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author:("Pathak, rupa")
1.  C/EBPδ Deficiency Sensitizes Mice to Ionizing Radiation-Induced Hematopoietic and Intestinal Injury 
PLoS ONE  2014;9(4):e94967.
Knowledge of the mechanisms involved in the radiation response is critical for developing interventions to mitigate radiation-induced injury to normal tissues. Exposure to radiation leads to increased oxidative stress, DNA-damage, genomic instability and inflammation. The transcription factor CCAAT/enhancer binding protein delta (Cebpd; C/EBPδ is implicated in regulation of these same processes, but its role in radiation response is not known. We investigated the role of C/EBPδ in radiation-induced hematopoietic and intestinal injury using a Cebpd knockout mouse model. Cebpd−/− mice showed increased lethality at 7.4 and 8.5 Gy total-body irradiation (TBI), compared to Cebpd+/+ mice. Two weeks after a 6 Gy dose of TBI, Cebpd−/− mice showed decreased recovery of white blood cells, neutrophils, platelets, myeloid cells and bone marrow mononuclear cells, decreased colony-forming ability of bone marrow progenitor cells, and increased apoptosis of hematopoietic progenitor and stem cells compared to Cebpd+/+ controls. Cebpd−/− mice exhibited a significant dose-dependent decrease in intestinal crypt survival and in plasma citrulline levels compared to Cebpd+/+ mice after exposure to radiation. This was accompanied by significantly decreased expression of γ-H2AX in Cebpd−/− intestinal crypts and villi at 1 h post-TBI, increased mitotic index at 24 h post-TBI, and increase in apoptosis in intestinal crypts and stromal cells of Cebpd−/− compared to Cebpd+/+ mice at 4 h post-irradiation. This study uncovers a novel biological function for C/EBPδ in promoting the response to radiation-induced DNA-damage and in protecting hematopoietic and intestinal tissues from radiation-induced injury.
PMCID: PMC3991713  PMID: 24747529
2.  Metabolomic Changes in Gastrointestinal Tissues after Whole Body Radiation in a Murine Model 
Molecular bioSystems  2013;9(4):723-731.
Exposure to ionizing radiation (IR) elicits a set of complex biological responses involving gene expression and protein turnover that ultimately manifest as dysregulation of metabolic processes representing the cellular phenotype. Although radiation biomarkers have been reported in urine and serum, they are not informative about IR mediated tissue or organ specific injury. In the present study we report IR induced metabolic changes in gastrointestinal (GI) tissue of CD2F1 mice using ultra-performance liquid chromatography (UPLC) coupled with electrospray time-of-flight mass spectrometry. Post-radiation GI injury is a critical determinant of survival after exposure to IR. Our results show a distinct dose and time dependent response to GI tissue injury.
PMCID: PMC3601576  PMID: 23403731
3.  Reduction of radiation-induced vascular nitrosative stress by the vitamin E analog, γ-tocotrienol: evidence of a role for tetrahydrobiopterin 
The vitamin E analog γ-tocotrienol (GT3) is a powerful radioprotector. GT3 reduces post-radiation vascular peroxynitrite production, an effect dependent on inhibition of hydroxy-methyl-glutaryl coenzyme A (HMG-CoA) reductase. HMG-CoA reductase inhibitors mediate their pleiotropic effects via eNOS that requires the co-factor tetrahydrobiopterin (BH4). This study investigated the effects of radiation on BH4 bioavailability and of GT3 on BH4 metabolism.
Methods and Materials
Mice were exposed to 8.5 Gy total body irradiation (TBI). Lung BH4 and total biopterin concentrations were measured 0, 3.5, 7, 14 and 21 days after TBI using differential oxidation followed by HPLC. The effect of exogenous GT3 and BH4 treatment on post-radiation vascular oxidative stress and bone marrow colony-forming units (BM-CFU) were assessed in vivo. The effect of GT3 on endothelial cell apoptosis and endothelial expression of GTP cyclohydrolase 1 (GTPCH), GTPCH regulatory protein (GFRP), GFRP transcription, GFRP protein levels, and GFRP-CTPCH protein binding were determined in vitro.
Compared to baseline levels, lung BH4 concentrations decreased by 24% at 3.5 days after TBI, an effect that was reversed by GT3. At 14 and 21 days after TBI, compensatory increases in BH4 (58% and 80%, respectively) were observed. Relative to vehicle-treated controls, both GT3 and BH4 supplementation reduced post-irradiation vascular peroxynitrite production at 3.5 days (by 66% and 33%, respectively), and BH4 resulted in a 68% increase in BM-CFU. GT3 ameliorated endothelial cell apoptosis and reduced endothelial GFRP protein levels and GFRP-GTPCH binding by decreasing transcription of the GFRP gene.
BH4 bioavailability is reduced in the early post-radiation phase. Exogenous administration of BH4 reduces post-irradiation vascular oxidative stress. GT3 potently reduces the expression of GFRP, one of the key regulatory proteins in the BH4 pathway, and may thus exert some of its beneficial effects on post-radiation free-radical production partly by counteracting the decrease in BH4.
PMCID: PMC3023840  PMID: 20950957
radiation; oxidative stress; nitric oxide synthase; tetrahydrobiopterin; vitamin E; endothelial cells
4.  Differential radio-sensitivities of human chromosomes 1 and 2 in one donor in interphase- and metaphase-spreads after 60Co γ-irradiation 
Radiation-induced chromosome aberrations lead to a plethora of detrimental effects at cellular level. Chromosome aberrations provide broad spectrum of information ranging from probability of malignant transformation to assessment of absorbed dose. Studies mapping differences in radiation sensitivities between human chromosomes are seldom undertaken. Consequently, health risk assessment based on radio-sensitivities of individual chromosomes may be erroneous. Our efforts in this article, attempt to demonstrate differences in radio-sensitivities of human chromosome-1 and/or -2, both in interphase and metaphase spreads.
Upon blood collection, dosimetry and irradiation were performed. Lymphocytes were isolated after whole-blood irradiation with 60Co γ-rays in the dose range of 0–5 Gy for both interphase, and metaphase aberration studies. Induction of premature chromosome condensation in interphase cells was accomplished using a phosphatase inhibitor, calyculin-A. Metaphase spreads were harvested from short-term peripheral blood lymphocyte cultures following colcemid arrest and using an automated metaphase harvester and spreader. Aberration analysis in both interphase and metaphase spreads were done using FISH.
In interphase, aberrant cell and aberration frequency involving chromosome 1 and/or 2 increased linearly with radiation dose. In metaphase, aberrations increased in a linear-quadratic manner with dose. Our studies ascertain that chromosome-2 is more radio-sensitive than chromosome-1 in both interphase and metaphase stages, albeit the DNA content of chromosome-2 is lesser than chromosome-1 by almost 10 million base pairs.
Differences in radio-sensitivities of chromosomes have implications in genetic damage, chromosome organization, and chromosome function. Designing research experiments based on our vital findings may bring benefit to radiation-induced risk assessment, therapeutics and development of chromosome specific biomarkers.
PMCID: PMC2704179  PMID: 19531236

Results 1-4 (4)