Altered Redox Potential Research Articles

Replacement of Tyrosines by Unnatural Amino Acid Aminophenylalanine Leads to Metal-Mediated Aniline Free Radical Formation in a Copper Amine Oxidase.

Copper amine oxidases (CAOs) catalyze the oxidative deamination of primary amines to aldehyde, ammonia, and hydrogen peroxide as products and are widely distributed in bacteria, plants, and eukaryotes. These enzymes initiate the single turnover, post-translational conversion of an active site tyrosine to the redox cofactor 2,4,5-trihydroxyphenylalanine quinone (TPQ), subsequently employing TPQ to catalyze steady-state amine oxidation. The mechanisms of TPQ biogenesis and steady-state amine oxidation have been studied extensively, with consensus mechanisms proposed for both reactions. One unresolved issue has been whether the Cu2+ center must undergo formal reduction to Cu1+ in the course of the reaction. Herein, we investigate the properties of the active site of a yeast (Hansenula polymorpha) amine oxidase (HPAO) that has undergone site-specific insertion of a para-aminophenylalanine (pAF) into the position of either the precursor tyrosine to TPQ (Y405) or the two strictly conserved neighboring tyrosines (Y305 and Y407). While our original intention was to interrogate cofactor biogenesis using a precursor unnatural amino acid (UAA) of altered redox potential and pKa, we instead observe an unanticipated reaction assigned to an intramolecular electron transfer from pAF to the active site copper ion. We establish the generality of the observed active site chemistry using exogenously added, aniline-containing substrates under conditions that prevent side chain amine oxidation. The results support previous proposals that the activation of the TPQ precursor occurs in the absence of a formal valence change at the active site copper site. The described reaction of pAFs with the active site redox Cu2+ center of HPAO provides a prototype for either the engineering of the enzymatic oxidation of exogenous anilines or the insertion of site-specific free radical probes within proteins.

AMP, ADP, and ATP Concentrations Differentially Affected by Meat Processing, Manufacturing, and Nonmeat Ingredients

Given its presence in a wide spectrum of soils relevant to food process hygiene, the biological metabolite adenosine triphosphate (ATP) is used as a target for surface hygiene assessments in food processing facilities. Yet, ample evidence demonstrates that ATP is depleted into adenosine di- (ADP) and monophosphate (AMP) homologs resulting in a loss of sensitivity for ATP-based hygiene assays. Yet, there are few studies that denote the degree of these shifts under routine processing conditions such as those encountered during various meat processing steps that may likely alter redox potential and adenosine profiles (e.g., tissue/cellular disruption, application of reducing additives, fermentation, or thermal treatment steps). In this study, meat samples were collected from homogenized beef tissue treated with nonmeat ingredients (sodium chloride, sodium nitrite, sodium erythorbate, natural smoke condensate, and sodium acid pyrophosphate) during manufacture at predetermined steps, and from retail meat products purchased from local markets. Concentrations of ATP, ADP, AMP, and AXP (sum concentration of all homologs) in a lab setting and in situ meat processing venues were determined and compared. Greater differences in AXP were seen during manufacture, where ADP generally comprised ∼90% as a mole fraction of AXP across all treatments, with the exception of the final cook step where AMP predominated. ATP concentrations averaged 2 log values lower than ADP and AMP. Adenosine profiles in retail samples followed similar trends with minimal ATP concentrations with ADP predominant in uncooked samples and AMP predominant in cooked samples. Resultingly, meat processing steps during product manufacture will alter AXP-reliant test sensitivities which should be considered when such technologies are utilized for hygiene verification in meat processing.

Dopant-driven recombination delay and ROS enhancement in nanoporous Cd1-xCuxS heterogeneous photocatalyst for the degradation of DR-23 dye under visible light irradiation

