Glutathione peroxidase and glutathione S-transferase activity of platelets

Metabolic phenotyping in phenylketonuria reveals disease clustering independently of metabolic control

Phenylketonuria (PKU, MIM #261600) is one of the most common inborn errors of metabolism (IEM) with an incidence of 1:10000 in the European population. PKU is caused by autosomal recessive mutations in phenylalanine hydroxylase (PAH) and manifests with elevation of phenylalanine (Phe) in plasma and urine. Untreated PKU manifests with intellectual disability including seizures, microcephaly and behavioral abnormalities. Early treatment and good compliance result in a normal intellectual outcome in many but not in all patients. This study examined plasma metabolites in patients with PKU (n = 27), hyperphenylalaninemia (HPA, n = 1) and healthy controls (n = 32) by LC- MS/MS. We hypothesized that PKU patients would exhibit a distinct "submetabolome" compared to that of healthy controls. We further hypothesized that the submetabolome of PKU patients with good metabolic control would resemble that of healthy controls. Results from this study show: (i) Distinct clustering of healthy controls and PKU patients based on polar metabolite profiling, (ii) Increased and decreased concentrations of metabolites within and afar from the Phe pathway in treated patients, and (iii) A specific PKU-submetabolome independently of metabolic control assessed by Phe in plasma. We examined the relationship between PKU metabolic control and extended metabolite profiles in plasma. The PKU submetabolome characterized in this study represents the combined effects of dietary adherence, adjustments in metabolic pathways to compensate for defective Phe processing, as well as metabolic derangements that could not be corrected with dietary management even in patients classified as having good metabolic control. New therapeutic targets may be uncovered to approximate the PKU submetabolome to that of healthy controls and prevent long-term organ damage.

Oxidative stress in phenylketonuria-evidence from human studies and animal models, and possible implications for redox signaling

Phenylketonuria (PKU) is one of the commonest inborn error of amino acid metabolism. Before mass neonatal screening was possible, and the success of introducing diet therapy right after birth, the typical clinical finds in patients ranged from intellectual disability, epilepsy, motor deficits to behavioral disturbances and other neurological and psychiatric symptoms. Since early diagnosis and treatment became widespread, usually only those patients who do not strictly follow the diet present psychiatric, less severe symptoms such as anxiety, depression, sleep pattern disturbance, and concentration and memory problems. Despite the success of low protein intake in preventing otherwise severe outcomes, PKU's underlying neuropathophysiology remains to be better elucidated. Oxidative stress has gained acceptance as a disturbance implicated in the pathogenesis of PKU. The conception of oxidative stress has evolved to comprehend how it could interfere and ultimately modulate metabolic pathways regulating cell function. We summarize the evidence of oxidative damage, as well as compromised antioxidant defenses, from patients, animal models of PKU, and in vitro experiments, discussing the possible clinical significance of these findings. There are many studies on oxidative stress and PKU, but only a few went further than showing macromolecular damage and disturbance of antioxidant defenses. In this review, we argue that these few studies may point that oxidative stress may also disturb redox signaling in PKU, an aspect few authors have explored so far. The reported effect of phenylalanine on the expression or activity of enzymes participating in metabolic pathways known to be responsive to redox signaling might be mediated through oxidative stress.

Platelet Selenium Indices as Useful Diagnostic Surrogate for Assessment of Selenium Status in Lambs: an Experimental Comparative Study on the Efficacy of Sodium Selenite vs. Selenium Nanoparticles

