Peptide secretion in the cutaneous glands of South American tree frog Phyllomedusa bicolor: an ultrastructural study

The importance of antimicrobial peptides (AMPs) in amphibian skin defense

Antimicrobial peptides (AMPs) are produced for defense in nearly all taxa from simple bacteria to complex mammalian species. Some amphibian families have developed this defensive strategy to a high level of sophistication by loading the AMPs into specialized granular glands within the dermis. Enervated by the sympathetic nervous system, the granular glands are poised to deliver an array of AMPs to cleanse the wound and facilitate healing. There have been a number of excellent review publications in recent years that describe amphibian AMPs with an emphasis on their possible uses for human medicine. Instead, my aim here is to review what is known about the nature of amphibian AMPs, the diversity of amphibian AMPs, regulation of their production, and to provide the accumulated evidence that they do, indeed, play an important role in the protection of amphibian skin, vital for survival. While much has been learned about amphibian AMPs, there are still important gaps in our understanding of peptide synthesis, storage, and functions.

The Complex Bridge between Aquatic and Terrestrial Life: Skin Changes during Development of Amphibians

Amphibian skin is a particularly complex organ that is primarily responsible for respiration, osmoregulation, thermoregulation, defense, water absorption, and communication. The skin, as well as many other organs in the amphibian body, has undergone the most extensive rearrangement in the adaptation from water to land. Structural and physiological features of skin in amphibians are presented within this review. We aim to procure extensive and updated information on the evolutionary history of amphibians and their transition from water to land-that is, the changes seen in their skin from the larval stages to adulthood from the points of morphology, physiology, and immunology.

The Amazonian kambô frog Phyllomedusa bicolor (Amphibia: Phyllomedusidae): Current knowledge on biology, phylogeography, toxinology, ethnopharmacology and medical aspects

Phyllomedusa bicolor (Phyllomedusidae), popularly known as the kambô in Brazil, is a tree frog that is widely distributed in South American countries and is known for producing a skin secretion that is rich in bioactive peptides, which are often used in indigenous rituals. The biological effects of the skin secretion were observed in the first studies with indigenous communities. Over the last six decades, researchers have been studying the chemical composition in detail, as well as the potential pharmacological applications of its constituents. For this reason, indigenous communities and health agents fear the misuse of the kambô, or the inappropriate use of the species, which can result in health complications or even death of users. This article seeks to provide a transdisciplinary review that integrates knowledge regarding the biology of P. bicolor, ethnoknowledge about the ritual of the kambô, and the chemistry and pharmacology of the skin secretion of this species, in addition to medical aspects of the indiscriminate use of the kambô. Furthermore, this review seeks to shed light on perspectives on the future of research related to the kambô.

KAMBO: NATURAL DRUG OR POTENTIAL TOXIC AGENT? A LITERATURE REVIEW OF ACUTE POISONING CASES

Kambo is the name of a natural substance derived from the glandular secretions of the amphibian Phyllomedusa bicolor, a species native to regions in South America. The communities living in these areas administer the substance generally transdermally during rituals for religious-purifying purposes, producing small skin burns. The scientific literature has reported some cases of intoxication following the use of Kambo but this aspect is still poorly understood. In fact, no shared therapy protocols exist for these events nor any real legislation on Kambo. The purpose of this work was to examine all cases of acute intoxication resulting from the administration of Kambo and published over the last 10 years, illustrating clinical signs, laboratory findings, instrumental tests, and therapy. The several cases identified in our review confirm that acute Kambo intoxication can occur, with serious and life-threatening effects. We developed a protocol aimed at the early diagnosis of cases of suspected acute intoxication by creating a treatment algorithm. The study aims to investigate the pathophysiology of these events in humans, proposing a protocol for the diagnosis and treatment of these cases that can be used by healthcare professionals.

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The use of Kambo has spread for distribution worldwide through numerous websites.

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The literature review confirmed that acute Kambo intoxication include possible side effects.

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Intoxication may affect various systems with laboratory or instrumental alterations.

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Intoxication may be reversible if promptly diagnosed and treated.

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An algorithm with adequate triage can support diagnosis and treatment.

Review of the physiological effects of Phyllomedusa bicolor skin secretion peptides on humans receiving Kambô

Kambô is an Amazonian ritual which includes the application of the defensive secretion of the Phyllomedusa bicolor frog to superficial burns made on the skin of human participants. The secretion, which contains a range of biologically active linear peptides, induces a short purgative experience that is extensively reported by participants to leave them with positive physical, emotional and spiritual after-effects. Various peptides identified in the secretion exert analgesic, vascular, and gastric effects in vivo, and antimicrobial and anti-cancer effects, among others, in vitro. While there has been some investigation into the physiological effects of various individual peptides isolated from the P. bicolor secretion, very little is known about the putative synergistic effects of concurrent administration of the complete substance through the transdermal methods used traditionally in the Kambô ritual. In this review and commentary, the authors summarize the existing biological information from animal research on peptides from the P. bicolor secretion, then consider the evidence in the context of Kambô administration to humans. The presented information suggests that specific peptides are likely to contribute to analogous physiological effects of Kambô in humans. The possibility that beyond their physiological action, the experiential or phenomenological component of these effects may have therapeutic applications is discussed, concluding with a consideration of the feasibility of human clinical research.

