Dependence of Electric Pulse Mediated Growth Factor Release on the Platelet Rich Plasma Separation Method

Platelet rich plasma (PRP) has been explored for multiple clinical applications, including dentistry, orthopedics, sports medicine, diabetic foot ulcers, and cosmetic treatments. Topical applications of PRP typically use thrombin to induce platelet activation, which is accompanied by growth factor release and clotting of the PRP, prior to treatment. Injectable PRP treatments typically use non-activated PRP under the assumption that collagen at the site of the injury mediates platelet activation to ensure growth factor release in vivo. Ex-vivo electrical stimulation of platelets is emerging as a robust, easy to use, instrument-based PRP activation technique to facilitate growth factor release with or without clotting, while providing tunability of growth factor release, clot mechanical properties (when desired), and serotonin release from the dense granules. This paper briefly reviews the key results of the electrical activation of platelets and demonstrates successful growth factor release by electrical ex-vivo stimulation without clotting for three types of PRP separated from whole blood using available commercial kits: Harvest, EmCyte and Eclipse. While these three types of PRP feature a wide range of platelet and red blood cell content compared to whole blood, we demonstrate that pulsed electric fields enable growth factor release for all these biological matrices generated using whole blood from four human donors. These experiments open opportunities for using electrically stimulated PRP with released growth factors without clotting for injectable platelet treatments in relevant clinical applications.

Biofluid-Triggered Burst Release from an Adaptive Covalently Assembled Dipeptide Nanocontainer for Emergency Treatment

The construction of quickly dissociating containers holding bioactive components that meet the extreme requirements of emergency treatment is highly desirable but remains a great challenge. Here the use of small-molecule-induced dynamic covalent assembly is reported for simple and tunable fabrication of a biocompatible diphenylalanine-based nanocontainer toward rapidly responsive cargo delivery. The assembled nanocontainer can adaptively encapsulate various charged or neutral molecules. Upon biofluid trigger, the encapsulated molecules and bioactive proteins are released in a burst (within 5 s) from the nanocontainer due to highly sensitive deprotonation-mediated disruption of hydrogen bonding. This highlighted feature allows the nanocontainer as an excellent "fast dissolving" delivery vehicle available in spray dosage form for medical emergencies, as demonstrated by in vivo application for massive hemorrhage.

Modification of Pulsed Electric Field Conditions Results in Distinct Activation Profiles of Platelet-Rich Plasma

Background

Activated autologous platelet-rich plasma (PRP) used in therapeutic wound healing applications is poorly characterized and standardized. Using pulsed electric fields (PEF) to activate platelets may reduce variability and eliminate complications associated with the use of bovine thrombin. We previously reported that exposing PRP to sub-microsecond duration, high electric field (SMHEF) pulses generates a greater number of platelet-derived microparticles, increased expression of prothrombotic platelet surfaces, and differential release of growth factors compared to thrombin. Moreover, the platelet releasate produced by SMHEF pulses induced greater cell proliferation than plasma.

Aims

To determine whether sub-microsecond duration, low electric field (SMLEF) bipolar pulses results in differential activation of PRP compared to SMHEF, with respect to profiles of activation markers, growth factor release, and cell proliferation capacity.

Methods

PRP activation by SMLEF bipolar pulses was compared to SMHEF pulses and bovine thrombin. PRP was prepared using the Harvest SmartPreP2 System from acid citrate dextrose anticoagulated healthy donor blood. PEF activation by either SMHEF or SMLEF pulses was performed using a standard electroporation cuvette preloaded with CaCl₂ and a prototype instrument designed to take into account the electrical properties of PRP. Flow cytometry was used to assess platelet surface P-selectin expression, and annexin V binding. Platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF), endothelial growth factor (EGF) and platelet factor 4 (PF4), and were measured by ELISA. The ability of supernatants to stimulate proliferation of human epithelial cells in culture was also evaluated. Controls included vehicle-treated, unactivated PRP and PRP with 10 mM CaCl₂ activated with 1 U/mL bovine thrombin.

