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Monthly Archives: December 2020

  • The Development and Use of Peptides as Therapeutics

    Peptides refer to biologically active molecules that contain at least two amino acids, interlinked by a peptide bond. Unlike large proteins, they are small in size and a typical chain will usually not go past 100 amino acids.

    Since peptides are highly selective and also known to have relatively safe characteristics, their pharmacological profiles have always appealed to the research world. They are readily available in the human body where they play diverse biological roles.

    For most applications, they mainly act as regulatory and signaling molecules in various physiological processes. Back in the day, the instability of peptides limited their use in the design and development of human drugs, but due to technological breakthroughs, the instability challenges have all been overcome, greatly increasing the broad application of peptides.
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  • The Use of Therapeutic Peptides in Cancer Treatments

    Cancer and cardiovascular diseases are among the major causes of death in most developed countries. Most of the conventional approaches to treating cancer are quickly losing their therapeutic relevance due to the lack of tumor selectivity, drug resistance, and solubility. As such, there is a great need for the development of new therapeutic agents and treatment plans. Over the years, therapeutic peptides have provided a glimmer of hope, and they are currently being considered as a novel approach to treating a variety of diseases, including various forms of cancer.

    This is because they come with a variety of advantages over normal proteins and antibodies. Some of these advantages include easy synthesis, high target selectivity, and specificity, and very low toxicity. They, however, have some drawbacks, with their stability and short half-life being among major concerns. In this piece, we will be looking at some of the therapeutic peptides receiving the most attention currently and some of the strategies being used to overcome some of the peptide limitations.
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  • Promising Cancer Therapies With Peptide-Based Treatments

    What are Peptides and How are They Used?

    Peptides are molecules consisting of various chains of amino acids joined by peptides bonds through the process of a dehydration-condensation reaction. There are various places, or various origins of peptides, including but not limited to direct synthesis by the body, artificial synthesis, or through processes such as proteolysis. They play a huge role in the treatment of a variety of diseases, and they are currently at the center stage in the development of various types of vaccines and for the use of targeted therapy.
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  • Interesting Findings About Peptide Immunotherapeutics

    The development of peptide vaccines has been in the works for a very long time, but with minimal success. However, current advancements in medical technology, as well as an increased understanding of the immune system – more specifically the operations of the antigenic epitopes in stimulating an immune response, have opened a whole new field and made the development of peptide vaccines possible.

    Peptide-based vaccines – technically known as epitope ensemble vaccines, are viewed as a viable alternative approach to the discovery and development of not just targeted therapy but also prophylactic vaccines.
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  • Peptides as Therapeutic Agents for Inflammatory-Related Diseases

    An inflammation is the body's normal response to lesions and infections. The immune system cells move to the site of the injury or infection, and cause an inflammation. To treat this disorder, unspecific small molecule drugs are used, which may cause some side effects.
    The inflammation produces mediators such as cytokines, interleukins, and growth factors. It is necessary to regulate the inflammation to stabilize or heal the damaged cells or tissues.

    A lot of research is being made, and peptides have been used as an alternative anti-inflammatory therapy. Actually, peptides are considered effective compounds, and show an innovative strategy by stopping, diminishing, and/or changing the expression and activity of mediators.
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  • What are the benefits of peptides in cosmetics ?

    The cosmetic industry represents a huge worldwide sector. Between skincare, makeup, and haircare, it is growing faster than most other industries, and its market value is estimated to be worth almost $805 billion by 2023.

    The key to this evolution is innovation. Every brand tries to create new products with new compositions in order to target a maximum of people. More and more people are very careful about each product’s contents, which is why brands always have to conduct lots of research and find a way to make the perfect product, containing the best natural elements possible.
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  • Antimicrobial Peptides in Human Health

    The human body has always been special to scientists because it has this amazing capacity to repair itself (like a broken bone) and to protect itself from any kind of exterior aggressions. After studies and a lot of research, it was discovered that peptides in the body are one of the reasons why it can face pathogens and stay healthy.

