Online hate network spreads malicious COVID-19 content outside the control of individual social media platforms

We show that malicious COVID-19 content, including racism, disinformation, and misinformation, exploits the multiverse of online hate to spread quickly beyond the control of any individual social media platform. We provide a first mapping of the online hate network across six major social media platforms. We demonstrate how malicious content can travel across this network in ways that subvert platform moderation efforts. Machine learning topic analysis shows quantitatively how online hate communities are sharpening COVID-19 as a weapon, with topics evolving rapidly and content becoming increasingly coherent. Based on mathematical modeling, we provide predictions of how changes to content moderation policies can slow the spread of malicious content.

Hidden order across online extremist movements can be disrupted by nudging collective chemistry

Disrupting the emergence and evolution of potentially violent online extremist movements is a crucial challenge. Extremism research has analyzed such movements in detail, focusing on individual- and movement-level characteristics. But are there system-level commonalities in the ways these movements emerge and grow? Here we compare the growth of the Boogaloos, a new and increasingly prominent U.S. extremist movement, to the growth of online support for ISIS, a militant, terrorist organization based in the Middle East that follows a radical version of Islam. We show that the early dynamics of these two online movements follow the same mathematical order despite their stark ideological, geographical, and cultural differences. The evolution of both movements, across scales, follows a single shockwave equation that accounts for heterogeneity in online interactions. These scientific properties suggest specific policies to address online extremism and radicalization. We show how actions by social media platforms could disrupt the onset and 'flatten the curve' of such online extremism by nudging its collective chemistry. Our results provide a system-level understanding of the emergence of extremist movements that yields fresh insight into their evolution and possible interventions to limit their growth.

A preliminary study of cerebral blood flow, aging and dementia in people with Down syndrome

BACKGROUND

People with Down syndrome (DS) develop Alzheimer's disease (AD) at an earlier age of onset than those with sporadic AD. AD neuropathology is typically present in DS by 40 years of age with an onset of dementia approximately 10 years later. This early onset is due to the overexpression of amyloid precursor protein from the third copy of chromosome 21. Cerebrovascular neuropathology is thought to contribute in 40-60% of cases sporadic AD. However, the vascular contribution to dementia in people with DS has been relatively unexplored. We hypothesised that vascular perfusion is compromised in older adults with DS relative to younger individuals and is further exacerbated in those with dementia.

METHOD

Cerebral blood flow (CBF) was measured using pulsed arterial spin labelling in 35 cognitively characterised adults with DS (26-65 years). DS participants were also compared with 15 control subjects without DS or dementia (26-65 years). Linear regression evaluated the difference in CBF across groups and diagnosis along with assessing the association between CBF and cognitive measures within the DS cohort.

RESULTS

Cerebral blood flow was significantly lower among DS participants with probable AD compared with controls (P = 0.02) and DS participants with no dementia (P = 0.01). Within the DS cohort, CBF was significantly associated with the Severe Impairment Battery (SIB) measure and the Dementia Questionnaire for People with Learning Disabilities (DLD) rating (F_3,25  = 5.13; P = 0.007). Both the SIB (β = 0.74; t = 2.71; P = 0.01) and DLD (β = -0.96; t = -3.87; P < 0.001) indicated greater impairment as global CBF decreased. Age was significantly associated with CBF among participants with DS. There was a non-linear effect of age, whereby CBF declined more rapidly after 45 years of age.

CONCLUSIONS

This preliminary study of CBF in DS indicates that cerebrovascular pathology may be a significant contributor to dementia in DS. CBF was associated with diagnosis, cognition and age. Notably, CBF decreases at a greater rate after age 45 and may represent a significant prodromal event in AD progression.

Riparian forest fragments in rice fields under different management: differences on hymenopteran parasitoids diversity

Hymenopteran parasitoids are important biological control agents in agroecosystems, and their diversity can be increased with habitat heterogeneity. Thus, the purpose of the study is to evaluate the influence of distance of rice-growing areas from natural fragment, type of crop management (organic and conventional) and crop stages (vegetative and reproductive stages) on parasitoids family diversity. The work took place in two irrigated rice crops, one with organic management (O.M.) and another one with conventional management (C.M.), in the municipality of Nova Santa Rita, RS, Brazil, during the 2013/2014 and 2014/2015 seasons. The parasitoids were collected with Malaise trap arranged at different distances in relation to the native vegetation surrounding the rice crop in both places. Specimens were collected twice a month from seeding until the rice harvest. Average abundance between management, distances and rice development were compared. The most abundant families were Platygastridae, Mymaridae, Encyrtidae, Eulophidae and Trichogrammatidae. Parasitoid average abundance was significantly higher on OM only in the second season. There was a negative correlation between distance from native vegetation and parasitoid abundance in C.M. areas. There were differences in the composition of the parasitoid assembly between the phenological stages of rice.

