Chemopreventive Potential of Caryophyllane Sesquiterpenes: An Overview of Preliminary Evidence

Chemoprevention is referred to as a strategy to inhibit, suppress, or reverse tumor development and progression in healthy people along with high-risk subjects and oncologic patients through using pharmacological or natural substances. Numerous phytochemicals have been widely described in the literature to possess chemopreventive properties, although their clinical usefulness remains to be defined. Among them, caryophyllane sesquiterpenes are natural compounds widely occurring in nature kingdoms, especially in plants, fungi, and marine environments. Several structures, characterized by a common caryophyllane skeleton with further rearrangements, have been identified, but those isolated from plant essential oils, including β-caryophyllene, β-caryophyllene oxide, α-humulene, and isocaryophyllene, have attracted the greatest pharmacological attention. Emerging evidence has outlined a complex polypharmacological profile of caryophyllane sesquiterpenes characterized by blocking, suppressing, chemosensitizing, and cytoprotective properties, which suggests a possible usefulness of these natural substances in cancer chemoprevention for both preventive and adjuvant purposes. In the present review, the scientific knowledge about the chemopreventive properties of caryophyllane sesquiterpenes and the mechanisms involved have been collected and discussed; moreover, possible structure-activity relationships have been highlighted. Although further high-quality studies are required, the promising preclinical findings and the safe pharmacological profile encourage further studies to define a clinical usefulness of caryophyllane sesquiterpenes in primary, secondary, or tertiary chemoprevention.

Voltage-gating of aquaporins, a putative conserved safety mechanism during ionic stresses

Aquaporins are transmembrane water channels found in almost every living organism. Numerous studies have brought a good understanding of both water transport through their pores and the regulations taking place at the molecular level, but subtleties remain to be clarified. Recently, a voltage-related gating mechanism involving the conserved arginine of the channel's main constriction was captured for human aquaporins through molecular dynamics studies. With a similar approach, we show that this voltage-gating could be conserved among this family and that the underlying mechanism could explain part of plant AQPs diversity when contextualized to high ionic concentrations provoked by drought. Finally, we identified residues as adaptive traits which constitute good targets for drought resistance plant breeding research.

1-benzyl-1,4-diazepane reduces the efflux of resistance-nodulation-cell division pumps in Escherichia coli

Aim: To investigate the action mechanism of 1-benzyl-1,4-diazepane (1-BD) as efflux pump inhibitor (EPI) in Escherichia coli mutants: ΔacrAB or overexpressing AcrAB and AcrEF efflux pumps. Materials & methods: Effect of 1-BD on: antibiotic potentiation, by microdilution method; membrane functionality, by fluorimetric assays; ethidium bromide accumulation, by fluorometric real-time efflux assay; AcrB expression, by quantitative photoactivated localization microscopy. Results: 1-BD decreases the minimal inhibitory concentration of levofloxacin and other antibiotics and increase ethidium bromide accumulation in E. coli overexpressing efflux pumps but not in the ΔacrAB strain. 1-BD increases membranes permeability, without sensibly affecting inner membrane polarity and decreases acrAB transcription. Conclusion: 1-BD acts as an EPI in E. coli with a mixed mechanism, different from that of major reference EPIs.

Antimicrobial effects of three herbs (Brassica juncea, Forsythia suspensa, and Inula britannica) on membrane permeability and apoptosis in Salmonella

AIMS

This study aimed synergistic effects of three herbs in Salmonella via increased membrane permeability and apoptosis.