    One kind of peptide is very important in the body, which is the antimicrobial peptide (AMP). These peptides are essential to the body's natural defense against diseases. They ward off invading microbial pathogens such as viruses and bacteria. Also, they have had a major role in the development of therapeutic agents to prevent and treat diseases, which has become even more important, considering the situation we are facing now.
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  • The Potential of Antifungal Peptides as Therapeutic Agents

    Fungi have been used for centuries for food and beverage processing. In recent years, a better understanding of science and advancement in medical technology has shone a spotlight on their potential for being used as antibiotics to overcome the well-known deficits of the current antibiotics in use. However, it should not be forgotten that fungi are also responsible for causing a myriad of infectious diseases. There is well-documented evidence of an increase in the number of cases for community-acquired fungal infections over the past decade.

    Furthermore, a rise in the number of immunodeficiency-related cases, antibiotic resistance development, and limited therapeutic options, have made the search for alternatives a serious concern, and one which the research world is currently heavily involved. There is a need for the new antifungals being formulated, currently to be less toxic for the host, and it is also vital for them to have broader or targeted antimicrobial spectra, and have very little chances for triggering resistance in the long run.

    With such criteria in mind, a lot of focus has been turned towards antimicrobial peptides that exhibit antifungal properties. These peptides are currently being viewed as powerful potential candidates because of their high efficacy, as well as high selectivity. In this piece, we will be providing an overview of the classification, as well as the bioactivity of both natural and synthetic antifungal peptides, including their modes of action, as well as the specific advantages they have over the current drugs being used, as antifungal therapies.

    Types of Antifungal Peptides and Bioactivity

    Currently, it is estimated that there are about 1,133 peptides that possess antifungal properties – this is according to the information availed by Antimicrobial Peptide Database (APD). Below is a classification of antifungal peptides, based on their structure or mode of operation. However, the most acceptable classification is usually based on whether they are natural, synthetic, or semisynthetic.

    Natural Antifungal Peptides

    Natural antifungal peptides originate from a variety of species of bacteria, eukarya, and archae obtained from various natural sources. A good number of the natural antifungal bacteria thought antagonist activity testing in vitro on known pathogenic fungi. But with the increased use of sequencing technologies, new strategies have been formulated for predicting and discovering new natural antifungal peptides.

    Some of the notable new methods that are currently being used for the discovery and prediction of these peptides include the hidden Markov model, docking simulations, and various template-based and sequence-based methods that make it possible for the novel in silico prediction of the antifungal peptides.

    In most cases, natural antifungal peptides usually have an alpha-helix structure, beta-hairpin (or sheet), or a blend between alpha/beta-sheet structures whenever they interact with the membranes. Some of the natural antifungal peptides are rich in certain amino acids, causing them to be classified as glycine-rich arginine-rich, tryptophan-rich, histidine-rich, and proline-rich amino acids. However, the actual structure of most of the antifungal peptides is yet to be fully determined.

    Synthetic and Semisynthetic Peptides and Structure-Activity Relationship

    Antifungal synthetic and semisynthetic peptides are designed with the aim of improving the pharmacological properties, lowering immunogenicity, and reducing some of the undesirable side effects of the natural peptides. The pharmacological alterations also help in enhancing the bioavailability, as well as the stability of the peptides. A very good example of such pharmacological transformation is the reduction of the hemolytic activity of echinocandin B antifungal peptide, which was achieved by replacing the linoleoyl side-chain, with a pentyloxy terphenyl or octyloxy benzoyl side chains.

    Structure-activity relationships (SAR) are vital factors of considerations in the design and development of synthetic peptides. There are lots of biophysical properties that can be used in the determination of antifungal activities, with the common ones being the peptide length, the secondary structure, amphipathicity, hydrophobicity, net charge, and stereospecificity among others. Some of these characteristics are interdependent on each other, while others are completely independent.

    It should be noted, however, that most of the antifungal peptides are non-stereospecific and in a similar manner, we don’t have any dominant conformations among the antifungal peptides. Consequently, the main differentiating factors among the peptides originate from the variations of the sequences in both primary and secondary structures.

    Amphipathicity and hydrophobicity are vital factors when it comes to the interactions at the peptide membranes, as well as the processes of membrane permeabilization, not forgetting vital variables in designing synthetic peptides. A rise in hydrophobicity and amphipathicity correlates positively to a rise in antifungal activities, as well as an increase in hemolytic activities. Studies also suggest that tryptophan can lead to an increase in hemolytic activities, because of its ability to alter lipid polymorphism in the membranes.

