Alzheimer's Disease: Innovative Therapeutic Approaches Based on Peptides and Nanoparticles

Alzheimer's disease (AD) is the main cause of dementia in the world and its etiology is not yet fully understood. The pathology of AD is primarily characterized by intracellular neurofibrillary tangles and extracellular amyloid-β plaques. Unfortunately, few treatment options are available, and most treat symptoms, as is the case of acetylcholinesterase inhibitors (IAChE) and N-methyl-d-aspartate receptor antagonists. For more than 20 years pharmaceutical research has targeted the "amyloid cascade hypothesis," but this has not produced meaningful results, leading researchers to focus now on other characteristics of the disease and on multitarget approaches. This review aims to evaluate some new treatments that are being developed and studied. Among these are new treatments based on peptides, which have high selectivity and low toxicity; however, these compounds have a short half-life and encounter challenges when crossing the blood-brain barrier. The present review discusses up-and-coming peptides tested as treatments and explores some nanotechnological strategies to overcome the downsides. These compounds are promising, as they not only act on the symptoms but also aim to prevent progressive neuronal loss.

A Concise Review on the Role of Natural and Synthetically Derived Peptides in Colorectal Cancer

Colorectal cancer being the second leading cause of cancer-associated deaths has become a significant health concern around the globe. Though there are various cancer treatment approaches, many of them show adverse effects and some compromise the health of cancer patients. Hence, significant efforts are being made for the evolution of a novel biological therapeutic approach with better efficacy and minimal side effects. Current research suggests that the application of peptides in colorectal cancer therapeutics holds the possibility of the emergence of an anticancer reagent. The primary beneficial factors of peptides are their comparatively rapid and easy process of synthesis and the enormous potential for chemical alterations that can be evaluated for designing novel peptides and enhancing the delivery capacity of peptides. Peptides might be utilized as agents with cytotoxic activities or as a carrier of a specific drug or as cytotoxic agents that can efficiently target the tumor cells. Further, peptides can also be used as a tool for diagnostic purposes. The recent analysis aims at developing peptides that have the potential to efficiently target the tumor moieties without harming the nearby normal cells. Additionally, decreasing the adverse effects, and unfolding the other therapeutic properties of potential peptides, are also the subject matter of in-depth analysis. This review provides a concise summary of the function of both natural and synthetically derived peptides in colorectal cancer therapeutics that are recently being evaluated and their potent applications in the clinical field.

FT-MS in the de novo top-down sequencing of natural nontryptic peptides

The present review covers available results on the application of FT-MS for the de novo sequencing of natural peptides of various animals: cones, bees, snakes, amphibians, scorpions, and so forth. As these peptides are usually bioactive, the animals efficiently use them as a weapon against microorganisms or higher animals including predators. These peptides represent definite interest as drugs of future generations since the mechanism of their activity is completely different in comparison with that of the modern antibiotics. Utilization of those peptides as antibiotics can eliminate the problem of the bacterial resistance development. Sequence elucidation of these bioactive peptides becomes even more challenging when the species genome is not available and little is known about the protein origin and other properties of those peptides in the study. De novo sequencing may be the only option to obtain sequence information. The benefits of FT-MS for the top-down peptide sequencing, the general approaches of the de novxxo sequencing, the difficult cases involving sequence coverage, isobaric and isomeric amino acids, cyclization of short peptides, the presence of posttranslational modifications will be discussed in the review.

Monocyclic Peptides: Types, Synthesis and Applications

Peptides are considered to be appropriate tools in various biological fields. They can be primarily used for the rational design of bioactive molecules. They can act as ligands in the development of targeted therapeutics as well as diagnostics, can be used in the design of vaccines or can be employed in agriculture. Peptides can be classified in two broad structural classes: linear and cyclic peptides. Monocyclic peptides are a class of polypeptides with one macrocyclic ring that bears advantages, such as more selective binding and uptake by the target receptor, as well as higher potency and stability compared to linear types. This paper provides an overview of the categories, synthesis methods and various applications of cyclic peptides. The various applications of cyclic peptides include their use as pro-apoptotic and anti-microbial agents, their application as targeting ligands in drug delivery and diagnostic agents, as well as agricultural and therapeutics applications that are elaborated and discussed in this paper.

Lactoferrin-Derived Peptides as a Control Strategy against Skinborne Staphylococcal Biofilms

Coagulase-negative staphylococci (CoNS) widely colonize the human skin and play an active role in host defense. However, these bacteria may cause malodours and increase infection incidence rate in immune-compromised patients and individuals with catheters and implants. CoNS spreading is favored by biofilm formation that also promotes the release of virulence factors and drug resistance. Biofilm control or eradication by antimicrobial peptides (AMPs) represents an attractive strategy which is worth investigating. In this work, bovine lactoferrin (BLF) hydrolysate (HLF) was in vitro evaluated for its antimicrobial and antibiofilm activities against skin-related coagulase negative and positive staphylococci. Despite a minimal inhibitory concentration (MIC) recorded for HLF ranging from 10 to more than 20 mg/mL, a minimal biofilm inhibitory concentration (MIBC) equal to 2.5 mg/mL was found for most target strains. Conversely, MIBC values referred to the individual peptides, LFcinB or LFmpin (herein purified and identified) were significantly lower. Finally, the application of 2.5 mg/mL HLF solution by dipping and spraying on biofilm-attached glass surfaces also caused a high biofilm eradication rate depending on the incubation time, thus attracting interest for future applications in cosmetic formulation for skin care.

