Marked elevations in lung and plasma ceramide in COVID-19 linked to microvascular injury

The pathogenesis of the marked pulmonary microvasculature injury, a distinguishing feature of COVID-19 acute respiratory distress syndrome (COVID-ARDS), remains unclear. Implicated in the pathophysiology of diverse diseases characterized by endothelial damage, including ARDS and ischemic cardiovascular disease, ceramide and in particular palmitoyl ceramide (C16:0-ceramide) may be involved in the microvascular injury in COVID-19. Using deidentified plasma and lung samples from COVID-19 patients, ceramide profiling by mass spectrometry was performed. Compared with healthy individuals, a specific 3-fold C16:0-ceramide elevation in COVID-19 patient plasma was identified. Compared with age-matched controls, autopsied lungs of individuals succumbing to COVID-ARDS displayed a massive 9-fold C16:0-ceramide elevation and exhibited a previously unrecognized microvascular ceramide-staining pattern and markedly enhanced apoptosis. In COVID-19 plasma and lungs, the C16-ceramide/C24-ceramide ratios were increased and reversed, respectively, consistent with increased risk of vascular injury. Indeed, exposure of primary human lung microvascular endothelial cell monolayers to C16:0-ceramide-rich plasma lipid extracts from COVID-19, but not healthy, individuals led to a significant decrease in endothelial barrier function. This effect was phenocopied by spiking healthy plasma lipid extracts with synthetic C16:0-ceramide and was inhibited by treatment with ceramide-neutralizing monoclonal antibody or single-chain variable fragment. These results indicate that C16:0-ceramide may be implicated in the vascular injury associated with COVID-19.

Molecular Profiling of Coronavirus Disease 2019 (COVID-19) Autopsies Uncovers Novel Disease Mechanisms

Current understanding of coronavirus disease 2019 (COVID-19) pathophysiology is limited by disease heterogeneity, complexity, and a paucity of studies assessing patient tissues with advanced molecular tools. Rapid autopsy tissues were evaluated using multiscale, next-generation RNA-sequencing methods (bulk, single-nuclei, and spatial transcriptomics) to provide unprecedented molecular resolution of COVID-19-induced damage. Comparison of infected/uninfected tissues revealed four major regulatory pathways. Effectors within these pathways could constitute novel therapeutic targets, including the complement receptor C3AR1, calcitonin receptor–like receptor, or decorin. Single-nuclei RNA sequencing of olfactory bulb and prefrontal cortex highlighted remarkable diversity of coronavirus receptors. Angiotensin-converting enzyme 2 was rarely expressed, whereas basigin showed diffuse expression, and alanyl aminopeptidase, membrane, was associated with vascular/mesenchymal cell types. Comparison of lung and lymph node tissues from patients with different symptoms (one had died after a month-long hospitalization with multiorgan involvement, and the other had died after a few days of respiratory symptoms) with digital spatial profiling resulted in distinct molecular phenotypes. Evaluation of COVID-19 rapid autopsy tissues with advanced molecular techniques can identify pathways and effectors, map diverse receptors at the single-cell level, and help dissect differences driving diverging clinical courses among individual patients. Extension of this approach to larger data sets will substantially advance the understanding of the mechanisms behind COVID-19 pathophysiology.

Tissue-based SARS-CoV-2 detection in fatal COVID-19 infections: Sustained direct viral-induced damage is not necessary to drive disease progression

