Natural Polymer-Based Nanogel for pH-Responsive Delivery of Sorafenib Tosylate in Hemangiosarcoma.

Smart nanomedicinal treatment for cancer manifests a solubility challenge with inherent nanoscale size and nonspecific release with stimuli-responsive potential. This is the limelight in novel chemotherapy to pursue physiochemical differences between the tumor microenvironment (TME) and normal cells, which introduces active groups of nanocarriers responding to various stimuli, endowing them with concise responses to various tumor-related signals. The nanogels were successfully prepared by a modified solvent evaporation technique. Nine batches were formulated by changing the chitosan concentration (12, 14, 16 mg/ml) and sonication time (5, 10, 15 min). The formulations were optimized for particle size and zeta potential with high percent entrapment efficiency (%EE) through Central Composite Design software. The optimized batch F7 had a 182-nm size and high zeta potential (64.5 mV) with 98% EE. The drug release of F7 was higher at pH 6 (97.556%) than at pH 7.4 (45.113%). The pharmacokinetic study shows that the release follows the Hixon plot model (R2 = 0.9334) that shifts to zero order (R2 = 0.9149). The nanogel F7 was observed for stability and showed an absence of color change, phase separation, and opacity for 6 months. In the present study, the pH difference between cancer cells and normal cells is the key point of the smart nanogel. This study is promising but challenging depending on the in vivo study. The nanogel was successfully prepared and evaluated for pH-responsive release. As hemangiosarcoma commonly occurs in dogs, this formulation helps to limit the difficulties with administration.

Isoquinoline-based intrinsic fluorescence assessment of erythropoiesis-stimulating agent, Roxadustat (FG-4592), in tablets: applications to content uniformity and human plasma evaluation.

In the present study, a first validated and green spectrofluorimetric approach for its assessment and evaluation in different matrices was investigated. After using an excitation wavelength of 345 nm, Roxadustat (ROX) demonstrates a highly native fluorescence at an emission of 410 nm. The influences of experimental factors such as pH, diluting solvents, and different organized media were tested, and the most appropriate solvent choice was ethanol. It was confirmed that there was a linear relationship between the concentration of ROX and the relative fluorescence intensity in the range 60.0-1000.0 ng ml-1, with the limit of detection and limit of quantitation, respectively, being 17.0 and 53.0 ng ml-1. The mean recoveries % [±standard deviation (SD), n = 5] for pharmaceutical preparations were 100.11% ± 2.24%, whereas for plasma samples, they were 100.08 ± 1.08% (±SD, n = 5). The results obtained after the application of four greenness criteria, Analytical Eco-Scale metric, NEMI, GAPI, and AGREE metric, confirmed its eco-friendliness. In addition, the whiteness meter (RGB12) confirmed its level of sustainability. The International Council for Harmonisation (ICH) criteria were used to verify the developed method through the study in both spiked plasma samples and content uniformity evaluation. An appropriate standard for various applications in industry and quality control laboratories was developed.

Interconnections between the Cation/Alkaline pH-Responsive Slt and the Ambient pH Response of PacC/Pal Pathways in Aspergillus nidulans.

In the filamentous ascomycete Aspergillus nidulans, at least three high hierarchy transcription factors are required for growth at extracellular alkaline pH: SltA, PacC and CrzA. Transcriptomic profiles depending on alkaline pH and SltA function showed that pacC expression might be under SltA regulation. Additional transcriptional studies of PacC and the only pH-regulated pal gene, palF, confirmed both the strong dependence on ambient pH and the function of SltA. The regulation of pacC expression is dependent on the activity of the zinc binuclear (C6) cluster transcription factor PacX. However, we found that the ablation of sltA in the pacX- mutant background specifically prevents the increase in pacC expression levels without affecting PacC protein levels, showing a novel specific function of the PacX factor. The loss of sltA function causes the anomalous proteolytic processing of PacC and a reduction in the post-translational modifications of PalF. At alkaline pH, in a null sltA background, PacC72kDa accumulates, detection of the intermediate PacC53kDa form is extremely low and the final processed form of 27 kDa shows altered electrophoretic mobility. Constitutive ubiquitination of PalF or the presence of alkalinity-mimicking mutations in pacC, such as pacCc14 and pacCc700, resembling PacC53kDa and PacC27kDa, respectively, allowed the normal processing of PacC but did not rescue the alkaline pH-sensitive phenotype caused by the null sltA allele. Overall, data show that Slt and PacC/Pal pathways are interconnected, but the transcription factor SltA is on a higher hierarchical level than PacC on regulating the tolerance to the ambient alkalinity in A. nidulans.