Hidden resilience and adaptive dynamics of the global online hate ecology

Online hate and extremist narratives have been linked to abhorrent real-world events, including a current surge in hate crimes^1-6 and an alarming increase in youth suicides that result from social media vitriol⁷; inciting mass shootings such as the 2019 attack in Christchurch, stabbings and bombings^8-11; recruitment of extremists^12-16, including entrapment and sex-trafficking of girls as fighter brides¹⁷; threats against public figures, including the 2019 verbal attack against an anti-Brexit politician, and hybrid (racist-anti-women-anti-immigrant) hate threats against a US member of the British royal family¹⁸; and renewed anti-western hate in the 2019 post-ISIS landscape associated with support for Osama Bin Laden's son and Al Qaeda. Social media platforms seem to be losing the battle against online hate^19,20 and urgently need new insights. Here we show that the key to understanding the resilience of online hate lies in its global network-of-network dynamics. Interconnected hate clusters form global 'hate highways' that-assisted by collective online adaptations-cross social media platforms, sometimes using 'back doors' even after being banned, as well as jumping between countries, continents and languages. Our mathematical model predicts that policing within a single platform (such as Facebook) can make matters worse, and will eventually generate global 'dark pools' in which online hate will flourish. We observe the current hate network rapidly rewiring and self-repairing at the micro level when attacked, in a way that mimics the formation of covalent bonds in chemistry. This understanding enables us to propose a policy matrix that can help to defeat online hate, classified by the preferred (or legally allowed) granularity of the intervention and top-down versus bottom-up nature. We provide quantitative assessments for the effects of each intervention. This policy matrix also offers a tool for tackling a broader class of illicit online behaviours^21,22 such as financial fraud.

Emergent dynamics of extremes in a population driven by common information sources and new social media algorithms

We quantify how and when extreme subpopulations emerge in a model society despite everyone having the same information and available resources – and show that counterintuitively these extremes will likely be enhanced over time by new social media algorithms designed to reduce division. We verify our analysis mathematically, and show it reproduces (a) the time-dependent behavior observed in controlled experiments on humans, (b) the findings of a recent study of online behavior by Facebook concerning the impact of ‘soft’ and ‘hard’ news, (c) the observed temporal emergence of extremes in U.S. House of Representatives voting, and (d) the real-time emergence of a division in national opinion during the ongoing peace process in Colombia. We uncover a novel societal tipping point which is a ‘ghost’ of a nearby saddle-node bifurcation from dynamical systems theory, and which provides a novel policy opportunity for preventing extremes from emerging.

Universality and correlations in individuals wandering through an online extremist space

The "out of the blue" nature of recent terror attacks and the diversity of apparent motives highlight the importance of understanding the online trajectories that individuals follow prior to developing high levels of extremist support. Here we show that the physics of stochastic walks, with and without temporal correlation, provides a unifying description of these online trajectories. Our unique data set comprising all users of a global social media site reveals universal characteristics in individuals' online lifetimes. Our accompanying theory generates analytical and numerical solutions that describe the characteristics shown by individuals that go on to develop high levels of extremist support and those that do not. Going forward, it is conceivable that a deeper understanding of these temporal and many-body correlations may eventually contribute to the important task of better countering the spread of radical propaganda online.

Multiscale dynamical network mechanisms underlying aging of an online organism from birth to death

We present the continuous-time evolution of an online organism network from birth to death which crosses all organizational and temporal scales, from individual components through to the mesoscopic and entire system scale. These continuous-time data reveal a lifespan driven by punctuated, real-time co-evolution of the structural and functional networks. Aging sees these structural and functional networks gradually diverge in terms of their small-worldness and eventually their connectivity. Dying emerges as an extended process associated with the formation of large but disjoint functional sub-networks together with an increasingly detached core. Our mathematical model quantifies the very different impacts that interventions will have on the overall lifetime, period of initial growth, peak of potency, and duration of old age, depending on when and how they are administered. In addition to their direct relevance to online extremism, our findings may offer insight into aging in other network systems of comparable complexity for which extensive in vivo data is not yet available.

Age-related increases in right frontal activation during task switching are mediated by reaction time and white matter microstructure

Age-related increases in right frontal cortex activation are a common finding in the neuroimaging literature. However, neurocognitive factors contributing to right frontal over-recruitment remain poorly understood. Here we investigated the influence of age-related reaction time (RT) slowing and white matter (WM) microstructure reductions as potential explanatory factors for age-related increases in right frontal activation during task switching. Groups of younger (N=32) and older (N=33) participants completed a task switching paradigm while functional magnetic resonance imaging (fMRI) was performed, and rested while diffusion tensor imaging (DTI) was performed. Two right frontal regions of interest (ROIs), the dorsolateral prefrontal cortex (DLPFC) and insula, were selected for further analyses from a common network of regions recruited by both age groups during task switching. Results demonstrated age-related activation increases in both ROIs. In addition, the older adult group showed longer RT and decreased fractional anisotropy in regions of the corpus callosum with direct connections to the fMRI ROIs. Subsequent mediation analyses indicated that age-related increases in right insula activation were mediated by RT slowing and age-related increases in right DLPFC activation were mediated by WM microstructure. Our results suggest that age-related RT slowing and WM microstructure declines contribute to age-related increases in right frontal activation during cognitive task performance.

