In recent years, the number of patients presenting with fungal infections has increased, and the emergence of pathogenic fungi has seriously affected human health and safety. Of the several common pathogenic fungi that occur clinically,
Antimicrobial peptides (AMPs), also known as host defense peptides, are biologically active molecules produced by various organisms as important components of their innate immune response (Yan et al. 2018). AMPs not only have strong antimicrobial efficacy but also have activity against viruses, parasites and tumor cells (Ren et al. 2012; Patnaik et al. 2013; Tindwa et al. 2013). In addition to strong antimicrobial efficacy, AMPs have low hemolytic and cytotoxic activities (Edwards et al. 2016). For example, (Quintana et al. 2014) found that the AMP subtilosin has antiviral and viricidal effects against herpes simplex virus type 2 (HSV-2). (Kovalchuk et al. 2007) showed that a complex of natural cytokines and AMPs (CCAP or Superlymph) inhibits virus proliferation
AMP-17 is encoded by a specific highly expressed gene extracted from the
In this study, the
To better evaluate the antifungal activity of AMP-17, the MICs and MFCs for several common clinical pathogens were determined. MIC and MFC values of AMP-17 against
MIC values of AMP-17 against the fungi species tested.
Peptide | MIC (μg/ml) | ||||
---|---|---|---|---|---|
AMP-17 | 18.75 | 18.75 | 18.75 | 18.75 | 9.375 |
MFC values of AMP-17 against the fungi species tested.
Peptide | MIC (μg/ml) | ||||
---|---|---|---|---|---|
AMP-17 | 37.5 | 37.5 | 37.5 | 37.5 | 18.75 |
Influences of temperature and the number of freeze-thaw times on the antifungal activity of AMP-17.
Temperature (98°C) | Colony count | Temperature (−80°C) | Colony count |
---|---|---|---|
5 | 69.50 ± 4.95** | 1 | (240.50 ± 3.54**) × 102 |
20 | 6.00 ± 2.83** | 2 | (273.50±3.54**) × 102 |
30 | 4.50 ± 2.12** | 4 | (342.00 ± 8.49**) × 102 |
60 | 6.50 ± 0.71** | 6 | (357.00 ± 1.41**) × 102 |
90 | 9.50 ± 3.54** | 8 | (351.50 ± 6.36**) × 102 |
120 | 3.50 ± 0.71** | 10 | (370.50 ± 3.54**) × 102 |
Negative control (ddH2O) | 565900.00 ± 17112.00 | Negative control (ddH2O) | (5507.00 ± 147.08) × 102 |
Note: Compared with ddH2O as a control, ** p < 0.01
With the increase in the incidence of pathogenic fungal infections, antifungal drugs are increasingly being used in clinical practice; however, drug-resistant strains are also gradually increasing, posing a serious health problem (Loeffler and Stevens 2003). Therefore, the development of new natural antifungal drugs has become a hot topic of current research, with research on AMP functions from
(Guo et al. 2017) identified AMP-17 protein as a new AMP, which has a strong antifungal activity against
Although AMP-17 has good antifungal activity against several common clinical pathogenic fungi, its physicochemical properties were not known, which prompted us to carry out the experiments in the current study. It was found that AMP-17 protein had good thermal stability, antifreeze and salt stability; however, its antifungal activity was easily destroyed by protease. Under the action of proteases (trypsin, pepsin and proteinase K), the antifungal activity of AMP-17 protein decreased with time of treatment, to the point when it was lost. (Tang et al. 2015) also found that an AMP was weakened by protease action. It was suggested that under certain temperature conditions, a variety of proteases could hydrolyze the carboxyl-terminal peptide bond of AMP-17 protein, destroying the spatial structure of the protein and leading to loss of antifungal activity; however, the specific mechanisms need further verification. In this study, it was also found that on exposure to a high-temperature environment (98°C) for 5 to 120 minutes, the antifungal activity of AMP-17 did not decrease, but increased. This was in contrast to (Zhang et al. 2017). The reason for the increase in activity of AMP-17 protein against
Cytotoxicity, as measured by human red blood cell hemolysis, is an important factor in new drug development. Hemolysis concentration-50 (HC50), as one of the most commonly used indicators of cytotoxicity, provides strong technical support in the development of new drugs (Konai et al. 2014). At present, although AMPs are expected to be the best substitute for antibiotics, most AMPs still show cell hemolysis, which limits their use as drugs. For example, (Chang et al. 2017) found that the AMP TP4 residue A12I/A15I had a higher hemolytic activity, which may be due to the increased hydrophobicity in the main helix caused by the A12I/A15I mutation, which reduces bacterial outer membrane target protein, OprI, binding, and bactericidal activity, but increases hemolytic activity. The phenomenon is similar to that of (Chen et al. 2005), who also found that the hemolysis of AMP was related to the content of hydrophobic residues. As the hydrophobicity increased, the helicity and self-assembly ability of the AMP also increased. As a new type of potential AMP, the cell hemolysis characteristics of AMP-17 could be key in drug design. Surprisingly, hemolysis by AMP-17 protein was much lower than the prescribed drug hemolysis standard (5%), making it a promising antifungal agent.
In conclusion, AMP-17 protein has extensive antifungal activity against several common pathogens. Besides, it has strong stability and low hemolytic activity. These characteristics make AMP-17 protein an attractive molecule for development and application in medicine.