Red cell superoxide dismutase, glutathione peroxidase and catalase in Down syndrome patients with and without manifestations of Alzheimer disease

Peripheral Oxidation Markers in Down Syndrome Patients: The Better and the Worse

Oxidative stress plays an important role in Down syndrome (DS) pathology since the gene dose effect leads to abnormal levels of certain enzymes and metabolites. In this review, we focused on relatively easy-to-obtain, peripheral markers of oxidative stress and inflammation, in order to compare the levels of these markers in DS patients and chromosomally healthy persons. Studies taking into account age- and sex-matched control groups were of particular interest in this context. We analyzed the factors that influence the levels of said markers in both groups (i.e., the usefulness of the markers), including the age of DS patients, occurrence of regular trisomy 21 or mosaicism, physical activity of patients, and the onset of Alzheimer's disease in DS. This paper was conceived as a handbook-to help for selecting suitable, easy-to-obtain markers for monitoring of the health status of DS patients (e.g., in nutritional studies and during dietary supplementation).

Erythrocyte membrane stability to hydrogen peroxide is decreased in Alzheimer disease

The brain and erythrocytes have similar susceptibility toward free radicals. Therefore, erythrocyte abnormalities might indicate the progression of the oxidative damage in Alzheimer disease (AD). The aim of this study was to investigate erythrocyte membrane stability and plasma antioxidant status in AD. Fasting blood samples (from 17 patients with AD and 14 healthy controls) were obtained and erythrocyte membrane stability against hydrogen peroxide and 2,2'-azobis-(2-amidinopropane) dihydrochloride (AAPH), serum Trolox equivalent antioxidant capacity (TEAC), residual antioxidant activity or gap (GAP), erythrocyte catalase activity (CAT), erythrocyte superoxide dismutase (SOD) activity, erythrocyte nonproteic thiols, and total plasma thiols were determined. A significant decrease in erythrocyte membrane stability to hydrogen peroxide was found in AD patients when compared with controls (P<0.05). On the contrary, CAT activity (P<0.0001) and total plasma thiols (P<0.05) were increased in patients with AD compared with controls. Our results indicate that the most satisfactory measurement of the oxidative stress level in the blood of patients with AD is the erythrocyte membrane stability to hydrogen peroxide. Reduced erythrocyte membrane stability may be further evaluated as a potential peripheral marker for oxidative damage in AD.

Erythrocyte phospholipid molecular species and fatty acids of Down syndrome children compared with non-affected siblings

The majority of children with Down syndrome (DS) develop Alzheimer's disease (AD) at an early age. Although long-chainn-3 fatty acids (FA) are protective of neurodegeneration, little is known about the FA status in DS. In the present study, we aimed to investigate whether children with DS presented altered plasma and erythrocyte membrane phospholipids (PL) FA composition, when compared with their non-affected siblings. Venous blood samples were analysed for plasma and erythrocyte membrane FA composition by TLC followed by GC techniques. Lipid molecular species were determined by electrospray ionisation/tandem MS (ESI-MS/MS). FA analysis measured by standard GC showed an increased concentration of MUFA and a decreased concentration of plasmalogens in major PL fractions, but there were no differences in the concentrations of arachidonic acid or DHA. However, as identified by ESI-MS/MS, children with DS had increased levels of the following erythrocyte PL molecular species: 16 : 0–16 : 0, 16 : 0–18 : 1 and 16 : 0–18 : 2n-6, with reduced levels of 16 : 0–20 : 4n-6 species. Children with DS presented significantly higher levels of MUFA in both plasma and erythrocyte membrane, as well as higher levels of saturated and monounsaturated molecular species. Of interest was the almost double proportion of 16 : 0–18 : 2n-6 and nearly half the proportion of 16 : 0–20 : 4n-6 of choline phosphoacylglycerol species in children with DS compared with their non-affected siblings. These significant differences were only revealed by ESI-MS/MS and were not observed in the GC analysis. Further investigations are needed to explore molecular mechanisms and to test the association between the pathophysiology of DS and the risk of AD.

Redox proteomics analysis of HNE-modified proteins in Down syndrome brain: clues for understanding the development of Alzheimer disease

Down syndrome (DS) is the most common genetic cause of intellectual disability, due to partial or complete triplication of chromosome 21. DS subjects are characterized by a number of abnormalities including premature aging and development of Alzheimer disease (AD) neuropathology after approximately 40 years of age. Several studies show that oxidative stress plays a crucial role in the development of neurodegeneration in the DS population. Increased lipid peroxidation is one of the main events causing redox imbalance within cells through the formation of toxic aldehydes that easily react with DNA, lipids, and proteins. In this study we used a redox proteomics approach to identify specific targets of 4-hydroxynonenal modifications in the frontal cortex from DS cases with and without AD pathology. We suggest that a group of identified proteins followed a specific pattern of oxidation in DS vs young controls, probably indicating characteristic features of the DS phenotype; a second group of identified proteins showed increased oxidation in DS/AD vs DS, thus possibly playing a role in the development of AD. The third group of comparison, DS/AD vs old controls, identified proteins that may be considered specific markers of AD pathology. All the identified proteins are involved in important biological functions including intracellular quality control systems, cytoskeleton network, energy metabolism, and antioxidant response. Our results demonstrate that oxidative damage is an early event in DS, as well as dysfunctions of protein-degradation systems and cellular protective pathways, suggesting that DS subjects are more vulnerable to oxidative damage accumulation that might contribute to AD development. Further, considering that the majority of proteins have been already demonstrated to be oxidized in AD brain, our results strongly support similarities with AD in DS.

