Hydrophilic interaction liquid chromatography based method for simultaneous determination of purines and their derivatives in food spices

This work presents method for separation and quantification of adenine, guanine, xanthine, hypoxanthine, uric acid, and creatinine in food spices using hydrophilic interaction liquid chromatography with UV detection. Optimized conditions allowed separation with mobile phases containing acetonitrile and additives ammonium acetate (90:10, v/v, pH 6.1) or formate (90:10, v/v, pH 3.2). In food spices no uric acid was detected, creatinine (16 ± 2 μg g-1) was found only in instant dried yeast. The highest content of purines was determined in dried yeast (xanthine 110 ± 8 μg g-1, hypoxanthine 441 ± 24 μg g-1, adenine 84 ± 16 μg g-1, guanine 163 ± 12 μg g-1), high in curry, herbal pepper, and chicken seasoning, the lowest concentration was in black pepper (hypoxanthine 12 ± 2 μg g-1, adenine 27 ± 3 μg g-1). To best of our knowledge, no such complementary method and obtained data have been reported so far.

Exposure of children to brominated flame retardants and heavy metals in Morocco: Urine and blood levels in association with global cytosine and adenine methylation

Persistent pollutants, namely brominated flame retardants (BFRs) and heavy metals, are compounds that are added to a wide range of products and materials for preventing ignition, increasing the functionality of materials or improving their performance, e.g. electric conductivity. The exposure of children might consequently be inferred, through indoor dust and hand-to-mouth or toy-chewing behaviors. The current study is aimed at assessing the exposure of Moroccan children to BFRs and heavy metal elements, and evaluating their associations with global DNA methylation. First, parents responded to a questionnaire pertaining to children's lifestyle, then blood and urine samples were collected from (n = 93) children aged between 5 and 11 years for biomonitoring and DNA methylation analysis. BFRs were detected in 54.84% of samples with a median concentration of 0.01 nmol/mL (range: 0.004-0.051 nmol/mL) while metal elements were detected in more than 90% of samples. BFRs showed no variations with global DNA methylation, unlike metal elements, which revealed significant associations with global DNA methylation markers, namely 5-mC, 5-hmC and N⁶-mA levels. Moroccan children may be exposed to flame retardants and heavy metals through several routes. Further research is required to assess the exposure and the health impacts of environmental pollutants and ultimately protect the Moroccan population by the prevention of adverse health effects.

Exploiting Purine as an Internal Standard for SERS Quantification of Purine Derivative Molecules Released by Bacteria

Surface-enhanced Raman scattering (SERS) is a highly sensitive technique used in diverse biomedical applications including rapid antibiotic susceptibility testing (AST). However, signal fluctuation in SERS, particularly the widespread of signals measured from different batches of SERS substrates, compromises its reliability and introduces potential errors in SERS-AST. In this study, we investigate the use of purine as an internal standard (IS) to recalibrate SERS signals and quantify the concentrations of two important purine derivatives, adenine and hypoxanthine, which are the most important biomarkers used in SERS-AST. Our findings demonstrate that purine IS effectively mitigates SERS signal fluctuations and enables accurate prediction of adenine and hypoxanthine concentrations across a wide range (5 orders of magnitude). Calibrations with purine as an IS outperform those without, exhibiting a 10-fold increase in predictive accuracy. Additionally, the calibration curve obtained from the first batch of SERS substrates remains effective for 64 additional substrates fabricated over a half-year period. Measurements of adenine and hypoxanthine concentrations in bacterial supernatants using SERS with purine IS closely align with the liquid chromatography-mass spectrometry results. The use of purine as an IS offers a simple and robust platform to enhance the speed and accuracy of SERS-AST, while also paving the way for in situ SERS quantification of purine derivatives released by bacteria under various stress conditions.

Genome-wide DNA N6-adenine methylation in sea buckthorn (Hippophae rhamnoides L.) fruit development

As a new epigenetic mark, DNA N6-adenine (6mA) methylation plays an important role in various biological processes and has been reported in many prokaryotic organisms in recent years. However, the distribution patterns and functions of DNA 6mA modification have been poorly studied in non-model crops. In this study, we observed that the methylation ratio of 6mA was about 0.016% in the sea buckthorn (Hippophae rhamnoides L.) genome using mass spectrometry. We first constructed a comprehensive 6mA landscape in sea buckthorn genome using nanopore sequencing at single-base resolution. Distribution analysis suggested that 6mA methylated sites were widely distributed in the sea buckthorn chromosomes, which were similar to those in Arabidopsis and rice. Furthermore, reduced 6mA DNA methylation is associated with different expression of genes related to the fruit-ripening process in sea buckthorn. Our results revealed that 6mA DNA modification could be considered an important epigenomic mark and contributes to the fruit ripening process in plants.

Incorporation of a FRET Pair into a Riboswitch RNA to Measure Mg2+ Concentration and RNA Conformational Change in Cell

Riboswitches are natural biosensors that can regulate gene expression by sensing small molecules. Knowledge of the structural dynamics of riboswitches is crucial to elucidate their regulatory mechanism and develop RNA biosensors. In this work, we incorporated the fluorophore, Cy3, and its quencher, TQ3, into a full-length adenine riboswitch RNA and its isolated aptamer domain to monitor the dynamics of the RNAs in vitro and in cell. The adenine riboswitch was sensitive to Mg²⁺ concentrations and could be used as a biosensor to measure cellular Mg²⁺ concentrations. Additionally, the TQ3/Cy3-labeled adenine riboswitch yielded a Mg²⁺ concentration that was similar to that measured using a commercial assay kit. Furthermore, the fluorescence response to the adenine of the TQ3/Cy3-labeled riboswitch RNA was applied to determine the proportions of multiple RNA conformational changes in cells. The strategy developed in this work can be used to probe the dynamics of other RNAs in cells and may facilitate the developments of RNA biosensors, drugs and engineering.

Surface-enhanced Raman scattering of DNA bases using frozen silver nanoparticle dispersion as a platform

Raman spectroscopy is a powerful method to characterize molecules in various media. Although surface-enhanced Raman scattering (SERS) is often employed to compensate for the intrinsically poor sensitivity of Raman spectroscopy, there remain serious tasks, such as simple preparations of SERS substrates, sensitivity control, and reproducible measurements. Here, we propose freezing as an efficient way to overcome these problems in SERS measurements using DNA bases as model targets. Solutes are expelled from ice crystals and concentrated in the liquid phase upon freezing. Silver nanoparticles (AgNPs) are also concentrated in the liquid phase to aggregate with Raman target analytes. The SERS signal intensity is maximized when the AgNP concentration exceeds the critical aggregation value. Freezing allows up to 5000 times enhancements of the SERS signal. Thus, an efficient SERS platform is prepared by simple freezing. The simultaneous detection of four DNA bases effectively eliminates variations of signal intensities and allows the reliable determination of concentration ratios.

