Functional changes in the rat distal colon after whole-body irradiation: dose-response and temporal relationships

Spectroscopic study of the effect of low dose fast neutrons on the hemoglobin structure

Cosmic rays, nuclear accidents, and neutron therapy could be sources for exposure to low-dose fast neutrons. However, the study of low dose effects needs sentient techniques to detect slight alteration happen by this low dose. Herein, the effects of low-dose fast neutrons on the structure of hemoglobin (Hb) using spectroscopic techniques, namely, Fourier transform infrared (FTIR), Raman, and ultraviolet-visible (UV-Vis) spectroscopic. Forty (20 control/20 irradiated) female Wistar rats were used in this work. The irradiated rats were irradiated to low-dose at a total dose of 10 mGy from a fast neutron source (241Am-Be, 0.2 mGy/h). Multivariate analyses were applied to differentiate between the control and irradiated rats' Raman spectra. The erythrocytes samples were isolated from whole blood to explore the Hb structure. FTIR results revealed changes in the ν(S-H) bond of α-104 and β-93 cysteines by low-dose fast neutrons. Raman spectra showed changes in the spin state and oxidation state of the iron atom of the Hb. Besides, deformation in methine C-H was recorded. UV-Vis spectroscopy disclosed that the irradiated rats might be more susceptive to oxidation than control rats. The study deduced that the low dose fast neutron could cause tiny Hb structure changes by indirect effects. Besides, the spectroscopic techniques showed a potent ability to reveal tiny changes in the Hb structure that happened by a low dose of fast neutrons.

Effect of low-dose fast neutrons on the protein components of peripheral blood mononuclear cells of whole-body irradiated Wistar rats

The immune system is exposed to extremely low doses of neutrons under different circumstances, such as through exposure to cosmic rays, nuclear accidents, and neutron therapy. Peripheral blood mononuclear cells (PBMCs) are the primary immune cells that exhibit selective immune responses. Changes in the functions of the protein components of PBMC can be induced by structural modifications of these proteins themselves. Herein, we have investigated the effect of low-dose fast neutrons on PBMC proteins at 0, 2, 4, and 8 days post-whole body irradiation. 64 Wistar rats were used in this study of which, 32 were exposed to fast neutrons at a total dose of 10 mGy (²⁴¹Am-Be, 0.2 mGy/h), and the other 32 were used as controls. Blood samples were drawn, and PBMCs were isolated from whole blood. Fourier transform infrared (FTIR) spectroscopy and fluorescence spectroscopy were used to estimate the changes in the proteins of PBMCs. An alkaline comet assay was performed to assess DNA damage. Hierarchical cluster analysis (HCA) and principal components analysis (PCA) were utilized to discriminate between irradiated and non-irradiated samples. FTIR and fluorescence spectra of the tested samples revealed alterations in the amides and tryptophan, and therefore protein structure at time intervals of 2 and 4 days post-irradiation. No changes were recorded in samples tested at time intervals of 0 and 8 days post-irradiation. The FTIR band intensities of the PBMC proteins of the irradiated samples decreased slightly and were statistically significant. Curve fitting of the amide I band in the FTIR spectra showed changes in the secondary structure of the proteins. At 2 days post-irradiation, fluorescence spectra of the tested samples revealed decreases in the band tryptophan. The comet assay revealed low levels of DNA damage. In conclusion, low-dose fast neutrons can affect the proteins of PBMC.

