Glycosylation-modified antigens as a tolerance-inducing vaccine platform prevent anaphylaxis in a pre-clinical model of food allergy

The only FDA-approved oral immunotherapy for a food allergy provides protection against accidental exposure to peanuts. However, this therapy often causes discomfort or side effects and requires long-term commitment. Better preventive and therapeutic solutions are urgently needed. We develop a tolerance-inducing vaccine technology that utilizes glycosylation-modified antigens to induce antigen-specific non-responsiveness. The glycosylation-modified antigens are administered intravenously (i.v.) or subcutaneously (s.c.) and traffic to the liver or lymph nodes, respectively, leading to preferential internalization by antigen-presenting cells, educating the immune system to respond in an innocuous way. In a mouse model of cow's milk allergy, treatment with glycosylation-modified β-lactoglobulin (BLG) is effective in preventing the onset of allergy. In addition, s.c. administration of glycosylation-modified BLG shows superior safety and potential in treating existing allergies in combination with anti-CD20 co-therapy. This platform provides an antigen-specific immunomodulatory strategy to prevent and treat food allergies.

Synthetically mannosylated antigens induce antigen-specific humoral tolerance and reduce anti-drug antibody responses to immunogenic biologics

Immunogenic biologics trigger an anti-drug antibody (ADA) response in patients that reduces efficacy and increases adverse reactions. Our laboratory has shown that targeting protein antigen to the liver microenvironment can reduce antigen-specific T cell responses; herein, we present a strategy to increase delivery of otherwise immunogenic biologics to the liver via conjugation to a synthetic mannose polymer, p(Man). This delivery leads to reduced antigen-specific T follicular helper cell and B cell responses resulting in diminished ADA production, which is maintained throughout subsequent administrations of the native biologic. We find that p(Man)-antigen treatment impairs the ADA response against recombinant uricase, a highly immunogenic biologic, without a dependence on hapten immunodominance or control by T regulatory cells. We identify increased T cell receptor signaling and increased apoptosis and exhaustion in T cells as effects of p(Man)-antigen treatment via transcriptomic analyses. This modular platform may enhance tolerance to biologics, enabling long-term solutions for an ever-increasing healthcare problem.

Synthetically mannosylated antigens induce antigen-specific humoral tolerance and reduce anti-drug antibody responses to immunogenic biologics

Immunogenic biologics trigger an anti-drug antibody (ADA) response in patients, which reduces efficacy and increases adverse reactions. Our laboratory has previously shown that targeting protein antigen to the liver microenvironment can reduce antigen-specific T cell responses; herein, we present a strategy to increase delivery of otherwise immunogenic biologics to the liver via conjugation to a synthetic mannose polymer (p(Man)). This delivery leads to reduced antigen-specific T follicular helper cell and B cell responses resulting in diminished ADA production, which is maintained throughout subsequent administrations of the native biologic. We found that p(Man)-antigen treatment impairs the ADA response against recombinant uricase, a highly immunogenic biologic, without a dependence on hapten immunodominance or control by Tregs. We identify increased TCR signaling and increased apoptosis and exhaustion in T cells as effects of p(Man)-antigen treatment via transcriptomic analyses. This modular platform may enhance tolerance to biologics, enabling long-term solutions for an ever-increasing healthcare problem.

Synthetically glycosylated antigens for the antigen-specific suppression of established immune responses

Inducing antigen-specific tolerance during an established immune response typically requires non-specific immunosuppressive signalling molecules. Hence, standard treatments for autoimmunity trigger global immunosuppression. Here we show that established antigen-specific responses in effector T cells and memory T cells can be suppressed by a polymer glycosylated with N-acetylgalactosamine (pGal) and conjugated to the antigen via a self-immolative linker that allows for the dissociation of the antigen on endocytosis and its presentation in the immunoregulatory environment. We show that pGal-antigen therapy induces antigen-specific tolerance in a mouse model of experimental autoimmune encephalomyelitis (with programmed cell-death-1 and the co-inhibitory ligand CD276 driving the tolerogenic responses), as well as the suppression of antigen-specific responses to vaccination against a DNA-based simian immunodeficiency virus in non-human primates. Our findings show that pGal-antigen therapy invokes mechanisms of immune tolerance to resolve antigen-specific inflammatory T-cell responses and suggest that the therapy may be applicable across autoimmune diseases.

Semaphorin 3A delivered by a rapidly polymerizing click hydrogel overcomes impaired implant osseointegration in a rat type 2 diabetes model

Semaphorin 3A (sema3A) is an osteoprotective factor that enhances bone formation while inhibiting osteoclast bone resorption. It is produced by rat calvarial osteoblasts cultured on grit-blasted/acid-etched microtextured (SLA) titanium surfaces at higher levels than on tissue culture polystyrene, suggesting that it may improve performance of titanium implants in vivo, particularly in conditions characterized by compromised bone quality. To test this, we established a clinically relevant type 2 diabetes mellitus (T2DM) rat model and used a non-toxic click hydrogel that rapidly polymerizes in situ (GEL) to provide localized controlled delivery of sema3A. In vitro studies confirmed that sema3A released from GEL was biologically active, increasing osteoblast differentiation of a pre-osteoblast cell-line. Whereas increased sema3A production was not observed in T2DM calvarial osteoblasts cultured on SLA, exogenous sema3A enhanced surface-induced osteoblast differentiation, indicating that it would be a viable candidate for in vivo use. Delivery of sema3A either by GEL or by local injection to bone defects enhanced osseointegration of SLA implants in the T2DM rats. Trabecular bone mass and bone-to-implant contact were decreased in T2DM rats compared to normal rats; sema3A delivered locally improved both parameters. These findings suggest that reduced trabecular bone contributes to poor osseointegration in T2DM patients and support GEL as a promising treatment option for sustained release of therapeutic doses of sema3A. Moreover, using this clinically translatable T2DM model and developing a biocompatible, Cu-free click chemistry hydrogel platform for the non-invasive delivery of therapeutics has major implications for regenerative medicine as a whole. STATEMENT OF SIGNIFICANCE: Osseointegration is compromised in patients with poor bone quality due to conditions like type 2 diabetes mellitus (T2DM). Previously, we showed that semaphorin 3A (sema3A) production is increased when human bone marrow stromal cells are cultured on titanium substrates that support osseointegration in vivo, suggesting it may enhance peri-implant osteogenesis in diabetes. Here we established a spontaneously developing T2DM rat model with clinical translatability and used it to assess sema3A effectiveness. Sema3A was delivered to the implant site via a novel copper-free click hydrogel, which has minimal swelling behavior and superior rheological properties. Osseointegration was successfully restored, and enhanced compared to burst release through injections. This study provides scientific evidence for using sema3A to treat impaired osseointegration in T2DM patients.

