Is Platelet-Rich Plasma a Future Therapy in Pain Management?

Platelet-rich plasma (PRP) has the potential to regenerate tissues and decrease pain through the effects of bioactive molecules and growth factors present in alpha granules. Several PRP preparation systems are available with varying end products, doses of growth factors, and bioactive molecules. This article presents the biology of PRP, the preparation of PRP, and the effects PRP-related growth factors have on tissue healing and repair. Based on available evidence-based literature, the success of PRP therapy depends on the method of preparation and composition of PRP, the patient's medical condition, anatomic location of the injection, and the type of tissue injected.

The basic science of platelet-rich plasma (PRP): what clinicians need to know

Platelet-rich plasma (PRP) has been advocated for the biological augmentation of tissue healing and regeneration through the local introduction of increased levels (above baseline) of platelets and their associated bioactive molecules. In theory, the increased levels of autologous growth factors and secretory proteins provided by the concentrated platelets may enhance the wound healing process, especially in degenerative tissues or biologically compromised individuals. Although PRP has been increasingly utilized in the treatment of a variety of sports-related injuries, improvements in healing and clinical outcomes have not been universally reported. One reason for this may be the fact that all PRP preparations are not the same. Variations in the volume of whole blood taken, the platelet recovery efficacy, the final volume of plasma in which the platelets are suspended, and the presence or absence of white blood cells, and the addition of exogenous thrombin to activate the platelets or calcium chloride to induce fibrin formation, can all affect the character and potential efficacy of the final PRP product. This article will review the basic principles involved in creating PRP and examine the potential basic scientific significance of the individual blood components contained in the various forms of PRP currently used in sports medicine.

Optimization of leukocyte concentration in platelet-rich plasma for the treatment of tendinopathy

BACKGROUND

Numerous methods are available for platelet-rich plasma (PRP) generation, but evidence defining the optimum composition is lacking. We hypothesized that leukocyte-reduced PRP would result in lower inflammatory cytokine expression compared with concentrated-leukocyte PRP and that maintaining the platelet:white blood cell (WBC) ratio would compensate for the effect of increased WBC concentration.

METHODS

Blood and flexor digitorum superficialis tendons were collected from young adult horses. Three PRP groups were generated with the same platelet concentration but different WBC concentrations: intermediate-concentration standard PRP, leukocyte-reduced PRP, and concentrated-leukocyte PRP. An additional high-concentration PRP group was generated with the same WBC concentration as the concentrated-leukocyte PRP group and the same platelet:WBC ratio as the standard PRP group. The PRP groups were used as media for flexor digitorum superficialis tendon explants in culture for seventy-two hours with 10% plasma in Dulbecco modified Eagle medium (DMEM) serving as control. Tendon gene expression for collagen types I (COL1A1) and III (COL3A1), cartilage oligomeric matrix protein (COMP), matrix metalloproteinase (MMP-13), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) was performed.

RESULTS

The desired PRP groups were successfully generated. The expression of COMP, the COL1A1:COL3A1 ratio, and the expression of MMP-13 in flexor digitorum superficialis tendon explants was not different between PRP groups. The expression of COMP (p = 0.0027) and the COL1A1:COL3A1 ratio (p < 0.0001) were increased in the PRP groups as compared with the control group, and the expression of MMP-13 was decreased in the PRP groups as compared with the control group (p < 0.0001). The expression of IL-1β was lowest in leukocyte-reduced PRP and highest in concentrated-leukocyte PRP (p = 0.0001). The leukocyte-reduced PRP group and the control group had the lowest TNF-α expression, whereas the high-concentration PRP and concentrated-leukocyte PRP groups had the highest expression (p = 0.0224).

CONCLUSIONS

A high absolute WBC concentration in PRP contributes to the expression of inflammatory cytokines in flexor digitorum superficialis tendon explants, and maintenance of the platelet:WBC ratio is not able to counteract this effect.

CLINICAL RELEVANCE

The optimum composition of PRP for the treatment of tendinopathy has not been directly investigated. Persistent inflammation results in inferior repair with scar tissue. The present study indicates that in an animal model, WBC in PRP contributes to inflammatory cytokine production. Therefore, leukocyte-reduced PRP may be the optimum preparation to stimulate superior healing without scar tissue formation.

