Wound dressings containing complexes of transition metals and alginate for elastase sequestering
Transition metal (e.g., silver and copper) derivatized phosphorylated polysaccharides (cellulose, starch, gauze) provide antimicrobial and elastase sequestration properties to wound dressings, and the wound dressing have enhanced water sorption and elastase sequestration when used with alginates. Wound dressings with alginates (e.g., silver alginate, crosslinked alginates, etc.) provide enhanced wound fluid absorption as well as elastase sequestration.
This is a continuation-in-part of application Ser. No. 10/446,806 filed May 29, 2003, which is a continuation-in-part of U.S. patent application Ser. No. 09/515,172, entitled “Wound Dressing with Protease-Lowering Activity,” filed on Feb. 29, 2000, that are incorporated herein in entirety by reference.
FIELD OF THE INVENTIONThe invention generally relates to wound dressings and their methods of use. In particular, the invention provides wound dressings with associated active agents such as protease inhibitors and sequestrants which enhance the healing of wounds, especially chronic wounds.
BACKGROUND OF THE INVENTIONThe normal response to tissue injury is a timely and orderly reparative process that results in sustained restoration of anatomic and functional integrity.(Lazarus, et al. 1994). In contrast, in chronic ulcers, the healing process is prolonged, incomplete and proceeds in an uncoordinated manner resulting in poor anatomical and functional outcome. Clinically, wounds are categorized as acute and chronic based on the timeliness of healing.
Most chronic ulcers are associated with a small number of well-defined clinical entities particularly chronic venous stasis, diabetes mellitus, and pressure ulcers. These conditions are responsible collectively for approximately 70% of all chronic ulcers (Nwomeh et al. 1998). The incidence and prevalence of chronic ulcers vary considerably but are especially high in spinal cord injury patients as well as the elderly and nursing home population. As our society continues to age it is predicted that the incidence of chronic ulcers will continue to increase dramatically. Patients with pressure ulcers also have a significant socioeconomic impact on our society. For example, health care expenditures for treating pressure ulcers alone have been estimated to exceed $3 billion a year (Nwomeh, et al. 1998). Normal healing involves a complex cascade of events involving interaction among many cell types, soluble factors and matrix components. Healing can be arbitrarily divided into overlapping temporal phases of coagulation, inflammation fibroplasia and finally remodeling. Most of the events are cytokine regulated. Normally, during the inflammatory phase, polymorphonuclear leukocytes (PMNs) are the first of the leukocytes to appear. They produce various proteases such as MMP-8 (collagenase) and elastase, which help to remove damaged matrix and aid in healing. In both the open acute and chronic wound, various cytokines are important in contraction and spontaneous closure of the wound as well as angiogenesis. Under normal circumstances, closure of the open wound is aided further by epithelization as these surface cells seal the final closure.
Chronic wounds are very different. For example, pressure ulcers are characterized by deep tissue necrosis with loss of muscle and fat that is disproportionately greater then the loss of overlying skin (Falanga, et al. 1998). These defects are common among the immobilized and debilitated. There are approximately 225,000 spinal cord injury patients in the United States and approximately 9,000 new cases per year. Approximately 60% of these patients develop pressure ulcers and the annual cost is greater then $25,000 per patient for medically related care.(Allman, 1998) If the elderly nursing home population with pressure ulcers in added to the spinal cord injury population then the figure for the care of all pressure ulcers is enormous.
To date, the majority of the effort to improve rates of healing of chronic wounds have focused on the use of exogenous peptide growth factors and cell based products such as cytokines. For the most part, these attempts have met with little notable success. Another alternative approach has been the use of “skin substitutes” such as Apligraf (matrix+cells) and Dermagraft (matrix+cells). While this second approach has shown some promise, its expense presently greatly limits its use to the richer developed countries. Various modifications of the wound dressings have also been suggested as a means to augment would healing.
Further examples include:
U.S. Pat. No. 5,098,417 to Yamazaki et al. teaches the ionic bonding of physiologically active agents to cellulosic wound dressings.
U.S. Pat. No. 4,453,939 to Zimmerman et al. teaches the inclusion of aprotonin in composition for “sealing and healing” of wounds. U.S. Pat. No. 5,807,555 to Bonte et al. teaches the inclusion of inhibition for alpha-1-protease, collagenase, and elastase in pharmaceutical compositions for promotion of collagen synthesis.
U.S. Pat. No. 5,696,101 to. Wu et al., teaches use of oxidized cellulose (e.g. Oxycel) as a bactericide and hemostat in treatment of wounds.
World Patent WO 98/00180 to Watt et al. teaches complexation of oxidized cellulose with structural proteins (e.g. collagen) for chronic wound healing; and references the utility of oligosaccharide fragments produced by the breakdown of oxidized cellulose in vivo in the promotion of wound healing.
