Dermonecrosis caused by a spitting cobra snakebite results from toxin potentiation and is prevented by the repurposed drug varespladib

Snakebite envenoming is a neglected tropical disease that causes substantial mortality and morbidity globally. The venom of African spitting cobras often causes permanent injury via tissue-destructive dermonecrosis at the bite site, which is ineffectively treated by current antivenoms. To address this therapeutic gap, we identified the etiological venom toxins in Naja nigricollis venom responsible for causing local dermonecrosis. While cytotoxic three-finger toxins were primarily responsible for causing spitting cobra cytotoxicity in cultured keratinocytes, their potentiation by phospholipases A2 toxins was essential to cause dermonecrosis in vivo. This evidence of probable toxin synergism suggests that a single toxin-family inhibiting drug could prevent local envenoming. We show that local injection with the repurposed phospholipase A2-inhibiting drug varespladib significantly prevents local tissue damage caused by several spitting cobra venoms in murine models of envenoming. Our findings therefore provide a therapeutic strategy that may effectively prevent life-changing morbidity caused by snakebite in rural Africa.

Snakebite drug discovery: high-throughput screening to identify novel snake venom metalloproteinase toxin inhibitors

Snakebite envenoming results in ∼100,000 deaths per year, with close to four times as many victims left with life-long sequelae. Current antivenom therapies have several limitations including high cost, variable cross-snake species efficacy and a requirement for intravenous administration in a clinical setting. Next-generation snakebite therapies are being widely investigated with the aim to improve cost, efficacy, and safety. In recent years several small molecule drugs have shown considerable promise for snakebite indication, with oral bioavailability particularly promising for community delivery rapidly after a snakebite. However, only two such drugs have entered clinical development for snakebite. To offset the risk of attrition during clinical trials and to better explore the chemical space for small molecule venom toxin inhibitors, here we describe the first high throughput drug screen against snake venom metalloproteinases (SVMPs)-a pathogenic toxin family responsible for causing haemorrhage and coagulopathy. Following validation of a 384-well fluorescent enzymatic assay, we screened a repurposed drug library of 3,547 compounds against five geographically distinct and toxin variable snake venoms. Our drug screen resulted in the identification of 14 compounds with pan-species inhibitory activity. Following secondary potency testing, four SVMP inhibitors were identified with nanomolar EC50s comparable to the previously identified matrix metalloproteinase inhibitor marimastat and superior to the metal chelator dimercaprol, doubling the current global portfolio of SVMP inhibitors. Following analysis of their chemical structure and ADME properties, two hit-to-lead compounds were identified. These clear starting points for the initiation of medicinal chemistry campaigns provide the basis for the first ever designer snakebite specific small molecules.

Repurposed drugs and their combinations prevent morbidity-inducing dermonecrosis caused by diverse cytotoxic snake venoms

Morbidity from snakebite envenoming affects approximately 400,000 people annually. Tissue damage at the bite-site often leaves victims with catastrophic life-long injuries and is largely untreatable by current antivenoms. Repurposed small molecule drugs that inhibit specific snake venom toxins show considerable promise for tackling this neglected tropical disease. Using human skin cell assays as an initial model for snakebite-induced dermonecrosis, we show that the drugs 2,3-dimercapto-1-propanesulfonic acid (DMPS), marimastat, and varespladib, alone or in combination, inhibit the cytotoxicity of a broad range of medically important snake venoms. Thereafter, using preclinical mouse models of dermonecrosis, we demonstrate that the dual therapeutic combinations of DMPS or marimastat with varespladib significantly inhibit the dermonecrotic activity of geographically distinct and medically important snake venoms, even when the drug combinations are delivered one hour after envenoming. These findings strongly support the future translation of repurposed drug combinations as broad-spectrum therapeutics for preventing morbidity caused by snakebite.

Machine-learning guided Venom Induced Dermonecrosis Analysis tooL: VIDAL

Snakebite envenoming is a global public health issue that causes significant morbidity and mortality, particularly in low-income regions of the world. The clinical manifestations of envenomings vary depending on the snake's venom, with paralysis, haemorrhage, and necrosis being the most common and medically relevant effects. To assess the efficacy of antivenoms against dermonecrosis, a preclinical testing approach involves in vivo mouse models that mimic local tissue effects of cytotoxic snakebites in humans. However, current methods for assessing necrosis severity are time-consuming and susceptible to human error. To address this, we present the Venom Induced Dermonecrosis Analysis tooL (VIDAL), a machine-learning-guided image-based solution that can automatically identify dermonecrotic lesions in mice, adjust for lighting biases, scale the image, extract lesion area and discolouration, and calculate the severity of dermonecrosis. We also introduce a new unit, the dermonecrotic unit (DnU), to better capture the complexity of dermonecrosis severity. Our tool is comparable to the performance of state-of-the-art histopathological analysis, making it an accessible, accurate, and reproducible method for assessing dermonecrosis in mice. Given the urgent need to address the neglected tropical disease that is snakebite, high-throughput technologies such as VIDAL are crucial in developing and validating new and existing therapeutics for this debilitating disease.

Refining an ecological momentary assessment study of binge eating among sexual minority and heterosexual young women: a mixed methods pilot study

Background

Ecological momentary assessment (EMA) is used to capture daily lived experiences, states, and environments. Although EMA is commonly used in behavioral health research, there remains a dearth of literature on how researchers account for design considerations of EMA techniques when designing studies. The goal of this formative mixed methods study was to elicit feedback on EMA study procedures and materials from the target populations for a larger study about binge eating among sexual minority and heterosexual young women, in which data are collected entirely remotely.

Methods

Sexual minority (n=12) and heterosexual (n=9) women ages 18-30 who binge ate took part in a pilot EMA study and exit interview and survey. As part of the consent and orientation process, participants reviewed video and written materials describing the study purpose and procedures. Using a smartphone app, for seven consecutive days they completed a survey each morning, 5 random surveys per day, and self-initiated a survey each time they binge ate. Participants then provided feedback on the study via a 1-hour virtual interview and online survey. Interviews were transcribed and reviewed by two coders to identify themes on the acceptability and feasibility of the EMA procedures with a focus on: (I) the training and study description materials; (II) general smartphone app and survey preferences; and (III) specific EMA survey question content and wording.

Results

The qualitative and quantitative data converged to suggest participants were able to easily download and use the app to complete surveys and report on binge eating events. Participants provided feedback that was incorporated into revisions on general study procedures, the training video content, and EMA question content for binge eating, identity-related stressors, and appearance-related pressures. No systematic themes in the quantitative or qualitative data emerged to suggest questions were perceived differently by sexual minority and heterosexual young women.

Conclusions

These findings provide evidence for the feasibility of conducting a remote EMA study to assess young women's experiences around binge eating. This formative study provides an example of how a mixed methods approach can be used to refine EMA study methods and questions to improve study design.

Rationale and Design of an Ecological Momentary Assessment Study Examining Predictors of Binge Eating Among Sexual Minority and Heterosexual Young Women: Protocol for the Health and Experiences in Real Life (HER Life) Study

BACKGROUND

Previous research has identified health disparities between sexual minority and heterosexual women, including increased rates of obesity and binge eating in sexual minority women. Established predictors of binge eating behavior include negative emotions and sociocultural processes; however, these studies are generally conducted in samples of young women where sexual identity is not known or reported. There is a dearth of research evaluating how sexual minority-specific factors (eg, minority stress and connectedness to the lesbian, gay, bisexual, transgender, and queer community) may affect binge eating in sexual minority women. In addition, no studies have examined these processes in racially diverse samples or considered how intersecting minority identities (eg, Black and sexual minority) may affect eating behaviors.

OBJECTIVE

The Health and Experiences in Real Life (HER Life) Project aims to clarify real-world predictors of binge eating in young heterosexual and sexual minority women using ecological momentary assessment. The role of affective, social, and health behavior factors in binge eating will be examined for all women (aim 1), and sexual minority-specific predictors will also be considered for sexual minority women participants (aim 2). Person-level moderators of race, body- and eating-related factors, and sexual minority-specific factors will also be examined to better understand how real-world binge eating predictors may differ for various demographic groups (aim 3).