Dementia and mild cognitive impairment in adults with intellectual disability: issues of diagnosis

Individuals with intellectual disability (ID) are now living longer with the majority of individuals reaching middle and even "old age." As a consequence of this extended longevity they are vulnerable to the same age-associated health problems as elderly adults in the general population without ID. This includes dementia, a general term referring to a variety of diseases and conditions causing substantial loss of cognitive ability and functional declines; adults with Down syndrome are at especially high risk. A great deal of recent effort has focused on the very earliest detectable indicators of decline (and even prodromal stages of dementia-causing diseases). A condition called mild cognitive impairment (MCI) has been conceptually defined as a decline in functioning that is more severe than expected with typical brain aging but not severe enough to meet criteria for a diagnosis of dementia. Consensus criteria for both dementia and MCI have been developed for typically developing adults but are of limited applicability for adults with ID, given their pre-existing cognitive impairments. Early diagnosis will continue to be of growing importance, both to support symptomatic treatment and to prevent irreversible neuropathology when interventions are developed to slow or halt the progression of underlying disease. While the intellectual and developmental disabilities field has for some time recognized the need to develop best-practices for the diagnosis of MCI and dementia, there remains a pressing need for empirically based assessment methods and classification criteria.

The effects of levosimendan exposure on oxidant/antioxidant status and trace element levels in the pulmonary artery of rats

We investigated both the effect of levosimendan and the role of oxidant/antioxidant status and trace element levels in the pulmonary artery of rats. Fourteen male Wistar albino rats were randomly divided into two groups of seven animals each. Group 1 was not exposed to levosimendan and served as a control. Levosimendan (12 μg/kg) diluted in 10 ml 0.9 % NaCl was administered intraperitoneally to group 2. Animals of both groups were killed after 3 days, and their pulmonary arteries were harvested to determine changes in tissue oxidant/antioxidant status and trace element levels. The animals in both groups were killed 72 h after the levosimendan exposure treatment, and pulmonary arteries were harvested to determine levels of the lipid peroxidation product MDA and the antioxidant GSH as well as the decreased activity of antioxidant enzymes such as SOD, GSH-Px and CAT. It was found that MDA levels increased in pulmonary artery tissues of rats after levosimendan administration. The GSH level decreased in the pulmonary artery of rats after levosimendan treatment. Co, Mn, Fe, Cd and Pb levels were significantly higher (P < 0.001) and Mg, Zn and Cu levels significantly lower (P < 0.001) in the levosimendan group compared to the control group. These results suggest that levosimendan treatment caused an increase in free radical production and a decrease in antioxidant enzyme activity in the pulmonary artery of levosimendan-treated rats. It also caused a decrease or increase in the levels of many minerals in the pulmonary artery, which is an undesirable condition for normal pharmacological function.

Oxidative stress: A bridge between Down's syndrome and Alzheimer's disease

Besides the genetic, biochemical and neuropathological analogies between Down's syndrome (DS) and Alzheimer's disease (AD), there is ample evidence of the involvement of oxidative stress (OS) in the pathogenesis of both disorders. The present paper reviews the publications on DS and AD in the past 10 years in light of the "gene dosage" and "two-hit" hypotheses, with regard to the alterations caused by OS in both the central nervous system and the periphery, and the main pipeline of antioxidant therapeutic strategies. OS occurs decades prior to the signature pathology and manifests as lipid, protein and DNA oxidation, and mitochondrial abnormalities. In clinical settings, the assessment of OS has traditionally been hampered by the use of assays that suffer from inherent problems related to specificity and/or sensitivity, which explains some of the conflicting results presented in this work. For DS, no scientifically proven diet or drug is yet available, and AD trials have not provided a satisfactory approach for the prevention of and therapy against OS, although most of them still need evidence-based confirmation. In the future, a balanced up-regulation of endogenous antioxidants, together with multiple exogenous antioxidant supplementation, may be expected to be one of the most promising treatment methods.

Could cholesterol bound to haemoglobin be a missing link for the occasional inverse relationship between superoxide dismutase and glutathione peroxidase activities?

The concept of an anti-oxidant defence system as a means to prevent oxidative cell damage implies balanced activities of anti-oxidant defence enzymes. As well as positive correlations between anti-oxidant enzyme activities in human erythrocytes, it has been observed that sometimes when glutathione peroxidase activity is increased, CuZn-superoxide dismutase activity is decreased. In our current study we have examined the plasma lipid profile and the anti-oxidant defence enzymes in erythrocytes from humans, pigs, and bulls. We found that a negative correlation existed between CuZn-superoxide dismutase and glutathione peroxidase activities in human erythrocytes when the concentrations of both plasma triglycerides and total cholesterol were high. This correlation was also found in pig erythrocytes, but not in bull erythrocytes. We propose that cholesterol could affect membrane lipid peroxidation and superoxide generation in erythrocytes via the recently found fraction of cholesterol bound to haemoglobin, termed haemoglobin-cholesterol.

Oxidative stress and hematologic and biochemical parameters in individuals with Down syndrome

OBJECTIVE

To evaluate the levels of thiobarbituric acid reactive substances (TBARS), uric acid, and seric superoxide dismutase and catalase activities, as well as total serum iron, total iron-binding capacity (TIBC), erythrocyte osmotic fragility, and hemograms in people with Down syndrome.

PARTICIPANTS AND METHODS

The study sampled (July to December 2003) 50 people with Down syndrome and 50 individuals without Down syndrome (control group) matched by age and sex. The levels of TBARS were measured by the TBARS method. Serum superoxide dismutase and catalase activities and uric acid levels were determined spectrophotometrically. Erythrocyte osmotic fragility was assessed by the percentage of hemolysis. Hemograms, total serum iron level, and TIBC were determined with automated systems.