Radiation-induced hyposuppression of the hypothalamic-pituitary-adrenal axis is associated with alterations of hippocampal corticosteroid receptor expression

Therapeutic brain irradiation in children can cause a progressive decline in cognitive functions through a diminished capability to learn and memorize. Because of the known involvement of the hippocampus in memory consolidation, this study was aimed at examining the late effects of gamma radiation on hypothalamic-pituitary-adrenal (HPA) axis activity and hippocampal corticosteroid receptor expression in an animal model of cranial radiotherapy. In the late-response phase, the basal and stress-induced corticosterone levels were not affected by radiation, but the suppression of glucocorticoid negative feedback by dexamethasone was attenuated in irradiated rats. Western blot analyses showed that exposure to radiation led to a decrease of cytosolic glucocorticoid receptor (GR) levels and a concomitant elevation of mineralocorticoid receptor (MR). The results obtained were complemented by those of RT-PCR, since the ratio of GR/MR mRNA was also decreased after radiation exposure. Dexamethasone appeared to be much less effective in shifting GR to the nuclear compartment in irradiated rats than in sham-irradiated animals. However, the expression of chaperones that aid GR intracellular trafficking, Hsp90 and Hsp70, remained unaffected. In conclusion, our data suggest that the hallmark of the late response to gamma radiation is a hyposuppressive state of the HPA axis that is associated with a decrease in both the GR/MR ratio and the nuclear accumulation of dexamethasone-activated GR in the hippocampus.

Effects of Zinc Compound on Body Weight and Recovery of Bone Marrow in Mice Treated with Total Body Irradiation

This study aimed to investigate if zinc compound would have effects on body weight loss and bone marrow suppression induced by total body irradiation (TBI). ICR mice were divided randomly into two groups and treated with test or control compounds. The test compound contained zinc (amino acid chelated with bovine prostate extract), and the control was reverse osmosis pure water (RO water). One week after receiving the treatment, mice were unirradiated, or irradiated with 6 or 3 Gy by 6 MV photon beams to the total body. Body weight changes were examined at regular intervals. Three and 5 weeks after the radiation, animals were sacrificed to examine the histologic changes in the bone marrow. Lower body weight in the period of 1-5 weeks after radiation and poor survival rate were found after the 6 Gy TBI, as compared with the 3 Gy groups. The median survival time after 6 Gy and 3 Gy TBI for mice given the test compound were 26 and 76 days, respectively, and the corresponding figures were 14 and 70 days, respectively, for mice given the control compound (p < 0.00001). With zinc supplement, the mean body weight in mice which received the same dose of radiation was 7-8 g heavier than in the water-supplement groups during the second and third weeks (p < 0.05). Hence, there was no statistically significant difference in survival rate between zinc and water supplement in mice given the same dose of irradiation. Histopathologically, there was less recovery of bone marrow cells in the 6 Gy groups compared with the 3 Gy groups. In the 3 Gy water-supplement group, the nucleated cells and megakaryocytes were recovered in the fifth week when recovery was still not seen in the 6 Gy group. With zinc supplement, these cells were recovered in the third week. In this study, we found that zinc is beneficial to body weight in mice treated with TBI. Histologic examination of bone marrow showed better recovery of bone marrow cells in groups of mice fed with zinc. This study suggests that zinc can be used as supplements in cancer patients receiving radiotherapy to reduce radiation-induced complications.

Absorption, accumulation and biological effects of depleted uranium in Peyer's patches of rats

The digestive tract is the entry route for radionuclides following the ingestion of contaminated food and/or water wells. It was recently characterized that the small intestine was the main area of uranium absorption throughout the gastrointestinal tract. This study was designed to determine the role played by the Peyer's patches in the intestinal absorption of uranium, as well as the possible accumulation of this radionuclide in lymphoid follicles and the toxicological or pathological consequences on the Peyer's patch function subsequent to the passage and/or accumulation of uranium. Results of experiments performed in Ussing chambers indicate that the apparent permeability to uranium in the intestine was higher (10-fold) in the mucosa than in Peyer's patches ((6.21+/-1.21 to 0.55+/-0.35)x10(-6)cm/s, respectively), demonstrating that the small intestinal epithelium was the preferential pathway for the transmucosal passage of uranium. A quantitative analysis of uranium by ICP-MS following chronic contamination with depleted uranium during 3 or 9 months showed a preferential accumulation of uranium in Peyer's patches (1355% and 1266%, respectively, at 3 and 9 months) as compared with epithelium (890% and 747%, respectively, at 3 and 9 months). Uranium was also detected in the mesenteric lymph nodes ( approximately 5-fold after contamination with DU). The biological effects of this accumulation of depleted uranium after chronic contamination were investigated in Peyer's patches. There was no induction of the apoptosis pathway after chronic DU contamination in Peyer's patches. The results indicate no change in the cytokine expression (Il-10, TGF-beta, IFN-gamma, TNF-alpha, MCP-1) in Peyer's patches and in mesenteric lymph nodes, and no modification in the uptake of yeast cells by Peyer's patches. In conclusion, this study shows that the Peyer's patches were a site of retention for uranium following the chronic ingestion of this radionuclide, without any biological consequences of such accumulation on Peyer's patch functions.

