The expression of trefoil factor family member 2 in increased at an acidic pH

Trefoil factor family member 2 (Tff2) is significantly involved in intestinal tumor growth in ApcMin/+ mice, which can be used as a human colon cancer model. TFF2, which encodes TFF2 (spasmolytic protein 1) is highly expressed in human cancer tissues, including the pancreas, colon and bile ducts, as well as in normal gastric and duodenum tissues. By contrast, TFF2 exhibits low expression levels in other normal tissues, including the small and large intestine. Furthermore, TFF2 expression has not been detected in DLD-1 cells, a cell line derived from human colon cancer. What induces TFF2 expression in normal and tumor cells is still unknown. Highly malignant tumor tissues are characterized by higher temperatures and lower pH (6.2-6.9) than in normal tissues, where normal pH ranges from 7.2 to 7.4. This microenvironment exacerbates malignancy by promoting the acquisition of cell death resistance, drug resistance and immune escape. Therefore, the present study examined how TFF2 expression is affected in cultured cells that imitate the tumor tissue microenvironment. The incubation temperature was increased from 37 to 40°C, but no expression of TFF2 was induced. Subsequently, a culture solution with an acidic pH was prepared to simulate the Warburg effect in tumors. TFF2 expression was increased by 42.8- and 5.8-fold in cells cultured in acidic medium at pH 6.5 and 6.8 compared with at pH 7.4, respectively, as determined using the relative quantification method following quantitative polymerase chain reaction. The present study also analyzed fluctuations in the expression levels of genes other than TFF2, under acidic conditions. Acidic conditions upregulated the expression of genes related to cell membranes and glycoproteins, based on the Database for Annotation, Visualization, and Integrated Discovery. In conclusion, TFF2 was highly expressed under acidic conditions, implying that it may have an important function in protecting the plasma membrane from acidic environments in both normal and cancer cells. These findings warrant further investigation of TFF2 as a target of cancer therapy and diagnosis.

Emulsifying properties of O/W emulsion stabilized by soy protein isolate and γ-polyglutamic acid electrostatic complex

In order to improve the emulsifying properties of soy protein around isoelectric point, soy protein isolate (SPI) and γ-polyglutamic acid (γ-PGA) complexes were prepared by electrostatic interaction. The formation of SPI-γ-PGA electrostatic complex and emulsifying properties were investigated by monitoring turbidity, zeta potential, intrinsic fluorophores, emulsion characterization, and microstructure observation. The results showed that the formation of SPI-γ-PGA electrostatic complex was identified through turbidimetric analysis and zeta-potential measurement. Intrinsic fluorescence spectrum indicated internal structure changes of electrostatic complexes. Furthermore, SPI-γ-PGA complex-stabilized emulsions showed better stability with small droplet sizes and slow growth as well as the uniform microstructure around the isoelectric point (pH 4.0-5.0) than SPI-formed emulsions. Under the different thermal treatments and ionic strengths, emulsions stabilized by SPI-γ-PGA-soluble complex resulted in improved emulsion stability to environmental stresses. This may be attributed to the increased steric repulsion and electrostatic repulsion by SPI-γ-PGA complexes at oil-water interfaces. The findings derived from this research would provide theoretical reference about SPI-γ-PGA electrostatic complex that can be applied in acid beverages and developed a novel plant-based sustainable stabilizer for emulsions. PRACTICAL APPLICATION: The electrostatic interaction between SPI and γ-PGA improved the emulsifying characteristics of soy protein around isoelectric point. The results derived from this research would expand applications of SPI-γ-PGA-soluble electrostatic complex that can be applied in acid beverages, as well as a novel plant-based sustainable stabilizer for emulsions.

Clinically relevant mutations in the PhoR sensor kinase of host-adapted Mycobacterium abscessus isolates impact response to acidic pH and virulence

IMPORTANCE

Difficult-to-treat pulmonary infections caused by nontuberculous mycobacteria of the Mycobacterium abscessus group have been steadily increasing in the USA and globally. Owing to the relatively recent recognition of M. abscessus as a human pathogen, basic and translational research to address critical gaps in diagnosis, treatment, and prevention of diseases caused by this microorganism has been lagging behind that of the better-known mycobacterial pathogen, Mycobacterium tuberculosis. To begin unraveling the molecular mechanisms of pathogenicity of M. abscessus, we here focus on the study of a two-component regulator known as PhoPR which we found to be under strong evolutionary pressure during human lung infection. We show that PhoPR is activated at acidic pH and serves to regulate a defined set of genes involved in host adaptation. Accordingly, clinical isolates from chronically infected human lungs tend to hyperactivate this regulator enabling M. abscessus to escape macrophage killing.

Acidic pH modulates Burkholderia cenocepacia antimicrobial susceptibility in the cystic fibrosis nutritional environment

IMPORTANCE

Burkholderia cenocepacia causes severe infections in cystic fibrosis (CF) patients. CF patients are prone to reoccurring infections due to the accumulation of mucus in their lungs, where bacteria can adhere and grow. Some of the antibiotics that inhibit B. cenocepacia in the laboratory are not effective for CF patients. A major contributor to poor clinical outcomes is that antibiotic testing in laboratories occurs under conditions that are different from those of sputum. CF sputum may be acidic and have increased concentrations of iron and zinc. Here, we used a medium that mimics CF sputum and found that acidic pH decreased the activity of many of the antibiotics used against B. cenocepacia. In addition, we assessed susceptibility to more than 500 antibiotics and found four active compounds against B. cenocepacia. Our findings give a better understanding of the lack of a relationship between susceptibility testing and the clinical outcome when treating B. cenocepacia infections.

Rhodamine-Based Cyclic Hydroxamate as Fluorescent pH Probe for Imaging of Lysosomes

Monitoring the microenvironment within specific cellular regions is crucial for a comprehensive understanding of life events. Fluorescent probes working in different ranges of pH regions have been developed for the local imaging of different pH environments. Especially, rhodamine-based fluorescent pH probes have been of great interest due to their ON/OFF fluorescence depending on the spirolactam ring's opening/closure. By introducing the N-alkyl-hydroxamic acid instead of the alkyl amines in the spirolactam of rhodamine, we were able to tune the pH range where the ring opening and closing of the spirolactam occurs. This six-membered cyclic hydroxamate spirolactam ring of rhodamine B proved to be highly fluorescent in acidic pH environments. In addition, we could monitor pH changes of lysosomes in live cells and zebrafish.

Mycobacterium tuberculosis response to cholesterol is integrated with environmental pH and potassium levels via a lipid utilization regulator

How bacterial response to environmental cues and nutritional sources may be integrated in enabling host colonization is poorly understood. Exploiting a reporter-based screen, we discovered that overexpression of Mycobacterium tuberculosis (Mtb) lipid utilization regulators altered Mtb acidic pH response dampening by low environmental potassium (K+). Transcriptional analyses unveiled amplification of Mtb response to acidic pH in the presence of cholesterol, a major carbon source for Mtb during infection, and vice versa. Strikingly, deletion of the putative lipid regulator mce3R resulted in loss of augmentation of (i) cholesterol response at acidic pH, and (ii) low [K+] response by cholesterol, with minimal effect on Mtb response to each signal individually. Finally, the ∆mce3R mutant was attenuated for colonization in a murine model that recapitulates lesions with lipid-rich foamy macrophages. These findings reveal critical coordination between bacterial response to environmental and nutritional cues, and establish Mce3R as a crucial integrator of this process.

