Cyclopeptides with anti-inflammatory activity from seeds of Annona montana

Improvement effects of cyclic peptides from Annona squamosa on cognitive decline in neuroinflammatory mice

Cyclic peptides can resist enzymatic hydrolysis to pass through the intestine barrier, which may reduce the risk of mild cognition decline. But evidence is lacking on whether they work by alleviating neuroinflammation. A cylic peptide from Annona squamosa, Cylic(PIYAG), was biologically evaluated in vivo and in vitro. Cylic(PIYAG) enhanced the spatial memory ability of LPS-induced mice. And treatment with Cylic(PIYAG) markedly reduced the iNOS, MCP-1, TNF-α, and gp91phox expression induced by LPS. Cylic(PIYAG, 0.01, 0.05 and 0.2 μM) could significantly reduce the protein expression level of COX-2 and iNOS (P < 0.05) in BV2 cells. The concentration of Cylic(PIYAG) in blood reached a peak of 3.64 ± 1.22 μg/ml after intragastric administration in 1 h. And fluorescence microscope shows that Cylic(PIYAG) mainly locates and may play an anti-inflammatory role in the cytoplasm of microglia. This study demonstrates that the peptidic can prevent microglia activation, decrease the inflammatory reaction, improve the cognition of LPS-induced mice.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-023-01441-8.

Plant peptides - redefining an area of ribosomally synthesized and post-translationally modified peptides

Covering 1965 to February 2024Plants are prolific peptide chemists and are known to make thousands of different peptidic molecules. These peptides vary dramatically in their size, chemistry, and bioactivity. Despite their differences, all plant peptides to date are biosynthesized as ribosomally synthesized and post-translationally modified peptides (RiPPs). Decades of research in plant RiPP biosynthesis have extended the definition and scope of RiPPs from microbial sources, establishing paradigms and discovering new families of biosynthetic enzymes. The discovery and elucidation of plant peptide pathways is challenging due to repurposing and evolution of housekeeping genes as both precursor peptides and biosynthetic enzymes and due to the low rates of gene clustering in plants. In this review, we highlight the chemistry, biosynthesis, and function of the known RiPP classes from plants and recommend a nomenclature for the recent addition of BURP-domain-derived RiPPs termed burpitides. Burpitides are an emerging family of cyclic plant RiPPs characterized by macrocyclic crosslinks between tyrosine or tryptophan side chains and other amino acid side chains or their peptide backbone that are formed by copper-dependent BURP-domain-containing proteins termed burpitide cyclases. Finally, we review the discovery of plant RiPPs through bioactivity-guided, structure-guided, and gene-guided approaches.

Traditional Uses, Phytochemistry and Pharmacological Activities of Annonacae

In 1789, the Annonaceae family was catalogued by de Jussieu. It encompasses tropical and subtropical plants which are widespread in distribution across various continents such as Asia, South and Central America, Australia and Africa. The genus of Annona is one of 120 genera of the Annonaceae family and contains more than 119 species of trees and shrubs. Most species are found in tropical America, where over 105 species have been identified. Due to its edible fruits and medicinal properties, Annona is the most studied genus of Annonaceae family. To date, only a limited number of these species have economic value, including A. squamosa L. (sugar apple), A. cherimola Mill. (Cherimoya), A. muricata L. (guanabana or soursop), A. atemoya Mabb. (atemoya), a hybrid between A. cherimola and A. squamosa, A. reticulata L. (custard apple), A. glabra L. (pond-apple) and A. macroprophyllata Donn. Sm. (ilama). Phytochemically, several classes of secondary metabolites, including acetogenins, essential oils, alkaloids, terpenoids and flavonoids. The pharmacological activities of Annona species leaves and seeds include antibacterial, anticancer, antidiabetic and anti-inflammatory properties.