Developing an efficient heterogeneous photocatalyst for environmental remediation and treatment strategies using visible light harvesting processes is promising but challenging. Herein, Cd1-xCuxS materials have been synthesized and characterized by precise analytical tools. Cd1-xCuxS materials exhibited excellent photocatalytic activity for direct Red 23 (DR-23) dye degradation in visible light irradiation. The operational parameters, like dopant concentration, photocatalyst dose, pH, and initial concentration of dye were investigated during the process. The photocatalytic degradation process follows pseudo-first-order kinetics. As compared to other tested materials, 5% Cu doped CdS material revealed superior photocatalytic performance for the degradation of DR-23 (k = 13.96 × 10−3 min−1). Transient absorption spectroscopy, EIS, PL, and transient photocurrent indicated that adding copper to the CdS matrix improved the separation of photo-generated charge carriers by lowering the recombination rate. Spin-trapping experiments recognized the photodegradation primarily based on secondary redox products, i.e., hydroxyl and superoxide radicals. According to by Mott-Schottky curves, photocatalytic mechanism and photo-generated charge carrier density were elucidated regarding dopant-induced valence and conduction bands shifting. Thermodynamic probability of radical formation in line with the altered redox potentials by Cu doping has been discussed in the mechanism. The identification of intermediates by mass spectrometry study also showed a plausible breakdown mechanism for DR-23. Moreover, samples treated with nanophotocatalyst displayed excellent results when tested for water quality metrics such as DO, TDS, BOD, and COD. Developed nanophotocatalyst shows high recyclability with superior heterogeneous nature. 5% Cu-doped CdS also exhibit strong photocatalytic activity for the degradation of colourless pollutant bisphenol A (BPA) under visible light (k = 8.45 × 10−3 min−1). The results of this study offer exciting opportunities to alter semiconductors' electronic band structures for visible-light-induced photocatalytic activity for wastewater treatment.

Gut redox potential affects host susceptibility to pathogen infection

Redox potential is a key environmental indicator in the gut and also significantly affects host health. To study the influence of gut redox potential on the infection of hosts by pathogen, we employed zebrafish and common carp as animal models to investigate the relationship between gut redox potential and host susceptibility. Our results proved that gut redox potential was significantly elevated after host infection with pathogenic bacteria. Moreover, the level of reactive oxygen species (ROS) was significantly and positively correlated with gut redox potential. Reduction of the gut redox potential with antioxidants significantly improved host resistance to pathogen infections. In addition, when the host was infected with pathogen, the reduction of gut redox potential could improve survival. Interestingly, the combination of antioxidants and low concentrations of antibiotics could achieve a similar therapeutic effect to that of a single high concentration of antibiotics by reducing the gut redox potential. Overall, this study proved that altered redox potential could aid in the host resistance to infection, and also provides new perspectives for the treatment of pathogen infections.

Dual-Targeted Hyaluronic Acid/Albumin Micelle-Like Nanoparticles for the Vectorization of Doxorubicin.

Drug targeting of tumor cells is one of the great challenges in cancer therapy; nanoparticles based on natural polymers represent valuable tools to achieve this aim. The ability to respond to environmental signals from the pathological site (e.g., altered redox potential), together with the specific interaction with membrane receptors overexpressed on cancer cells membrane (e.g., CD44 receptors), represent the main features of actively targeted nanoparticles. In this work, redox-responsive micelle-like nanoparticles were prepared by self-assembling of a hyaluronic acid–human serum albumin conjugate containing cystamine moieties acting as a functional spacer. The conjugation procedure consisted of a reductive amination step of hyaluronic acid followed by condensation with albumin. After self-assembling, nanoparticles with a mean size of 70 nm and able to be destabilized in reducing media were obtained. Doxorubicin-loaded nanoparticles modulated drug release rate in response to different redox conditions. Finally, the viability and uptake experiments on healthy (BALB-3T3) and metastatic cancer (MDA-MB-231) cells proved the potential applicability of the proposed system as a drug vector in cancer therapy.

Involvements of Hyperhomocysteinemia in Neurological Disorders

Homocysteine (HCY), a physiological amino acid formed when proteins break down, leads to a pathological condition called hyperhomocysteinemia (HHCY), when it is over a definite limit. It is well known that an increase in HCY levels in blood, can contribute to arterial damage and several cardiovascular disease, but the knowledge about the relationship between HCY and brain disorders is very poor. Recent studies demonstrated that an alteration in HCY metabolism or a deficiency in folate or vitamin B12 can cause altered methylation and/or redox potentials, that leads to a modification on calcium influx in cells, or into an accumulation in amyloid and/or tau protein involving a cascade of events that culminate in apoptosis, and, in the worst conditions, neuronal death. The present review will thus summarize how much is known about the possible role of HHCY in neurodegenerative disease.

Compensation of Mutation in Arabidopsis glutathione transferase (AtGSTU) Genes under Control or Salt Stress Conditions.