New dynamical scaling universality for quantum networks across adiabatic quantum phase transitions

We reveal universal dynamical scaling behavior across adiabatic quantum phase transitions in networks ranging from traditional spatial systems (Ising model) to fully connected ones (Dicke and Lipkin-Meshkov-Glick models). Our findings, which lie beyond traditional critical exponent analysis and adiabatic perturbation approximations, are applicable even where excitations have not yet stabilized and, hence, provide a time-resolved understanding of quantum phase transitions encompassing a wide range of adiabatic regimes. We show explicitly that even though two systems may traditionally belong to the same universality class, they can have very different adiabatic evolutions. This implies that more stringent conditions need to be imposed than at present, both for quantum simulations where one system is used to simulate the other and for adiabatic quantum computing schemes.

Theory of enhanced performance emerging in a sparsely connected competitive population

We provide an analytic theory to explain Anghel et al's recent numerical finding whereby a maximum in the global performance emerges for a sparsely connected competitive population [Phys. Rev. Lett. 92, 058701 (2004)]. We show that the effect originates in the highly correlated dynamics of strategy choice, and can be significantly enhanced using a simple modification to the model.

Systematics, evolution, and biology of scelionid and platygastrid wasps

The Platygastroidea comprises two families of parasitoids, Scelionidae and Platygastridae, and nearly 4500 described species. They parasitize a diverse array of insects as well as spiders. Idiobiont endoparasitism of eggs is the putative ground plan biology, as reflected by all scelionids, but most Platygastridae are koinobiont endoparasitoids of immature Auchenorrhyncha, Sternorrhyncha, and Cecidomyiidae. The superfamily is demonstrably monophyletic but its phylogenetic position remains uncertain. Relationships within the Platygastroidea are also poorly known and the group is in need of comprehensive phylogenetic study. Significant information is available on host relationships and biology, although much of this is biased to a few genera of Telenominae that are employed as biocontrol agents. Hosts for many genera are unknown, in particular those that inhabit leaf litter or parasitize solitary host eggs. The Trissolcus basalis-Nezara viridula parasitoid-host association has become a favored model system in ecological, behavioral, and physiological research on insects.

Theory of networked minority games based on strategy pattern dynamics

We formulate a theory of agent-based models in which agents compete to be in a winning group. The agents may be part of a network or not, and the winning group may be a minority group or not. An important feature of the present formalism is its focus on the dynamical pattern of strategy rankings, and its careful treatment of the strategy ties which arise during the system's temporal evolution. We apply it to the minority game with connected populations. Expressions for the mean success rate among the agents and for the mean success rate for agents with k neighbors are derived. We also use the theory to estimate the value of connectivity p above which the binary-agent-resource system with high resource levels makes the transition into the high-connectivity state.

Enhanced winning in a competing population by random participation

We study a version of the minority game in which one agent is allowed to join the game in a random fashion. It is shown that in the crowded regime, i.e., for small values of the memory size m of the agents in the population, the agent performs significantly well if she decides to participate the game randomly with a probability q and she records the performance of her strategies only in the turns that she participates. The information, characterized by a quantity called the inefficiency, embedded in the agent's strategies performance turns out to be very different from that of the other agents. Detailed numerical studies reveal a relationship between the success rate of the agent and the inefficiency. The relationship can be understood analytically in terms of the dynamics in which the various possible histories are being visited as the game proceeds. For a finite fraction of randomly participating agents up to 60% of the population, it is found that the winning edge of these agents persists.

Predictability of large future changes in a competitive evolving population

The dynamical evolution of many economic, sociological, biological, and physical systems tends to be dominated by a relatively small number of unexpected, large changes ("extreme events"). We study the large, internal changes produced in a generic multiagent population competing for a limited resource, and find that the level of predictability increases prior to a large change. These large changes hence arise as a predictable consequence of information encoded in the system's global state.

Deterministic dynamics in the minority game

The minority game (MG) behaves as a stochastically disturbed deterministic system due to the coin toss invoked to resolve tied strategies. Averaging over this stochasticity yields a description of the MG's deterministic dynamics via mapping equations for the strategy score and global information. The strategy-score map contains both restoring-force and bias terms, whose magnitudes depend on the game's quenched disorder. Approximate analytical expressions are obtained and the effect of "market impact" is discussed. The global-information map represents a trajectory on a de Bruijn graph. For small quenched disorder, a Eulerian trail represents a stable attractor. It is shown analytically how antipersistence arises. The response to perturbations and different initial conditions is also discussed.

Generalized strategies in the minority game

We show analytically how the fluctuations (i.e., standard deviation sigma) in the minority game can decrease below the random coin-toss limit if the agents use more general, stochastic strategies. This suppression of sigma results from a cancellation between the actions of a crowd, in which agents act collectively and make the same decision, and those of an anticrowd, in which agents act collectively by making the opposite decision to the crowd.

Theory of the evolutionary minority game

We present a theory describing a recently introduced model of an evolving, adaptive system in which agents compete to be in the minority. The agents themselves are able to evolve their strategies over time in an attempt to improve their performance. The theory explicitly demonstrates the self-interaction, or market impact, that agents in such systems experience.

