Human neutrophil elastase and collagenase sequestration with phosphorylated cotton wound dressings

Abstract

The design and preparation of wound dressings that redress the protease imbalance in chronic wounds is an important goal of wound healing and medical materials science. Chronic wounds contain high levels of tissue and cytokine-destroying proteases including matrix metalloprotease and neutrophil elastase. Thus, the lowering of excessive protease levels in the wound environment by wound dressing sequestration prevents the breakdown of extracellular matrix proteins and growth factors necessary for wound healing. Phosphorylated cotton wound dressings were prepared to target sequestration of proteases from chronic wound exudate through a cationic uptake binding mechanism involving salt bridge formation of the positively charged amino acid side chains of proteases with the phosphate counterions of the wound dressing fiber. Dressings were prepared by applying sodium hexametaphosphate and diammonium phosphate in separate formulations to cotton gauze by pad/dry/cure methods. Phosphorylated cotton dressings were assessed for their ability to lower elastase and collagenase activity. The phosphorylated cotton dressings lowered elastase and collagenase activity 40-80% more effectively than the untreated cotton wound dressings under conditions that mimic chronic wound exudate. Efficacy of the phosphorylated cotton was found to be related to the level of phosphorylation and a lower pH due to protonated phosphate at the surface of the dressing. The capacity of the modified gauze to sequester continued elastase secretions similar to that found in a chronic wound over a 24-h period was retained within a 80% retention of elastase sequestration and was dose-dependent.

Development of a Continuous Finishing Chemistry Process for Manufacture of a Phosphorylated Cotton Chronic Wound Dressing

“…Assessment of the phosphorylated cotton gauze's protease-lowering efficacy, when cured under stationary oven conditions, showed that DAP : urea at a percent ratio by weight of 30 : 10 (urea : PO4) gave higher protease-lowering activity when compared with SMP as the phosphorylating reagent (Figure 4(a) and (d)). This result of higher add-ons correlating with better protease sequestrant efficacy is consistent with previous work, where the increase in cellulose phosphorylation was correlated to an increase in protease sequestrant efficacy [16]. Thus, to improve whiteness and retain efficacy a series of formulations containing a combination of DAP and SMP were cured on the cotton gauze.…”

“…Urea promotes the biphasic reaction between the cellulose and the phosphorylating reagent (see reaction schematic shown in Figure 3), and the release of ammonia from urea decomposition during the reaction required engineering exhaustion of ammonia from the curing oven (see conditions stated in Figure 2 inset). The effect of the two different finishes on the protease sequestrant efficacy of the phosphorylated cotton wound dressing has been previously reported [16]. The typical temperature range for assessing the curing conditions with SMP was 160-175 C.…”

The effects of pH on wound healing, biofilms, and antimicrobial efficacy

“…These proteases, including MMPs and neutrophil elastase, augment tissue and cytokine destruction. Products which lower the levels of these proteases in the wound environment help to prevent the breakdown of extracellular matrix proteins and growth factors that are crucial for wound repair . In a study by Edwards and Howley in 2007, phosphorylated cotton dressings were tested for their ability to sequester elastase and collagenase activity in vitro.…”

Ovine forestomach matrix biomaterial is a broad spectrum inhibitor of matrix metalloproteinases and neutrophil elastase

“…Inhibition of tissue proteases by biomaterials has traditionally been demonstrated using solid‐state assays, whereby the intact samples are incubated in enzyme solutions and then the residual enzyme activity quantified following removal of the sample (14–19,22,29). In the case of soluble or partially soluble biomaterials, such as OFM and ORC/C, reductions in enzyme activity using this approach can be accounted for either by (i) surface adsorption of the enzyme to the biomaterial; or (ii) dissolution of soluble inhibitory components.…”