Expression and distribution of antimicrobial peptides in the skin of healthy beagles

Efficacy of Short Novel Antimicrobial Peptides in a Mouse Model of Staphylococcus pseudintermedius Skin Infection

As the clinical application of antibiotics for bacterial skin infections in companion animals becomes increasingly prevalent, the issue of bacterial resistance has become more pronounced. Antimicrobial peptides, as a novel alternative to traditional antibiotics, have garnered widespread attention. In our study, synthetic peptides ADD-A and CBD3-ABU were tested against Staphylococcus pseudintermedius skin infections in KM mice. ADD-A was applied topically and through intraperitoneal injection, compared with control groups and treatments including CBD3-ABU, ampicillin sodium, and saline. Wound contraction, bacterial counts and histology were assessed on days 3 and 11 post-infection. ADD-A and ampicillin treatments significantly outperformed saline in wound healing (p < 0.0001 and p < 0.001, respectively). ADD-A also showed a markedly lower bacterial count than ampicillin (p < 0.0001). Histologically, ADD-A-applied wounds had better epidermal continuity and a thicker epidermis than normal, with restored follicles and sebaceous glands. ADD-A's effectiveness suggests it as a potential alternative to antibiotics for treating skin infections in animals.

Antimicrobial Peptide Reduces Cytotoxicity and Inflammation in Canine Epidermal Keratinocyte Progenitor Cells Induced by Pseudomonas aeruginosa Infection

The direct effects and antimicrobial activity of synthetic antimicrobial peptides (AMPs) obtained from dogs, including cBD, cBD103, and cCath, against P. aeruginosa wild-type strain PAO1 and canine keratinocytes were analyzed. Antibacterial effects on planktonic bacteria were assessed by determining the minimum bactericidal concentrations (MBCs) of AMPs and by a time-kill assay. Antibiofilm effects were assessed using the microtiter plate assay. We also evaluated the effects of AMPs on cell cytotoxicity and host immune response induced by stimulating canine epidermal keratinocyte progenitor (CPEK) cells with PAO1 and its LPS. cBD, cBD103, and cCath all exhibited dose-dependent antimicrobial and antibiofilm effects. In particular, 25 μg/mL cBD103 showed rapid bactericidal activity within 60 min and inhibited biofilm formation. In addition, pretreatment with cBD103 (25 µg/mL) and cCath (50 µg/mL) 1 h before stimulation significantly reduced the cytotoxicity of the CPEK cells by PAO1 and LPS-induced IL-6 and TNF-a expressions. cBD had little effect on the response to PAO1 and LPS in the cells. These results indicate the therapeutic potential of AMPs in P. aeruginosa skin infections. However, further studies on the mechanism of action of AMPs in keratinocytes and clinical trials are needed.

Comparison of the quantity and antimicrobial activity of host defence peptides in ear canals between healthy and atopic dogs: A preliminary study

BACKGROUND

Host defence peptides (HDPs) are involved in cutaneous immune defence. The secretion of HDPs in the ears of healthy normal and noninfected atopic dogs has not been measured.

HYPOTHESES/OBJECTIVES

The aim of this study was to quantify the concentrations of β-defensins (cBD3)-like and cathelicidin (cCath) HDPs in ears of healthy and atopic dogs without infectious otitis, additionally to evaluate the antimicrobial effect of the HDPs obtained.

ANIMALS

Ten healthy and 20 atopic dogs with mild inflammatory, noninfectious otitis were included.

MATERIALS AND METHODS

Absence of infection was determined by cytological evaluation, and the severity of clinical signs, if present, was assessed by a previously validated score (Otitis Externa Scoring System for Clinical Study, OTIS-3). The left ear canal of each dog was rinsed with 2 mL of sodium phosphate buffer. The solution obtained was analysed by enzyme-linked immunosorbent assay to quantify HDPs. Additionally, aural secretions were incubated with two concentrations (5 × 105 and 5 × 104 colony-forming units/mL) of Staphylococcus pseudintermedius and the bacterial density measured after 24 h of incubation. Data were statistically analysed. Significance was set as p ≤ 0.05.

RESULTS

There was a significantly lower concentration of HDPs from atopic ears when compared with those from normal healthy dogs (cBD3-like: p = 0.0007; cCath: p = 0.049). There was minimal to variable antimicrobial activity in the aural secretions of both groups.

