Mechanistic models to meet the challenge of climate change in plant-pathogen systems

Evidence that climate change will impact the ecology and evolution of individual plant species is growing. However, little, as yet, is known about how climate change will affect interactions between plants and their pathogens. Climate drivers could affect the physiology, and thus demography, and ultimately evolutionary processes affecting both plant hosts and their pathogens. Because the impacts of climate drivers may operate in different directions at different scales of infection, and, furthermore, may be nonlinear, abstracting across these processes may mis-specify outcomes. Here, we use mechanistic models of plant-pathogen interactions to illustrate how counterintuitive outcomes are possible, and we introduce how such framing may contribute to understanding climate effects on plant-pathogen systems. We discuss the evidence-base derived from wild and agricultural plant-pathogen systems that could inform such models, specifically in the direction of estimates of physiological, demographic and evolutionary responses to climate change. We conclude by providing an overview of knowledge gaps and directions for future research in this important area. This article is part of the theme issue 'Infectious disease ecology and evolution in a changing world'.

Assessing the risk of vaccine-driven virulence evolution in SARS-CoV-2

The evolution of SARS-CoV-2 virulence, or lethality, threatens to exacerbate the burden of COVID-19 on society. How might COVID-19 vaccines alter selection for increased SARS-CoV-2 virulence? Framing current evidence surrounding SARS-CoV-2 biology and COVID-19 vaccines in the context of evolutionary theory indicates that prospects for virulence evolution remain uncertain. However, differential effects of vaccinal immunity on transmission and disease severity between respiratory compartments could select for increased virulence. To bound expectations for this outcome, we analyse an evo-epidemiological model. Synthesizing model predictions with vaccine efficacy data, we conclude that while vaccine-driven virulence remains a theoretical possibility, the risk is low if vaccines provide sustained robust protection against infection. Furthermore, we found that any increases in transmission concomitant with increases in virulence would be unlikely to threaten prospects for herd immunity in a highly immunized population. Given that virulence evolution would nevertheless impact unvaccinated individuals and populations with low vaccination rates, it is important to achieve high vaccination rates worldwide and ensure that vaccinal immunity provides robust protection against both infection and disease, potentially through the use of booster doses.

Challenges in modeling the emergence of novel pathogens

The emergence of infectious agents with pandemic potential present scientific challenges from detection to data interpretation to understanding determinants of risk and forecasts. Mathematical models could play an essential role in how we prepare for future emergent pathogens. Here, we describe core directions for expansion of the existing tools and knowledge base, including: using mathematical models to identify critical directions and paths for strengthening data collection to detect and respond to outbreaks of novel pathogens; expanding basic theory to identify infectious agents and contexts that present the greatest risks, over both the short and longer term; by strengthening estimation tools that make the most use of the likely range and uncertainties in existing data; and by ensuring modelling applications are carefully communicated and developed within diverse and equitable collaborations for increased public health benefit.

Variation in SARS-CoV-2 outbreaks across sub-Saharan Africa

A surprising feature of the SARS-CoV-2 pandemic to date is the low burdens reported in sub-Saharan Africa (SSA) countries relative to other global regions. Potential explanations (for example, warmer environments1, younger populations2-4) have yet to be framed within a comprehensive analysis. We synthesized factors hypothesized to drive the pace and burden of this pandemic in SSA during the period from 25 February to 20 December 2020, encompassing demographic, comorbidity, climatic, healthcare capacity, intervention efforts and human mobility dimensions. Large diversity in the probable drivers indicates a need for caution in interpreting analyses that aggregate data across low- and middle-income settings. Our simulation shows that climatic variation between SSA population centers has little effect on early outbreak trajectories; however, heterogeneity in connectivity, although rarely considered, is likely an important contributor to variance in the pace of viral spread across SSA. Our synthesis points to the potential benefits of context-specific adaptation of surveillance systems during the ongoing pandemic. In particular, characterizing patterns of severity over age will be a priority in settings with high comorbidity burdens and poor access to care. Understanding the spatial extent of outbreaks warrants emphasis in settings where low connectivity could drive prolonged, asynchronous outbreaks resulting in extended stress to health systems.

High variation expected in the pace and burden of SARS-CoV-2 outbreaks across sub-Saharan Africa

A surprising feature of the SARS-CoV-2 pandemic to date is the low burdens reported in sub-Saharan Africa (SSA) countries relative to other global regions. Potential explanations (e.g., warmer environments1, younger populations2-4) have yet to be framed within a comprehensive analysis accounting for factors that may offset the effects of climate and demography. Here, we synthesize factors hypothesized to shape the pace of this pandemic and its burden as it moves across SSA, encompassing demographic, comorbidity, climatic, healthcare and intervention capacity, and human mobility dimensions of risk. We find large scale diversity in probable drivers, such that outcomes are likely to be highly variable among SSA countries. While simulation shows that extensive climatic variation among SSA population centers has little effect on early outbreak trajectories, heterogeneity in connectivity is likely to play a large role in shaping the pace of viral spread. The prolonged, asynchronous outbreaks expected in weakly connected settings may result in extended stress to health systems. In addition, the observed variability in comorbidities and access to care will likely modulate the severity of infection: We show that even small shifts in the infection fatality ratio towards younger ages, which are likely in high risk settings, can eliminate the protective effect of younger populations. We highlight countries with elevated risk of 'slow pace', high burden outbreaks. Empirical data on the spatial extent of outbreaks within SSA countries, their patterns in severity over age, and the relationship between epidemic pace and health system disruptions are urgently needed to guide efforts to mitigate the high burden scenarios explored here.

