Tryptophan metabolism and oxidative stress in patients with Huntington's disease

Abnormalities in the kynurenine pathway may play a role in Huntington's disease (HD). In this study, tryptophan depletion and loading were used to investigate changes in blood kynurenine pathway metabolites, as well as markers of inflammation and oxidative stress in HD patients and healthy controls. Results showed that the kynurenine : tryptophan ratio was greater in HD than controls in the baseline state and after tryptophan depletion, indicating increased indoleamine dioxygenase activity in HD. Evidence for persistent inflammation in HD was provided by elevated baseline levels of C-reactive protein, neopterin and lipid peroxidation products compared with controls. The kynurenate : kynurenine ratio suggested lower kynurenine aminotransferase activity in patients and the higher levels of kynurenine in patients at baseline, after depletion and loading, do not result in any differences in kynurenic acid levels, providing no supportive evidence for a compensatory neuroprotective role for kynurenic acid. Quinolinic acid showed wide variations in blood levels. The lipid peroxidation data indicate a high level of oxidative stress in HD patients many years after disease onset. Levels of the free radical generators 3-hydroxykynurenine and 3-hydroxyanthranilic acid were decreased in HD patients, and hence did not appear to contribute to the oxidative stress. It is concluded that patients with HD exhibit abnormal handling of tryptophan metabolism and increased oxidative stress, and that these factors could contribute to ongoing brain dysfunction.     

Kynurenines,neurodegeneration and Alzheimer’s disease

Alzheimer’s disease (AD) is one of the major causes of dementia. The pathogenesis of the disease is not entirely understood, but the amyloid β peptide (Aβ) and the formation of senile plaques seem to play pivotal roles. Oligomerization of the Aβ is thought to trigger a cascade of events, including oxidative stress, glutamate excitotoxicity and inflammation. The kynurenine (KYN) pathway is the major route for the metabolism of the essential amino acid tryptophan. Some of the metabolites of this pathway, such as 3-hydroxykynurenine and quinolinic acid, are known to have neurotoxic properties, whereas others, such as kynurenic acid, are putative neuroprotectants. Among other routes, the KYN pathway has been shown to be involved in AD pathogenesis, and connections to other known mechanisms have also been demonstrated. Oxidative stress, glutamate excitotoxicity and the neuroinflammation involved in AD pathogenesis have been revealed to be connected to the KYN pathway. Intervention at these key steps may serve as the aim of potential therapy.     

The relationship between oxidative/nitrative stress and pathological inclusions in Alzheimer's and Parkinson's diseases

Alzheimer's (AD) and Parkinson's diseases (PD) are late-onset neurodegenerative diseases that have tremendous impact on the lives of affected individuals, their families, and society as a whole. Remarkable efforts are being made to elucidate the dominant factors that result in the pathogenesis of these disorders. Extensive postmortem studies suggest that oxidative/nitrative stresses are prominent features of these diseases, and several animal models support this notion. Furthermore, it is likely that protein modifications resulting from oxidative/nitrative damage contribute to the formation of intracytoplasmic inclusions characteristic of each disease. The frequent presentation of both AD and PD in individuals and the co-occurrence of inclusions characteristic of AD and PD in several other neurodegenerative diseases suggests the involvement of a common underlying aberrant process. It can be surmised that oxidative/nitrative stress, which is cooperatively influenced by environmental factors, genetic predisposition, and senescence, may be a link between these disorders.     

DJ-1 deficiency in astrocytes selectively enhances mitochondrial Complex I inhibitor-induced neurotoxicity

Parkinson's disease (PD) brains show evidence of mitochondrial respiratory Complex I deficiency, oxidative stress, and neuronal death. Complex I-inhibiting neurotoxins, such as the pesticide rotenone, cause neuronal death and parkinsonism in animal models. We have previously shown that DJ-1 over-expression in astrocytes augments their capacity to protect neurons against rotenone, that DJ-1 knock-down impairs astrocyte-mediated neuroprotection against rotenone, and that each process involves astrocyte-released factors. To further investigate the mechanism behind these findings, we developed a high-throughput, plate-based bioassay that can be used to assess how genetic manipulations in astrocytes affect their ability to protect co-cultured neurons. We used this bioassay to show that DJ-1 deficiency-induced impairments in astrocyte-mediated neuroprotection occur solely in the presence of pesticides that inhibit Complex I (rotenone, pyridaben, fenazaquin, and fenpyroximate); not with agents that inhibit Complexes II-V, that primarily induce oxidative stress, or that inhibit the proteasome. This is a potentially PD-relevant finding because pesticide exposure is epidemiologically-linked with an increased risk for PD. Further investigations into our model suggested that astrocytic GSH and heme oxygenase-1 antioxidant systems are not central to the neuroprotective mechanism.     

