Dysregulation of tyrosinase activity: a potential link between skin disorders and neurodegeneration

OBJECTIVES

The co-occurrence of melanoma and Parkinson's disease (PD) is higher than expected. We review the relationship between melanoma and PD, then proffer a hypothesis of how dysregulated human tyrosinase could be involved in both diseases via the loss of dopamine and neuromelanin-positive neurons in PD and the genesis alterations in melanin content during melanoma.

KEY FINDINGS

There are a surprising number of links between skin disorders and neurodegenerative diseases. Some risk factors related to the co-occurrence of PD and melanoma have been extensively investigated over the past 15 years. It has been proposed that human tyrosinase, an enzyme participating in the biosynthesis of neuromelanin in the brain and of melanin in the skin, plays a role. Abnormally dysregulated human tyrosinase impacts the genesis and progression of melanoma and PD.

SUMMARY

The dual role of human tyrosinase places it as the potential critical link between these seemingly distinct conditions. Detecting and monitoring human tyrosinase activity in the progression of melanoma and PD opens new opportunities for early diagnosis and treatment of both diseases.

Fabrication of Antibacterial and Antioxidant ZnO-Impregnated Amine-Functionalized Chitosan Bio-Nanocomposite Membrane for Advanced Biomedical Applications

Developing a variety of safe and effective functioning wound dressings is a never-ending objective. Due to their exceptional antibacterial activity, biocompatibility, biodegradability, and healing-promoting properties, functionalized chitosan nanocomposites have attracted considerable attention in wound dressing applications. Herein, a novel bio-nanocomposite membrane with a variety of bio-characteristics was created through the incorporation of zinc oxide nanoparticles (ZnONPs) into amine-functionalized chitosan membrane (Am-CS). The developed ZnO@Am-CS bio-nanocomposite membrane was characterized by various analysis tools. Compared to pristine Am-CS, the developed ZnO@Am-CS membrane revealed higher water uptake and adequate mechanical properties. Moreover, increasing the ZnONP content from 0.025 to 0.1% had a positive impact on antibacterial activity against Gram-positive and Gram-negative bacteria. A maximum inhibition of 89.4% was recorded against Escherichia coli, with a maximum inhibition zone of 38 ± 0.17 mm, and was achieved by the ZnO (0.1%)@Am-CS membrane compared to 72.5% and 28 ± 0.23 mm achieved by the native Am-CS membrane. Furthermore, the bio-nanocomposite membrane demonstrated acceptable antioxidant activity, with a maximum radical scavenging value of 46%. In addition, the bio-nanocomposite membrane showed better biocompatibility and reliable biodegradability, while the cytotoxicity assessment emphasized its safety towards normal cells, with the cell viability reaching 95.7%, suggesting its potential use for advanced wound dressing applications.

Antioxidant and Antibacterial Activity of Four Tannins Isolated from Different Sources and Their Effect on the Shelf-Life Extension of Vacuum-Packed Minced Meat

Four tannin samples extracted from chestnut wood (tannin oenologique, TO), grape (tannin VR grape, TVG), oak gall (tannin galalcool, TG), and oak tree (tannin VR supra elegance, TE) were evaluated for antioxidant and antibacterial activity. The highest total phenolic content (TPC) values were observed in the order of TVG > TG > TE > TO (p < 0.05). The antioxidant activities of all samples were determined in terms of DPPH radical scavenging activity, reducing power, metal-chelating activity, and linoleic acid peroxidation assay. The antioxidant activities of all samples vary and no correlation was observed with the respective TPC values of each sample. Antibacterial activities indicate that all samples showed more or less inhibitory effects against selected Gram-positive and Gram-negative bacteria. Based on antioxidant and antibacterial activity, TO and TVG were selected for the beef mince quality preservation study during refrigerated storage. Both TO and TVG at two different concentrations, 0.25 and 0.5%, could cease the chemical and microbial changes as compared to the control sample. Although total viable count (TVC) did not show a significant difference, the H2S-producing bacteria count was lower in all samples treated with TO and TVG compared to sodium metabisulfite (SMS) and the control sample (p < 0.05). Therefore, TO and TVG could be promising natural food preservatives during refrigerated storage.