Unlike in human medicine, information on the platelet selenium (Se) concentration and glutathione peroxidase (GPx) activity, as potential biomarkers of Se status, is lacking in the field of veterinary medicine. The aims of this study were to compare the effects of sodium selenite (SeS) and Se nanoparticles (SeN) on platelet Se indices, and compare the results with those of conventional indices of Se status in sheep. Eighteen lambs with marginal Se status were assigned to a control (CON) group and two Se-treated groups administered either a single dose of Se at 0.055 mg/kg BW subcutaneously as SeS or SeN. The Se concentration and GPx activity in plasma, erythrocytes, whole blood, and platelets were assessed at 14 time points during 90 days. In Se-treated groups, Se concentrations and GPx activity increased significantly in plasma, whole blood, erythrocytes, and platelets. However, the responses in SeS group often started and peaked earlier and, in almost all time points, were more pronounced than the SeN group (P < 0.001), indicating that SeS compared to SeN was more biopotent in raising Se biomarkers. Se indices in platelets started and peaked later than those of short-term (in plasma) and earlier than those of long-term indices (in erythrocytes) indicating that platelet indices can serve as intermediate-term biomarkers of Se status. In conclusion, platelet indices of Se are promising proxy for currently used indices of Se status in sheep, regardless of Se source.

Hyperphenylalaninemia Correlated with Global Decrease of Antioxidant Genes Expression in White Blood Cells of Adult Patients with Phenylketonuria

BACKGROUND

Several studies have highlighted disturbance of redox homeostasis in patients with phenylketonuria (PKU) which may be associated with neurological disorders observed in patients, especially during adulthood when phenylalanine restrictive diets are not maintained. The aim of this study was to assess the antioxidant profile in a cohort of PKU patients in comparison to the controls and to evaluate its relation to biochemical parameters especially phenylalaninemia.

METHODS

We measured RNA expression of 22 antioxidant genes and reactive oxygen species (ROS) levels in white blood cells of 10 PKU patients and 10 age- and gender-matched controls. We also assessed plasma amino acids, vitamins, oligo-elements, and urinary organic acids concentrations. Then we evaluated the relationship between redox status and biochemical parameters.

RESULTS

In addition to expected biochemical disturbances, we highlighted a significant global decrease of antioxidant genes expression in PKU patients in comparison to the controls. This global decrease of antioxidant genes expression, including various isoforms of peroxiredoxins, glutaredoxins, glutathione peroxidases, and superoxide dismutases, was significantly correlated to hyperphenylalaninemia.

CONCLUSION

This study is the first to evaluate the expression of 22 antioxidant genes in white blood cells regarding biochemical parameters in PKU. These findings highlight the association of hyperphenylalaninemia with antioxidant genes expression. New experiments to specify the role of oxidative stress in PKU pathogenesis may be useful in suggesting new recommendations in PKU management and new therapeutic trials based on antioxidant defenses.

The relative importance of oxidative stress versus arylation in the mechanism of quinone-induced cytotoxicity to platelets

Our previous studies demonstrated that menadione is cytotoxic to rat platelets. In an attempt to assess the relative contributions of enzymatic redox cycling versus arylation in menadione-induced cytotoxicity, we have studied three quinones with different mechanisms of action: 2,3-dimethoxy-1,4-naphthoquinone (DMNQ; pure redox cycler), menadione (both redox cycler and arylator), and 1,4-benzoquinone (BQ; pure arylator). BQ was more toxic to rat platelets than menadione, while DMNQ did not cause LDH leakage at all. Cellular uptake kinetics revealed that DMNQ concentration taken up by the cells was equivalent to that decreased in incubation medium. On the other hand, the concentrations of BQ and menadione taken into the cells were significantly lower than the decreases in concentrations seen in the incubation medium. This suggests indirectly that BQ and menadione may have undergone arylation, binding to glutathione (GSH) or protein thiols. The difference in arylation capacity between BQ and menadione was well correlated with their relative cytotoxicity (LDH leakage) observed in platelets. All three quinones caused a rapid, extensive depletion of intracellular GSH in platelets. Treatments with BQ and menadione did not result in formation of oxidized glutathione (GSSG), whereas DMNQ showed a time-dependent increase in GSSG. Altogether, these results suggest that enzymatic redox cycling does not play a critical role in quinone-induced cytotoxicity in rat platelets, while arylation is likely to be quinone's primary mechanism of action.

Biological chemistry of thiols in the vasculature and in vascular-related disease

For all their similarities in structure and common chemistry, the functions of the amino thiols in vascular biology are remarkably different. This review details the basic chemistry of sulfhydryls that dictates their functions in health and disease. In addition, the biochemistry and metabolism of each thiol are outlined, in an effort to highlight its specific contributions to the normal biology and physiology of blood vessels and to the pathogenesis of vascular-related disease.

