Inducible expression of defensins and cathelicidins by nutrients and associated regulatory mechanisms

Oleanolic acid improved intestinal immune function by activating and potentiating bile acids receptor signaling in E. coli-challenged piglets

BACKGROUND

Infection with pathogenic bacteria during nonantibiotic breeding is one of the main causes of animal intestinal diseases. Oleanolic acid (OA) is a pentacyclic triterpene that is ubiquitous in plants. Our previous work demonstrated the protective effect of OA on intestinal health, but the underlying molecular mechanisms remain unclear. This study investigated whether dietary supplementation with OA can prevent diarrhea and intestinal immune dysregulation caused by enterotoxigenic Escherichia coli (ETEC) in piglets. The key molecular role of bile acid receptor signaling in this process has also been explored.

RESULTS

Our results demonstrated that OA supplementation alleviated the disturbance of bile acid metabolism in ETEC-infected piglets (P < 0.05). OA supplementation stabilized the composition of the bile acid pool in piglets by regulating the enterohepatic circulation of bile acids and significantly increased the contents of UDCA and CDCA in the ileum and cecum (P < 0.05). This may also explain why OA can maintain the stability of the intestinal microbiota structure in ETEC-challenged piglets. In addition, as a natural ligand of bile acid receptors, OA can reduce the severity of intestinal inflammation and enhance the strength of intestinal epithelial cell antimicrobial programs through the bile acid receptors TGR5 and FXR (P < 0.05). Specifically, OA inhibited NF-κB-mediated intestinal inflammation by directly activating TGR5 and its downstream cAMP-PKA-CREB signaling pathway (P < 0.05). Furthermore, OA enhanced CDCA-mediated MEK-ERK signaling in intestinal epithelial cells by upregulating the expression of FXR (P < 0.05), thereby upregulating the expression of endogenous defense molecules in intestinal epithelial cells.

CONCLUSIONS

In conclusion, our findings suggest that OA-mediated regulation of bile acid metabolism plays an important role in the innate immune response, which provides a new diet-based intervention for intestinal diseases caused by pathogenic bacterial infections in piglets.

Prophybiotics for in-ovo stimulation; validation of effects on gut health and production of broiler chickens

Probiotics and phytobiotics have demonstrated effective improvement of gut health in broiler chickens when individually administered in-ovo. However, their combined use in-ovo, has not been studied to date. We coined the term "prophybiotic" (probiotic + phytobiotic) for such a combination. The current study therefore, aimed to elucidate the effects of combined use of a selected probiotic and a phytobiotic in-ovo, on broiler gut health and production parameters, as opposed to use of probiotics alone. ROSS 308 hatching eggs were injected with either Leuconostoc mesenteroides (probiotic: PB) or L. mesenteroides with garlic aqueous extract (prophyiotic: PPB) on the 12th day of incubation. Relative abundances of bacteria in feces and cecal content (qPCR), immune related gene expression in cecal mucosa (qPCR) and histomorphology of cecal tissue (PAS staining) were analyzed along with production parameters (hatch quality, body weight, feed efficiency and slaughter and meat quality). PPB treatment increased the abundance of faecalibacteria and bifidobacteria in feces (d 7) and Akkermansia sp. in cecal content. Moreover, it decreased Escherichia coli abundance in both feces (d 34) and cecal content. PB treatment only increased the faecalibacteria in feces (d 7) and Akkermansia sp. in the cecal content. Moreover, PPB treatment resulted in up-regulation of immune related genes (Avian beta defensing 1, Free fatty acid receptor 2 and Mucin 6) and increased the crypt depth in ceca whereas PB treatment demonstrated a higher crypt depth and a tendency to increase Mucin 6 gene expression. Both treatments did not impair the production parameters studied. In conclusion, our results suggest that in-ovo PPB treatment may have enhanced potential in boosting the immune system without compromising broiler production and efficiency, as compared to the use of probiotic alone. Our study, highlights the potential of carefully selected PPB combinations for better results in improving gut health of broiler chickens.