Treatment of peanut allergy and colitis in mice via the intestinal release of butyrate from polymeric micelles

The microbiome modulates host immunity and aids the maintenance of tolerance in the gut, where microbial and food-derived antigens are abundant. Yet modern dietary factors and the excessive use of antibiotics have contributed to the rising incidence of food allergies, inflammatory bowel disease and other non-communicable chronic diseases associated with the depletion of beneficial taxa, including butyrate-producing Clostridia. Here we show that intragastrically delivered neutral and negatively charged polymeric micelles releasing butyrate in different regions of the intestinal tract restore barrier-protective responses in mouse models of colitis and of peanut allergy. Treatment with the butyrate-releasing micelles increased the abundance of butyrate-producing taxa in Clostridium cluster XIVa, protected mice from an anaphylactic reaction to a peanut challenge and reduced disease severity in a T-cell-transfer model of colitis. By restoring microbial and mucosal homoeostasis, butyrate-releasing micelles may function as an antigen-agnostic approach for the treatment of allergic and inflammatory diseases.

Synthetically glycosylated antigens as an inverse vaccine platform to prevent and treat food allergies

The only FDA-approved oral immunotherapy for a food allergy provides protection against accidental exposure to peanuts. However, this therapy often causes discomfort or side effects and requires long-term commitment. Better preventive and therapeutic solutions are urgently needed. We have developed a technology for inverse vaccination using glyco-polymerized antigens to induce antigen-specific non-responsiveness. We have demonstrated that following subcutaneous (SC) administration, glyco-polymer conjugates traffic to draining lymph nodes (LNs) and are preferentially internalized by antigen presenting cells, educating the immune system to respond to these antigens in an innocuous way. Here, we tested SC administration of glyco-polymerized β-lactoglobulin (BLG) in a murine model of cow’s milk allergy. Two doses of glyco-polymerized BLG given one week apart (prior to sensitization) prevented an allergic response to BLG upon intragastric challenge as measured by reductions in BLG-specific IgG, IgG1, and IgE production as well as BLG-specific type 2 T helper cell (Th2) responses in vitro. We further explored the therapeutic potential of glyco-polymerized BLG. Unlike unmodified BLG, two SC injections of glyco-polymerized BLG after sensitization did not cause anaphylactic reactions in allergic mice and inhibited cellular Th2 cytokines upon BLG restimulation. Since pre-existing humoral immunity inhibited the therapeutic effect of our glyco-polymerized BLG, we introduced a co-therapy (anti-CD20) to blunt the humoral response and observed ameliorated anaphylactic responses following glyco-polymerized BLG therapy. This platform may provide a potential T cell-modulating strategy to prevent and treat food allergies.

This work was supported in part by seed funding from the Chicago Immunoengineering Innovation Center at the University of Chicago as well as the Food Allergy Fund. 

Generation of potent cellular and humoral immunity against SARS-CoV-2 antigens via conjugation to a polymeric glyco-adjuvant

The SARS-CoV-2 virus has caused an unprecedented global crisis, and curtailing its spread requires an effective vaccine which elicits a diverse and robust immune response. We have previously shown that vaccines made of a polymeric glyco-adjuvant conjugated to an antigen were effective in triggering such a response in other disease models and hypothesized that the technology could be adapted to create an effective vaccine against SARS-CoV-2. The core of the vaccine platform is the copolymer p(Man-TLR7), composed of monomers with pendant mannose or a toll-like receptor 7 (TLR7) agonist. Thus, p(Man-TLR7) is designed to target relevant antigen-presenting cells (APCs) via mannose-binding receptors and then activate TLR7 upon endocytosis. The p(Man-TLR7) construct is amenable to conjugation to protein antigens such as the Spike protein of SARS-CoV-2, yielding Spike-p(Man-TLR7). Here, we demonstrate Spike-p(Man-TLR7) vaccination elicits robust antigen-specific cellular and humoral responses in mice. In adult and elderly wild-type mice, vaccination with Spike-p(Man-TLR7) generates high and long-lasting titers of anti-Spike IgGs, with neutralizing titers exceeding levels in convalescent human serum. Interestingly, adsorbing Spike-p(Man-TLR7) to the depot-forming adjuvant alum amplified the broadly neutralizing humoral responses to levels matching those in mice vaccinated with formulations based off of clinically-approved adjuvants. Additionally, we observed an increase in germinal center B cells, antigen-specific antibody secreting cells, activated T follicular helper cells, and polyfunctional Th1-cytokine producing CD4+ and CD8+ T cells. We conclude that Spike-p(Man-TLR7) is an attractive, next-generation subunit vaccine candidate, capable of inducing durable and robust antibody and T cell responses.

Lymph Node-Targeted Synthetically Glycosylated Antigen Leads to Antigen-Specific Immunological Tolerance

Inverse vaccines that tolerogenically target antigens to antigen-presenting cells (APCs) offer promise in prevention of immunity to allergens and protein drugs and treatment of autoimmunity. We have previously shown that targeting hepatic APCs through intravenous injection of synthetically glycosylated antigen leads to effective induction of antigen-specific immunological tolerance. Here, we demonstrate that targeting these glycoconjugates to lymph node (LN) APCs under homeostatic conditions leads to local and increased accumulation in the LNs compared to unmodified antigen and induces a tolerogenic state both locally and systemically. Subcutaneous administration directs the polymeric glycoconjugate to the draining LN, where the glycoconjugated antigen generates robust antigen-specific CD4+ and CD8+ T cell tolerance and hypo-responsiveness to antigenic challenge via a number of mechanisms, including clonal deletion, anergy of activated T cells, and expansion of regulatory T cells. Lag-3 up-regulation on CD4+ and CD8+ T cells represents an essential mechanism of suppression. Additionally, presentation of antigen released from the glycoconjugate to naïve T cells is mediated mainly by LN-resident CD8+ and CD11b+ dendritic cells. Thus, here we demonstrate that antigen targeting via synthetic glycosylation to impart affinity for APC scavenger receptors generates tolerance when LN dendritic cells are the cellular target.

