Proteases and pH in chronic wounds

The use of MelMax in the healing of chronic wounds

Chronic wounds can have detrimental consequences for the quality of life of patients as well as presenting a huge financial burden to the NHS. An imbalance in the level of matrix metalloproteinases (MMPs) and the tissue inhibitors of MMPs (TIMPs) in chronic wounds impedes the healing process. In addition, high levels of bacteria in the wound bed are a common feature of chronic wounds and also cited as a major cause of delayed healing. The aim of this article is to look in more detail at the role of MMPs in wound healing as well as the antimicrobial properties of honey when combined with a dressing to combat wound infection. The article also introduces a new dressing, MelMax (distributed by CliniMed), which utilizes protease regulation and the antimicrobial properties of honey when addressing chronic wound infection. Short-term case studies are used to demonstrate how the dressing was successfully incorporated into the author's practice.

The impact of Manuka honey dressings on the surface pH of chronic wounds

Chronic non healing wounds have an elevated alkaline environment. The acidic pH of Manuka honey makes it a potential treatment for lowering wound pH, but the duration of effect is unknown. Lowering wound pH can potentially reduce protease activity, increase fibroblast activity and increase oxygen release consequently aiding wound healing. The aim of this study was to analyse the changes in surface pH and size of non healing ulcers following application of Manuka honey dressing after 2 weeks. The study was an open label, non randomised prospective study. Patients presenting consecutively with non healing chronic superficial ulcers, determined by aetiology and no reduction in wound size in previous 3 weeks. Single pH measurements recorded using Blueline 27 glass surface electrode and R 315 pH meter set (Reagecon/Alkem, Co. Clare Ireland). Area determined using Visitrak (Smith & Nephew, Mull, UK) digital planimetry. Apinate (Manuka honey) (Comvita, Slough, UK) applied to wounds for 2 weeks after which wounds re-evaluated. Eight males and nine females with 20 ulcers (3 bilateral) were included: venous, 50% (n = 10); mixed aetiology, 35% (n = 7); arterial, 10% (n = 2) and pressure ulcer, 5% (n = 1). Reduction in wound pH after 2 weeks was statistically significant (P < 0.001). Wounds with pH >or= 8.0 did not decrease in size and wounds with pH <or= 7.6 had a 30% decrease in size. A reduction in 0.1 pH unit was associated with an 8.1% reduction in wound size (P < 0.012). The use of Manuka honey dressings was associated with a statistically significant decrease in wound pH and a reduction in wound size. Elevated pH readings at the start were associated with minimal reduction in size. Surface wound pH measurements may contribute to objective wound assessments, but further research is necessary to determine its exact contribution.

Current therapeutic options of chronic leg ulcers

Wound treatment is continually becoming more complex and difficult. In the following review, we focus on the different options of wound debridement, stimulation of granulation tissue, different wound dressings, and therapeutic strategies in hard-to-heal-wounds. We also present some future treatment options for chronic wounds.

Evaluation of pH measurement as a method of wound assessment

OBJECTIVE

To assess variations in wound pH levels and explore the relationship between wound pH and the state of wound healing.

METHOD

Fifty patients with acute or chronic wounds attending the wound clinic at University Hospital,Varanasi, India were included. Wound pH was measured using litmus paper strips and recorded weekly. Other parameters recorded were the wound condition, exudate level and culture.

RESULTS

The baseline pH of most of the wounds was greater than 8.5. As the wound condition improved and exudate levels decreased, the pH reduced to less than 8.0. Fifty-eight per cent of the wounds were culture positive, and an association was observed between the type of organism present and the wound pH.

CONCLUSION

Wound pH measurements can be performed efficiently and are non-invasive, causing no discomfort to the patient. As the wounds healed, the pH reduced. This change in pH can help predict the likelihood of wound healing.