Human Neutrophil Alpha-Defensins Promote NETosis and Liver Injury in Alcohol-Related Liver Cirrhosis: Potential Therapeutic Agents

Background: Neutrophils are thought to play a pivotal role in the pathogenesis of many inflammatory diseases, such as hepatitis, liver cirrhosis, etc. Activated human neutrophils release human neutrophil peptides (HNP1-3) or alpha-defensins that are antimicrobial peptides in azurophil granules. Furthermore, HNP1-3 build a scaffold of neutrophil extracellular traps (NETs) and promote the process of programmed cell death called NETosis. Our study aimed to investigate the role of alpha-defensins in the pathogenesis of alcohol-related liver cirrhosis (ALC). Methods: The concentrations of alpha-defensins in the plasma of 62 patients with ALC and 24 healthy subjects were measured by ELISA. The patients with ALC were prospectively recruited based on the severity of liver dysfunction according to the Child-Pugh and Model of End-Stage Liver Disease-Natrium (MELD-Na) scores, modified Maddrey's Discriminant Function (mDF), and the presence of ALC complications. Results: The concentrations of alpha-defensins in plasma were significantly higher in the ALC patients than in the controls. The plasma levels of HNP1-3 correlated with the MELD and mDF scores. ALC subgroups with MELD > 20 and mDF > 32 displayed significantly higher HNP1-3 concentrations. The plasma levels of HNP1-3 revealed a good predictive AUC for hepatic encephalopathy and ascites development (0.81 and 0.74, respectively) and for patient survival (0.87) in those over 40 years of age. Conclusion: These findings suggest that alpha-defensins play an important role in the assessment of ALC.

Can mesenchymal stem/stromal cells and their secretomes combat bacterial persisters?

The increasing number of life-threatening infections caused by persister bacteria is associated with various issues, including antimicrobial resistance and biofilm formation. Infections due to persister cells are often difficult to suppress without the use of last-resort antibiotics. Throughout the world, bacterial persistence and resistance create an unmet clinical demand for the exploration of newly introduced therapeutic approaches. Mesenchymal stem / stromal cells (MSCs) have an antimicrobial activity to protect against bacterial infections, including those caused by bacterial persisters. MSCs have substantial potential to secrete antimicrobial peptides (AMPs), including cathelicidin, beta-defensins, lipocalin-2, hepcidin, indoleamine 2,3-dioxygenase (IDO), cysteine proteases, and inducible nitric oxide synthases (iNOS). MSCs possess the potential to contribute to innate immunity by regulating the immune response. Recently, MSCs and their secreted components have been reported to improve antimicrobial activity. Bactericidal activity by MSCs and their secretomes has been shown to be mediated in part by the secretion of AMPs. Even though they were discovered more than 80 years ago, therapeutic options for persisters are restricted, and there is an urgent need for alternative treatment regimens. Hence, this review intends to critically assess the current literature on the effects of MSCs and their secretomes on persister bacteria. MSCs and their secretome-based therapies could be preferred as an up-and-coming approach to reinforce the antimicrobial efficiency in persister infections.

The deubiquitinase OTUD4 inhibits the expression of antimicrobial peptides in Paneth cells to support intestinal inflammation and bacterial infection

Dysfunction of the intestinal epithelial barrier causes microbial invasion that would lead to inflammation in the gut. Antimicrobial peptides (AMPs) are essential components of the intestinal epithelial barrier, while the regulatory mechanisms of AMPs expression are not fully characterized. Here, we report that the ovarian tumor family deubiquitinase 4 (OTUD4) in Paneth cells restricts the expression of AMPs and thereby promotes experimental colitis and bacterial infection. OTUD4 is upregulated in the inflamed mucosa of ulcerative colitis patients and in the colon of mice treated with dextran sulfate sodium salt (DSS). Knockout of OTUD4 promotes the expression of AMPs in intestinal organoids after stimulation with lipopolysaccharide (LPS) or peptidoglycan (PGN) and in the intestinal epithelial cells (IECs) of mice after DSS treatment or Salmonella typhimurium (S.t.) infection. Consistently, Vil-Cre;Otud4fl/fl mice and Def-Cre;Otud4fl/fl mice exhibit hyper-resistance to DSS-induced colitis and S.t. infection compared to Otud4fl/fl mice. Mechanistically, knockout of OTUD4 results in hyper K63-linked ubiquitination of MyD88 and increases the activation of NF-κB and MAPKs to promote the expression of AMPs. These findings collectively highlight an indispensable role of OTUD4 in Paneth cells to modulate AMPs production and indicate OTUD4 as a potential target for gastrointestinal inflammation and bacterial infection.