METHODS AND RESULTS

Using high-performance liquid chromatography, four types of phenylethyl glycosides and a lignan were detected in the herb mixture (Brassica juncea, Forsythia suspensa, and Inula britannica). During treatment with the herb mixture (1×, 2×, or 4× the MIC), viable cells decreased to 1·87 log CFU per ml (Salmonella Gallinarum) and 2·33 log CFU per ml (Salmonella Enteritidis) after 12 h of incubation according to inhibition of tricarboxylic acid cycle (P < 0·01). In addition, N-phenyl-1-naphthylamine uptake increased from 229·00 to 249·67 AU in S. Gallinarum and from 232·00 to 250·67 AU in S. Enteritidis (P < 0·05), whereas membrane potential decreased from 8855·00 to 3763·25 AU and from 8703·67 to 4300·38 AU, respectively. Apoptotic Salmonella cells were observed by confocal laser scanning microscopy and flow cytometry. Transmission electron microscopy observations with negative staining showed protein leakage from damaged Salmonella.

CONCLUSIONS

These results showed the synergistic effect of the three herbs against avian pathogenic Salmonella induced by membrane damage and apoptosis.

SIGNIFICANCE AND IMPACT OF THE STUDY

Salmonella causes enormous economic losses in the poultry industry. These results indicated that potency of natural antimicrobial agents due to apoptosis in Salmonella.

Repurposing Antispasmodic Agent Otilonium Bromide for Treatment of Staphylococcus aureus Infections

Recently, the problem of bacterial resistance has been brought into focus, which makes the development of new antibiotics become a necessity. Compared with traditional development approaches, drug repurposing provides a faster and more effective approach to find new antimicrobial agents. In this study, we found that antispasmodic agent otilonium bromide had strong antibacterial ability and bactericidal activity against Staphylococcus aureus, with minimal inhibitory concentrations (MICs) of 4-8 μg/ml, and bacteria could be killed completely after treatment with 2× MIC of otilonium bromide for 5 h. Furthermore, it had a potent effect on eradicating biofilm at concentrations ranging from 16 to 64 μg/ml. At the same time, it had low tendency to develop resistance and possessed limited cytotoxicity. In the methicillin-resistant S. aureus-infected mouse peritonitis model, it was also effective to cure mice and improve their survival rate. In addition, we observed that otilonium bromide changed the permeability of bacterial membrane and caused membrane damage, and it is probably the antibacterial mechanism of otilonium bromide. Taken together, our results indicated that otilonium bromide could be a new antimicrobial agent to treat S. aureus infections more safely and efficiently.

Synergistic antibacterial and anti-biofilm activity of nisin like bacteriocin with curcumin and cinnamaldehyde against ESBL and MBL producing clinical strains

Bacteriocins are small peptides that can inhibit the growth of a diverse range of microbes. There is a need to identify bacteriocins that are effective against biofilms of resistant clinical strains. The present study focussed on the efficacy of purified nisin like bacteriocin-GAM217 against extended spectrum β-lactamase (ESBL) and metallo-beta-lactamase (MBL) producing clinical strains. Bacteriocin-GAM217 when combined with curcumin and cinnamaldehyde, synergistically enhanced antibacterial activity against planktonic and biofilm cultures of Staphylococcus epidermidis and Escherichia coli. Bacteriocin-GAM217 and phytochemical combinations inhibited biofilm formation by >80%, and disrupted the biofilm for selected ESBL and MBL producing clinical strains. The anti-adhesion assay showed that these combinatorial compounds significantly lowered the attachment of bacteria to Vero cells and that they elicited membrane permeability and rapid killing as viewed by confocal microscopy. This study demonstrates that bacteriocin-GAM217 in combination with phytochemicals can be a potential anti-biofilm agent and thus has potential for biomedical applications.

Anthrax Protective Antigen 63 (PA63): Toxic Effects in Neural Cultures and Role in Gulf War Illness (GWI)