Apoptosis is a pathway responsible for the resolution of endotoxin-induced alveolar type II cell hyperplasia in the rat

Previous studies showed that intratracheal instillation of endotoxin induces transient type II cell hyperplasia in the rat lung and described some of the mechanisms involved in the proliferative response of type II cells. The purpose of the present study was to investigate how long the type II cell hyperplasia persists and how it is resolved. The portion of epithelial cells in hyperplastic lesions of the rat lung expressing cyclin D1, an indicator for cells in the G1 phase of the cell cycle, was greatest at 3 d post instillation and decreased after 4 and 6 d. The fate of the proliferating epithelial cells was traced by injecting the rats with 5-bromo-2' deoxy uridine (BrdU) 2 d post instillation, the peak time point for maximum incorporation of BrdU. Exfoliated BrdU-positive epithelial cells were detected in the alveolar spaces in tissue sections from rats 4, 5, and 6 d post instillation. BrdU-positive epithelial cells showed flattened nuclei at 6 and 10 d post instillation. Expression of the 116 kD poly(ADP-ribose) polymerase (PARP) was low in type II cells from control rats, and was increased at 3, 4, and 6 d post instillation. In cells obtained by lavage, only a 35 kD cleavage product of PARP was detected, which is an indicator of necrotic cell death. In isolated type II cells from rats 3, 4, and 6 d post endotoxin instillation, progressive cleavage of the PARP to its 89 kD residual fragment was detected, which is a direct evidence for the activation of caspases. Furthermore, apoptotic epithelial cells with condensed nuclei were identified by electron microscopy in rats 4 d post instillation. These results indicate that apoptosis is an additional mechanism for the resolution of endotoxin-induced lung epithelial hyperplasias.

Immunologic specificity of lymphocyte cell lines from dogs exposed to beryllium oxide

We have reported that dogs exposed twice to aerosols of beryllium oxide (BeO) developed Be-specific immune responses within the lung, along with granulomatous and fibrotic lung lesions. To evaluate the specificity of the immune response, lymphocytes from lungs and blood of BeO-exposed dogs were co-cultured over an irradiated blood monocyte layer, alternately with interleukin 2 and BeSO4. Resultant cell lines were then tested for their response to different metal cations, common canine recall antigens, and BeSO4 in an in vitro cell proliferation assay. The cell lines responded to BeSO4 in a dose-dependent fashion, with mean stimulation indices of 7, 58, 119, and 112 at concentrations of 0.01, 1.0, 10, and 100 microM BeSO4 respectively. Cells not proliferate when incubated with ZnSO4 or NiSO4, or with canine distemper, leptospira, adenovirus 2, parvovirus, or parainfluenza antigens. Lymphocytes from normal vaccinated dogs proliferated markedly when cultured with these antigens. Cells from the cultured cell lines (91%) stained with Thy-1 (a pan T-cell marker) and 96% stained with DT2 (a helper T-cell marker). Furthermore, the Be-induced proliferative response was restricted by major histocompatibility (MHC) class II antigens. These data reinforce the premise that inhalation exposure of dogs to BeO produces lung lesions and MHC class II restricted immunologic responses mediated by Be-specific, helper T-Cells. These data further confirm the hypothesis that antigen localized to the lung results in the recruitment of T-cells to the lung, followed by localized antigen-specific, cell-mediated immune responses.

p53, Cip1, and Gadd153 expression following treatment of A549 cells with natural and man-made vitreous fibers

DNA damage induced by chemicals and ionizing radiation is associated with the expression of negative regulators of the cell cycle. The arrest of cells in G1 and G2 phases of the cell cycle provides time for DNA repair. Asbestos fibers are carcinogenic when inhaled by both humans and animals; however, the mechanism by which the fibers exert their effect is unknown. This work was undertaken to determine whether the expression of DNA damage-inducible genes differs between crocidolite, a fiber positive for lung tumors, and JM 100 glass microfiber, which is negative for lung tumors when inhaled by rats. Temporal and dose-related expressions of p53, Cip1, and Gadd153 proteins were determined in cultured A549 cells treated with either Union Internationale Contre le Cancer crocidolite or JM 100 for 20 hr and cultured in fresh media. Immunolabeled cells were analyzed by flow cytometry, and the increased number of protein-expressing cells was determined by subtracting the expression in unexposed cells from exposed cells. Crocidolite induced the expression of all three proteins with a maximum expression after approximately 18 hr in fresh media. At a similar time point, JM 100 did not markedly induce the three proteins. Crocidolite also induced a dose-dependent increase in the number of cells in the G2 phase of the cell cycle. These results show that asbestos behaves like ionizing radiation and genotoxic chemicals by inducing proteins associated with DNA damage and cell-cycle arrest. The clear difference in response between crocidolite and JM 100 may help elucidate the mechanism of action of toxic and nontoxic fibers.