Glutathione transferases (GSTs) play a crucial role in detoxification processes due to the fact of their glutathione (GSH) conjugating activity, and through glutathione peroxidase or dehydroascorbate reductase (DHAR) activities, they influence the redox state of GSH and ascorbate (AsA). The plant-specific tau (GSTU) group is the largest class of Arabidopsis GSTs, and their members are involved in responses to different abiotic stresses. We investigated the effect of salt stress on two-week-old Arabidopsis thaliana wild-type (Col-0), Atgstu19 and Atgstu24 mutant plants after applying 150 mM NaCl for two days. The Atgstu19 seedlings had lower GST activity and vitality both under control conditions and after salt stress than the wild-type, but the level of total ROS was similar to the Col-0 plants. The GST activity of the knockout Atgstu24 mutant was even higher under control conditions compared to the Col-0 plants, while the ROS level and its vitality did not differ significantly from the wild-type. Analysis of the AtGSTU expression pattern revealed that the mutation in a single AtGSTU gene was accompanied by the up- and downregulation of several other AtGSTUs. Moreover, elevated AsA and GSH levels, an altered GSH redox potential and increased DHAR and glutathione reductase activities could help to compensate for the mutation of AtGSTU genes. The observed changes in the mutants suggest that the investigated isoenzymes influence the redox homeostasis under control conditions and after NaCl treatment in Arabidopsis seedlings. These data indicate for the first time the more general role of a temporary shift of redox status as part of GST mechanisms and regulation.

Multiple sclerosis drug FTY-720 toxicity is mediated by the heterotypic fusion of organelles in neuroendocrine cells

FTY-720 (Fingolimod) was one of the first compounds authorized for the treatment of multiple sclerosis. Among its other activities, this sphingosine analogue enhances exocytosis in neuroendocrine chromaffin cells, altering the quantal release of catecholamines. Surprisingly, the size of chromaffin granules is reduced within few minutes of treatment, a process that is paralleled by the homotypic fusion of granules and their heterotypic fusion with mitochondria, as witnessed by dynamic confocal and TIRF microscopy. Electron microscopy studies support these observations, revealing the fusion of several vesicles with individual mitochondria to form large, round mixed organelles. This cross-fusion is SNARE-dependent, being partially prevented by the expression of an inactive form of SNAP-25. Fused mitochondria exhibit an altered redox potential, which dramatically enhances cell death. Therefore, the cross-fusion of intracellular organelles appears to be a new mechanism to be borne in mind when considering the effect of FTY-720 on the survival of neuroendocrine cells.

Agroecological assessment of the effectiveness of irrigation of tomato using electrolyzed water

Aim. The purpose of the research is to quantify the agroecological response of plants and the bio‐productivity of crops to irrigation using electrochemical water treatment technology. Material and Methods. The study was carried out using the tomato (Solanum lycoparsicum, hybrid Pink Paradise F1) in a protected ground culture as an example. The experimental site is located in the dry‐steppe zone of light chestnut soils of the Lower Volga region (48о56΄46˝N44о51΄45˝E). The magnitude of the electrochemically initiated shift of the redox potential of irrigation water and the options for combining the use of electrochemically treated water were taken as variable experimental factors. Results. It was established that the magnitude of the electrochemically initiated shift of the redox potential of irrigation water has a predominant effect on the estimated biometric indicators: the coefficient of variation of the indicators for this factor reached 9.5‐38.0%. The influence of the method of using electrochemically treated water is estimated at 4.12‐10.24%, but regarding net assimilation the significance of this factor is not statistically proven. The highest estimates of linear growth – 2.21 m, maximum leaf area – 43.4 thousand m2/ha, accumulated biomass – 13.39 t/ha, photosynthetic potential – 3617 thousand m2 days/ha and tomato biological yield – 140.0 t/ha, obtained by the combined use of a catholyte for vegetation and fertilizer irrigation with an electrochemically initiated shift of the redox potential (‐500) mV. Conclusion. The studies have proved the statistical significance of the biometric response of tomato plants to the use of water with electrochemically altered redox potential for vegetation and fertilizer irrigation.

