Dose-dependent Increase In Frequency Research Articles

Linear dose response of acrocentric chromosome associations to gamma irradiation in human lymphocytes.

The frequency of acrocentric chromosome associations (ACA) was studied to determine the possible dose-response relationship of gamma irradiation in human lymphocytes. Peripheral blood collected from three healthy donors was irradiated with 0, 0.1, 0.25, 0.5, 0.75, 1, 2, 3, 4, and 5 Gy of gamma radiation. Chromosomal preparations were made after 48 h of culture as per standard guidelines. The experiment was repeated three times, with adifferent donor each time. The ACA frequency in irradiated lymphocytes increased with radiation dose. The D-G type of association was most prominent and showed asignificant dose-dependent increase in frequency. The dose response of ACA frequency to radiation was found to be linear: ACA frequency = 0.2923 (±0.0276) + 0.1846 (±0.0307) × D (correlation coefficient r = 0.9442). As expected, dicentric chromosome (DC) frequencies followed the linear quadratic fit model, with DC frequency = 0.0015 (±0.0013) + 0.0220 (±0.0059) × D + 0.0215 (±0.0018) × D^2 (correlation coefficient r = 0.9982). Acorrelation curve was prepared for ACA frequency versus DC frequency, resulting in the regression equation y = 1.130x + 0.4051 (R2 = 0.7408; p = 0.0014). Our results showed an increase in ACA frequency in irradiated lymphocytes with an increase in radiation dose; thus, ACA may serve as acandidate cytogenetic biomarker for radiation biodosimetry.

An integrated analysis of herpes virus infections from eight randomized clinical studies of baricitinib in adults with moderate-to-severe atopic dermatitis.

Atopic dermatitis (AD) is associated with an increased risk for viral infections including those caused by herpes simplex virus and varicella zoster virus. This study examined treatment-emergent (TE) herpes simplex infection including eczema herpeticum (EH), and herpes zoster (HZ), in adult patients with AD receiving ≥1 dose of baricitinib (BARI), an oral selective inhibitor of Janus kinase 1/2. We evaluated data from six double-blinded, randomized, placebo-controlled (PC) trials and two long-term extension studies, within three analysis sets: PC, 2-4-mg BARI extended and All-BARI-AD. Frequency, incidence rate (IR)/100 person-years (PYs) and clinical characteristics of TE-herpes simplex, EH and HZ were reported. In the All-BARI-AD dataset (n = 2531; 2247 PYs), herpes simplex was reported in 8.9% of patients (n = 224; IR = 10.3). Most herpes simplex events were rated as mild or moderate (93.3%), rarely led to permanent discontinuation (2.2%) and presented mostly as oral/perioral herpes simplex (51.3%). TE-EH occurred at a low frequency (All-BARI-AD 1.7% n = 43; IR = 2.0) and were reported in 0.5%, 0.2% and 1.4% of patients receiving placebo, 2-mg or 4-mg BARI respectively. In the All-BARI-AD dataset, most events were investigator-rated as mild/moderate (79.1%), affected ≤2% of the body surface area (74.2%) and occurred as single events (88.4%). Serious TE-EH (n = 11) occurred exclusively in patients with poor disease control (vIGA-AD™ score ≥3) at infection onset. TE-HZ was reported in 2.1% of BARI patients (n = 53; IR = 2.3), without a dose relationship during the PC period (IR = 2.7 and IR = 0.0) or the extended dataset (IR = 3.7 and IR = 1.7) for 2- or 4-mg BARI respectively. TE-herpes simplex was common, while occurrence of EH was uncommon. Most events of EH were localized with involvement of a small BSA and were linked to poor disease control. Events of HZ were rare in the PC dataset and without a dose dependent increase in frequency.