Risk assessment of antimony-arsenic contaminated soil remediated using zero-valent iron at different pH values combined with freeze-thaw cycles.

Soil in mining wastelands is seriously polluted with heavy metals. Zero-valent iron (ZVI) is widely used for remediation of heavy metal-polluted soil because of its excellent adsorption properties; however, the remediation process is affected by complex environmental conditions, such as acid rain and freeze-thaw cycles. In this study, the effects of different pH values and freeze-thaw cycles on remediation of antimony (Sb)- and arsenic (As)-contaminated soil by ZVI were investigated in laboratory simulation experiments. The stability and potential human health risks associated with the remediated soil were evaluated. The results showed that ZVI has a significant stabilizing effect on Sb and As in both acidic and alkaline soils contaminated with dual levels of Sb and As, and the freeze-thaw process in different pH value solution systems further enhances the ability of ZVI to stabilize Sb and As, especially in acidic soils. However, it should be noted that apart from the pH=1.0 solution environment, ZVI's ability to stabilize As is attenuated under other circumstances, potentially leading to leaching of its unstable form and thereby increasing contamination risks. This indicates that the F1 (2% ZVI+pH=1 solution+freeze-thaw cycle) processing exhibits superior effectiveness. After F1 treatment, the bioavailability of Sb and As in both soils also significantly decreased during the gastric and intestinal stages (about 60.00%), the non-carcinogenic and carcinogenic risks of Sb and As in alkaline soils are eliminated for children and adults, with a decrease ranging from 60.00% to 70.00%, while in acidic soil, the non-carcinogenic and carcinogenic risks of As to adults and children is acceptable, but Sb still poses non-carcinogenic risks to children, despite reductions of about 65.00%. These findings demonstrate that soil pH is a crucial factor influencing the efficacy of ZVI in stabilizing Sb and As contaminants during freeze-thaw cycles. This provides a solid theoretical foundation for utilizing ZVI in the remediation of Sb- and As-contaminated soils, emphasizing the significance of considering both pH levels and freeze-thaw conditions to ensure effective and safe treatment.

The protective effect of a new absorbent incontinence design against an alkaline pH challenge on the epidermal barrier.

BACKGROUND: Incontinence-associated dermatitis (IAD) is one of the most common complications of incontinence. Improved diaper designs can minimize the occurrence of IAD. PURPOSE: To develop a novel diaper design to minimize the damaging effects of incontinence on the epidermal barrier. METHODS: An optimized diaper design was tested for surface dryness (ie, rewet), maintenance of a skin-adapted surface pH of 5.5, and ability to protect epidermal barrier function from an alkaline pH 10.7 challenge. RESULTS: The diapers released a mean (standard deviation [SD]) of 1.2 (0.2) mg/cm2 of solution under pressure after the first loading and a mean of 2.9 (1.7) mg/cm2 after the second loading. The surface pH remained between 4.5 and 5.5 over 5 hours. In healthy skin, transepidermal water loss (TEWL) increased by a mean of 3.43 (4.67) g/m2/h after the alkaline urine solution challenge with the new diaper design versus a mean of 8.38 (5.67) g/m2/h with a cellulose patch (P < .001) as a control. The mean erythema readings were 1.18 (1.30) g/m2/h for the new design and 2.56 (1.25) g/m2/h for the cellulose patches (P < .001). CONCLUSION: The new diaper design minimizes rewetting, maintains an acidic surface, and protects the epidermal barrier against an alkaline pH challenge. This design may help prevent IAD.

Dual pH/redox-responsive hyperbranched polymeric nanocarriers with TME-trigger size shrinkage and charge reversible ability for amplified chemotherapy of breast cancer.