Disease and healthcare burden of COVID-19 in the United States

As of 24 April 2020, the SARS-CoV-2 epidemic has resulted in over 830,000 confirmed infections in the United States¹. The incidence of COVID-19, the disease associated with this new coronavirus, continues to rise. The epidemic threatens to overwhelm healthcare systems, and identifying those regions where the disease burden is likely to be high relative to the rest of the country is critical for enabling prudent and effective distribution of emergency medical care and public health resources. Globally, the risk of severe outcomes associated with COVID-19 has consistently been observed to increase with age^2,3. We used age-specific mortality patterns in tandem with demographic data to map projections of the cumulative case burden of COVID-19 and the subsequent burden on healthcare resources. The analysis was performed at the county level across the United States, assuming a scenario in which 20% of the population of each county acquires infection. We identified counties that will probably be consistently, heavily affected relative to the rest of the country across a range of assumptions about transmission patterns, such as the basic reproductive rate, contact patterns and the efficacy of quarantine. We observed a general pattern that per capita disease burden and relative healthcare system demand may be highest away from major population centers. These findings highlight the importance of ensuring equitable and adequate allocation of medical care and public health resources to communities outside of major urban areas.

Vaccine-driven virulence evolution: consequences of unbalanced reductions in mortality and transmission and implications for pertussis vaccines

Many vaccines have heterogeneous effects across individuals. Additionally, some vaccines do not prevent infection, but reduce disease-associated mortality and transmission. Both of these factors will alter selection pressures on pathogens and thus shape the evolution of pathogen virulence. We use a mathematical modelling framework to show that (i) the balance of how vaccines reduce transmission versus mortality and (ii) individual variability in protection conferred both shape the evolution of pathogen virulence. Epidemiological (burden of disease) and evolutionary (pathogen virulence) outcomes are both worse when vaccines confer smaller reductions in transmission than in mortality. Furthermore, outcomes are modulated by variability in vaccine effects, with increased variability limiting the extent of virulence evolution but in some cases preventing eradication. These findings are pertinent to current concerns about the global resurgence of pertussis and the efficacy of pertussis vaccines, as the two classes of these vaccines may reduce disease symptoms without preventing infection and differ in their ability to reduce transmission. Furthermore, these findings point to the importance of generating precise predictions for virulence evolution in Bordetella pertussis (and other similar pathogens) by incorporating empirical characterizations of vaccine effects into models capturing the epidemiological details of this system.

Quantitative uniqueness of human brain evolution revealed through phylogenetic comparative analysis

While the human brain is clearly large relative to body size, less is known about the timing of brain and brain component expansion within primates and the relative magnitude of volumetric increases. Using Bayesian phylogenetic comparative methods and data for both extant and fossil species, we identified that a distinct shift in brain-body scaling occurred as hominins diverged from other primates, and again as humans and Neanderthals diverged from other hominins. Within hominins, we detected a pattern of directional and accelerating evolution towards larger brains, consistent with a positive feedback process in the evolution of the human brain. Contrary to widespread assumptions, we found that the human neocortex is not exceptionally large relative to other brain structures. Instead, our analyses revealed a single increase in relative neocortex volume at the origin of haplorrhines, and an increase in relative cerebellar volume in apes.

Estimating infection prevalence: Best practices and their theoretical underpinnings

Accurately estimating infection prevalence is fundamental to the study of population health, disease dynamics, and infection risk factors. Prevalence is estimated as the proportion of infected individuals ("individual-based estimation"), but is also estimated as the proportion of samples in which evidence of infection is detected ("anonymous estimation"). The latter method is often used when researchers lack information on individual host identity, which can occur during noninvasive sampling of wild populations or when the individual that produced a fecal sample is unknown. The goal of this study was to investigate biases in individual-based versus anonymous prevalence estimation theoretically and to test whether mathematically derived predictions are evident in a comparative dataset of gastrointestinal helminth infections in nonhuman primates. Using a mathematical model, we predict that anonymous estimates of prevalence will be lower than individual-based estimates when (a) samples from infected individuals do not always contain evidence of infection and/or (b) when false negatives occur. The mathematical model further predicts that no difference in bias should exist between anonymous estimation and individual-based estimation when one sample is collected from each individual. Using data on helminth parasites of primates, we find that anonymous estimates of prevalence are significantly and substantially (12.17%) lower than individual-based estimates of prevalence. We also observed that individual-based estimates of prevalence from studies employing single sampling are on average 6.4% higher than anonymous estimates, suggesting a bias toward sampling infected individuals. We recommend that researchers use individual-based study designs with repeated sampling of individuals to obtain the most accurate estimate of infection prevalence. Moreover, to ensure accurate interpretation of their results and to allow for prevalence estimates to be compared among studies, it is essential that authors explicitly describe their sampling designs and prevalence calculations in publications.