A Mildly Acidic Environment Alters Pseudomonas aeruginosa Virulence and Causes Remodeling of the Bacterial Surface

Pseudomonas aeruginosa is a versatile pathogen that resists environmental stress, such as suboptimal pH. As a result of exposure to environmental stress, P. aeruginosa shows an altered virulence-related phenotype. This study investigated the modifications that P. aeruginosa undertakes at a mildly low pH (pH 5.0) compared with the bacteria grown in a neutral medium (pH 7.2). Results indicated that in a mildly acidic environment, expression of two-component system genes (phoP/phoQ and pmrA/pmrB), lipid A remodeling genes such as arnT and pagP and virulence genes, i.e., pqsE and rhlA, were induced. Moreover, lipid A of the bacteria grown at a mildly low pH is modified by adding 4-amino-arabinose (l-Ara4N). Additionally, the production of virulence factors such as rhamnolipid, alginate, and membrane vesicles is significantly higher in a mildly low-pH environment than in a neutral medium. Interestingly, at a mildly low pH, P. aeruginosa produces a thicker biofilm with higher biofilm biomass. Furthermore, studies on inner membrane viscosity and permeability showed that a mildly low pH causes a decrease in the inner membrane permeability and increases its viscosity. Besides, despite the importance of PhoP, PhoQ, PmrA, and PmrB in Gram-negative bacteria for responding to low pH stress, we observed that the absence of each of these two-component systems does not meaningfully impact the remodeling of the P. aeruginosa envelope. Given that P. aeruginosa is likely to encounter mildly acidic environments during infection in its host, the alterations that the bacterium undertakes under such conditions must be considered in designing antibacterial strategies against P. aeruginosa. IMPORTANCE P. aeruginosa encounters environments with acidic pH when establishing infections in hosts. The bacterium develops an altered phenotype to tolerate a moderate decrease in the environmental pH. At the level of the bacterial envelope, modified lipid A composition and a reduction of the bacterial inner membrane permeability and fluidity are among the changes P. aeruginosa undergoes at a mildly low pH. Also, the bacterium is more likely to form biofilm in a mildly acidic environment. Overall, these alterations in the P. aeruginosa phenotype put obstacles in the way of antibacterial activities. Thus, considering physiological changes in the bacterium at low pH helps design and implement antimicrobial approaches against this hostile microorganism.

Acid-sensing ion channel blocker diminazene facilitates proton-induced excitation of afferent nerves in a similar manner that Na+/H+ exchanger blockers do

Tissue acidification causes sustained activation of primary nociceptors, which causes pain. In mammals, acid-sensing ion channels (ASICs) are the primary acid sensors; however, Na⁺/H⁺ exchangers (NHEs) and TRPV1 receptors also contribute to tissue acidification sensing. ASICs, NHEs, and TRPV1 receptors are found to be expressed in nociceptive nerve fibers. ASIC inhibitors reduce peripheral acid-induced hyperalgesia and suppress inflammatory pain. Also, it was shown that pharmacological inhibition of NHE1 promotes nociceptive behavior in acute pain models, whereas inhibition of TRPV1 receptors gives relief. The murine skin-nerve preparation was used in this study to assess the activation of native polymodal nociceptors by mild acidification (pH 6.1). We have found that diminazene, a well-known antagonist of ASICs did not suppress pH-induced activation of CMH-fibers at concentrations as high as 25 μM. Moreover, at 100 μM, it induces the potentiation of the fibers' response to acidic pH. At the same time, this concentration virtually completely inhibited ASIC currents in mouse dorsal root ganglia (DRG) neurons (IC₅₀ = 17.0 ± 4.5 μM). Non-selective ASICs and NHEs inhibitor EIPA (5-(N-ethyl-N-isopropyl)amiloride) at 10 μM, as well as selective NHE1 inhibitor zoniporide at 0.5 μM induced qualitatively the same effects as 100 μM of diminazene. Our results indicate that excitation of afferent nerve terminals induced by mild acidification occurs mainly due to the NHE1, rather than acid-sensing ion channels. At high concentrations, diminazene acts as a weak blocker of the NHE. It lacks chemical similarity with amiloride, EIPA, and zoniporide, so it may represent a novel structural motif for the development of NHE antagonists. However, the effect of diminazene on the acid-induced excitation of primary nociceptors remains enigmatic and requires additional investigations.

In Vitro Activity of Finafloxacin against Panels of Respiratory Pathogens

This study determined the in vitro activity of finafloxacin against panels of bacterial strains, representative of those associated with infection in cystic fibrosis patients and predominately isolated from clinical cases of respiratory disease. Many of these isolates were resistant to various antimicrobials evaluated including the aminoglycosides, cephalosporins, carbapenems and fluoroquinolones. Broth microdilution assays were performed at neutral and acidic pH, to determine antimicrobial activity. Finafloxacin demonstrated superior activity at reduced pH for all of the bacterial species investigated, highlighting the requirement to determine the activity of antimicrobials in host-relevant conditions.

Structural insights at acidic pH of dye-decolorizing peroxidase from Bacillus subtilis

Dye-decolorizing peroxidases (DyPs), a type of heme-containing oxidoreductase enzymes, catalyze the peroxide-dependent oxidation of various industrial dyes as well as lignin and lignin model compounds. In our previous work, we have recently reported the crystal structures of class A-type DyP from Bacillus subtilis at pH 7.0 (BsDyP7), exposing the location of three binding sites for small substrates and high redox-potential substrates. The biochemical studies revealed the optimum acidic pH for enzyme activity. In the present study, the crystal structure of BsDyP at acidic pH (BsDyP4) reveals two-monomer units stabilized by intermolecular salt bridges and a hydrogen bond network in a homo-dimeric unit. Based on the monomeric structural comparison of BsDyP4 and BsDyP7, minor differences were observed in the loop regions, that is, LI (Ala64-Gln71), LII (Glu96-Lys108), LIII (Pro117-Leu124), and LIV (Leu295-Asp303). Despite these differences, BsDyP4 adopts similar heme architecture as well as three substrate-binding sites to BsDyP7. In BsDyP4, a shift in Asp187, heme pocket residue discloses the plausible reason for optimal acidic pH for BsDyP activity. This study provides insight into the structural changes in BsDyP at acidic pH, where BsDyP is biologically active.

Seneca Valley virus enters cells through multiple pathways and traffics intracellularly via the endolysosomal pathway

Seneca Valley virus (SVV, also known as Senecavirus A), an oncolytic virus, is a nonenveloped, positive-strand RNA virus and the sole member of the genus Senecavirus within the family Picornaviridae. The mechanisms of SVV entry into cells are currently almost unknown. In the present study, we found that SVV entry into HEK293T cells is acidic pH-dependent by using ammonium chloride (NH₄Cl) and chloroquine, both of which could inhibit SVV infection. We confirmed that dynamin II is required for SVV entry by using dynasore, silencing the dynamin II protein, or expressing the dominant-negative (DN) K44A mutant of dynamin II. Then, we discovered that chlorpromazine (CPZ) treatment or knockdown of the clathrin heavy chain (CLTC) protein significantly inhibited SVV infection. In addition, overexpression of CLTC promoted SVV infection. Caveolin-1 and membrane cholesterol were also required for SVV endocytosis. Notably, utilizing genistein, EIPA or nocodazole, we observed that macropinocytosis and microtubules are not involved in SVV entry. Furthermore, overexpression of the Rab7 and Rab9 proteins but not the Rab5 or Rab11 proteins promoted SVV infection. The findings were further validated by the knockdown of four Rabs and Lamp1 proteins, indicating that after internalization, SVV is transported from late endosomes to the trans-Golgi network (TGN) or lysosomes, respectively, eventually releasing its RNA into the cytosol from the lysosomes. Our findings concretely revealed SVV endocytosis mechanisms in HEK293T cells and provided an insightful theoretical foundation for further research into SVV oncolytic mechanisms.