RESULTS

The results showed that levels of TBARS, uric acid, and seric superoxide dismutase and catalase activities were higher in the Down syndrome group compared with the control group. We also observed a slight increase in erythrocyte osmotic fragility in the Down syndrome group, but the total serum iron levels, TIBC, and hemograms for both groups were within the age-related reference values.

CONCLUSION

This was the first time, to our knowledge, that increases in seric superoxide dismutase and catalase activities were observed in people with Down syndrome. Although other studies are necessary, our results add to the understanding of the mechanisms responsible for the increased oxidative stress observed in individuals with Down syndrome and may be useful in supporting future antioxidant therapies that will improve the lives of people with Down syndrome.

Trisomy 21: conference report and 1990 update

The most relevant data and stimulating ideas presented and discussed at the symposium are briefly summarized. They centered around four major foci: the genotype, the phenotype, the pathogenesis of Down syndrome (DS), and the Down person. The molecular genetic approaches to the isolation of genes encoded by chromosome 21, the definition of a possible "critical region," and the acquisition of further insights on the origin of trisomy 21 were the main topics of the analysis of the genotype. The study of the phenotype concentrated essentially on three complex traits related to the nervous, immune, and hematologic systems, which show great sensitivity to developmental disturbances, with major effects on DS subjects' health and behavior. The difficulties of investigating the pathogenesis of the syndrome were outlined, but the theoretical bases for devising sound and complete experimental approaches were also delineated. Finally, the special attention that in the last decade the medical and sociopsychological sciences gave to Down persons was also underlined, and future developments indicated. DS still remains a challenge to science and medicine; however, from the symposium emerged a less pessimistic view on actual potentialities for a decisive advancement in its basic knowledge.

Oxidative stress related markers in the “VITA” and the centenarian projects

Oxidative stress seems to play an important role in the pathophysiology of Alzheimer's disease (AD). At present there are no easily accessible biochemical markers for AD. We performed activity assays for platelet MAO-B and erythrocyte Cu/Zn-SOD as well as Western blotting for these two proteins. Moreover, we assessed plasma lactoferrin and performed RFLP-analysis for the MAO-B-intron-13-polymorphism in patients from the Vienna-Transdanube Aging (VITA) and from the so called centenarian project. The first one, VITA, is a community-based cohort study of all 75 years old inhabitants of a geographical region of Vienna. The centenarian project investigates chronic care in-old patients suffering from AD. In both sexes platelet MAO-B activity increased significantly in the AD group, and Cu/Zn-SOD activity decreased, but the latter effect was significant only in females. No significant difference was found regarding plasma lactoferrin. No correlation was found between MAO-Bi13 and MAO-B platelet activity or allele MAO-Bi13 and disease frequency. These results point to the possibility that a combination of MAO-B and SOD activity levels might be useful tools for an early diagnosis of AD.

Anti-oxidant gene expression imbalance, aging and Down syndrome

The expression of copper zinc superoxide dismutase (SOD1), manganese superoxide dismutase (SOD2), glutathione peroxidase (GPx), and catalase (CAT) genes have been detected in human skin fibroblast cells for 2 year normal child (control), 50 year old normal male and female and a 1 year old Down Syndrome (DS) male and female with established trisomy karyotype using the RT-PCR technique. Differential expression of these genes is quantified individually against a beta-Actin gene that has been employed as an internal control. The immunoblotting of cell lysate proteins with polyclonal antibodies exhibit SOD1 (16 kD), SOD2 (40 kD), GPx (23 and 92 kD), CAT (64 kD), and Actin (43 kD) as translational products. The results demonstrate that the enhancement in the level of mRNAs encoding SOD1 in DS male and female, as well as aged male and female are 51, 21, 31 and 50% respectively compared to the normal child (control). In SOD2, DS male and female display higher (176%) and lower (26%) levels of expression whereas aged male and female exhibit enhanced levels of expression (66 and 119%) respectively compared to the control. This study demonstrates that DS affects the female less than the male whereas in the aging process, the female is more prone to oxidative damage than the male. These results not only indicate that the level of GPx mRNA is constant except in DS male, which shows a downward regulation but that even CAT mRNA is upward regulated in aged as well as in DS males and females. These disproportionate changes in anti-oxidant genes, which are incapable of coping with over expressed genes, may contribute towards the aging process, dementia and Down syndrome.

Impact of trisomy 21 on human trophoblast behaviour and hormonal function

Although trisomy 21 (T21) is the most frequent genetic abnormality and some maternal serum markers for this fetoplacental aneuploidy are of placental origin, little is known of its impact on placental development. We therefore studied the influence of T21 on trophoblast behaviour. Using cultured cells from 46 human T21 pregnancies, we confirmed the defective morphological and functional differentiation of the villous cytotrophoblast in this setting; indeed, villous cytotrophoblast cells aggregate normally but fuse inefficiently to form the syncytiotrophoblast. This is in part related to the abnormal oxidative status of the T21 cytotrophoblast, characterized by a gene dosage-related increase in SOD-1 (copper-zinc superoxide dismutase) expression and activity. This was associated with a significant (P < 0.01) increase in catalase activity but no significant change in glutathione peroxidase activity. On the basis of these in vitro findings and studies of large panels of maternal serum, we propose a pathophysiological explanation for trisomy 21 maternal serum markers of placental origin.

S100B content and SOD activity in amniotic fluid of pregnancies with Down syndrome

OBJECTIVES

We measured S100B levels and superoxide dismutase (SOD) activity retrospectively in amniotic fluid samples from pregnancies with normal and Down syndrome (DS) fetuses.

DESIGN AND METHODS

Samples from 26 normal and 71 Down syndrome fetuses were studied. S100B protein levels were determined using LIA-mat Sangtec kit, and SOD activity was measured with the RANSOD kit.

