Angiotensin II inhibitor facilitates epidermal wound regeneration in diabetic mice

Lychnophora ericoides Mart. (Brazilian arnica) ethanol extract accelerates the skin wound healing process: Evidence for its mechanism of action

BACKGROUND

Lychnophora ericoides Mart, also known as the Brazilian arnica or fake arnica, belongs to the Asteraceae family. Leaves and roots are used in alcoholic and hydroalcoholic preparations for the treatment of wounds, inflammation, and pain.

PURPOSE

The present study aimed to investigate the effects of L. ericoides ethanolic extract (EELE) on cutaneous wound healing and the mechanisms of action involved.

METHODS

A total of 72 C57BL/6 mice were randomly divided into four groups of six animals each. An excisional wound was made in the dorsal region of each mouse. The test groups were topically treated with the vehicle, a positive control commercial reference drug, EELE ointment (5%), and EELE ointment (10%). The treatments were applied over 14 days. The wound area was measured every two days to verify the wound closure kinetics. On days 3, 7, and 14 the wound tissue samples were processed for Hematoxylin and Eosin, Masson-Trichrome, and Toluidine blue staining. The expression of renin-angiotensin system (RAS) components, the vascular growth factor-A (VEGF-A), the basic fibroblast growth factor (FGF-2), and type I collagen genes were evaluated. Phytochemical analyses were performed using HPLC-DAD and HPLC-MS/MS.

RESULTS

The EELE (10%) significantly reduced the wound area compared to the treatments used for the other groups. Histological analysis demonstrated that wounds treated with L. ericoides for 14 days developed improved anatomical skin features, healed with hair follicles and sebaceous glands, increased collagen production and angiogenesis, and decreased the number of mast cells at the injury site. Real-time PCR data demonstrated that groups treated with EELE (10%) showed increased Type I collagen, VEGF-A, FGF-2, and AT1R and decreased ACE II and receptor MAS. The healing action of L. ericoides may be related to the presence of phenolic compounds, such as phenolic acids, chlorogenic acid derivatives, and C-glycoside flavonoids.

CONCLUSION

Topical treatment with EELE increases important factors for wound healing: FGF, VEGF, collagen formation, and the expression of the proliferative axis of the renin-angiotensin system. For the first time, the present study shows the healing action of L. ericoides at the molecular level in an animal model. This process can be used as an alternative therapy for wound healing and the development of herbal therapy.

Potential use of angiotensin receptor blockers in skin pathologies

Renin-angiotensin system (RAS) components such as angiotensin II, angiotensin receptors (AT₁R and AT₂R), and angiotensin-converting enzyme (ACE) are expressed in different cell types of the skin. Through AT1R, angiotensin II increases proinflammatory cytokines contributing to fibrosis, angiogenesis, proliferation, and migration of immune cells to the skin. In contrast, AT₂R suppresses the effects mentioned above. Many studies show that angiotensin receptor blockers (ARBs) and angiotensin-converting enzymes (ACEi) reduce the proinflammatory cytokines and fibrogenic factors including transforming growth factor β (TGF-β), Connective tissue growth factor (CTGF), and IL-6. This review article provides a detailed research study on the implications of ARBs in wound healing, hypertrophic scar, and keloids. We further discuss the therapeutic potentials of ARBs in autoimmune and autoinflammatory skin diseases and cancer, given their anti-fibrotic and anti-inflammatory effects.

Effect of the renin-angiotensin system on the exacerbation of adrenal glucocorticoid steroidogenesis in diabetic mice: Role of angiotensin-II type 2 receptor

