Rapid and reliable HILIC-MS/MS method for monitoring allantoin as a biomarker of oxidative stress.

Allantoin is an excellent biomarker of oxidative stress in humans as the main product of uric acid oxidation by reactive oxygen species. Yet, allantoin determination is still not routinely performed in clinical laboratories. Therefore, we developed a fast, simple, selective, and sensitive UHPLC-MS/MS method for allantoin determination in human serum using an isotopically labeled internal standard. Our analytical protocol provided high sensitivity by mass spectrometry detection and high throughput by HILIC-MS/MS analysis within 4 min, with one-step serum sample preparation approximately within 7 min. Lastly, our protocol was fully validated to demonstrate its reliability in allantoin determination in human serum. The method showed an excellent linear range from 0.05 to 100 µM, with precision ranging from 1.8 to 11.3% (RSD), and with accuracy (relative error %) within ±6.0%. The method was then applied to analyze the concentration of allantoin in serum samples from 71 patients with chronic gout without treatment with xanthine oxidase inhibitors. The median serum allantoin concentration in the cohort was 2.8 µM (n = 71). Overall, our simple analytical protocol has the potential to be easily implemented in clinical routine practice for monitoring allantoin as a key oxidative stress biomarker.

Serum uric acid increases in patients with systemic autoimmune rheumatic diseases after 3 months of treatment with TNF inhibitors.

In patients with gout, the serum uric acid (SUA) is usually lower during acute gouty attacks than during intercritical periods. It has been suggested that systemic inflammatory response can cause this phenomenon. The objective is to determine whether therapy with TNF inhibitors (TNFis) affects SUA levels in patients with systemic autoimmune rheumatic diseases (SARDs) and whether SUA changes correlate with pro-inflammatory cytokines or with the oxidative stress marker allantoin. In this study, SUA, CRP, creatinine, MCP-1, IFN-α2, IFN-γ, Il-1ß, IL-6, IL-8, IL-10, IL-12, IL-17a, IL-18, IL-23, IL-33, TNF-α, and allantoin levels were measured prior to and after 3 months of TNFis treatment in patients with SARDs. The values obtained in the biochemical assays were then tested for associations with the patients' demographic and disease-related data. A total of 128 patients (rheumatoid arthritis, n = 44; ankylosing spondylitis, n = 45; psoriatic arthritis, n = 23; and adults with juvenile idiopathic arthritis, n = 16) participated in this study. Among the entire patient population, SUA levels significantly increased 3 months after starting treatment with TNFis (279.5 [84.0] vs. 299.0 [102.0] µmol/l, p < 0.0001), while the levels of CRP, IL-6, IL-8, and MCP-1 significantly decreased. Male sex was the most powerful baseline predictor of ΔSUA in univariate and multivariate models. None of the measured laboratory-based parameters had statistically significant effects on the magnitude of ΔSUA. 3 months of anti-TNF therapy increased the levels of SUA in patients with SARDs, but neither the measured pro-inflammatory cytokines nor the oxidation to allantoin appeared responsible for this effect.

Serum metabolites are associated with all-cause mortality in chronic kidney disease.

Chronic kidney disease (CKD) involves significant metabolic abnormalities and has a high mortality rate. Because the levels of serum metabolites in patients with CKD might provide insight into subclinical disease states and risk for future mortality, we determined which serum metabolites reproducibly associate with mortality in CKD using a discovery and replication design. Metabolite levels were quantified via untargeted liquid chromatography and mass spectroscopy from serum samples of 299 patients with CKD in the Modification of Diet in Renal Disease (MDRD) study as a discovery cohort. Six among 622 metabolites were significantly associated with mortality over a median follow-up of 17 years after adjustment for demographic and clinical covariates, including urine protein and measured glomerular filtration rate. We then replicated associations with mortality in 963 patients with CKD from the African American Study of Kidney Disease and Hypertension (AASK) cohort over a median follow-up of ten years. Three of the six metabolites identified in the MDRD cohort replicated in the AASK cohort: fumarate, allantoin, and ribonate, belonging to energy, nucleotide, and carbohydrate pathways, respectively. Point estimates were similar in both studies and in meta-analysis (adjusted hazard ratios 1.63, 1.59, and 1.61, respectively, per doubling of the metabolite). Thus, selected serum metabolites were reproducibly associated with long-term mortality in CKD beyond markers of kidney function in two well characterized cohorts, providing targets for investigation.

