Diminished blood levels of reduced glutathione and alpha-tocopherol in two triosephosphate isomerase-deficient brothers

Metabolic Shades of S-D-Lactoylglutathione

S-D-lactoylglutathione (SDL) is an intermediate of the glutathione-dependent metabolism of methylglyoxal (MGO) by glyoxalases. MGO is an electrophilic compound that is inevitably produced in conjunction with glucose breakdown and is essentially metabolized via the glyoxalase route. In the last decades, MGO metabolism and its cytotoxic effects have been under active investigation, while almost nothing is known about SDL. This article seeks to fill the gap by presenting an overview of the chemistry, biochemistry, physiological role and clinical importance of SDL. The effects of intracellular SDL are investigated in three main directions: as a substrate for post-translational protein modifications, as a reservoir for mitochondrial reduced glutathione and as an energy currency. In essence, all three approaches point to one direction, namely, a metabolism-related regulatory role, enhancing the cellular defense against insults. It is also suggested that an increased plasma concentration of SDL or its metabolites may possibly serve as marker molecules in hemolytic states, particularly when the cause of hemolysis is a disturbance of the pay-off phase of the glycolytic chain. Finally, SDL could also represent a useful marker in such metabolic disorders as diabetes mellitus or ketotic states, in which its formation is expected to be enhanced. Despite the lack of clear-cut evidence underlying the clinical and experimental findings, the investigation of SDL metabolism is a promising field of research.

Excitotoxins, Mitochondrial and Redox Disturbances in Multiple Sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS). There is increasing evidence that MS is not only characterized by immune mediated inflammatory reactions, but also by neurodegenerative processes. There is cumulating evidence that neurodegenerative processes, for example mitochondrial dysfunction, oxidative stress, and glutamate (Glu) excitotoxicity, seem to play an important role in the pathogenesis of MS. The alteration of mitochondrial homeostasis leads to the formation of excitotoxins and redox disturbances. Mitochondrial dysfunction (energy disposal failure, apoptosis, etc.), redox disturbances (oxidative stress and enhanced reactive oxygen and nitrogen species production), and excitotoxicity (Glu mediated toxicity) may play an important role in the progression of the disease, causing axonal and neuronal damage. This review focuses on the mechanisms of mitochondrial dysfunction (including mitochondrial DNA (mtDNA) defects and mitochondrial structural/functional changes), oxidative stress (including reactive oxygen and nitric species), and excitotoxicity that are involved in MS and also discusses the potential targets and tools for therapeutic approaches in the future.

Early mitochondrial dysfunction leads to altered redox chemistry underlying pathogenesis of TPI deficiency

Triose phosphate isomerase (TPI) is responsible for the interconversion of dihydroxyacetone phosphate to glyceraldehyde-3-phosphate in glycolysis. Point mutations in this gene are associated with a glycolytic enzymopathy called TPI deficiency. This study utilizes a Drosophila melanogaster model of TPI deficiency; TPI(sugarkill) is a mutant allele with a missense mutation (M80T) that causes phenotypes similar to human TPI deficiency. In this study, the redox status of TPI(sugarkill) flies was examined and manipulated to provide insight into the pathogenesis of this disease. Our data show that TPI(sugarkill) animals exhibit higher levels of the oxidized forms of NAD(+), NADP(+) and glutathione in an age-dependent manner. Additionally, we demonstrate that mitochondrial redox state is significantly more oxidized in TPI(sugarkill) animals. We hypothesized that TPI(sugarkill) animals may be more sensitive to oxidative stress and that this may underlie the progressive nature of disease pathogenesis. The effect of oxidizing and reducing stressors on behavioral phenotypes of the TPI(sugarkill) animals was tested. As predicted, oxidative stress worsened these phenotypes. Importantly, we discovered that reducing stress improved the behavioral and longevity phenotypes of the mutant organism without having an effect on TPI(sugarkill) protein levels. Overall, these data suggest that reduced activity of TPI leads to an oxidized redox state in these mutants and that the alleviation of this stress using reducing compounds can improve the mutant phenotypes.