The redox-dependent regulation of satellite cells following aseptic muscle trauma (SpEED): study protocol for a randomized controlled trial

BackgroundMuscle satellite cells (SCs) are crucial for muscle regeneration following muscle trauma. Acute skeletal muscle damage results in inflammation and the production of reactive oxygen species (ROS) which may be implicated in SCs activation. Protection of these cells from oxidative damage is essential to ensure sufficient muscle regeneration. The aim of this study is to determine whether SCs activity under conditions of aseptic skeletal muscle trauma induced by exercise is redox-dependent.Methods/designBased on the SCs content in their vastus lateralis skeletal muscle, participants will be classified as either high or low respondents. In a randomized, double-blind, crossover, repeated-measures design, participants will then receive either placebo or N-acetylcysteine (alters redox potential in muscle) during a preliminary 7-day loading phase, and for eight consecutive days following a single bout of intense muscle-damaging exercise. In both trials, blood samples and muscle biopsies will be collected, and muscle performance and soreness will be measured at baseline, pre-exercise, 2 and 8 days post exercise. Biological samples will be analyzed for redox status and SCs activity. Between trials, a 4-week washout period will be implemented.DiscussionThis study is designed to investigate the impact of redox status on SCs mobilization and thus skeletal muscle potential for regeneration under conditions of aseptic inflammation induced by exercise. Findings of this trial should provide insight into (1) molecular pathways involved in SCs recruitment and muscle healing under conditions of aseptic skeletal muscle trauma present in numerous catabolic conditions and (2) whether skeletal muscle’s potential for regeneration depends on its basal SCs content.Trial registrationClinicalTrials.gov, ID: NCT03711838. Registered on 19 Oct 2018.

Changes in the microbial consortium during dark hydrogen fermentation in a bioelectrochemical system increases methane production during a two-stage process

BackgroundBioelectrochemical systems (BESs) are an innovative technology developed to influence conventional anaerobic digestion. We examined the feasibility of applying a BES to dark hydrogen fermentation and its effects on a two-stage fermentation process comprising hydrogen and methane production. The BES used low-cost, low-reactivity carbon sheets as the cathode and anode, and the cathodic potential was controlled at − 1.0 V (vs. Ag/AgCl) with a potentiostat. The operation used 10 g/L glucose as the major carbon source.ResultsThe electric current density was low throughout (0.30–0.88 A/m2 per electrode corresponding to 0.5–1.5 mM/day of hydrogen production) and water electrolysis was prevented. At a hydraulic retention time of 2 days with a substrate pH of 6.5, the BES decreased gas production (hydrogen and carbon dioxide contents: 52.1 and 47.1%, respectively), compared to the non-bioelectrochemical system (NBES), although they had similar gas compositions. In addition, a methane fermenter (MF) was applied after the BES, which increased gas production (methane and carbon dioxide contents: 85.1 and 14.9%, respectively) compared to the case when the MF was applied after the NBES. Meta 16S rRNA sequencing revealed that the BES accelerated the growth of Ruminococcus sp. and Veillonellaceae sp. and decreased Clostridium sp. and Thermoanaerobacterium sp., resulting in increased propionate and ethanol generation and decreased butyrate generation; however, unknowingly, acetate generation was increased in the BES.ConclusionsThe altered redox potential in the BES likely transformed the structure of the microbial consortium and metabolic pattern to increase methane production and decrease carbon dioxide production in the two-stage process. This study showed the utility of the BES to act on the microbial consortium, resulting in improved gas production from carbohydrate compounds.

Stimuli-responsive polymeric micelles for drug delivery and cancer therapy.

Polymeric micelles (PMs) have been widely investigated as nanocarriers for drug delivery and cancer treatments due to their excellent physicochemical properties, drug loading and release capacities, facile preparation methods, biocompatibility, and tumor targetability. They can be easily engineered with various functional moieties to further improve their performance in terms of bioavailability, circulation time, tumor specificity, and anticancer activity. The stimuli-sensitive PMs capable of responding to various extra- and intracellular biological stimuli (eg, acidic pH, altered redox potential, and upregulated enzyme), as well as external artificial stimuli (eg, magnetic field, light, temperature, and ultrasound), are considered as “smart” nanocarriers for delivery of anticancer drugs and/or imaging agents for various therapeutic and diagnostic applications. In this article, the recent advances in the development of stimuli-responsive PMs for drug delivery, imaging, and cancer therapy are reviewed. The article covers the generalities of stimuli-responsive PMs with a focus on their major delivery strategies and newly emerging technologies/nanomaterials, discusses their drawbacks and limitations, and provides their future perspectives.

