Differential basal expression of genes associated with stress response, damage control, and DNA repair among mouse tissues

Safety evaluation of ethanolic extract from aerial flowering part of spiny globe thistle (Echinops spinosus) in mice: Phytochemical screening and genotoxicity

Echinops spinosus is widely used by the population due to its therapeutic potential; however, there is no evidence in the literature that substantiates its safety. Therefore, this study aimed to identify the chemical constituents of E. spinosus extract via GC/MS analysis and evaluate its cytotoxicity and genotoxicity. Male mice were orally given three doses of E. spinosus extract (250, 500, and 1000 mg/kg) for four weeks. Blood and tissue samples were collected after the end of treatment. GC-MS results revealed 73 compounds in the E. spinosus extract, including sugars, sugar alcohols, fatty acids, organic acids, amino acids, and nitrogenous compounds. In vitro experiments revealed that E. spinosus was not cytotoxic to human colon, prostate, or breast cancer cells. In vivo experiments showed that E. spinosus extract did not significantly induce chromosomal damage in the bone marrow, primary spermatocyte, or sperm morphology abnormalities at doses up to 1000 mg/kg/day. This extract also did not induce DNA damage at doses ≤ 500 mg/kg/day in the bone marrow, spleen, testis, or spermatozoa and at 250 mg/kg/day in the liver or kidney. However, treatment with a high dose of E. spinosus caused significant disturbances in liver and kidney functions, oxidative stress indicators, comet tail formation, and histological architecture of the liver, kidney, and testis. In conclusion, E. spinosus extract is nontoxic, with an oral LD50 > 5000 mg/kg. The extract showed negative genotoxicity within the safety threshold of ≤ 500 mg/kg/day and positive genotoxicity at a dose of 1000 mg/kg/day.

Effects of low-dose, short-duration periods of asymmetric radiation on colony formation of C6 glioma cell cultures

Background/Aim: Previous studies on fractionation in radiation therapy have been mainly based on applying equal doses over at least 6 h. The main purpose of fractionation is to increase normal tissue tolerance rather than tumor sensitivity. Thus, one can apply higher doses to the tumor. In contrast, new molecular studies indicate that high and low doses of radiation act by different mechanisms. This study was conducted to investigate the radiobiological effect of asymmetrical radiation doses. Methods: This is an experimental study done in vitro with a G6 glioma cell line to investigate the responses when C6 glioma cells are irradiated with single doses of 30 and 230 cGy using an orthovoltage therapy device or doses split into 30 and 200 and 115 and 115 cGy within periods of 15 and 30 min. A total of 5 × 103 cells were transferred to polyethylene culture flasks for colony formation. A cluster containing more than 30 cells was considered a new colony. Results: A single dose of 230 cGy caused a 56.8% reduction in colony formation. However, when 230 cGy was divided over 15- and 30-min periods in fractions of 30 and 200 cGy, colony formation was significantly reduced compared to the control group (68.13% and 52.64%, P = 0.030, respectively). This effect continued when the radiation dose was divided into equal fractions (115 and 115 cGy) with periods of 15 and 30 min (42.60%, P = 0.021 and 20.77%, P = 0.008, respectively). Conclusion: According to these results, (i) short interval (15 and 30 min) fractionation significantly reduces colony formation compared to a single equal dose; and (ii) the protective mechanisms activated in cell response probably vary at different radiation doses and different fractions.

