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The oral cavity is a frequent site for head and neck cancers, which rank as the sixth most common cancer globally, with a 5-year survival rate slightly over 50%. Current treatments are limited, and resistance to therapy remains a significant clinical obstacle. IsCT1, a membrane-active peptide derived from the venom of the scorpion Opisthacanthus madagascariensis , has shown antitumor effects in various cancer cell lines, including breast cancer and chronic myeloid leukemia. However, its hemolytic action limits its potential therapeutic use. This study aims to assess the antitumor and antiproliferative activities of synthetic peptides derived from IsCT1 (IsCT-P, AC-AFPK-IsCT1, AFPK-IsCT1, AC-KKK-IsCT1, and KKK-IsCT1) in the context of oral squamous cell carcinoma. We evaluated the cytotoxic effects of these peptides on tongue squamous cell carcinoma cells and normal cells, as well as their impact on cell cycle phases, the expression of proliferation markers, modulators of cell death pathways, and mitochondrial potential. Our results indicate that the IsCT1 derivatives IsCT-P and AC-AFPK-IsCT1 possess cytotoxic properties towards squamous cell carcinoma cells, reducing mitochondrial membrane potential and the proliferative index. The treatment of cancer cells with AC-AFPK-IsCT1 led to a positive modulation of pro-apoptotic markers p53 and caspases 3 and 8, a decrease in PCNA and Cyclin D1 expression, and cell cycle arrest in the S phase. Notably, contrary to the parental IsCT1 peptide, AC-AFPK-IsCT1 did not exhibit hemolytic activity or cytotoxicity towards normal cells. Therefore, AC-AFPK-IsCT1 might be a viable therapeutic option for head and neck cancer treatment.

Malaria can have severe long-term effects. Even after treatment with antimalarial drugs eliminates the parasite, survivors of cerebral malaria may suffer from irreversible brain damage, leading to cognitive deficits. Angiotensin II, a natural human peptide hormone that regulates blood pressure, has been shown to be active against Plasmodium spp., the etiologic agent of malaria. Here, we tested two Ang II derivatives that do not elicit vasoconstriction in mice: VIPF, a linear tetrapeptide, which constitutes part of the hydrophobic portion of Ang II; and Ang II-SS, a disulfide-bridged derivative. The antiplasmodial potential of both peptides was evaluated with two mouse models: an experimental cerebral malaria model and a mouse model of non-cerebral malaria. The latter consisted of BALB/c mice infected with Plasmodium berghei ANKA. The peptides had no effect on mean blood pressure and significantly reduced parasitemia in both mouse models. Both peptides reduced the SHIRPA score, an assay used to assess murine health and behavior. However, only the constrained derivative (Ang II-SS), which was also resistant to proteolytic degradation, significantly increased mouse survival. Here, we show that synthetic peptides derived from Ang II are capable of conferring protection against severe manifestations of malaria in mouse models while overcoming the vasoconstrictive side effects of the parent peptide., (© 2024. The Author(s).)

Triple-negative breast cancer is the most aggressive subtype of breast cancer, with worse clinical evolution and tumor-free survival, leading to the need to develop new effective therapies for its control. The present study evaluated the action of tumor-penetrating peptide BR2 associated with 2-aminoethyl dihydrogen phosphate (2-AEH 2 P) on triple-negative breast tumor cells. Cell viability was evaluated by the MTT colorimetric method, mitochondrial electrical potential, and proteins involved in cell proliferation and death control were evaluated by flow cytometry and structural and morphological analysis by confocal microscopy. The results obtained showed that the peptide BR2 and the association 2-AEH 2 P + BR2 promoted significant cytotoxicity in tumor lines, compared to 2-AEH 2 P alone. In addition, the association 2-AEH 2 P + BR2 promoted tumor cells arrest in the G0/G1 phases. Interestingly, both treatments modulated the expression of markers CD44, CD34, CD24, cyclin D1, and Bcl-2, increased p21, Bax, and released cytochrome c. The association proved to be more effective, providing modulation of proteins involved in cell death and senescence, more pronounced cytotoxicity for tumor cells compared to normal cells, and the reduction of markers related to aggressiveness profile, progression, and tumor metastasis., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022. Published by Elsevier Masson SAS.)

