RBCs Regulate Platelet Function and Hemostasis under Shear Conditions through Biophysical and Biochemical Means.

Red blood cells (RBCs) have been hypothesized to support hemostasis by facilitating platelet margination and releasing platelet-activating factors such as adenosine diphosphate (ADP). Significant knowledge gaps remain regarding how RBCs influence platelet function, especially in (patho)physiologically relevant hemodynamic conditions. Here we present results showing how RBCs affect platelet function and hemostasis in conditions of anemia, thrombocytopenia, and pancytopenia, and how the biochemical and biophysical properties of RBCs regulate platelet function at the blood-vessel wall interface and in the fluid phase under flow conditions. We found that RBCs promoted platelet deposition to collagen under flow conditions in moderate (50  103/L) but not severe (10  103/L) thrombocytopenia in vitro. Reduction in hematocrit by 45% led to increased bleeding in mice with hemolytic anemia. In contrast, bleeding diathesis was observed in mice with a 90% but not with a 60% reduction in platelet counts. RBC transfusion improved hemostasis by enhancing fibrin clot formation at the site of vascular injury in mice with severe pancytopenia induced by total body irradiation. Altering membrane deformability changed the ability of RBCs to promote platelet aggregation. RBC-derived ADP contributed to platelet activation and aggregation in vitro under pathologically high shear stresses, as observed in patients supported by left ventricular assist devices. These findings demonstrate that RBCs support platelet function and hemostasis through multiple mechanisms, both at the blood-vessel wall interface and in the fluidic phase of circulation.

Hyperbaric treatment of platelets is comparable to cold storage alone over 14 days.

BACKGROUND: Platelets stored at room temperature (22-24°C) for transfusion purposes have a shelf life of 5-7 days, or 72 h when stored refrigerated (1-6°C). The limited shelf life of platelet products severely compromises platelet inventory. We hypothesized that cold storage of platelets in 100% plasma using xenon gas under high pressure would extend shelf life to 14 days. STUDY DESIGN AND METHODS: Double apheresis platelet units were collected and split equally between two bags. One unit was placed in a hyperbaric chamber, pressurized to 4 bars with a xenon/oxygen gas mixture, and placed in a refrigerator for 14 days (Xe). The remaining unit was aliquoted into mini-bags (10 ml) for storage at room temperature (RTP) or in cold (CSP). Samples were assayed on days 5 (RTP) or 14 (Xe and CSP) for count, metabolism, clot strength, platelet aggregation, and activation markers. RESULTS: The platelet count in Xe samples was lower than that of RTP but significantly higher than CSP. Despite similar levels of glucose and lactate, the pH of Xe samples was significantly lower than CSP. Glycoprotein expression was better preserved by Xe storage compared to CSP, but no differences in activation were observed. Thromboelastography and aggregometry results were comparable between all groups. DISCUSSION: Cold storage of platelets in plasma with hyperbaric xenon provides no significant improvement in platelet function over cold storage alone. The use of a hyperbaric chamber and the slow off-gassing of Xe-stored units complicate platelet storage and delivery logistics.

Nicotine Affects Murine Aortic Stiffness and Fatigue Response During Supraphysiological Cycling.

Nicotine exposure is a major risk factor for several cardiovascular diseases. Although the deleterious effects of nicotine on aortic remodeling processes have been studied to some extent, the biophysical consequences are not fully elucidated. In this investigation, we applied quasi-static and dynamic loading to quantify ways in which exposure to nicotine affects the mechanical behavior of murine arterial tissue. Segments of thoracic aortas from C57BL/6 mice exposed to 25 mg/kg/day of subcutaneous nicotine for 28 days were subjected to uniaxial tensile loading in an open-circumferential configuration. Comparing aorta segments from nicotine-treated mice relative to an equal number of control counterparts, stiffness in the circumferential direction was nearly twofold higher (377 kPa ± 165 kPa versus 191 kPa ± 65 kPa, n = 5, p = 0.03) at 50% strain. Using a degradative power-law fit to fatigue data at supraphysiological loading, we observed that nicotine-treated aortas exhibited significantly higher peak stress, greater loss of tension, and wider oscillation band than control aortas (p ≤ 0.01 for all three variables). Compared to simple stress relaxation tests, fatigue cycling is shown to be more sensitive and versatile in discerning nicotine-induced changes in mechanical behavior over many cycles. Supraphysiological fatigue cycling thus may have broader potential to reveal subtle changes in vascular mechanics caused by other exogenous toxins or pathological conditions.