RESULTS

We observed significantly higher levels of S100B in the Down group (median of 1.24 microg/l) than in the control group (median 0.69 microg/l). S100B concentration in DS samples increased from the 13th to the 18th week of gestation and was positively correlated with gestational age. The amniotic fluid SOD activity in the DS group (16.60 U/mg/prot) was significantly higher than in the normal one (10.78 U/mg/prot).

CONCLUSIONS

This study indicates that S100B and SOD in amniotic fluid could be used as additional parameters for prenatal screening of trissomy 21 and that S100B values are associated with the gestational age.

Relevance of drug uptake, cellular distribution and cell membrane fluidity to the enhanced sensitivity of Down's syndrome fibroblasts to anticancer antibiotic-mitoxantrone

Sensitivity of human fibroblasts derived from Down's syndrome (DS) individuals (S-240, T-158, T-74, T-164) and normal donors (S-126, WA-1) to anticancer antibiotic-mitoxantrone (1,4-dihydroxy-5,8-bis((2-((2-hydroxy-ethyl)amino)ethyl)amino)-9,10-anthracenedione dihydrochloride; MIT) and its relationship to the transport rate, cellular distribution and interaction with cell membrane were studied. The survival assay showed that MIT was more toxic to trisomic fibroblast lines than to normal cells. Studies of transport kinetics indicated that the amount of drug taken up and extruded by DS cells was diminished, compared to control cells. In contrast, the cellular level of MIT associated with DNA was greater in trisomic than in normal cells. The fluorescence anisotropy measurements of TMA-DPH and 12-AS demonstrated that the fluidity of the polar region of the outer lipid monolayer of DS cell membrane was decreased in comparison with normal cells. MIT treatment decreased fluidity of the inner hydrophobic region of plasma membrane, but only slightly influenced the fluidity of the outer surface of the cell membrane. Finally, we concluded that lowered membrane fluidity, diminished amount of MIT extruded by cells and the enhanced level of the drug associated with DNA could be responsible for the enhanced sensitivity of DS fibroblasts to the MIT treatment.

Selenium intake, mood and other aspects of psychological functioning

Selenium is an essential trace element although the level of selenium in food items reflects the soil in which they were grown and thus varies markedly between different parts of the world. The metabolism of selenium by the brain differs from other organs in that at times of deficiency the brain retains selenium to a greater extent. The preferential retention of selenium in the brain suggests that it plays important functions. To date mood is the clearest example of an aspect of psychological functioning that is modified by selenium intake. Five studies have reported that a low selenium intake was associated with poorer mood. The underlying mechanism is unclear although a response to supplementation was found with doses greater than those needed to produce maximal activity of the selenoprotein glutathione peroxidase. Although the functions of many selenoproteins are unknown some play important roles in anti-oxidant mechanisms. As there are suggestions that oxidative injury plays a role in normal aging, schizophrenia, Parkinson's and Alzheimer's disease, the possible role of selenium is considered. Although there is evidence that supplementation with anti-oxidant vitamins shown some promise with Alzheimer's patients, and in preventing the development of tardive dyskinesia in schizophrenics taking neuroleptics, a role for selenium has been little considered.

Mitochondrial dysfunction and Down's syndrome

Neither the pathogenesis nor the aetiology of Down's syndrome (DS) are clearly understood. Numerous studies have examined whether clinical features of DS are a consequence of specific chromosome 21 segments being triplicated. There is no evidence, however, that individual loci are responsible, or that the oxidative damage in DS could be solely explained by a gene dosage effect. Using astrocytes and neuronal cultures from DS fetuses, a recent paper shows that altered metabolism of the amyloid precursor protein and oxidative stress result from mitochondrial dysfunction.1 These findings are consistent with considerable data implicating the role of the mitochondrial genome in DS pathogenesis and aetiology.

Protein levels of human peroxiredoxin subtypes in brains of patients with Alzheimer's disease and Down syndrome

Human peroxiredoxin (Prx) play important roles in eliminating hydrogen peroxide generated during cellular mechanisms using electrons from thioredoxin (Trx). Oxidative stress induced by reactive oxygen species (ROS) such as hydrogen peroxide has been implicated in the pathogenesis of several neurodegenerative diseases. We applied the proteomic approach to study protein levels of three subtypes of human Prx in brain regions from patients with Alzheimer's disease (AD) and Down Syndrome (DS). Protein levels of Prx-I and Prx-II were significantly increased in AD and DS. Protein levels of Prx-III, a mitochondrial protein, however, were significantly decreased. We conclude that increased protein levels of Prx-I and Prx-II could provide protection against neuronal cell death induced by hydrogen peroxide. Decreased protein levels of Prx-III could be caused by mitochondrial damage shown in AD and DS. Showing upregulated Prx protein levels provides evidence for the involvement of ROS in the pathogenesis of AD and DS.

Influence of age on activities of antioxidant enzymes and lipid peroxidation products in erythrocytes and neutrophils of Down syndrome patients

Thirty-seven individuals with Down syndrome (DS) were divided into four age categories: (i) 1 to < 6 years, (ii) 6 to < 13 years, (iii) 13 to < 20 years, and (iv) over 20 years. Activities of antioxidant enzymes found in individual age categories were different, but the differences between age groups were not statistically significant. We confirmed significantly higher activities of Cu/Zn superoxide dismutase (SOD) and glutathione peroxidase (GPx) in blood cells of people with DS as compared to 35 controls, which consisted, for the first time, of siblings of children with DS. No significant differences were found in activities of catalase and glutathione reductase in DS vs. controls. A significant difference was observed in serum concentration of malondialdehyde (MDA) in DS vs. controls (8.39 +/- 0.34 micromol/l vs. 7.34 +/- 0.27 micromol/l; p = .021) and concentration of MDA in erythrocytes of individuals with DS between the third and fourth age group (p = .05). In DS persons, an elevated ratio of SOD to catalase plus GPx with respect to the controls in all age categories was found, suggesting oxidative imbalance, potentially contributing to accelerated aging observed in these persons.

