Hx Concentrations Research Articles

BCNO quantum dots-based ratiometric fluorescence platform integrated with portable device: Hypoxanthine sensing for on-site assessment of meat freshness with deep learning

Deep learning algorithms have been applied to digital image colorimetry (DIC) to improve color measurement and analysis, enabling the identification and quantification of analytes. In this work, we developed a smartphone-assisted platform for the detection of hypoxanthine (Hx) based on a ratiometric fluorescent probe (RF-probe) and deep learning algorithm for the first time with advantages of high sensitivity, in-field and simple operation, and accurate detection. Through an enzymatic cascade reaction, xanthine oxidase (XOD) degraded Hx to uric acid (UA) and H2O2, o-phenylenediamine (OPD) was converted to 2,3-diaminophenoxazine (DAP) by catalytic oxidation of H2O2 and OPD under horseradish peroxidase (HRP). The presence of DAP led to fluorescence quenching of BCNO quantum dots (BCNO QDs) at 440 nm and fluorescence enhancement of DAP at 570 nm due to the internal filtration effect (IFE). With the addition of Hx, the fluorescence color changed from blue to yellow. A good linear relationship was between I570/I440 and the Hx concentration in the range of 3-100 µM with a detection limit of 50 nM. Fluorescent color images of solution and test strips were acquired and extracted with a smartphone of our designed miniature device, which could be used to establish DIC for the detection of Hx with the linear relationship ranging from 0-100 μM and 0-40 μM, respectively. Then YOLOv5-assisted deep learning was applied to recognize and deal with the images, which offered improved accuracy, faster inference speed, flexibility, and efficient training. Therefore, our simple DIC platform was established for the in-field detection of Hx in real meat samples which was significant for the analysis of meat freshness and provided broad application potential for the analysis of other targets in food safety.

Co-products from the Atlantic salmon filleting industry – Their properties, stability and potential as human food ingredients

The present study impacts the growing knowledge about co-products obtained from the primary processing of Atlantic salmon (Salmo Salar L.) as food ingredients by highlighting their microbial and chemical composition and stability. The proximate composition varied between the co-products from the fatty belly-flap (34% lipid, 15% protein) to the leaner deboned meat (10% fat, 22% protein) (p < 0.001), whereas no differences were observed between the superior and production qualities (p > 0.31). However, the co-products from the processing of production quality salmon had a higher microbial load of psychotropic aerobic-, H2S-producing- and Pseudomonas spp. bacteria than those of superior quality salmon origin (4.0, 5.2, and 4.3 log CFU/g units higher, respectively). Fatty co-products, such as the belly flap, were especially susceptible to ATP degradation, giving higher Hx concentrations after 7/10 days of ice-storage than leaner fractions (p < 0.001). Moreover, a positive correlation between the lipid level and degradation of ATP was observed (r = 0.62, p = 0.006). To conclude, co-products from superior and production quality salmon contain valuable nutrients suitable for human consumption. However, the co-products are vulnerable to microbial and chemical deterioration, presumably due to disruption of biological membranes during processing, and should be handled accordingly.

Downregulation of Peroxidase Activity of Platinum Cube Enables Minute-Time Scale Colorimetric Signaling of Hypoxanthine for Fish Freshness Monitoring.

Due to its unique biological composition, aquatic products, especially fish, are extremely perishable compared to other muscle products. Herein, we proposed an artificial nanozyme-based colorimetric detection of hypoxanthine (Hx), the indicator of fish freshness, in a minute-time scale without the assistance of a natural enzyme (hypoxanthine oxidase). The principle is based on the interaction between Hx and polyvinylpyrrolidone-modified platinum cubic nanomaterials (PVP-PtNC), in which the catalytic active sites of PVP-PtNC's surface were blocked by Hx. This causes the downregulation of PVP-PtNC's catalytic ability and weakened its ability to catalyze the oxidization of 3,3',5,5'-Tetramethylbenzidine (TMB) by H2O2. Accordingly, the decrease in the UV-vis absorption and the weakening of the colorimetric reaction color is proportional to the Hx concentration. On this basis, a target-triggered colorimetric method for detecting Hx is developed for fish freshness monitoring with a fast detection speed, low cost, high accuracy, and simplified operation. Experiments reveal that the correlation response of Hx is from 0.5 μM to 10 mM with a limit of detection of 0.16 μM. In particular, the Hx detected from real fish indicates that the method possesses a promising potential for practical application. All of these features are expected to promote the development of online detection tools for food safety monitoring.