Natural bioeffective cyclooligopeptides from plant seeds of Annona genus

The Annona L. is one of the most significant genus of the Annonaceae family due to its widespread medicinal properties. This genus has a variety of active metabolites, including alkaloids, isoquinolines, peptides, acetogenins, lectins, volatile oils etc. Due to the constitution of cyclopeptides with an expanded spectrum of distinctive bioproperties, this genus is predominantly preferred over other species. The cytotoxicity, vasorelaxant activity, anti-inflammatory and other properties exhibited by cyclooligopeptides from seeds of Annona genus plants make these metabolites attractive leads for the drug discovery process. The present review covers the structural characteristics, structure activity relationship, synthesis strategies, pharmacological properties of plant seeds-originated bioactive peptides from Annona genus, which may be vital for the development of novel therapeutics based on peptide skeleton.

Recent advances in the biosynthesis of RiPPs from multicore-containing precursor peptides

Ribosomally synthesized and post-translationally modified peptides (RiPPs) compose a large structurally and functionally diverse family of natural products. The biosynthesis system of RiPPs typically involves a precursor peptide comprising of a leader and core motif and nearby processing enzymes that recognize the leader and act on the core for producing modified peptides. Interest in RiPPs has increased substantially in recent years as improvements in genome mining techniques have dramatically improved access to these peptides and biochemical and engineering studies have supported their applications. A less understood, intriguing feature in the RiPPs biosynthesis is the precursor peptides of multiple RiPPs families produced by bacteria, fungi and plants carrying multiple core motifs, which we term "multicore". Herein, we present the prevalence of the multicore systems, their biosynthesis and engineering for applications.

Natural Bioactive Thiazole-Based Peptides from Marine Resources: Structural and Pharmacological Aspects

Peptides are distinctive biomacromolecules that demonstrate potential cytotoxicity and diversified bioactivities against a variety of microorganisms including bacteria, mycobacteria, and fungi via their unique mechanisms of action. Among broad-ranging pharmacologically active peptides, natural marine-originated thiazole-based oligopeptides possess peculiar structural features along with a wide spectrum of exceptional and potent bioproperties. Because of their complex nature and size divergence, thiazole-based peptides (TBPs) bestow a pivotal chemical platform in drug discovery processes to generate competent scaffolds for regulating allosteric binding sites and peptide–peptide interactions. The present study dissertates on the natural reservoirs and exclusive structural components of marine-originated TBPs, with a special focus on their most pertinent pharmacological profiles, which may impart vital resources for the development of novel peptide-based therapeutic agents.

Cyclic Peptides in Seed of Annona muricata Are Ribosomally Synthesized

Small, cyclic peptides are reported to have many bioactivities. In bacteria and fungi, they can be made by nonribosomal peptide synthetases, but in plants they are exclusively ribosomal. Cyclic peptides from the Annona genus possess cytotoxic and anti-inflammatory activities, but their biosynthesis is unknown. The medicinal soursop plant, Annona muricata, contains annomuricatins A (cyclo-PGFVSA) and B (cyclo-PNAWLGT). Here, using de novo transcriptomics and tandem mass spectrometry, we identify a suite of short transcripts for precursor proteins for 10 validated annomuricatins, 9 of which are novel. In their precursors, annomuricatins are preceded by an absolutely conserved Glu and each peptide sequence has a conserved proto-C-terminal Pro, revealing parallels with the segetalin orbitides from the seed of Vaccaria hispanica, which are processed through ligation by a prolyl oligopeptidase in a transpeptidation reaction.

Discovery of Kynurenines Containing Oligopeptides as Potent Opioid Receptor Agonists

Kynurenine (kyn) and kynurenic acid (kyna) are well-defined metabolites of tryptophan catabolism collectively known as "kynurenines", which exert regulatory functions in host-microbiome signaling, immune cell response, and neuronal excitability. Kynurenine containing peptides endowed with opioid receptor activity have been isolated from natural organisms; thus, in this work, novel opioid peptide analogs incorporating L-kynurenine (L-kyn) and kynurenic acid (kyna) in place of native amino acids have been designed and synthesized with the aim to investigate the biological effect of these modifications. The kyna-containing peptide (KA1) binds selectively the m-opioid receptor with a Ki = 1.08 ± 0.26 (selectivity ratio m/d/k = 1:514:10000), while the L-kyn-containing peptide (K6) shows a mixed binding affinity for m, d, and k-opioid receptors, with efficacy and potency (E_max = 209.7 + 3.4%; LogEC₅₀ = -5.984 + 0.054) higher than those of the reference compound DAMGO. This novel oligopeptide exhibits a strong antinociceptive effect after i.c.v. and s.c. administrations in in vivo tests, according to good stability in human plasma (t_1/2 = 47 min).

