Use of a Cyclooxygenase-2 Inhibitor Does Not Inhibit Platelet Activation or Growth Factor Release From Platelet-Rich Plasma

Interactions Between Biologic Therapies and Other Treatment Modalities

Biologic therapies are becoming increasingly utilized by veterinarians. The literature regarding the interaction of biologic therapies with other therapeutics is still in its infancy. Initial studies have examined the effects of exercise, stress, various pharmaceutical interventions, extracorporeal shockwave, therapeutic laser, and hyperbaric oxygen on biologic therapies. Continued research is imperative as owners and veterinarians increasingly choose a multimodal approach to injury and illness. Further, understanding the effects of concurrently administered treatments and pharmaceuticals as well as the health status of the horse is imperative to providing the optimal therapeutic outcome.

Equine Platelet-Rich Plasma

Platelet-rich plasma (PRP) is an orthobiologic therapy composed of platelets, leukocytes, red blood cells, and plasma proteins. PRP has been used for 20 years, but progress determining efficacy has been slow. The definitions and classification of PRP are reviewed, and the use of PRP for tendon, ligament, and joint disease is discussed with a focus on findings of basic science and clinical studies, platelet activation, concurrent administration of nonsteroidal anti-inflammatory drugs, and treatment complications. Finally, the advantages of platelet lysates and freeze-dried platelets are discussed. The promising results of a PRP lysate optimized for antibiofilm and antimicrobial properties are introduced.

Submucosal Injection of Activated Platelet-Rich Plasma for Treatment of Periodontal Disease in Dogs

Periodontal disease is the most common oral disease seen in dogs, and its routine treatment usually involves dental scaling. Platelet-rich plasma (PRP) therapy may enhance the effectiveness of treatment of periodontal disease, delay the progression of the disease and decrease the time under anesthesia. However, its application in dogs is rarely discussed. The objective of this study was to evaluate the benefits of activated PRP for treatment of periodontal disease in dogs. 43 mL of whole blood was collected from six adult dogs and PRP extracted using the double centrifugation tube method. Subsequently, the PRP was activated using calcium chloride (A-PRP). Significantly elevated concentrations of PDGF-BB (7000.28 pg/mL), TGF-β (378.98 pg/mL), and VEGF (7.14 pg/mL) were detected in the A-PRP. Additionally, three of the dogs with stage 2-3 periodontal disease were enrolled in the clinical trial. Periodontal pocket depth, stage of periodontal disease, gingival index, horizontal bone loss, and alveolar bone density involving the maxillary third and fourth premolar and first molar teeth (107, 108, 109, 207, 208, and 209) were evaluated. Teeth were treated by dental scaling alone (control group) or by dental scaling followed by submucosal injection of 0.1 mL A-PRP per site. After 56 days, significant improvement in periodontal pocket depth, stage of periodontal disease, gingival index, and horizontal bone loss was observed in dogs injected with A-PRP. The high concentrations of growth factors in A-PRP likely contributed to this effect. The use of submucosal injections of A-PRP to treat canine stage 2-3 periodontal disease appears safe and effective for clinical practice.

Medium-Term Effect of Treatment with Intra-Articular Injection of Sodium Hyaluronate, Betamethasone and Platelet-Rich Plasma in Patients with Temporomandibular Arthralgia: A Retrospective Cohort Study

Temporomandibular joint disorders are associated with pain and reduced jaw mobility. The aim of this study was to compare the long-term effect on pain of intra-articular TMJ injections of betamethasone, sodium hyaluronate and platelet-rich plasma. The sample was made up of 114 patients, who were randomly distributed into three groups at least three years ago and who achieved a total remission of pain after treatment. We found that the median number of months without pain was, according to each group, as follows: platelet-rich plasma: 33; sodium hyaluronate: 28; betamethasone: 19. Both platelet-rich plasma and sodium hyaluronate lead to significant pain-free time after treatment; when we compare bethametasone with the two other substances, it proved to be very ineffective.

Common Medications Which Should Be Stopped Prior to Platelet-Rich Plasma Injection

Osteoarthritis (OA) is an extremely prevalent joint condition in the United States, affecting over 30 million people [...]

Effect of Leukoreduced Platelet Rich Plasma on Intra-Articular Pro-Inflammatory Cytokines in a Canine Pilot Study

Simple Summary

This study provides initial information on the effect of platelet rich plasma in some of the most important pro-inflammatory cytokines identified in osteoarthritic stifle joint in dogs. The use of platelet rich plasma is getting more popular in the veterinary field but its effect in those cytokines is not known.

