Mechanisms of cold-induced platelet actin assembly

Platelet dysfunction reversal with cold-stored vs room temperature-stored platelet transfusions

ABSTRACT

Platelets are stored at room temperature for 5 to 7 days (room temperature-stored platelets [RSPs]). Because of frequent and severe shortages, the US Food and Drug Administration recently approved up to 14-day cold-stored platelets (CSPs) in plasma. However, the posttransfusion function of CSPs is unknown and it is unclear which donors are best suited to provide either RSPs or CSPs. In this study, we sought to evaluate the posttransfusion platelet function and its predictors for platelets stored for the maximum approved storage times (7-day RSPs and 14-day CSPs) in healthy volunteers on acetylsalicylic acid (ASA). We conducted a randomized crossover study in 10 healthy humans. Individuals donated 1 platelet unit, stored at either 22°C or 4°C based on randomization. Before transfusion, participants ingested ASA to inhibit endogenous platelets. Transfusion recipients were tested for platelet function and lipid mediators. Platelet units were tested for lipid mediators only. A second round of transfusion with the alternative product was followed by an identical testing sequence. RSPs reversed platelet inhibition significantly better in αIIbβ3 integrin activation-dependent assays. In contrast, CSPs in recipients led to significantly more thrombin generation, which was independent of platelet microparticles. Lysophosphatidylcholine-O species levels predicted the procoagulant capacity of CSPs. In contrast, polyunsaturated fatty acid concentrations predicted the aggregation response of RSPs. In summary, we provide, to our knowledge, the first efficacy data of extended-stored CSPs in plasma. Our results suggest that identifying ideal RSP and CSP donors is possible, and pave the way for larger studies in the future. This trial is registered at www.ClinicalTrials.gov as #NCT0511102.

Cold temperature induces a TRPM8-independent calcium release from the endoplasmic reticulum in human platelets

The detection of temperature by the human sensory system is life-preserving and highly evolutionarily conserved. Platelets are sensitive to temperature changes and are activated by a decrease in temperature, akin to sensory neurons. However, the molecular mechanism of this temperature-sensing ability is unknown. Yet, platelet activation by temperature could contribute to numerous clinical sequelae, most importantly to reduced quality of ex vivo-stored platelets for transfusion. In this multidisciplinary study, we present evidence for the expression of the temperature-sensitive ion channel transient receptor potential cation channel subfamily member 8 (TRPM8) in human platelets and precursor cells. We found the TRPM8 mRNA and protein in MEG-01 cells and platelets. Inhibition of TRPM8 prevented temperature-induced platelet activation and shape change. However, chemical agonists of TRPM8 did not seem to have an acute effect on platelets. When exposing platelets to below-normal body temperature, we detected a cytosolic calcium increase which was independent of TRPM8 but was completely dependent on the calcium release from the endoplasmic reticulum. Because of the high interindividual variability of TRPM8 expression, a population-based approach should be the focus of future studies. Our study suggests that the cold response of platelets is complex and TRPM8 appears to play a role in early temperature-induced activation of platelets, while other mechanisms likely contribute to later stages of temperature-mediated platelet response.

Evaluating stored platelet shape change using imaging flow cytometry

Platelets are routinely stored at room temperature for 5-7 days before transfusion. Stored platelet quality is traditionally assessed by Kunicki's morphology score. This method requires extensive training, experience, and is highly subjective. Moreover, the number of laboratories familiar with this technique is decreasing. Cold storage of platelets has recently regained interest because of potential advantages such as reduced bacterial growth and preserved function. However, platelets exposed to cold temperatures change uniformly from a discoid to a spherical shape, reducing the morphology score outcomes to spheroid versus discoid during cooling. We developed a simpler, unbiased screening tool to measure temperature-induced platelet shape change using imaging flow cytometry. When reduced to two dimensions, spheres appear circular, while discs are detected on a spectrum from fusiform to circular. We defined circular events as having a transverse axis of >0.8 of the longitudinal axis and fusiform events ≤0.8 of the longitudinal axis. Using this assay, mouse and human platelets show a temperature and time-dependent, two-dimensional shape change from fusiform to circular, consistent with their three-dimensional change from discs to spheres. The method we describe here is a valuable tool for detecting shape change differences in response to agonists or temperature and will help screening for therapeutic measures to mitigate the cold-induced storage lesion.

Cold-stored platelets for acute bleeding in cardiac surgical patients: a narrative review

PURPOSE

Cold-stored platelets (CSP) are an increasingly active topic of international research. They are maintained at 1-6 °C, in contrast to standard room-temperature platelets (RTP) kept at 20-24 °C. Recent evidence suggests that CSP have superior hemostatic properties compared with RTP. This narrative review explores the application of CSP in adult cardiac surgery, summarizes the preclinical and clinical evidence for their use, and highlights recent research.

SOURCE

A targeted search of MEDLINE and other databases up to 24 February 2022 was conducted. Search terms combined concepts such as cardiac surgery, blood, platelet, and cold-stored. Searches of trial registries ClinicalTrials.gov and WHO International Clinical Trials Registry Platform were included. Articles were included if they described adult surgical patients as their population of interest and an association between CSP and clinical outcomes. References of included articles were hand searched.

PRINCIPAL FINDINGS

When platelets are stored at 1-6 °C, their metabolic rate is slowed, preserving hemostatic function for increased storage duration. Cold-stored platelets have superior adhesion characteristics under physiologic shear conditions, and similar or superior aggregation responses to physiologic agonists. Cold-stored platelets undergo structural, metabolic, and molecular changes which appear to "prime" them for hemostatic activity. While preliminary, clinical evidence supports the conduct of trials comparing CSP with RTP for patients with platelet-related bleeding, such as those undergoing cardiac surgery.

CONCLUSION

Cold-stored platelets may have several advantages over RTP, including increased hemostatic capacity, extended shelf-life, and reduced risk of bacterial contamination. Large clinical trials are needed to establish their potential role in the treatment of acutely bleeding patients.

Cold temperature induces a TRPM8-independent calcium release from the endoplasmic reticulum in human platelets

Platelets are sensitive to temperature changes and akin to sensory neurons, are activated by a decrease in temperature. However, the molecular mechanism of this temperature-sensing ability is unknown. Yet, platelet activation by temperature could contribute to numerous clinical sequelae, most importantly to reduced quality of ex vivo-stored platelets for transfusion. In this interdisciplinary study, we present evidence for the expression of the temperature-sensitive ion channel transient receptor potential cation channel subfamily member 8 (TRPM8) in human platelets and precursor cells. We found the TRPM8 mRNA and protein in MEG-01 cells and platelets. Inhibition of TRPM8 prevented temperature-induced platelet activation and shape change. However, chemical agonists of TRPM8 did not seem to have an acute effect on platelets. When exposing platelets to below-normal body temperature, we detected a cytosolic calcium increase which was independent of TRPM8 but was completely dependent on the calcium release from the endoplasmic reticulum. Because of the high interindividual variability of TRPM8 expression, a population-based approach should be the focus of future studies. Our study suggests that the cold response of platelets is complex and TRPM8 appears to play a role in early temperature-induced activation of platelets, while other mechanisms likely contribute to later stages of temperature-mediated platelet response.