Soluble N-Acetylgalactosamine-Modified Antigens Enhance Hepatocyte-Dependent Antigen Cross-Presentation and Result in Antigen-Specific CD8+ T Cell Tolerance Development

Hepatocytes compose up to 80% of the total liver and have been indicated as important players in the induction of immunologic tolerance in this organ. We show that hepatocytes possess the molecular machinery required for the cross-presentation of extracellular antigens. Using a derivative of the model antigen ovalbumin (OVA) covalently modified with a polymer containing multiple N-acetylgalactosamine residues (pGal-OVA) that enhance extracellular antigen uptake by mimicking the glycome of apoptotic debris, we show efficient hepatocyte-dependent induction of cross-tolerance of both adoptively transferred OT-I cells and endogenous OVA-specific CD8+ T lymphocytes, for example inducing tolerance to OVA-expressing skin transplants. Our study confirms that hepatocytes are capable of inducing peripheral tolerogenesis and provides proof of concept that they may be a valuable candidate for in vivo targeted tolerogenic treatments.

Abstract 4582: Tumor matrix-targeted polymeric glyco-adjuvant for in situ cancer vaccination

Cancer vaccination is challenging due to a lack of strong, clinically approved adjuvants and difficulty in identifying cancer-specific antigens. Here, in order to address these challenges, we report the creation of a targeted therapeutic cancer vaccine with two components: (1) a mannosylated, toll-like receptor 7 (TLR7)-agonizing polymer, p(Man-TLR7), and (2) a fusion protein consisting of serum albumin (SA) fused to a collagen binding domain (CBD), namely the A3 domain of von Willebrand factor. p(Man-TLR7) has been shown to elicit strong CD8+ T cell responses, which are vital for the success of cancer vaccines. As such, we hypothesized that chemically linking p(Man-TLR7) to a tumor-targeting protein would localize our polymeric glyco-adjuvant to the tumor, promoting the immunogenic processing of endogenous tumor antigens and bypassing the need to pre-identify tumor-specific antigens. In the approach presented here, CBD-SA acts as our tumor-targeting protein by actively binding to collagen in the tumor microenvironment via the CBD, in addition to utilizing the passive targeting of SA. Upon successful and reproducible generation of CBD-SA-p(Man-TLR7) conjugates, we observed that the conjugates retained the ability to bind both collagen I and collagen III. We then assessed the in vivo anti-tumor efficacy of our conjugates in B16F10 tumor-bearing mice, testing both murine CBD-SA-p(Man-TLR7) and human CBD-SA-p(Man-TLR7) conjugates to evaluate the translatability of our approach. We observed an 84% decrease in average B16F10 tumor size and improved overall survival compared to untreated controls when mice were treated with intravenously-delivered murine CBD-SA-p(Man-TLR7) in combination with anti-PD-1 and anti-CTLA-4 antibodies. In the case of intravenously-delivered human CBD-SA-p(Man-TLR7), a 60% decrease in average tumor size compared to untreated controls was observed when mice were treated with our vaccine as a monotherapy. Further improved anti-tumor efficacy (an 85% decrease in average tumor size compared to untreated controls) and improved overall survival were observed when we combined our human CBD-SA-p(Man-TLR7) vaccination with anti-PD-1 and anti-CTLA-4 antibodies. In conclusion, in situ vaccination with CBD-SA-p(Man-TLR7) is a translatable approach that synergizes with checkpoint antibody therapy to provide therapeutic benefit in treatment of a poorly immunogenic melanoma model.

Citation Format: Laura T. Gray, D. Scott Wilson, Jun Ishihara, Koichi Sasaki, Michal Raczy, Melody Swartz, Jeffrey Hubbell. Tumor matrix-targeted polymeric glyco-adjuvant for in situ cancer vaccination [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4582.

Antigen-specific suppression of previously activated T cell responses via polymeric GalNAc antigen conjugation

Current treatments for autoimmunity, allergy, and drug hypersensitivity require continuous global immune suppression. Here we demonstrate in vivo therapeutic efficacy of antigen-specific T cell tolerance induction following prior immunization in various models of murine immunity. Our lab has engineered an N-acetylgalactosamine polymer (pGal) that can be conjugated to protein antigen and delivered intravenously to immunosuppressive hepatic antigen presenting cells, thereby inducing lasting immune regulation without off target effects. In this work, we show treatment with pGal-ovalbumin (OVA) conjugates can suppress previously activated T cells in an antigen-specific fashion. We describe the suppressive effects and underlying signatures of tolerogenic T cell reprogramming by comparing treatment with native OVA to pGal-OVA. Therapeutic treatment with pGal-OVA results in reduced T cell expansion and activation after secondary challenge, higher expression levels of suppressive/exhausted markers such as PD1 and TOX, and markedly lower production of cytokines including IFNg, TNFa, and IL-17 following in vitro restimulation with antigen. Further investigation of antigen-specific tolerance induction utilizing pGal-conjugates can lead to potentially curative approaches for controlling aberrant immunity to self or innocuous foreign protein.

Antigens reversibly conjugated to a polymeric glyco-adjuvant induce protective humoral and cellular immunity

Fully effective vaccines for complex infections must elicit a diverse repertoire of antibodies (humoral immunity) and CD8⁺ T-cell responses (cellular immunity). Here, we present a synthetic glyco-adjuvant named p(Man-TLR7), which, when conjugated to antigens, elicits robust humoral and cellular immunity. p(Man-TLR7) is a random copolymer composed of monomers that either target dendritic cells (DCs) via mannose-binding receptors or activate DCs via Toll-like receptor 7 (TLR7). Protein antigens are conjugated to p(Man-TLR7) via a self-immolative linkage that releases chemically unmodified antigen after endocytosis, thus amplifying antigen presentation to T cells. Studies with ovalbumin (OVA)-p(Man-TLR7) conjugates demonstrate that OVA-p(Man-TLR7) generates greater humoral and cellular immunity than OVA conjugated to polymers lacking either mannose targeting or TLR7 ligand. We show significant enhancement of Plasmodium falciparum-derived circumsporozoite protein (CSP)-specific T-cell responses, expansion in the breadth of the αCSP IgG response and increased inhibition of sporozoite invasion into hepatocytes with CSP-p(Man-TLR7) when compared with CSP formulated with MPLA/QS-21-loaded liposomes-the adjuvant used in the most clinically advanced malaria vaccine. We conclude that our antigen-p(Man-TLR7) platform offers a strategy to enhance the immunogenicity of protein subunit vaccines.

Improving the immunogenicity of dendritic cell-derived exosome-based vaccines for the immunotherapy of melanoma

Dendritic cell (DC)-derived exosomes (Dexo) are promising vaccine candidates for the treatment of cancer.

We aimed at identifying a Dexo formulation with stronger immune stimulatory properties and efficacy as compared to the Dexo vaccines previously tested in pre-clinical and clinical settings of cancer immunotherapy. We therefore produced Dexo from DCs loaded with specific antigens and matured with the Toll-like receptor (TLR)-3 ligand poly(I:C) as danger signal.

