA/cm2, n = 19, vs. 115.4 +/- 8.2 microA/cm2, n = 63, for control rats) and unchanged at day 7. Dissociation constant was decreased at day 4 (0.73 +/- 0.29 nM, n = 10, vs. 2.14 +/- 0.39 nM, n = 13, for control rats) but unchanged at day 7, without change in binding site number. Thus total body irradiation induces a temporary stimulation of cholinergic regulation of mucosal intestinal function that may result in radiation-induced diarrhea.

Inhibition of lipid absorption as an approach to the treatment of obesity

A reduction in fat intake may be achieved by making educated choices to reduce total calorie intake, to consume a lower quantity of total fats, or to modify the ratio of saturated-to-polyunsaturated lipids. Leptin agonists or NPY or CCK antagonists may prove to be useful to diminish appetite and thereby reduce the total intake of food. But eating has such cultural, social, and hedonistic attributes that such a single-pronged approach is unlikely to be successful. The use of fat substitutes may prove to be popular to provide a wide range of snack food options, but these are likely to be of minimal use in weight reduction programs because of their distribution of additives in only a limited number of foods. The inhibitors of lipid digestion will be modestly successful in the short term; their long-term success will be influenced by gastrointestinal adverse effects and the need to consume fat-soluble vitamin supplements to prevent the development of fat-soluble vitamin deficiencies. The inhibition of lipid absorption is an attractive targeted approach for the treatment of obesity, since this would reduce the uptake of visible as well as invisible fats, which would potentially offer convenient dosing, and could also be a means to inhibit secondarily the uptake of carbohydrate calories.

Refeeding varying fatty acid and cholesterol diets alters phospholipids in rat intestinal brush border membrane

Refeeding a diet initially given shortly after weaning results in a different adaptive change in the in vitro intestinal uptake of sugars and lipids than if the diet is given for the first time at a later age. This study was undertaken in rats to test the hypothesis that changes in nutrient uptake associated with refeeding diets containing beef tallow (S), beef tallow plus 1% cholesterol (Sc), fish oil (F), or fish oil plus cholesterol (Fc) are associated with changes in the brush border membrane (BBM) phospholipids and phospholipid fatty acids. Weanling Sprague-Dawley rats were fed ad libitum one of the four diets. At 35 d of age (about 2 wk after weaning), the rats were maintained on either the same diet used at weaning, or were switched to one of the other semisynthetic diets which were then fed for a further 7 wk. At week nine (2 + 7) the rats were either continued on the same diet or were switched back to the original diet for 2 wk (2 + 7 + 2). The groups of animals which were compared included SSSc vs. ScSSc; ScScS vs. SScS; FFFc vs. FcFFc; and FcFcF vs. FFcF. Refeeding S, Sc, F, or Fc had no effect on food consumption or on body weight gain. Refeeding Fc resulted in increased ileal BBM total phospholipids, whereas rechallenge with F resulted in a decline in the jejunal BBM ratio of phospho-lipid/cholesterol. Refeeding Sc resulted in a decrease in the ileal BBM phosphatidylcholine (PC). In rats rechallenged with Fc, there was increased ileal BBM sphingomyelin (SM), increased ileal BBM phosphatidylethanolamine (PE), decreased ileal BBM PC/PE, and an increased ileal BBM SM/PC. Refeeding had no effect on the fatty acyl constituents of the jejunal of ileal BBM PC or PE. These results suggest that there are late effects of the early introduction of dietary cholesterol on intestinal BBM phospholipid content and composition that may contribute to the previously reported changes in intestinal nutrient absorption.

Crypt cell production rate, enterocyte turnover time and appearance of transport along the jejunal villus of the rat

Intestinal nutrient absorption is subject to adaptation with, for example, diabetes, diet lipid variations (isocaloric semisynthetic diets enriched with saturated (S) or polyunsaturated (P) fatty acids), ileal resection and abdominal irradiation. These models were used in rats to assess dynamic morphology and distribution of amino acid transporter along the villus. The enterocyte migration rate (EMR) was measured using [3H]thymidine; the vincristine metaphase arrest technique was used to determine the crypt cell production rate (CCPR); quantitative autoradiography was used to assess the time and age of enterocytes when the uptake of 1 and 20 mM [3H]leucine and [3H]lysine was initiated along the villus. The enhanced jejunal uptake of nutrients which occurs after a 50% distal enterectomy was associated with a fall in EMR and CCPR, yet the enhanced nutrient uptake which occurs in diabetes is not associated with any alteration in EMR, CCPR, enterocyte transport pool (ETP), i.e., the length of the enterocyte column along with the villus containing amino acid transporter) or expression of transporter along the villus. The reduced uptake of nutrients in rats fed P as compared with S was associated with increased rather than decreased ETP and age of the enterocytes at the tip of the villus. The reduced nutrient uptake which occurs 3 days after abdominal irradiation was associated with increased EMR and CCPR, and reduced ETP and age of enterocytes of the tip of the villus. However, 14 days after irradiation when nutrient transport remains reduced, these parameters have returned to normal. Thus, alterations in nutrient transport may be associated with changes in the dynamic morphology of the intestine, but the two processes are not necessarily interdependent. We speculate that the changes in the dynamic morphology of the intestine, and the changes of amino acid transport which occurs in these models of intestinal adaptation, are independently controlled.

