Platelet lysates represent an emerging tool for the treatment of ocular surface diseases. Here, we propose a method for the preparation, dispensation, storage, and characterization of platelet lysate collected from platelet donors.
Various ocular surface diseases are treated with blood-derived eye drops. Their use has been introduced in clinical practice because of their metabolite and growth factor content, which promotes eye surface regeneration. Blood-based eye drops can be prepared from different sources (i.e., whole blood or platelet apheresis donation), as well as with different protocols (e.g., different dilutions and freeze/thaw cycles). This variability hampers the standardization of clinical protocols and, consequently, the evaluation of their clinical efficacy. Detailing and sharing the methodological procedures may contribute to defining common guidelines. Over the last years, allogenic products have been diffusing as an alternative to the autologous treatments since they guarantee higher efficacy standards; among them, the platelet-rich plasma lysate (PRP-L) eye drops are prepared with simple manufacturing procedures. In the transfusion medicine unit at AUSL-IRCCS di Reggio Emilia, Italy, PRP-L is obtained from platelet-apheresis donation. This product is initially diluted to 0.3 x 109 platelets/mL (starting from an average concentration of 1 x 109 platelets/mL) in 0.9% NaCl. Diluted platelets are frozen/thawed and, subsequently, centrifuged to eliminate debris. The final volume is split into 1.45 mL aliquots and stored at −80 °C. Before being dispensed to patients, eye drops are tested for sterility. Patients may store platelet lysates at −15 °C for up to 1 month. The growth factor composition is also assessed from randomly selected aliquots, and the mean values are reported here.
Blood-derived products are widely used in wound care1, maxillofacial and orthopedic surgery, and for the treatment of different ocular surface diseases2 such as dry eye disease (DED)3. In DED, the tear film homeostasis is impaired as a consequence of the abnormal functioning of different factors involved in tear production and ocular surface integrity4,5.
DED is characterized by heterogeneity in causes and severity6,7,8 and may be a consequence of different factors like aging, sex9, contact lenses, topical or systemic medications10, or pre-existing conditions like Sjögren's syndrome10. Despite having mild symptoms, DED affects millions of people worldwide, impacting their quality of life and the health system as well6.
Many treatments have been reported for this pathology, but there is still no consensus on the most effective solution12. To date, artificial tears are the first line of therapy aimed at restoring the aqueous composition of the tear film, albeit these substitutes do not contain the main biologically active solutes of natural tears6,11. Platelet-based products are considered a valid alternative12,13 to artificial tears, although their clinical efficacy, recommendations for use, and methods of preparations are still a matter of debate3.
Blood-based products share with tears a similar composition in terms of metabolites14, proteins, lipids, vitamins, ions, growth factors (GFs), antioxidant compounds11 and osmolarity (300 mOsm/L)11. Through the synergistic activity of their components, they promote the regeneration of the corneal epithelium, inhibit the release of inflammatory cytokines, and increase the number of goblet cells and the expression of mucins in the conjunctiva2,3.
So far, heterogeneity in ophthalmic blood-based products has been documented in the literature; these products can be classified according to the blood donors' origin, i.e., autologous, or allogenic, as well as the blood source, i.e., peripheral blood, cord blood, serum, or platelets.
Although autologous products were the most widespread3, allogenic ones are now becoming the preferred choice, since they ensure higher efficacy and safety standards15, together with a significant reduction in costs16,17. Previous studies, indeed, proved that blood-based products obtained from patients with autoimmune and/or systemic diseases may show altered quality and functionality6,16,17. Despite the fact that serum-based eye drops are the most widespread, platelets-based products are recently becoming affirmed as a valid alternative, as they can be easily prepared while maintaining significant levels of efficacy3,11. Currently available platelet-based products can be divided in platelet-rich plasma (PRP), platelet-rich plasma lysate (PRP-L), and plasma rich in growth factors (PRGF)3.
Among them, PRP-L has the advantage of being a long-life frozen product. PRP-L can be prepared from apheresis, buffy-coats, or even from expiring platelets (PLTs)18,19, preciously reducing their wastage. The aliquots can be stored for months in the blood transfusions centers at −80 °C or even at patients' homes at −15 °C for shorter periods.