Platelet count, temperature and pH value differentially affect hemostatic and immunomodulatory functions of platelets

Platelets are primarily recognized for their role in hemostasis, but also regulate immune responses by interacting with leukocytes. Their highly sensitive nature enables platelets to rapidly respond to micro-environmental changes, which is crucial under physiological condition but can jeopardize in vitro analyses. Thus, we tested how platelet count and changes in pH and temperatures, which are commonly experienced during inflammation and infection but also affected by ex vivo analyses, influence platelet-leukocyte interaction and immunomodulation. Reducing platelet count by up to 90 % slightly decreased platelet activation and platelet-leukocyte aggregate formation, but did not affect CD11b activation nor CD62L shedding of monocytes or neutrophils. Acidosis (pH 6.9) slightly elevated platelet degranulation and binding to innate leukocytes, though pH changes did not modulate leukocyte activation. While platelet responsiveness was higher at room temperature than at 37 °C, incubation temperature did not affect platelet-leukocyte aggregate formation. In contrast, platelet-mediated CD11b activation and CD62L expression increased with temperature. Our data thus demonstrate the importance of standardized protocols for sample preparation and assay procedure to obtain comparable data. Further, unspecific physiologic responses such as thrombocytopenia, acidosis or temperature changes may contribute to platelet dysfunction and altered platelet-mediated immunomodulation in inflammatory and infectious disease.

Rho GTPase Signaling in Platelet Regulation and Implication for Antiplatelet Therapies

Platelets play a vital role in regulating hemostasis and thrombosis. Rho GTPases are well known as molecular switches that control various cellular functions via a balanced GTP-binding/GTP-hydrolysis cycle and signaling cascade through downstream effectors. In platelets, Rho GTPases function as critical regulators by mediating signal transduction that drives platelet activation and aggregation. Mostly by gene targeting and pharmacological inhibition approaches, Rho GTPase family members RhoA, Rac1, and Cdc42 have been shown to be indispensable in regulating the actin cytoskeleton dynamics in platelets, affecting platelet shape change, spreading, secretion, and aggregation, leading to thrombus formation. Additionally, studies of Rho GTPase function using platelets as a non-transformed model due to their anucleated nature have revealed valuable information on cell signaling principles. This review provides an updated summary of recent advances in Rho GTPase signaling in platelet regulation. We also highlight pharmacological approaches that effectively inhibited platelet activation to explore their possible development into future antiplatelet therapies.

Platelet storage: Progress so far

There is a crucial need for platelet transfusion during an emergency-surgery and treatment of platelet disorders. The unavailability of donors has furthermore increased the demand for platelet storage. Platelets have limited shelf life due to bacterial contamination and storage lesions. Temperature, materials, oxygen availability, media, platelet processing and manufacturing methods influence the platelet quality and viability during storage. The conception of various platelet additive solutions along with the advent of plastic storage during the 1980s led to enormous developments in platelet storage strategies. Cold storage of platelets gained attention despite its inability to contribute to platelet survival post-transfusion as it offers faster haemostasis. Several developments in platelet storage strategies over the years have improved the quality and shelf-life of stored platelets. Despite the progress, the efficacy of platelets during storage beyond a week has not been achieved. Antioxidants as additives have been explored in platelet storage and have proven to enhance the efficacy of platelets during prolonged storage. However, the molecular interactions of antioxidants in platelets can provide a better understanding of their mechanism of action. Optimization of dosage concentrations of antioxidants is also a critical parameter to be considered as they tend to exhibit toxicity at certain levels. This review provides comprehensive insights into the critical factors affecting platelet storage and the evolution of platelet storage. It also emphasizes the role of antioxidants as additives in platelet storage solutions and their future prospects towards better platelet banking.

There and Back Again: The Once and Current Developments in Donor-Derived Platelet Products for Products for Hemostatic Therapy

Over 100 years ago, Duke transfused whole blood to a thrombocytopenic patient to raise the platelet count and prevent bleeding. Since then, platelet transfusions have undergone numerous modifications from whole blood-derived platelet-rich plasma to apheresis-derived platelet concentrates. Similarly, the storage time and temperature have changed. The mandate to store platelets for a maximum of 5-7 days at room temperature has been challenged by recent clinical trial data, ongoing difficulties with transfusion-transmitted infections, and recurring periods of shortages, further exacerbated by the COVID-19 pandemic. Alternative platelet storage approaches are as old as the first platelet transfusions. Cold-stored platelets may offer increased storage times (days) and improved hemostatic potential at the expense of reduced circulation time. Frozen (cryopreserved) platelets extend the storage time to years but require storage at -80 °C and thawing before transfusion. Lyophilized platelets can be powder-stored for years at room temperature and reconstituted within minutes in sterile water but are probably the least explored alternative platelet product to date. Finally, whole blood offers the hemostatic spectrum of all blood components but has challenges, such as ABO incompatibility. While we know more than ever before about the in vitro properties of these products, clinical trial data on these products are accumulating. The purpose of this review is to summarize the findings of recent preclinical and clinical studies on alternative, donor-derived platelet products.

Recent lessons learned for ex-vivo platelet production

PURPOSE OF REVIEW

Platelet transfusion can be life-saving but carries a risk of infection or alloimmunization and is limited by insufficient donor sources and restricted unit shelf life. Generating sufficient platelets in vitro to replace a unit of collected blood remains a challenge. Here, we examine the latest advances in the regulation of megakaryocyte maturation and expansion along with platelet formation and survival. We also discuss alternative therapies investigated to induce platelet production.

RECENT FINDINGS

Recent studies examined candidate niche cells in the bone marrow microenvironment for promoting platelet formation and developed an explant-based bioreactor to enhance platelet production ex vivo. Chemical inhibitors were examined for their ability to promote megakaryocyte maturation and expansion. Microparticles from megakaryocytes or platelets were found to improve megakaryocyte maturation and platelet formation. Membrane budding was identified as a novel mode of platelet formation. Lastly, a chemical inhibitor to improve cold-stored platelets was identified.

SUMMARY

Recent advances in the regulation of megakaryocyte expansion and platelet production provide exciting promise for the development of improved approaches to generate platelets in vitro. These findings bring the field one step closer to achieving the ultimate goal of creating a unit of platelets without the need for donation.

