Introduction
Exuberant granulation tissue (EGT) is a common complication associated with healing of distal limb wounds in horses. EGT forms when there is a dysregulation in the inflammatory phase of wound healing resulting in chronic inflammation and excessive fibroplasia.1–3 Control of EGT remains problematic despite many treatments being evaluated to manage this process. These wounds often require repeated surgical debridement to remove the EGT to allow contraction and epithelialization.4
A primary driver of proliferation is tissue growth factor-β (TGF-β), which is found in high concentration in equine limb wounds and has been hypothesized to promote EGT.5,6 Specifically, TGF-β1 is critical to the formation of granulation tissue through modulation of fibronectin production. Modulation of TGF-β1 limits profibrotic actions, reduces the differentiation and production of extracellular matrix, and has resulted in changes in fibroblast morphology, proliferation rates, gene expression, and contractile capacity.7,8 TGF-β1 has been identified in pathologic healing in multiple species including humans.9 Nonhealing diabetic foot ulcers and keloids in humans have marked similarities to EGT in horses when considering the chronic inflammatory processes, vascular endothelial dysfunction and microvascular occlusion, and fibroproliferation.7,10–13
Several in vitro and in vivo human studies have evaluated the delivery of silicon or derivatives such as orthosilicic acid to wounds.14–16 Orthosilicic acid regulates growth factors such as basic fibroblast growth factor,15 resulting in production of homogenous collagen and elastic fiber formation16 and reduced chronic inflammation.14 Orthosilicic acid modulates inflammation by decreasing production of proinflammatory IL-1β, IL-6, and IL-8.14 Furthermore, orthosilicic acid reduces TGF-β1–induced differentiation of fibroblasts, having an antifibrotic action and improved wound contraction, resulting in decreased scarring.14
Zarasyl Equine is a patented barrier cream listed with the FDA as an unapproved drug with marketing approval to sell as labeled. It is composed of tailored amorphous silicate nanoparticles and 2 different molecular weights of polyethylene glycol. Amorphous silicate nanoparticles deliver orthosilicic acid up to its solubility limit as they dissolve, resulting in a slow-release mechanism to maintain its presence in the wound environment.15 The proposed mechanism for improved wound healing and decrease in EGT is through the effects of orthosilicic acid, resulting in modulation of the microenvironment. Polyethylene glycol works as an antibacterial osmotic compound, maintaining a moist healing environment, which helps to prevent scar formation and to enhance repair of damaged skin.17
The objective of this retrospective case series was to report clinical outcomes of horses with distal limb wounds treated with an amorphous silicate dressing. We hypothesized that wounds treated with an amorphous silicate dressing would have minimal complications and lesion resolution without formation of EGT.
Materials and Methods
Eight veterinary hospitals across the US were surveyed for equine wound cases that were treated with an amorphous silicate topical (Zarasyl Equine Cream; Zarasyl Ltd). Pertinent case information was acquired by review of medical records provided by the attending veterinarian. Inclusion criteria for case enrollment were equine limb wounds treated with an amorphous silicate topical and followed from initiation of treatment to wound resolution by the veterinarian. Wounds that were considered must have been evaluated as either chronic wounds (wounds with delayed healing) or wounds unable to be managed with primary closure due to excessive tension, contamination, or patient behavior.
Eleven cases that fit the inclusion criteria were identified between May 2021 and May 2022. Additional information was gathered from the medical records for analysis. All wounds were initially clipped, cleaned, and debrided (to remove necrotic tissue or EGT), as deemed necessary by the attending veterinarian. Timing of initiation of treatment with amorphous silicate topical varied between cases from time of presentation to after an established bed of granulation tissue had formed. A thin layer of amorphous silicate topical was applied, covering the surface area of the wound every 1 to 3 days. Wounds were bandaged as deemed necessary by the veterinarian. The wounds were gently cleaned with water or sterile saline (0.9% NaCl) solution prior to each reapplication of the topical. Wound dimensions were determined using a standard ruler. A rectangular area was approximated on the basis of width and height measurements. Tissue planes affected were determined by visual assessment and wound exploration performed by the attending veterinarian. Wound contracture was monitored by photographs including a standard measuring card at the level of the wound. All cases were followed by veterinarians until they deemed the wound resolved on the basis of complete epithelialization. Data are reported as median and ranges.
Statistical analysis
Wound surface area (cm2) affected was calculated on the basis of wound dimensions. Correlation between time to complete healing (days) and surface area of the wound (cm2) was evaluated with a linear regression model. Correlation between time to complete healing (days) and tissue planes affected was evaluated with a pairwise Wilcoxon rank sum test (JMP version 16.0.0; SAS Institute Inc) with significance set to P < .05.