Abstract

Evaluation of effect of Leukoreduced Platelet Rich Plasma (LrPRP) on TNF-α and IL-6 (pro-inflammatory cytokines) in joint fluid in dogs with cranial cruciate ligament rupture (CCLR). Eight client-owned dogs with CCLR were assigned to treatment (2 mL LrPRP) or control (2 mL saline) injection groups. Day of evaluation (day 0) and day of surgery (day 10–14), joint fluid was collected and joint injected. Joint fluid was also collected on day of suture removal (day 20–28). TNF-α and IL-6 concentrations of joint fluid were measured using a bead-based antibody assay. Concentrations at the later time points were expressed as a ratio to the initial level within each stifle. LrPRP had a mean concentration of platelets 1.7 times higher that of whole blood on day of evaluation and 1.4 times higher on day of the surgery. Leukocytes were reduced by 99.7%. On day of surgery, TNF-α ratios in the joint fluid from dogs injected with LrPRP were significantly different that TNF-α ratios of control group. On the day of suture removal ratios of IL-6 and TNF-α were lower in LrPRP treatment group compared with control group; however, differences were not significant. LrPRP modulate ratios of pro-inflammatory cytokine TNF-α in dogs with CCLR.

Platelet-Rich Plasma as an Orthobiologic: Clinically Relevant Considerations

Platelet-rich plasma (PRP) is an autologous blood-derived product processed to concentrate platelets and the associated growth factors. PRP has been shown to be relatively well-tolerated and safe to use for a number of conditions in humans, equines, and canines. There are multiple commercial systems that have been validated for canine use. These systems use a variety of methodologies to produce a PRP product. However, PRP products have been shown to differ greatly between systems. Further study is needed to fully elucidate optimal component concentrations for various indications.

Device-Based Enrichment of Knee Joint Synovial Cells to Drive MSC Chondrogenesis Without Prior Culture Expansion In Vitro: A Step Closer to 1-Stage Orthopaedic Procedures

BACKGROUND

Synovial fluid (SF) mesenchymal stem cells (MSCs) are derived from the synovial membrane and have cartilage repair potential. Their current use in clinical practice is largely exploratory. As their numbers tend to be small, therapeutic procedures using MSCs typically require culture expansion. Previous reports indicate that the stem cell-mobilizing device (STEM device) intraoperatively increases SF-MSCs.

PURPOSE

This study evaluated the chondrogenic potential of non-culture expanded synovium-mobilized MSCs and SF-microfragments obtained after enrichment using the STEM device and ascertained if device-mediated synovial membrane manipulation facilitated ongoing MSC release.

STUDY DESIGN

Controlled laboratory study.

METHODS

Two samples of aspiration fluid were collected intraoperatively before and after STEM device utilization from patients (n = 16) undergoing diagnostic or therapeutic knee arthroscopy. Human knee synovium (n = 5) was collected during total knee replacement, and a suspended culture was performed to assess the effect of the STEM device on ongoing MSC release. Colony forming unit-fibroblastic assays were used to determine the number of MSCs. Additionally, cytometric characterization of stromal and immune cells and chondrogenesis differentiation assay were performed without culture expansion. Filtered platelet concentrates were prepared using the HemaTrate system.

RESULTS

After STEM device use, a significant increase was evident in SF-MSCs (P = .03) and synovial fluid-resident synovial tissue microfragments (P = .03). In vitro-suspended synovium released significantly more MSCs following STEM device use than nonstimulated synovium (P = .01). The STEM device-released total cellular fraction produced greater in vitro chondrogenesis with significantly more glycosaminoglycans (GAGs; P < .0001) when compared with non-STEM device synovial fluid material. Nonexpanded SF-MSCs and SF-microfragments combined with autologous filtered platelet concentrate produced significantly more GAGs than the complete chondrogenic media (P < .0001). The STEM device-mobilized cells contained more M2 macrophage cells and fewer M1 cells.

CONCLUSION

Non-culture expanded SF-MSCs and SF-microfragments had the potential to undergo chondrogenesis without culture expansion, which can be augmented using the STEM device with increased MSC release from manipulated synovium for several days. Although preliminary, these findings offer proof of concept toward manipulation of the knee joint environment to facilitate endogenous repair responses.