Regulation of Host Defense Peptide Synthesis by Polyphenols

The rise of antimicrobial resistance has created an urgent need for antibiotic-alternative strategies for disease control and prevention. Host defense peptides (HDPs), which have both antimicrobial and immunomodulatory properties, are an important component of the innate immune system. A host-directed approach to stimulate the synthesis of endogenous HDPs has emerged as a promising solution to treat infections with a minimum risk for developing antimicrobial resistance. Among a diverse group of compounds that have been identified as inducers of HDP synthesis are polyphenols, which are naturally occurring secondary metabolites of plants characterized by the presence of multiple phenol units. In addition to their well-known antioxidant and anti-inflammatory activities, a variety of polyphenols have been shown to stimulate HDP synthesis across animal species. This review summarizes both the in vitro and in vivo evidence of polyphenols regulating HDP synthesis. The mechanisms by which polyphenols induce HDP gene expression are also discussed. Natural polyphenols warrant further investigation as potential antibiotic alternatives for the control and prevention of infectious diseases.

Induction of Endogenous Antimicrobial Peptides to Prevent or Treat Oral Infection and Inflammation

Antibiotics are often used to treat oral infections. Unfortunately, excessive antibiotic use can adversely alter oral microbiomes and promote the development of antibiotic-resistant microorganisms, which can be difficult to treat. An alternate approach could be to induce the local transcription and expression of endogenous oral antimicrobial peptides (AMPs). To assess the feasibility and benefits of this approach, we conducted literature searches to identify (i) the AMPs expressed in the oral cavity; (ii) the methods used to induce endogenous AMP expression; and (iii) the roles that expressed AMPs may have in regulating oral inflammation, immunity, healing, and pain. Search results identified human neutrophil peptides (HNP), human beta defensins (HBD), and cathelicidin AMP (CAMP) gene product LL-37 as prominent AMPs expressed by oral cells and tissues. HNP, HBD, and LL-37 expression can be induced by micronutrients (trace elements, elements, and vitamins), nutrients, macronutrients (mono-, di-, and polysaccharides, amino acids, pyropeptides, proteins, and fatty acids), proinflammatory agonists, thyroid hormones, and exposure to ultraviolet (UV) irradiation, red light, or near infrared radiation (NIR). Localized AMP expression can help reduce infection, inflammation, and pain and help oral tissues heal. The use of a specific inducer depends upon the overall objective. Inducing the expression of AMPs through beneficial foods would be suitable for long-term health protection. Additionally, the specialized metabolites or concentrated extracts that are utilized as dosage forms would maintain the oral and intestinal microbiome composition and control oral and intestinal infections. Inducing AMP expression using irradiation methodologies would be applicable to a specific oral treatment area in addition to controlling local infections while regulating inflammatory and healing processes.

A review on curcumin colon-targeted oral drug delivery systems for the treatment of inflammatory bowel disease

Synthetic drugs and monoclonal antibodies are the typical treatments to combat inflammatory bowel disease (IBD). However, side effects are present when these treatments are used, and their continued application could be restricted by the high relapse rate of the disease. One potential alternative to these treatments is the use of plant-derived products. The use curcumin is one such treatment option that has seen an increase in usage in treating IBD. Curcumin is derived from a rhizome of turmeric (Curcuma longa), and the results of studies on the use of curcumin to treat IBD are promising. These studies suggest that curcumin interacts with cellular targets such as NF-κB, JAKs/STATs, MAPKs, TNF-α, IL-6, PPAR, and TRPV1 and may reduce the progression of IBD. Potentially, curcumin can be used as a therapeutic agent for patients with IBD when it reduces the incidence of clinical relapse. This review discusses the strategies utilized in designing and developing an oral colonic delivery dosage form of curcumin.

