The effect of platelet releasate on wound healing in animal models

THERAPEUTIC EFFECT OF USING AUTOLOGOUS PLATELET CONCENTRATE IN VITRECTOMY FOR MACULAR HOLE: A Systematic Review and Meta-Analysis

PURPOSE

To summarize the current evidence regarding the therapeutic effect of using autologous platelet concentrate (APC) in vitrectomy for macular hole (MH).

METHODS

The PubMed, Web of Science, and Embase databases were searched according to the PROSPERO protocol (CRD42022366202). Controlled trials comparing whether APC was used in the vitrectomy of MH were included. The primary outcome was the closure rate of MH and postoperative best-corrected visual acuity, and the secondary outcome was the incidence of different types of complications.

RESULTS

Seven studies that included 634 eyes were eligible. For the primary outcome, the usage of APC significantly improved the closure rate of MH in vitrectomy (odds ratio [OR] = 5.34, 95% confidence interval, 2.83-10.07, P < 0.001). Postoperative visual acuity did not significantly differ between the APC group and similar baseline controls (SMD = -0.07, 95% confidence interval, -0.35 to 0.22, P = 0.644). For the secondary outcome, using APC did not result in additional complications regarding postoperative retinal detachment or the recurrence of MH.

CONCLUSION

The use of APC in vitrectomy was associated with a superior closure rate of the hole and no additional complications; therefore, it is effective and safe in MH surgery.

Vitreoretinal Interface Changes After Anti-vascular Endothelial Growth Factor Treatment in Highly Myopic Eyes: A Real-World Study

INTRODUCTION

To investigate changes in the vitreoretinal interface after anti-vascular endothelial growth factor (anti-VEGF) treatment in highly myopic eyes.

METHODS

Eyes with myopic choroidal neovascularization (mCNV) treated with intravitreal injection of anti-VEGF in a single-center were retrospectively reviewed. Fundus abnormalities and features of optical computed tomography were studied.

RESULTS

A total of 295 eyes from 254 patients were recruited to the study. Prevalence of myopic macular retinoschisis (MRS) was 25.4%, and the rates of progression and onset of MRS were 75.9% and 16.2%, respectively. Outer retinal schisis (β = 8.586, p = 0.003) and lamellar macular hole (LMH) (β = 5.015, p = 0.043) at baseline were identified risk factors for progression and onset of MRS, whereas male sex (β = 9.000, p = 0.039) and outer retinal schisis at baseline (β = 5.250, p = 0.010) were risk factors for MRS progression. Progression of MRS was first detected in outer retinal layers in 48.3% of eyes. Thirteen eyes required surgical intervention. Spontaneous improvements of MRS were observed in five eyes (6.3%).

CONCLUSION

Changes in the vitreoretinal interface, such as progression, onset, and improvement of MRS, were observed after anti-VEGF treatment. Outer retinal schisis and LMH were risk factors of progression and onset of MRS after anti-VEGF treatment. Intravitreal injection of ranibizumab and retinal hemorrhage were protective factors for surgical intervention for vision-threatening MRS.

Surgical Management of Recurrent and Persistent Macular Holes: A Practical Approach

Primary surgery for macular hole (MH) closure has a high success rate with current methods of pars plana vitrectomy and internal limiting membrane (ILM) peeling. When primary surgery fails, there are several options available for secondary repair, including extension of the ILM peel, creation of an ILM flap, pedunculated ILM flap, lens capsule flap transplantation, autologous retinal transplantation, use of a human amniotic membrane plug, adjuvant autologous platelet concentrate, induction of macular detachments with subretinal blebs, and creation of retinal incisions. In this review, we discuss the practical approach to each of these surgical techniques for the management of recurrent or persistent MHs.