A non-lethal method for studying scorpion venom gland transcriptomes, with a review of potentially suitable taxa to which it can be applied

Scorpion venoms are mixtures of proteins, peptides and small molecular compounds with high specificity for ion channels and are therefore considered to be promising candidates in the venoms-to-drugs pipeline. Transcriptomes are important tools for studying the composition and expression of scorpion venom. Unfortunately, studying the venom gland transcriptome traditionally requires sacrificing the animal and therefore is always a single snapshot in time. This paper describes a new way of generating a scorpion venom gland transcriptome without sacrificing the animal, thereby allowing the study of the transcriptome at various time points within a single individual. By comparing these venom-derived transcriptomes to the traditional whole-telson transcriptomes we show that the relative expression levels of the major toxin classes are similar. We further performed a multi-day extraction using our proposed method to show the possibility of doing a multiple time point transcriptome analysis. This allows for the study of patterns of toxin gene activation over time a single individual, and allows assessment of the effects of diet, season and other factors that are known or likely to influence intraindividual venom composition. We discuss the gland characteristics that may allow this method to be successful in scorpions and provide a review of other venomous taxa to which this method may potentially be successfully applied.

Exposure to Batrachochytrium dendrobatidis affects chemical defences in two anuran amphibians, Rana dalmatina and Bufo bufo

Background

Batrachochytrium dendrobatidis (Bd) is the causative agent of chytridiomycosis, one of the major causes of worldwide amphibian biodiversity loss. Many amphibians exhibit skin-based chemical defences, which may play an important role against invading pathogens, but whether the synthesis of these chemical compounds is enhanced or suppressed in the presence of pathogens is largely unknown. Here we investigated direct and indirect effects of larval exposure to the globally distributed and highly virulent Bd-GPL strain on skin secreted chemical defences and life history traits during early ontogeny of agile frogs (Rana dalmatina) and common toads (Bufo bufo).

Results

Exposure to Bd during the larval stage did not result in enhanced synthesis of the antimicrobial peptide Brevinin-1 Da in R. dalmatina tadpoles or in increased production of bufadienolides in B. bufo tadpoles. However, exposure to Bd during the larval stage had a carry-over effect reaching beyond metamorphosis: both R. dalmatina and B. bufo froglets contained smaller quantities of defensive chemicals than their Bd-naïve conspecifics in the control treatment. Prevalence of Bd and infection intensities were very low in both larvae and metamorphs of R. dalmatina, while in B. bufo we observed high Bd prevalence and infection intensities, especially in metamorphs. At the same time, we did not find a significant effect of Bd-exposure on body mass or development rate in larvae or metamorphs in either species.

Conclusions

The lack of detrimental effect of Bd-exposure on life history traits, even parallel with high infection intensities in the case of B. bufo individuals, is surprising and suggests high tolerance of local populations of these two species against Bd. However, the lowered quantity of defensive chemicals may compromise antimicrobial and antipredatory defences of froglets, which may ultimately contribute to population declines also in the absence of conspicuous mass-mortality events.

The sexual dimorphic inguinal glands of the frog species Ololygon centralis (Anura: Hylidae) at light and transmission electron microscopy

The anuran skin characteristically has different types of glands, most of which are microscopic and are spread throughout the skin. Some species have specialized regions where glands agglomerate, forming macroglands. The description of the external morphology of Ololygoncentralis (Pombal & Bastos, 1996) revealed the presence of an inguinal gland. Ololygoncentralis is the only species of the genus that has a macrogland. The present study found these inguinal macroglands to be present only on male specimens, thus characterizing it as a sexually dimorphic skin gland. Microscopic analysis revealed that these glands are composed of many syncytial units involved by myoepithelial cells. The center of the syncytium is full of a proteinaceous secretion with a basic pH and the absence of sugar residues. Similar glands observed in other anuran species have been associated with pheromone production, suggesting that the inguinal glands described for O.centralis males may have a similar function.