Coronavirus disease 2019 (COVID-19) is an ongoing pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Although viral infection is known to trigger inflammatory processes contributing to tissue injury and organ failure, it is unclear whether direct viral damage is needed to sustain cellular injury. An understanding of pathogenic mechanisms has been handicapped by the absence of optimized methods to visualize the presence and distribution of SARS-CoV-2 in damaged tissues. We first developed a positive control cell line (Vero E6) to validate SARS-CoV-2 detection assays. We then evaluated multiple organs (lungs, kidneys, heart, liver, brain, intestines, lymph nodes, and spleen) from fourteen COVID-19 autopsy cases using immunohistochemistry (IHC) for the spike and the nucleoprotein proteins, and RNA in situ hybridization (RNA ISH) for the spike protein mRNA. Tissue detection assays were compared with quantitative polymerase chain reaction (qPCR)-based detection. SARS-CoV-2 was histologically detected in the Vero E6 positive cell line control, 1 of 14 (7%) lungs, and none (0%) of the other 59 organs. There was perfect concordance between the IHC and RNA ISH results. qPCR confirmed high viral load in the SARS-CoV-2 ISH-positive lung tissue, and absent or low viral load in all ISH-negative tissues. In patients who die of COVID-19-related organ failure, SARS-CoV-2 is largely not detectable using tissue-based assays. Even in lungs showing widespread injury, SARS-CoV-2 viral RNA or proteins were detected in only a small minority of cases. This observation supports the concept that viral infection is primarily a trigger for multiple-organ pathogenic proinflammatory responses. Direct viral tissue damage is a transient phenomenon that is generally not sustained throughout disease progression.

Pathophysiology of SARS-CoV-2: the Mount Sinai COVID-19 autopsy experience

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its associated clinical syndrome COVID-19 are causing overwhelming morbidity and mortality around the globe and disproportionately affected New York City between March and May 2020. Here, we report on the first 100 COVID-19-positive autopsies performed at the Mount Sinai Hospital in New York City. Autopsies revealed large pulmonary emboli in six cases. Diffuse alveolar damage was present in over 90% of cases. We also report microthrombi in multiple organ systems including the brain, as well as hemophagocytosis. We additionally provide electron microscopic evidence of the presence of the virus in our samples. Laboratory results of our COVID-19 cohort disclose elevated inflammatory markers, abnormal coagulation values, and elevated cytokines IL-6, IL-8, and TNFα. Our autopsy series of COVID-19-positive patients reveals that this disease, often conceptualized as a primarily respiratory viral illness, has widespread effects in the body including hypercoagulability, a hyperinflammatory state, and endothelial dysfunction. Targeting of these multisystemic pathways could lead to new treatment avenues as well as combination therapies against SARS-CoV-2 infection.

Analysis of sex-specific risk factors and clinical outcomes in COVID-19

Background

Sex has consistently been shown to affect COVID-19 mortality, but it remains unclear how each sex's clinical outcome may be distinctively shaped by risk factors.

Methods

We studied a primary cohort of 4930 patients hospitalized with COVID-19 in a single healthcare system in New York City from the start of the pandemic till August 5, 2020, and a validation cohort of 1645 patients hospitalized with COVID-19 in the same healthcare system from August 5, 2020, to January 13, 2021.

Results

Here we show that male sex was independently associated with in-hospital mortality, intubation, and ICU care after adjusting for demographics and comorbidities. Using interaction analysis and sex-stratified models, we found that hypoxia interacted with sex to preferentially increase women's mortality risk while obesity interacted with sex to preferentially increase women's risk of intubation and intensive care in our primary cohort. In the validation cohort, we observed that male sex remained an independent risk factor for mortality, but sex-specific interactions were not replicated.

Conclusions

We conducted a comprehensive sex-stratified analysis of a large cohort of hospitalized COVID-19 patients, highlighting clinical factors that may contribute to sex differences in the outcome of COVID-19.

Intestinal Host Response to SARS-CoV-2 Infection and COVID-19 Outcomes in Patients With Gastrointestinal Symptoms

BACKGROUND & AIMS

Given that gastrointestinal (GI) symptoms are a prominent extrapulmonary manifestation of COVID-19, we investigated intestinal infection with SARS-CoV-2, its effect on pathogenesis, and clinical significance.