METHODS

Researchers aim to recruit 150 sexual minority and 150 heterosexual women from across the United States, including at least 50 Black women for each group, using web-based recruitment methods. The eligibility criteria include identifying as a woman, being aged between 18 and 30 years, and having had at least two binge eating episodes in the last 2 weeks. Participants must endorse being only or mostly attracted to men (considered heterosexual) or only or mostly attracted to women or having a current or most recent female partner (considered sexual minority). Eligible participants complete an initial web-based baseline survey and then 14 days of ecological momentary assessment involving the completion of a morning and before-bed survey and 5 prompted surveys per day as well as a user-initiated survey after binge eating episodes. The data will be analyzed using a series of multilevel models.

RESULTS

Data collection started in February 2021. We have currently enrolled 129 sexual minority women and 146 heterosexual women. Data collection is expected to conclude in fall 2022.

CONCLUSIONS

The Health and Experiences in Real Life Project aims to elucidate potential differences between sexual minority and heterosexual women in within-person factors predicting binge eating and inform eating disorder interventions for sexual minority women. The challenges in recruiting sexual minority women, including the determination of eligibility criteria and considerations for remote data collection, are discussed.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/41199.

Associations between body dissatisfaction and relationship functioning among same-sex female couples: An actor-partner interdependence model

Nearly all past research about body dissatisfaction and romantic relationship factors is among heterosexual couples; little is known about these associations in sexual minority couples. The present study aimed to fill gaps in the current literature by using actor-partner interdependence models (APIMs) to examine dyadic patterns of association between body dissatisfaction and different aspects of relationship functioning among same-sex female couples. Participants were 163 same-sex female romantic dyads (326 women) between the ages of 18-35 years who completed measures of body dissatisfaction and relationship factors. Results from significance testing of actor and partner effects indicated higher levels of women's own body dissatisfaction were associated with lower levels of their own, but not their partner's, relationship satisfaction, closeness, sexual satisfaction, and intimacy/connectedness. Significance testing alone indicated that the association between one's own body dissatisfaction and their partner's relationship satisfaction was not significant. However, dyadic pattern testing identified a partner pattern for this effect, which suggests that the association between one's own body dissatisfaction and one's own relationship satisfaction is similar in magnitude and direction as that between an individuals' own body dissatisfaction and their partner's relationship satisfaction. In this study, women's own body dissatisfaction was found to be negatively associated with their own relationship functioning, which is consistent with findings of women in male-female couples. Thus, these findings highlight the important role that body dissatisfaction plays in women's relationship experiences. More research is needed to better understand potential cross-partner effects of body dissatisfaction and relationship factors in same-sex female couples. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Exploring the Utility of Recombinant Snake Venom Serine Protease Toxins as Immunogens for Generating Experimental Snakebite Antivenoms

Snakebite is a neglected tropical disease that causes high rates of global mortality and morbidity. Although snakebite can cause a variety of pathologies in victims, haemotoxic effects are particularly common and are typically characterised by haemorrhage and/or venom-induced consumption coagulopathy. Despite polyclonal antibody-based antivenoms being the mainstay life-saving therapy for snakebite, they are associated with limited cross-snake species efficacy, as there is often extensive toxin variation between snake venoms, including those used as immunogens for antivenom production. This restricts the therapeutic utility of any antivenom to certain geographical regions. In this study, we explored the feasibility of using recombinantly expressed toxins as immunogens to stimulate focused, pathology-specific, antibodies in order to broadly counteract specific toxins associated with snakebite envenoming. Three snake venom serine proteases (SVSP) toxins, sourced from geographically diverse and medically important viper snake venoms, were successfully expressed in HEK293F mammalian cells and used for murine immunisation. Analyses of the resulting antibody responses revealed that ancrod and RVV-V stimulated the strongest immune responses, and that experimental antivenoms directed against these recombinant SVSP toxins, and a mixture of the three different immunogens, extensively recognised and exhibited immunological binding towards a variety of native snake venoms. While the experimental antivenoms showed some reduction in abnormal clotting parameters stimulated by the toxin immunogens and crude venom, specifically reducing the depletion of fibrinogen levels and prolongation of prothrombin times, fibrinogen degradation experiments revealed that they broadly protected against venom- and toxin-induced fibrinogenolytic functional activities. Overall, our findings further strengthen the case for the use of recombinant venom toxins as supplemental immunogens to stimulate focused and desirable antibody responses capable of neutralising venom-induced pathological effects, and therefore potentially circumventing some of the limitations associated with current snakebite therapies.

Recruiting Cisgender Female Couples for Health Disparity-Focused Daily Diary Research: Challenges, Successes, and Lessons Learned

The underlying mechanisms of sexual minority women's (SMW's) numerous physical and mental health disparities compared to heterosexual women are not well understood. The contribution of relationship factors is particularly understudied; few studies collect data from both same-sex female partners. Further, most research among SMW is cross sectional which limits our understanding of day-to-day experiences of same-sex women's couples. This paper aimed to describe the feasibility of recruiting a large sample of SMW and their female partners for a disparity-focused daily diary study investigating alcohol use and mental health. A firm specializing in sexual minority market research was enlisted to help with recruitment from multiple sources and conducted an initial pre-screening of SMW and their female partners, at least one of whom drank alcohol regularly. A total of 4182 individuals completed the pre-screener, with information for 930 individuals (465 couples) being sent to the research team. From this, 376 individuals (188 couples) completed the study screener, met the inclusion criteria, and were invited to participate. Ultimately, 326 individuals (163 couples) consented and completed baseline. A total of 321 individuals, from 162 couples, began the daily diary portion of the study. Compliance with study procedures was excellent. The use of multiple recruitment sources increased the diversity of the sample. Challenges to recruitment, changes in protocol, and characteristics of the final sample are discussed.

Does Assessment Alter Responses? An Examination of Measurement Reactivity in an Ecological Momentary Assessment of Body Comparisons

Introduction: Body comparisons have been implicated in body dissatisfaction and eating disorder development. Ecological momentary assessment (EMA) has been used to capture body comparisons in everyday life; however, the potential for measurement reactivity this approach has on EMA responses has yet to be examined. The present study systematically evaluated measurement reactivity in EMA of body comparisons. Methods: Undergraduate women (N = 75) completed four surveys daily for 11 days; Days 1–4 did not include comparison assessments and Days 5–11 did. Changes were examined in related EMA measures between these time periods and individual difference measures pre- and post-EMA. Results: A within-person MANOVA showed no significant change in the individual difference measures. Multilevel analyses revealed that participants reported fewer comparisons as day of study increased. When they completed EMA with versus without comparison items, they reported fewer occasions of loss of control while eating and less pleasant social company at time of assessment. Discussion: Findings suggest limited concern for reactivity in this approach, though researchers examining body comparisons, loss of control eating, and perceptions of social company should be cautious when interpreting their findings and consider examining reactivity directly. Future research on body comparisons should also consider using run-in periods to improve data quality.

Evaluating study procedure training methods for a remote daily diary study of sexual minority women

BACKGROUND

Ecological momentary assessment (EMA) methods can be used to remotely assess physical and mental health in daily life for hard-to-reach, marginalized, and geographically dispersed populations in the U.S., such as sexual minority women (e.g., lesbian, bisexual). However, EMA studies are often complex, and engaging participants from afar can be a challenge. This study experimentally examined whether adding videos to written recruitment materials would improve consent rates, reduce dropout rates, and improve survey completion rates for an online daily diary study.

METHODS

As part of a 2-week study of same-sex female couples' health, 376 women ages 18-35 were recruited from across the U.S. using a market research firm. Couples were randomized to an introductory information condition (written + video materials or written-only materials) prior to informed consent.

RESULTS

Overall, 97.1% of eligible women reviewed introductory materials and of these 96.7% consented; consent rates did not differ by condition (written + video: 97.1%, written-only: 97.1%). Dropout rates were low (5.4%) and survey completion rates were high (90.4% of surveys completed); there were no group differences for study dropout (written + video: 3.6%, written-only: 7.0%) or survey completion (written + video: 92.5%, written-only: 88.4%). Data from women randomized to receive videos indicated more than half (53.3%) did not watch any of the five videos in full. However, among those who viewed the videos, time spent watching videos, watching more videos in full, and watching at least one video in full were each positive associated with survey completion rates.

