Do Platelets and Keratinocytes Enhance Skin Graft Donor Site Healing?

Platelets are the unsung heroes of healing. They stop bleeding by actively participating in the clotting cascade and releasing several growth factors and cytokines reported to attract and stimulate the fibroblasts, endothelial cells, and keratinocytes that replace lost skin structures. Would it stimulate healing if these tiny growth factor and cytokine “factories” were applied directly to a wound? If so, how would healing differ and how long would the effect last? Recent research has started to answer these questions by applying platelet concentrate directly to wounds. This month’s Evidence Corner describes 2 recent randomized controlled trials (RCTs) that applied topical dressings containing concentrated platelets to split-thickness skin graft donor sites (SSDS)¹ or burns.² As with much promising research, these studies report interesting results and open opportunities to answer even more interesting questions.

References: Guerid S, Darwiche SE, Berger MM, Applegate LA, Benathan M, Raffoul W. Autologous keratinocyte suspension in platelet concentrate accelerates and enhances wound healing - a prospective randomized clinical trial on skin graft donor sites: platelet concentrate and keratinocytes on donor sites. Fibrogenesis Tissue Repair. 2013;6(1):1-8.   Rationale: Topically applied individual growth factors such as platelet-derived growth factor (PDGF), epidermal growth factor (EGF), and fibroblast growth factor (FGF) have produced inconclusive results during treatment. Platelets and keratinocytes both play essential roles in healing, releasing physiologic levels of these key growth factors involved in healing.   Objective: Test whether a platelet concentrate or keratinocytes suspended in a platelet concentrate could enhance SSDS healing.   Methods: A prospective Swiss study randomly assigned 15 subjects with an SSDS 0.2 mm deep on the anterolateral thigh, not exceeding 15% of body surface area, to 1 of 3 groups. After appropriate institutional review and consent, grafts were harvested to cover mainly burns, trauma wounds, ulcers, or cutaneous tumor excisions. Individuals taking immunosuppressive agents, with severe peripheral arteriopathy or renal insufficiency were excluded from study. Immediately after harvesting the graft, all SSDS sites were temporarily covered with gauze impregnated with 2 mg/L adrenaline in saline solution until hemostasis was achieved. Split-thickness skin graft donor sites treated with platelet concentrate (PC group) were then sprayed with 4 ml of 10 parts 2,300 × 106 autologous platelets aseptically prepared using a 1-step procedure, then delivered plus 1 part 10% calcium chloride. This combination was allowed to coagulate in situ before applying 3 layers of paraffin gauze. Individuals treated with additional keratinocytes (PC + K group), received a similar dose of autologous platelets plus 22.6 × 106 aseptically prepared autologous keratinocytes using the same 4 ml spray delivery system. Control subjects received similar treatment without the platelet concentrate or keratinocytes. All 3 groups were dressed with 3 layers of paraffin gauze held in place by a standardized wrap and elastic bandage until postoperative day 5, when epithelization and a 0-10 Visual Analogue Scale (VAS) for patient-reported wound pain were evaluated by observers who were blinded to treatment. After the day 5 dressing change, the wound was covered by paraffin gauze with an outer layer of dry dressings. Evaluations continued every 2 days until healing was complete. One-way analysis of variance with Tukey post hoc comparisons tested differences between groups, with the probability of incorrectly concluding efficacy set at 5%.   Results: The 3 groups were comparable at baseline on all characteristics. Split-thickness skin graft donor sites treated with PC + K healed in a mean of 5.7 days, faster (P < 0.01) than the 7.2 days for the PC group, which also healed faster (P < 0.01) than the 13.9 days for control subjects. Significant reductions in day 5 postoperative wound pain paralleled the healing results.   Author’s Conclusions: Platelet concentrates improve wound healing and can be used to deliver keratinocytes to wounds, which also enhance healing, though cost and complexity must be reduced before the technique can be used as a standard protocol.

