Combination of a pH-responsive peptide amphiphile and a conventional antibiotic in treating Gram-negative bacteria

BACKGROUND

Clinical treatments ofgastric infections using antibiotics suffer from the undesired killing of commensal bacteria and emergence of antibiotic resistance. It is desirable to develop pH-responsive antimicrobial peptides (AMPs) that kill pathogenic bacteria such as H. pyloriand resistant E. coli under acidic environment with minimal impact to commensal bacteria whilst not causing antibiotic resistance.

EXPERIMENTS

Using a combined approach of cell assays, molecular dynamics (MD) simulations and membrane models facilitating biophysical and biochemical measurements including small angle neutron scattering (SANS), we have characterized the pH-responsive physiochemical properties and antimicrobial performance of two amphiphilic AMPs, GIIKDIIKDIIKDI-NH2 and GIIKKIIDDIIKKI-NH2 (denoted as 3D and 2D, respectively), that were designed by selective substitutions of cationic residues of Lys (K) in the extensively studied AMP G(IIKK)3I-NH2 with anionic residue Asp (D).

FINDINGS

Whilst 2D kept non-ordered coils across the entire pH range studied, 3D displayed a range of secondary structures when pH was shifted from basic to acidic, with distinct self-assembly into nanofibers in aqueous environment. Further experimental and modeling studies revealed that the AMPs interacted differently with the inner and outer membranes of Gram-negative bacteria in a pH-responsive manner and that the structural features characterized by membrane leakage and intramembrane nanoaggregates revealed from fluorescence spectroscopy and SANS were well linked to antimicrobial actions. Different antimicrobial efficacies of 2D and 3D were underlined by the interplay between their ability to bind to the outer membrane lipid LPS (lipopolysaccharide), outer membrane permeability change and inner membrane depolarization and leakage. Furthermore, AMP's binding with the inner membrane under acidic condition caused both the dissipation of membrane potential (Δψ) and the continuous dissipation of transmembrane ΔpH, with Δψ and ΔpH being the key components of the proton motive force. Combinations of antibiotic (Minocycline) with the pH-responsive AMP generated the synergistic effects against Gram-negative bacteria only under acidic condition. These features are crucial to target applications to gastric infections, anti-acne and wound healing.

Effective Treatment of Helicobacter pylori Infection Using Supramolecular Antimicrobial Peptide Hydrogels

Helicobacter pylori can cause various gastric conditions including stomach cancer in an acidic environment. Although early H. pylori infections can be treated by antibiotics, prolonged antibiotic administrations may lead to the development of antimicrobial resistance, compromising the effectiveness of the treatments. Antimicrobial peptides (AMPs) have been reported to possess unique advantages against antimicrobial-resistant bacteria due to their rapid physical membrane disruptions and anti-inflammation/immunoregulation properties. Herein, we have developed an AMP hydrogel, which can be orally administered for the treatment of H. pylori infection. The hydrogel has potent antimicrobial activity against H. pylori, achieving bacterial eradication within minutes of action. Compared with the AMP solution, the hydrogel formulation significantly reduced the cytotoxicity and enhanced proteolytic stability. In vivo experiments suggested that the hydrogel formed at pH 4 had superior therapeutic effects to those at pH 7 and 10 hydrogels, attributed to its rapid release and bactericidal action within the acidic stomach environment. Compared to conventional antibiotic treatments, the AMP hydrogel had the advantages of fast bacterial killing in the gastric juice and obviated proton pump inhibitors during the treatment. Although both the AMP hydrogel and antibiotics suppressed the expression of pro-inflammatory cytokines, the former uniquely promoted inflammation resolution. These results indicate that the AMP hydrogels with effectiveness and biosafety may be potential candidates for the clinical treatment of H. pylori infections.

Unraveling How Membrane Nanostructure Changes Impact the Eye Irritation of Nonionic Alkyl Ethoxylate Surfactants

Nonionic surfactants used in agri-spraying processes may cause varying degrees of corneal irritation when they come in direct contact with farmers' eyes, and the exact irritations are thought to be determined by how surfactants interact with corneal cell membranes. However, how nonionic surfactants interact with cell membranes at the molecular and nano levels remains largely unexplored. In this study, the interactions between nonionic surfactants (alkyl ethoxylate, C12Em) and lipid membranes were examined by membrane permeability measurement, quartz crystal microbalance with dissipation, dual polarization interferometry, confocal laser scanning microscopy, and neutron reflection, aiming to reveal complementary structural features at the molecular and nano levels. Apart from the extremely hydrophobic surfactant C12E2, all nonionic surfactants studied could penetrate the model cell membrane composed of a phosphocholine lipid bilayer. Nonionic surfactants with intermediate amphiphilicity (C12E6) rapidly fused into the lipid membrane and stimulated the formation of pores across the lipid bilayer, consistent with the cytoplasm leakage and fast cell necrosis observed from the cytotoxicity study of corneal cells. In comparison, while hydrophobic and hydrophilic surfactants [those with long and short ethoxylates (C12E4,12,23)] could cause mild structural alteration to the outer lipid layer of the membrane, these structural changes were insufficient to elicit large cytoplasmic leakage rapidly and instead cell death occurred over longer periods of time due to changes in the membrane permeability. These results reveal the strong link of surfactant-lipid membrane interactions to surfactant cytotoxicity and the association with amphiphilicity of nonionic surfactants.