Co(OH)2/MXene-Ti3C2 nanocomposites with triple-enzyme mimic activities as hydrogel sensing platform for on-site detection of hypoxanthine.

Novel Co(OH)2/MXene-Ti3C2 nanocomposites with oxidase (OXD)-mimic, peroxidase (POD)-mimic, and catalase (CAT)-mimic activities were prepared by asimple two-step method. The Co(OH)2/MXene-Ti3C2 nanocomposites with triple-enzyme mimic activities were embedded into sodium alginate (SA) gels for the first time to fabricate a target-responsive hydrogel-assisted assay. The catalytic mechanism and steady-state kinetics of Co(OH)2/MXene-Ti3C2 nanocomposites were investigated. Subsequently, hypoxanthine (Hx) was catalyzed by xanthine oxidase (XOD) to form H2O2, which reacts with 3,3',5,5'-tetramethyl-benzidine (TMB) in the presence of Co(OH)2/MXene-Ti3C2 nanocomposites to form a blue oxide (ox-TMB) in the hydrogel. The visible color change of the hydrogel with the increase of Hx concentration can be recognized through a smartphone App to transfer the red (R), green (G), and blue (B) values for the quantitative determination of Hx, with adetection range from 5 to 250μM, and detection limit of0.2μM. Themethod was applied to the determination of Hx content in different aquatic products. The spiked recoveries of the aquatic products were from 94.1 to 106.4%, and the relative standard deviations (RSD) were less than 5.4%. Our results show that the Co(OH)2/MXene-Ti3C2 nanocomposites hydrogel-assisted colorimetric biosensor is cost-effective, sensitive, and selective andhas excellent application prospects forin-the-field determinationof Hx.

Cu nanoclusters decorated Ti3C2 nanosheets composite with tetraenzyme mimic activities and the application for smartphone-assisted detection of hypoxanthine

MXene-based nanozymes have increased research enthusiasm in the field of food safety and environment monitoring. Herein, the Cu NCs/Ti3C2 NSs nanocomposites were prepared by modifying copper nanoclusters (Cu NCs) on the surface of Ti3C2 nanosheets (NSs) with a simple two-step method. The Cu NCs/Ti3C2 NSs nanocomposites had outstanding tetraenzyme mimic activities, i.e. peroxidase (POD)-mimics, catalase (CAT)-mimics, ascorbic acid oxidase (AAO)-mimics and superoxide dismutase (SOD)-mimics. Modification of Cu NCs on Ti3C2 NSs can enhance tetraenzyme mimic activities because of the synergistic catalytic effect between Cu NCs and Ti3C2 NSs. The catalytic mechanism and steady-state kinetics of Cu NCs/Ti3C2 NSs were also investigated. Based on the POD-mimic activity of Cu NCs/Ti3C2 NSs, a simple and rapid colorimetric method was established for the on-site detection of hypoxanthine (Hx), with the linear range of 5–200 μM and limit of detection (LOD) was 0.25 μM. The visible color change with the increase of Hx concentration can be recognized by a smartphone APP to transfer the red (R), green (G) and blue (B) value for the quantitative analysis of Hx, with the linear range of 10–200 μM, which provided a convenient method for the real-time detection of Hx. This work not only provides a significant route to fabricate nanocomposite with outstanding tetraenzyme mimic activities but also offers a low-cost and rapid method for monitoring the freshness of aquatic products.