Results

PRP activated with SMLEF bipolar pulses or thrombin had similar light scatter profiles, consistent with the presence of platelet-derived microparticles, platelets, and platelet aggregates whereas SMHEF pulses primarily resulted in platelet-derived microparticles. Microparticles and platelets in PRP activated with SMLEF bipolar pulses had significantly lower annexin V-positivity than those following SMHEF activation. In contrast, the % P-selectin positivity and surface P-selectin expression (MFI) for platelets and microparticles in SMLEF bipolar pulse activated PRP was significantly higher than that in SMHEF-activated PRP, but not significantly different from that produced by thrombin activation. Higher levels of EGF were observed following either SMLEF bipolar pulses or SMHEF pulses of PRP than after bovine thrombin activation while VEGF, PDGF, and PF4 levels were similar with all three activating conditions. Cell proliferation was significantly increased by releasates of both SMLEF bipolar pulse and SMHEF pulse activated PRP compared to plasma alone.

Conclusions

PEF activation of PRP at bipolar low vs. monopolar high field strength results in differential platelet-derived microparticle production and activation of platelet surface procoagulant markers while inducing similar release of growth factors and similar capacity to induce cell proliferation. Stimulation of PRP with SMLEF bipolar pulses is gentler than SMHEF pulses, resulting in less platelet microparticle generation but with overall activation levels similar to that obtained with thrombin. These results suggest that PEF provides the means to alter, in a controlled fashion, PRP properties thereby enabling evaluation of their effects on wound healing and clinical outcomes.

Platelet-rich plasma stimulated by pulse electric fields: Platelet activation, procoagulant markers, growth factor release and cell proliferation

Therapeutic use of activated platelet-rich plasma (PRP) has been explored for wound healing, hemostasis and antimicrobial wound applications. Pulse electric field (PEF) stimulation may provide more consistent platelet activation and avoid complications associated with the addition of bovine thrombin, the current state of the art ex vivo activator of therapeutic PRP. The aim of this study was to compare the ability of PEF, bovine thrombin and thrombin receptor activating peptide (TRAP) to activate human PRP, release growth factors and induce cell proliferation in vitro. Human PRP was prepared in the Harvest SmartPreP2 System and treated with vehicle, PEF, bovine thrombin, TRAP or Triton X-100. Platelet activation and procoagulant markers and microparticle generation were measured by flow cytometry. Released growth factors were measured by ELISA. The releasates were tested for their ability to stimulate proliferation of human epithelial cells in culture. PEF produced more platelet-derived microparticles, P-selectin-positive particles and procoagulant annexin V-positive particles than bovine thrombin or TRAP. These differences were associated with higher levels of released epidermal growth factor after PEF than after bovine thrombin or TRAP but similar levels of platelet-derived, vascular-endothelial, and basic fibroblast growth factors, and platelet factor 4. Supernatant from PEF-treated platelets significantly increased cell proliferation compared to plasma. In conclusion, PEF treatment of fresh PRP results in generation of microparticles, exposure of prothrombotic platelet surfaces, differential release of growth factors compared to bovine thrombin and TRAP and significant cell proliferation. These results, together with PEF's inherent advantages, suggest that PEF may be a superior alternative to bovine thrombin activation of PRP for therapeutic applications.

Aptamer-functionalized solid phase microextraction-liquid chromatography/tandem mass spectrometry for selective enrichment and determination of thrombin

In this publication, a novel solid phase microextraction (SPME) coating functionalized with a DNA aptamer for selective enrichment of a low abundance protein from diluted human plasma is described. This approach is based on the covalent immobilization of an aptamer ligand on electrospun microfibers made with the hydrophilic polymer poly(acrylonitrile-co-maleic acid) (PANCMA) on stainless steel rods. A plasma protein, human α-thrombin, was employed as a model protein for selective extraction by the developed Apt-SPME probe, and the detection was carried out with liquid chromatography/tandem mass spectrometry (LC-MS/MS). The SPME probe exhibited highly selective capture, good binding capacity, high stability and good repeatability for the extraction of thrombin. The protein selective probe was employed for direct extraction of thrombin from 20-fold diluted human plasma samples without any other purification. The Apt-SPME method coupled with LC-MS/MS provided a good linear dynamic range of 0.5-50 nM in diluted human plasma with a good correlation coefficient (R(2)=0.9923), and the detection limit of the proposed method was found to be 0.30 nM. Finally, the Apt-SPME coupled with LC-MS/MS method was successfully utilized for the determination of thrombin in clinical human plasma samples. One shortcoming of the method is its reduced efficiency in undiluted human plasma compared to the standard solution. Nevertheless, this new aptamer affinity-based SPME probe opens up the possibility of selective enrichment of a given targeted protein from complex sample either in vivo or ex vivo.