Storage temperature determines platelet GPVI levels and function in mice and humans

Platelets are currently stored at room temperature before transfusion to maximize circulation time. This approach has numerous downsides, including limited storage duration, bacterial growth risk, and increased costs. Cold storage could alleviate these problems. However, the functional consequences of cold exposure for platelets are poorly understood. In the present study, we compared the function of cold-stored platelets (CSP) with that of room temperature-stored platelets (RSP) in vitro, in vivo, and posttransfusion. CSP formed larger aggregates under in vitro shear while generating similar contractile forces compared with RSP. We found significantly reduced glycoprotein VI (GPVI) levels after cold exposure of 5 to 7 days. After transfusion into humans, CSP were mostly equivalent to RSP; however, their rate of aggregation in response to the GPVI agonist collagen was significantly lower. In a mouse model of platelet transfusion, we found a significantly lower response rate to the GPVI-dependent agonist convulxin and significantly lower GPVI levels on the surface of transfused platelets after cold storage. In summary, our data support an immediate but short-lived benefit of cold storage and highlight the need for thorough investigations of CSP. This trial was registered at www.clinicaltrials.gov as #NCT03787927.

Frozen and cold-stored platelets: reconsidered platelet products

Platelet transfusion, both prophylactic and therapeutic, is a key element in modern medicine. Currently, the standard platelet product for clinical use is platelet concentrates at room temperature (20-24°C) under gentle agitation. As this temperature favors bacterial growth, storage is limited to 5-7 days, which result in high wastage rate, and complicates inventory and product availability at remote areas. Frozen and/or cold storage would ameliorate those disadvantages by reducing the risk of bacterial contamination and by extending the product shelf-life to weeks or even years. Consequently, the usefulness in transfusion medicine of platelet cryopreservation and refrigeration, two old and scarcely used platelet storage approaches, is reemerging. Indeed, there have been substantial recent research efforts to characterize both cold and cryopreserved platelets. Most recent studies indicate that cryopreserved and cold platelets display a pro-coagulant profile that may produce the rapid hemostatic response which is needed in bleeding patients. Thus, it seems appropriate that blood banks and blood transfusion centers explore the possibility of split platelet inventories consisting of platelets stored at room temperature and cryopreserved and cold-stored platelets.

Effects of storage time and temperature on thromboelastographic analysis in dogs and horses

BACKGROUND

The accessibility of thromboelastography (TEG) to general practitioners is limited by short sample storage times (30 minutes) and storage temperatures (20-23°C).

OBJECTIVES

We aimed to evaluate the stability of canine and equine citrated blood samples when stored for extended periods of time, both at room temperature (RT) (20-23°C) and refrigerator temperature (FT) (2-7.5°C).

METHODS

Citrated whole blood samples from healthy dogs and horses (n = 10 for each) were stored for 30 minutes (baseline) at RT before TEG analysis. Baseline values for TEG variables R, K, α, MA, LY30, and LY60 were compared with those from samples stored for 2, 8, and 22.5 h, at RT and FT. Results were compared using an ANOVA (P < .05). Total allowable analytical error (TE_a ) based on biological variation data was used to evaluate stability.

RESULTS

In dogs, statistically significant differences included shorter R, longer K, decreased MA, and increased LY60 at various time points and storage temperatures from 2 h onward. Only samples stored for 2 h at FT showed acceptable stability compared with TE_a . In horses, statistically significant differences included shorter R and K, and decreased α, LY30, and LY60 at various time points and storage temperatures from 2 h onward. Samples were not stable at any time compared with TE_a , regardless of the temperature.

CONCLUSIONS

In this study, canine samples could be stored for up to 2 h at FT without affecting TEG results; equine samples should be stored for 30 minutes at RT.

Calcium Ion Chelation Preserves Platelet Function During Cold Storage

OBJECTIVE

Platelet transfusion is a life-saving therapy to prevent or treat bleeding in patients with thrombocytopenia or platelet dysfunction. However, for >6 decades, safe and effective strategies for platelet storage have been an impediment to widespread use of platelet transfusion. Refrigerated platelets are cleared rapidly from circulation, precluding cold storage of platelets for transfusion. Consequently, platelets are stored at room temperature with an upper limit of 5 days due to risks of bacterial contamination and loss of platelet function. This practice severely limits platelet availability for transfusion. This study is to identify the mechanism of platelet clearance after cold storage and develop a method for platelet cold storage. Approach and Results: We found that rapid clearance of cold-stored platelets was largely due to integrin activation and apoptosis. Deficiency of integrin β3 or caspase-3 prolonged cold-stored platelets in circulation. Pretreatment of platelets with EGTA, a cell impermeable calcium ion chelator, reversely inhibited cold storage-induced platelet activation and consequently prolonged circulation of cold-stored platelets. Moreover, transfusion of EGTA-treated, cold-stored platelets, but not room temperature-stored platelets, into the mice deficient in glycoprotein Ibα significantly shortened tail-bleeding times and diminished blood loss.

CONCLUSIONS

Integrin activation and apoptosis is the underlying mechanism of rapid clearance of platelets after cold storage. Addition of a cell impermeable calcium ion chelator to platelet products is potentially a simple and effective method to enable cold storage of platelets for transfusion.

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.

Antioxidant prevents clearance of hemostatically competent platelets after long-term cold storage

BACKGROUND

Cold storage of platelets (PLTs) has the potential advantage of prolonging storage time while reducing posttransfusion infection given the decreased likelihood of bacterial outgrowth during storage and possibly beneficial effects in treating bleeding patients. However, cold storage reduces PLT survival through the induction of complex storage lesions, which are more accentuated when storage is prolonged.

STUDY DESIGN AND METHODS

Whole blood-derived PLT-rich plasma concentrates from seven PLT pools (n = 5 donors per pool). PLT additive solution was added (67%/33% plasma) and the product was split into 50-mL bags. Split units were stored in the presence or absence of 1 mM of N-acetylcysteine (NAC) under agitation for up to 14 days at room temperature or in the cold and were analyzed for PLT activation, fibrinogen-dependent spreading, microparticle formation, mitochondrial respiratory activity, reactive oxygen species (ROS) generation, as well as in vivo survival and bleeding time correction in immunodeficient mice.

RESULTS

Cold storage of PLTs for 7 days or longer induces significant PLT activation, cytoskeletal damage, impaired fibrinogen spreading, enhances mitochondrial metabolic decoupling and ROS generation, and increases macrophage-dependent phagocytosis and macrophage-independent clearance. Addition of NAC prevents PLT clearance and allows a correction of the prolonged bleeding time in thrombocytopenic, aspirin-treated, immunodeficient mice.