In vivo, Dexo produced from DCs loaded with OVA and stimulated with poly(I:C) could induce efficient activation of endogenous OVA-specific CD4+ and CD8+ T cells, leading to pro-inflammatory Th1 immune responses.

We subsequently produced Dexo from DCs matured with poly(I:C) and cultured in the presence of oxidized B16F10 cell lysates (Dexo(B16+pIC)) as a source of B16F10 antigens.

Mice bearing subcutaneous B16F10 tumors were vaccinated intradermally to target tumor-draining lymph nodes (tdLN), resulting in reduced tumor growth, limited metastasis burden and, most importantly, in prolonged survival of the mice vaccinated with Dexo(B16+pIC). Such benefits were associated with increased frequencies of effector CD8+ T cells in the tdLNs, spleen and tumor masses, reduced frequencies of tumor-infiltrating exhausted PD-1+ CD8+ T cells and increased frequencies of tumor-infiltrating NK and NK-T cells obtained upon vaccination with Dexo(B16+pIC) as compared to Dexo(B16), which instead are devoid of poly(I:C) and resemble the Dexo vaccines previously tested in human patients.

Our results demonstrate that poly(I:C) is a promising candidate for the production of Dexo vaccines with improved immune stimulatory properties suitable for the immunotherapy of cancer.

Hepatocyte-dependent cross-presentation of soluble antigens induces antigen-specific CD8+ T cell tolerance

The ability of hepatocytes to cross-present soluble extracellular antigens and the related immunological outcomes remain poorly investigated.

Our work shows that murine primary hepatocytes actively uptake and process extracellular antigens in EEA1+ and TAP1+ phagosomes, which are functionally related to cross-presentation. In fact EEA1+TAP1+ organelles, which are one of the signatures of professional cross-presenting cells, are also found in the cytoplasm of hepatocytes. Moreover, in vitro hepatocyte-dependent cross-presentation of OVA to OT-I cells is sensitive to specific drug inhibitors of endosomal and proteasomal activity, providing direct evidence that endocytosed antigens enter the cross-presentation pathway.

In vivo, cross-presenting hepatocytes induce tolerance of adoptively transferred OT-I cells by clonal deletion, as pro-apoptotic markers are upregulated on hepatocyte-educated OT-I cells. Non-deleted OT-I cells show instead significantly reduced response to vaccination, indicative of anergy. Active engulfment or emperipolesis of antigen cross-presenting hepatocytes by OT-I cells is also detected in vitro, as an additional means of T cell deletion.

PD-1/PD-L1 interactions participate in the induction of hepatocyte-dependent cross-tolerance, as specific blockage of PD-L1 on hepatocytes significantly reduces the development of hepatocyte-dependent cross-tolerance.

Due to their physiologic metabolic functions and their capacity to cross-present extracellular antigens here described, we propose hepatocytes as one of the major players in the establishment of antigen-specific CD8+ T cell peripheral tolerance.

Costs and limits of phenotypic plasticity

The costs and limits of phenotypic plasticity are thought to have important ecological and evolutionary consequences, yet they are not as well understood as the benefits of plasticity. At least nine ideas exist regarding how plasticity may be costly or limited, but these have rarely been discussed together. The most commonly discussed cost is that of maintaining the sensory and regulatory machinery needed for plasticity, which may require energy and material expenses. A frequently considered limit to the benefit of plasticity is that the environmental cues guiding plastic development can be unreliable. Such costs and limits have recently been included in theoretical models and, perhaps more importantly, relevant empirical studies now have emerged. Despite the current interest in costs and limits of plasticity, several lines of reasoning suggest that they might be difficult to demonstrate.

Adaptation and Natural Selection revisited

In Adaptation and Natural Selection, George C. Williams linked the distinction between group and individual adaptation with the distinction between group and individual selection. Williams' Principle, as we will call it, says that adaptation at a level requires selection at that level. This is a necessary but not a sufficient condition; for example, group adaptation requires group selection, but the fact that group selection influences a trait's evolution does not suffice for the resulting trait frequency to be a group adaptation. What more is required? In this paper, we describe an answer to this question that has been developed in multilevel selection theory. We also discuss an alternative framework for defining units of adaptation that violates Williams' Principle.

Orally delivered thioketal nanoparticles loaded with TNF-α-siRNA target inflammation and inhibit gene expression in the intestines

Small interfering RNAs (siRNAs) directed against proinflammatory cytokines have the potential to treat numerous diseases associated with intestinal inflammation; however, the side-effects caused by the systemic depletion of cytokines demands that the delivery of cytokine-targeted siRNAs be localized to diseased intestinal tissues. Although various delivery vehicles have been developed to orally deliver therapeutics to intestinal tissue, none of these strategies has demonstrated the ability to protect siRNA from the harsh environment of the gastrointestinal tract and target its delivery to inflamed intestinal tissue. Here, we present a delivery vehicle for siRNA, termed thioketal nanoparticles (TKNs), that can localize orally delivered siRNA to sites of intestinal inflammation, and thus inhibit gene expression in inflamed intestinal tissue. TKNs are formulated from a polymer, poly-(1,4-phenyleneacetone dimethylene thioketal), that degrades selectively in response to reactive oxygen species (ROS). Therefore, when delivered orally, TKNs release siRNA in response to the abnormally high levels of ROS specific to sites of intestinal inflammation. Using a murine model of ulcerative colitis, we demonstrate that orally administered TKNs loaded with siRNA against the proinflammatory cytokine tumour necrosis factor-alpha (TNF-α) diminish TNF-α messenger RNA levels in the colon and protect mice from ulcerative colitis.

Complex foraging polymorphism in bluegill sunfish

The bluegill sunfish (Lepomis macrochirus) is considered a generalist predator, adept at feeding in both the littoral and open-water habitats of North American freshwater lakes. We demonstrate adaptive intraspecific variation in morphology and foraging behaviors within single lakes. This variation appears to make individual fish specialized for feeding in either the littoral or open-water habitat. Discovery of a complex polymorphism in such a well-studied species suggests that adaptive variation may be more common than is currently perceived.

Social semantics: toward a genuine pluralism in the study of social behaviour

Pluralism is the coexistence of equivalent theoretical frameworks, either because they are historically entrenched or because they achieve separate insights by viewing the same process in different ways. A recent article by West et al. [Journal of Evolutionary Biology (2007) vol. 20, 415-432] attempts to classify the many equivalent frameworks that have been developed to study the evolution of social behaviour. This article addresses shortcomings in the West et al.'s article, especially with respect to multilevel selection, in a common effort to maximize the benefits of pluralism while minimizing the semantic costs.