Hypoxanthine Reduces Radiation Damage in Vascular Endothelial Cells and Mouse Skin by Enhancing ATP Production via the Salvage Pathway

An effective method that can protect radiation-damaged tissues from apoptosis and promote tissue repair has not been reported to date. Hypoxanthine (Hx) is an intermediate metabolite in the purine degradation system that serves as a substrate for ATP synthesis via the salvage pathway. In this study, we focused on the transient decrease in intracellular ATP concentration after radiation exposure and examined the protective effect of Hx against radiation-induced tissue damage. Human umbilical vein endothelial cells were X irradiated, and the cell viability and incidence of apoptosis and DNA double-strand breaks (DSBs) were evaluated at different Hx concentrations. We found that in the presence of 2-100 µM Hx, the percentages of DSBs and apoptotic cells after 2, 6 and 10 Gy dose of radiation significantly decreased, whereas cell viability increased in a concentration-dependent manner. Moreover, the addition of Hx increased the levels of AMP, ADP, and ATP in the cells at 2 h postirradiation, suggesting that Hx was used for adenine nucleotide synthesis through the salvage pathway. Administration of a xanthine oxidoreductase inhibitor to a mouse model of radiation dermatitis resulted in increased blood Hx levels that inhibited severe dermatitis and accelerated recovery. In conclusion, the findings provide evidence that increasing the levels of Hx to replenish ATP could be an effective strategy to reduce radiation-induced tissue damage and elucidating the detailed mechanisms underlying the protective effects of Hx could help develop new protective strategies against radiation.

Smart phone assisted paper-based biosensor system for hypoxanthine detection in fish meat samples

In this work, we present the development of a paper-based, low-cost, sensitive, quantitative and stable platform proper for smartphone-assisted colorimetric detection of the fresh fish product to eliminate people’s concerns while consuming seafood. Biocompatible zones were prepared onto the paper filter material by chitosan modification an d mu lti-enzyme immobilization in the developed biosensor system. The visual detected result was connected with the hypoxanthine (Hx) amount by using a smartphone app that can perform image processing to evaluate the quantitative detection. Selectivity, specificity, stability, and direct real sample tests indicated the potential usability of the developed paper-based biosensor system for Hx detection in meat samples with an easy-to-use method. An application for examination of Hx concentration in real fish meat was achieved by placing the paper-based biosensor in contact with fish skin. As a future perspective, the developed method can be practical in developing portable biosensors to assess the fish freshness grade.

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 (H2O2), which was due to both the oxidation of H2O2 towards Cys-CuNCs and the resulting Cu(II). Owing to that Hx can generate H2O2 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 8–400 μmol/L has a good linear relationship with the fluorescence quenching efficiency, and the detection limit is 0.7 μmol/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.

Diffusion and Solubility of Common Microelectronic Airborne Molecular Contaminants into PEI Thin Polymer Membranes and its Related Contamination Control Applications

Sorption and outgassing mechanisms of corrosive gases in relation with wafers lost yield due to polymer container Front Opening Unified Pod (FOUP), is crucial information to understand the cross contamination between FOUP and wafers. This occurs when FOUPs (made in polymers) outgas contaminants into the wafer surrounding minienvironment. Gas sorption is governed by surface adsorption, followed by diffusion and solubility and then, permeability appears as a key parameter to understanding these cross contamination phenomena. In this work, we present the transport coefficients obtained for gaseous HF and HCl at cleanroom conditions (Patm, 21 ± 2°C &amp; 40% RH) at two different HX concentrations using the sorption kinetic method, based on Fick’s law, for thin films (≈50μm) of PEI. Finally, we establish the relationship between the sorption parameters of a polymer thin film and the potential contamination transfer from a FOUP whose main polymer material is similar.

An electrochemical biosensor for hypoxanthine detection in vitreous humor: A potential tool for estimating the post-mortem interval in forensic cases

In this study, a simple electrochemical method was developed for fast and convenient detection of hypoxanthine (Hx) and subsequent estimation of the post-mortem interval (PMI) in forensic cases. A polydopamine-modified carbon nanofibers (CNFs) electrode was utilized with xanthine oxidase (XOD) for Hx detection in vitreous humor (VH) samples for the first time. Fourier transform infrared (FT-IR) spectra and electrochemical characterization revealed the PDA-coated CNFs exhibited good biocompatibility for XOD immobilization and fast electron transfer. Under the optimal conditions, acceptable stability and reproducibility of the assay were achieved. Additionally, this enzymatic electrochemical biosensor showed a good linear relationship between the current response and Hx concentrations in the range of 5 − 60 µM and a detection limit of 2 μM. Consequently, the possible interferences in VH samples were studied to verify the selectivity of this device, and the findings confirmed the excellent detection specificity of this assay for the analysis of real samples. Moreover, the recycling experiments conducted in VH samples showed the practical application of this microdevice. In addition, the analysis of Hx concentration allowed for accurate PMI prediction, compared with known PMI values. These results indicated that the Hx biosensor may be a promising tool for the estimation of PMI in forensic investigations.

