Enantiomeric 9‐mer peptide analogs of protaetiamycine with bacterial cell selectivities and anti‐inflammatory activities

Protaetiamycine is an insect defensin, derived from the larvae of the beetle Protaetia brevitarsis. In our previous work, we designed 9‐mer peptide analogs of protaetiamycine, including 9Pbw2 (RLWLAIKRR‐NH₂), 9Pbw3 (RLWLAIWRR‐NH₂), and 9Pbw4 (RLWLAWKRR‐NH₂). 9Pbw2 and 9Pbw4 showed high antimicrobial activity without cytotoxicity, while 9Pbw3 with higher hydrophobicity compared to 9Pbw2 and 9Pbw4 showed high cytotoxicity as well as high antimicrobial activity (Shin et al., J. Pept. Sci. 2009; 15: 559–568). In this study, we investigated the anti‐inflammatory activities of 9Pbw2, 9Pbw3, and 9Pbw4 by quantitation of NO production in LPS‐stimulated RAW264.7 cells. The results showed that only 9Pbw3 has strong inhibition of NO production, implying that Trp⁷ as well as optimum level of hydrophobicity may play key roles in the anti‐inflammatory activity of 9Pbw3. In order to design potent anti‐inflammatory peptide with lower cytotoxicity as well as high stability from cleavage by protease compared to 9Pbw3, we synthesized 9Pbw3‐D , the all‐D ‐amino acid analog of 9Pbw3. 9Pbw3‐D showed less cytotoxicity against RAW264.7 cells as well as considerably stronger inhibition of NO production and inflammation‐induced cytokine production in LPS‐stimulated RAW264.7 cells than 9Pbw3. 9Pbw3‐D inhibited the gene expression of inflammatory‐induced cytokine significantly more than 9Pbw3 and showed high resistance to proteolytic digestion. Binding of 9Pbw3‐D with LPS caused higher enhancement of the FITC fluorescence as a result of its stronger interaction with LPS compared to that of 9Pbw3 and this result is in good agreement with their anti‐inflammatory activities. 9Pbw3‐D with higher anti‐inflammatory activity as well as lower cytotoxicity against mammalian cell compared to 9Pbw3 can be a potent noncytotoxic antibiotic candidates. Copyright © 2011 European Peptide Society and John Wiley & Sons, Ltd.     

Effects of arginine and leucine substitutions on anti‐endotoxic activities and mechanisms of action of cationic and amphipathic antimicrobial octadecapeptide from rice α‐amylase

Previously, we showed that the antimicrobial cationic and amphipathic octadecapeptide AmyI‐1‐18 from rice α‐amylase (AmyI‐1) inhibited the endotoxic activity of lipopolysaccharide (LPS) from Escherichia coli. In addition, we demonstrated that several AmyI‐1‐18 analogs containing arginine or leucine substitutions, which were designed on the basis of the helical wheel projection of AmyI‐1‐18, exhibited higher antimicrobial activity against human pathogenic microorganisms than AmyI‐1‐18. In the present study, anti‐inflammatory (anti‐endotoxic) activities of five AmyI‐1‐18 analogs containing arginine or leucine substitutions were investigated. Two single arginine‐substituted and two single leucine‐substituted AmyI‐1‐18 analogs inhibited the production of LPS‐induced nitric oxide in mouse macrophages (RAW264) more effectively than AmyI‐1‐18. These data indicate that enhanced cationic and hydrophobic properties of AmyI‐1‐18 are associated with improved anti‐endotoxic activity. In subsequent chromogenic Limulus amebocyte lysate assays, 50% inhibitory concentrations (IC₅₀) of the three AmyI‐1‐18 analogs (G12R, D15R, and E9L) were 0.11–0.13 μm , indicating higher anti‐endotoxic activity than that of AmyI‐1‐18 (IC_50, 0.22 μm ), and specific LPS binding activity. In agreement, surface plasmon resonance analyses confirmed direct LPS binding of three AmyI‐1‐18 analogs. In addition, AmyI‐1‐18 analogs exhibited little or no cytotoxic activity against RAW264 cells, indicating that enhancements of anti‐inflammatory and LPS‐neutralizing activities following replacement of arginine or leucine did not result in significant increases in cytotoxicity. This study shows that the arginine‐substituted and leucine‐substituted AmyI‐1‐18 analogs with improved anti‐endotoxic and antimicrobial activities have clinical potential as dual‐function host defense agents. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.     