Prior investigation shows an increase in the activity of both hypothalamus-pituitary-adrenal (HPA) axis and the renin-angiotensin system (RAS) in diabetic patients. Moreover, activation of angiotensin-II type 1 receptor (AT₁) has been associated with adrenal steroidogenesis. This study investigates the role of RAS on the overproduction of corticosterone in diabetic mice. Diabetes was induced by intravenous injection of alloxan into fasted Swiss-webster mice. Captopril (angiotensin-converting enzyme inhibitor), Olmesartan (AT₁ receptor antagonist), CGP42112A (AT₂ receptor agonist) or PD123319 (AT₂ receptor antagonist) were administered daily for 14 consecutive days, starting 7 days post-alloxan. Plasma corticosterone was evaluated by ELISA, while adrenal gland expressions of AT₁ receptor, AT₂ receptor, adrenocorticotropic hormone receptor MC2R, pro-steroidogenic enzymes steroidogenic acute regulatory protein (StAR), and 11β-hydroxysteroid dehydrogenase type 1 (11βHSD1) were assessed using immunohistochemistry or western blot. Diabetic mice showed adrenal gland overexpression of AT₁ receptor, MC2R, StAR, and 11βHSD1 without altering AT₂ receptor levels, all of which were sensitive to Captopril or Olmesartan treatment. In addition, PD123319 blocked the ability of Olmesartan to reduce plasma corticosterone levels in diabetic mice. Furthermore, CGP42112A significantly decreased circulating corticosterone levels in diabetic mice, without altering the overexpression of MC2R and StAR in the adrenal glands. Our findings revealed that inhibition of both angiotensin synthesis and AT₁ receptor activity reduced the high production of corticosterone in diabetic mice via the reduction of MC2R signaling expression in the adrenal gland. Furthermore, the protective effect of Olmesartan on the overproduction of corticosterone by adrenals in diabetic mice depends on both AT₁ receptor blockade and AT₂ receptor activation.

Valsartan nano-filaments alter mitochondrial energetics and promote faster healing in diabetic rat wounds

Chronic wounds are a common and debilitating condition associated with aging populations that impact more than 6.5 million patients in the United States. We have previously demonstrated the efficacy of daily topical 1% valsartan in treating wounds in diabetic mouse and pig models. Despite these promising results, there remains a need to develop an extended-release formulation that would reduce patient burden by decreasing the frequency of daily applications. Here, we used nanotechnology to self-assemble valsartan amphiphiles into a filamentous structure (val-filaments) that would serve as a scaffold in wound beds and allow for steady, localised and tunable release of valsartan amphiphiles over 24 days. Two topical treatments of this peptide-based hydrogel on full-thickness wounds in Zucker Diabetic Fatty rats resulted in faster rates of wound closure. By day 23, all val-filament treated wounds were completely closed, as compared to one wound closed in the placebo group. Mechanistically, we observed enrichment of proteins involved in cell adhesion and energetics pathways, downregulation of Tgf-β signalling pathway mediators (pSmad2, pSmad3 and Smad4) and increased mitochondrial metabolic pathway intermediates. This study demonstrates the successful synthesis of a sustained-release valsartan filament hydrogel, its impact on mitochondrial energetics and efficacy in treating diabetic wounds.

Valsartan solid lipid nanoparticles integrated hydrogel: A challenging repurposed use in the treatment of diabetic foot ulcer, in-vitro/in-vivo experimental study

The article presents an experimental study on the possible repurposed use of valsartan (Val), in the local treatment of uncontrolled diabetic foot ulcer. Solid lipid nanoparticles (SLN), loaded with Val were prepared by applying 3² full factorial design using modified high shear homogenization method. The lipid phase composed of Precirol® ATO 5 (P ATO 5) and/or Gelucire 50/13 (G 50/13) in different ratios and a nonionic emulsifier, Pluronic 188 (P188), was used in different percentages. Optimized formulation was further integrated in hydroxyl propyl methyl cellulose (HPMC) gel for the ease of administration. In-vitro and in-vivo characterizations were investigated. The prepared nanoparticles showed small particle size, high entrapment efficiency and sustained drug release. Microbiologically, Val-SLN showed a prominent decrease in the biofilm mass formation for both gram-positive and gram-negative bacteria, as well as a comparable minimum inhibitory concentration level to levofloxacin alone. Diabetes was induced in 32 neonatal Sprague-Dawley rats. At 8 weeks of age, rats with blood sugar level >160 were subjected to surgically induced ulcer. Treatment with Val-SLN for 12 days revealed enhanced healing characteristics through cyclooxygenase-2 (COX-2), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), nitric oxide (NO), transforming growth factor-beta (TGF-β), matrix metalloproteinase (MMPs) and vascular endothelial growth factor (VEGF) pathways. Histological examination revealed re-epithelization in Val-SLN treated ulcer, as well as decrease in collagen using trichrome histomorphometric analysis.

Macrophage mediation in normal and diabetic wound healing responses

PURPOSE

The failure in timely healing of wounds is a central feature in chronic wounds that leads to physiological, psychological and economic burdens. Macrophages have been demonstrated to have various functions in wounds including host defense, the promotion and resolution of inflammation, the removal of apoptotic cells and tissue restoration following injury. Accumulated evidence suggests that macrophage dysfunction is a component of the pathogenesis of non-healing wounds. While the overall signaling cascades have been well understood, their complex interplay and a detailed characterization of events that are disrupted in chronic wounds have still not emerged satisfactorily.

