Dried urine swabs as a tool for monitoring metabolite excretion.

AIM: We tested a large set (n = 181) of wet urine and dried urine samples spotted on regular cosmetic cotton swabs for comparative UHPLC-MS/MS analysis of various metabolites across a wide polarity and structural range. Results/methodology: The agreement of measurements between conventional 24 h urines and dried urine spots made from them in situ was evaluated by Passing-Bablok regression and Bland-Altman analysis after creatinine correction. There was full agreement in qualitative results but quantitative analysis revealed underestimation of dried urine spots in some cases. The dried urine samples contained analytes at measurable levels for at least 9 months. CONCLUSION: Although this technique seems very promising more methodological studies have to be conducted in order to improve applicability of dried urine microvolume fluidic sampling for quantitative analysis.

Short-term effects of dietary advanced glycation end products in rats.

Dietary advanced glycation end products (AGE) formed during heating of food have gained interest as potential nutritional toxins with adverse effects on inflammation and glucose metabolism. In the present study, we investigated the short-term effects of high and low molecular weight (HMW and LMW) dietary AGE on insulin sensitivity, expression of the receptor for AGE (RAGE), the AGE receptor 1 (AGER1) and TNF-α, F2-isoprostaglandins, body composition and food intake. For 2 weeks, thirty-six Sprague-Dawley rats were fed a diet containing 20% milk powder with different proportions of this being given as heated milk powder (0, 40 or 100%), either native (HMW) or hydrolysed (LMW). Gene expression of RAGE and AGER1 in whole blood increased in the group receiving a high AGE LMW diet, which also had the highest urinary excretion of the AGE, methylglyoxal-derived hydroimidazolone 1 (MG-H1). Urinary excretion of N ε-carboxymethyl-lysine increased with increasing proportion of heat-treated milk powder in the HMW and LMW diets but was unrelated to gene expression. There was no difference in insulin sensitivity, F2-isoprostaglandins, food intake, water intake, body weight or body composition between the groups. In conclusion, RAGE and AGER1 expression can be influenced by a high AGE diet after only 2 weeks in proportion to MG-H1 excretion. No other short-term effects were observed.

Effect of dietary advanced glycation end products on postprandial appetite, inflammation, and endothelial activation in healthy overweight individuals.

PURPOSE: Advanced glycation end products (AGEs) formed in food during high-heat cooking may induce overeating and inflammation. We investigated whether AGE contents in a single meal affect postprandial appetite and markers of inflammation, endothelial activation, and oxidative stress. METHODS: In total, 19 healthy overweight individuals completed a crossover meal test with two meals of identical ingredients prepared by roasting (H-AGE) or steaming (L-AGE), respectively. Postprandial blood samples were analysed for N(ε)-carboxymethyl-lysine (CML), appetite-regulating gut hormones, glucose, insulin, triacylglycerol, and markers of inflammation and endothelial activation. Subjective appetite ratings and subsequent food intake were also assessed, and urine was analysed for CML, methylglyoxal-derived hydroimidazolone (MG-H1), and F2-isoprostanes. RESULTS: CML content of the H- and L-AGE meals was 5.0 and 2.8 mg, respectively. Plasma CML and urinary CML and MG-H1 tended to be higher after the H-AGE meal. There was no change in subsequent food intake, appetite sensations, or appetite hormone responses between meals, except for the overall ghrelin response, which was higher after the H-AGE meal compared with the L-AGE meal (p = 0.016). There was an increased glycaemic response to the H-AGE meal (p = 0.027) compared with the L-AGE meal. Inflammatory and endothelial activation markers did not differ between meals, but there was an overall effect on endothelial activation (p = 0.021) and on the oxidative marker, F2-isoprostanes, in urine (p = 0.013). CONCLUSION: The present study did not show any pronounced effects of AGEs on appetite and markers of inflammation, but did indicate that AGEs may affect postprandial ghrelin, oxidative stress, and glucose responses.

Monitoring of PQQ-dependent glucose dehydrogenase substrate specificity for its potential use in biocatalysis and bioanalysis.

Substrate specificity of 2,7,9-tricarboxypyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase was investigated in biosensor arrangement for understanding the suitability and the limitations of its use in bioanalysis and bioproduction of chemicals. The study demonstrated a very broad substrate specificity of biosensor utilising soluble form of PQQ-dependent glucose dehydrogenase. Nineteen saccharides out of 31 were oxidised by the sensor. Investigation confirmed strong importance of hydroxyl configuration in the positions 2 and 5 of oxidised saccharides. The broad specificity suggests that the PQQ-dependent glucose dehydrogenase could be utilised for analysis of other sugars than glucose in food samples for various production processes and for biofuel cells. In addition, the results showed that the substrate specificity of enzymes can be effectively and generally studied by biosensor arrangement for research purposes. This layout utilising immobilised enzyme allowed performing comprehensive study using a small amount of enzymes and thus saving the costs and time.