Controlled dissolution from wax-coated aerosol particles in canine lungs

Treatment of pulmonary and systemic diseases may be improved and toxicity reduced by pulmonary deposition of drug-containing aerosols exhibiting delayed dissolution. Aqueous disodium fluorescein and pentamidine aerosols were dried, concentrated, and condensation coated with paraffin wax. The apparent mass median aerodynamic diameters of the coated fluorescein particles were 2.8-4.0 microns. Wax-to-fluorescein ratios were 0.38-1.05. The dissolution half times determined using a single-pass flow system were 1.5 min for uncoated fluorescein and 0.8 min for uncoated pentamidine. These increased over threefold when the aerosols were coated with paraffin wax to maxima of 5.3 and 2.6 min, respectively. Wax-coated aerosols generated from fluorescein mixed with 99mTc-labeled iron oxide colloid delivered to the canine lungs demonstrated a 3.4-fold increase in the absorption half time of disodium fluorescein compared with uncoated fluorescein (11.2 vs. 38.4 min). The absence of changes in pulmonary function on inhalation of these wax-coated aerosols, together with a high drug load and delayed release, establishes a foundation for future therapeutic applications.

Effect of particle morphology on emitted dose of fatty acid-treated disodium cromoglycate powder aerosols

These studies assess the quantity and morphology of the emitted aerosolized dose of irregularly shaped disodium cromoglycate particles in the fine particle fraction using in vitro methods. Disodium cromoglycate was treated with a homologous series of saturated fatty acids, between C8 and C18, in a range of concentrations. The products of these treatments were powders with a variety of particle size, shape, and aggregation characteristics. Samples of these powders were loaded in gelatin capsules, generated as aerosols from a Rotahaler and collected in a two-stage liquid impinger or eight-stage inertial impactor. Particles were examined directly by scanning electron microscopy and subsequently the images were analyzed to define morphology. The aerodynamic fine-particle fraction determined by the two-stage impinger increased approximately twofold with lauric acid treatment (0.0317 g/g, 6.7%) and threefold with stearic acid treatment (0.58 g/g; 9.7%) compared with disodium cromoglycate alone (0 g/g, 3.56%). The lauric acid formulation appeared to alter deposition primarily by changing particle morphology. Stearic acid altered particle shape to some extent and the increase in the fine-particle fraction appeared to be attributable to improved particle dispersion properties. The uncontrolled presence of irregular-shaped particles can introduce dosing errors due to effects on dispersion and aerodynamic behavior. Conversely, controlled particle morphology and size may be employed to optimize the dose delivered to the lungs particularly if particle-particle and particle-surface interactions can be minimized.

Stationary and nonstationary correlation-frequency analysis of heterodyne mode laser light scattering: magnitude and periodicity of canine tracheal ciliary beat frequency in vivo

Stationary and nonstationary correlation-frequency analysis of heterodyne laser light scattering were utilized to make automated, on-line, objective measurements of tracheal ciliary beat frequency (CBF) in intact, anesthetized canines. The stationary correlation-frequency analysis laser light-scattering technique was used to assess the magnitude of the CBF stimulatory responses induced by aerosolized 10(-5) M fenoterol (sympathomimetic), and 10(-8) M and 10(-6) M methacholine (parasympathomimetic) delivered to the whole lungs of eight barbiturate-anesthetized beagles. The nonstationary correlation-frequency analysis laser light-scattering technique was used to measure the effect on tracheal CBF of increasing the cytosolic calcium ion concentration with a calcium ionophore, A23187. Aerosolized A23187 was delivered to the isolated tracheal lumens of eight beagle dogs in cumulative doses ranging from 10(-9)M to 10(-6) M. Administration of the ionophore synchronized the CBF with a period of 5.3 min. Dose dependencies were observed in both the time to the peak CBF stimulation and the magnitude of the stimulatory response. The magnitude of CBF stimulation was inhibited by prior administration of aerosolized nifedipine (2 mg/ml), a voltage-operated calcium channel blocker. The A23187-induced modulation period of tracheal CBF, was unchanged by nifedipine. These are the first data to demonstrate that the magnitude and periodicity of CBF are two independent coupled processes. The cooperativity of these two processes could be determined in the effectiveness of mucociliary transport.

Nature of the mammalian ciliary metachronal wave

The temporal and spatial coordination of ciliary beat (metachronicity) is fundamental to effective mucociliary transport. Metachronal wave period (MWP) and ciliary beat frequency (CBF) of fresh excised sheep and canine tracheal epithelial tissues were measured with the use of a newly developed alternating focal spot laser light scattering system. MWP was determined from cross correlation of the heterodyne signals from the alternating focal spots. CBF was determined by autocorrelation of the heterodyne signals from each of the spots. MWP and CBF were measured in four sheep tracheal epithelial tissues with the use of longitudinal interfocal spot distances of 6 and 18 microns. In three canine tracheal epithelial tissues MWP and CBF were measured both longitudinally and circumferentially with interfocal spot distances of 5, 15, 65, 87, and 96 microns. For the sheep tracheal epithelial tissues the mean CBF was 5.9 +/- 0.4 Hz (mean of means; range 3.6 +/- 0.5 to 9.9 +/- 1.5 Hz), whereas the mean MWPs for 6- and 18-microns interfocal spot distances were 0.50 +/- 0.1 and 0.47 +/- 0.1 s, respectively. For the canine tracheal epithelial tissues the mean CBF was 4.0 +/- 0.2 Hz (2.0 +/- 0.8 to 7.2 +/- 3.2 Hz), whereas the mean longitudinal MWP was 1.5 s and the mean circumferential MWP was 2.1 s. Geometric combination of the MWP components leads to a derived MWP of 2.6 s with a propagation direction of 54 degrees with respect to the longitudinal axis of the trachea. MWP was found to be episode modulated with 12- to 20-min intervals in the longitudinal direction, but modulation was not as apparent in the circumferential direction. These data suggest that MWP and CBF are regulated by separate intracellular, intercellular, and intraciliary mechanisms.