Platelet derived cytokine accumulation in platelet concentrates treated for pathogen reduction

BACKGROUND

Pathogen reduction technologies (PRTs) prevent replication and proliferation of pathogens in platelet (PLT) concentrates (PCs) by modifying nucleic acids. Due to increased cell activation, PRT may also lead to increased cytokine release from α granules and promote adverse transfusion reactions in the recipient.

DESIGN

Fifteen double-dose leukoreduced apheresis PCs were collected on the Trima Accel platform (vs. 5.2.) allowing for the resuspension in PLT additive solution (PAS) immediately after collection. After a 2-h resting period (1st hour without, 2nd hour with agitation), splitting was performed: one unit remained untreated to serve as control (C), while the other was riboflavin-UVB treated using the Mirasol-PRT system according to the manufacturer's instructions (M). During 8 days of storage, PCs were analyzed for contaminating white and red blood cells, bacterial growth, PLT activation, LDH and cytokine release (MIP-1 α, RANTES, PF4, and TGF-β-1). Results obtained were opposed to a former study, where triple-dose PCs underwent Mirasol-PRT prior to resuspension or the INTERCEPT BLOOD SYSTEM (psoralen-UVA) or remained untreated.

RESULTS

Despite similar LDH release, PRT treatment was associated with significantly higher (p<0.05) cell activation but only slightly higher cytokine accumulation during storage. Differences became significant only for PF4 and RANTES at day 8 of storage. On the other hand, in the investigation on triple-dose PCs (yielding higher cytokine levels), TGF beta-1 and RANTES remained significantly (p<0.05) lower after PRT treatment compared to untreated units.

CONCLUSION

Factors, such as collection modality, onset of resuspension and additional amounts of magnesium/potassium in the PAS used may be of equal or even greater impact for cytokine accumulation in stored PCs than PRT treatment.

Pilot analysis of cytokines levels in stored granulocyte-colony-stimulating factor-mobilized peripheral blood stem cell concentrates

BACKGROUND

The transfusion of peripheral blood stem cell (PBSC) concentrates is sometimes associated with febrile transfusion reactions. PBSC concentrates contain large numbers of white blood cells, and during storage the levels of soluble cytokines that could cause transfusion reactions may increase.

STUDY DESIGN AND METHODS

Aliquots of granulocyte-colony-stimulating factor (CSF)-mobilized PBSC concentrates from nine healthy subjects were stored in bags at 2 to 8°C for 48 hours. The levels of 19 growth factors and biologic response modifiers were measured in the plasma of PBSC concentrates at 0, 24, and 48 hours of storage using a nested enzyme-linked immunosorbent assay. The same 19 factor levels were also measured in blood plasma from six healthy subjects.

RESULTS

There were no significant differences in the PBSC and plasma levels of soluble interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α, which can cause febrile reactions. The levels of TGF-β1, matrix metalloproteinase-8, CCL5/(reduced on activation normal T expressed and secreted), and platelet (PLT)-derived growth factor-AB were significantly greater in PBSCs than in plasma and the level of CCL2/MCP-1 was significantly less in PBSCs. Duration of PBSC storage had no effect on the levels of these five factors. There was a trend for reduced levels of IL-1β, IL-2, IL-7, IL-8, IL-12p70, IL-15, interferon-γ, CD40L, and granulocyte-macrophage-CSF and increased levels of TNF-α and IL-10 levels in PBSC concentrates, but the differences were not significant.

CONCLUSIONS

There was no increase in stored PBSC concentrates of cytokines that have been associated with febrile transfusion reactions; however, the levels of other factors that were likely released by PLTs and granulocytes during the collection process were elevated.