Selenium in uremia

The importance of selenium as an essential trace element for man has been increasingly recognized during the last several years. Selenium deficiency has been associated with cases of congestive cardiomyopathy, skeletal myopathy, anemia, enhanced cancer risk, elevated incidence of cardiovascular disease, immune system alterations, hair and nail changes, and abnormalities in thyroid hormone metabolism. These symptoms are frequently present in chronic uremic patients. Nevertheless, the prevalence and significance of selenium deficiency in the uremic syndrome is still not clearly defined. This article reviews the selenium status in chronic uremic patients, the supposed pathogenetic mechanisms of selenium disturbance in uremia, and the possible role of selenium deficiency on some uremic abnormalities.

Glutathione metabolic enzyme activities in diabetic platelets as a function of glycemic control

Type 1 diabetic subjects categorized on the basis of the glycated haemoglobin content of their blood (low less than 7%; medium, greater than 7% and less than 11%; high, greater than 11%) were analyzed for total intraplatelet GSH as well as for the steady-state kinetic parameters (apparent KM and apparent Vmax) of some glutathione metabolic enzymes including glutathione reductase, glutathione peroxidase, gamma-glutamyltrans-peptidase and glutathione-S-transferase. This study indicates that intraplatelet GSH content of subjects with low glycated-haemoglobin is approximately 2-fold higher than those with medium glycated-haemoglobin. There was no further decrease in intraplatelet-GSH in subjects with high glycated-haemoglobin. The kinetic parameters of the platelet-enzymes studied (glutathione reductase, gamma-glutamyltranspeptidase and glutathione-S-transferase) were essentially independent of the glycation state of the subject. However, the apparent KM of glutathione peroxidase was approximately 4-fold higher in the subjects with high glycated-haemoglobin, in comparison to low subjects. This decrease in affinity could possibly result from the susceptibility of this enzyme to non-enzymatic glucosylation as purified samples of glutathione peroxidase incubated in vitro with glucose showed similar increases in apparent KM. These results are discussed in terms of the potential contribution of glutathione peroxidase impairment, to the hyperaggregability of the diabetic platelet.

Antioxidant status (selenium, vitamins A and E) and aging

Antioxidant status can be evaluated by blood selenium, vitamins A and E. The level of selenium was determined in whole blood, erythrocytes and plasma of 170 French people (70-95 years old) healthy and with intercurrent illness, by using PIXE (proton-induced X-ray emission analysis). These results are discussed with other values from the literature. Plasma levels of vitamins A and E have been measured by HPLC. All data were compared with those obtained for younger subjects. Healthy elderly people residing in a geriatric home received selenium supplements during 1 month. The influence of this supplementation brought to light a deficiency for this trace element. The correlation of aging and nutritional requirements with immune function, heart and cancer death rate is presented and discussed.

Selenium and vitamin E status of healthy and institutionalized elderly subjects: analysis of plasma, erythrocytes and platelets

Levels of selenium in whole blood, plasma, erythrocytes and platelets, glutathione peroxidase (EC 1.11.1.9; GSH-Px) activity in erythrocytes and platelets and vitamin E, low-density-lipoprotein (LDL)-cholesterol and vitamin E: LDL cholesterol in plasma were measured in seventy-five healthy subjects aged less than 65 years and twenty-eight healthy and twenty-three institutionalized elderly people aged greater than 65 years. Healthy elderly subjects had significantly lower levels of Se in whole blood and plasma when compared with younger subjects. Other measurements of Se status were not significantly different. In the healthy subjects plasma levels of vitamin E and LDL-cholesterol increased with age to 60 years and decreased above 80 years. Vitamin E: LDL cholesterol values were not affected by age. Measurements of Se and vitamin E status in the institutionalized elderly compared with the healthy elderly were all reduced with the exception of platelet Se levels and erythrocyte GSH-Px activity. Ageing per se had minimal effect on Se and vitamin E status but intercurrent illness and decreased food intake can lead to reduced levels in the elderly.