CONCLUSIONS

Long-term cold storage induces mitochondrial uncoupling and increased proton leak and ROS generation. The resulting ROS is a crucial contributor to the increased macrophage-dependent and -independent clearance of functional PLTs and can be prevented by the antioxidant NAC in a magnesium-containing additive solution.

Cold-Stored Platelets: Review of Studies in Humans

Although numerous reviews and editorials have been published about the biologic features of platelets exposed to cold temperature and their in vitro function, none has focused on the data from studies after transfusion in healthy human participants and patients. This may, in part, be due to the paucity of well-controlled in vivo investigations of cold-stored platelets. Although numerous studies are looking into the recovery and survival of cold-stored platelets (ie, the percentage of infused platelets maintained in circulation over time), very few assess in vivo platelet function. Another caveat is that most studies were performed in the 1960s and 1970s, at a time when platelet collection and storage were different compared to today. Despite these limitations, we believe the transfusion community can take valuable information from these studies. This review is limited to data on cold-stored platelets in plasma or additive solution and does not include data on whole blood or resuspended whole blood from components because the hemostatic properties of whole blood are likely very different (the interested reader is referred to the review article focused on the hemostatic properties of platelets stored in whole blood by van der Meer et al in this special edition of Transfusion Medicine Reviews). In this review, we report that room temperature storage consistently results in a longer in vivo platelet circulation time at the expense of bacterial growth and shorter storage duration, resulting in expiration, wastage, and regional and national shortages. Cold storage of platelets universally results in moderately reduced recovery and markedly reduced survival. We found inconsistent data about the efficacy of cold-stored platelets likely due to study design differences. The analysis of the available data suggests that there is a short-lasting hemostatic effect of cold-stored platelets. Storage time or choice of anticoagulant did not have a clear effect on platelet efficacy after cold storage. In summary, more data and clinical trials are needed to better understand the effect of cold-stored platelets after transfusion into humans.

Therapeutic Utility of Cold-Stored Platelets or Cold-Stored Whole Blood for the Bleeding Hematology-Oncology Patient

Bleeding related to thrombocytopenia is common in hematology-oncology patients. Platelets stored at room temperature (RTPs) are the current standard of care. Platelets stored in the cold (CSPs) have enhanced hemostatic function relative to RTPs. CSPs were reported to reduce bleeding in hematology-oncology patients. Recent studies have confirmed the enhanced hemostatic properties of CSPs. CSPs may be the better therapeutic option for this population. CSPs may also offer a preferable immune profile, reduced thrombotic risk, and reduced transfusion-transmitted infection risk. The logistical advantages of CSPs would improve outcomes for many patients who currently cannot access platelet transfusions.

Refrigeration, cryopreservation and pathogen inactivation: an updated perspective on platelet storage conditions

Conventional storage of platelet concentrates limits their shelf life to between 5 and 7 days due to the risk of bacterial proliferation and the development of the platelet storage lesion. Cold storage and cryopreservation of platelets may facilitate extension of the shelf life to weeks and years, and may also provide the benefit of being more haemostatically effective than conventionally stored platelets. Further, treatment of platelet concentrates with pathogen inactivation systems reduces bacterial contamination and provides a safeguard against the risk of emerging and re-emerging pathogens. While each of these alternative storage techniques is gaining traction individually, little work has been done to examine the effect of combining treatments in an effort to further improve product safety and minimize wastage. This review aims to discuss the benefits of alternative storage techniques and how they may be combined to alleviate the problems associated with conventional platelet storage.

Cold platelets for trauma-associated bleeding: regulatory approval, accreditation approval, and practice implementation-just the "tip of the iceberg"

BACKGROUND

Laboratory and clinical evidence suggest that cold-stored platelets (CS-PLTs) might be preferable to room temperature platelets (RT-PLTs) for active bleeding. Ease of prehospital use plus potential hemostatic superiority led our facility to pursue approval of CS-PLTs for actively bleeding trauma patients.

STUDY DESIGN AND METHODS

From November 18, 2013, through October 8, 2015, correspondence was exchanged between our facility, the AABB, and the US Food and Drug Administration (FDA). An initial AABB variance request was for 5-day CS-PLTs without agitation. The AABB deferred its decision pending FDA approval to use our platelet (PLT) bags for CS-PLTs. On March 27, 2015, the FDA approved 3-day CS-PLTs without agitation. On October 8, 2015, the AABB approved 3-day CS-PLTs without agitation and without bacterial testing for actively bleeding trauma patients. Our facility's goal is to carry CS-PLTs on air ambulances.

RESULTS

CS-PLTs have been used for trauma patients at our facility since October 2015. As of August 2016, a total of 21 (19.1%) of 119 CS-PLTs have been transfused. The short 3-day storage period combined with the formation of clots in plasma-rich CS-PLTs during storage have been the major causes of a high (80.9%) discard rate.

CONCLUSION

In the future, pathogen-reduced (PR), PLT additive solution (PAS) CS-PLTs seem more practical due to low risks of bacterial contamination and storage-related clotting. This should make longer storage of CS-PLTs feasible (e.g., 10 days or more). With a longer shelf life, PR PAS CS-PLTs could potentially be used in a wider range of patient populations.

Temperature effects on the activity, shape, and storage of platelets from 13-lined ground squirrels

The objective of this study is to determine how a hibernating mammal avoids the formation of blood clots under periods of low blood flow. A microfluidic vascular injury model was performed to differentiate the effects of temperature and shear rate on platelet adhesion to collagen. Human and ground squirrel whole blood was incubated at 15 or 37 °C and then passed through a microfluidic chamber over a 250-µm strip of type I fibrillar collagen at that temperature and the shear rates of 50 or 300 s^-1 to simulate torpid and aroused conditions, respectively. At 15 °C, both human and ground squirrel platelets showed a 90-95% decrease in accumulation on collagen independent of shear rate. At 37 °C, human platelet accumulation reduced by 50% at 50 s^-1 compared to 300 s^-1, while ground squirrel platelet accumulation dropped by 80%. When compared to platelets from non-hibernating animals, platelets from animals collected after arousal from torpor showed a 60% decrease in binding at 37 °C and 300 s^-1, but a 2.5-fold increase in binding at 15 °C and 50 s^-1. vWF binding in platelets from hibernating ground squirrels was decreased by 50% relative to non-hibernating platelets. The source of the plasma that platelets were stored in did not affect the results indicating that the decreased vWF binding was a property of the platelets. Upon chilling, ground squirrel platelets increase microtubule assembly leading to the formation of long rods. This shape change is concurrent with sequestration of platelets in the liver and not the spleen. In conclusion, it appears that ground squirrel platelets are sequestered in the liver during torpor and have reduced binding capacity for plasma vWF and lower accumulation on collagen at low shear rates and after storage at cold temperatures, while still being activated by external agonists. These adaptations would protect the animals from spontaneous thrombus formation during torpor but allow them to restore normal platelet function upon arousal.