Neutrophils are a predominant infiltrating inflammatory cell type present in the acute inflammatory response. Neutrophils function primarily to destroy invading pathogens and to debride devitalized tissue at the site of injury. The normal adult produces approximately 10.sup.11 neutrophils per day. To function effectively in host defense, they must migrate to the site of inflammation and release selectively a large repertoire of lytic enzymes, antimicrobial peptides, and potent oxidants from cytoplasmic granules. Under other conditions, the neutrophil has been implicated in causing disease by damaging normal host tissue. Such inflammatory tissue injury are important in the pathogenesis of a variety of clinical disorders including arthritis, ischemia-reperfusion tissue injury and systemic inflammatory response syndrome (SIRS) and the acute respiratory distress syndrome(ARDS).(Weiss, 1989) There is strong evidence that neutrophils also may have a significant role in the pathophysiology of pressure ulcers.
Neutrophils are a prevalent cell type in pressure ulcers.(Diegelmann, et al. 1999; Paloahti. et al. 1993; Rogers et al. 1995) In addition, there is direct evidence correlating neutrophil products with chronic pressure ulcers.(Yager, et al. 1996; Yager, et al. 1997). This includes neutrophil elastase, gelatinase (MMP-9) as well as collagenase (MMP-8).(Wysocki, 1996; Wysocki et al, 1993; Yager et al. 1997; Yager et al. 1996). Therefore, these observations and the evidence that neutrophils have been implicated in tissue destruction in other inflammatory processes give strong credence to the hypothesis that neutrophil products are involved in the pathogenesis of pressure sores and subsequent failure to heal. Neutrophil-derived MMP-8 has been shown to be the predominant collagenase in both acute and chronic wounds.(Nwomeh, et al. 1999).
Neutrophils contain large amounts of elastase (1 pg /cell). This serine protease has a broad substrate spectrum. As with neutrophil-derived MM-8, elastase levels have also been found to be significantly elevated in fluid derived from pressure ulcers.(Yager et al. 1997) The presence of high levels of active elastase with a wound site may have important implications for wound healing therapies utilizing peptide growth factors. Elastase present in chronic wounds can degrade peptide growth factors such as PDGF and TGF-b.(Yager et al. 1997). Moreover, cell surface receptors for peptide growth factors may themselves be functionally inactivated by the actions of elastase. Elastase may also contribute to the overall proteolytic environment of chronic wounds. It is known to proteolytically inactivate the specific inhibitor, Tissue Inhibitor of Metalloproteinases (TIMP). In addition, elastase itself may participate in proteolytically activating collagenase and gelatinase zymogens. Obviously, an unregulated proteolytic environment can be a significant aspect of the pathophysiology of chronic wounds.
It would be highly beneficial to have available additional methods for enhancing wound healing. In particular, methods directed to bringing the proteolytic environment of wounds under control in order to promote wound repair would be desirable. Such methods would be useful in the treatment of wounds in general, and chronic wounds in particular. Further, it would be highly beneficial if such methods were inexpensive and thus widely accessible.
A number of patents and patent applications describe the use of alginates in the treatment of burns or wounds. For example, U.S. Pat. No. 6,696,077 to Scherr describes various silver alginate foam compositions, and U.S. Pat. No. 6,809,231 to Edwards describes cross-linked alginate formulations.
A number of patents and patent applications describe the use of silver ions as antimicrobial agents. For example, U.S. Patent Publication 2005/010900 to Qin describes polysaccharide fibers formed with alginate that contain a silver compound as an antimicrobial agent, and U.S. Patent Publication 2004/0241213 to Bray describes carboxymethyl cellulose or alginate fibers in a mixture that contains silver ions. Neither reference describes a configuration where alginates are position in a wound dressing for sequestration of elastase.
SUMMARY OF THE INVENTIONIt is an object of this invention to provide novel wound dressings for the treatment of wounds, especially for the treatment of chronic, non-healing wounds. The wound dressings of the instant invention are comprised of a support matrix which is preferably cellulose, carboxymethylated cellulose, dialdehyde gauze, sulfonated gauze, and phosphorylated gauze, in combination with silver or copper, alginate or silver alginate. The wound dressings combine antimicrobial activity together with elastase sequestration and provide for enhanced wound healing in burns, surgical wounds, ulcers and chronic wounds, etc. For example, in some embodiments, the gauze may be derivatives with silver and then coated with alginate. In other cases, the gauze may be coated with silver alginate which may be bound to the support matrix or be able to dissociate from the support matrix so as to allow migration in the wound microenvironment. When phosphorylated gauze, sulfonated gauze or dialdehyde gauze is used as a support matrix, the wound dressing benefits from elastaste sequestration by the gauze itself as well as by the alginate. The sequestrants bind proteases found in the wound fluid and remove them from the wound microenvironment.
The invention also provides methods of use for the wound dressings, including a method for sequestering elastase at a wound site. This method comprises the step of contacting the wound site with a wound dressing selected form the group consisting of carboxymethylcellulose, dialdehyde gauze, sulfonated gauze, and phosphorylated gauze together with transition metal such as silver and alginate.
The dressings may be applied to wounds in order to enhance would healing, especially the healing of chronic wounds.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 2A-C. Reaction progress curves for gauze-treated solutions of elastase. Substrate hydrolysis was performed with a 60 .mu.M solution of MeOSuc-Ala-Ala-Pro-Val-pNA and reaction rates monitored by spectrophotometric measurement of the release of p-nitroaniline at 405 nm. 25, 50 and 75 mg samples of phosphorylated cotton gauze (PSC, 5A), sulfonated cotton gauze (SOC, 5B) and dialdehyde cotton gauze (DAG, 5C) were compared with 75 mg of untreated cotton gauze (UT).