Antispasmodic activity of the ethanol extract of Citrullus lanatus seeds: Justifying ethnomedicinal use in Pakistan to treat asthma and diarrhea

ETHNOPHARMACOLOGICAL RELEVANCE

Citrullus lanatus (Thunb.) belongs to the ground family, Cucurbitaceae, known for edible fruit. Besides nutritional benefits, the traditional herbal practitioners in Pakistan and India used their seeds to treat gastrointestinal, respiratory, and urinary disorders. In Northern Sudan, its seeds are often used as a laxative. Its root is laxative and emetic at a high dose. Its seeds are also used to treat bedwetting and urinary tract obstruction.

AIM OF THE STUDY

This study aimed to elucidate the multi-target mechanisms of Citrullus lanatus seeds to treat asthma and diarrhea. The pharmacological experiments were designed and conducted, along with the pharmacology network and molecular docking predictions, to verify the seeds biopotency for antispasmodic and bronchodilator properties.

METHODS

LC ESI-MS/MS were performed to identify the potentially active compounds in hydroethanolic extract of Citrullus lanatus seeds, then to quantify them by HPLC. The quantified bioactive compounds of Citrullus lanatus, i.e., stigmasterol, quinic acid, malic acid, epicatechin, caffeic acid, rutin, p-coumaric acid, quercetin, ferulic acid, scopoletin, apigenin, and kaempferol were subjected to in silico studies for molecular docking. The hydroethanolic extract of Citrullus lanatus seeds was examined on isolated rabbit tissue, i.e., jejunum, trachea, and urinary bladder. The antiperistalsis, antidiarrheal and antisecretory studies were also performed in animal models.

RESULTS

In silico studies revealed that bioactive compounds of C. lanatus seeds interfere with asthma and diarrhea-associated target genes, which are a member of calcium mediate signaling, regulation of cytosolic calcium concentration, smooth muscle contraction, and inflammatory responses. It was also found that rutin, quercetin, kaempferol, and scopoletin were stronger binding to voltage-gated calcium channels, calcium/calmodulin-dependent protein kinase, myosin light chain kinase, and phosphoinositide phospholipase C, thus, exerting calcium channel blocker activity. The hydroethanolic extract of C. lanatus seeds exerted a concentration-dependent relaxant response for the spasmolytic response on isolated jejunum and trachea preparations and caused relaxation of spastic contraction of K⁺ (80 mM). Furthermore, it caused a non-parallel rightward shift with suppression of calcium concentration-response curves. In animal models, the Cl.EtOH showed antiperistalsis, antidiarrheal and antisecretory response.

CONCLUSION

Thus, we confirm Citrullus lanatus seeds have some medicinal effects by regulating the contractile response through target proteins of calcium mediates signaling and can be a promising component in the medical treatment for asthma and diarrhea.

A lipoglycopeptide antibiotic for Gram-positive biofilm-related infections

Drug-resistant Gram-positive bacterial infections are still a substantial burden on the public health system, with two bacteria ( Staphylococcus aureus and Streptococcus pneumoniae ) accounting for over 1.5 million drug-resistant infections in the United States alone in 2017. In 2019, 250,000 deaths were attributed to these pathogens globally. We have developed a preclinical glycopeptide antibiotic, MCC5145, that has excellent potency (MIC 90 ≤ 0.06 μg/ml) against hundreds of isolates of methicillin-resistant S. aureus (MRSA) and other Gram-positive bacteria, with a greater than 1000-fold margin over mammalian cell cytotoxicity values. The antibiotic has therapeutic in vivo efficacy when dosed subcutaneously in multiple murine models of established bacterial infections, including thigh infection with MRSA and blood septicemia with S. pneumoniae , as well as when dosed orally in an antibiotic-induced Clostridioides difficile infection model. MCC5145 exhibited reduced nephrotoxicity at microbiologically active doses in mice compared to vancomycin. MCC5145 also showed improved activity against biofilms compared to vancomycin, both in vitro and in vivo, and a low propensity to select for drug resistance. Characterization of drug action using a transposon library bioinformatic platform showed a mechanistic distinction from other glycopeptide antibiotics.