Reference: Maghsoudi H, Nezami N, Mirzajanzadeh M. Enhancement of burn wounds healing by platelet dressing. Int J Burns Trauma. 2013;3(2):96-101.   Rationale: Rapid burn healing improves patient outcomes. Platelets release cytokines and growth factors that foster healing, so applying platelets to a burn wound may enhance healing rates.   Objective: This RCT compared healing efficacy of clinical burns treated with a concentrated homologous platelet dressing or a standard of care, a silver sulfadiazine (SSD) gauze dressing.   Methods: Fifty patients with second or third degree burns over < 20% of their total body surface area, admitted to a trauma and burn center in Tabriz, Iran, participated in this study after proper review and patient consent. Two burn sites on each patient, matched as closely as possible on depth, area, and location, were assigned randomly to receive either a standard of care SSD gauze dressing with no occlusive cover dressing, or concentrated hemologically compatible cross-matched platelets on the wound with no antiseptic. The platelet-treated group was treated topically with an unspecified number of platelets prepared by the center’s blood bank and sealed over the burn surface beneath an occlusive dressing. All wounds were evaluated daily until healed after a nurse removed the dressing and cleaned the wound. A clinician blinded to treatment group recorded wound area, epithelization, granulation tissue formation, and subject-reported pain on a 0-10 VAS. Each wound was cultured on admission and again 5 days later. Deep second and third degree burns were grafted once covered with granulation tissue. Statistical methods were not specified.   Results: Burn sites treated with the platelets or SSD were comparable on enrollment. The occluded and platelet-treated burns epithelized in a mean of 9.5 days and granulated sufficiently for grafting in a mean of 9.8 days. These results were 2 to 3 days faster on average than burns treated with SSD gauze without an occlusive cover dressing (P < 0.007). All patients reported less pain with the platelet preparation covered by an occlusive dressing.   Author’s Conclusions: The platelet dressing improved burn wound healing and significantly reduced healing time. Further study is required to optimize the platelet dose in the dressing, frequency of application and potential interactions between platelets and other factors promoting burn wound healing.   Clinical Perspective: These results seem to support the value of adding topical platelets to the list of evidence-based care for SSDS¹ and second and third degree burns.² Best available evidence suggests further research before reaching this conclusion. Guerid et al¹ conducted a study showing that adding autologous platelets to standard care with gauze-based dressing improves SSDS healing rates and related pain. They also showed that adding autologous keratinocytes further improves SSDS healing rates, but did not test whether effects of these topical additions exceeded the effects of sealing in endogenous cells, molecules and fluids. Maghsoud et al² explored effects of adding topical platelets to burns, but topical platelets were not the only treatment changed: they also added an occlusive film dressing to seal the platelets in place. Silver sulfadiazine control subjects were not dressed with such an occlusive dressing. Disregarding the potential for mild healing delay reported if 1% SSD cream is applied topically to full-thickness excisions in vivo,³ absence of an occlusive dressing is a key factor that may have accounted for the slower healing of the SSD control burns.⁴   Scientific support for replacing gauze with occlusive dressings that seal and heal acute and chronic wounds, preserving a moist environment, has been growing for more than half a century.⁵ A compelling meta-analysis of evidence supported use of moist wound healing with hydrocolloid dressings to reduce SSDS healing time, pain, and incidence of infection, compared to gauze, or saline- or paraffin-impregnated gauze.⁶ This conclusion was recently verified by a large prospective RCT⁷ comparing the effects of alginate (n = 45), film (n = 49), gauze (n = 50), hydrocolloid (n = 49), hydrofiber (n = 47), or silicone (n = 48) dressings on SSDS healing, pain, and infection incidence. Hydrocolloid-dressed wounds healed 7 days faster than those with any other dressing. Gauze dressings more than doubled the incidence of infection: 18% compared to 7.6% for all other dressings.   An unanswered question remains for both studies: what if the rich broth of keratinocytes, fibroblasts, endothelial cells, smooth muscle cells, and natural growth factors and cytokines normally bathing wounds had been sealed over the SSDS or burn wound surface? Impregnated gauze dressings absorb healing fluids. Impregnated gauze is no longer recognized as an adequate standard of care.^8,9 Unless compared to a best standard of care control dressing that seals healing cells, molecules, and fluid over the wound surface, healing effects of treating any wound with any topical agent remain questionable.