CLINICAL RELEVANCE

Although numbers were small, this study highlights 3 factors relevant to 1-stage joint repair using the STEM device: increased SF-MSCs and SF-microfragments and prolonged synovial release of MSCs. Joint repair strategies involving endogenous MSCs for cartilage repair without the need for culture expansion in a 1-stage procedure may be possible.

Is Antiplatelet Therapy Contraindicated After Platelet-Rich Plasma Treatment? A Narrative Review

Background

Antiplatelet therapies are often withheld before and after platelet-rich plasma product (PRPP) administration due to theoretical concerns that therapies that inhibit the function of platelets would inhibit the effects of PRPP.

Purpose/Hypothesis

The purpose of this study was to evaluate the effect that antiplatelet therapies have on the ability of PRPP to stimulate wound healing and tissue regeneration. Our hypothesis was that antiplatelet therapies would have highly heterogeneous effects on the biological activity of PRPP.

Study Design

Narrative review.

Methods

The Medline database was searched via PubMed to identify all studies related to PRPP and antiplatelet therapies, yielding 1417 publications. After the search was confined to articles published after 1995, there were 901 articles remaining. All abstracts were then screened to identify animal or human clinical studies that focused on growth factor or inflammatory cytokine production or treatment outcomes. We limited our analysis to studies reporting on orthopaedic pathologies and in vitro studies of antiplatelet therapies. Ultimately, 12 articles fit the search criteria.

Results

The majority of studies reported on the use of nonsteroidal anti-inflammatory drugs as antiplatelet therapy. The majority of studies were in vitro analyses of growth factors, inflammatory cytokines, or cell viability, whereas 1 study examined clinical outcomes in an animal model. None of the studies investigated clinical outcomes in humans. All of the studies showed no effect or mixed effects of antiplatelet therapies on PRPP efficacy. One study showed PRPP recovery to baseline function after a 1-week washout period.

Conclusion

The literature did not provide support for the common clinical practice of withholding antiplatelet therapies in patients being treated with PRPP.

Intra-articular injections of platelet-rich plasma in symptomatic knee osteoarthritis: a consensus statement from French-speaking experts

PURPOSE

There has been much debate regarding the use of intra-articular injections of platelet-rich plasma (PRP) as symptomatic treatment for knee osteoarthritis. The objective of this consensus was to develop guidelines for PRP injections in knee osteoarthritis according to the French National Authority for Health recommendations.

METHODS

Fifteen physicians from different French-speaking countries (10 rheumatologists, 4 specialists in rehabilitation and sports medicine and 1 radiologist) were selected for their expertise in the areas of PRP and osteoarthritis. A comprehensive literature review was conducted on Medline including all published therapeutic trials, open studies, meta-analysis and systematic reviews focusing on the effects of PRP in knee OA, as well as fundamental studies concerning the characteristics of the various types of PRP and their mechanisms, indexed before April 2019. Using the method recommended by the French National Authority for Health inspired by the Delphi consensus process, 25 recommendations were finally retained and evaluated. The recommendations were classified as appropriate or not appropriate, with strong or relative agreement, or uncertain if a consensus was not achieved.

RESULTS

Among the 25 recommendations selected, the main ones are the following: (1) Intra-articular injections of PRP are an effective symptomatic treatment for early to moderate knee osteoarthritis. This recommendation was considered appropriate with a relative agreement (Median = 8; rank = 6-9). Level of evidence 1A. (2) A PRP treatment sequence in knee osteoarthritis may include 1-3 injections. This recommendation was considered appropriate with a strong agreement (Median = 9; rank = 7-9). Level of evidence 1A. (3) Leucocytes-poor PRP should be preferred in knee osteoarthritis. This recommendation was considered appropriate with a relative agreement (Median = 8; rank = 5-9). Level of evidence 5. (4) Intra-articular PRP knee injections should be performed under ultrasound or fluoroscopic guidance. This recommendation was considered uncertain with no consensus (Median = 8; rank = 3-9). Level of evidence 5. (5) PRP should not be mixed with an anesthetic or intra-articular corticosteroid. This recommendation was considered appropriate with a relative agreement (Median = 9; rank = 6-9). Level of evidence 5 CONCLUSION: Those 25 recommendations should standardize and facilitate the use of IA PRP injections, which are considered by experts as an effective treatment especially in early or moderate knee OA. Although a strong or relative agreement from the experts was obtained for most of the recommendations, many of them had a very low level of evidence (Level 5) and were principally based on the clinical experience of the experts.