CONCLUSIONS

In summary, we had high consent rates, low dropout rates, and high survey completion rates regardless of video instructions. Although sexual minority women can be hard to reach, our potential participants appeared highly motivated to take part in research, and thus video recruitment materials were not necessary to improve participation. Future experimental research to maximize EMA study design and implementation could be important for populations less inclined to participate in EMA studies, or who are less familiar with research.

A therapeutic combination of two small molecule toxin inhibitors provides broad preclinical efficacy against viper snakebite

Snakebite is a medical emergency causing high mortality and morbidity in rural tropical communities that typically experience delayed access to unaffordable therapeutics. Viperid snakes are responsible for the majority of envenomings, but extensive interspecific variation in venom composition dictates that different antivenom treatments are used in different parts of the world, resulting in clinical and financial snakebite management challenges. Here, we show that a number of repurposed Phase 2-approved small molecules are capable of broadly neutralizing distinct viper venom bioactivities in vitro by inhibiting different enzymatic toxin families. Furthermore, using murine in vivo models of envenoming, we demonstrate that a single dose of a rationally-selected dual inhibitor combination consisting of marimastat and varespladib prevents murine lethality caused by venom from the most medically-important vipers of Africa, South Asia and Central America. Our findings support the translation of combinations of repurposed small molecule-based toxin inhibitors as broad-spectrum therapeutics for snakebite.

Sexual Minority Stress and Social Support Explain the Association between Sexual Identity with Physical and Mental Health Problems among Young Lesbian and Bisexual Women

Bisexual women report more physical and psychological health problems than lesbian women do, which may be attributed to greater sexual minority stress and less social support. However, many studies combine lesbian and bisexual women into a single group. The current study examined if sexual minority stress and social support mediated the association between women's sexual identity (lesbian or bisexual) and health-related outcomes. A total of 650 U.S. young adult lesbian (n = 227) and bisexual (n = 423) women completed an online survey about sexual minority stress, social support, and physical and mental health problems. Bisexual women reported more physical and mental health problems. A sequential mediation model showed that bisexual women reported greater sexual minority stress than lesbian women, which in turn was associated with less social support, which was associated with more physical and mental health problems. Greater sexual minority stress and lower social support may help explain why bisexual women report more health-related problems than lesbian women. The results of the present study support the importance of examining risk and protective factors for health problems separately for lesbian and bisexual women. Health-related intervention programs that target sexual minority women may need to be tailored differently for lesbian and bisexual women.

Rationale and Design of a Remote Web-Based Daily Diary Study Examining Sexual Minority Stress, Relationship Factors, and Alcohol Use in Same-Sex Female Couples Across the United States: Study Protocol of Project Relate

Background

The Healthy People 2020 initiative aims to reduce health disparities, including alcohol use, among sexual minority women (SMW; eg, lesbian, bisexual, queer, and pansexual). Compared with heterosexual women, SMW engage in more hazardous drinking and report more alcohol-related problems. Sexual minority stress (ie, the unique experiences associated with stigmatization and marginalization) has been associated with alcohol use among SMW. Among heterosexuals, relationship factors (eg, partner violence and drinking apart vs together) have also been associated with alcohol use. Negative affect has also been identified as a contributor to alcohol use. To date, most studies examining alcohol use among SMW have used cross-sectional or longitudinal designs.

Objective

Project Relate was designed to increase our understanding of alcohol use among young SMW who are at risk for alcohol problems. The primary objectives of this study are to identify daily factors, as well as potential person-level risk and protective factors, which may contribute to alcohol use in SMW. Secondary objectives include examining other physical and mental concerns in this sample (eg, other substance use, eating, physical activity, and stress).

Methods

Both partners of a female same-sex couple (aged 18-35 years; n=150 couples) are being enrolled in the study following preliminary screening by a market research firm that specializes in recruiting sexual minority individuals. Web-based surveys are being used to collect information about the primary constructs of interest (daily experiences of alcohol use, sexual minority stress, relationship interactions, and mood) as well as secondary measures of other physical and mental health constructs. Data are collected entirely remotely from women across the United States. Each member of eligible couples completes a baseline survey and then 14 days of daily surveys each morning. Data will be analyzed using multilevel structural equation modeling.

Results

To date, 208 women (ie, 104 couples) were successfully screened and enrolled into the study. In total, 164 women have completed the 14-day daily protocol. Compliance with completing the daily diaries has been excellent, with participants on average completing 92% of the daily diaries. Data collection will be completed in fall 2018, with results published as early as 2019 or 2020.

Conclusions

Project Relate is designed to increase our understanding of between- and within-person processes underlying hazardous drinking in understudied, at-risk SMW. The study includes a remote daily diary methodology to provide insight into variables that may be associated with daily hazardous alcohol use. Before the development of programs that address hazardous alcohol use among young SMW, there is a need for better understanding of individual and dyadic variables that contribute to risk in this population. The unique challenges of recruiting and enrolling SMW from across the United States in a daily diary study are discussed.

International Registered Report Identifier (IRRID)

DERR1-10.2196/11718

An exploration of spatial risk assessment for soil protection: estimating risk and establishing priority areas for soil protection

Methods for the spatial estimation of risk of harm to soil by erosion by water and wind and by soil organic matter decline are explored. Rates of harm are estimated for combinations of soil type and land cover (as a proxy for hazard frequency) and used to estimate risk of soil erosion and loss of soil organic carbon (SOC) for 1 km(2)pixels. Scenarios are proposed for defining the acceptability of risk of harm to soil: the most precautionary one corresponds to no net harm after natural regeneration of soil (i.e. a 1 in 20 chance of exceeding an erosion rate of <1 tha(-1)y(-1) and SOC content decline of 0 kg t(-1)y(-1) for mineral soils and a carbon stock decline of 0 tha(-1)y(-1) for organic soils). Areas at higher and lower than possible acceptable risk are mapped. The veracity of boundaries is compromised if areas of unacceptable risk are mapped to administrative boundaries. Errors in monitoring change in risk of harm to soil and inadequate information on risk reduction measures' efficacy, at landscape scales, make it impossible to use or monitor quantitative targets for risk reduction adequately. The consequences for priority area definition of expressing varying acceptable risk of harm to soil as a varying probability of exceeding a fixed level of harm, or, a varying level of harm being exceeded with a fixed probability, are discussed. Soil data and predictive models for rates of harm to soil would need considerable development and validation to implement a priority area approach robustly.

Lung tissue mitochondrial benzodiazepine receptors increase in a model of pulmonary inflammation

Pulmonary inflammation induced in the rabbit lung by the intravenous injection of complete Freund's adjuvant (CFA) increases the lung uptake of 14C-diazepam from the pulmonary circulation. The objective of this study was to determine the extent to which mitochondrial (or peripheral) benzodiazepine receptors (mBRs) may contribute to this increased uptake. To this end, we measured the pulmonary venous effluent concentration versus time for 14C-diazepam following its injection into the pulmonary artery of isolated perfused normal and CFA inflamed lungs with and without an inhibitor (PK11195) of diazepam binding to mBRs. The results demonstrate that this model of pulmonary inflammation is associated with an increase in lung tissue mBR. Lung tissue caspase-3 activity was also measured as one index of lung inflammation, and we found that in inflamed lungs, there was an inverse correlation between mBR density and lung tissue capase-3 activity. This is consistent with observations in other organs and a role for mBRs in apoptotic elimination of inflammatory cells in the resolution of this inflammatory response. The results suggest the potential utility of mBR ligands for noninvasive detection and/or characterization of pulmonary inflammation, e.g., via nuclear medicine methods.

Pulmonary arterial morphometry from microfocal X-ray computed tomography

The objective of this study was to develop an X-ray computed tomographic method for pulmonary arterial morphometry. The lungs were removed from a rat, and the pulmonary arterial tree was filled with perfluorooctyl bromide to enhance X-ray absorbance. At each of four pulmonary arterial pressures (30, 21, 12, and 5.4 mmHg), the lungs were rotated within the cone of the X-ray beam that was projected from a microfocal X-ray source onto an image intensifier, and 360 images were obtained at 1 degrees increments. The three-dimensional image volumes were reconstructed with isotropic resolution with the use of a cone beam reconstruction algorithm. The luminal diameter and distance from the inlet artery were measured for the main trunk, its immediate branches, and several minor trunks. These data revealed a self-consistent tree structure wherein the portion of the tree downstream from any vessel of a given diameter has a similar structure. Self-consistency allows the entire tree structure to be characterized by measuring the dimensions of only the vessels comprising the main trunk of the tree and its immediate branches. An approach for taking advantage of this property to parameterize the morphometry and distensibility of the pulmonary arterial tree is developed.