Change in Lactate, Ammonia, and Hypoxanthine Concentrations in a 1-Year Training Cycle in Highly Trained Athletes: Applying Biomarkers as Tools to Assess Training Status.

Włodarczyk, M, Kusy, K, Słomińska, E, Krasiński, Z, and Zieliński, J. Change in lactate, ammonia, and hypoxanthine concentrations in a 1-year training cycle in highly trained athletes: applying biomarkers as tools to assess training status. J Strength Cond Res 34(2): 355-364, 2020-The aim was to determine changes in biomarker (LA, NH3, purine metabolites) blood concentration during graded exercise and recovery throughout an annual training cycle in highly trained athletes of different training profiles. The study included 12 sprinters (SP, 21-30 years), 11 triathletes (TR, 20-31 years), 12 futsal players (FU, 19-31 years), and 13 amateur runners (AM, 20-33 years). Purine metabolite (hypoxanthine, xanthine, uric acid), ammonia (NH3), and lactate (LA) concentrations were determined at rest, during an incremental treadmill exercise test (every 3 minutes), and during recovery (5, 10, 15, 20, and 30 minutes postexercise) in 4 phases of an annual training cycle. Purine metabolite concentration was determined from plasma, whereas LA and NH3 from whole blood. For LA during exercise and recovery, certain significant differences between training phases within groups were observed for FU, TR, and SP but not for AM. For NH3, the greatest differences between examination points were observed for SP and TR near maximal exercise and in the first few stages of recovery. For hypoxanthine (Hx), the largest amount of differences between examination points was observed for FU, TR, and FU throughout the entire exercise spectrum. Biomarker concentration dynamics change during an incremental exercise test and postexercise in an annual training cycle. Biomarker responses differ depending on training type and magnitude of training loads used in various phases of an annual training cycle. When assessing training status using an incremental exercise test throughout an annual training cycle, NH3 and Hx concentration changes are more sensitive compared with LA.

Changes in Blood Concentration of Adenosine Triphosphate Metabolism Biomarkers During Incremental Exercise in Highly Trained Athletes of Different Sport Specializations.

Włodarczyk, M, Kusy, K, Słomińska, E, Krasiński, Z, and Zieliński, J. Changes in blood concentration of adenosine triphosphate metabolism biomarkers during incremental exercise in highly trained athletes of different sport specializations. J Strength Cond Res 33(5): 1192-1200, 2019-We hypothesized that (a) high-level specialized sport training causes different adaptations that induce specific biomarker release dynamics during exercise and recovery and (b) skeletal muscle mass affects biomarker release. Eleven sprinters (21-30 years), 16 endurance runners (18-31 years), 12 futsal players (18-29 years), and 12 amateur runners as controls (22-33 years) were examined. Hypoxanthine (Hx), xanthine (X), uric acid (UA), ammonia (NH3), and lactate (LA) concentrations were determined at rest, during an incremental treadmill exercise test (every 3 minutes), and during recovery (5, 10, 15, 20, and 30 minutes after exercise). Hx, X, and UA concentration was determined from plasma, while LA and NH3 from whole blood, and muscle mass was assessed using dual X-ray absorptiometry method. At rest, during incremental exercise, and up to 30 minutes into the postexercise recovery period, sprinters had lowest Hx, X, and UA concentrations, and endurance athletes had lowest NH3 concentrations. For LA during exercise, the lowest concentrations were noted in endurance athletes, except when reaching maximum intensity, where the differences between groups were not significant. There were no significant correlations observed between skeletal muscle mass and biomarker concentration at maximal intensity and recovery in any group. In conclusion, the magnitude of exercise-induced biomarker concentration is only related to training adaptations through specific training profile but not to muscle mass. In addition, the results suggest that combined measuring of LA, NH3, and Hx concentration in blood is useful in indirectly reflecting key changes in exercise- and training-induced energy status. Further research should focus on studying how specific training sessions affect individual biomarker response in highly trained athletes.