Zinc and selenium supplement mitigated valproic acid-induced testis toxicity by modulating the oxidative redox balance in male rats

Valproic acid (VPA) is widely used antiepileptic agent which is associated with reproductive toxicity via impairment in oxidative redox. Zinc (Zn) and selenium (Se) are trace element with antioxidant effect that known to be essential for spermatogenesis. In the current study, the protective effect of co-administration of Zn and Se on VPA-induced reproductive toxicity in male rats was evaluated. Forty-eight male rats were divided into 8 groups of six (n=6): Control group (treated with normal saline); VPA only (250, 500, 1,000 mg/kg) group; VPA (500 mg/kg) plus Zn (2 mg/kg) group; VPA (500 mg/kg) plus Se (1.5 mg/kg) group; VPA (500 mg/kg) plus a combination of Zn and Se group; and VPA+vitamin E (20 mg/kg) group. The Animals were sacrificed after 28 days of treatment and sperm analysis was taken. Also, evaluation of oxidative stress markers including malondialdehyde (MDA), protein carbonyl (PC), glutathione (GSH) and histopathological changes were done on testis tissue. Morphological changes and a significant decrease in motility and sperm count in rats treated with VPA were observed. Also, an increase in oxidative stress marker, including MDA and PC and a decrease in GSH level was evident in VPA group. Zn and Se administration was able to protect against sperm abnormality, ameliorate the histological change in testis tissue, and suppressed the increase in oxidative stress markers induced by VPA. These results indicated that combination therapy with Zn and Se showed better an ameliorative effect than each one alone. Therefore, it can be suggested as an effective supplement for reproductive impairment in VPA-treated patient.

Genotoxicity of cationic lipopeptide nanoparticles

The genotoxicity of cationic lipopeptide nanoparticles (cLPNPs) was evaluated in vivo and in vitro comet assay and the in vivo chromosome aberrations test. In vitro comet assay, human blood cells were exposed to cLPNPs at the concentration of 2.5, 5, 10, 20, 40 and 100 μg/mL. Significant DNA damage was observed after 1 h exposure, but no effects were detected after 3 h. In vivo, cLPNPs were administered in single or five daily injection doses at 8, 20 and 40 mg/kg of body weight by subcutaneous injection to male mice. The cLPNPs caused DNA damage in the liver, lung and kidney, but not in the spleen. The kidney was more prone to genotoxic effects that persisted from 24 h to 14d after a single injection of cLPNPs. No statistically significant increase in the percentage of cells with chromosomal aberrations above the vehicle control was observed in mice bone marrow after a single or repeated injection of cLPNPs. In summary, cLPNPs shown to be genotoxic both in vivo and in vitro. The results suggest the importance of the use of highly sensitive methods, such as the comet assay, in order to determine the full genotoxic potential of nanoparticles.

Toxicity assessment of chlorpyrifos on different organs of rat: exploitation of microbial-based enzymatic system for neutralization

This study was aiming to treat the chlorpyrifos (CPF), an organophosphate (OP) pesticide with microbial enzyme extract, and assess the toxicity effects of CPF before/after its treatment on the integrity of DNA (deoxyribonucleic acid) and the activities of enzymes AChE (acetylcholinestrase), GST (glutathione S-transferase), SOD (superoxide dismutase), CAT (catalase), and MDA (malondialdehyde) in different organs of rat. The untreated CPF in rat significantly increased the DNA damage and decreased the activities of all these enzymes. Among all the organs studied, the liver was the most affected organ. Further, CPF was treated with an OPH (organophosphate hydrolase) enzyme obtained from CPF degrading bacterial laboratory isolate Pseudomonas sp. (ChlD) to neutralize the toxicity of CPF. The crude intracellular enzyme extract degraded > 90% of added CPF and > 80% of its toxic intermediate 3,5,6-trichloropyridinol (TCP) which resulted in > 80% reduction of CPF toxicity in different organs of rat. Thus, this study not only illustrated the adverse effect of OPs on mammalian system but also suggested a highly efficient and eco-friendly way to remove the harmful pesticide from the environment and agricultural food products which may help to reduce the exposure of humans to such lethal toxicants.