Pulmonary arterial dilation by inhaled NO: arterial diameter, NO concentration relationship

The objective of this study was to determine the nitric oxide (NO) concentration and vessel diameter dependence of the pulmonary arterial dilation induced by inhaled NO. Isolated dog lung lobes were situated between a microfocal X-ray source and X-ray detector and perfused with either blood or plasma. Boluses of radiopaque contrast medium were injected into the lobar artery under control conditions, when the pulmonary arteries were constricted by infusion of serotonin and when the serotonin infusion was accompanied by inhalation of from 30 to 960 parts/million NO. Arterial diameter measurements were obtained from X-ray images of vessels having control diameters in the 300- to 3,400-microm range. Serotonin constricted the vessels throughout the size range studied, with an average decrease in diameter of approximately 20%. The fractional reversal of the serotonin-induced constriction by inhaled NO was directly proportional to inhaled NO concentration, inversely proportional to vessel size, and greater with plasma than with blood perfusion in vessels as large as 3 mm in diameter. The latter indicates that intravascular hemoglobin affected the bronchoalveolar-to-arterial luminal NO concentration gradient in fairly large pulmonary arteries. The data provide information regarding pulmonary arterial smooth muscle accessibility to intrapulmonary gas that should be useful as part of the database for modeling the communication between intrapulmonary gas and pulmonary arterial smooth muscle cells in future studies.

Oxygen dependency of monoamine oxidase activity in the intact lung

Hydrogen peroxide generated by monoamine oxidase (MAO)-mediated deamination of biogenic amines has been implicated in cell signaling and oxidative injury. Because the pulmonary endothelium is a site of metabolism of monoamines present in the venous return, this brings into question a role for MAO in hyperoxic lung injury. The objective of this study was to evaluate the O(2) dependency of the MAO reaction in the lung. To this end, we measured the pulmonary venous effluent concentrations of the MAO substrate [(14)C]phenylethylamine and its metabolite [(14)C]phenylacetic acid after the bolus injection of either phenylethylamine or phenylacetic acid into the pulmonary artery of perfused rabbit lungs over a range of PO(2) values from 16 to 518 Torr. The apparent Michaelis constant for O(2) was approximately 18 microM, which is more than an order of magnitude less that measured for purified MAO. The results suggest a minimal influence of high O(2) on MAO activity in the normal lung and demonstrate the importance of measuring reaction kinetics in the intact organ.

The arterial site of action of nitric oxide in the neonatal pig lung determined by microfocal angiography

To determine the site of action of inhaled nitric oxide (iNO) in the newborn pig lung, lungs were isolated and perfused at constant flow for microfocal x-ray angiography. Measurements of pulmonary arterial diameters were made on arteries in the 100--2500 microm diameter range under control conditions, during vasoconstriction caused by hypoxia (decreasing PO(2) from approximately 120 to approximately 50 Torr), or N(omega)-nitro-L-arginine methylester (L-NAME 10(-4) M) administration, with or without vasodilation induced by iNO (40 ppm) or by the NO donor S-nitroso-N-acetylpenicillamine (SNAP 5 x 10(-6) M) given intravascularly. Hypoxia caused constriction only in smaller arteries whereas L-NAME constricted arteries throughout the size range studied. iNO dilated the smaller arteries more than the larger arteries under all study conditions. SNAP was used to provide an intravascular source of NO for comparison to iNO. SNAP also dilated smaller arteries more than larger arteries, but it had a significantly greater effect on the large arteries than did iNO. This suggests that differential accessibility of the vascular smooth muscle to NO between sources, air and blood, is a factor in the diameter dependence of the responses.

Microfocal X-ray CT imaging and pulmonary arterial distensibility in excised rat lungs

The objective of this study was to develop an X-ray computed tomographic method for measuring pulmonary arterial dimensions and locations within the intact rat lung. Lungs were removed from rats and their pulmonary arterial trees were filled with perfluorooctyl bromide to enhance X-ray absorbance. The lungs were rotated within the cone of the X-ray beam projected from a microfocal X-ray source onto an image intensifier, and 360 images were obtained at 1 degrees increments. The three-dimensional image volumes were reconstructed with isotropic resolution using a cone beam reconstruction algorithm. The vessel diameters were obtained by fitting a functional form to the image of the vessel circular cross section. The functional form was chosen to take into account the point spread function of the image acquisition and reconstruction system. The diameter measurements obtained over a range of vascular pressures were used to characterize the distensibility of the rat pulmonary arteries. The distensibility coefficient alpha [defined by D(P) = D(0)(1 + alphaP), where D(P) is the diameter at intravascular pressure (P)] was approximately 2.8% mmHg and independent of vessel diameter in the diameter range (about 100 to 2,000 mm) studied.

Pulmonary reduction of an intravascular redox polymer

Pulmonary endothelial cells in culture reduce external electron acceptors via transplasma membrane electron transport (TPMET). In studying endothelial TPMET in intact lungs, it is difficult to exclude intracellular reduction and reducing agents released by the lung. Therefore, we evaluated the role of endothelial TPMET in the reduction of a cell-impermeant redox polymer, toluidine blue O polyacrylamide (TBOP(+)), in intact rat lungs. When added to the perfusate recirculating through the lungs, the venous effluent TBOP(+) concentration decreased to an equilibrium level reflecting TBOP(+) reduction and autooxidation of its reduced (TBOPH) form. Adding superoxide dismutase (SOD) to the perfusate increased the equilibrium TBOP(+) concentration. Kinetic analysis indicated that the SOD effect could be attributed to elimination of the superoxide product of TBOPH autooxidation rather than of superoxide released by the lungs, and experiments with lung-conditioned perfusate excluded release of other TBOP(+) reductants in sufficient quantities to cause significant TBOP(+) reduction. Thus the results indicate that TBOP(+) reduction is via TPMET and support the utility of TBOP(+) and the kinetic model for investigating TPMET mechanisms and their adaptations to physiological and pathophysiological stresses in the intact lung.

A rat lung model of instilled liquid transport in the pulmonary airways

When a liquid is instilled in the pulmonary airways during medical therapy, the method of instillation affects the liquid distribution throughout the lung. To investigate the fluid transport dynamics, exogenous surfactant (Survanta) mixed with a radiopaque tracer is instilled into tracheae of vertical, excised rat lungs (ventilation 40 breaths/min, 4 ml tidal volume). Two methods are compared: For case A, the liquid drains by gravity into the upper airways followed by inspiration; for case B, the liquid initially forms a plug in the trachea, followed by inspiration. Experiments are continuously recorded using a microfocal X-ray source and an image-intensifier, charge-coupled device image train. Video images recorded at 30 images/s are digitized and analyzed. Transport dynamics during the first few breaths are quantified statistically and follow trends for liquid plug propagation theory. A plug of liquid driven by forced air can reach alveolar regions within the first few breaths. Homogeneity of distribution measured at end inspiration for several breaths demonstrates that case B is twice as homogeneous as case A. The formation of a liquid plug in the trachea, before inspiration, is important in creating a more uniform liquid distribution throughout the lungs.

A rat lung model of instilled liquid transport in the pulmonary airways

When a liquid is instilled in the pulmonary airways during medical therapy, the method of instillation affects the liquid distribution throughout the lung. To investigate the fluid transport dynamics, exogenous surfactant (Survanta) mixed with a radiopaque tracer is instilled into tracheae of vertical, excised rat lungs (ventilation 40 breaths/min, 4 ml tidal volume). Two methods are compared: For case A, the liquid drains by gravity into the upper airways followed by inspiration; for case B, the liquid initially forms a plug in the trachea, followed by inspiration. Experiments are continuously recorded using a microfocal X-ray source and an image-intensifier, charge-coupled device image train. Video images recorded at 30 images/s are digitized and analyzed. Transport dynamics during the first few breaths are quantified statistically and follow trends for liquid plug propagation theory. A plug of liquid driven by forced air can reach alveolar regions within the first few breaths. Homogeneity of distribution measured at end inspiration for several breaths demonstrates that case B is twice as homogeneous as case A. The formation of a liquid plug in the trachea, before inspiration, is important in creating a more uniform liquid distribution throughout the lungs.