METHODS

Human intestinal biopsy tissues were obtained from patients with COVID-19 (n = 19) and uninfected control individuals (n = 10) for microscopic examination, cytometry by time of flight analyses, and RNA sequencing. Additionally, disease severity and mortality were examined in patients with and without GI symptoms in 2 large, independent cohorts of hospitalized patients in the United States (N = 634) and Europe (N = 287) using multivariate logistic regressions.

RESULTS

COVID-19 case patients and control individuals in the biopsy cohort were comparable for age, sex, rates of hospitalization, and relevant comorbid conditions. SARS-CoV-2 was detected in small intestinal epithelial cells by immunofluorescence staining or electron microscopy in 15 of 17 patients studied. High-dimensional analyses of GI tissues showed low levels of inflammation, including down-regulation of key inflammatory genes including IFNG, CXCL8, CXCL2, and IL1B and reduced frequencies of proinflammatory dendritic cells compared with control individuals. Consistent with these findings, we found a significant reduction in disease severity and mortality in patients presenting with GI symptoms that was independent of sex, age, and comorbid illnesses and despite similar nasopharyngeal SARS-CoV-2 viral loads. Furthermore, there was reduced levels of key inflammatory proteins in circulation in patients with GI symptoms.

CONCLUSIONS

These data highlight the absence of a proinflammatory response in the GI tract despite detection of SARS-CoV-2. In parallel, reduced mortality in patients with COVID-19 presenting with GI symptoms was observed. A potential role of the GI tract in attenuating SARS-CoV-2-associated inflammation needs to be further examined.

The human leukocyte antigen as a candidate tumor suppressor

Here we argue in support of the human leukocyte antigen (HLA) supergene as a tumor suppressor. HLA is a recurring mutational target in a large and diverse group of malignancies. The tumor suppressor function of HLA is linked to an embryonic/stemness and drug resistance phenotype. A deeper understanding of the distinct roles of HLA, including immunosurveillance, stemness, and tumor suppressor functions, could illuminate the limited responses in cancer patients. Furthermore, it would provide guidelines for the design of new therapeutic strategies, including the potential of modulating HLA expression in the tumor stem cell compartment.

Postmortem Findings Associated With SARS-CoV-2: Systematic Review and Meta-analysis

Coronavirus Disease 2019 (COVID-19), caused by the novel Severe Acute Respiratory Syndrome-associated Coronavirus 2 (SARS-CoV-2), has become a global threat to public health. COVID-19 is more pathogenic and infectious than the prior 2002 pandemic caused by SARS-CoV-1. The pathogenesis of certain disease manifestations in COVID-19 such as diffuse alveolar damage (DAD) are thought to be similar to SARS-CoV-1. However, the exact pathogenesis of COVID-19 related deaths remains poorly understood. The aim of this article was to systematically summarize the rapidly emerging literature regarding COVID-19 autopsies. A meta-analysis was also conducted based on data accrued from preprint and published articles on COVID-19 (n=241 patients) and the results compared with postmortem findings associated with SARS-CoV-1 deaths (n=91 patients). Both autopsy groups included mostly adults of median age 70 years with COVID-19 and 50 years with SARS-CoV-1. Overall, prevalence of DAD was more common in SARS-CoV-1 (100.0%) than COVID-19 (80.9%) autopsies (P=0.001). Extrapulmonary findings among both groups were not statistically significant except for hepatic necrosis (P <0.001), splenic necrosis (P<0.006) and white pulp depletion (P <0.001) that were more common with SARS-CoV-1. Remarkable postmortem findings in association with COVID-19 apart from DAD include pulmonary hemorrhage, viral cytopathic effect within pneumocytes, thromboembolism, brain infarction, endotheliitis, acute renal tubular damage, white pulp depletion of the spleen, cardiac myocyte necrosis, megakaryocyte recruitment, and hemophagocytosis.