Evaluation of topologically distinct constrained antimicrobial peptides with broad-spectrum antimicrobial activity

Antimicrobial peptides (AMPs) are short cationic peptides with a high affinity for membranes and emerged as a promising therapeutic approach with potential for treating infectious diseases. Chemical stabilization of short peptides proved to be a successful approach for enhancing their bio-physical properties. Herein, we designed and synthesized a panel of conformationally constrained antimicrobial peptides with either α-helical or β-hairpin conformation using templating strategies. These synthetic short constrained peptides possess different topological distributions of hydrophobic and hydrophilic residues and displayed distinct antimicrobial activity. Notably, the conformationally constrained α-helical peptides displayed a faster internalization into the bacteria cells compared to their β-hairpin analogues. These synthetic short constrained peptides showed killing effects on a broad spectrum of microorganisms mainly through pore formation and membrane damage which provided a potentially promising skeleton for the next generation of stabilized antimicrobial peptides.

Sclerin, a New Cytotoxic Cyclononapeptide from Annona scleroderma

A new cytotoxic cyclononapeptide, sclerin, cyclo(–Dab¹–Ser²–Tyr³–Gly⁴–Thr⁵–Val⁶–Ala⁷– Ile⁸–Pro⁹–) (1), was isolated from the methanol extract of the seeds of Annona scleroderma, together with the known metabolite, cyclosenegalin A, cyclo(–Pro¹–Gly²–Leu³–Ser⁴–Ala⁵–Val⁶–Thr⁷–) (2). The planar structures for the two compounds were established by comprehensive analysis of NMR and ESI-HRMS data, and the absolute stereochemistry was stablished by Marfey’s method. Compound 1 showed moderate cytotoxic activity against the human prostate carcinoma cell line DU-145 at µM concentration.

Combining JBCA and Marfey's methodology to determine the absolute configuration of threonines: the case of gunungamide A, a new cyclic depsipeptide containing chloropyrrole from the sponge Discodermia sp

JBCA and Marfey's allowed us to distinguish threonines diasteroisomers.

Antiinflammatory peptides: current knowledge and promising prospects

BACKGROUND

Inflammation is part of the regular host reaction to injury or infection caused by toxic factors, pathogens, damaged cells, irritants, and allergens. Antiinflammatory peptides (AIPs) are present in all living organisms, and many peptides from herbal, mammalian, bacterial, and marine origins have been shown to have antimicrobial and/or antiinflammatory properties.

METHODS

In this study, we investigated the effects of antiinflammatory peptides on inflammation, and highlighted the underlying mechanisms responsible for these effects.

RESULTS

In multicellular organisms, including humans, AIPs constitute an essential part of their immune system. In addition, numerous natural and synthetic AIPs are effective immunomodulators and can interfere with signal transduction pathways involved in inflammatory cytokine expression. Among them, some peptides such as antiflammin, N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP), and those derived from velvet antler proteins, bee venom, horse fly salivary gland, and bovine β-casein have received considerable attention over the past few years.

CONCLUSION

This article presents an overview on the major properties and mechanisms of action associated with AIPs as immunomodulatory, chemotactic, antioxidant, and antimicrobial agents. In addition, the results of various studies dealing with effects of AIPs on numerous classical models of inflammation are reviewed and discussed.

Potential therapeutic applications of the genus Annona: Local and traditional uses and pharmacology

ETHNO-PHARMACOLOGICAL RELEVANCE

Annona species (Annonaceae) have long been used as traditional herbal medicines by native peoples in tropical areas. In different countries they are used against a large variety of illnesses, such as parasitic and infectious diseases, cancer, diabetes, peptic ulcers, and mental disorders.