Syzygium cumini (L.) Skeels extracts; in vivo anti-nociceptive, anti-inflammatory, acute and subacute toxicity assessment

ETHNOPHARMACOLOGICAL RELEVANCE

Syzygium cumini (L.) Skeels has been extensively used in the ancient medical system of Pakistan, India, Bangladesh, and Sri Lanka to combat diabetes, inflammation, and renal disorders. These health-promoting aspects of S. cumini are related to bioactive metabolites such as phenolic acids, anthocyanins, tannins, and flavonoids.

AIM OF THE STUDY

Earlier to this study, we have reported S. cumini extracts as potential sources of bioactive compounds bearing antioxidant and anti-inflammatory properties. However, prior further suggesting S. cumini fruit extracts for consumption against inflammatory disorders, it was mandatory to validate the claim and explore toxicity of the extracts. This study aims to determine the in vivo anti-nociceptive, anti-inflammatory, acute, and subacute toxicity properties of S. cumini crude extracts, followed by identifying and quantifying bioactive metabolites.

MATERIAL AND METHODS

In the present study, the anti-nociceptive and anti-inflammatory potential of S. cumini sequential crude extracts were evaluated using formalin and glutamate-induced paw licking method in mice. The acute and sub-acute toxicity assessment of active extract was performed by oral administration in rats. An acute toxicity trial was performed with two different doses, i.e., 2000 mg/kg and 3000 mg/kg for consecutive 14 days, whereas a sub-acute toxicity study was conducted at doses of 750 mg/kg and 1500 mg/kg for the next 28 days. Identification of bioactive compounds was performed using HPLC, and at the end, in silico docking calculations of identified compounds were performed.

RESULTS

The 100% methanolic extract (SCME) protected the mice from painful stimulation of formalin and glutamate in a dose-dependent manner with the maximum effect of 49% and 67% at 200 mg/kg, respectively, followed by moderate and non-influential effects of 50% methanolic extract and dichloromethane (DCM) extracts when compared to control, i.e., normal saline. The results of acute toxicity recorded LD₅₀ of SCME over 3000 mg/kg, and no antagonistic effects were recorded during the subacute study when SCME dispensed at the rate of 750 mg/kg and 1500 mg/kg. SCME was found to induce no adverse effects to kidney, heart, liver, spleen, and paired lungs examined by hematological, serum biochemical, histological analysis. HPLC analysis of S. cumini 100% methanolic extracts revealed the presence of delphinidin 3-glucoside, peonidin-3,5-diglucoside, scopoletin, and umbelliferone at the concentration of 127.4, 2104, 31.3, 10.4 μg/g whereas in 50% methanolic extract, the quinic acid, catechin, and myricetin were present at the concentration of 54.9, 63.7, 12.3 μg/g, respectively. Umbelliferone and scopoletin are newly reported compounds in the present study. In silico docking calculations of these compounds indicated the potential of anti-nociceptive and anti-inflammatory activities.

CONCLUSIONS

These findings validate that S. cumini fruit extracts are a rich source of bioactive compounds that needs to be considered to enhance biological activities with lesser side effects.

Phytochemical Profile, Biological Properties, and Food Applications of the Medicinal Plant Syzygium cumini

Syzygium cumini, locally known as Jamun in Asia, is a fruit-bearing crop belonging to the Myrtaceae family. This study aims to summarize the most recent literature related to botany, traditional applications, phytochemical ingredients, pharmacological activities, nutrition, and potential food applications of S. cumini. Traditionally, S. cumini has been utilized to combat diabetes and dysentery, and it is given to females with a history of abortions. Anatomical parts of S. cumini exhibit therapeutic potentials including antioxidant, anti-inflammatory, analgesic, antipyretic, antimalarial, anticancer, and antidiabetic activities attributed to the presence of various primary and secondary metabolites such as carbohydrates, proteins, amino acids, alkaloids, flavonoids (i.e., quercetin, myricetin, kaempferol), phenolic acids (gallic acid, caffeic acid, ellagic acid) and anthocyanins (delphinidin-3,5-O-diglucoside, petunidin-3,5-O-diglucoside, malvidin-3,5-O-diglucoside). Different fruit parts of S. cumini have been employed to enhance the nutritional and overall quality of jams, jellies, wines, and fermented products. Today, S. cumini is also used in edible films. So, we believe that S. cumini’s anatomical parts, extracts, and isolated compounds can be used in the food industry with applications in food packaging and as food additives. Future research should focus on the isolation and purification of compounds from S. cumini to treat various disorders. More importantly, clinical trials are required to develop low-cost medications with a low therapeutic index.