The reduction of nitroblue tetrazolium by red blood cells: a measure of Red Cell membrane antioxidant capacity and hemoglobin-membrane binding sites

The reduction of nitroblue tetrazolium (NBT) with intact Red Blood Cells (RBCs) is biphasic with an initial rapid reduction followed by a slower second phase. This biphasic kinetics has been explained with the initial rapid phase attributed to antioxidants in the red cell which reduce membrane bound NBT and the slower phase associated with the reaction of NBT with membrane bound hemoglobin. This model has been confirmed by a utilization of a number of red cell modifications which either increase the red cell antioxidants (vitamin C and vitamin E) or damage the red cell membrane (cumene hydroperoxide and N-ethylmaleimide). The utilization of this assay for human blood samples was investigated by studying a series of 20 human subjects ranging between 34 and 87 years of age. It was possible to fit all of these samples with two adjustable parameters which reflect the red cell membrane antioxidant capacity (x) and the hemoglobin membrane interactions (m). The antioxidant capacity shows a significant (p < .002; R = -.67) decrease with age. This finding is consistent with a decrease in the level of antioxidants in aged subjects. In addition, the number of hemoglobin membrane sites are negatively correlated with the antioxidant capacity (p < .02; R = -.52) suggesting that the oxidative stress associated with reduced antioxidants results in increased hemoglobin-membrane interactions.

Down syndrome: advances in molecular biology and the neurosciences

The entire DNA sequence for human chromosome 21 is now complete, and it is predicted to contain only about 225 genes, which is approximately three-fold fewer than the number initially predicted just 10 years ago. Despite this remarkable achievement, very little is known about the mechanism(s) whereby increased gene copy number (gene dosage) results in the characteristic phenotype of Down syndrome. Although many of the phenotypic traits show large individual variation, neuromotor dysfunction and cognitive and language impairment are observed in virtually all individuals. Currently, there are no efficacious biomedical treatments for these central nervous system-associated impairments. To develop novel therapeutic strategies, the effects of gene dosage imbalance need to be understood within the framework of those critical biological events that regulate brain organization and function.

Correlations of glutathione peroxidase activity with memory impairment in adults with Down syndrome

BACKGROUND

Down syndrome (DS) is a genetic disorder (trisomy 21 in 96% of cases), associated with an excess of a key enzyme involved with free radical metabolism (FRM), superoxide dismutase-1 (SOD-1), that is encoded by a gene on chromosome 21. Consequently, SOD-1 activity is elevated in DS, which also occurs in conditions of oxidative stress, and is associated with a compensatory increase in glutathione peroxidase activity (GSHPx).

METHODS

This study examined the relationship of memory function with erythrocyte SOD-1, GSHPx and catalase (CAT) activity in 22-51 year old adults with DS.

RESULTS

Mean erythrocyte SOD-1 (p < .02) and GSHPx (p < .01), but not CAT (p = .76), activities were significantly greater in the DS group than the controls. In the DS group, erythrocyte GSHPx, but not SOD-1 or CAT activities, was significantly correlated with memory function (r = .625, p < .025, df = 13 for savings score, r = .631, p < .01, df = 14 for intrusion errors) but not with intelligence quotients.

CONCLUSIONS

These observations suggest a possible relationship between altered FRM with memory deficits among adults with DS within the age-range in that an age-related increase in the prevalence for Alzheimer's neuropathology is known to be robust before reaching a plateau of 100%.

Effect of vitamin E on chromosomal aberrations in lymphocytes from patients with Down's syndrome

A possible protective effect of vitamin E (DL-alpha-tocopherol) on chromosomal damage was evaluated in lymphocytes from patients with Down's syndrome (DS) and from controls. This included the analysis of the basal and G2 chromosomal aberration frequencies in lymphocytes cultured with and without 100 microM vitamin E. The chromosomal damage in G2 was determined by scoring the number of chromosomal aberrations in lymphocyte cultures treated with 5 mM caffeine, 2 h before harvesting. Vitamin E treatment decreased the basal and G2 chromosomal aberrations both in control and DS lymphocytes. In DS cells, this protective effect, expressed as a decrease in the chromosomal damage, was greater (50%) than in controls (30%). These results suggest that the increment in basal and G2 aberrations yield in DS lymphocytes may be related to the increase in oxidative damage reported in these patients.

Antioxidant enzymes and fatty acid status in erythrocytes of Down syndrome patients

The excess of genetic information in patients with Down syndrome (DS) produces an increase in the catalytic activity of superoxide dismutase (SOD1), an antioxidant enzyme coded on chromosome 21. It has been suggested that an increase in oxidative stress in DS patients may cause adverse effects in the cell membranes through the oxidation of polyunsaturated fatty acids (PUFAs). The aim of this study was to evaluate the cellular antioxidant system by determining the catalytic activity of the SOD1, glutathione peroxidase (GPx), catalase (CAT), and glutathione reductase (GR) enzymes and the concentrations of α-tocopherol in red blood cells (RBCs) in a group of 72 DS patients. The profile of fatty acids in the phospholipids of RBC membranes was also evaluated. The activity of the erythrocyte antioxidant enzymes is significantly higher in the DS group than in the control group (SOD1, 635 ± 70 U/g Hb vs 476 ± 67 U/g Hb; CAT, 1843 ± 250 U/g Hb vs 1482 ± 250 U/g Hb; GPx, 23.2 ± 5.3 U/g Hb vs 21.5 ± 3.6 U/g Hb; and GR, 9.32 ± 1.4 U/g Hb vs 6.9 ± 1.3 U/g Hb, respectively). No differences were observed in RBC α-tocopherol concentrations between the two groups studied. Long-chain n6 PUFA (C20:3n6, C20:4n6) concentrations were increased in DS patients, suggesting enhanced Δ-6-desaturase activity. The long-chain n3 PUFA (docosahexenoic acid) does not appear to be affected by increased oxidative stress, probably because of the existence of compensatory antioxidant mechanisms.