Limited Treatment Options for Diabetic Wounds: Barriers to Clinical Translation Despite Therapeutic Success in Murine Models

Significance: Millions of people worldwide suffer from diabetes mellitus and its complications, including chronic diabetic wounds. To date, there are few widely successful clinical therapies specific to diabetic wounds beyond general wound care, despite the vast number of scientific discoveries in the pathogenesis of defective healing in diabetes. Recent Advances: In recent years, murine animal models of diabetes have enabled the investigation of many possible therapeutics for diabetic wound care. These include specific cell types, growth factors, cytokines, peptides, small molecules, plant extracts, microRNAs, extracellular vesicles, novel wound dressings, mechanical interventions, bioengineered materials, and more. Critical Issues: Despite many research discoveries, few have been translated from their success in murine models to clinical use in humans. This massive gap between bench discovery and bedside application begs the simple and critical question: what is still missing? The complexity and multiplicity of the diabetic wound makes it an immensely challenging therapeutic target, and this lopsided progress highlights the need for new methods to overcome the bench-to-bedside barrier. How can laboratory discoveries in animal models be effectively translated to novel clinical therapies for human patients? Future Directions: As research continues to decipher deficient healing in diabetes, new approaches and considerations are required to ensure that these discoveries can become translational, clinically usable therapies. Clinical progress requires the development of new, more accurate models of the human disease state, multifaceted investigations that address multiple critical components in wound repair, and more innovative research strategies that harness both the existing knowledge and the potential of new advances across disciplines.

Therapeutic Efficacy of Autologous Platelet Concentrate Injection on Macular Holes with High Myopia, Large Macular Holes, or Recurrent Macular Holes: A Multicenter Randomized Controlled Trial

We aimed to evaluate the anatomical and functional outcomes of pars-plana vitrectomy (PPV) with or without autologous platelet concentrate (APC) injection in patients with recurrent macular holes (MHs), large MHs, or MHs with high myopia. This multicenter, prospective, interventional randomized controlled trial was conducted from March 2017 to April 2020. Participants were randomly allocated to a PPV group or a PPV+APC group. All participants underwent standard 25-gauge PPV, and eyes in the PPV+APC group underwent PPV with intravitreal APC injection before air-gas exchange. A total of 117 patients were enrolled (PPV group: n = 59, PPV+APC group: n = 58). Hole closure was achieved in 47 participants (79.7%) in the PPV group and 52 participants (89.7%) in the PPV+APC group. There were no between-group differences in the anatomical closure rate or functional outcomes including best-corrected visual acuity, metamorphopsia, pattern-reversal visual evoked potential, or Visual Function Questionnaire-25 score. The use of APC injection does not improve the anatomical and functional outcomes of surgery for large MHs, recurrent MHs, or MHs with high myopia. The adjunctive use of APC can be considered in selected cases because it is not inferior to conventional MH surgery, is relatively simple to perform, and is not affected by the surgeon’s skill.

Extracellular Polyphosphate Promotes Macrophage and Fibrocyte Differentiation, Inhibits Leukocyte Proliferation, and Acts as a Chemotactic Agent for Neutrophils

Fibrocytes are monocyte-derived fibroblast like cells that participate in wound healing, but little is known about what initiates fibrocyte differentiation. Blood platelets contain 60-100-mer polymers of phosphate groups called polyphosphate, and when activated, platelets induce blood clotting (the first step in wound healing) in part by the release of polyphosphate. We find that activated platelets release a factor that promotes fibrocyte differentiation. The factor is abolished by treating the crude platelet factor with the polyphosphate-degrading enzyme polyphosphatase, and polyphosphate promotes fibrocyte differentiation. Macrophages and recruited neutrophils also potentiate wound healing, and polyphosphate also promotes macrophage differentiation and induces chemoattraction of neutrophils. In support of the hypothesis that polyphosphate is a signal that affects leukocytes, we observe saturable binding of polyphosphate to these cells. Polyphosphate also inhibits leukocyte proliferation and proteasome activity. These results suggest new roles for extracellular polyphosphate as a mediator of wound healing and inflammation and also provide a potential link between platelet activation and the progression of fibrosing diseases.

Effect of microfracture and autologous-conditioned plasma application in the focal full-thickness chondral defect of the knee: an experimental study on rabbits

Purpose

The aim of the present study was to evaluate the effect of microfracture and intraarticular autologous conditioned plasma (ACP) injection on cartilage regeneration in a focal full-thickness chondral defect model created in the knee joint.