Multidrug-resistant bacteria represent a global health problem increasingly leading to infections that are untreatable with our existing antibiotic arsenal. Therefore, it is critical to identify novel effective antimicrobials. Venoms represent an underexplored source of potential antibiotic molecules. Here, we engineered a peptide (IsCT1-NH 2 ) derived from the venom of the scorpion Opisthacanthus madagascariensis , whose application as an antimicrobial had been traditionally hindered by its high toxicity. Through peptide design and the knowledge obtained in preliminary studies with single and double-substituted analogs, we engineered IsCT1 derivatives with multiple amino acid substitutions to assess the impact of net charge on antimicrobial activity and toxicity. We demonstrate that increased net charge (from +3 to +6) significantly reduced toxicity toward human erythrocytes. Our lead synthetic peptide, [A] 1 [K] 3 [F] 5 [K] 8 -IsCT1-NH 2 (net charge of +4), exhibited increased antimicrobial activity against Gram-negative and Gram-positive bacteria in vitro and enhanced anti-infective activity in a mouse model. Mechanism of action studies revealed that the increased antimicrobial activity of our lead molecule was due, at least in part, to its enhanced ability to permeabilize the outer membrane and depolarize the cytoplasmic membrane. In summary, we describe a simple method based on net charge tuning to turn highly toxic venom-derived peptides into viable therapeutics.

Chagas disease is caused by Trypanosoma cruzi and affects approximately 10 million people a year worldwide. The only two treatment options, benznidazole and nifurtimox, have low efficacy and high toxicity towards human cells. Mastoporan peptide (MP) a small cationic AMP from the venom of the wasp Polybia paulista has been reported as a potent trypanocidal agent. Thus, we evaluated the antichagasic effect of another AMP from the venom of the same wasp Polybia paulista, polybia-CP (ILGTILGLLSKL-NH 2 ), and investigated its mechanism of action against different stages of the trypanosomal cells life cycle. Polybia-CP was tested against the epimastigote, trypomastigote and amastigote forms of the T. cruzi Y strain (benznidazole-resistant strain) and inhibited the development of these forms. We also assessed the selectivity of the AMP against mammalian cells by exposing LLC-MK2 cells to polybia-CP, the peptide presented a high selectivity index (>106). The mechanism of action of polybia-CP on trypanosomal cells was investigated by flow cytometry, scanning electron microscopy (SEM) and enzymatic assays with T. cruzi GAPDH (tcGAPDH), enzyme that catalyzes the sixth step of glycolysis. Polybia-CP induced phosphatidylserine exposure, it also increased the formation of reactive species of oxigen (ROS) and reduced the transmembrane mitochondrial potential. Polybia-CP also led to cell shrinkage, evidencing apoptotic cell death. We did not observe the inhibition of tcGAPDH or autophagy induction. Altogether, polybia-CP has shown the features of a promising template for the development of new antichagasic agents., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The wasp venom-derived antimicrobial peptide polybia-CP has been previously shown to exhibit potent antimicrobial activity, but it is also highly toxic. Previously, using a physicochemical-guided peptide design strategy, we reversed its toxicity while preserving and even enhancing its antibacterial properties. Here, we report on several additional unanticipated biological properties of polybia-CP and derivatives, namely their ability to target Plasmodium sporozoites and cancer cells. We leverage a physicochemical-guided approach to identify features that operate as functional hotspots making these peptides viable antiplasmodial and anticancer agents. Helical content and net positive charge are identified as key structural and physicochemical determinants for antiplasmodial activity. In addition to helicity and net charge, hydrophobicity-related properties of polybia-CP and derivatives were found to be equally critical to target cancer cells. We demonstrate that by tuning these physicochemical parameters, it is possible to design synthetic peptides with enhanced submicromolar antiplasmodial potency and micromolar anticancer activity. This study reveals novel and previously undescribed functions for Polybia-CP and analogs. Additionally, we demonstrate that a physicochemical-guided rational design strategy can be used for identifying functional hotspots in peptide molecules and for tuning structure-function to generate novel and potent new-to-nature therapies., (© 2020 The Authors. Bioengineering & Translational Medicine published by Wiley Periodicals, Inc. on behalf of The American Institute of Chemical Engineers.)