Enhancement of the anti‐inflammatory activity of temporin‐1Tl‐derived antimicrobial peptides by tryptophan,arginine and lysine substitutions

Temporin‐1Tl (TL) is a 13‐residue frog antimicrobial peptide (AMP) exhibiting potent antimicrobial and anti‐inflammatory activity. To develop novel AMP with improved anti‐inflammatory activity and antimicrobial selectivity, we designed and synthesized a series of TL analogs by substituting Trp, Arg and Lys at selected positions. Except for Escherichia coli and Staphylococcus epidermidis, all TL analogs exhibited retained or increased antimicrobial activity against seven bacterial strains including three methicillin‐resistant Staphylococcus aureus strains compared with TL. TL‐1 and TL‐4 showed a little increase in antimicrobial selectivity, while TL‐2 and TL‐3 displayed slightly decreased antimicrobial selectivity because of their about twofold increased hemolytic activity. All TL analogs demonstrated greatly increased anti‐inflammatory activity, evident by their higher inhibition of the production tumor necrosis factor‐α (TNF‐α) and nitric oxide and the mRNA expression of inducible nitric oxide synthase and TNF‐α in lipopolysaccharide (LPS)‐stimulated RAW264.7 macrophage cells, compared with TL. Taken together, the peptide anti‐inflammatory activity is as follows: TL‐2 ≈ TL‐3 ≈ TL‐4 > TL‐1 > TL. In addition, LPS binding ability of the peptides corresponded with their anti‐inflammatory activity. These results apparently suggest that the anti‐inflammatory activity of TL analogs is associated with the direct binding ability between these peptides and LPS. Collectively, our designed TL analogs possess improved anti‐inflammatory activity and retain antimicrobial activity without a significant increase in hemolysis. Therefore, it is evident that our TL analogs constitute promising candidates for the development of peptide therapeutics for gram‐negative bacterial infection. Copyright © 2015 European Peptide Society and John Wiley & Sons, Ltd.     

Antibacterial activity of bactenecin 5 fragments and their interaction with phospholipid membranes.

Bactenecin 5 (Bac 5) is an antibacterial 43mer peptide isolated from bovine neutrophils. It consists of an Arg-rich N-terminal region and successive repeats of Arg-Pro-Pro-Ile (or Phe). We synthesized Bac 5(1-23) and several related peptides to clarify the roles these regions play in antibacterial activity. An assay of antibacterial activity revealed that such activity requires the presence of Arg residues at or near the N-terminus, as well as a chain length exceeding 15 residues. None of the peptides exhibited haemolytic activity. Polyproline II-like CD curves were observed for most of the peptides. Measurements of the membrane perturbation and fusion indicated that the perturbation and fusogenic activities of the peptides were, generally, parallel to their antibacterial activities. Amino acid substitution in the repeating region had some effect on antibacterial activity.     