Neutron reflection and scattering in characterising peptide assemblies

Self-assemblies of de novo designed short peptides at interface and in bulk solution provide potential platforms for developing applications in many medical and technological areas. However, characterising how bioinspired supramolecular nanostructures evolve with dynamic self-assembling processes and respond to different stimuli remains challenging. Neutron scattering technologies including small angle neutron scattering (SANS) and neutron reflection (NR) can be advantageous and complementary to other state-of-the-art techniques in tracing structural changes under different conditions. With more neutron sources now available, SANS and NR are becoming increasingly popular in studying self-assembling processes of diverse peptide and protein systems, but the difficulty in experimental manipulation and data analysis can deter beginners. This review will introduce the basic theory, general experimental setup and data analysis of SANS and NR, followed by provision of their applications in characterising interfacial and solution self-assemblies of representative peptides and proteins. SANS and NR are remarkably effective in determining the morphological features self-assembled short peptides, especially size and shape transitions as a result of either sequence changes or in response to environmental stimuli, demonstrating the unique capability of NR and SANS in unravelling the interactive processes. These examples highlight the potential of NR and SANS in supporting the development of novel short peptides and proteins as biopharmaceutical candidates in the fight against many diseases and infections that share common features of membrane interactive processes.

How do antimicrobial peptides disrupt the lipopolysaccharide membrane leaflet of Gram-negative bacteria?

HYPOTHESIS

It is widely regarded that antimicrobial peptides (AMPs) kill bacteria by physically disrupting microbial membranes and causing cytoplasmic leakage, but it remains unclear how AMPs disrupt the outer membrane (OM) of Gram-negative bacteria (GNB) and then compromise the inner membrane. We hypothesise that different AMPs impose different structural disruptions, with direct implications to their antimicrobial efficacies.

EXPERIMENTS

The antimicrobial activities of three typical AMPs, including the designed short AMP, G₃, and two natural AMPs, melittin and LL37, against E. coli and their haemolytic activities were studied. Lipopolysaccharide (LPS) and anionic di-palmitoyl phosphatidyl glycerol (DPPG) monolayer models were constructed to mimic the outer membrane and inner membrane leaflets of Gram-negative bacteria. The binding and penetration of AMPs to the model lipid monolayers were systematically studied by neutron reflection via multiple H/D contrast variations.

FINDING

G₃ has relatively high antimicrobial activity, low cytotoxicity, and high proteolytic stability, whilst melittin has significant haemolysis and LL37 has weaker antimicrobial activity. G₃ could rapidly lyse LPS and DPPG monolayers within 10-20 min. In contrast, melittin was highly active against the LPS membrane, but the dynamic process lasted up to 80 min, with excessive stacking in the OM. LL37 caused rather weak destruction to LPS and DPPG monolayers, leading to massive adsorption on the membrane surface without penetrating the lipid tail region. These findings demonstrate that the rationally designed AMP G₃ was well optimised to impose most effective destruction to bacterial membranes, consistent with its highest bactericidal activity. These different interfacial structural features associated with AMP binding shed light on the future development of active and biocompatible AMPs for infection and wound treatments.

Competitive Adsorption of a Monoclonal Antibody and Nonionic Surfactant at the PDMS/Water Interface

Interfacial adsorption of monoclonal antibodies (mAbs) can cause structural deformation and induce undesired aggregation and precipitation. Nonionic surfactants are often added to reduce interfacial adsorption of mAbs which may occur during manufacturing, storage, and/or administration. As mAbs are commonly manufactured into ready-to-use syringes coated with silicone oil to improve lubrication, it is important to understand how an mAb, nonionic surfactant, and silicone oil interact at the oil/water interface. In this work, we have coated a polydimethylsiloxane (PDMS) nanofilm onto an optically flat silicon substrate to facilitate the measurements of adsorption of a model mAb, COE-3, and a commercial nonionic surfactant, polysorbate 80 (PS-80), at the siliconized PDMS/water interface using spectroscopic ellipsometry and neutron reflection. Compared to the uncoated SiO₂ surface (mimicking glass), COE-3 adsorption to the PDMS surface was substantially reduced, and the adsorbed layer was characterized by the dense but thin inner layer of 16 Å and an outer diffuse layer of 20 Å, indicating structural deformation. When PS-80 was exposed to the pre-adsorbed COE-3 surface, it removed 60 wt % of COE-3 and formed a co-adsorbed layer with a similar total thickness of 36 Å. When PS-80 was injected first or as a mixture with COE-3, it completely prevented COE-3 adsorption. These findings reveal the hydrophobic nature of the PDMS surface and confirm the inhibitory role of the nonionic surfactant in preventing COE-3 adsorption at the PDMS/water interface.

Intramembrane Nanoaggregates of Antimicrobial Peptides Play a Vital Role in Bacterial Killing

Recent developments in antimicrobial peptides (AMPs) have focused on the rational design of short sequences with less than 20 amino acids due to their relatively low synthesis costs and ease of correlation of the structure-function relationship. However, gaps remain in the understanding of how short cationic AMPs interact with the bacterial outer and inner membranes to affect their antimicrobial efficacy and dynamic killing. The membrane-lytic actions of two designed AMPs, G(IIKK)₃ I-NH₂ (G₃ ) and G(IIKK)₄ I-NH₂ (G₄ ), and previously-studied controls GLLDLLKLLLKAAG-NH₂ (LDKA, biomimetic) and GIGAVLKVLTTGLPALISWIKRKR-NH₂ (Melittin, natural) are examined. The mechanistic processes of membrane damage and the disruption strength of the four AMPs are characterized by molecular dynamics simulations and experimental measurements including neutron reflection and scattering. The results from the combined studies are characterized with distinctly different intramembrane nanoaggregates formed upon AMP-specific binding, reflecting clear influences of AMP sequence, charge and the chemistry of the inner and outer membranes. G₃ and G₄ display different nanoaggregation with the outer and inner membranes, and the smaller sizes and further extent of insertion of the intramembrane nanoaggregates into bacterial membranes correlate well with their greater antimicrobial efficacy and faster dynamic killing. This work demonstrates the crucial roles of intramembrane nanoaggregates in optimizing antimicrobial efficacy and dynamic killing.