METHODS

The existing literature was reviewed to summarize the regulation of macrophage polarization in wound closure and dysregulation in non-healing wounds. Further, the review also underscored the role of Nrf2 in promoting macrophage-mediated regulation in wound responses and in particular, macrophage involvement in iron homeostasis that is impaired in chronic wounds such as in diabetes.

RESULTS

The mechanisms involved in the reprogramming of macrophage subtypes in chronic wounds are still emerging. Furthermore, treating non-healing wounds has increasingly been shifting focus from generic treatments to the development of targeted therapies. Increasing evidence suggests the need for modeling wound tissue in vitro which may very well serve a critical aspect to characterize the relevant factors that sustain chronic wounds in vivo such as the constant iron overload at the wound site from recurrent infection and bleeding.

CONCLUSION

The development of targeted therapies and also developing a reliable means to monitor assisted healing of chronic wounds are two major goals to be pursued. In addition, identifying molecular targets that can regulate macrophages to aid tissue restoration in chronic wounds would serve the crucial step in realizing both aforementioned goals.

Wound healing is promoted by Musa paradisiaca (banana) extract in diabetic rats

Introduction

Impairments in wound healing commonly occur among patients with diabetes. Herbal medicines have a long history of usage in wound care management. Super green (SG) is a newly discovered natural product obtained from Musa paradisiaca. This study aimed to investigate the efficacy of the topical application of SG in healing surgical wounds in diabetic rats.

Material and methods

Wistar rats received a one-time intraperitoneal injection of streptozotocin to induce type 1 diabetes. Full-thickness excisional skin wounds were created on the backs of the rats. The relevant groups were topically treated with the indicated concentrations of SG or vehicle dressing throughout the study duration. Histological analysis was performed and the mRNA levels of proinflammatory cytokines were measured to evaluate the improvement of wound closure.

Results

The wound area ratio of the SG (1/6000 dilution)-treated group was greatly reduced compared to that of the vehicle-treated group. The histological analysis showed fewer inflammatory cells, accelerated re-epithelialization, and increased collagen deposition in SG 1/6000-treated wounds. The gene expression levels of tumor necrosis factor-α, interleukin-1β, and interleukin-6 were decreased and the levels of type I and type III collagen were increased after SG treatment.

Conclusions

These results show that the most therapeutically efficacious concentration of SG (1/6000 dilution) can enhance wound repair in diabetic rats. SG has the potential to be a new treatment strategy for diabetic wounds.

Parallels between wound healing, epimorphic regeneration and solid tumors

Striking similarities between wound healing, epimorphic regeneration and the progression of solid tumors have been uncovered by recent studies. In this Review, we discuss systemic effects of tumorigenesis that are now being appreciated in epimorphic regeneration, including genetic, cellular and metabolic heterogeneity, changes in circulating factors, and the complex roles of immune cells and immune modulation at systemic and local levels. We suggest that certain mechanisms enabling regeneration may be co-opted by cancer to promote growth at primary and metastatic sites. Finally, we advocate that working with a unified approach could complement research in both fields.

Tissue repair brakes: A common paradigm in the biology of regeneration

To date, most attention on tissue regeneration has focused on the exploration of positive cues promoting or allowing the engagement of natural cellular restoration upon injury. In contrast, the signals fostering cell identity maintenance in the vertebrate body have been poorly investigated; yet they are crucial, for their counteraction could become a powerful method to induce and modulate regeneration. Here we review the mechanisms inhibiting pro-regenerative spontaneous adaptive cell responses in different model organisms and organs. The pharmacological or genetic/epigenetic modulation of such regenerative brakes could release a dormant but innate adaptive competence of certain cell types and therefore boost tissue regeneration in different situations.