Quantitative analysis of m6A RNA modification by LC-MS

N6-adenosine methylation (m6A) of messenger RNA (mRNA) plays key regulatory roles in gene expression. Accurate measurement of m6A levels is thus critical to understand its dynamic changes in various biological settings. Here, we provide a protocol to quantitate the levels of adenosine and m6A in cellular mRNAs. Using nuclease and phosphatase, we digest mRNA into nucleosides, which are subsequently quantified using liquid chromatography mass spectrometry. For complete details on the use and execution of this protocol, please refer to Cho et al. (2021).

Tenofovir and emtricitabine concentrations in hair are comparable between individuals on tenofovir disoproxil fumarate versus tenofovir alafenamide-based ART

Tenofovir disoproxil fumarate (TDF) in combination with emtricitabine (FTC) is the backbone for both human immunodeficiency virus (HIV) treatment and pre-exposure prophylaxis (PrEP) worldwide. Tenofovir alafenamide (TAF) with FTC is increasingly used in HIV treatment and was recently approved for PrEP among men-who-have-sex-with-men. TDF and TAF are both metabolized into tenofovir (TFV). Antiretrovirals in plasma are taken up into hair over time, with hair levels providing a long-term measure of adherence. Here, we report a simple, robust, highly sensitive, and validated high-performance liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS)-based analytical method for analyzing TFV and FTC from individuals on either TDF/FTC or TAF/FTC in small hair samples. TFV/FTC are extracted from ~5 mg hair and separated on a column using a gradient elution. The lower quantification limits are 0.00200 (TFV) and 0.0200 (FTC) ng/mg hair; the assay is linear up to 0.400 (TFV) and 4.00 (FTC) ng/mg hair. The intra-day and inter-day coefficients of variance (CVs) are 5.39-12.6% and 6.40-13.5% for TFV and 0.571-2.45% and 2.45-5.16% for FTC. TFV concentrations from participants on TDF/FTC-based regimens with undetectable plasma HIV RNA were 0.0525 ± 0.0295 ng/mg, whereas those from individuals on TAF/FTC-based regimens were 0.0426 ± 0.0246 ng/mg. Despite the dose of TFV in TDF being 10 times that of TAF, hair concentrations of TFV were not significantly different for those on TDF versus TAF regimens. Pharmacological enhancers (ritonavir and cobicistat) did not boost TFV concentrations in hair. In summary, we developed and validated a sensitive analytical method to analyze TFV and FTC in hair and found that hair concentrations of TFV were essentially equivalent among those on TDF and TAF.

Decoding the epitranscriptional landscape from native RNA sequences

Traditional epitranscriptomics relies on capturing a single RNA modification by antibody or chemical treatment, combined with short-read sequencing to identify its transcriptomic location. This approach is labor-intensive and may introduce experimental artifacts. Direct sequencing of native RNA using Oxford Nanopore Technologies (ONT) can allow for directly detecting the RNA base modifications, although these modifications might appear as sequencing errors. The percent Error of Specific Bases (%ESB) was higher for native RNA than unmodified RNA, which enabled the detection of ribonucleotide modification sites. Based on the %ESB differences, we developed a bioinformatic tool, epitranscriptional landscape inferring from glitches of ONT signals (ELIGOS), that is based on various types of synthetic modified RNA and applied to rRNA and mRNA. ELIGOS is able to accurately predict known classes of RNA methylation sites (AUC > 0.93) in rRNAs from Escherichiacoli, yeast, and human cells, using either unmodified in vitro transcription RNA or a background error model, which mimics the systematic error of direct RNA sequencing as the reference. The well-known DRACH/RRACH motif was localized and identified, consistent with previous studies, using differential analysis of ELIGOS to study the impact of RNA m6A methyltransferase by comparing wild type and knockouts in yeast and mouse cells. Lastly, the DRACH motif could also be identified in the mRNA of three human cell lines. The mRNA modification identified by ELIGOS is at the level of individual base resolution. In summary, we have developed a bioinformatic software package to uncover native RNA modifications.

Silver-Based SERS Pico-Molar Adenine Sensor

Adenine is an important molecule for biomedical and agricultural research and applications. The detection of low concentration adenine molecules is thus desirable. Surface-enhanced Raman scattering (SERS) is a promising label-free detection and fingerprinting technique for molecules of significance. A novel SERS sensor made of clusters of silver nanostructures deposited on copper bumps in valleys of an etched silicon substrate was previously reported to exhibit a low and reproducible detection limit for a 10⁻¹¹ M neutral adenine aqueous solution. Reflection of laser illumination from the silicon surface surrounding a valley provides additional directions of laser excitation to adenine molecules adsorbing on a silver surface for the generation of enhanced SERS signal strength leading to a low detection limit. This paper further reports a concentration dependent shift of the ring-breathing mode SERS adenine peak towards 760 cm⁻¹ with decreasing concentration and its pH-dependent SERS signal strength. For applications, where the pH value can vary, reproducible detection of 10⁻¹² M adenine in a pH 9 aqueous solution is feasible, making the novel SERS structure a desirable pico-molar adenine sensor.

Ground and Excited States of Gas-Phase DNA Nucleobase Cation-Radicals. A UV-vis Photodisociation Action Spectroscopy and Computational Study of Adenine and 9-Methyladenine

Cation radicals of adenine (A^•+) and 9-methyladenine (MA^•+) were generated in the gas phase by collision-induced intramolecular electron transfer in copper-terpyridine-nucleobase ternary complexes and characterized by collision-induced dissociation (CID) mass spectra and UV-vis photodissociation action spectroscopy in the 210-700 nm wavelength region. The action spectra of both A^•+ and MA^•+ displayed characteristic absorption bands in the near-UV and visible regions. Another tautomer of A^•+ was generated as a minor product by multistep CID of protonated 9-(2-bromoethyl)adenine. Structure analysis by density functional theory and coupled-clusters ab initio calculations pointed to the canonical 9-H-tautomer Ad1^•+ as the global energy minimum of adenine cation radicals. The canonical tautomer MA1^•+ was also calculated to be a low-energy structure among methyladenine cation radicals. However, two new noncanonical tautomers were found to be energetically comparable to MA1^•+. Vibronic absorption spectra were calculated for several tautomers of A^•+ and MA^•+ and benchmarked on equation-of-motion coupled-clusters excited-state calculations. Analysis of the vibronic absorption spectra of A^•+ tautomers pointed to the canonical tautomer Ad1^•+ as providing the best match with the action spectrum. Likewise, the canonical tautomer MA1^•+ was the unequivocal best match for the MA^•+ ion generated in the gas phase. According to potential-energy mapping, MA1^•+ was separated from energetically favorable noncanonical cation radicals by a high-energy barrier that was calculated to be above the dissociation threshold for loss of a methyl hydrogen atom, thus preventing isomerization. Structures and energetics of all four DNA nucleobase cation radicals are compared and discussed.