Punicalagin Mollifies Lead Acetate-Induced Oxidative Imbalance in Male Reproductive System

Punicalagin (PU) is a known antioxidant. The present study examined PU to protect against lead-induced oxidative stress (OS) testicular damage in mice. Significant increase in lipid peroxidation (LPO) after intraperitoneal injection of lead acetate (LA) indicated enormous generation of reactive oxygen species (ROS). Lead-induced OS has a direct effect on the differentiation of spermatogonial cells, showing a significant decline in sperm count. Supplementation of PU significantly changes values of LPO and glutathione (GSH) with a concomitant increase in sperm count, a marked decrease in the abnormal sperms, and a decline in the morphologically abnormal sperm population. Moreover, the histopathological evaluation of testes and epididymides showed severe changes in mice treated with LA. PU significantly induced nuclear factor erythroid-2 related factor 2-like 2 (Nrf2) expression and phase II enzymes, and data suggest that PU may inhibit OS through Nrf2 activation. The fertility test proved that PU might play an important role in male infertility treatment, especially in the type of infertility induced by OS.

Advances in radiation biology: effect on nuclear medicine

Over the past 15 years and more, extensive research has been conducted on the responses of biological systems to radiation delivered at a low dose or low dose rate. This research has demonstrated that the molecular-, cellular-, and tissue-level responses are different following low doses than those observed after a single short-term high-dose radiation exposure. Following low-dose exposure, 3 unique responses were observed, these included bystander effects, adaptive protective responses, and genomic instability. Research on the mechanisms of action for each of these observations demonstrates that the molecular and cellular processes activated by low doses of radiation are often related to protective responses, whereas high-dose responses are often associated with extensive damage such as cell killing, tissue disruption, and inflammatory diseases. Thus, the mechanisms of action are unique for low-dose radiation exposure. When the dose is delivered at a low dose rate, the responses typically differ at all levels of biological organization. These data suggest that there must be a dose rate effectiveness factor that is greater than 1 and that the risk following low-dose rate exposure is likely less than that for single short-term exposures. All these observations indicate that using the linear no-threshold model for radiation protection purposes is conservative. Low-dose research therefore supports the current standards and practices. When a nuclear medical procedure is justified, it should be carried out with optimization (lowest radiation dose commensurate with diagnostic or therapeutic outcome).

Evaluation of DNA damage and cytotoxicity induced by three commonly used organophosphate pesticides individually and in mixture, in rat tissues

Organophosphate pesticides are among the most widely used synthetic chemicals for controlling a wide variety of pests. Chlorpyrifos (CPF), methyl parathion (MPT), and malathion (MLT) are among the most extensively used organophosphate (OP) pesticides. The main target of action of OP compounds is the central and peripheral nervous system, although it has also been postulated that these compounds in both acute and chronic intoxication, disturb the redox processes and thus induce oxidative stress. The excessive generation of reactive oxygen species (ROS) causes damage to all vital macromolecules including lipids, proteins, and DNA. This study was aimed to investigate the genotoxicity and cytotoxicity of CPF, MPT, and MLT when given singly or in combination. The DNA damage was measured by alkaline single-cell gel electrophoresis or comet assay and expressed as DNA damage index. The results showed that both acute and chronic exposure with CPF, MPT, and MLT, caused significantly marked DNA damage in rat tissues namely, liver, brain, kidney, and spleen, when measured 24 hour posttreatment. It was also observed that MPT caused highest level of DNA damage and brain was maximally affected by these OP compounds. When these pesticides were given in mixture, the damage was not the sum of damage caused by individual pesticide, confirming that these pesticides do not potentiate the toxicity of each other. When the DNA damage was measured 48 and 72 hour posttreatment, the damage was partially repaired. Pesticide exposure also caused histopathological changes in rat tissues.

Assessment of genotoxic effects of flumorph by the comet assay in mice organs

The present study investigated the genotoxic effects of flumorph in various organs (brain, liver, spleen, kidney and sperm) of mice. The DNA damage, measured as comet tail length (µm), was determined using the alkaline comet assay. The comet assay is a sensitive assay for the detection of genotoxicity caused by flumorph using mice as a model. Statistically significant increases in comet assay for both dose-dependent and duration-dependent DNA damage were observed in all the organs assessed. The organs exhibited the maximum DNA damage in 96 h at 54 mg/kg body weight. Brain showed maximum DNA damage followed by spleen > kidney > liver > sperm. Our data demonstrated that flumorph had induced systemic genotoxicity in mammals as it caused DNA damage in all tested vital organs, especially in brain and spleen.