AIM OF THE STUDY

This review aims to achieve a comprehensive understanding of the research conducted so far on the local and traditional uses, pharmacological activities, mechanism of actions of active compounds, toxicity, and possible interactions with other drugs of the Annona species. Through analysis of these findings, evidences supporting their applications in ethno-medicines are described. We discuss the possible research opportunities and stand out the weak points in our knowledge that deserves further investigation.

MATERIAL AND METHODS

Information on ethno-medicinal uses and pharmacological activities of the Annona genus was collected. The main scientific biomedical literature databases (Cochrane, PubMed, Scopus, Lilacs, SeCiMed, Elsevier, SpringerLink, Google Scholar, SciFinder) were consulted. The search covered all the literature available until September 2017. National and regional databases of Herbal Medicine and Complementary and Alternative Medicine were also revised in order to explore further data. For a better understanding of the therapeutic importance of these species, we have classified the pharmacological activities within each group of disorders. The International Classification of Diseases (ICD), used from WHO Member States, was chosen as the reference classification.

RESULTS

From among the 27 species revised, four species are highlighted for their important pharmacological activities in most of the groups of illnesses: A. muricata, A. squamosa, A. senegalensis, and A. cherimola. Many investigations have been performed with extracts from the leaves, bark, fruit and seeds and have shown a wide range of pharmacological activities, such as antiprotozoal, antitumoural, antidiabetic, hepato-protective, anti-inflammatory and anxiolytic activities. The chemistry on the annonaceous acetogenins (ACGs) has been extensively investigated due to their potent antitumoural activity. Many of the assays were carried out with the isolated acetogenins in different lines of tumour culture cells and were found effective at very low doses even in multidrug-resistant tumours, and hence constitute promising compounds in the treatment of different types of cancers. No studies were found with extracts rich in acetogenins in the clinical field.

CONCLUSIONS

The experimental results from the pharmacological research enable the validation of their traditional uses in several of the groups of diseases in the countries of origin and reveal these plants to be a valuable source for therapeutic molecules. However, more toxicity assays and clinical trials would be necessary to establish optimal and safe doses of consumption on the application of these medicinal plants.

Annonaceae: Breaking the Wall of Inflammation

Inventories of tropical forests have listed Annonaceae as one of the most diverse plant families. For centuries, it is employed in traditional medicines to cure various pathological conditions including snakebite, analgesic, astringent, diarrhea, dysentery, arthritis pain, rheumatism, neuralgia, and weight loss etc. Phytochemical analysis of Annonaceae family have reported the occurrence of alkaloids, flavonoids, triterpenes, diterpenes and diterpene flavone glycosides, sterols, lignans, and annonaceous acetogenin characteristically affiliated with Annonaceae sp. Numerous past studies have underlined the pleotropic pharmacological activities of the crude extracts and isolated compounds from Annonaceae species. This review is an effort to abridge the ethnobotany, morphology, phytochemistry, toxicity, and particularly focusing on the anti-inflammatory activity of the Annonaceae species.

Toward the Synthesis and Pharmacological Screening of a Natural Cycloheptapeptide of Plant Origin

The solution-phase synthesis of a proline and glycine-rich plant-derived cyclic heptapeptide, gypsophin E (8), is reported via coupling of a tetrapeptide unit Glycyl-L-leucyl-L-valyl-L-proline-OMe with a tripeptide unit Boc-L-isoleucyl-glycyl-L-proline-OH, followed by cyclization of the linear fragment having seven amino acid units. The structure of the newly synthesized cycloheptapeptide was confirmed by means of chemical and spectroscopic methods. The newly synthesized cyclopolypeptide displayed potent antifungal and anthelmintic activities against the pathogenic yeast Candida albicans, the dermatophytes Trichophyton mentagrophytes and Microsporum audouinii at the 6 μg/mL level, and the earthworms Megascoplex konkanensis, Pontoscotex corethruses and Eudrilus eugeniea at a concentration of 2 mg/mL.