Temporal growth factor release from platelet-rich plasma, trehalose lyophilized platelets, and bone marrow aspirate and their effect on tendon and ligament gene expression

Platelet-rich plasma (PRP) has generated substantial interest for tendon and ligament regeneration because of the high concentrations of growth factors in platelet alpha-granules. This study compared the temporal release of growth factors from bone marrow aspirate (BMA), PRP, and lyophilized platelet product (PP), and measured their effects on tendon and ligament gene expression. Blood and BMA were collected and processed to yield PRP and plasma. Flexor digitorum superficialis tendon (FDS) and suspensory ligament (SL) explants were cultured in 10% plasma in DMEM (control), BMA, PRP, or PP. TGF-beta1 and PDGF-BB concentrations were determined at 0, 24, and 96 h of culture using ELISA. Quantitative RT-PCR for collagen types I and III (COL1A1, COL3A1), cartilage oligomeric matrix protein (COMP), decorin, and matrix metalloproteinases-3 and 13 (MMP-3, MMP-13) was performed. TGF-beta1 and PDGF-BB concentrations were highest in PRP and PP. Growth factor quantity was unchanged in BMA, increased in PRP, and decreased in PP over 4 days. TGF-beta1 and platelet concentrations were positively correlated. Lyophilized PP and PRP resulted in increased COL1A1:COL3A1 ratio, increased COMP, and decreased MMP-13 expression. BMA resulted in decreased COMP and increased MMP-3 and MMP-13 gene expression. Platelet concentration was positively correlated with COL1A1, ratio of COL1A1:COL3A1, and COMP, and negatively correlated with COL3A1, MMP-13, and MMP-3. White blood cell concentration was positively correlated with COL3A1, MMP3, and MMP13, and negatively correlated with a ratio of COL1A1:COL3A1, COMP, and decorin. These findings support further in vivo investigation of PRP and PP for treatment of tendonitis and desmitis.

Thrombin-induced interleukin 1beta synthesis in platelet suspensions: impact of contaminating leukocytes

A controversial discussion as to whether human platelets are capable of regulated protein synthesis has been ongoing for over half a century. A previous study has suggested that human platelets synthesize large amounts of interleukin 1beta (IL-1beta) in response to external cues and in a physiologically significant manner. However, cytokines such as IL-1beta are generally considered to be products of leukocytes and it could not be completely excluded that contaminating leukocytes may have contributed to the IL-1beta results in platelet preparations. It was therefore our intention to investigate whether residual leukocytes had an impact on thrombin-induced IL-1beta synthesis. Using various methods to reduce the level of contaminating leukocytes, we found that IL-1beta production in platelet-rich suspensions is dependent on the presence of leukocytes, as it was decreased by reducing the number of leukocytes. In addition, we found that thrombin-induced IL-1beta synthesis was completely eliminated in leukocyte-free platelet preparations and could be restored by adding leukocytes. IL-1beta synthesis could be detected in platelet suspensions contaminated with at least 1 leukocyte per 10(5) platelets. This study demonstrated that platelets are incapable of synthesizing detectable amounts of IL-1beta on their own. We suggest that any IL-1beta synthesis detected is a by-product of leukocytes contaminating the platelet preparations. Thus, the hypothesis that platelets producing IL-1beta, provide a new link between thrombosis and inflammation needs to be reconsidered.

Transforming growth factor-beta1, Th1 responses, and autoimmune liver disease

Transforming growth factor-beta1 (TGF-beta1) is released during the storage of blood components, particularly platelet concentrates, and transfusion recipients are exposed to high levels of TGF-beta1. Because TGF-beta1 is one of the most potent immunosuppressive cytokines known, understanding the immunobiologic functions of TGF-beta1 may be relevant for understanding the immunobiologic effects of transfusion. Our laboratory studies the biologic effects of TGF-beta1 in the immune system. Mice deficient in TGF-beta1 spontaneously develop autoimmunity, confirming the important role of this cytokinean an immune regulator. A few years ago, my laboratory made the observation that genetic background strongly affects the phenotype of TGF-beta1-/- mice. TGF-beta1-/- mice on the BALB/c background rapidly develop an aggressive T-cell-mediated hepatitis, whereas TGF-beta1-/- mice on the 129/CF-1 background do not. In this review, I summarize findings published or in press from our laboratory on disease pathogenesis in TGF-beta1-/- mice and then discuss some of the exciting (as-yet-unpublished) directions our laboratory is currently taking.