Free Copper,Ferroxidase and SOD1 Activities,Lipid Peroxidation and NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Content in the CSF. A Different Marker Profile in Four Neurodegenerative Diseases

The understanding of oxidative damage in different neurodegenerative diseases could enhance therapeutic strategies. Our objective was to quantify lipoperoxidation and other oxidative products as well as the activity of antioxidant enzymes and cofactors in cerebrospinal fluid (CSF) samples. We recorded data from all new patients with a diagnosis of either one of the four most frequent neurodegenerative diseases: Parkinson’s disease (PD), Alzheimer’s disease (AD), Huntington’s disease (HD) and lateral amyotrophic sclerosis (ALS). The sum of nitrites and nitrates as end products of nitric oxide (NO) were increased in the four degenerative diseases and fluorescent lipoperoxidation products in three (excepting ALS). A decreased Cu/Zn-dependent superoxide dismutase (SOD) activity characterized the four diseases. A significantly decreased ferroxidase activity was found in PD, HD and AD, agreeing with findings of iron deposition in these entities, while free copper was found to be increased in CSF and appeared to be a good biomarker of PD.     

Kynurenine 3-monooxygenase inhibition in blood ameliorates neurodegeneration

Metabolites in the kynurenine pathway, generated by tryptophan degradation, are thought to play an important role in neurodegenerative disorders, including Alzheimer's and Huntington's diseases. In these disorders, glutamate receptor-mediated excitotoxicity and free radical formation have been correlated with decreased levels of the neuroprotective metabolite kynurenic acid. Here, we describe the synthesis and characterization of JM6, a small-molecule prodrug inhibitor of kynurenine 3-monooxygenase (KMO). Chronic oral administration of JM6 inhibits KMO in the blood, increasing kynurenic acid levels and reducing extracellular glutamate in the brain. In a transgenic mouse model of Alzheimer's disease, JM6 prevents spatial memory deficits, anxiety-related behavior, and synaptic loss. JM6 also extends life span, prevents synaptic loss, and decreases microglial activation in a mouse model of Huntington's disease. These findings support a critical link between tryptophan metabolism in the blood and neurodegeneration, and they provide a foundation for treatment of neurodegenerative diseases.     

Integrative hypothesis for Huntington's disease: a brief review of experimental evidence

Huntington's disease (HD) is a demential, neurodegenerative inheritable disease affecting middle-aged patients. HD is characterized by uncontrolled choreiform movements, psychiatric symptoms and cognitive decline. Histopathological changes in HD brains reveal a considerable damage to basal ganglia, particularly affecting middle-sized spiny neurons from the caudate-putamen region. Neurochemical changes are specifically oriented to deplete GABAergic and cholinergic systems, while molecular alterations include an increased expression of CAG trinucleotide at exon 1 from the huntingtin (htt) gene, as well as aggregation of mutant htt. Although several hypotheses regarding the mechanisms by which neurotoxicity is triggered in HD brains have been suggested on the basis of experimental evidence, so far it remains not clear which of them are predominant or whether they are complementary. Recent experimental evidence through transgenic mice models reveal an interesting interaction between expanded CAG triplets, mutant htt, and the increase in toxic metabolites from the kynurenine pathway. Further evidence supports the assumption that different toxic mechanisms (i.e. excitotoxicity, energy metabolism impairment, inflammatory events, oxidative stress, etc.) are confluent and depend on each other. In this review we will briefly summarize some of those findings and propose a final integrative hypothesis for HD.     

Expression of mutant huntingtin in glial cells contributes to neuronal excitotoxicity

Huntington disease (HD) is characterized by the preferential loss of striatal medium-sized spiny neurons (MSNs) in the brain. Because MSNs receive abundant glutamatergic input, their vulnerability to excitotoxicity may be largely influenced by the capacity of glial cells to remove extracellular glutamate. However, little is known about the role of glia in HD neuropathology. Here, we report that mutant huntingtin accumulates in glial nuclei in HD brains and decreases the expression of glutamate transporters. As a result, mutant huntingtin (htt) reduces glutamate uptake in cultured astrocytes and HD mouse brains. In a neuron-glia coculture system, wild-type glial cells protected neurons against mutant htt-mediated neurotoxicity, whereas glial cells expressing mutant htt increased neuronal vulnerability. Mutant htt in cultured astrocytes decreased their protection of neurons against glutamate excitotoxicity. These findings suggest that decreased glutamate uptake caused by glial mutant htt may critically contribute to neuronal excitotoxicity in HD.     

