Name: protocol to create chronic wounds in diabetic mice
Uploaded: 2019-09-25T13:30:00
Description: Watch this Scientific Journal Video about Protocol to Create Chronic Wounds in Diabetic Mice at JoVE.com

The authors have no acknowledgements.

All experiments were completed in accordance and compliance with federal regulations and University of California policy and procedures have been approved by the University of California, Riverside IACUC.
1. Animal
<ol>
	<li>Use diabetic and obese B6.BKS(D)-Leprdb/J mice for the chronic wound model. Purchasing options include either heterozygotes for breeding or homozygotes directly for experiments.</li>
	<li>Breed heterozygote males and females to produce offspring. Only...

Once chronic wounds are created on the mice, the model can be used to study impaired wound healing processes involved in the initiation of chronicity. The model can also be used to test the efficacy of a wide range of chemicals and drugs that can reverse chronic wound development and impaired healing and lead to wound closure and healing. Different time points after the onset of chronicity can be studied: e.g., days 1-5 after wounding for early onset of chronicity and days 20 and beyond for full strength chronic...

Wound healing involves complex cellular and molecular processes that are temporally and spatially regulated, organized in sequential and overlapping stages that involve many different cell types including but not limited to the immune response and the vascular system1. Immediately after the skin sustains an injury, factors and blood cells aggregate to the wound site and initiate the coagulation cascade to form a clot. After homeostasis is achieved, the blood vessels dilate to let into the wound site oxygen, nutrients, enzymes, antibodies and chemotactic factors that chemoattract polymorphonucleocytes to clear the wound bed of foreign debris and secrete proteolytic enzymes2. Activated platelets secrete a variety of growth factors to stimulate the keratinocytes at the wound edge to re-epithelialize the wounded area. Monocytes recruited to the wound site differentiate into macrophages which phagocytose bacteria and dead neutrophils and secrete additional factors to maintain keratinocyte proliferative and pro-migratory signals. In the proliferation phase, while re-epithelialization continues, new granulation tissue composed of fibroblasts, monocytes/macrophages, lymphocytes, and endothelial cells continue the rebuilding process2. Angiogenesis is stimulated by promoting endothelial cell proliferation and migration, resulting in new vessel development. Epithelialization and remodeling of the extracellular matrix construct a barrier against the environment. As the wound heals and granulation tissue evolves into a scar, apoptosis eliminates inflammatory cells, fibroblasts, and endothelial cells without causing additional tissue damage. The tensile strength of the tissue is enhanced by fibroblasts remodeling various components of the extracellular matrix, like collagen, so that the newly formed tissue is almost as strong and flexible as unwounded skin2.
Any deviation from this highly concerted progression towards wound closure leads to impaired and/or chronic wounds3. Chronic wounds are characterized by increased oxidative stress, chronic inflammation, damaged microvasculature, and abnormal collagen matrix in the wound4. Oxidative stress, especially in the wound, can delay wound closure2,5. When, in the first stage of wound healing, the inflammatory phase becomes unregulated, the host tissue assumes extensive damage due to a continuous influx of inflammatory cells5 that release cytotoxic enzymes, an increase in free oxygen radicals, and unregulated inflammatory mediators, resulting in cell death6,7.
In this destructive microenvironment, biofilm-forming bacteria take advantage of host nutrients and contribute to the damage of the host tissue2. These biofilms are difficult to control and remove because the hydrated extracellular polymeric substances composed of proteins, DNA, RNA, and polysaccharides allows bacteria harbored within to be tolerant to conventional antibiotic therapies and evade the host&#39;s innate and adaptive immune response2,8,9.
Studying chronic wounds is crucial because they impact ~6.5 million people and cost ~$40 billion per year in the US alone10. Patients with diabetes have increased risks for developing chronic wounds that require amputation in order to contain the spread of infection. These patients have a 50% mortality risk within 5 years of amputation that is attributed to the pathophysiology mechanism of diabetes11. The relationship between the host&#39;s immune system and the microbiome in wound healing is a vital topic of ongoing research because consequences of chronic wounds, if unresolved, include amputation and death12.
Although a significant effort has been invested in understanding how chronic wounds develop in humans, it is still unclear how and why chronic wounds form. Experiments to study the mechanisms of impaired healing is difficult to conduct in humans, and wound healing specialists only see patients with chronic wounds that have already reached chronicity for weeks to months. Thus, specialists are unable to study what processes went wrong that lead the wound to develop to become chronic2. There is a lack of animal models that recapitulate the complexity of human chronic wounds. Until our model was developed, no model for chronic wound studies existed.
The chronic wound model was developed in mice that have a mutation in the leptin receptor (db/db-/-)13. These mice are obese, diabetic, and have impaired healing but do not develop chronic wounds14. Blood glucose levels average around 200 mg/dL, but can be as high as 400 mg/dL15. When high levels of oxidative stress (OS) in the wound tissue are induced immediately after wounding, the wound becomes chronic16. The db/db-/- wounds are considered chronic by 20 days and remain open for 60 days or more. Biofilm produced by bacteria can be seen developing beginning three days after wounding; a mature biofilm can be seen 20 days after wounding and persists until either wound closure. The biofilm-forming bacteria we find in these mice are also found in human diabetic chronic wounds.
Oxidative stress is induced by treating the wounds with two inhibitors of antioxidant enzymes, catalase and glutathione peroxidase, two enzymes with the capacity to break down hydrogen peroxide. Hydrogen peroxide is a reactive oxygen species and can cause cellular damage through the oxidation of proteins, lipids, and DNA. Catalase catalyzes the decomposition of hydrogen peroxide into less harmful chemicals oxygen and water. 3-Amino-1,2,4-triazole (ATZ) inhibits catalase by binding specifically and covalently to the active center of the enzyme, inactivating it17,18,19. ATZ has been used to study the effects of oxidative stress both in vitro and in vivo through the inhibition of catalase20,21,22,23,24. Glutathione peroxidase catalyzes the reduction of hydrogen peroxide through the antioxidant, glutathione, and is an important enzyme that protects the cell against oxidative stress25. Mercaptosuccinic acid (MSA) inhibits glutathione peroxidase by binding to the selenocysteine active site of the enzyme with thiol, inactivating it26. MSA has been used to study the effects of oxidative stress in vitro and in vivo as well20,27,28.
This novel model of chronic wounds is a powerful model to study because it shares many of the same features observed in human diabetic chronic wounds, including prolonged inflammation from increased OS and natural biofilm formation from skin microbiome. The wounds have impaired dermal-epidermal interaction, abnormal matrix deposition, poor angiogenesis and damaged vasculature. Chronic wounds will develop in both male and female mice, so both sexes can be used to study chronic wounds. Therefore, the chronic wound model can contribute significantly to advance fundamental understanding of how such wounds begin. Using this chronic wound model can provide answers to fundamental questions about how chronicity is initiated/achieved through contributions from the physiology of impaired wound healing and the microbiome of the host.