Metabolic adaptations of cancer in extreme tumor microenvironments

Cancer cells are highly heterogeneous to adapt to extreme tumor microenvironments (TMEs). TMEs challenge cancer cells via hypoxia, nutrition starvation, and acidic pH, promoting invasion and metastasis concomitant with genetic, epigenetic, and metabolic alterations. Metabolic adaptation to an extreme TME could allow cancer cells to evade cell death and immune responses, as well as resulting in drug resistance, recurrence, and poor patient prognosis. Therefore, elucidation of the metabolic adaptation of malignant cancer cells within TMEs is necessary, however, most are still elusive. Recently, adaptation of cancer cells within the TME can be analyzed via cell-cell interactions at the single-cell level. In addition, information into organelle-organelle interactions has recently been obtained. These cell-cell, and organelle-organelle interactions demonstrate the potential as new cancer therapy targets, as they play essential roles in the metabolic adaptation of cancer cells to the TME. In this manuscript, we review (1) metabolic adaptations within tumor microenvironments through (2) cell-to-cell, and (3) organelle-organelle metabolic interactions.

Comparative Transcriptome Analysis Unveils the Molecular Mechanism Underlying Sepal Colour Changes under Acidic pH Substratum in Hydrangea macrophylla

The hydrangea (Hydrangea macrophylla (Thunb). Ser.), an ornamental plant, has good marketing potential and is known for its capacity to change the colour of its inflorescence depending on the pH of the cultivation media. The molecular mechanisms causing these changes are still uncertain. In the present study, transcriptome and targeted metabolic profiling were used to identify molecular changes in the RNAome of hydrangea plants cultured at two different pH levels. De novo assembly yielded 186,477 unigenes. Transcriptomic datasets provided a comprehensive and systemic overview of the dynamic networks of the gene expression underlying flower colour formation in hydrangeas. Weighted analyses of gene co-expression network identified candidate genes and hub genes from the modules linked closely to the hyper accumulation of Al³⁺ during different stages of flower development. F3'5'H, ANS, FLS, CHS, UA3GT, CHI, DFR, and F3H were enhanced significantly in the modules. In addition, MYB, bHLH, PAL6, PAL9, and WD40 were identified as hub genes. Thus, a hypothesis elucidating the colour change in the flowers of Al³⁺-treated plants was established. This study identified many potential key regulators of flower pigmentation, providing novel insights into the molecular networks in hydrangea flowers.

Structure and surface dynamics of genomic DNA as probed with surface-enhanced Raman spectroscopy: Trace level sensing of nucleic acids extracted from plants

In this work surface-enhanced Raman spectra of nucleic acids from in vitro grown Solanum tuberosum L. cultivars and populations (Buzau population, Lazarea population, Patraque d'Auvergne, RFA Roclas Clone 2.6 Ferma, Vitelotte Negresse, Roclas Clone C, Blue Congo) were measured with 532 nm laser line. Main surface-enhanced Raman modes of these DNAs have been analyzed. Also, DNA from two grapevine (Vitis vinifera L.) varieties were studied at acidic pHs by surface-enhanced Raman spectroscopy. Modified SERS intensities and wavenumber shifts of nucleic acids bands were observed upon lowering the pH, being a proof of binding affinity changes of DNA with silver nanoparticles (AgNPs) and of structural modifications induced at acidic pHs in DNA molecular groups. Furthermore, the (sub)picosecond surface dynamics of DNA extracted from leaf tissues of grapevine (Vitis vinifera L.) varieties was investigated. In this work, the bands full widths at half-maximum (FWHMs) have values in the wavenumber range from 8 to 34 cm^-1. (Sub)picosecond molecular dynamics of DNA groups with global relaxation times between 0.31 ps - 1.33 ps has been found.

Heparin promotes rapid fibrillation of the basic Parathyroid Hormone at physiological pH

In acidic secretory granules of mammalian cells, peptide hormones including the parathyroid hormone (PTH) are presumably stored in the form of functional amyloid fibrils. Mature PTH, however, is considerably positively charged in acidic environments, a condition known to impede unassisted self-aggregation into fibrils. Here, we studied the role of the polyanion heparin on promoting fibril formation of PTH. Employing ITC, CD spectroscopy, NMR, SAXS and fluorescence-based assays we could demonstrate that heparin binds PTH with submicromolar affinity and facilitates its conversion into fibrillar seeds, enabling rapid formation of amyloid fibrils under acidic conditions. In absence of heparin, PTH remained in a soluble monomeric state. We suspect that heparin-like surfaces are required in vivo to convert PTH efficiently into fibrillar deposits.

Structural Insights into the Ligand-Binding and -Releasing Mechanism of Helicoverpa armigera Pheromone-Binding Protein PBP1

Cotton bollworm (Helicoverpa armigera) is a worldwide agricultural pest in which the transport of pheromones is indispensable and perceived by pheromone-binding proteins (PBPs). However, three-dimensional structure, pheromone binding, and releasing mechanisms of PBPs are not completely illustrated. Here, we solved three structures of the cotton bollworm HarmPBP1 at different pH values and its complex with ligand, Z-9-hexadecenal. Although apo-HarmPBP1 adopts a common PBP scaffold of six α-helices surrounding a predominantly hydrophobic central pocket, the conformation is greatly distinct from other apo-PBPs. The Z-9-hexadecenal is bound mainly by hydrophobic interaction. The pheromone can enter this cavity through an opening between the helices α5 and α6, as well as the loop between α3 and α4. Structural analysis suggests that ligand entry into the pocket is followed by a shift of Lys94 and Lys138, which may act as a lid at the opening of the pocket. Acidic pH will cause a subtle structural change of the lid, which in turn affects its ligand-binding ability, differently from other family proteins. Taken together, this study provides structural bases for the interactions between pheromones and PBPs, the pH-induced conformational switch, and the design of small inhibitors to control cotton bollworms by disrupting male–female chemosensory communication.

Acidic Microenvironment Determines Antibiotic Susceptibility and Biofilm Formation of Pseudomonas aeruginosa

Pseudomonas aeruginosa is the most prevalent bacterial species that contribute to cystic fibrosis (CF) respiratory failure. The impaired function of CF transmembrane conductance regulator leads to abnormal epithelial Cl^-/HCO₃ ^- transport and acidification of airway surface liquid. However, it remains unclear why the CF lung is most commonly infected by Pseudomonas aeruginosa versus other pathogens. We carried out studies to investigate if lower pH helps Pseudomonas aeruginosa adapt and thrive in the CF-like acidic lung environment. Our results revealed that Pseudomonas aeruginosa generally forms more biofilm, induces antibiotic resistance faster in acidic conditions, and can be reversed by returning the acidic environment to physiologically neutral conditions. Pseudomonas aeruginosa appears to be highly adaptive to the CF-like acidic pH environment. By studying the effects of an acidic environment on bacterial response, we may provide a new therapeutic option in preventing chronic Pseudomonas aeruginosa infection and colonization.

Tumor Microenvironment Features and Chemoresistance in Pancreatic Ductal Adenocarcinoma: Insights into Targeting Physicochemical Barriers and Metabolism as Therapeutic Approaches

Currently, the median overall survival of PDAC patients rarely exceeds 1 year and has an overall 5-year survival rate of about 9%. These numbers are anticipated to worsen in the future due to the lack of understanding of the factors involved in its strong chemoresistance. Chemotherapy remains the only treatment option for most PDAC patients; however, the available therapeutic strategies are insufficient. The factors involved in chemoresistance include the development of a desmoplastic stroma which reprograms cellular metabolism, and both contribute to an impaired response to therapy. PDAC stroma is composed of immune cells, endothelial cells, and cancer-associated fibroblasts embedded in a prominent, dense extracellular matrix associated with areas of hypoxia and acidic extracellular pH. While multiple gene mutations are involved in PDAC initiation, this desmoplastic stroma plays an important role in driving progression, metastasis, and chemoresistance. Elucidating the mechanisms underlying PDAC resistance are a prerequisite for designing novel approaches to increase patient survival. In this review, we provide an overview of the stromal features and how they contribute to the chemoresistance in PDAC treatment. By highlighting new paradigms in the role of the stromal compartment in PDAC therapy, we hope to stimulate new concepts aimed at improving patient outcomes.