Use of dry powder inhalers in COPD

INTRODUCTION

This was a study of 30 chronic obstructive pulmonary disease (COPD) patients to assess the ease of use and preference of four dry powder inhalers -- accuhaler, aerolizer, handihaler, turbohaler -- the accuhaler and turbohaler are multidose devices, whereas the aerolizer and handihaler are single dose devices.

METHOD

None of the subjects had previous experience of dry powder inhalers. The correct technique for each inhaler was divided into 12 steps including one critical step that if not performed would result in no drug delivery. Subjects were shown the correct technique for each inhaler in a random order and were assessed immediately and 1 h later. Each subject was asked to rank the four devices for preference and ease of use, as well as to assess how comfortable it felt to inhale through the device using a visual analogue scale.

RESULTS

The numbers of perfect scores were not significantly different between devices, but the number of fatal errors that would result in no drug delivery was significantly more common in single dose devices (p < 0.01). There were significant differences in the rankings of each device (Friedman test, p < 0.005) with the turbohaler being ranked first most often and the handihaler last. The turbohaler scored highest for comfort of inhalation and the accuhaler lowest, but differences were small.

CONCLUSIONS

In COPD patients starting on dry powder inhalers, multidose devices appear to be preferred, have fewer problems and are easier to use effectively.

Chemical potentials and phase equilibria of Lennard-Jones mixtures: a self-consistent integral equation approach

We explore the vapor-liquid phase behavior of binary mixtures of Lennard-Jones-type molecules where one component is supercritical, given the system temperature. We apply the self-consistency approach to the Ornstein-Zernike integral equations to obtain the correlation functions. The consistency checks include not only thermodynamic consistencies (pressure consistency and Gibbs-Duhem consistency), but also pointwise consistencies, such as the zero-separation theorems on the cavity functions. The consistencies are enforced via the bridge functions in the closure which contain adjustable parameters. The full solution requires the values of not only the monomer chemical potentials, but also the dimer chemical potentials present in the zero-separation theorems. These are evaluated by the direct chemical-potential formula [L. L. Lee, J. Chem. Phys. 97, 8606 (1992)] that does not require temperature nor density integration. In order to assess the integral equation accuracy, molecular-dynamics simulations are carried out alongside the states studied. The integral equation results compare well with simulation data. In phase calculations, it is important to have pressure consistency and valid chemical potentials, since the matching of phase boundaries requires the equality of the pressures and chemical potentials of both the liquid and vapor phases. The mixtures studied are methane-type and pentane-type molecules, both characterized by effective Lennard-Jones potentials. Calculations on one isotherm show that the integral equation approach yields valid answers as compared with the experimental data of Sage and Lacey. To study vapor-liquid phase behavior, it is necessary to use consistent theories; any inconsistencies, especially in pressure, will vitiate the phase boundary calculations.

Replica Ornstein-Zernike self-consistent theory for mixtures in random pores

We present a self-consistent integral equation theory for a binary liquid in equilibrium with a disordered medium, based on the formalism of the replica Ornstein-Zernike (ROZ) equations. Specifically, we derive direct formulas for the chemical potentials and the zero-separation theorems (the latter provide a connection between the chemical potentials and the fluid cavity distribution functions). Next we solve a modified-Verlet closure to ROZ equations, which has built-in parameters that can be adjusted to satisfy the zero-separation theorems. The degree of thermodynamic consistency of the theory is also kept under control. We model the binary fluid in random pores as a symmetrical binary mixture of nonadditive hard spheres in a disordered hard-sphere matrix and consider two different values of the nonadditivity parameter and of the quenched matrix packing fraction, at different mixture concentrations. We compare the theoretical structural properties as obtained through the present approach with Percus-Yevick and Martinov-Sarkisov integral equation theories, and assess both structural and thermodynamic properties by performing canonical standard and biased grand canonical Monte Carlo simulations. Our theory appears superior to the other integral equation schemes here examined and provides reliable estimates of the chemical potentials. This feature should be useful in studying the fluid phase behavior of model adsorbates in random pores in general.

Extra-articular migration of the patellar component following total knee arthroplasty

Complications related to patellar resurfacing are well recognized. We present an unusual case where the patellar button, after separating from the patella, extruded from the knee joint to lie within the extra-articular soft tissues.

One-step purification of recombinant proteins using a nanomolar-affinity streptavidin-binding peptide, the SBP-Tag

We describe the use of the SBP-tag, a new streptavidin-binding peptide, for both the one-step purification and the detection of recombinant proteins. The SBP-tag sequence is 38 amino acids long and binds to streptavidin with an equilibrium dissociation constant of 2.5 nM. We demonstrate that a single-step purification of SBP-tagged proteins from bacterial extract yields samples that are more pure than those purified using maltose-binding protein or the His-tag. The capacity of the immobilized streptavidin used to purify SBP-tagged proteins is about 0.5 mg per milliliter of matrix, which is high enough to isolate large quantities of proteins for further study. Also, the elution conditions from the streptavidin column are very mild and specific, consisting of the wash buffer plus biotin. This combination of high-affinity, high-yield, mild elution conditions, and simplicity of use makes the SBP-tag suitable for high-throughput protein expression/purification procedures, including robotically manipulated protocols with microtiter plates. Additionally, the SBP-tag can be used for detection since a wide variety of streptavidin-conjugated fluorescent and enzymatic systems are commercially available. We also present a new, rapid, method for the measurement of protein-protein, protein-peptide, or protein-small molecule equilibrium dissociation constants that require as little as 1 fmol of labeled protein. We call this method the spin-filter binding inhibition assay.

High Risk Drug Use Sites, Meaning and Practice: Implications for AidS Prevention

A study of drug use locations in Hartford, CT, Is designed to understand the environmental and social conditions within “high risk sites” where drug users inject drugs or smoke crack, In order to develop AIDS prevention models that build upon the physical and social organization of these locations. The study assesses high-risk sites characterized on the basis of type of location or structure, presence and strength of gatekeepers, and presence and strength of HIV prevention opportunities and pressures. A combination of ethnographic, epidemiological, and social network methods are used to document the characteristics, social organization, natural history, and dynamics of these sites, the network relations of site users, and the various opportunities for, or barriers to, on-site social-level HIV prevention intervention. This paper provides an overview of the study and presents preliminary findings, Including the degree to which drug injectors and crack smokers use specific types of sites in Hartford. The paper also discusses the ways these findings Inform development of on-site, type-specific and peer-led or structural HIV-prevention Interventions.

