A ratiometric fluorescent probe for hypoxanthine detection in aquatic products based on the enzyme mimics and fluorescence of cobalt-doped carbon nitride

A ratiometric fluorescent probe for hypoxanthine(Hx)detection was established based on the mimic enzyme and fluorescence characteristics of cobalt-doped graphite-phase carbon nitride(Co doped g-C_(3)N_(4)).In addition to emitting strong fluorescence,the peroxidase activity of Co doped g-C_(3)N_(4)can catalyze the reaction of O-phenylenediamine and H_(2)O_(2)to produce diallyl phthalate which can emit yellow fluorescence at 570 nm.Through the decomposition of Hx by xanthine oxidase,Hx can be indirectly detected by the generating hydrogen peroxide based on the measurement of fluorescent ratio I(F_(570)/F_(370)).The linear range was 1.7-272.2 mg/kg(R^(2)=0.997),and the detection limit was 1.52 mg/kg(3σ/K,n=9).The established method was applied to Hx detection in bass,grass carp,and shrimp,and the data were verified by HPLC.The result shows that the established probe is sensitive,accurate,and reliable,and can be used for Hx detection in aquatic products.

Voltammetric Detection of Nanomolar Levels of Hypoxanthine in the Presence of Copper(Ⅱ) at Glassy Carbon Electrode

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X-Ray Induced Mutation Frequency at the <i>Hypoxanthine Phosphoribosyltransferase</i>Locus in Clinically Relevant Radioresistant Cells

To elucidate the molecular mechanisms underlying cellular radioresistance, clinically relevant radioresistant cell lines were established via long-term exposure to X-rays with stepwise dose escalation. Established cells continue to proliferate despite exposure to 2 Gy X-rays/day for more than 30 days, a standard protocol in cancer radiotherapy. DNA repair fidelity in radioresistant and the parental cells by evaluating the mutation frequency at the hypoxanthine phosphoribosyltransferase (HPRT) locus after exposure to X-rays was determined. Mutation spectrum at the HPRT locus was examined by multiplex polymerase chain reaction. Rejoining kinetics of X-ray-induced DNA double strand breaks (dsbs) was evaluated by the detection of phosphorylated histone H2AX (γH2AX) after X-irradiation. The fold increase in the HPRT mutation frequency due to acute radiation was similar between radioresistant and the parental cell lines. However, fractionated radiation (FR) consisting of 2 Gy X-rays/day increased the mutation frequency at the HPRT locus in parental but not in radioresistant cells. Analysis of the FR-induced mutations at the HPRT locus revealed a high frequency of deletion mutations (>70%) in parental but not in radioresistant cells. As assessed by γH2AX immunostaining, DNA dsbs induced by acute exposure to 10 Gy of X-rays were repaired to the control level within 7 days in radioresistant but not in the parental cells. Moreover, 2 Gy × 5 FR increased the number of γH2AX-positive cells in parental cultures but not in radioresistant cultures. DNA dsbs induced by 2 Gy/day FR are repaired with fidelity in radioresistant but not in parental cells.

Determination of Hypoxanthine in the Presence of Copper by Adsorptive Stripping Voltammetry

A stripping method for the determination of hypoxanthine in the presence of copper at the submicromolar concentration levels is described. The method is based on controlled adsorptive accumulation of hypoxanthine-copper at the thin-film mercury electrode followed by a fast linear scan voltammetric measurement of the surface species. Optimum experimental conditions were found to be the use of 1.0 × 10﹣3 mol·L﹣1 NaOH solution as electrolyte supporting, an accumulation potential of ﹣0.50 V and a linear scan rate of 200 mV·s﹣1. The response of hypoxanthine-copper is linear over the concentration ranges of 10 - 60 ppb. For an accumulation time of 30 minutes, the detection limit was found to be 250 ppt (1.8 × 10﹣9 mol·L﹣1). Adequate conditions for measuring the hypoxanthine in the presence of metal ions, xanthine, uric acid and other nitrogenated bases were also investigated. The utility of the method is demonstrated by the presence of hypoxanthine associated in ATP or ssDNA.

On-line electrochemical measurements of cerebral hypoxanthine of freely moving rats

This study demonstrates an on-line method for continuous measurements of cerebral hypoxanthine in the freely moving rats with integration of selective electrochemical biosensing with in vivo microdialysis sampling. The selective electrochemical biosensing is achieved by using xanthine oxidase (XOD) as the specific sensing element and Prussian blue (PB) as the electrocatalyst for the reduction of H2O2 generated from the oxidase-catalyzed reaction. The method is virtually interference-free from the co-existing electroactive species in the brain and exhibits a good stability and reproducibility. Upon integrated with in vivo microdialysis, the on-line method is well suitable for continuous measurements of cerebral hypoxanthine of freely moving rats, which is illustrated by the measurements of the microdi-alysates after the hypoxanthine standard was externally infused into the rat brain. This study essentially offers a facile on-line electrochemical approach to continuous measurements of cerebral hypoxanthine and could find some interesting applications in physiological and pathological investigations associated with hypoxanthine.