Influence of Low-pH Beverages on the Two-Body Wear of CAD/CAM Monolithic Materials

The aim of this in vitro study is to evaluate the effect of different acidic media on volumetric wear and surface roughness of CAD/CAM monolithic materials. Forty-eight rectangular specimens were prepared using different CAD/CAM monolithic materials: nanohybrid composite (Grandio Blocks, Voco), resin-based composite (Cerasmart, GC), lithium disilicate (E-Max, Ivoclar), and high-translucency zirconia (Katana STML, Kuraray Noritake). After storage in distilled water at 37 °C for two days, the specimens were tested using a chewing machine with a stainless-steel ball as an antagonist (49N loads, 250,000 cycles). Testing was performed using distilled water, Coca-Cola, and Red Bull as abrasive media. Wear and surface roughness analyses of the CAD/CAM materials were performed using a 3D profilometer and analyzed with two-way analysis of variance and post hoc pairwise comparison procedures. Worn surfaces were examined using scanning electron microscopy. Resin-based materials suffered higher volumetric wear than ceramics (p = 0.00001). Water induced significantly less volumetric wear than the other tested solutions (p = 0.0014), independent of the material tested. High-translucency zirconia showed less surface roughness than all the other materials tested. The selection of monolithic CAD/CAM materials to restore worn dentition due to erosive processes could impact restorative therapy stability over time. Resin-based materials seem to be more influenced by the acidic environment when subjected to a two-body wear test.

How the PhoP/PhoQ System Controls Virulence and Mg2+ Homeostasis: Lessons in Signal Transduction, Pathogenesis, Physiology, and Evolution

The PhoP/PhoQ two-component system governs virulence, Mg2+ homeostasis, and resistance to a variety of antimicrobial agents, including acidic pH and cationic antimicrobial peptides, in several Gram-negative bacterial species. Best understood in Salmonella enterica serovar Typhimurium, the PhoP/PhoQ system consists o-regulated gene products alter PhoP-P amounts, even under constant inducing conditions. PhoP-P controls the abundance of hundreds of proteins both directly, by having transcriptional effects on the corresponding genes, and indirectly, by modifying the abundance, activity, or stability of other transcription factors, regulatory RNAs, protease regulators, and metabolites. The investigation of PhoP/PhoQ has uncovered novel forms of signal transduction and the physiological consequences of regulon evolution.

Design and Engineering of Hypoxia and Acidic pH Dual-Stimuli-Responsive Intelligent Fluorescent Nanoprobe for Precise Tumor Imaging

Stimulus-responsive fluorescence imaging modality shows great promise for detection of tumor due to the advantages of high sensitivity, simplicity and noninvasiveness. However, some non-cancer regions including nodules and inflammation may also exhibit a stimulus-related characteristic, which cause the problem of nonspecific responsiveness and then cause "false positive" results for tumor recognition. Herein, hypoxia and acidic pH, two typical features strongly associated with tumor invasion, progression and metastasis in tumor microenvironment (TME), are chosen as dual stimuli to fabricate "dual lock-and-key" fluorescent nanoprobe for highly specific and precise imaging of tumor cells. Mesoporous silica coated gold nanorods (AuNR@mSiO₂ ) are employed as nanocarrier and nanoquencher to load the pH-sensitive fluorescent reporter (Rho-TP). Azobenzene (azo) which can be reduced to amines by the highly expressed azoreductase under hypoxic conditions, is elected as the effective gatekeeper for AuNR@mSiO₂ by forming complex with β-cyclodextrin polymer via host-guest interaction (azo/β-CDP). By elaborately combining the hypoxia-responsive gatekeeper and pH-responsive fluorescent signal reporter into one nanoprobe, sensitive and specific imaging of tumor cells can be realized. The fabricated dual lock-and-key fluorescent nanoprobe successfully further apply in tumor-bearing mice model, which indicate potential of early diagnosis and assessment of cancer treatment.

Downregulation of a novel flagellar synthesis regulator AsiR promotes intracellular replication and systemic pathogenicity of Salmonella typhimurium

The intracellular pathogen Salmonella enterica serovar Typhimurium (S. Typhimurium) exploits host macrophage as a crucial survival and replicative niche. To minimize host immune response stimulated by flagellin, the expression of flagellar genes is downregulated during S. Typhimurium growth within host macrophages. However, the underlying mechanisms are largely unknown. In this study, we show that STM14_1285 (named AsiR), a putative RpiR-family transcriptional regulator, which is downregulated within macrophages as previously reported and also confirmed here, positively regulates the expression of flagellar genes by directly binding to the promoter of flhDC. By generating an asiR mutant strain and a strain that persistently expresses asiR gene within macrophages, we confirmed that the downregulation of asiR contributes positively to S. Typhimurium replication in macrophages and systemic infection in mice, which could be attributed to decreased flagellar gene expression and therefore reduced flagellin-stimulated secretion of pro-inflammatory cytokines IL-1β and TNF-α. Furthermore, the acidic pH in macrophages is identified as a signal for the downregulation of asiR and therefore flagellar genes. Collectively, our results reveal a novel acidic pH signal-mediated regulatory pathway that is utilized by S. Typhimurium to promote intracellular replication and systemic pathogenesis by repressing flagellar gene expression.

Novel Functions and Signaling Specificity for the GraS Sensor Kinase of Staphylococcus aureus in Response to Acidic pH

Although the GraS sensor kinase of Staphylococcus aureus is known for the sensing of and resistance to cationic antimicrobial peptides (CAMPs), we recently established that it also signals in response to acidic pH, which is encountered on human skin concurrently with CAMPs, antimicrobial unsaturated free fatty acids (uFFA), and calcium. We therefore evaluated how these environmental signals would affect GraS function and resistance to antimicrobial uFFA. Growth at pH 5.5 promoted increased resistance of S. aureus USA300 to linoleic and arachidonic acids but not palmitoleic or sapienic acid. However, enhanced resistance to these C_16:1 uFFA was achieved by supplementing acidic medium with 0.5 mM calcium or subinhibitory CAMPs. Enhanced resistance to uFFA at acidic pH was dependent on GraS and GraS-dependent expression of the lysyl-phosphatidylglycerol synthase enzyme MprF, through a mechanism that did not require the lysyl-transferase function of MprF. In addition to enhanced resistance to antimicrobial uFFA, acidic pH also promoted increased production of secreted proteases in a GraS-dependent manner. During growth at pH 5.5, downstream phenotypes of signaling through GraS, including resistance to uFFA, MprF-dependent addition of positive charge to the cell surface, and increased production of secreted proteases, all occurred independently of acidic amino acids in the extracytoplasmic sensor loop of GraS that were previously found to be required for sensing of CAMPs. Cumulatively, our data indicate that signaling through GraS at acidic pH occurs through a mechanism that is distinct from that described for CAMPs, leading to increased resistance to antimicrobial uFFA and production of secreted proteases.IMPORTANCE Staphylococcus aureus asymptomatically colonizes 30% of humans but is also a leading cause of infectious morbidity and mortality. Since infections are typically initiated by the same strain associated with asymptomatic colonization of the nose or skin, it is important to understand how the microbe can endure exposure to harsh conditions that successfully restrict the growth of other bacteria, including a combination of acidic pH, antimicrobial peptides, and antimicrobial fatty acids. The significance of our research is in showing that acidic pH combined with antimicrobial peptide or environmental calcium can signal through a single membrane sensor protein to promote traits that may aid in survival, including modification of cell surface properties, increased resistance to antimicrobial fatty acids, and enhanced production of secreted proteases.