Refrigerated storage of platelets initiates changes in platelet surface marker expression and localization of intracellular proteins

BACKGROUND

Platelets (PLTs) are currently stored at room temperature (22°C), which limits their shelf life, primarily due to the risk of bacterial growth. Alternatives to room temperature storage include PLT refrigeration (2-6°C), which inhibits bacterial growth, thus potentially allowing an extension of shelf life. Additionally, refrigerated PLTs appear more hemostatically active than conventional PLTs, which may be beneficial in certain clinical situations. However, the mechanisms responsible for this hemostatic function are not well characterized. The aim of this study was to assess the protein profile of refrigerated PLTs in an effort to understand these functional consequences.

STUDY DESIGN AND METHODS

Buffy coat PLTs were pooled, split, and stored either at room temperature (20-24°C) or under refrigerated (2-6°C) conditions (n = 8 in each group). PLTs were assessed for changes in external receptor expression and actin filamentation using flow cytometry. Intracellular proteomic changes were assessed using two-dimensional gel electrophoresis and Western blotting.

RESULTS

PLT refrigeration significantly reduced the abundance of glycoproteins (GPIb, GPIX, GPIIb, and GPIV) on the external membrane. However, refrigeration resulted in the increased expression of high-affinity integrins (αIIbβ3 and β1) and activation and apoptosis markers (CD62P, CD63, and phosphatidylserine). PLT refrigeration substantially altered the abundance and localization of several cytoskeletal proteins and resulted in an increase in actin filamentation, as measured by phalloidin staining.

CONCLUSION

Refrigerated storage of PLTs induces significant changes in the expression and localization of both surface-expressed and intracellular proteins. Understanding these proteomic changes may help to identify the mechanisms resulting in the refrigeration-associated alterations in PLT function and clearance.

Evaluation of in vitro storage characteristics of cold stored platelet concentrates with N acetylcysteine (NAC)

Platelets play a vital role in hemostasis and thrombosis, and their demand and usage has multiplied many folds over the years. However, due to the short life span and storage constraints on platelets, it is allowed to store them for up to 7 days at room temperature (RT); thus, there is a need for an alternative storage strategy for extension of shelf life. Current investigation involves the addition of 50 mM N acetylcysteine (NAC) in refrigerated concentrates. Investigation results revealed that addition of NAC to refrigerated concentrates prevented platelet activation and reduced the sialidase activity upon rewarming as well as on prolonged storage. Refrigerated concentrates with 50 mM NAC expressed a 23.91 ± 6.23% of CD62P (P-Selectin) and 22.33 ± 3.42% of phosphotidylserine (PS), whereas RT-stored platelets showed a 46.87 ± 5.23% of CD62P and 25.9 ± 6.48% of phosphotidylserine (PS) after 5 days of storage. Further, key metabolic parameters such as glucose and lactate accumulation indicated reduced metabolic activity. Taken together, investigation and observations indicate that addition of NAC potentially protects refrigerated concentrates by preventing platelet activation, stabilizing sialidase activity, and further reducing the metabolic activity. Hence, we believe that NAC can be a good candidate for an additive solution to retain platelet characteristics during cold storage and may pave the way for extension of storage shelf life.

New explanations for old observations: marginal band coiling during platelet activation

Blood platelets are tiny cell fragments derived from megakaryocytes. Their primary function is to control blood vessel integrity and ensure hemostasis if a vessel wall is damaged. Circulating quiescent platelets have a flat, discoid shape maintained by a circumferential microtubule bundle, called the marginal band (MB). In the case of injury platelets are activated and rapidly adopt a spherical shape due to microtubule motor-induced elongation and subsequent coiling of the MB. Platelet activation and shape change can be transient or become irreversible. This depends on the strength of the activation stimulus, which is translated into a cytoskeletal crosstalk between microtubules, their motors and the actomyosin cortex, ensuring stimulus-response coupling. Following microtubule motor-driven disc-to-sphere transition, a strong stimulus will lead to compression of the sphere through actomyosin cortex contraction. This will concentrate the granules in the center of the platelet and accelerate their exocytosis. Once granules are released, platelets have crossed the point of no return to irreversible activation. This review summarizes the current knowledge of the molecular mechanism leading to platelet shape change, with a special emphasis on microtubules, and refers to previously published observations, which have been essential for generating an integrated view of cytoskeletal rearrangements during platelet activation.

Short-term moderate hypothermia stimulates alkaline phosphatase activity and osteocalcin expression in osteoblasts by upregulating Runx2 and osterix in vitro

Exposure of Normal Human Osteoblast cells (NHOst) to a period of hypothermia may interrupt their cellular functions, lead to changes in bone matrix and disrupt the balance between bone formation and resorption, resulting in bone loss or delayed fracture healing. To investigate this possibility, we exposed NHOst cells to moderate (35 °C) and severe (27 °C) hypothermia for 1, 12, 24 and 72 h. The effects of hypothermia with respect to cell cytoskeleton organization, metabolic activity and the expression of cold shock chaperone proteins, osteoblast transcription factors and functional markers, were examined. Our findings showed that prolonged moderate hypothermia retained the polymerization of the cytoskeletal components. NHOst cell metabolism was affected differently according to hypothermia severity. The osteoblast transcription factors Runx2 and osterix were necessary for the transcription and translation of bone matrix proteins, where alkaline phosphatase (Alp) activity and osteocalcin (OCN) bone protein were over expressed under hypothermic conditions. Consequently, bone mineralization was stimulated after exposure to moderate hypothermia for 1 week, indicating bone function was not impaired. The cold shock chaperone protein Rbm3 was significantly upregulated (p<0.001) during the cellular stress adaption under hypothermic conditions. We suggest that Rbm3 has a dual function: one as a chaperone protein that stabilizes mRNA transcripts and a second one in enhancing the transcription of Alp and Ocn genes. Our studies demonstrated that hypothermia permitted the in vitro maturation of NHOst cells probably through an osterix-dependent pathway. For that reason, we suggest that moderate hypothermia can be clinically applied to counteract heat production at the fracture site that delays fracture healing.