DNA damage-inducible genes as biomarkers for exposures to environmental agents

A biodosimetric approach to determine alpha-particle dose to the respiratory tract epithelium from known exposures to radon has been developed in the rat. Cytotoxicity assays have been used to obtain dose-conversion factors for cumulative exposures typical of those encountered by underground uranium miners. However, this approach is not sensitive enough to derive dose-conversion factors for indoor radon exposures. The expression of DNA damage-inducible genes is being investigated as a biomarker of exposure to radon progeny. Exposure of cultures of A549 cells to alpha particles resulted in an increase in the protein levels of the DNA damage-inducible genes, p53, Cip1, and Gadd45. These protein changes were associated with a transient arrest of cells passing through the cell cycle. This arrest was typified by an increase in the number of cells in the G1 and G2 phases and a decrease in the number of cells in the S phase. The effect of inhaled alpha particles (radon progeny) in rats was examined in the epithelial cells of the lateral well of the anterior nasal cavity. Exposures to radon progeny resulted in a significant increase in the number of cells in the G1 phase and a decrease in the number of cells in the S phase. These cell-cycle changes were concomitant with an increase in the number of cells containing DNA strand breaks. These results suggest a commonality between cell-cycle events in vitro and in vivo following exposure to ionizing radiation. In addition to ionizing radiation, A549 cells were exposed to 4-nitroquinoline-1-oxide, methyl methanesulphonate, crocidolite asbestos, and glass microfiber. These studies showed that physical and chemical agents induce different expression patterns of p53, Cip1, and Gadd153 proteins and they could be used to discriminate between toxic and nontoxic materials such as asbestos and glass microfiber. The measurement of gene expression in A549 cells may provide a means to identify a broad spectrum of physical and chemical toxicants encountered in the environment.

Kinetics of nasal epithelial cell loss and proliferation in F344 rats following a single exposure to 0.5 ppm ozone

Repeated exposure to 0.5 ppm ozone (O3) induces mucous cell metaplasia in the nasal transitional epithelium (NTE) of rats. The cellular events which commit the NTE to undergo this phenotypic alteration occur during the first 3 days of exposure. To examine the kinetics of the early cellular responses of NTE to O3, F344 rats were exposed to filtered air or 0.5 ppm O3 for 8 hr and euthanized 2, 4, 6, 8, 12, 16, 20, 24, and 36 hr postexposure (PE). Two hours before euthanization, rats were injected with bromodeoxyuridine (BrdU) to label S-phase cells. The nasal cavities were fixed and processed for light microscopy. Sections from the anterior nasal cavity were immunostained to detect BrdU-labeled cells and analyzed to determine the numeric densities of NTE cells and intraepithelial neutrophils, and the labeling index (LI; [BrdU-labeled epithelial cells/total epithelial cells] x 100) and unit length labeling index (ULLI; BrdU-labeled epithelial cells/mm basal lamina) of the NTE overlying maxilloturbinates. O3 exposure induced a transient influx of neutrophils 2-4 hr PE and a significant (17%) loss of NTE cells 2-4 hr PE. An increase in epithelial DNA synthesis was first detected 12 hr PE. In this study, there was no difference in the sensitivity of the two measures of epithelial cell DNA synthesis. Both the LI and ULLI were greatest 20-24 hr PE and were reduced, but still greater than those of controls, by 36 hr PE. The numeric density of NTE cells returned to control levels 20-24 hr PE. This study has defined the kinetics of acute O3-induced NTE cell injury, loss, and proliferation in vivo. The transit time from Go to S, after O3-induced injury, was 12-20 hr and the duration of G2 + M was 8-12 hr. These data may be used to further explore the early cellular and molecular events that lead to ozone-induced mucous cell metaplasia.

Induction of mesothelioma after intrapleural inoculation of F344 rats with silicon carbide whiskers or continuous ceramic filaments

OBJECTIVE

To find whether continuous ceramic filaments (CCFs) and silicon carbide whiskers (SiCWs), which are used in many industries as reinforcing materials in advanced ceramic composites, are carcinogenic in the intrapleural inoculation assay.

METHODS

Samples of SiCWs, CCF, International Union Against Cancer crocidolite, or saline were injected into the pleural cavities of female F344/N rats to find whether the samples of SiCW and CCF had the potential to induce mesotheliomas after the direct application of the materials to the surface of the pleural mesothelium.

RESULTS

Rats injected with two of the three individual samples of SiCW or the crocidolite had significantly reduced life spans compared with the rats treated with saline, CCFs, or the third SiCW sample. Rats treated with either of the two SiCW samples or crocidolite developed mesotheliomas. By contrast, rats treated with saline or CCF did not. The two SiCW samples that induced shortened life spans also induced a higher rate of mesothelioma (87%-90%), than the crocidolite (57%) and the third SiCW sample (23%).

CONCLUSION

SiCWs but not CCFs could induce mesotheliomas after intrapleural injection in rats. The difference in biological activity between the SiCW samples could not be explained on the basis of their physical dimensions or biological activity toward cultured cells. Results from this study indicated that SiCWs should be handled with care as they might be carcinogenic if inhaled. However, there is controversy as to whether results of intrapleural injection assays are sufficient to determine a fibre's carcinogenic activity. The results also showed that a collection of fibrous materials such as SiCWs could have considerably different biological activities despite similar physical dimensions.