Results
Medical history
Eleven horses were treated with an amorphous silicate dressing and included in analysis. Four Quarter Horses, 2 Thoroughbreds, 1 Paint Horse, 1 Tennessee Walking Horse, 1 Warmblood, 1 Welsh cross, and 1 Mustang were included. Ages ranged from 1 to 26 years with a median age of 7 years. All wounds included were limb wounds (6 left hind limb, 3 right hind limb, and 2 right front limb), with 8 of them located on the metacarpus/metatarsus, 1 on the fetlock, 1 on the pastern, and 1 over the femoropatellar joint. The size of wounds varied from 5 to 20 cm in length with a median of 10 cm and from 2 to 15 cm in width with a median of 5 cm. At presentation, 1 case (case 6; Table 1) had a sequestrum (9 X 2 cm) associated with the wound that was radiographically identified on the dorsolateral aspect of the third metatarsus. The sequestrum was removed and the parent bone surgically debrided under standing sedation and local analgesia prior to wound treatment. Three wounds included transection of the extensor tendons and exposure of the third metatarsal bone. No other wounds had bone exposure on presentation. The duration of the wounds at the time of presentation varied from acute (n = 2), 2 to 14 days (6), 1 month (1), and > 3 months (2).
Case data including wound size (cm) and tissue planes affected at the time of presentation and subsequent progression of wound healing, including time to 50% reduction in size and time to resolution.
| Case No. | Size of wound (height X width cm) | Tissue planes affected | Time to 50% wound contraction (d) | Time to resolution (d) |
|---|---|---|---|---|
| 1 | 13 X 5 cm | Skin, subcutaneous | 40 | 70 |
| 2 | 8 X 8 cm | Skin, subcutaneous | 21 | 49 |
| 3 | 15 X 8 cm | Skin, subcutaneous, tendon, bone exposure | 50 | 100 |
| 4 | 13 X 2 cm | Skin | 7 | 14 |
| 5 | 8 X 13 cm | Skin | 90 | 120 |
| 6 | 3 X 5 cm | Skin, subcutaneous | 20 | 35 |
| 7 | 2 X 4 cm | Skin | 15 | 28 |
| 8 | 20 X 10 cm | Skin, subcutaneous | 17 | 37 |
| 9 | 10 X 15 cm | Skin, subcutaneous, tendon, bone exposure | 60 | 126 |
| 10 | 3 X 5 cm | Skin, subcutaneous | 15 | 30 |
| 11 | 15 X 5 cm | Skin, subcutaneous, tendon, bone exposure | 33 | 75 |
Prior to treatment with the topical amorphous silicate, medical treatment included manuka honey (n = 3), systemic antimicrobial therapy (8), systemic nonsteroidal anti-inflammatories (5), Dermalone Ointment (1), Derma Gel (1), silicone gel dressing (1), and wet-to-dry bandage (3).
Outcomes
None of the wounds required EGT debridement following treatment with the topical amorphous silicate. None of the horses had complications associated with the topical amorphous silicate treatment including but not limited to cutaneous reactions, infection, or other adverse reactions. Time to 50% wound contracture ranged from 7 to 60 days with a median of 21 days. Time to resolution varied greatly from 14 to 126 days with a median of 49 days (Table 1). Wounds affecting all 4 tissue planes (skin, subcutaneous, tendon, and bone exposure) took significantly longer to heal than wounds affecting skin and subcutaneous tissues only (P = .037). There was a moderate positive correlation between healing time (days) and area of the wound (cm2; r = 0.55; 95% CI, –0.07 to 0.86), but it was not statistically significant (P = .078). No other significant differences were noted between time to heal and depth of wound. All referring veterinarians and owners were satisfied with wound healing following the use of the topical amorphous silicate treatment. Representative wound healing progression over time is demonstrated (Figures 1–4).
Progressive healing of a 7-year-old Quarter Horse mare that presented for a laceration on the dorsomedial aspect of the right metatarsus. The extensor tendon was transected, and 15 cm of the metatarsus was exposed. Fifty days after treatment with a topical amorphous silicate, the wound had contracted to 50% the original width.
Citation: Journal of the American Veterinary Medical Association 261, 6; 10.2460/javma.22.11.0490
Progressive healing of a 1-year-old Tennessee Walking Horse filly that presented for a wound to the dorsomedial metatarsus bone of the right hind limb. The wound extended 20 cm in length and 10 cm in width. Seventeen days after treatment with a topical amorphous silicate, the wound had contracted to 50% the original width. The wound had resolved by day 37 without formation of exuberant granulation tissue.