Low dose radiation response curves, networks and pathways in human lymphoblastoid cells exposed from 1 to 10cGy of acute gamma radiation

We investigated the low dose dependency of the transcriptional response of human cells to characterize the shape and biological functions associated with the dose-response curve and to identify common and conserved functions of low dose expressed genes across cells and tissues. Human lymphoblastoid (HL) cells from two unrelated individuals were exposed to graded doses of radiation spanning the range of 1-10cGy were analyzed by transcriptome profiling, qPCR and bioinformatics, in comparison to sham irradiated samples. A set of ∼80 genes showed consistent responses in both cell lines; these genes were associated with homeostasis mechanisms (e.g., membrane signaling, molecule transport), subcellular locations (e.g., Golgi, and endoplasmic reticulum), and involved diverse signal transduction pathways. The majority of radiation-modulated genes had plateau-like responses across 1-10cGy, some with suggestive evidence that transcription was modulated at doses below 1cGy. MYC, FOS and TP53 were the major network nodes of the low-dose-response in HL cells. Comparison our low dose expression findings in HL cells with those of prior studies in mouse brain after whole body exposure, in human keratinocyte cultures, and in endothelial cells cultures, indicates that certain components of the low dose radiation response are broadly conserved across cell types and tissues, independent of proliferation status.

Structure-mutagenicity relationship of kaurenoic acid from Xylopia sericeae (Annonaceae)

Kaurane diterpenes are considered important compounds in the development of new highly effective anticancer chemotherapeutic agents. Genotoxic effects of anticancer drugs in non-tumour cells are of special significance due to the possibility that they induce secondary tumours in cancer patients. In this context, we evaluated the genotoxic and mutagenic potential of the natural diterpenoid kaurenoic acid (KA), i.e. (-)-kaur-16-en-19-oic acid, isolated from Xylopia sericeae St. Hill, using several standard in vitro and in vivo protocols (comet, chromosomal aberration, micronucleus and Saccharomyces cerevisiae assays). Also, an analysis of structure-activity relationships was performed with two natural diterpenoid compounds, 14-hydroxy-kaurane (1) and xylopic acid (2), isolated from X. sericeae, and three semi-synthetic derivatives of KA (3-5). In addition, considering the importance of the exocyclic double bond (C16) moiety as an active pharmacophore of KA cytotoxicity, we also evaluated the hydrogenated derivative of KA, (-)-kauran-19-oic acid (KAH), to determine the role of the exocyclic bond (C16) in the genotoxic activity of KA. In summary, the present study shows that KA is genotoxic and mutagenic in human peripheral blood leukocytes (PBLs), yeast (S. cerevisiae) and mice (bone marrow, liver and kidney) probably due to the generation of DNA double-strand breaks (DSB) and/or inhibition of topoisomerase I. Unlike KA, compounds 1-5 and KAH are completely devoid of genotoxic and mutagenic effects under the experimental conditions used in this study, suggesting that the exocyclic double bond (C16) moiety may be the active pharmacophore of the genetic toxicity of KA.

NASA Radiation Biomarker Workshop, September 27-28, 2007

A summary is provided of presentations and discussions at the NASA Radiation Biomarker Workshop held September 27-28, 2007 at NASA Ames Research Center in Mountain View, CA. Invited speakers were distinguished scientists representing key sectors of the radiation research community. Speakers addressed recent developments in the biomarker and biotechnology fields that may provide new opportunities for health-related assessment of radiation-exposed individuals, including those exposed during long-duration space travel. Topics discussed included the space radiation environment, biomarkers of radiation sensitivity and individual susceptibility, molecular signatures of low-dose responses, multivariate analysis of gene expression, biomarkers in biodefense, biomarkers in radiation oncology, biomarkers and triage after large-scale radiological incidents, integrated and multiple biomarker approaches, advances in whole-genome tiling arrays, advances in mass spectrometry proteomics, radiation biodosimetry for estimation of cancer risk in a rat skin model, and confounding factors. A summary of conclusions is provided at the end of the report.