Detection of salivary heat shock protein 27 by enzyme-linked immunosorbent assay and its correlation with histopathology of oral leukoplakia.

Context:Salivary analytes may be used as biomarkers for translational and clinical applications. Heat shock proteins (Hsps) are ubiquitous, highly conserved proteins found in all prokaryotic and eukaryotic species. Hsp27, a low molecular weight protein, may act as a salivary biomarker. Leukoplakia is the most common oral potentially malignant disorder and various salivary biomarkers such as interleukin-6, 8, tumor necrosis factor-α and MMPs have been detected in it. Oral leukoplakia presents clinically as homogenous and nonhomogenous forms; the microscopic pattern ranges from simple epithelial hyperplasia to carcinoma in situ.Aims:This study aims to detect salivary Hsp27 in oral leukoplakia by enzyme-linked immunosorbent assay (ELISA) and to correlate its expression pattern with histopathology.Materials and Methods:A total of 45 cases had constituted the study group. Salivary Hsp27 levels were assessed by ELISA in histopathologically confirmed cases of oral leukoplakia and were compared with that of healthy volunteers.Statistical Analysis:Mann–Whitney U-test and Spearman's correlation coefficient were used for the detection of Hsp27 and its correlation with mean absorbance levels.Results:The mean absorbance values had shown elevated expression of Hsp27 in oral leukoplakia when compared to that in healthy volunteers.Conclusions:The present study had shown elevated expression of salivary Hsp27 in oral leukoplakia which could be attributed to altered redox potential.

013 Prostaglandin D2 enhances testosterone metabolism by ROS-mediated altered redox potential in keratinocytes

013 Prostaglandin D2 enhances testosterone metabolism by ROS-mediated altered redox potential in keratinocytes

Multifunctional Liposomes.

Liposomes have come a long way since their conception in the 1960s, when they were envisioned primarily for drug delivery. Besides serving the important function of the delivery of a variety of drugs, liposomes offer a platform for the co-delivery of a range of therapeutic and diagnostic agents with different physicochemical properties. They are also amenable to the addition of various targeting moieties such as proteins, sugars, and antibodies for selective targeting at a desired site, including tumors. Currently, the design of stimuli-sensitive liposomes for drug delivery is a lively area of research. Compared to conventional liposomes, stimuli-sensitive nanoplatforms respond to local conditions that are characteristics of the pathological area of interest, allowing the release of active agents at the targeted site. Acidic pH, abnormal levels of enzymes, temperature, altered redox potential, and external magnetic field are examples of internal and external stimuli exploited in the design of stimuli-sensitive liposomes. The penetration of the liposomes into the cells can be enhanced with the help of a variety of cell penetrating peptides, which can be incorporated into the liposomes with the help of various lipid-polymer conjugates. Liposomes are now being employed in diagnostics as well. Imaging of a tumor can be made easier by the inclusion of fluorescent probes. They can also be used for gamma or MR imaging using chelated reporter metals and incorporating them either into the core of the liposome or in the lipid bilayer facing outwards. In this chapter, we discuss methods that are commonly used for the preparation of liposomes with a vast range of functions to meet a variety of needs in diagnostics and drug delivery.

Phase 3 Study of L-Glutamine Therapy in Sickle Cell Anemia and Sickle β0-Thalassemia Subgroup Analyses Show Consistent Clinical Improvement