Platelet dynamics during natural and pharmacologically induced torpor and forced hypothermia

Hibernation is an energy-conserving behavior in winter characterized by two phases: torpor and arousal. During torpor, markedly reduced metabolic activity results in inactivity and decreased body temperature. Arousal periods intersperse the torpor bouts and feature increased metabolism and euthermic body temperature. Alterations in physiological parameters, such as suppression of hemostasis, are thought to allow hibernators to survive periods of torpor and arousal without organ injury. While the state of torpor is potentially procoagulant, due to low blood flow, increased viscosity, immobility, hypoxia, and low body temperature, organ injury due to thromboembolism is absent. To investigate platelet dynamics during hibernation, we measured platelet count and function during and after natural torpor, pharmacologically induced torpor and forced hypothermia. Splenectomies were performed to unravel potential storage sites of platelets during torpor. Here we show that decreasing body temperature drives thrombocytopenia during torpor in hamster with maintained functionality of circulating platelets. Interestingly, hamster platelets during torpor do not express P-selectin, but expression is induced by treatment with ADP. Platelet count rapidly restores during arousal and rewarming. Platelet dynamics in hibernation are not affected by splenectomy before or during torpor. Reversible thrombocytopenia was also induced by forced hypothermia in both hibernating (hamster) and non-hibernating (rat and mouse) species without changing platelet function. Pharmacological torpor induced by injection of 5'-AMP in mice did not induce thrombocytopenia, possibly because 5'-AMP inhibits platelet function. The rapidness of changes in the numbers of circulating platelets, as well as marginal changes in immature platelet fractions upon arousal, strongly suggest that storage-and-release underlies the reversible thrombocytopenia during natural torpor. Possibly, margination of platelets, dependent on intrinsic platelet functionality, governs clearance of circulating platelets during torpor.

Wiskott-Aldrich syndrome protein (WASp) controls the delivery of platelet transforming growth factor-β1

Platelets are immunologically competent cells containing cytokines such as TGF-β1 that regulate cell-mediated immunity. However, the mechanisms underlying cytokine secretion from platelets are undefined. The Wiskott-Aldrich syndrome protein (WASp) regulates actin polymerization in nucleated hematopoietic cells but has other role(s) in platelets. WASp-null (WASp(-/-)) platelets stimulated with a PAR-4 receptor agonist had increased TGF-β1 release compared with WT platelets; inhibiting WASp function with wiskostatin augmented TRAP-induced TGF-β1 release in human platelets. TGF-β1 release is dissociated from α-granule secretion (P-selectin up-regulation) and occurs more gradually, with ∼10-15% released after 30-60 min. Blockade of Src family kinase-mediated WASp Tyr-291/Tyr-293 phosphorylation increased TGF-β1 release, with no additive effect in WASp(-/-) platelets, signifying that phosphorylation is critical for WASp-limited TGF-β1 secretion. Inhibiting F-actin assembly with cytochalasin D enhanced secretion in WT platelets and further increased TGF-β1 release in WASp(-/-) platelets, indicating that WASp and actin assembly independently regulate TGF-β1 release. A permeabilized platelet model was used to test the role of upstream small GTPases in TGF-β1 release. N17Cdc42, but not Rac1 mutants, increased TGF-β1 secretion and abrogated WASp phosphorylation. We conclude that WASp function restricts TGF-β1 secretion in a Cdc42- and Src family kinase-dependent manner and independently of actin assembly.

Simplified platelet sample preparation for SDS-PAGE-based proteomic studies

PURPOSE

The goal of this study was to design an easy and simple protocol for platelet isolation and sample preparation for proteomic studies based on 2DE (IEF-SDS-PAGE) followed by Coomassie blue staining.

EXPERIMENTAL DESIGN

Blood was collected by venipuncture into tubes coated with EDTA and platelet-rich plasma (PRP) was immediately obtained by centrifugation. PRP was stored refrigerated in closed Falcon tubes for 0, 1, 2, 3, 5, and 7 days and platelets were isolated by centrifugation. 2DE gels were stained with colloidal Coomassie blue stain and evaluated using the Progenesis SameSpots software. Spots that differed significantly in the gels of fresh and stored platelet samples were excised, digested with trypsin, and further analyzed using nanoLC-MS/MS.

RESULTS

During the 7-day follow-up period, we found 20 spots that differed significantly (ANOVA p <0.05). During the first 2 days of PRP storage in test tubes, however, only nine spots significantly differed in all donors. In these spots, we identified 14 different proteins.

CONCLUSIONS AND CLINICAL RELEVANCE

In conclusion, for proteome investigations, whenever it is not feasible to prepare washed platelets immediately after blood collection, the EDTA-anticoagulated PRP can be stored in test tubes at 4°C for up to 2 days for the platelet proteome investigation.

Regulation of actin dynamics by protein kinase R control of gelsolin enforces basal innate immune defense

Primary resistance to pathogens is reliant on both basal and inducible immune defenses. To date, research has focused upon inducible innate immune responses. In contrast to resistance via cytokine induction, basal defense mechanisms are less evident. Here we showed that the antiviral protein kinase R (PKR) inhibited the key actin-modifying protein gelsolin to regulate actin dynamics and control cytoskeletal cellular functions under homeostatic conditions. Through this mechanism, PKR controlled fundamental innate immune, actin-dependent processes that included membrane ruffling and particle engulfment. Accordingly, PKR counteracted viral entry into the cell. These findings identify a layer of host resistance, showing that the regulation of actin-modifying proteins during the innate immune response bolsters first-line defense against intracellular pathogens and has a sustained effect on virus production. Moreover, these data provide proof of principle for a concept in which the cell cytoskeleton could be targeted to elicit broad antiviral protection.

Arachidonic acid depletion extends survival of cold-stored platelets by interfering with the [glycoprotein Ibα--14-3-3ζ] association

BACKGROUND

Cold storage of platelets reduces bacterial growth and preserves their hemostatic properties better than current procedures do. However, storage at 0°C induces [14-3-3ζ-glycoprotein Ibα] association, 14-3-3ζ release from phospho-Bad, Bad activation and apoptosis.

DESIGN AND METHODS

We investigated whether arachidonic acid, which also binds 14-3-3ζ, contributes to coldinduced apoptosis.

RESULTS

Cold storage activated P38-mitogen-activated protein kinase and released arachidonic acid, which accumulated due to cold inactivation of cyclooxygenase-1/thromboxane synthase. Accumulated arachidonic acid released 14-3-3ζ from phospho-Bad and decreased the mitochondrial membrane potential, which are steps in the induction of apoptosis. Addition of arachidonic acid did the same and its depletion made platelets resistant to cold-induced apoptosis. Incubation with biotin-arachidonic acid revealed formation of an [arachidonic acid-14-3-3ζ-glycoprotein Ibα] complex. Indomethacin promoted complex formation by accumulating arachidonic acid and released 14-3-3ζ from cyclo-oxygenase-1. Arachidonic acid depletion prevented the cold-induced reduction of platelet survival in mice.