DNA damage in tissues and organs of mice treated with diphenyl diselenide

Diphenyl diselenide (DPDS) is an organoselenium compound with interesting pharmacological activities and various toxic effects. In previous reports, we demonstrated the pro-oxidant action and the mutagenic properties of this molecule in bacteria, yeast and cultured mammalian cells. This study investigated the genotoxic effects of DPDS in multiple organs (brain, kidney, liver, spleen, testes and urinary bladder) and tissues (bone marrow, lymphocytes) of mice using in vivo comet assay, in order to determine the threshold of dose at which it has beneficial or toxic effects. We assessed the mechanism underlying the genotoxicity through the measurement of GSH content and thiobarbituric acid reactive species, two oxidative stress biomarkers. Male CF-1 mice were given 0.2-200 micromol/kg BW DPDS intraperitonially. DPDS induced DNA damage in brain, liver, kidney and testes in a dose response manner, in a broad dose range at 75-200 micromol/kg with the brain showing the highest level of damage. Overall, our analysis demonstrated a high correlation among decreased levels of GSH content and an increase in lipid peroxidation and DNA damage. This finding establishes an interrelationship between pro-oxidant and genotoxic effects. In addition, DPDS was not genotoxic and did not increase lipid peroxidation levels in any organs at doses < 50 micromol/kg. Finally, pre-treatment with N-acetyl-cysteine completely prevented DPDS-induced oxidative damage by the maintenance of cellular GSH levels, reinforcing the positive relationship of DPDS-induced GSH depletion and DNA damage. In summary, DPDS induces systemic genotoxicity in mammals as it causes DNA damage in vital organs like brain, liver, kidney and testes.

Enhanced Spontaneous and Benzo(a)pyrene-Induced Mutations in the Lung of Nrf2-Deficient gpt Delta Mice

The lung is an organ that is sensitive to mutations induced by chemicals in ambient air, and transgenic mice harboring guanine phosphoribosyltransferase (gpt) gene as a target gene are a well-established model system for assessing genotoxicity in vivo. Transcription factor Nrf2 mediates inducible and constitutive expression of cytoprotective enzymes against xenobiotics and mutagens. To address whether Nrf2 is also involved in DNA protection, we generated nrf2+/−::gpt and nrf2−/−::gpt mice. The spontaneous mutation frequency of the gpt gene in the lung was approximately three times higher in nrf2-null (nrf2−/−) mice than nrf2 heterozygous (nrf2+/−) and wild-type (nrf2+/+) mice, whereas in the liver, the mutation frequency was higher in nrf2−/− and nrf2+/− mice than in nrf2+/+ wild-type mice. By contrast, no difference in mutation frequency was observed in testis among the three genotypes. A single intratracheal instillation of benzo(a)pyrene (BaP) increased the lung mutation frequency 3.1- and 6.1-fold in nrf2+/− and nrf2−/− mice, respectively, compared with BaP-untreated nrf2+/− mice, showing that nrf2−/− mice are more susceptible to genotoxic carcinogens. Surprisingly, mutation profiles of the gpt gene in BaP-treated nrf2+/− mice was substantially different from that in BaP-untreated nrf2−/− mice. In nrf2−/− mice, spontaneous and BaP-induced mutation hotspots were observed at nucleotides 64 and 140 of gpt, respectively. These results thus show that Nrf2 aids in the prevention of mutations in vivo and suggest that Nrf2 protects genomic DNA against certain types of mutations. [Cancer Res 2007;67(12):5643–8]

Extracting gene networks for low-dose radiation using graph theoretical algorithms

