Hydrophobicity Determines the Bacterial Killing Rate of α-Helical Antimicrobial Peptides and Influences the Bacterial Resistance Development.

Rapid antimicrobial action is an important advantage of antimicrobial peptides (AMPs) over antibiotics, which is also a reason for AMPs being less likely to induce bacterial resistance. However, the structural parameters and underlying mechanisms affecting the bacterial killing rate of AMPs remain unknown. In this study, we performed a structure-activity relationship (SAR) study using As-CATH4 and 5 as templates. We revealed that hydrophobicity, rather than other characteristics, is the critical structural parameter determining the bacterial killing rate of α-helical AMPs. With the hydrophobicity increase, the action rates of AMPs including bacterial binding, lipopolysaccharides neutralization, and outer and inner membrane permeabilization increased. Additionally, the higher hydrophobic AMPs with enhanced bacterial killing rates possess better in vivo therapeutic potency and a lower propensity to induce bacterial resistance. These findings revealed the importance of the bacterial killing rate for AMPs and are of great significance to the design and optimization of AMP-related drugs.

Antimicrobial peptides, conventional antibiotics, and their synergistic utility for the treatment of drug-resistant infections.

Antimicrobial peptides (AMPs), also known as host defense peptides (HDPs), are important effector immune defense molecules in multicellular organisms. AMPs exert their antimicrobial activities through several mechanisms; thus far, induction of drug resistance through AMPs has been regarded as unlikely. Therefore, they have great potential as new generation antimicrobial agents. To date, more than 30 AMP-related drugs are in the clinical trial phase. In recent years, studies show that some AMPs and conventional antibiotics have synergistic effects. The combined use of AMPs and antibiotics can kill drug-resistant pathogens, prevent drug resistance, and significantly improve the therapeutic effects of antibiotics. In this review, we discuss the progress in synergistic studies on AMPs and conventional antibiotics. An overview of the current understanding of the functional scope of AMPs, ongoing clinical trials, and challenges in the development processes are also presented.

Defensing role of novel piscidins from largemouth bass (Micropterus salmoides) with evidence of bactericidal activities and inducible expressional delineation.

Micropterus salmoides is an economical important species of freshwater-cultured fish, the in-depth knowledge of its immune system is in urgent development to cope with serious infectious diseases. Piscidin is an important antimicrobial peptide (AMP) family existing in almost all teleosts. However, no piscidin has been reported in largemouth bass. In this study, three novel piscidins (MSPiscidin-1, -2, and -3) were firstly identified and characterized from the largemouth bass. The predicted mature peptides of MSPiscidin-1, -2, and -3 (consists of 24, 27, 25 amino acid residues, respectively) all adopted an amphipathic α-helical conformation representative of cationic AMPs that are important for membrane permeabilization and antibacterial activity. MSPiscidin-2 and -3 indeed displayed strong, broad-spectrum, and highly efficient antimicrobial activities in vitro against aquatic pathogens, but MSPiscidin-1 didn't show direct antimicrobial activity. MSPiscidin-2 and -3 killed bacteria mainly by inducing membrane permeabilization, in addition, they also can interact with bacterial genomic DNA, which might influence the DNA replication and transcription. Besides, MSPiscidin-2 and -3 could effectively inhibit the formation of the bacterial biofilm and eliminate the preformed biofilms. In vivo, MSPiscidin-1-3 genes showed an inducible expression pattern in the tested tissues upon Vibrio harveyi infection, which further indicated the key roles of piscidins in innate immunity in largemouth bass. Overall, this study will supplement the understanding of M. salmoides innate immune system and provide candidates for the design of novel peptide antibacterial agents used in aquaculture.

A novel anionic cathelicidin lacking direct antimicrobial activity but with potent anti-inflammatory and wound healing activities from the salamander Tylototriton kweichowensis.

Cathelicidin is a family of antimicrobial peptides (AMPs) existing in vertebrates, which play multiple functions in host responses against environmental stresses. All cathelicidins identified to date are cationic, no anionic member with net negative charges has been reported. In the present study, a novel anionic cathelicidin (TK-CATH) with a net charge of -3 was identified from the skin of the salamander, T. kweichowensis. Unlike most other cathelicidin members, it didn't exhibit direct antimicrobial activity. However, it demonstrated strong anti-inflammatory activity. It effectively inhibited the LPS-induced pro-inflammatory cytokine gene expression and protein production in amphibian leukocytes and mouse macrophages by inhibiting the LPS-activated mitogen-activated protein kinase (MAPK) signaling pathways. Besides, TK-CATH showed potent wound healing activity. It could effectively induce the production of several cytokines, chemokines and growth factors relating to wound healing, promote the motility and proliferation of keratinocytes, and accelerate the skin wound healing in a mouse full-thickness wound model. These results imply that TK-CATH participates in both the inflammatory phase and new tissue formation phase of wound repair process. Meanwhile, TK-CATH exhibited weak but effective free radical scavenging activity and low cytotoxicity. All the results above indicate that TK-CATH is a multifunctional peptide in the skin of the salamander T. kweichowensis. It may play important roles in host immune responses against bacterial infection and skin wound repair.