Methods

Full-thickness chondral defects of 3 × 6 mm² were surgically created in right medial femoral condyles (MFC) of New Zealand rabbits, and the rabbits were then divided into three groups according to treatment: Group 1 received only microfracture (mfx), Group 2 received mfx plus intraarticular ACP, and Group 3 received mfx; the defect was covered by the periosteum, and then, ACP was applied subperiosteally and intraarticularly. Twelve weeks after injection, the animals were sacrificed and the femoral condyles were evaluated macroscopically and histologically by hematoxylin-eosin staining. Then, histological sections were scored using the International Cartilage Repair Society (ICRS) visual histological scale.

Results

Findings showed that in both mfx/ACP-treated groups, the defects were filled regularly and smoothly, the defects had a greater fill and good integration into the surrounding host tissue, and the repair matrix had more hyaline-like character. On the other hand, defects were filled with an irregular, fibrous cartilage in the mfx-treated group. Histological scores in Group 2 and Group 3 were better compared to Group 1.

Conclusion

In the present study, we were able to demonstrate a beneficial effect of intraarticular administration of ACP as a coadjuvant of microfractures in order to regenerate hyaline-like cartilage in full-thickness chondral lesions in a rabbit model.

Platelet-rich plasma for enhancing surgical rotator cuff repair: evaluation and comparison of two application methods in a rat model

PURPOSE

Platelet-rich plasma (PRP) is a natural concentrate of autologous growth factors now being widely tested in different fields of medicine for its potential in enhancing the regeneration of tissue with low healing potential. However, studies of PRP in enhancing rotator cuff repair have been contradictory, perhaps because of how PRP is administered. The purpose of this study is to evaluate the effect of PRP and compare two different application methods of PRP on rotator cuff healing.

METHODS

The supraspinatus tendons of 48 mature, male Wistar-Albino rats were detached from their insertion on the humerus. The animals were divided into four groups: (1) no repair, (2) primary repair, (3) repair plus PRP injections into the tendon-bone interface, and (4) repair plus PRP absorbed from a sponge carrier to the tendon-bone interface. The tendons were evaluated biomechanically and histologically at week 8.

RESULTS

Cuffs repaired with PRP had significantly greater mean (SD) load-to-failure rates [11.1 (6.5) and 11.6 (3.9) N; P < 0.05] and stiffness [3.5 (2.3) and 1.6 (0.75) N; P < 0.05] than did cuffs repaired without PRP. The groups receiving PRP did not differ significantly on these variables. Histological evaluation showed no significant differences among the four groups.

CONCLUSIONS

The application of PRP, independent of the application method, significantly improved biomechanical properties at the rotator cuff tendon-bone interface. The type of application, injection or absorption from a sponge did not influence the effect of PRP on rotator cuff healing.

Effects of platelet-rich plasma on the repair of wounds on the distal aspect of the forelimb in horses

OBJECTIVE

To evaluate the effect of platelet-rich plasma on wounds on the distal aspect of the forelimb in horses.

ANIMALS

6 mixed-breed 10- to 15-year-old mares.

PROCEDURES

3 wounds were created on metacarpal regions in each of 6 horses (n = 36 wounds total). Eighteen wounds were treated with platelet-rich plasma and bandaged, whereas 18 control wounds were similarly bandaged with no prior topical treatment. Decrease in wound surface area and the required number of excisions of exuberant granulation tissue were recorded until complete healing. Tissue specimens were taken from wounds at 1 week for histologic examination and measurement of transforming growth factor-beta1 concentrations and at closure for histologic examination, biomechanical evaluation, and measurement of collagen type I and type III mRNA.

RESULTS

Platelet-rich plasma favored excessive development of granulation tissue and significantly slowed wound healing at 1, 2, and 3 weeks after surgery. Transforming growth factor-beta1 had a 1.6-fold higher concentration in treated wounds, compared with untreated wounds. Histologic, biomechanical, and gene expression data did not differ significantly between treated and control wounds.

CONCLUSIONS AND CLINICAL RELEVANCE

Topical application of autologous platelet-rich plasma did not accelerate or improve the quality of repair of small granulating wounds on limbs of horses. This treatment may better suit wounds with massive tissue loss or, alternatively, chronic wounds that would benefit from a fresh source of mediators to accelerate the healing process.

