Two arginine residues in the COOH-terminal of human β-defensin-3 constitute an essential motif for antimicrobial activity and IL-6 production

Efficient titanium surface modified using bifunctional chimeric peptides to prevent biofilm formation by multiple microorganisms

It is still a challenge to prevent the formation of bacterial biofilms on the surfaces of oral implants. A chemical peptide with binding and antibacterial properties may be a promising agent if used to modify titanium (Ti) surfaces to inhibit biofilm formation. In this study, peptides were designed by linking the antimicrobial sequence derived from human β-defensin-3 (hBD-3) to the Ti-binding peptide-1 (TBP-1) sequence by using a triple glycine (G) linker. The antimicrobial activity and biocompatibility characteristics of the chemical-peptide-modified Ti surface were then evaluated and the potential antibacterial mechanism was investigated. This study demonstrated that the chemical-peptide-modified surface exhibited satisfactory bactericidal activities against Streptococcus gordonii, Fusobacterium nucleatum, and Porphyromonas gingivalis. In addition to its potent bacteria-killing efficacy, the surface-immobilised chemical peptide also demonstrated excellent biocompatibility to L929 cells. Moreover, the disruption of the integrity of the bacterial membrane partially revealed the antibacterial mechanism of the peptide. This study demonstrated the potential of chemical-peptide-modified Ti surfaces for preventing the occurrence of peri-implant diseases, thereby providing a promising approach to improving the survival rate of oral implants.

The C-Terminus of Panusin, a Lobster β-Defensin, Is Crucial for Optimal Antimicrobial Activity and Serum Stability

β-defensins are one of the most abundant and studied families of antimicrobial peptides (AMPs). Because of their selective toxicity to bacterial membranes and a broad spectrum of microbicidal action, β-defensins are regarded as potential therapeutic agents. This work focuses on a β-defensin-like AMP from the spiny lobster Panulirus argus (hereafter referred to as panusin or PaD). This AMP is structurally related to mammalian defensins via the presence of an αβ domain stabilized by disulfide bonds. Previous studies of PaD suggest that its C-terminus (Ct_PaD) contains the main structural determinants of antibacterial activity. To confirm this hypothesis, we made synthetic versions of PaD and Ct_PaD to determine the influence of the C-terminus on antimicrobial activity, cytotoxicity, proteolytic stability, and 3D structure. After successful solid-phase synthesis and folding, antibacterial assays of both peptides showed truncated Ct_PaD to be more active than native PaD, confirming the role of the C-terminus in activity and suggesting that cationic residues in that region enhance binding to negatively charged membranes. On the other hand, neither PaD nor Ct_PaD were hemolytic or cytotoxic in human cells. Proteolysis in human serum was also studied, showing high (>24 h) t_1/2 values for PaD and lower but still considerable for Ct_PaD, indicating that the missing native disulfide bond in Ct_PaD alters protease resistance, albeit not decisively. NMR-2D experiments in water agree with the results obtained by circular dichroism (CD), where in SDS micelles, CD showed both peptides adopting an increasingly ordered structure in a hydrophobic environment, in tune with their ability to perturb bacterial membrane systems. In conclusion, while the β-defensin features of PaD are confirmed as advantageous in terms of antimicrobial activity, toxicity, and protease stability, the results of the present work suggest that these same features are preserved, even enhanced, in the structurally simpler Ct_PaD, which must therefore be viewed as a valuable lead for the development of novel anti-infectives.

Structure-activity relationships of antibacterial peptides

Antimicrobial peptides play a crucial role in innate immunity, whose components are mainly peptide-based molecules with antibacterial properties. Indeed, the exploration of the immune system over the past 40 years has revealed a number of natural peptides playing a pivotal role in the defence mechanisms of vertebrates and invertebrates, including amphibians, insects, and mammalians. This review provides a discussion regarding the antibacterial mechanisms of peptide-based agents and their structure-activity relationships (SARs) with the aim of describing a topic that is not yet fully explored. Some growing evidence suggests that innate immunity should be strongly considered for the development of novel antibiotic peptide-based libraries. Also, due to the constantly rising concern of antibiotic resistance, the development of new antibiotic drugs is becoming a priority of global importance. Hence, the study and the understanding of defence phenomena occurring in the immune system may inspire the development of novel antibiotic compound libraries and set the stage to overcome drug-resistant pathogens. Here, we provide an overview of the importance of peptide-based antibacterial sources, focusing on accurately selected molecular structures, their SARs including recently introduced modifications, their latest biotechnology applications, and their potential against multi-drug resistant pathogens. Last, we provide cues to describe how antibacterial peptides show a better scope of action selectivity than several anti-infective agents, which are characterized by non-selective activities and non-targeted actions toward pathogens.