Short KR‐12 analogs designed from human cathelicidin LL‐37 possessing both antimicrobial and antiendotoxic activities without mammalian cell toxicity

KR‐12 (residues 18–29 of LL‐37) was known to be the smallest peptide of human cathelicidin LL‐37 possessing antimicrobial activity. In order to optimize α‐helical short antimicrobial peptides having both antimicrobial and antiendotoxic activities without mammalian cell toxicity, we designed and synthesized a series of KR‐12 analogs. Highest hydrophobic analogs KR‐12‐a5 and KR‐12‐a6 displayed greater inhibition of lipopolysaccharide (LPS)‐stimulated tumor necrosis factor‐α production and higher LPS‐binding activity. We have observed that antimicrobial activity is independent of charge, but LPS neutralization requires a balance of hydrophobicity and net positive charge. Among KR‐12 analogs, KR‐12‐a2, KR‐12‐a3 and KR‐12‐a4 showed much higher cell specificity for bacteria over erythrocytes and retained antiendotoxic activity, relative to parental LL‐37. KR‐12‐a5 displayed the strongest antiendotoxic activity but almost similar cell specificity as compared with LL‐37. Also, these KR‐12 analogs (KR‐12‐a2, KR‐12‐a3, KR‐12‐a4 and KR‐12‐a5) exhibited potent antimicrobial activity (minimal inhibitory concentration: 4 μM) against methicillin‐resistant Staphylococcus aureus. Taken together, these KR‐12 analogs have the potential for future development as a novel class of antimicrobial and anti‐inflammatory therapeutic agents. Copyright © 2013 European Peptide Society and John Wiley & Sons, Ltd.     

The synthesis and activity evaluation of N‐acylated analogs of echinocandin B with improved solubility and lower toxicity

Presently, echinocandins have been recommended as the first‐line drugs for the treatment of invasive candidiasis. However, low oral bioavailability and solubility limit their application. To improve this situation, this study chose amino acid and fatty acid as raw materials to modify the nucleus of echinocandin B. Six N‐acylated analogs were screened from the derivatives that possessed potent antifungal activity and good water solubility. Based on antifungal susceptibility and hemolytic toxicity, compound 5 as the candidate had good antifungal activity and no hemolytic effect. Moreover, compared with anidulafungin, compound 5 showed a comparable fungicidal effect, much higher solubility, and lower toxicity. In conclusion, compound 5 has the potential for further research and development on account of reserved antifungal activity, high solubility, and low toxicity.     

Anti‐inflammatory and anti‐endotoxin properties of peptides derived from the carboxy‐terminal region of a defensin from the tick Ornithodoros savignyi

Antimicrobial peptides are small cationic peptides that possess a large spectrum of bioactivities, including antimicrobial, anti‐inflammatory and antioxidant activities. Several antimicrobial peptides are known to inhibit lipopolysaccharide (LPS)‐induced inflammation in vitro and to protect animals from sepsis. In this study, the cellular anti‐inflammatory and anti‐endotoxin activities of Os and Os‐C, peptides derived from the carboxy‐terminal of a tick defensin, were investigated. Both Os and Os‐C were found to bind LPS in vitro, albeit to a lesser extent than polymyxin B and melittin, known endotoxin‐binding peptides. Binding to LPS was found to reduce the bactericidal activity of Os and Os‐C against Escherichia coli confirming the affinity of both peptides for LPS. At a concentration of 25 µM, the nitric oxide (NO) scavenging activity of Os was higher than glutathione, a known NO scavenger. In contrast, Os‐C showed no scavenging activity. Os and Os‐C inhibited LPS/IFN‐γ induced NO and TNF‐α production in RAW 264.7 cells in a concentration‐dependent manner, with no cellular toxicity even at a concentration of 100 µM. Although inhibition of NO and TNF‐α secretion was more pronounced for melittin and polymyxin B, significant cytotoxicity was observed at concentrations of 1.56 µM and 25 µM for melittin and polymyxin B, respectively. In addition, Os, Os‐C and glutathione protected RAW 264.7 cells from oxidative damage at concentrations as low as 25 µM. This study identified that besides previously reported antibacterial activity of Os and Os‐C, both peptides have in addition anti‐inflammatory and anti‐endotoxin properties. Copyright © 2015 European Peptide Society and John Wiley & Sons, Ltd.     

