The Antimicrobial Peptides Human β-Defensins Induce the Secretion of Angiogenin in Human Dermal Fibroblasts

Antimicrobial peptides in bone regeneration: mechanism and potential

INTRODUCTION

Antimicrobial peptides (AMPs) are small-molecule peptides with a unique antimicrobial mechanism. Other notable biological activities of AMPs, including anti-inflammatory, angiogenesis, and bone formation effects, have recently received widespread attention. These remarkable bioactivities, combined with the unique antimicrobial mechanism of action of AMPs, have led to their increasingly important role in bone regeneration.

AREAS COVERED

In this review, on the one hand, we aimed to summarize information about the AMPs that are currently used for bone regeneration by reviewing published literature in the PubMed database. On the other hand, we also highlight some AMPs with potential roles in bone regeneration and their possible mechanisms of action.

EXPERT OPINION

The translation of AMPs to the clinic still faces many problems, but their unique antimicrobial mechanisms and other conspicuous biological activities suggest great potential. An in-depth understanding of the structure and mechanism of action of AMPs will help us to subsequently combine AMPs with different carrier systems and perform structural modifications to reduce toxicity and achieve stable release, which may be a key strategy for facilitating the translation of AMPs to the clinic.

Local Defense Factors in Cleft-Affected Palate in Children before and during Milk Dentition Age: A Pilot Study

One of the most frequent congenital orofacial defects is the cleft lip and palate. Local tissue defense factors are known to be important in immune response and inflammatory and healing processes in the cleft tissue; however, they have only been researched in older children during mixed dentition. Thus, the aim of this study is to assess the distribution of LL-37, CD-163, IL-10, HBD-2, HBD-3, and HBD-4 in children before and during milk dentition. The unique and rare material of palate tissue was obtained from 13 patients during veloplastic surgeries during the time span of 20 years. Immunohistochemistry, light microscopy, semi-quantitative evaluation, and non-parametric statistical analysis were used. A significant decrease in HBD-3 and HBD-4 in the connective tissue was found, as well as several mutual statistically significant and strong correlations between HBD-2, HBD-3, HBD-4, and LL-37. Deficiency of HBD-3 and HBD-4 suggests promotion of chronic inflammation. The scarcity of HBD-4 could be connected to the different signaling pathways of dental pulp cells. Mutual correlations imply changes in the epithelial barrier, amplified healing efficiency, and increased antibacterial line of defense. Deprivation of changes in IL-10 quantity points to possible suppression of the factor. The presence of similar CD-163 immunoreactive substances produced by M2 macrophages was also observed.

Human α-Defensin 51-9 and Human β-Defensin 2 Improve Metabolic Parameters and Gut Barrier Function in Mice Fed a Western-Style Diet

Obesity and metabolic comorbidities are associated with gut permeability. While high-fructose and Western-style diet (WSD) disrupt intestinal barrier function, oral administration of human α-defensin 5 (HD5) and β-defensin 2 (hBD2) is believed to improve intestinal integrity and metabolic disorders. Eighty-four male C57BL/6J mice were fed a WSD or a control diet (CD) ± fructose (F) for 18 weeks. In week 13, mice were randomly divided into three intervention groups, receiving defensin fragment HD51-9, full-length hBD2, or bovine serum albumin (BSA)-control for six weeks. Subsequently, parameters of hepatic steatosis, glucose metabolism, and gut barrier function were assessed. WSDF increased body weight and hepatic steatosis (p < 0.01) compared to CD-fed mice, whereas peptide intervention decreased liver fat (p < 0.05) and number of hepatic lipid droplets (p < 0.01) compared to BSA-control. In addition, both peptides attenuated glucose intolerance by reducing blood glucose curves in WSDF-fed mice. Evaluation of gut barrier function revealed that HD51-9 and hBD2 improve intestinal integrity by upregulating tight junction and mucin expression. Moreover, peptide treatment restored ileal host defense peptides (HDP) expression, likely by modulating the Wnt, Myd88, p38, and Jak/STAT pathways. These findings strongly suggest that α- and β-defensin treatment improve hepatic steatosis, glucose metabolism, and gut barrier function.