Cholesterol lowering treatment restores blood global DNA methylation in chronic kidney disease (CKD) patients.

BACKGROUND AND AIMS: Chronic kidney disease (CKD) is characterized by increased oxidative stress (OS). In consideration of the well-known link between OS and DNA methylation we assessed DNA methylcytosine (mCyt) concentrations in CKD patients at baseline and during cholesterol lowering treatment. METHODS AND RESULTS: DNA methylation and OS indices (malonyldialdehyde, MDA; allantoin/uric acid ratio, All/UA) were measured in 30 CKD patients randomized to three cholesterol lowering regimens for 12 months (simvastatin 40 mg/day, ezetimibe/simvastatin 10/20 mg/day, or ezetimibe/simvastatin 10/40 mg/day) and 30 age- and sex-matched healthy controls. DNA methylation was significantly lower in CKD patients vs. controls (4.06 ± 0.20% vs. 4.27 ± 0.17% mCyt, p = 0.0001). Treatment significantly increased mCyt DNA concentrations in all patients (4.06 ± 0.04% at baseline; 4.12 ± 0.03% at 4 months; 4.17 ± 0.03% at 8 months; and 4.20 ± 0.02% at 12 months, p = 0.0001 for trend). A trend for a greater effect on DNA methylation was observed with combined treatment ezetimibe/simvastatin 10/40 mg/day (+5.2% after one year treatment). The treatment-associated mCyt increase was significantly correlated with the concomitant reduction in MDA concentrations and All/AU ratios. CONCLUSION: Our results demonstrate that CKD patients have a lower degree of DNA methylation and that cholesterol lowering treatment restores mCyt DNA concentrations to levels similar to healthy controls. The treatment-associated increase in DNA methylation is correlated with a concomitant reduction in OS markers. The study was registered at clinicaltrials.gov (NCT00861731).

Serum allantoin and aminothiols as biomarkers of chronic heart failure.

Background Oxidative stress (OS) represents the primary mediator of chronic heart failure (CHF) development and progression. It is well established that homocysteine is able to generate reactive oxygen species. Small amounts of allantoin in human serum result from free radical action on urate and may provide a stable marker for in vivo free radical activity. To investigate whether some easily measurable indexes such as antioxidants (uric acid, glutathione) and related molecules (allantoin, homocysteine and cysteine) can serve as OS biomarkers. Methods We investigated 75 stable CHF patients. Aminothiols and purine compound levels were determined by capillary electrophoresis. Results The homocysteine level was markedly elevated in CHF patients, whatever the aetiology. Parameters of the transsulfuration pathway and the investigated purine compounds were significantly increased. Conversely, total glutathione was decreased. The allantoin/uric acid ratio was significantly higher in CHF patients with an hyperhomocysteinaemia >17 µmol/L. All parameters of the transsulfuration and purine degadation pathways were significantly correlated, suggesting an OS in CHF patients. Conclusion Our data show an imbalance of serum aminothiols and purine compounds in these CHF patients on adapted therapy. We suggest that the evaluation and control of these new markers may help improve the OS that participates in the progression of the disease.

The relationship between hypertension and plasma allantoin, uric acid, xanthine oxidase activity and nitrite, and their predictive capacity in severe preeclampsia.

It is controversial that uric acid (UA) levels are related to the severity of hypertension in preeclampsia (PE). Our aim in this study was to determine whether UA, xanthine oxidase activity (XOA), allantoin and nitrite levels are related to arterial blood pressure (BP) in PE. We formed a control group (n = 20) and a PE group (n = 20) for the study. Their BPs and plasma UA, XOA, allantoin and nitrite levels were measured. The values from the control and PE pregnant women were assessed via a Wilcoxon matched-pairs test. A Pearson correlation test was also performed. In addition, the diagnostic value of these tests was evaluated via receiver operating characteristic (ROC) analysis. The BP, UA, XOA and allantoin levels in the PE patients were found to be higher when compared with those of the pregnant controls. The UA, XOA and allantoin levels showed high correlations with BP in cases of PE. However, there was no superiority among the correlations. No differences were observed between the groups in terms of nitrite levels and the relationship between nitrite and BP. UA, XOA and allantoin levels may be high due to placental cell death because of abnormal trophoblastic activity observed in PE. Moreover, the reactive oxygen products that are created during the genetic material degradation may explain how UA, XOA and allantoin levels are related to BP. According to ROC analysis, UA, XOA and allantoin assays are reliable predictors for the determination of PE.