Serine/threonine ligation for natural cyclic peptide syntheses

The effectiveness of Ser/Thr ligation-mediated peptide cyclization has been demonstrated by the synthesis of cyclic peptide natural products, such as daptomycin, cyclomontanin B, yunnanin C and mahafacyclin B.

Tropical Plant Extracts as Sources of Grain-Protectant Compounds Against Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae)

The toxicity of organic plant extracts to Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) was assessed for three tropical plant species: branches, leaves, and seeds of Annona montana (Annonaceae), branches of Aristolochia paulistana (Aristolochiaceae), and leaves and branches of Casearia sylvestris (Salicaceae). The screening assay resulted that the extracts of A. montana seeds obtained with hexane (LC50 = 534.75 mg kg(-1) and LT50 = 6.10 days) and with dichloromethane (LC50 = 424.67 mg kg(-1) and LT50 = 5.03 days) were the most promising treatments, followed by the extract prepared from A. montana leaves with hexane (LC50 = 837.70 mg kg(-1) and LT50 = 4.90 days). Moreover, extracts (at 1,500 mg kg(-1)) prepared from C. sylvestris branches with dichloromethane and A. paulistana with hexane caused significant mortality (37% and 41.5%, respectively) beyond sublethal effects on S. zeamais. Therefore, based on the biological assays, extraction yield, and evaluation of the chromatographic profile of the crude extracts by TLC, the hexane extract of A. montana seeds was selected and fractioned using liquid-liquid partitioning. The hydroalcoholic fraction caused mortality of 55.5%, significantly superior to dichloromethane fraction, which caused 35.5% of mortality. Chemical analyses ((1)H NMR, HPLC, and TLC) were performed, and the results showed the presence of alkaloids and acetogenins in both active fractions, which have been associated with bioactivity. Therefore, extracts prepared from A. montana seeds (especially) is an interesting source of new compounds with promising grain-protectant properties.

Design and synthesis of tryptophan containing dipeptide derivatives as formyl peptide receptor 1 antagonist

Our previous studies identified an Fmoc-(S,R)-tryptophan-containing dipeptide derivative, 1, which selectively inhibited neutrophil elastase release induced by formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) in human neutrophils. In an attempt to improve pharmacological activity, a series of tryptophan-containing dipeptides were synthesized and their pharmacological activities were investigated in human neutrophils. Of these, five compounds 3, 6, 19a, 24a, and 24b exhibited potent and dual inhibitory effects on FMLP-induced superoxide anion (O2˙(-)) generation and neutrophil elastase release in neutrophils with IC50 values of 0.23/0.60, 1.88/2.47, 1.87/3.60, 0.12/0.37, and 1.32/1.03 μM, respectively. Further studies indicated that inhibition of superoxide production in human neutrophils by these dipeptides was associated with the selective inhibition of formyl peptide receptor 1 (FPR1). Furthermore, the results of structure-activity relationship studies concluded that the fragment N-benzoyl-Trp-Phe-OMe (3) was most suitable as a core structure for interaction with FPR1, and may be approved as a lead for the development of new drugs in the treatment of neutrophilic inflammatory diseases. As some of the synthesized compounds exhibited separable conformational isomers, and showed diverse bioactivities, the conformation analysis of these compounds is also discussed herein.

Insights on the phytochemical profile (cyclopeptides) and biological activities of Calotropis procera latex organic fractions