Discovery of Novel Caeridins from the Skin Secretion of the Australian White's Tree Frog, Litoria caerulea

Abundant biologically active peptides have been discovered from frog skin secretions, a rich natural source of bioactive compounds with great potential in drug discovery. In this study, three Caeridin peptides, namely, Caeridin-1, S5-Caeridin-1, and Caeridin-a1, were discovered from the skin secretion of the Australian White's tree frog, Litoria caerulea, for the first time, by means of combining transcriptomic and peptidomic analyses. It also represents the first report on bioactive Caeridins since this family of peptides was initially studied 20 years ago. Chemically synthetic versions of each natural Caeridin demonstrated promising bioactivities either on rat smooth muscles or against microbial growth. Specifically, Caeridin-1 produced contraction of rat bladder smooth muscle, while S5-Caeridin-1 induced relaxation of rat ileum smooth muscle, both at nanomolar concentrations. Moreover, Caeridin-a1 was shown to potently inhibit the growth of the planktonic Gram-positive bacteria Staphylococcus aureus (S. aureus), methicillin-resistant S. aureus (MRSA), and Enterococcus faecalis (E. faecalis), the Gram-negative bacterium, Escherichia coli (E. coli), and the yeast, Candida albicans (C. albicans). The discovery of these Caeridins may induce further intensive and systematic studies of frog skin peptides to promote the discovery of natural templates as lead compounds for drug discovery and therapeutic application.

Characterization, Stability and Biological Activity In Vitro of Cathelicidin-BF-30 Loaded 4-Arm Star-Shaped PEG-PLGA Microspheres

BF-30 is a single chain polypeptide of an N-segment with an α-helix from cathelicidin gene encoding, and it contains 30 amino acid residues, with a relative molecular mass and isoelectric point of 3637.54 and 11.79, respectively. Cathelicidin-BF-30 was entrapped in four-arm star-shaped poly(ethylene glycol-b-dl-lactic acid-co-glycolic acid) block copolymers (4-arm-PEG-PLGA) by a double-emulsion solvent-evaporation method. Three release phases of cathelicidin-BF-30loaded 4-arm-PEG-PLGA microspheres were observed, including an initial burst-release phase, followed by a lag phase with minimal drug release and finally a secondary zero-order release phase. The delivery system released BF-30 over more than 15 days in vitro. Furthermore, the material for preparing the microspheres has good biocompatibility and biodegradability. Additionally, based on the drug resistance of food pathogenic bacteria, the antibacterial effects of BF-30 on Shigella dysenteriae CMCC 51105 (Sh. dysenteriae CMCC 51105), Salmonella typhi (S. typhi) and Staphylococcus aureus (S. aureus) as well as the stability of the in vitro release of the BF-30-loded microspheres were studied. The α-helix secondary structure and antibacterial activity of released BF-30 were retained and compared with native peptide. These BF-30 loaded microspheres presented <10% hemolysis and no toxicity for HEK293T cells even at the highest tested concentration (150 μg/mL), indicating that they are hemocompatible and a promising delivery and protection system for BF-30 peptide.

The Biological Effects of Kambo: Is There a Relationship Between its Administration and Sudden Death?

Kambo is a substance obtained from the skin secretions of a frog, Phyllomedusa bicolor, popular in the Amazon region, which is administered via the transdermal route. We report a case of 42-year-old man found dead in his house. Near the corpse, a plastic box labeled as "Kambo sticks" was found. The man was a chronic consumer of Kambo and no previous pathology or genetic disease emerged in clinical history from the declaration of his general practitioner. Autopsy investigations and toxicological analysis were performed. The histopathological examination showed left ventricular hypertrophy. Toxicological screening was negative for ethanol and other drugs. Phyllocaerulein, phyllokinin, and deltorphin A were isolated from the Kambo sticks but, only deltorphin A was detected in blood sample. We describe the first forensic case of death associated with Kambo administration. We attempt to explain how its use could be related to the cause of sudden death in this case.

Immunoreactivities of NF-κB, IL-1β and IL-1R in the skin of Chinese brown frog (Rana dybowskii)

The cytokine interleukin-1 beta (IL-1β) is an evolutionarily conserved molecule that was originally identified in the immune system. Nuclear factor κB (NF-κB) plays a critical role in the activation of immune cells by upregulating the expression of many cytokines. In this study, we investigated the localization and expression level of IL-1β, its functional membrane receptor type I (IL-1R1) and NF-κB in the skin of Rana dybowskii during the breeding period and pre-hibernation. Histologically, the skin of Rana dybowskii consists of epidermis and dermis, and four kinds of cells were identified in the epidermis during the breeding period and pre-hibernation, while the dermis was composed of homogenous gel, mucous glands and granular glands. IL-1β, IL-1R1 and NF-κB were immunolocalized in the epithelial and glandular cells in both periods. Western blotting showed that there was no significant difference in the expression of IL-1β between the breeding period and pre-hibernation, whereas IL-1R1 and NF-κB were significantly higher in the pre-hibernation compared to the breeding period. These results suggested that IL-1β and NF-κB may collectively play important roles in the skin immune system of Rana dybowskii during the breeding period and pre-hibernation.