Zingiber officinale exhibits behavioral radioprotection against radiation-induced CTA in a gender-specific manner

At the organismic level, exposure to radiation can produce taste aversion (CTA) learning and emesis, which have been proposed as behavioral endpoints that are mediated by harmful effects of radiations on peripheral systems, primarily the gastrointestinal system. Thus, the aim of the present investigation was to study the gastroprotective action of hydroalcoholic extract of zingiber rhizome (Zingiber officinale Rosc.) against radiation-induced conditioned taste aversion (CTA) in both male and female species of animals, for testing its potential as a behavioral radioprotector. Administration of zingiber extract 1 h before 2-Gy gamma-radiation was significantly effective in blocking the saccharin avoidance response, with 200 and 250 mg/kg b.wt. i.p., being the most effective doses for male and female rats, respectively. A comparison of the efficacy of zingiber extract with two antiemetic drugs, ondansteron and dexamethasone, revealed that the extract rendered comparable protection against radiation-induced CTA. Our experiments also confirmed the existence of sex dichotomy (i.e., the sex of animal greatly influenced response towards radiation exposure) in relation to behavioral responses (CTA) or differential metabolism. The observed gender variations were hypothesized to be a result of hormonal fluctuations and differences in pharmacological parameters in male and female rats. To correlate the mechanism of action, the free-radical-scavenging potential of zingiber extract to scavenge hydroxyl ion and nitric oxide was also tested, in cell-free system and a concentration of 1000 microg/ml, was found to be the most potent, which has been proposed as one the many activities assisting in its overall ability to modulate radiation-induced taste aversion. The results demonstrate that Z. officinale possesses antioxidant, radioprotective and neuromodulatory properties that can be effectively utilized for behavioral radioprotection and for efficiently mitigating radiation-induced CTA in both males and females species.

Differential qualitative and temporal changes in the response of the hypothalamus-pituitary-adrenal axis in rats after localized or total-body irradiation

Stress such as exposure to ionizing radiation is able to activate the hypothalamus-pituitary-adrenal axis. The present study sought to examine the effects of different configurations of a 10-Gy gamma irradiation in rats on the hypothalamus-pituitary-adrenal axis to understand the mechanism of negative feedback by glucocorticoids induced by ionizing radiation. Specifically, we determined adrenocorticotropin and corticosterone levels in plasma as well as corticotrophin-releasing factor expression in the paraventricular nucleus of the hypothalamus by in situ hybridization from 6 h to 4 days after total-body, abdominal or head irradiation. In this study, we found an activation of the hypothalamus-pituitary-adrenal axis after radiation exposure. Plasma adrenocorticotropin and corticosterone levels were significantly increased after total-body and abdominal irradiation 3 days after exposure, in parallel with decreased labeling of corticotrophin-releasing factor mRNA in the parvocellular region of the paraventricular nucleus of the hypothalamus. Our results suggest that ionizing radiation activates the neuroendocrine system to protect the organism from the occurrence of radiation-induced inflammation.