Protective antigen (PA) 63 (PA63) is a protein derived from the PA83 component contained in the anthrax vaccine. The anthrax vaccine ("Biothrax") was administered together with other vaccines to Gulf War veterans, about 35% of whom later developed a multisymptom disease (Gulf War Illness [GWI]), with prominent neurological/cognitive/mood symptoms, among others. The disease has been traditionally attributed to exposures to toxic chemicals during the war but other factors could be involved, including vaccines received. Of these, the anthrax vaccine is the most toxic. Here, we assessed directly the PA63 toxin's harmful effects on cultured neuroblastoma 2A (N2A) cells with respect to cell spreading, process formation, apoptosis, and integrity of cell membrane, cytoskeleton, and mitochondria. We found that, when added in N2A cultures, PA63 toxin led to decreased cell spreading and cell aggregation, leading to apoptosis. The mechanisms of PA63-induced cell damage included compromised cell membrane permeability indicated by enhanced access of propidium iodide in cells. In addition, signaling pathways leading to organization of N2A cytoskeleton were negatively affected, as both actin and microtubular networks were compromised. Finally, the mitochondrial membrane potential was impaired in specific assays. Altogether, these alterations led to apoptosis as a collective toxic effect of PA63 which was substantially reduced by the concomitant addition of specific antibodies against PA63.

Berberine derivatives with a long alkyl chain branched by hydroxyl group and methoxycarbonyl group at 9-position show improved anti-proliferation activity and membrane permeability in A549 cells

Berberine (BBR) exhibits diverse bioactivities, including anticancer activity; but its poor druggability limits its applications. In this study, we designed and synthesized a series of 9-O position modified BBR derivatives aiming to improve its cell permeability and anticancer activity, utilizing a long alkyl chain branched by hydroxyl group and methoxycarbonyl group. Among these compounds, B10 showed 3.6-fold higher intracellular concentration than BBR, as well as 60-fold increased anti-proliferation activity against human lung cancer A549 cells compared with BBR. Treatment with B10 (1, 2 μM) induced apoptosis of A549 cells. Further investigations showed that B10 treatment dose-dependently affected mitochondrial functions, including oxygen consumption rate (OCR), mitochondrial membrane potential (MMP) and the morphology of mitochondria in A549 cells. Therefore, this work offers a new way for BBR structural modification through improving cell membrane permeability to affect mitochondrial functions and potential anti-tumor therapy in the future.

Combined Effect of Nitrofurantoin and Plant Surfactant on Bacteria Phospholipid Membrane

Due to the increasing use of antibiotics, measures are being taken to improve their removal from the natural environment. The support of biodegradation with natural surfactants that increase the bioavailability of impurities for microorganisms that degrade them, raises questions about their effect on bacterial cells. In this paper we present analysis of the interaction of nitrofurantoin (NFT) and saponins from the Saponaria officinalis on the environmental bacteria membrane and the model phospholipid membrane mimicking it. A wide perspective of the process is provided with the Langmuir monolayer technique and membrane permeability test with bacteria. The obtained results showed that above critical micelle concentration (CMC), saponin molecules are incorporated into the POPE monolayer, but the NFT impact was ambiguous. What is more, differences in membrane permeability between the cells exposed to NFT in comparison to that of the non-exposed cells were observed above 1.0 CMC for Achromobacter sp. KW1 or above 0.5 CMC for Pseudomonas sp. MChB. In both cases, NFT presence lowered the membrane permeability. Moreover, the Congo red adhesion to the cell membrane also decreased in the presence of a high concentration of surfactants and NFT. The results suggest that saponins are incorporated into the bacteria membrane, but their sugar hydrophilic part remains outside, which modifies the adsorption properties of the cell surface as well as the membrane permeability.

Hypoalbuminemia: a price worth paying for improved dialytic removal of middle-molecular-weight uremic toxins?