Cold-stored platelets have better preserved contractile function in comparison with room temperature-stored platelets over 21 days.

Although it is well established that transfusion of platelets in cases of severe bleeding reduces mortality, the availability of platelets is hampered by harsh restrictions on shelf life due to elevated risks of microbial contamination and functional losses with room temperature-stored platelets (RTP) kept at 22°C. In contrast, many recent studies have shown that 4°C cold-stored platelets (CSP) are able to overcome these shortcomings leading to the recent Food and Drug Administration licensure for 14-day stored CSP when conventional platelets are unavailable. This work expands the evidence supporting superiority of CSP function by assaying the less explored platelet-mediated clot retraction of RTP and CSP in either autologous plasma (AP) or platelet additive solution (PAS) for up to 21 days. The results demonstrate that CSP have better preservation of contractile function, exhibiting retraction for up to 21 days in both AP and PAS and forming highly ordered fibrin scaffolds similar to those of fresh platelets. In contrast, RTP stored in AP showed impaired contractile function by Day 5 with no retraction after 10 days, whereas PAS-stored RTP retained contractile function for up to 21 days. Collectively, these findings support extended storage of CSP and suggest that storage in PAS can mitigate functional losses in RTP.

Cold storage of platelets in platelet additive solution maintains mitochondrial integrity by limiting initiation of apoptosis-mediated pathways.

BACKGROUND: Cold storage of platelets in plasma maintains hemostatic function and is an attractive alternative to room temperature platelets (RTPs). We have recently shown that functional differences between cold-stored platelets (CSPs) and RTPs after 5-day storage are associated with mitochondrial respiration and that CSPs in platelet (PLT) additive solution (PAS) can maintain hemostatic function for at least 15 days. STUDY DESIGN AND METHODS: This study tested the hypothesis that cold storage in PAS preserves mitochondrial integrity by reducing PLT apoptosis. CSPs and RTPs in plasma or PAS were stored and assayed for up to 15 days for mitochondrial function and integrity, mitochondrial-associated mRNA transcript expression, apoptotic proteins, and apoptotic flow cytometry metrics. RESULTS: CSP preserved mitochondria-associated mRNA comparable to baseline levels, improved mitochondrial respiration, and minimized depolarization to Day 15. Additionally, CSPs had minimal induction of caspases, preservation of plasma membrane integrity, and low expression of pro-apoptotic Bax. Storage in PAS appeared to be protective for RTPs in some parameters and enhanced the effects of CSPs. CONCLUSION: Mitochondrial function and molecular analyses defined CSP priming as distinctly different from the well-documented RTP storage lesion. While current blood bank storage at room temperature is limited to 5 to 7 days, refrigeration and storage in PAS for up to 15 days may represent an opportunity to enhance inventories and access to PLT hemostatic support for bleeding patients.

Design Considerations and Assays for Hemocompatibility of FDA-Approved Nanoparticles.

Nanoparticles have numerous biomedical applications including, but not limited to, targeted drug delivery, diagnostic imaging, sensors, and implants for a wide range of diseases including cancer, diabetes, heart disease, and tuberculosis. Although the mode of delivery of the nanoparticles depends on the application and the disease, the nanoparticles are often in immediate contact with the systemic circulation either because of intravenous administration or their ability to enter the bloodstream with relative ease or their longer survival time in circulation. Once in circulation, the nanoparticles may elicit unintended hemostatic and inflammatory responses, and hence the design of nanoparticles for therapeutic applications should take broad hemocompatibility concerns into consideration. In this review, we present the principles underlying the structural and functional design of various classes of nanoparticles that are currently approved by the US Food and Drug Administration, categorize these particles based on their interactions with cardiovascular tissues and ensuing adverse events, and also describe various in vitro assays that may be used evaluate their hemocompatibility.

Influence of membrane cholesterol on monocyte chemotaxis.