Converging genetic and epigenetic drivers of paediatric acute lymphoblastic leukaemia identified by an information-theoretic analysis

In cancer, linking epigenetic alterations to drivers of transformation has been difficult, in part because DNA methylation analyses must capture epigenetic variability, which is central to tumour heterogeneity and tumour plasticity. Here, by conducting a comprehensive analysis, based on information theory, of differences in methylation stochasticity in samples from patients with paediatric acute lymphoblastic leukaemia (ALL), we show that ALL epigenomes are stochastic and marked by increased methylation entropy at specific regulatory regions and genes. By integrating DNA methylation and single-cell gene-expression data, we arrived at a relationship between methylation entropy and gene-expression variability, and found that epigenetic changes in ALL converge on a shared set of genes that overlap with genetic drivers involved in chromosomal translocations across the disease spectrum. Our findings suggest that an epigenetically driven gene-regulation network, with UHRF1 (ubiquitin-like with PHD and RING finger domains 1) as a central node, links genetic drivers and epigenetic mediators in ALL.

Circulating Levels of Calcitonin Gene-Related Peptide Are Lower in COVID-19 Patients

Background

To better understand the biology of COVID-19, we have explored the behavior of calcitonin gene-related peptide (CGRP), an angiogenic, vasodilating, and immune modulating peptide, in severe acute respiratory syndrome coronavirus 2 positive patients.

Methods

Levels of CGRP in the serum of 57 COVID-19 patients (24 asymptomatic, 23 hospitalized in the general ward, and 10 admitted to the intensive care unit) and healthy donors (n = 24) were measured by enzyme-linked immunosorbent assay (ELISA). In addition, to better understand the physiological consequences of the observed variations, we investigated by immunofluorescence the distribution of receptor activity modifying protein 1 (RAMP1), one of the components of the CGRP receptor, in autopsy lung specimens.

Results

CGRP levels were greatly decreased in COVID-19 patients (P < 0.001) when compared to controls, and there were no significant differences due to disease severity, sex, age, or comorbidities. We found that COVID-19 patients treated with proton pump inhibitors had lower levels of CGRP than other patients not taking this treatment (P = 0.001). RAMP1 immunoreactivity was found in smooth muscle cells of large blood vessels and the bronchial tree and in the airways´ epithelium. In COVID-19 samples, RAMP1 was also found in proliferating type II pneumocytes, a common finding in these patients.

Conclusions

The lower levels of CGRP should negatively impact the respiratory physiology of COVID-19 patients due to vasoconstriction, improper angiogenesis, less epithelial repair, and faulty immune response. Therefore, restoring CGRP levels in these patients may represent a novel therapeutic approach for COVID-19.

Gastrointestinal involvement attenuates COVID-19 severity and mortality

Given that gastrointestinal (GI) symptoms are a prominent extrapulmonary manifestation of coronavirus disease 2019 (COVID-19), we investigated intestinal infection with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) and its effect on disease pathogenesis. SARS-CoV-2 was detected in small intestinal enterocytes by immunofluorescence staining or electron microscopy, in 13 of 15 patients studied. High dimensional analyses of GI tissues revealed low levels of inflammation in general, including active downregulation of key inflammatory genes such as IFNG, CXCL8, CXCL2 and IL1B and reduced frequencies of proinflammatory dendritic cell subsets. To evaluate the clinical significance of these findings, examination of two large, independent cohorts of hospitalized patients in the United States and Europe revealed a significant reduction in disease severity and mortality that was independent of gender, age, and examined co-morbid illnesses. The observed mortality reduction in COVID-19 patients with GI symptoms was associated with reduced levels of key inflammatory proteins including IL-6, CXCL8, IL-17A and CCL28 in circulation but was not associated with significant differences in nasopharyngeal viral loads. These data draw attention to organ-level heterogeneity in disease pathogenesis and highlight the role of the GI tract in attenuating SARS-CoV-2-associated inflammation with related mortality benefit.

ONE SENTENCE SUMMARY

Intestinal infection with SARS-CoV-2 is associated with a mild inflammatory response and improved clinical outcomes.