Calotropis procera is a medicinal plant whose pharmacological properties are associated with its latex. Here, the Calotropis procera latex fractions were investigated in an attempt to trace its phytochemical profile and measure its anti-inflammatory and toxicity activity. The crude latex was partitioned, yielding five fractions (49.4% hexane, 5.2% dichloromethane, 2.0% ethyl acetate, 2.1% n-butanol, and 41.1% aqueous). Phytochemical screening and spectroscopy analysis revealed that dichloromethane is the most chemically diverse fraction. Triterpenes were detected in both the hexane and dichloromethane fractions, while flavonoids were detected in the dichloromethane and ethyl acetate fractions. These fractions were cytotoxic to cancer cell lines (LD₅₀ 0.05 to 3.9 μg/mL) and lethal to brine shrimp (LD₅₀ 10.9 to 65.7 μg/mL). Reduced neutrophil migration in rats was observed in carrageenan-induced peritonitis for the dichloromethane (67%), ethyl acetate (56%), and aqueous (72%) fractions. A positive reaction with tolidine and ninhydrin suggested that cyclopeptides are in the ethyl acetate fraction. It is therefore concluded that Calotropis procera latex dichloromethane and ethyl acetate fractions exhibit both in vitro and in vivo activities as well as anti-inflammatory properties. Cyclopeptide detection is especially interesting because previous attempts to investigate these low-molecular cyclic amino acid sequences in C. procera have failed.

Composition and evaluation of the anti-inflammatory and anticancer activities of the essential oil from Annona sylvatica A. St.-Hil

The essential oil from the leaves of Annona sylvatica (EOAS) was extracted by hydrodistillation, and the analysis was performed by gas chromatography-mass spectrometry. The main compounds identified in the EOAS were sesquiterpenes, such as hinesol, z-caryophyllene, β-maaliene, γ-gurjunene, silphiperfol-5-en-3-ol, ledol, cubecol-1-epi, and muurola-3,5-diene. Oral administration of the EOAS (20 and 200 mg/kg) and subcutaneous injection of dexamethasone (0.5 mg/kg, reference drug) significantly inhibited carrageenan- and complete Freund's adjuvant-induced mouse paw edema. The anticancer activity the EOAS showed growth inhibitory activity on all cell lines when administered in a high concentration. The EOAS inhibited the growth of human cancer cell lines with GI(50) values in the range of 36.04-45.37 μg/mL on all of the cell lines tested. This work describes for the first time the anti-inflammatory and anticancer effects of the essential oil of A. sylvatica and its composition. Considering that drugs currently available for the treatment of inflammatory and cancer conditions show undesirable side-effects, the present results may have clinical relevance and open new possibilities for the development of novel anti-inflammatory and anticancer drugs.

Single molecule studies of cyclic peptides using molecular matrix at liquid/solid interface by scanning tunneling microscopy

We report in this work the single molecule studies of cyclic peptide, cyclosporine A (CsA), using a molecular network formed by star-shaped oligofluorene (StOF-COOH(3)) at the liquid/solid interface by scanning tunneling microscopy (STM). Individual cyclosporine A can be identified and resolved in the molecular network, and the high-resolution STM images of CsA show polygon-like characteristics with a diameter of approximately 1.7 nm. Furthermore, the complex of CsA and Mg(2+) has also been observed to adsorb inside of the molecular matrix. The STM results reveal two adsorption characteristics for the CsA-Mg(2+) complex, which is suggestive of asymmetrical configurations of the complex. The difference in binding energy between the two observed adsorption configurations is estimated to be 1.88 kJ·mol(-1). These results help set the stage for studying the fine structures and functions of various cyclic peptides at the liquid/solid interface.

Synthesis of Aib-containing cyclopeptides via the ‘azirine/oxazolone method’

The cyclic pentapeptide cyclo[Gly-Phe(2Me)-Aib-Aib-Gly], containing three α,α-disubstituted α-amino acids, was prepared by cyclization of H-Gly-Phe(2Me)-Aib-Aib-Gly-OH with diphenyl phosporazidate (DPPA) in 60% yield. The synthesis of the linear precursor was performed by using the ‘azirine/oxazolone method’, in which the α,α-disubstituted α-amino acids were introduced by coupling of the corresponding amino or peptide acid with a 2,2-disubstituted 3-amino-2H-azirine. Whereas the cyclization of an analogous hexapeptide afforded the cyclopeptide in 42% yield, the corresponding tetrapeptide yielded a 1:2 mixture of the monomeric and dimeric cyclopeptide. In the case of the tripeptide H-Gly-Phe(2Me)-Aib-OH, the cyclization with DPPA led to the dimeric cyclohexapeptide exclusively.