A novel pH/redox-responsive hyperbranched MeO-PEG-b-(NIPAAm-co-PBAE) nanoparticles (NPs) were designed with size shrinkage and charge-reversible potential for targeted delivery of docetaxel (DTX) to MDA-MB-231 cell lines. In the tumor microenvironment (TME), amine protonation induces charge reversal and disulfide bond cleavage under high TME GSH concentration causing size shrinkage, improved deep tumor penetration, and active targeting of the therapeutic agents. These nano drug delivery systems (NDDSs) significantly promoted cancer cell uptake (~ 100% at 0.5 h), facilitating site-specific delivery and deep tumor penetration. The MTT assay revealed significantly higher cytotoxicity (P value < 0.0001) for DTX-loaded NPs compared to free DTX. Cell cycle analysis revealed G2/M (58.3 ± 2.1%) and S (21.5 ± 1.3%) arrest for DTX-loaded NPs, while free DTX caused G2/M (67.9 ± 1.1%) and sub-G1 (10.3 ± 0.8%) arrest. DTX-loaded NPs induced higher apoptosis (P value < 0.001) in MDA-MB-231 cells (71.5 ± 2.8%) compared to free DTX (42.3 ± 3.1%). Western blotting and RT-PCR assays confirmed significant up-regulation of protein levels and apoptotic genes by DTX-loaded NPs compared to free DTX. In conclusion, TME-responsive charge reversal and size-shrinkable smart NDDSs designed based on low pH, and high glutathione (GSH), offer more effective site-specific delivery of therapeutic agents to tumors.

Macrophage membrane-camouflaged pH-sensitive nanoparticles for targeted therapy of oral squamous cell carcinoma.

BACKGROUND: Oral cancer is the most common malignant tumor of the head and neck, and 90% of cases are oral squamous cell carcinoma (OSCC). Chemotherapy is an important component of comprehensive treatment for OSCC. However, the clinical treatment effect of chemotherapy drugs, such as doxorubicin (DOX), is limited due to the lack of tumor targeting and rapid clearance by the immune system. Thus, based on the tumor-targeting and immune evasion abilities of macrophages, macrophage membrane-encapsulated poly(methyl vinyl ether alt maleic anhydride)-phenylboronic acid-doxorubicin nanoparticles (MM@PMVEMA-PBA-DOX NPs), briefly as MM@DOX NPs, were designed to target OSCC. The boronate ester bonds between PBA and DOX responded to the low pH value in the tumor microenvironment, selectively releasing the loaded DOX. RESULTS: The results showed that MM@DOX NPs exhibited uniform particle size and typical core-shell structure. As the pH decreased from 7.4 to 5.5, drug release increased from 14 to 21%. The in vitro targeting ability, immune evasion ability, and cytotoxicity of MM@DOX NPs were verified in HN6 and SCC15 cell lines. Compared to free DOX, flow cytometry and fluorescence images demonstrated higher uptake of MM@DOX NPs by tumor cells and lower uptake by macrophages. Cell toxicity and live/dead staining experiments showed that MM@DOX NPs exhibited stronger in vitro antitumor effects than free DOX. The targeting and therapeutic effects were further confirmed in vivo. Based on in vivo biodistribution of the nanoparticles, the accumulation of MM@DOX NPs at the tumor site was increased. The pharmacokinetic results demonstrated a longer half-life of 9.26 h for MM@DOX NPs compared to 1.94 h for free DOX. Moreover, MM@DOX NPs exhibited stronger tumor suppression effects in HN6 tumor-bearing mice and good biocompatibility. CONCLUSIONS: Therefore, MM@DOX NPs is a safe and efficient therapeutic platform for OSCC.

Reversible pH-Gated MXene Membranes with Ultrahigh Mono-/Divalent-Ion Selectivity.

Artificial ion channel membranes hold high promise in water treatment, nanofluidics, and energy conversion, but it remains a great challenge to construct such smart membranes with both reversible ion-gating capability and desirable ion selectivity. Herein, we constructed a smart MXene-based membrane via p-phenylenediamine functionalization (MLM-PPD) with highly stable and aligned two-dimensional subnanochannels, which exhibits reversible ion-gating capability and ultrahigh metal ion selectivity similar to biological ion channels. The pH-sensitive groups within the MLM-PPD channel confers excellent reversible Mg2+-gating capability with a pH-switching ratio of up to 100. The mono/divalent metal-ion selectivity up to 1243.8 and 400.9 for K+/Mg2+ and Li+/Mg2+, respectively, outperforms other reported membranes. Theoretical calculations combined with experimental results reveal that the steric hindrance and stronger PPD-ion interactions substantially enhance the energy barrier for divalent metal ions passing through the MLM-PPD, and thus leading to ultrahigh mono/divalent metal-ion selectivity. This work provides a new strategy for developing artificial-ion channel membranes with both reversible ion-gating functionality and high-ion selectivity for various applications.