Hemodiafiltration (HDF) increases the removal of middle-molecular-weight uremic toxins and may improve outcomes in patients with end-stage kidney disease (ESKD), but it requires complex equipment and comes with risks associated with infusion of large volumes of substitution solution. New high-flux hemodialysis membranes with improved diffusive permeability profiles do not have these limitations and offer an attractive alternative to HDF. However, both strategies are associated with increased albumin loss into the dialysate, raising concerns about the potential for decreased serum albumin concentrations that have been associated with poor outcomes in ESKD. Many factors can contribute to hypoalbuminemia in ESKD, including protein energy wasting, inflammation, volume expansion, renal loss and loss into the dialysate; of these factors, loss into the dialysate is not necessarily the most important. Furthermore, recent studies suggest that mild hypoalbuminemia per se is not an independent predictor of increased mortality in dialysis patients, but in combination with inflammation it is a poor prognostic sign. Thus, whether hypoalbuminemia predisposes to increased morbidity and mortality may depend on the presence or absence of inflammation. In this review we summarize recent findings on the role of dialysate losses in hypoalbuminemia and the importance of concomitant inflammation on outcomes in patients with ESKD. Based on these findings, we discuss whether hypoalbuminemia may be a price worth paying for increased dialytic removal of middle-molecular-weight uremic toxins.

Comparative Proteomics of Extended-Spectrum Cephalosporin-Resistant Neisseria gonorrhoeae Isolates Demonstrates Altered Protein Synthesis, Metabolism, Substance Transport, and Membrane Permeability

Neisseria gonorrhoeae isolates exhibit resistance to extended-spectrum cephalosporins (ESCs), the last remaining option for first-line empirical monotherapy. Here, we investigated the proteomic profiles of N. gonorrhoeae clinical isolates with ESC-resistance to support exploration of the antimicrobial resistance mechanisms for N. gonorrhoeae. We used comparative iTRAQ quantitative proteomics to investigate differential protein expression of three ESC-resistant N. gonorrhoeae clinical isolates using N. gonorrhoeae ATCC49226 as a reference strain. The expression of 40 proteins was downregulated and expression of 56 proteins was upregulated in all three ESC-resistant N. gonorrhoeae isolates. Proteins with predicted function of translation, ribosomal structure and biogenesis, as well as components of the Type IV secretory systems, were significantly upregulated. Two differentially expressed proteins of ABC transporters were also reported by other teams in proteomics studies of N. gonorrhoeae isolates under antimicrobial stress conditions. Differentially expressed proteins are involved in energy production and metabolism of carbohydrates and amino acids. Our results indicated that amino acid and carbohydrate metabolism, cell membrane structure, interbacterial DNA transfer, and ribosome components might be involved in mediating ESC-resistance in N. gonorrhoeae. These findings facilitate a better understanding of the mechanisms of ESC-resistance in N. gonorrhoeae and provide useful information for identifying novel targets in the development of antimicrobials against N. gonorrhoeae.

Structural Plasticity of EAK-16 Peptide Inducing Vesicle Membrane Leakage

BACKGROUND

Ionic complementary peptide EAK-16 has been studies for anticancer drug delivery application. This is a 16 residues, short sequence peptide has ability to trosnform into micro/nanoparticle via self-assembly. However, it is still not clear that how this can bind with cell membrane to induce membrane leakage or delivering their cargo inside cell membrane.

OBJECTIVE

The main objective of this work was to understand behaviour of secondary structure conformation of peptide in solution and at lipid membrane interfaces and membrane permeability of synthetic ionic complementary peptide EAK-16. The corresponding secondary structure conformation was evaluated.

METHODS

We performed biophysical investigation to probe the interaction of synthesised ionic complementary peptide (EAK-16) with dimyristoylphospholcholine (DMPC) and dimyristoylphosphoserine (DMPS) membrane interfaces. The folding behaviours of EAK-16 were studied with Circular Dichroism (CD) spectroscopy. Membrane leakage with peptide was confirmed with calcein leakage assay.

RESULTS

Our finding of this study showed that in aqueous phase EAK-16 was predominantly folded into β-sheets. The temperature could alter the β-sheets. However, in DMPC and DMPS membrane interfaces, EAK-16 adopted helical conformation. EAK-16 has preference in perturbing anionic compared Zwitterionic lipid vesicles. This study proposed that hydrophobic grooves of EAK-16 might be a key in the association with lipid bilayers. Secondly, a charge distribution of ionic residues would also support the orientation at lipid bilayers. This peptide membrane association would facilitate the membrane destabilisation.