Induction of EGF receptor and erbB-2 during endotoxin-induced alveolar type II cell proliferation in the rat lung

The overall purpose of this study was to produce a model of transient type II cell hyperplasia to enable comparisons of changes in gene expression in the remodelling epithelium with those in carcinogen-induced hyperplastic lesions. Rats instilled with endotoxin had increased numbers of neutrophils in the bronchoalveolar lavage fluid (BALF) by 3 hours that reached maximum levels at 48 hours and returned to background levels 168 hours after instillation. The number of macrophages in the BALF increased throughout the 168 hours following instillation. Epithelial cell hyperplasia was maximum at 96 hours post-instillation in areas of extensive inflammation. The number of alveolar epithelial cells that exhibited bromodeoxyuridine nuclear incorporation reached maximum levels 48 hours after endotoxin treatment and decreased to near background levels at 96 hours. Ultrastructural studies of hyperplastic cells showed the presence of lamellar bodies and condensed chromosomes, characteristics of type II cells in mitosis. At 168 hours after instillation, the hyperplasia regressed to form normal-appearing alveolar structure with few focal lesions. Specific immunostaining for the proto-oncogenes, EGF receptor and erbB-2, on tissue sections increased during the endotoxin-induced hyperplasia. Furthermore, the induction of the 170 kDa and 180 kDa glycoproteins in type II cells isolated from endotoxin-instilled rats was shown by Western analysis. These proto-oncogenes, often thought to be markers of early events during neoplasia, may, therefore, also be associated with wound repair mechanisms after hyperplasia.

Silicon carbide whiskers: characterization and aerodynamic behaviors

Silicon carbide (SiC) whiskers are fiberlike materials with a wide range of industrial applications. Industrial hygiene samplings of the material are taken to monitor and control possible exposures to workers. This study characterizes an SiC whisker in detail, including its width-length distribution, aspect ratio, particle density, and aerodynamic size distribution. The SiC whiskers were aerosolized, and samples from a filter, cascade impactor, and aerosol centrifuge were taken. The diameter-length distribution of SiC fibers determined by electron microscopy from filter samples was found to follow the bivariate lognormal distribution. The aerodynamic size of a fiber aerosol depends not only on the particle dimension and density but also on the orientation of its axis with respect to flow. The results show that the aerodynamic size distribution obtained from the impactor was consistent with the predicted value, assuming the long axis of the fiber was parallel to the flow toward the collection substrate. On the other hand, the aerodynamic size in the aerosol centrifuge was consistent with results for a perpendicular orientation. A larger aerodynamic size (20-25%) was obtained in the case of impactor data as compared with centrifuge data. The respirable fraction estimated from the cascade impactor data was 65%, consistent with the estimate from bivariate analysis (67%) but smaller than the estimated fraction from the aerosol centrifuge (76%). The results show that the data obtained with the bivariate analysis of fiber dimensions had good correlation with the cascade impactor data, and this approach can be used to predict the aerodynamic size distribution and the size-selective fractions for fiber aerosols from filter samples.

An improved method for the isolation of type II and Clara cells from mice

Identifying the causal events and temporal aspects of lung cancer development requires the ability to isolate target and nontarget cells for comparative analyses. Current methodology can either isolate only one pure specific cell population from a lung or multiple cell types at lower purity. Previous studies in our laboratory have identified the alveolar type II cell as the progenitor cell for tumor development in the A/J mouse. The purpose of this study was to develop new protocols for the isolation and culture of type II and Clara cells from the mouse lung. Both type II and Clara cells were obtained in high purity using a sequential centrifugal elutriation protocol. In the first elutriation, cell fractions were collected using a Standard chamber. The type II and Clara cell fractions were then elutriated separately (two different separations) using a Sanderson chamber. The final purity of the type II and Clara cell preparations was 73% and 76%, respectively. Colonies of 4 to 20 Clara cells exhibiting epithelial morphology were evident 1 wk after plating in low serum medium. The growth of type II cells required the addition of bronchioalveolar lavage fluid and acidic fibroblast growth factor to the medium. The isolation of viable mouse type II and Clara cells in high purity should facilitate the identification of cell-specific changes in gene expressions or in enzymatic pathways following in vivo or in vitro exposure to environmental carcinogens.

An overview of animal models for assessing synthetic vitreous fibers (SVFs) safety

Synthetic vitreous fibers (SVFs) are materials with many important commercial applications. The fibrous nature of the SVFs raises concerns about their potential human health hazards. However, sufficient epidemiological data do not exist to establish the hazardous nature of all SVFs. In addition, the cellular and molecular mechanisms underlying the induction of pulmonary lesions are only partially understood. Without sufficient evidence to associate fiber exposure and lung disease, animal bioassays have been used to identify specific hazardous fibers. These bioassays include inhalation exposures, intratracheal instillation, and intracavitary injection (intrapleural and intraperitoneal). Inhalation exposures of animals most closely represent the human experience, but these exposures are costly and time-consuming to conduct. Intratracheal and intracavitary administrations of fiber are alternatives to inhalation exposures; however, they do not represent human exposures and can give false positive results. The limitations of the noninhalation approaches must be considered when addressing the potential for a respirable fiber to induce human lung disease. In addition, when the results from inhalation exposures do not agree with the alternative animal assays, most weight should be given to the animal inhalation assays because of the limitations of the alternative approaches. To determine the safety of SVFs, both the inhalation and noninhalation approaches are suggested.