CONCLUSIONS AND CLINICAL RELEVANCE

This study showed, for the first time, that the ear canals of atopic dogs with mild noninfectious otitis contain a lower concentration of cBD3-like and cCath HDPs than those of healthy dogs with normal ears. A consistent antimicrobial activity was not present in the aural secretions from either group.

Evaluation of the effects of chlorhexidine digluconate with and without cBD103 or cCath against multidrug-resistant clinical isolates of Staphylococcus pseudintermedius

Background

Because of the increased incidence of multidrug‐resistant (MDR) bacteria, the use of disinfectants over antibiotics has been encouraged. However, the interactions between disinfectants and host local immunity are poorly understood.

Objective

To assess the effects of chlorhexidine digluconate (Chx), with and without selected host defence peptides (HDPs), against MDR Staphylococcus pseudintermedius (MDR‐SP).

Methods and materials

Ten clinical isolates of MDR‐SP were tested, using a modified microbroth dilution method. Four two‐fold dilutions of 2% Chx and 1 μg/mL the HDPs synthetic canine β‐defensin 103 (cBD103) or cathelicidin (cCath) were tested alone or in combination. Colony counts after 5, 15, 30 and 60 min, and a minimum inhibitory concentration (MIC) after 24 h were recorded. Friedman followed by Dunn’s multiple comparison tests with significance of P < 0.05 were used for statistical analysis. Synergy, additivity/neutrality or antagonism were calculated.

Results

Growth was not inhibited by either HDP alone. An MIC of 0.312 μg/mL Chx was achieved for nine of the isolates. One isolate had an MIC of 0.078 μg/mL Chx. A MIC₉₀ (in nine of 10 isolates) of 0.312 µg/mL was seen for Chx in combination with either HDP. Synergy was seen in the combination Chx/cCath used at the highest concentrations of Chx (0.624 µg/mL and 0.312 µg/mL) after 30 and 60 min incubation. Additivity/neutrality was seen for most of the other concentrations and times of incubation.

Conclusions and clinical importance

These results suggest a synergistic/additive effect between Chx and HDPs in dogs. Further studies evaluating the mechanisms behind this effect are needed.

Antimicrobial peptides in domestic animals and their applications in veterinary medicine

Antimicrobial peptides (AMPs) are molecules with a broad-spectrum activity against bacteria, fungi, protozoa, and viruses. These peptides are widely distributed in insects, amphibians and mammals. Indeed, they are key molecules of the innate immune system with remarkable antimicrobial and immunomodulatory activity. Besides, these peptides have also shown regulatory activity for gut microbiota and have been considered inductors of growth performance. The current review describes the updated findings of antimicrobial peptides in domestic animals, such as bovines, goats, sheep, pigs, horses, canines and felines, analyzing the most relevant aspects of their use as potential therapeutics and their applications in Veterinary medicine.

Exploring Pleiotropic Functions of Canine β-Defensin 103: Nasal Cavity Expression, Antimicrobial Activity, and Melanocortin Receptor Activity

Canine β-defensin 103 (cBD103) and its common variant cBD103ΔG23 are multitasking polypeptides. As a β-defensin, cBD103 is one of many antimicrobial agents used by the innate immunity to thwart pathogenic colonization. In this study, we showed that cBD103 was expressed throughout the nasal cavity, with primary expression in the nares as well as respiratory and olfactory epithelia. In the rostral nasal concha, cBD103 was expressed in the epithelium, and to a lesser degree in the lamina propria, but was absent in goblet cells. In the main olfactory epithelium, virtually all cells in the epithelial layer and select cells associated with Bowman's glands expressed cBD103. We also showed that the ΔG23 mutation did not appreciably alter the antimicrobial activity of the peptide against several species of microorganisms tested in nutrient-rich or minimal media or minimal media with salt added. Moreover, we showed antimicrobial activity in minimal media did not necessarily predict the inhibitory action of the peptide in nutrient-rich media. Both forms of cBD103 caused ultrastructural changes (membrane blebbing, condensation of intracellular contents and cell wall lysis) in Escherichia coli and Staphylococcus aureus. As a ligand of the melanocortin receptors, we showed that cBD103ΔG23 increased ERK1/2 activation and cAMP accumulation when bound to the human or canine melanocortin-4 receptor, acting as a weak allosteric agonist.