In-Membrane Nanostructuring of Cationic Amphiphiles Affects Their Antimicrobial Efficacy and Cytotoxicity: A Comparison Study between a De Novo Antimicrobial Lipopeptide and Traditional Biocides

Cationic biocides have been widely used as active ingredients in personal care and healthcare products for infection control and wound treatment for a long time, but there are concerns over their cytotoxicity and antimicrobial resistance. Designed lipopeptides are potential candidates for alleviating these issues because of their mildness to mammalian host cells and their high efficacy against pathogenic microbial membranes. In this study, antimicrobial and cytotoxic properties of a de novo designed lipopeptide, CH₃(CH₂)₁₂CO-Lys-Lys-Gly-Gly-Ile-Ile-NH₂ (C₁₄KKGGII), were assessed against that of two traditional cationic biocides C_nTAB (n = 12 and 14), with different critical aggregation concentrations (CACs). C₁₄KKGGII was shown to be more potent against both bacteria and fungi but milder to fibroblast host cells than the two biocides. Biophysical measurements mimicking the main features of microbial and host cell membranes were obtained for both lipid monolayer models using neutron reflection and small unilamellar vesicles (SUVs) using fluorescein leakage and zeta potential changes. The results revealed selective binding to anionic lipid membranes from the lipopeptide and in-membrane nanostructuring that is distinctly different from the co-assembly of the conventional C_nTAB. Furthermore, C_nTAB binding to the model membranes showed low selectivity, and its high cytotoxicity could be attributed to both membrane lysis and chemical toxicity. This work demonstrates the advantages of the lipopeptides and their potential for further development toward clinical application.

Contrasting impacts of mixed nonionic surfactant micelles on plant growth in the delivery of fungicide and herbicide

HYPOTHESIS

Nonionic alkyl ethoxylate surfactants are widely used in agrochemicals to facilitate the permeation of systemic herbicides and fungicides across the plant waxy film. Industrial grade surfactants are often highly mixed and how the mixing affects their interactions with pesticides and wax films remains largely unexplored. A better understanding could enable design of mixed nonionic surfactants for herbicides and fungicides to maximize their efficiency and reduce wastage whilst controlling their impact on plant wax films.

EXPERIMENT

In this study, nonionic surfactants with general structure n-oxyethylene glycol monododecyl ether (C₁₂E_n) were used to form surfactant mixtures with the same average ethoxylate numbers but different hydrophilic-lipophilic balance (HLB) values. Their mixed micellar systems were then used to solubilize a herbicide diuron (DN) and a fungicide cyprodinil (CP), followed by plant wax solubilization upon contact with wax films. These processes were monitored by ¹H NMR and SANS.

FINDING

Pesticide solubilization made surfactant micelles effectively more hydrophobic but subsequent wax dissolution caused pesticide release and the restoration of the micellar amphiphilicity. Nonionic surfactants with lower HLBs form larger nanoaggregates, show enhanced wettability, and have better ability to solubilize and permeate pesticides across the wax film, but may cause significant damage to plant growth. These observations help explain why herbicides applied on weeds would benefit from surfactants with lower HLB values while fungicides require surfactants with HLBs to balance between delivery efficiency and potential phytotoxicity risks.

Implications of surfactant hydrophobic chain architecture on the Surfactant-Skin lipid model interaction

Although surfactants have been widely used in skin care and other related applications, our knowledge about how surfactants interact with stratum corneum (SC) lipids remains limited. This work reports how surfactants interact with a lipid SC model by neutron diffraction and molecular dynamics (MD) simulations, focusing on examining the impact of surfactant molecular architecture. The surfactant-SC mixed membrane was constructed by an equimolar mixture of ceramide/cholesterol/fatty acids and surfactant at 1% molar ratio of total lipids. The arrangements of water and surfactant molecules in the membrane were obtained through neutron scattering length density (NSLD) profiles via contrast variation method, meanwhile, MD simulation clearly demonstrated the mechanism of hydration change in the surfactant-model SC mixed membrane. No drastic difference was detected in the repeating distance of the short periodicity phase (SPP) upon adding surfactants, however, it significantly enhanced the membrane hydration and reduced the amount of phase separated crystalline cholesterol, showing a strong dependence on surfactant chain length, branching and double bond. This work clearly demonstrates how surfactant architecture affects its interaction with the SC membrane, providing useful guidance for either choosing an existing surfactant or designing a new one for surfactant-based transdermal application.

How do terminal modifications of short designed IIKK peptide amphiphiles affect their antifungal activity and biocompatibility?

HYPOTHESIS

The widespread and prolonged use of antifungal antibiotics has led to the rapid emergence of multidrug resistant Candida species that compromise current treatments. Natural and synthetic antimicrobial peptides (AMPs) offer potential alternatives but require further development to overcome some of their current drawbacks. AMPs kill pathogenic fungi by permeabilising their membranes but it remains unclear how AMPs can be designed to maximise their antifungal potency whilst minimising their toxicity to host cells.

EXPERIMENTS

We have designed a group of short (IIKK)₃ AMPs via selective terminal modifications ending up with different amphiphilicities. Their antifungal performance was assessed by minimum inhibition concentration (MICs) and dynamic killing to 4 Candida strains and Cryptococcus neoformans, and the minimum biofilm-eradicating concentrations to kill 95% of the C. albicans biofilms (BEC₉₅). Different antifungal actions were interpreted on the basis of structural disruptions of the AMPs to small unilamellar vesicles from fluorescence leakage, Zeta potential, small angle neutron scattering (SANS) and molecular dynamics simulations (MD).

FINDING

AMPs possess high antifungal activities against the Candida species and Cryptococcus neoformans; some of them displayed faster dynamic killing than antibiotics like amphotericin B. G(IIKK)₃I-NH₂ and (IIKK)₃II-NH₂ were particularly potent against not only planktonic microbes but also fungal biofilms with low cytotoxicity to host cells. It was found that their high selectivity and fast action were well correlated to their fast membrane lysis, evident from data measured from Zeta potential measurements, SANS and MD, and also consistent with the previously observed antibacterial and anticancer performance. These studies demonstrate the important role of colloid and interface science in further developing short, potent and biocompatible AMPs towards clinical treatments via structure design and optimization.