Acidic Submucosal Gland pH and Elevated Protein Concentration Produce Abnormal Cystic Fibrosis Mucus

In response to respiratory insults, airway submucosal glands secrete copious mucus strands to increase mucociliary clearance and protect the lung. However, in cystic fibrosis, stimulating submucosal glands has the opposite effect, disrupting mucociliary transport. In cystic fibrosis (CF) pigs, loss of cystic fibrosis transmembrane conductance regulator (CFTR) anion channels produced submucosal gland mucus that was abnormally acidic with an increased protein concentration. To test whether these variables alter mucus, we produced a microfluidic model of submucosal glands using mucus vesicles from banana slugs. Acidic pH and increased protein concentration decreased mucus gel volume and increased mucus strand elasticity and tensile strength. However, once mucus strands were formed, changing pH or protein concentration largely failed to alter the biophysical properties. Likewise, raising pH or apical perfusion did not improve clearance of mucus strands from CF airways. These findings reveal mechanisms responsible for impaired mucociliary transport in CF and have important implications for potential treatments.

Insulin-Loaded Barium Salt Particles Facilitate Oral Delivery of Insulin in Diabetic Rats

Oral delivery is considered as the most preferred and yet most challenging mode of drug administration; especially a fragile and sensitive peptide like insulin that shows extremely low bioavailability through the gastro-intestinal (GIT) route. To address this problem, we have designed a novel drug delivery system (DDS) using precipitation-induced Barium (Ba) salt particles. The DDS can load insulin molecules and transport them through the GIT route. There were several in vitro simulation tests carried out to prove the efficiency of Ba salt particles as oral delivery candidates. All three Ba salt particles (BaSO₄, BaSO_3, and BaCO₃) showed very good loading of insulin (>70% in all formulations) and a degree of resistance throughout a wide range of pHs from basic to acidic conditions when assessed by spectrophotometry. Particles and insulin-associated particles were morphologically assessed and characterized using FE-SEM and FT-IR. A set of tests were designed and carried out with mucin to predict whether the particles are potentially capable of overcoming one of the barriers for crossing intestinal epithelium. The mucin binding experiment demonstrated 60–100% of mucin adhesion to the three different particles. FT-IR identifies the characteristic peaks for mucin protein, particles, and particle-mucin complex re-confirming mucin adhesion to the particles. Finally, the effectiveness of nano-insulin was tested on streptozotocin (STZ) induced diabetic rats. A short acting human insulin analog, insulin aspart, was loaded into Ba salt particles at a dose of 100 IU/Kg prior to oral administration. Among the three formulations, insulin aspart-loaded BaSO₄ and BaCO₃ particles dramatically reduced the existing hyperglycemia. BaSO₄ with loaded Insulin showed an onset of glucose-lowering action within 1 hr, with blood glucose level measured significantly lower compared to the 2nd and 3rd h (p < 0.05). Insulin-loaded BaCO₃ particles showed a significant decrease in blood glucose level at 1–2 h, although the glucose level started to show a slight rise at 3rd h and by 4th h, it was back to baseline level. However, although BaSO₃ particles with loaded insulin showed a trend of reduction in blood glucose level, the reduction was not found to be significant (p < 0.05) at any point in time. Therefore, oral formulations of insulin/BaSO₄ and insulin/BaCO₃ particles were observed as effective as native insulin aspart subcutaneous formulation in terms of onset and duration of action. Further investigation will be needed to reveal bioavailability and mechanism of action of this novel Nano-Insulin formulations.

Activity of (-)-Camphene Derivatives Against Mycobacterium tuberculosis in Acidic pH

BACKGROUND

For more than 60 years, the lack of new anti-tuberculosis drugs and the increase of resistant Mycobacterium tuberculosis lineages exhibit a therapeutic challenge, demanding new options for the treatment of resistant tuberculosis.

OBJECTIVE

Herein, we determined the (i) activities of (-)-camphene and its derivatives and (ii) combinatory effect with pyrazinamide (PZA) against Mycobacterium tuberculosis in acidic pH and (iii) cytotoxicity on VERO cells.

METHODS

The activity of (-)-camphene and its 15 derivatives was determined in M. tuberculosis H37Rv in culture medium at pH 6.0 by Resazurin Microtiter Assay Plate (REMA). The activity and combinatory study of three (-)-camphene derivatives with PZA was carried out on seven multidrugresistant (MDR) clinical isolates by REMA and Checkerboard, respectively. The assay of 3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyltetrazolium (MTT) bromide in VERO cells was used to determine the derivatives' cytotoxicity.

RESULTS

Four (-)-camphene derivatives, (4), (5a) (5d) and (5h), showed a reduction in the MIC value at pH 6.0 compared to the MIC detected at pH 6.8 in M. tuberculosis H₃₇Rv and multidrug resistant clinical isolates. Three (-)-camphene derivatives, (4), (5d) and (5h), showed synergistic effect (FICI ≤ 0.5) combined with PZA and were more selective for M. tuberculosis than VERO cell (selective index from 7.7 to 84.2).

CONCLUSION

Three (-)-camphene derivatives have shown to be promising anti-TB molecule scaffolds due to their low MIC values in acidic pH against MDR M. tuberculosis clinical isolates, synergism with PZA and low cytotoxicity.

A New pH-Dependent Macrocyclic Rhodamine B-Based Fluorescent Probe for Copper Detection in White Wine

For efficiently measuring copper (II) ions in the acidic media of white wine, a new chemosensor based on rhodamine B coupled to a tetraazamacrocyclic ring (13aneN₄CH₂NH₂) was designed and synthesized by a one-pot reaction using ethanol as a green solvent. The obtained chemosensor was characterized via NMR, UV and fluorescent spectra. It was marked with no color emission under neutral pH conditions, with a pink color emission under acidic conditions, and a magenta color emission under acidic conditions where copper (II) ions were present. The sensitivity towards copper (II) ions was tested and verified over Ca²⁺, Ag⁺, Zn²⁺, Mg²⁺, Co²⁺, Ni²⁺, Fe²⁺, Pb²⁺, Cd²⁺, Fe³⁺, and Mn²⁺, with a detection limit of 4.38 × 10^-8 M in the fluorescence spectrum.

YaeB, Expressed in Response to the Acidic pH in Macrophages, Promotes Intracellular Replication and Virulence of Salmonella Typhimurium

Salmonella enterica serovar Typhimurium is a facultative intracellular pathogen that infects humans and animals. Survival and growth in host macrophages represents a crucial step for S. Typhimurium virulence. Many genes that are essential for S. Typhimurium proliferation in macrophages and associated with virulence are highly expressed during the intracellular lifecycle. yaeB, which encodes an RNA methyltransferase, is also upregulated during S. Typhimurium growth in macrophages. However, the involvement of YaeB in S. Typhimurium pathogenicity is still unclear. In this study, we investigated the role of YaeB in S. Typhimurium virulence. Deletion of yaeB significantly impaired S. Typhimurium growth in macrophages and virulence in mice. The effect of yaeB on pathogenicity was related to its activation of pstSCAB, a phosphate (P_i)-specific transport system that is verified here to be important for bacterial replication and virulence. Moreover, qRT-PCR data showed YaeB was induced by the acidic pH inside macrophages, and the acidic pH passed to YeaB through inhibiting global regulator histone-like nucleoid structuring (H-NS) which confirmed in this study can repress the expression of yaeB. Overall, these findings identified a new virulence regulatory network involving yaeB and provided valuable insights to the mechanisms through which acidic pH and low P_i regulate virulence.