The present invention is based upon the previously unrecognized discovery that active agents such as inhibitors and sequestrants of proteases may be used as healing accelerants of wounds, and of chronic wounds in particular. These inhibitors and sequestrants may be physically applied on wound dressings, or in the alternative may be ionically or covalently conjugated to a wound dressing material for purposes of sustained release of active agent or sequestration of endogenous constituents from the wound environment. In a preferred embodiment of the present invention, the active agents inhibit or bind cationic, neutrophil-derived proteases such as neutrophil elastase.
Specific pharmacological effects of proteases inhibitors and sequences associated with wound dressings include inhibition of the breakdown of growth factors that stimulate migration of cells to the ulcer site of the wound, leading to the growth of new tissue that heals the open wound. This technology is broadly applicable to all forms of chronic wounds including diabetic ulcers and decubitus bedsores. Both peripheral and central administration of the compounds formulated on wound dressings accelerate wound healing of chronic wounds. Silver complexed to matrix and silver alginate are shown herein to have potent elastase sequestering properties which were heretofore previously unrecognized and thereby inhibit proteases such as human elastase and thus prevent growth factor and tissue degradation. Alternatively, the silver alginate may be bound (chemically (ionic or covalently) or physically) to the wound dressing. As a component of such a matrix, they are able to sequester destructive proteases from the microenvironment of the wound, thus preventing the degradation of growth factors and fibronectin that would otherwise occur.
The therapeutic administration of the modified wound dressings containing inhibitors include a pharmacologically effective dose of the inhibitor or sequestrant (e.g., silver alginate, or silver alginate in combination with a phosporylated, sulfonated or dialdehyde gauze) when used tin the treatment of a patient in need thereof. The dose of inhibitor or sequestrant required on the wound dressing to promote accelerated healing in the patient ranges from about 0.2 mg/gram fiber to about 200 mg/gram fiber per day, with this in turn being dependent upon specific factors including patient health, wound type, etc. The term “patient” used herein is taken to mean mammals such as sheep, horses, cattle, pigs, dogs, cats, rats, mice and primates, including humans.
The term “wound dressing” used herein is taken to include any pharmaceutically acceptable wound covering or support matrix such as:
a) films, including those of a semipermeable or a semi-occlusive nature such as polyurethane copolymers, acrylamides, acrylates, paraffin, polysaccharides, cellophane and lanolin.
b) hydrocolloids including carboxymethylcellulose protein constituents of gelatin, pectin, and complex polysaccharides including Acacia gum, guar gum and karaya. These materials may be utilized in the form of a flexible foam or, in the alternative, formulated in polyurethane or, in a further alternative, formulated as an adhesive mass such as polyisobutylene.
c) hydrogens such as agar, starch or propylene glycol; which typically contain about 80% to about 90% water and are conventionally formulated as sheets, powders, pastes and gels in conjunction with cross-linked polymers such as polyethylene oxide, polyvinyl pyrollidone, acrylamide, propylene glycol.
d) foams such as polysaccharide which consist of a hydrophilic open-celled contact surface and hydrophobic closed-cell polyurethane.
e) impregnates including pine mesh gauze, paraffin and lanolin-coated gauze, polyethylene glycol-coated gauze, knitted viscose, rayon, and polyester.
f) cellulose-like polysaccharide such as alginates, including calcium alginate, which may be formulated as non-woven composites of fibers or spun into woven composites.
Preferred wound dressings are polysaccharide containing support matrices which are derivatized with silver or copper and/or which have silver alginate bound to or placed upon them, and it is envisioned to include chitosans, alginates (e.g., cross-linked or in a form other than silver alginate) and cotton or carboxymethylated cotton in the form of gauze, films, hydrocolloide, hydrogels, hydroactives, foams, impregnates, absorptive powders and pastes,
Especially preferred wound dressings include cotton cellulose formed as woven or non-woven gauze. This type of wound dressing has the advantage of being readily available and relatively inexpensive. In this case, the protease sequestrant or inhibitor may be linked to the cellulose polysaccharide chain through a chemical substituent such as amino, carboxylate, citrate, phosphate, sulfonate, chloride, bromide, mono-carboxylic acid, di-carboxylic acid, tri-carboxylic acid; or, any pharmaceutically acceptable salt thereof. Exemplary salts are seen to include those of acids such as acetic, glycolic, lactic, pyruvic, malonic, succinic, glutaric, fumaric, malic, tartaric, ascorbic, maleic, hydroxymaleic, benzoic, hydroxybenzoic, phenylacetic, cinnamic, salicylic, and 2-phenoxyhenzoic; and sulfonic acids such as methane sulfonic acid and hydroxyethane sulfonic acid. Salts of the carboxy terminal amino acid moiety may include the nontoxic carboxylic acid salts formed with any suitable inorganic or organic bases. illustratively, these salts include those of alkali metals, as for example, sodium and potassium; alkaline earth metals, such as calcium and magnesium; light metals of Group IIA elements including aluminum, and organic primary, secondary, and tertiary amines, as for example, trialkylamines, including triethylamine, procaine, dibenzylamine, 1-ethenamine, N,N′-dibenzylethylenediamine, dihydroabietylamine, N-alkylpiperidine and any other suitable amine.