Independent and additive stimulation of tendon repair by thrombin and platelets

BACKGROUND

Platelet concentrate application with added thrombin improves Achilles tendon repair in the rat. Upon tissue injury, platelets are activated by thrombin, which has many biological properties in common with growth factors. We wanted to differentiate the effect of platelets from that of thrombin.

METHODS

The Achilles tendon was transected in 50 rats. Platelet gel was prepared from the blood of 10 other rats. The rats were given either platelet gel with active or neutralized thrombin implanted into the defect during the operation, or a local injection 6h postoperatively with 50 microL of either platelet concentrate, thrombin or saline. The rats were killed after 14 days and the tendons were mechanically tested.

RESULTS

Compared to saline, platelet gel caused a 42% increase in force at failure, a 90% increase in energy, and a 61% increase in ultimate stress. Platelet gel with neutralized thrombin caused a 22% increase in force at failure, and energy and stress were less elevated. Injected platelet concentrate caused a 24% increase in force at failure, and thrombin caused a 10% increase. These effects and the differences between treatments were statistically significant.

INTERPRETATION

Platelets and thrombin had independent and additive stimulatory effects on tendon repair. The clinical relevance is so far unknown.

Bone formation in the maxillary sinus by using platelet-rich plasma: an experimental study in sheep

Recently, platelet-rich plasma (PRP) has been proven to be an effective regeneration adjunct when combined with autogenous bone in the reconstruction of mandibular defects. However, little is known about the effect of PRP when combined with a bone allograft in the maxillary sinus. The purpose of this study was to quantitatively evaluate the ability of PRP to enhance bone regeneration in the maxillary sinus of sheep when combined with demineralized freeze-dried bone allograft (DFDBA) and cortical cancellous freeze-dried bone allograft (CCFDBA). Ten sheep were selected for bilateral sinus augmentation DFDBA + CCFDBA + PRP (test) and DFDBA + CCFDBA (control). Five were sacrificed at 3 months and the other 5 at 6 months. Hematology tests were performed for platelet count, and histology slides were obtained for histomorphometric analysis taking 2 measures of interest: total area (square millimeters) and percentage of bone fill. Student t tests showed no significant difference between test and control groups for total area (P > .25) and percentage of bone fill (P > .80) at either 3 or 6 months. The control group showed no statistical difference for total area (P < .095) and percentage of bone fill (P <.60) between 3- and 6-month healing times. The test group, however, showed a significant increase in total area (P <.025) but not in percentage of bone fill (P <.40) for the 2 healing periods. When the treatments were compared for interactions within the animal model, no clear tendency was evident for the test group to perform in relation to the control group regarding total area (r = .766, P < .01). A moderate tendency existed between the percentages of bone filled (r = .824, P < .005). Platelet-rich plasma showed higher platelet count than did the whole blood (2 to 5 times). However, no correlation was found between the log ratio and the bone measures. Within the limitations of this study, PRP failed to enhance or accelerate bone regeneration in the maxillary sinus of sheep when combined with bone allograft.

Autologous platelets for macular hole surgery: the Sussex Eye Hospital experience

PURPOSE

To evaluate the anatomical and visual outcomes of patients managed by macular hole surgery with adjunctive use of autologous platelets at Sussex Eye Hospital, UK.

METHODS

A retrospective non-comparative consecutive interventional case series was conducted. Standard macular hole vitrectomy surgery was combined with autologous platelets. No other adjuncts were used, nor internal limiting membrane peeling performed. The main outcome measure was anatomical closure of the macular hole. Secondary outcome measures included: visual outcome (best postoperative best corrected visual acuity [BCVA] and final BCVA), hole reopening and/or re-operation, complications, and time to and influence of cataract surgery.