Effects of vitamin E therapy on ethanol-induced changes in platelet aggregation, thromboxane formation, factor VIII levels and serum lipids

A transient increase in platelet thromboxane formation has been observed in non-alcoholics during acute ethanol intoxication and in alcoholics shortly after ethanol withdrawal. Whether these effects are related to the generation of free radicals and lipid peroxidation was investigated by using vitamin E as a free radical scavenger and inhibitor of lipid peroxide formation. The results demonstrate that a high dose of vitamin E (1800 IU) taken daily by non-alcoholic men slightly (P less than 0.05) decreases aggregation-associated platelet thromboxane formation during ethanol oxidation. Likewise, vitamin E prevents the ethanol-induced increase (P less than 0.01) in factor VIII coagulant activity. These observations suggest that the enhancement of platelet thromboxane formation and factor VIII coagulant activity by acute ethanol ingestion may be related to stimulated lipid peroxidation. By contrast, similar effects of vitamin E were not found in alcoholics shortly after ethanol withdrawal suggesting other mechanisms for their platelet hyperreactivity.

Selenium deficiency

Selenium is undoubtedly an essential trace element: its involvement in GPx structure, the presence of deleterious effects of selenium deficiency in animals, and the recognition of deficiency states in man attest to its importance. However, if the consequences of selenium deficiency in man are now widely recognized, the mechanisms underlying these conditions are poorly understood. The definition of the exact role of selenium in human homeostasis has been hampered by the lack of a sensitive parameter, usable in routine investigation, to assess selenium status. Measurements of plasma and urinary levels, although useful in clinical practice, are inadequate indicators. The only true evidence of selenium deficiency lies in a positive response to selenium therapy. Deficiency states have been demonstrated for inhabitants of regions where selenium supply is limited, in protein-energy malnutrition, and in patients maintained on total parenteral nutrition without selenium supplementation. The benefit of selenium supplementation, together with other antioxidant drugs, in non-deficient subjects is still a matter of debate; its protective effect in neoplastic, cardiovascular and neurological degenerative diseases is not yet proven.

Effect of GSH depletion by 1-chloro-2,4-dinitrobenzene on human platelet aggregation, arachidonic acid oxidative metabolism and cytoskeletal proteins

Platelet reduced glutathione (GSH) is completely depleted by 1-chloro-2,4-dinitrobenzene (CDNB), which is a substrate for GSH-S-transferase. GSH-depleted platelets: a) aggregate normally at high inducer concentration; b) respond with increased (after arachidonic acid) or depressed (after collagen) aggregability at low inducer concentration; c) show almost no arachidonic acid-induced stimulation of the hexose monophosphate shunt; d) are sensitized to oxidant agents such as diamide, which elicits a faster cytoskeletal protein oxidative polymerization and reversible aggregation. Our results suggest that GSH acts as a reducing cofactor and/or free radical scavenger in the PG-hydroperoxidase step of the cyclooxygenase pathway; moreover, GSH protects membrane and cytoskeletal protein -SH groups from oxidation.

Selenium intake of infants and young children, healthy children and dietetically treated patients with phenylketonuria

In 20 healthy infants and children, 5-20 months old, the Se intake was estimated by analysing food samples by instrumental neutron activation analysis. The intake was calculated by weighing the portions offered and actually consumed. The median Se content of the food amounted to 27 ng/g wet weight (gww) and median daily Se intake to 33.5 micrograms. The Se intake was not equally distributed over the day. About 50% of the daily Se intake was derived from the supper. The main Se sources (41%) for young children were cereal paps. Commercially available meals (30 ng/g) contained less Se than home-made ones (50 ng/g). In nine dietetically treated patients with phenylketonuria the median Se intake amounted only to 6.9 micrograms/day corresponding to a mean Se content of the diet of 7.9 ng/g. The main Se source in the diet was vegetables (36.3%) and 20% derived from their protein supplements. The Se intake of young children, healthy or dietetically treated, cannot be calculated accurately from tables but must be estimated by measuring the Se content of the local food because cereals and vegetables--the main Se sources--exhibit great regional variations.