The wound dressings of the instant invention may be used alone or as an adjunct to other therapeutic measures. For example, the wound dressings may be used together with the administration of exogenous growth factors. Obviously, conditions that increase the stability of an exogenous peptide growth factor or its receptor will likely promote its efficacy. The wound dressings of the present invention may also be used in conjunction with skin grafts, in which case a proteolytic environment that is under control will less likely cause the “rejection” or melting of a skin substitute graft.
The wound dressings may also include other therapeutically beneficial substances such as antibiotics, vitamins, and the like.
The dressings and methods of the present invention may be utilized to treat any type of appropriate wound. In a preferred embodiment, the wound that is treated is a chronic, non-healing wound.
The invention is illustrated by the following Examples which are intended to be illustrative but should in no way be construed as limiting.
EXAMPLESCarboxymethylated and Dialdehyde Cotton Gauze
Methods
Preparation of Dialdehyde Cotton Gauze
Dialdehyde cotton gauze (also referred to as 2,3 dialdehyde-anhydroglucos-cellulose, oxidized cellulose, oxycellulose, or periodate-oxidized cellulose) was prepared as follows: cotton gauze (12 ply-4 in.×4 in.), USP type VII, were treated under three different reaction conditions in lots of 50 gauze sponges as follows: Treatment 1: a 0.07 M solution of sodium periodate for 1 h at 45° C. with a solution pH of 4.2. Treatment 2: a 0.2 M solution of sodium periodate for 1.5 h at 45° C. with a solution pH of 4.5. Treatment 3: a 0.2 M solution of sodium periodate for 3 h at 45° C. with a solution pH of 4.5. Following the treatment excess periodate was removed by rinsing the gauze through a screen under running tap water. Following the rinse cycle the gauze samples were passed through a conventional ringer to remove excess moisture. The samples were then separated and placed on a wire rack to air dry overnight. The dried gauzes were placed in Chex all II.™. instant sealing pouches (5 in.×10 in.) and sterilized with ethylene oxide gas by Micro Test Laboratories, Agauam, Mass.
Preparation of Carboxymethylated Cotton Gauze
Carboxymethylation was completed as outlined previously (Liyanage et al, 1995). A solution was made by mixing 24 parts of dichloroacetic acid with 24 parts of water, and while cooling in an ice bath, stirring in 75 parts of sodium hydroxide solution. This solution was used to pad a sample of cotton gauze to a wet pickup of 135%. The wet sample was then placed in an oven at 100° C. and dried/cured for 10 minutes.
Determination of Dialdehyde Content and Degree of Substitution of Carboxymethylcellulose
Previously outlined procedures were employed to determine the dialdehyde content (Hofreiter et al. 1995) and the degree of substitution for the carboxymethylated gauze (Reinhardt et al.)
Assay of Treated Gauze for Elastase Activity
Treated and untreated gauze samples were submerged in 1 milliliter of buffer containing 0.1 units/ml of human neutrophil elastase. The samples were allowed to incubate for one hour at room temperature, and the gauze samples were removed and placed in a press to drain unbound buffer and enzyme. The unbound buffer and enzyme fractions were combined and assayed for elastase activity as described below.
Enzyme Assays
Enzyme assays of the solutions containing unbound human neutrophil elastase were conducted in pH 7.6 buffer composed of 0.1 M sodium phosphate, 0.5 M NaCl, and 3.3% DMSO and subjected to spectrophotometric measurement of the release of p-nitroaniline at 410 nm from the enzymatic hydrolysis of MeOSuc-Ala-Ala-Pro-Val-pNA (Sigma). The spectrophotometric kinetic assays were performed in a BioRad Microplate Reader (Hercules, Calif.) with a 96-well format. 200 microliter aliquots of a elatase solution (0.2 units) were assayed to initiate the enzyme reaction.
Results
The gauze finishes employed in this study were prepared to assess the effect of 1) both sterilization and variation of the sodium periodate finishing conditions on the activity of dialdehyde cotton gauze in reducing elastase activity; and 2) the effect of the degree of substitution of carboxymethylated gauze in reducing elastase activity.
As shown in
Two different degree of substitution (DS) levels of carboxy methylated cotton cellulose were also compared. As shown in
Correlation of decreased enzyme activity with number of carboxylate or aldehyde sites on cellulose observed within a narrow range of enzyme rates of activity suggests that the cotton derivatized aldehyde and carboxylates bind elastase into readily accessible binding sites in the modified cotton fiber of the gauze.
These results suggest that dialdehyde cotton gauze and carboxymethylated gauze can be used to effect the sequestration of the protease elastase from solutions of the enzyme.