Deletion in KRT75L4 linked to frizzle feather in Xiushui Yellow Chickens

Bird feathers are the product of interactions between natural and artificial selection. Feather-related traits are important for chicken selection and breeding. Frizzle feather is characterized by the abnormally development of feathers in chickens. In the current study, frizzle feather characteristics were observed in a local breed called Xiushui Yellow Chicken in Jiangxi, China. To determine the molecular mechanisms that underlie frizzle feather in Xiushui Yellow Chicken, four populations of three breeds (Xiushui Yellow Chicken with frizzle feathers, Xiushui Yellow Chicken with normal feathers, Guangfeng White-Ear Yellow Chicken, and Ningdu Yellow Chicken) were selected for whole-genome resequencing. Using a comparative genome strategy and genome-wide association study, a missense mutation (g.5281494A>G) and a 15-bp deletion (g.5285437-5285451delGATGCCGGCAGGACG) in KRT75L4 were identified as candidate mutations associated with frizzle feather in Xiushui Yellow Chicken. Based on genotyping performed in a large Xiushui Yellow Chicken population, the g.5285437-5285451delGATGCCGGCAGGACG mutation in KRT75L4 was confirmed as the putative causative mutation of frizzle feather. These results deepen the understanding of the molecular mechanisms responsible for frizzle feather, as well as facilitating the molecular detection and selection of the feather phenotype in Xiushui Yellow Chickens.

How do chain lengths of acyl-l-carnitines affect their surface adsorption and solution aggregation?

HYPOTHESIS

l-carnitines in our body systems can be readily converted into acyl-l-carnitines which have a prominent place in cellular energy generation by supporting the transport of long-chain fatty acids into mitochondria. As biocompatible surfactants, acyl-l-carnitines have potential to be useful in technical, personal care and healthcare applications. However, the lack of understanding of the effects of their molecular structures on their physical properties has constrained their potential use.

EXPERIMENTS

This work reports the study of the influence of the acyl chain lengths of acyl-l-carnitines (C_nLC) on solubility, surface adsorption and aggregation. Critical micellar concentrations (CMCs) of C_nLC were determined by surface tension measurements. Neutron reflection (NR) was used to further examine the structure and composition of the adsorbed C_nLC layer. The structural changes of the micellar aggregates under different concentrations of C_nLC, pH and ionic strength were determined by dynamic light scattering (DLS) and small angle neutron scattering (SANS).

FINDINGS

C₁₂LC is fully soluble over a wide temperature and concentration range. There is however a strong decline of solubility with increasing acyl chain length. The adsorption and aggregation behavior of C₁₄LC was therefore studied at 30 °C and C₁₆LC at 45 °C. The solubility boundaries displayed distinct hysteresis with respect to heating and cooling. The CMCs of C₁₂LC, C₁₄LC and C₁₆LC at pH 7 were 1.1 ± 0.1, 0.10 ± 0.02 and 0.010 ± 0.005 mM, respectively, with the limiting values of the area per molecule at the CMC being 45.4 ± 2, 47.5 ± 2 and 48.8 ± 2 Å² and the thicknesses of the adsorbed C_nLC layers at the air/water interface increasing from 21.5 ± 2 to 22.6 ± 2 to 24.2 ± 2 Å, respectively. All three surfactants formed core-shell spherical micelles with comparable dimensional parameters apart from an increase in core radius with acyl chain length. This study outlines the effects of acyl chain length on the physicochemical properties of C_nLCs under different environmental conditions, serving as a useful basis for developing their potential applications.

[Treatment efficacy of dietary supplement Licofor for dry eye associated with meibomian gland dysfunction]

Objective: To evaluate the clinical efficacy of dietary supplement Licofor in the treatment of dry eye associated with meibomian gland dysfunction (MGD). Methods: This was a prospective, randomized controlled clinical trial. Sixty patients [25 males, 35 females, aged (42±13) years] who had dry eye associated with MGD were recruited in Xiangya Hospital of Central South University from December 2018 to October 2019. The patients were equally divided into two groups: 30 cases (60 eyes) in the experimental group and 30 cases (60 eyes) in the control group. All subjects were treated with eye hot compress, artificial tears and antibiotic ointment. After that, the experimental group and control group were received dietary supplementary Licofor or placebo daily for 12 weeks. The symptoms and signs of dry eye, morphology and function of meibomian gland, and inflammatory response were assessed at the beginning, 4^th, 8^th and 12^th week of treatment. Results: After 12 weeks of treatment, statistically significant improvements in ocular surface disease index (OSDI) scores, tear break-up time (TBUT), corneal fluorescein staining (CFS), the morphology of eyelid margin, meibomian gland orifice, meibomian gland expressibility, meibum quality, and periglandular inflammatory cell density were determined in both groups (all P<0.05). In the Licofor group, the improvement of OSDI scores [16.7 (12.5, 20.8) vs 20.8 (18.8, 22.9), P<0.001], the morphology of eyelid margin, meibomian gland orifice and periglandular inflammatory cell density [443 (318, 513) vs 553 (415, 676)/mm², P=0.002] were more significant (all P<0.05). Conclusion: The combined treatment of licofor and conventional treatment can significantly improve symptoms of dry eye, the morphology of eyelid margin, meibomian gland orifice, meibum quality, and eyelid inflammation response of dry eye associated with MGD.