Cholesterol content influences several important physiological functions due to its effect on membrane receptors. In this work, we tested the hypothesis that cellular cholesterol alters chemotactic response of monocytes to Monocyte Chemoattractant Protein-1 (MCP-1) due to their effect on the receptor, CCR2. We used Methyl-ß-cyclodextrin (MßCD) to alter the baseline cholesterol in human monocytic cell line THP-1, and evaluated their chemotactic response to MCP-1. Compared to untreated cells, cholesterol enrichment increased the number of monocytes transmigrated in response to MCP-1 while depletion had opposite effect. Using imaging flow cytometry, we established that these differences were due to alterations in expression levels, but not the surface distribution, of CCR2.

Cholesterol Regulates Monocyte Rolling through CD44 Distribution.

Cholesterol is an important risk factor of atherosclerosis, due to its active uptake by monocytes/macrophages. Monocyte recruitment from flowing blood to atherosclerotic foci is the key first step in the development of atherosclerosis. Cholesterol content alters cell membrane stiffness, and lateral lipid and protein diffusion. We hypothesized that cholesterol content will modulate the recruitment of monocytes to inflamed endothelial surface by altering the dynamics of adhesion receptors. We depleted or enriched the cellular cholesterol levels using methyl-ß-cyclodextran in freshly isolated human monocytes. We investigated the effect of these changes on the mechanics of monocyte rolling on E-selectin surfaces at 1 dyn/cm2 in microchannels. Using imaging flow cytometry and atomic force microscopy, we characterized the distribution of lipid rafts and the E-selectin counterreceptor CD44 on the monocyte surface. We observed that lower levels of cholesterol resulted in the uniform, CD44-mediated rolling of monocytes on the E-selectin-coated surfaces. We also observed that cells depleted of cholesterol had higher membrane fluidity, and more uniform distribution of CD44 counterreceptor, which resulted in smooth motion of the cells compared to cells enriched with cholesterol. This work demonstrates that cholesterol can modulate monocyte adhesion by regulating the receptor mobility, and our results provide insights into the biophysical regulation of inflammation for the better understanding of diseases like atherosclerosis and hypercholesterolemia.

Platelets stored at 4°C contribute to superior clot properties compared to current standard-of-care through fibrin-crosslinking.

Currently, platelets for transfusion are stored at room temperature (RT) for 5-7 days with gentle agitation, but this is less than optimal because of loss of function and risk of bacterial contamination. We have previously demonstrated that cold (4°C) storage is an attractive alternative because it preserves platelet metabolic reserves, in vitro responses to agonists of activation, aggregation and physiological inhibitors, as well as adhesion to thrombogenic surfaces better than RT storage. Recently, the US Food and Drug Administration clarified that apheresis platelets stored at 4°C for up to 72 h may be used for treating active haemorrhage. In this work, we tested the hypothesis that cold-stored platelets contribute to generating clots with superior mechanical properties compared to RT-stored platelets. Rheological studies demonstrate that the clots formed from platelets stored at 4°C for 5 days are significantly stiffer (higher elastic modulus) and stronger (higher critical stress) than those formed from RT-stored platelets. Morphological analysis shows that clot fibres from cold-stored platelets were denser, thinner, straighter and with more branch points or crosslinks than those from RT-stored platelets. Our results also show that the enhanced clot strength and packed structure is due to cold-induced plasma factor XIII binding to platelet surfaces, and the consequent increase in crosslinking.

Screening a Commercial Library of Pharmacologically Active Small Molecules against Staphylococcus aureus Biofilms.

It is now well established that bacterial infections are often associated with biofilm phenotypes that demonstrate increased resistance to common antimicrobials. Further, due to the collective attrition of new antibiotic development programs by the pharmaceutical industries, drug repurposing is an attractive alternative. In this work, we screened 1,280 existing commercially available drugs in the Prestwick Chemical Library, some with previously unknown antimicrobial activity, against Staphylococcus aureus, one of the commonly encountered causative pathogens of burn and wound infections. From the primary screen of the entire Prestwick Chemical Library at a fixed concentration of 10 µM, 104 drugs were found to be effective against planktonic S. aureus strains, and not surprisingly, these were mostly antimicrobials and antiseptics. The activity of 18 selected repurposing candidates, that is, drugs that show antimicrobial activity that are not already considered antimicrobials, observed in the primary screen was confirmed in dose-response experiments. Finally, a subset of nine of these drug candidates was tested against preformed biofilms of S. aureus We found that three of these drugs, niclosamide, carmofur, and auranofin, possessed antimicrobial activity against preformed biofilms, making them attractive candidates for repurposing as novel antibiofilm therapies.