Metabonomics revealed xanthine oxidase-induced oxidative stress and inflammation in the pathogenesis of diabetic nephropathy.

Diabetic nephropathy (DN) is a serious complication of diabetes mellitus (DM), which is a major public health problem in the world. To reveal the metabolic changes associated with DN, we analyzed the serum, urine, and renal extracts obtained from control and streptozotocin (STZ)-induced DN rats by (1)H NMR-based metabonomics and multivariate data analysis. A significant difference between control and DN rats was revealed in metabolic profiles, and we identified several important DN-related metabolites including increased levels of allantoin and uric acid (UA) in the DN rats, suggesting that disturbed purine metabolism may be involved in the DN. Combined with conventional histological and biological methods, we further demonstrated that xanthine oxidase (XO), a key enzyme for purine catabolism, was abnormally activated in the kidney of diabetic rats by hyperglycemia. The highly activated XO increased the level of intracellular ROS, which caused renal injury by direct oxidative damage to renal cells, and indirect inducing inflammatory responses via activating NF-κB signaling pathway. Our study highlighted that metabonomics is a promising tool to reveal the metabolic changes and the underlying mechanism involved in the pathogenesis of DN.

Impact of cholesterol lowering treatment on plasma kynurenine and tryptophan concentrations in chronic kidney disease: relationship with oxidative stress improvement.

BACKGROUND AND AIM: Tryptophan (Trp) degradation via indoleamine (2,3)-dioxygenase (IDO), with consequent increased in kynurenine (Kyn) concentrations, has been proposed as marker of immune system activation. Oxidative stress (OS) might contribute to the pro-inflammatory state in chronic kidney disease (CKD) through the activation of NF-kB, with consequent activation and recruitment of immune cells. METHODS AND RESULTS: Serum concentrations of Trp and Kyn, oxidative stress indices malondialdehyde (MDA) and allantoin/uric acid (All/UA) ratio and anti-oxidant amino acid taurine were measured in 30 CKD patients randomized to 40 mg/day simvastatin (group 1), ezetimibe/simvastatin 10/20 mg/day (group 2) or ezetimibe/simvastatin 10/40 mg/day (group 3) and treated for 12 months. Baseline Kyn and Kyn/Trp ratio were higher in CKD patients vs. healthy controls (1.67 ± 0.62 µmol/L vs 1.25 ± 0.40 µmol/L, p < 0.01 and 0.036 ± 0.016 vs 0.023 ± 0.010, p < 0.001 respectively). Both Kyn and Kyn/Trp ratio significantly decreased after cholesterol lowering treatment, to values comparable with healthy controls after one year treatment (1.67 ± 0.62 µmol/L vs 1.31 ± 0.51 µmol/L, p < 0.0001 and 0.036 ± 0.016 vs 0.028 ± 0.012 p < 0.0001, respectively). This was paralleled by a significant decrease in MDA (218 ± 143 nmol/L vs 176 ± 123 nmol/L, p < 0.01) and All/UA ratio (1.47 ± 0.72 vs 1.19 ± 0.51, p < 0.01) in CKD patients. CONCLUSIONS: Amelioration of both oxidative and inflammation status after cholesterol lowering treatment in CKD might be mediated by restoration of antioxidant taurine concentrations during therapy (from 51.1 ± 13.3 µmol/L at baseline to 63.1 ± 16.4 µmol/L, p < 0.001 by ANOVA), suggesting that improvement of both oxidative and inflammation status in CKD patients could be explained, at least partly, by the cholesterol lowering effects.

Oxidative stress improvement is associated with increased levels of taurine in CKD patients undergoing lipid-lowering therapy.