RESULTS

Seventy eyes of 65 patients underwent macular hole surgery with vitrectomy and autologous platelets. There were 14 stage 2 holes, 52 stage 3 holes and four stage 4 holes. Mean follow up was 29 months (range 1.5-78 months). Primary anatomical success (hole closure) was 95.7% (n = 67); however, six (8.5%) holes reopened at a mean of 12.7 months (range 3.6-36.3 months) after their initial surgery. Final surgical success was 98.5% (65/66) in those eyes of patients electing re-operation procedures. Seventy-seven per cent (n = 54) of patients obtained 2 or more lines of visual acuity improvement at final follow up with a mean improvement of 4 lines (range -3 to +12 lines). Forty per cent (n = 28) achieved final BCVA of 6/12 or better, which improved to 51% (n = 36) if best postoperative BCVA was considered.

CONCLUSIONS

Adjunctive use of autologous platelets at the time of macular hole surgery yields good surgical and visual results, without significant complications, and should remain a considered option in the surgical management of macular holes. Improved macular hole closure with autologous platelets (compared with vitrectomy alone) has previously been demonstrated in a randomized controlled trial. Visual outcome benefit of platelets remains to be investigated by randomized controlled trial and any planned trials should include an autologous platelets intervention arm along with visual acuity as a primary outcome measure.

Intraoperative adjunctive agents in vitrectomy: serum, cytokines, and glue

The surgical goal in the treatment of retinal breaks is to seal the edges of the break, and traditionally, photocoagulation and cryocoagulation have been used to accomplish this. However, it is sometimes difficult in complicated retinal detachments to maintain the seal against tractional forces. Adhesion is achieved through a process of cell necrosis, inflammation and subsequent fibrovascular proliferation. This strategy, however, may not be appropriate in vision-sensitive areas such as macular holes. To improve the success rate of macular hole surgery, a number of authors have advocated the use of biological modifiers, such as transforming growth factor beta, human autologous serum, tissue glue, or platelet concentrates. These materials may enhance the adhesion of the detached retina and therefore lead to a better anatomical and functional success. We have reviewed the advances of intraoperative application of synthetic or biological adhesives. However, through the improvement of surgical techniques and surgeons' skills in recent years, the anatomical success rate of macular hole surgery has increased in most institutions without adjunctive additives. Thus, many surgeons believe that adjunctive additives may not be necessary for most idiopathic macular holes.

Synthesis and activity of NH2- and COOH-terminal elastase recognition sequences on cotton

The application of peptide recognition sequences of elastase to fibers of wound dressings is a possible route to inhibiting high levels of destructive elastase in the chronic wound. For this reason we have synthesized the elastase recognition sequence Val-Pro-Val on both cotton cellulose, and carboxymethylated cellulose cotton (CMC) and prepared chromatography columns of these to examine elastase retention. The tripeptide was synthesized on cotton-based cellulose fibers both in sequence and as a tripeptide methyl ester. Glycine was employed as a linker of the recognition sequence to the cotton cellulose. Pre-treatment of cotton cellulose with cellulase improved the substitution level of glycine. The peptidocellulose conjugates were employed as a chromatographic stationary phase to assess elastase retention. The sequence Val-Pro-Val-OMe was amino-terminally anchored to carboxymethylated cotton and demonstrated retention of up to 58% of elastase when first applied to the column. Higher repetitive retention was demonstrated subsequently. Cotton gauze similarly modified with Val-Pro-Val-Gly cellulose was compared with untreated gauze for reduction of elastase activity in buffered saline. Solutions of elastase that were treated with Val-Pro-Val-Gly cellulose cotton gauze, demonstrated reduced elastase activity. This study demonstrates the use of elastase recognition sequences as sequestering agents of elastase when attached to cotton fibers and constitutes a model for the design of peptidocellulose analogs in dressing fibers for chronic wounds.

Effect of autologous platelet concentrate in surgery for idiopathic macular hole: results of a multicenter, double-masked, randomized trial. Platelets in Macular Hole Surgery Group

OBJECTIVE

To evaluate prospectively the efficacy and safety of autologous platelet concentrate (APC) as an adjuvant in surgery for idiopathic macular hole.

DESIGN

Multicenter, double-masked, randomized clinical trial.

SETTING

Four university-based ophthalmology clinics.

PARTICIPANTS

One hundred ten patients with stage 3 or 4 idiopathic full-thickness macular holes of less than 3 years' duration were randomized (53 eyes to the platelet group and 57 eyes to the control group).