Shear stress upregulates IL-1ß secretion by Chlamydia pneumoniae- infected monocytes.

Infectious agents are increasingly implicated in the development and progression of chronic inflammatory diseases. Several lines of evidence suggest that the common intracellular respiratory pathogen, Chlamydia pneumoniae contributes to the well-established risk factors of atherosclerosis but the exact mechanism is not well understood. It is believed that C. pneumoniae-infected monocytes travel from the lung to the atherosclerotic foci, during which the cells experience mechanical stimuli due to blood flow. In this work, we characterized the effect of physiological levels of shear stress on C. pneumoniae-infected human monocytes in an in vitro flow model. We found that a shear stress of 5 dyn/cm(2) enhanced the expression of pro-inflammatory cytokine IL-1ß only in infected, but not in uninfected, monocytes. We also found that this enhancement is due to the upregulation of IL-1ß gene expression due to shear stress. Our results demonstrate that mechanotransduction is an important, heretofore unaddressed, determinant of inflammatory response to an infection.

Effect of silver nanoparticle geometry on methicillin susceptible and resistant Staphylococcus aureus, and osteoblast viability.

Orthopedic implant failure as a result of bacterial infection affects approximately 0.5-5% of patients. These infections are often caused by Staphylococcus aureus which is capable of attaching and subsequently forming a biofilm on the implant surface, making it difficult to eradicate with systemic antibiotics. Further, with the emergence of antibiotic-resistant bacteria, alternative treatments are necessary. Silver nanoparticles have received much attention for their broad spectrum antibacterial activity which has been reported to be both size and shape dependent. The purpose of this study was therefore to evaluate the effect of three different geometries on their effect on microbial susceptibility as well as evaluate their effect on bone cell viability. Silver nanoparticles of spherical, triangular and cuboid shapes were synthesized by chemical reduction methods. The susceptibility of S. aureus and methicillin-resistant S. aureus was evaluated a 24 h period and determined using a colorimetric assay. Further, the viability of human fetal osteoblast (hFOB) cells in the presence of the silver nanoparticles was evaluated over a period of 7 days by AlmarBlue fluorescence assay. hFOB morphology was also evaluated by light microscopy imaging. Results indicated that silver nanoparticle geometry did not have an effect on microbiota susceptibility or hFOB viability. However, high concentrations of silver nanoparticles (0.5 nM) conferred significant susceptibility towards the bacteria and significantly reduced hFOB viability. It was also found that the hFOBs exhibited an increasingly reduced viability to lower silver nanoparticle concentrations with an increase in exposure time.

Monocytes mediate metastatic breast tumor cell adhesion to endothelium under flow.

Endothelial adhesion is necessary for the hematogenous dissemination of tumor cells. However, the metastatic breast tumor cell MDA-MB-231 does not bind to the endothelium under physiological flow conditions, suggesting alternate mechanisms of adhesion. Since monocytes are highly represented in the tumor microenvironment, and also bind to endothelium during inflammation, we hypothesized that the monocytes assist in the arrest of MDA-MB-231 on the endothelium. Using in vitro models of the dynamic shear environment of the vasculature, we show that TNF-α-activated THP1/primary human monocytes and MDA-MB-231 cells form stable aggregates, and that the monocytes in these aggregates mediate the adhesion of otherwise nonadherent MDA-MB-231 cells to inflamed endothelium under flow (55±2.4 vs. 1.7±0.82 at a shear stress of 0.5 dyn/cm(2), P<0.01). We also show that the hydrodynamic forces determine the size and orientation of aggregates adhered to the endothelium, and strongly favor the attachment of small aggregates with tumor cells downstream of flow (74-86% doublets at 0.5-2 dyn/cm(2), P<0.01). The 5-fold up-regulation of ICAM-1 on TNF-α-activated MDA-MB-231 cells through the Nf-κB pathway was found to be critical in MDA-MB-231-monocyte aggregation and endothelial adhesion. Our results demonstrate that, under inflammatory conditions, monocytes may serve to disseminate tumor cells through circulation, and the tumor-monocyte-endothelial axis may represent a new therapeutic target to reduce cancer metastasis.

