Separation and determination of 11 marker pteridines in human urine by liquid chromatography and fluorimetric detection

Pyrazines in food samples: Recent update on occurrence, formation, sampling, pretreatment and analysis methods

Pyrazines are a class of active aromatic substances existing in various foods. The accumulation of pyrazines has an impact on flavor and quality of food products. This review encompasses the formation mechanisms and control strategies of pyrazines via Maillard reaction (MR), including the new reactants and emerging techniques. Pyrazines characteristics are better understood through the developed sample pretreatments and detection methods. Herein, an in-depth review of pretreatments and analysis methods since 2010 is presented to explore the simple, fast, green, and effective strategies. Sample preparation methods include liquid phase extraction, solid phase extraction, supercritical fluid extraction, and microextraction methods such as liquid phase microextraction, and solid phase microextraction, etc. Detections are made by chromatographic methods, and sensors, etc. Advantages and limitations are discussed and compared for providing insights to further studies.

Urinary neopterin and biopterin indicate that inflammation has a role in autism spectrum disorder

Inflammation is thought to be involved in the pathogenesis of autism spectrum disorder (ASD). Pteridine metabolites are biomarkers of inflammation that increase on immune system activation. In this study, we investigated the urinary pteridine metabolites in ASD patients as a possible biomarker for immune activation and inflammation. This observational, cross-sectional, prospective study collected urine samples from 212 patients with ASD and 68 age- and sex-matched healthy individuals. Urine neopterin (NE) and biopterin (BIO) levels were measured. Patients who had chronic disorders, active infection at the time of sampling, or high C-reactive protein levels were excluded. The urine NE and BIO concentrations were determined by high-performance liquid chromatography. The ratios of both NE and BIO to creatinine (CRE) were used to standardise the measurements. The NE/CRE and NE/BIO levels were significantly higher in ASD patients than controls. Univariate and multivariate models revealed a significant increase in NE/CRE and NE/BIO in ASD patients. There was a significant relationship between the NE/BIO [average area under the curve (AUC) = 0.717; range: 0.637-0.797] and NE/CRE (average AUC = 0.756; range: 0.684-0.828) ratios, which distinguished individuals with ASD from controls. The elevated NE/CRE and NE/BIO ratios suggest that inflammation and T cell-mediated immunity are involved in the pathophysiology of autism. NE/BIO could serve as a diagnostic inflammatory marker in the pathogenesis of ASD.

A simple and useful method for evaluation of oxidative stress in vivo by spectrofluorometric estimation of urinary pteridines

Pteridine derivatives are intermediate metabolites of folic acid and its cofactors. Oxidized-form pteridines, but not reduced-form pteridines, are fluorescent substances. The purpose of this study was to clarify whether oxidized-form pteridine level in urine, estimated by spectrofluorometry, reflects oxidative stress in vivo. The subjects were healthy middle-aged men (n = 258). Urinary pteridine level was estimated by spectrofluorometry with an excitation wavelength of 360 nm and an emission wavelength of 450 nm. Relationships of urinary pteridines with oxidative stress markers (urinary DNA/RNA oxidation products and 15-isoprostane F_2t) and with smoking were analyzed. Concentrations of pteridines, DNA/RNA oxidation products and 15-isoprostane F_2t were used after logarithmic transformation in linear analyses. Pteridine levels were significantly correlated with levels of DNA/RNA oxidation products (Pearson’s correlation coefficient: 0.626, p < 0.01) and 15-isoprostane F_2t (Pearson’s correlation coefficient: 0.695, p < 0.01). These correlations were not confounded by age, body mass index, history of smoking and estimated glomerular filtration rate in multivariate analysis. The mean urinary pteridine level was significantly higher in heavy smokers (16 cigarettes or more per day) than in nonsmokers and light smokers (less than 16 cigarettes per day) and was higher in light smokers than in nonsmokers. Thus, urinary fluorometric pteridine levels were shown to be associated with known biomarkers of oxidative stress as well as smoking, which causes oxidative stress in vivo. We propose spectrofluorometrical estimation of urinary pteridines as a simple and useful method for evaluation of oxidative stress in vivo.

Simultaneous determination of twelve polar pteridines including dihydro- and tetrahydropteridine in human urine by hydrophilic interaction liquid chromatography with tandem mass spectrometry

Pteridines and their derivatives are important cofactors in the process of cell metabolism, and the level of urinary excretion of these compounds is considered as an important clinical criterion. In this work, a new separation method involving hydrophilic interaction chromatography (HILIC) with tandem mass spectrometric detection has been developed for the simultaneous analysis of 12 pteridines including oxidized, di- and tetrahydroforms, namely neopterin, 7,8-dihydroneopterin, biopterin, 7,8-dihydrobiopterin, 5,6,7,8-tetrahydrobiopterin, dimethylpterin, dimethyltetrahydropterin, pterin, isoxanthopterin, xanthopterin, sepiapterin and pterin-6-carboxylic acid, in human urine without oxidative pretreatments. The stabilizing agent (dithiothreitol) at various concentrations and the stability of oxidized, di- and tetrahydroforms during the sample's short-term storage and processing and of the extracts were tested. In the developed method, 12 pteridines were chromatographically separated on an ZIC-HILIC column by gradient elution, and the run time was 20 min. Matrix effect was evaluated and several dilutions of urine were tested in order to study the evolution of signal suppression. Spiked recovery studies demonstrated that the technique was both accurate (83.1-116.7%) and precise (RSD 1.4-15.6%). Finally, several clinical urine specimens without oxidative pretreatments were examined with the new technique and compared with previous reports.

