Sample preparation technique and white cell content influence the detectable levels of growth factors in platelet concentrates

Preparation of highly concentrated and white cell-poor platelet-rich plasma by plateletpheresis

BACKGROUND AND OBJECTIVES

Contaminating white blood cells (WBC) contribute remarkably to the overall growth factor content of locally applicable platelet-rich plasma (PRP) or platelet (PLT) gel and change the relative proportions of the contained growth factors.

MATERIALS AND METHODS

To study the independent effects of locally applicated highly concentrated PLTs, the development of preparations is needed that contain large amounts of PLTs and no or at least very few leucocytes. Therefore, 20 plateletpheresis procedures were performed in voluntary blood donors to get highly concentrated and extremely WBC-poor plateletpheresis concentrates. The degree of spontaneous PLT activation, the PLT aggregation response to agonists and the level of the growth factor TGF-beta1 (transforming growth factor beta1) were measured immediately after the donation and 1 day later.

RESULTS

The concentrates contained 1.96 +/- 0.36 x 10e11 PLTs per unit in 55.2 +/- 7.9 ml, respectively. In comparison to the donors' blood, the PLT-enrichment factor was 15.3 +/- 5.4. At the same time, the concentrates contained extremely low residual numbers of WBCs (0.8 +/- 3.3 x 10e3/ml). The concentration of the growth factor TGF-beta1 was 743.2 +/- 243.9 ng/ml. On day 1, the PLT concentration and the TGF-beta1 content of the PLT concentrates had not decreased.

CONCLUSIONS

In summary, plateletpheresis is suited to provide PRP products with higher concentrations of human platelets and platelet-derived growth factors than previously reported PRP preparation methods but with extremely low numbers of contaminating leucocytes.

Sinus floor elevation using autogenous bone or bone substitute combined with platelet-rich plasma

OBJECTIVE

Sinus augmentation is a common approach for patients with severe alveolar ridge atrophy. However, autogenous bone sometimes results in donor site complications. Bone substitutes with platelet-rich plasma (PRP) promote early bone formation with autogenous bone. Use of PRP on autogenous bone and a bovine bone substitute were investigated in this split-mouth animal study.

STUDY DESIGN

Premolars were extracted from minipigs. Each animal received sinus augmentation using a lateral approach with simultaneous insertion of 3 implants in each site. Groups were randomized using autogenous bone alone and combined with PRP or a bovine hydroxyapatite alone in combination with PRP.

RESULTS

Microradiographic findings in the autogenous group did not show significantly different rates by using autogenous bone alone or combined with PRP. Using the bovine hydroxyapatite as augmentation material only at 8 weeks, a nonsignificant effect in the PRP group could be seen. At all other observation periods, no significant influence was observed.

CONCLUSION

No significant influence of PRP was found.

Human platelet lysate can replace fetal bovine serum for clinical-scale expansion of functional mesenchymal stromal cells

BACKGROUND

Human multipotent mesenchymal stromal cells (MSCs) are promising candidates for a growing spectrum of regenerative and immunomodulatory cellular therapies. Translation of auspicious experimental results into clinical applications has been limited by the dependence of MSC propagation from fetal bovine serum (FBS).

STUDY DESIGN AND METHODS

The capacity of human platelet lysate (HPL) to replace FBS for clinical-scale MSC propagation was analyzed.

RESULTS

HPL could be efficiently produced from buffy coats. Multiplex analyses allowed a distinct HPL growth factor profile to be delineated. With a previously established two-step clinical-scale procedure, HPL was reproducibly more efficient than FBS in supporting MSC outgrowth. With only 3 x 10(5) primary culture-derived MSCs, a mean of 4.36 x 10(8) HPL-MSCs (range, 3.01 x 10(8)-5.40 x 10(8)) was obtained within a single secondary 11- to 13-day culture step. Although morphologically distinct, HPL-MSCs and FBS-MSCs did not differ significantly in terms of immunophenotype, differentiation potential in vitro, and lack of tumorigenicity in nude mice in vivo.