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			<td height="42" style="height:42px;width:308px;">B6.BKS(D)-Leprdb/J&#160;</td>
			<td style="width:176px;">The Jackson Laboratory&#160;</td>
			<td style="width:107px;">00697</td>
			<td style="width:204px;">Homozygotes and heterozygotes available&#160;</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:308px;">Nair Hair Remover Lotion with Soothing Aloe and Lanolin</td>
			<td style="width:176px;">Nair</td>
			<td style="width:107px;"></td>
			<td style="width:204px;">a chemical depilatory</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:308px;">Buprenex (buprenorphine HCl)</td>
			<td style="width:176px;">Henry Stein Animal Health</td>
			<td style="width:107px;">059122</td>
			<td style="width:204px;">0.3 mg/ml, Class 3</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:308px;">3-Amino-1,2,4-triazole (ATZ)</td>
			<td style="width:176px;">TCI</td>
			<td style="width:107px;">A0432</td>
			<td style="width:204px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:308px;">Mercaptosuccinic acid (MSA)</td>
			<td style="width:176px;">Aldrich</td>
			<td style="width:107px;">88460</td>
			<td style="width:204px;"></td>
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			<td height="21" style="height:21px;width:308px;">Phosphate buffer solution (PBS)</td>
			<td style="width:176px;"></td>
			<td style="width:107px;"></td>
			<td style="width:204px;">autoclave steriled</td>
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		<tr height="42">
			<td height="42" style="height:42px;width:308px;">Isoflurane</td>
			<td style="width:176px;">Henry Schein Animal Health</td>
			<td style="width:107px;">029405</td>
			<td style="width:204px;">NDC 11695-6776-2</td>
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			<td height="42" style="height:42px;width:308px;">Oxygen</td>
			<td style="width:176px;"></td>
			<td style="width:107px;"></td>
			<td style="width:204px;">Tank must be compatible with vaporizing system</td>
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			<td height="21" style="height:21px;width:308px;">Isoflurane vaporizer</td>
			<td style="width:176px;">JA Baulch &#38; Associates&#160;</td>
			<td style="width:107px;"></td>
			<td style="width:204px;"></td>
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			<td height="21" style="height:21px;width:308px;">Wahl hair clipper</td>
			<td style="width:176px;">Wahl</td>
			<td style="width:107px;"></td>
			<td style="width:204px;">Lithium Ion Pro</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:308px;">Acu Punch 7mm skin biopsy punches</td>
			<td style="width:176px;">Acuderm Inc.</td>
			<td style="width:107px;">P750</td>
			<td style="width:204px;"></td>
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			<td height="42" style="height:42px;width:308px;">Tegaderm&#160;</td>
			<td style="width:176px;">3M</td>
			<td style="width:107px;">Ref: 1624W</td>
			<td style="width:204px;">Transparent film dressing (6 cm x 7 cm)</td>
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			<td height="21" style="height:21px;width:308px;">Heating pad</td>
			<td style="width:176px;">Conair</td>
			<td style="width:107px;"></td>
			<td style="width:204px;">Moist Dry Heating Pad</td>
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			<td height="42" style="height:42px;width:308px;">Insulin syringes</td>
			<td style="width:176px;">BD</td>
			<td style="width:107px;">329461</td>
			<td style="width:204px;">0.35 mm (28G) x 12.7 mm (1/2&#34;)</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:308px;">70% ethanol</td>
			<td style="width:176px;"></td>
			<td style="width:107px;"></td>
			<td style="width:204px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:308px;">Kimwipes</td>
			<td style="width:176px;"></td>
			<td style="width:107px;"></td>
			<td style="width:204px;"></td>
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			<td height="21" style="height:21px;width:308px;">Tweezers</td>
			<td style="width:176px;"></td>
			<td style="width:107px;"></td>
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			<td height="21" style="height:21px;width:308px;">Sharp surgical scissors</td>
			<td style="width:176px;"></td>
			<td style="width:107px;"></td>
			<td style="width:204px;"></td>
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			<td height="21" style="height:21px;width:308px;">Thin metal spatula</td>
			<td style="width:176px;"></td>
			<td style="width:107px;"></td>
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			<td height="21" style="height:21px;width:308px;">Tubing</td>
			<td style="width:176px;"></td>
			<td style="width:107px;"></td>
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			<td height="21" style="height:21px;width:308px;">Mouse nose cone</td>
			<td style="width:176px;"></td>
			<td style="width:107px;"></td>
			<td style="width:204px;"></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:308px;">Gloves</td>
			<td style="width:176px;"></td>
			<td style="width:107px;"></td>
			<td style="width:204px;"></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:308px;">small plastic containers</td>
			<td style="width:176px;"></td>
			<td style="width:107px;"></td>
			<td style="width:204px;"></td>
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protocol to create chronic wounds in diabetic mice