Lipid-lowering therapy has been reported to reduce several oxidative stress (OS) markers in hypercholesterolemia. Since OS is frequently associated with renal dysfunction, we aimed to investigate the effect of hypolipidemic drugs on oxidative stress and plasma taurine (Tau), a sulfur amino acid with a marked antioxidant effect, in chronic kidney disease (CKD). We enrolled 30 CKD randomized to receive three different hypolipidemic regimens for 12 months: simvastatin alone (40 mg/day) or ezetimibe/simvastatin combined therapy (10/20 or 10/40 mg/day). Low molecular weight (LMW) thiols including homocysteine, cysteine, cysteinylglycine, glutathione, and glutamylcysteine in their reduced and total form and oxidative stress indices as malondialdehyde (MDA) and allantoin/uric acid (All/UA) ratio were also evaluated. Tau concentration significantly increased throughout the therapy. The rise of taurine was more striking for the group with the concomitant administration of ezetimibe/simvastatin 10/40 mg/day (+31.6% after 1 year of therapy). A significant decrease of both MDA and All/UA ratio was observed during therapy for all patients (-19% for both MDA and All/UA ratio) with a more pronounced effect in patients treated with ezetimibe/simvastatin 10/40 mg/day (-26% for MDA and -28% for All/UA ratio). Besides, an increase of thiols reduced forms was found (+20.7% of LMW thiols redox status) with a greater effect in subjects treated with ezetimibe/simvastatin 10/40 mg/day (+24.7%). Moreover, we demonstrated that oxidative stress improvement during therapy was correlated with increased taurine levels. We hypothesize that taurine may be responsible for the oxidative stress improvement observed during lipid-lowering treatment through the reduction of superoxide anion production at the respiratory chain activity level.

Relationship between serum allantoin and urate in healthy subjects and effects of benzbromarone in gout patients.

BACKGROUND: Although hyperuricemia is suggested to increase allantoin production in both pro- and antioxidant manners, it remains undetermined whether it increases the serum concentration of allantoin. In addition, since uric acid has both pro- and antioxidant actions, a decrease in the serum concentration of uric acid may have an effect on the pro-oxidant-antioxidant balance. METHODS: To examine whether serum allantoin is correlated with serum urate, we measured those levels as well as other parameters in 63 healthy subjects. In addition, to determine whether serum allantoin is correlated with reactive oxygen species (ROS) biomarkers, we measured 8-hydroxy deoxyguanosine and 15-F2t-isoprostane, markers of ROS, in urine samples from 30 gout patients before and 1 year after benzbromarone treatment (50 mg/d). RESULTS: The serum concentration of allantoin was correlated with that of urate in healthy subjects (R = 0.27, p < 0.05). Benzbromarone treatment in the patients decreased the concentrations of allantoin and urate in serum by 17% (p < 0.05) and 49% (p < 0.05), respectively, and the benzbromarone-induced change in serum allantoin was correlated with that in serum urate (R = 0.39, p < 0.05). However, benzbromarone treatment did not change the ratios of 8-hydroxydeoxyguanosine/creatinine or 15-F2t-isoprostane/creatinine in urine. CONCLUSIONS: Our findings suggest that hyperuricemia contributes to an increase in serum concentration of allantoin, though they do not indicate that hyperuricemia is a major factor for controlling oxidative stress in vivo.

Enhancement of androgen action in the kidneys of transgenic mice harboring the mutant human UMOD gene.

Uromodulin storage diseases are characterized by hyperuricemia of underexcretion type and renal insufficiency. Although these diseases are caused by mutations in the UMOD gene that encodes the kidney-specific glycoprotein uromodulin, the effect of uromodulin mutation on the kidney has not been clearly established. In this study, we investigated the effect by comparing transgenic mice expressing human uromodulin with and without mutation. Change in the intracellular localization of human uromodulin protein was shown in the kidney of transgenic mice expressing mutant human uromodulin by a deglycosylation experiment. Then, we determined by microarray technology and quantitative real-time PCR that the strongly induced gene in the kidney of these mice was 5-α-reductase 2, an enzyme that converts testosterone into the more potent androgen. Moreover, the expressions of androgen-induced genes ß-glucuronidase, ornithine decarboxylase structural 1, and cytochrome P450 4a12a were increased. The increase in mRNA levels of urate reabsorptive transport system urate transporter 1 could be investigated, but the changes in its protein level and renal urate handling could not be demonstrated. Therefore, it is suggested that a uromodulin mutation may be responsible for the enhancement of renal androgen action.