First pregnancies and livebirths from transfer of sodium alginate encapsulated embryos in a rodent model

OBJECTIVE

To determine the effect of sodium alginate encapsulation of rodent embryos on in vitro embryonic cleavage rates, implantation rates, and livebirth rates, and to find the in vivo degradation time for the capsules.

DESIGN

Studies were conducted using both CB6F1 mice and Golden Syrian hamsters.

RESULTS

Capsules made with 3.0% sodium alginate degraded in vivo within 24 to 48 hours after transfer. In vitro embryonic cleavage of encapsulated embryos was not impaired, nor were implantation rates in CB6F1 mice. Finally, 8.6% of transferred encapsulated embryos resulted in livebirths.

CONCLUSIONS

Encapsulation of rodent embryos in 3.0% sodium alginate is not detrimental to embryonic development, implantation rates, or fetal development. Because the capsule degrades within 48 hours after transfer, encapsulating embryos may be beneficial for human in vitro fertilization and embryo transfer.

A model for thromboembolization on biomaterials

A model was developed to describe the kinetics of protein and platelet deposition and embolization on biomaterials. The model assumes that proteins can be adequately represented by fibrinogen, albumin, and Factor XII, that protein adsorption is Langmuir-type, that surfaces are homogeneous, and that all adsorption and deposition steps are first order. Eleven model parameters were determined from literature experimental data from ex vivo experiments utilizing canine and baboon blood on Silastic, one parameter came from adsorption of Factor XII on glass, and three parameters were obtained by minimizing differences between experimental and predicted fibrinogen adsorption, and platelet deposition and embolization behavior. The model well predicted observed behavior for fibrinogen adsorption, platelet deposition, and platelet embolization on Silastic, and platelet embolization from both polyacrylamide and HEMA-MAAC.

A pore transport model for pulmonary alveolar epithelium

Hydrodynamic heteropore flow models for transport of solutes across alveolar epithelial tissue have been developed. A two-size cylindrical pore model and a similar parallel-plate model were formulated, tested and used to predict effective pore sizes from literature data on transport in bullfrog, canine and rat lungs. The best fit equivalent pore-size estimates were obtained using a modified, nonlinear least squares procedure, with alveolar surface area to volume ratio (S/V) and small-pore area fraction of total pore area as parameters. Small-pore and large-pore width estimates of 4 nm (84% of total flow area) and 10 nm, respectively, with an average deviation of 20% from experimentally derived permeabilities were obtained from the bullfrog alveolar epithelium parallel-plate pore model (13 solutes, diameters 0.3 to 2.8 nm). The equivalent cylindrical pore model diameter estimates were 5 nm and 10 nm, with small-pore area fraction and percentage deviations similar to the parallel-plate model estimates. Eighty-eight percent of the bulk water driven by a sucrose osmotic gradient was predicted to be transported through the small pores. The rat alveolus parallel-plate pore model (6 solutes) yielded small-pore and large-pore widths of 0.4 nm and 50 nm, respectively. Clearance rate-constant data for dextran macromolecules (3,000 to 250,000 Daltons), using a single parallel-plate pore model, resulted in a pore width estimate of 98 nm for canine alveoli with an average deviation of the predicted rate constants of 18% from literature experimental values. In all cases tested, the parallel-plate pore model predicted lower small-pore size estimates than did the cylindrical pore model, and both models had appreciably smaller percentage deviations from experimental data than previous models.

Work of adhesion of respiratory tract mucus

A method was devised to measure the work of adhesion (WA) to a substrate of mucus, a viscoelastic gel, from the measured contact angle of glycerol on a mucus substrate and the known physical properties of a Teflon surface. Fifteen sputum samples from cystic fibrosis (CF) patients were compared with 25 mucus samples from canine tracheal pouches (CP), studied in the hydrated and partially dehydrated states. Apparent viscosity (eta A) and recoverable shear strain (SR) were measured by fluxgate magnetometry, and water content was inferred from vapor pressure osmometry. Na+, K+, and Ca2+ concentrations were measured with specific ion electrodes and Cl- with a chloridimeter. The Cl- concentration of the CP mucus was inversely proportional to its osmolality, and the Cl- concentration of the CP mucus was 102.5 +/- 1.6 meq/l compared with 55.6 +/- 2.5 meq/l for CF sputum. When CP mucus osmolality was increased from 316.0 +/- 5.5 to 430.0 +/- 7.5 mosmol/kg, WA increased from 25.1 +/- 1.8 to 31.1 +/- 1.2 ergs/cm2 and eta A increased from 391 +/- 55 to 622 +/- 121 P, respectively. CF sputum WA was 30.2 +/- 0.6 ergs/cm2, eta A was 1,110 +/- 316 P, and osmolality was 466.0 +/- 14.0 mosmol/kg. The increased WA and eta A of mucus in CF patients may thus be dependent on the hydration of mucus, which is related to the documented Cl- transport defect.