Changed serum trace element profile in Down's syndrome

Being cofactors of important antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPx), which are significantly modified in Down's syndrome (trisomy 21), serum levels of microtrace elements zinc, copper, and selenium and of macroelement magnesium are reported in 16 subjects with Down's syndrome (DS) and their respective well age- and sex-matched controls. Serum zinc and selenium levels were significantly lowered in DS subjects, whereas copper levels were elevated. Consequently, a marked increase (40%) of the copper/zinc ratio in DS persons was observed. There were no differences in serum levels of magnesium between DS and control subjects.

Free radical pathology in schizophrenia: a review

There is evidence that free radicals are involved in membrane pathology, and may play a role in schizophrenia. Free radicals are reactive chemical species generated during normal metabolic processes, and, in excess, can damage lipids, proteins, and DNA. Regions of high oxygen consumption, lipid content, and transition metals are at particular risk. Hence, neuronal membranes are uniquely vulnerable to radical-mediated damage. Elaborate antioxidant defense systems exist to protect against oxidative stress. In schizophrenia there is evidence for dysregulation of free radical metabolism, as detected by abnormal activities of critical antioxidant enzymes and other indices of lipid peroxidation in plasma, red blood cells, and cerebrospinal fluid. Such abnormalities have been associated with tardive dyskinesia, negative symptoms, neurological signs, poor premorbid function, and CT scan abnormalities. Studies to date have generally been exploratory. Further elucidation of the role of free radicals and antioxidants in schizophrenia and its treatment will require systematic investigation.

Evidence against the involvement of reactive oxygen species in the pathogenesis of neuronal death in Down's syndrome and Alzheimer's disease

It has been proposed that the pathogenesis of Down's Syndrome (DS) involves reactive oxygen species (ROS) arising from a gene dosage effect that disproportionately elevates superoxide dismutase (SOD1) activity. It was also suggested that generation of ROS might be responsible for neuronal death in Alzheimer's Disease (AD). Little data on brain ROS in DS and AD exist; therefore, we determined activities of choline acetyltransferase (ChAT) and of the oxidative defense enzymes SOD1 and glutathione peroxidase (GSHPx) in frontal cortex of aged patients with DS and AD. We also measured levels of malondialdehyde, which reflects lipid peroxidation, and o-tyrosine, which represents the hydroxyl radical attack. ChAT was significantly reduced in cortex of patients with DS (-68%) and AD (-66%) as compared to controls. There were no statistically significant differences, however, between controls and both neurodegenerative disorders for SOD1, GSHPx, malondialdehyde and o-tyrosine. Our data contradict the only previous finding on increased SOD1 and ROS in brains of patients with DS: age as well as methodological differences might account for the discrepancy. In conclusion, no evidence for a pathogenetic role of SOD1, GSHPx, lipid peroxidation or hydroxyl radical attack in aged patients with DS and AD could be provided.

Peripheral antioxidant enzyme activities and selenium in elderly subjects and in dementia of Alzheimer's type--place of the extracellular glutathione peroxidase

Defenses against free radical damage were determined in red blood cells and plasma from 40 patients with dementia of the Alzheimer-type (DAT) and 34 aged control subjects with normal cognitive function. No crude significant difference in erythrocyte copper-zinc superoxide dismutase (E-CuZnSOD), seleno-dependent glutathione peroxidase (E-GSH-Px), glutathione reductase (E-GSSG-RD) activities, and selenium (Se) concentration was found between DAT cases and control subjects. The peroxidation products evaluated in plasma by the thiobarbituric-reactive material (TBARS) were at the same level in the DAT group as compared to controls. In the DAT group, plasma GSH-Px (P-GSH-Px) activity and plasma Se (P-Se) were negatively correlated with age (r = -0.58; p < 0.001 and r = -0.63; p < 0.001 respectively). Moreover, erythrocyte GSH-Px activity and Se were also negatively correlated with age (r = -0.40; p < 0.01 and r = -0.46; p < 0.01, respectively). No significant correlation with age was observed in the controls. When controlling for age, a significant increase for P-GSH-Px activity and P-Se was observed in DAT patients as compared to controls. These significant differences mostly appeared in DAT subjects under 80 years. Some correlations were only observed in the DAT group such as P-GSH-Px and E-GSH-Px (r = +0.68; p < 0.001); P-GSH-Px and E-Se (r = +0.79; p < 0.001). Correlations between P-GSH-Px and P-Se, E-GSH-Px and P-Se, and P-Se with E-Se are greater in the DAT group (r = +0.84; p < 0.001; r = +0.76; p < 0.001 and r = 0.75; p < 0.001) than in the control group (r = 0.54, pI < 0.01; r = 0.43, p < 0.01 and r = +0.34, p < 0.05 respectively). The fact that first -- a significant increase in P-GSH-Px and P-Se, second -- some modifications in the relationships between antioxidant parameters, and third -- age-dependent decreases of glutathione-peroxidase activities and their cofactor, appeared only in the DAT group suggest that DAT is associated with an oxidative stress due to an imbalance between reactive oxygen species and the peripheral antioxidant opposing forces.