Chronic wounds develop as a result of defective regulation in one or more complex cellular and molecular processes involved in proper healing. They impact ~6.5M people and cost ~$40B/year in the US alone. Although a significant effort has been invested in understanding how chronic wounds develop in humans, fundamental questions remain unanswered. Recently, we developed a novel mouse model for diabetic chronic wounds that have many characteristics of human chronic wounds. Using db/db-/- mice, we can generate chronic wounds by inducing high levels of oxidative stress (OS) in the wound tissue immediately after wounding, using a one-time treatment with inhibitors specific to the antioxidant enzymes catalase and glutathione peroxidase. These wounds have high levels of OS, develop biofilm naturally, become fully chronic within 20 days after treatment and can remain open more for more than 60 days. This novel model has many features of diabetic chronic wounds in humans and therefore can contribute significantly to advancing fundamental understanding of how wounds become chronic. This is a major breakthrough because chronic wounds in humans cause significant pain and distress to patients and result in amputation if unresolved. Moreover, these wounds are very expensive and time-consuming to treat, and lead to significant loss of personal income to patients. Advancements in this field of study through the use of our chronic wound model can significantly improve health care for millions who suffer under this debilitating condition. In this protocol, we describe in great detail the procedure to cause acute wounds to become chronic, which has not been done before.

Figure 5 depicts an example of a wound without treatment of inhibitors progressing towards wound closure and a wound with treatment of inhibitors progressing towards chronicity. The transparent dressing has been left in place on the chronic wound so that biofilm and fluid accumulation can be seen.
Chronic wound initiation takes place in less than 6 hours and the wound margin is visibly altered from ...

Watch this Scientific Journal Video about Protocol to Create Chronic Wounds in Diabetic Mice at JoVE.com

Protocol to Create Chronic Wounds in Diabetic Mice

Chronic wounds are developed from acute wounds on a diabetic mouse model by inducing high levels of oxidative stress after a full-thickness cutaneous wound. The wound is treated with inhibitors for catalase and glutathione peroxidase, resulting in impaired healing and biofilm development by bacteria present in the skin microbiome.

Chronic wounds develop as a result of defective regulation in one or more complex cellular and molecular processes involved in proper healing. They impact ...

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