Redox imbalance in Parkinson's disease

Parkinson's disease (PD) is an adult-onset neurodegenerative disorder characterized by preferential loss of dopaminergic neurons in an area of the midbrain called the substantia nigra (SN) along with occurrence of intraneuronal inclusions called Lewy bodies. The majority of cases of PD are sporadic in nature with late onset (95% of patients); however a few PD cases (5%) are seen in familial clusters with generally earlier onset. Although PD has been heavily researched, so far the exact cause of the rather selective cell death is unknown. Multiple lines of evidence suggest an important role for oxidative stress. Dopaminergic neurons (DA) are particularly prone to oxidative stress due to DA metabolism and auto-oxidation combined with increased iron, decreased total glutathione levels and mitochondrial complex I inhibition-induced ROS production in the SN which can lead to cell death by exceeding the oxidative capacity of DA-containing cells in the region. Enhancing antioxidant capabilities and chelating labile iron pools in this region therefore constitutes a rational approach to prevent or slow ongoing damage of DA neurons. In this review, we summarize the various sources of reactive oxygen species that may cause redox imbalance in PD as well as potential therapeutic targets for attenuation of oxidative stress associated with PD.     

Purine,kynurenine, neopterin and lipid peroxidation levels in inflammatory bowel disease

The kynurenine metabolites of tryptophan may be involved in the regulation of neuronal activity and thus gut motility and secretion. We have now performed a pilot study to measure serum concentrations of purines and kynurenines in patients with mild inflammatory bowel disease, as well as in sex- and age-matched control subjects. For some analyses, the patients were subdivided into subgroups of those with Crohn's disease and those with ulcerative colitis. The analyses indicated an increased activity in one branch of the kynurenine pathway. While there was no demonstrable difference in neopterin levels in either of the patient groups compared with controls, indicating that the disorders were in an inactive quiescent phase, both groups showed significantly higher levels of lipid peroxidation products. This suggests the presence of increased oxidative stress even during relative disease inactivity. The increased level of kynurenic acid may represent either a compensatory response to elevated activation of enteric neurones or a primary abnormality which induces a compensatory increase in gut activity. In either case, the data may indicate a role for kynurenine modulation of glutamate receptors in the symptoms of inflammatory bowel disease.     

Kynurenine Pathway Measurements in Huntington''s Disease Striatum: Evidence for Reduced Formation of Kynurenic Acid

Recent evidence suggests that there may be overactivation of the N-methyl-D-aspartate (NMDA) subtype of excitatory amino acid receptors in Huntington's disease (HD). Tryptophan metabolism by the kynurenine pathway produces both quinolinic acid, an NMDA receptor agonist, and kynurenic acid, an NMDA receptor antagonist. In the present study, multiple components of the tyrosine and tryptophan metabolic pathways were quantified in postmortem putamen of 35 control and 30 HD patients, using HPLC with 16-sensor electrochemical detection. Consistent with previous reports in HD putamen, there were significant increases in 5-hydroxyindoleacetic acid, 5-hydroxytryptophan, and serotonin concentrations. Within the kynurenine pathway, the ratio of kynurenine to kynurenic acid was significantly (p less than 0.01) increased twofold in HD patients as compared with controls, consistent with reduced formation of kynurenic acid in HD. CSF concentrations of kynurenic acid were significantly reduced in HD patients as compared with controls and patients with other neurologic diseases. Because kynurenic acid is an endogenous inhibitor of excitatory neurotransmission and can block excitotoxic degeneration in vivo, a relative deficiency of this compound could directly contribute to neuronal degeneration in HD.     