    The length of the antifungal peptides is also vital for the secondary structure, as well as the mode of action. Most of the already-discovered antifungal peptides have between 11 and 40 residues. Studies show that about 7 – 8 amino acids are necessary for the formation of amphipathic structures in antimicrobial peptides. Studies also postulate that longer lengths of the amino acids may have potential impacts on the stability, cytotoxicity, and manufacturing costs.

    To go around these hurdles, short microbial peptides with no more than amino ten amino acids are coming out as potential alternatives, because they are more stable and they have low toxicity. In general, short antimicrobial peptides comprise simple amino acids, and it is easy to synthesize and modify them chemically, which brings a lot of control over toxicity, half-life, specificity, and stability. They have also been found to be less immunogenic.

    The Potential of Antifungal Peptides as Therapeutic Agents

    Mechanisms of Actions of Antifungal Peptides

    Peptides with antifungal properties have a very broad range of antimicrobial spectrum including viruses, fungi, and bacteria. Below is a brief look at the hypothetical mechanisms of how antifungal peptides operate when fighting fungal pathogens.

    Inhibiting the Actions of 1,3-β-Glucan Synthesis

    β-glucan synthesis is important for the integrity of the cell walls. However, cyclic lipoproteins may succeed to non-competitively inhibit it causing the destabilization of the cell wall, making it prone to cell lysis and osmotic stress.

    1,3-β-Glucans are heavily involved with processes such as septum division and assembly of the walls – an action that makes it possible for β-Glucan synthase inhibitors to affect the structures of the cell walls. When β-Glucan synthase is inhibited, it leads to negative feedback, which puts the cell cycles to rest.

    Inhibitions of Chitin Biosynthesis in the Cell Walls

    Chitin is present in the walls of the fungal cells. It is a vital amino acid in marinating cell integrity. Aureobasidins belong to this category, and they are cyclic lipophilic 8-mer depsipeptides, with two major modes of action: interrupting sphingolipid synthesis and interrupting cell wall membranes by changing the accumulation of actin.

    Various members of aureobasidin family display anti-candida activity. These antifungal peptides are also known to interfere with the synthesis of chitin found in C. Albicans, as it was observed in various in vivo and in vitro studies.

    Selective Activities on Membranes

    One of the natural antifungal peptides that have shown selective activity on the cell membranes, is Rs-ARF2. This is a 50 amino acid residue obtained from plant defensin and exhibits three-stranded alpha-helix and beta-sheets structures. The amino acid residue has shown super effective properties in targeting fungus-specific membrane glucosylceramide, which is known to induce membrane permeability that further leads to increased uptake of Ca ions and medium alkalinization.

    The defending is also known to cause an increase in the formation of toxic and reactive oxygen species intracellularly. Rs-ARF2 does not have this particular fungus-specific ceramide. They have very little cytotoxicity on mammalian cells when administered in dosages that might cause fungal pathogen inhibition.

    Iturins are also natural antifungal peptides with very interesting selective activities on the cell membranes. They are cyclic peptides with a lipophilic amino acid attached to the L and D acids. They are mostly produced by Bacilus Subtilis, and they are very well-known to cause pore formation in the membranes, leading to leakage of certain key ions.

    They have very limited antimicrobial activities with very little effect on bacteria. Sadly, these peptides have been discovered to be toxic to mammalian cell membranes. Also interestingly, the bulk of antimicrobial peptides are usually cationic, but iturins are also cationic but may sometimes be anionic or neutral. Bacillomycin F is a member of this family and it is known to effectively inhibit the actions of C. Tropicalis, C. Albicans, and A. niger.

    Histatin 5 is another natural antimicrobial peptide whose activities on the cell membranes are worth pointing out. It is a mammalian peptide with four arginines, seven histidines, and three lysines. Such a structure causes it to adopt an alpha-helical structure when present in non-aqueous environments.

    The peptide works by binding itself to Ssa2p –a cell wall protein that is necessary for internalizing histatin5 into the cells. For the smooth uptake of this peptide, the polyamine transporters of Dur31 and Dur3 are always necessary. These have to be translocated into the cells.