Andrographolide and 4-Phenylbutyric Acid Administration Increase the Expression of Antimicrobial Peptides Beta-Defensin-1 and Cathelicidin and Reduce Mortality in Murine Sepsis

Antibiotic resistance is a global threat and requires the search for new treatment strategies. Natural antimicrobial peptides (AMPs) have pronounced antibacterial, antiviral, antifungal, and antitumor activity. AMPs’ clinical use is complicated by the high synthesis costs and rapid proteolytic degradation. The search for small molecules, inducers of endogenous AMP expression, could become a new approach. Here, we investigated for the first time the effect of seven small molecules (andrographolide, levofloxacin, azithromycin, montelukast, 4-phenylbutyric acid, rosuvastatin and valsartan) on AMP (beta-defensin-1, hBD-1 and cathelicidin, LL-37) serum levels in rats. In control groups, the level of hBD-1 was 295.0 (292.9–315.4) pg/mL, and for LL-37, it was 223.8 (213.3–233.6) pg/mL. Andrographolide (ANDR) and 4-phenylbutyric acid (4-PHBA) administration significantly enhanced the level of both AMPs. The hBD-1 level was 581.5 (476.3–607.7) pg/mL for ANDR and 436.9 (399.0–531.6) pg/mL for 4-PHBA. The LL-37 level was 415.4 (376.2–453.8) pg/mL for ANDR and 398.9 (355.7–410.1) pg/mL for 4-PHBA. Moreover, we have shown that these compounds reduce mortality in a murine model of sepsis caused by a carbapenem-resistant Klebsiella aerogenes isolate. From our point of view, these small molecules are promising candidates for further study as potent AMP inducers. The data obtained allow the development of new strategies to combat antibiotic resistance and infectious diseases.

High-Throughput Identification of Epigenetic Compounds to Enhance Chicken Host Defense Peptide Gene Expression

Enhancing the synthesis of endogenous host defense peptides (HDPs) has emerged as a novel antibiotic-free approach to infectious disease control and prevention. A number of epigenetic compounds have been identified as HDP inducers and several have proved beneficial in antimicrobial therapy. However, species-specific regulation of HDP synthesis is evident. In attempt to identify epigenetic compounds with potent HDP-inducing activity for poultry-specific application, we developed a stable luciferase reporter cell line, known as HTC/AvBD10-luc, following our earlier construction of HTC/AvBD9-luc. HTC/AvBD10-luc was developed through permanent integration of a chicken macrophage cell line, HTC, with a lentiviral luciferase reporter vector driven by a 4-Kb AvBD10 gene promoter. Using a high throughput screening assay based on the two stable cell lines, we identified 33 hits, mostly being histone deacetylase (HDAC) inhibitors, from a library of 148 epigenetic compounds. Among them, entinostat and its structural analog, tucidinostat, were particularly effective in promoting multiple HDP gene expression in chicken macrophages and jejunal explants. Desirably, neither compounds triggered an inflammatory response. Moreover, oral gavage of entinostat significantly enhanced HDP gene expression in the chicken intestinal tract. Collectively, the high throughput assay proves to be effective in identifying HDP inducers, and both entinostat and tucidinostat could be potentially useful as alternatives to antibiotics to enhance intestinal immunity and disease resistance.