Elevated Risk Analysis Index (RAI) Frailty Scores Are Independently Associated with Adverse Outcomes in Lower Extremity Surgical Revascularizations Similarly Across Genders

The Risk Analysis Index (RAI) frailty scoring system has recently undergone revision and external validation using the National Surgical Quality Improvement Program (NSQIP) database. We set forth to evaluate the association of RAI-rev ranges with outcomes following lower extremity surgical revascularization and verify equivalent applicability across genders. All elective NSQIP Targeted Lower Extremity Open cases from 2015-2019 were divided by EMR-recorded gender. Aggregate demographics, perioperative factors, and 30-day outcomes were compared using unpaired t-test and Fisher's exact test. Adjusted odds-ratios (aOR) for each outcome were generated by applying a multivariate binary logistic regression model (IBM SPSSTM) for five-point RAI-rev score increments from 25-45 and a most-frail group with scores >45 with a non-frail reference of <25. Covariates included surgical indication, prior ipsilateral revascularization, graft utilization, dirty/infected wound, smoking, hypertension, diabetes, and steroid use. 8,155 cases included 2,498 (31%) performed in women who demonstrated slightly lower RAI-rev scores than men (22.1 ± 5.8 vs. 24.2 ± 5.1; P = 0.0001). Univariate trends demonstrated dose-dependent increases in frequency of most outcomes with rising frailty score ranges, most substantially regarding mortality (0.4% non-frail to 14.7% most-frail), disposition to skilled nursing facility (8% non-frail to 27% most-frail), and extended length of stay (16% non-frail to 44% most-frail). After adjusting for co-variates, patients with RAI-rev scores of 26-30 had aOR of 1.4 (95% CI: 1.2-1.6; P < 0.001), 1.9 (95% CI: 1.6-2.2; P < 0.001), and 2.4 (95% CI:1.3-4.4; P < 0.001) for extended stay, disposition to skilled nursing, and mortality respectively. Trends were similar across genders in both univariate and multivariate analyses. Mortality, extended stay, and increased rehabilitation needs after surgical revascularization were associated with higher RAI-rev score ranges in a dose dependent manner similarly across genders.

Protective role of eugenol on arsenic induced oxidative DNA damage and modulatory effect of GSTO2 polymorphism

Arsenic exposure is one of the major health problem worldwide. It is related with various cancers and numerous other pathological effects. The present work was aimed to study the ameliorative effects of eugenol against arsenic mediated oxidative DNA damage using Sister chromatid exchanges (SCE), comet, and lipid peroxidation assays as biomarkers. For the genotyping of GSTO2, PCR RFLP method was used. The treatment with sodium arsenite showed dose dependent increase in frequency of SCE, comet tail moment (Tm), and lipid peroxidation (TBARS levels). On administration of eugenol (10 and 20 µM) significant dose dependent decrease in the number of SCE, Tm value, and TBARS levels observed in arsenic treated cultured peripheral blood lymphocytes. Nonsignificant effects of GSTO2 polymorphism perceived on arsenic genotoxicity and eugenol antigenotoxicity. The results of the present work suggest a protective role of eugenol against arsenic induced genotoxic and oxidative damage in cultured human peripheral blood lymphocytes. Practical application Arsenic contamination of groundwater is one of the leading environmental issues worldwide. Chronic exposure of arsenic cause several health problems including tumor manifestation. The results of the present study suggest the use of indigenous dietary elements, herbs, shrubs as a safer and effective preventative medicine against heavy metal induced genotoxicity and oxidative stress.