Cutaneous inflammation differentially regulates the expression and function of Angiotensin-II types 1 and 2 receptors in rat primary sensory neurons

Neuropathic and inflammatory pain results from cellular and molecular changes in dorsal root ganglion (DRG) neurons. The type-2 receptor for Angiotensin-II (AT2R) has been involved in this type of pain. However, the underlying mechanisms are poorly understood, including the role of the type-1 receptor for Angiotensin-II (AT1R). Here, we used a combination of immunohistochemistry and immunocytochemistry, RT-PCR and in vitro and in vivo pharmacological manipulation to examine how cutaneous inflammation affected the expression of AT1R and AT2R in subpopulations of rat DRG neurons and studied their impact on inflammation-induced neuritogenesis. We demonstrated that AT2R-neurons express C- or A-neuron markers, primarily IB4, trkA, and substance-P. AT1R expression was highest in small neurons and co-localized significantly with AT2R. In vitro, an inflammatory soup caused significant elevation of AT2R mRNA, whereas AT1R mRNA levels remained unchanged. In vivo, we found a unique pattern of change in the expression of AT1R and AT2R after cutaneous inflammation. AT2R increased in small neurons at 1 day and in medium size neurons at 4 days. Interestingly, cutaneous inflammation increased AT1R levels only in large neurons at 4 days. We found that in vitro and in vivo AT1R and AT2R acted co-operatively to regulate DRG neurite outgrowth. In vivo, AT2R inhibition impacted more on non-peptidergic C-neurons neuritogenesis, whereas AT1R blockade affected primarily peptidergic nerve terminals. Thus, cutaneous-induced inflammation regulated AT1R and AT2R expression and function in different DRG neuronal subpopulations at different times. These findings must be considered when targeting AT1R and AT2R to treat chronic inflammatory pain. Cover Image for this issue: doi: 10.1111/jnc.14737.

Balance and circumstance: The renin angiotensin system in wound healing and fibrosis

The tissue renin angiotensin system (tRAS) is a locally-acting master-modulator of tissue homeostasis and regeneration. Through these abilities, it is emerging as an attractive target for therapies aiming to restore tissue homeostasis in conditions associated with disturbed wound healing. The tRAS can be divided into two axes - one being pro-inflammatory and pro-fibrotic and one being anti-inflammatory and anti-fibrotic. However, the division of the axes is fuzzy and imperfect as the axes are codependent and the outcome of tRAS activation is determined by the context. Although the tRAS is a local system it shares its key enzymes, ligands and receptors with the systemic RAS and is consequently also targeted by repurposing of drugs developed against the systemic RAS to manage hypertension. With a focus on the skin we will here discuss the tRAS, its involvement in physiological and pathological wound healing, and the therapeutic aptitude of its targeting to treat chronic wounds and fibrosis.

Angiotensin-converting enzyme inhibitor reduces scar formation by inhibiting both canonical and noncanonical TGF-β1 pathways

Angiotensin-converting enzyme inhibitors (ACEIs) can improve the fibrotic processes in many internal organs. Recent studies have shown a relationship between ACEI with cutaneous scar formation, although it has not been confirmed, and the underlying mechanism is unclear. In this study, we cultured mouse NIH 3T3 fibroblasts with different concentrations of ACEI. We measured cell proliferation with a Cell Counting Kit-8 and collagen expression with a Sirius Red Collagen Detection Kit. Flow cytometry and western blotting were used to detect transforming growth factor β1 (TGF-β1) signaling. We also confirmed the potential antifibrotic activity of ACEI in a rat scar model. ACEI reduced fibroblast proliferation, suppressed collagen and TGF-β1 expression, and downregulated the phosphorylation of SMAD2/3 and TAK1, both in vitro and in vivo. A microscopic examination showed that rat scars treated with ramipril or losartan were not only narrower than in the controls, but also displayed enhanced re-epithelialization and neovascularization, and the formation of organized granulation tissue. These data indicate that ACEI inhibits scar formation by suppressing both TGF-β1/SMAD2/3 and TGF-β1/TAK1 pathways, and may have clinical utility in the future.

Topical Reformulation of Valsartan for Treatment of Chronic Diabetic Wounds

Chronic wounds are among the most devastating and difficult to treat consequences of diabetes. Dysregulation of the skin renin-angiotensin system is implicated in abnormal wound healing in diabetic and older adults. Given this, we sought to determine the effects of topical reformulations of the angiotensin type 1 receptor blockers losartan and valsartan and the angiotensin-converting enzyme inhibitor captopril on wound healing in diabetic and aged mice with further validation in older diabetic pigs. The application of 1% valsartan gel compared with other tested formulations and placebo facilitated and significantly accelerated closure time and increased tensile strength in mice, and was validated in the porcine model. One percent of valsartan gel-treated wounds also exhibited higher mitochondrial content, collagen deposition, phosphorylated mothers against decapentaplegic homologs 2 and 3 and common mothers against decapentaplegic homolog 4, alpha-smooth muscle actin, CD31, phospho-vascular endothelial growth factor receptor 2, and p42/44 mitogen-activated protein kinase. Knockout of the angiotensin subtype 2 receptors abolished the beneficial effects of angiotensin type 1 receptor blockers, suggesting a role for angiotensin subtype 2 receptors in chronic wound healing.