CONCLUSIONS

We conclude that cold storage induced apoptosis through an [arachidonic acid-14-3-3ζ-glycoprotein Ibα] complex, which released 14-3-3ζ from Bad in an arachidonic acid-dependent manner. Although arachidonic acid depletion reduced agonist-induced thromboxane A(2) formation and aggregation, arachidonic acid repletion restored these functions, opening ways to reduce apoptosis during storage without compromising hemostatic functions post-transfusion.

Dual roles for hepatic lectin receptors in the clearance of chilled platelets

Chilling rapidly (<4 h) clusters Glycoprotein - (GP)Ib receptors on blood platelets, and ß2-integrins of hepatic macrophages bind ßGlcNAc residues in the clusters leading to rapid clearance of acutely chilled platelets following transfusion. Although capping the ßGlcNAc moieties by galactosylation prevents clearance, this strategy is ineffective after prolonged (>24 h) refrigeration. We report here that prolonged refrigeration increases the density/concentration of exposed galactose residues such that hepatocytes become increasingly involved in the removal of platelets using their Ashwell-Morell receptors. Macrophages always rapidly remove a large fraction of transfused platelets (~40%). With platelet cooling, hepatocyte-dependent clearance further diminishes their recoveries following transfusion.

The platelet storage lesion

The continuous increase in the demand for platelet transfusion has necessitated the need to establish standards for determining the quality of platelets during storage. Bacterial contamination of platelet products and deleterious changes in structure and function referred to as the platelet storage lesion (PSL), have restricted the platelet shelf life to 5 days. The PSL and platelet health variables have been well studied and documented. The precise correlation between in vitro assays and in vivo platelet recovery and survival is yet to be established. This review presents an overview of the current understanding of PSL and the novel approaches being developed to negate the storage lesion.

Combined electrostatics and hydrogen bonding determine intermolecular interactions between polyphosphoinositides

Membrane lipids are active contributors to cell function as key mediators in signaling pathways controlling cell functions including inflammation, apoptosis, migration, and proliferation. Recent work on multimolecular lipid structures suggests a critical role for lipid organization in regulating the function of both lipids and proteins. Of particular interest in this context are the polyphosphoinositides (PPI's), especially phosphatidylinositol (4,5) bisphosphate (PIP 2). The cellular functions of PIP 2 are numerous but the organization of PIP 2 in the inner leaflet of the plasma membrane, as well as the factors controlling targeting of PIP 2 to specific proteins, remains poorly understood. To analyze the organization of PIP 2 in a simplified planar system, we used Langmuir monolayers to study the effects of subphase conditions on monolayers of purified naturally derived PIP 2 and other anionic or zwitterionic phospholipids. We report a significant molecular area expanding effect of subphase monovalent salts on PIP 2 at biologically relevant surface densities. This effect is shown to be specific to PIP 2 and independent of subphase pH. Chaotropic agents (e.g., salts, trehalose, urea, temperature) that disrupt water structure and the ability of water to mediate intermolecular hydrogen bonding also specifically expanded PIP 2 monolayers. These results suggest a combination of water-mediated hydrogen bonding and headgroup repulsion in determining the organization of PIP 2, and may contribute to an explanation for the unique functionality of PIP 2 compared to other anionic phospholipids.

Storage of buffy-coat-derived platelets in additive solutions at 4 °C and 22 °C: flow cytometry analysis of platelet glycoprotein expression

BACKGROUND

The aim of our in vitro study is to compare the effects on platelet membrane glycoproteins that play an important role in the main functions of platelets, when platelets are stored for a period of 21 days at 4 degrees C or 22 degrees C.

STUDY DESIGN AND METHODS

Platelet concentrates (PC) were prepared from pooled buffy-coats (BC) for paired studies (total eight pools from 80 BCs) by using the OrbiSac system. We divided each pool into two PCs and stored them at 4 degrees C or 22 degrees C.

RESULTS

The activation marker CD62 remained almost unchanged during storage in all units. The expression of CD63 was higher in PCs stored at 22 degrees C than in those stored at 4 degrees C. No significant difference in CD41 expression was detected over time. The expression of CD42b declined during storage and even more in PCs stored at 4 degrees C until day 21 [day 14: mean flourscence intensity: 32.5 +/- 13.1 vs. 46.5 +/- 19.1], but the percentage of platelets expressing CD42b remained high in platelets stored at 4 degrees C, but gradually decreased at 22 degrees C (day 14: 95.0 +/- 1.5 vs. 59.0 +/- 9.9). Storage at 4 degrees C reduced the rate of glycolysis and maintained the pH better after day 10 than in PCs stored at 22 degrees C (day 14: 7.009 +/- 0.067 vs. 7.233 +/- 0.125). The concentration of regulated upon activation of normal T-cells expressed and secreted was higher in PCs stored at 22 degrees C than at 4 degrees C (day 7: 414.7 +/- 32.3 vs. 49.6 +/- 19.0). No response to extent of shape change and no swirling were detected at 4 degrees C.

CONCLUSION

Platelets stored at 4 degrees C retain their in vitro characteristics better than those stored at 22 degrees C, except for parameters that reflect changes in shape. Storage at 4 degrees C is not associated with an increased expression of glycoprotein (GpIb, GpIIb/IIIa) and platelet activation markers (CD62p and CD63) as compared with storage at 22 degrees C.

Metabolic energy reduction by glucose deprivation and low gas exchange preserves platelet function after 48 h storage at 4 °C

INTRODUCTION

We showed earlier that metabolically suppressed platelets (MSP) prepared by incubation in glucose-free, antimycin A medium at 37 degrees C better sustained storage at 4 degrees C than untreated controls at 22 degrees C. However, the use of the mitochondrial inhibitor antimycin A is incompatible with platelet transfusion.

OBJECTIVES

The aim of this study was to investigate how energy-reduced (ER) platelets could be prepared in the absence of antimycin A.

STUDY DESIGN AND METHODS

Platelets in gas-impermeable bags in glucose-free medium were kept at 22 degrees C for 4 h to reduce energy stores and thereafter stored at 4 degrees C (ER22-4). Controls were energy-reduced platelets without prior incubation at 22 degrees C (ER4), and MSPs in test tubes and untreated platelets in gas-permeable bags with glucose and stored at 22 degrees C (C22) and 4 degrees C (C4).

RESULTS

After 48 h storage, ER22-4 were superior to C22 with respect to pH preservation (6 x 4 +/- 0 x 4 vs. 5 x 0 +/- 0 x 4, n= 4), platelet count (800 +/- 225 vs. 650 +/- 150 x 10(9)), thrombin receptor-activating peptide-induced aggregation (50 +/- 15 vs. 10 +/- 5%) and glycoprotein (GP)Ib alpha expression (60 +/- 15% vs. 28 +/- 15). GPIb alpha expression was higher in ER22-4 than in ER4, indicating that energy suppression preserved GPIb alpha during cold storage.