CONCLUSIONS

Replacing FBS with HPL prevents bovine prion, viral, and zoonose contamination of the stem cell product. This new efficient FBS-free two-step procedure for clinical-scale MSC propagation may represent a major step toward challenging new stem cell therapies.

Trehalose lyophilized platelets for wound healing

Fresh platelet preparations are utilized to treat a wide variety of wounds, although storage limitations and mixed results have hampered their clinical use. We hypothesized that concentrated lyophilized and reconstituted platelet preparations, preserved with trehalose, maintain and possibly enhance fresh platelets' ability to improve wound healing. We studied the ability of a single dose of trehalose lyophilized and reconstituted platelets to enhance wound healing when topically applied on full-thickness wounds in the genetically diabetic mouse. We compared these results with the application of multiple doses of fresh platelet preparations and trehalose lyophilized and reconstituted platelets as well as multiple doses of vascular endothelial growth factor (VEGF) and wounds left untreated. Trehalose lyophilized and reconstituted platelets, in single and multiple applications, multiple applications of fresh platelets and multiple applications of VEGF increased granulation tissue deposition, vascularity, and proliferation when compared with untreated wounds, as assessed by histology and immunohistochemistry. Wounds treated with multiple doses of VEGF and a single dose of freeze-dried platelets reached 90% closure faster than wounds left untreated. A single administration of trehalose lyophilized and reconstituted platelet preparations enhanced diabetic wound healing, therefore representing a promising strategy for the treatment of nonhealing wounds.

Platelet-rich plasma: a review of biology and applications in plastic surgery

Healing of hard and soft tissue is mediated by a complex array of intracellular and extracellular events that are regulated by signaling proteins, a process that is, at present, incompletely understood. What is certain, however, is that platelets play a prominent if not deciding role. Controlled animal studies of soft and hard tissues have suggested that the application of autogenous platelet-rich plasma can enhance wound healing. The clinical use of platelet-rich plasma for a wide variety of applications has been reported; however, many reports are anecdotal and few include controls to definitively determine the role of platelet-rich plasma. The authors describe platelet biology and its role in wound healing; the preparation, characterization, and use of platelet-rich plasma; and those applications in plastic surgery for which it may be useful.

Effect of platelet-rich plasma on migration and proliferation of SaOS-2 osteoblasts: role of platelet-derived growth factor and transforming growth factor-beta

Platelet-enriched plasma (PRP) is used in therapy as a source of growth factors in bone fracture and wound healing; however, few data exist on its role in the different aspects of the healing process. The effect of PRP and of the two main growth factors present in this preparation (platelet-derived growth factor [PDGF] and transforming growth factor-beta [TGF-beta]) was evaluated in vitro using the human osteoblastic cell line SaOS-2, which was shown by reverse transcription-polymerase chain reaction to express both PDGF-alpha and -beta receptors. Batroxobine-activated PRP was added in different concentrations to SaOS-2 cells to assess cell migration (by a microchemotaxis assay) and cell proliferation (by [3H]-thymidine incorporation into the DNA). Immunoneutralization with anti-PDGF-beta or anti-TGF-beta antibodies allowed the assessment of the specific role of these growth factors. The overall results obtained indicate that PRP dose-dependently stimulates both chemotaxis and cell proliferation. PDGF and TGF-beta appear to exert distinct effects on the two parameters, the former involved in stimulating cell migration and the latter in inhibiting cell proliferation. It is concluded that the different growth factors present in activated PRP can specifically contribute to the main processes of tissue regeneration.