Random mutagenesis by PCR

Error-prone PCR (EP-PCR) is the method of choice for introducing random mutations into a defined segment of DNA that is too long to be chemically synthesized as a degenerate sequence. Using EP-PCR, the 5' and 3' boundaries of the mutated region may be defined by the choice of PCR primers. Accordingly, it is possible to mutagenize an entire gene or merely a segment of a gene. The average number of mutations per DNA fragment can be controlled as a function of the number of EP-PCR doublings performed. The EP-PCR technique described here is for a 400-bp sequence, and an Alternate Protocol is for a library. EP-PCR takes advantage of the inherently low fidelity of Taq DNA polymerase, which may be further decreased by the addition of Mn2+, increasing the Mg2+ concentration, and using unequal dNTP concentrations.

The use of mRNA display to select high-affinity protein-binding peptides

We report the use of "mRNA display," an in vitro selection technique, to identify peptide aptamers to a protein target. mRNA display allows for the preparation of polypeptide libraries with far greater complexity than is possible with phage display. Starting with a library of approximately 10(13) random peptides, 20 different aptamers to streptavidin were obtained, with dissociation constants as low as 5 nM. These aptamers function without the aid of disulfide bridges or engineered scaffolds, yet possess affinities comparable to those for monoclonal antibody-antigen complexes. The aptamers bind streptavidin with three to four orders of magnitude higher affinity than those isolated previously by phage display from lower complexity libraries of shorter random peptides. Like previously isolated peptides, they contain an HPQ consensus motif. This study shows that, given sufficient length and diversity, high-affinity aptamers can be obtained even from random nonconstrained peptide libraries. By engineering structural constraints into these ultrahigh complexity peptide libraries, it may be possible to produce binding agents with subnanomolar binding constants.

Religious groups as adaptive units

This essay provides a sketch of religion as a set of biologically and culturally evolved adaptations that enable human groups to function as adaptive units. Recent developments in evolutionary biology make such a group-level interpretation of religion more plausible than in the past. A brief survey of relevant concepts is followed by a relatively detailed interpretation of Calvinism as a religious system in which explicit behavioral prescriptions, beliefs about God and his relationship with people, and numerous social control mechanisms combined to change the city of Geneva from a collection of warring factions to a unified population.

Artificial selection of microbial ecosystems for 3-chloroaniline biodegradation

We present a method for selecting entire microbial ecosystems for bioremediation and other practical purposes. A population of ecosystems is established in the laboratory, each ecosystem is measured for a desired property (in our case, degradation of the environmental pollutant 3-chloroaniline), and the best ecosystems are used as 'parents' to inoculate a new generation of 'offspring' ecosystems. Over many generations of variation and selection, the ecosystems become increasingly well adapted to produce the desired property. The procedure is similar to standard artificial selection experiments except that whole ecosystems, rather than single individuals, are the units of selection. The procedure can also be understood in terms of complex system theory as a way of searching a vast combinatorial space (many thousands of microbial species and many thousands of genes within species) for combinations that are especially good at producing the desired property. Ecosystem-level selection can be performed without any specific knowledge of the species that comprise the ecosystems and can select ensembles of species that would be difficult to discover with more reductionistic methods. Once a 'designer ecosystem' has been created by ecosystem-level selection, reductionistic methods can be used to identify the component species and to discover how they interact to produce the desired effect.

Artificial ecosystem selection

Artificial selection has been practiced for centuries to shape the properties of individual organisms, providing Darwin with a powerful argument for his theory of natural selection. We show that the properties of whole ecosystems can also be shaped by artificial selection procedures. Ecosystems initiated in the laboratory vary phenotypically and a proportion of the variation is heritable, despite the fact that the ecosystems initially are composed of thousands of species and millions of individuals. Artificial ecosystem selection can be used for practical purposes, illustrates an important role for complex interactions in evolution, and challenges a widespread belief that selection is most effective at lower levels of the biological hierarchy.

In vitro selection of functional nucleic acids

In vitro selection allows rare functional RNA or DNA molecules to be isolated from pools of over 10(15) different sequences. This approach has been used to identify RNA and DNA ligands for numerous small molecules, and recent three-dimensional structure solutions have revealed the basis for ligand recognition in several cases. By selecting high-affinity and -specificity nucleic acid ligands for proteins, promising new therapeutic and diagnostic reagents have been identified. Selection experiments have also been carried out to identify ribozymes that catalyze a variety of chemical transformations, including RNA cleavage, ligation, and synthesis, as well as alkylation and acyl-transfer reactions and N-glycosidic and peptide bond formation. The existence of such RNA enzymes supports the notion that ribozymes could have directed a primitive metabolism before the evolution of protein synthesis. New in vitro protein selection techniques should allow for a direct comparison of the frequency of ligand binding and catalytic structures in pools of random sequence polynucleotides versus polypeptides.

Population viscosity and the evolution of altruism

The term population viscosity refers to limited dispersal, which increases the genetic relatedness of neighbors. This effect both supports the evolution of altruism by focusing the altruists' gifts on relatives of the altruist, and also limits the extent to which altruism may emerge by exposing clusters of altruists to stiffer local competition. Previous analyses have emphasized the way in which these two effects can cancel, limiting the viability of altruism. These papers were based on models in which total population density was held fixed. We present here a class of models in which population density is permitted to fluctuate, so that patches of altruists are supported at a higher density than patches of non-altruists. Under these conditions, population viscosity can support the selection of both weak and strong altruism.

Constructing high complexity synthetic libraries of long ORFs using in vitro selection

We present a method that can significantly increase the complexity of protein libraries used for in vitro or in vivo protein selection experiments. Protein libraries are often encoded by chemically synthesized DNA, in which part of the open reading frame is randomized. There are, however, major obstacles associated with the chemical synthesis of long open reading frames, especially those containing random segments. Insertions and deletions that occur during chemical synthesis cause frameshifts, and stop codons in the random region will cause premature termination. These problems can together greatly reduce the number of full-length synthetic genes in the library. We describe a strategy in which smaller segments of the synthetic open reading frame are selected in vitro using mRNA display for the absence of frameshifts and stop codons. These smaller segments are then ligated together to form combinatorial libraries of long uninterrupted open reading frames. This process can increase the number of full-length open reading frames in libraries by up to two orders of magnitude, resulting in protein libraries with complexities of greater than 10(13). We have used this methodology to generate three types of displayed protein library: a completely random sequence library, a library of concatemerized oligopeptide cassettes with a propensity for forming amphipathic alpha-helical or beta-strand structures, and a library based on one of the most common enzymatic scaffolds, the alpha/beta (TIM) barrel.