Skin of the Red Eye Tree Frog Agalychnis Callidryas (Hylidae, Phyllomedusinae) Contains Lipid Glands of the Type Described in the Genus Phyllomedusa

Several anuran species of the genus Phyllomedusa are known to possess specialized cutaneous glands producing lipids and exhibit a peculiar wiping behavior. This behavior is a stereotyped repertory of fore and hind limb movements distributing hydrophobic molecules onto the body surface and reducing evaporative water loss. No reports are presently available on the occurrence of lipid glands in other phyllomedusine genera, and data on the structure of the secretory units specialized for the production of cutaneous lipids are still unclear. The present report is aimed to answer both questions: it describes lipid glands of the Phyllomedusa type in Agalychnis callidryas and provides light and transmission electron microscope evidence of the syncytial structure of their secretory units, a typical feature of serous glands in anuran skin. This morphological trait supports the hypothesis that lipid glands are a specialized subset of the anuran serous glands, and underlines their flexible role in the skin adaption to sub-aerial environments. Anat Rec, 300:503-506, 2017. © 2016 Wiley Periodicals, Inc.

[Amphibian skin as a source of therapeutic peptides]

The search for new bioactive molecules that could be used in therapeutics is a major public health issue, particularly in the treatment of certain diseases such as cancer. In this context the exploration of the venom of animals (snakes, amphibians, cones, scorpions, insects...) that produce molecules of various structures and biological activities, is a very promising direction. Research in this area led to the discovery of neuropeptides, hormones, toxins, antimicrobial peptides and other extremely potent mediators. These are now used in many areas both in fundamental research and in translational research, respectively, to understand biochemical and physiological mechanisms, or to use as medical diagnostic tools and for therapeutic purposes. Pr. V. Erspamer is the first researcher to have shown, in the 1930s, that in addition to biogenic amines and alkaloids, granular glands from the skin of amphibians also produced huge amounts of peptides with various structures and biological activities. He also showed that these peptides had their counterparts, most often in the form of identical or similar peptides, in the central nervous system and the gastrointestinal tract of mammals. These observations are summarized in the form of a triangle concept of "brain-gut-skin" that states that any peptide found in a compartment should be present in the other two. In addition, abundance, ease of extraction and identification of peptides from amphibian skin make this model a means to search for their counterparts in mammals where they are present in minute quantities. This approach has two advantages: (i) at the fundamental level, the large peptide diversity, ubiquity and multiplicity of functions to which they participate, constitute a true chemical library to understand the mechanisms of recognition and signal transduction and study the physicochemical basic of the specificity; and (ii) in terms of applications, the relative simplicity of these peptides and the rise of the production techniques by chemical or recombinant synthesis offer an innovative potential for the development of molecules with pharmacological or therapeutic purposes.

Life history linked to immune investment in developing amphibians

The broad diversity of amphibian developmental strategies has been shaped, in part, by pathogen pressure, yet trade-offs between the rate of larval development and immune investment remain poorly understood. The expression of antimicrobial peptides (AMPs) in skin secretions is a crucial defense against emerging amphibian pathogens and can also indirectly affect host defense by influencing the composition of skin microbiota. We examined the constitutive or induced expression of AMPs in 17 species at multiple life-history stages. We found that AMP defenses in tadpoles of species with short larval periods (fast pace of life) were reduced in comparison with species that overwinter as tadpoles and grow to a large size. A complete set of defensive peptides emerged soon after metamorphosis. These findings support the hypothesis that species with a slow pace of life invest energy in AMP production to resist potential pathogens encountered during the long larval period, whereas species with a fast pace of life trade this investment in defense for more rapid growth and development.

Charge and aggregation pattern govern the interaction of plasticins with LPS monolayers mimicking the external leaflet of the outer membrane of Gram-negative bacteria

Bacterial resistance to antibiotics has become today a major public health issue. In the development of new anti-infectious therapies, antimicrobial peptides appear as promising candidates. However, their mechanisms of action against bacterial membranes are still poorly understood. We describe for the first time the interaction and penetration of plasticins into lipid monolayers and bilayers modeling the two leaflets of the asymmetrical outer membrane of Gram-negative bacteria. The lipid composition of these monolayers mimics that of each leaflet: mixtures of LPS Re 595 mutant and wild type S-form from Salmonella enterica for the external leaflet, and SOPE/SOPG/cardiolipin (80/15/5) for the inner one. The analysis of the interfacial behavior of native (PTCDA1) and modified (PTCDA1-KF) antimicrobial plasticins showed that PTCDA1-KF exhibited better surface properties than its unmodified counterpart. Both peptides could penetrate into the model monolayers at concentrations higher than 0.1 μM. The penetration was particularly enhanced for PTCDA1-KF into the mixed LPS monolayer, due to attractive electrostatic interactions. Grazing X-ray diffraction and atomic force microscopy studies revealed the changes in LPS monolayers organization upon peptide insertion. The interaction of plasticins with liposomes was also monitored by light scattering and circular dichroism techniques. Only the cationic plasticin achieved full disaggregation and structuration in α helices, whereas the native one remained aggregated and unstructured. The main steps of the penetration mechanism of the two plasticins into lipid models of the external leaflet of the outer membrane of Gram-negative bacteria have been established.