PRP-L are highly enriched in GFs, which have been proved to stimulate eye surface regeneration12,20,21. Nevertheless, there are only few reported clinical studies in this area, and all of them used autologous sources3,22. PRP-L still needs further validation and characterization before it can be routinely used for the treatment of eye surface diseases, since there are no standardized guidelines for its preparation, dispensation, and storage3.
Herein, a detailed protocol is shared for the production of PRP-L used at the Transfusion Medicine Unit in AUSL-IRCCS di Reggio Emilia, Italy, and dispensation to patients with DED. We aim to help the scientific community to develop standard methods of preparation, which may increase homogeneity and consistency in worldwide studies and clinical approaches.
PRP-L used for the quantitative assessment of growth factors were collected within a wider study on the characterization of PRP products for regenerative purposes, carried out at the AUSL-IRCCS di Reggio Emilia and approved by the Area Vasta Emilia Nord Ethical Committee on 10 January, 2019 (protocol number 2019/0003319). Donors gave their informed consent as per the Declaration of Helsinki. No ethical approval was necessary for collecting the aggregated, anonymous data of the Ocular Surface Disease Index (OSDI) questionnaire, which is routinely used by clinicians to monitor dry eye syndrome symptoms. Figure 1A shows an outline of the protocol followed, while the pictures in Figure 1B depict the main steps of the procedure.
1. Platelet-rich plasma (PRP) collection
2. Platelet-rich plasma lysate (PRP-L) preparation
3. PRP-L dispensation
The rationale for the use of serum-derived eye drops (which is the blood-based product most frequently used for the treatment of eye surface diseases) lies in their content of GFs, which are almost completely derived from circulating platelets. PRP contains a significantly higher number of platelets (and, consequently, of platelet-derived GFs) compared to peripheral blood serum, ranging between 0.15 x 109-0.45 x 109 PLTs/mL. According to Italian laws, the platelet count in PRP units should be at least 0.9 x 109-1 x 109 PLTs/mL. Therefore, to obtain a product that simulates the efficacy of serum eye drops, PRP should be diluted to the physiological platelet content before lysate preparation.
Nevertheless, since tissue repair is mainly driven by platelet-derived GFs, the PLT scount alone might be misleading for an effective therapy of eye surface diseases. In DED, which is the eye disease most commonly treated with blood-derived eye drops, tear film production and homeostasis are impaired. Platelet-based products for the treatment of DED, therefore, should also mimic the physiological content of tears.
To identify the most suitable PRP-L for treating eye surface diseases, described in step 1.3.2. of the present protocol, we preliminarily assessed different PRP dilutions, according to their PLTs content (between 0.7 x 109/mL and 0.3 x 109/mL), and some representative GFs from those that are known to be involved in eye tissue repair12,20,21.
Platelet count was performed with a hemocytometer, while GFs were assessed by means of a multiplex protein quantification assay. The assay was performed as previously described25 according to the manufacturer's instructions. GFs shown in this manuscript were selected for quantification after a preliminary screening of 36 GFs and GFRs performed on PRP lysate with a semi-quantitative protein array. Luminex quantification was performed on 3 out of the 36 screened GFs: EGF and PDGF (which turned out to be the most abundant ones in our PRP lysates) and TGFβ-1,2,3 isoforms (for which the content is important for the eye surface treatment21). EGF and PDGF content were measured as they may influence the efficacy of PRP-L22, while TGFβ isoforms were selected for their known role in immune signaling regualtion21.
Since protein arrays are part of another in vitro study on the characterization of different PRP26, those data are not presented in this manuscript.
We quantitatively assessed EGF, PDGF, and TGFβ in PRP lysates from two different donors (D1 and D2), previously diluted between 0.7 x 109-0.3 x 109 PLTs/mL in 0.9% NaCl. Figure 2 shows the results of the 0.3 x 109 PLTs/mL dilution, which turned out to be most similar to tear composition.
The 0.3 x 109 PLTs/mL dilution was selected based on literature data on tear composition. The EGF values were found to be quite low compared to the mean tear value but still in the range of normality27. Even PDGF, despite being highly variable between the two donors considered, was always comparable to the concentration found in normal tears20. Finally, TGFβ-1 was found to be the most abundant isoform in PRP-L, similar to tears21.
