Inhibitory Effects of the Peptide (CKPV)2 on Endotoxin-Induced Host Reactions

Innate Inspiration: Antifungal Peptides and Other Immunotherapeutics From the Host Immune Response

The purpose of this review is to describe antifungal therapeutic candidates in preclinical and clinical development derived from, or directly influenced by, the immune system, with a specific focus on antimicrobial peptides (AMP). Although the focus of this review is AMP with direct antimicrobial effects on fungi, we will also discuss compounds with direct antifungal activity, including monoclonal antibodies (mAb), as well as immunomodulatory molecules that can enhance the immune response to fungal infection, including immunomodulatory AMP, vaccines, checkpoint inhibitors, interferon and colony stimulating factors as well as immune cell therapies. The focus of this manuscript will be a non-exhaustive review of antifungal compounds in preclinical and clinical development that are based on the principles of immunology and the authors acknowledge the incredible amount of in vitro and in vivo work that has been conducted to develop such therapeutic candidates.

Alpha-melanocyte stimulating hormone: an emerging anti-inflammatory antimicrobial peptide

The alpha-melanocyte stimulating hormone (α-MSH) is a neuropeptide belonging to the melanocortin family. It is well known for its anti-inflammatory and antipyretic effects and shares several characteristics with antimicrobial peptides (AMPs). There have been some recent reports about the direct antimicrobial activity of α-MSH against various microbes belonging to both fungal and bacterial pathogens. Similar to α-MSH's anti-inflammatory properties, its C-terminal residues also exhibit antimicrobial activity parallel to that of the entire peptide. This review is focused on the current findings regarding the direct antimicrobial potential and immunomodulatory mechanism of α-MSH and its C-terminal fragments, with particular emphasis on the prospects of α-MSH based peptides as a strong anti-infective agent.

The synthetic melanocortin (CKPV)2 exerts anti-fungal and anti-inflammatory effects against Candida albicans vaginitis via inducing macrophage M2 polarization

In this study, we examined anti-fungal and anti-inflammatory effects of the synthetic melanocortin peptide (Ac-Cys-Lys-Pro-Val-NH₂)₂ or (CKPV)₂ against Candida albicans vaginitis. Our in vitro results showed that (CKPV)₂ dose-dependently inhibited Candida albicans colonies formation. In a rat Candida albicans vaginitis model, (CKPV)₂ significantly inhibited vaginal Candida albicans survival and macrophages sub-epithelial mucosa infiltration. For mechanisms study, we observed that (CKPV)₂ inhibited macrophages phagocytosis of Candida albicans. Meanwhile, (CKPV)₂ administration inhibited macrophage pro-inflammatory cytokines (TNF-α, IL-1β and IL-6) release, while increasing the arginase activity and anti-inflammatory cytokine IL-10 production, suggesting macrophages M1 to M2 polarization. Cyclic AMP (cAMP) production was also induced by (CKPV)₂ administration in macrophages. These above effects on macrophages by (CKPV)₂ were almost reversed by melanocortin receptor-1(MC1R) siRNA knockdown, indicating the requirement of MC1R in the process. Altogether, our results suggest that (CKPV)₂ exerted anti-fungal and anti-inflammatory activities against Candida albicans vaginitis probably through inducing macrophages M1 to M2 polarization and MC1R activation.

Antimicrobial peptides for therapeutic applications: a review

Antimicrobial peptides (AMPs) have been considered as potential therapeutic sources of future antibiotics because of their broad-spectrum activities and different mechanisms of action compared to conventional antibiotics. Although AMPs possess considerable benefits as new generation antibiotics, their clinical and commercial development still have some limitations, such as potential toxicity, susceptibility to proteases, and high cost of peptide production. In order to overcome those obstacles, extensive efforts have been carried out. For instance, unusual amino acids or peptido-mimetics are introduced to avoid the proteolytic degradation and the design of short peptides retaining antimicrobial activities is proposed as a solution for the cost issue. In this review, we focus on small peptides, especially those with less than twelve amino acids, and provide an overview of the relationships between their three-dimensional structures and antimicrobial activities. The efforts to develop highly active AMPs with shorter sequences are also described.

Melanocortin peptides inhibit urate crystal-induced activation of phagocytic cells

INTRODUCTION

The melanocortin peptides have marked anti-inflammatory potential, primarily through inhibition of proinflammatory cytokine production and action on phagocytic cell functions. Gout is an acute form of arthritis caused by the deposition of urate crystals, in which phagocytic cells and cytokines play a major pathogenic role. We examined whether alpha-melanocyte-stimulating hormone (alpha-MSH) and its synthetic derivative (CKPV)2 influence urate crystal-induced monocyte (Mo) activation and neutrophil responses in vitro.

METHODS

Purified Mos were stimulated with monosodium urate (MSU) crystals in the presence or absence of melanocortin peptides. The supernatants were tested for their ability to induce neutrophil activation in terms of chemotaxis, production of reactive oxygen intermediates (ROIs), and membrane expression of CD11b, Toll-like receptor-2 (TLR2) and TLR4. The proinflammatory cytokines interleukin (IL)-1beta, IL-8, and tumor necrosis factor-alpha (TNF-alpha) and caspase-1 were determined in the cell-free supernatants. In parallel experiments, purified neutrophils were preincubated overnight with or without melanocortin peptides before the functional assays.