Phyllomedusa bicolor skin secretion and the Kambô ritual

The ritual of Kambô or Sapo is a type of voluntary envenomation. During this purification ritual a shaman healer, from various South American countries, deliberately burns the right shoulder with a glowing stick from a fireplace. Excretions of Phyllomedusa bicolor (or Giant Leaf Frog, Kambô or Sapo) are then applied to these fresh wounds. This ritual is used as a means of purification of the body, supposedly brings luck to hunters, increases stamina and enhances physical and sexual strength. All the peripheral and most of the central effects of the secretion can be ascribed to the exceptionally high content of active peptides, easily absorbed through burned skin. This article describes the ritual and the bio-active peptides from the secretion.

Tagging frogs with passive integrated transponders causes disruption of the cutaneous bacterial community and proliferation of opportunistic fungi

Symbiotic bacterial communities play a key role in protecting amphibians from infectious diseases including chytridiomycosis, caused by the pathogenic fungus Batrachochytrium dendrobatidis. Events that lead to the disruption of the bacterial community may have implications for the susceptibility of amphibians to such diseases. Amphibians are often marked both in the wild and in captivity for a variety of reasons, and although existing literature indicates that marking techniques have few negative effects, the response of cutaneous microbial communities has not yet been investigated. Here we determine the effects of passive integrated transponder (PIT) tagging on culturable cutaneous microbial communities of captive Morelet's tree frogs (Agalychnis moreletii) and assess the isolated bacterial strains for anti-B. dendrobatidis activity in vitro. We find that PIT tagging causes a major disruption to the bacterial community associated with the skin of frogs (∼12-fold increase in abundance), as well as a concurrent proliferation in resident fungi (up to ∼200-fold increase). Handling also caused a disruption the bacterial community, although to a lesser extent than PIT tagging. However, the effects of both tagging and handling were temporary, and after 2 weeks, the bacterial communities were similar to their original compositions. We also identify two bacterial strains that inhibit B. dendrobatidis, one of which increased in abundance on PIT-tagged frogs at 1 day postmarking, while the other was unaffected. These results show that PIT tagging has previously unobserved consequences for cutaneous microbial communities of frogs and may be particularly relevant for studies that intend to use PIT tagging to identify individuals involved in trials to develop probiotic treatments.

Molecular cloning of skin peptide precursor-encoding cDNAs from tibial gland secretion of the Giant Monkey Frog, Phyllomedusa bicolor (Hylidae, Anura)

The skins of phyllomedusine frogs have long been considered as being tremendously rich sources of bioactive peptides. Previous studies of both peptides and cloning of their precursor encoding cDNAs have relied upon methanolic skin extracts or the dissected skins of recently deceased specimens and have not considered the different glands in isolation. We therefore focused our attention on the tibial gland of the Giant Monkey Frog, Phyllomedusa bicolor and constructed a cDNA library from the skin secretion that was obtained via mechanical stimulation of this macrogland. Using shotgun cloning, four precursors encoding host-defense peptides were identified: two archetypal dermaseptins, a phyllokinin and a phylloseptin that is new for this species but has been recently described from the Waxy Monkey Leaf Frog, Phyllomedusa sauvagii. Our study is the first to report defensive peptides specifically isolated from anuran tibial glands, confirming the hypothesis that these glands also contribute to chemical defense. Moreover, the discovery of novel compounds for this otherwise very well characterized species suggests that this largely neglected gland might possess a different cocktail of secretions from glands elsewhere in the same animal. We will also discuss some evolutionary implications of our findings with respect to the adaptive plasticity of secretory glands.

Skin micro-organs from several frog species secrete a repertoire of powerful antimicrobials in culture

This work is an attempt to take advantage of the rich biodiversity that exists in Colombia in order to start a systematic analysis of antimicrobial substances that have emerged through amphibian evolution. For this purpose we have developed a technique to grow intact frog skin derived micro-organs (SMOs) in vitro in the absence of serum. We show that in SMOs, the skin glands remain intact and continue to secrete into the medium substances with potent antibacterial activity, for several days in culture. Our strategy has been to create a bank of substances secreted by amphibian skin from different species. This bank contains at present around 50 species and is of particular importance as some of the species are in danger of disappearing. We show that some of the species tested displayed very strong antibacterial activity without being toxic to somatic cell lines, even at 10-fold higher concentration.