Once the most suitable PLT dilution to prepare apheresis PRP-L had been identified, the Transfusion Medicine Unit started distributing these products to patients affected by eye surface disorders in 2015. The ophthalmologists routinely collected the OSDI questionnaires to monitor DED symptoms; the OSDI test assesses quality of life measures, such as the perception of ocular irritation and how it affects the functioning related to vision. The questionnaire, created by the Outcomes Research Group at Allergan Inc. in 1995 and now accepted as a valid instrument to monitor DED, is submitted to patients and analyzed as previously described28,29.
Here, we show the aggregate results of OSDI tests of DED patients treated between January 2020 and January 2021 (n = 27). After a 6 month therapy with PRP-L, the OSDI scores decreased from 56 ± 21 to 45 ± 21, indicating an improvement in patients' quality of life (Figure 3).
Despite these data still being in the severe range and not relating to clinical outcomes of efficacy, they suggest that DED patients consider PRP-L a useful product that ameliorates ocular discomfort; this aspect should be further investigated in prospective clinical trials aimed at assessing its efficacy in treating ocular surface diseases.
In Table 1, we report a comparison of the present method of production with another method for preparing allogenic PRP-L for eye drops30 and for other purposes22. To our knowledge, Zhang's30 protocol and the current protocol are the only published methods to produce PRP-L for the eye surface. In both, PRP-L is obtained from apheresis; differences between the two protocols, mainly relating to the number of freeze and thaw cycles and centrifugation steps, should be compared in order to improve PRP-L production. Nevertheless, these methodological differences have not been proved to be detrimental to the regenerative capacity of PRP-L tested on other tissues22.
Figure 1: Main steps of the protocol for the preparation of PRP-L. (A) Scheme of the protocol, from PRP collection to PRP-L preparation and dispensation. (B) Representative pictures of the main steps of the protocols. Please click here to view a larger version of this figure.
Figure 2: Luminex quantification of platelet-derived growth factors for the 0.3 x 109/mL dilution of PRP-L. (A) Epidermal growth factor (EGF); (B) platelet-derived growth factor (PDGF); (C) transforming growth factor-beta isoform 1 (TGFβ1); (D) transforming growth factor-beta isoform 2 (TGFβ2); (E) transforming growth factor-beta isoform 3 (TGFβ3). Values are expressed as pg/mL, mean ± standard deviation of three independent measurements. D1 and D2 are two different platelet donors. Please click here to view a larger version of this figure.
Figure 3: Aggregate OSDI scores of DED patients treated with PRP-L between January 2020 and January 2021 at the Ophthalmology Unit of the AUSL-IRCCS di Reggio Emilia. N = 27 patients. OSDI score aggregate results are represented as mean ± standard error, p-value was calculated with a paired t-test with data analysis software. Please click here to view a larger version of this figure.
This article | PRP-L for the eye (in vitro study)29 | PRP-L for other purposes21 | |
Source | PLTs apheresis | PLTs apheresis | Apheresis and whole blood |
Freeze and thaw cycles | 1 (at -80 °C) | 2 (at -80 °C) | 1-3 (at -20 °C and -80 °C) |
Storage temperature | at -80 °C | at -80 °C | at -20 °C and -80 °C |
Centrifugation speed before storage | 3000 x g/30 min | 3500 x g/30 min | 400-3000 x g/6 min -30 min |
Filtration before storage | No | Yes | No/Yes |
Table 1: Comparison of protocols to prepare allogenic PRP-L from platelet-based products collected by apheresis.
In recent years, the clinical use of platelet-based products for ocular surface pathologies has increased, but their diffusion is hampered by the lack of scientific robustness. This is mainly caused by wide heterogeneity in donor sources and preparation protocols, which are often not fully disclosed or not specifically designed for the purpose for which they are dispensed. Particularly, information about platelet-based products collected by apheresis is still lacking. Therefore, the aim of the present work was to describe the step-by-step processing of platelet-rich plasma lysates (PRP-L) obtained by apheresis for the treatment of DED.
PRP-L is an optimal source for the production of eye drops since it contains more GFs than the other blood-based products22, and, when compared to serum or PRP, its production or storage are inexpensive and simple. To obtain PRP-L, platelets are subjected to lysis (usually through one or more freeze and thaw cycles) to release their content. This process guarantees a solution enriched in active molecules that stimulate tissue regeneration22,26. An increasing number of diseases have been treated with PRP-L22, but the indication for use in ophthalmology is still weak due to the low standardization criteria in platelet collection and PRP-L production3,22.