Antimicrobial activity,bactericidal mechanism and LPS‐neutralizing activity of the cell‐penetrating peptide pVEC and its analogs

pVEC is a cell‐penetrating peptide derived from the murine vascular endothelial‐cadherin protein. To evaluate the potential of pVEC as antimicrobial peptide (AMP), we synthesized pVEC and its analogs with Trp and Arg/Lys substitution, and their antimicrobial and lipopolysaccharide (LPS)‐neutralizing activities were investigated. pVEC and its analogs displayed a potent antimicrobial activity (minimal inhibitory concentration: 4–16 μM) against Gram‐positive and Gram‐negative bacteria but no or less hemolytic activity (less than 10% hemolysis) even at a concentration of 200 μM. These peptides induced a near‐complete membrane depolarization (more than 80%) at 4 μM against Staphylococcus aureus and a significant dye leakage (35–70%) from bacterial membrane‐mimicking liposome at a concentration as low as 1 μM. The fluorescence profiles of pVEC and its analogs in dye leakage from liposome and membrane depolarization were similar to those of a frog‐derived AMP, magainin 2. These results suggest that pVEC and its analogs kill bacteria by forming a pore or ion channel in the cytoplasmic membrane. pVEC and its analogs significantly inhibited nitric oxide production or tumor necrosis factor‐α release in LPS‐stimulated mouse macrophage RAW264.7 cells at 10 to 50 μM, in which RAW264.7 were not damaged. Taken together, our results suggest that pVEC and its analogs with potent antimicrobial and LPS‐neutralizing activities can serve as AMPs for the treatment of microbial infection and sepsis. Copyright © 2011 European Peptide Society and John Wiley & Sons, Ltd.     

An artificial self‐sufficient cytochrome P450 directly nitrates fluorinated tryptophan analogs with a different regio‐selectivity

Aromatic nitration is an immensely important industrial process to produce chemicals for a variety of applications, but it often suffers from multiple unsolved challenges. Enzymes as biocatalysts have been increasingly used for organic chemistry synthesis due to their high selectivity and environmental friendliness, but nitration has benefited minimally from the development of biocatalysis. In this work, we aimed to develop TxtE as practical biocatalysts for aromatic nitration. TxtE is a unique class I cytochrome P450 enzyme that nitrates the indole of l ‐tryptophan. To develop cost‐efficient nitration processes, we fused TxtE with the reductase domains of CYP102A1 (P450BM3) and of P450RhF to create class III self‐sufficient biocatalysts. The best engineered fusion protein was comparable with wild type TxtE in terms of nitration performance and other key biochemical properties. To demonstrate the application potential of the fusion enzyme, we nitrated 4‐F‐dl ‐tryptophan and 5‐F‐l ‐tryptophan in large scale enzymatic reactions. Tandem MS/MS and NMR analyses of isolated products revealed altered nitration sites. To our knowledge, these studies represent the first practice in developing biological nitration approaches and lay a solid basis to the use of TxtE‐based biocatalysts for the production of valuable nitroaromatics.     

High efficacy and minimal peptide required for the anti‐angiogenic and anti‐hepatocarcinoma activities of plasminogen K5