Integument structure and function in juvenile Xenopus laevis with disrupted thyroid balance

The skin is the largest organ in the body and is a barrier between the internal and external environment. The present study evaluates how PTU, a goitrogen, that is used to treat hyperthyroidism affects the structure and electrical properties of the frog (Xenopus laevis) skin. The results are considered in the context of the two-membrane model established in the seminal work of Ussing and collegues in the 1940s and 1950s. In vitro experiments with skin from Xenopus adults revealed that PTU can act directly on skin and causes a significant increase (p<0.05, One-way ANOVA) in short circuit current (Isc) via an amiloride-insensitive mechanism. Juvenile Xenopus exposed to waterborne PTU (5 mg/L) had a significantly bigger and more active thyroid gland (p<0.01, Student's t-test) than control Xenopus. The bioelectric properties of skin taken from Xenopus juveniles treated with PTU in vivo had a lower Isc, (3.05±0.4, n=13) and Rt (288.2±39.5) than skin from control Xenopus (Isc, 4.19±1.14, n=14; Rt, 343.3±43.3). A histological assessment of skin from PTU treated Xenopus juveniles revealed the epidermis was significantly thicker (p<0.01, Student's t-test) and had a greater number of modified exocrine glands (p<0.01, Student's t-test) in the dermis compared to control skin. Modifications in skin structure are presumably the basis for its changed bioelectric properties and the study highlights a site of action for environmental chemicals which has been largely neglected.

Experimental strategies for the analysis of D-amino acid containing peptides in crustaceans: a review

Detection of D-amino acids in natural peptides has been, and remains a challenging task, as peptidyl isomerization is a peculiar and subtle posttranslational modification that does not induce any change in primary sequence or in physicochemical properties of the molecule such as molecular mass or pI. Therefore, the presence of a D-amino acid residue in a peptide chain is generally transparent to classical methods of peptide analysis (electrophoresis, chromatography, mass spectrometry, molecular biology). In this article, we will review the various experimental strategies and analytical techniques, which have been used to characterize and to study D-amino acid containing peptides in crustaceans.

Emerging knowledge of regulatory roles of D-amino acids in bacteria

The d-enantiomers of amino acids have been thought to have relatively minor functions in biological processes. While l-amino acids clearly predominate in nature, d-amino acids are sometimes found in proteins that are not synthesized by ribosomes, and d-Ala and d-Glu are routinely found in the peptidoglycan cell wall of bacteria. Here, we review recent findings showing that d-amino acids have previously unappreciated regulatory roles in the bacterial kingdom. Many diverse bacterial phyla synthesize and release d-amino acids, including d-Met and d-Leu, which were not previously known to be made. These noncanonical d-amino acids regulate cell wall remodeling in stationary phase and cause biofilm dispersal in aging bacterial communities. Elucidating the mechanisms by which d-amino acids govern cell wall remodeling and biofilm disassembly will undoubtedly reveal new paradigms for understanding how extracytoplasmic processes are regulated as well as lead to development of novel therapeutics.

Antimicrobial peptides from Phyllomedusa frogs: from biomolecular diversity to potential nanotechnologic medical applications

Screening for new bioactive peptides in South American anurans has been pioneered in frogs of the genus Phyllomedusa. All frogs of this genus have venomous skin secretions, i.e., a complex mixture of bioactive peptides against potential predators and pathogens that presumably evolved in a scenario of predator-prey interaction and defense against microbial invasion. For every new anuran species studied new peptides are found, with homologies to hormones, neurotransmitters, antimicrobials, and several other peptides with unknown biological activity. From Vittorio Erspamer findings, this genus has been reported as a "treasure store" of bioactive peptides, and several groups focus their research on these species. From 1966 to 2009, more than 200 peptide sequences from different Phyllomedusa species were deposited in UniProt and other databases. During the last decade, the emergence of high-throughput molecular technologies involving de novo peptide sequencing via tandem mass spectrometry, cDNA cloning, pharmacological screening, and surface plasmon resonance applied to peptide discovery, led to fast structural data acquisition and the generation of peptide molecular libraries. Research groups on bioactive peptides in Brazil using these new technologies, accounted for the exponential increase of new molecules described in the last decade, much higher than in any previous decades. Recently, these secretions were also reported as a rich source of multiple antimicrobial peptides effective against multidrug resistant strains of bacteria, fungi, protozoa, and virus, providing instructive lessons for the development of new and more efficient nanotechnological-based therapies for infectious diseases treatment. Therefore, novel drugs arising from the identification and analysis of bioactive peptides from South American anuran biodiversity have a promising future role on nanobiotechnology.