Triosephosphate isomerase deficiency: new insights into an enigmatic disease

The triosephosphate isomerase (TPI) functions at a metabolic cross-road ensuring the rapid equilibration of the triosephosphates produced by aldolase in glycolysis, which is interconnected to lipid metabolism, to glycerol-3-phosphate shuttle and to the pentose phosphate pathway. The enzyme is a stable homodimer, which is catalytically active only in its dimeric form. TPI deficiency is an autosomal recessive multisystem genetic disease coupled with hemolytic anemia and neurological disorder frequently leading to death in early childhood. Various genetic mutations of this enzyme have been identified; the mutations result in decrease in the catalytic activity and/or the dissociation of the dimers into inactive monomers. The impairment of TPI activity apparently does not affect the energy metabolism at system level; however, it results in accumulation of dihydroxyacetone phosphate followed by its chemical conversion into the toxic methylglyoxal, leading to the formation of advanced glycation end products. By now, the research on this disease seems to enter a progressive stage by adapting new model systems such as Drosophila, yeast strains and TPI-deficient mouse, which have complemented the results obtained by prediction and experiments with recombinant proteins or erythrocytes, and added novel data concerning the complexity of the intracellular behavior of mutant TPIs. This paper reviews the recent studies on the structural and catalytic changes caused by mutation and/or nitrotyrosination of the isomerase leading to the formation of an aggregation-prone protein, a characteristic of conformational disorders.

Enhanced methylglyoxal formation in the erythrocytes of hemodialyzed patients

Methylglyoxal (MG) contributes significantly to the carbonyl stress in uremia; however, the reason for its increased concentration is not clear. Thus, the present study was aimed to investigate the formation and degradation of MG in the erythrocytes of hemodialyzed (HD) patients with end-stage renal disease. In 22 nondiabetic patients on long-term HD, erythrocyte MG and d-lactate levels, glyoxalase activities, and whole blood reduced glutathione content were determined. The data were compared with those from 22 healthy controls. Erythrocyte MG and d-lactate production were also investigated in vitro under normoglycemic (5 mmol/L) and hyperglycemic (50 mmol/L) conditions. The erythrocyte MG levels were elevated (P < .001) in the HD patients. The blood reduced glutathione content and glyoxalase I activity were similar to the control levels, but the glyoxalase II activity was significantly (P < .005) increased. In the normoglycemic in vitro model, production of both MG (P < .001) and d-lactate (P < .002) was significantly enhanced in the HD erythrocytes relative to the controls. During hyperglycemia, the MG formation and degradation rates were further increased (P < .001). The present study demonstrated an increased formation of MG in the erythrocytes of HD patients. This seemed to be related to a glucose metabolism disturbance of the cells. The degradation system of MG was also activated; still, it was not able to counteract the high rate of MG formation. The alterations and imbalance of these metabolic processes may contribute to the carbonyl overload and stress in the HD patients.

Degradation of functional triose phosphate isomerase protein underlies sugarkill pathology

Triose phosphate isomerase (TPI) deficiency glycolytic enzymopathy is a progressive neurodegenerative condition that remains poorly understood. The disease is caused exclusively by specific missense mutations affecting the TPI protein and clinically features hemolytic anemia, adult-onset neurological impairment, degeneration, and reduced longevity. TPI has a well-characterized role in glycolysis, catalyzing the isomerization of dihydroxyacetone phosphate (DHAP) to glyceraldehyde-3-phosphate (G3P); however, little is known mechanistically about the pathogenesis associated with specific recessive mutations that cause progressive neurodegeneration. Here, we describe key aspects of TPI pathogenesis identified using the TPI(sugarkill) mutation, a Drosophila model of human TPI deficiency. Specifically, we demonstrate that the mutant protein is expressed, capable of forming a homodimer, and is functional. However, the mutant protein is degraded by the 20S proteasome core leading to loss-of-function pathogenesis.