Oxidized, Sulfonated, and Phosphorylated Cotton Gauze Dressings Selectively Absorb
Neutrophil Elasase Activity in Solution
Methods
Preparation of Periodate-Oxidized, Sulfonated, and Phosphorylated Cotton
2,3 dialdehyde-anhydroglucose-cellulose (i.e. periodate oxidized) cotton. Cotton gauze (12 ply-4 in.×0.4 in.), USP type VII, was treated in lots of 50 gauze sponges in a 0.07 M solution of sodium periodate for 1 h at 45° C. with a solution pH of 4.2. Alternatively, cotton gauze was oxidized with 0.2M sodium metaperiodate (pH 5) at 40° C. for 3 hours. Following the treatment excess periodate was removed by rinsing the gauze through a screen under running tap water. Following the rinse cycle, the gauze were passed through a conventional ringer to remove excess moisture. The samples were then separated and placed on a wire rack to air dry overnight. The dried gauze are placed in a Chex all II.™. instant sealing pouch (5×10 in.) and sterilized with ethylene oxide gas by Micro Test Laboratories, Agauam, Mass.
Sulfonated cotton. The cotton gauze may be sulfonated by washing the dialdehyde oxycellulose with 5% sodium bisulfite (NaHSO3) under pH 4.5, liquor ratio 1:60 for 3 hours. Excess sodium bisulfite may be removed by rinsing with water under running tap water. Following the rinse cycle the gauze are passed through a conventional ringer to remove excess moisture. The samples are then separated and placed on a wire rack to air dry overnight.
Phosphorylated cotton. Phosphorylation of cotton gauze is accomplished by applying inorganic phosphate salt (sodium hexametaphosphate) to cotton gauze in 4-16% composition. Urea is usually included in the formulation on a 2:1 weight ratio of urea to phosphate. All formulations contained 0.1% Triton X-100 as a wetting agent. The cotton gauze is padded to 80-90% wet pickup and then dried at 60° C. The samples are cured at 160° C. for 7 min.
The phosphorylated and sulfonated cotton cellulose D.S. levels were 0.035 and 0.011 respectively, as measured by elemental analysis.
Carboxymethylated Cotton Gauze
Carboxymethylation was completed as outlined previously (Reinhart et al. 1957). A solution was made by mixing 24 parts of dichloroacetic acid with 24 parts of water and while cooling in an ice bath stirring in 75 parts of sodium hydroxide solution. This solution was used to pad a sample of cotton gauze to a wet pickup of 135%. The wet sample was then placed in an oven at 100° C., and dried/cured for 10 minutes.
Free-Swell Absorbency and Wicking Test
A free-swell absorbency test was performed as follows: A 0.5 gram sample of the cotton gauze was placed in 30 mL of a 0.9% by weight aqueous saline solution and left for 5 minutes. The cotton textile was then filtered through a sintered Mark 1 funnel of pore size 100-160 microns and is left for 5 minutes, or until it stops dripping. The water filtered through the funnel was weighed and the weight of water absorbed by the filaments is calculated by subtraction. A wicking test was made by immersing the cotton gauze in deionized water containing foxboro red dye such that the gauze was just touching the water surface. The time required for the dye solution to migrate 1.5 cm on the gauze strip was measured.
Patients and Wound Fluid
Informed consent was obtained for all procedures, and approval was received from the Virginia Commonwealth University Committee on the Conduct of Human Research, in accordance with the 1975 Declaration of Helsinki. Fluids were harvested from a grade III trochanteric pressure ulcer of a patient with spinal cord injury using a sub-atmospheric device (V.A.C.R™., KCl, San Antonio, Tex.). Fluids were clarified by centrifugation at 14,000 g for 15 min at 4° C. The protein concentration was determined with the Bio-Rad Protein assay (Richmond, Calif.) with bovine serum albumin as a quantitation standard.
Assay of Wound Fluid
The patient wound fluid was diluted (1:100; wound fluid: buffer; v:v) at a volume of 3 mL with buffer (0.1M sodium phosphate, 0.5 M NaCl, and 3.3% DMSO) and incubated with weighed samples of gauze ranging from 75 mg to 700 mg. The gauze samples were soaked in the wound fluid solutions for one hour whereupon the solutions were filtered from the gauze under pressure applied to the gauss using a Whatman Autovial (0.45 micron PFTE membrane). Recovery of the wound fluid solution from the gauze was judged to be 90%. The wound fluid solution was assayed for elastase activity in a manner similar to the elastase enzyme assay described below. Rates of substrate hydrolysis were measured on a reaction progress curve of absorbance versus time.
Sequestration and Inhibition of Elastase Activity by Finished Cotton Gauze
The effect of a variety of cotton gauze finishes was tested to assess extraction of elastase from solution. Carboxymethylated, sulfonated, phosphorylated, and oxidized cotton gauze were assayed as 50 and 75 milligram samples of type VII cotton gauze (used typically in patients with chronic wounds). Treated and untreated gauze samples were submerged in 1 milliliter of buffer containing 1 unit/mL of human neutrophil elastase. The samples were allowed to incubate for one hour at room temperature, and each individual gauze sample was removed and placed in an Autovial press filter (Whatman,) to extract unbound buffer and enzyme. The filtered fraction of each individual sample was re-combined with solution not taken up by the gauze and assayed for elastase activity.