Field-amplified sample injection combined with pressure-assisted capillary electrophoresis UV detection for the simultaneous analysis of allantoin, uric acid, and malondialdehyde in human plasma.

The allantoin/uric acid (All/UA) ratio and malondialdehyde (MDA) plasma levels have been proposed as important markers for monitoring oxidation triggered by the action of free radicals (FR). Here, we describe an easy field amplified sample injection capillary electrophoresis method with UV detection for the separation and quantification of All, UA, and free MDA in human plasma. The plasma samples were simply filtered through centrifugation membrane tubes for protein elimination and directly injected on a capillary without complex cleanup and/or sample derivatization procedures. The use of a run buffer composed of 300 mmol/L sodium borate at pH 10 with 50 mmol/L of N-methyl-D: -glucamine and an overimposed pressure/voltage of 0.1 psi during the electrophoretic run allows basline resolution of the analytes within 17 min. The electrokinetic injection allows a detection limit of 15 nmol/L for All, 20 nmol/L for UA and 10 nmol/L for MDA in a plasma sample, thus significantly improving the LOD of previous described methods based on capillary electrophoresis. Precision tests indicate a good repeatability of our method both for migration times (CV = 1.85%) and areas (CV = 2.87%). Moreover, a good reproducibility of intra- and inter-assay tests was obtained (CV = 4.63% and CV = 6.59% respectively). The suitability of the method was tested by measuring analyte levels in 40 healthy volunteers.

Trientine and renin-angiotensin system blockade ameliorate progression of glomerular morphology in hypertensive experimental diabetic nephropathy.

A comparison of the efficacy of the copper chelator, trientine, with combined renin angiotensin system (RAS) blockade on the progression of glomerular pathology in the diabetic (mREN-2)27 rat is reported. Animals were treated for 2 months with trientine, combined RAS blockers, combined trientine plus RAS blockers or none. Treatments began after inducing diabetes with streptozotocin. Physiological data were recorded monthly and light microscopic glomerular features were scored. Plasma allantoin and both plasma and renal protein carbonyls were measured as markers of oxidative stress. Trientine and RAS blockade decreased proteinuria and albuminuria and prevented an increase in creatinine clearance and kidney weight. Both reduced the diabetes-related glomerular features of mesangiolysis and glomerular segmental hypocellularity and trientine prevented severe tuft-to-capsule adhesion and reduced tubularization. Hypertension-related severe mesangial matrix expansion and global hypercellularity were increased by both treatments, which may reflect repair of mesangiolysis. Trientine reduced plasma but not renal protein carbonyls or plasma allantoin. In this model, trientine prevented the development of many diabetes-specific features similarly to RAS blockade. Amelioration of oxidative stress and features commonly observed in human diabetic nephropathy (DN), support a diabetes-related defect in copper (Cu) metabolism. The addition of Cu(II) chelation may improve current DN therapy.

Patients with REM sleep behavior disorder have higher serum levels of allantoin.

INTRODUCTION: Rapid eye movement (REM) sleep behavior disorder (RBD) is associated with an increased risk of developing Parkinson's disease (PD). Low uric acid (UA) levels are associated with the risk of development and progression of PD. Allantoin is the major oxidation product of UA and is considered as a biomarker of oxidative stress. We aimed to compare serum levels of UA, allantoin, and allantoin/UA ratio in RBD patients with those in healthy controls, and to examine their associations with clinical severity. METHODS: We evaluated serum levels of UA, allantoin, and allantoin/UA ratio in 38 RBD patients (one female, mean age 66.8 (SD 6.3) years) and in 47 controls (four females, 66.8 (7.6) years). All RBD patients were assessed according to an examination protocol, which included structured interview, Montreal Cognitive Assessment (MoCA), Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS), and dopamine transporter single-photon emission computed tomography (DAT-SPECT). The lower putaminal binding ratio from both hemispheres was used for analysis. RESULTS: Mean serum allantoin concentration and allantoin/UA ratio were significantly increased in the RBD group compared to controls (2.6 (1.8) vs. 1.4 (0.7) µmol/l, p = 0.0004, and 0.008 (0.004) vs. 0.004 (0.002), p < 0.0001, respectively). There were no significant differences in UA levels between the two groups. No significant associations between any biochemical parameter and RBD duration, putaminal binding ratio on DAT-SPECT, MDS-UPDRS, or MoCA score were found. CONCLUSION: Serum allantoin and allantoin/UA ratio are increased in RBD patients in comparison to controls, which may reflect increased systemic oxidative stress in prodromal synucleinopathy.