Development of an in vitro high content imaging assay for quantitative assessment of CAR-dependent mouse, rat, and human primary hepatocyte proliferation

Rodent liver tumors promoted by constitutive androstane receptor (CAR) activation are known to be mediated by key events that include CAR-dependent gene expression and hepatocellular proliferation. Here, an in vitro high content imaging based assay was developed for quantitative assessment of nascent DNA synthesis in primary hepatocyte cultures from mouse, rat, and human species. Detection of DNA synthesis was performed using direct DNA labeling with the nucleoside analog 5-ethynyl-2′-deoxyuridine (EdU). The assay was multiplexed to enable direct quantitation of DNA synthesis, cytotoxicity, and cell count endpoints. An optimized defined medium cocktail was developed to sensitize hepatocytes to cell cycle progression. The baseline EdU response to defined medium was greatest for mouse, followed by rat, and then human. Hepatocytes from all three species demonstrated CAR activation in response to the CAR agonists TCPOBOP, CITCO, and phenobarbital based on increased gene expression for Cyp2b isoforms. When evaluated for a proliferation phenotype, TCPOBOP and CITCO exhibited significant dose-dependent increases in frequency of EdU labeling in mouse and rat hepatocytes that was not observed in hepatocytes from three human donors. The observed species differences are consistent with CAR activators inducing a proliferative response in rodents, a key event in the liver tumor mode of action that is not observed in humans.

Embryo Microinjection of Selenomethionine Reduces Hatchability and Modifies Oxidant Responsive Gene Expression in Zebrafish

In previous studies we demonstrated that exposure to selenomethionine (SeMet) causes developmental toxicities in zebrafish (Danio rerio). The objectives of this study were to establish a dose-response relationship for developmental toxicities in zebrafish after embryo microinjection of Se (8, 16 or 32 μg/g dry mass of eggs) in the form of SeMet, and to investigate potential underlying mechanism(s) of SeMet-induced developmental toxicities. A dose-dependent increase in frequencies of mortality and total deformities, and reduced hatchability were observed in zebrafish exposed to excess Se via embryo microinjection. The egg Se concentration causing 20% mortality was then used to investigate transcript abundance of proteins involved in antioxidant protection and methylation. Excess Se exposure modified gene expression of oxidant-responsive transcription factors (nuclear factor erythroid 2-related factor nrf2a and nrf2b), and enzymes involved in cellular methylation (methionine adenosyltransferase mat1a and mat2ab) in zebrafish larvae. Notably, excess Se exposure up-regulated transcript abundance of aryl hydrocarbon receptor 2 (ahr2), a signalling pathway involved in the toxicity of dioxin-related compounds. Our findings suggest that oxidative stress or modification of methylation, or a combination of these mechanisms, might be responsible for Se-induced developmental toxicities in fishes.

Clinical Efficacy and Tolerability of the Nicotinic Channel Modulator Dexmecamylamine in Subjects with Overactive Bladder

We evaluated the efficacy and tolerability of the nicotinic channel modulator dexmecamylamine for overactive bladder. This was a randomized, double-blind, placebo controlled trial in 768 randomized subjects. Those with at least a 6-month history of overactive bladder were randomized to 0.5, 1 or 2 mg dexmecamylamine or placebo in a ratio of 1:1:1:2, respectively. Subjects completed a 3-day diary before each visit associated with the 12-week treatment period. They were required to have 8 or more micturitions per day and 3 or more urinary urge incontinent episodes per day if overactive bladder wet at the end of a placebo run-in period. Co-primary end points for the study included a change from baseline 1) in micturition frequency per 24 hours at week 12 and 2) in urge urinary incontinence episodes per 24 hours at week 12. Secondary end points were voided volume, nocturia episodes, OABq (Overactive Bladder Questionnaire) and urgency questionnaire. Dexmecamylamine (2 mg) produced a statistically significant decrease in micturition frequency (p = 0.03) but did not produce a statistically significant decrease in urge incontinence (wet) episodes (p = 0.38). Secondary end points, including volume voided in the 1 mg group only, CGI-I (Clinical Global Impression of Improvement), visual analog scale urgency impact, intensity and severity, were statistically significant at week 12 for the 2 mg dose. Dexmecamylamine was well tolerated in this subject population with a low incidence of discontinuations due to adverse effects. Constipation, dry mouth and urinary tract infection showed a dose dependent increase in frequency. Dexmecamylamine does not appear to offer an enhanced therapeutic profile for the treatment of overactive bladder relative to current therapies.