Layer-by-layer electrochemical biosensors configuring xanthine oxidase and carbon nanotubes/graphene complexes for hypoxanthine and uric acid in human serum solutions

A selective biosensing platform for the determination of hypoxanthine (Hx) and uric acid (UA) concentrations in both buffer and human serum sample solutions was developed. The biosensor features the layer-by-layer (LbL) self-assembly of negatively charged xanthine oxidase (XOD) and positively charged poly(diallyldimethyl ammonium chloride) (PDDA) wrapped oxidized multi-walled carbon nanotubes and graphene (CNTs-G) complexes (PDDA-CNTs-G) on screen printed carbon electrode (SPCE) surfaces. Catalytic responses of the XOD modified biosensor with the chosen optimum number of layers for LbL assembly on SPCE towards Hx in buffer solutions were first investigated using both cyclic and square wave voltammetries. The peak current at around 0.08 V (vs. Ag/AgCl) associated with the production of UA increased as a function of the Hx concentration due to the surface selective catalytic reaction of XOD and Hx. A linear dynamic range of 5–50 µM Hx with a detection limit of 4.40 µM was obtained and the sensor was further applied to the analysis of Hx in normal human serum solutions in addition to myocardial infarction (MI) patient serum sample solutions from a local hospital. Since untreated serum solutions contain a certain amount of UA, a XOD free SPCE biosensor consisted of only PDDA-CNTs-G was also employed to evaluate the native concentration of UA in the serum and further assist the determination of Hx concentration when using the developed LbL biosensor. Our sensing results for the real biological fluidic solutions were finally validated by comparing to those using liquid chromatography-mass spectrometry(LC-MS).

Room Temperature Phase Transition in Methylammonium Lead Iodide Perovskite Thin Films Induced by Hydrohalic Acid Additives.

Although reactive additives have been employed in perovskite solar cells to enhance film morphology and significantly increase device performance, little is known about the effect of these additives on perovskite structural and optical properties. Here we report a systematic study of how the properties of methylammonium lead iodide perovskite (CH3 NH3 PbI3 ) are influenced by hydrohalic acid additives (HX; X=I, Br, Cl) in the precursor solution. Detailed structural and optical spectroscopic analysis reveals that all three acids affect the optical properties and alter the unit cell lattice parameters. Depending on the identity and concentration of HX, optical bandgaps widen or compress: addition of HBr yields a wider bandgap, whereas HI compresses the gap at high concentrations; HCl, on the other hand, has no significant effect on the bandgap. These changes can be understood by correlating them with the types of defects present in polycrystalline perovskite thin films in combination with the structural strain induced in very small crystallites. The presence of extra halides from HX in the precursor solution enables filling of the lattice vacancies in the perovskite, thereby altering metal-halogen-metal bond connectivity and consequently cell volumes and optical bandgaps. Remarkably, a room temperature tetragonal→cubic phase transition is observed for CH3 NH3 PbI3 films treated with high HX concentrations. Further insights into this anomalous phase transformation are obtained from in situ variable-temperature X-ray diffraction in the 25-55 °C (298-328 K) range, revealing a monotonic fall in transition temperature with increasing precursor solution HX concentration.

Different target specificities of haptoglobin and hemopexin define a sequential protection system against vascular hemoglobin toxicity

Free hemoglobin (Hb) triggered vascular damage occurs in many hemolytic diseases, such as sickle cell disease, with an unmet need for specific therapeutic interventions. Based on clinical observations the Hb and heme scavenger proteins haptoglobin (Hp) and hemopexin (Hx) have been characterized as a sequential defense system with Hp as the primary protector and Hx as a backup when all Hp is depleted during more severe intravascular hemolysis. In this study we present a mechanistic rationale for this paradigm based on a combined biochemical and cell biological approach directed at understanding the unique roles of Hp and Hx in Hb detoxification. Using a novel in vitro model of Hb triggered endothelial damage, which recapitulates the well-characterized pathophysiologic sequence of oxyHb(Fe2+) transformation to ferric Hb(Fe3+), free heme transfer from ferric Hb(Fe3+) to lipoprotein and subsequent oxidative reactions in the lipophilic phase. The accumulation of toxic lipid peroxidation products liberated during oxidation reactions ultimately lead to endothelial damage characterized by a specific gene expression pattern with reduced cellular ATP and monolayer disintegration. Quantitative analysis of key chemical and biological parameters allowed us to precisely define the mechanisms and concentrations required for Hp and Hx to prevent this toxicity. In the case of Hp we defined an exponential relationship between Hp availability relative to oxyHb(Fe2+) and related protective activity. This exponential relationship demonstrates that large Hp quantities are required to prevent Hb toxicity. In contrast, the linear relationship between Hx concentration and protection defines a highly efficient backup scavenger system during conditions of large excess of free oxyHb(Fe2+) that occurs when all Hp is consumed. The diverse protective function of Hp and Hx in this model can be explained by the different target specificities of the two proteins.