Branching exponent heterogeneity and wall shear stress distribution in vascular trees

A bifurcating arterial system with Poiseuille flow can function at minimum cost and with uniform wall shear stress if the branching exponent (z) = 3 [where z is defined by (D(1))(z) = (D(2))(z) + (D(3))(z); D(1) is the parent vessel diameter and D(2) and D(3) are the two daughter vessel diameters at a bifurcation]. Because wall shear stress is a physiologically transducible force, shear stress-dependent control over vessel diameter would appear to provide a means for preserving this optimal structure through maintenance of uniform shear stress. A mean z of 3 has been considered confirmation of such a control mechanism. The objective of the present study was to evaluate the consequences of a heterogeneous distribution of z values about the mean with regard to this uniform shear stress hypothesis. Simulations were carried out on model structures otherwise conforming to the criteria consistent with uniform shear stress when z = 3 but with varying distributions of z. The result was that when there was significant heterogeneity in z approaching that found in a real arterial tree, the coefficient of variation in shear stress was comparable to the coefficient of variation in z and nearly independent of the mean value of z. A systematic increase in mean shear stress with decreasing vessel diameter was one component of the variation in shear stress even when the mean z = 3. The conclusion is that the influence of shear stress in determining vessel diameters is not, per se, manifested in a mean value of z. In a vascular tree having a heterogeneous distribution in z values, a particular mean value of z (e.g., z = 3) apparently has little bearing on the uniform shear stress hypothesis.

Purified recombinant A. fumigatus allergens induce different responses in mice

Aspergillus fumigatus an opportunistic fungus is associated with a number of diseases in humans. Allergy resulting from exposure to the A. fumigatus allergens has been recognized frequently. The damage caused by the disease is very striking in patients with atopy and those with cystic fibrosis. Avoidance to exposure is not feasible because A. fumigatus spores are ubiquitously distributed in the environment. Hence, immunotherapeutic regimens in severe forms of A. fumigatus allergy may have a high potential. However, before such forms of therapy can be envisaged, it is essential to understand the immunopathogenesis. In the present study, we investigated the role of purified A. fumigatus allergens in the development of allergic asthma in mice. We have used four major recombinant A. fumigatus allergens in the murine model. Mice exposed to Asp f 1, f 3, and f 4 showed inflammatory changes in the lungs and airway hyperreactivity. The immune responses, including elevated serum IgE, enhanced eosinophils, recruitment in the peripheral blood and lungs, and expression of regulatory cytokines, are characteristic of a Th2 response. Asp f 6 demonstrated only a reduced response in these animals. The results suggest that the pathology induced by crude A. fumigatus extract results from the cumulative effects of the allergens and the individual responses varied considerably with different purified antigens.

Hypoxic pulmonary vasoconstriction is modified by P-450 metabolites

20-Hydroxyeicosatetraenoic acid (20-HETE) is a cytochrome P-450 4A (CYP4A) metabolite of arachidonic acid (AA) in human and rabbit lung microsomes and is a dilator of isolated human pulmonary arteries (PA). However, little is known regarding the contribution of P-450 metabolites to pulmonary vascular tone. We examined 1) the effect of two mechanistically distinct omega- and omega1-hydroxylase inhibitors on perfusion pressures in isolated rabbit lungs ventilated with normoxic or hypoxic gases, 2) changes in rabbit PA ring tone elicited by 20-HETE or omega- and omega1-hydroxylase inhibitors, and 3) expression of CYP4A protein in lung tissue. A modest increase in perfusion pressure (55 +/- 11% above normoxic conditions) was observed in isolated perfused lungs during ventilation with hypoxic gas (FI(O(2)) = 0.05). Inhibitors of 20-HETE synthesis, 17-oxydecanoic acid (17-ODYA) or N-methylsulfonyl-12,12-dibromododec-11-enamide (DDMS), increased baseline perfusion pressure above that of vehicle and amplified hypoxia-induced increases in perfusion pressures by 92 +/- 11% and 105 +/- 11% over baseline pressures, respectively. 20-HETE relaxed phenylephrine (PE)-constricted PA rings. Treatment with 17-ODYA enhanced PE-induced contraction of PA rings, consistent with inhibition of a product that promotes arterial relaxation, whereas 6-(20-propargyloxyphenyl)hexanoic acid (PPOH), an epoxygenase inhibitor, blunted contraction to PE. Conversion of AA into 20-HETE was blocked by 17-ODYA, DDMS, and hypoxia. CYP4A immunospecific protein confirms expression of CYP4A in male rabbit lung tissue. Our data suggest that endogenously produced 20-HETE could modify rabbit pulmonary vascular tone, particularly under hypoxic conditions.

Lung redox homeostasis: emerging concepts

This symposium was organized to present some aspects of current research pertaining to lung redox function. Focuses of the symposium were on roles of pulmonary endothelial NADPH oxidase, xanthine oxidase (XO)/xanthine dehydrogenase (XDH), heme oxygenase (HO), transplasma membrane electron transport (TPMET), and the zinc binding protein metallothionein (MT) in the propagation and/or protection of the lung or other organs from oxidative injury. The presentations were chosen to reflect the roles of both intracellular (metallothionein, XO/XDH, and HO) and plasma membrane (NADPH oxidase, XO/XDH, and unidentified TPMET) redox proteins in these processes. Although the lung endothelium was the predominant cell type under consideration, at least some of the proposed mechanisms operate in or affect other cell types and organs as well.

Effects of hypoxia on pulmonary microvascular volume

To determine the effects of alveolar hypoxia on pulmonary microvascular volume, X-ray microfocal angiographic images of isolated perfused dog lung lobes were obtained during passage of a bolus of radiopaque contrast medium during both normoxic (alveolar gas, 15% O(2), 6% CO(2), and 79% N(2)) and hypoxic (3% O(2), 6% CO(2), and 91% N(2)) conditions. Regions of interest (ROIs) over the lobar artery and vein at low magnification and a feeding artery ( approximately 500 microm diameter) and the nearby microvasculature (vessels smaller than approximately 50 microm) at high magnification were identified, and X-ray absorbance vs. time curves were acquired under both conditions from the same ROIs. The total pulmonary vascular volume was calculated from the flow and the mean transit time for the contrast medium passage from the lobar artery to lobar vein. The fractional changes in microvascular volume were determined from the areas under the high-magnification X-ray absorbance curves. Hypoxia decreased lobar volume by 13 +/- 3% (SE) and regional microvascular volume by 26 +/- 4% (SE). Given the morphometry of the lung vasculature, these results suggest that capillary volume was decreased by hypoxia.

Transport and reaction at endothelial plasmalemma: distinguishing intra- from extracellular events

The pulmonary endothelium is a chemical reactor that modifies blood composition in several ways, including reduction of the oxidized forms of certain redox active substances in the blood. The physiological functions of the transplasma membrane electron transport systems involved in the latter are not fully understood, but an argument is made that they are involved in antioxidant defense. In addition, the experimental approaches used to characterize the process, including studies at whole organ, cell culture, and subcellular levels, along with the use of mathematical modeling, may be representative of the physiome concept wherein a goal is the integration of information obtained at all levels of biological organization. In this article, separation of intra- and extracellular events involved in the disposition of redox active probes within the lungs is the particular example.

Systemic lobar shunting induces advanced pulmonary vasculopathy

OBJECTIVES

We characterized the morphology and vasomotor responses of a localized, high-flow model of pulmonary hypertension.

METHODS

An end-to-side anastomosis was created between the left lower lobe pulmonary artery and the aorta in 23 piglets. Control animals had a thoracotomy alone or did not have an operation. Eight weeks later, hemodynamic measurements were made. Then shunted and/or nonshunted lobes were removed for determination of vascular resistance and compliance by occlusion techniques under conditions of normoxia, hypoxia (FIO (2) = 0.03), and inspired nitric oxide administration. Quantitative histologic studies of vessel morphology were performed.