Background: Sickle cell disease (SCD) is characterized by continuous oxidative stress through various mechanisms contributing to the pathophysiology and clinical course of sickle cell crises (SCC) and organ damage. L-glutamine is a precursor for the synthesis of essential metabolic redox cofactors including Nicotinamide Adenine Dinucleotide (NAD). Early studies have demonstrated that altered erythrocyte NAD redox potential was improved by oral L-glutamine therapy, suggesting that higher L-glutamine utilization in SCD exceeded de novo synthesis and its depletion played a role in oxidative stress.A Phase 2 study of Pharmaceutical Grade L-glutamine (L-glutamine) versus placebo showed promising results on clinical endpoints. In a Phase 3 study with 230 SCD patients, randomized 2:1 to L-glutamine or placebo, the median number of SCCs was 25% lower for L-glutamine than placebo (L-glutamine 3.0 vs. placebo 4.0). An analysis of SCC events showed significant differences between groups (p < 0.01). Categories for pre-specified subgroups for Age, Gender and Hydroxyurea (HU) use were defined in the statistical plan. HU use was also a randomization stratification factor since HU is the only FDA-approved drug for SCD treatment. Examination of the HU subgroup for differences in L-glutamine effect across categories (HU vs. no HU) was appropriate since approximately 66% of patients remained on HU throughout the Phase 3 study. To investigate the subgroup treatment effect size, treatment by subgroup interaction and consistency of the primary endpoint across the categories of the subgroups, an examination was performed following the guidelines for reporting subgroup analysis.Methods: The Negative Binomial Regression (NBR) model was utilized to generate an estimate of treatment effect and treatment by subgroup interactions of the three pre-specified subgroups. SCC events are most accurately described as counts and NBR is specifically intended for modeling count variables, usually for over-dispersed counts as seen in SCD studies. Rates of SCC for each treatment arm in a subgroup (Rate L-glutamine per 48 weeks / Rate placebo per 48 weeks) provide rate ratios, and an estimate of effect size, with 95% confidence intervals. A rate ratio <1.0 favored L-glutamine. Tests for treatment by subgroup interactions were conducted simultaneously. A significant interaction could be seen if the treatment is better than placebo for one category and worse than placebo for the other. Predefined categories for subgroups with corresponding sample sizes were as follows: Age: 5 - 18 years (n = 118) and ≥ 18 years (n = 111); Gender: Females (n = 124) and Males (n = 105). HU use before and during study: Yes (n = 153) and No (n = 76). Data for this Phase 3 subgroup report were obtained from an integrated dataset and the NBR model with treatment, subgroup, region and HU use as main effects and a treatment by subgroup interaction term was run with log (time on study) as an offset.Results:Age Subgroup:Both the 5 - 18 years and the > 18 years groups had a lower rate of SCCs per 48 weeks in the L-glutamine arm relative to placebo. The rate ratio was 0.93 [0.67 - 1.29] for the 5 - 18 years group and 0.64 [0.45 - 0.89] in the > 18 years group. There was no treatment by Age Group interaction (p = 0.118).Gender Subgroup: Both the Female and the Male groups had a lower rate of SCCs per 48 weeks in the L-glutamine treatment arm. The rate ratio was 0.81 [0.59 -1.12] for the Female group and 0.73 [0.51 - 1.05] for the Male group, indicating consistent treatment effects across genders. There was no treatment by Gender interaction (p = 0.683).Hydroxyurea Use Subgroup: Both HU groups had a lower rate of SCCs per 48 weeks in the L-glutamine arm. The treatment effects were consistent across groups, with a rate ratio of 0.78 [0.51 - 1.20] for the group without HU use and 0.77 [0.58 - 1.03] for the group with HU use. There was no treatment by HU use interaction (p = 0.961). See Figure 1 for a graphic example.Conclusion: For the Age and Gender subgroups, both categories in each subgroup benefited from L-glutamine but to varying degrees noted by the difference in rate ratios. For the HU use subgroup, both categories (on HU and not on HU) benefited from L-glutamine similarly. Lack of interactions in all subgroups indicated that regardless of category within a subgroup, treatment effect by Pharmaceutical Grade L-glutamine was beneficial. [Display omitted] DisclosuresNiihara:Emmaus Medical, Inc.: Employment, Equity Ownership. Viswanathan:Novartis: Speakers Bureau. Razon:Emmaus Medical, Inc.: Employment. Tran:Emmaus Medical, Inc.: Employment, Equity Ownership. Stark:Emmaus Medical, Inc.: Employment, Equity Ownership.

O ascorbato de sódio promove a resistência de união após técnicas de clareamento dental?

Objective: To summarize and discuss the available information concerning the effectiveness of sodium ascorbate in improving bond strength after dental bleaching procedures. Methods: Information of original articles or reviews listed in PubMed database using searching terms: (“sodium ascorbate” OR antioxidant) AND (bleaching OR hydrogen peroxide OR carbamide peroxide), were included in the review. Results: Most of studies revealed that sodium ascorbate could restore the altered redox potential of the oxidized bonding substrate, thus reversing the compromised bonding. However, several protocols of this antioxidant have been used in combination with different peroxide concentrations and exposure time to bleaching agents. Conclusion: Studies should be conducted to establish an appropriate application protocol and to evaluate the effect of sodium ascorbate in other dental properties.