Mitochondrial involvement in Parkinson's disease, Huntington's disease, hereditary spastic paraplegia and Friedreich's ataxia

Respiratory chain dysfunction has been identified in several neurodegenerative disorders. In Friedreich's ataxia (FA) and Huntington's disease (HD), where the respective mutations are in nuclear genes encoding non-respiratory chain mitochondrial proteins, the defects in oxidative phosphorylation are clearly secondary. In Parkinson's disease (PD) the situation is less clear, with some evidence for a primary role of mitochondrial DNA in at least a proportion of patients. The pattern of the respiratory chain defect may provide some clue to its cause; in PD there appears to be a selective complex I deficiency; in HD and FA the deficiencies are most severe in complex II/III with a less severe defect in complex IV. Aconitase activity in HD and FA is severely decreased in brain and muscle, respectively, but appears to be normal in PD brain. Free radical generation is thought to be of importance in both HD and FA, via excitotoxicity in HD and abnormal iron handling in FA. The oxidative damage observed in PD may be secondary to the mitochondrial defect. Whatever the cause(s) and sequence of events, respiratory chain deficiencies appear to play an important role in the pathogenesis of neurodegeneration. The mitochondrial abnormalities induced may converge on the function of the mitochondrion in apoptosis. This mode of cell death is thought to play an important role in neurodegenerative diseases and it is tempting to speculate that the observed mitochondrial defects in PD, HD and FA result directly in apoptotic cell death, or in the lowering of a cell's threshold to undergo apoptosis. Clarifying the role of mitochondria in pathogenesis may provide opportunities for the development of treatments designed to reverse or prevent neurodegeneration.     

Nrf2-ARE信号通路在神经退行性疾病中的作用研究进展

神经退行性疾病(Neurodegenerative disease)是一类以神经元退行性病变为基础的慢性、进行性、不可逆的神经系统疾病的总称,主要包括阿尔茨海默病(Alzheimer's disease,AD)、帕金森病(Parkinson's disease,PD)、亨廷顿舞蹈病(Huntington disease,HD)、肌萎缩侧索硬化症(amyotrophic lateral sclerosis,ALS)、脊髓肌萎缩症(spinal muscular atrophy,SMA)、不同类型脊髓小脑共济失调(spinal cerebella ataxias,SCA)等。其病因和发病机制十分复杂,其中,氧化应激学说近年来受到了人们的广泛关注和普遍认可。而研究表明,Nrf2-ARE信号通路是体内抗氧化应答机制中最重要的通路之一,其能对氧化应激导致的神经细胞损伤产生保护作用,即阻止神经细胞的病变和凋亡,进而延缓神经退行性疾病的发生发展,因而有望成为神经退行性疾病的有效治疗靶标。本文就Nrf2-ARE信号通路结构特点及Nrf2-ARE信号通路在神经退行性疾病中的作用研究进展作一综述。     

Effect of centrophenoxine against rotenone-induced oxidative stress in an animal model of Parkinson's disease

Oxidative stress has been implicated in the etiology of Parkinson's disease (PD). The important biochemical features of PD, being profound deficit in dopamine (DA) content, reduced glutathione (GSH), and enhanced lipid peroxidation (LPO) in dopaminergic (DA-ergic) neurons resulting in oxidative stress, mitochondrial dysfunction and apoptosis. Rotenone-induced neurotoxicity is a well acknowledged preclinical model for studying PD in rodents as it produces selective DA-ergic neuronal degeneration. In our previous study, we have shown that chronic administration of rotenone to rats is able to produce motor dysfunction, which increases progressively with rotenone treatment and centrophenoxine (CPH) co-treatment is able to attenuate these motor defects. The present study was carried out to evaluate the antioxidant potential of CPH against rotenone-induced oxidative stress. Chronic administration of rotenone to SD rats resulted in marked oxidative damage in the midbrain region compared to other regions of the brain and CPH co-treatment successfully attenuated most of these changes. CPH significantly attenuated rotenone-induced depletion in DA, GSH and increase in LPO levels. In addition, the drug prevented the increase in nitric oxide (NO) and citrulline levels and also enhanced the activity of catalase and superoxide dismutase (SOD). Histological analysis carried out using hematoxylin and eosin staining has indicated severe damage to mid brain in comparison to cortex and cerebellum and this damage is attenuated by CPH co-treatment. Our results strongly indicate the possible therapeutic potential of centrophenoxine as an antioxidant in Parkinson's disease and other movement disorders where oxidative stress is a key player in the disease process.     