Pteridine determination in human serum with special emphasis on HPLC methods with fluorimetric detection

Conjugated and unconjugated pteridines and their derivatives are important cofactors in cellular metabolism. Hence, the amount of unconjugated pteridines in biological fluids has been found to be modified as a result of several disorders. It is necessary to note that while for the control of pteridines in urine samples there are numerous reference data, the literature referred to for the analysis of these analytes in serum/plasma is scarce. In biological fluids, pteridines can exist in different oxidation states, and these compounds can be classified into two groups according to: (a) oxidized or aromatic pteridines and (b) reduced pteridines. Oxidized pteridines yield a strong fluorescence signal, whereas reduced pteridines present a low quantum yield of fluorescence. In order to enable the analysis of the reduced forms, several preoxidation procedures to generate aromatic rings have been established. Also, stabilization of the reduced forms by the addition of reducing agents has been widely reported. The objective of this paper is to show possibilities and different approaches in the analysis of pteridines in serum samples. We have mainly focused on the description of the current situation in the application of high-performance chromatography methods with fluorimetric detection.

The role of urinary pteridines as disease biomarkers

Pteridines and their derivatives function as intermediates in the metabolism of several vitamins and cofactors, and their relevance to disease has inspired new efforts to study their roles as disease biomarkers. Recent analytical advances, such as the emergence of sensitive mass spectrometry techniques, new workflows for measuring pteridine derivatives in their native oxidation states and increased multiplexing capacities for the simultaneous determination of many pteridine derivatives, have enabled researchers to explore the roles of urinary pteridines as disease biomarkers at much lower levels with greater accuracy than with previous technologies or methods. As a result, urinary pteridines are being increasingly studied as putative cancer biomarkers with promising results being reported from exploratory studies. In addition, the role of urinary neopterin as a universal biomarker for immune system activation is being investigated in new diseases where it is anticipated to become a useful supplementary marker in clinical diagnostic settings. In summary, this review provides an overview of recent developments in the clinical study of urinary pteridines as disease biomarkers, covers the most promising aspects of advanced analytical techniques being developed for the determination of urinary pteridines and discusses the major challenges associated with implementing pteridine biomarkers in clinical laboratory settings.

HPLC determination of serum pteridine pattern as biomarkers

Pteridinic derivatives are important biomolecules considered as biomarkers for several diseases, especially in cancer and infectious pathologies. A new fluorimetric-HPLC method for the analysis of nine pteridines in human serum has been reported. Two analytical columns composed by C18 porous and fused core particles were assayed and the results compared. Fused core particle column allows us adequate separation, in only one run and in 15 min. Acid precipitation step of the proteins and clean-up process with an Isolute ENV+ (hydroxylated polystyrene-divinylbenzene copolymer) cartridge of the serum samples have been optimized. Analytes were determined by fluorimetric detection, exciting at 272 nm and measuring the fluorescence emission at 410 nm for isoxanthopterin, at 465 nm for xanthopterin, and at 445 nm for the analysis of the other pteridines. Detection limits between 0.07 and 0.61 ng mL(-1) were calculated according to Clayton criterium. Intraday precision varied from 1.2 to 5.3 and interday precision between 1.2 and 7.4, both expressed as RSD (%). External standard and standard addition calibrations were compared in the analysis of serum samples. The pteridine amounts in serum (expressed as ng mL(-1) ± confidence interval) were 3.69 ± 1.78; 1.35 ± 0.24; 0.46 ± 0.14; 0.54 ± 0.24; 0.84 ± 0.55; 2.10 ± 0.51 and 0.23 ± 0.11 for XAN, NEO, MON, ISO, BIO and 6HMPT, respectively, using the external standard method. Comparable results were obtained by the standard addition method. It is noticeable that 7BIO was not detected in the healthy serum samples analyzed.

Determination of pteridines in biological samples with an emphasis on their stability

Pteridines are a group of endogenous heterocyclic compounds whose concentrations in biological fluids may be increased in some disorders, such as infections, autoimmune disorders and cancer. In particular, pteridine concentrations in urine may represent promising noninvasive markers. However, their specificity requires further investigation. Pteridines can occur in three oxidation states with different stability. In order to enable the analysis of the unstable di- and tetra-hydroforms either an oxidation (mainly with iodine) or stabilization by reducing agents is applied. Due to the high polarity of pteridines, many analytical procedures employed ion-pair, ion-exchange or hydrophilic interaction liquid chromatography using mostly fluorescence detection. In the last decade, MS was found to be applicable. The objective of this Review is to show possibilities and different approaches in pteridine analysis in biological samples.