Platelet-rich plasma loaded with antibiotics as an affiliated treatment for infected bone defect by combining wound healing property and antibacterial activity

To be faced with an infected bone defect and the need to accelerate bone union while controlling infection is a welcome challenge for orthopedists. Platelet-rich plasma (PRP) has been applied in tissue defects given their composition of growth factors however the weak antibacterial effects have limited the use of PRP in the clinical setting. Therefore, the aim of this study was to explore the feasibility of using PRP in a local antibiotic delivery system (PADS) with the characteristics of promoting wound healing of bone infection. PADS was prepared with the addition of antibiotics or no antibiotics as control after PRP was prepared by a two-step centrifugation procedure. Antibacterial tests showed zones of inhibition produced by antibiotics were not significantly different with antibiotics combined with PRP. HPLC analysis demonstrated that about 60% of the total vancomycin (VAN) and ceftazidime (CAZ) dose were released within 10 min, then the release rate gradually decreased. However, 90% clindamycin was released within 10 min. Interestingly, above 10 times the minimum inhibitory concentration was presented after 72 h. Additionally, ELISA and morphology studies of PADS indicated that loaded antibiotics could reduce the PRP-released growth factor concentration and disturb the structure of platelet-fibrin beams and fibrin network in a dose-dependent manner. Fortunately, the lower dose of antibiotics maintained their anti-microbial effect, meanwhile growth factors released from PADS, the structure of platelet-fibrin beams, fibrin network remained unaffected. In addition, a patient experiencing infected bone defect receiving this PADS treatment achieved union within the 15-month follow-up. Therefore, this novel PADS approach might represent a potential therapy for patients who have sustained infected bone defects.

Effects of Antiplatelet and Nonsteroidal Anti-inflammatory Medications on Platelet-Rich Plasma: A Systematic Review

Background:

Platelet-rich plasma (PRP) has wide applications in orthopaedic care. Its beneficial effects are attributed to the growth factor profile from the platelet secretome. In theory, these effects would be diminished by medications that inhibit platelet activation and/or the subsequent release of growth factors.

Purpose:

To determine whether commonly used antiplatelets, nonsteroidal anti-inflammatory drugs (NSAIDs), or anticoagulant medications affect platelet growth factor release in PRP.

Study Design:

Systematic review; Level of evidence, 2.

Method:

A systematic review of the literature related to antiplatelet, anti-inflammatory, and anticoagulant drugs was performed following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. We used the Downs and Black objective quality scoring system. The literature search consisted of PubMed and Cochrane Library databases. Search terms consisted of 1 item selected from “platelet-rich plasma,” “platelet-derived growth factor,” and “platelet-rich plasma AND growth factor” combined with 1 item from “antiplatelet,” “aspirin,” “anticoagulant,” and “NSAID.” Only studies published within the past 25 years were included.

Results:

A total of 15 studies met the inclusion criteria: 7 studies detected no significant decrease in growth factors or mitogenesis, whereas 6 detected a decrease with antiplatelet agents, 1 detected mixed results with an antiplatelet agent, and 1 had mixed results with an antiplatelet agent/vasodilator. In terms of PRP activation, all 3 studies assessing collagen, the 2 studies analyzing adenosine diphosphate alone, and the 1 study investigating arachidonic acid found a decrease in growth factor concentration.

Conclusion:

Antiplatelet medications may decrease the growth factor release profile in a cyclooxygenase 1– and cyclooxygenase 2–dependent manner. Eight of 15 studies found a decrease in growth factors or mitogenesis. However, more studies are needed to comprehensively understand antiplatelet effects on the PRP secretome.

Post-Procedure Protocols Following Platelet-Rich Plasma Injections for Tendinopathy: A Systematic Review

OBJECTIVE

Platelet-rich plasma (PRP) has been increasingly studied as a treatment for tendinopathy. Many factors may influence outcomes after PRP, including different protocols following administration. It was hypothesized that there would be heterogeneity in post-PRP protocols.

LITERATURE SURVEY

A systematized review of the literature on post-PRP protocols for tendinopathy was conducted using an electronic search of MEDLINE and Embase databases through September 2018.