The Chemical Composition and Health-Promoting Effects of the Grewia Species-A Systematic Review and Meta-Analysis

Globally grown and organoleptically appreciated Grewia species are known as sources of bioactive compounds that avert the risk of communicable and non-communicable diseases. Therefore, in recent years, the genus Grewia has attracted increasing scientific attention. This is the first systematic review which focusses primarily on the nutritional composition, phytochemical profile, pharmacological properties, and disease preventative role of Grewia species. The literature published from 1975 to 2021 was searched to retrieve relevant articles from databases such as Google Scholar, Scopus, PubMed, and Web of Science. Two independent reviewers carried out the screening, selection of articles, and data extraction. Of 815 references, 56 met our inclusion criteria. G. asiatica and G. optiva were the most frequently studied species. We found 167 chemical compounds from 12 Grewia species, allocated to 21 categories. Flavonoids represented 41.31% of the reported bioactive compounds, followed by protein and amino acids (10.7%), fats and fatty acids (9.58%), ash and minerals (6.58%), and non-flavonoid polyphenols (5.96%). Crude extracts, enriched with bioactive compounds, and isolated compounds from the Grewia species show antioxidant, anticancer, anti-inflammatory, antidiabetic, hepatoprotective/radioprotective, immunomodulatory, and sedative hypnotic potential. Moreover, antimicrobial properties, improvement in learning and memory deficits, and effectiveness against neurodegenerative ailments are also described within the reviewed article. Nowadays, the side effects of some synthetic drugs and therapies, and bottlenecks in the drug development pathway have directed the attention of researchers and pharmaceutical industries towards the development of new products that are safe, cost-effective, and readily available. However, the application of the Grewia species in pharmaceutical industries is still limited.

Cyclic Dipeptides: The Biological and Structural Landscape with Special Focus on the Anti-Cancer Proline-Based Scaffold

Cyclic dipeptides, also know as diketopiperazines (DKP), the simplest cyclic forms of peptides widespread in nature, are unsurpassed in their structural and bio-functional diversity. DKPs, especially those containing proline, due to their unique features such as, inter alia, extra-rigid conformation, high resistance to enzyme degradation, increased cell permeability, and expandable ability to bind a diverse of targets with better affinity, have emerged in the last years as biologically pre-validated platforms for the drug discovery. Recent advances have revealed their enormous potential in the development of next-generation theranostics, smart delivery systems, and biomaterials. Here, we present an updated review on the biological and structural profile of these appealing biomolecules, with a particular emphasis on those with anticancer properties, since cancers are the main cause of death all over the world. Additionally, we provide a consideration on supramolecular structuring and synthons, based on the proline-based DKP privileged scaffold, for inspiration in the design of compound libraries in search of ideal ligands, innovative self-assembled nanomaterials, and bio-functional architectures.

Syzygium cumini(L.),Skeels fruit extracts: In vitro and in vivo anti-inflammatory properties

ETHNOPHARMACOLOGICAL RELEVANCE

Syzygium cumini (L.) Skeels is an important medicinal plant utilized in the health care systems of Pakistan, India, Sri Lanka, and Bangladesh. S. cumini have been used to treat renal issues, indigestion, diabetes, dysentery, and employed in folk medicine to treat inflammations. It is known to anticipate antioxidant, anti-inflammatory, anticancer, anti-diabetic, anti-bacterial, antifungal, activities, and radioprotective activities.