Structural Disruptions of the Outer Membranes of Gram-Negative Bacteria by Rationally Designed Amphiphilic Antimicrobial Peptides

Gram-negative bacteria are covered by both an inner cytoplasmic membrane (IM) and an outer membrane (OM). Antimicrobial peptides (AMPs) must first permeate through the OM and cell wall before attacking the IM to cause cytoplasmic leakage and kill the bacteria. The bacterial OM is an asymmetric bilayer with the outer leaflet primarily composed of lipopolysaccharides (LPSs) and the inner leaflet composed of phospholipids (PLs). Two cationic α-helical AMPs were designed to target Gram-negative bacteria, a full peptide G(IIKK)₃I-NH₂ (G₃), and a hydrophobic lipopeptide C₈-G(IIKK)₂I-NH₂ (C₈G₂, with C₈ denoting the octanoyl chain). LPS dominates OM functions as the first line of defense against antibiotics, thereby reducing drug susceptibility. This work explores how the two AMPs interact with LPS through several carefully chosen OM models that facilitated measurements from solid-state nuclear magnetic resonance (ss-NMR), small-angle neutron scattering (SANS), and neutron reflectivity (NR). The results revealed that G₃ molecules bound preferably to the LPS head region and functioned as bridge molecules to reassemble the dislocated lipids into bilayer stacks. In contrast, C₈G₂ lipopeptides could quickly penetrate into the central region of the OM to cause direct removal of some membrane lipids. Different structural disruptions implicated different antimicrobial efficacies from these AMPs. The demonstration of the structural features underlying different susceptibilities of the OM to AMPs offers a useful route for the future development of strain-specific AMPs against antimicrobial-resistant pathogens.

What happens when pesticides are solubilised in binary ionic/zwitterionic-nonionic mixed micelles?

HYPOTHESIS

Surfactants have been widely used as adjuvants in agri-sprays to enhance the solubility of pesticides in foliar spray deposits and their mobility through leaf cuticles. Previously, we have characterised pesticide solubilisation in nonionic surfactant micelles, but what happens when pesticides become solubilised in anionic, cationic and zwitterionic and their mixtures with nonionic surfactants remain poorly characterised.

EXPERIMENTS

To facilitate characterisations by SANS and NMR, we used nonionic surfactant hexaethylene glycol monododecyl ether (C₁₂E₆), anionic sodium dodecylsulphate (SDS), cationic dodecyltrimethylammonium bromide (DTAB) and zwitterionic dodecylphosphocholine (C₁₂PC) as model adjuvant systems to solubilise 3 pesticides, Cyprodinil (CP), Azoxystrobin (AZ) and Difenoconazole (DF), representing different structural features. The investigation focused on the influence of solubilisates in driving changes to the micellar nanostructures in the absence or presence of electrolytes. NMR and NOESY were applied to investigate the solubility and location of each pesticide in the micelles. SANS was used to reveal subtle changes to the micellar structures due to pesticide solubilisation with and without electrolytes.

FINDINGS

Unlike nonionic surfactants, the ionic and zwitterionic surfactant micellar structures remain unchanged upon pesticide solubilisation. Electrolytes slightly elongate the ionic surfactant micelles but have no effect on nonionic and zwitterionic surfactants. Pesticide solubilisation could alter the structures of the binary mixtures of ionic/zwitterionic and ionic/nonionic micelles by causing elongation, shell shrinkage and dehydration, with the exact alteration being determined by the molar ratio in the mixture.

Surface adsorption and solution aggregation of a novel lauroyl-l-carnitine surfactant

HYPOTHESIS

l-carnitine plays a crucial role in the cellular production of energy by transporting fatty acids into mitochondria. Acylated l-carnitines are amphiphilic and if appropriate physical properties were demonstrated, they could replace many currently used surfactants with improved biocompatibility and health benefits.

EXPERIMENTS

This work evaluated the surface adsorption of lauroyl-l-carnitine (C₁₂LC) and its aggregation behavior. The size and shape of the aggregates of C₁₂LC surfactant were studied at different temperatures, concentrations, pH and ionic strength by dynamic light scattering (DLS) and small-angle neutron scattering (SANS). Surface tension measurements were carried out to determine the critical micellar concentration (CMC) of C₁₂LC. Combining with the Gibbs equation, the surface excess at different concentrations could be determined. Neutron reflection (NR) was used to determine the structure of the adsorbed layer at the air/water interface with the help of isotopic contrast variations.

FINDINGS

At pH 7, the limiting area per molecule (A_CMC) of the zwitterionic C₁₂LC adsorbed layer at the air/water interface was found to be 46 Å² from surface tension and neutron reflection, smaller than the values of C₁₂PC, C₁₂E₅, DTAB, C₁₂C₄betaine and C₁₂C₈betaine but close to that of SDS. A pronounced surface tension minimum at pH 2 at the low ionic strength was linked to a minimum value of area per molecule of about 30 Å², indicating the competitive adsorption from traces of lauric acid produced by hydrolysis of C₁₂LC. As the concentration increased, area per molecule reached a plateau of 37-39 Å², indicating the dissolution of the more surface-active lauric acid into the micelles of C₁₂LC. DLS and SANS showed that the size and shape of micelles had little response to temperature, concentration, ionic strength or pH. The SANS profiles measured under 3 isotopic contrasts could be well fitted by the core-shell model, giving a spherical core radius of 15.7 Å and a shell thickness of 10.5 Å. The decrease of pH led to more protonated carboxyl groups and more positively charged micelles, but the micellar structures remained unchanged, in spite of their stronger interaction. These features make C₁₂LC potentially attractive as a solubilizing agent.

A technical review of face mask wearing in preventing respiratory COVID-19 transmission

Since the outbreak of the COVID-19 pandemic, most countries have recommended their citizens to adopt social distance, hand hygiene, and face mask wearing. However, wearing face masks has not been well adopted by many citizens. While the reasons are complex, there is a general perception that the evidence to support face mask wearing is lacking, especially for the general public in a community setting. Face mask wearing can block or filter airborne virus-carrying particles through the working of colloid and interface science. This paper assesses current knowledge behind the design and functioning of face masks by reviewing the selection of materials, mask specifications, relevant laboratory tests, and respiratory virus transmission trials, with an overview of future development of reusable masks for the general public. This review highlights the effectiveness of face mask wearing in the prevention of COVID-19 infection.