CONCLUSION

This study demonstrated the supporting evidence that EAK-16 could interact with lipid membranes and conforming to helical structure, while the helical conformation induced the lipid membrane leakage. Overall, this study provides a physical rationale that ionic complementary peptide can be a useful tool for designing and development of novel antibiotics and anticancer agents along its previous drug delivery applications.

Localized Axolemma Deformations Suggest Mechanoporation as Axonal Injury Trigger

Traumatic brain injuries are a leading cause of morbidity and mortality worldwide. With almost 50% of traumatic brain injuries being related to axonal damage, understanding the nature of cellular level impairment is crucial. Experimental observations have so far led to the formulation of conflicting theories regarding the cellular primary injury mechanism. Disruption of the axolemma, or alternatively cytoskeletal damage has been suggested mainly as injury trigger. However, mechanoporation thresholds of generic membranes seem not to overlap with the axonal injury deformation range and microtubules appear too stiff and too weakly connected to undergo mechanical breaking. Here, we aim to shed a light on the mechanism of primary axonal injury, bridging finite element and molecular dynamics simulations. Despite the necessary level of approximation, our models can accurately describe the mechanical behavior of the unmyelinated axon and its membrane. More importantly, they give access to quantities that would be inaccessible with an experimental approach. We show that in a typical injury scenario, the axonal cortex sustains deformations large enough to entail pore formation in the adjoining lipid bilayer. The observed axonal deformation of 10–12% agree well with the thresholds proposed in the literature for axonal injury and, above all, allow us to provide quantitative evidences that do not exclude pore formation in the membrane as a result of trauma. Our findings bring to an increased knowledge of axonal injury mechanism that will have positive implications for the prevention and treatment of brain injuries.

Tumor-Targeted, Cytoplasmic Delivery of Large, Polar Molecules Using a pH-Low Insertion Peptide

Tumor-targeted drug delivery systems offer not only the advantage of an enhanced therapeutic index, but also the possibility of overcoming the limitations that have largely restricted drug design to small, hydrophobic, "drug-like" molecules. Here, we explore the ability of a tumor-targeted delivery system centered on the use of a pH-low insertion peptide (pHLIP) to directly deliver moderately polar, multi-kDa molecules into tumor cells. A pHLIP is a short, pH-responsive peptide capable of inserting across a cell membrane to form a transmembrane helix at acidic pH. pHLIPs target the acidic tumor microenvironment with high specificity, and a drug attached to the inserting end of a pHLIP can be translocated across the cell membrane during the insertion process. We investigate the ability of wildtype pHLIP to deliver peptide nucleic acid (PNA) cargoes of varying sizes across lipid membranes. We find that pHLIP effectively delivers PNAs up to ∼7 kDa into cells in a pH-dependent manner. In addition, pHLIP retains its tumor-targeting capabilities when linked to cargoes of this size, although the amount delivered is reduced for PNA cargoes greater than ∼6 kDa. As drug-like molecules are traditionally restricted to sizes of ∼500 Da, this constitutes an order-of-magnitude expansion in the size range of deliverable drug candidates.

Antibiotic Uptake Across Gram-Negative Outer Membranes: Better Predictions Towards Better Antibiotics

Crossing the Gram-negative bacterial membrane poses a major barrier to antibiotic development, as many small molecules that can biochemically inhibit key bacterial processes are rendered microbiologically ineffective by their poor cellular uptake. The outer membrane is the major permeability barrier for many drug-like molecules, and the chemical properties that enable efficient uptake into mammalian cells fail to predict bacterial uptake. We have developed a computational method for accurate prospective prediction of outer membrane uptake of drug-like molecules, which we combine with a new medium-throughput experimental assay of outer membrane vesicle swelling. Parallel molecular dynamics simulations of compound uptake through Escherichia coli (E. coli) OmpF are used to successfully and quantitatively predict experimental permeabilities measured via either outer membrane swelling or prior liposome-swelling measurements. These simulations are analyzed using an inhomogeneous solubility-diffusion model to yield predictions of permeability. For most polar molecules we test, outer membrane permeability also correlates well with whole-cell uptake. The ability to accurately predict and measure outer membrane uptake of a wide variety of small molecules will enable simpler determination of which molecular scaffolds and which derivatives are most promising prior to extensive chemical synthesis. It will also assist in formulating a more systematic understanding of the chemical determinants of outer membrane permeability.