IsCT1-NH 2 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-NH 2 , [K] 3 -IsCT1-NH 2 , or [F] 5 -IsCT1-NH 2 ) showed no significant change in an activity relative to IsCT1-NH 2 . The addition of a proline residue at position 8 ([P] 8 -IsCT1-NH 2 ) 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-NH 2 ) 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-NH 2 , 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., (© 2019 European Peptide Society and John Wiley & Sons, Ltd.)

About 1 in 8 U.S. women (≈12%) will develop invasive breast cancer over the course of their lifetime. Surgery, chemotherapy, radiotherapy, and hormone manipulation constitute the major treatment options for breast cancer. Here, we show that both a natural antimicrobial peptide (AMP) derived from wasp venom (decoralin, Dec-NH 2 ), and its synthetic variants generated via peptide design, display potent activity against cancer cells. We tested the derivatives at increasing doses and observed anticancer activity at concentrations as low as 12.5 μmol L -1 for the selective targeting of MCF-7 breast cancer cells. Flow cytometry assays further revealed that treatment with wild-type (WT) peptide Dec-NH 2 led to necrosis of MCF-7 cells. Additional atomic force microscopy (AFM) measurements indicated that the roughness of cancer cell membranes increased significantly when treated with lead peptides compared to controls. Biophysical features such as helicity, hydrophobicity, and net positive charge were identified to play an important role in the anticancer activity of the peptides. Indeed, abrupt changes in peptide hydrophobicity and conformational propensity led to peptide inactivation, whereas increasing the net positive charge of peptides enhanced their activity. We present peptide templates with selective activity towards breast cancer cells that leave normal cells unaffected. These templates represent excellent scaffolds for the design of selective anticancer peptide therapeutics.

Antimicrobial peptides are considered promising drug candidates due to their broad range of activity. VmCT1 (Phe-Leu-Gly-Ala-Leu-Trp-Asn-Val-Ala-Lys-Ser-Val-Phe-NH 2 ) is an α-helical antimicrobial peptide that was obtained from the Vaejovis mexicanus smithi scorpion venom. Some of its analogs showed to be as antimicrobial as the wild type, and they were designed for understanding the influence of physiochemical parameters on antimicrobial and hemolytic activity. Some cationic antimicrobial peptides exhibit anticancer activity so VmCT1 analogs were tested to verify the anticancer activity of this family of peptides. The analogs were synthesized, purified, characterized, and the conformational studies were performed. The anticancer activity was assessed against MCF-7 mammary cancer cells. The results indicated that [Glu] 7 -VmCT1-NH 2 , [Lys] 3 -VmCT1-NH 2 , and [Lys] 7 -VmCT1-NH 2 analogs presented moderated helical tendency (0.23-0.61) and tendency of anticancer activity at 25 μmol/L in 24 hr of experiment; and [Trp] 9 -VmCT1-NH 2 analog that presented low helical tendency and moderated anticancer activity at 50 μmol/L. These results demonstrated that single substitutions on VmCT1 led to different physicochemical features and could assist on the understanding of anticancer activity of this peptide family., (© 2017 John Wiley & Sons A/S.)