Silver SERS Adenine Sensors with a Very Low Detection Limit

The detection of adenine molecules at very low concentrations is important for biological and medical research and applications. This paper reports a silver-based surface-enhanced Raman scattering (SERS) sensor with a very low detection limit for adenine molecules. Clusters of closely packed silver nanoparticles on surfaces of discrete ball-like copper bumps partially covered with graphene are deposited by immersion in silver nitrate. These clusters of silver nanoparticles exhibit abundant nanogaps between nanoparticles, where plasmonic coupling induces very high local electromagnetic fields. Silver nanoparticles growing perpendicularly on ball-like copper bumps exhibit surfaces of large curvature, where electromagnetic field enhancement is high. Between discrete ball-like copper bumps, the local electromagnetic field is low. Silver is not deposited on the low-field surface area. Adenine molecules interact with silver by both electrostatic and functional groups and exhibit low surface diffusivity on silver surface. Adenine molecules are less likely to adsorb on low-field sensor surface without silver. Therefore, adenine molecules have a high probability of adsorbing on silver surface of high local electric fields and contribute to the measured Raman scattering signal strength. We demonstrated SERS sensors made of clusters of silver nanoparticles deposited on discrete ball-like copper bumps with very a low detection limit for detecting adenine water solution of a concentration as low as 10⁻¹¹ M.

DNA N6-methyladenine increased in human esophageal squamous cell carcinoma

Esophageal cancer is one of the most common malignancies worldwide. DNA N6-methyladenine (6mA) has been well-studied in prokaryotes, while the distribution and biological functions of DNA 6mA in eukaryotic cells remain to be elucidated. Recently, DNA 6mA epigenetic modification was found in human gastric and liver cancers. To explore the status of DNA 6mA epigenetic modification in esophageal cancer, 101 cases of human esophageal squamous cell carcinoma (ESCC) and matched adjacent normal tissue samples were analyzed by dot blot assay. The levels of genomic DNA 6mA were significantly higher in ESCC tissue samples than in matched adjacent normal tissue samples (P<0.001). Increased DNA 6mA was associated with poor tumor differentiation (P<0.05), while no association was found between 6mA modification and gender, age, tumor size, TNM stage, lymph node metastasis, smoking, alcohol intake, or family history (all P>0.05). In conclusion, DNA 6mA epigenetic modification increased in human ESCC and may serve as a prognostic marker.

Voltammetric determination of adefovir dipivoxil by using a nanocomposite prepared from molecularly imprinted poly(o-phenylenediamine), multi-walled carbon nanotubes and carbon nitride

An electrochemical sensor for adefovir dipivoxil (ADV) detection was prepared by electropolymerization of o-phenylenediamine in the presence of ADV on a glassy carbon electrode modified with multi-walled carbon nanotubes and carbon nitride. The electrode was characterized by field emission scanning electron microscopy and differential pulse voltammetry. The performance was optimized by response surface methodology. The changes in differential pulse voltammetric peak currents of the redox probe, ferricyanide, were linear to ADV concentrations in the range from 0.1 to 9.9 μmol L^-1, with the detection limit of 0.05 μmol L^-1 (S/N = 3). The sensor was applied to the determination of ADV in drug formulations, human serum and urine samples. It is selective due to the use of an imprinted material, well reproducible, long-term stable, and regenerable. Graphical abstract By merging the unique properties of carbon nitride with intrinsic properties of MWCNTs, and molecularly imprinted polymers, a novel electrochemical sensor with selective binding sites was prepared for determination of adefovir dipivoxil in pharmaceutical and biological samples.

Using artificial neural network and multivariate calibration methods for simultaneous spectrophotometric analysis of Emtricitabine and Tenofovir alafenamide fumarate in pharmaceutical formulation of HIV drug

Spectrophotometric analysis method based on artificial neural network (ANN), partial least squares regression (PLS) and principal component regression (PCR) models was proposed for the simultaneous determination of Emtricitabine (ETB) and Tenofovir alafenamide fumarate (TAF) in human immunodeficiency virus (HIV) drug. An artificial neural network consisting of two, five, and seven layers with 2,3,5,7, and 9 neurons was trained by applying a feed forward back-propagation learning. In this method, Levenberg-Marquardt (LM) and gradient descent with momentum and adaptive learning rate back propagation (GDX) algorithms were used. Statistical parameters indicated that the ability of LM was better than GDX algorithm. Also, root mean square error (RMSE) and recovery (%) of the PLS and PCR methods showed that PLS has worked better than PCR. The proposed models were compared to the high- performance liquid chromatography (HPLC) as a reference method. Furthermore, the obtained results of the one-way analysis of variance (ANOVA) test at the 95% confidence level represented that there was no significant difference between the proposed and reference methods.

Real Time Normalization of Fast Photochemical Oxidation of Proteins Experiments by Inline Adenine Radical Dosimetry

Hydroxyl radical protein footprinting (HRPF) is a powerful method for measuring protein topography, allowing researchers to monitor events that alter the solvent accessible surface of a protein (e.g., ligand binding, aggregation, conformational changes, etc.) by measuring changes in the apparent rate of reaction of portions of the protein to hydroxyl radicals diffusing in solution. Fast Photochemical Oxidation of Proteins (FPOP) offers an ultrafast benchtop method for radical generation for HRPF, photolyzing hydrogen peroxide using a UV laser to generate high concentrations of hydroxyl radicals that are consumed on roughly a microsecond time scale. The broad reactivity of hydroxyl radicals means that almost anything added to the solution (e.g., ligands, buffers, excipients, etc.) will scavenge hydroxyl radicals, altering their half-life and changing the effective radical concentration experienced by the protein. Similarly, minute changes in peroxide concentration, laser fluence, and buffer composition can alter the effective radical concentration, making reproduction of data challenging. Here, we present a simple method for radical dosimetry that can be carried out as part of the FPOP workflow, allowing for measurement of effective radical concentration in real time. Additionally, by modulating the amount of radical generated, we demonstrate that effective hydroxyl radical yields in FPOP HRPF experiments carried out in buffers with widely differing levels of hydroxyl radical scavenging capacity can be compensated on the fly, yielding statistically indistinguishable results for the same conformer. This method represents a major step in transforming FPOP into a robust and reproducible technology capable of probing protein structure in a wide variety of contexts.