Magnetic resonance measurements of cellular and sub-cellular membrane structures in live and fixed neural tissue

We develop magnetic resonance (MR) methods for real-time measurement of tissue microstructure and membrane permeability of live and fixed excised neonatal mouse spinal cords. Diffusion and exchange MR measurements are performed using the strong static gradient produced by a single-sided permanent magnet. Using tissue delipidation methods, we show that water diffusion is restricted solely by lipid membranes. Most of the diffusion signal can be assigned to water in tissue which is far from membranes. The remaining 25% can be assigned to water restricted on length scales of roughly a micron or less, near or within membrane structures at the cellular, organelle, and vesicle levels. Diffusion exchange spectroscopy measures water exchanging between membrane structures and free environments at 100 s^-1.

Disruption of the Ergosterol Biosynthetic Pathway Results in Increased Membrane Permeability, Causing Overproduction and Secretion of Extracellular Monascus Pigments in Submerged Fermentation

Because Monascus pigments (MPs) predominantly accumulate in the cytoplasm during submerged fermentation, many biotechnologies are applied to enhance the production of extracellular MPs (exMPs) to reduce the downstream processing costs. In this study, the genes monascus_7017 and monascus_8018, identified as ERG4 genes, were knocked out to disrupt the ergosterol biosynthetic pathway and enhance the production of exMPs in Monascus purpureus LQ-6. Double-deletion of EGR4 in M. purpureus LQ-6 reduced ergosterol concentration by 57.14% and enhanced exMP production 2.06-fold. In addition, integrated transcriptomic and proteomic analyses were performed to elucidate the transmembrane secretion mechanism of exMPs based on the relationship between ergosterol synthesis and membrane permeability, which revealed that several metabolic pathways were noticeably dynamic, including fatty acid degradation, amino acid metabolism, energy metabolism, carbohydrate metabolism, and transport. These findings therefore clarified the secretion mechanism of exMPs and provide a novel strategy for further enhancement of exMP production in submerged fermentation.

Characterization of Endophytic Streptomyces griseorubens MPT42 and Assessment of Antimicrobial Synergistic Interactions of its Extract and Essential Oil from Host Plant Litsea cubeba

The present study aimed to evaluate the synergistic effects of the crude ethyl acetate extract (CEAE) from endophytic actinomycete MPT42 and essential oil (EO) of the same host plant Litsea cubeba. The isolate MPT42, exhibiting broad-spectrum antimicrobial activities and harboring all three antibiotic-related biosynthetic genes pks-I, pks-II, and nrps, was identified as Streptomycete griseorubens based on an analysis of the morphology, physiology, and 16S rDNA sequence. Minimum inhibitory concentrations (MICs) and the fractional inhibitory concentration index were used to estimate the synergistic effects of various combined ratios between CEAE or antibiotics (erythromycin, vancomycin) and EO toward 13 microbial strains including pathogens. L. cubeba fruit EO, showing the main chemical constituents of 36.0% citral, 29.6% carveol, and 20.5% limonene, revealed an active-low against tested microbes (MICs ≥ 600 μg/mL). The CEAE of S. griseorubens culture exhibited moderate–strong antimicrobial activities against microbes (MICs = 80–600 μg/mL). Analysis of the mechanism of action of EO on Escherichia coli ATCC 25922 found that bacterial cells were dead after 7 h of the EO treatment at 1 MIC (5.5 mg/mL), where 62% cells were permeabilized after 2 h and 3% of them were filament (length ≥ 6 μm). Combinations of CEAE, erythromycin, or vancomycin with EO led to significant synergistic antimicrobial effects against microbes with 4–16 fold reduction in MIC values when compared to their single use. Interestingly, the vancomycin–EO combinations exhibited a strong synergistic effect against five Gram-negative bacterial species. This could assume that the synergy was possibly due to increasing the cell membrane permeability by the EO acting on the bacterial cells, which allows the uptake and diffusion of antimicrobial substances inside the cell easily. These findings in the present study therefore propose a possible alternative to combat the emergence of multidrug-resistant microbes in veterinary and clinics.