Assessment of toxicity and genotoxicity of low doses of 5-fluorouracil in zebrafish (Danio rerio) two-generation study

Residues of anti-neoplastic drugs represent new and emerging pollutants in aquatic environments. Many of these drugs are genotoxic, and it has been postulated that they can cause adverse effects in aquatic ecosystems. 5-Fluorouracil (5-FU) is one of the most extensively used anti-neoplastic drugs in cancer therapy, and this article describes the results of the first investigation using a two-generation toxicity study design with zebrafish (Danio rerio). Exposure of zebrafish to 5-FU (0.01, 1.0 and 100 μg/L) was initiated with adult zebrafish (F0 generation) and continued through the hatchings and adults of the F1 generation, and the hatchings of the F2 generation, to day 33 post-fertilisation. The exposure did not affect survival, growth and reproduction of the zebrafish; however, histopathological changes were observed in the liver and kidney, along with genotoxic effects, at all 5-FU concentrations. Increases in DNA damage determined using the comet assay were significant in the liver and blood cells, but not in the gills and gonads. In erythrocytes, a significant, dose-dependent increase in frequency of micronuclei was observed at all 5-FU concentrations. Whole genome transcriptomic analysis of liver samples of F1 generation zebrafish exposed to 0.01 μg/L and 1 μg/L 5-FU revealed dose-dependent increases in the number of differentially expressed genes, including up-regulation of several DNA-damage-responsive genes and oncogenes (i.e., jun, myca). Although this chronic exposure to environmentally relevant concentrations of 5-FU did not affect the reproduction of the exposed zebrafish, it cannot be excluded that 5-FU can lead to degenerative changes, including cancers, which over long-term exposure of several generations might affect fish populations. The data from this study contribute to a better understanding of the potential consequences of chronic exposure of fish to low concentrations of anti-neoplastic drugs, and they demonstrate that further studies into multi-generation toxicity are needed.

Orexin receptor antagonism: an ascending multiple-dose study with almorexant

The objectives of this study were to investigate the multiple-dose tolerability, safety, pharmacokinetics, and pharmacodynamics of the dual orexin receptor antagonist almorexant. Healthy subjects received daily doses of almorexant (100, 200, 400 or 1000 mg) or placebo in the morning for four days followed by two days with evening administration (Days 5-6). Each dose level was investigated in a new group of 10 subjects (eight active, two placebo, 1:1 sex). Dose-dependent increases in frequency and intensity were observed for somnolence and other adverse events. Pharmacokinetics at steady state showed rapid absorption, low concentrations eight hours post-dose, and minimal accumulation. Following evening, administration absorption was delayed and C(max) decreased. Almorexant at 400 and 1000 mg administered in the morning reduced vigilance, alertness, visuomotor coordination, and motor coordination assessed in a psychometric test battery. Polysomnography recordings following evening administration showed a trend towards shorter latency to sleep stages 3 and 4, and shorter latency to, and longer time in, rapid-eye-movement sleep at higher doses when compared to placebo. Whether these findings in healthy subjects translate into relevant sleep-enabling effects in insomnia patients needs to be investigated in future studies.

Hematotoxicity and Genotoxicity of Mercuric Chloride Following Subchronic Exposure Through Drinking Water in Male Rats

Erythrocytes are a convenient model to understand the subsequent oxidative deterioration of biological macromolecules in metal toxicities. The present study examined the variation of hematoxic and genotoxic parameters following subchronic exposure of mercuric chloride via drinking water and their possible association with oxidative stress. Male rats were exposed to 50 ppm (HG1) and 100 ppm (HG2) of mercuric chloride daily for 90 days. A significant dose-dependent decrease was observed in red blood cell count, hemoglobin, hematocrit, and mean cell hemoglobin concentration in treated groups (HG1 and HG2) compared with controls. A significant dose-dependent increase was observed in lipid peroxidation; therefore, a significant variation was found in the antioxidant enzyme activities, such as superoxide dismutase, catalase, and glutathione peroxidase. Interestingly, mercuric chloride treatment showed a significant dose-dependent increase in frequency of total chromosomal aberration and in percentage of aberrant bone marrow metaphase of treated groups (p < 0.01). The oxidative stress induced by mercury treatment may be the major cause for chromosomal aberration as free radicals lead to DNA damage. These data will be useful in screening the antioxidant activities of natural products, which may be specific to the bone marrow tissue.