Changes in platelet phospholipase C protein level and activity in Alzheimer's disease

We have previously demonstrated that PLC-delta was abnormally accumulated in autopsied brains with Alzheimer's disease (AD). As nonneuronal tissue involvement in AD is also suggested and PLC activity is reduced in AD platelets, we examined the changes of the protein level of PLC-delta and its enzyme activity in platelets taken from patients with AD and age-matched controls. PLC-delta in human platelets was detected as a 72 kDa protein using a specific antibody against PLC-delta. Western blots revealed that the protein level of PLC-delta was significantly higher in the cytosolic fraction prepared from AD platelets compared to controls. We investigated the activity of PLC-delta which hydrolyzes phosphatidylinositol and found that the PLC-delta activity in the cytosolic fraction from AD platelets was significantly reduced compared to the control. This finding that the enzyme activity per PLC-delta molecule is reduced in AD platelets is consistent with the study using Alzheimer brains. These results suggest that aberrant phosphoinositide metabolism is present in nonneuronal tissues as well as the brains of patients with AD.

Carnitine, carnitine acetyltransferase, and glutathione in Alzheimer brain

Glutathione and "total" carnitine (i.e., free carnitine plus acid-soluble carnitine esters) were measured in an affected (superior frontal gyrus; SFG) and unaffected (cerebellum: CBL) region of Alzheimer disease (AD) and control brains. Average glutathione content in AD SFG (n = 13) and AD CBL (n = 7) (7.9 +/- 2.1 and 11.9 +/- 4.0 nmol/mg protein, respectively (mean +/- S.D.)) was similar to that in control SFG (n = 13) and CBL (n = 6) (7.7 +/- 2.0 and 11.6 +/- 2.6 nmol/mg protein, respectively). However, glutathione increased significantly with age in AD brain (p = 0.003) but not in control brain. Average total carnitine in AD SFG (84 +/- 47 pmol/mg protein; n = 10) and AD CBL (108 +/- 86 pmol/mg protein; n = 7) was not significantly different from that in the corresponding regions of control brain (148 +/- 97 (n = 10) and 144 +/- 107 (n = 6) pmol/mg protein, respectively). However, a significant decline of total carnitine with age in both regions was noted for AD brain, but not for control brain. Carnitine acetyltransferase activity in the AD SFG (n = 13) was not significantly different from that of control SFG (n = 13) (1.83 +/- 1.05 and 2.04 +/- 0.82 nmol/min/mg protein, respectively). However, carnitine acetyltransferase activity of AD CBL (n = 7) was significantly lower than that of control CBL (n = 6) (1.33 +/- 0.88 versus 2.26 +/- 0.66 nmol/min/mg protein; p = 0.05).

Cu/Zn superoxide dismutase in patients with non-familial Alzheimer's disease

Chromosome 21 contains genes whose altered expression has long been associated with Down's syndrome and whose altered structure with some cases of Alzheimer's disease (AD). The gene for the Cu/Zn superoxide dismutase enzyme (SOD-1), a key enzyme in the metabolism of oxygen free radicals, is located on the distal portion of chromosome 21. Due to the triplication of the SOD-1 gene, patients with Down's syndrome have an almost 50% increase in their SOD activity. On the other hand, almost 25% of the patients with Down's syndrome over 40 years of age develop progressive dementia, with clinical symptoms of AD. Therefore, we decided to evaluate whether abnormalities in the production of free radicals could be detected in blood cells from AD patients, and whether they correlated with molecular variations in the Cu/Zn SOD-1 gene. Superoxide anion production was evaluated spectrophotometrically in suspensions of monocytes from 9 sporadic AD patients, and from 9 aged-matched apparently normal controls. After stimulation with increasing concentrations of n-formyl-methionyl-leucyl-phenylalanine (fMLP) or Ca ionophore A23187, monocyte free radical generation was quantitatively and qualitatively normal. Furthermore, restriction fragment length polymorphism (RFLP) analysis of leukocyte DNA digested with a variety of enzymes, gave comparable results in patients and controls. Our data support the possibility that in addition to the generation of free radicals, other directions should be explored to elucidate the mechanisms of dementia in AD.

Analysis of the functional effects of a mutation in SOD1 associated with familial amyotrophic lateral sclerosis

Mutations in the Cu, Zn superoxide dismutase (SOD1) gene have been reported in some pedigrees with Familial Amyotrophic Lateral Sclerosis (FALS). We have investigated the functional and structural effects of a Gly-->Ser mutation at codon 41 of SOD1 in a pedigree with FALS and the topography of SOD1 expression in the mammalian CNS. These analyses show that the 41Gly-->Ser mutation causes a 27% reduction in Cu, Zn SOD activity. SOD1 is transcribed at high levels in rat motoneurons and four other types of neurons homologous to upper motoneurons that degenerate in human ALS. However, SOD1 is transcribed at lower levels in other types of neurons, such as cerebellar Purkinje cells, which are not usually involved significantly in human ALS. On the other hand, immunocytochemical studies indicate that most types of rat neurons contain similar levels of Cu, Zn SOD immunoreactive protein. Nevertheless, these results suggest that the essential feature causing this subtype of ALS is either a reduction in Cu, Zn SOD activity in cell types that presumably critically require Cu, Zn SOD for protection against oxidative damage or the fact that the mutation in SOD1 associated with FALS results in a novel gain of function that is particularly deleterious to those cell types expressing SOD1 at high levels.