RESULTS

Eighty-three percent of animals having a shunt survived to final study. Aortic pressure, main pulmonary artery and wedge pressures, cardiac output, blood gases, and weight gain were not different between control pigs and those receiving a shunt. Six of 9 shunted lobes demonstrated systemic levels of pulmonary hypertension in vivo. Arterial resistance was higher (24.3 +/- 12.0 vs 1.3 +/- 0. 2 mm Hg. mL(-1). s(-1), P =.04) and arterial compliance was lower (0. 05 +/- 0.01 vs 0.16 +/- 0.03 mL/mm Hg, P =.02) in shunted compared with nonshunted lobes. Hypoxic vasoconstriction was blunted in shunted lobes compared with nonshunted lobes (31% +/- 13% vs 452% +/- 107% change in arterial resistance, during hypoxia, P <.001). Vasodilation to inspired nitric oxide was evident only in shunted lobes (34% +/- 6% vs 1.8% +/- 8.2% change in arterial resistance during administration of inspired nitric oxide, P =.008). Neointimal and medial proliferation was found in shunted lobes with approximately a 10-fold increase in wall/luminal area ratio.

CONCLUSIONS

An aorta-lobar pulmonary artery shunt produces striking vasculopathy. The development of severe pulmonary hypertension within a short time frame, low mortality, and localized nature of the vasculopathy make this model highly attractive for investigation of mechanisms that underlie pulmonary hypertension.

An iterative approach to the beam hardening correction in cone beam CT

In computed tomography (CT), the beam hardening effect has been known to be one of the major sources of deterministic error that leads to inaccuracy and artifact in the reconstructed images. Because of the polychromatic nature of the x-ray source used in CT and the energy-dependent attenuation of most materials, Beer's law no longer holds. As a result, errors are present in the acquired line integrals or measurements of the attenuation coefficients of the scanned object. In the past, many studies have been conducted to combat image artifacts induced by beam hardening. In this paper, we present an iterative beam hardening correction approach for cone beam CT. An algorithm that utilizes a tilted parallel beam geometry is developed and subsequently employed to estimate the projection error and obtain an error estimation image, which is then subtracted from the initial reconstruction. A theoretical analysis is performed to investigate the accuracy of our methods. Phantom and animal experiments are conducted to demonstrate the effectiveness of our approach.

Cyanide increases reduction but decreases sequestration of methylene blue by endothelial cells

The mechanisms of endothelial cell transplasma membrane electron transport (TMET) have not been completely identified. Redox probes such as methylene blue (MB) can be useful tools, but the complexity of their disposition upon exposure to the cells can hinder interpretation. For example, MB is reduced on the cell surface by TMET, but after entering the cell in reduced form, it is reoxidized and sequestered within the cell. We developed a method to separately quantify the reduction and reoxidation rates such that it can be determined whether a metabolic inhibitor such as cyanide affects the reduction or oxidation process. MB was introduced at the inlet to a column filled with endothelial cell covered beads either as a short 12 s injection (bolus) or a long 45 min infusion (pulse), and its effluent concentration was measured as a function of time. The cells extracted 56% of the MB from the bolus, but only 41% during the pulse steady state. In the presence of cyanide, these extractions increased to 70% and decreased to 4%, respectively. Mathematical model results support the interpretation that these paradoxical effects on bolus and pulse extractions reflect the differential effects of cyanide on extracellular reduction and intracellular oxidation, i.e., cyanide increased the reduction rate from 7.3 to 13.0 cm s-1 X 10(-5) and decreased the oxidation rate from 1.09 to 0.02 cm s-1 X 10(-3). Cyanide also increased intracellular NADH by almost eight times, suggesting that TMET is sensitive to the cell redox status, i.e., NADH is a direct or indirect electron source. The cyanide-induced decrease in sequestration indicates a cyanide-sensitive intracellular oxidation mechanism. The results also demonstrate the potential utility of this approach for further evaluation of these endothelial redox mechanisms.

Toluidine blue O and methylene blue as endothelial redox probes in the intact lung

There is increasing evidence that the redox activities of the pulmonary endothelial surface may have important implications for the function of both lungs and blood. Because of the inherent complexity of intact organs, it can be difficult to study these activities in situ. Given the availability of appropriate indicator probes, the multiple-indicator dilution (MID) method is one approach for dealing with some aspects of this complexity. Therefore, the objectives of the present study were to 1) evaluate the potential utility of two thiazine redox indicators, methylene blue (MB) and toluidine blue O (TBO), as MID electron acceptor probes for in situ pulmonary endothelium and 2) develop a mathematical model of the pulmonary disposition of these indicators as a tool for quantifying their reduction on passage through the lungs. Experiments were carried out using isolated rabbit lungs perfused with physiological salt solution with or without plasma albumin over a range of flow rates. A large fraction of the injected TBO disappeared from the perfusate on passage through the lungs. The reduction of its oxidized, strongly polar, relatively hydrophilic blue form to its colorless, highly lipophilic reduced form was revealed by the presence of the reduced form in the venous effluent when plasma albumin was included in the perfusate. MB was also lost from the perfusate, but the fraction was considerably smaller than for TBO. A distributed-in-space-and-time model was developed to estimate the reduction rate parameter, which was approximately 29 and 1.0 ml/s for TBO and MB, respectively, and almost flow rate independent for both indicators. The results suggest the utility particularly of TBO as an electron acceptor probe for MID studies of in situ pulmonary endothelium and of the model for quantitative evaluation of the data.

Pulmonary inflammation alters the lung disposition of lipophilic amine indicators

Many lipophilic amine compounds are rapidly extracted from the blood on passage through the pulmonary circulation. The extent of their extraction in normal lungs depends on their physical-chemical properties, which affect their degree of ionization, lipophilicity, and propensity for interacting with blood and tissue constituents. The hypothesis of the present study was that changes in the tissue composition that occur during pulmonary inflammation would have a differential effect on the pulmonary extraction of lipophilic amines having different properties. If so, measurement of the extraction patterns for a group of lipophilic amines, having different physical-chemical properties, might provide a means for detecting and identifying lung tissue abnormalities. To evaluate this hypothesis, we measured the pulmonary extraction patterns for four lipophilic amines, [(14)C]diazepam, [(3)H]alfentanil, [(14)C]lidocaine, and [(14)C]codeine, along with two hydrophilic compounds, (3)HOH and [(14)C]phenylethylamine, after the bolus injection of these indicators into the pulmonary artery of isolated lungs from normal rabbits and from rabbits with pulmonary inflammation induced by an intravenous injection of complete Freund's adjuvant. The pulmonary extraction patterns, parameterized using a previously developed mathematical model, were, in fact, differentially altered by the inflammatory response. For example, the tissue sequestration rate, k(seq) (ml/s), per unit (3)HOH accessible extravascular lung water volume significantly increased for diazepam and lidocaine, but not for codeine and alfentanil. The results are consistent with the above hypothesis and suggest the potential for using lipophilic amines as indicators for detection and quantification of changes in lung tissue composition associated with lung injury and disease.

Detection of changes in lung tissue properties with multiple-indicator dilution

We evaluated the potential utility of a group of indicators, each of which targets a particular tissue property, as indicators in the multiple-indicator dilution method to detect and to identify abnormalities in lung tissue properties resulting from lung injury models. We measured the pulmonary venous outflow concentration vs. time curves of [14C]diazepam, 3HOH, [14C]phenylethylamine, and a vascular reference indicator following their bolus injection into the pulmonary artery of isolated perfused rabbit lungs under different experimental conditions, resulting in changes in the lung tissue composition. The conditions included granulomatous inflammation, induced by the intravenous injection of complete Freund's adjuvant (CFA), and intratracheal fluid instillation, each of which resulted in similar increases in lung wet weight. Each of these conditions resulted in a unique pattern among the concentration vs. time outflow curves of the indicators studied. The patterns were quantified by using mathematical models describing the pulmonary disposition of each of the indicators studied. A unique model parameter vector was obtained for each condition, demonstrating the ability to detect and to identify changes in lung tissue properties by using the appropriate group of indicators in the multiple-indicator dilution method. One change that was particularly interesting was a CFA-induced change in the disposition of diazepam, suggestive of a substantial increase in peripheral-type benzodiazepine receptors in the inflamed lungs.