Kringle 5(K5) is the fifth kringle domain of human plasminogen and its anti‐angiogenic activity is more potent than angiostatin that includes the first four kringle fragment of plasminogen. Our recent study demonstrated that K5 suppressed hepatocarcinoma growth by anti‐angiogenesis. To find high efficacy and minimal peptide sequence required for the anti‐angiogenic and anti‐tumour activities of K5, two deletion mutants of K5 were generated. The amino acid residues outside kringle domain of intact K5 (Pro452‐Ala542) were deleted to form K5mut1(Cys462‐Cys541). The residue Cys462 was deleted again to form K5mut2(Met463‐Cys541). K5mut1 specifically inhibited proliferation, migration and induced apoptosis of endothelial cells, with an apparent two‐fold enhanced activity than K5. Intraperitoneal injection of K5mut1 resulted in more potent tumour growth inhibition and microvessel density reduction than K5 both in HepA‐grafted and Bel7402‐xenografted hepatocarcinoma mouse models. These results suggested that K5mut1 has more potent anti‐angiogenic activity than intact K5. K5mut2, which lacks only the amino terminal cysteine of K5mut1, completely lost the activity, suggesting that the kringle domain is essential for the activity of K5. The activity was enhanced to K5mut1 level when five acidic amino acids of K5 in NH₂ terminal outside kringle domain were replaced by five serine residues (K5mut3). The shielding effect of acidic amino acids may explain why K5mut1 has higher activity. K5, K5mut1 and K5mut3 held characteristic β‐sheet spectrum while K5mut2 adopted random coil structure. These results suggest that K5mut1 with high efficacy is the minimal active peptide sequence of K5 and may have therapeutic potential in liver cancer.     

Residual FDG‐PET metabolic activity in metastatic melanoma patients with prolonged response to anti‐PD‐1 therapy

18‐Fluorodeoxyglucose positron emission tomography (FDG‐PET) scans were performed on 27 patients with unresectable stage IIIC or IV melanoma after prolonged treatment with anti‐PD‐1 antibodies to examine the hypothesis that patients with prolonged response to treatment may have metabolically inactive lesions by FDG‐PET. Scans were performed at a median of 15.2 months (range 12–29 months) after starting treatment. Overall, 15 of 27 (56%) patients had a positive FDG‐PET scan. Eight patients with positive scans underwent biopsy; 5 of 8 (62%) were melanoma and 3 of 8 (38%) were immune cell infiltrates. Of the 12 patients with negative FDG‐PET scans, six had residual computerized tomography‐visible lesions, five have ceased treatment, and none have recurred with follow‐up of 6–10 months. Patients with residual metastases after a prolonged period without progression on anti‐PD‐1 therapy may have metabolically inactive lesions. Isolated metabolically active lesions in clinically well patients may reveal immune cell infiltrates rather than melanoma.     

Design,synthesis and biological activity of cell‐penetrating peptide‐modified octreotide analogs

Four novel octreotide analogs with cell‐penetrating peptides (CPPs) at the N‐terminus or C‐terminus were synthesized by a stepwise Fmoc solid‐phase synthesis strategy. The synthesized peptides were analyzed and characterized using reverse phase HPLC and MALDI‐TOF mass spectrometry. The antiproliferative activity of the analogs was tested in vitro on human gastric (SGC‐7901) and hepatocellular cancer (BEL7402) cell lines using the 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assay. Interestingly, these analogs showed a higher anticancer activities than the parent octreotide except CMTPT03 analog. The results demonstrate that the designed octreotide analogs enhance their anticancer activity after linking together the CPPs to octreotide at the N‐terminus, and are potential molecules for future use in cancer therapy and drug targeting. Copyright © 2009 European Peptide Society and John Wiley & Sons, Ltd.     

The dipteran parasitoid Exorista bombycis induces pro‐ and anti‐oxidative reactions in the silkworm Bombyx mori: Enzymatic and genetic analysis

Hymenopteran parasitoids inject various factors including polydnaviruses along with their eggs into their host insects that suppress host immunity reactions to the eggs and larvae. Less is known about the mechanisms evolved in dipteran parasitoids that suppress host immunity. Here we report that the dipteran, Exorista bombycis, parasitization leads to pro‐oxidative reactions and activation of anti‐oxidative enzymes in the silkworm Bombyx mori larva. We recorded increased activity of oxidase, superoxide dismutase, thioredoxin peroxidase, catalase, glutathione‐S‐transferase (GST), and peroxidases in the hemolymph plasma, hemocytes, and fat body collected from B. mori after E. bombycis parasitization. Microarray and qPCR showed differential expression of genes encoding pro‐ and anti‐oxidant enzymes in the hemocytes. The significance of this work lies in increased understanding of dipteran parasitoid biology.     