Single blinded, randomized, placebo-controlled study on the effects of ciclosporin on cutaneous barrier function and immunological response in atopic beagles

Ciclosporin (CsA) is a common treatment for canine atopic dermatitis (cAD). cAD is a very common skin disease with a multifactorial pathogenesis due to complex interactions between the host and the environment. The purpose of this study was to describe the physical and immunological effects of CsA in cAD using a canine model of AD. Fourteen beagles were enrolled; seven received CsA orally every 24 h for 28 days, and seven received placebo. All dogs were exposed to relevant allergens, house dust mite solution, one day prior to treatment and once weekly thereafter for 28 consecutive days. Canine atopic dermatitis extent and severity index-03 (CADESI-03) and skin biopsies were performed on day 0, 14, and 28. Quantitative RT-PCR was used to determine levels of cutaneous cytokines and barrier function markers. Indirect immunofluorescence was used to determine protein expression and distribution of nuclear messengers, barrier function and inflammatory [thymic stromal lymphopoietin (TSLP)] markers. The data were tested for normality and then the upaired two samples Student's t-test and the repeated measurements ANOVA, followed by the Dunnett's Multiple Comparison Test as post-hoc analysis, were performed. A P value of <0.05 was considered statistically significant. A significant decrease in CADESI-03 occurred for the treatment group compared to placebo (p = 0.023) on day 28. On day 14, a significant increase in TSLP protein expression [p = 0.019 (placebo); p = 0.02 (CsA)] and a significant decrease in Transforming Growth Factor (TGF)-β mRNA [p = 0.01 (placebo); p = 0.015 (CsA)] were noted in both groups compared to baseline. On day 28, a significant increase in canine beta defensin (cBD)103 [p = 0.012 (placebo)] and cBD3-like mRNAs [p = 0.044 (placebo)], and filaggrin [p = 0.035 (CsA)] and TSLP protein expressions [p = 0.0092 (CsA)] were seen compared to baseline. In contrast, a significant decrease in mRNA of Tumor Necrosis factor (TNF)-α [p = 0.013 (CsA)], Interleukin (IL)-10 [p = 0.038 (CsA)], TGF-β [p = 0.017 (CsA)], and caspase 14 [p = 0.014 (CsA)] was seen on day 28 compared to baseline. Comparison of the groups revealed no significant effect on skin immunologic milieu or barrier markers despite evident improvement of physical signs in the treatment group. Although this study confirmed the usefulness of CsA for the treatment of cAD, a clear involvement of CsA on some of the currently known immunological alterations present in cAD was not determined. However, it is important to note that there was no measurable exacerbation of skin barrier dysfunction secondary to CsA administration in this model.

Salivary proteomics of healthy dogs: An in depth catalog

Objective

To provide an in-depth catalog of the salivary proteome and endogenous peptidome of healthy dogs, evaluate proteins and peptides with antimicrobial properties, and compare the most common salivary proteins and peptides between different breed phylogeny groups.

Methods

36 healthy dogs without evidence of periodontal disease representing four breed phylogeny groups, based upon single nucleotide polymorphism haplotypes (ancient, herding/sighthound, and two miscellaneous groups). Saliva collected from dogs was pooled by phylogeny group and analyzed using nanoscale liquid chromatography-tandem mass spectrometry. Resulting tandem mass spectra were compared to databases for identification of endogenous peptides and inferred proteins.

Results

2,491 proteins and endogenous peptides were found in the saliva of healthy dogs with no periodontal disease. All dog phylogeny groups’ saliva was rich in proteins and peptides with antimicrobial functions. The ancient breeds group was distinct in that it contained unique proteins and was missing many proteins and peptides present in the other groups.

Conclusions and clinical relevance

Using a sophisticated nanoscale liquid chromatography-tandem mass spectrometry, we were able to identify 10-fold more salivary proteins than previously reported in dogs. Seven of the top 10 most abundant proteins or peptides serve immune functions and many more with various antimicrobial mechanisms were found. This is the most comprehensive analysis of healthy canine saliva to date, and will provide the groundwork for future studies analyzing salivary proteins and endogenous peptides in disease states.