Monitoring of monosaccharides, oligosaccharides, ethanol and glycerol during wort fermentation by biosensors, HPLC and spectrophotometry.

The aim of the present study was to analyze sugar levels (namely maltose, maltotriose, glucose and fructose) and alcohols (ethanol and glycerol) during the fermentation process in wort samples by amperometric enzymatic biosensors developed by our research group for industrial application, HPLC and spectrophotometry, and to compare the suitability of the presented methods for determination of individual analytes. We can conclude that for the specific monitoring of maltose or maltotriose only the HPLC method was suitable. On the other hand, biosensors and spectrophotometry reflected a decrease in total sugar concentration better and were able to detect both glucose and fructose in the later stages of fermentation, while HPLC was not. This can be attributed to the low detection limits and good sensitivity of the proposed methods. For the ethanol and glycerol analysis all methods proved to be suitable. However, concerning the cost expenses and time analysis, biosensors represented the best option.

Amperometric glucose biosensor utilizing FAD-dependent glucose dehydrogenase immobilized on nanocomposite electrode.

Amperometric glucose biosensors utilizing commercially available FAD-dependent glucose dehydrogenases from two strains of Aspergillus species are described. Enzymes were immobilized on nanocomposite electrode consisting of multi-walled carbon nanotubes by entrapment between chitosan layers. Unlike the common glucose oxidase based biosensor, the presented biosensors appeared to be O(2)-independent. The optimal amount of enzymes, working potential and pH value of working media of the glucose biosensors were determined. The biosensor utilizing enzyme isolated from Aspergillus sp. showed linearity over the range from 50 to 960 µM and from 70 to 620 µM for enzyme from Aspergillus oryzae. The detection limits were 4.45 µM and 4.15 µM, respectively. The time of response was found to be 60 s. The biosensors showed excellent operational stability - no loss of sensitivity after 100 consecutive measurements and after the storage for 4 weeks at 4 °C in phosphate buffer solution. When biosensors were held in a dessicator at room temperature without use, they kept the same response ability at least after 6 months. Finally, the results obtained from measurements of beverages and wine samples were compared with those obtained with the enzymatic-spectrophotometric and standard HPLC methods, respectively. Good correlation between results in case of analysis of real samples and good analytical performance of presented glucose biosensor allows to use presented concept for mass production and commercial use.

Application of electrochemical biosensors in clinical diagnosis.

Analyses in the clinical area need quick and reliable analytical methods and devices. For this purpose, biosensors can be a suitable option, whereas they are constructed to be simple for use, specific for the target analyte, capable of continuous monitoring and giving quick results, potentially low-costing and portable. In this article, we describe electrochemical biosensors developed for clinical diagnosis, namely for glucose, lactate, cholesterol, urea, creatinine, DNA, antigens, antibodies, and cancer markers assays. Chosen biosensors showed desirable sensitivity, selectivity, and potential for application on real samples. They are often designed to avoid interference with undesired components present in the monitored systems.

Multienzymatic amperometric biosensor based on gold and nanocomposite planar electrodes for glycerol determination in wine.

Amperometric biosensors based on gold planar or nanocomposite electrode containing multiwalled carbon nanotubes for determination of glycerol were developed. The biosensors were constructed by immobilization of a novel multienzyme cascade consisting of glycerol kinase/creatine kinase/creatinase/sarcosine oxidase/peroxidase between a chitosan "sandwich." A measuring buffer contained adenosine 5'-triphosphate (ATP), creatine phosphate, and an artificial electrochemical mediator ferrocyanide. The currents proportional to glycerol concentration were measured at working potential of -50 mV against Ag/AgCl reference electrode. The biosensors showed linearity over the ranges of 5-640 µM and 5-566 µM with detection limits of 1.96 and 2.24 µM and sensitivities of 0.80 and 0.81 nA µM(-1), respectively. Both types of biosensors had a response time of 70s. The biosensors demonstrated satisfactory operational stability (no loss of sensitivity after 90 consecutive measurements) and excellent storage stability (90% of the initial sensitivity after 15 months of storage at room temperature). The results obtained from measurements of wines correlated well with those obtained with an enzymatic-spectrophotometric assay. The presented multienzyme cascade can be used also for determination of triglycerides or various kinase substrates when glycerol kinase is replaced by other kinases.