Dermaseptins and magainins: antimicrobial peptides from frogs' skin-new sources for a promising spermicides microbicides-a mini review

Sexually transmitted infections (STIs) and human immunodeficiency virus (HIV), the causative agents of acquired immunodeficiency syndrome (AIDS), are two great concerns in the reproductive health of women. Thus, the challenge is to find products with a double activity, on the one hand having antimicrobial/antiviral properties with a role in the reduction of STI, and on the other hand having spermicidal action to be used as a contraceptive. In the absence of an effective microbicide along with the disadvantages of the most commonly used spermicidal contraceptive worldwide, nonoxynol-9, new emphasis has been focused on the development of more potential intravaginal microbicidal agents. Topical microbicides spermicides would ideally provide a female-controlled method of self-protection against HIV as well as preventing pregnancies. Nonoxynol-9, the only recommended microbicide spermicide, damages cervicovaginal epithelium because of its membrane-disruptive properties. Clearly, there is an urgent need to identify new compounds with dual potential microbicidal properties; antimicrobial peptides should be candidates for such investigations. Dermaseptins and magainins are two classes of cationic, amphipathic alpha-helical peptides that have been identified in the skin extracts of frogs Phyllomedusa sauvagei and Xenopus laevis. Regarding their contraceptive activities and their effect against various STI-causing pathogens, we believe that these two peptides are appropriate candidates in the evaluation of newer and safer microbicides spermicides in the future.

Distinguishing and quantifying peptides and proteins containing D-amino acids by tandem mass spectrometry

Tandem mass spectrometry (MS/MS) utilizing both electron capture dissociation (ECD) and collisionally activated dissociation (CAD) was used to develop a qualitative and quantitative analytical method for chiral analysis of individual amino acid residues in polypeptides. ECD produced a more distinct chiral recognition than CAD, which is attributed to the smaller degree of vibrational excitation in ECD. Several peptide and protein model systems were used in this study, including the smallest known protein, tryptophan cage, a lactoferrin peptide, and the biologically relevant opioid peptide, dermorphin. An adaptation of the kinetic method was used to quantify the degree of separation between fragmentation patterns of stereoisomeric peptides as a function of fragment ion abundances. The obtained calibration scale for relative abundances of d-amino acids in diastereomeric peptide mixtures was accurate to 1% for ECD and to 3-5% for CAD. It was found that separation and quantification of stereoisomers could be advantageously performed by nanoflow reversed-phase liquid chromatography, with the objective of on-line MS/MS limited to stereoisomer identification. This technique shows promise for the analysis of chiral substitution in peptides and proteins, broadening the application area for tandem mass spectrometry.

Schistosoma mansoni dermaseptin-like peptide: structural and functional characterization

Analysis of the Schistosoma mansoni peptidome for immunomodulatory molecules by solvent extraction and reverse-phase HPLC revealed a 27-amino-acid residue peptide from an extract of cercariae. Using matrix-assisted, laser desorption-ionization, time-of-flight mass spectrometry, the peptide yielded a protonated molecular ion [M + H]+ of m/z 2789. The unequivocal sequence was deduced by automated Edman degradation as: DLWNSIKDMAAAAGRAALNAVTGMVNQ. The peptide exhibited an 80.76% identity with dermaseptin 3.1 from the leaf frog Agalychnis annae, and was therefore named Schistosoma mansoni dermaseptin-like peptide (SmDLP). Immunocytochemical staining using a primary antidermaseptin B2 antibody located SmDLP in acetabular glands of cercariae, in and around schistosomula, and in adult worms and their eggs. Dot-blotting confirmed its presence in extracts (cercariae and worms) and excretion/secretion (E/S) products (transforming cercariae and eggs). This was corroborated by use of a MALDI-ToF spectra database of E/S products from cercariae. Functional characterization of the peptide indicated that SmDLP had typical amphipathic antimicrobial peptide properties, i.e., the ability to lyse human erythrocytes causing a decrease in the levels of nitric oxide produced by monocytic cells. This last function strongly suggests that SmDLP plays a vital role in the parasite's immunoevasion strategy. The possibility that schistosomes acquired this gene from amphibians has been discussed by constructing a phylogenetic tree.

Serous cutaneous glands of the Pacific tree-frog Hyla regilla (Anura, Hylidae): Patterns of secretory release induced by nor-epinephrine

The serous (poison) cutaneous glands of the Pacific tree-frog Hyla regilla were induced to release their product by 10(-3)M nor-epinephrine stimulation. After discharge structural and ultrastructural features of the cutaneous glands involved in release were observed. Furthermore, the discharged product, consisting of discrete, secretory granules, was collected and processed for transmission electron microscope analysis. As indicated by patterns found in the myoepithelium encircling the syncytial secretory unit, gland discharge is caused by contraction of the peripheral myocytes. Muscle cell compression dramatically affects the syncytium and results in degenerative changes, including expulsion of the secretory unit nuclei. Therefore, the structural collapse in depleted glands has been ascribed to the mechanical activity performed by the myoepithelium during discharge, rather than cytoplasm involution described in conventional, holocrine glands. TEM investigation revealed that the secretory granules collected after discharge maintain their peculiar traits: they consist of recurrent patterns of thin subunits, acquired during serous maturation and provided with remarkable structural stability.

