Significance: The regeneration of healthy and functional skin remains a huge challenge due to its multilayer structure and the presence of different cell types within the extracellular matrix in an organized way. Despite recent advances in wound care products, traditional therapies based on natural origin compounds, such as plant extracts, honey, and larvae, are interesting alternatives. These therapies offer new possibilities for the treatment of skin diseases, enhancing the access to the healthcare, and allowing overcoming some limitations associated to the modern products and therapies, such as the high costs, the long manufacturing times, and the increase in the bacterial resistance. This article gives a general overview about the recent advances in traditional therapies for skin wound healing, focusing on the therapeutic activity, action mechanisms, and clinical trials of the most commonly used natural compounds. New insights in the combination of traditional products with modern treatments and future challenges in the field are also highlighted. Recent Advances: Natural compounds have been used in skin wound care for many years due to their therapeutic activities, including anti-inflammatory, antimicrobial, and cell-stimulating properties. The clinical efficacy of these compounds has been investigated through in vitro and in vivo trials using both animal models and humans. Besides the important progress regarding the development of novel extraction methods, purification procedures, quality control assessment, and treatment protocols, the exact mechanisms of action, side effects, and safety of these compounds need further research. Critical Issues: The repair of skin lesions is one of the most complex biological processes in humans, occurring throughout an orchestrated cascade of overlapping biochemical and cellular events. To stimulate the regeneration process and prevent the wound to fail the healing, traditional therapies and natural products have been used with promising results. Although these products are in general less expensive than the modern treatments, they can be sensitive to the geographic location and season, and exhibit batch-to-batch variation, which can lead to unexpected allergic reactions, side effects, and contradictory clinical results. Future Directions: The scientific evidence for the use of traditional therapies in wound healing indicates beneficial effects in the treatment of different lesions. However, specific challenges remain unsolved. To extend the efficacy and the usage of natural substances in wound care, multidisciplinary efforts are necessary to prove the safety of these products, investigate their side effects, and develop standard controlled trials. The development of good manufacturing practices and regulatory legislation also assume a pivotal role in order to improve the use of traditional therapies by the clinicians and to promote their integration into the national health system. Current trends move to the development of innovative wound care treatments, combining the use of traditional healing agents and modern products/practices, such as nanofibers containing silver nanoparticles, Aloe vera loaded into alginate hydrogels, propolis into dressing films, and hydrogel sheets containing honey.

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Traditional Therapies for Skin Wound Healing.

A conceptually new approach to polymer-based enzyme-triggered release is described, whereby the selective catalytic action of (disease-specific) enzymes triggers a charge-induced swelling response in chemically crosslinked hydrogel particles, resulting in the release of physically entrapped macromolecules (see figure).

Enzyme-responsive polymer hydrogel particles for controlled release

Previous hypotheses about the causes of venous ulceration are inconsistent with recently published data. In patients with chronic venous insufficiency the number of functioning capillary loops visible in the skin on microscopy fell after the legs had been dependent for 30 minutes. Another study had shown that leucocytes became trapped in the circulation in dependent legs. A new hypothesis linking these two findings proposes that the trapped white cells occlude the capillaries and result in ischaemia of the skin of the leg.

Causes of venous ulceration: A new hypothesis

Objective To compare the clinical effectiveness of larval therapy with a standard debridement technique (hydrogel) for sloughy or necrotic leg ulcers.
 
Design Pragmatic, three armed randomised controlled trial.
 
Setting Community nurse led services, hospital wards, and hospital outpatient leg ulcer clinics in urban and rural settings, United Kingdom.
 
Participants 267 patients with at least one venous or mixed venous and arterial ulcer with at least 25% coverage of slough or necrotic tissue, and an ankle brachial pressure index of 0.6 or more. Interventions Loose larvae, bagged larvae, and hydrogel.
 
Main outcome measures The primary outcome was time to healing of the largest eligible ulcer. Secondary outcomes were time to debridement, health related quality of life (SF-12), bacterial load, presence of meticillin resistant Staphylococcus aureus, adverse events, and ulcer related pain (visual analogue scale, from 0 mm for no pain to 150 mm for worst pain imaginable).
 
Results Time to healing was not significantly different between the loose or bagged larvae group and the hydrogel group (hazard ratio for healing using larvae v hydrogel 1.13, 95% confidence interval 0.76 to 1.68; P=0.54). Larval therapy significantly reduced the time to debridement (2.31, 1.65 to 3.2; P<0.001). Health related quality of life and change in bacterial load over time were not significantly different between the groups. 6.7% of participants had MRSA at baseline. No difference was found between larval therapy and hydrogel in their ability to eradicate MRSA by the end of the debridement phase (75% (9/12) v 50% (3/6); P=0.34), although this comparison was underpowered. Mean ulcer related pain scores were higher in either larvae group compared with hydrogel (mean difference in pain score: loose larvae v hydrogel 46.74 (95% confidence interval 32.44 to 61.04), P<0.001; bagged larvae v hydrogel 38.58 (23.46 to 53.70), P<0.001).
 
Conclusions Larval therapy did not improve the rate of healing of sloughy or necrotic leg ulcers or reduce bacterial load compared with hydrogel but did significantly reduce the time to debridement and increase ulcer pain.
 
Trial registration Current Controlled Trials ISRCTN55114812 and National Research Register N0484123692.

https://www.bmj.com/content/bmj/338/bmj.b773.full.pdf

Larval therapy for leg ulcers (VenUS II): randomised controlled trial

Detection and partial characterisation of two antibacterial factors from the excretions/secretions of the medicinal maggot Lucilia sericata and their activity against methicillin-resistant Staphylococcus aureus (MRSA).

Summary

Background Larvae of the greenbottle fly Lucilia sericata are used routinely for the clinical treatment of difficult necrotic and infected wounds. Degradation by proteinases contained in larval excretory/secretory (ES) products is thought to contribute to wound debridement by removal of dead tissue. However, proteinase activity may also affect host tissue remodelling processes.



Objectives  To identify proteolytic enzymes derived from L. sericata ES products with activities against fibrin and extracellular matrix (ECM) components.



Methods  Larval proteinase activities were assayed in vitro using class-specific substrates and inhibitors. Their action against fibrin and ECM components was examined using sodium dodecyl sulphate–polyacrylamide gel electrophoresis.



Results  Three classes of proteolytic enzyme were detected in the secretions using fluorescein isothiocyanate-labelled casein as a model substrate. The predominant activity belonged to serine proteinases (pH optima 8–9) of two different subclasses (trypsin-like and chymotrypsin-like), with a weaker aspartyl proteinase (pH 5) and a metalloproteinase (pH 9) with exopeptidase characteristics also present. Using skin-relevant ECM components as substrates L. sericata ES products solubilized fibrin clots and degraded fibronectin, laminin and acid-solubilized collagen types I and III. Hydrolysis of ECM macromolecules was inhibited by preincubating ES products with phenylmethylsulphonyl fluoride but not 4-amidinophenylmethylsulphonyl fluoride, indicating that degradation was due to the ‘chymotrypsin-like’ serine proteinase.



Conclusions  These data suggest that a combination of L. sericata ES proteinases involving chymotrypsin-like and trypsin-like activities could potentially influence wound healing events when maggots are introduced into necrotic and infected wounds, with the chymotrypsin-like activity involved in the remodelling of ECM components.

Degradation of extracellular matrix components by defined proteinases from the greenbottle larva Lucilia sericata used for the clinical debridement of non-healing wounds.

J.C.T. Church

Papers

Degradation of extracellular matrix components by defined proteinases from the greenbottle larva Lucilia sericata used for the clinical debridement of non-healing wounds.