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.

The influence of platelet additive solutions on cytokine levels and complement activation in platelet concentrates during storage

BACKGROUND AND OBJECTIVES

The accumulation of platelet-derived cytokines in platelet concentrates (PC) during storage may contribute towards non-haemolytic transfusion reactions (NHTR). We investigated the effect of platelet storage medium on platelet activation, complement activation and cytokine levels in leucocyte-reduced PC.

MATERIALS AND METHODS

Hyperconcentrated platelets (3000-6000 x 109/l) were collected by apheresis and diluted in 100% plasma, 70% PASIII, or 70% or 80% PASIII supplemented with magnesium and potassium (PAS IIIM).

RESULTS

Levels of transforming growth factor-beta (TGF-beta) and regulated on activation, normal, T-cell expressed, and secreted (RANTES) increased during storage, as did the expression of P-selectin (CD62P), and were highest in PC stored in PASIII. In PC stored in PASIIIM, however, levels of TGF-beta and RANTES were not significantly different from PC stored in plasma. Levels of CD62P expression, however, remained higher in PASIIIM PC than in those stored in plasma by day 5, but were lower than PC stored in PASIII. C3a des arg levels increased during storage in all media with the exception of PASIII and, on day 7, were higher in PC stored in plasma compared to PC stored in the other media.

CONCLUSIONS

Our results indicate that replacing plasma in PC with unmodified PASIII for storage results in higher levels of platelet-derived cytokines in PC. Furthermore, it appears that the nature of the medium used for storage of PC has a significant impact on platelet activation and cytokine levels of the PC. These implications should be taken into account when considering replacement of plasma with PAS.

Phosphatidylserine exposure in platelet concentrates during the storage period: differences between the platelets collected with different cell separators

BACKGROUND AND OBJECTIVES

Platelet alterations occur during the production and storage of platelet concentrates, the so called "storage lesion". We studied the platelet alterations during the storage period in apheresis concentrates, employing flow cytometry for phosphatidylserine (PS) detection on platelets during the five days of storage.

MATERIAL AND METHODS

Twenty-seven single donor platelet concentrates harvested with the Cobe Trima, Baxter Amicus, or Haemonetics MCS+ were analyzed for PS exposure by flow cytometry on the day of production (day 1) and on days 3 and 5 of storage. Furthermore PS expression was analyzed in platelet donors' blood samples withdrawn before plateletpheresis.

RESULTS

PS expression on platelets gave the following median values: in blood donors before apheresis it was 1.12% (0.13-1.78) in platelets concentrates on the first day (2 h after apheresis) 2.06% (0.66-15.2), the third day 6.57% (1.98-51.13) and the fifth day 23.04% (3.86-80.23). All differences between median values of PS expression in blood samples before apheresis, and platelets concentrates on days 1, 3 and 5 of storage, are statistically significant. The expression of PS in platelet concentrates was analyzed in relation to the blood cell separator used for the collection procedure and showed the following results: on day 1 the median values of PS in platelet concentrates collected with the three different blood cell separators, Trima, Cobe and MCS, did not show statistically significant differences. On day 3, the platelets concentrates collected with the Trima and with the MCS showed differences that were statistically significant. Those were respectively 10.59% (4.56-51.13) and 3.53% (1.98-12.61), p = 0.005. The PS expression in platelet concentrates collected with the Trima and MCS showed differences that are also statistically significant on day 5 at respectively 32.4% (9.61-80.23) and 8.57% (3.86-48.42), p = 0.005.

CONCLUSIONS

PS exposure in platelet concentrates on days 3 and 5 rise to levels that could compromise the quality of the platelet units. Improvements in standardized platelet quality controls, and in platelet collection systems are required to reduce the storage lesions in platelets concentrates.