Drug susceptibility of matrix-encapsulated Candida albicans nano-biofilms.

The rise in the use of biomedical devices and implants has seen a concomitant surge in the advent of device-related nosocomial (hospital-acquired) infections of bacterial and fungal origins. The most common nosocomial fungal infection is candidiasis caused mainly by Candida albicans biofilms. Candidiasis is associated with an unacceptably high mortality rate, and there is an urgent need for the discovery of new antifungal drugs that prevent or control biofilm formation. To this end, we recently developed an ultra-high-throughput microarray platform consisting of nano-scale biofilms of C. albicans encapsulated in collagen or alginate hydrogel matrices for antifungal drug screening. Here, we report that the choice of matrix influences the apparent susceptibility of C. albicans to the common antifungal drugs, amphotericin B, and caspofungin. While amphotericin B is equally effective against biofilms grown in collagen and alginate matrices, caspofungin is effective only against biofilms grown only in alginate, but not in collagen. We demonstrate differences in the distribution of the drugs in the two matrices may contribute to the susceptibility of C. albicans nano-biofilms. In a larger context, our results highlight the importance of the choice of matrix as a parameter in 3D cell encapsulation, and suggest a screening strategy to predict drug performance in vivo.

Overcoming antifungal resistance.

Fungal infections have become one of the major causes of morbidity and mortality in immunocompromised patients. Despite increased awareness and improved treatment strategies, the frequent development of resistance to the antifungal drugs used in clinical settings contributes to the increasing toll of mycoses. Although a natural phenomenon, antifungal drug resistance can compromise advances in the development of effective diagnostic techniques and novel antifungals. In this review, we will discuss the advent of cellular-micro- arrays, microfluidics, genomics, proteomics and other state-of-the art technologies in conquering antifungal drug resistance.

Clots reveal anomalous elastic behavior of fiber networks.

The adaptive mechanical properties of soft and fibrous biological materials are relevant to their functionality. The emergence of the macroscopic response of these materials to external stress and intrinsic cell traction from local deformations of their structural components is not well understood. Here, we investigate the nonlinear elastic behavior of blood clots by combining microscopy, rheology, and an elastic network model that incorporates the stretching, bending, and buckling of constituent fibrin fibers. By inhibiting fibrin cross-linking in blood clots, we observe an anomalous softening regime in the macroscopic shear response as well as a reduction in platelet-induced clot contractility. Our model explains these observations from two independent macroscopic measurements in a unified manner, through a single mechanical parameter, the bending stiffness of individual fibers. Supported by experimental evidence, our mechanics-based model provides a framework for predicting and comprehending the nonlinear elastic behavior of blood clots and other active biopolymer networks in general.

High-throughput screening of a collection of known pharmacologically active small compounds for identification of Candida albicans biofilm inhibitors.

Candida albicans is the most common etiologic agent of systemic fungal infections with unacceptably high mortality rates. The existing arsenal of antifungal drugs is very limited and is particularly ineffective against C. albicans biofilms. To address the unmet need for novel antifungals, particularly those active against biofilms, we have screened a small molecule library consisting of 1,200 off-patent drugs already approved by the Food and Drug Administration (FDA), the Prestwick Chemical Library, to identify inhibitors of C. albicans biofilm formation. According to their pharmacological applications that are currently known, we classified these bioactive compounds as antifungal drugs, as antimicrobials/antiseptics, or as miscellaneous drugs, which we considered to be drugs with no previously characterized antifungal activity. Using a 96-well microtiter plate-based high-content screening assay, we identified 38 pharmacologically active agents that inhibit C. albicans biofilm formation. These drugs were subsequently tested for their potency and efficacy against preformed biofilms, and we identified three drugs with novel antifungal activity. Thus, repurposing FDA-approved drugs opens up a valuable new avenue for identification and potentially rapid development of antifungal agents, which are urgently needed.

Enhanced shear-induced platelet aggregation due to low-temperature storage.