Recurrence rates of urinary calculi according to stone composition and morphology

Few studies have examined the relative risk of recurrence of different stone types. The object of the present study was to evaluate the tendency for stone recurrence as a function of major mineral composition of the stones and morphological characteristics of the stones. This study was carried out using 38,274 stones for which we had data available to specify if the stone was from the first or a subsequent urinary stone episode. Stones were analyzed for morphology by stereomicroscope and for composition by infrared spectroscopy. Overall, 42.7% of stones were from patients who had had a previous stone event, with these being more frequent in men (44.4%) than in women (38.9%, p < 0.0001). Age of first stone occurrence was lowest for dihydroxyadenine (15.7 ± 16.6 years) and highest for anhydrous uric acid (62.5 ± 14.9 years), with the average age of first stones of calcium oxalate falling in the middle (40.7 ± 14.6 years for calcium oxalate dihydrate, and 48.4 ± 15.1 years for calcium oxalate monohydrate, COM). By composition alone, COM was among the least recurrent of stones, with only 38.0% of COM stones coming from patients who had had a previous episode; however, when the different morphological types of COM were considered, type Ic-which displays a light color, budding surface and unorganized section-had a significantly greater rate of recurrence, at 82.4% (p < 0.0001), than did other morphologies of COM. Similarly, for stones composed of apatite, morphological type IVa2-a unique form with cracks visible beneath a glossy surface-had a higher rate of recurrence than other apatite morphologies (78.8 vs. 39-42%, p < 0.0001). Stone mineral type alone is insufficient for identifying the potential of recurrence of the stones. Instead, the addition of stone morphology may allow the diagnosis of highly recurrent stones, even among common mineral types (e.g., COM) that in general are less recurrent.

Multiporous molybdenum carbide nanosphere as a new charming electrode material for highly sensitive simultaneous detection of guanine and adenine

By introduction of Mo metal species (molybdenum-based polyoxometalates) into the Cu-MOF as co-precursor, molybdenum carbide nanosphere (Mo_xC@C) was prepared via a simple calcining routine and a further etching the metallic Cu process. The obtained Mo_xC@C showed a unique structure where well-dispersed Mo_xC nanoparticles (NPs) were encapsulated in porous carbon matrix. As-fabricated novel 3D porous architecture Mo_xC@C nanosphere exhibited a potent and persistent electro-oxidation behavior followed by well-separated oxidation peaks (peak to peak voltage is about 350 mV) toward adenine (A) and guanine (G) by differential pulse voltammetry (DPV). This excellent electrochemical performance can be attributed to the unique structure and composition of 3D Mo_xC@C. Furthermore, 3D Mo_xC@C also revealed high selectivity and sensitivity, good reproducibility, excellent stability and anti-interference ability. The calibration curves for quantitive analysis of G and A were obtained: 0.03-122 µM, and 0.02-122 µM, respectively, the detection limits were 0.0085 µM, 0.008 µM, respectively. The proposed procedure was successfully applied to detect G and A in human urine and serum samples with satisfactory recovery, which manifests its viability application for practical analysis.

HPLC-Based Metabolomic Analysis of Normal and Inflamed Gut

The idiopathic inflammatory bowel diseases, which include Crohn's disease and ulcerative colitis, are multifactorial chronic conditions that result in numerous perturbations of metabolism in the gastrointestinal mucosa. Thus, methodologies for the qualitative and quantitative analysis of small molecule metabolites in mucosal tissues are important for further elucidation of mechanisms driving inflammation and the metabolic consequences of inflammation. High-performance liquid chromatography (HPLC) is a ubiquitous analytical technique that can be adapted for both targeted and non-targeted metabolomic analysis. Here, protocols for reversed-phase (RP) HPLC-based methods using two different detection modalities are presented. Ultraviolet detection is used for the analysis of adenine nucleotide metabolites, whereas electrochemical detection is used for the analysis of multiple amino acid metabolites. These methodologies provide platforms for further characterization of the metabolic changes that occur during gastrointestinal inflammation.

[Determination of Nucleosides and Nucleobases in Natural, Cultured and Tissue Culture Anoectochilus roxburghii Using LC-MS]

OBJECTIVE

To establish a method for simultaneous determination of nucleosides and nucleobases in natural, cultured and tissue culture Anoectochilus roxburghii by high performance liquid chromatography-electrospray ionization/ion trap mass spectrometry (HPLC-ESI/MS).

METHODS

The separation was performed on a Welch Ultimate XB-C18 column (250 mm x 4.6 mm,5 μm). 20 mmol/L ammonium acetate solution and methanol were adopted as the mobile phase with gradient elution. The flow rate was 1.0 mL/min. The injection volume was 20 μL. The column temperature and UV wavelength were set at 30 degrees C and 260 nm, respectively.

RESULTS

Cytosine, uracil, cytidine, uridine, hypoxanthine, adenine, inosine, guanosine,fl-thymidine and adenosine were identified in natural, cultured and tissue culture Anoectochilus roxburghii. The total content of nucleosides and nucleotides in Anoectochilus roxburghii were 1.6639, 1.8568 and 2.2013 mg/g,respectively.

CONCLUSION

The contents of nucleosides and nucleobases in herb are affected by its growth pattern. The total content of nucleosides and nucleotides was tissue culture herb > cultured herb > natural herb. This investigation would provide the theoretic basis for quality standards and applications of Anoectochilus roxburghii in clinical research.

Nucleobase Recognition by Truncated α-Hemolysin Pores

The α-hemolysin (αHL) protein nanopore has been investigated previously as a base detector for the strand sequencing of DNA and RNA. Recent findings have suggested that shorter pores might provide improved base discrimination. New work has also shown that truncated-barrel mutants (TBM) of αHL form functional pores in lipid bilayers. Therefore, we tested TBM pores for the ability to recognize bases in DNA strands immobilized within them. In the case of TBMΔ6, in which the barrel is shortened by ∼16 Å, one of the three recognition sites found in the wild-type pore, R1, was almost eliminated. With further mutagenesis (Met113 → Gly), R1 was completely removed, demonstrating that TBM pores can mediate sharpened recognition. Remarkably, a second mutant of TBMΔ6 (Met113 → Phe) was able to bind the positively charged β-cyclodextrin, am7βCD, unusually tightly, permitting the continuous recognition of individual nucleoside monophosphates, which would be required for exonuclease sequencing mediated by nanopore base identification.

Simultaneous Determination of Adenine and Guanine Using Cadmium Selenide Quantum Dots-Graphene Oxide Nanocomposite Modified Electrode

A novel electrochemical sensor was fabricated by immobilizing Cadmium Selenide Quantum Dots (CdSe QDs)-Graphene Oxide (GO) nanocomposite on a paraffin wax impregnated graphite electrode (PIGE) and was used for the simultaneous determination of adenine and guanine. The CdSe QDs-GO nanocomposite was prepared by ultrasonication and was characterized with spectroscopic and microscopic techniques. The nanocomposite modified electrode was characterized by cyclic voltammetry (CV). The modified electrode showed excellent electrocatalytic activity towards the oxidative determination of adenine and guanine with a good peak separation of 0.31 V. This may be due to the high surface area and fast electron transfer kinetics of the nanocomposite. The modified electrode exhibited wide linear ranges from 0.167 μM to 245 μM for Guanine and 0.083 μM to 291 μM for Adenine with detection limits of 0.055 μM Guanine and 0.028 μM of Adenine (S/N = 3) respectively. Further, the modified electrode was used for the quantitative determination of adenine and guanine in herring sperm DNA with satisfactory results. The modified electrode showed acceptable selectivity, reproducibility and stability under optimal conditions.