Identification and characterization of novel bi-functional cathelicidins from the black-spotted frog (Pelophylax nigromaculata) with both anti-infective and antioxidant activities.

Cathelicidins are an important family of antimicrobial peptides (AMPs), which play pivotal roles in vertebrate immune responses against microbial infections. They are regarded as potential drug leads for the development of novel antimicrobial agents and three related drugs have been developed into clinical trials. Thus, it is meaningful to identify more cathelicidins from vertebrate species. Cathelicidins from ranid frogs possess special structural characteristics and activities, but to date only 12 ranid frog cathelicidins have been identified. In the present study, two novel cathelicidins (PN-CATH1 and 2) were identified from the black-spotted frog, Pelophylax nigromaculata. PN-CATHs possess low sequence similarity with the known cathelicidins. They exhibited moderate, but broad-spectrum and rapid antimicrobial activities against the tested bacteria. They kill bacteria by mainly inducing bacterial membrane disruption and possibly generating intracellular ROS formation. They also possess potent anti-biofilm and persister cell killing activity, indicating their potential in combating infections induced by biofilms-forming bacteria. Besides direct antimicrobial activity, they exhibited potent anti-inflammatory activity by effectively inhibiting the LPS-induced production of pro-inflammatory cytokines in mouse macrophages, which could be partly ascribed to their direct LPS-neutralizing ability. Furthermore, PN-CATHs demonstrated powerful in vitro free radical scavenging activities. Ultraviolet radiation significantly increased their in vivo gene expression in frog skin. Meanwhile, they possess weak cytotoxic activity and extremely low hemolytic activity. PN-CATHs represent the first discovery of cathelicidins family AMPs with both potent anti-infective and antioxidant activities. The discovery of PN-CATHs provides potential peptide leads for the development of novel anti-infective and antioxidant drugs.

Design of a Sea Snake Antimicrobial Peptide Derivative with Therapeutic Potential against Drug-Resistant Bacterial Infection.

Infections caused by drug-resistant pathogens are a worldwide challenge for public health. Antimicrobial peptides (AMPs) are regarded as promising antibiotic alternatives for the treatment of drug-resistant infections. In the present study, a series of small peptides were designed based on our previously reported sea snake AMP Hc-CATH. From them, the lead peptide HC1-D2, a truncated peptide entirely substituted by d-amino acids, was selected. HC1-D2 exhibited significantly improved stability and antibiofilm and anti-inflammatory activities. Meanwhile, HC1-D2 retained potent, broad-spectrum, and rapid antimicrobial properties against bacteria and fungi, especially drug-resistant bacteria. Moreover, HC1-D2 showed low propensity to induce bacterial resistance and low cytotoxicity and hemolytic activity. Notably, HC1-D2 showed potent in vivo anti-infective ability in mouse peritonitis models infected by both standard and drug-resistant bacteria. It significantly decreased the bacterial counts in the abdominal cavity and spleen of mice and apparently increased the survival rates of the mice. Acting through the MAPKs inflammatory pathway, HC1-D2 selectively induced the production of chemokine and the subsequent immune cell recruitment to the infection site, while inhibiting the production of pro-inflammatory cytokines with undesirable toxicities. These much improved properties make HC1-D2 a promising candidate for the development of novel peptide anti-infective agents against drug-resistant infections.

TCM treatment for 40 cases of rheumatoid arthritis with channel blockage due to yin deficiency.

To verify the therapeutic effects of the method of softening and lubricating the joints, and calming the endogenous wind in case of rheumatoid arthritis (RA) with the syndrome of channel blockage due to yin deficiency, 60 RA patients with the syndrome of channel blockage due to yin deficiency were randomly divided into a treatment group (40 cases) and a control group (20 cases) and treated respectively by the above method for the former and with Zheng Qing Feng Tong Ning Tablets ([symbol: see text]) for the latter. The result turned out to be that the effect in the treatment group was very satisfying. The treatment group obtained a better result in the accumulated points of syndrome and RA, morning rigidity of the joints, grip strength, 20m walking time and erythrocyte sedimentation rate (ESR) (P < 0.01 or P < 0.05). The above indicates that channel blockage due to yin deficiency is an important pathogenesis of RA, and calming the endogenous wind is a method of choice for treating RA.