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.

Thinking on the Construction of Antimicrobial Peptide Databases: Powerful Tools for the Molecular Design and Screening

With the accelerating growth of antimicrobial resistance (AMR), there is an urgent need for new antimicrobial agents with low or no AMR. Antimicrobial peptides (AMPs) have been extensively studied as alternatives to antibiotics (ATAs). Coupled with the new generation of high-throughput technology for AMP mining, the number of derivatives has increased dramatically, but manual running is time-consuming and laborious. Therefore, it is necessary to establish databases that combine computer algorithms to summarize, analyze, and design new AMPs. A number of AMP databases have already been established, such as the Antimicrobial Peptides Database (APD), the Collection of Antimicrobial Peptides (CAMP), the Database of Antimicrobial Activity and Structure of Peptides (DBAASP), and the Database of Antimicrobial Peptides (dbAMPs). These four AMP databases are comprehensive and are widely used. This review aims to cover the construction, evolution, characteristic function, prediction, and design of these four AMP databases. It also offers ideas for the improvement and application of these databases based on merging the various advantages of these four peptide libraries. This review promotes research and development into new AMPs and lays their foundation in the fields of druggability and clinical precision treatment.

Recombinant human β-defensin130 inhibited the growth of foodborne bacteria through membrane disruption and exerted anti-inflammatory activity

Foodborne pathogens causing food poisoning and infections are detrimental to human health, and the abuse of antibiotics induced severe antibiotic resistance in past decades. Thus, it is urgent to develop new antimicrobial agents. In the current study, human β-defensin 130 (hBD130), which is an antimicrobial peptide identified in human macrophages in 2017, was initially produced in Pichia pastoris. The purified hBD130 demonstrated broad bactericidal spectrum against foodborne pathogens through a membrane disruption, with concentrations ranging from 10 to 45 μg/mL. Moreover, hBD130 showed a low hemolytic effect and nearly no cytotoxicity to mammalian cells with a dosage of 400 μg/mL. In addition, the secretion amounts and mRNA levels of NO, IL-6, IL-1β, and TNF-α in LPS-induced mouse macrophage were significantly decreased with 1 mg/mL of hBD130. Taken together, these results showed that hBD130 is a promising antimicrobial agent to treat foodborne bacterial infections and inflammation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-022-01087-y.

Identification of a crocodylian β-defensin variant from Alligator mississippiensis with antimicrobial and antibiofilm activity

β-defensin host defense peptides are important components of the innate immune system of vertebrates. Although evidence of their broad antimicrobial, antibiofilm and immunomodulatory activities in mammals have been presented, β-defensins from other vertebrate species, like crocodylians, remain largely unexplored. In this study, five new crocodylian β-defensin variants from Alligator mississippiensis and Crocodylus porosus were selected for synthesis and characterization based on their charge and hydrophobicity values. Linear peptides were synthesized, folded, purified and then evaluated for their antimicrobial and antibiofilm activities against the bacterial pathogens, Salmonella enterica serovar Typhimurium, Staphylococcus aureus, Enterobacter cloacae and Acinetobacter baumannii. The Am23SK variant (SCRFSGGYCIWNWERCRSGHFLVALCPFRKRCCK) from A. mississippiensis displayed promising activity against both planktonic cells and bacterial biofilms, outperforming the human β-defensin 3 under the experimental conditions. Moreover, Am23SK exhibited no cytotoxicity towards mammalian cells and exerted immunomodulatory effects in vitro, moderately suppressing the production of proinflammatory mediators from stimulated human bronchial epithelial cells. Overall, our results have expanded the activity landscape of crocodylian and reptilian β-defensin in general.