In vitro diffusion bed, 3-day repeat challenge 'capacity' test for antimicrobial wound dressings

The aim of this study was to develop an in vitro wound infection model that allows the comparison of the bacterial kill rate of antimicrobial wound dressings over the course of 3 days, with renewed microbial challenges each day, under realistic wound-like conditions. A test bed model of a moderately exuding wound was constructed from a hydrogel containing releasable foetal calf serum (FCS), and cellulose discs dosed with test microbes (Methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa) suspended in 50% FCS applied at the interface between the test dressing and the hydrogel test bed. Freshly prepared discs were used to challenge the same dressing over a 23-hour period for a course of 3 days. Different test dressings produced differing kill rates, allowing quantitative comparison of both their immediate activity and their capacity to continue working over 3 days, within a fluid-donating system similar to the situation in vivo. The reported method has significant advantages over established test procedures since it enables the researcher to assess the antimicrobial capacity of wound dressings to continue working under conditions that match those encountered in wounds. These key conditions are those that would be expected to impede the action of the dressing and protect the infecting organisms.

Influence of pH on wound-healing: a new perspective for wound-therapy?

Wound healing is a complex regeneration process, which is characterised by intercalating degradation and re-assembly of connective tissue and epidermal layer. The pH value within the wound-milieu influences indirectly and directly all biochemical reactions taking place in this process of healing. Interestingly it is so far a neglected parameter for the overall outcome. For more than three decades the common assumption amongst physicians was that a low pH value, such as it is found on normal skin, is favourable for wound healing. However, investigations have shown that in fact some healing processes such as the take-rate of skin-grafts require an alkaline milieu. The matter is thus much more complicated than it was assumed. This review article summarises the existing literature dealing with the topic of pH value within the wound-milieu, its influence on wound healing and critically discusses the currently existing data in this field. The conclusion to be drawn at present is that the wound pH indeed proves to be a potent influential factor for the healing process and that different pH ranges are required for certain distinct phases of wound healing. Further systematic data needs to be collected for a better understanding of the pH requirements under specific circumstances. This is important as it will help to develop new pH targeted therapeutic strategies.

Experimental models and high-throughput diagnostics for tissue regeneration

During wound healing, cells recreate functional structures to regenerate the injured tissue. Understanding the healing process is essential for the development of new concepts and the design of novel biomimetic approaches for delivery of cells, genes and growth factors to accelerate tissue regeneration. To this end, realistic experimental models and high-throughput diagnostics are necessary to understand the molecular mechanisms of healing and reveal the genetic networks that determine tissue repair versus regeneration. Following a brief overview of the biology of wound healing, this review covers the in vitro and in vivo models that are employed at present to study the healing process. Discussion then covers the application of high-throughput genomic and proteomic technologies in epithelial development, living skin substitutes and wound healing. Finally, this review provides a perspective on novel technologies that should be developed to facilitate the understanding of wound healing complications and the design of therapeutics that target the underlying deficiencies.

Real-time monitoring of drug-induced changes in the stomach acidity of living rats using improved pH-sensitive nitroxides and low-field EPR techniques

New improved pH-sensitive nitroxides were applied for in vivo studies. An increased stability of the probes towards reduction was achieved by the introduction of the bulky ethyl groups in the vicinity of the paramagnetic NO fragment. In addition, the range of pH sensitivity of the approach was extended by the synthesis of probes with two ionizable groups, and, therefore, with two pKa values. Stability towards reduction and spectral characteristics of the three new probes were determined in vitro using 290 MHz radiofrequency (RF)- and X-band electron paramagnetic resonance (EPR), longitudinally detected EPR (LODEPR), and field-cycled dynamic nuclear polarization (FC-DNP) techniques. The newly synthesized probe, 4-[bis(2-hydroxyethyl)amino]-2-pyridine-4-yl-2,5,5-triethyl-2,5-dihydro-1H-imidazol-oxyl, was found to be the most appropriate for the application in the stomach due to both higher stability and convenient pH sensitivity range from pH 1.8 to 6. LODEPR, FC-DNP and proton-electron double resonance imaging (PEDRI) techniques were used to detect the nitroxide localization and acidity in the rat stomach. Improved probe characteristics allowed us to follow in vivo the drug-induced perturbation in the stomach acidity and its normalization afterwards during 1 h or longer period of time. The results show the applicability of the techniques for monitoring drug pharmacology and disease in the living animals.