Induced Karyomorphological Variations in Three Phenodeviants of Capsicum annuum L.

EMS was used as a mutagen in Capsicum annuum L. to isolate karyomorphological mutants. Seeds of Capsicum annuum L. var Azad were first pre-soaked in distilled water and then treated with 0.5% solution of EMS for 3 durations, i.e. 3, 5, and 7 h, and genetic segregation was closely observed. Many chromosomal anomalies like stickiness, bridges, and multivalent, secondary associations, laggards, and precocious movement were observed after all 3 durations of treatment. These anomalies showed a dose-dependent increase in frequency. The morphological parameters showed a decreasing trend along with the increasing dose. However, with the 7-h dose 3 morphologically distinct plants were isolated, which varied not only from other sib plants but also from control plants. Their cytological analysis revealed a predominance of bridges and increased frequency of bridges in all 3 plants. Therefore, it can be presumed that these 2 factors together may be responsible for creating deviations in these 3 plants.

Folic acid deficiency increases chromosomal instability, chromosome 21 aneuploidy and sensitivity to radiation-induced micronuclei

Folic acid deficiency can lead to uracil incorporation into DNA, hypomethylation of DNA, inefficient DNA repair and increase chromosome malsegregation and breakage. Because ionising radiation increases demand for efficient DNA repair and also causes chromosome breaks we hypothesised that folic acid deficiency may increase sensitivity to radiation-induced chromosome breakage. We tested this hypothesis by using the cytokinesis-block micronucleus assay in 10 day WIL2-NS cell cultures at four different folic acid concentrations (0.2, 2, 20, and 200 nM) that span the “normal” physiological range in humans. The study showed a significant dose-dependent increase in frequency of binucleated cells with micronuclei and/or nucleoplasmic bridges with decreasing folic acid concentration ( P < 0.0001, P = 0.028, respectively). These biomarkers of chromosomal instability were also increased in cells irradiated (1.5 Gy γ-rays) on day 9 relative to un-irradiated controls ( P < 0.05). Folic acid deficiency and γ-irradiation were shown to have a significant interactive effect on frequency of cells containing micronuclei (two-way ANOVA, interaction P = 0.0039) such that the frequency of radiation-induced micronucleated cells (i.e. after subtracting base-line frequency of un-irradiated controls) increased with decreasing folic acid concentration ( P-trend < 0.0001). Aneuploidy of chromosome 21, apoptosis and necrosis were increased by folic acid deficiency but not by ionising radiation. The results of this study show that folate status has an important impact on chromosomal stability and is an important modifying factor of cellular sensitivity to radiation-induced genome damage.

Effects of alpha-adrenergic stimuli on mesenteric collecting lymphatics in the rat.