Angiotensin II (Ang II) is a natural mammalian hormone that has been described to exhibit antiplasmodial activity therefore constituting a promising alternative for the treatment of malaria. Despite its promise, the development of Ang II as an antimalarial is limited by its potent induction of vasoconstriction and its rapid degradation within minutes. Here, we used peptide design to perform targeted chemical modifications to Ang II to generate conformationally restricted (disulfide-crosslinked) peptide derivatives with suppressed vasoconstrictor activity and increased stability. Designed constrained peptides were synthesized chemically and then tested for antiplasmodial activity. Two lead constrained peptides were identified (i.e., peptides 1 and 2), each composed of 10 amino acid residues. These peptides exhibited very promising activity in both our Plasmodium gallinaceum (>80%) and Plasmodium falciparum (>40%) models, an activity that was equivalent to that of Ang II, and led to complete suppression of vasoconstriction. In addition, peptide 5 exhibited selective activity towards the pre-erythrocytic stage (98% of activity against P. gallinaceum), thus suggesting that it may be possible to design peptides that target specific stages of the malaria life cycle. The Ang II derived stable scaffolds presented here may provide the basis for development of a new generation of peptide-based drugs for the treatment of malaria.

Angiotensin II (AngII) is the final active product of the renin enzymatic cascade, which is responsible for sustaining blood pressure. To investigate the effect of N-terminal cyclization on AT 1 activation and tachyphylaxis, we designed conformationally constrained analogues with an i-(i + 1) lactam bridge. All analogues presented the same binding coefficient and tachyphylactic index, but some of them such as Cyclo (0-1a) [Glu 0 , endo-(Lys 1a )]-AngII and Cyclo (0-1a) [Asp 0 , endo-(Orn 1a )]-AngII showed higher potency. The same tachyphylactic index presented by AngII and cyclic analogues was surprising. We expected a variation after the modification of AngII N-terminal region., (© 2016 John Wiley & Sons A/S.)

This article reports the in vitro antiplasmodial activity of two endoperoxides of the class 1,2-dioxetanes against Plasmodium falciparum: bis(adamantyl)-1,2-dioxetane and 3,3,4,4-tetramethyl-1,2-dioxetane. The results reveal that bis(adamantyl)-1,2-dioxetane displays substantial antiplasmodial activity, at least two orders of magnitude higher than that of artemisinin, while 3,3,4,4-tetramethyl-1,2-dioxetane is less active., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The antimalarial activity of peroxides most likely originates from their interaction with iron(II) species located inside the malaria parasite, which forms destructive radical species through a Fenton-like mechanism. This article reports the first evaluation of the in vitro antimalarial activity of three peroxides of the class 1,2-dioxetanes against Plasmodium falciparum; the results reveal that the studied 3-methoxy-1,2-dioxetanes display significant antimalarial activity, at a similar level as artemisinin and also that their reactivity toward iron(II) correlate linearly with their antimalarial activity., (© 2015 John Wiley & Sons A/S.)

Background: Antiplasmodial activities of angiotensin II and its analogues have been extensively investigated in Plasmodium gallinaceum and Plasmodium falciparum parasite species. Due to its vasoconstrictor property angiotensin II cannot be used as an anti-malarial drug., Methods: This work presents the solid-phase syntheses and liquid chromatography and mass spectrometry characterization of ten linear peptides related to angiotensin II against mature P. gallinaceum sporozoites and erythrocyte invasion by P. falciparum. Conformational analyses were performed by circular dichroism. IC50 assays were performed to identify the ideal concentration used on the biological tests and haemolytical erythrocytic assays were made to verify the viability of the biological experiments. The contractile responses of the analogues were made to evaluate if they are promising candidates to be applied as antiplasmodial drugs., Results: The results indicate two short-peptides constituted by hydrophobic residues (5 and 6) with antiplasmodial activity in these models, 89 and 94 % of biological activity against P. gallinaceum sporozoite, respectively, and around 50 % of activity against P. falciparum. Circular dichroism spectra suggested that all the peptides adopted β-turn conformation in different solutions, except peptide 3. Besides the biological assays IC50, the haemolysis assays and contractile response activities were applied for peptides 5 and 6, which did not present expressive results., Conclusions: The hydrophobic portion and the arginine, tyrosine, proline, and phenylalanine, when present on peptide primary sequence, tend to increase the antiplasmodial activity. This class of peptides can be explored, as anti-malarial drugs, after in vivo model tests. Graphical abstract: The most active peptide presented 94 % activity on P. gallinaceum sporozoites and 53 % inhibited P. falciparum ring forms invasion.