COVID-19: Staging of a New Disease

Coronavirus disease 2019 (COVID-19), like cancer, is a complex disease with clinical phases of progression. Initially conceptualized as a respiratory disease, COVID-19 is increasingly recognized as a multi-organ and heterogeneous illness. Disease staging is a method for measuring the progression and severity of an illness using objective clinical and molecular criteria. Integral to cancer staging is "metastasis," defined as the spread of a disease-producing agent, including neoplastic cells and pathogens such as certain viruses, from the primary site to distinct anatomic locations. Staging provides valuable frameworks and benchmarks for clinical decision-making in patient management, improved prognostication, and evidence-based treatment selection.

Cardiogenic Shock and Mitral Valve Chord Rupture: A Rare Presentation of Libman-Sacks Endocarditis

Distinguishing Libman-Sacks endocarditis from other valvular heart disease etiologies has important implications for management. We present a case of a 23-year-old man who presented in extremis with fever and cardiogenic shock caused by Libman-Sacks endocarditis with associated mitral valve chord rupture. (Level of Difficulty: Beginner.)

Anticoagulation, Bleeding, Mortality, and Pathology in Hospitalized Patients With COVID-19

Background

Thromboembolic disease is common in coronavirus disease-2019 (COVID-19). There is limited evidence on the association of in-hospital anticoagulation (AC) with outcomes and postmortem findings.

Objectives

The purpose of this study was to examine association of AC with in-hospital outcomes and describe thromboembolic findings on autopsies.

Methods

This retrospective analysis examined the association of AC with mortality, intubation, and major bleeding. Subanalyses were also conducted on the association of therapeutic versus prophylactic AC initiated ≤48 h from admission. Thromboembolic disease was contextualized by premortem AC among consecutive autopsies.

Results

Among 4,389 patients, median age was 65 years with 44% women. Compared with no AC (n = 1,530; 34.9%), therapeutic AC (n = 900; 20.5%) and prophylactic AC (n = 1,959; 44.6%) were associated with lower in-hospital mortality (adjusted hazard ratio [aHR]: 0.53; 95% confidence interval [CI]: 0.45 to 0.62 and aHR: 0.50; 95% CI: 0.45 to 0.57, respectively), and intubation (aHR: 0.69; 95% CI: 0.51 to 0.94 and aHR: 0.72; 95% CI: 0.58 to 0.89, respectively). When initiated ≤48 h from admission, there was no statistically significant difference between therapeutic (n = 766) versus prophylactic AC (n = 1,860) (aHR: 0.86; 95% CI: 0.73 to 1.02; p = 0.08). Overall, 89 patients (2%) had major bleeding adjudicated by clinician review, with 27 of 900 (3.0%) on therapeutic, 33 of 1,959 (1.7%) on prophylactic, and 29 of 1,530 (1.9%) on no AC. Of 26 autopsies, 11 (42%) had thromboembolic disease not clinically suspected and 3 of 11 (27%) were on therapeutic AC.

Conclusions

AC was associated with lower mortality and intubation among hospitalized COVID-19 patients. Compared with prophylactic AC, therapeutic AC was associated with lower mortality, although not statistically significant. Autopsies revealed frequent thromboembolic disease. These data may inform trials to determine optimal AC regimens.

Comparison of SARS-CoV-2 detection from nasopharyngeal swab samples by the Roche cobas 6800 SARS-CoV-2 test and a laboratory-developed real-time RT-PCR test