How do Self-Assembling Antimicrobial Lipopeptides Kill Bacteria?

Antimicrobial peptides are promising alternatives to traditional antibiotics. A group of self-assembling lipopeptides was formed by attaching an acyl chain to the N-terminus of α-helix-forming peptides with the sequence C_x-G(IIKK)_yI-NH₂ (C_xG_y, x = 4-12 and y = 2). C_xG_y self-assemble into nanofibers above their critical aggregation concentrations (CACs). With increasing x, the CACs decrease and the hydrophobic interactions increase, promoting secondary structure transitions within the nanofibers. Antimicrobial activity, determined by the minimum inhibition concentration (MIC), also decreases with increasing x, but the MICs are significantly smaller than the CACs, suggesting effective bacterial membrane-disrupting power. Unlike conventional antibiotics, both C₈G₂ and C₁₂G₂ can kill Staphylococcus aureus and Escherichia coli after only minutes of exposure under the concentrations studied. C₁₂G₂ nanofibers have considerably faster killing dynamics and lower cytotoxicity than their nonaggregated monomers. Antimicrobial activity of peptide aggregates has, to date, been underexploited, and it is found to be a very promising mechanism for peptide design. Detailed evidence for the molecular mechanisms involved is provided, based on superresolution fluorescence microscopy, solid-state nuclear magnetic resonance, atomic force microscopy, neutron scattering/reflectivity, circular dichroism, and Brewster angle microscopy.

MicroRNA-381 inhibits lung adenocarcinoma cell biological progression by directly targeting LMO3 through regulation of the PI3K/Akt signaling pathway and epithelial-to-mesenchymal transition

OBJECTIVE

To investigate the role of miR-381 in the progression of lung adenocarcinoma (LA) and its underlying mechanism.

PATIENTS AND METHODS

A total of 54 pairs of LA tissues and para-carcinoma tissues were obtained from May 2015 to April 2017 in our hospital. Four human LA cell lines (A549, SPC-A1, H1299, and PC-9) and one normal human pulmonary epithelial cell line BEAS-2B were obtained and cultured. The protein and mRNA expression levels were detected by quantitative Real Time-Polymerase Chain Reaction (qRT-PCR) and Western blot, respectively. Additionally, cell proliferation assays and cell migration and invasion assays were used. Furthermore, tumor xenograft model in nude mice was made in this study.

RESULTS

miR-381 was notably downregulated in LA tissues. Moreover, low miR-381 expression was confirmed to be strongly correlated with poor prognosis and aggressive clinicopathological characteristics of LA patients. Exogenous miR-381 overexpression was found to notably restrict LA cell proliferation, migration, and invasion; additionally, miR-381 overexpression could significantly reduce tumor growth in vivo. Mechanistically, LMO3 was determined as a novel direct target for miR-381 in LA cells. In clinical LA tissues, the LMO3 expressions were clearly overexpressed. Furthermore, miR-381 overexpression affected the PI3K/Akt pathway and EMT in LA.

CONCLUSIONS

MiR-381 played key roles in LA progression, partially via directly targeting LMO3 and regulating the PI3K/Akt signaling pathway and EMT. Thus, the miR-381/ LMO3 axis has clinical significance in the therapy of patients with LA.

Aggregated Amphiphilic Antimicrobial Peptides Embedded in Bacterial Membranes

Molecular dynamics (MD) simulations, stochastic optical reconstruction microscopy (STORM), and neutron reflection (NR) were combined to explore how antimicrobial peptides (AMPs) can be designed to promote the formation of nanoaggregates in bacterial membranes and impose effective bactericidal actions. Changes in the hydrophobicity of the designed AMPs were found to have a strong influence on their bactericidal potency and cytotoxicity. G(IIKK)₃I-NH₂ (G₃) achieved low minimum inhibition concentrations (MICs) and effective dynamic kills against both antibiotic-resistant and -susceptible bacteria. However, a G₃ derivative with weaker hydrophobicity, KI(KKII)₂I-NH₂ (KI), exhibited considerably lower membrane-lytic activity. In contrast, the more hydrophobic G(ILKK)₃L-NH₂ (GL) peptide achieved MICs similar to those observed for G₃ but with worsened hemolysis. Both the model membranes studied by Brewster angle microscopy, zeta potential measurements, and NR and the real bacterial membranes examined with direct STORM contained membrane-inserted peptide aggregates upon AMP exposure. These structural features were well supported by MD simulations. By revealing how AMPs self-assemble in microbial membranes, this work provides important insights into AMP mechanistic actions and allows further fine-tuning of antimicrobial potency and cytotoxicity.

How does substrate hydrophobicity affect the morphological features of reconstituted wax films and their interactions with nonionic surfactant and pesticide?

HYPOTHESIS

Surfactants are widely used in agri-sprays to improve pesticide efficiency, but the mechanism underlying their interactions with the surface wax film on plants remains poorly understood. To facilitate physical characterisations, we have reconstituted wheat cuticular wax films onto an optically flat silicon substrate with and without octadecyltrimethoxysilane modification to control surface hydrophobicity.

EXPERIMENTS

Imaging techniques including scanning electron microscopy (SEM) unravelled morphological features of the reconstituted wax films similar to those on leaves, showing little impact from the different substrates used. Neutron reflection (NR) established that reconstituted wax films were comprised of an underlying wax film decorated with top surface wax protrusions, a common feature irrespective of substrate hydrophobicity and highly consistent with what was observed from natural wax films. NR measurements, with the help of isotopic H/D substitutions to modify the scattering contributions of the wax and solvent, revealed different wax regimes within the wax films, illustrating the impact of surface hydrophilicity on the nanostructures within the wax films.