Charge-Reversal NaCl/G-Quartets for Aggregation-Induced Mitochondrial MicroRNA Imaging and Ion-Interference Therapy.

Mitochondrial therapy is a promising new strategy that offers the potential to achieve precise disease diagnosis or maximum therapeutic response. However, versatile mitochondrial theranostic platforms that integrate biomarker detection and therapy have rarely been exploited. Here, we report a charge-reversal nanomedicine activated by an acidic microenvironment for mitochondrial microRNA (mitomiR) detection and ion-interference therapy. The transporter liposome (DD-DC) was constructed from a pH-responsive polymer and a positively charged phospholipid, encapsulating NaCl nanoparticles with coloading of the aggregation-induced emission (AIE) fluorogens AIEgen-DNA/G-quadruplexes precursor and brequinar (NAB@DD-DC). The negatively charged nanomedicine ensured good blood stability and high tumor accumulation, while the charge-reversal to positive in response to the acidic pH in the tumor microenvironment (TME) and lysosomes enhanced the uptake by tumor cells and lysosome escape, achieving accumulation in mitochondria. The subsequently released Na+ in mitochondria not only contributed to the formation of mitomiR-494 induced G-quadruplexes for AIE imaging diagnosis but also led to an osmolarity surge that was enhanced by brequinar to achieve effective ion-interference therapy.

Multistress Interplay: Time and Duration of Ocean Acidification Modulate the Toxicity of Mercury and Other Metals.

The current understanding of multistress interplay assumes stresses occur in perfect synchrony, but this assumption is rarely met in the natural marine ecosystem. To understand the interplay between nonperfectly overlapped stresses in the ocean, we manipulated a multigenerational experiment (F0-F3) to explore how different temporal scenarios of ocean acidification will affect mercury toxicity in a marine copepod Pseudodiaptomus annandalei. We found that the scenario of past acidification aggravated mercury toxicity but current and persistent acidification mitigated its toxicity. We specifically performed a proteomics analysis for the copepods of F3. The results indicated that current and persistent acidification initiated the energy compensation for development and mercury efflux, whereas past acidification lacked the barrier of H+ and had dysfunction in the detoxification and efflux system, providing a mechanistic understanding of mercury toxicity under different acidification scenarios. Furthermore, we conducted a meta-analysis on marine animals, demonstrating that different acidification scenarios could alter the toxicity of several other metals, despite evidence from nonsynchronous scenarios remaining limited. Our study thus demonstrates that time and duration of ocean acidification modulate mercury toxicity in marine copepods and suggests that future studies should move beyond the oversimplified scenario of perfect synchrony in understanding multistress interaction.

The fundamental role of pH in CH4 bioconversion into polyhydroxybutyrate in mixed methanotrophic cultures.

Climate change and plastic pollution are likely the most relevant challenges for the environment in the 21st century. Developing cost-effective technologies for the bioconversion of methane (CH4) into polyhydroxyalkanoates (PHAs) could simultaneously mitigate CH4 emissions and boost the commercialization of biodegradable polymers. Despite the fact that the role of temperature, nitrogen deprivation, CH4:O2 ratio or micronutrients availability on the PHA accumulation capacity of methanotrophs has been carefully explored, there is still a need for optimization of the CH4-to-PHA bioconversion process prior to becoming a feasible platform in future biorefineries. In this study, the influence of different cultivation broth pH values (5.5, 7, 8.5 and 10) on bacterial biomass growth, CH4 bioconversion rate, PHA accumulation capacity and bacterial community structure was investigated in a stirred tank bioreactor under nitrogen deprivation conditions. Higher CH4 elimination rates were obtained at increasing pH, with a maximum value of 50.4 ± 2.7 g CH4·m-3·h-1 observed at pH 8.5. This was likely mediated by an increased ionic strength in the mineral medium, which enhanced the gas-liquid mass transfer. Interestingly, higher PHB accumulations were observed at decreasing pH, with the highest PHB contents recorded at a pH 5.5 (43.7 ± 3.4 %w·w-1). The strong selective pressure of low pH towards the growth of Type II methanotrophic bacteria could explain this finding. The genus Methylocystis increased its abundance from 34 % up to 85 and 90 % at pH 5.5 and 7, respectively. On the contrary, Methylocystis was less abundant in the community enriched at pH 8.5 (14 %). The accumulation of intracellular PHB as energy and carbon storage material allowed the maintenance of high CH4 biodegradation rates during 48 h after complete nitrogen deprivation. The results here obtained demonstrated for the first time a crucial and multifactorial role of pH on the bioconversion performance of CH4 into PHA.