The present study examined the effects of alpha 1- and alpha 2-adrenergic stimuli on rat mesenteric collecting lymphatics in vivo. Sprague-Dawley rats were anesthetized, and the mesentery was prepared for intravital microscopic study. Mesenteric collecting lymphatic diameter was continuously monitored by using a computerized video tracking system, and indexes of lymphatic pumping (e.g., contraction frequency, stroke volume, ejection fraction, and muscle shortening velocity) were determined from the diameter record. Contractile activity was monitored before and during the administration of various adrenergic agonists and antagonists. The receptor antagonists prazosin (alpha 1) and yohimbine (alpha 2) did not significantly alter baseline diameter or contractile activity, which suggests that lymphatics possess no basal adrenergic tone. Norepinephrine and phenylephrine (01-1.0 microM) produced dose-dependent increases in frequency and decreases in diameter. Lymphatic pump flow increased in direct proportion to frequency, because stroke volume did not change. The changes in lymphatic pumping produced by 1 microM norepinephrine were completely blocked by prazosin or phentolamine and only partially blocked by yohimbine. The alpha 2-adrenoceptor agonist (alpha-methyl-norepinephrine) produced no changes in lymphatic activity. This latter observation suggests that a role for postjunctional alpha 2-adrenoceptors in modulating mesenteric lymphatic smooth muscle is unlikely. The results of these studies support the existence of alpha-adrenoceptors on lymphatic smooth muscle. It is concluded that conditions characterized by increased sympathetic outflow may augment lymphatic function through alpha 1- but not alpha 2-adrenoceptors.

Mutational spectra of the dietary carcinogen 2-amino-1-methyl-6- phenylimidazo[4,5-b]pyridine(PhIP) at the Chinese hamsters hprt locus.

The mutagenic 'fingerprint' of the cooked food carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) was determined in a Chinese hamster cell line genetically engineered to express human CYP1A2 (XEMh1A2-MZ). The parental Chinese hamster V79 and XEMh1A2-MZ cells were exposed to PhIP at various concentrations for 24h. There was a dose-dependent increase in frequency of mutations at the hypoxanthine-guanine phosphoribosyltransferase (hprt) locus only in the metabolically competent XEMh1A2-MZ cells. The mutant frequency ranged from 25 to 90 X 10(-6) with final concentrations of 2.5 to 100 microM PhIP compared to 8 X 10(-6) in the solvent controls and the V79MZ cells. The molecular nature of the PhIP-induced mutations in XEMh1A2-MZ cells was determined by examining DNA sequence modifications at the hprt locus in forty five 6-thioguanine resistant (6-TGr) mutant clones. Single base substitutions predominantly GC-->TA transversions, were the major class of PhIP-induced mutation. However, a -1 frameshift 'hotspot' in a 5'-GGGA sequence was also observed. With the exception of a compound modification, all of the PhIP-induced mutations involved G.C base pairs. This is consistent with the previously observed PhIP-induced mutations in cultured mammalian cells and 32P-postlabelling experiments that show PhIP adducts to the guanine base and that major adduct is at the C8 position. Furthermore, nearly all of these mutations involved guanine bases on the non-transcribed strand which is possibly indicative of preferential repair of PhIP adducts from the transcribed strand. Nearest neighbor analysis of induced base substitutions indicates a preference for 5' guanine and 3' adenine. These data effectively define a mutation 'fingerprint' for PhIP, which may provide the basis for definitive studies on the role of PhIP in diet associated cancers such as tumours of colon. It is, therefore, intriguing that in their recent report of mutation in tumours of the colon induced by PhIP in male rate Kakiuchi et al. (Proc. Natl Acad. Sci. USA, 92, 910-914) report that four out of eight tumors had identical mutation of the tumour suppressor gene apc which is comprised of a -1 G frameshift in a 5'-GGGA sequence.

Role of excitatory amino acids in the generation and transmission of respiratory drive in neonatal rat.