Allogenic platelet-based products should be preferred since they are more standardizable than autologous ones, both in terms of donor characteristics and method of preparation. The patient health status may affect the quality of the product6,16,17, while the in-house kits to collect autologous platelets from whole blood when transfusion services are not directly available do not meet the standard quality required in transfusion medicine31.
To our knowledge, there are no clinical studies characterizing the usage of allogenic PRP-L in ophthalmology3, while there are few reports regarding autologous PRP-L eye drops3 and only one study using allogenic PRP-L obtained from cord blood to treat patients with eye surface diseases32. Although allogenic PRP-L is listed in the clinical guidelines24 and its usage has been proposed3,30, there is still a lack of evidence on its efficacy compared to other treatments and to other blood-based products (e.g., serum). Here, the protocol presented aims to help the scientific community to develop common methods of production and to shed light on the methodological differences.
Here, we described PRP-L production starting from allogenic PRP collected by apheresis. Platelet-based allogenic products to obtain platelet lysates may also be collected from buffy-coats (BCs), and both sources have been equally reported31. BCs are obtained from pooled donors (usually four or five), thus minimizing the inter-individual differences. Conversely, pooling increases the risk of transmitting infectious agents or prions or stimulating an allogenic response31,33. Apheresis is a complex and invasive procedure, and only a minority of donors are eligible for or compliant with it34. Nevertheless, platelet-based products obtained by apheresis are free from other residual circulating blood cells and contain a higher amount of PLTs35. For these reasons, the current work is focused on developing clinical studies to compare PRP-L from these two different sources.
In this protocol, the starting concentration of PLTs in PRP units collected by apheresis was on average 1 x 109/mL, which is consistent with the reported concentrations for other platelet-based products22. In this method, PLTs are diluted afterward with 0.9% NaCl solution to 0.3 x 109/mL. Other protocols report the use of plasma for the dilution22.
Few studies have reported the use of PRP-L in ophthalmology; in these cases, autologous eye drops were prepared at concentrations of PLTs ranging from 0.5 x 109/mL-1 x 109/mL36,37,38. As discussed earlier, standardization markers are desirable and would also help in determining the proper dilution. Here, for instance, we report the concentration of some pivotal GFs in the PRP-L. EGF and PDGF content influence the efficacy of PRP-L22, while TGFβ isoforms are involved in regulating immune signaling21,39, and their concentration is finely regulated. Therefore, TGFβ concentration in platelet-based eye drops may influence not only the efficacy but also elicit potential detrimental effects39; thus, it should be carefully investigated before defining the proper dilution. Nonetheless, the dilution selected-0.3 x 109 PLTs/mL-was based on the GFs content in tears21,25. Zhang et al. previously compared serum-based eye drops, both autologous and allogenic, and platelet-based lysates for their content in GFs and for their capability to promote the regeneration of corneal cells in vitro30. The study showed how these products have comparable features, with PRP-L having higher EGF concentration but lower fibronectin. In their protocol, the freeze/thaw process was repeated twice, the centrifuge performed at 3500 x g for 30 min, and the platelet lysate stored at −80 °C30.
Freezing and thawing is indeed a critical step; most of the protocols (including this one) were developed with −80 °C freezing and 37 °C thawing, but freezing has also been reported at −24 °C, −196 °C, and −150 °C22,33 Even the number of freeze/thaw cycles performed are variable, ranging from 1 to 522,33. A limited number of studies also reported sonication or solvent/detergent treatment to obtain platelet lysates22,33. Other methodological variables previously reported in the preparation of PRP-L concern the centrifugation step-between 300 x g and 10000 x g, from 2 min to 60 min-and the long-term storage, which, in most cases, is at −80 °C, albeit that similar products have been also been directly stored at −20 °C22. Storage conditions, in particular, should be carefully monitored since they might affect the availability and activity of GFs contained in lysates. In this highly heterogeneous context, quality controls and clinical studies taking into consideration the release of biogenic factors and the differences in the therapeutic effect should be urgently evaluated.