Specific Interactions between Rifamycin Antibiotics and Water Influencing Ability To Overcome Natural Cell Barriers and the Range of Antibacterial Potency

Rifamycins are a group of macrocyclic antibiotics mainly used for the treatment of various bacterial infections including tuberculosis. Spectroscopic studies of rifamycins evidence the formation of temperature- and solvent-dependent equilibria between A-, B-, and C-type conformers in solutions. The B- and C-type conformers of rifamycin antibiotics are exclusively formed in the presence of water molecules. A- and B-type conformers exhibit a hydrophilic and "open" ansa-bridge nature whereas the C-type conformer is more lipophilic due to the presence of a "closed" ansa-bridge structure. The involvement of the lactam moiety of the ansa-bridge in intramolecular H-bonds within rifapentine and rifampicin implicates the formation of a more hydrophilic A-type conformer. In contrast to rifampicin and rifapentine, for rifabutin and rifaximin, the "free" lactam group enhances conformational flexibility of the ansa-bridge, thereby enabling interconversion between A- and C-type conformers. In turn, an equilibrium between A- and C-type conformers for rifamycins improves their adaptation to the changing nature of bacteria cell membranes, especially those of Gram-negative strains and/or to efflux pump systems.

Proteomic Analysis of Rhizobium favelukesii LPU83 in Response to Acid Stress

Acid soils constitute a severe problem for leguminous crops mainly through a disturbance in rhizobium-legume interactions. Rhizobium favelukesii-an acid-tolerant rhizobium able to nodulate alfalfa-is highly competitive for nodule occupation under acid conditions but inefficient for biologic nitrogen fixation. In this work, we obtained a general description of the acid-stress response of R. favelukesii LPU83 by means of proteomics by comparing the total proteome profiles in the presence or absence of acid stress by nanoflow ultrahigh-performance liquid chromatography coupled to mass spectrometry. Thus, a total of 336 proteins were identified with a significant differential expression, 136 of which species were significantly overexpressed and 200 underexpressed in acidity. An in silico functional characterization with those respective proteins revealed a complex and pleiotropic response by these rhizobia involving components of oxidative phosphorylation, glutamate metabolism, and peptidoglycan biosynthesis, among other pathways. Furthermore, a lower permeability was evidenced in the acid-stressed cells along with several overexpressed proteins related to γ-aminobutyric acid metabolism, such as the gene product of livK, which gene was mutated. This mutant exhibited an acid-sensitive phenotype in agreement with the proteomics results. We conclude that both the γ-aminobutyric acid metabolism and a modified cellular envelope could be relevant to acid tolerance in R. favelukesii.

Natural Flavones from Morus alba against Methicillin-Resistant Staphylococcus aureus via Targeting the Proton Motive Force and Membrane Permeability

The emergence and rapid spread of methicillin-resistant Staphylococcus aureus (MRSA) critically requires alternative therapeutic options. New antibacterial drugs and strategies are urgently needed to combat MRSA-associated infections. Here, we investigated the antibacterial activity of flavones from Morus alba and the potential mode of action against MRSA. Kuwanon G, kuwanon H, mulberrin, and morusin displayed high efficiency in killing diverse MRSA isolates. On the basis of structure-activity analysis, the cyclohexene-phenyl ketones and isopentenyl groups were critical to increase the membrane permeability and to dissipate the proton motive force. Meanwhile, mechanistic studies further showed that kuwanon G displayed rapid bactericidal activity in vitrowith difficulty in developing drug resistance. Kuwanon G targeted phosphatidylglycerol and cardiolipin in the cytoplasmic membrane through the formation of hydrogen bonds and electrostatic interactions. Additionally, kuwanon G promoted wound healing in a mouse model of MRSA skin infection. In summary, these results indicate that flavones are promising lead compounds to treat MRSA-associated infections through disrupting the proton motive force and membrane permeability.