On the interaction of the liposomal membrane with blood components

Liposome-encapsulated hemoglobin (LEH) has been shown to be a viable candidate as a blood replacement. However, few data have been presented as to how LEH interacts with normal blood components. Liposomes were prepared from egg lecithin, cholesterol, and dicetyl phosphate or phosphatidic acid, and mixed with fresh blood plasma or whole blood. Erythrocyte osmotic fragility, prothrombin time (extrinsic coagulation efficiency), activated partial thromboplastin time (intrinsic coagulation efficiency), plasma clot stability in urea (fibrin stabilizing factor), and clot retraction (platelet activation) were measured. Although liposomes were found to bind extensively to erythrocytes, all tests indicated that the liposomes had no significant adverse effects, provided that normal levels of plasma Ca++ were maintained. The ability of liposomes to absorb Ca++ from the plasma was related directly to the amount of dicetyl phosphate or phosphatidic acid present and thus, presumably, to the presence of negatively charged species in the membrane. The mechanics of deformation of the LEH membrane were investigated by encapsulating Hemoglobin S in liposomes. Liposomes containing Hemoglobin S were found to sickle when deoxygenated, but not liposomes containing normal hemoglobin. Shape analysis of sickled liposomes yielded a deforming stress of 10(6) dynes/cm2, about 50 times greater than the reported limit for shear elasticity of the erythrocyte membrane.

Pathways of substance P stimulation of canine tracheal ciliary beat frequency

Substance P (SP), an inflammatory neuropeptide, may be released by intraepithelial nerves in response to an irritant or inflammatory stimulus. To investigate the neural and humoral pathways mediating the response of tracheal ciliary beat frequency (CBF) to topically applied SP, CBF was measured on the ventral midtracheal surface of anesthetized beagles by using heterodyne-mode correlation analysis laser light scattering. In the first study, aerosolized SP, delivered to the lungs of eight beagle dogs, stimulated CBF in a dose-dependent manner from a baseline of 4.9 +/- 0.4 Hz to a maximum of 14.9 +/- 1.5 Hz at dose of 10(-7) M. In the second study, the tracheal lumen was isolated from the bronchial airways by inflating the cuff of an endotracheal tube near the carina. Intravenous hexamethonium bromide (2 mg/kg), ipratropium bromide (0.5 micrograms/kg), and indomethacin (2 mg/kg) were used as blocking agents to inhibit the nicotinic, muscarinic, and cyclooxygenase pathways, respectively. Aerosolized 10(-9), 10(-8), or 10(-7) M SP was delivered sequentially to the tracheal lumen for 3 min at 30-min intervals. SP caused two distinct CBF stimulatory episodes at 4 min (mean time of the maximal response) and at 18 min (mean time of the maximal response) after onset of delivery and returned to baseline after 25 min. SP stimulated CBF from the baseline of 5.1 +/- 0.4 Hz to a maximum of 14.2 +/- 2.5 Hz during the first episode (P less than 0.01) and to 10.4 +/- 0.6 Hz during the second episode (P less than 0.01) at dose of 10(-8) M. These responses were inhibited by all the blocking agents. These data suggest that SP stimulates CBF via a cyclooxygenase-dependent parasympathetic reflex.

Stimulation of tracheal ciliary beat frequency by capsaicin

To determine the possible involvement of neural and cyclooxygenase pathways whereby irritants might affect cilia activity in vivo, the temporal response of canine tracheal ciliary beat frequency (CBF) to the inhaled surrogate irritant capsaicin was studied. CBF was measured on the ventral midtracheal surface of barbiturate-anesthetized eucapnically ventilated beagle dogs by heterodyne-mode laser light scattering. After base-line CBF was established, hexamethonium bromide (2 mg/kg iv), ipratropium bromide (0.5 microgram/kg iv), indomethacin (2 mg/kg iv), or intravenous 0.9% saline was administered. Aerosolized 3 Z 10(-9) M capsaicin in 0.9% saline was delivered for 2 min, and CBF was measured for the following 60 min. Control experiments used 0.9% saline sham aerosol with a 0.9% saline sham block. Aerosolized capsaicin stimulated CBF from a base line of 6.2 +/- 1.4 (SD) Hz (n = 230) to a mean maximum of 17.7 +/- 7.3 Hz (n = 16) 23 min after aerosol delivery, and CBF returned to base line within 60 min. Neither hexamethonium bromide, ipratropium bromide, nor indomethacin changed CBF from base-line values. The episodic CBF stimulatory response to capsaicin after commencement of aerosol was completely inhibited by hexamethonium bromide. Ipratropium bromide partially inhibited the first 15 min and totally inhibited the following 45 min of stimulatory response. Indomethacin inhibited the initial 15 min but had less effect on the following 45 min of stimulatory response. These data indicate that multiple stimulatory mechanisms function over a prolonged period of time to affect the removal of irritants from the airways and that these mechanisms differ from those involved in the maintenance of basal CBF.