1. The involvement of excitatory amino acids in the generation and transmission of rhythmic respiratory drive was studied in an in vitro neonatal rat brain stem-spinal cord preparation. The subclasses of excitatory amino acid receptors studied included: (i) N-methyl-D-aspartate (NMDA) receptors, (ii) (R, S)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid hydrobromide (AMPA) and kainate (non-NMDA) receptors and (iii) 2-amino-4-phosphonobutyric acid (AP-4)-sensitive receptors. Respiratory motoneurone population discharge was recorded from glossopharyngeal (IX), vagus (X), and hypoglossal (XII) cranial nerves, as well as cervical (C1-C5) and thoracic (T2-T5) spinal ventral roots. This activity is generated in the motoneurone pools that transmit respiratory drive to upper airway, accessory, diaphragm and intercostal muscles. Perturbations of motor nerve discharge were analysed after excitatory amino acid receptor antagonists or agonists were added to bathing solutions surrounding either the spinal cord or brain stem. The excitatory amino acid receptor antagonists included: (i) NMDA receptor antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imin-H-maleate (MK-801) and (ii) non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). The agonists included: (i) NMDA, (ii) non-NMDA receptor agonists AMPA and kainic acid. The effects of perturbations of AP-4-sensitive receptors with AP-4, and of inhibiting excitatory amino acid uptake with dihydrokainic acid (DHK) were also studied. 2. Block of non-NMDA receptors in the medulla by CNQX resulted in an antagonist concentration-dependent decrease in the respiratory motoneuronal burst frequency. Non-NMDA receptor activation with kainic acid or AMPA caused a concentration-dependent increase in burst frequency, with competitive interactions with CNQX. 3. Inhibition of excitatory amino acid uptake in the medulla with DHK resulted in a reversible, dose-dependent increase in respiratory frequency. A similar increase in respiratory frequency was induced by DHK when medullary NMDA receptors were blocked with MK-801, confirming that endogenously released excitatory amino acids act at non-NMDA receptors to modulate rhythm. 4. Non-NMDA receptor block reduced and ultimately abolished the amplitude of integrated cranial and spinal respiratory motoneuronal discharge when added to the solution bathing the medulla and spinal cord, respectively. 5. NMDA receptor block in the medulla with MK-801 did not perturb the spontaneous respiratory burst frequency, although bath application of NMDA produced a dose-dependent increase in frequency, with non-competitive interactions with MK-801. MK-801 also did not perturb the amplitude of cranial or bulbospinal premotoneurone discharge.(ABSTRACT TRUNCATED AT 400 WORDS)

Use of a cell hybrid test system to demonstrate that benomyl induces aneuploidy and polyploidy

We have monitored the segregation of a single human chromosome in a human-Chinese hamster hybrid cell line, EUBI, following exposure to benomyl. We found a dose-dependent increase in frequency of aneuploidy, but a much more marked induction of polyploidy was noted at the highest benomyl concentration. We confirm the usefulness of this assay for determining genetic risk associated with human exposure to environmental chemicals.

Carcinogens can induce homologous recombination between duplicated chromosomal sequences in mouse L cells.

The ability of a series of DNA-damaging agents to induce homologous intrachromosomal recombination between duplicated genes in the chromosome of mouse cells was investigated. The target cells were the thymidine kinase-deficient mouse L-cell strain 333M, which contains a single integrated copy of a plasmid with two herpes simplex virus thymidine kinase (Htk) genes, each containing an 8-base-pair XhoI linker inserted at a unique site. Expression of a functional Htk enzyme requires a productive recombinational event between the two nonfunctional genes. The spontaneous rate of recombination in this strain is 3 per 10(6) cells per generation. The agents tested represent physical carcinogens (UV and ionizing radiation), a simple alkylating agent (N-methyl-N'-nitro-N-nitrosoguanidine), an alkylating cross-linking agent (mitomycin C), and a reactive metabolite of a polycyclic aromatic hydrocarbon ((+/-)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10- tetrahydrobenzo[a]pyrene [BPDE] ). The background frequency of tk+ recombinants in the untreated population averaged 18 X 10(-6) +/- 5 X 10(-6). Ionizing radiation had little or no effect on recombination; exposure to mitomycin C, N-methyl-N'-nitro-N-nitrosoguanidine, BPDE, or UV, at doses that lowered the survival to between 90 and 10% of the control, caused a dose-dependent increase in frequency of recombinants, reaching 50 X 10(-6) to 100 X 10(-6). No tk+ cells could be generated with a control cell line that contained only one mutant copy of the Htk gene. Molecular hybridization analysis showed that 85 to 90% of the tk+ recombinants retained the Htk gene duplication, consistent with nonreciprocal transfer of wild-type genetic information, gene conversion. In the rest, only a single copy of the Htk gene remained, reflecting a single reciprocal exchange within a chromatid or a single unequal exchange between sister chromatids. Each recombinant tested contained an XhoI-resistant (wild-type) Htk gene.