INTERVENTIONS

Standardized macular hole surgery versus surgery combined with injection of an APC. In all cases, the procedure consisted of three-port pars plana vitrectomy, posterior hyaloid separation, and nonexpansile fluid-gas exchange. After the fluid-gas exchange, patients were randomized to receive either injection of an APC or no adjunctive treatment. After surgery, patients were positioned face down for 12 days. Platelet counts showed that the concentrates contained a mean of 96.106 platelets (range, 82-102).

MAIN OUTCOME MEASURES

Anatomic and functional evaluations were performed at 1, 3, and 6 months after surgery in a double-masked fashion by an independent observer. The main outcome was reapposition of the edge of the macular hole 1 month after surgery. Secondary outcomes were anatomic status at 3 and 6 months, changes in Early Treatment Diabetic Retinopathy Study score, and complications.

RESULTS

One month after surgery, the anatomic success rate in the platelet group was 52 of 53 (98%; 95% confidence interval, 0.90-1.00) versus 47 of 57 (82%; 95% confidence interval, 0.70-0.91) in the control group (P = 0.009, Fisher's exact test; relative risk, 0.11; 95% confidence interval, 0.01-0.81). Visual acuity was not significantly different between the two groups at any timepoint. There were no complications specifically attributable to the platelet injection.

CONCLUSION

Injection of APC improved significantly the anatomic success rate of surgery for idiopathic macular holes of less than 3 years' duration, but postoperative visual acuity of the platelet group was not statistically different from the control group.

Inhibition of elastase by a synthetic cotton-bound serine protease inhibitor: in vitro kinetics and inhibitor release

A cotton-bound serine protease inhibitor of elastase (fiber-inhibitor) has been formulated for in vitro evaluation in chronic wound fluid. As a model to understand the properties of the inhibitor in wound dressings, the kinetic profile and in vitro release of the fiber-inhibitor formulation have been examined. The elastase inhibitor N-Methoxysuccinyl-Ala-Ala-Pro-Val-chloromethylketone was modified onto cotton cellulose fibers and assayed as a colloidal system. Amino acid analysis and reversed phase high performance liquid chromatography were compared as semiquantitative methods to assess elastase inhibitor release from the cotton fibers. The kinetics of inhibition was assessed on treated fibers of synthetic dressings such that a colloidal suspension of the fiber-inhibitor and elastase was employed as an assay. A dose-response relationship was observed in the kinetics of substrate hydrolysis catalyzed by three elastases: porcine pancreatic elastase, which was employed to model this approach; human leukocyte elastase; and elastase in human chronic wound fluid. Both freely dissolved and fiber-bound inhibitors were studied. The initial rates of substrate hydrolysis were inversely linear with freely dissolved inhibitor dose. The apparent first order rate constants, kobs, for the elastase-inhibitor complex were calculated from the kinetic profiles. The kobs for inhibitor bound enzyme varied as a function of inhibitor vs. enzyme concentration and based on the order of mixing of substrate, inhibitor and enzyme in the assay. Enzyme inhibition by the fiber-inhibitor was measured as inhibitor concentration at 50% inhibition (I50). I50 values measured from the colloidal assay with fiber-released inhibitor were within the same range to those for freely dissolved inhibitor. Inhibition of elastase activity in chronic wound fluid was observed with 1-5 mg of fiber-inhibitor formulation. This approach constitutes an in vitro assessment of synthetic serine protease inhibitors on fibers and may be employed to evaluate structure vs. function of elastase inhibition in the modified fibers of wound dressing composites.

Autologous platelet concentrate as an adjunct in macular hole healing: a pilot study

PURPOSE

A pilot study was undertaken to assess the efficacy of autologous platelets in macular hole healing.

PATIENTS AND METHODS

Eight eyes of eight patients with stage 3 or 4 macular holes, two of which had failed to heal after previous vitrectomy and gas tamponade, were included. The procedure consisted of pars plana vitrectomy with removal of posterior cortical vitreous, stripping of associated epimacular membranes, 15% perfluoroethane-air tamponade, and instillation of autologous platelet concentrate onto the posterior pole. Strict postoperative facedown positioning was observed for 12 days. Postoperative evaluation included visual acuity measurement, biomicroscopic macular appearance and scanning laser ophthalmoscope examination. The follow-up period ranged from 3 to 13 months (mean, 7 months).