The modified gauze containing bound elastase was assessed for recoverable enzyme activity by pooling gauze samples and extracting bound elastase with 20% acetic acid solution. Samples of 1-2 grams of modified gauze were soaked in acetic acid solutions, filtered and the solutions lyophilized to dryness. The lyophilized pellet was resuspended in buffer, filtered on a sintered glass filter funnel and the resulting solution was assayed in 200 microliter aliquots. Elastase activities recovered from the gauze were 43 milliunits per gram in untreated gauze and 160 milliunits per gram from dialdehyde cotton gauze.
Enzyme Assays
Enzyme assays of the solutions containing unbound human neutrophil elastase were conducted in pH 7.6 buffer composed of 0.1M sodium phosphate, 0.5 M NaCl, and 3.3% DMSO and subjected to spectrophotomeric measurement of the release of p-nitroaniline at 410 nm from the enzymatic hydrolysis of N-Methoxysuccinyl-Ala-Ala-Pro-Val-p-nitoranilide (Sigma) (Nakajima et al. 1979). The spectrophotometric kinetic assays were performed in a Bio-Rad Microplate Reader (Hercules, Calif.) with a 96-well format. Two hundred microliter aliquots of an elastase solution (0.2 units) were assayed per well, and 20 microliters of a 60 micromolar substrate solution was added to initate the enzyme reaction.
Inhibition of Elastase Activity with Dialdehyde Starch
Elastase activity was measured in dialdehyde starch solutions. Solutions of dialdehyde starch (Sigma) were prepared in the buffer described above at concentrations of 100 to 0.1 micromolar. The dialdehyde starch solutions were incubated with stirring in Reacti-Vials with 0.2 units/mL of elastase for an hour. The solutions were centrifuged at 1200×g for five minutes and the supernatant was assayed for elastase activity as described above.
Results
Cotton gauze was subjected to phosphorylation, oxidation, and sulfonation. The degree of substitution (D.S.) was determined by a standard degree of substitution relationship for cellulose (based on the per cent of total phosphorous and sulfur for the phosphorylated and sulfonated samples). Base titration of free carboxyls was employed to determine D.S. levels on carboxymethylated cotton cellulose (CMC). The phosphorylated and sulfonated cotton cellulose D.S. levels were 0.035 and 0.011 respectively. This corresponds to one phosphate for every 28 anhydroglucose units and one sulfate for every 91 anhydroglucose units. The degree of substitution for the dialdehyde was also 0.011 since the bisulfite addition reaction is utilized to determine D.S. levels for dialdehyde cotton. The degree of substitution for CMC was 1.4.
Effect of Modified Gauzes on Elastase Activity
Initial experiments examined the ability of the modified cotton celluloses to absorb purified neutrophil elastase. Twenty-five, fifty and seventy-five milligram quantities of gauze were soaked to saturation for an hour in one milliliter of buffered solution containing 0.2 units of elastase. Unbound enzyme was removed by filtration followed by pressing under high pressure. The recovery of buffer from the filtration process was found to be 90%.
The assessment of elastase activity in solution exposed to the treated gauze was performed on the unbound enzyme. Acid-extractable elastase activity was assayed in a 96-well format using MeOSuc-Ala-Ala-Pro-Val-pNa for substrate hydrolysis. The kinetics of elastase activity is based on the relative initial velocity (v.sub.o) values for enzyme solutions exposed to cotton gauze. In this study 0.2 units of elastase were tested per sample. Measurement of elastase activity remaining in solution upon treatment with the gauze was accomplished by monitoring the reaction rate within a thirty-minute time frame. The reaction progress curves for the treated samples are shown in
The lower vo values for the treated samples when compared with the untreated cotton gauze suggests that the elastase activity is retained in the treated cotton gauze due to selected modifications on the gauze. Retention of elastase activity in treated gauze was found to be four-fold higher than in untreated gauze.
To assess whether the dialdehyde cotton gauze may act through active site uptake of elastase, dialdehyde starch was employed as a soluble aldehydic polysaccharide that may bind elastase. The results demonstrated that inhibition of elastase by dialdehyde starch is observed within a low micromole range, which is an inhibitory concentration within the titer of aldehydes per gram of dialdehyde cotton used in the current study. Thus, inhibition of elastase activity by a soluble form of a high molecular weight aldehydic carbohydrate suggests that the dialdehyde cotton gauze may function as a serine protease sequestrant through active site access to elastase.
Non-specific binding of the enzyme by the dialdehyde cotton gauze is an alternative explanation for elastase inhibition by dialdehyde cotton gauze. Since aldehydes can form Schiff bases with protein amino groups the potential for Schiff base formation between the protein amino groups of elastase and the aldehydes of dialdehyde cotton (DAG) was a concern. To mimic the effect of protein amines a high molecular weight polylysine was employed. Polylysine is a single amino acid biopolymer containing only epsilon amines as the side chains of the primary amino acid structure. To test for a potential non-specific Schiff base reaction effect between the elastase and the DAG, the dialdehyde cotton was incubated in a polylysine solution and elastase added to the solution to test for retention of elastase-lowering activity. DAG retained its inhibitory effect on elastase in the presence of polylysine. Based on this result it may be inferred that proteinaceous amines do not interfere with the observed elastase-lowering effects of the dialdehyde cotton gauze.