IsCT‐based analogs intending better biological activity

IsCT1‐NH₂ is a cationic antimicrobial peptide isolated from the venom of the scorpion Opisthacanthus madagascariensis that has a tendency to form an α‐helical structure and shows potent antimicrobial activity and also inopportunely shows hemolytic effects. In this study, five IsCT1 (ILGKIWEGIKSLF)‐based analogs with amino acid modifications at positions 1, 3, 5, or 8 and one analog with three simultaneous substitutions at the 1, 5, and 8 positions were designed. The net charge of each analog was between +2 and +3. The peptides obtained were characterized by mass spectrometry and analyzed by circular dichroism for their structure in different media. Studies of antimicrobial activity, hemolytic activity, and stability against proteases were also carried out. Peptides with a substitution at position 3 or 5 ([L]³‐IsCT1‐NH₂, [K]³‐IsCT1‐NH₂, or [F]⁵‐IsCT1‐NH₂) showed no significant change in an activity relative to IsCT1‐NH₂. The addition of a proline residue at position 8 ([P]⁸‐IsCT1‐NH₂) reduced the hemolytic activity as well as the antimicrobial activity (MIC ranging 3.13‐50 μmol L^?1), and the addition of a tryptophan residue at position 1 ([W]¹‐IsCT1‐NH₂) increased the hemolytic activity (MHC = 1.56 μmol L^?1) without an improvement in antimicrobial activity. The analog [A]¹[F]⁵[K]⁸‐IsCT1‐NH₂, which carries three simultaneous modifications, presented increasing or equivalent values in antimicrobial activity (MIC approximately 0.38 and 12.5 μmol L^?1) with a reduction in hemolytic activity. In addition, this analog presented the best resistance against proteases. This kind of strategy can find functional hotspots in peptide molecules in an attempt to generate novel potent peptide antibiotics.     

A novel human anti‐VCAM‐1 monoclonal antibody ameliorates airway inflammation and remodelling

Asthma is a chronic inflammatory disease induced by Type 2 helper T cells and eosinophils. Vascular cell adhesion molecule‐1 (VCAM‐1) has been implicated in recruiting eosinophils and lymphocytes to pathological sites in asthma as a regulatory receptor. Accordingly, monoclonal antibody (mAb) against VCAM‐1 may attenuate allergic inflammation and pathophysiological features of asthma. We attempted to evaluate whether a recently developed human anti‐VCAM‐1 mAb can inhibit the pathophysiological features of asthma in a murine asthma model induced by ovalbumin (OVA). Leucocyte adhesion inhibition assay was performed to evaluate the in vitro blocking activity of human anti‐VCAM‐1 mAb. OVA‐sensitized BALB/c mice were treated with human anti‐VCAM‐1 mAb or isotype control Ab before intranasal OVA challenge. We evaluated airway hyperresponsiveness (AHR) and bronchoalveolar lavage fluid analysis, measured inflammatory cytokines and examined histopathological features. The human anti‐VCAM‐1 mAb bound to human and mouse VCAM‐1 molecules and inhibited adhesion of human leucocytes in vitro. AHR and inflammatory cell counts in bronchoalveolar lavage fluid were reduced in mice treated with human anti‐VCAM‐1 mAb as compared with a control Ab. The levels of interleukin (IL)‐5 and IL‐13, as well as transforming growth factor‐β, in lung tissue were decreased in treated mice. Human anti‐VCAM‐1 mAb reduced goblet cell hyperplasia and peribronchial fibrosis. In vivo VCAM‐1 expression decreased in the treated group. In conclusion, human anti‐VCAM‐1 mAb attenuated allergic inflammation and the pathophysiological features of asthma in OVA‐induced murine asthma model. The results suggested that human anti‐VCAM‐1 mAb could potentially be used as an additional anti‐asthma therapeutic medicine.     