Fluorescent Copper Nanoclusters for Highly Sensitive Monitoring of Hypoxanthine in Fish

Hypoxanthine(Hx)is an important freshness indicator reflecting the initial freshness of aquatic products.In this work,a novel fluorescence method was established based on cysteine functionalized copper nanoclusters(Cys-CuNCs)for monitoring Hx in fish.The as-synthesized Cys-CuNCs exhibit favorable fluorescent property.Importantly,the fluorescence can be quenched significantly when the solution contained a small amount of hydrogen peroxide(H_(2)O_(2)),which was due to both the oxidation of H_(2)O_(2) towards Cys-CuNCs and the resulting Cu(II).Owing to that Hx can generate H_(2)O_(2) under dissolved oxygen and xanthine oxidase(XOD),a fluorescent method for Hx was established.Under the optimal conditions,the Hx concentration in the range of 8–400μmol/L has a good linear relationship with the fluorescence quenching e fficiency,and the detection limit is 0.7μmol/L.Finally,the as-established sensor was applied to determine Hx content in carp.By comparing to the total volatile basic nitrogen(TVB-N)results,the proposed method was feasible in the evaluation of carp freshness.

Utility of cardiac biomarkers in sports medicine:Focusing on troponin,natriuretic peptides,and hypoxanthine

Evidence-based consensus suggests that physical activity and regular exercise training can reduce modifiable risk factors as well as rate of mortality and morbidity in patients with chronic diseases,such as cardiovascular disease(CVD),diabetes,obesity and cancer.Conversely,long-term exercise training and drastic increase in vigorous physical activity may also cause acute cardiovascular events(e.g.acute myocardial infarction)and deleterious cardiac remodeling,particularly when exercise is performed by unfit or susceptible individuals.There is a reversed J-shaped hormesis-like curve between the duration and intensity of exercise and level of CVD risks.Therefore,it is important for an early detection of cardiac injuries in professional and amateur athletes.Under this context,this article focuses on the use of biomarker testing,an indispensable component in the current clinical practices especially in Cardiology and Oncology.We attempt to justify the importance of using circulating biomarkers in routine practices of Sports Medicine for an objective assessment of CVD events following exercise.Special attentions are dedicated to three established or emerging cardiac biomarkers(i.e.cardiac troponins,natriuretic peptides,hypoxanthine)for myocardial tissue hypoxia/ischemia events,muscle stress,and the consequent cellular necrotic injury.Based on these focused analyses,we propose use of circulating biomarker testing in both laboratory and point-of-care settings with an increasingly broader involvement or participation of team physicians,trainers,coaches,primary care doctors,as well as educated athlete community.This diagnostic approach may improve the quality of medical surveillance and preventive measures on exercise-related CVD risks/outcomes.

Chemical Quality Indexes of Mullet (<i>Mugil platanus</i>) Stored on Ice

The present study was conducted aiming at establishing chemical quality parameters to assess ice stored mullet (0℃ ± 1℃) through the evaluation of nucleotide (adenosine monophosphate [AMP], inosine [HxR] and hypoxanthine [Hx]) degradation, biogenic amine (histamine [HI], putrescine [PU], cadaverine [CA] and tyramine [TI]) quantification and mesophilic and psychrotrophic bacteria count monitoring. The microbial load of 7 log CFU·g–1 established as maximum acceptable limit was attained after the 20th day of ice storage. IMP concentration declined during the storage period to levels below the detection limit. HxR content increased only up to time T3 and then declined. Hx level increased during all the storage period. CA and HI content increase was not observed, on the other hand, PU and TI contents significantly increased (p < 0.05) at time T5. We concluded that IMP and Hx concentrations can be adequate parameters to assess mullet quality under the study conditions. HxR proved to be adequate to evaluate the freshness of mullet in the first days of storage while the amines, PU and TI, can be used to assess loss of quality. Mullet obtained in conditions similar to those of the present study and maintained at 0℃ ± 1℃ can be consumed up to the 20th storage day.

Disposable amperometric biosensors based on xanthine oxidase immobilized in the Prussian blue modified screen-printed three-electrode system

The screen-printed three-electrode system was applied to fabricate a new type of disposable amperometric xanthine oxidase biosensor.Carbon-working,carbon-counter and Ag/AgCl reference electrodes were all manually printed on the polyethylene terephthalate substrate forming the screen-printed three-electrode system by the conventional screen-printing process.As a mediator,Prussian blue could not only catalyze the electrochemical reduction of hydrogen peroxide produced from the enzyme reaction,but also keep the favorable potential around 0 V.The optimum operational conditions,including pH,potential and temperature,were investigated.The sensitivities of xanthine and hypoxanthine detections were 13.83 mA/M and 25.56 mA/M,respectively.A linear relationship was obtained in the concentration range between 0.10μM and 4.98μM for xanthine and between 0.50μM and 3.98μM for hypoxanthine.The small Michaelis-menten constant value of the xanthine oxidase biosensor was calculated to be 3.90 μM.The results indicate that the fabricated xanthine oxidase biosensor is effective and sensitive for the detection of xanthine and hypoxanthine.