Influence of recanalization on uric acid patterns in acute ischemic stroke.

BACKGROUND: Most epidemiological studies have reported a significant association between elevated serum levels of uric acid (UA) and increased cardiovascular disease. On the other hand, UA is the most abundant antioxidant in the human body. We hypothesized that UA levels would change noticeably in association with the degree of oxidative stress in acute ischemic stroke. METHODS: We analyzed consecutive patients with acute ischemic stroke in the anterior circulation system within 24 h of symptom onset, confirmed by diffusion-weighted imaging (DWI), and with a modified NIH Stroke Scale (mNIHSS) score of 5 or greater. Baseline demographics, serial clinical scores, serial UA and allantoin (a nonenzymatic metabolite of UA) levels, UA change (baseline UA - UA at 48 h), and DWI lesion volumes were compared between 45 patients with recanalized vessels (RV) and 43 patients with nonrecanalized vessels (NV) in follow-up imaging. RESULTS: The RV (vs. NV) patients were more likely to receive thrombolytic treatment (p = 0.005), achieve a reduction in day-14-mNIHSS scores (p = 0.001), and greater changes in UA (p = 0.024) and allantoin levels (p = 0.003). The UA levels dropped at 48 h and gradually increased in a U-shaped pattern. UA change (r = 0.360; p = 0.001) rather than baseline UA (r = 0.044; p = 0.681) was significantly correlated with infarct volume. In the RV (vs. NV) patients, there was a stronger association between infarct volume and UA change (r = 0.483; p = 0.001) or allantoin levels (r = 0.466; p = 0.017). CONCLUSION: Our results suggest that UA might be a consumptive and reproducible antioxidant in acute ischemic stroke, and this pattern appears to be influenced by recanalization success and infarct volume size.

Aminothiols and allantoin in chronic dialysis patients: effects of hemodialysis sessions.

BACKGROUND: To investigate the possible relationship between homocysteine and allantoin levels in hemodialyzed patients, serum levels of thiols and purine compounds were analyzed before and after dialysis sessions. METHODS: 16 clinically stable non-diabetic patients hemodialyzed on polysulfone membranes were compared with 36 control subjects. Serum samples were collected before and after hemodialysis sessions. Total homocysteine, cysteine, glutathione, cysteinylglycine, uric acid, hypoxanthine, and allantoin were measured by capillary electrophoresis. RESULTS: Pre-dialysis homocysteine, allantoin, and uric acid were significantly elevated in dialysis patients as compared to controls. Cysteine, glutathione, and hypoxanthine levels were similar in both groups. Homocysteine significantly decreased, but did not normalize after dialysis sessions. Glutathione and cysteinylglycine levels remained unchanged after dialysis sessions, whereas cysteine decreased. Uric acid, hypoxanthine, and allantoin levels were significantly reduced by dialysis sessions. The allantoin/uric acid ratio was higher in dialyzed patients before hemodialysis (0.049 +/- 0.023 vs. 0.016 +/- 0.012 in controls; p < 0.001), and became elevated after a dialysis session (0.084 +/- 0.033; p = 0.002). CONCLUSIONS: Despite the use of biocompatible membranes, homeostasis of thiols and purine compounds is disturbed in hemodialysed patients. We suggest that allantoin could be used as a marker for oxidative stress in hemodialyzed patients.

A 12-week aerobic training programme reduced plasmatic allantoin in adolescents with Down syndrome.