Iron plaque formation in the roots of Pistia stratiotes L.: importance in phytoremediation of cadmium

Aquatic macrophytes play an important role in the removal of toxic metals from wastewater. Therefore, the induction of Fe plaque on the roots, and its consequences on Cd tolerance investigated in an aquatic macrophyte Pistia stratiotes L. The presence of Fe²⁺ ion but not Fe³⁺ resulted in Fe plaque formation. Induction of Fe plaque decreased Ca and increased K and Fe accumulations in the root. Plaque formed plants had accumulated less Cd until 50.0 µM CdCl₂ treatments because plaque acted as a barrier to Cd exposure. However, at higher concentrations (500.0 µM CdCl₂), plaque formed plants contained more Cd in the roots. Cadmium inducible ion leakage in the root and lowering of the photosynthetic pigment content were less in plants with a plaque. Stretching of aromatic carbonyl groups and alkyl groups among plaque formed plants upon Cd treatments indicated the putative role of phenolics in Cd detoxification.

Therapeutic Strategies Targeting Cariogenic Biofilm Microenvironment

Cariogenic biofilms are highly structured microbial communities embedded in an extracellular matrix, a multifunctional scaffold that is essential for the existence of the biofilm lifestyle and full expression of virulence. The extracellular matrix provides the physical and biological properties that enhance biofilm adhesion and cohesion, as well as create a diffusion-modulating milieu, protecting the resident microbes and facilitating the formation of localized acidic pH niches. These biochemical properties pose significant challenges for the development of effective antibiofilm therapeutics to control dental caries. Conventional approaches focusing solely on antimicrobial activity or enhancing remineralization may not achieve maximal efficacy within the complex biofilm microenvironment. Recent approaches disrupting the biofilm microbial community and the microenvironment have emerged, including specific targeting of cariogenic pathogens, modulation of biofilm pH, and synergistic combination of bacterial killing and matrix degradation. Furthermore, new "smart" nanotechnologies that trigger drug release or activation in response to acidic pH are being developed that could enhance the efficacy of current and prospective chemical modalities. Therapeutic strategies that can locally disrupt the pathogenic niche by targeting the biofilm structure and its microenvironment to eliminate the embedded microorganism and facilitate the action of remineralizing agents may lead to enhanced and precise anticaries approaches.

Degenerate intervertebral disc-like pH induces a catabolic mechanoresponse in human nucleus pulposus cells

Mechanical stimulation is known to influence intervertebral disc (IVD) cell behavior and function, but the effect on disc cells is routinely considered in isolation from other microenvironmental factors. Acidic pH has been shown to be a prominent and detrimental microenvironmental factor present in degenerate IVDs, but its influence on the human disc cell mechanoresponse has never been studied. We investigated the response of agarose-encapsulated human nucleus pulposus (NP) cells to 0.004 MPa, 1.0 Hz and 1 hour of compression (Flexcell FX4000 Compression System) under pH conditions representative of nondegenerate (pH 7.1) and degenerate (pH 6.5) IVDs. Cell viability, extracellular matrix production, and expression of anabolic/anti-catabolic and catabolic genes were assessed. We report that preculture of NP cells in agarose gels was required in order for cells to be mechanoresponsive, and this correlated with increased type VI collagen, α5β1 integrin, and fibronectin expression. Furthermore, the matrix homeostatic response observed at pH 7.1 (representative of nondegenerate IVDs; increased aggrecan [AGC], tissue inhibitor of metalloproteinases-1 [TIMP1], matrix metalloproteinase-3 [MMP3], a disintegrin and metalloproteinase with thrombospondin motif-5 [ADAMTS5] gene expression) was RGD-integrin dependent, whereas only MMP3 remained mechanoresponsive at pH 6.5, and this was independent of RGD-integrins. Our findings suggest differential mechanotransduction pathways operating for specific genes, with RGD-integrin dependent AGC expression, but not RGD-independent MMP3 expression, inhibited at pH representative of degenerate IVDs (pH 6.5), which could contribute to the catabolic phenotype observed during IVD degeneration.

CLINICAL SIGNIFICANCE

Characterizing the influence of the mechanical and chemical intervertebral disc microenvironment on disc cells, particularly in disc degeneration, could help develop future therapeutic strategies for the treatment of discogenic back pain.

Two distinct penicillin binding proteins promote cell division in different Salmonella lifestyles

The bacterial cell wall preserves cell integrity in response to external insults and the internal turgor pressure. The major component of the cell wall is the peptidoglycan (PG); a giant macromolecule formed by glycan chains cross-linked by short peptides. The PG is synthesized by a stepwise process that includes cytosolic and periplasmic reactions. The building subunits -muropeptides- are incorporated into the growing macromolecule by transglycolyslation (TG) and transpeptidation (TP) reactions, which constitute the last biosynthetic steps. TP reactions, involving cleavage of the terminal D Ala-D-Ala bond in the stem peptide, are carried out by enzymes known generically as penicillin-binding proteins (PBPs) due to their capacity to bind β lactam antibiotics, which are D Ala-D-Ala structural analogues. On an average, bacterial genomes harbour a minimum of 10 PBP-encoding genes, most of them non-essential. This dispensability has led to the widely accepted concept of functional redundancy for many PBPs. An exemption is the PBP dedicated to build the septal PG required to separate daughter cells during cell division. To date, this division specific PBP was reported as unique in all known bacteria and, as a consequence, “essential”. Our recent results obtained in the intracellular bacterial pathogen Salmonella enterica serovar Typhimurium challenges this view since this bacterium has two PBPs that can independently build the division septum. One of these two division PG enzymes is orthologue of the division-specific PBP3 of Escherichia coli. The second enzyme, named PBP3_SAL, is absent in non-pathogenic bacteria and, at least in S. Typhimurium, displays PG biosynthetic activity restricted to acidic conditions. Our work also revealed that it is possible to generate a S. Typhimurium mutant defective in PBP3, which cannot divide at neutral pH.

Two Elution Mechanisms of MEP Chromatography

MEP (mercapto-ethyl-pyridine) HyperCel is one of the hydrophobic charge induction chromatography (HCIC) resins. Under normal operation, proteins are bound to the MEP resin at neutral pH, at which MEP is not charged, mostly via hydrophobic interaction. MEP has a pyridine group, whose pK is 4.8, and hence is positively charged at acidic pH range. Based on the binding mechanism (i.e., hydrophobic interaction) and the induced positive charge at acidic pH, there may be two ways to elute the bound proteins. One way is to bring the pH down to protonate both MEP resin and the bound protein, leading to charge repulsion and thereby elution. Another way is to use hydrophobic interaction modifiers, which are often used in hydrophobic interaction chromatography, to reduce hydrophobic interaction. Here, we summarize such two possible elution approaches.

Triportheus albus Cope, 1872 in the Blackwater, Clearwater, and Whitewater of the Amazon: A Case of Phenotypic Plasticity?

The Amazon basin includes 1000s of bodies of water, that are sorted according to their color in three types: blackwater, clearwater, and whitewater, which significantly differ in terms of their physicochemical parameters. More than 3,000 species of fish live in the rivers of the Amazon, among them, the sardine, Triportheus albus, which is one of the few species that inhabit all three types of water. The purpose of our study was to analyze if the gene expression of T. albus is determined by the different types of water, that is, if the species presents phenotypic plasticity to live in blackwater, clearwater, and whitewater. Gills of T. albus were collected at well-characterized sites for each type of water. Nine cDNA libraries were constructed, three biological replicates of each condition and the RNA was sequenced (RNA-Seq) on the MiSeq^® Platform (Illumina^®). A total of 51.6 million of paired-end reads, and 285,456 transcripts were assembled. Considering the FDR ≤ 0.05 and fold change ≥ 2, 13,754 differentially expressed genes were detected in the three water types. Two mechanisms related to homeostasis were detected in T. albus that live in blackwater, when compared to the ones in clearwater and whitewater. The acidic blackwater is a challenging environment for many types of aquatic organisms. The first mechanism is related to the decrease in cellular permeability, highlighting the genes coding for claudin proteins, actn4, itgb3b, DSP, Gap junction protein, and Ca²⁺-ATPase. The second with ionic and acid-base regulation [rhcg1, slc9a6a (NHE), ATP6V0A2, Na⁺/K⁺-ATPase, slc26a4 (pedrin) and slc4a4b]. We suggest T. albus is a good species of fish for future studies involving the ionic and acid-base regulation of Amazonian species. We also concluded that, T. albus, shows well defined phenotypic plasticity for each water type in the Amazon basin.