To find effective new candidate antimalarial drugs, bradykinin and its analogs were synthesized and tested for effectiveness against Plasmodium gallinaceum sporozoites and Plasmodium falciparum on erythrocytes. Among them, bradykinin and its P2 analog presented high activity against Plasmodium gallinaceum, but they degrade in plasma. On the other hand, RI-BbKI did not degrade and reached high activity. No analog was active against Plasmodium falciparum., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The anti-plasmodium activity of angiotensin II and its analogs have been described in different plasmodium species. Here we synthesized angiotensin II Ala-scan analogs to verify peptide-parasite invasion preservation with residue replacements. The analogs were synthesized by 9-fluorenylmethoxycarbonyl (Fmoc) and tert-butyloxycarbonyl (t-Boc) solid phase methods, purified by liquid chromatography and characterized by mass spectrometry. The results obtained in Plasmodium falciparum assays indicated that all analogs presented some influence in parasite invasion, except [Ala(4)]-Ang II (18% of anti-plasmodium activity) that was not statistically different from control. Although [Ala(8)]-Ang II presented a lower biological activity (20%), it was statistically different from control. The most relevant finding was that [Ala(5)]-Ang II preserved activity (45%) relative to Ang II (47%). In the results of Plasmodium gallinaceum assays all analogs were not statistically different from control, except [Ala(6)]-Ang II, which was able to reduce the parasitemia about 49%. This approach provides insight for understanding the importance of each amino acid on the native Ang II sequence and provides a new direction for the design of potential chemotherapeutic agents without pressor activity., (Copyright © 2015 Elsevier Inc. All rights reserved.)

A model octapeptide peptide consisting of an alternating sequence of arginine (Arg) and phenylalanine (Phe) residues, namely, [Arg-Phe]4, was prepared, and its self-assembly in solution studied. The simple alternating [Arg-Phe]4 peptide sequence allows for unique insights into the aggregation process and the structure of the self-assembled motifs. Fluorescence and UV-vis assays were used to determine critical aggregation concentrations, corresponding to the formation of oligomeric species and β-sheet rich structures organized into both spheroidal aggregates and highly ordered fibrils. Electron and atomic force microscopy images show globular aggregates and long unbranched fibers with diameters ranging from ∼4 nm up to ∼40 nm. Infrared and circular dichroism spectroscopy show the formation of β-sheet structures. X-ray diffraction on oriented stalks show that the peptide fibers have an internal lamellar structure, with an orthorhombic unit cell with parameters a ∼ 27.6 Å, b ∼ 9.7 Å, and c ∼ 9.6 Å. In situ small-angle X-ray scattering (SAXS) shows the presence of low molecular weight oligomers in equilibrium with mature fibers which are likely made up from 5 or 6 intertwined protofilaments. Finally, weak gel solutions are probed under gentle shear, suggesting the ability of these arginine-rich fibers to form networks.

The anti-plasmodial activity of conformationally restricted analogs of angiotensin II against Plasmodium gallinaceum has been described. To observe activity against another Plasmodium species, invasion of red blood cells by Plasmodium falciparum was analyzed. Analogs restricted with lactam or disulfide bridges were synthesized to determine their effects and constraints in the peptide-parasite interaction. The analogs were synthesized using tert-butoxycarbonyl and fluoromethoxycarbonyl solid phase methods, purified by liquid chromatography, and characterized by mass spectrometry. Results indicated that the lactam bridge restricted analogs 1 (Glu-Asp-Arg-Orn-Val-Tyr-Ile-His-Pro-Phe) and 3 (Asp-Glu-Arg-Val-Orn-Tyr-Ile-His-Pro-Phe) showed activity toward inhibition of ring formation stage of P. falciparum erythrocytic cycle, preventing invasion in about 40% of the erythrocytes. The disulfide-bridged analog 10 (Cys-Asp-Arg-Cys-Val-Tyr-Ile-His-Pro-Phe) was less effective yet significant, showing a 25% decrease in infection of new erythrocytes. In all cases, the peptides presented no pressor activity, and hydrophobic interactions between the aromatic and alkyl amino acid side chains were preserved, a factor proven important in efficacy against P. gallinaceum. In contrast, hydrophilic interactions between the Asp(1) carboxyl and Arg(2) guanidyl groups proved not to be as important as they were in the case of P. gallinaceum, while interactions between the Arg(2) guanidyl and Tyr(4) hydroxyl groups were not important in either case. The β-turn conformation was predominant in all of the active peptides, proving importance in anti-plasmodial activity. This approach provides insight for understanding the importance of each amino acid residue on the native angiotensin II structure and a new direction for the design of potential chemotherapeutic agents., (Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.)