CONCLUSION

Metabolic suppression without the use of antimycin A could be mimicked by storage of platelets in glucose-free medium in gas-impermeable bags. Energy suppression preserved GPIb alpha expression during storage at 4 degrees C.

Platelet binding and phagocytosis by macrophages

BACKGROUND

Earlier it was reported that metabolic arrest followed by incubation at 4 degrees C reduces the platelet (PLT) storage defect. Here it is reported that this treatment also reduces binding and phagocytosis by macrophages.

STUDY DESIGN AND METHODS

Phagocytosis of mepacrine-labeled PLTs by macrophages changes the latter into bright fluorescent particles easily detected by fluorescence-activated cell sorting.

RESULTS

In combination with conventional binding analysis it was found that binding to phorbol 12-myristate 13-acetate-matured THP-1 cells is primarily regulated by PLT P-selectin expression and phagocytosis by combined phosphatidylserine (PS) exposure and glycoprotein (GP) Ibalpha clustering. It was found that trapping of PLT Ca2+ and raising cAMP reduces phagocytosis by lowering PS exposure. Chilling of PLTs leads to an increase in binding and PS- and GPIbalpha-mediated phagocytosis. Prior depletion of PLT energy stores prevents this increase by preserving low Ca2+ concentration, PS exposure, and PS-mediated phagocytosis.

CONCLUSION

These data characterize the individual factors that control PLT binding and phagocytosis and might help to define conditions that improve the survival of stored PLTs after transfusion.

Control and regulation of the cellular responses to cold shock: the responses in yeast and mammalian systems

Although the cold-shock response has now been studied in a number of different organisms for several decades, it is only in the last few years that we have begun to understand the molecular mechanisms that govern adaptation to cold stress. Notably, all organisms from prokaryotes to plants and higher eukaryotes respond to cold shock in a comparatively similar manner. The general response of cells to cold stress is the elite and rapid overexpression of a small group of proteins, the so-called CSPs (cold-shock proteins). The most well characterized CSP is CspA, the major CSP expressed in Escherichia coli upon temperature downshift. More recently, a number of reports have shown that exposing yeast or mammalian cells to sub-physiological temperatures (<30 or <37 degrees C respectively) invokes a co-ordinated cellular response involving modulation of transcription, translation, metabolism, the cell cycle and the cell cytoskeleton. In the present review, we summarize the regulation and role of cold-shock genes and proteins in the adaptive response upon decreased temperature with particular reference to yeast and in vitro cultured mammalian cells. Finally, we present an integrated model for the co-ordinated responses required to maintain the viability and integrity of mammalian cells upon mild hypothermic cold shock.

The cold-shock response in cultured mammalian cells: harnessing the response for the improvement of recombinant protein production

There are a growing number of reports on the sub-physiological temperature culturing (<37 degrees C) of mammalian cells for increased recombinant protein yield, although the effect is variable between cell lines, expression systems, and the product of interest. What is becoming clear is that exposing mammalian cells to sub-physiological temperatures invokes a coordinated cellular response involving modulation of the cell cycle, metabolism, transcription, translation, and the cell cytoskeleton. Opportunities currently exist for further enhancement of the cold-shock effect on recombinant protein production in mammalian cells through advancements in our understanding of the mechanisms involved in the cold-shock response.

Storage of buffy coat-derived platelets in additive solutions: in vitro effects of storage at 4oC

BACKGROUND

The aims of this in vitro study were to compare the storage of platelets (PLTs) at 4 degrees C with those stored at 22 degrees C and to determine the in vitro effects of preincubation at 37 degrees C for 1 hour before the analysis on the basis of the maintenance of PLT metabolic and cellular integrity.

STUDY DESIGN AND METHODS

PLT concentrates (PCs) were prepared from pooled buffy coats (BCs) for paired studies (total eight pools from 160 BCs). Each pool was divided into four PCs and stored under different conditions: at 20 to 24 degrees C on a flatbed agitator, at 20 to 24 degrees C on a flatbed agitator and with incubation of the samples at 37 degrees C for 1 hour before the analysis, at 4 degrees C, and at 4 degrees C and with incubation of the samples at 37 degrees C for 1 hour before the analysis.

RESULTS

Storage of PLTs at 4 degrees C resulted in reductions in the rate of glycolysis and better retention of pH after Day 10 than in PCs stored at 22 degrees C (Day 14, 7.003 +/- 0.047 vs. 7.201 +/- 0.146). Hypotonic shock response and extent of shape change were higher at 22 degrees C than at 4 degrees C and in preincubated PCs stored at 22 degrees C than in reference PCs stored at the same temperature (Day 5, 45.6 +/- 2.7 vs. 36.5 +/- 3.9 and 24.1 +/- 2.0 vs. 15.5 +/- 1.8). The concentration of RANTES was higher in PCs stored at 22 degrees C than at 4 degrees C (Day 7, 179 +/- 25 vs. 79 +/- 32).

CONCLUSION

PLTs stored at 4 degrees C without agitation maintain metabolic and cellular characteristics to a great extent during 21 days of storage. These studies confirm the view that PLTs lose their discoid shape and that this loss with storage at 4 degrees C is associated with reductions in metabolic rate and in their release of alpha-granule content.

Flavonoid-mediated inhibition of actin polymerization in cold-activated platelets

The response of human platelets to low temperature (below 15 degrees C) requires that they are stored at elevated temperatures and limits their storage time to 5 days for use in transfusion. Prolonged storage at room temperature leads to loss of platelet function and risk of septic conditions. The need for improved platelet storage is an important issue, and finding a key component allowing platelets to be maintained at low temperatures would have significant practical benefit. Developing such a component is challenging, because the process of cold-activation resembles that of a physiological agonist-mediated activation, but without a specific receptor that can be inhibited. A component preventing platelets' low temperature response will potentially inhibit their physiological function, making them less useful after transfusion. In the present study, we report that pretreatment of platelets with flavonoids before chilling prevents an increase in cytosolic calcium concentration, actin polymerization and platelet shape change. After warming, platelets that were chilled in the presence of flavonoids retain a normal shape change and aggregation response after stimulation by thrombin. Additionally, cold platelet activation does not increase platelet procoagulant activity evaluated by annexin V-FITC binding in the presence and absence of flavonoids. These data confirm the important links that exist between agonist- and cold-mediated platelet activation, suggesting a possible advantage of incorporating the use of flavonoids to allow platelet hypothermic-storage.