Regulatory pathways for the stimulation of canine tracheal ciliary beat frequency by bradykinin

1. The effects of bradykinin, a potent inflammatory nanopeptide, on tracheal ciliary beat frequency in vivo were investigated using barbiturate-anaesthetized beagles. Tracheal ciliary beat frequency was measured using heterodyne mode correlation analysis laser light scattering, a technique that does not require surgical intervention. 2. Aerosolized 10(-5) M-bradykinin in 0.9% saline administered for 3 min to eight barbiturate-anaesthetized beagles stimulated tracheal ciliary beat frequency from the baseline of 5.3 +/- 0.1 Hz to a maximum of 16.6 +/- 2.0 Hz, 8 min after aerosol delivery, and ciliary beat frequency remained above baseline for the following 35 min. 3. Intravenously injected hexamethonium bromide, ipratropium bromide or indomethacin did not change baseline tracheal ciliary beat frequency. That down-regulation of ciliary beat frequency below baseline values was not observed with either the neural or the cyclooxygenase blocking agents suggests that neither of these pathways is involved in the maintenance of the observed basal ciliary beat frequency. 4. Bradykinin-induced stimulation of tracheal ciliary beat frequency is blocked by hexamethonium bromide, ipratropium bromide or indomethacin. These data suggest that the stimulation of ciliary beat frequency by bradykinin acts through both cellular cyclooxygenase and parasympathetic pathways in series.

Ultrasonic evaluation of erythrocyte aggregation dynamics

The dynamics of aggregation and disaggregation of blood of varying hematocrit in oscillatory flow in a distensible horizontal tube was determined by measuring the developing echo intensity of the blood samples with a 10 MHz B-mode ultrasonic scanner. Early aggregation could be detected within 10 sec. of stoppage of flow. The rate of echo intensity buildup and thus, presumably the rate of aggregation when flow was stopped was inversely related to hematocrit, as was the rate of echo intensity reduction when flow was resumed. Polycythemic blood of 60% hematocrit showed no echo intensity increase over 5 min. Increasing the shear stress when flow was resumed resulted in rapid decreases in aggregation. In all cases, disaggregation following flow resumption was faster than aggregation following flow stoppage.

Oxidative interactions between hemoglobin and egg lecithin liposomes

The oxidative interaction between hemoglobin and unsaturated egg lecithin liposomes, characterized by the consumption of oxygen and the production of methemoglobin over time, was measured and modelled. The oxygen and methemoglobin profiles were fit by a mathematical model, using numerical integration techniques. From the model, it was determined that the catalytic rate constants for the effect of hemoglobin on lipid peroxidation varied with hemoglobin type, as deoxyhemoglobin greater than oxyhemoglobin = methemoglobin. Under in vivo conditions of oxygen tension, reaction rates were oxyhemoglobin greater than deoxyhemoglobin greater than methemoglobin. Vitamin E had about 35 times the antioxidant activity of cholesterol, as determined by the model. Both additives, together, appeared to stabilize the liposomal membrane, as manifested by their ability to prevent oxidation of approximately 95% of the available lipid.

Regulation of ciliary beat frequency by autonomic mechanisms: in vitro

The ciliated epithelium of the mammalian trachea separates the neurohumoral milieu of the tissue from that of the environment of the airway lumen. To determine whether specific autonomic receptors regulating ciliary beat frequency (CBF) were located on mucosal or serosal sides, we measured CBF by heterodyne mode correlation analysis laser light scattering in bovine tracheal tissues mounted in a two-sided chamber. A beta 2-adrenergic agonist, fenoterol, at 10(-7) M, stimulated serosal CBF from 7.9 +/- 1.3 to 20.2 +/- 5.8 Hz (P less than 0.01) and mucosal CBF from 6.6 +/- 0.9 to 14.7 +/- 4.6 Hz (P less than 0.01). A muscarinic cholinergic agonist, methacholine, at 10(-7) M, increased mucosal CBF from 8.4 +/- 1.0 to 19.5 +/- 5.5 Hz (P less than 0.01) and serosal CBF from 8.0 +/- 0.9 to 15.4 +/- 5.0 Hz (P less than 0.01). The differences in stimulation of CBF on the mucosal and serosal sides between fenoterol and methacholine were significant (P less than 0.01). Studies in which these autonomic agonist stimulating effects were inhibited by their respective antagonists, propranolol and atropine sulfate, demonstrated that CBF can be regulated independently by mediators both in the submucosa and within the mucus lining.

Development of the polyurethane sponge as a delivery system for aryl 4-guanidinobenzoates

The Today Contraceptive Sponge was evaluated as a vehicle for the delivery of aryl 4-guanidinobenzoates (AGs) which are highly active sperm acrosin inhibitors. Studies in animals have shown that several AGs are more potent vaginal contraceptives and less irritating to the vagina than nonoxynol-9 (N-9), the most frequently used active ingredient in commercial vaginal contraceptive formulations. Neither nonoxynol-9 nor the material that could be solubilized from the sponge matrix altered the enzyme-inhibitory activity of 4'-acetamidophenyl 4-guanidinobenzoate HCl (AGB), 4'-carboxyphenyl 4-guanidinobenzoate HCl (EGB) or 4'-carbomethoxyphenyl 4-guanidinobenzoate HCl (MSGB). Besides being acrosin inhibitors, all three AGs exhibited antimotility activity towards human spermatozoa, EGB being as potent as N-9. The antimotility effects of the AGs and N-9 were additive. For subsequent studies, AGB was used as the model compound. Manufacture of the AGB-containing sponges did not affect the chemical structure of AGB. Good release rates of AGB were obtained from the sponges over a 7-day period. The release rates were 20-50% higher when the sponges also contained N-9. These results indicate that certain AGs exert a dual contraceptive action on spermatozoa by inhibiting both the sperm enzyme acrosin and sperm motility. Furthermore, the polyurethane sponge appears to be a convenient and satisfactory long-term delivery system for the AGs. A mixture of N-9 and AG can be used clinically because these compounds have no adverse effects on each other.