MATERIAL AND METHODS

We examined the in vitro anti-inflammatory activities of S. cumini fruit extracts, evaluated using membrane stabilization, egg albumin denaturation, and bovine serum albumin denaturation assays. In vivo anti-inflammatory activity was also assessed, using murine models of carrageenan, formaldehyde, and PGE2 induced paw edema. Fractionation of active extracts was performed using HPLC, followed by LC-ESI-MS/MS analysis to identify the bioactive compounds responsible for anti-inflammatory activity.

RESULTS

The crude methanolic extract showed stronger in vitro and in vivo anti-inflammatory activities compared to other extracts. The most potent effects were observed in the formaldehyde induced paw edema assay wherein methanolic extract and standard indomethacin induced 72% and 88% inhibition against paw edema volume in comparison to control (normal saline) respectively. In the bovine serum albumin denaturation assay the methanolic extract induced 82% inhibition against denaturation as compared to control (phosphate buffer) while standard diclofenac sodium induced 98% inhibition. In contrast, 50% v/v MeOH:H2O or 100% dichloromethane extracts displayed moderate to weak effects in the anti-inflammatory models. HPLC fractionation provided 6 active sub-fractions, four (MF2, MF3, MF6, MF7) from the 100% methanolic extract and two (HAF1, HAF3) from the 50% methanolic extract. The MF2, MF7, and HAF1 sub-fractions displayed potent activity in all studied in vitro assays. LC-ESI-MS-MS analysis tentatively identified delphinidin 3-glucoside, peonidin-3,5-diglucoside, gallic acid, liquitrigenin, scopoletin, umbelliferon, and rosmanol from the 100% methanolic fractions. Myricetin, catechin, quinic acid, chlorogenic acid, ellagic acid, gallic acid, and caffeic acid were identified in the 50% methanolic fractions.

CONCLUSIONS

These results demonstrate that S. cumini fruit extracts are a rich source of bioactive compounds that are worthy of further investigation as leads for anti-inflammatory drug discovery.

Solid-Phase Synthesis of Octapeptin Lipopeptides

Octapeptins are naturally derived cyclic lipopeptide antibiotics with activity against a range of Gram-negative pathogens, including highly resistant strains. Octapeptin C4, an exemplar of the class, was synthesized using a combination of Fmoc solid-phase peptide synthesis (SPPS) and solution-phase cyclization. Utilizing H-L-Leu-2-chlorotrityl resin, peptide couplings were performed using HCTU and collidine in DMF. The linear sequence was terminated by N-acylation with 3-(R)-hydroxydecanoic acid. The residue Dab-2 was orthogonally protected with 1-(4,4-dimethyl-2,6-dioxocyclohex-1-ylidene)isovaleryl group (ivDde) to enable selective side-chain deprotection prior to resin cleavage. Resin cleavage was accomplished with hexafluoroisopropanol in DCM, followed by cyclization with diphenylphosphoryl azide (DPPA) and solid sodium bicarbonate in DMF.

Non-antibiotic antimicrobial agents to combat biofilm-forming bacteria

Biofilms can be produced by multiple species or by a single strain of bacteria. The biofilm state enhances the resistance of the resident microorganisms to antimicrobial agents by producing extracellular polymeric substances. Typically, antibiotics are used to stop the growth of bacteria, but emerging resistance has limited their effectiveness. Bacteria in biofilms are less susceptible to antibiotics compared with their free-floating state, as biofilms impair antibiotic penetration. To obviate this challenge, non-antibiotic antimicrobial agents are needed. This review describes two classes of these agents, namely antimicrobial nanoparticles and antimicrobial peptides. Applications of these antimicrobials in the food industry and medical applications are discussed, and the directions for future research are highlighted.

Hydroxyl substituted benzoic acid/cinnamic acid derivatives: Tyrosinase inhibitory kinetics, anti-melanogenic activity and molecular docking studies