Evaluation of single and double centrifugation tube methods for concentrating equine platelets

The aim of this study was to evaluate single and double centrifugation tube methods for concentrating equine platelets. Whole blood samples were collected from clinically normal horses and processed by use of single and double centrifugation tube methods to obtain four platelet concentrates (PCs): PC-A, PC-B, PC-C, and PC-D, which were analyzed using a flow cytometry hematology system for hemogram and additional platelet parameters (mean platelet volume, platelet distribution width, mean platelet component concentration, mean platelet component distribution width). Concentrations of transforming growth factor beta 1 (TGF-beta(1)) were determined in all the samples. Platelet concentrations for PC-A, PC-B, PC-C, and PC-D were 45%, 44%, 71%, and 21% higher, respectively, compared to the same values for citrated whole blood samples. TGF-beta(1) concentrations for PC-A, PC-B, PC-C, and PC-D were 38%, 44%, 44%, and 37% higher, respectively, compared to citrated whole blood sample values. In conclusion, the single and double centrifugation tube methods are reliable methods for concentrating equine platelets and for obtaining potentially therapeutic TGF-beta(1) levels.

Platelet content and growth factor release in platelet-rich plasma: a comparison of four different systems

BACKGROUND

Different systems for preparation of platelet-rich plasma are commercially available, but data for comparison of these systems have not been published so far.

MATERIALS AND METHODS

We investigated the performance of Vivostat PRF Preparation Kit, PCCS Platelet Concentrate Collection System, Harvest SmartPReP 2 APC 60 Process, and Fibrinet Autologous Fibrin & Platelet System. The preparations provided by these systems are platelet concentrates with high numbers of platelets in a small volume of plasma and PDGF-AB is released continuously during the 5 days after preparation.

RESULTS

Vivostat PRF Preparation Kit, PCCS Platelet Concentrate Collection System, Harvest SmartPReP 2 APC 60 Process are comparable in platelet yield and total amount of released PDGF-AB after 120 h while with Fibrinet the lowest platelet yield and PDGF-AB content of supernatant was achieved. The ability of growth factor release was equal in all four systems.

CONCLUSION

In conclusion, all four systems for preparation of platelet-rich plasma investigated result in considerable growth factor release. In what extent the total content of PDGF-AB as a consequence of platelet yield has an impact on wound healing has to be further investigated.

Lack of beneficial effects of platelet-rich plasma on sinus augmentation using a fluorohydroxyapatite or autogenous bone: an explorative study

BACKGROUND

Maxillary sinus augmentation is frequently necessary before placement of dental implants in the posterior maxilla. Besides autogenous bone graft, various bone substitutes have been used, with favourable results. Although platelet-rich plasma (PRP) has been used in the field of oral and maxillofacial surgery for years, its beneficial effects on osseous regeneration still remain unclear. The aim of this study was to evaluate the short and long time effects of PRP on single-stage sinus augmentation using autogenous bone or a fluorohydroxyapatite (Algipore) in a randomized prospective animal study.

METHODS

After extraction of maxillary premolars of sixteen minipigs, the wounds were allowed to heal for 2 months. Then, sinus augmentations were performed bilaterally using one of the following grafting materials: autogenous bone and Algipore with or without PRP. Three dental implants (Ankylos) were installed in each sinus simultaneously. Four animals were euthanized at each period of observation (1, 2, 8 and 12 months). Implant-bearing specimens were sectioned bucco-lingually along the long axis of implants and undecalcified ground specimens were prepared. The bone-implant-contact (BIC) was measured by means of microradiographic examination. For histological evaluation, the specimens were stained with toluidin blue, and the percentage of the newly formed bone and the remaining bone substitute were evaluated.

RESULTS

The grafting materials chosen showed increasing levels of BIC and newly formed bone throughout the period of observation in both PRP and non-PRP groups. Adding PRP resulted in lower BIC and newly formed bone compared with autogenous bone grafts or Algipore alone. However, a statistical significance was not found. The percentages of the remaining bone substitute in both the PRP and non-PRP groups were closely comparable in all observation periods.