Elastase-Lowering Activity in Wound Fluid
The dialdehyde cotton gauze (DAG) was selected for further evaluation using human wound fluid. To assess the ability of the modified gauze to lower wound fluid-containing elastase activity in comparison to untreated gauze (UT), DAG samples and UT were placed in wound fluid in a range of 2.5 to 20 milligrams of gauze per microliter of patient wound fluid. After exposure to the DAG or UT, the solutions of chronic wound fluid were assessed for residual elastase activity using a known elastase substrate
The results showed that the chronic wound fluid which had been exposed to DAG possessed less elastase activity than that which had been exposed to UT at each quantity of gauze tested. This suggests that more elastase has been sequestered by DAG than by UT. Increasing the quantity of DAG resulted in a dose dependent decrease in the amount of retained elastase activity.
These results reflect the superior ability of the DAG samples to remove elastase activity from wound fluid as compared to untreated cotton gauze. Dialdehyde cotton gauze extracted 2-5 fold more elastase activity with increased gauze loading per volume of wound fluid when compared with untreated gauze.
Measurement of protein levels remaining in the wound fluid following incubation with the gauzes was performed to compare the relative amounts of protein taken up by treated and untreated gauze. Lower levels of protein were found in the wound fluid soaked with DAG than with the untreated cotton. This is consistent with the lower activity of elastase found in the wound fluid soaked with DAG samples.
The results obtained demonstrate that dialdehyde cotton effects the sequestration of the protease elastase from wound fluid.
We have optimized phosphorylation of cellulosic materials to achieve products with exceptional sequestering properties for elastase and other proteases. These optimization involved utilization various phosphorylation reagents, achieving products with great sequestering properties at high product throughput and lower reagent utilization.
Moreover, by incorporating alginates and starches into cellulosic products we have made products with high liquid sorption and liquid retention capabilities. In experiments described below we used ammonium alginate, Protamon S obtained from FMC Biopolymer, Philadelphia Pa. Other types of alginates such as sodium alginate, potassium alginate, magnesium alginate or alginic acid could be used as well in the wound dressing applications contemplated by this invention. Alginates are biopolymers of mannuronic (M) and glucoronic (G) acids. Alginate occurs in the seaweed as a mix of calcium, magnesium, sodium and potassium salts. The process of manufacturing of this product from the seaweed involves extraction of the alginic acid from the weed followed by neutralization by different salts to prepare appropriate product. Depending on the source of the seaweed and the extraction process different grades of product with different M and G ratio and sequence and molecular weight are obtained. Depending on the molecular weight of the alginate, different viscosity is obtained at the same concentration. Above 2.5% wt/wt solution the ammonium alginate we used produced solutions with viscosity over 200 centipoise at room temperature so we kept concentration below this value.
Elastase Sequestering Performance:
The elastase sequestering performance of our products was measured by placing 50 mg of the product in 1.00 ml of Simulated Wound Fluid (SMFL). SMFL was prepared by dissolving leukocyte elastase into buffer at concentration of 20 m. unit/ml. Included in SMFL is 0.1% bovine serum albumin (BSA) to simulate average chronic wound. We have found that this formulation has activity similar to “average” chronic wound and allows us to compare performance of different wound care product to each other and to controls. The elastase sequestering performance of the product is obtained by comparing the activity of the SMFL fluid before and after equilibration (2 hr) of the fluid with the product.
Competitive Liquid Sorption and Retention
This procedure is to simulate the performance of products according to the invention when they are in touch with another liquid absorber. These absorptive materials retain fluid better than the standard cotton dressing. Therefore there is not only absorption of fluid, but he absorb fluid is retained within the dressing. Clinically this means that dressing could be left in the wound for longer period of time and the normal skin adjacent to the wound would be less likely to be macerated. This procedure is to simulate fluid sorption capacity of wound care products according to the invention as compared to average liquid sorption capacity of cotton gauze or paper towel. The experiment is carried out in the following manner. A piece of the product (0.1 to 1.00 gram) is allowed to come in contact with water for 60 seconds. The amount of the water used in this experiment is in excess of total sorption capacity of the product and we keep it to 1.5 ml water per 0.1 g of the product. So if the wound care product is 0.2 gram, we use 3.0 ml and if 0.5 gram, we use 7.5 ml of water.
After the product has soaked the water, it is removed and placed flat on 10 folds of dry paper towels allowing excess water to drain away for 90 seconds. The product is then weighed accurately and the % water retained under this competitive condition is calculated as described below;
% Competitive Water Sorption/Retentive=100×(Wt90 sec−WtOriginal)/WtOriginal
Where Wt90 sec is the weight of the dressing after 90 second of contact with the dry paper towel and WtOriginal is the original weight of the dressing. This property will be referred to % water retention throughout this patent (% WRC).
Alginate and Silver Alginate Solution Preparation
Preparation of 2.2% Alginate Solution:
Dissolved 10.0 gram of ammonium alginate in 449.0 grams of water and mixed overnight to achieve uniform solution. Solutions above 3% had too high viscosity and were difficult to handle without heating.