Alpha-particle-induced p53 protein expression in a rat lung epithelial cell strain

Other investigators have shown that both sparsely ionizing and UV radiation cause cell cycle arrest that is associated with increased expression of wild-type p53 protein. The effect of exposure to alpha-particles from 238Pu on the induction of the p53 protein has now been examined in cultured lung epithelial cells derived from male F344 rats. The number of cells having increased levels of p53 protein was determined by flow cytometry after the cells had been stained with a monoclonal antibody to p53. alpha-Particle irradiation caused a dose-dependent increase in p53 protein levels detectable at doses as low as 0.6 cGy, with no evidence of a threshold. An increase in p53 protein also occurred in X-irradiated cells. However, no increase was seen in cells exposed to less than 10 cGy of X-rays, indicating the existence of a relatively higher DNA damage threshold for sparsely ionizing radiation. In addition, more cells exposed to low doses of alpha radiation had increased p53 protein levels than would be predicted based on the number of nuclei expected to be traversed by an alpha-particle, suggesting that alpha-particles cause genetic damage by mechanisms in addition to direct interactions with DNA.

Phagosomal pH and glass fiber dissolution in cultured nasal epithelial cells and alveolar macrophages: a preliminary study

The dissolution rate of glass fibers has been shown to be pH sensitive using in vitro lung fluid simulant models. The current study investigated whether there is a difference in phagosomal pH (ppH) between rat alveolar macrophages (AM) and rat nasal epithelial cells (RNEC) and whether such a difference would influence the dissolution of glass fibers. The ppH was measured in cultured AM and RNEC using flow cytometric, fluorescence-emission rationing techniques with fluorescein-labeled, amorphous silica particles. Glass fiber dissolution was determined in AM and RNEC cultured for 3 weeks with fast dissolving glass fibers (GF-A) or slow dissolving ones (GF-B). The mean diameters of GF-A were 2.7 microns and of GF-B, 2.6 microns, the average length of both fibers was approximately 22 to 25 microns. Dissolution was monitored by measuring the length and diameter of intracellular fibers and estimating the volume, assuming a cylindrical morphology. The ppH of AM was 5.2 to 5.8, and the ppH of RNEC was 7.0 to 7.5. The GF-A dissolved more slowly in RNEC than in AM, and no dissolution was evident in either cell type with GF-B. The volume loss with GF-A after a 3-week culture with AM was 66% compared to 45% for cultured RNEC. These results are different from those obtained using in vitro lung fluid-simulant models where dissolution is faster at higher pH. This difference suggests that dissolution rates of glass fibers in AM should not be applied to the dissolution of fibers in epithelial cells.

Estimation of the dose of radon progeny to the peripheral lung and the effect of exposure to radon progeny on the alveolar macrophage

Groups of rats were exposed to radon progeny attached to a vector aerosol of cigarette smoke particles in a closed-loop exposure system. The total exposures ranged from 70 to 1020 WLM over a 3-5-h period. Alveolar macrophages were lavaged from exposed and control rats (exposed to the vector aerosol alone). There were no differences between phagocytic capabilities of the macrophages lavaged from the controls and any group of exposed rats. The increases in the numbers of binucleated/multinucleated and micronucleated macrophages were enumerated using cytological preparations of lavaged alveolar macrophages after exposure compared to the numbers in the control rats. The peak response in numbers of binucleated/multinucleated and micronucleated macrophages occurred at 21 days after exposure, beyond which the numbers decreased. This peak response showed a significant exposure-dependent relationship. The number of micronuclei provided a sensitive indicator of exposure. The lowest exposure level used (70 WLM) resulted in a significant difference in the number of micronucleated macrophages between control and exposed rats. The alpha-particle dose to the peripheral lung was estimated by comparing formation of micronuclei in cultured macrophages exposed to alpha particles from 238Pu (where the dose was known) to micronuclei in lavaged macrophages from animals exposed to radon progeny (where the exposure concentration was known, but the dose was not known). The dose estimated in this way for the peripheral lung was 9.8 +/- 1.2 mGy/WLM. This value is three to five times higher than predicted from mathematical models currently available.