CONCLUSIONS

The application of PRP could not reveal significant beneficial effects on the BIC, the percentage of the newly formed bone and the remaining bone substitute in this study.

Platelet Rich Plasma: Biology and New Technology

Platelets play a central role in hemostasis and wound healing. The latter is mediated by release of secretory proteins on platelet activation, which directly or indirectly influences virtually all aspects of the wound healing cascade. Studies in basic science have shown a dose-response relationship between the platelet concentration and levels of secretory proteins, as well as between platelet concentration and certain proliferative events of significance to the healing wound. Technologies to provide autologous platelet rich plasma to the repair site are now being used in a wide variety of clinical applications, with the majority of such studies suggesting a role in the surgeon's armamentarium. Little standardization in the field exists, which has made it difficult to fully evaluate the literature on the subject and unequivocally establish applications for which the technology truly has merit. This article presents fundamental background on platelet biology and the role of platelets in both hemostasis and wound healing, as well as methods of preparing, characterizing, and using platelet rich plasma, to provide the reader a foundation on which to critically evaluate prior studies and plan future work.

Tissue regeneration and in loco administration of platelet derivatives: clinical outcome, heterogeneous products, and heterogeneity of the effector mechanisms

BACKGROUND

In loco administration of platelet (PLT) derivatives is a relatively new auxiliary treatment for tissue regeneration to be hastened. Enthusiastic reports are faced by more critical ones. The more obvious rationale for the in vivo administration of PLT derivatives resides in their growth factor content.

STUDY DESIGN AND METHODS

The relevant literature was systematically reviewed. Close scrutiny of the technical details was carried out to find out the procedural differences accounting for conflicting results.

RESULTS

An impressively vast heterogeneity of conduct was found in both in vitro and in vivo studies. Major outcome-affecting variables were recognized such as those associated with PLT preparation; growth factor measurement; proliferation test; dose, timing, and administration of the PLT derivatives; study design; and primary endpoints.

CONCLUSIONS

So many variables were found making standardization or confrontation of the in vitro and the in vivo studies barely conceivable or manageable. The mechanisms of action are very complex. The attribution of tissue regeneration capacity of PLT derivatives solely to the PLT-derived growth factors is simplistic. The results obtained through in vitro experiments are indicative for general mechanisms. Their simplistic hold to the complex in vivo environment may be misleading.

The utilization of autologous growth factors for the facilitation of fusion in complex neuropathic fractures in the diabetic population

A review of current knowledge of autologous growth factors as used in foot and ankle surgery is presented. This knowledge is clinically correlated with 50 Charcot's foot reconstruction patients who had diabetes and who were randomized to a platelet-rich plasma (PRP) concentration system (Symphony, DePuy, Warsaw, Indiana) or a hollow-fiber hemoconcentration system (Interpore Cross AGF, Interpore Cross, Irvine, California) trial. Although the literature supports the notion that Symphony produces a higher yield of intact platelets more consistently, clinically, a statistically significantly higher number of patients treated with Interpore Cross AGF went on to solid fusion. The findings may indicate that one type of PRP may be indicated for a particular clinical circumstance based on the patient's medical history and resultant local wound environment.

Platelet-rich plasmas: growth factor content and roles in wound healing

Platelet-rich plasmas (PRPs) are used in a variety of clinical applications, based on the premise that higher growth factor content should promote better healing. In this study, we have determined the effects of calcium and thrombin on the release of EGF, TGF-alpha, IGF-1, Ang-2 and IL-1beta from PRPs, and assessed the mitogenic potential of PRP supernatants on osteoblast and endothelial cell division. ELISA assays indicate that (i) mean growth factor concentrations vary from traces (TGF-alpha) to 5.5 ng/mL (IGF-1), (ii) there are significant variations in growth factor concentrations between individuals, and (iii) calcium and thrombin regulate growth factor release, synthesis, and/or degradation in stereotyped patterns that are specific to each growth factor. PRP supernatants promote strong osteoblast and endothelial cell divisions, supporting the concept that PRPs may be beneficial in wound healing.