METHODOLOGY

After duplicates were removed, English language articles involving adult patients who received PRP for tendinopathy were reviewed. Exclusion criteria included studies with fewer than 10 patients, PRP used to treat pathology other than tendinopathy, multiple protocols in one study, and surgical settings. Protocol specifics were extracted including nonsteroidal anti-inflammatory drugs (NSAID) restrictions before and after injection, postinjection restrictions on movement and weight bearing, use of orthoses, activity modifications, and postinjection rehabilitation protocols. Given limitations in the data, a meta-analysis was not performed.

SYNTHESIS

Eighty-four studies met inclusion criteria. Following PRP injection, weight-bearing restrictions were mentioned rarely (12% of protocols). Orthosis use was uncommon overall (18%) but more common in Achilles tendinopathy protocols (53%). The majority of protocols instituted a period of stretching (51%) and strengthening (54%). Stretching programs generally began 2-7 days following injection, and strengthening programs began within 2-3 weeks. Preinjection NSAID restriction was reported rarely (20%), whereas postinjection NSAID restriction was more common (56%), with a typical restriction of greater than 2 weeks (38%). Return to play or full activity was reported in 42% of protocols, most commonly at 4-6 weeks following injection.

CONCLUSION

Although the clinical effectiveness of PRP remains controversial, even less is known about the effect of post-PRP protocols, which may affect the outcomes attributed to PRP itself. No studies directly compare post-PRP protocols, and the protocols studied demonstrate substantial heterogeneity. Some consensus regarding post-PRP protocols exists, although the rationale for these recommendations is limited.

Effects of Aspirin on Growth Factor Release From Freshly Isolated Leukocyte-Rich Platelet-Rich Plasma in Healthy Men: A Prospective Fixed-Sequence Controlled Laboratory Study

BACKGROUND

The benefits of platelet-rich plasma (PRP) are believed to be in part dependent on growth factor release after platelet activation. Platelet activation is complex and involves multiple mechanisms. One important mechanism is driven by cyclooxygenase 1 (COX-1)-mediated conversion of arachidonic acid (AA) to precursor prostaglandins that then mediate proinflammatory responses that trigger growth factor release. Acetylsalicylic acid (ASA; also known as aspirin) is known to irreversibly inhibit COX-1, thereby blocking AA-mediated signaling; however, it is unclear whether ASA use alters growth factor release from freshly isolated PRP.

PURPOSE

To assess the effects of low-dose ASA use on activation of growth factor release from freshly isolated human PRP via AA and thrombin (TBN).

STUDY DESIGN

Controlled laboratory study.

METHODS

Twelve healthy men underwent blood collection and leukocyte-rich PRP (LR-PRP) preparation through a double-spin protocol to obtain baseline whole blood and PRP counts the same day. PRP was aliquoted into 3 groups: nonactivated, AA activated, and TBN activated. Immediately after activation, the concentrations of transforming growth factor β1 (TGF-β1), vascular endothelial growth factor (VEGF), and platelet-derived growth factor AB (PDGF-AB) were measured using enzyme-linked immunosorbent assays (ELISAs). The same 12 participants were then placed on an 81-mg daily dose of oral ASA for 14 days. Repeat characterization of whole blood and PRP analyses was done on day 14, followed by repeat ELISAs of growth factors under the same nonactivated and activated settings as previously stated.

RESULTS

Fourteen days of daily ASA had no effect on the number of platelets and leukocytes measured in whole blood and LR-PRP. Compared with nonactivated LR-PRP, AA- and TBN-mediated activation led to significant release of VEGF and PDGF-AB. In contrast, release of TGF-β1 from LR-PRP was observed only with activation by AA, not with TBN. Consistent with its inhibitory role in AA signaling, ASA significantly inhibited AA-mediated release of all 3 growth factors measured in this study. Although ASA had no effect on TBN-mediated release of VEGF and TGF-β1 from LR-PRP, ASA did partially block TBN-mediated release of PDGF-AB, although the mechanism remains unclear.

CONCLUSION

Daily use of low-dose ASA reduces VEGF, PDGF-AB, and TGF-β1 expression in freshly isolated human LR-PRP when activated with AA.

CLINICAL RELEVANCE

Reduction in growth factor release attributed to daily use of low-dose ASA or other COX inhibitors can be mitigated when PRP samples are activated with TBN. Clinical studies are needed to determine whether activation before PRP injection is needed in all applications where ASA is in use and to what extent ASA may inhibit growth factor release in vivo at the site of injury.