The immune function of dermal fibroblasts in skin defence against pathogens

Dermal fibroblasts are the main resident cells of the dermis. They have several significant functions related to wound healing, extracellular matrix production and hair cycling. Dermal fibroblasts can also act as sentinels in defence against infection. They express pattern recognition receptors such as toll-like receptors to sense pathogen components, followed by the synthesis of pro-inflammatory cytokines (including IL-6, IFN-β and TNF-α), chemokines (such as IL-8 and CXCL1) and antimicrobial peptides. Dermal fibroblasts also secrete other molecules-like growth factors and matrix metalloproteinases to benefit tissue repair from infection. Crosstalk between dermal fibroblasts and immune cells may amplify the immune response against infection. Moreover, the transition of a certain adipogenic fibroblasts to adipocytes protects skin from bacterial infection. Together, we discuss the role of dermal fibroblasts in the war against pathogens in this review. Dermal fibroblasts have important immune functions in anti-infection immunity, which should not be overlooked.

Antimicrobial Peptides and Interleukins in Cleft Soft Palate

Cleft palate is one of the most common and well-studied congenital anomalies; however, the role of protective tissue factors in its pathophysiology is still debated. The aim of our study was to evaluate interleukin and antimicrobial peptide appearance and distribution in cleft palate. Eight soft palate samples were obtained during veloplasty procedures. Immunohistochemical staining was applied to detect HBD-2-, HBD-3-, HBD-4-, LL-37-, IL-10-, and CD-163-positive cells via light microscopy. For statistical evaluation, the Mann-Whitney U test and Spearman's rank correlation coefficient were used. A significant difference between study groups was observed for HBD-2 and IL-10 in epithelial and connective tissue as well as HBD-4 in connective tissue. The number of HBD-3-positive cells was moderate in the patients, and few were observed in the controls. The number of LL-37-positive cells varied from a moderate amount to a numerous amount in both study groups, whilst CD-163 marked a moderate number of positive cells in patients, and a few-to-moderate amount was observed in the controls. Numerous correlations between studied factors were revealed in cleft tissues. The increase in antimicrobial peptides HBD-2 and HBD-4 and anti-inflammatory cytokine IL-10 suggested a wide compensatory elevation of the local immune system against cleft-raised tissue changes. The correlations between the studied factors (HBD-2, HBD-3, HBD-4, LL-37, and IL-10) proved the synergistic involvement of common local defense factors in postnatal cleft palate morphopathogenesis.

Antibacterial peptides-loaded bioactive materials for the treatment of bone infection

Bacterial bone infection in open fractures is an urgent problem to solve in orthopedics. Antimicrobial peptides (AMPs), as a part of innate immune defense, have good biocompatibility. Their antibacterial mechanism and therapeutic application against bacteria have been widely studied. Compared with traditional antibiotics, AMPs do not easily cause bacterial resistance and can be a reliable substitute for antibiotics in the future. Therefore, various physical and chemical strategies have been developed for the combined application of AMPs and bioactive materials to infected sites, which are conducive to maintaining the local stability of AMPs, reducing many complications, and facilitating bone infection resolution. This review explored the molecular structure, function, and direct and indirect antibacterial mechanisms of AMPs, introduced two important AMPs (LL-37 and β-defensins) in bone tissues, and reviewed advanced AMP loading strategies and different bioactive materials. Finally, the latest progress and future development of AMPs-loaded bioactive materials for the promotion of bone infection repair were discussed. This study provided a theoretical basis and application strategy for the treatment of bone infection with AMP-loaded bioactive materials.

Role of defensins in diabetic wound healing

The adverse consequences resulting from diabetes are often presented as severe complications. Diabetic wounds are one of the most commonly occurring complications in diabetes, and the control and treatment of this is costly. Due to a series of pathophysiological mechanisms, diabetic wounds remain in the inflammatory phase for a prolonged period of time, and face difficulty in entering the proliferative phase, thus leading to chronic non-healing wounds. The current consensus on the treatment of diabetic wounds is through multidisciplinary comprehensive management, however, standard wound treatment methods are still limited and therefore, more effective methods are required. In recent years, defensins have been found to play diverse roles in a variety of diseases; however, the molecular mechanisms underlying these activities are still largely unknown. Defensins can be constitutively or inductively produced in the skin, therefore, their local distribution is affected by the microenvironment of these diabetic wounds. Current evidence suggests that defensins are involved in the diabetic wound pathogenesis, and can potentially promote the early completion of each stage, thus making research on defensins a promising area for developing novel treatments for diabetic wounds. In this review, we describe the complex function of human defensins in the development of diabetic wounds, and suggest potential thera-peutic benefits.