Vaginal deployment and tenofovir delivery by microbicide gels

Gels are one of the soft material platforms being evaluated to deliver topically acting anti-HIV drugs (microbicides) to the vaginal environment. For each drug, its loaded concentration, gel properties and applied volume, and frequency of dosing can be designed to optimize PK and, thence, PD. These factors also impact user sensory perceptions and acceptability. Deterministic compartmental modeling of vaginal deployment and drug delivery achieved by test gels can help delineate how multiple parameters characterizing drug, vehicle, vaginal environment, and dosing govern details of PK and PD and also gel leakage from the canal. Such microbicide delivery is a transport process combining convection, e.g., from gel spreading along the vaginal canal, with drug diffusion in multiple compartments, including gel, mucosal epithelium, and stroma. The present work builds upon prior models of gel coating flows and drug diffusion (without convection) in the vaginal environment. It combines and extends these initial approaches in several key ways, including: (1) linking convective drug transport due to gel spreading with drug diffusion and (2) accounting for natural variations in dimensions of the canal and the site of gel placement therein. Results are obtained for a leading microbicide drug, tenofovir, delivered by three prototype microbicide gels, with a range of rheological properties. The model includes phosphorylation of tenofovir to tenofovir diphosphate (which manifests reverse transcriptase activity in host cells), the stromal concentration distributions of which are related to reference prophylactic values against HIV. This yields a computed summary measure related to gel protection ("percent protected"). Analyses illustrate tradeoffs amongst gel properties, drug loading, volume and site of placement, and vaginal dimensions, in the time and space history of gel distribution and tenofovir transport to sites of its anti-HIV action and concentrations and potential prophylactic actions of tenofovir diphosphate therein.

Identification, synthesis and characterization of new impurities in tenofovir

A detailed impurity study was conducted on tenofovir, (R)-({[1-(6-amino-9H-purin-9-yl)propan-2-yl]oxy}methyl)phosphonic acid (1), which is the key starting material of manufacturing the active pharmaceutical ingredient (API) tenofovir disoproxil fumarate (2) based on a recently reported procedure. The major impurities generated in the production of tenofovir (1) have been synthesized, characterized and confirmed. The possible formation mechanisms of these impurities were elucidated herein, which would help to understand the process. In addition, this work will also improve the quality control during manufacturing tenofovir and tenofovir disoproxil fumarate (2).

Self-assembled large-area annular cavity arrays with tunable cylindrical surface plasmons for sensing

Surface plasmons that propagate along cylindrical metal/dielectric interfaces in annular apertures in metal films, called cylindrical surface plasmons (CSPs), exhibit attractive optical characteristics. However, it is challenging to fabricate these nanocoaxial structures. Here, we demonstrate a practical low-cost route to manufacture highly ordered, large-area annular cavity arrays (ACAs) that can support CSPs with great tunability. By employing a sol-gel coassembly method, reactive ion etching and metal sputtering techniques, regular, highly ordered ACAs in square-centimeter-scale with a gap width tunable in the range of several to hundreds of nanometers have been produced with good reproducibility. Ag ACAs with a gap width of 12 nm and a gap height of 635 nm are demonstrated. By finite-difference time-domain simulation, we confirm that the pronounced dips in the reflectance spectra of ACAs are attributable to CSP resonances excited in the annular gaps. By adjusting etching time and Ag film thickness, the CSP dips can be tuned to sweep the entire optical range of 360 to 1800 nm without changing sphere size, which makes them a promising candidate for forming integrated plasmonic sensing arrays. The high tunability of the CSP resonant frequencies together with strong electric field enhancement in the cavities make the ACAs promising candidates for surface plasmon sensors and SERS substrates, as, for example, they have been used in liquid refractive index (RI) sensing, demonstrating a sensitivity of 1505 nm/RIU and a figure of merit of 9. One of the CSP dips of ACAs with a certain geometry size is angle- (0-70 degrees) and polarization-independent and can be used as a narrow-band absorber. Furthermore, the nano annular cavity arrays can be used to construct solar cells, nanolasers and nanoparticle plasmonic tweezers.

Electrocatalytic activity of molybdenum disulfide nanosheets enhanced by self-doped polyaniline for highly sensitive and synergistic determination of adenine and guanine

Recently, easy, green, and low-cost liquild exfoliation of bulk materials to obtain thin-layered nanostructure significantly emerged. In this work, thin-layered molybdenum disulfide (MoS2) nanosheets were fabricated through intercalation of self-doped polyaniline (SPAN) to layer space of bulk MoS2 by ultrasonic exfoliating method to effectively prevent reaggregation of MoS2 nanosheets. The obtained hybrid showed specific surface area, a large number of electroactive species, and open accessible space, accompanied by rich negative charged and special conjugated structure, which was applied to adopt positively charged guanine and adenine, based on their strong π-π* interactions and electrostatic adsorption. Also, the SPAN-MoS2 interface exhibited the synergistic effect and good electrocatalytic activity compared with the sole SPAN or MoS2 modified electrode.

Mapping antiretroviral drugs in tissue by IR-MALDESI MSI coupled to the Q Exactive and comparison with LC-MS/MS SRM assay

This work describes the coupling of the IR-MALDESI imaging source with the Q Exactive mass spectrometer. IR-MALDESI MSI was used to elucidate the spatial distribution of several HIV drugs in cervical tissues that had been incubated in either a low or high concentration. Serial sections of those analyzed by IR-MALDESI MSI were homogenized and analyzed by LC-MS/MS to quantify the amount of each drug present in the tissue. By comparing the two techniques, an agreement between the average intensities from the imaging experiment and the absolute quantities for each drug was observed. This correlation between these two techniques serves as a prerequisite to quantitative IR-MALDESI MSI. In addition, a targeted MS(2) imaging experiment was also conducted to demonstrate the capabilities of the Q Exactive and to highlight the added selectivity that can be obtained with SRM or MRM imaging experiments.

Highly sensitive and synergistic detection of guanine and adenine based on poly(xanthurenic acid)-reduced graphene oxide interface

In order to achieve the large direct electrochemical signals of guanine and adenine, an urgent request to explore novel electrode materials and interfaces has been put forward. In this paper, a poly(xanthurenic acid, Xa)-reduced graphene oxide (PXa-ERGNO) interface, which has rich negatively charged active sites and accelerated electron transfer ability, was fabricated for monitoring the positively charged guanine and adenine. Scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectra, X-ray photoelectron spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and differential pulse voltammetry were adopted to characterize the morphology and prove the electrochemical properties of the prepared interface. The PXa-ERGNO interface with rich negative charge and large electrode surface area was an excellent sensing platform to prompt the adsorption of the positively charged guanine and adenine via strong π-π* interaction or electrostatic adsorption. The PXa-ERGNO interface exhibited prominent synergistic effect and good electrocatalytic activity for sensitive determination of guanine and adenine compared with sole PXa or ERGNO modified electrode. The sensing platform we built could be further applied in the adsorption and detection of other positively charged biomolecules or aromatic molecules.