A Chimeric Cationic Peptide Composed of Human β-Defensin 3 and Human β-Defensin 4 Exhibits Improved Antibacterial Activity and Salt Resistance

Human beta-defensins (hBDs) play an important role in the host defense against various microbes, showing different levels of antibacterial activity and salt resistance in vitro. It is of interest to investigate whether can chimeric hBD analogs enhanced antibacterial activity and salt resistance. In this study, we designed a chimeric human defensin, named H4, by combining sequences of human beta-defensin-3 (hBD-3) and human beta-defensin-4 (hBD-4), then evaluated its antibacterial activity, salt resistance, and cytotoxic effects. The result showed that the antibacterial activity of H4 against most tested strains, including Klebsiella pneumonia, Enterococcus faecalis, Staphyloccocus aureus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumonia, and Acinetobacter baumannii was significantly improved compared to that of hBD-3 and hBD-4. Notably, H4 exhibited significantly better antibacterial activity against multidrug resistant isolate A. baumannii MDR-ZJ06 than commonly used antibiotics. Chimeric H4 still showed more than 80% antibacterial activity at high salt concentration (150 μM), which proves its good salt tolerance. The cytotoxic effect assay showed that the toxicity of H4 to Hela, Vero, A549 cells and erythrocytes at a low dose (<10 μg/ml) was similar to that of hBD-3 and hBD-4. In conclusion, given its broad spectrum of antibacterial activity and high salt resistance, chimeric H4 could serve as a promising template for new therapeutic antimicrobial agents.

Beta defensin 3 enhances ovarian granulosa cell proliferation and migration via ERK1/2 pathway in vitro†

Antimicrobial peptides (AMPs) are regarded as host defense peptides that possess bactericidal activity as well as immunomodulatory function. However, the role of AMP in the mammalian ovary is unknown. In the present study, porcine granulosa cells were utilized in a cell model to study the role of porcine beta defensin 2 (pBD2; pDEFB4B) and 3 (pBD3; pDEFB103A) during ovarian follicular development. Granulosa cells were cultured in the absence and presence of 1, 10, and 50 μg/ml of pDEFB4B or pDEFB103A. After 24 h of treatment, pDEFB103A but not pDEFB4B stimulated granulosa cell proliferation in a concentration-dependent manner (P < 0.05). This effect was dependent on the stage of follicular development. In addition, transwell cell migration assay showed that in the presence of pDEFB103A (10 μg/ml), a 2.5-fold increase in cell migration was achieved. Furthermore, further study revealed that pDEFB103A increased the mRNA levels of cyclin D1 (CCND1) and proliferating cell nuclear antigen (PCNA), both associated with cell proliferation. To study the potential pathway involved in pDEFB103A-induced cell proliferation and migration, western blots were performed. It was found that pDEFB103A significantly increased the phosphorylated-ERK1/2 to nonphosphorylated ratio. Moreover, pretreatment with the U0126, a specific ERK1/2 phosphorylation inhibitor, suppressed PDEFB103A inducing GCs ERK1/2 phosphorylation, as well as proliferation and migration, suggesting that PDEFB103A may act via activating the ERK1/2 pathway. Furthermore, using a signal transduction pathway Elk-1 trans-reporting system, the activation of ERK1/2 pathway by PDEFB103A was further confirmed. Our data suggest that AMP may play a physiological role in the mammalian ovary.

Effect of Bifunctional β Defensin 2-Modified Scaffold on Bone Defect Reconstruction