ABBREVIATIONS

PRPs, platelet-rich plasmas; GFs, growth factors; EGF, epidermal growth factor; TGF-alpha, transforming growth factor-alpha; IGF-1, insulin-like growth factor-1; Ang-2, angiopoietin-2; IL-1beta, interleukin-1 beta; HUVECs, human umbilical vein endothelial cells; hFOB 1.19, human fetal osteoblasts; and FBS, fetal bovine serum.

Plateletpheresis does not cause long-standing platelet-derived growth factor release into the donor blood

BACKGROUND

Recently, long-standing elevations of soluble growth factors released from platelets (PLTs) after contact with artificial surfaces during dialysis were described. They could be jointly responsible for the high frequency of death from cardiovascular diseases in dialysis patients. There are no comparable data on the extent and the duration of a growth factor release by plateletpheresis procedures.

STUDY DESIGN AND METHODS

A total of 37 plateletpheresis procedures were performed with two different devices. PLT-derived growth factor (PDGF) isoform AB, transforming growth factor (TGF)-beta1, and beta-thromboglobulin (beta-TG) were measured in the donors' plasma samples, and PLT activation and function were measured by cytometry and aggregometry before and after plateletpheresis and 1 and 24 hours later.

RESULTS

Before apheresis, the following mean plasma levels were found: beta-TG, 98.6 +/- 37.3 IU per mL; PDGF-AB, 71.5 +/- 38.5 pg per mL; and TGF-beta1, 2.24 +/- 0.80 ng per mL. At the end of the apheresis procedures, the mean PDGF-AB level had increased by a factor of 1.8 (p < 0.05). One hour later, the mean PDGF-AB level had normalized again. No significant change in the levels of beta-TG and TGF-beta1 was found by the apheresis procedures. There was no influence of the blood cell separator type on the results.

CONCLUSION

Only a slight and rapidly reversible increase in soluble PDGF-AB was found during plateletpheresis and no increase in soluble TGF-beta1 and beta-TG was found. This change should not be harmful to the donor.

Platelet-Released Supernatant Increases Matrix Metalloproteinase-2 Production, Migration, Proliferation, and Tube Formation of Human Umbilical Vascular Endothelial Cells

BACKGROUND

Local application of platelets represents a promising tool to enhance bone regeneration. New bone formation strictly requires blood vessel formation, a sequential process involving matrix degradation, migration, proliferation, and tube formation of endothelial cells. Here we investigated the impact of secreted granula products from activated platelets on endothelial cells, and determined the involvement of extracellular signal-regulated kinase (ERK) signaling.

METHODS

The effects of platelet-released supernatant on endothelial cells were investigated using in vitro models. Matrix metalloproteinase-2 (MMP-2) release, migration, proliferation, and tube formation of human umbilical vascular endothelial cells (HUVEC) were determined in response to platelet-released supernatant by gelatine zymography, Boyden chamber assay, 3[H]thymidine incorporation, and basement membrane assay, respectively. All experiments were performed in the presence of the ERK signaling inhibitor PD98059. ERK phosphorylation was detected by Western blot analysis.

RESULTS

Incubation with platelet-released supernatant increased the production of MMP-2, migration, proliferation, and tube formation of HUVEC. Platelet-released supernatant also stimulated ERK phosphorylation in HUVEC. Inhibition of ERK signaling decreased platelet-released supernatant-stimulated endothelial cell proliferation, but not MMP-2 activity, migration, and the formation of capillary tubes.

CONCLUSIONS

Our data suggest that secreted granula products from platelets can enhance different stages of blood vessel formation, and that ERK signaling is required to mediate the mitogenic effects of the supernatant. These findings support the hypothesis of a potential link between platelet activation and blood vessel formation during bone regeneration.