The inhibition of tyrosinase is an established strategy for treating hyperpigmentation. Our previous findings demonstrated that cinnamic acid and benzoic acid scaffolds can be effective tyrosinase inhibitors with low toxicity. The hydroxyl substituted benzoic and cinnamic acid moieties of these precursors were incorporated into new chemotypes that displayed in vitro inhibitory effect against mushroom tyrosinase. The most active compound, (2-(3-methoxyphenoxy)-2-oxoethyl (E)-3-(4-hydroxyphenyl) acrylate) 6c, inhibited tyrosinase with an IC₅₀ of 5.7 µM, while (2-(3-methoxyphenoxy)-2-oxoethyl 2, 4-dihydroxybenzoate) 4d had an IC₅₀ of 23.8 µM. In comparison, the positive control, kojic acid showed tyrosinase inhibition with an IC₅₀ = 16.7 µM. Analysis of enzyme kinetics revealed that 6c and 4d displayed noncompetitive reversible inhibition of the second tyrosinase enzymatic reaction with K_i values of 11 µM and 130 µM respectively. In silico docking studies with mushroom tyrosinase (PDB ID 2Y9X) predicted possible binding modes in the catalytic site for these active compounds. The phenolic para-hydroxy group of the most active compound 6c is predicted to interact with the catalytic site Cu⁺⁺ ion. The methoxy part of this compound is predicted to form a hydrogen bond with Arg 268. Compound 6c had no observable toxic effects on cell morphology or cell viability at the highest tested concentration of 91.4 µM. When dosed at 91.4 µM onto B16F10 melanoma cells in vitro6c showed anti-melanogenic effects equivalent to kojic acid at 880 µM. 6c displayed no PAINS (pan-assay interference compounds) alerts. Our results show that compound 6c is a more potent tyrosinase inhibitor than kojic acid and is a candidate for further development. Our exposition of the details of the interactions between 6c and the catalytic pocket of tyrosinase provides a basis for rational design of additional potent inhibitors of tyrosinase, built on the cinnamic acid scaffold.

Quinolone antibiotics

The quinolone antibiotics arose in the early 1960s, with the first examples possessing a narrow-spectrum of activity with unfavorable pharmacokinetic properties. Over time, the development of new quinolone antibiotics has led to improved analogues with an expanded spectrum and high efficacy. Nowadays, quinolones are widely used for treating a variety of infections. Quinolones are broad-spectrum antibiotics that are active against both Gram-positive and Gram-negative bacteria, including mycobacteria, and anaerobes. They exert their actions by inhibiting bacterial nucleic acid synthesis through disrupting the enzymes topoisomerase IV and DNA gyrase, and by causing breakage of bacterial chromosomes. However, bacteria have acquired resistance to quinolones, similar to other antibacterial agents, due to the overuse of these drugs. Mechanisms contributing to quinolone resistance are mediated by chromosomal mutations and/or plasmid gene uptake that alter the topoisomerase targets, modify the quinolone, and/or reduce drug accumulation by either decreased uptake or increased efflux. This review discusses the development of this class of antibiotics in terms of potency, pharmacokinetics and toxicity, along with the resistance mechanisms which reduce the quinolones' activity against pathogens. Potential strategies for future generations of quinolone antibiotics with enhanced activity against resistant strains are suggested.

Enhancement of antibiotic-activity through complexation with metal ions - Combined ITC, NMR, enzymatic and biological studies

Alternative solutions need to be developed to overcome the growing problem of multi-drug resistant bacteria. This study explored the possibility of creating complexes of antibiotics with metal ions, thereby increasing their activity. Analytical techniques such as isothermal titration calorimetry and nuclear magnetic resonance were used to examine the structure and interactions between Cu(II), Ag(I) or Zn(II) and β-lactam antibiotics. The metal-β-lactam complexes were also tested for antimicrobial activity, by micro-broth dilution and disk diffusion methods, showing a synergistic increase in the activity of the drugs, and enzymatic inhibition assays confirming inhibition of β-lactamases responsible for resistance. The metal-antibiotic complex concept was proven to be successful with the activity of the drugs enhanced against β-lactamase-producing bacteria. The highest synergistic effects were observed for complexes formed with Ag(I).