FINDINGS

It was observed from both spectroscopic ellipsometry and NR measurements that wax films formed on the hydrophobic substrate were more robust and durable against attack by nonionic surfactant C₁₂E₆ solubilised with pesticide Cyprodinil (CP) than films coated on the bare hydrophilic silica. Thus, the former could be a more feasible model for studying the wax-surfactant-pesticide interactions.

[A multicenter survey of the accessibility of essential medicines for children in China]

Objective: To investigate the availability, prices and affordability of essential medicines in pediatric population across China, in the hope of improving rational use of medicines. Methods: A multicenter cross-sectional survey of medicine prices, availability and affordability was conducted in 17 provinces, municipalities and autonomous region across east, south-central part, west and north of China. Data on 42 medicines used in pediatric population, both original and generic, were collected in 55 public hospitals from May 26 to June 2, 2017. Availability was expressed as the percentage of hospitals with stock of the target medicine on the day of data collection,and median price ratio (MPR) was the ratio of price upon investigation to international reference. Based on national minimum daily wage, affordability represents the number of working days needed to earn the expense which covers a standard course using the target medicine. Statistical software SPSS 13.0 was applied for descriptive analysis of availability, MPR and affordability. Results: Mean Availability of original and generic medicine was 33% and 32%, with median MPR being 5.43 and 1.55. Among the 19 medicines with price information for both original and generic product, the median MPR was 7.73 and 2.04 respectively. Regarding the five medicines used to treat four common pediatric diseases (pneumonia,peptic ulcer, congenital hypothyroidism, refractory nephrotic syndrome), the affordability was 0.63 (0.16-6.17) d for generic medicine, and 1.03 (0.16-11.53) d for its original counterpart. Conclusions: The availability to both original and generic products of the 42 medicines used in pediatric population was low in China. The prices of generic medicines seem to be lower and affordability higher than those of original medicines. There is an urgent need to improve the availability and affordability of pediatric medicines.

Phylogenetic classification of hemagglutinin gene of H9N2 avian influenza viruses isolated in China during 2012-2016 and evaluation of selected candidate vaccine strains

H9N2 subtype avian influenza virus (AIV) was the highly contagious pathogen which has caused severe losses in the poultry industry throughout China in recent years. Using current epidemic viruses as vaccine was an effective way to prevent infection of H9N2 subtype AIV. In this study, a total of 23 H9N2 subtype AIV strains were isolated in 200 samples from 13 provinces of China during 2012-2016. The sequencing and phylogenetic analysis of the hemagglutinin gene sequence of the isolation strains showed that 22 isolation strains were clustered to h9.4.2.5 lineage, while only 1 belonged to h9.4.2.6. The data of cross-HI, neutralization and cross-immune protection shown that the A/chicken/Hunan/HN/2015 (HN) and A/chicken/Shandong/SD/2014 (SD) strains as vaccine could effectively protect present viruses infection compared with other strains. These results indicated that current epidemic viruses were mainly belong to h9.4.2.5 lineage and HN and SD strains as candidate vaccine strains were potentiality for the protection of present H9N2 subtype AIV infection.

Catechol-cation adhesion on silica surfaces: molecular dynamics simulations

Understanding the interaction mechanism between catechol-cation and inorganic surfaces is vital for controlling the interfacial adhesion behavior. In this work, molecular dynamics simulations are employed to study the adhesion of siderophore analogues (Tren-Lys-Cam, Tren-Arg-Cam and Tren-His-Cam) on silica surfaces with different degrees of ionization and the effects of cationic amino acids and ionic strength on adhesion are discussed. Simulation results indicate that adhesion of catechol-cation onto the ionized silica surface is dominated by electrostatic interactions. At different degrees of ionization, the rank of the adhesions of three siderophore analogues on silica is different. Further analysis shows that the amino acid terminus has a large influence on the adhesion process, especially histidine adhesion on negatively charged surfaces. Tren-Lys-Cam (TLC) has a larger adhesion free energy than Tren-Arg-Cam (TAC) at a higher degree of ionization (18%); both the bulkier structure and delocalized charge of Arg decreased the cation's electrostatic interaction with the charged silica. In addition, the adhesion free energy on ionized silica surfaces decreased with increasing ionic strength of aqueous solutions. A linear correlation between the potential of mean force obtained from umbrella sampling and the rupture force via steered molecular dynamics simulations for siderophore analogue adhesion on silica surfaces is also found. This work may provide some guidance for developing the next generation underwater adhesives.

Mesoscopic Structures of Poly(carboxybetaine) Block Copolymer and Poly(ethylene glycol) Block Copolymer in Solutions

The antifouling property of exogenous materials is vital for their in vivo applications. In this work, dissipative particle dynamics simulations are performed to study the self-assembled morphologies of two copolymer systems containing poly(ethylene glycol) (PEG) and poly(carboxybetaine) (PCB) in aqueous solutions. Effects of polymer composition and polymer concentration on the self-assembled structures of the two copolymers (PLA-PEG and PLA-PCB) are investigated, respectively [PLA represents poly(lactic acid)]. Results show that whatever the copolymer composition is, PLA-PEG systems will self-assemble into core-shell structures, whereas onion-like and vesicle structures are also found for the PLA-PCB systems. Different morphologies are obtained at different polymer concentrations in both copolymer systems. Simulation results demonstrate that PCB is more stable than PEG in maintaining self-assembled spherical structures of copolymer systems because PLA-PEG forms dumbbell-like structures whereas PLA-PCB is spherical under the same polymer concentration. Although both copolymer systems can self-assemble into core-shell nanoparticles when the block ratio of PLA:PEG or PLA:PCB is 80:20, the core-shell structures of the nanoparticles are quite different. The shell layers formed by PEG in PLA-PEG nanoparticles are inhomogeneous in size because of the amphiphilicity of PEG, whereas the shell layers in PLA-PCB nanoparticles are homogenous because of the strong hydrophilicity of the zwitterionic PCB polymer block.