Natural Cyclooxygenase-2 Inhibitors Synergize With Butyrate to Augment Chicken Host Defense Peptide Gene Expression

Enhancing the synthesis of microbicidal and immunomodulatory host defense peptides (HDP) is a promising host-directed antimicrobial strategy to combat a growing threat of antimicrobial resistance. Here we investigated the effect of several natural cyclooxygenase-2 (COX-2) inhibitors on chicken HDP gene regulation. Our results indicated that phenolic COX-2 inhibitors such as quercetin, resveratrol, epigallocatechin gallate, anacardic acid, and garcinol enhanced HDP gene expression in chicken HTC macrophage cell line and peripheral blood mononuclear cells (PBMCs). Moreover, these natural COX-2 inhibitors showed a strong synergy with butyrate in augmenting the expressions of multiple HDP genes in HTC cells and PBMCs. Additionally, quercetin and butyrate synergistically promoted the expressions of mucin-2 and claudin-1, two major genes involved in barrier function, while suppressing lipopolysaccharide-triggered interleukin-1β expression in HTC macrophages. Mechanistically, we revealed that NF-κB, p38 mitogen-activated protein kinase, and cyclic adenosine monophosphate signaling pathways were all involved in the avian β-defensin 9 gene induction, but histone H4 was not hyperacetylated in response to a combination of butyrate and quercetin. Because of their HDP-inducing, barrier-protective, and antiinflammatory activities, these natural COX-2 inhibitors, when combined with butyrate, may be developed as novel host-directed antimicrobial therapeutics.

Butyrate, Forskolin, and Lactose Synergistically Enhance Disease Resistance by Inducing the Expression of the Genes Involved in Innate Host Defense and Barrier Function

The rising concern of antimicrobial resistance highlights a need for effective alternatives to antibiotics for livestock production. Butyrate, forskolin, and lactose are three natural products known to induce the synthesis of host defense peptides (HDP), which are a critical component of innate immunity. In this study, the synergy among butyrate, forskolin, and lactose in enhancing innate host defense, barrier function, and resistance to necrotic enteritis and coccidiosis was investigated. Our results indicated that the three compounds synergistically augmented the expressions of multiple HDP and barrier function genes in chicken HD11 macrophages. The compounds also showed an obvious synergy in promoting HDP gene expressions in chicken jejunal explants. Dietary supplementation of a combination of 1 g/kg sodium butyrate, 10 mg/kg forskolin-containing plant extract, and 10 g/kg lactose dramatically improved the survival of chickens from 39% to 94% (p < 0.001) in a co-infection model of necrotic enteritis. Furthermore, the three compounds largely reversed growth suppression, significantly alleviated intestinal lesions, and reduced colonization of Clostridium perfringens or Eimeria maxima in chickens with necrotic enteritis and coccidiosis (p < 0.01). Collectively, dietary supplementation of butyrate, forskolin, and lactose is a promising antibiotic alternative approach to disease control and prevention for poultry and possibly other livestock species.

A bridge for short-chain fatty acids to affect inflammatory bowel disease, type 1 diabetes, and non-alcoholic fatty liver disease positively: by changing gut barrier

PURPOSE

In previous studies, short-chain fatty acids (SCFAs) have been found to regulate gut microbiota and change gut barrier status, and the potential positive effects of SCFAs on inflammatory bowel disease (IBD), type 1 diabetes mellitus (T1D), and non-alcoholic fatty liver disease (NAFLD) have also been found, but the role of SCFAs in these three diseases is not clear. This review aims to summarize existing evidence on the effects of SCFAs on IBD, T1D, and NHFLD, and correlates them with gut barrier and gut microbiota (gut microbiota barrier).

METHODS

A literature search in PubMed, Web of Science, Springer, and Wiley Online Library up to October 2020 was conducted for all relevant studies published.

RESULTS

This is a retrospective review of 150 applied research articles or reviews. The destruction of gut barrier may promote the development of IBD, T1D, and NAFLD. SCFAs seem to maintain the gut barrier by promoting the growth of intestinal epithelial cells, strengthening the intestinal tight connection, and regulating the activities of gut microbiota and immune cells, which might result possible beneficial effects on the above three diseases at a certain dose.

CONCLUSIONS

Influencing gut barrier health may be a bridge for SCFAs (especially butyrate) to have positive effects on IBD, T1D, and NAFLD. It is expected that this article can provide new ideas for the subsequent research on the treatment of diseases by SCFAs and help SCFAs be better applied to precise and personalized treatment.