SiRNA Delivery by Stimuli-Sensitive Nanocarriers.

Since its discovery in the late 1990, small interfering RNA (siRNA) have quickly crept into the biopharmaceutical research as a new and powerful tool for the treatment of different human diseases based on altered gene-expression. Despite promising data from many pre-clinical studies, concrete hurdles still need to be overcome to bring therapeutic siRNAs in clinic. The design of stimuli-sensitive nanopreparations for gene therapy is a lively area of the current research. Compared to conventional systems for siRNA delivery, this type of platform can respond to local stimuli that are characteristics of the pathological area of interest, allowing the release of nucleic acids at the desired site. Acidic pH, de-regulated levels of enzymes, altered redox potential and magnetic field are examples of stimuli exploit to design stimuli-sensitive nanoparticles. In this review, we discuss on recent stimulisensitive strategies for siRNA delivery and we highlight on the potential of combining multiple stimuli-sensitive strategies in the same nano-platform for a better therapeutic outcome.

Novel Redox-Responsive Amphiphilic Copolymer Micelles for Drug Delivery: Synthesis and Characterization.

A novel redox-responsive amphiphilic polymer was synthesized with bioreductive trimethyl-locked quinone propionic acid for a potential triggered drug delivery application. The aim of this study was to synthesize and characterize the redox-responsive amphiphilic block copolymer micelles containing pendant bioreductive quinone propionic acid (QPA) switches. The redox-responsive hydrophobic block (polyQPA), synthesized from QPA-serinol and adipoyl chloride, was end-capped with methoxy poly(ethylene glycol) of molecular weight 750 (mPEG750) to achieve a redox-responsive amphiphilic block copolymer, polyQPA-mPEG750. PolyQPA-mPEG750 was able to self-assemble as micelles to show a critical micelle concentration (CMC) of 0.039% w/v (0.39mg/ml, 0.107mM) determined by a dye solubilization method using 1,6-diphenyl-1,3,5-hexatriene (DPH) in phosphate-buffered saline (PBS). The mean diameter of polymeric micelles was found to be 27.50nm (PI = 0.064) by dynamic light scattering. Furthermore, redox-triggered destabilization of the polymeric micelles was confirmed by (1)H-NMR spectroscopy and particle size measurements in a simulated redox state. PolyQPA-mPEG750 underwent triggered reduction to shed pendant redox-responsive QPA groups and its polymeric micelles were swollen to be dissembled in the presence of a reducing agent, thereby enabling the release of loaded model drug, paclitaxel. The redox-responsive polyQPA-mPEG750 polymer micelles would be useful as a drug delivery system allowing triggered drug release in an altered redox state such as tumor microenvironments with an altered redox potential and/or redox enzyme upregulation.

Redox Modulation of Flavin and Tyrosine Determines Photoinduced Proton-coupled Electron Transfer and Photoactivation of BLUF Photoreceptors

Photoinduced electron transfer in biological systems, especially in proteins, is a highly intriguing matter. Its mechanistic details cannot be addressed by structural data obtained by crystallography alone because this provides only static information on a given redox system. In combination with transient spectroscopy and site-directed manipulation of the protein, however, a dynamic molecular picture of the ET process may be obtained. In BLUF (blue light sensors using FAD) photoreceptors, proton-coupled electron transfer between a tyrosine and the flavin cofactor is the key reaction to switch from a dark-adapted to a light-adapted state, which corresponds to the biological signaling state. Particularly puzzling is the fact that, although the various naturally occurring BLUF domains show little difference in the amino acid composition of the flavin binding pocket, the reaction rates of the forward reaction differ quite largely from a few ps up to several hundred ps. In this study, we modified the redox potential of the flavin/tyrosine redox pair by site-directed mutagenesis close to the flavin C2 carbonyl and fluorination of the tyrosine, respectively. We provide information on how changes in the redox potential of either reaction partner significantly influence photoinduced proton-coupled electron transfer. The altered redox potentials allowed us furthermore to experimentally describe an excited state charge transfer intermediately prior to electron transfer in the BLUF photocycle. Additionally, we show that the electron transfer rate directly correlates with the quantum yield of signaling state formation.