Aspergillus fumigatus antigen exposure results in pulmonary airway resistance in wild-type but not in IL-4 knockout mice

Inhalation of Aspergillus fumigatus, a ubiquitous fungus, results in the development of allergic bronchopulmonary aspergillosis, a disabling allergic lung disease. For better patient management early diagnosis is essential, and understanding of the immune mechanism is important in achieving this goal. Although animal model studies have contributed to the understanding of the disease mechanism, details on the immunopathogenesis are still lacking. In the present study, we have developed an allergic aspergillosis model in wild-type and IL-4 knockout mice and studied the immune and airway responses. The results indicate that the immune response, pulmonary pathology, and airway reactivity comparable to allergic bronchopulmonary aspergillosis are reproducible in wild mice. IL-4 knockout mice showed similar pulmonary pathology, but no increase in airway resistance, suggesting that IgE and hence IL-4 may be important in eliciting the airway response, while other factors may be involved in the inflammatory process.

A murine model of latex allergy-induced airway hyperreactivity

Sensitization to latex proteins can cause immediate IgE mast cell-mediated reactions. Health care workers have been found to be particularly at risk because of high exposure. Latex allergy can be produced in mice as demonstrated by IgE and eosinophil responses. Thus the mouse is a potential animal model for studying this disease, but the airway response to latex sensitization in mice has not been evaluated previously. In the present study, we immunized BALB/c mice intranasally with nonammoniated latex proteins. Animals were anesthetized, and lung mechanics were evaluated plethysmographically. Changes in pulmonary conductance (GL) and compliance (Cdyn) were measured in response to a nonspecific challenge with methacholine or to a direct challenge with intravenous latex antigen. Latex sensitization resulted in elevated levels of IgE and latex-specific IgG1 as well as interstitial infiltrates consistent with an allergic response. The methacholine dose-response ED50 for GL was 116.4 microg for the control mice and fell significantly to 20.9 microg for latex-sensitized mice. The ED50 calculated for Cdyn was also significantly lower after latex sensitization. The GL in latex-sensitized mice challenged with latex antigen fell significantly from a prechallenge value of 1.87 +/- 0.41 (S.E.) to 0. 198 +/- 0.03 ml x s-1 x cmH2O after latex antigen challenge. The results indicate that latex-sensitized mice did exhibit increased airway reactivity in the methacholine challenge test. The latex allergic response in mice is unique in that direct challenge with latex antigen itself also resulted in a significant airway response.

Structure-function relationships in the pulmonary arterial tree

Knowledge of the relationship between structure and function of the normal pulmonary arterial tree is necessary for understanding normal pulmonary hemodynamics and the functional consequences of the vascular remodeling that accompanies pulmonary vascular diseases. In an effort to provide a means for relating the measurable vascular geometry and vessel mechanics data to the mean pressure-flow relationship and longitudinal pressure profile, we present a mathematical model of the pulmonary arterial tree. The model is based on the observation that the normal pulmonary arterial tree is a bifurcating tree in which the parent-to-daughter diameter ratios at a bifurcation and vessel distensibility are independent of vessel diameter, and although the actual arterial tree is quite heterogeneous, the diameter of each route, through which the blood flows, tapers from the arterial inlet to essentially the same terminal arteriolar diameter. In the model the average route is represented as a tapered tube through which the blood flow decreases with distance from the inlet because of the diversion of flow at the many bifurcations along the route. The taper and flow diversion are expressed in terms of morphometric parameters obtained using various methods for summarizing morphometric data. To help put the model parameter values in perspective, we applied one such method to morphometric data obtained from perfused dog lungs. Model simulations demonstrate the sensitivity of model pressure-flow relationships to variations in the morphometric parameters. Comparisons of simulations with experimental data also raise questions as to the "hemodynamically" appropriate ways to summarize morphometric data.

Proline in vasoactive peptides: consequences for peptide hydrolysis in the lung

To examine the hypothesis that trans isomers of bradykinin and [Gly6]bradykinin are preferentially hydrolyzed by lung peptidases, we studied the fractional inactivation of these peptides in the perfused rat lung using a bioassay after a single-pass bolus injection and high-performance liquid chromatography after lung recirculation. In the bioassay studies, when the peptides passed through the lung, 25.6-fold more bradykinin or 7-fold more [Gly6]bradykinin was required to elicit a contraction equivalent to that produced when the peptides did not pass through the lung. In the recirculation studies, hydrolysis progress curves with rapid and slow phases were observed, with a higher fraction of bradykinin than [Gly6]bradykinin hydrolyzed in the rapid phase. Cyclophilin increased the hydrolysis rate during the slow phase for both peptides. Kinetic analysis indicated that the slowly hydrolyzed peptide fraction, presumably the cis fraction, was 0.13 for bradykinin and 0.43 for [Gly6]bradykinin with cis-trans isomerization rate constants of 0.074 and 0.049 s-1, respectively, consistent with published nuclear magnetic resonance studies.

Immune response and airway reactivity in wild and IL-4 knockout mice exposed to latex allergens

BACKGROUND

Natural rubber latex has been reported as a major cause of allergy and asthma in a number of individuals. One of the occupational groups most affected by latex allergy are the health care workers who are frequently exposed to natural rubber latex products in their patient care activities. The immunopathogenesis of latex allergy is not well understood. In order to understand the immune mechanism in latex allergy, we have developed a mouse model of latex allergy.

METHODS

Both wild-type and IL-4 knockout BALB/c mice were challenged intranasally with latex proteins and their immune responses, lung pathology, and airway reactivity were evaluated.

RESULTS

The total serum IgE and latex specific IgE, IgG1, and peripheral blood and lung eosinophil levels in wild type BALB/c mice were enhanced by the latex exposure, while no IgE or eosinophil were detected in IL-4 knockout mice. Latex-specific IgG1 levels in the sera were lower in IL-4 knockout animals compared to wild mice. However, latex-specific IgG2a antibody was higher in all the IL-4 knockout mice compared to wild type mice. Both the wild type and IL-4 knockout animals developed increased airway resistance after antigen challenge when compared to control animals, although the airway resistance response of IL-4 knockout animals was attenuated compared to the wild-type animals. The histology of the lungs of these two groups of animals was similar.

CONCLUSION

In spite of the differences in the immune responses in the two groups of mice, there were comparable lung inflammatory responses, suggesting a multifactorial pathogenetic mechanism.

Accounting for the heterogeneity of capillary transit times in modeling multiple indicator dilution data

To mathematically model multiple indicator dilution (MID) data for the purpose of estimating parameters descriptive of indicator-tissue interactions, it is necessary to account for the effects of the distribution of capillary transit times, h(c)(t). In this paper, we present an efficient approach for incorporating h(c)(t) in the mathematical modeling of MID data. In this method, the solution of the model partial differential equations obtained at different locations along the model capillary having the longest transit time provides the outflow concentrations for all capillaries. When weighted by h(c)(t), these capillary outflow concentrations provide the outflow concentration versus time curve for the capillary bed. The method is appropriate whether the available data on capillary dispersion are in terms of capillary transit time or relative flow distributions, and whether the dispersion results from convection time differences among heterogeneous parallel pathways or axial diffusion along individual pathways. Finally, we show that the knowledge of a relationship among the moments of h(c)(t), rather than h(c)(t) per se, is sufficient information to account for the effect of h(c)(t) in the mathematical modeling interpretation of MID data. This relationship can be determined by including a flow-limited indicator in the injected bolus, thus providing an efficient means for obtaining the experimental data sufficient to account for capillary flow and transit time heterogeneity in MID modeling.

Transit time dispersion in the pulmonary arterial tree

Knowledge of the contributions of arterial and venous transit time dispersion to the pulmonary vascular transit time distribution is important for understanding lung function and for interpreting various kinds of data containing information about pulmonary function. Thus, to determine the dispersion of blood transit times occurring within the pulmonary arterial and venous trees, images of a bolus of contrast medium passing through the vasculature of pump-perfused dog lung lobes were acquired by using an X-ray microfocal angiography system. Time-absorbance curves from the lobar artery and vein and from selected locations within the intrapulmonary arterial tree were measured from the images. Overall dispersion within the lung lobe was determined from the difference in the first and second moments (mean transit time and variance, respectively) of the inlet arterial and outlet venous time-absorbance curves. Moments at selected locations within the arterial tree were also calculated and compared with those of the lobar artery curve. Transit times for the arterial pathways upstream from the smallest measured arteries (200-micron diameter) were less than approximately 20% of the total lung lobe mean transit time. Transit time variance among these arterial pathways (interpathway dispersion) was less than approximately 5% of the total variance imparted on the bolus as it passed through the lung lobe. On average, the dispersion that occurred along a given pathway (intrapathway dispersion) was negligible. Similar results were obtained for the venous tree. Taken together, the results suggest that most of the variation in transit time in the intrapulmonary vasculature occurs within the pulmonary capillary bed rather than in conducting arteries or veins.