RESULTS

The supernatants from MSU crystal-stimulated Mos exerted chemoattractant and priming activity on neutrophils, estimated as ROI production and CD11b membrane expression. The supernatants of Mos stimulated with MSU in the presence of melanocortin peptides had less chemoattractant activity for neutrophils and less ability to prime neutrophils for CD11b membrane expression and oxidative burst. MSU crystal-stimulated Mos produced significant levels of IL-1beta, IL-8, TNF-alpha, and caspase-1. The concentrations of proinflammatory cytokines, but not of caspase-1, were reduced in the supernatants from Mos stimulated by MSU crystals in the presence of melanocortin peptides. Overnight incubation of neutrophils with the peptides significantly inhibited their ability to migrate toward chemotactic supernatants and their capacity to be primed in terms of ROI production.

CONCLUSIONS

Alpha-MSH and (CKPV)2 have a dual effect on MSU crystal-induced inflammation, inhibiting the Mos' ability to produce neutrophil chemoattractants and activating compounds and preventing the neutrophil responses to these proinflammatory substances. These findings reinforce previous observations on the potential role of alpha-MSH and related peptides as a new class of drugs for treatment of inflammatory arthritis.

In vitro antimicrobial activity of alpha-melanocyte stimulating hormone against major human pathogen Staphylococcus aureus

Alpha-melanocyte stimulating hormone (alpha-MSH) is an endogenous anti-inflammatory peptide reported to possess antimicrobial properties, however their role as antibacterial peptides is yet to be established. In the present study, we examined in vitro antibacterial activity of alpha-MSH against S. aureus strain ISP479C and several methicillin-sensitive (MSSA) and methicillin-resistant (MRSA) S. aureus strains. Antibacterial activity was examined by varying several parameters, viz., bacterial cell densities, growth phase, pH, salt concentration, and temperature. Antibacterial activity was also examined in complex biomatrices of rat whole blood, plasma and serum as well as in biofilm form of bacteria. Our results showed that alpha-MSH possessed significant and rapid antibacterial activity against all the studied strains including MRSA (84% strains were killed on exposure to 12 microM of alpha-MSH for 2h). pH change from 7.4 to 4 increased alpha-MSH staphylocidal activity against ISP479C by 21%. Antibacterial activity of alpha-MSH was dependent on bacterial cell density and independent of growth phase. Moreover, antimicrobial activity was retained when alpha-MSH was placed into whole blood, plasma, and serum. Most importantly, alpha-MSH exhibited antibacterial activity against staphylococcal biofilms. Multiple membrane permeabilization assays suggested that membrane damage was, at least in part, a major mechanism of staphylocidal activity of alpha-MSH. Collectively the above findings suggest that alpha-MSH could be a promising candidate of a novel class of antimicrobial agents.

The synthetic melanocortin (CKPV)2 exerts broad anti-inflammatory effects in human neutrophils

Natural melanocortin peptides exert broad effects on the host and they have remarkable therapeutic potential. However, successful use of melanocortins as therapeutic agents depends on the design of molecules that have more stable pharmacological profiles. The synthetic peptide (CKPV)(2), based on the C-terminal sequence of alpha-melanocyte stimulating hormone (alpha-MSH), has anti-tumor necrosis factor-alpha (TNF-alpha) effects in vitro and in vivo and is a promising candidate to treat inflammation. Because neutrophil activity is a major target for anti-inflammatory therapies, we determined whether (CKPV)(2) modulates human neutrophil functions in vitro. Incubation of freshly-separated human neutrophils with 10(-12)-10(-6)M (CKPV)(2) significantly inhibited activities relevant to the inflammatory reaction. Neutrophil migration toward the two chemoattractants interleukin 8 (IL-8) and N-formyl-methionyl-leucyl-phenylalanine (fMLP) was significantly inhibited by (CKPV)(2). (CKPV)(2) also inhibited reactive oxygen intermediate (ROI) production induced by phorbol 12-myristate 13-acetate (PMA), but not that induced by fMLP. Because these effects of (CKPV)(2) were abolished by the adenylyl cyclase inhibitor 2',5'-dideoxyadenosine (ddAdo), they appear to be cAMP-dependent. Finally, the peptide reduced lipopolysaccharide (LPS)-stimulated expression of TNF-alpha, interleukin-1beta (IL-1beta), interleukin-8 (IL-8), and intercellular adhesion molecule 1 (ICAM-1), as well as TNF-alpha protein release in cell supernatants. The data indicate that (CKPV)(2) modulates broad cAMP-dependent, anti-inflammatory pathways in human neutrophils.

The melanocortin system in leukocyte biology

The melanocortin system is composed of the melanocortin peptides, adrenocorticotropic hormone and alpha-, beta-, and gamma-melanocyte-stimulating hormone, the melanocortin receptors (MCRs), and the endogenous antagonists agouti- and agouti-related protein. Melanocortin peptides exert multiple effects upon the host, including anti-inflammatory and immunomodulatory effects. Leukocytes are a source of melanocortins and a major target for these peptides. Because of reduced translocation of the nuclear factor NF-kappaB to the nucleus, MCR activation by their ligands causes a collective reduction of the most important molecules involved in the inflammatory process. This review examines how melanocortin peptides and their receptors participate in leukocyte biology.