Sonoporation of Cells by a Parallel Stable Cavitation Microbubble Array

Sonoporation is a targeted drug delivery technique that employs cavitation microbubbles to generate transient pores in the cell membrane, allowing foreign substances to enter cells by passing through the pores. Due to the broad size distribution of microbubbles, cavitation events appear to be a random process, making it difficult to achieve controllable and efficient sonoporation. In this work a technique is reported using a microfluidic device that enables in parallel modulation of membrane permeability by an oscillating microbubble array. Multirectangular channels of uniform size are created at the sidewall to generate an array of monodispersed microbubbles, which oscillate with almost the same amplitude and resonant frequency, ensuring homogeneous sonoporation with high efficacy. Stable harmonic and high harmonic signals emitted by individual oscillating microbubbles are detected by a laser Doppler vibrometer, which indicates stable cavitation occurred. Under the influence of the acoustic radiation forces induced by the oscillating microbubble, single cells can be trapped at an oscillating microbubble surface. The sonoporation of single cells is directly influenced by the individual oscillating microbubble. The parallel sonoporation of multiple cells is achieved with an efficiency of 96.6 ± 1.74% at an acoustic pressure as low as 41.7 kPa.

Sonoporation of Cells by a Parallel Stable Cavitation Microbubble Array

Sonoporation is a targeted drug delivery technique that employs cavitation microbubbles to generate transient pores in the cell membrane, allowing foreign substances to enter cells by passing through the pores. Due to the broad size distribution of microbubbles, cavitation events appear to be a random process, making it difficult to achieve controllable and efficient sonoporation. In this work a technique is reported using a microfluidic device that enables in parallel modulation of membrane permeability by an oscillating microbubble array. Multirectangular channels of uniform size are created at the sidewall to generate an array of monodispersed microbubbles, which oscillate with almost the same amplitude and resonant frequency, ensuring homogeneous sonoporation with high efficacy. Stable harmonic and high harmonic signals emitted by individual oscillating microbubbles are detected by a laser Doppler vibrometer, which indicates stable cavitation occurred. Under the influence of the acoustic radiation forces induced by the oscillating microbubble, single cells can be trapped at an oscillating microbubble surface. The sonoporation of single cells is directly influenced by the individual oscillating microbubble. The parallel sonoporation of multiple cells is achieved with an efficiency of 96.6 ± 1.74% at an acoustic pressure as low as 41.7 kPa.

Modulation of membrane permeability by carbon dioxide

Promoting drug delivery across the biological membrane is a common strategy to improve bioavailability. Inspired by the observation that carbonated alcoholic beverages can increase the absorption rate of ethanol, we speculate that carbon dioxide (CO₂ ) molecules could also enhance membrane permeability to drugs. In the present work, we have investigated the effect of CO₂ on the permeability of a model membrane formed by 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine lipids to three drug-like molecules, namely, ethanol, 2',3'-dideoxyadenosine, and trimethoprim. The free-energy and fractional-diffusivity profiles underlying membrane translocation were obtained from μs-timescale simulations and combined in the framework of the fractional solubility-diffusion model. We find that addition of CO₂ in the lipid environment results in an increase of the membrane permeability to the three substrates. Further analysis of the permeation events reveals that CO₂ expands and loosens the membrane, which, in turn, facilitates permeation of the drug-like molecules. © 2019 Wiley Periodicals, Inc.