Angiotensin II (AII) as well as analog peptides shows antimalarial activity against Plasmodium gallinaceum and Plasmodium falciparum, but the exact mechanism of action is still unknown. This work presents the solid-phase synthesis and characterization of eight peptides corresponding to the alanine scanning series of AII plus the amide-capped derivative and the evaluation of the antiplasmodial activity of these peptides against mature P. gallinaceum sporozoites. The Ala screening data indicates that the replacement of either the Ile(5) or the His(6) residues causes minor effects on the in vitro antiplasmodial activity compared with AII, i.e. AII (88%), [Ala(6) ]-AII (79%), and [Ala(5) ]-AII (75%). Analogs [Ala(3) ]-AII, [Ala(1) ]-AII, and AII-NH2 showed antiplasmodial activity around 65%, whereas the activity of the [Ala(8) ]-AII, [Ala(7) ]-AII, [Ala(4) ]-AII, and [Ala(2) ]-AII analogs is lower than 45%. Circular dichroism data suggest that AII and the most active analogs adopt a β-fold conformation in different solutions. All AII analogs, except [Ala(4) ]-AII and [Ala(8) ]-AII, show contractile responses and interact with the AT1 receptor, [Ala(5) ]-AII and [Ala(6) ]-AII. In conclusion, this approach is helpful to understand the contribution of each amino acid residue to the bioactivity of AII, opening new perspectives toward the design of new sporozoiticidal compounds., (Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.)

Leptin is a cytokine that regulates food intake, energy expenditure and hematopoiesis. Based on the tridimensional structure of the human leptin molecule, six fragments have been synthesized, (Ac-Lep23-47-NH2, [LEP1]; Ac-Lep48-71-NH2, [LEP2]; Ac-Lep72-88-NH2, [LEP3]; Ac-Lep92-115-NH2, [LEP4], Ac-[Ser(117)]-Lep116-140-NH2, [LEP5] and Ac-Lep141-164-NH2, [LEP6]), and their effects on hematopoiesis were evaluated. The mice were treated with 1mg/kg LEP5 for 3 days. The mature and primitive hematopoietic populations were quantified. We observed that the mature populations from the bone marrow and spleen were not affected by LEP5. However, the peptide caused at least a two-fold increase in the number of hematopoietic stem cells, the most primitive population of the bone marrow. Additionally, the number of granulocyte/macrophage colony-forming units produced by bone marrow cells in methylcellulose also increased by 40% after treatment with LEP5, and the leptin receptor was activated. These results show that the leptin fragment LEP5 is a positive modulator of the in vivo expansion of hematopoietic stem cells., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Controlling the dissemination of malaria requires the development of new drugs against its etiological agent, a protozoan of the Plasmodium genus. Angiotensin II and its analog peptides exhibit activity against the development of immature and mature sporozoites of Plasmodium gallinaceum. In this study, we report the synthesis and characterization of angiotensin II linear and cyclic analogs with anti-plasmodium activity. The peptides were synthesized by a conventional solid-phase method on Merrifield's resin using the t-Boc strategy, purified by RP-HPLC and characterized by liquid chromatography/ESI (+) MS (LC-ESI(+)/MS), amino acid analysis, and capillary electrophoresis. Anti-plasmodium activity was measured in vitro by fluorescence microscopy using propidium iodine uptake as an indicator of cellular damage. The activities of the linear and cyclic peptides are not significantly different (p < 0.05). Kinetics studies indicate that the effects of these peptides on plasmodium viability overtime exhibit a sigmoidal profile and that the system stabilizes after a period of 1 h for all peptides examined. The results were rationalized by partial least-square analysis, assessing the position-wise contribution of each amino acid. The highest contribution of polar amino acids and a Lys residue proximal to the C-terminus, as well as that of hydrophobic amino acids in the N-terminus, suggests that the mechanism underlying the anti-malarial activity of these peptides is attributed to its amphiphilic character., (Copyright © 2013 European Peptide Society and John Wiley & Sons, Ltd.)