RESULTS

Of eight eyes, flattening of the surrounding retina and closure of the hole were achieved in seven (87.5%). Visual acuity improved two lines or more in four eyes (50%) Four eyes (50%) reached a postoperative visual acuity of 20/50 or more. Increased nuclear sclerosis was observed in six eyes (75%), and retinal detachment occurred in two eyes (25%).

CONCLUSIONS

Autologous platelet concentrate administered peroperatively in full-thickness macular holes seems to be a safe and effective adjunct to vitrectomy with removal of posterior hyaloid and gas tamponade. A larger multicenter randomized prospective study is underway to verify these encouraging results before advocating the use of autologous platelets in macular hole surgery.

Surgery for idiopathic full-thickness macular holes

BACKGROUND

Idiopathic full-thickness macular holes (FTMH) are an important cause of loss of central vision in the elderly. Improved understanding of the natural history and pathophysiology of FTMH has led to recent advances in the surgical management of patients with this hitherto untreatable condition.

METHODS

The current concepts of the natural history and surgical treatment are reviewed. Pilot studies of vitrectomy undertaken to relieve the tangential traction at the vitreomacular interface and the role of growth factors as promoters of a limited healing response are reviewed and illustrated by the results of surgical treatment of macular holes obtained by the author and others.

RESULTS

Whereas early pilot studies of vitrectomy of impending (stage I) macular hole suggested beneficial results (80-95% of operated eyes did not progress to FTMH), no such benefit could be demonstrated by a subsequent randomised treatment trial. In a study of early vitrectomy and partial fluid-gas exchange hole closure was achieved in 88% of patients with stage II FTMH with visual improvement in 67%. In other studies of FTMH (stages II-IV) the addition of adjunctive substances such as growth factors, autologous serum, plasma or platelet concentrate has resulted in closure in 77-100% of cases. However, similar results have also been reported with vitrectomy and gas tamponade alone. Histologically the closure of the FTMH is associated with glial proliferation.

CONCLUSION

Vitrectomy and intraocular tamponade appear to be beneficial in patients with FTMH. The role of adjunctive substances, such as growth factors and other promoters of the healing response, requires clarification by randomised treatment trials.

Autologous platelet concentrate for the treatment of full-thickness macular holes

BACKGROUND

To improve the anatomic success rate in the surgery of full-thickness macular holes, we tested, in a prospective pilot study, the effects of autologous platelet concentrate deposited on the macula at the end of surgery.

METHODS

Two consecutive groups of patients were compared. Twenty eyes (group 1, mean symptom duration 11 months) were operated on with injection of an autologous platelet concentrate on the macula after fluid-gas exchange. Another 20 eyes (group 2, mean symptom duration 11 months) were subsequently operated on without autologous platelet concentrate. For all stage 3 holes, posterior hyaloid was detached en bloc at the level of the optic disc. The patient was left supine for 24 h after surgery, and then remained face down for 10 days.

RESULTS

In group 1, 19 cases were an anatomic success, i.e. there was flattening of the retina surrounding the hole and reattachment of the edge of the hole to the retinal pigment epithelium; in 9 cases the hole was even undetectable. Final visual acuity was 0.5 or more in 9 eyes, and 0.4 or more in 14. Visual acuity improved by two lines or more in 17 of the 19 successfully operated eyes. In group 2, only 13 cases were an anatomic success. The functional results for the successfully operated eyes were identical to those of group 1.

CONCLUSION

These results strongly suggested that autologous platelet concentrate could significantly improve the success rate in macular hole surgery and led us to begin a comparative, prospective, randomized trial.