Nitric oxide increases the survival of rats with a high oxygen exposure

The purpose of this study was to begin to examine the influence of inhaled NO on O2 toxicity. The survival of Sprague-Dawley rats exposed to >95% O2, >95% O2 + 10 ppm NO, >95% O2 + 100 ppm NO, and >95% O2 + 3 ppm NO2 was determined. Survival at 120 h was 2/24 in >95% O2, 2/12 in >95% O2 + 10 ppm NO, and 1/12 in >95% O2 + 3 ppm NO2. Survival at 120 h was 21/30 in >95% O2 + 100 ppm NO (p < 0.01 compared with >95% O2). Three additional groups of rats were exposed for 60 h to: 21% O2, >95% O2, or >95% O2 + 100 ppm NO. The lungs were then assayed for total protein, reduced (GSH) and oxidized glutathione (GSSG), and 4-hydroxy-2(E)-nonenal. Both of the high O2 groups had significantly (p < 0.05) lower GSH/mg protein and GSH/GSSG ratios compared with the 21% O2 group. The >95% O2 group had a higher 4-hydroxy-2(E)-nonenal/mg of protein than either the 21% O2 group (p < 0.05), or the >95% O2 + 100 ppm NO group (p < 0.05 compared with >95% O2, not different from the 21% O2 group). Additional groups of rats were exposed to either 21% O2, >95% O2, or >95% O2 + 100 ppm NO for 0, 24, 48, and 60 h. The lungs were examined for neutrophil accumulation, which was increased at 60 h in the two groups exposed to >95% O2, but adding NO had no effect. Thus, the overall result was that 100 ppm inhaled NO improved the survival of rats in high O2.

Activation by systemic angiotensin II of neurochemically identified neurons in rat hypothalamic paraventricular nucleus

Using the immunohistochemical localization of the protein product of the immediate early gene, c-fos, to localize activated neurons in the paraventricular nucleus of the hypothalamus (PVN), we studied the chemical phenotypes of neurons activated by circulating angiotensin II (AII). We determined the proportions of activated PVN neurons that expressed AII type I receptor-like immunoreactivity (AT1-L) or the neurohormones vasopressin (VP) and oxytocin (OXY). In addition, we identified activated PVN neurons that putatively produce nitric oxide (NO) on the basis of histochemical staining for nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d). Conscious rats received intravenous AII infusions at a rate sufficient to elevate mean arterial pressure by 40-60 mmHg for 90 min; control rats received infusions of vehicle. Brains were prepared for double immunohistochemistry [Fos-like immunoreactivity (FLI)/AT1-L, FLI/VP or FLI/OXY] or FLI/ NADPH-d histochemistry. Systemic AII infusions led to activation of 149+/-14 PVN neurons per section. In contrast, control animals showed activation of 21+/-6 PVN neurons per section. AII infusions elicited the activation of the following numbers of chemically identified PVN neurons per section: AT1-L, 24+/-5; VP, 26+/-5; OXY, 11+/-2; NADPH-d, 22+/-4. Control animals had few activated PVN neurons per section. For each of the chemically identified populations of PVN neurons, the following proportions were activated: AT1-L, 12.5%; VP, 15.2%; OXY, 7.2%; NADPH-d, 17.3%. The results suggest that PVN neurons producing the AT1 receptor, VP, OXY, and NO, participate in the mediation of the central responses to circulating AII.

Ascorbate-mediated transplasma membrane electron transport in pulmonary arterial endothelial cells

Pulmonary endothelial cells are capable of reducing certain electron acceptors at the luminal plasma membrane surface. Motivation for studying this phenomenon comes in part from the expectation that it may be important both as an endothelial antioxidant defense mechanism and in redox cycling of toxic free radicals. Pulmonary arterial endothelial cells in culture reduce the oxidized forms of thiazine compounds that have been used as electron acceptor probes for studying the mechanisms of transplasma membrane electron transport. However, they reduce another commonly studied electron acceptor, ferricyanide, only very slowly by comparison. In the present study, we examined the influence of ascorbate [ascorbic acid (AA)] and dehydroascorbate [dehydroascorbic acid (DHAA)] on the ferricyanide and thiazine reductase activities of the bovine pulmonary arterial endothelial cell surface. The endothelial cells were grown on microcarrier beads so that the reduction of ferricyanide and methylene blue could be studied colorimetrically in spectrophotometer cuvettes and in flow-through cell columns. The ferricyanide reductase activity could be increased 80-fold by adding DHAA to the medium, with virtually no effect on methylene blue reduction. The DHAA effect persisted after the DHAA was removed from the medium. AA also stimulated the ferricyanide reductase activity but was less potent, and the relative potencies of AA and DHAA correlated with their relative rates of uptake by the cells. The results are consistent with the hypothesis that AA is an intracellular electron donor for an endothelial plasma membrane ferricyanide reductase and that the stimulatory effect of DHAA is the result of increasing intracellular AA. Adding sufficient DHAA to markedly increase extracellular ferricyanide reduction had little effect on the plasma membrane methylene blue reductase activity, suggesting that pulmonary arterial endothelial cells have at least two separate transplasma membrane electron transport systems.

Feldkamp and circle-and-line cone-beam reconstruction for 3D micro-CT of vascular networks

Detailed morphometric knowledge of the microvascular network is needed for studies relating structure to haemodynamic function in organs like the lung. Clinical volumetric CT is limited to millimetre-order spatial resolution. Since evidence suggests that small arterioles (50 to 300 micrometres) dominate pulmonary haemodynamics, we built a micro-CT scanner, capable of imaging excised lungs in 3D with 100 microm resolution, for basic physiology research. The scanner incorporates a micro-focal (3 microm) x-ray source, an xyz theta stage and a CCD-coupled image intensifier detector. We imaged phantoms and contrast-enhanced rat lungs, reconstructing the data with either the Feldkamp or the circle-and-line cone-beam reconstruction algorithm. We present reconstructions using 180 views over 360 degrees for the circular trajectory, augmented with views from a linear scan for the circle-and-line algorithm. Especially for platelike features perpendicular to the rotation axis and remote from the midplane, the circle-and-line algorithm produces superior reconstructions compared with Feldkamp's algorithm. We conclude that the use of nonplanar source trajectories to perform micro-CT on contrast-enhanced, excised lungs can provide data useful for morphometric analysis of vascular trees, currently down to the 130 microm level.

Pulmonary disposition of lipophilic amine compounds in the isolated perfused rabbit lung

We measured the pulmonary venous concentration vs. time curves for [3H]alfentanil, [14C]lidocaine, and [3H]codeine after the bolus injection of each of these lipophilic amine compounds (LAC) and a vascular-reference indicator (fluorescein isothiocyanate-dextran) into the pulmonary artery of isolated perfused rabbit lungs. A range of flows and perfusate albumin concentrations was studied. To evaluate the information content of the data, we developed a kinetic model describing the pulmonary disposition of these LAC that was based on indicator dilution theory, and we sought a robust approach for interpreting the estimated model parameters. We found that the distribution of the kinetic model rate constants of the lipophilic amine-tissue interactions can be described by alpha, H, and psi, where alpha is a measure of the capacity of the rapidly equilibrating interactions between the lipophilic amine and the tissue; H is a measure of the equilibrium capacity of the slowly equilibrating interactions between the lipophilic amine and the tissue; and psi is the mean sojourn time. The values of alpha, H, and psi were 0.8 +/- 0.1 (SE), 0.6 +/- 0.1, and 1.6 +/- 0.5 s; 1.9 +/- 0.1, 5.3 +/- 0.4, and 5.6 +/- 0.5 s; and 1.1 +/- 0.1, 9.8 +/- 0.4, and 4.7 +/- 0.2 s for alfentanil, lidocaine, and codeine, respectively. These values for alpha, H, and psi reveal the relative dominance of the slowly equilibrating interactions for lidocaine and codeine in comparison with alfentanil. This approach to data analysis may have utility for the potential use of LAC to reveal and to quantify changes in lung tissue composition associated with lung disease.