Pharmacodynamic Evaluation of Fosfomycin against Escherichia coli and Klebsiella spp. from Urinary Tract Infections and the Influence of pH on Fosfomycin Activities

Fosfomycin is widely used for the treatment of uncomplicated urinary tract infection (UTI), and it has recently been recommended that fosfomycin be used to treat infections caused by multidrug-resistant (MDR) Gram-negative bacilli. Whether urine acidification can improve bacterial susceptibility to fosfomycin oral dosing regimens has not been analyzed. The MIC of fosfomycin for 245 Gram-negative bacterial isolates, consisting of 158 Escherichia coli isolates and 87 Klebsiella isolates which were collected from patients with urinary tract infections, were determined at pH 6.0 and 7.0 using the agar dilution method. Monte Carlo simulation of the urinary fosfomycin area under the concentration-time curve (AUC) after a single oral dose of 3,000 mg fosfomycin and the MIC distribution were used to determine the probability of target attainment (PTA). Fosfomycin was effective against E. coli (MIC₉₀ ≤ 16 μg/ml) but not against Klebsiella spp. (MIC₉₀ > 512 μg/ml). Acidification of the environment increased the susceptibility of 71% of the bacterial isolates and resulted in a statistically significant decrease in bacterial survival. The use of a regimen consisting of a single oral dose of fosfomycin against an E. coli isolate with an MIC of ≤64 mg/liter was able to achieve a PTA of ≥90% for a target pharmacodynamic index (AUC/MIC) of 23 in urine; PTA was not achieved when the MIC was higher than 64 mg/liter. The cumulative fractions of the bacterial responses (CFR) were 99% and 55% against E. coli and Klebsiella spp., respectively, based on simulated drug exposure in urine with an acidic pH of 6.0. A decrease of the pH from 7.0 to 6.0 improved the PTA and CFR of the target pharmacodynamic index in both E. coli and Klebsiella isolates.

Improving the water solubility of Monascus pigments under acidic conditions with gum arabic

BACKGROUND

Monascus pigments (Mps) are natural food colorants and their stability in acidic solutions is important for application in the food industry. This study aimed to evaluate the use of gum arabic (GA) as a stabilizer for maintaining the solubility of Mps in an acidic aqueous solution exposed to a high temperature, and to analyze the molecular interactions between GA and Mps.

RESULTS

Mps dispersed (0.2 g kg^-1 ) in deionized water at pH 3.0-4.0 without GA formed precipitates but remained in a stable solution in the presence of GA (1 g kg^-1 ). The significant improvement of Mps water solubility under acidic conditions was attributed to the formation of Mps-GA complexes, as indicated by a sharp increase in the fluorescence intensity. The results on particle size, zeta potential, and transmission electron microscopy further suggested that molecular binding of Mps to GA, electrostatic repulsion, and steric hindrance of GA were contributing factors to preventing the aggregation of Mps in acidic solutions. A mechanistic model was presented for GA-Mps interactions and complex structures.

CONCLUSION

GA was proven to be an effective stabilizer of natural food colorants in acidic solutions. © 2016 Society of Chemical Industry.

Effects of intermolecular interactions on the stability of carbon nanotube-gold nanoparticle conjugates in solution

This work deals with the role of intermolecular interactions in the stability of a carbon nanotube (CNT) capped by functionalized gold nanoparticles (AuNPs). The importance of such a system is due to its potential application as a pH-controlled drug carrier. Our preliminary experimental studies showed that fabrication of such a nanobottle/nanocontainer is feasible and it is possible to encapsulate the anticancer drug cisplatin inside the inner space of a CNT and seal its ends by functionalized AuNPs. The expected behavior, that is, detachment of AuNPs at acidic pH and the release of cisplatin, was, however, not observed. On the other hand, our theoretical studies of chemically identical system led to the conclusion that the release of cisplatin at acidic pH should be observed. Therefore, in this work, a deeper theoretical analysis of various factors that could be responsible for the disagreement between experimental and theoretical results were performed. The study found that the major factor is a large dispersion interaction component acting between CNT and AuNP in solution in the case of the experimental system. This factor can be controlled to some extent by tuning the system size or the ratio between AuNP diameter and CNT diameter. Thus, such kind of a pH-sensitive drug carrier is still of great interest, but its structural parameters need to be properly adjusted.

Adaptation in Bacillus cereus: From Stress to Disease

Bacillus cereus is a food-borne pathogen that causes diarrheal disease in humans. After ingestion, B. cereus experiences in the human gastro-intestinal tract abiotic physical variables encountered in food, such as acidic pH in the stomach and changing oxygen conditions in the human intestine. B. cereus responds to environmental changing conditions (stress) by reversibly adjusting its physiology to maximize resource utilization while maintaining structural and genetic integrity by repairing and minimizing damage to cellular infrastructure. As reviewed in this article, B. cereus adapts to acidic pH and changing oxygen conditions through diverse regulatory mechanisms and then exploits its metabolic flexibility to grow and produce enterotoxins. We then focus on the intricate link between metabolism, redox homeostasis, and enterotoxins, which are recognized as important contributors of food-borne disease.

Asymmetric structure of the influenza A virus and novel function of the matrix protein M1

Influenza virus is an enveloped virus. It comprises two major modules: external lipoprotein envelope and internal ribonucleoprotein (RNP) containing the genomic negative-strand RNA. Lipoprotein envelope contains four vital proteins: hemagglutinin (HA), neuraminidase (NA), transmembrane ionic channel M2, and minor amounts of nuclear export protein NEP. RNP contains RNA and four polypeptides: major nucleocapsid protein NP and three polymerase subunits PB1, PB2, PA. Both modules are linked with each other by matrix M1 maintaining the virus integrity. According to the structural function, NP and M1 are predominant in virus particle in the amounts of 1000 and 3000 molecules, respectively. In addition to the structural function, M1 plays a role in regulation of intracellular and nuclear migration of viral RNP and virus assembly, referred as budding process, at the plasma membrane in infected cells. The bipolar structure of the influenza virus characterized by asymmetric location of RNP and nonregular distribution of M1 and M2 inside the virion is reviewed. The role of M1 in maintaining the asymmetric structure of the virus particle and regulation of RNP transport inside virus particle is considered. First experimental data confirming (i) intravirion RNP transport and its outside exit directed by the M1 and (ii) the importance of this process in virus uncoating and initiation of infection in target cell are discussed. A novel class of antiviral agents activating ATP-ase of the early endosome compartment in the target cell is discussed.