[Determination of four kinds of purines in deer fetus soft capsule by HPLC]

OBJECTIVE

To establish an HPLC method for simultaneous determination of four kinds of purines in deer fetus soft capsule.

METHODS

Four kinds of purines were detected and determined by HPLC. The mobile phase was 0.02 mol/L KH2PO4 (containing 1 mmol/L heptane sulfonic acid sodium, pH = 3.8)-methanol = 97:3. Detection wavelength was 254 nm and flow rate was 1.5 ml min. The linear relationship of four kinds of purines was as follows: hypoxanthine: Y1 = 83695X1 + 355 (r1 = 0.9998), with the linear range 0.040-0.667 mg/mL; xanthine: Y2 = 50638X2 + 39 (r2 = 0.9989), with the linear range 0.008-0.119 mg/mL; guanine: Y3 = 30269X3-9562 (r3 = 0.9924), with the linear range 0.018 - 0.279 mg/mL; adenine: Y4 = 38975X4-8671 (r4 = 0.9989), with the linear range 0.027-0.399 mg/mL The average sample recovery rate of hypoxanthine, xanthine, guanine and adenine were 98.1%, 98.6%, 98.0% and 97.5%, with RSD 1.0%, 0.4%, 0.8% and 0.6%, respectively.

RESULTS

The content of hypoxanthine, xanthine, guanine and adenine in 3 lots of deer fetus soft capsule were 116.5-132.0 microg/capsule, 21.2-23.0 microg/capsule, 48.6-54.3 microg/capsule and 68.9-75.2 microg/capsule, respectively.

CONCLUSIONS

This method is simple,accurate and reproducible, which provides a basis for quality control of purines in deer fetus soft capsule.

Comparative studies on chemical parameters and antioxidant properties of stipes and caps of shiitake mushroom as affected by different drying methods

BACKGROUND

Shiitake, the second most cultivated mushroom, is famous for its high nutritional value and medicinal properties. In this study, various chemical parameters and antioxidant properties of caps and stipes of shiitake mushroom dried by different methods (freeze-drying, shade drying and hot air drying) were comparatively investigated by spectrophotometric assays, high-performance liquid chromatography, 1,1'-diphenyl-2-picrylhydrazyl assay, ferric reducing power assay and lipid peroxidation inhibition assay.

RESULTS

The contents of amino acids, neutral sugar and total phenolics in stipes were higher than those in caps of shiitake, while caps showed advantages in terms of their contents of protein and eritadenine. The chemical parameters and antioxidant activities of shiitake were significantly affected by the drying method used.

CONCLUSION

The contents of total phenolics, amino acids and neutral sugar in stipes were higher than those in caps of shiitake, which suggested that stipes were more nutritional than caps in some respects. Hot air drying at 50 °C resulted in high total phenolic, amino acid, uronic acid and neutral sugar contents and antioxidant activities, which could be useful for the application of shiitake and related products in the food industry.

Lower concentrations of B-vitamin subgroups in the serum and amniotic fluid correlate to cleft lip and palate appearance in the offspring of A/WySn mice

PURPOSE

The pathogenesis and prevention of cleft lip and palate (CL/P) have been studied mainly in clinical and animal experiments. A prophylactic poly-B-vitamin substitution during the first months of pregnancy has provided the most encouraging results for the prevention of CL/P recurrence in families at risk. In vitro studies of the palatal organ in an A/WySn mouse model have confirmed the positive influence of B-vitamins on palatal development. The present animal study was performed to analyze different B-vitamin concentrations in the serum and amniotic fluid of A/WySn mice according to the appearance of CL/P in their offspring.

MATERIAL AND METHODS

Concentrations of different B-vitamins (B1, B2, B3, B5, B6, and folic acid) in serum and amniotic fluid were analyzed by high-performance liquid chromatographic detection. Immunohistochemical staining against thiamin-1 receptor was performed on histologic midface sections of A/WySn fetuses with (n = 12) and without (n = 14) CL/P.

RESULTS

Vitamin B5 (P < .001) and folic acid (P < .004) concentrations in the amniotic fluid of dams with CL/P were significantly lower than in dams without CL/P. Serum concentrations of folic acid (P = .5) and B5 (P = .4) showed no difference between the 2 groups. Dams with CL/P had significantly lower thiamine concentrations in serum (P = .01) and amniotic fluid (P < .001). Histologic midface sections presented high thiamin-1 receptor expression in the palatal shelf of fetuses with CL/P.

CONCLUSION

A decreased use or uptake of some B-vitamin subgroups (B1, B5, and folic acid) in amniotic fluid and serum (vitamin B1) was correlated to an increased cleft appearance in A/WySn mice. The high thiamin-1 receptor expression in the palatal tissue of mouse fetuses with CL/P may be caused by a decreased availability of vitamin B1.

SERS study on adenine using a Ag/poly(t-butylacrylate) nanocomposite

Enhancement of Raman signals of the nucleobase adenine on an Ag based composite was studied using the 1064 nm laser line. The composite comprise emulsions of Ag nanoparticles encapsulated in poly(t-butylacrylate) (PtBA) beads that act as substrate for the Surface-Enhanced Raman Scattering (SERS) of adenine. For this system, Raman enhancement was observed for the ring-stretching vibrational mode of adenine after aggregation of the Ag/poly(t-butylacrylate) emulsion and isolation of the solid composite. This is a convenient and alternative analytical approach to SERS monitoring of solutions of adenine over the more common use of pure Ag colloids. As a consequence, this research contributes to develop innovative studies on DNA fragments using polymeric platforms that can act as highly sensitive SERS substrates.

Participation of Gs-proteins in the action of relaxin-like gonad-stimulating substance (GSS) for 1-methyladenine production in starfish ovarian follicle cells

Gonad-stimulating substance (GSS) in starfish is the only known invertebrate peptide hormone responsible for final gamete maturation, rendering it functionally analogous to gonadotropins in vertebrates. Recently, we purified GSS from radial nerves in the starfish Asterina pectinifera and identified the chemical structure as a heterodimer composed of two different peptides (A- and B-chain) with disulfide cross-linkages. This study examined the hormonal action of GSS on ovarian follicle cells obtained from ovaries in growing (stage IV) and fully grown (stage V) stages, and particularly the mode of signal transduction. The action of GSS on 1-MeAde production by follicle cells in stage V was mediated through the production of cAMP. In contrast, GSS failed to induce 1-MeAde and cAMP production by follicle cells in stage IV. According to competitive experiments using radioiodinated and radioinert GSS, highly specific binding was observed in follicle cells, though their affinities and numbers in stage IV were inferior to those in stage V. Interestingly, Gsα was not detected immunologically in follicle cell membranes of stage IV. Gβ was also faint in stage IV. Although adenylyl cyclase activity in stage V was dose-dependently activated by GSS in the presence of GTP, neither GSS in the presence of GTP nor nonhydrolyzable GTP analogs were effective on the activity in stage IV. These findings strongly suggest that the failure of GSS to produce 1-MeAde is because of a lack of Gs-proteins in follicle cells at stage IV.