神经退化性疾病生物能量代谢和氧化应激研究进展

衰老是导致几种常见的神经系统退化性疾病的主要危险因素,包括帕金森氏病（Ｐａｒｋｉｎｓｏｎ’ｓ ｄｉｓｅａｓｅ ＰＤ）,肌萎缩性侧索硬化（Ａｍｙｏｔｒｏｐｈｉｃ ｌａｔｅｒａｌ ｓｃｌｅｒｏｓｉｓ,ＡＬＳ）,早老性痴呆（Ａｌｚｈｅｉｍｅｒ’ｓ ｄｉｓｅａｓｅ ＡＤ）和亨廷顿氏病（Ｈｕｎｔｉｎｇｔｏｎ’ｓ ｄｉｓｅａｓｅ ＨＤ）。最近研究表明,神经退化性疾病涉及到线粒体缺陷,氧化应激等因素。在脑和其它组织中,老化可导致线粒体功能的损伤和氧化损伤的增强。ＰＤ病人中,已发现线粒体复合酶体Ⅰ活性降低,氧化损伤增加和抗氧化系统活性的改变。在几例家族性ＡＬＳ病人中,也发现Ｃｕ、Ｚｎ超氧化物歧化酶（Ｃｕ,Ｚｎ ＳＯＤ）基因的突变,导致Ｃｕ、Ｚｎ超氧化物歧化酶活性减低;散发的ＡＬＳ病人氧化损伤增高。在ＨＤ病人中已发现能量代谢异常     

Levodopa therapy reduces DNA damage in peripheral blood cells of patients with Parkinson’s disease

Oxidative stress seems to play a major role in the pathogenesis of neurodegeneration. In Parkinson’s disease (PD) patients, the dopaminergic neurons are subjected to oxidative stress resulting from reduced levels of antioxidant defenses such as glutathione and high amount of intracellular iron. Levodopa (LD) is widely used for the symptomatic treatment of PD, but its role in oxidative damage control is still unclear. The aim of this study was to analyze the presence of DNA damage in peripheral blood lymphocytes (PBL) of PD patients, during a washout and a controlled LD dosage and to evaluate the oxidative damage fluctuation after LD intake. The standard and the Fpg-modified version of Comet assay were applied in analyzing DNA damage in PBL from blood samples of nine PD patients and nine matched controls. Due to the limited number of patients we cannot reach definite conclusions even if our data confirm the accumulation of DNA lesions in PD patients; these lesions decrease after LD intake.     

Plasma protein thiolation index (PTI) as a biomarker of thiol-specific oxidative stress in haemodialyzed patients

The role of oxidative stress in patients with end stage renal disease (ESRD), which occurs at significantly higher levels than in the general population, is often underestimated in clinical practice. Emerging evidence highlights the strong correlation of oxidative stress with chronic inflammation and cardiovascular disease, which are highly prevalent in most patients on maintenance haemodialysis (HD) and are a major risk factor for mortality in this population. In this study, total plasma thiols and plasma S-thiolated proteins were measured in patients with ESRD, before and after a regular HD session, and compared to age-matched healthy subjects. We found a significant decrease in the level of total plasma thiols and, conversely, a significant increase in the level of S-thiolated proteins in these patients. In most patients, post-HD plasma level of total thiols did not differ from the one in healthy subjects, whereas plasma level of S-thiolated proteins was lower in HD patients than in age-matched healthy controls. This suggests that a single HD session restores plasma thiol redox status and re-establishes the antioxidant capacity of plasma thiols. Additionally, we determined protein thiolation index (PTI), i.e., the molar ratio between the sum of all low molecular mass thiols bound to S-thiolated plasma proteins and protein free cysteinyl residues. Patients with ESRD had a significantly higher PTI compared to age-matched healthy subjects and HD was associated with a decrease in PTI to normal, or lower than normal, levels. Although this study is limited in size, our results suggest that PTI is a useful indicator of thiol-specific oxidative stress in patients with ESRD on maintenance HD. This study also emphasizes that PTI determination is a cheap and simple tool suitable for large-scale clinical studies that could be used for routine screening of thiol-specific oxidative stress.     

Proteasome and oxidative phoshorylation changes may explain why aging is a risk factor for neurodegenerative disorders

Neurodegenerative disorders (ND) belong to the most devastating diseases in the industrialized western world. Alzheimer disease (AD) is the most prevalent among these disorders followed by Parkinson disease (PD). Huntington disease (HD) is an autosomal dominantly inherited condition with a single mutation that causes disease in almost 100% of all cases. In this review we used previously published proteomics studies on AD, PD and HD to find cellular pathways changed similarly in ND and aging. All studies employed large gel two dimensional gel electrophoresis for protein separation and mass spectrometry for protein identification. Altered proteins were subjected to a KEGG pathway analysis and altered pathways determined for each disorder and aging. We found that besides the mitochondrial oxidative phosphorylation, the proteasome system are altered in aging and ND. The proteasome facilitates protein degradation which is commonly perturbed in ND which may link neurodegeneration to its largest risk factor—aging.