Bone tissue engineering has emerged as an effective alternative treatment to the problem of bone defect. To repair a bone defect, antibiosis and osteogenesis are two essential aspects of the repair process. By searching the literature and performing exploratory experiments, we found that β defensin 2 (BD2), with bifunctional properties of antibiosis and osteogenesis, was a feasible alternative for traditional growth factors. The antimicrobial ability of BD2 against Staphylococcus aureus and Escherichia coli was studied by the spread plate and live/dead staining methods (low effective concentration of 20 ng/mL). BD2 was also demonstrated to enhance osteogenesis, with higher messenger RNA (mRNA) and protein expression of the osteogenic markers collagen I (Col1), runt-related transcription factor 2 (Runx2), osteopontin (Opn), and osteocalcin (Ocn) in vitro (1.5-2.5-fold increase compared with the control group in the most effective concentration group), which was consistent with the alkaline phosphatase (ALP) and alizarin red S (ARS) staining results. We implanted poly(sebacoyl diglyceride) (PSeD) combined with BD2 and rat bone tissue-derived mesenchymal stem cells (rBMSCs) under the back skin of rats and found that the inflammatory response was significantly lower with this combination than with the PSeD/rBMSCs scaffold without BD2 and the pure PSeD group and was similar to the control group. Importantly, when assessed in a critical-sized in vivo rat 8 m diameter calvaria defect model, a scaffold we developed combining bifunctional BD2 with porous organic polymer displayed an osteogenic effect that was 160-200% greater than the control group. The in vivo study results revealed a significant osteogenic response and antimicrobial effect and were consistent with the in vitro results. In summary, BD2 displayed a great potential of simultaneously promoting bone regeneration and preventing infection and could provide a viable alternative to traditional growth factors applied in bone defect repair.

Modification of the surface of titanium with multifunctional chimeric peptides to prevent biofilm formation via inhibition of initial colonizers

Background

Prevention of bacterial colonization remains a major challenge in the field of oral implant devices. Chimeric peptides with binding, antimicrobial, and osteogenesis motifs may provide a promising alternative for the inhibition of biofilm formation on titanium (Ti) surfaces.

Methods

In this study, chimeric peptides were designed by connecting an antimicrobial sequence from human β-defensin-3 with a Ti-binding sequence and arginine-glycine-aspartic acid using a glycine-glycine-glycine linker. Binding to the Ti substrate and antimicrobial properties against streptococci were evaluated. Significant improvement in reduction of bacterial colonization onto the Ti surface was observed, with or without the presence of saliva or serum. The MC3T3-E1 cells grew well on the modified Ti surfaces compared with the control group.

Results

The data showed that the three peptide functional motifs maintained their respective functions, and that the antibiofilm mechanism of the chimeric peptide was via suppression of sspA and sspB gene expression.

Conclusion

These results indicated that the endogenous peptide fragments engineered on the Ti surface could provide an environmentally friendly approach for improving the biocompatibility of oral implants.

Engineered chimeric peptides with antimicrobial and titanium-binding functions to inhibit biofilm formation on Ti implants

Titanium (Ti) implants have been commonly used in oral medicine. However, despite their widespread clinical application, these implants are susceptible to failure induced by microbial infection due to bacterial biofilm formation. Immobilization of chimeric peptides with antibacterial properties on the Ti surface may be a promising antimicrobial approach to inhibit biofilm formation. Here, chimeric peptides were designed by connecting three sequences (hBD-3-1/2/3) derived from human β-defensin-3 (hBD-3) with Ti-binding peptide-l (TBP-l: RKLPDAGPMHTW) via a triple glycine (G) linker to modify Ti surfaces. Using X-ray photoelectron spectroscopy (XPS), the properties of individual domains of the chimeric peptides were evaluated for their binding activity toward the Ti surface. The antimicrobial and anti-biofilm efficacy of the peptides against initial settlers, Streptococcus oralis (S. oralis), Streptococcus gordonii (S. gordonii) and Streptococcus sanguinis (S. sanguinis), was evaluated with confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Transmission electron microscopy (TEM) and real-time quantitative PCR (qRT-PCR) were used to study cell membrane changes and the underlying antimicrobial mechanism. Compared with the other two peptides, TBP-1-GGG-hBD3-3 presented stronger antibacterial activity and remained stable in saliva and serum. Therefore, it was chosen as the best candidate to modify Ti surfaces in this study. This peptide inhibited the growth of initial streptococci and biofilm formation on Ti surfaces with no cytotoxicity to MC3T3-E1 cells. Disruption of the integrity of bacterial membranes and decreased expression of adhesion protein genes from S. gordonii revealed aspects of the antibacterial mechanism of TBP-1-GGG-hBD3-3. We conclude that engineered chimeric peptides with antimicrobial activity provide a potential solution for inhibiting biofilm formation on Ti surfaces to reduce or prevent the occurrence of peri-implant diseases.