Using blood hemoglobin for blood analysis

This paper demonstrates that the spectrophotometric properties of blood hemoglobin (Hb) can be used for the direct determination of biochemical compounds in blood. Glucose is used as a model, but the methodology can be applied to many other compounds (only a previous enzymatic reaction producing H(2)O(2) is needed). In order to develop the method, a model relating the Hb absorbance variation during the reaction with the glucose concentration has been developed to provide theoretical support for the method and to predict its application to other compounds. In addition, clear blood samples need to be prepared without pre-treatment and lateral reactions of H(2)O(2) with other blood constituents need to be blocked; this has been achieved with 100 : 1 v/v blood dilution in bi-distilled water and azide addition. The linear response range of the method can be fitted between 2 and 540 mg dL(-1) glucose relative to the original blood sample (RSD about 4%, 70 mg dL(-1)). The analyte concentration can be obtained by an absolute calibration method or by the standard addition method; both have been applied for direct glucose determination in several blood samples and good correlations with those obtained by an automatic analyzer have been obtained.

Drosophila model of human inherited triosephosphate isomerase deficiency glycolytic enzymopathy

Heritable mutations, known as inborn errors of metabolism, cause numerous devastating human diseases, typically as a result of a deficiency in essential metabolic products or the accumulation of toxic intermediates. We have isolated a missense mutation in the Drosophila sugarkill (sgk) gene that causes phenotypes analogous to symptoms of triosephosphate isomerase (TPI) deficiency, a human familial disease, characterized by anaerobic metabolic dysfunction resulting from pathological missense mutations affecting the encoded TPI protein. In Drosophila, the sgk gene encodes the glycolytic enzyme TPI. Our analysis of sgk mutants revealed TPI impairment associated with reduced longevity, progressive locomotor deficiency, and neural degeneration. Biochemical studies demonstrate that mutation of this glycolytic enzyme gene does not result in a bioenergetic deficit, suggesting an alternate cause of enzymopathy associated with TPI impairment.

Triosephosphate isomerase deficiency: consequences of an inherited mutation at mRNA, protein and metabolic levels

Triosephosphate isomerase (TPI) deficiency is a unique glycolytic enzymopathy coupled with neurodegeneration. Two Hungarian compound heterozygote brothers inherited the same TPI mutations (F240L and E145Stop), but only the younger one suffers from neurodegeneration. In the present study, we determined the kinetic parameters of key glycolytic enzymes including the mutant TPI for rational modelling of erythrocyte glycolysis. We found that a low TPI activity in the mutant cells (lower than predicted from the protein level and specific activity of the purified recombinant enzyme) is coupled with an increase in the activities of glycolytic kinases. The modelling rendered it possible to establish the steady-state flux of the glycolysis and metabolite concentrations, which was not possible experimentally due to the inactivation of the mutant TPI and other enzymes during the pre-steady state. Our results showed that the flux was 2.5-fold higher and the concentration of DHAP (dihydroxyacetone phosphate) and fructose 1,6-bisphosphate increased 40- and 5-fold respectively in the erythrocytes of the patient compared with the control. Although the rapid equilibration of triosephosphates is not achieved, the energy state of the cells is not 'sick' due to the activation of key regulatory enzymes. In lymphocytes of the two brothers, the TPI activity was also lower (20%) than that of controls; however, the remaining activity was high enough to maintain the rapid equilibration of triosephosphates; consequently, no accumulation of DHAP occurs, as judged by our experimental and computational data. Interestingly, we found significant differences in the mRNA levels of the brothers for TPI and some other, apparently unrelated, proteins. One of them is the prolyl oligopeptidase, the activity decrease of which has been reported in well-characterized neurodegenerative diseases. We found that the peptidase activity of the affected brother was reduced by 30% compared with that of his neurologically intact brother.

Quantitative assessment of the glyoxalase pathway in Leishmania infantum as a therapeutic target by modelling and computer simulation