Immunomodulatory Properties of Host Defence Peptides in Skin Wound Healing

Cutaneous wound healing is a vital biological process that aids skin regeneration upon injury. Wound healing failure results from persistent inflammatory conditions observed in diabetes, or autoimmune diseases like psoriasis. Chronic wounds are incurable due to factors like poor oxygenation, aberrant function of peripheral sensory nervature, inadequate nutrients and blood tissue supply. The most significant hallmark of chronic wounds is heavily aberrant immune skin function. The immune response in humans relies on a large network of signalling molecules and their interactions. Research studies have reported on the dual role of host defence peptides (HDPs), which are also often called antimicrobial peptides (AMPs). Their duality reflects their potential for acting as antibacterial peptides, and as immunodulators that assist in modulating several biological signalling pathways related to processes such as wound healing, autoimmune disease, and others. HDPs may differentially control gene regulation and alter the behaviour of epithelial and immune cells, resulting in modulation of immune responses. In this review, we shed light on the understanding and most recent advances related to molecular mechanisms and immune modulatory features of host defence peptides in human skin wound healing. Understanding their functional role in skin immunity may further inspire topical treatments for chronic wounds.

A High-Throughput Comparative Proteomics of Milk Fat Globule Membrane Reveals Breed and Lactation Stages Specific Variation in Protein Abundance and Functional Differences Between Milk of Saanen Dairy Goat and Holstein Bovine

Large variations in the bioactivities and composition of milk fat globule membrane (MFGM) proteins were observed between Saanen dairy goat and Holstein bovine at various lactation periods. In the present study, 331, 250, 182, and 248 MFGM proteins were characterized in colostrum and mature milk for the two species by Q-Orbitrap HRMS-based proteomics techniques. KEGG pathway analyses displayed that differentially expressed proteins in colostrum involved in galactose metabolism and an adipogenesis pathway, and the differentially expressed proteins in mature milk associated with lipid metabolism and a PPAR signaling pathway. These results indicated that the types and functions of MFGM proteins in goat and bovine milk were different, and goat milk had a better function of fatty acid metabolism and glucose homeostasis, which can enhance our understanding of MFGM proteins in these two species across different lactation periods, and they provide significant information for the study of lipid metabolism and glycometabolism of goat milk.

Mutual interaction between gut microbiota and protein/amino acid metabolism for host mucosal immunity and health

In recent years, many studies have shown that the intestinal microflora has various effects that are linked to the critical physiological functions and pathological systems of the host. The intestinal microbial community is widely involved in the metabolism of food components such as protein, which is one of the essential nutrients in diets. Additionally, dietary protein/amino acids have been shown to have had a profound impact on profile and operation of gut microbiota. This review summarizes the current literature on the mutual interaction between intestinal microbiota and protein/amino acid metabolism for host mucosal immunity and health.

L-Threonine upregulates the expression of β-defensins by activating the NF-κB signaling pathway and suppressing SIRT1 expression in porcine intestinal epithelial cells