The urgent need to implement and rapidly expand testing for severe acute respiratory syndrome coronavirus‐2 (SARS‐CoV‐2) infection has led to the development of multiple assays. How these tests perform relative to one another is poorly understood. We evaluated the concordance between the Roche Diagnostics cobas 6800 SARS‐CoV‐2 test and a laboratory‐developed test (LDT) real‐time reverse transcription‐polymerase chain reaction based on a modified Centers for Disease Control and Prevention protocol, for the detection of SARS‐CoV‐2 in samples submitted to the Clinical Laboratories of the Mount Sinai Health System. A total of 1006 nasopharyngeal swabs in universal transport medium from persons under investigation were tested for SARS‐CoV‐2 as part of routine clinical care using the cobas SARS‐CoV‐2 test with subsequent evaluation by the LDT. Cycle threshold values were analyzed and interpreted as either positive (“detected” or “presumptive positive”), negative (not detected), inconclusive, or invalid. Statistical analysis was performed using GraphPad Prism 8. The cobas SARS‐CoV‐2 test reported 706 positive and 300 negative results. The LDT reported 640 positive, 323 negative, 34 inconclusive, and 9 invalid results. When excluding inconclusive and invalid results, the overall percent agreement between the two platforms was 95.8%. Cohen's κ coefficient was 0.904 (95% confidence interval, 0.875‐0.933), suggesting almost perfect agreement between both platforms. An overall discordance rate of 4.2% between the two systems may reflect differences in primer sequences, assay limit of detection, or other factors, highlighting the importance of comparing the performance of different testing platforms.

In this study, we compared the detection of SARS‐CoV‐2 in clinical samples from patients being evaluated for CoVID‐19 infection by two different RT‐PCR assays, the cobas® 6800 SARS‐CoV‐2 test from Roche Molecular Systems and a laboratory‐developed test (LDT) using the Centers for Disease Control and Prevention 2019‐nCoV primers and probes. Overall there was excellent agreement between the two tests methods, although our results suggest that the cobas® SARSCoV‐2 test may have a lower limit of detection than the LDT.

A Dysregulated DNA Methylation Landscape Linked to Gene Expression in MLL-Rearranged AML

Translocations of the KMT2A (MLL) gene define a biologically distinct and clinically aggressive subtype of acute myeloid leukaemia (AML), marked by a characteristic gene expression profile and few cooperating mutations. Although dysregulation of the epigenetic landscape in this leukaemia is particularly interesting given the low mutation frequency, its comprehensive analysis using whole genome bisulphite sequencing (WGBS) has not been previously performed. Here we investigated epigenetic dysregulation in nine MLL-rearranged (MLL-r) AML samples by comparing them to six normal myeloid controls, using a computational method that encapsulates mean DNA methylation measurements along with analyses of methylation stochasticity. We discovered a dramatically altered epigenetic profile in MLL-r AML, associated with genome-wide hypomethylation and a markedly increased DNA methylation entropy reflecting an increasingly disordered epigenome. Methylation discordance mapped to key genes and regulatory elements that included bivalent promoters and active enhancers. Genes associated with significant changes in methylation stochasticity recapitulated known MLL-r AML expression signatures, suggesting a role for the altered epigenetic landscape in the transcriptional programme initiated by MLL translocations. Accordingly, we established statistically significant associations between discordances in methylation stochasticity and gene expression in MLL-r AML, thus providing a link between the altered epigenetic landscape and the phenotype.

Regulated noise in the epigenetic landscape of development and disease

In this Perspective, we synthesize past and present observations in the field of epigenetics to propose a model in which the epigenome can modulate cellular plasticity in development and disease by regulating the effects of noise. In this model, the epigenome facilitates phase transitions in development and reprogramming and mediates canalization, or the ability to produce a consistent phenotypic outcome despite being challenged by variable conditions, during cell fate commitment. After grounding our argument in a discussion of stochastic noise and nongenetic heterogeneity, we explore the hypothesis that distinct chromatin domains, which are known to be dysregulated in disease and remodeled during development, might underlie cellular plasticity more generally. We then present a modern portrayal of Waddington's epigenetic landscape through a mathematical formalism. We speculate that this new framework might impact how we approach disease mechanisms. In particular, it may help to explain the observation that the variability of DNA methylation and gene expression are increased in cancer, thus contributing to tumor cell heterogeneity.