The glyoxalase pathway of Leishmania infantum was kinetically characterized as a trypanothione-dependent system. Using time course analysis based on parameter fitting with a genetic algorithm, kinetic parameters were estimated for both enzymes, with trypanothione derived substrates. A K(m) of 0.253 mm and a V of 0.21 micromol.min(-1).mg(-1)for glyoxalase I, and a K(m) of 0.098 mm and a V of 0.18 micromol.min(-1).mg(-1) for glyoxalase II, were obtained. Modelling and computer simulation were used for evaluating the relevance of the glyoxalase pathway as a potential therapeutic target by revealing the importance of critical parameters of this pathway in Leishmania infantum. A sensitivity analysis of the pathway was performed using experimentally validated kinetic models and experimentally determined metabolite concentrations and kinetic parameters. The measurement of metabolites in L. infantum involved the identification and quantification of methylglyoxal and intracellular thiols. Methylglyoxal formation in L. infantum is nonenzymatic. The sensitivity analysis revealed that the most critical parameters for controlling the intracellular concentration of methylglyoxal are its formation rate and the concentration of trypanothione. Glyoxalase I and II activities play only a minor role in maintaining a low intracellular methylglyoxal concentration. The importance of the glyoxalase pathway as a therapeutic target is very small, compared to the much greater effects caused by decreasing trypanothione concentration or increasing methylglyoxal concentration.

Methotrexate inhibits the glyoxalase system in vivo in children with acute lymphoid leukaemia

The inhibition of glyoxalase I leads to antitumour activity through the accumulation of methylglyoxal. Our earlier observations suggested that methotrexate (MTX) may affect the glyoxalase system. This prompted a serial study of the drug on this metabolic pathway. Ten children with acute lymphoid leukaemia (ALL), admitted to our department between January 2002 and July 2003, were enrolled. Plasma D-lactate was assayed before, 24 and 72 h after the start of four consecutive MTX infusions (5 g/m(2)/24 h) in each patient. Inhibition of glyoxalase I was tested in vitro, using human erythrocyte lysates and yeast enzyme. The elevated initial plasma D-lactate levels (P<0.02) fell significantly (P<0.001) in response to 24 h MTX infusions. In vitro, MTX, folic and folinic acids inhibited the activity of glyoxalase I. Thus, MTX seems to affect the alpha-oxoaldehyde metabolism in vivo, as a likely consequence of glyoxalase I inhibition. This action probably contributes to the anticancer activity and toxicity of the drug.

Chronic axonal neuropathy with triosephosphate isomerase deficiency

A patient with triosephosphate isomerase deficiency resulting from compound heterozygote mutation is described. Chronic axonal neuropathy was identified on clinical and neurophysiologic grounds and confirmed by sural nerve biopsy. This report describes the first biopsy-proven case confirming that peripheral neuropathy can occur with triosephosphate isomerase deficiency.

Adverse effects of dopamine potentiation by long-term treatment with selegiline

A patient with triosephosphate isomerase (TPI) deficiency exhibited worsening of abnormal involuntary movements of the dystonic type and developed psychiatric symptoms while on selegiline. When selegiline was stopped after 9 years of treatment, abnormal involuntary movements improved to pretreatment level and psychiatric behaviour returned to normal. Monoamine oxidase-B platelet activity was low in this patient.

Increased formation of methylglyoxal and protein glycation, oxidation and nitrosation in triosephosphate isomerase deficiency

Triosephosphate isomerase deficiency is associated with the accumulation of dihydroxyacetonephosphate (DHAP) to abnormally high levels, congenital haemolytic anaemia and a clinical syndrome of progressive neuromuscular degeneration leading to infant mortality. DHAP degrades spontaneously to methylglyoxal (MG)--a potent precursor of advanced glycation endproducts (AGEs). MG is detoxified to D-lactate intracellularly by the glyoxalase system. We investigated the changes in MG metabolism and markers of protein glycation, oxidation and nitrosation in a Hungarian family with two germline identical brothers, compound heterozygotes for triosephosphate isomerase deficiency, one with clinical manifestations of chronic neurodegeneration and the other neurologically intact. The concentration of MG and activity of glyoxalase I in red blood cells (RBCs) were increased, and the concentrations of D-lactate in blood plasma and D-lactate urinary excretion were also increased markedly in the propositus. There were concomitant increases in MG-derived AGEs and the oxidative marker dityrosine in hemoglobin. Smaller and nonsignificant increases were found in the neurologically unaffected brother and parents. There was a marked increase (15-fold) in urinary excretion of the nitrosative stress marker 3-nitrotyrosine in the propositus. The increased derangement of MG metabolism and associated glycation, oxidative and nitrosative stress in the propositus may be linked to neurodegenerative process in triosephosphate isomerase deficiency.