    The Broad Range of Antimicrobial Peptides

    Most of the antimicrobial peptides have various ways of affecting a number of microorganisms. Such organisms include fungi, envelope-containing viruses, and bacteria. Most of the antimicrobial peptides can be collectively grouped as cyclic peptides or linear peptides.

    Examples of cyclic peptides include poultry gallinacean, syringomycins, macrocyclic peptides, and mammalian defensin among others. Examples of linear peptides include magainins, cathelicidins, lactoferrin-derived peptides, and bombinins.

    Most of these peptides are known to cause membrane disruption by forming a toroidal pore that causes essential molecules to leak through the membranes, hence, greatly compromising the integrity and functionality of the membrane.

    Other mechanisms of the antimicrobial peptide actions include demixing and clustering, alteration of membrane potential, lipid flip-flop, the formation of anionic lipid-peptide domains, and membrane thinning, among others. Additionally, some of these antimicrobial peptides may influence cell processes such as inhabitation of DNA replication, cell apoptosis induction, damage of the DNA and protein, and RNA synthesis among others.

    Advantages of Antifungal Peptides

    The current antifungal agents have a wide range of shortcomings that hamper their efficacy as therapeutic tools in the fight against fungal infections. There is just a handful of approved antifungal drugs but their future as antifungal therapies is shrouded with a lot of uncertainties because of the persistent resistance to those therapies.

    Apart from the antifungal resistance, the current therapies have a low diversity of mechanisms of action. Some of them also exhibit adverse reactions on the hosts while others also affect common eukaryotic targets present in both human cells and pathogenic fungi cells. These challenges have caused serious problems in the design and development of novel efficient and non-toxic antifungal therapies.

    Antifungal peptides are currently being viewed as the best alternatives for overcoming the shortcomings of the current antifungal drugs. This is because antifungal peptides have multiple microbial targets and this helps to reduce the possibility of the development of resistance as is the case with most antifungal drugs. Some of the notable antimicrobial targets include molecules for physiological processes such as DNA and RNA, cell cycle, protein synthesis, and different cell wall components.

    Due to the lack of side effects, a good number of antifungal peptides are able to target very specific fungal molecules. This ability leads to high pathogen selectivity and also helps to reduce the chances of cytotoxicity on mammalian cells. Sadly, this is not an assurance that there will be no cytotoxicity. However, most of the antifungal peptides have highly reduced cytotoxicity.

    This is believed to be the case because of two reasons. One: It is believed that there exists a stronger interaction between the cationic charges of the peptide and the negatively charged fungal membrane. Two, some of the antifungal peptides target membrane lipids, which are unique to the fungi and are not found in mammalian cells. This phenomenon greatly helps to reduce toxicity.

    More and more evidence is being gathered to show that antimicrobial peptides and antifungal peptides are multifactorial. Host defense peptides such as the cathelicidins and defensins are known to be anti-inflammatory, immunomodulatory, and angiogenic.

    They also display the ability to initiate adaptive immune responses. With further insights in the development of antifungal therapies using antifungal peptides, resistance to the current antifungal drugs will be a thing of the past, and there will be a whole new regime for dealing with fungal and microbial infections.