Antimicrobial activity of human α‐defensin 6 analogs: insights into the physico‐chemical reasons behind weak bactericidal activity of HD6 in vitro

Human α‐defensin 6 (HD6), unlike other mammalian defensins, does not exhibit bactericidal activity, particularly against aerobic bacteria. Monomeric HD6 has a tertiary structure similar to other α‐defensins in the crystalline state. However, the physico‐chemical reasons behind the lack of antibacterial activity of HD6 are yet to be established unequivocally. In this study, we have investigated the antimicrobial activity of HD6 analogs. A linear analog of HD6, in which the distribution of arginine residues was similar to active α‐defensins, shows broad‐spectrum antimicrobial activity, indicating that atypical distribution of arginine residues contributes to the inactivity of HD6. Peptides spanning the N‐terminal cationic segment were active against a wide range of organisms. Antimicrobial potency of these shorter analogs was further enhanced when myristic acid was conjugated at the N‐terminus. Cytoplasmic localization of the analogs without fatty acylation was observed to be necessary for bacterial killing, while they exhibited fungicidal activity by permeabilizing Candida albicans membranes. Myristoylated analogs and the linear full‐length arginine analog exhibited activity by permeabilizing bacterial and fungal membranes. Our study provides insights into the lack of bactericidal activity of HD6 against aerobic bacteria. Copyright © 2015 European Peptide Society and John Wiley & Sons, Ltd.     

Investigations on the interactions between naphthalimide‐based anti‐tumor drugs and human serum albumin by spectroscopic and molecular modeling methods

The interactions between the three kinds of naphthalimide‐based anti‐tumor drugs (NADA, NADB, NADC) and human serum albumin (HSA) under simulated physiological conditions were investigated by fluorescence spectroscopy, circular dichroism spectroscopy and molecular modeling. The results of the fluorescence quenching spectroscopy showed that the quenching mechanisms for different drugs were static and their affinity was in a descending order of NADA > NADB > NADC. The relative thermodynamic parameters indicated that hydrophobic force was the predominant intermolecular force in the binding of NAD to HSA, while van der Waals interactions and hydrogen bonds could not be ignored. The results of site marker competitive experiment confirmed that the binding site of HSA primarily took place in site I. Furthermore, the molecular modeling study was consistent with these results. The study of circular dichroism spectra demonstrated that the presence of NADs decreased the α‐helical content of HSA and induced the change of the secondary structure of HSA. Copyright © 2015 John Wiley & Sons, Ltd.     

Antimicrobial activity of leucine‐substituted decoralin analogs with lower hemolytic activity

Linear cationic α‐helical antimicrobial peptides are promising chemotherapeutics. Most of them act by different mechanisms, making it difficult to microorganisms acquiring resistance. Decoralin is an example of antimicrobial peptide; it was described by Konno et al. and presented activity against microorganisms, but with pronounced hemolytic activity. We synthesized leucine‐substituted decoralin analogs designed based on important physicochemical properties, which depend on the maintenance of the amphiphilic α‐helical tendency of the native molecule. Peptides were synthesized, purified, and characterized, and the conformational studies were performed. The results indicated that the analogs presented both higher therapeutic indexes, but with antagonistic behavior. While [Leu]¹⁰‐Dec‐NH₂ analog showed similar activity against different microorganisms (c.a. 0.4–0.8 μmol L^?1), helical structuration, and some hemolytic activity, [Leu]⁸‐Dec‐NH₂ analog did not tend to helical structure and presented antimicrobial activities two orders higher than the other two peptides analyzed. On the other hand, this analog showed to be the less hemolytic (MHC value = 50.0 μmol L^?1). This approach provided insight for understanding the effects of the leucine substitution in the amphiphilic balance. They led to changes on the conformational tendency, which showed to be important for the mechanism of action and affecting antimicrobial and hemolytic activities. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.