Chitosan-coated anisotropic silver nanoparticles as a SERS substrate for single-molecule detection

Surface-enhanced Raman spectroscopy (SERS) is a technique that has become widely used for identifying and providing structural information about molecular species in low concentration. There is an ongoing interest in finding optimum particle size, shape and spatial distribution for optimizing the SERS substrates and pushing the sensitivity toward the single-molecule detection limit. This work reports the design of a novel, biocompatible SERS substrate based on small clusters of anisotropic silver nanoparticles embedded in a film of chitosan biopolymer. The SERS efficiency of the biocompatible film is assessed by employing Raman imaging and spectroscopy of adenine, a significant biological molecule. By combining atomic force microscopy with SERS imaging we find that the chitosan matrix enables the formation of small clusters of silver nanoparticles, with junctions and gaps that greatly enhance the Raman intensities of the adsorbed molecules. The study demonstrates that chitosan-coated anisotropic silver nanoparticle clusters are sensitive enough to be implemented as effective plasmonic substrates for SERS detection of nonresonant analytes at the single-molecule level.

Testing a portable Raman instrument: the detection of biomarkers in gypsum powdered matrix under gypsum crystals

In this study the possibility to detect biomarkers in experimentally prepared evaporitic matrices using a portable Raman instrument was estimated. Testing of the instrument was carried-out under the Alpine conditions outdoors at a low ambient temperature of -10 °C and at an altitude of 2860 m (Pitztal, Austria). Amino acids glycine and l-alanine, nucleo bases thymine and adenine, and metabolite urea were the organics mixed with gypsum powder. In this step it was shown that portable Raman spectroscopic instrumentation is capable of detecting biomarkers in complex samples in a host geological matrix. Such detection is possible even when the laser beam was focussed through the gypsum crystals 3-9 mm thick. For exobiology areas, this is an important fact, because life and/or related biomolecules are likely to be found in cavities under the surface of partially transparent evaporitic minerals that provide them a shelter from the hostile surrounding environment. For influencing the intensity of Raman bands the thickness of covering crystals is not as important as is the actual concentration of the biomarkers. This work and similar experiments serve for better evaluation of Raman spectroscopy as a method for future planetary exploration mission adoption.

Simultaneous determination of five nucleosides and nucleobases of Rehmannia glutinosa Libosch. by high performance liquid chromatography

This study is to establish a method for simultaneously determination of five nucleosides and nucleobases, including hypoxanthine, uridine, adenine, guanosine and adenosine in Rehmannia glutinosa Libosch. which was collected from different regions in China. A Diamonsil C18 column (250 mm x 4.6 mm, 5 microm) was used. Acetonitrile and 0.04 mol L(-1) potassium dihydrogen phosphate solution were adopted as mobile phase with gradient elution. The flow rate was 1 mL min(-1) and column temperature was 30 degrees C. The detection wavelength was at 254 nm. The method had good linearity over the range of 1.0 - 16.0 microg mL(-1) (r2 = 0.999 8), 5.0 - 80.0 microg mL(-1) (r2 = 0.999 8), 1.0 - 16.0 microg mL(-1) (r2 = 0.999 5), 1.25 - 20.0 microg mL(-1) (r2 = 0.999 8) and 1.0 - 16.0 microg mL(-1) (r2 = 0.999 8) for hypoxanthine, uridine, adenine, guanosine and adenosine, respectively. The average recoveries were between 98.8% and 100.7%. The content of hypoxanthine, uridine, adenine, guanosine and adenosine in Rehmannia glutinosa Libosch. from different regions was significantly different. This established method was sensitive and reliable for the quantification of five chemical constituents in Rehmannia glutinosa Libosch.

RNA oxidation adducts 8-OHG and 8-OHA change with Aβ42 levels in late-stage Alzheimer's disease

While research supports amyloid-β (Aβ) as the etiologic agent of Alzheimer's disease (AD), the mechanism of action remains unclear. Evidence indicates that adducts of RNA caused by oxidation also represent an early phenomenon in AD. It is currently unknown what type of influence these two observations have on each other, if any. We quantified five RNA adducts by gas chromatography/mass spectroscopy across five brain regions from AD cases and age-matched controls. We then used a reductive directed analysis to compare the RNA adducts to common indices of AD neuropathology and various pools of Aβ. Using data from four disease-affected brain regions (Brodmann's Area 9, hippocampus, inferior parietal lobule, and the superior and middle temporal gyri), we found that the RNA adduct 8-hydroxyguanine (8-OHG) decreased, while 8-hydroxyadenine (8-OHA) increased in AD. The cerebellum, which is generally spared in AD, did not show disease related changes, and no RNA adducts correlated with the number of plaques or tangles. Multiple regression analysis revealed that SDS-soluble Aβ₄₂ was the best predictor of changes in 8-OHG, while formic acid-soluble Aβ₄₂ was the best predictor of changes in 8-OHA. This study indicates that although there is a connection between AD related neuropathology and RNA oxidation, this relationship is not straightforward.

Plasmonic coupling of silver nanoparticles covered by hydrogen-terminated graphene for surface-enhanced Raman spectroscopy

We report on strong plasmonic coupling from silver nanoparticles covered by hydrogen-terminated chemically vapor deposited single-layer graphene, and its effects on the detection and identification of adenine molecules through surface-enhanced Raman spectroscopy (SERS). The high resistivity of the graphene after subjecting to remote plasma hydrogenation allows plasmonic coupling induced strong local electromagnetic fields among the silver nanoparticles to penetrate the graphene, and thus enhances the SERS efficiency of adenine molecules adsorbed on the film. The graphene layer protects the nanoparticles from reactive and harsh environments and provides a chemically inert and biocompatible carbon surface for SERS applications.

Sensitive and selective detection of adenine using fluorescent ZnS nanoparticles

We have used fluorescent ZnS nanoparticles as a probe for the determination of adenine. A typical 2 × 10(-7) M concentration of adenine quenches 39.3% of the ZnS fluorescence. The decrease in ZnS fluorescence as a function of adenine concentration was found to be linear in the concentration range 5 × 10(-9)-2 × 10(-7) M. The limit of detection (LOD) of adenine by this method is 3 nM. Among the DNA bases, only adenine quenched the fluorescence of ZnS nanoparticles in the submicromolar concentration range, thus adding selectivity to the method. The amino group of adenine was important in determining the quenching efficiency. Steady-state fluorescence experiments suggest that one molecule of adenine is sufficient to quench the emission arising from a cluster of ZnS consisting of about 20 molecules. Time-resolved fluorescence measurements indicate that the adenine molecules block the sites on the surface of ZnS responsible for emission with the longest lifetime component. This method may be applied for the determination of adenine in biological samples since the measurements have been carried out at pH 7.