A sensitive strategy for label-free and time-resolved fluorescence assay of thrombin using Tb-complex and unmodified gold nanoparticles

Gold nanoparticles (GNPs) can effectively differentiate the unfolded and folded aptamer, and quench the fluorescence of terbium ternary complexes (Tb-complexes), thus the authors herein report a sensitive strategy for protein detection, using label-free aptamer, Tb-complexes and GNPs. In the presence of thrombin, the aptamer is inclined to form G-quartet, and the folded aptamer cannot adsorb on the surface of GNPs, inducing the GNPs aggregation in the presence of 0.5 mol L(-1) salt. After centrifugation at low speed to remove the aggregated GNPs, the quenching capability of the supernatant for Tb-complexes is decreased. The fluorescence intensity of Tb-complexes increases as the concentration of thrombin increases. Due to the highly specific recognition ability of the aptamer for thrombin and the strong quenching property of GNPs for Tb-complexes, the proposed protocol has good selectivity and high sensitivity for thrombin. Under the optimum conditions, a linear range from 1.0 × 10(-9) M to 1.0 × 10(-8) M is obtained with a detection limit of 0.14 nM, which is much lower than those commonly obtained for colorimetric sensors and some fluorescent sensors. The signal of Tb-complexes can be measured by time-resolved manner which made most of the unspecific fluorescent background signals be eliminated. The proposed sensor has been successfully applied in complicated biological samples for thrombin detection, and it can provide a promising potential for label-free aptamer-based protein detection.

Time-resolved fluorescence aptamer-based sandwich assay for thrombin detection

In the present study, the authors report a novel sensitive method for the detection of thrombin using time-resolved fluorescence sensing platform based on two different thrombin aptamers. The thrombin 15-mer aptamer as a capture probe was covalently attached to the surface of glass slide, and the thrombin 29-mer aptamer was fluorescently labeled as a detection probe. A bifunctional europium complex was used as the fluorescent label. The introduction of thrombin triggers the two different thrombin aptamers and thrombin to form a sandwich structure. The fluorescence intensity is proportional to the thrombin concentration. The present sensing system could provide both a wide linear dynamic range and a low detection limit. The proposed sensing system also presented satisfactory specificity and selectivity. Results showed that thrombin was retained at the aptamer-modified glass surface while nonspecific proteins were removed by rinsing with buffer solution. This approach successfully showed the suitability of aptamers as low molecular weight receptors on glass slides for sensitive and specific protein detection.

Highly sensitive detection of human thrombin in serum by affinity capillary electrophoresis/laser-induced fluorescence polarization using aptamers as probes

The detection and quantification of disease-related proteins play critical roles in clinical practice and diagnostic assays. We present an affinity probe capillary electrophoresis/laser-induced fluorescence polarization (APCE/LIFP) assay for detection of human thrombin using a specific aptamer as probe. In the APCE/LIFP assay, the mobility and fluorescence polarization of complex are measured simultaneously during CE analysis. The affinity complex of human thrombin can be well separated from unbound aptamer on CE and clearly identified on the basis of its fluorescence polarization and migration. Because of the binding favorable G-quartet conformation potentially involved in the specific aptamer, it was assumed that monovalent and bivalent cations promoting the formation of a stable G quadruplex conformation in the aptamer may enhance the binding of the aptamer and thrombin. Therefore, we investigated the effects of various metal cations on the binding of human thrombin and the aptamer. Our results show that cations like K(+) and Mg(2+) could not stabilize the affinity complex. Without the use of typical cations, a highly sensitive assay of human thrombin was developed with the corresponding detection limits of 4.38x10(-19) and 2.94x10(-19)mol in mass for standard solution and human serum, respectively.