BACKGROUND: Refrigeration of platelets (PLTs) offers an attractive alternative to the currently practiced storage at room temperature since it may mitigate problems associated with bacterial contamination and extend storage lifetime. Refrigeration causes a number of biophysical and biochemical changes in PLTs and decreases PLT circulation time in vivo. However, the effect of refrigeration on PLT hemostatic functions under physiologic and pathophysiologic shear conditions has not been adequately characterized. STUDY DESIGN AND METHODS: Washed PLTs prepared from either fresh PLT-rich plasma (PRP) or PRP stored at 4°C for 2 days was mixed with exogenous von Willebrand factor (VWF) and fibrinogen and sheared in a cone-and-plate viscometer. PLT aggregation, activation, and VWF binding after shear and glycoprotein (GP) Ibα receptor expression and ristocetin-induced PLT agglutination were measured. RESULTS: PLTs stored at 4°C for 2 days aggregated significantly more than fresh PLTs particularly at high shear rates (10,000/sec), and this increase was independent of PLT concentration or suspension viscosity. Further, refrigerated PLTs showed a greater increase in GP Ibα-dependent PLT activation under shear and also bound more VWF than fresh PLTs. However, the GP Ibα expression levels as measured by three different antibodies were significantly lower in refrigerated PLTs than in fresh PLTs, and refrigeration resulted in a modest decrease in ristocetin-induced PLT agglutination. CONCLUSION: The combined results demonstrate that refrigeration increases PLT aggregation under high shear, but not static, conditions and also increases shear-induced VWF binding and PLT activation. Clinically, enhanced shear-induced PLT aggregation due to low temperature storage may be a beneficial strategy to prevent severe bleeding in trauma.

Primary hemostatic capacity of whole blood: a comprehensive analysis of pathogen reduction and refrigeration effects over time.

BACKGROUND: Whole blood (WB) has been used in combat since World War I as it is readily available and replaces every element of shed blood. Component therapy has become standard; however, recent military successes with WB resuscitation have revived the debate regarding wider WB use. Characterization of optimal WB storage is needed. We hypothesized that refrigeration preserves WB function and that a pathogen reduction technology (PRT) based on riboflavin and ultraviolet light has no deleterious effect over 21 days of storage. STUDY DESIGN AND METHODS: WB units were stored for 21 days either at 4°C or 22°C. Half of each temperature group underwent PRT, yielding four final treatment groups (n = 8 each): CON 4 (WB at 4°C); CON 22 (WB at 22°C); PRT 4 (PRT WB at 4°C); and PRT 22 (PRT WB at 22°C). Testing was at baseline, Days 1-7, 10, 14, and 21. Assays included coagulation factors; platelet activation, aggregation, and adhesion; and thromboelastography (TEG). RESULTS: Prothrombin time (PT) and partial thromboplastin time increased over time; refrigeration attenuated the effects on PT (p ≤ 0.009). Aggregation decreased over time (p ≤ 0.001); losses were attenuated by refrigeration (p ≤ 0.001). Refrigeration preserved TEG parameters (p ≤ 0.001) and PRT 4 samples remained within normal limits throughout the study. Refrigeration in combination with PRT inhibited fibrinolysis (p ≤ 0.001) and microparticle formation (p ≤ 0.031). Cold storage increased shear-induced platelet aggregation and ristocetin-induced platelet agglutination (p ≥ 0.032), as well as GPIb-expressing platelets (p ≤ 0.009). CONCLUSION: The in vitro hemostatic function of WB is largely unaffected by PRT treatment and better preserved by cold storage over 21 days. Refrigerated PRT WB may be suitable for trauma resuscitation. Clinical studies are warranted.

A low-cost, high-throughput microfluidic nano-culture platform for functional metagenomics.

Functional metagenomics is an attractive culture-independent approach for functional screening of diverse microbiomes to identify known and novel genes. Since functional screening can involve sifting through tens of thousands of metagenomic library clones, an easy high-throughput screening approach is desirable. Here, we demonstrate a proof-of-concept application of a low-cost, high-throughput droplet based microfluidic assay to the selection of antibiotic resistance genes from a soil metagenomic library. Metagenomic library members encapsulated in nanoliter volume water-in-oil droplets were printed on glass slides robotically, and cell growth in individual drops in the presence of ampicillin was imaged and quantified to identify ampicillin-resistant clones. From the hits, true positives were confirmed by sequencing and functional validation. The ease of liquid handling, ease of set-up, low cost, and robust workflow makes the droplet-based nano-culture platform a promising candidate for screening and selection assays for functional metagenomic libraries.