Development of a polymeric releasing device for 2'-carbomethoxyphenyl 4-guanidinobenzoate (a proteinase inhibitor): release rate, in vitro antifibrinolytic activity and in utero contraceptive effect

A polymeric delivery system consisting of ethylene-vinyl acetate copolymer (EVAc) was developed for 2'-carbomethoxyphenyl 4-guanidinobenzoate (MSGB), a potent inhibitor of the sperm enzyme acrosin. The optimal device consists of copolymer with 40% vinyl acetate by weight (EVAc/40), 65% drug loading and MSGB with a particle size of 250-499 micron. This formulation yields a device that is highly flexible and can be shaped to many forms and sizes. Construction of the device does not alter the properties of MSGB. Well controlled release of MSGB from the device occurs in vitro and in the uteri of rats. The in vitro release rate under "infinite sink" conditions is essentially the same as the in vivo release rate. The contraceptive effect of the MSGB-releasing device was tested in rabbits by placing a blank (control) device in one uterine horn and an MSGB-releasing device in the contralateral horn. In contrast to blank devices, MSGB-releasing devices completely prevent pregnancy, not only by inhibiting fertilization but also by decreasing implantation. MSGB possesses high in vitro antifibrinolytic activity. These results indicate that a very flexible device can be constructed for uterine application which retains its contraceptive effect by release of MSGB. The antifibrinolytic activity of MSGB may further decrease the menorrhagia that can be associated with IUD use.

Stimulation of ciliary beat frequency by autonomic agonists: in vivo

beta 2-Adrenergic bronchodilator and muscarinic cholinergic bronchoconstrictor agonists both stimulate ciliary activity in vitro. To test the hypothesis that increases in autonomic activity would result in increases in ciliary beat frequency (CBF) in vivo, a correlation analysis heterodyne laser light-scattering system was developed and validated to measure the stimulating effects of sympathomimetic and parasympathomimetic agonists on tracheal CBF in intact, anesthetized beagles. The mean baseline CBF from 42 studies of 274 measurements in 9 (5 male and 4 female) adult beagles was 6.6 +/- 1.1 Hz. The stimulating effects of a beta 2-adrenergic agonist, fenoterol, and a muscarinic cholinergic agonist, methacholine, on CBF were studied on four and eight beagles, respectively. The studies were randomized and blinded. Aerosolized 10(-5) M fenoterol stimulated the CBF from the base line of 6.8 +/- 2.5 to 32.0 +/- 17.9 Hz in four dogs. Aerosolized methacholine stimulated the CBF from the base line of 5.8 +/- 0.7 to 9.4 +/- 3.0 Hz for 10(-8) M, and to 12.6 +/- 3.1 Hz for 10(-6) M in eight dogs. These are the first data obtained in intact animals that demonstrate CBF in the lower respiratory tract is regulated by autonomic agonists.

Hemodynamic effects of exchange transfusions with liposome-encapsulated hemoglobin

The ability of liposome-encapsulated hemoglobin (LEH) to sustain life in rats at hematocrits 45% below lethal levels was demonstrated by virtually total exchange transfusions. All control animals (transfused with 7% albumin in Erilyte) died at a mean hematocrit of 5.35%, with corresponding oxygen-carrying capacity of 2.65 ml/100 ml. All LEH animals survived with a final RBC hematocrit of 2.96% and an oxygen-carrying capacity of 7.05 ml/100 ml. LEH animals maintained normal blood pressures and essentially normal cardiac output, while control animals failed to do so. Systemic vascular resistance of control animals at 78% exchange was reduced to 33% of baseline, while of LEH animals at 92% exchange, to 80% of baseline. In-vitro measurements were made of LEH and RBC suspension viscosity as a function of shear rate, suspension concentration, and lipid membrane composition. The viscous behavior of the LEH suspensions was non-Newtonian and nearly the same as suspensions of natural RBC prepared similarly, though LEH suspensions had slightly higher viscosity.

Cardiorespiratory effects of exchange transfusions with synthetic erythrocytes in rats

Synthetic erythrocytes (SE) can maintain life with near-normal hemodynamics in rats with hematocrits (Hct) 45% below the lethal levels, as shown when we exchanged virtually all their blood. We compared cardiorespiratory variables between the SE and control animals, which were hemodiluted with 7% albumin, at the 78% exchange level. In addition, SE animals at 92% exchange were compared with the 78% exchange and baseline levels. All our control rats died at Hct above 5% with corresponding oxygen-carrying capacity of 2.65 ml/dl. All SE rats survived, having a final Hct of 2.96% with an oxygen-carrying capacity of 7.05 ml/dl. SE animals maintained normal BP and marginally increased cardiac output, while control animals did not. Vascular resistance of control animals at 78% exchange was reduced to 30%, while in SE animals at 92% exchange, vascular resistance was lowered to 80% of baseline values.

Measurements of viscosity of synthetic erythrocyte suspensions

Measurements were made of the viscosity of suspensions of synthetic erythrocytes composed of hemoglobin solutions encapsulated in liposomes, as a function of shear rate, temperature, suspension concentration, lipid membrane composition, and the viscosity of the suspending medium. It was found that the viscous behavior of the synthetic erythrocyte suspensions was non-Newtonian and nearly the same as that of suspensions of natural erythrocytes prepared similarly, with the major difference being that synthetic erythrocyte suspensions are somewhat more viscous. Suspensions of Fluosol FC-43 prepared similarly were found to be essentially Newtonian fluids, and substantially different and more viscous than either erythrocyte suspension. The higher viscosity of synthetic erythrocyte suspensions probably accounts for the ability of these suspensions to maintain normal systemic vascular resistance in transfusion experiments, in spite of the fact that synthetic erythrocytes are smaller than natural erythrocytes.