Carcinogens can induce homologous recombination between duplicated chromosomal sequences in mouse L cells.

The ability of a series of DNA-damaging agents to induce homologous intrachromosomal recombination between duplicated genes in the chromosome of mouse cells was investigated. The target cells were the thymidine kinase-deficient mouse L-cell strain 333M, which contains a single integrated copy of a plasmid with two herpes simplex virus thymidine kinase (Htk) genes, each containing an 8-base-pair XhoI linker inserted at a unique site. Expression of a functional Htk enzyme requires a productive recombinational event between the two nonfunctional genes. The spontaneous rate of recombination in this strain is 3 per 10(6) cells per generation. The agents tested represent physical carcinogens (UV and ionizing radiation), a simple alkylating agent (N-methyl-N'-nitro-N-nitrosoguanidine), an alkylating cross-linking agent (mitomycin C), and a reactive metabolite of a polycyclic aromatic hydrocarbon ((+/-)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10- tetrahydrobenzo[a]pyrene [BPDE] ). The background frequency of tk+ recombinants in the untreated population averaged 18 X 10(-6) +/- 5 X 10(-6). Ionizing radiation had little or no effect on recombination; exposure to mitomycin C, N-methyl-N'-nitro-N-nitrosoguanidine, BPDE, or UV, at doses that lowered the survival to between 90 and 10% of the control, caused a dose-dependent increase in frequency of recombinants, reaching 50 X 10(-6) to 100 X 10(-6). No tk+ cells could be generated with a control cell line that contained only one mutant copy of the Htk gene. Molecular hybridization analysis showed that 85 to 90% of the tk+ recombinants retained the Htk gene duplication, consistent with nonreciprocal transfer of wild-type genetic information, gene conversion. In the rest, only a single copy of the Htk gene remained, reflecting a single reciprocal exchange within a chromatid or a single unequal exchange between sister chromatids. Each recombinant tested contained an XhoI-resistant (wild-type) Htk gene.

Improved benefit/risk ratio of higher-dose metoclopramide therapy during cisplatin-induced emesis.

Metoclopramide (Paspertin) was infused intravenously in the high doses of 1.75, 3.5, 7.0, and 14 mg/kg body wt. per treatment cycle as antiemetic therapy for cisplatin-induced emesis (363 cycles, 25-120 mg/m2). The antiemetic potency of metoclopramide increased in a log linear manner, giving from 40% to 95% protection against emesis. Gastrointestinal motility showed a similar increase, i.e. diarrhoea. In contrast, the extrapyramidal reactions, namely akathisia, rigidity and acute dystonia, did not show a dose-dependent increase in frequency and remained constant over the dose range of 3.5-14 mg/kg per cycle. The results suggest increasing benefit of metoclopramide treatment with increasing doses of the drug.

Genetic Effects of Impure and Pure Saccharin in Yeast

Yeast cells were grown in media containing impure or purified saccharin preparations. Dose-dependent increases in frequencies of cells possessing aberrant cell morphologies were revealed by light microscopy. At each test dose, cells grown in impure saccharin exhibited up to sevenfold higher frequencies of mitotic crossing-over or gene conversion in three of four assays for genetic recombination than cells grown in purified saccharin from the same lot. With one exception, the sweetener produced by the Maumee process caused larger increases in recombination and gene reversion than the sweetener produced by the Remsen-Fahlberg process. The several test markers did not respond equally to any test saccharin. Cells grown in liquid media containing no saccharin or two of three test concentrations of saccharin produced cell titers that were approximately equivalent.