We report for the first time on the self-assembly of nanostructures composed exclusively of alternating positively charged and hydrophobic amino acids. A novel arginine/phenylalanine octapeptide, RF8, was synthesized. Because the low hydrophobicity of this sequence makes its spontaneous ordering through solution-based methods difficult, a recently proposed solid-vapor approach was used to obtain nanometric architectures on ITO/PET substrates. The formation of the nanostructures was investigated under different preparation conditions, specifically, under different gas-phase solvents (aniline, water, and dichloromethane), different peptide concentrations in the precursor solution, and different incubation times. The stability of the assemblies was experimentally studied by electron microscopy and thermogravimetric analysis coupled with mass spectrometry. The secondary structure was assessed by infrared and Raman spectroscopy, and the arrays were found to assume an antiparallel β-sheet conformation. FEG-SEM images clearly reveal the appearance of fibrillar structures that form extensive homogeneously distributed networks. A close relationship between the morphology and preparation parameters was found, and a concentration-triggered mechanism was suggested. Molecular dynamics simulations were performed to address the thermal stability and nature of intermolecular interactions of the putative assembly structure. Results obtained when water is considered as solvent shows that a stable lamellar structure is formed containing a thin layer of water in between the RF8 peptides that is stabilized by H-bonding.

The octarepeat domain in cellular prion protein (PrP(C)) has attracted much attention over the last 10 years because of its importance in the complexation of copper with PrP(C). The aim of this research was to study the UV-vis spectra of a peptide similar to the 1-repeat of the octarepeat region in PrP(C) using experimental and theoretical approaches and to gain insight into the complexation of the PrP(C) octarepeat domain with copper(II) ions in solution. We found that the copper atom was responsible for the peptide conformation, which allows for charge transfers between its two terminal residues., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Angiotensin II (AII) is the active octapeptide product of the renin enzymatic cascade, which is responsible for sustaining blood pressure. In an attempt to establish the AII-receptor-bound conformation of this octapeptide, we designed conformationally constrained analogues by scanning the entire AII sequence with an i-(i+2) and i-(i+3) lactam bridge consisting of an Asp-(Xaa)(n)-Lys scaffold. Most analogues presented low agonistic activity when compared to AII in the different bioassays tested. The exceptions are cyclo(0-1a) [Asp(0), endo-(Lys(1a))]-AII (1) and [Asp(0), endo-(Lys(1a))]-AII (2), both of which showed activity similar to AII. Based on peptide 1 and the analogue cyclo(3-5)[Sar(1), Asp(3), Lys(5)]-AII characterized by Matsoukas et al., we analyzed the agonistic and antagonistic activities, respectively, through a new monocyclic peptide series synthesized by using the following combinations of residues as bridgehead elements for the lactam bond formation: D- or L-Asp combined with D- or L-Lys or L-Glu combined with L-Orn. Six analogues showed an approximately 20% increase in biological activity when compared with peptide (1) and were equipotent to AII. In contrast, six analogues presented antagonistic activity. These results suggest that the position of the lactam bridge is more important than the bridge length or chirality for recognition of and binding to the angiotensin II AT1-receptor., (Copyright © 2011 Elsevier B.V. All rights reserved.)