Citation: Journal of the American Veterinary Medical Association 261, 6; 10.2460/javma.22.11.0490
Progressive healing of a 2-year-old Thoroughbred gelding presented for a laceration of its fetlock and metatarsus to the level of the third metacarpal bone. The wound extended 10 cm in height and 15 cm in width. Sixty days after treatment with a topical amorphous silicate, the wound had contracted to 50% the original width. The wound resolved by day 125 without formation of exuberant granulation tissue.
Citation: Journal of the American Veterinary Medical Association 261, 6; 10.2460/javma.22.11.0490
Progressive healing of a 26-year-old Warmblood gelding presented for full-thickness sloughing of the skin after a cellulitis of the right front dorsal fetlock. The wound extended 3 cm in length by 5 cm in width. Twenty days after initiation of topical amorphous silicate, the wound had contracted to 50% the original width.
Citation: Journal of the American Veterinary Medical Association 261, 6; 10.2460/javma.22.11.0490
Discussion
To the authors’ knowledge, this was the first report of clinical results using a topical barrier cream composed of silicate technology and polyethylene glycol in equids. The topical treatment was easy to perform and was not associated with complications. Treatment with a topical amorphous silicate led to resolution of the wounds without requiring further debridement of granulation beds.
The delivery of orthosilicic acid by this product may reduce chronic inflammation in the wound bed microenvironment, allowing improved healing and decreasing EGT by modulating basic fibroblast growth factor15; reducing inflammatory factors such as IL-1β, IL-6, and IL-814; and modulating TGF-β1–induced differentiation of fibroblasts.14 Additionally, TGF-β1 is implicated in fibroblast differentiation with elevated tissue levels, leading to increased scarring, and microvascular dysfunction, resulting in hypoxemic environments.5,8,18 Modulation of this high TGF-β1 environment via orthosilicic acid present in the product evaluated could result in a decrease in EGT. This study did not evaluate the mechanism of action of this product, and further work should be performed using a standard equine wound model to evaluate changes in the wound microenvironment and further elucidate the mechanism to prevent EGT.
This study was a multicenter retrospective clinical study that involved clinicians and clients across the US. It was a study that used clinical cases of wound management to demonstrate the effectiveness of the topical product without the limitations of an experimentally generated wound. Treatment with a topical amorphous silicate proved to be effective in a variety of wound sizes and depths, providing satisfactory wound resolution with minimal intervention required by the veterinarian.
There were several limitations to this study. The primary limitation was the variability in the timing of initiation and frequency of treatment. The product label instructed once- or twice-daily application. While this may be ideal, this is often not feasible for veterinarians or owners, and this study demonstrated positive healing despite varied treatment regimens. Additional limitations included chronicity of the wounds and the variability in earlier and concurrent management of the wounds, including previous debridement of EGT. Furthermore, the variability in management prior to starting the amorphous silicate topical treatment was a reflection that prior management of the wounds had been unsuccessful. Also there was no control group in which similar wounds were managed with another standard protocol to compare to the topical barrier cream reported here. Future studies comparing treatment time windows, size of wound, and mechanism of action are indicated to better understand the role that Zarasyl Equine plays in wound healing.
Nonhealing wounds and EGT in distal limb wounds of horses have a significant economic impact and require a large amount of labor from veterinarians and owners. Treatment of these wounds with a topical amorphous silicate provided positive results with resolution of all wounds.
Acknowledgments
Jacqueline M. Chevalier served as a student Associate Editor for the Journal of the American Veterinary Medical Association (JAVMA). She declares that she had no role in the editorial direction of this manuscript.
No external funding was used in this study. The product used was supplied by Zarasyl Ltd.
The authors declare that there were no conflicts of interest.
Case contributions were made by Drs. Baer, Barber, Connally, Fertig, Hunter, Hill, Kimmons, and Hayes and the Cornell University Equine Hospital.
References
- 1.↑
Theoret C, Wilmink JM. Equine Wound Management. 3rd ed. Wiley Blackwell; 2017. doi:10.1111/j.1751-0813.1992.tb09918.x
- 2.