OBJECTIVE: To assess the influence of a 12-week training programme on plasmatic levels of allantoin, an in vivo marker for oxidative stress, in adolescents with Down syndrome. This finding would be of great interest, since oxidative damage has been proposed as a pathogenic mechanism of several pathologies in this population. MATERIALS: To reach this goal, 31 male adolescents with Down syndrome (16.3 (1.1) years; 155.2 (5.7) cm; 70.8 (4.5) kg) performed a 12-week training programme, three sessions per week, consisting of warm-up (15 min) followed by a main part (20-35 min (increasing 5 min each 3 weeks)) at a work intensity of 60-75% of peak heart rate (increasing by 5% each 3 weeks) and then a cool-down period (10 min). According to previous studies, it should be emphasised that the maximal heart rate for individuals with Down syndrome was predicted by the equation HRmax = 194.5-(0.56 age). The control group included seven age-, sex- and BMI-matched adolescents with trisomy 21 that did not perform any training programme. The levels uric acid and allantoin were assayed in plasma by HPLC. This protocol was approved by an institutional ethics committee. RESULTS: When compared with baseline, plasmatic levels of allantoin were decreased significantly (22.09 (1.62) vs 18.74 (1.38) micromol/l; p<0.001) after being exercised. Furthermore, the allantoin/uric acid ratio was decreased significantly (0.071 (0.006) vs 0.059 (0.004); p<0.05). On the contrary, no changes were reported in controls. CONCLUSION: A 12-week aerobic programme significantly reduced oxidative damage expressed in terms of plasmatic allantoin content in adolescents with Down syndrome. Further studies on this topic are required.

Liver adenine nucleotides: fructose-induced depletion and its effect on protein synthesis.

Intravenous administration of D-fructose to rats rapidly depletes liver adenosine triphosphate and inorganic phosphate; marked elevations of uric acid and allantoin in plasma follow. Concomitantly the incorporation of DL-leucine-1-(14)C into liver protein is almost completely inhibited.

An enzyme cycling method for measurement of allantoin in human serum.

Current conventional measurement of allantoin levels in human serum uses an HPLC method. However, performing this assay is time-consuming and sample-intensive, and it requires expensive equipment. We have developed a novel enzyme cycling method for measuring allantoin concentrations in human serum. In the first step, serum allantoin is converted to allantoate by the action of allantoinase (EC 3.5.2.5), and endogenous ammonia is simultaneously removed by the action of glutamine synthetase II (EC 6.3.1.2). In the second step, l-methionine sulfoximine is used to inhibit glutamine synthetase II, and ammonia is liberated from allantoate by the activity of allantoate amidohydrolase (EC 3.5.3.9). In the final step, the ammonia is then converted to NAD by NAD synthetase (EC 6.3.1.5). Subsequent action of glucose dehydrogenase (EC 1.1.1.47) and diaphorase (EC 1.6.99.2) in the presence of glucose and 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium (WST-1) acts to cycle the formed NAD between its oxidized and reduced forms, resulting in the production of WST-1 formazan, which is monitored at 450 nm. The assay standard curve is linear from 0 to 70 muM allantoin. The level of allantoin in healthy subjects was measured to be 8.2+/-3.1 microM (n=30).

Coenzyme Q10 and oxidative imbalance in Down syndrome: biochemical and clinical aspects.

Down syndrome (DS) is a chromosomal abnormality (trisomy 21) associated with mental retardation and Alzheimer-like dementia, characteristic change of the individual's phenotype and premature ageing. Oxidative stress is known to play a major role in this pathology since a gene dose effect leads to elevated ratio of superoxide dismutase to catalase/glutathione peroxidase compared to controls in all age categories suggesting that oxidative imbalance contributes to the clinical manifestation of DS. Hyperuricemia is another feature of DS that has an interesting relationship with oxidative stress since uric acid represents an important free radical scavenger. However its formation is connected to the conversion of Xanthine dehydrogenase (XDH) to Xanthine oxidase (XO) which leads to concomitant production of free radicals. Here we report that plasma samples from DS patients in pediatric age, despite an increased total antioxidant capacity, largely due to elevated Uric acid content (UA), present significantly elevated markers of oxidative damage such as increased allantoin levels. Moreover DS plasma samples do not differ from healthy control ones in terms of Coenzyme Q10 and susceptibility to peroxidative stimuli. On the contrary, lymphocyte and platelet CoQ10 content was significantly lower in DS patients, a fact that might underlie oxidative imbalance at a cellular level.