Ethanol Concentration Influences the Mechanisms of Wine Tannin Interactions with Poly(L-proline) in Model Wine

Changes in ethanol concentration influence red wine astringency, and yet the effect of ethanol on wine tannin-salivary protein interactions is not well understood. Isothermal titration calorimetry (ITC) was used to measure the binding strength between the model salivary protein, poly(L-proline) (PLP) and a range of wine tannins (tannin fractions from a 3- and a 7-year old Cabernet Sauvignon wine) across different ethanol concentrations (5, 10, 15, and 40% v/v). Tannin-PLP interactions were stronger at 5% ethanol than at 40% ethanol. The mechanism of interaction changed for most tannin samples across the wine-like ethanol range (10-15%) from a combination of hydrophobic and hydrogen binding at 10% ethanol to only hydrogen binding at 15% ethanol. These results indicate that ethanol concentration can influence the mechanisms of wine tannin-protein interactions and that the previously reported decrease in wine astringency with increasing alcohol may, in part, relate to a decrease tannin-protein interaction strength.

Anti-cooperative ligand binding and dimerisation in the glycopeptide antibiotic dalbavancin

Dalbavancin, a semi-synthetic glycopeptide with enhanced antibiotic activity compared to vancomycin and teicoplanin, binds to the C-terminal lysyl-d-alanyl-d-alanine subunit of Lipid II, inhibiting peptidoglycan biosynthesis. In this study, micro-calorimetry and electrospray ionization (ESI)-MS have been used to investigate the relationship between oligomerisation of dalbavancin and binding of a Lipid II peptide mimic, diacetyl-Lys-d-Ala-d-Ala (Ac2-Kaa). Dalbavancin dimerised strongly in an anti-cooperative manner with ligand-binding, as was the case for ristocetin A, but not for vancomycin and teicoplanin. Dalbavancin and ristocetin A both adopt an 'closed' conformation upon ligand binding, suggesting anti-cooperative dimerisation with ligand-binding may be a general feature of dalbavancin/ristocetin A-like glycopeptides. Understanding these effects may provide insight into design of novel dalbavancin derivatives with cooperative ligand-binding and dimerisation characteristics that could enhance antibiotic activity.

Polymer-peptide hybrids as a highly immunogenic single-dose nanovaccine

AIM

To explore four-arm star poly(t-butyl)acrylate (P(t)BA)-peptide and linear P(t)BA-peptide conjugates as a vaccine-delivery system against Group A Streptococcus.

MATERIALS & METHODS

P(t)BA nanoparticles bearing J14 peptide epitopes were prepared via alkyne-azide 1,3-dipolar cycloaddition 'click' reaction. The conjugated products were self-assembled into small or large nanoparticles. These nanoparticle vaccine candidates were evaluated in vivo and J14-specific antibody titers were assessed.

RESULTS & DISCUSSION

Mice vaccinated with the nanoparticles were able to produce J14-specific IgG antibodies without the use of an external adjuvant after a single immunization. We have demonstrated for the first time that the immune responses against self-assembled P(t)BA nanoparticles are stronger for the smaller sized (~20 nm) nanoparticles compared with the larger (~500 nm) P(t)BA nanoparticles.

CONCLUSION

PtBA analogs have the potential to be developed as potent carrier systems for single-dose synthetic vaccines.

Effect of unsaturated bonds in the sn-2 acyl chain of phosphatidylcholine on the membrane-damaging action of Clostridium perfringens alpha-toxin toward liposomes

Clostridium perfringens alpha-toxin degrades phosphatidylcholine (PC) in the bilayer of liposomes and destroys the membrane. The effect of the type and position of unsaturation in the fatty acyl chain of PC (18:0/18:1 PC) synthesized on the toxin-induced leakage of carboxyfluorescein (CF) from PC liposomes was examined. Differential scanning calorimetry showed that the phase transition temperature (T(m)) was minimal when the triple bond was positioned at C (9) in the sn-2 acyl chain. The toxin-induced CF leakage decreased with the migration of the bond from C (9) to either end of the acyl chain in PC. The PC containing the cis-double bond had a similar T(m) to that with the triple bond, but a lower value than the PC containing the trans-double bond. Furthermore, the toxin-induced leakage from liposomes composed of PC containing the cis-double bond resembled that with PC having the triple bond and was greater than that from liposomes with PC having the trans-double bond. The binding of a H148G mutant to PC liposomes showed a reciprocal relationship in terms of the T(m) value of PC containing the triple bond. These results indicate that the toxin-induced membrane damage is closely related to membrane fluidity in liposomes.