In an attempt to identify regions in the leptin molecule responsible for its bioactivity, we tested six related-leptin peptide fragments denoted: Ac-hLEP(23-47)-NH(2) (I), Ac-hLEP(48-71)-NH(2) (II), Ac-hLEP(72-88)-NH(2) (III), Ac-hLEP(92-115)-NH(2) (IV), Ac-[Ser(117)]-hLEP(116-140)-NH(2) (V), Ac-hLEP(141-164)-NH(2) (VI) and their correspondent disulfide bridged dimer forms. The activity of the fragments was evaluated in comparision to leptin, by their ability to interact with leptin receptor using a cytosensor microphysiometer. Our results indicated that the fragments IV and V and [D-Leu(4)]-OB(3) and its human sequence analog were recognized by leptin receptor present in HP-75 cells, in agreement with the results obtained by other workers, validating that this region of the molecule contain the functional epitope of the leptin molecule.

Gomesin is an antimicrobial peptide isolated from hemocytes of the Brazilian spider Acanthoscurria gomesiana that contains two disulfide bridges Cys(2-15)/Cys(6-11) and presents a beta-hairpin structure. To investigate the role of the disulfide bridges on gomesin conformation, bioactivities, and serum stability, structure-activity relationship (SAR) studies were conducted. Initially, gomesin and variants lacking one or both disulfide bridges were synthesized. CD studies showed that the gomesin structure is very rigid independently of the solvent environment. On the other hand, the linearized analogues adopted secondary structures according to the environment, while the monocyclic disulfide-bridged peptides had a tendency to adopt a turn structure. The absence of one or both bridges resulted in a decrease in the antimicrobial and hemolytic activities. In addition, serum stability studies revealed that, contrasting to gomesin that was stable even after 48 h of incubation, the linearized analogues were rapidly degraded. The replacement of the disulfide bounds by lactam bridges led to monocyclic and bicyclic compounds. SAR studies indicated that the monocyclic lactam-bridged analogues tend to assume a alpha-helical structure being less potent, hemolytic, and serum stable than the wild-type gomesin. On the other hand, the bicyclic lactam/disulfide-bridged analogues displayed a similar conformation and degradation kinetics identical to gomesin. However, the antimicrobial activity appeared to be dependent on the lactam bridge position and size. These findings indicated that (i) the secondary structure plays a pivotal role for the full activity of gomesin; (ii) the antimicrobial and hemolytic activities of gomesin are correlated events; (iii) while at least one of the disulfide bridges is needed for the maintenance of a significant antimicrobial activity of gomesin, both bridges are required for high serum stability and optimal conformation; and finally (iv) the best analogue obtained was the bicyclo (2-15,6-11)[Glu2, Cys(6,11), Lys15]-Gm since it is as stable and potent as gomesin.

Leptin presents an important role in energy balance and neuroendocrine control in mammals. In an attempt to identify regions of the leptin molecule responsible for its bioactivity, we have synthesized six peptides based on the protein three-dimensional structure. Fragments were synthesized by the solid-phase methodology, purified by reverse-phase high-performance liquid chromatography (RP-HPLC), and characterized by liquid chromatography-electrospray ionization mass spectrometry (LC/ESI-MS). They were injected intravenously and their ability to induce Fos immunoreactivity (Fos-ir) in rat hypothalamus was compared with that of the recombinant human leptin and saline. Fragment Ac-[Ser117]Lep116-140-NH2 (V) induced Fos-ir in hypothalamic nuclei that express leptin receptor long form. No similar ability was observed for the other five fragments. To investigate whether Fos-ir was induced in the same neuronal group activated by leptin, we proceeded with a dual-label immunohistochemistry for cocaine- and amphetamine-regulated transcript (CART), a neuropeptide related to leptin action in rat hypothalamus. We found that Ac-[Ser117]Lep116-140-NH2 (V) differentially activates CART neurons through the rostrocaudal extension of the arcuate nucleus. These results suggest that this fragment acts in the same group of neurons that mediate leptin response. This approach may offer the basis for the development of leptin-related compounds, having potential application in human or veterinary medicine.