Activity-stability trade-off observed in variants at position 315 of the GH10 xylanase XynR.

XynR is a thermostable alkaline GH10 xylanase, for which we have previously examined the effects of saturation mutagenesis at position 315 on enzyme alkaliphily, and found that at pH 10, the activities of variants could be ordered as follows: T315Q > T315S = T315N > T315H = wild-type XynR (WT) > 15 other variants. In this study, we sought to elucidate the mechanisms underlying the variable activity of these different variants. Crystallographic analysis revealed that the Ca2+ ion near position 315 in WT was absent in the T315Q variant. We accordingly hypothesized that the enhancement of alkaliphily in T315Q, and probably also in the T315H, T315N, and T315S variants, could be ascribed to an activity-stability trade-off associated with a reduction in stability due to the lack of this Ca2+ ion. Consistent with expectations, the alkaline resistance of T315H, T315N, T315Q, and T315S, evaluated through the pH-dependence of stability at 0 mM CaCl2 under alkaline conditions, was found to be lower than that of WT: the residual activity at pH 11 of WT was 78% while those of T315H, T315N, T315Q, and T315S were 0, 9, 0, and 43%, respectively. In addition, the thermostabilities of these four variants, as assessed using the denaturing temperatures (Tm) at 0 mM CaCl2 based on ellipticity at 222 nm in circular dichroism measurements, were lower than that of WT by 2-8 °C. Furthermore, the Tm values of WT and variants at 5 mM CaCl2 were higher than those at 0 mM CaCl2 by 6-11 °C. Collectively, our findings in this study indicate that mutation of the T residue at position 315 of XynR to H, N, Q, and S causes an increase in the alkaliphily of this enzyme, thereby reducing its stability.

Harnessing alkaline-pH regulatable promoters for efficient methanol-free expression of enzymes of industrial interest in Komagataella Phaffii.

BACKGROUND: The yeast Komagataella phaffii has become a very popular host for heterologous protein expression, very often based on the use of the AOX1 promoter, which becomes activated when cells are grown with methanol as a carbon source. However, the use of methanol in industrial settings is not devoid of problems, and therefore, the search for alternative expression methods has become a priority in the last few years. RESULTS: We recently reported that moderate alkalinization of the medium triggers a fast and wide transcriptional response in K. phaffii. Here, we present the utilization of three alkaline pH-responsive promoters (pTSA1, pHSP12 and pPHO89) to drive the expression of a secreted phytase enzyme by simply shifting the pH of the medium to 8.0. These promoters offer a wide range of strengths, and the production of phytase could be modulated by adjusting the pH to specific values. The TSA1 and PHO89 promoters offered exquisite regulation, with virtually no enzyme production at acidic pH, while limitation of Pi in the medium further potentiated alkaline pH-driven phytase expression from the PHO89 promoter. An evolved strain based on this promoter was able to produce twice as much phytase as the reference pAOX1-based strain. Functional mapping of the TSA1 and HSP12 promoters suggests that both contain at least two alkaline pH-sensitive regulatory regions. CONCLUSIONS: Our work shows that the use of alkaline pH-regulatable promoters could be a useful alternative to methanol-based expression systems, offering advantages in terms of simplicity, safety and economy.

Codelivery of anti-CD47 antibody and chlorin e6 using a dual pH-sensitive nanodrug for photodynamic immunotherapy of osteosarcoma.

Osteosarcoma is a malignant tumor originating from bone tissue that progresses rapidly and has a poor patient prognosis. Immunotherapy has shown great potential in the treatment of osteosarcoma. However, the immunosuppressive microenvironment severely limits the efficacy of osteosarcoma treatment. The dual pH-sensitive nanocarrier has emerged as an effective antitumor drug delivery system that can selectively release drugs into the acidic tumor microenvironment. Here, we prepared a dual pH-sensitive nanocarrier, loaded with the photosensitizer Chlorin e6 (Ce6) and CD47 monoclonal antibodies (aCD47), to deliver synergistic photodynamic and immunotherapy of osteosarcoma. On laser irradiation, Ce6 can generate reactive oxygen species (ROS) to kill cancer cells directly and induces immunogenic tumor cell death (ICD), which further facilitates the dendritic cell maturation induced by blockade of CD47 by aCD47. Moreover, both calreticulin released during ICD and CD47 blockade can accelerate phagocytosis of tumor cells by macrophages, promote antigen presentation, and eventually induce T lymphocyte-mediated antitumor immunity. Overall, the dual pH-sensitive nanodrug loaded with Ce6 and aCD47 showed excellent immune-activating and anti-tumor effects in osteosarcoma, which may lay the theoretical foundation for a novel combination model of osteosarcoma treatment.