Cytokine levels as performance indicators for white blood cell reduction of platelet concentrates

BACKGROUND AND OBJECTIVES

With the implementation of universal white blood cell (WBC) reduction in the UK, in-process WBC-reduction filters for pooled buffy coat (BC)-derived platelet concentrates (PCs) and apheresis methods are used routinely for the production of WBC-reduced PCs. While these strategies meet the specification for WBC reduction (< 5 x 10(6) WBCs/unit), the products from these processes may differ depending on the process employed and its performance. The aim of this study was therefore to investigate whether PCs prepared using various WBC-reduction processes are sufficiently depleted of WBCs to limit cytokine accumulation during storage and to assess if cytokine levels detected in platelet products can serve as indicators of acceptable platelet activation as a result of the WBC-reduction process.

MATERIALS AND METHODS

We measured the levels of cytokines predominantly derived from WBCs [e.g. interleukin-8 (IL-8)] and platelets [e.g. regulated on activation, normal, T-cell expressed, and secreted (RANTES) and transforming growth factor-beta(1) (TGF-beta(1))] under the present experimental conditions in different WBC-reduced PCs, i.e. PCs prepared from three different WBC-reduction filters and control non-filtered PCs using pooled BCs from the same donors and three apheresis types. Supernatant plasma was collected at the beginning (day 1) and end (day 5) of the shelf life of each PC, and the cytokine content was determined using appropriate enzyme-linked immunosorbent assays (ELISAs). Process efficiency was assessed by platelet yield and residual WBC count.

RESULTS

We found that products from the apheresis process involving a filtration step (Haemonetics MCS+) showed a lower cytokine content on both day 1 and day 5 in comparison with the fluidized bed (COBE Spectra) or elutriation (Amicus) processes. WBC reduction of BC-PCs of the same origin using three different filters showed comparable levels of cytokines on day 1 in all units. After storage for 5 days, the levels of IL-8 remained essentially unchanged in filtered BC-PCs but increased by more than threefold in control non-filtered BC-PCs, suggesting IL-8 release by residual WBCs present in the control PCs. The concentration of platelet-derived cytokines such as RANTES and TGF-beta(1), however, increased significantly in all filtered and control non-filtered PCs during the storage period.

CONCLUSION

These results show that markers of cytokine release from both WBCs and platelets are useful indicators of the performance and efficacy of the WBC-reduction process and of platelet quality.

Pathophysiology of febrile nonhemolytic transfusion reactions

Most febrile nonhemolytic transfusion reactions (FNHTR) to platelets are caused by cytokines that accumulate in the product during storage. There have been numerous studies that have demonstrated high concentrations of leukocyte- and platelet-derived cytokines in stored platelet products. The mechanism of cytokine accumulation is not understood; however, recent studies have suggested that leukocyte apoptosis and/or monocyte activation during the manufacturing process may play a role. Additional support of cytokines as a cause of FNHTR is provided by a recently published randomized controlled trial that shows that removal of the supernatant plasma from platelets before transfusion significantly lowers the frequency of reactions and eliminates most of the severe reactions associated with platelet transfusions. Although cytokines appear to play a major role in causing platelet reactions, there is little evidence to support their role in causing erythrocyte reactions. Hence, it appears that most febrile nonhemolytic transfusion reactions to erythrocytes are probably the result of an incompatibility between leukocytes in the erythrocyte product and antibodies in the recipient's plasma. Recent studies have confirmed that the concentrations of proinflammatory cytokines in a wide variety of stored erythrocyte products are low. Also, there is no clinical evidence to suggest that the small quantities of cytokines present in stored erythrocyte products contribute to acute reactions to these products when transfused.

Storage of blood components

Recent studies have shown that a restrictive transfusion policy results in lower mortality in patients undergoing surgery. The negative effects of red cell transfusion are associated with the presence of contaminating leukocytes, leukocyte products, and probably also with effects of nonviable and poorly functioning red cells. By relatively simple means it is possible to improve the quality of red cells in these respects. The removal of leukocytes from platelet concentrates (PCs) is even more important because of high immunogenicity and capacity to produce cytokines under the storage conditions applied. Prestorage leukocyte removal has clear advantages. Bacterial contamination of PCs is common, but fatal bacterial complications are rare because most contaminating microorganisms grow slowly and do not produce toxins, which are frequent causes of death. Suitable methods for routine bacterial culture of PCs are available and used in some countries.