Differential effects of Losartan and Atorvastatin in partial and full thickness burn wounds

Healing of burn wounds is often associated with scar formation due to excessive inflammation and delayed wound closure. To date, no effective treatment is available to prevent the fibrotic process. The Renin Angiotensin System (RAS) was shown to be involved in fibrosis in various organs. Statins (e.g. Atorvastatin), Angiotensin receptor antagonists (e.g. Losartan) and the combination of these drugs are able to reduce the local RAS activation, and reduced fibrosis in other organs. We investigated whether inhibition of the RAS could improve healing of burn wounds by treatment with Atorvastatin, Losartan or the combination of both drugs. Therefore, full and partial thickness burn wounds were inflicted on both flanks of Yorkshire pigs. Oral administration of Atorvastatin, Losartan or the combination was started at post-burn day 1 and continued for 28 days. Full thickness wounds were excised and transplanted with an autologous meshed split-thickness skin graft at post-burn day 14. Partial thickness wounds received conservative treatment. Atorvastatin treatment resulted in enhanced graft take and wound closure of the full thickness wounds, faster resolution of neutrophils compared to all treatments and reduced alpha-smooth muscle actin positive cells compared to control treatment. Treatment with Losartan and to a lesser extent the combination therapy resulted in diminished graft take, increased wound contraction and poorer scar outcome. In contrast, Losartan treatment in partial thickness wounds decreased the alpha-smooth muscle actin+ fibroblasts and contraction. In conclusion, we showed differential effects of Losartan and Atorvastatin in full and partial thickness wounds. The extensive graft loss seen in Losartan treated wounds is most likely responsible for the poor clinical outcome of these full thickness burn wounds. Therefore, Losartan treatment should not be started before transplantation in order to prevent graft loss. Atorvastatin seems to accelerate the healing process in full thickness wounds possibly by dampening the pro-inflammatory response.

Pathomechanisms of Altered Wound Healing in Recessive Dystrophic Epidermolysis Bullosa

Individuals with recessive dystrophic epidermolysis bullosa (RDEB), a rare genetic skin disease, carry mutations in the COL7A1 gene that codes for type VII collagen, an extracellular matrix component of the basement membrane zone forming the anchoring fibrils. As a consequence, RDEB individuals manifest unremitting skin blistering that evolves into chronic wounds, inflammation, and fibrosis. These features play a central role in the development of more severe disease complications, such as mitten deformities of hands and feet and aggressive epithelial cancers. Despite being recognized as a central clinical issue for RDEB, wound healing impairment has been only marginally investigated. Recently, studies with disease mouse models started to shed light on the molecular mechanisms underlying the altered healing response of RDEB. In turn, alterations found in RDEB skin cell behavior fostered the understanding of mechanisms that may be responsible for defective skin repair. This review summarizes findings related to healing impairment in RDEB, and highlights therapeutic strategies for ameliorating healing.

Signalling by Transforming Growth Factor Beta Isoforms in Wound Healing and Tissue Regeneration

Transforming growth factor beta (TGFβ) signalling is essential for wound healing, including both non-specific scar formation and tissue-specific regeneration. Specific TGFβ isoforms and downstream mediators of canonical and non-canonical signalling play different roles in each of these processes. Here we review the role of TGFβ signalling during tissue repair, with a particular focus on the prototypic isoforms TGFβ1, TGFβ2, and TGFβ3. We begin by introducing TGFβ signalling and then discuss the role of these growth factors and their key downstream signalling mediators in determining the balance between scar formation and tissue regeneration. Next we discuss examples of the pleiotropic roles of TGFβ ligands during cutaneous wound healing and blastema-mediated regeneration, and how inhibition of the canonical signalling pathway (using small molecule inhibitors) blocks regeneration. Finally, we review various TGFβ-targeting therapeutic strategies that hold promise for enhancing tissue repair.