The effect of acidic pH and presence of metals as parameters in establishing a sulfidogenic process in anaerobic reactor

The successful use of anaerobic reactors for bioremediation of acid mine drainage has been shown in systems with neutral pH. However, the choice of an efficient and suitable process for such wastewater must consider the capability of operating at acidic pH and in the presence of metals. This work studies the performance of an anaerobic batch reactor, under conditions of varying initial pH for its efficiencies in sulfate removal and metal precipitation from synthetic acid mine drainage. The chemical oxygen demand/sulfate (COD/SO4(2-)) ratio used was 1.00, with ethanol chosen as the only energy and carbon source. The initial pH of the synthetic drainage was progressively set from 7.0 to 4.0 to make it as close as possible to that of real acid mine drainage. Metals were also added starting with iron, zinc, and finally copper. The effectiveness of sulfate and COD removal from the synthetic acid mine drainage increased as the initial pH was reduced. The sulfate removal increased from 38.5 ± 3.7% to 52.2 ± 3%, while the removal of organic matter started at 91.7 ± 2.4% and ended at 99 ± 1%. These results indicate that the sulfate reducing bacteria (SRB) community adapted to lower pH values. The metal removal observed was 88 ± 7% for iron, 98.0 ± 0.5% for zinc and 99 ± 1% for copper. At this stage, an increase in the sulfate removal was observed, which reaches up to 82.2 ± 5.8%. The kinetic parameters for sulfate removal were 0.22 ± 0.04 h(-1) with Fe, 0.26 ± 0.04 h(-1) with Fe and Zn and 0.44 ± 0.04 h(-1) with Fe, Zn, and Cu.

Acidic pH-targeted chitosan capped mesoporous silica coated gold nanorods facilitate detection of pancreatic tumors via multispectral optoacoustic tomography

We present a cancer nanomedicine based on acidic pH targeted gold nanorods designed for multispectral optoacoustic tomography (MSOT). We have designed gold nanorods coated with mesoporous silica and subsequently capped with chitosan (CMGs). We have conjugated pH-sensitive variant 7 pHLIP peptide to the CMGs (V7-CMG) to provide targeting specificity to the acidic tumor microenvironment. In vitro, treatment of S2VP10 and MiaPaca2 cells with V7-CMG containing gemcitabine resulted in significantly greater cytotoxicity with 97% and 96.5% cell death, respectively than gemcitabine alone 60% and 76% death at pH 6.5 (S2VP10 pH 6.5 p=0.009; MiaPaca2 pH 6.5 p=0.0197). In vivo, the V7-CMGs provided the contrast and targeting specificity necessary for MSOT of retroperitoneal orthotopic pancreatic tumors. In the in vivo S2VP10 model, the V7-CMG particle preferentially accumulated within the tumor at 17.1 MSOT a.u. signal compared with 0.7 MSOT a.u. in untargeted CMG control in tumor (P = 0.0002). Similarly, V7-CMG signal was 9.34 MSOT a.u. in the S2013 model compared with untargeted CMG signal at 0.15 MSOT a.u. (P = 0.0004). The pH-sensitivity of the targeting pHLIP peptide and chitosan coating makes the particles suitable for simultaneous in vivo tumor imaging and drug delivery.

The pH-sensing receptor OGR1 improves barrier function of epithelial cells and inhibits migration in an acidic environment

The pH-sensing receptor ovarian cancer G protein-coupled receptor 1 (OGR1; GPR68) is expressed in the gut. Inflammatory bowel disease is typically associated with a decrease in local pH, which may lead to altered epithelial barrier function and subsequent gastrointestinal repair involving epithelial cell adhesion and migration. As the mechanisms underlying the response to pH changes are not well understood, we have investigated OGR1-mediated, pH-dependent signaling pathways in intestinal epithelial cells. Caco-2 cells stably overexpressing OGR1 were created and validated as tools to study OGR1 signaling. Barrier function, migration, and proliferation were measured using electric cell-substrate impedance-sensing technology. Localization of the tight junction proteins zonula occludens protein 1 and occludin and the rearrangement of cytoskeletal actin were examined by confocal microscopy. Paracellular permeability and protein and gene expression analysis using DNA microarrays were performed on filter-grown Caco-2 monolayers. We report that an acidic pH shift from pH 7.8 to 6.6 improved barrier function and stimulated reorganization of filamentous actin with prominent basal stress fiber formation. Cell migration and proliferation during in vitro wound healing were inhibited. Gene expression analysis revealed significant upregulation of genes related to cytoskeleton remodeling, cell adhesion, and growth factor signaling. We conclude that acidic extracellular pH can have a signaling function and impact the physiology of intestinal epithelial cells. The deconstruction of OGR1-dependent signaling may aid our understanding of mucosal inflammation mechanisms.

Characterization of the arginine decarboxylase gene (ORF HP0422, speA) involved in acid tolerance in Helicobacter pylori

BACKGROUND

Helicobacter pylori is a motile microaerophilic bacterium that colonizes the human stomach. H. pylori infection triggers gastric diseases, such as gastritis, peptic ulcer and gastric cancer. Stomach represents a barrier for microorganism colonization, particularly because of its high hydrochloric acid concentration. The main mechanism developed by H. pylori to maintain intracellular pH homeostasis in this environment is the urease activity. However, urease negative strains can be also isolated from clinical samples, suggesting that H. pylori presents other components involved in acid resistance.

OBJECTIVE

Here, we present some evidence that the arginine decarboxylase gene (speA) in H. pylori could be involved in an acid adaptation mechanism similar to the one in Enterobacteriaceae, which is dependent on the presence of arginine.

METHODS

Indeed, speA mRNA and protein expression are acutely induced by acid stress.

RESULTS

Moreover, we showed that H. pylori uses arginine in an acid response mechanism required for its growth in acid conditions.

CONCLUSION

Altogether, these results provide novel information regarding the H. pylori physiology and acid response mechanism.

Structural insights into the aggregation behavior of Murraya koenigii miraculin-like protein below pH 7.5

Murraya koenigii miraculin-like protein (MKMLP) gradually precipitates below pH 7.5. Here, we explore the basis for this aggregation by identifying the aggregation-prone regions via comparative analysis of crystal structures acquired at several pH values. The prediction of aggregation-prone regions showed the presence of four short peptides either in beta sheets or loops on surface of the protein. These peptides were distributed in two patches far apart on the surface. Comparison of crystal structures of MKMLP, determined at 2.2 Å resolution in pH 7.0 and 4.6 in the present study and determined at 2.9 Å in pH 8.0 in an earlier reported study, reveal subtle conformational differences resulting in gradual exposure of aggregation-prone regions. As the pH is lowered, there are alterations in ionic interactions within the protein interactions of the chain with water molecules and exposure of hydrophobic residues. The analysis of symmetry-related molecular interfaces involving one patch revealed shortening of nonpolar intermolecular contacts as the pH decreased. In particular, a decrease in the intermolecular distance between Trp103 of the aggregation-prone peptide WFITTG (103-108) unique to MLPs was observed. These results demonstrated that aggregation occurs due to the cumulative effect of the changes in interactions in two aggregation-prone defined regions.

Amyloid-β peptide (1-42) aggregation induced by copper ions under acidic conditions

It is well known that the aggregation of amyloid-β peptide (Aβ) induced by Cu²⁺ is related to incubation time, solution pH, and temperature. In this work, the aggregation of Aβ₁₋₄₂ in the presence of Cu²⁺ under acidic conditions was studied at different incubation time and temperature (e.g. 25 and 37°C). Incubation temperature, pH, and the presence of Cu²⁺ in Aβ solution were confirmed to alter the morphology of aggregation (fibrils or amorphous aggregates), and the morphology is pivotal for Aβ neurotoxicity and Alzheimer disease (AD) development. The results of atomic force microscopy (AFM) indicated that the formation of Aβ fibrous morphology is preferred at lower pH, but Cu²⁺ induced the formation of amorphous aggregates. The aggregation rate of Aβ was increased with the elevation of temperature. These results were further confirmed by fluorescence spectroscopy and circular dichroism spectroscopy and it was found that the formation of β-sheet structure was inhibited by Cu²⁺ binding to Aβ. The result was consistent with AFM observation and the fibrillation process was restrained. We believe that the local charge state in hydrophilic domain of Aβ may play a dominant role in the aggregate morphology due to the strong steric hindrance. This research will be valuable for understanding of Aβ toxicity in AD.