Genes with common functions often exhibit correlated expression levels, which can be used to identify sets of interacting genes from microarray data. Microarrays typically measure expression across genomic space, creating a massive matrix of co-expression that must be mined to extract only the most relevant gene interactions. We describe a graph theoretical approach to extracting co-expressed sets of genes, based on the computation of cliques. Unlike the results of traditional clustering algorithms, cliques are not disjoint and allow genes to be assigned to multiple sets of interacting partners, consistent with biological reality. A graph is created by thresholding the correlation matrix to include only the correlations most likely to signify functional relationships. Cliques computed from the graph correspond to sets of genes for which significant edges are present between all members of the set, representing potential members of common or interacting pathways. Clique membership can be used to infer function about poorly annotated genes, based on the known functions of better-annotated genes with which they share clique membership (i.e., "guilt-by-association"). We illustrate our method by applying it to microarray data collected from the spleens of mice exposed to low-dose ionizing radiation. Differential analysis is used to identify sets of genes whose interactions are impacted by radiation exposure. The correlation graph is also queried independently of clique to extract edges that are impacted by radiation. We present several examples of multiple gene interactions that are altered by radiation exposure and thus represent potential molecular pathways that mediate the radiation response.

Cypermethrin-induced DNA damage in organs and tissues of the mouse: Evidence from the comet assay

Cypermethrin is the most widely used Type II pyrethroid pesticide because of its high effectiveness against target species and its low mammalian toxicity reported so far. It is a fast-acting neurotoxin and is known to cause free radical-mediated tissue damage. The present study investigates the genotoxic effects of cypermethrin in multiple organs (brain, kidney, liver, spleen) and tissues (bone marrow, lymphocytes) of the mouse, using the alkaline comet assay. Male Swiss albino mice were given 12.5, 25, 50, 100, 200 mg/kg BW of cypermethrin intraperitoneally, daily for 5 consecutive days. A statistically significant (p<0.05) dose-dependent increase in DNA damage was observed in all the organs assessed, as evident from the comet-assay parameters, viz., Olive tail moment (OTM; arbitrary unit), tail DNA (%) and tail length (microm). Brain showed maximum DNA damage followed by spleen>kidney>bone marrow>liver>lymphocytes, as evident by the OTM. Our data demonstrate that cypermethrin induces systemic genotoxicity in mammals as it causes DNA damage in vital organs like brain, liver, kidney, apart from that in the hematopoietic system.

Low-dose irradiation alters the transcript profiles of human lymphoblastoid cells including genes associated with cytogenetic radioadaptive response

Low-dose ionizing radiation alters the gene expression profiles of mammalian cells, yet there is little understanding of the underlying cellular mechanisms responsible for these changes or of their consequences for genomic stability. We investigated the cytogenetic adaptive response of human lymphoblastoid cell lines exposed to 5 cGy (priming dose) followed by 2 Gy (challenge dose) compared to cells that received a single 2-Gy dose to (a) determine how the priming dose influences subsequent gene transcript expression in reproducibly adapting and non-adapting cell lines, and (b) identify gene transcripts that are associated with reductions in the magnitude of chromosomal damage after the challenge dose. The transcript profiles were evaluated using oligonucleotide arrays and RNA obtained 4 h after the challenge dose. A set of 145 genes (false discovery rate = 5%) with transcripts that were affected by the 5-cGy priming dose fell into two categories: (a) a set of common genes that were similarly modulated by the 5-cGy priming dose irrespective of whether the cells subsequently adapted or not and (b) genes with differential transcription in accordance with the cell lines that showed either adaptive or non-adaptive outcomes. The common priming-dose response genes showed up-regulation for protein synthesis genes and down-regulation of metabolic and signal transduction genes (>10-fold differences). The genes associated with subsequent adaptive and non-adaptive outcomes involved DNA repair, stress response, cell cycle control and apoptosis. Our findings support the importance of TP53-related functions in the control of the low-dose cytogenetic radioadaptive response and suggest that certain low-dose-induced alterations in cellular functions are predictive for the risk of subsequent genomic damage.