Finally, here we show how this method has been significantly evaluated with a positive result from an aggregate analysis of patients with dry eye disease receiving PRP-L for 6 months (OSDI questionnaire3). Although promising, OSDI alone is not sufficient to determine the efficacy of PRP-L in the treatment of DED and other ocular surface diseases, and clinical studies on the usage of allogenic PRP-L are warranted. Moreover, possible product composition differences due to alternative methodological steps (i.e., freeze and thaw, centrifugation, storage) should be compared in order to optimize the methodological procedure.
In conclusion, the high heterogeneity of blood sources and protocols still hampers the definitive translation of blood-based products to the clinical treatment of ocular surface diseases. Although PRP-L is an emerging product with some advantageous features, further studies are necessary to validate its use and to develop common guidelines. Sharing and detailing the protocol of preparation may expand the usability and shed light on the critical steps.
The authors have nothing to disclose.
The authors wish to thank "Casa del Dono di Reggio Emilia" for providing donor-derived platelet concentrates.
Equipments | |||
CompoSeal Mobilea II | Fresenius Kabi, Germany | bag sealer | |
HeraSafe hood | Heraeus Instruments, Germany | Class II biohazard hood | |
MCS+ 9000 Mobile Platelet Collection System | Haemonetics, Italy | automated plasma and multicomponent collection equipment for donating platelet, red cell, plasma, or combination blood components | |
Platelet shaker, PF396i | Helmer, USA | Platelet shaker | |
Raycell X-ray Blood Irradiator | MDS Nordion, Canada | X-ray Blood Irradiator | |
ROTIXA 50RS | Hettich Zentrifugen, Germany | High speed entrifuge | |
Sysmex XS-1000i | Sysmex Europe GMBH, Germany | haemocytometer for platelet count | |
Warm bath, WB-M15 | Falc Instruments, Italy | Warm bath | |
Materials | |||
ACD-A anticoagulant solution A | Fenwal Inc., USA | DIN 00788139 | anticoagulant solution for platelet apheresis (1000 ml) |
BD BACTEC Peds Plus/F Culture vials | BD Biosciences, USA | BD 442020 | Sterility assay |
BD BACTEC Peds Plus/F Culture vials | BD Biosciences, USA | 442020 | At least 2 vials for sterility assay |
BD Luer Lok Syringe | BD Plastipack, USA | 300865 | At least 4 sterile syringes (50 ml) |
Bio-Plex Human Cancer Panel 1 | BioRad Laboratories, USA | 171AC500M | Standard panel for PDGF isoforms assessment |
Bio-Plex Human Cancer Panel 2 | BioRad Laboratories, USA | 171AC600M | Standard panel for EGF assessment |
Bio-Plex MAGPIX Multiplex Reader | BioRad Laboratories, USA | Magpix | This instrument allows multiple immunoassays using functionalized magnetic beads. |
Bio-Plex Pro TGF-b Assay | BioRad Laboratories, USA | 10024984 | Set and standards for TGFb isoforms assessment |
BioRet | ARIES s.r.l., Italy | A2DH0020 | At least 4 piercing spike for blood bags |
Blood collection tube | BD Vacutainer, USA | 367835 | 1 tube, necessary to perform platelet counts |
Eye drops kit. COL Medical Device for the application and preservation of eye drops from haemocomponents | Biomed Device s.r.l., Italy | COLC50 | Eye drops kit. At least 2 kits for each PRP unit collected |
Human Cancer PDGF-AB/BB Set 1x96well | BioRad Laboratories, USA | 171BC511 | Set for PDGF isoforms assessment |
Human Cancer2 EGF Set 1x96well | BioRad Laboratories, USA | 171BC603M | Set for EGF assessment |
NaCl 0.9% sterile solution | Baxter S.p.A., Italy | B05BB01 | 1000 ml |
OSDI Questionnaire | Allergan Inc., USA | OSDI | Ocular Surface Disease Index Questionnaire |
Piercing spike | BioRet ARIES s.r.l., Italy | BS051004 | Spike |
Platelet Additive Solution A+ T-PAS+ | TERUMO BCT Inc., Italy | 40842 | preservative solution for platelet concentrates (1000 ml) |
Software Excel | Microsoft, USA | Excel | Data analysis software |
Teruflex Transfer bag 1000 ml | TERUMO BCT Inc., Italy | BB*T100BM | 1 for PRP dilution |
Teruflex Transfer bag 300 ml | TERUMO BCT Inc., Italy | BB*030CM | At least 6 for each PRP unit collected |