A cohort model of visual word recognition

A model of word recognition is proposed which assumes that when a word is encountered, the first available orthographic code activates all lexical entries that are positionally consistent with that information (i.e., the word's cohort). As subsequently encoded orthographic information becomes available, activation is withdrawn from lexical entries with which it is inconsistent, and the cohort is resolved when only a single candidate remains. The model is intended to characterize: (1) The initial encoding of the graphic information; (2) the recording of that information into an abstract orthographic form; (3) the manner in which the appropriate lexical entries are then activated; (4) the process whereby subsequent orthographic encoding resolves those activated entries to a single candidate; and finally (5) the way in which subjects use information for making decisions as it emerges during this processing. The model includes two critical points. The first is that letter identity information is encoded in the form of a complex orthographic unit termed a wickelgraph. A wickelgraph includes an encoding of the target letter's identity information as its core, plus, as a context, the identity of its two immediately adjacent letters. The set of possible wickelgraphs is assumed to instantiate the rules of orthography. The second point is that once a cohort is established, the perceiver can sample its status at any point during resolution and base a decision on the outcome of that sample. Some tasks (e.g., naming) may allow for a decision based on the initial status of the cohort, while others (e.g., lexical decision) can require its complete resolution. Six experiments are reported that illustrate some of these cohort effects in lexical access.

On the naming of color words and color patches

Subjects can name color words faster than they can name color patches. To account for that effect, a generic model of naming is described which assumes that words access the mental lexicon directly, whereas color patches do so only indirectly via an initial imaginal or semantic representation. However, Lund (1927) reported that the naming advantage for words disappeared when all the items to be named on a page were the same (i.e., they were blocked). In the present study, three experiments are reported that were designed to provide a clearer empirical definition of Lund's blocking effect and to ascertain the extent to which it requires a modification of the generic model. The blocked lists had 50 items arranged into 10 blocks, with each block homogeneous with respect to color. The block lengths were either all a predictable length of 5 items or they varied randomly from 1 to 9 items. The data indicated the following: (1) The blocking effect occurred even when the task required a full identification of each item, and (2) the blocking effect was confined to within-block transitions. Blocking seemed to eliminate the word advantage by allowing the subject to re-use the lexical entry used for the immediately prior items, which is consistent with the generic model.

The effect of semantic priming on the detection of letters within words

Smith (1979) reported an experiment in which subjects were to detect whether or not a displayed word contained a particular target letter. Her data indicated that if the word bearing the target letter was preceded by a semantically related item, the detection of the target letter was faster than it was if the preceding item was unrelated. Those results provided strong support for holistic models of word recognition, in which it is assumed that letter detection must be mediated by prior word recognition. That is, any facilitating effect of the prime on lexical access should be passed on to subsequent letter detection. The present experimental paradigm, which was very similar to (albeit different from) that of Smith, served to explore the generality of her effect, but the results did not confirm her findings. Although a lexical-decision task used in Experiments 2, 5, and 7 provided clear evidence that the priming items employed in these experiments did facilitate lexical processing, a letter-detection task used in Experiments 1, 3, 4, 6, and 8 failed to reveal any facilitating effect of semantic priming on letter detection. The conclusion is that the generality of Smith's effect is far too limited to offer support for holistic models of word recognition.

Fiber-induced hydroxyl radical formation: correlation with mesothelioma induction in rats and humans

As part of a program to study the effects of inhaled fibers, we characterized the capacity of various fibers to initiate hydroxyl radical (.OH) formation from hydrogen peroxide in a non-cellular system. We studied five natural fibers (erionite, crocidolite, amosite, anthophyllite and chrysotile) and two man-made fibers (JM code 100 glass fibers and glass wool). The fibers were incubated for 5 min at 37 degrees C with hydrogen peroxide and salicylic acid in pH 7.0 aqueous solutions. The salicylate reacted with any .OH formed in these mixtures to produce stable addition products. The amount of .OH addition products formed during the incubations was determined by the salicylate assay which uses HPLC with electrochemical detection. Erionite, JM code 100 and glass wool were the most effective initiators of .OH formation, followed, in order, by crocidolite, amosite and chrysotile. When the capacity of the natural fibers to initiate .OH formation was plotted versus either the values for tumor rates of rats that received pleural inoculations of fibers or the literature values for the human mesothelioma mortality rates, positive correlations (r2 > or = 0.896) were found. Similar correlations with man-made fibers were not found. No positive correlation could be made between .OH formation capacity versus the tumor rates of rats that received peritoneal injections of either type of fibers.

In vitro activity of silicon carbide whiskers in comparison to other industrial fibers using four cell culture systems

Silicon carbide whiskers (SiCW) and continuous glass filaments are important components of composite materials having potentially widespread use in the automotive, aerospace, and power generation industries. We determined the in vitro activity of three well-characterized samples of silicon carbide whiskers and a continuous glass filament sample in four different cellular assays and compared this to the activities of UICC crocidolite, JM Code 100 glass microfiber, and erionite in the same assay systems. The SiCW had a diameter range of 0.32-0.75 microns and a length range of 4.5-20.1 microns. The SiCW was significantly toxic; on a mass basis, one SiCW sample was more toxic than crocidolite; however, JM Code 100 glass microfiber, which is not toxic in vivo (i.e., it does not cause fibrogenesis or carcinogenesis when inhaled), was also more toxic than crocidolite. The glass filament sample was the least cytotoxic of all the samples tested. On a fiber number basis, all three SiCW samples were more toxic than crocidolite. The results of our study showed that SiCW exhibits significant in vitro biological reactivity. Thus, despite the caution that must be exercised in extrpolating the results of in vitro studies to conclusions about in vivo health effects, SiCW should be considered toxic until further toxicological data are available.