The role of soluble adenylyl cyclase in sensing and regulating intracellular pH.

Soluble adenylyl cyclase (sAC) differs from transmembrane adenylyl cyclases (tmAC) in many aspects. In particular, the activity of sAC is not regulated by G-proteins but by the prevailing bicarbonate concentrations inside cells. Therefore, sAC serves as an exquisite intracellular pH sensor, with the capacity to translate pH changes into the regulation of localization and/or activity of cellular proteins involved in pH homeostasis. In this review, we provide an overview of literature describing the regulation of sAC activity by bicarbonate, pinpointing the importance of compartmentalization of intracellular cAMP signaling cascades. In addition, examples of processes involving proton and bicarbonate transport in different cell types, in which sAC plays an important regulatory role, were described in detail.

Characterization of an extremophile bacterial acid phosphatase derived from metagenomics analysis.

Acid phosphatases are enzymes that play a crucial role in the hydrolysis of various organophosphorous molecules. A putative acid phosphatase called FS6 was identified using genetic profiles and sequences from different environments. FS6 showed high sequence similarity to type C acid phosphatases and retained more than 30% of consensus residues in its protein sequence. A histidine-tagged recombinant FS6 produced in Escherichia coli exhibited extremophile properties, functioning effectively in a broad pH range between 3.5 and 8.5. The enzyme demonstrated optimal activity at temperatures between 25 and 50°C, with a melting temperature of 51.6°C. Kinetic parameters were determined using various substrates, and the reaction catalysed by FS6 with physiological substrates was at least 100-fold more efficient than with p-nitrophenyl phosphate. Furthermore, FS6 was found to be a decamer in solution, unlike the dimeric forms of crystallized proteins in its family.

A new insight into the surface adsorption in the solution phase: A modification of the Langmuir isotherm.

The Langmuir isotherm, originally developed to study the adsorption of gases, has been modified in this research to investigate the adsorption of solutes in the solution phase. The modification considers the adsorption of solvent molecules and the interactions between adsorbed particles and the species in the solution. Three equations have been obtained to calculate the contribution of these additional effects on the Gibbs free energy, enthalpy, and entropy of solute adsorption based on the new isotherm. The study evaluated the efficiency of the new isotherm in the adsorption of some metal ions in an aqueous solution and found that it is more accurate than the Langmuir isotherm and provides a deeper insight into the adsorption process in the solution phase. PRACTITIONER POINTS: Modification of the Langmuir isotherm for adsorption in solution. Comparison of the efficiency of the Langmuir and modified Langmuir isotherms. Accurate determination of ∆ H ads o $$ \Delta {H}_{ads}^o $$ and ∆ S ads o $$ \Delta {S}_{ads}^o $$ for Pb(II), Cd(II), and Ni(II) adsorption.

Effect of pH on the ozonolysis degradation of p-nitrophenol in aquatic environment and the synergistic effect of hydroxy radical.

Density functional theory (DFT) was employed to elucidate the mechanisms for ozonolysis reaction of p-nitrophenol (PNP) and its anion form aPNP. Thermodynamic data, coupled with Average Local Ionization Energies (ALIE) analysis, reveal that the ortho-positions of the OH/O- groups are the most favorable reaction sites. Moreover, rate constant calculations demonstrate that the O3 attack on the C2-C3 bond is the predominant process in the reaction between neutral PNP and O3. For the aPNP + O3 reaction, the most favorable pathways involve O3 attacking the C1-C2 and C6-C1 bonds. The rate constant for PNP ozonolysis positively correlates with pH, ranging from 5.47 × 108 to 2.86 × 109 M-1 s-1 in the natural aquatic environment. In addition, the formation of hydroxyl radicals in the ozonation process of PNP and the mechanisms of its synergistic reaction of PNP with ozone were investigated. Furthermore, the ozonation and hydroxylation processes involving the intermediate OH-derivatives were both thermodynamically and kinetic analyzed, which illustrate that OH radicals could promote the elimination of PNP. Finally, the toxic of PNP and the main products for fish, daphnia, green algae and rat were assessed. The findings reveal that certain intermediates possess greater toxicity than the original reactant. Consequently, the potential health risks these compounds pose to organisms warrant serious consideration.