Clinical Update: Why PRP Should Be Your First Choice for Injection Therapy in Treating Osteoarthritis of the Knee

PURPOSE OF REVIEW

The purpose of this review is to update the reader on the current applications of platelet-rich plasma (PRP) in the treatment of knee osteoarthritis (KOA). This review will focus on PRP's effect on the osteoarthritic joint, how PRP compares to traditional treatments of KOA, and provide clinical feedback on the use of PRP in an orthopedic and sports medicine practice.

RECENT FINDINGS

Recent research into the applications of PRP for KOA has further indicated both the efficacy and safety of PRP treatment. Although research has shown a tendency toward better efficacy at earlier stages of osteoarthritis (OA), evidence exists to indicate positive effects at all stages of OA. In summary, since KOA is an extremely prevalent condition that can be a challenge to treat, it is imperative that safe and effective nonoperative treatment methods be available to individuals that are suffering from this condition.

The clinical efficacy of using autologous platelet-rich plasma in total hip arthroplasty: A retrospective comparative study

This study evaluated whether intra-articular platelet-rich plasma (PRP) might prevent postoperative bleeding in total hip arthroplasty (THA).In this study, 260 hips that underwent THA were evaluated randomly by paramedical staffs, 130 of which involved the intraoperative use of PRP, and 130 of which served as control group. Postoperative blood loss (drain bag volume), estimated blood loss, and change in hemoglobin (Hb) at day 1, 2, 4, and 7 were analyzed, respectively.PRP-treated group had a significant decrease in mean postoperative blood loss (92.6 ± 168.2 mL) compared to control group (682.3 ± 185.5 mL, P < .01). The mean postoperative estimated blood loss (526.1 ± 236.1 mL) in the PRP-treated group was significantly less than that in the control group (629.2.2 ± 142.3 mL, P < .01). There was a statistically significant difference in Hb value (mg/dL) at day 1, 2, 4, and 7 (-1.35 vs -1.98, -1.59 vs -2.52, -1.96 vs -2.82, and -1.76 vs -2.47, P < .05).We found a significant reduction in postoperative blood loss (drain bag volume), estimated blood loss, and change in Hb after the use of autologous platelet gel in patients of THA, and PRP appears to be effective in reducing postoperative bleeding in THA.

Assessment of Canine Autologous Conditioned PlasmaTM Cellular and Transforming Growth Factor-β1 Content

To evaluate (1) the cellular composition of canine ACP™ including using two different preparation protocols with variations on centrifugation time, (2) the effect of different activation protocols on the transforming growth factor (TGF)-β1 content in the ACP, and (3) patient factors that might influence platelet concentration of the ACP.

ACP was made with blood from 15 dogs using a manufacturer-recommended protocol^[1]. Each ACP sample was divided into three aliquots that were activated with calcium chloride (CaCl₂), human γ-thrombin (HGT), or not activated. TGF-β1 was quantified in each aliquot using an ELISA and comparisons among activation protocols were performed using a Skillings-Mack test. Correlations between platelet and TGF-β1 concentration were assessed with a Pearson correlation coefficient. ACP was subsequently prepared from an additional 17 dogs using a slightly modified centrifugation protocol and cellular composition was assessed. Effects of dog age, body weight, and hematocrit were assessed for their potential impact on ACP platelet concentration using a multiple linear regression analysis.

The mean increase in platelet concentration in the ACP above that in the whole blood was 1.2× (±std 0.62) and leukocyte concentration was a mean of 26% (0.37) that in the whole blood using the standard protocol. There was a significant (p < 0.01) effect of activation on TGF-β1 concentrations with mean concentrations of 4,538 (2,317), 14,948 (13,784), and 14,096 (15,210) pg/ml in aliquots that were not activated or were activated with thrombin or CaCl₂ respectively. There were significant correlations between the platelet concentration and TGF-β1 concentration in aliquots that were activated with either thrombin (r = 0.66; p < 0.01) or CaCl₂ (r = 0.86, p < 0.0001). The mean increase in platelet concentration was 1.4× (0.62) and the leukocyte concentration was 0.28× (0.13) that in whole blood using the modified ACP preparation protocol. Dog age, body weight, and hematocrit were not significant predictors of ACP platelet concentration.

These data show that on average this preparation protocol produces a mildly platelet-concentrated, leukoreduced platelet-rich plasma. Intentional activation had a significant effect on TGF-β1 concentrations with use of both CaCl₂ and thrombin resulting in higher TGF-β1 concentrations than that obtained in samples that are not activated.