Automated measurement of ciliary beat frequency

Measurements of ciliary beat frequency using video images are dependent on observer interpretation. To obtain objective estimates of ciliary beat frequency from video-image sequences, a computer-based method was developed. Regions of interest of video-image sequences were selected and digitized. Variations in numerical values representing light intensity resulting from cilia beating were extracted and analyzed using autocorrelation techniques. The ciliary beat frequencies obtained for 14 in vitro experiments on ciliated cells or epithelium from the frog palate (Rana catesbeiana) over the range of frequencies 2-25 Hz correlated well with independent observer measurements (r = 0.979). The addition of such computer-based methods to video observer-based systems allows more objective and efficient determinations of ciliary beat frequency.

Effects of lipid-soluble substances on the thermotropic properties of liposome filtration

Filtration of dimyristoyl phosphatidylcholine or dipalmitoyl phosphatidylcholine liposomes at various temperatures from 3 to 60 degrees C revealed a discontinuous change in filtration behavior centered about the gel-to-liquid crystal transition temperature. This change was continuous at temperatures immediately above or below the transition temperature. Although pure dipalmitoyl phosphatidylcholine liposomes are in the gel state at 22 degrees C, passage of liposomes composed of dipalmitoyl phosphatidylcholine and cholesterol through the filters at 22 degrees C gave results similar to those obtained with liquid-crystal liposomes. Low cholesterol concentrations were nearly as effective as high concentrations in producing this behavior; this observation is consistent with a shear mechanism for reduction of liposome size, since the stress induced by passage of the otherwise rigid liposome through a small pore would be relieved by fracture at a lattice imperfection. Liposomes composed of egg phosphatidylcholine and cholesterol were retained by the filters to a slightly greater extent than pure egg phosphatidylcholine liposomes; these results are consistent with the known condensing effect of cholesterol on liquid-crystal lipsomes and a shear mechanism occurring with filtration. Liposomes composed of dipalmitoyl phosphatidylcholine and either dipalmitoyl phosphatidic acid or dicetyl phosphate were filtered at 22 degrees C; they showed a filtration characteristic similar to liquid-crystal liposomes. Inclusion of the water-soluble dyes eosin Y or Evans blue in dipalmitoyl phosphatidylcholine liposomes resulted in filtration at 22 degrees C which was similar to that observed for liquid-crystal liposomes. The dyes, sodium fluorescein, 6-carboxyfluorescein and fluoresceinisothiocyanate dextran, did not alter 22 degrees C liposome filtration.

Synthetic erythrocytes from lipid encapsulated hemoglobin

Synthetic erythrocytes have been formed by encapsulating concentrated hemoglobin solutions in microcapsules consisting of phospholipid-cholesterol mixtures. The microcapsules (hemosomes) are of the order of one micron in diameter or smaller, are osmometers, are somewhat sturdier than erythrocytes (RBC), and are stable upon freezing. They have essentially the same oxygen and carbon dioxide carrying capacity as RBC, and can be tailored to have the same electrokinetic properties. They appear to evoke no immune response in the rat. In experiments involving complete replacement of natural blood hemosomes appear to sustain life. Rats can live and breathe normally without signs of hypoxia or acidosis for extended periods of time after the hematocrit of natural RBC drops well below the critical level. Synthetic erythrocytes do not appear to cause disseminated coagulation, microembolism, or any observable changes in internal organs.

Liposome filtration. Dependence on transition temperature

Liposomes formed by vortexing and passed through polycarbonate surface retention membranes showed appreciable differences in filtration behavior depending on the temperature of filtration relation relative to the liposome gel-liquid crystal transition temperature. Below transition, liposomes were filterable and size distributions could be determined; the cumulative volume distributions were log-normal. Above transition, liposomes were not filterable: smaller liposomes were formed until a limiting size was reached. These results suggest that liquid crystal liposome size distributions cannot be determined by filtration. This filtration behavior is a physical property of liposomes, related to the gel-liquid crystal transition, not previously reported. This property could be exploited as a new method for controlling liposome size distributions, but the implications for lipid membranes, including biological membranes, are general.

Kinetic studies of a doubly bound red cell antigen-antibody system

The Polybrene method for detection of red cell antibodies which utilizes continuous flow equipment was modified so that kinetic studies could be performed on red cell antibodies doubly bound between adjacent red cells. In the anti-Rh(o)-Rh(o) erythrocyte system, deaggregation by temperature was studied over an antibody concentration range of from approximately 1 to 500 antibody molecules per erythrocyte, a residence time range of approximately eightfold, and a temperature range of from 10 to 55 degrees C. The rate of dissociation of antigen-antibody complex, as determined from deaggregation of antibody-dependent red cell aggregates, was found to be of apparent zero order. The apparent activation energy for the antigen-antibody reaction under the experimental conditions was determined and found to be higher than would be expected for singly bound antigen-antibody systems. Possible explanations are considered for these findings in terms of an antigen-antibody bond-breaking model.