Wilmink JM, van Weeren PR, Stolk PWT, Van Mil FN, Barneveld A. Differences in second-intention wound healing between horses and ponies: histological aspects. Equine Vet J. 1999;31(1):61–67. doi:10.1111/j.2042-3306.1999.tb03792.x
- 3.↑
Wilmink JM, van Weeren PR. Second-intention repair in the horse and pony and management of exuberant granulation tissue. Vet Clin North Am Equine Pract. 2005;21(1):15–32. doi:10.1016/j.cveq.2004.11.014
- 4.↑
Hackett RP. How to Prevent and Treat Exuberant Granulation Tissue. Wound Orthop Manag. 2011; New York, (American Association of Equine Practitioners): 367.
- 5.↑
van den Boom R, Wilmink JM, O’Kane S, Wood J, Ferguson MWJ. Transforming growth factor-β levels during second-intention healing are related to the different course of wound contraction in horses and ponies. Wound Repair Regen. 2002;10(3):188–194. doi:10.1046/j.1524-475x.2002.10608.x
- 6.↑
De Martin I, Theoret CL. Spatial and temporal expression of types I and II receptors for transforming growth factor β in normal equine skin and dermal wounds. Vet Surg. 2004;33(1):70–76. doi:10.1111/j.1532-950x.2004.04008.x
- 7.↑
Wise LM, Stuart GS, Sriutaisuk K, Adams BR, Riley CB, Theoret CL. Anti-fibrotic actions of equine interleukin-10 on transforming growth factor-beta1-stimulated dermal fibroblasts isolated from limbs of horses. Front Vet Sci. 2020;7:577835. doi:10.3389/fvets.2020.577835
- 8.↑
Harman RM, Bihun IV, Van de Walle GR. Secreted factors from equine mesenchymal stromal cells diminish the effects of TGF-β1 on equine dermal fibroblasts and alter the phenotype of dermal fibroblasts isolated from cutaneous fibroproliferative wounds. Wound Repair Regen. 2017;25(2):234–247. doi:10.1111/wrr.12515
- 9.↑
Theoret CL, Barber SM, Moyana TN, Gordon JR. Expression of transforming growth factor β(1), β(3), and basic fibroblast growth factor in full-thickness skin wounds of equine limbs and thorax. Vet Surg. 2001;30(3):269–277. doi:10.1053/jvet.2001.23341
- 10.↑
Knottenbelt DC. Equine wound management: are there significant differences in healing at different sites on the body? Vet Dermatol. 1997;8(4):273–290. doi:10.1111/j.1365-3164.1997.tb00273.x
- 11.
Du Cheyne C, Martens A, De Spiegelaere W. High numbers of cd163-positive macrophages in the fibrotic region of exuberant granulation tissue in horses. Animals (Basel). 2021;11(9):2728. doi:10.3390/ani11092728
- 12.
Ud-Din S, Volk SW, Bayat A. Regenerative healing, scar-free healing and scar formation across the species: current concepts and future perspectives. Exp Dermatol. 2014;23(9):615–619. doi:10.1111/exd.12457
- 13.↑
Theoret CL, Olutoye OO, Parnell LKS, Hicks J. Equine exuberant granulation tissue and human keloids: a comparative histopathologic study. Vet Surg. 2013;42(7):783–789. doi:10.1111/j.1532-950X.2013.12055.x
- 14.↑
Grotheer V, Goergens M, Fuchs PC, et al. The performance of an orthosilicic acid-releasing silica gel fiber fleece in wound healing. Biomaterials. 2013;34(30):7314–7327. doi:10.1016/j.biomaterials.2013.06.012
- 15.↑
Quignard S, Coradin T, Powell JJ, Jugdaohsingh R. Silica nanoparticles as sources of silicic acid favoring wound healing in vitro. Colloids Surf B Biointerfaces. 2017;155:530–537. doi:10.1016/j.colsurfb.2017.04.049
- 16.↑
Herreros FOC, Cintra ML, Adam RL, de Moraes AM, Metze K. Remodeling of the human dermis after application of salicylate silanol. Arch Dermatol Res. 2007;299(1):41–45. doi:10.1007/s00403-007-0739-8
- 17.↑
Chirife J, Herszage L, Joseph A, Bozzini JP, Leardini N, Kohn ES. In vitro antibacterial activity of concentrated polyethylene glycol 400 solutions. Antimicrob Agents Chemother. 1983;24(3):409–412. doi:10.1128/AAC.24.3.409
- 18.↑
Chevalier J, Yin H, Arpino JM, et al. Obstruction of small arterioles in patients with critical limb ischemia due to partial endothelial-to-mesenchymal transition. iScience. 2020;23(6):101251. doi:10.1016/j.isci.2020.101251