Post-translational amino acid racemization in the frog skin peptide deltorphin I in the secretion granules of cutaneous serous glands

The dermal glands of the South American hylid frog Phyllomedusa bicolor synthesize and expel huge amounts of cationic, alpha-helical, 24- to 33-residue antimicrobial peptides, the dermaseptins B. These glands also produce a wide array of peptides that are similar to mammalian hormones and neuropeptides, including a heptapeptide opioid containing a D-amino acid, deltorphin I (Tyr-DAla-Phe-Asp-Val-Val-Gly NH2). Its biological activity is due to the racemization of L-Ala2 to D-Ala. The dermaseptins B and deltorphins are all derived from a single family of precursor polypeptides that have an N-terminal preprosequence that is remarkably well conserved, although the progenitor sequences giving rise to mature opioid or antimicrobial peptides are markedly different. Monoclonal and polyclonal antibodies were used to examine the cellular and ultrastructural distributions of deltorphin I and dermaseptin B in the serous glands by immunofluoresence confocal microscopy and immunogold-electron microscopy. Preprodeltorphin I and preprodermaseptins B are sorted into the regulated pathway of secretion, where they are processed to give the mature products. Deltorphin I, [l-Ala2]-deltorphin I and dermaseptin B are all stored together in secretion granules which accumulate in the cytoplasm of all serous glands. We conclude that the L- to D-amino acid isomerization of the deltorphin I occurs in the secretory granules as a post-translational event. Thus the specificity of isomerization depends on the presence of structural and/or conformational determinants in the peptide N-terminus surrounding the isomerization site.

Molecular strategies in biological evolution of antimicrobial peptides

Gene-encoded antimicrobial peptides that protect the skin of hylid and ranin frogs against noxious microorganisms are processed from a unique family of precursor polypeptides with a unique pattern of conserved and variable regions opposite to that of conventional secreted peptides. Precursors belonging to this family, designated the preprodermaseptin, have a common N-terminal preproregion that is remarkably well conserved both within and between species, but a hypervariable C-terminal domain corresponding to antimicrobial peptides with very different lengths, sequences, charges and antimicrobial spectra. Each frog species has its own distinct panoply of 10-20 antimicrobial peptides so that the 5000 species of ranids and hylids may produce approximately 100,000 different peptide antibiotics. The strategy that these frogs have evolved to generate this enormous array of peptides includes repeated duplications of a 150 million years old ancestral gene, focal hypermutation of the antimicrobial peptide domain maybe involving a mutagenic DNA polymerase similar to Escherichia coli Pol V, and subsequent actions of positive (diversifying) selection. The hyperdivergence of skin antimicrobial peptides can be viewed as the successful evolution of a multi-drug defense system that provides frogs with maximum protection against rapidly changing microbial biota and minimizes the chance of microorganisms developing resistance to individual peptides. The impressive variations in the expression of frog skin antimicrobial peptides may be exploited for discovering new molecules and structural motifs targeting specific microorganisms for which the therapeutic armamentarium is scarce.

Antimicrobial peptides from hylid and ranin frogs originated from a 150-million-year-old ancestral precursor with a conserved signal peptide but a hypermutable antimicrobial domain

The dermal glands of frogs produce antimicrobial peptides that protect the skin against noxious microorganisms and assist in wound repair. The sequences of these peptides are very dissimilar, both within and between species, so that the 5000 living anuran frogs may produce approximately 100 000 different antimicrobial peptides. The antimicrobial peptides of South American hylid frogs are derived from precursors, the preprodermaseptins, whose signal peptides and intervening sequences are remarkably conserved, but their C-terminal domains are markedly diverse, resulting in mature peptides with different lengths, sequences and antimicrobial spectra. We have used the extreme conservation in the preproregion of preprodermaseptin transcripts to identify new members of this family in Australian and South American hylids. All these peptides are cationic, amphipathic and alpha-helical. They killed a broad spectrum of microorganisms and acted in synergy. 42 preprodermaseptin gene sequences from 10 species of hylid and ranin frogs were analyzed in the context of their phylogeny and biogeography and of geophysical models for the fragmentation of Gondwana to examine the strategy that these frogs have evolved to generate an enormous array of peptide antibiotics. The hyperdivergence of modern antimicrobial peptides and the number of peptides per species result from repeated duplications of a approximately 150-million-year-old ancestral gene and accelerated mutations of the mature peptide domain, probably involving a mutagenic, error-prone, DNA polymerase similar to Escherichia coli Pol V. The presence of antimicrobial peptides with such different structures and spectra of action represents the successful evolution of multidrug defense by providing frogs with maximum protection against infectious microbes and minimizing the chance of microorganisms developing resistance to individual peptides. The hypermutation of the antimicrobial domain by a targeted mutagenic polymerase that can generate many sequence changes in a few steps may have a selective survival value when frogs colonizing a new ecological niche encounter different microbial predators.