High variation in hypoxanthine determination after analytical treatment of vitreous humor samples.

In the field of legal medicine the correct determination of the time of death is of great importance because an error in calculating the post-mortem interval (PMI) could be crucial in a criminal investigation. The quantification of hypoxanthine (Hx) concentration in the vitreous humor (VH) as a means to estimate PMI is useful when dealing with a recent time interval of death and has several advantages over other biological matrices. However, due to its viscous nature, VH has to be liquefied prior to its analysis, and the different procedures to liquefy it may cause alterations in Hx concentration, and hence in estimation of PMI. The aim of this study was to determine differences in Hx concentration after applying several pre-analytical treatments to different aliquots of the same VH sample. Enzymatic digestion, sonication, centrifugation and heat were the liquefying methods applied to reduce the viscosity of 105 VH samples. Analysis was performed using solid phase extraction and liquid chromatography in tandem with mass spectrometry. Statistically significant differences in the measured Hx concentrations were found between enzymatic digestion and the other three methods analyzed (sonication, centrifugation, and heat). Additionally, high data dispersion was found under heat treatment but was not observed for centrifugation or sonication, where similar and more moderate results were found. We conclude that high variations in Hx determination are observed when enzymatic digestion or heat treatment is used and we therefore recommend sonication or centrifugation to quantify Hx concentration in the VH.

Alterations in purine metabolism in middle-aged elite, amateur, and recreational runners across a 1-year training cycle

Changes in purine derivatives may be considered as signs of training-induced metabolic adaptations. The purpose of this study was to assess the effect of a 1-year training cycle on the response of hypoxanthine (Hx) concentration and Hx-guanine phosphoribosyltransferase (HGPRT) activity. Three groups of middle-aged male runners were examined: 11 elite master runners (EL; 46.0 ± 3.8 years), 9 amateur runners (AM; 45.1 ± 4.7 years), and 10 recreational runners (RE; 45.9 ± 6.1 years). Plasma Hx concentration and erythrocyte HGPRT activity were measured in three characteristic training phases of the annual cycle. Significant differences in post-exercise Hx concentration and resting HGPRT activity were demonstrated between the EL, AM, and RE groups across consecutive training phases. The EL group showed lowest Hx concentration and highest HGPRT activity compared to the AM and RE groups. Analogous differences were observed between the AM and RE groups during specific preparation. For the EL group, the changes were observed across all examinations and the lowest Hx concentration and highest HGPRT activity were found in the competition phase. Significant change was also revealed in the AM group between the general and specific preparation, but not in the competition phase. No significant changes were found in the RE runners who did not use anaerobic exercise in their training. In conclusion, a long-lasting endurance training, incorporating high-intensity exercise, results in significant changes in purine metabolism, whereas training characterized by constant low-intensity exercise does not. Plasma Hx concentration and erythrocyte HGPRT activity may be sensitive indicators of training adaptation and training status in middle-aged athletes.