Dose-response studies of depletion and repopulation of rat intestinal mucosal mast cells after irradiation

The effects of radiation on gut mucosal mast cells (MMC) and tissue eosinophils were examined. Groups of rat were given single doses of whole-body irradiation from 0.5 to 5 Gy. Serum rat mast cell protease II (RMCPII) concentration showed a significant dose-dependent fall after 1 Gy on day 3 and 1.5 Gy on day 7. MMC counts and tissue RMCPII values on day 7 decreased significantly by 70% after 1 Gy and were undetectable with larger doses. Rat with normal and expanded MMC populations were irradiated or given anaphylaxis. Serum RMCPII concentrations did not change after irradiation, but there was a 10-fold increase in RMCPII after anaphylaxis. Tissue eosinophils in jejunum were 50% of control at 7 days after 2 Gy, and this effect was progressively more marked with higher doses. Similar effects on MMC and eosinophils were demonstrated in ileum, ascending colon and rectum. After 4.5 Gy, repopulation of the gut with MMC did not occur until week 3-4 postirradiation and MMC counts were still 50% below those of controls at 5 weeks postirradiation. Counts of tissue eosinophils 5 weeks after 4.5 Gy irradiation had returned to control levels in jejunum but were still significantly depleted in colon. These experiments show that the high radiosensitivity of rat intestinal MMC is dose dependent, similar at four different levels in the gastrointestinal tract and does not lead to immediate release of granule protease; repopulation with MMC does not begin until at 3 weeks postirradiation.

Administration of milk from cows immunized with intestinal bacteria protects mice from radiation-induced lethality

Oral administration of "immune milk", that had been obtained from cows immunized with a variety of human gut bacteria containing E. coli, S. typhimurium, S. dysenteriae and 23 others, protected AKR/J mice from the lethal effect of radiation, when immune milk was orally given to mice at 150 g kg-1 day-1 for 7 days prior to gamma-irradiation of 8 Gy. Mean survival times were 24.8 days for the group given immune milk but only 16.8 days for the group given control milk from unimmunized cows. Enterobacteriaceae were detected in various organs such as liver, lung and kidney on day 13 after irradiation, whereas the numbers were significantly fewer in the study group as compared with the control group. And fewer number of intestinal Enterobacteriaceae were detected in the study group compared with the control group prior to irradiation. Immune milk also enhanced the mitogenic response to mesenteric lymph node cells, the redirected cytolytic activity of intestinal intraepithelial lymphocytes to P815 tumor cells with anti-CD3 mAb, and in vitro killing activities of the phagocytes in mesenteric lymph nodes to E. coli as compared with control milk. These results suggest that immune milk may reduce the number of bacteria translocating from the intestinal-tract and augment the activities of the gut-associated lymphoid tissues against the invasion of intestinal bacteria, causing protection against the lethal effect of radiation.

Lipid composition and peroxide levels of mucosal cells in the rat large intestine in relation to dietary fat

To examine whether dietary fat alters membrane lipid composition and peroxidation of polyunsaturated fatty acids in "non-proliferative" and "proliferative" cells in the large intestine, Sprague-Dawley rats were fed diets providing a polyunsaturated-to-saturated fatty acid ratio of 1.2 or 0.3 at a high or low level of fat intake for a 25-day period. Cell populations were isolated and the effect of dietary fat on membrane polyunsaturated fatty acid content and peroxide levels was determined. Neither fat level nor fatty acid composition of diet influenced total cholesterol, total phospholipids, and percentage of phospholipid classes in membrane phospholipids. Feeding the high fat and/or high polyunsaturated-to-saturated fatty acid ratio diet increased polyunsaturated fatty acid content of mucosal cell phospholipids. Increase in polyunsaturated fatty acid content was paralleled by a decrease in the monounsaturated fatty acid content of mucosal cell phospholipids. Membrane content of total saturated fatty acids was not significantly affected by diet. Variation in phospholipid fatty acid composition between "non-proliferative" and "proliferative" cells was observed. Lipid peroxide levels in mucosal cell lipid fractions were altered by dietary fat treatment. Animals fed high fat diets, compared to groups fed low fat diets, exhibited higher membrane peroxide levels when results are expressed as nmol/mg protein. Higher peroxide levels were observed in mucosal cells for rats fed high polyunsaturated-to-saturated fatty acid ratio diets when results were expressed per nmol of phospholipid. It is concluded that changes in fat level and fatty acid composition of the diet alters the mucosal cell membrane lipid composition in the rat large intestine and influences susceptibility of mucosal cell lipid to peroxidation. Further research is required to delineate which dietary factors--fat level, polyunsaturated-to-saturated fatty acid ratio, or both--have a primary influence on the degree of lipid peroxidation.