Preparation of 1.1 wt % Alginate 10% Neutralized with Silver Nitrate
Alginate solution was diluted by mixing 40 gram of the 2.2% alginate solution with 30 gram of DI water. Silver nitrate (Reagent Grade) from Baker was dissolved in DI water (77.4 mg in 5 ml) and added drop wise into the alginate solution with rapid agitation. A semi-clear solution resulted after overnight agitation. This “solution” will settle if left standing indicating gel formation. When we attempted to make higher concentration solutions, insoluble gels were formed which were hard to handle. Also when we attempted making silver alginate solutions above 10% neutralization (molar), gel formation made this product difficult to handle. Therefore a major drawback of making silver alginate and using them for making products is difficulty of handling gels. Despite this difficulty, in some applications, silver alginates may be preferred.
Highly liquid retentive dressings can be formed by coating of cotton or phosphorylate cotton with alginate and silver alginates as shown in Table 1.
In Table 1, PhosCot stands for phosphorylated cotton. Comparative Example 1 shows the behavior of common cotton which has low elastase sequestering performance and also low competitive liquid retention capacity. PhosCot (Comparative Example 2) has significantly higher elastase sequestering property, but it has low % CWR. Cotton coated with alginate (Competitive Example 3) has high % CWR, but it has low % elastase sequestering properties. On the other hand when phosphorylated cotton is coated with alginate (Example 1) or with silver alginate (Example 2) we have products with both good % Elastase sequestrations and % CWR. We can also achieve good performance when coating cotton with silver alginate (Example 3). As we have mentioned in the silver alginate solution preparation the viscosity and gel formation is a difficulty that could be avoided by other approaches of preparing these products by different processes as described below.
Desirable products (Table 2) were prepared by coating cotton (Example 4) or phosphorylated cotton (Example 5) with ammonium alginate in the first step, and then exposing the alginate coated fabric to silver nitrate solution to convert alginate into silver alginate to get product with high elastase sequestering properties (% CWR was not measured for these samples but were high). We used 1000 ppm silver nitrate solution for this derivatization. The advantage of this process is that one does not have to deal with gels of silver alginate, but the disadvantage of this process is that during the silver conversion a portion of the alginate is transferred into the silver nitrate solution (in form of gels) and from stand point of process control this type of product formation is not as desirable as process described below.
In this more preferred embodiment, the phosphorylated cotton gauze (Comparative 2) is reacted with soluble silver compounds such as silver nitrate or acetate to form silver complex with exceptional elastase sequestering capacity (Comparative 4). However the % CWR capacity of this product is not much different than that of cotton. When such a product is then coated with alginates, products with exceptional elastase sequestering and % CWR are obtained (Examples 6 and 7).
While phosphorylated cotton is preferred in the present invention, other polysaccharide derivatives may complex with silver such as phosphorylated starch, carboxymethyl cellulose, dialdehyde gauze, and sulfonated gauze, and those of skill in the art will recognize that the invention can be practiced with polysaccharides which have the capacity to form complexes with transition metals such as silver or copper.
It is also understood by those of skill in the art that these alginate containing products could be cross-linked by exposure to multivalent cations such as Ca2+, Cu2+, or Al3+ without affecting their elastase sequestering properties or their % CWR capacities as shown by examples that follow. In these examples, after coating the fabric with alginate or silver alginate, the products were brought in contact with 200 ppm calcium chloride (Ca) or copper sulfate (Cu) and then the performances were measured. As seen these products have great performances. Additionally these products having large supply of silver or copper will have antibacterial and antifungal properties.
These products have exceptional performance as dressings for chronic wounds where management of exudates fluids is critical in treatment of this class of wounds.
While the invention has been described in terms of its preferred embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the appended claims. Accordingly, the present invention should not be limited to the embodiments as described above, but should further include all modifications and equivalents thereof within the spirit and scope of the description provided herein.
Claims
1. A wound dressing, comprising:
- a phosphorylated polysaccharide substrate complexed with at least one transition metal; and
- an alginate coating.
2. The wound dressing of claim 1 wherein said phosphorylated polysaccharide is selected from the group consisting of phosphorylated cotton and phosphorylated gauze.
3. The wound dressing of claim 1 wherein said alginate coating is crosslinked.
4. The wound dressing of claim 1 wherein said alginate coating is silver alginate.
5. The wound dressing of claim 1 wherein the transition metal is selected from silver and copper.
6. A wound dressing comprising:
- a polysaccharide substrate; and
- an alginate coating mixed with at least one transition metal.
7. A method for treating a wound, comprising:
- contacting a wound with a wound dressing comprising a polysaccharide substrate with an alginate coating;
- absorbing wound fluid with said wound dressing; and
- sequestering elastase from said wound.
8. The method of claim 7 wherein said polysaccharide substrate is phosphorylated and is complexed with at least one transition metal.
9. The method of claim 7 wherein said alginate coating is mixed with at least one transition metal
Type: Application
Filed: Jul 7, 2006
Publication Date: Jan 11, 2007
Inventors: Kelman Cohen (Richmond, VA), Yousef Mohajer (Midlothian, VA)
Application Number: 11/482,193
International Classification: A61K 31/715 (20060101); A61L 15/00 (20060101); A61K 33/34 (20060101); A61K 33/38 (20060101);