The use of antimicrobial peptide (AMP), found in all forms of life and playing a pivotal role in the innate immune system, has been developed as a new strategy for maintaining intestinal health and reducing antibiotic usage due to its ability to resist pathogens and commensal microbes. The current study investigated the effects of l-threonine on β-defensin expression, the intestinal mucosal barrier and inflammatory cytokine expression in porcine intestinal epithelial cell lines (IPEC-J2). The results revealed that in IPEC-J2 cells, l-threonine significantly increased the expression of β-defensin (including pBD-1, pBD-2, and pBD-3) in a dose- and time-dependent manner (P < 0.05). By using different concentrations and treatment times of l-threonine, the results showed that the expression of β-defensin was upregulated to the greatest extent in IPEC-J2 cells cultured with 1 mM l-threonine for 24 h. Although the mRNA expression levels of β-defensins were markedly increased (P < 0.05), there was relatively little inducible pBD-1, pBD-2 and pBD-3 mRNA expression at the sub-confluent and confluent densities in comparison with post-confluent densities. Furthermore, we found that l-threonine enhanced the β-defensin expression by suppressing the expression of SIRT1, which increased acetylated p65 expression, and activating the NF-κB signaling pathway, which induced the translocation of p65 from the cytoplasm to the nucleus. In addition, l-threonine significantly prevented LPS-induced intestinal mucosal barrier damage by attenuating the decreasing tendency of the mRNA expression of Mucin1 and Mucin2 (P < 0.05). Simultaneously, l-threonine enhanced the expression of β-defensins upon LPS challenge in IPEC-J2 cells (P < 0.05). l-Threonine obviously decreased the mRNA expression of inflammatory cytokines compared to that in untreated cells (P < 0.05). In conclusion, l-threonine can upregulate β-defensin expression and reduce inflammatory cytokine expression in IPEC-J2 cells; meanwhile, l-threonine alleviates LPS-induced intestinal mucosal barrier damage in porcine intestinal epithelial cells. The l-threonine-mediated modulation of endogenous defensin expression may be a promising approach to reduce antibiotic use, enhance disease resistance and intestinal health in animals.

Avian host defense cathelicidins: structure, expression, biological functions, and potential therapeutic applications

Host defense peptides (HDP) are multifunctional effectors of the innate immune system, which has antimicrobial and pleiotropic immunomodulatory functions. Although there is a very sophisticated superposition of adaptive immune systems in vertebrates, this system is still essential. As an important family of HDP, cathelicidins are also known for their broad-spectrum antibacterial activity against bacteria, fungi, and enveloped viruses. It has been found in humans and other species, including cattle, pigs, sheep, goats, chickens, rabbits, and some kind of fish. Among them, cathelicidins in birds were described for the first time in 2005. This review focuses on the structure, biological activities, expression, and regulation of avian cathelicidin, especially main effects of host defense cathelicidin on potential therapeutic applications. According to the results obtained both in vitro and in vivo, good perspectives have been opened for cathelicidin. Nevertheless, further studies are needed to better characterize the mechanisms of action underlying the beneficial effects of cathelicidin as novel therapeutic alternatives to antibiotics.

Antibacterial activity of human defensins against Staphylococcus aureus and Escherichia coli

BACKGROUND

The global problem of antibiotic resistance requires the search for and development of new methods of treatment. One of the promising strategies is the use of low doses of antimicrobial peptides, in particular, human defensins HNP-1, hBD-1, and hBD-3, in combination with antibacterial drugs already used in clinical practice. This approach may be used to increase the effectiveness of conventional antibiotics. However, this requires thorough study of the effectiveness of defensins in combination with antibiotics against a large number of bacterial strains with known phenotypes of antibiotic resistance. The aim of this work was to study the antibacterial effect of HNP-1, hBD-1 and hBD-3 in combination with rifampicin or amikacin against clinical isolates of Staphylococcus aureus (n = 27) and Escherichia coli (n = 24) collected from hospitalized patients.

METHODS

The standard checkerboard assay was used to determine minimum inhibitory concentrations (MICs) of antimicrobials. The combined microbicidal effects of two substances (defensin + conventional antibiotic) were assessed by the fractional inhibitory concentration index (FICI).

RESULTS

The highest anti-staphylococcal activity (including methicillin-resistant strains) among defensins was demonstrated by hBD-3 that had MIC of 1 (0.5-4) mg/L (hereinafter, MIC values are presented as median and interquartile range). The MIC of HNP-1 against S. aureus was 4 (2-8) mg/L; the MIC of hBD-1 was 8 (4-8) mg/L. Against E. coli, the most effective was also found to be hBD-3 that had MIC of 4 (4-8) mg/L; the MIC of HNP-1 was 12 (4-32) mg/L. The combinations of HNP-1 + rifampicin and hBD-3 + rifampicin demonstrated synergistic effects against S. aureus. Against E. coli, combinations of HNP-1 + amikacin and hBD-3 + amikacin also showed synergy of action.