Training-induced adaptation in purine metabolism in high-level sprinters vs. triathletes

The aim of this study was to assess the effect of training loads on metabolic response of purine derivatives in highly trained sprinters (10 men, age range 20-29 yr) in a 1-yr cycle, compared with endurance-training mode in triathletes (10 men, age range 21-28 yr). A four-time measurement of respiratory parameters, plasma hypoxanthine (Hx) concentration, and erythrocyte hypoxanthine-guanine phosphoribosyl transferase (HGPRT) activity was administered in four characteristic training phases (general, specific, competition, and transition). A considerably lower postexercise plasma concentration of Hx in sprinters (8.1-18.0 μmol/l) than in triathletes (14.1-24.9 μmol/l) was demonstrated in all training phases. In both groups, a significant decrease in plasma Hx concentration in the competition phase and a considerable increase in the transition phase were observed. It was found that the resting erythrocyte HGPRT activity increased in the competition period and declined in the transition phase. Sprinters showed higher HGPRT activity (58.5-71.8 nmol IMP·mg Hb(-1)·h(-1)) than triathletes (55.8-66.6 nmol IMP·mg Hb(-1)·h(-1)) in all examinations. The results suggest a more effective use of anaerobic metabolic energy sources induced by sprint training characterized by higher amount of exercise in the anaerobic lactacid and the nonlactacid zone. The changes in plasma Hx concentration and erythrocyte HGPRT activity might serve as sensitive metabolic indicators in the training control, especially in sprint-trained athletes. These parameters may provide information about the energetic status of the muscles in highly trained athletes in which no significant adaptation changes are detected by means of commonly acknowledged biochemical and physiological parameters.

Effect of Training Load Structure on Purine Metabolism in Middle-Distance Runners

There are no studies analyzing the effect of training loads on purine metabolism during long training periods. The study's purpose was to evaluate the effect of training load changes and subsequent detraining on purine metabolism in middle-distance runners during a 1-yr cycle. In four characteristic points of the training cycle, loads assigned to five intensity zones, pre- and postexercise plasma hypoxanthine (Hx) and uric acid, and erythrocyte Hx-guanine phosphoribosyltransferase (HGPRT) activity were determined in 11 male middle-distance runners at the national level, practicing competitive sport for 8.1 ± 0.3 yr and with a mean age of 22.3 ± 0.7 yr, body mass of 73.0 ± 3.4 kg, and body height of 180 ± 2.2 cm. In the competition phase (CP), training loads in aerobic compensation and threshold zones decreased by 65.4% and by 20.5%, respectively. At the same time, anaerobic training loads increased by 132.5% in the VO(2max) zone and by 74.6% in the lactic acid tolerance zone. Postexercise Hx decreased significantly in CP by 6.2 μmol·L(-1). and increased in the transition phase (TP) by 17.4 μmol·L(-1). Both pre- and postexercise HGPRT activity increased significantly in CP by 9.3 nmol·mg(-1)·h(-1). and by 4.9 nmol·mg(-1)·h(-1). , respectively, and decreased significantly in TP by 10.6 nmol·mg(-1)·h(-1). and by 12.0 nmol·mg(-1)·h(-1). , respectively. A significant uric acid increase of 54 μmol·L(-1). was revealed merely in TP. The effect of anaerobic training on purine metabolism is significant despite of a very short total duration of anaerobic loads. Elevated preexercise HGPRT activity in CP suggests adaptation changes consisting in a "permanent readiness" for purine salvage. The detraining in TP leads to reverse adaptation changes. Probably, plasma Hx concentration and erythrocyte HGPRT activity may be considered as a useful measure of training status.

Hypoxanthine-based enzymatic sensor for determination of pork meat freshness

An enzyme sensor employing xanthine oxidase (XO), soluble or immobilised, in combination of an oxygen electrode has been developed and optimised to determinate the hypoxanthine (Hx) content in pork meat at different post-mortem times as measure of meat freshness. The amperometric signal obtained due to the oxygen depletion during the Hx oxidation was related with the consumed oxygen at 190 s in the soluble enzyme sensor or enzymatic rate at 10 s in the immobilised enzyme sensor. In both cases a linear relationship between the signal and the Hx concentration in the range 8.68–26.05 μM ( R 2 = 0.999) and 15.63–127 μM. ( R 2 = 0.995), respectively, was found. Both enzyme sensors exhibited very good working conditions and storage stability. A study of Hx oxidation was carried out in order to compare the Hx content measured by both sensors and those measured by high performance liquid chromatography (HPLC) obtaining a good agreement between both techniques. Therefore, the easy preparation and operation of both enzyme sensors suggests a reliable, rapid and an economical alternative for simple or multiple Hx measurements constituting a useful tool as quality control of meat freshness.