Snake Venom Cathelicidins as Natural Antimicrobial Peptides

Bioactive small molecules isolated from animals, plants, fungi and bacteria, including natural antimicrobial peptides, have shown great therapeutic potential worldwide. Among these peptides, snake venom cathelicidins are being widely exploited, because the variation in the composition of the venom reflects a range of biological activities that may be of biotechnological interest. Cathelicidins are short, cationic, and amphipathic molecules. They play an important role in host defense against microbial infections. We are currently facing a strong limitation on pharmacological interventions for infection control, which has become increasingly complex due to the lack of effective therapeutic options. In this review, we will focus on natural snake venom cathelicidins as promising candidates for the development of new antibacterial agents to fight antibiotic-resistant bacteria. We will highlight their antibacterial and antibiofilm activities, mechanism of action, and modulation of the innate immune response.

Synthesis and Evaluation of Spumigin Analogues Library with Thrombin Inhibitory Activity

Spumigins are marine natural products derived from cyanobacteria Nodularia spumigena, which mimics the structure of the d-Phe-Pro-Arg sequence and is crucial for binding to the active site of serine proteases thrombin and factor Xa. Biological evaluation of spumigins showed that spumigins with a (2S,4S)-4-methylproline central core represent potential lead compounds for the development of a new structural type of direct thrombin inhibitors. Herein, we represent synthesis and thrombin inhibitory activity of a focused library of spumigins analogues with indoline ring or l-proline as a central core. Novel compounds show additional insight into the structure and biological effects of spumigins. The most active analogue was found to be a derivative containing l-proline central core with low micromolar thrombin inhibitory activity.

Natural Peptides in Drug Discovery Targeting Acetylcholinesterase

Acetylcholinesterase-inhibitory peptide has gained much importance since it can inhibit acetylcholinesterase (AChE) and increase the availability of acetylcholine in cholinergic synapses, enhancing cholinergic transmission in pharmacological treatment of Alzheimer’s disease (AD). Natural peptides have received considerable attention as biologically important substances as a source of AChE inhibitors. These natural peptides have high potential pharmaceutical and medicinal values due to their bioactivities as neuroprotective and neurodegenerative treatment activities. These peptides have attracted great interest in the pharmaceutical industries, in order to design potential peptides for use in the prophylactic and therapy purposes. Some natural peptides and their derivatives have high commercial values and have succeeded in reaching the pharmaceutical market. A large number of peptides are already in preclinical and clinical pipelines for treatment of various diseases. This review highlights the recent researches on the various natural peptides and future prospects for AD management.

An unexpected cell-penetrating peptide from Bothrops jararaca venom identified through a novel size exclusion chromatography screening

Efficient drug delivery systems are currently one of the greatest challenges in pharmacokinetics, and the transposition of the gap between in vitro candidate molecule and in vivo test drug is, sometimes, poles apart. In this sense, the cell-penetrating peptides (CPP) may be the bridge uniting these worlds. Here, we describe a technique to rapidly identify unlabeled CPPs after incubation with liposomes, based on commercial desalting (size exclusion) columns and liquid chromatography-MS/MS, for peptide de novo sequencing. Using this approach, we found it possible to identify one new CPP - interestingly, a classical bradykinin-potentiating peptide - in the peptide-rich low molecular mass fraction of the Bothrops jararaca venom, which was also able to penetrate live cell membranes, as confirmed by classical approaches employing fluorescence-labeled analogues of this CPP. Moreover, both the labeled and unlabeled CPPs caused no metabolic, cell-cycle or morphologic alterations, proving to be unmistakably cargo deliverers and not drugs themselves. In sum, we have developed and validated a method for screening label-free peptides for CPP activity, regardless of their biological origin, which could lead to the identification of new and more efficient drug delivery systems. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.

Structural basis of peptide recognition by the angiotensin-1 converting enzyme homologue AnCE from Drosophila melanogaster

Human somatic angiotensin-1 converting enzyme (ACE) is a zinc-dependent exopeptidase, that catalyses the conversion of the decapeptide angiotensin I to the octapeptide angiotensin II, by removing a C-terminal dipeptide. It is the principal component of the renin-angiotensin-aldosterone system that regulates blood pressure. Hence it is an important therapeutic target for the treatment of hypertension and cardiovascular disorders. Here, we report the structures of an ACE homologue from Drosophila melanogaster (AnCE; a proven structural model for the more complex human ACE) co-crystallized with mammalian peptide substrates (bradykinin, Thr(6) -bradykinin, angiotensin I and a snake venom peptide inhibitor, bradykinin-potentiating peptide-b). The structures determined at 2-Å resolution illustrate that both angiotensin II (the cleaved product of angiotensin I by AnCE) and bradykinin-potentiating peptide-b bind in an analogous fashion at the active site of AnCE, but also exhibit significant differences. In addition, the binding of Arg-Pro-Pro, the cleavage product of bradykinin and Thr(6) - bradykinin, provides additional detail of the general peptide binding in AnCE. Thus the new structures of AnCE complexes presented here improves our understanding of the binding of peptides and the mechanism by which peptides inhibit this family of enzymes.

DATABASE

The atomic coordinates and structure factors for AnCE-Ang II (code 4AA1), AnCE-BPPb (code 4AA2), AnCE-BK (code 4ASQ) and AnCE-Thr6-BK (code 4ASR) complexes have been deposited in the Protein Data Bank, Research Collaboratory for Structural Bioinformatics, Rutgers University, New Brunswick, NJ (http://www.rcsb.org/)

STRUCTURED DIGITAL ABSTRACT

• AnCE cleaves Ang I by enzymatic study (View interaction) • Bradykinin and AnCE bind by x-ray crystallography (View interaction) • BPP and AnCE bind by x-ray crystallography (View interaction) • AnCE cleaves Bradykinin by enzymatic study (View interaction) • Ang II and AnCE bind by x-ray crystallography (View interaction).