Kinetics of selenium incorporation into tissues of female mallard ducks

Selenium is essential for both mammalian and avian species, although its metabolism in birds has been less thoroughly studied. Little information has been available on the kinetics of selenium in birds, especially as it relates to the teratogenicity seen in waterfowl consuming excessive amounts. This study describes the pharmacokinetics of small amounts of 75Se as selenious acid injected into female mallard ducks. Labeled selenium was injected into a wing vein of restrained animals and tissues taken at five different time points up to 24 h post-injection. Selenium levels as percent of injected dose were determined in liver, kidney, heart, lung, adrenals, thyroid, spleen, pancreas, ovaries, intestine, muscle and plasma. Estimates of kinetic parameters (uptake and elimination rates, time of maximum concentration and maximum concentration) were obtained with a non-linear kinetics computer program (PCNONLIN, SCI Software, Lexington, KY). Results showed four basic patterns of distribution, uptake and elimination. Visceral tissues exhibited a triphasic pattern with a rapid rise, a decline followed by a distinctive increase in levels between the last two time points. Brain uptake was continuous over the 24 h. Plasma rose rapidly and then declined to a constant level. The ovaries as a tissue of interest relating to the teratogenic effects of selenium showed the greatest relative increase at 24 h, suggesting kinetic mechanisms consistent with a pathway that might lead to accumulation of toxic levels and teratogenic effects during embryo development.

Direct regulation of rhodopsin 1 by Pax-6/eyeless in Drosophila: evidence for a conserved function in photoreceptors

Pax-6 is a transcription factor containing both a homeodomain (HD) and a Paired domain (PD). It functions as an essential regulator of eye development in both Drosophila and vertebrates, suggesting an evolutionarily conserved origin for different types of metazoan eyes. Classical morphological and phylogenetic studies, however, have concluded that metazoan eyes have evolved many times independently. These apparently contradictory findings may be reconciled if the evolutionarily ancient role of Pax-6 was to regulate structural genes (e.g., rhodopsin) in primitive photoreceptors, and only later did it expand its function to regulate the morphogenesis of divergent and complex eye structures. In support of this, we present evidence that eyeless (ey), which encodes the Drosophila homolog of Pax-6, directly regulates rhodopsin 1 (rh1) expression in the photoreceptor cells. We detect ey expression in both larval and adult terminally differentiated photoreceptor cells. We show that the HD of Ey binds to a palindromic HD binding site P3/RCS1 in the rh1 promoter, which is essential for rh1 expression. We further demonstrate that, in vivo, P3/RCS1 can be replaced by binding sites specific for the PD of Ey. P3/RCS1 is conserved in the promoters of all Drosophila rhodopsin genes as well as in many opsin genes in vertebrates. Mutimerized P3 sites in front of a basal promoter are able to drive the expression of a reporter gene in all photoreceptors. These results suggest that Pax-6/Ey directly regulates rhodopsin 1 gene expression by binding to the conserved P3/RCS1 element in the promoter.

CD18 antibody treatment limits early myocardial reperfusion injury after initial leukocyte deposition

Following myocardial ischemia, initial reperfusion with whole blood impairs the recovery of ventricular function. The exact mechanisms underlying early myocardial reperfusion injury are not clear, but leukocytes play an important role. In this study, we tested if treating the initial blood reperfusate with a monoclonal antibody (CL26) against the leukocyte adhesion protein (CD18 would reduce the leukocyte contribution to early reperfusion injury. We reasoned that blocking CD18 would reduce the initial retention of leukocytes in the heart and thereby limit the inflammatory response. Rat hearts were isolated and perfused at constant flow with a red cell-rich solution (K2RBC). The perfusate was not recirculated. Baseline measures were made of coronary flow, perfusion pressure, and ventricular pump function. No-flow, normothermic ischemia was induced for 30 min, followed immediately by reperfusion, at the preischemic flowrate, with diluted whole blood (DWB, treated with either vehicle or CL26). Reperfusion was continued with K2RBC for 40 min more, during which postischemic measures were made. We found that the cardiac retention of leukocytes was not significantly different for the two groups, nor were the recoveries of ventricular function. Later in reperfusion (R35), the coronary blood flowrate and the coronary vascular resistances were not different; however, the recoveries of ventricular pump function were significantly different (+dP/dt @ R35 (%Pre-I): Vehicle: 27 +/- 9% (n = 8); CL26: 51 +/- 6% (n = 7); P < 0.05). Also, at R35, the voltage required to capture and pace the vehicle-treated hearts was significantly greater than the voltage required to pace the CL26 hearts (P < 0.05). Because the coronary flowrate and leukocyte retention were similar for both groups, the improved recovery observed in the CL26-treated group was not due to either improved flow or to reduced leukocyte retention. Rather, the findings suggest that the beneficial effect of antibody treatment was to attenuate step(s) in the acute inflammatory response that occurred after the initial deposition of leukocytes in the heart.

Conservation and diversification in homeodomain-DNA interactions: a comparative genetic analysis

Nearly all metazoan homeodomains (HDs) possess DNA binding targets that are related by the presence of a TAAT sequence. We use an in vitro genetic DNA binding site selection assay to refine our understanding of the amino acid determinants for the recognition of the TAAT site. Superimposed upon the conserved ability of metazoan HDs to recognize a TAAT core is a difference in their preference for the bases that lie immediately 3' to it. Amino acid position 50 of the HD has been shown to discriminate among these base pairs, and structural studies have suggested that water-mediated hydrogen bonds and van der Waals contacts underlie for this ability. Here, we show that each of six amino acids tested at position 50 can confer a distinct DNA binding specificity.