Application of the new C18 speedisks to the analysis of polychlorinated dibenzo-p-dioxins and dibenzofurans in water and effluent samples

A recently introduced disk for solid-phase extraction of pollutants from water (C18 Speedisk) has been tested for the analysis of polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF). The complete procedure of analysis has been validated with spiked deionized water. The accuracy, expressed as recovery for the sum of 2,3,7,8-substituted congeners. is 92% and the precision, expressed as the RSD of reproducibility, is 5.8%. The limit of detection (LOD), using 2 l of water, is 4.2 pg/l (0.6 pg ITEQ/l) for the sum of 2,3,7,8-substituted congeners. Actually, the C18 Speedisks have substituted the use of other C18 membrane disks in our laboratory because they allow the fast and efficient analysis of samples with high content of suspended material and reduce the time of elution of free-particulate samples. These disks have been successfully applied to the analysis of water from different sources and with very different physical and chemical characteristics: seawater, rain water, an industrial effluent, a landfill leachate and the inlet and chlorinated and non-chlorinated outlet water from a wastewater treatment plant.

Genotoxicity of 17 gyrase- and four mammalian topoisomerase II-poisons in prokaryotic and eukaryotic test systems

The genotoxic potency of certain classes of topoisomerase II poisons is correlated with their affinity to the topoisomerase protein rather than with the presence of 'classical' structural alerts for DNA reactivity: bacterial topoisomerase II poisons (specifically named gyrase inhibitors) are highly genotoxic in prokaryotic systems; mammalian topoisomerase II poisons are potent mutagens/clastogens in eukaryotic systems. Studies with bacterial, lower eukaryotic and mammalian genotoxicity tests were performed to draw structure-activity conclusions and address risk-benefit considerations for the class of quinolone gyrase inhibitors. All 17 gyrase inhibitors investigated in this study showed genotoxic activity in Salmonella typhimurium strain TA102 and the SOS test. The genotoxic and the toxic activities increased in a highly parallel fashion from the parent compounds, nalidixic acid and oxolinic acid, to the new generation fluoroquinolones. Generally, the most potent fluoroquinolones also show clear-cut positive effects in eukaryotic test systems, although at concentrations 100-1000-fold higher than those effective in bacteria and also 100-1000-fold higher than the minimal genotoxic concentrations of antitumour topoisomerase II inhibitors (ellipticine, teniposide, mAMSA) used as reference compounds. However, subtle structural modifications of the quinolones can strongly diminish the preferential genotoxicity in the prokaryotic test systems.

A new aspect of the antiproliferative action of peripheral-type benzodiazepine receptor ligands

Ro 5-4864 (4-chlorodiazepam), PK 11195 (1-(2-chlorophenyl)-1,3-dihydro-1-methyl-propyl)isoquinoline carboxamide) and diazepam inhibit, in a concentration-dependent way, the proliferation of V79 Chinese hamster lung cells (IC50 values were: 65.0 +/- 3.73 microM, 57.70 +/- 4.75 microM and 106.80 +/- 8.89 microM, respectively) without being cytotoxic. This antiproliferative effect is mediated by mitosis arrest in the G2 + M stage without affecting DNA synthesis and seems unrelated to a specific interaction of these drugs with the peripheral-type benzodiazepine receptor.

Evaluation of the micronucleus test in vitro using Chinese hamster cells: results of four chemicals weakly positive in the in vivo micronucleus test

A rapid and simple procedure for the micronucleus test (MNT) in vitro using Chinese hamster ovary (CHO) cells was established in our laboratory. The assay is intended to quickly screen chromosomal aberrations in vitro within the framework of industrial genotoxicity studies. To test the sensitivity of the assay in the experiments described here, four substances, classified as noncarcinogens but reported as weak inducers of micronuclei (MN) in bone-marrow cells of mice, were evaluated in the MNT in vitro. Of the four compounds, ascorbic acid, phenol, and 2,6-diaminotoluene proved to be genotoxic in the MNT in vitro. Titanium dioxide, which could not be dissolved in the culture medium, did not induce MN. The MNT in vitro proved to be quick and relatively simple and to yield highly reproducible results when testing the four chemicals.