Molecular Understanding on the Underwater Oleophobicity of Self-Assembled Monolayers: Zwitterionic versus Nonionic

Molecular dynamics simulations are conducted to investigate the underwater oleophobicity of self-assembled monolayers (SAMs) with different head groups. Simulation results show that the order of underwater oleophobicity of SAMs is methyl < amide < oligo(ethylene glycol) (OEG) < ethanolamine (ETA) < hydroxyl < mixed-charged zwitterionic. The underwater-oil contact angles (OCAs) are <133° for all nonionic hydrophilic SAMs, while the mixed-charged zwitterionic SAMs are underwater superoleophobic (OCA can reach 180°). It appears that surfaces with stronger underwater oleophobicity have better antifouling performance. Further study on the effect of different alkyl ammonium ions on mixed-charged SAMs reveals that the underwater OCAs are >143.6° for all SAMs; mixed-charged SAMs containing primary alkyl ammonium ion are likely to possess the best underwater oleophobicity for its strong hydration capacity. It seems that alkyl sulfonate anion (SO₃^-) is more hydrophilic than alkyl trimethylammonium ion (NC₃⁺) for the hydrophobic methyl groups on nitrogen atoms and that the hydration of SO₃^- in mixed-charged SAMs can be seriously blocked by NC₃⁺. The monomer of SO₃^- should be slightly longer than that of NC₃⁺ to obtain better underwater oleophobicity in NC₃⁺-/SO₃^--SAMs. In addition, the underwater oleophobicity of SAMs might become worse at low grafting densities. This work systematically proves that a zwitterionic surface is more underwater oleophobic than a nonionic surface. These results will help for the design and development of superoleophobic surfaces.

The prevalence of and risk factors for prostatitis-like symptoms and its relation to erectile dysfunction in Chinese men

The aim of this study was to describe the prevalence of and risk factors for prostatitis-like symptoms and its relation to erectile dysfunction (ED) among southern Chinese men. Data were collected from 2790 men attending the Fangchenggang Area Male Healthy and Examination Survey from September 2009 to December 2009. The prostatitis-like symptoms were assessed by the NIH Chronic Prostatitis Symptom Index and ED was assessed using the 5-item International Index of Erectile Function. Lifestyle and demographic characteristics were obtained through a questionnaire. Prevalence of prostatitis-like symptoms was 12.4% among 2790 Chinese men aged 20-84 years. In smokers who smoked ≥20 cigarettes per day (age-adjusted OR = 1.29; 95% CI = 1.00-1.66; p = 0.04), physical inactivity (age-adjusted OR = 1.31; 95% CI = 1.03-1.66; p = 0.02) was a significant risk factor for prostatitis-like symptoms. Alcohol consumption (daily drinking) also was a risk factor for prostatitis-like symptoms, although the differences were not statistically significant (age-adjusted OR = 1.36; 95% CI = 0.96-1.92; p = 0.07). Those with diabetes may also be at higher risk for prostatitis-like symptoms (age-adjusted OR = 1.37; 95% CI = 0.85-2.21; p = 0.19). In addition, men with ED were more likely to have had prostatitis-like symptoms (age-adjusted OR = 1.86; 95% CI = 0.47-2.36; p < 0.0001), and the ORs increased with increasing severity of ED status (mild ED, mild to moderate ED, and moderate to severe ED were 1.57, 2.62, and 3.24, respectively. Test for trend, p = 0.0001). Our results show that prostatitis-like symptoms are prevalent in Southern China affecting men of all ages. Smoking, drinking, lack of physical activity, and elevated plasma glucose level were associated with an increased risk of prostatitis-like symptoms. In addition, our results reveal that ED accounted for a large proportion (61.5%) among men with prostatitis-like symptoms; we also confirm the magnitude of ED associated with prostatitis-like symptoms. Thus, interventions to evaluate and improve ED might help ameliorate prostatitis-like symptoms and vice versa.

The International Association for the Study of Lung Cancer Lung Cancer Staging Project: Proposals for the Revision of the Clinical and Pathologic Staging of Small Cell Lung Cancer in the Forthcoming Eighth Edition of the TNM Classification for Lung Cancer

INTRODUCTION

Small cell lung cancer (SCLC) is commonly classified as either limited or extensive, but the Union for International Cancer Control TNM Classification of Malignant Tumours seventh edition (2009) recommended tumor, node, and metastasis (TNM) staging based on analysis of the International Association for the Study of Lung Cancer (IASLC) database.

METHODS

Survival analyses were performed for clinically and pathologically staged patients presenting with SCLC from 1999 through 2010. Prognosis was compared in relation to the TNM seventh edition staging to serve as validation and analyzed in relation to proposed changes to the T descriptors found in the eighth edition.

RESULTS

There were 5002 patients: 4848 patients with clinical and 582 with pathological stages. Among these, 428 had both. Survival differences were confirmed for T and N categories and maintained in relation to proposed revisions to T descriptors for seventh edition TNM categories and proposed changes in the eighth edition. There were also survival differences, notably at 12 months, in patients with brain-only single-site metastasis (SSM) compared to SSM at other sites, and SSM without a pleural effusion showed a better prognosis than other patients in the M1b category.

CONCLUSION

We confirm the prognostic value of clinical and pathological TNM staging in patients with SCLC, and recommend continued usage for SCLC in relation to proposed changes to T, N, and M descriptors for NSCLC in the eighth edition. However, for M descriptors, it remains uncertain whether survival differences in patients with SSM in the brain simply reflect better treatment options rather than better survival based on anatomic extent of disease.