    References

    1. Andreu, D., and Rivas, L. (1998). Animal antimicrobial peptides: an overview. J. Pept. Sci. 47, 415–433. doi: 10.1002/(SICI)1097-0282(1998)47:6<415::AID-BIP2>3.0.CO;2-D
    2. Auchtung, T. A., Fofanova, T. Y., Stewart, C. J., Nash, A. K., Wong, M. C., Gesell, J. R., et al. (2018). Investigating colonization of the healthy adult gastrointestinal tract by fungi. mSphere 3:e00092–18. doi: 10.1128/mSphere.00092-18
    3. Bahar, A. A., and Ren, D. (2013). Antimicrobial peptides. Pharmaceuticals 6, 1543–1575. doi: 10.3390/ph6121543
    4. Balkovec, J. M., Black, R. M., Hammond, M. L., Heck, J. V., Zambias, R. A., Abruzzo, G., et al. (1992). Synthesis, stability, and biological evaluation of water-soluble prodrugs of a new echinocandin lipopeptide. Discovery of a potential clinical agent for the treatment of systemic candidiasis and Pneumocystis carinii pneumonia (PCP). J. Med. Chem. 35, 194–198. doi: 10.1021/jm00079a027
    5. Baltz, R. H. (2010). Streptomyces and Saccharopolyspora hosts for heterologous expression of secondary metabolite gene clusters. J. Ind. Microbiol. Biotechnol. 37, 759–772. doi: 10.1007/s10295-010-0730-9
    6. Bazinet, L., and Firdaous, L. (2013). Separation of bioactive peptides by membrane processes: technologies and devices. Recent. Pat. Biotechnol. 7, 9–27. doi: 10.2174/1872208311307010003
    7. Bechinger, B., and Lohner, K. (2006). Detergent-like actions of linear amphipathic cationic antimicrobial peptides. Biochim. Biophys. Acta 1758, 1529–1539. doi: 10.1016/j.bbamem.2006.07.001
    8. Bednarska, N. G., Wren, B. W., and Willcocks, S. J. (2017). The importance of the glycosylation of antimicrobial peptides: natural and synthetic approaches. Drug Discov. Today 22, 919–926. doi: 10.1016/j.drudis.2017.02.001
    9. Behrendt, R., White, P., and Offer, J. (2016). Advances in Fmoc solid-phase peptide synthesis. J. Pept. Sci. 22, 4–27. doi: 10.1002/psc.2836
    10. Belaid, A., and Hani, K. (2011). Antiviral and antifungal activity of some dermaseptin S4 analogues. Afr. J. Biotechnol. 10, 14962–14967. doi: 10.5897/AJB11.1108
    11. Besson, F., and Michel, G. (1984). Action of the antibiotics of the iturin group on artificial membranes. J. Antibiot. 37, 646–651. doi: 10.7164/antibiotics.37.646
    12. Bewley, C. A., and Faulkner, D. J. (1994). Theonegramide, an antifungal glycopeptide from the Philippine lithistid sponge Theonella swinhoei. J. Org. Chem. 59, 4849–4852. doi: 10.1021/jo00096a028
    13. Beyda, N. D., Lewis, R. E., and Garey, K. W. (2012). Echinocandin resistance in Candida species: mechanisms of reduced susceptibility and therapeutic approaches. Ann. Pharmacother. 46, 1086–1096. doi: 10.1345/aph.1R020
    14. Bhatla, S. C., Kaushik, V., and Yadav, M. K. (2010). Use of oil bodies and oleosins in recombinant protein production and other biotechnological applications. Biotechnol. Adv. 28, 293–300. doi: 10.1016/j.biotechadv.2010.01.001
    15. Bink, A., Kucharíková, S., Neirinck, B., Vleugels, J., van Dijck, P., Cammue, B. P. A., et al. (2012). The nonsteroidal antiinflammatory drug diclofenac potentiates the in vivo activity of caspofungin against Candida albicans biofilms. J. Infect. Dis. 206, 1790–1797. doi: 10.1093/infdis/jis594
    16. Blondelle, S. E., and Lohner, K. (2000). Combinatorial libraries: a tool to design antimicrobial and antifungal peptide analogues having lytic specificities for structure–activity relationship studies. J. Pept. Sci. 55, 74–87. doi: 10.1002/1097-0282(2000)55:1<74::AID-BIP70>3.0.CO;2-S
    17. Bondaryk, M., Staniszewska, M., Zielinska, P., and Urbanczyk-Lipkowska, Z. (2017). Natural antimicrobial peptides as inspiration for design of a new generation antifungal compounds. J. Fungi 3:46. doi: 10.3390/jof3030046
  • What You Need To Know About Antimicrobial Peptides

    The presence of various natural antimicrobial substances that contribute to a horde of body defense mechanisms was discovered during the late 19th century, and the research world has never relented since. It was in the year 1963 when in vitro antimicrobial activities of leukocyte extracts were discovered to be an activity of basic proteins. Since then, there have been discoveries of various cationic peptides with antimicrobial properties. Most of these peptides were discovered in host cells and tissues, and in virtually every other living species.
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