Physiological responses of European sea bass (Dicentrarchus labrax) exposed to increased carbon dioxide and reduced seawater salinities.

BACKGROUND: The iono- and osmoregulatory capacities of marine teleosts, such as European sea bass (Dicentrarchus labrax) are expected to be challenged by high carbon dioxide exposure, and the adverse effects of elevated CO2 could be amplified when such fish migrate into less buffered hypo-osmotic estuarine environments. Therefore, the effects of increased CO2 on the physiological responses of European sea bass (Dicentrarchus labrax) acclimated to 32 ppt, 10 ppt and 2.5 ppt were investigated. METHODS: Following acclimation to different salinities for two weeks, fish were exposed to present-day (400 µatm) and future (1000 µatm) atmospheric CO2 for 1, 3, 7 and 21 days. Blood pH, plasma ions (Na+, K+, Cl-), branchial mRNA expression of ion transporters such as Na+/K+-ATPase (NKA), Na+/K+/2Cl- co-transporters (NKCC) and ammonia transporters (e.g. Rhesus glycoproteins Rhbg, Rhcg1 and Rhcg2) were examined to understand the iono- and osmoregulatory consequences of elevated CO2. RESULTS: A transient but significant increase in the blood pH of exposed fish acclimated at 10 ppt (day 1) and 2.5 ppt (day 21) was observed possibly due to an overshoot of the blood HCO3- accumulation while a significant reduction of blood pH was observed after 21 days at 2.5ppt. However, no change was seen at 32 ppt. Generally, Na + concentration of control fish was relatively higher at 10 ppt and lower at 2.5 ppt compared to 32 ppt control group at all sampling periods. Additionally, NKA was upregulated in gill of juvenile sea bass when acclimated to lower salinities compared to 32 ppt control group. CO2 exposure generally downregulated NKA mRNA expression at 32ppt (day 1), 10 ppt (days 3, 7 and 21) and 2.5ppt (days 1 and 7) and also a significant reduction of NKCC mRNA level of the exposed fish acclimated at 32 ppt (1-3 days) and 10 ppt (7-21 days) was observed. Furthermore, Rhesus glycoproteins were generally upregulated in the fish acclimated at lower salinities indicating a higher dependance on gill ammonia excretion. Increased CO2 led to a reduced expression of Rhbg and may therefore reduce ammonia excretion rate. CONCLUSION: Juvenile sea bass were relatively successful in keeping acid base balance under an ocean acidification scenario. However, this came at a cost for ionoregulation with reduced NKA, NKCC and Rhbg expression rates as a consequence.

Effect of pH on the solubility and volumetric change of ready-to-use Bio-C Repair bioceramic material.

Acidic pH can modify the properties of repair cements. In this study, volumetric change and solubility of the ready-to-use bioceramic repair cement Bio-C Repair (BCR, Angelus, Londrina, PR, Brazil) were evaluated after immersion in phosphate-buffered saline (PBS) (pH 7.0) or butyric acid (pH 4.5). Solubility was determined by the difference in initial and final mass using polyethylene tubes measuring 4 mm high and 6.70 mm in internal diameter that were filled with BCR and immersed in 7.5 mL of PBS or butyric acid for 7 days. The volumetric change was established by using bovine dentin tubes measuring 4 mm long with an internal diameter of 1.5 mm. The dentin tubes were filled with BCR at 37°C for 24 hours. Scanning was performed with micro-computed tomography (micro-CT; SkyScan 1176, Bruker, Kontich, Belgium) with a voxel size of 8.74 µm. Then, the specimens were immersed in 1.5 mL of PBS or butyric acid at and 37 °C for 7 days. After this period, a new micro-CT scan was performed. Bio-C Repair showed greater mass loss after immersion in butyric acid when compared with immersion in PBS (p<0.05). Bio-C Repair showed volumetric loss after immersion in butyric acid and increase in volume after immersion in PBS (p<0.05). The acidic pH influenced the solubility and dimensional stability of the Bio-C Repair bioceramic cement, promoting a higher percentage of solubility and decrease in volumetric values.