Pentoxifylline reduces leukocyte retention in the coronary microcirculation early in reperfusion following ischemia

Using direct visualization techniques, we recently confirmed earlier histologic studies that leukocytes accumulate primarily in the coronary capillaries of ischemic hearts during early reperfusion. The purpose of this study was to determine if pentoxifylline (PTX) would reduce leukocyte trapping in postischemic hearts. Isolated rat hearts were subjected to 30 min of 37 degrees C, no-flow ischemia. Hearts were initially reperfused with diluted whole blood containing fluorescent leukocytes. At 5, (R5), 20, and 35 min of reperfusion, the deposition of leukocytes in the coronary capillaries and venules was observed directly using intravital fluorescence microscopy. Three groups were studied: a non-ischemic control group (group I) and postischemic groups reperfused with diluted whole blood treated with vehicle group II or PTX (5 mM; group III). Postischemic reperfusion with unactivated blood caused a significant trapping of leukocytes in coronary capillaries throughout reperfusion (R5, group I = 2.0 +/- 0.3 vs. group II = 5.7 +/- 0.6 leukocytes/capillary field, p < 0.05). The addition of PTX reduced capillary leukocyte trapping below control values throughout reperfusion (R5, group III = 1.6 +/- 0.2 leukocytes/capillary field, p < 0.05). At R5, there was no statistically significant difference in leukocyte accumulation in venules for all groups (group I = 1.5 +/- 0.6, group II = 3.2 +/- 0.4, group III = 3.3 +/- 0.4 leukocytes/100 microns venule). During the reperfusion period, leukocyte persistence in the capillaries of postischemic hearts (36%) was greater than in the venules (13%). These data indicate that early in reperfusion after myocardial ischemia, leukocyte trapping occurs primarily in the coronary capillaries. PTX reduced early leukocyte trapping in the capillaries. The results also demonstrate that during reperfusion, the mechanisms affecting capillary retention are more persistent than those in the venule. These findings suggest that attempts to attenuate the damaging potential of early leukostasis in capillaries consider the biophysical properties of the leukocyte.

Machiavellianism: a synthesis of the evolutionary and psychological literatures

Manipulative strategies of social conduct (Machiavellianism) have been studied by both psychologists and evolutionary biologists. The authors use the psychological literature as a database to test evolutionary hypotheses about the adaptive advantages of manipulative social behavior. Machiavellianism does not correlate with general intelligence and does not consistently lead to real-world success. It is best regarded as 1 of several social strategies, broadly similar to the "defect" strategy of evolutionary game theory, which is successful in some situations but not others. In general, human evolutionary psychology and evolutionary game theory provide useful frameworks for thinking about behavioral strategies, such as Machiavellianism, and identify a large number of specific hypotheses that have not yet been tested by personality and social psychologists.

Early in reperfusion following myocardial ischemia, leukocyte activation is necessary for venular adhesion but not capillary retention

OBJECTIVE

The pathobiology of leukocyte sequestration in the coronary microcirculation following ischemia is unclear. We examined the location(s) and persistence of leukocyte sequestration of unactivated and preactivated blood in the coronary microcirculation early during reperfusion following ischemia.

METHODS

Isolated rat hearts were subjected to 30 min of 37 degrees C, no-flow ischemia. Hearts were initially reperfused with diluted whole blood containing fluorescent leukocytes (DWB*). At 5, 20, and 35 min of reperfusion (R), the deposition of leukocytes in the coronary capillaries and venules was observed directly using intravital fluorescence microscopy. Four groups were studied: a nonischemic control group (Gr I), and postischemic groups reperfused with DWB* treated with vehicle (Gr II) or preactivated with 10(-8) M N-formylmethionyl-leucyl-phenylalanine (fMLP) (Gr III) or 10(-6) M fMLP (Gr IV).

RESULTS

At R5, postischemic reperfusion with unactivated blood caused a significant trapping of leukocytes in coronary capillaries (Gr I = 2.2 +/- 0.4 versus Gr II = 5.6 +/- 0.6 leukocytes per capillary field, P < 0.05). Hearts in Gr IV exhibited significantly greater leukocyte retention in capillaries compared to all other groups at R5 (R5, Gr IV = 8.8 leukocytes per capillary field, P < 0.05) and at R35. At R5, although more leukocytes were observed adhered to the venules in Gr II compared to Gr I, the difference was not statistically significant (Gr I = 1.7 +/- 0.7 versus Gr II = 3.4 +/- 0.5 leukocytes per 100 microns venule, P = 0.23). DWB* preactivated with the lower concentration of fMLP (10(-8) M) resulted in a significant increase in venular leukocyte adhesion at R5 compared to Gr I and Gr II (Gr III 6.1 +/- 0.5, P < 0.05). After 35 min of reperfusion, a greater percentage of leukocytes remained in the capillaries than in the venules.

CONCLUSIONS

These direct observations suggest that early in reperfusion after ischemia, both leukocyte and endothelial activation are necessary for venular adhesion, but that ischemia-induced coronary microvascular alterations are sufficient to promote leukocyte retention in coronary capillaries. These results also indicate that during 35 min of reperfusion, the degree of leukocyte washout is greater in the venules than in the capillaries. These results suggest that the mechanisms contributing to leukocyte retention early in reperfusion following myocardial ischemia are, indeed, different in the capillaries and venules and that the mechanisms affecting retention in capillaries are more persistent than those in the venules.

Left ventricular function after extended hypothermic preservation of the heart is dependent on functional coronary capillarity

BACKGROUND

A growing body of knowledge has led to the hypothesis that injury to the microcirculation during hypothermic myocardial preservation may result in decreased contractility of hearts upon reperfusion.

METHODS AND RESULTS

To test this hypothesis, we examined the relationship between no-reflow and left ventricular function after hypothermic cardiac preservation after reperfusion with solutions containing dilute whole blood (DWB) or washed red blood cells (K2RBC). Rat hearts were arrested with high-potassium cardioplegia, then flushed and stored for 6 hours in low-potassium cardioplegia at 4 degrees C. Hearts were reperfused at a constant flow rate (4 mL/min) with K2RBC for 60 minutes (group 1, n = 5) or DWB for 7 minutes followed by 53 minutes of K2RBC (group 2, n = 5). Left ventricular developed pressure (LVDP) was measured with an intraventricular balloon. Immediately after functional assessment, hearts were perfused with an india ink solution to mark flow, then glutaraldehyde. Morphometric techniques were used to determine the degree of capillary compression [delta d(c)], perfused capillary number per fiber area [QA(0)P], and perfused capillary surface area per fiber volume [Sv(c,f)P]. Capillaries were moderately compressed in both groups after reperfusion (group 1, 19 +/- 1%; group 2, 20 +/- 1%). QA(0)P and Sv(c,f)P were highly correlated with delta d(c) in hearts reperfused with K2RBC (r = .92 and r = .92; P < .01). Although statistically significant, the correlation was not as strong in DWB-reperfused hearts (r = .66 and r = .67; P < .05). LVDP was correlated to QA(0)P and Sv(c,f)P (r = .86 and r = .87, respectively) for groups 1 and 2.

CONCLUSIONS

The weaker correlation between capillary perfusion and capillary compression in DWB-reperfused hearts suggests that factors other than compression contribute to no-reflow after hypothermic preservation. Regardless of the composition of the reperfusate, recovery of left ventricular function after hypothermic ischemia is directly related to coronary capillary perfusion upon reperfusion.