Evaluation of the in vitro effect of Boldo and Meadowsweet plant extracts on the expression of antimicrobial peptides and inflammatory markers in canine keratinocytes

Dogs with allergies are prone to skin infections and treatments/preventatives to boost innate immune-defenses are beneficial. The aim of this study was to evaluate the effects of Boldo and Meadowsweet extracts on the expression of β-defensins (cBD), cathelicidin (cCath), and pro-inflammatory cytokines in canine keratinocyte. This study had two phases. Phase I evaluated mRNA expression of cBD103 and cCath, and secretion of cCath, IL-8 and TNF-α by keratinocytes harvested from healthy (n=5) and atopic (n=5) age-matched beagles exposed to Boldo (2% to 0.2%) and Meadowsweet (1% to 0.2%) extracts. Phase II focused on atopic keratinocytes (n=14) exposed to 0.2% Boldo, 0.2% Meadowsweet, and a mixture of 0.1% of both extracts. Phase I: cBD103 mRNA (all concentrations) and TNF-α secretion (2% Boldo) were increased in atopic compared with healthy keratinocytes. In atopic keratinocytes, cBD103 was increased after exposure to 1.5% and 0.2% Boldo. In healthy keratinocytes, 1% and 0.2% Meadowsweet, and 2% Boldo increased and decreased IL-8 secretion, respectively. In atopic keratinocytes, IL-8 increased after exposure to 1% and 0.4% Meadowsweet extract. Phase II: cBD103 mRNA increased after exposure to 0.2% Meadowsweet and to 0.1% mixture. cCath was increased after 0.2% Boldo, but decreased after 0.2% Meadowsweet or the 0.1% mixture. TNF-α secretion was decreased after 0.2% Boldo. It is concluded that low concentrations of both extracts and their combination may have some effects on cCath and cBD103 without stimulating an inflammatory response. However, more studies are needed to clarify the effects of these extracts on the local immunity.

The immunopathogenesis of staphylococcal skin infections - A review

Staphylococcus aureus and S. pseudintermedius are the major causes of bacterial skin disease in humans and dogs. These organisms can exist as commensals on the skin, but they can also cause severe or even devastating infections. The immune system has evolved mechanisms to deal with pathogenic microorganisms and has strategies to combat bacteria of this type. What emerges is a delicate "peace" between the opposing sides, but this balance can be disrupted leading to a full blown "war". In the ferocious battle that ensues, both sides attempt to get the upper hand, using strategies that are comparable to those used by modern day armies. In this review article, the complex interactions between the immune system and the organisms are described using such military analogies. The process is described in a sequential manner, starting with the invasion itself, and progressing to the eventual battlezone in which there are heavy casualties on both sides. By the end, the appearance of a simple pustule on the skin surface will take on a whole new meaning.

Antimicrobial peptides: agents of border protection for companion animals

Over the past 20 years, there have been significant inroads into understanding the roles of antimicrobial peptides in homeostatic functions and their involvement in disease pathogenesis. In addition to direct antimicrobial activity, these peptides participate in many cellular functions, including chemotaxis, wound healing and even determination of canine coat colour. Various biological and genetic approaches have helped to elucidate the role of antimicrobial peptides with respect to innate immunity and host defense.

Associations of antimicrobial peptides with various skin diseases, including psoriasis, rosacea and atopic dermatitis, have been documented in humans. In the longer term, therapeutic modulation of antimicrobial peptide expression may provide effective new treatments for disease.

This review highlights current knowledge about antimicrobial peptides of the skin and circulating leukocytes, with particular focus on relevance to physiology and disease in companion animals.

Activity, expression and genetic variation of canine β-defensin 103: a multifunctional antimicrobial peptide in the skin of domestic dogs

The skin functions as more than a physical barrier to infection. Epithelial cells of the skin can synthesize antimicrobial peptides, including defensins, which exhibit direct antimicrobial activity. Here we characterize the expression pattern, genetic variation and activity of the major β-defensin expressed in canine skin, canine β-defensin 103 (CBD103). The gene encoding CBD103 exhibits two forms of polymorphism: a common 3-basepair deletion allele and a gene copy-number variation. Golden retrievers and Labrador retrievers were the only breeds that encoded the variant allele of CBD103, termed CBD103ΔG23. Both these breeds also exhibited a CBD103 gene copy-number polymorphism that ranged from 2 to 4 gene-copies per diploid genome. Recombinant CBD103 and CBD103ΔG23, as well as the human ortholog human β-defensin 3 (hBD3) and hBD3ΔG23, showed potent and comparable antimicrobial killing against both methicillin-susceptible and methicillin-resistant Staphylococcus pseudintermedius. Skin biopsy specimens from dogs with atopic dermatitis revealed CBD103 expression levels similar to those in healthy controls and comparable at lesional and nonlesional sites. This expression pattern in dogs differs from the previously reported reduced expression of the human ortholog in atopic dermatitis. Overall, the similarities of CBD103 and its human ortholog reported here support the notion that the domestic dog may serve as a valuable model for studying β-defensin biology in the skin.