Fibroblast migration and proliferation during in vitro wound healing. A quantitative comparison between various growth factors and a low molecular weight blood dialysate used in the clinic to normalize impaired wound healing

During the formation of granulation tissue in a dermal wound, platelets, monocytes and other cellular blood constituents release various peptide growth factors to stimulate fibroblasts to migrate into the wound site and proliferate, in order to reconstitute the various connective tissue components. The effect on fibroblast migration and proliferation of these growth factors, and of Solcoseryl (HD), a deproteinized fraction of calf blood used to normalize wound granulation and scar tissue formation, was quantified in vitro. The presence of basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF), transforming growth factor-beta (TGF-beta) and hemodialysate (HD) increased the number of cells in the denuded area, i.e., in the "wound space" of an artificially ruptured monolayer of LM-fibroblasts (mouse lung fibroblasts). When cell proliferation was blocked with Mitomycin C, in the first 24 h all factors, i.e., bFGF, PDGF, TGF-beta and HD, promoted cell migration, whereas after 48 h it became obvious that each factor stimulated both migration and proliferation, each in a characteristic way. The effects were significant and more distinct after 48 h, following the order: PDGF (46%) approximately bFGF (87%) > HD (45%) approximately TGF-beta (40%) > control (62%). The relative contributions of migration after inhibiting proliferation are given in brackets. The modulatory activity of HD was localized in its hydrophilic fraction. It was destroyed by acid hydrolysis. Furthermore, this activity could be blocked by protamine sulfate, an inhibitor blocking peptide growth factor receptor binding.

Osteoconductive properties of methylpyrrolidinone chitosan in an animal model

Bone defects were surgically produced in the tibiae of rabbits and medicated with freeze-dried methylpyrrolidinone chitosan. Histological observations 60 d after surgery showed a considerable presence of neoformed bone tissue, as opposed to controls, originating from the pre-existing bone as well as from the periosteum. The cationic nature and the chelating ability of the methylpyrrolidinone chitosan apparently favoured mineralization. Endosteal-periosteal and bone marrow osteoblast-like precursors, stimulated by growth factors entrapped in the coagulum-polysaccharide mixture, gave rise to intramembranous bone formation. The ultrastructural examination evidenced that bone osteoid was followed by mineralization of the tissue.

The utility of collagen-based vehicles in delivery of growth factors for hard and soft tissue wound repair

Bovine demineralized bone powder and reconstituted bovine dermal collagen have been effectively utilized during the past several years to deliver a variety of growth factors in animal models of hard and soft tissue wound repair. Bone morphogenetic proteins have been delivered in a demineralized bone powder matrix to promote ectopic bone formation in the rat subcutaneous model with the objective of studying the process of endochondral bone formation and evaluating the utility of such factors in promoting repair of hard tissue defects. Reconstituted bovine dermal collagen gels and sponges, including composites of collagen and heparin, have been utilized to deliver growth factors such as platelet-derived growth factor (PDGF), transforming growth factor-beta (TGF-beta) and fibroblast growth factor (FGF) to study their effects in subcutaneous and incisional models of dermal wound repair. The results of these experimental animal studies have provided convincing evidence that the rheological properties, biocompatibility and resorbable nature of type I collagen make it an excellent delivery vehicle for evaluation of a variety of growth factors in human clinical studies of hard and soft tissue would repair.

Detection of undegraded fibrin and tumor necrosis factor-alpha in venous leg ulcers

The pathogenesis of venous leg ulcers is based on the leakage of fibrinogen leading to pericapillary fibrin cuff and plugging of capillaries by white blood cells. Eight patients with venous leg ulcers have been studied with a panel of antibodies reactive for fibrinogen, fibrin, fibrin degradation products, and various cell-associated markers for polymorphonuclear cells, monocytes, and B and T lymphocytes. Our results showed that pericapillary fibrin cuff was mainly composed of undegraded fibrin and that, in the granulation tissue, tumor necrosis factor-alpha and elastase activities were detectable in monocytes and polymorphonuclear cells, respectively. Only few activated lymphocytes were present. On the basis of these results, it is assumed that inflammation generated by activated white blood cells that accumulate under unrelieved pressure is the key event. Tumor necrosis factor-alpha synthesized by activated monocytes may therefore induce the formation of pericapillary fibrin cuffs. Pericapillary fibrin cuffs and toxic metabolites released by polymorphonuclear cells may explain the absence of wound repair.