Effect of radiation on cAMP, cGMP and Ca(2+)(i) pathways and their interactions in rat distal colon

The secretory response implicated in the intestinal response to luminal attack is altered by radiation. The cAMP, cGMP and Ca(2+)(i) pathways leading to secretion as well as the interactions between the cAMP pathway and the cGMP or Ca(2+)(i) pathway were studied in the rat distal colon 4 days after a 9-Gy abdominal X irradiation, when modifications mainly occurred. The secretory response in Ussing chambers and cAMP and cGMP accumulation in single isolated crypts were measured. The muscarinic receptor characteristics were determined in mucosal membrane preparations. The secretory response by the cAMP pathway (stimulated by vasoactive intestinal peptide or forskolin) and the cAMP accumulation in crypts were decreased (P < 0.05) after irradiation. The weak secretory response induced by the cGMP pathway (stimulated by nitric oxide or guanylin) was unaltered by radiation, and the small amount of cGMP determined in isolated crypts from the control group became undetectable in the irradiated group. Inducible NOS was not involved in the hyporesponsiveness to VIP after irradiation (there was no effect of an iNOS inhibitor). The secretory response by the Ca(2+)(i) pathway (stimulated by carbachol) was unaffected despite a decreased number and increased affinity of muscarinic receptors. The non-additivity of VIP and carbachol co-stimulated responses was unmodified. In contrast, VIP and SNP co-stimulation showed that NO enhanced the radiation-induced hyporesponsiveness to VIP through a reduced accumulation of cAMP in crypts. This study provides further understanding of the effect of ionizing radiation on the intracellular signaling pathways.

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.

Characterization of altered absorptive and secretory functions in the rat colon after abdominal irradiation: comparison with the effects of total-body irradiation

The aim of this work was to determine the alterations in the absorptive and secretory functions of the rat colon after abdominal irradiation and to compare the effects of abdominal and whole-body irradiation. Rats received an abdominal irradiation with 8 to 12 Gy and were studied at 1, 4 and 7 days after exposure. Water and electrolyte absorption was measured in vivo by insertion of an agarose cylinder into the colons of anesthetized rats. In vitro measurements of potential difference, short-circuit current and tissue conductance were performed in Ussing chambers under basal and agonist-stimulated conditions. Most of the changes appeared at 4 days after abdominal irradiation. At this time, a decrease in water and electrolyte absorption in the colon was observed for radiation doses > or = 9 Gy. The response to secretagogues (VIP, 5-HT and forskolin) was attenuated after 10 and 12 Gy. Epithelial integrity, estimated by potential difference and tissue conductance, was altered from 1 to 7 days after 12 Gy abdominal irradiation. These results show that the function of the colon was affected by abdominal irradiation. Comparison with earlier results for total-body irradiation demonstrated a difference of 2 Gy in the radiation dose needed to induce changes in the function of the colon.

Characterization of the acute inflammatory response after irradiation in mice and its regulation by interleukin 4 (Il4)

The aim of this study was to determine the effects of total-body irradiation of mice on the acute release of a panel of several mediators of inflammation and to evaluate the efficacy of Il4 in regulating these radiation-induced modifications. We studied the effects of exposure of C57BL6/J mice to 8 Gy gamma rays on the early release of cytokines, chemokines, acute-phase proteins, prostaglandins and corticosterone in either plasma or tissues compared to those observed after intraperitoneal injection of lipopolysaccharide from 1 h to 3 days after stimulation. During the characterization of the acute inflammatory response induced by radiation or lipopolysaccharide, we observed differences both in the type of mediators produced and in the time course of release. We next determined the anti-inflammatory potential of Il4 in this model of total-body irradiation. We found that Il4 was able to down-regulate the radiation-induced production of mediators of inflammation such as Gro1 (also known as KC, N51) in plasma and lung, corticosterone in blood, Il1b in lung, and prostaglandin E(2) in colon, suggesting the anti-inflammatory potential of Il4 in regulating the radiation-induced response.