Electrochemically fabricated self-aligned 2-D silver/alumina arrays as reliable SERS sensors

A novel SERS sensor for adenine molecules is fabricated electrochemically using an ordered two-dimensional array of self-aligned silver nanoparticles encapsulated by alumina. Silver is electro-deposited on the interior surfaces at the bottom of nano-channels in a porous anodic aluminum oxide (AAO) film. After etching aluminum, the back-end alumina serves as a SERS substrate. SERS enhancement factor greater than 10(6) is measured by 532 nm illumination. It exhibits robust chemical stability and emits reproducible Raman signals from repetitive uses for eight weeks. The inexpensive mass production process makes this reliable, durable and sensitive plasmon based optical device promising for many applications.

Concentrations of tenofovir and emtricitabine in breast milk of HIV-1-infected women in Abidjan, Cote d'Ivoire, in the ANRS 12109 TEmAA Study, Step 2

The aim was to evaluate emtricitabine (FTC) and tenofovir (TFV) neonatal ingestion through breast milk. Median TFV and FTC breast milk doses represented 0.03% and 2%, respectively, of the proposed oral infant doses. Neonatal simulated plasma concentrations were extremely low for TFV but between the half-maximal inhibitory concentration and the adult minimal expected concentration for FTC. The rare children who will acquire HIV despite TDF-FTC therapy will need to be monitored for viral resistance acquisition.

Fate of the antiretroviral drug tenofovir in agricultural soil

Tenofovir (9-(R)-(2-phosphonylmethoxypropyl)-adenine) is an antiretroviral drug widely used for the treatment of human immunodeficiency virus (HIV-1) and Hepatitis B virus (HBV) infections. Tenofovir is extensively and rapidly excreted unchanged in the urine. In the expectation that tenofovir could potentially reach agricultural lands through the application of municipal biosolids or wastewater, and in the absence of any environmental fate data, we evaluated its persistence in selected agricultural soils. Less than 10% of [adenine-8-(14)C]-tenofovir added to soils varying widely in texture (sand, loam, clay loam) was mineralized in a 2-month incubation under laboratory conditions. Tenofovir was less readily extractable from clay soils than from a loam or a sandy loam soil. Radioactive residues of tenofovir were removed from the soil extractable fraction with DT(50)s ranging from 24±2 to 67+22days (first order kinetic model) or 44+9 to 127+55days (zero order model). No extractable transformation products were detectable by HPLC. Tenofovir mineralization in the loam soil increased with temperature (range 4°C to 30°C), and did not occur in autoclaved soil, suggesting a microbial basis. Mineralization rates increased with soil moisture content, ranging from air-dried to saturated. In summary, tenofovir was relatively persistent in soils, there were no extractable transformation products detected, and the response of [adenine-8-(14)C]-tenofovir mineralization to soil temperature and heat sterilization indicated that the molecule was biodegraded by aerobic microorganisms. Sorption isotherms with dewatered biosolids suggested that tenofovir residues could potentially partition into the particulate fraction during sewage treatment.

Label-free and highly sensitive biomolecular detection using SERS and electrokinetic preconcentration

In this paper, we present a method combining surface-enhanced Raman scattering (SERS) spectroscopy to detect biomolecules in a label-free way with an electrokinetic preconcentration technique (electrophoresis) to amplify biomolecular signals at low concentrations. A constant electric field is applied to charged biomolecules in solution, attracting them to an oppositely charged electrode, which is also used as a SERS substrate. Within 5 min, we observed that the SERS signal of 10 fM adenine was amplified to the level of the signal of non-preconcentrated 1 microM adenine (sensitivity improvement by 8 orders of magnitude) and the method was effective over a wide range of concentrations (10 fM to 1 microM). The signals were further amplified under stronger electric field and longer application: The increase of the signal intensity was observed to be 51 times at -0.6 V cm(-1) after 25 min. The effectiveness of this method allows the creation of label-free, target-specific, and highly sensitive monitoring applications.

Alternative polyadenylation variants of the RNA binding protein, HuR: abundance, role of AU-rich elements and auto-Regulation

The RNA-binding protein, HuR, is involved in the stabilization of AU-rich element-containing mRNAs with products that are involved in cell-cycle progression, cell differentiation and inflammation. We show that there are multiple polyadenylation variants of HuR mRNA that differ in their abundance, using both bioinformatics and experimental approaches. A polyadenylation variant with distal poly(A) signal is a rare transcript that harbors functional AU-rich elements (ARE) in the 3'UTR. A minimal 60-nt region, but not a mutant form, fused to reporter-3'UTR constructs was able to downregulate the reporter activity. The most predominant and alternatively polyadenylated mature transcript does not contain the ARE. HuR itself binds HuR mRNA, and upregulated the activity of reporter from constructs fused with ARE-isoform and the HuR ARE. Wild-type tristetraprolin (TTP), but not the zinc finger mutant TTP, competes for HuR binding and upregulation of HuR mRNA. The study shows that the HuR gene codes for several polyadenylation variants differentially regulated by AU-rich elements, and demonstrates an auto-regulatory role of HuR.

Application of UV-spectrophotometric methods for estimation of tenofovir disoproxil fumarate in tablets

Two new, simple and cost effective UV-spectrophotometric and first order derivative methods were developed for estimation of tenofovir disoproxil fumarate in bulk and tablets. Tenofovir disoproxil fumarate was estimated at 260 nm in 0.1N HCl. In first order derivative, it showed amplitude at 273 nm. In both the methods linearity was found to be in the range of 5-40 micro/ ml; for UV-spectrophotometric method (Y=0.02586 x +0.0083; r(2)=0.9999) and for first order derivative spectrophotometric method (Y=0.00132 x +0.00035; r(2)=0.9995), respectively. These methods were tested and validated for various parameters according to USP guidelines. The quantitation limits were found to be 1.546 and 1.986 micro/ ml, for both the methods. The proposed methods were successfully applied for the determination of tenofovir disoproxil fumarate in pharmaceutical formulations. The results demonstrated that the procedure is accurate, precise and reproducible (relative standard deviation <2%), while being simple, cheap and less time consuming and can be suitably applied for the estimation of tenofovir disoproxil fumarate in different dosage forms.

[Study on HPLC fingerprint characteristic analysis of Cordyceps sinensis and its similar products]

OBJECTIVE

To study on HPLC fingerprint characteristic analysis of Cordyceps sinensis and its similar products.

METHODS

To determinate 13 samples of Cordyceps sinensis and its similar products by HPLC, and analyze the HPLC results with similar appraisal method and graphical methods of multivariate sample in two dimensional plane such as the methods of profile, radar chart and constellation graph.

RESULTS

The similar appraisal method might synthesize the similar degree in quantification, while the graphical methods such as profile graph, radar chart and constellation graph could show more details about the classification and the characteristic of varieties directly.

CONCLUSIONS

We recommend the combined application of similar appraisal method and the graphical methods due to its advantages on the judgment and characteristic analysis of fingerprint.