Immunoglobulin G subclasses in older persons with Down syndrome

IgG subclasses were measured in sera from 33 persons with Down syndrome (DS) (mean age 55 +/- 7 years) and 33 age- and sex-matched control individuals using a mouse monoclonal antibody based sandwich enzyme linked immunosorbent assay. Significantly higher levels of IgG1 and IgG3 and lower levels of IgG2 and IgG4 subclasses were found in the DS group compared to the control individuals. The higher levels of IgG1 and IgG3 subclasses found in DS persons were consistent with those seen in patients with autoimmune diseases and chronic viral infections; the lower levels of IgG2 and IgG4 subclasses were consistent with those seen in patients with recurrent infections. Our findings are similar to those reported in children with DS. We speculate that the subclass levels may have little or no relationship to the development of brain lesions typical of Alzheimer disease in older persons with DS. There were no significant differences between the levels of IgG subclasses of persons with DS showing signs of dementia of the Alzheimer type compared to those without such manifestations.

Age-associated chromosome 21 loss in Down syndrome: possible relevance to mosaicism and Alzheimer disease

We previously observed low level mosaicism (2-4% normal cells) in phytohemagglutinin-stimulated peripheral blood lymphocytes (PBL) in 29% of a small group of elderly persons with Down syndrome (DS). An analysis of cytogenetic data on 154 trisomy 21 cases (age 1 day to 68 years) showed that the proportion of diploid cells in such cultures significantly increased (P < 0.005) with advancing age. Thus, the "occult" mosaicism in PBL of the elderly persons with DS is likely due to the accumulation of cells that have lost a chromosome 21. A consequence of chromosome 21 loss could be uniparental disomy of the 2n cells, a factor that might have significant biological consequences if some chromosome 21 genes are imprinted. Loss of a chromosome 21 from trisomic cells might result in tissue-specific mosaicism and "classical" mosaicism in different age groups. Chromosome 21 loss might also be relevant to the development of Alzheimer-type dementia in DS and in the general population.

Selenium and oxygen-metabolizing enzymes in elderly community residents: a pilot epidemiological study

OBJECTIVE

To investigate the relationship of selenium and oxygen-deactivating enzymes with age in the elderly.

SAMPLE

The study sample consisted of volunteers recruited from the PAQUID study. This study is conducted in a representative sample of non-institutionalized individuals aged > or = 65 years living in Southwestern France; its main objective is to study longitudinally the incidence and risk factors of dementia.

METHODS

Plasma and erythrocyte selenium and activities of oxygen metabolizing enzymes in erythrocytes (GSH-Px, CuZn-SOD, and GSSG-RD) were measured in 239 volunteers (108 males and 131 females; mean age 73.7 years).

RESULTS

Plasma selenium (PSe) decreased significantly with age; a similar but non-significant trend was found for erythrocyte selenium (ESe). None of the enzyme activities showed a clear relationship with age. Women had significantly higher GSH-Px activities than men. For PSe levels lower than 77 ng/mL, there was a strong correlation between PSe and GSH-Px; above this value, the correlation decreased, suggesting that the selenium requirement for GSH-Px production had been satisfied. In this sample, CuZn-SOD was correlated negatively with GSH-Px (r = -0.18; P < or = 0.01) and positively with GSSG-RD (r = +0.20; P < or = 0.01).

CONCLUSIONS

In individuals aged > or = 65 years, we found that blood selenium levels were negatively correlated with age. Our analysis of the relationship between selenium and GSH-Px activity suggests that low selenium values are associated with decreased GSH-Px activity.

Increased radiosensitivity of cell lines derived from a Down's syndrome patient with ocular telangiectasia

Studies on radiosensitivity of cells from Down's syndrome (DS) patients were stimulated by the observation of their increased susceptibility to leukemia. While lymphocytes from DS patients were found to consistently show increased chromosomal aberrations after exposure to ionizing radiation, conflicting reports have been published on the radiosensitivity of fibroblasts and lymphoblastoid cell lines (LCL) derived from these patients. In the present study, cultured skin fibroblast lines developed from a DS patient with ocular telangiectasia and five normal subjects were compared for both cell killing and chromosomal aberrations (breaks, translocations, inversions, dicentrics, and rings) after low dose-rate gamma-irradiation. The LCLs developed from the patient and two normal persons were also compared for chromosomal radiosensitivity using the same irradiation protocol. A comparison of the D10 (radiation dose resulting in 10% survival) values estimated from the survival curves and the frequencies of induced chromosome aberrations in different cell lines showed that the DS cells were more radiosensitive than the respective controls. The increased cellular radiosensitivity of the DS patient reported here could be due to a combination of genetic factors (DS plus a gene for hypersensitivity to radiation) and, thus, may not be representative of all DS patients. Alternatively, the use of low dose-rate irradiation could be a factor in revealing the radiosensitivity of DS fibroblasts in general.

The role of alterations in free radical metabolism in mediating cognitive impairments in Down's syndrome

Down's syndrome (DS) is a genetic disorder involving an excess of chromosome 21 (trisomy 21) in approximately 96% of the cases and comprises approximately 15% of the population with mental retardation (Heller, 1969). In addition to the constitutional mental deficiencies associated with the syndrome many DS patients develop dementia associated with Alzheimer's disease (AD) in their later years of life (Thase et al., 1984). The genetic locus for Cu,Zn-superoxide dismutase (SOD1), a key enzyme in free radical metabolism, is located on chromosome 21, and the activity level of this enzyme is elevated by approximately 50% in a variety of cells of DS patients (see Kedziora and Bartosz, 1988; Sinet, 1982). Because alterations in free radical metabolism may be involved in neuronal death and may be associated with a number of pathological manifestations of DS, it is important to understand the role of free radical metabolism in cognitive impairments of DS, the topic discussed in this chapter.

Severe perinatal liver disease and Down syndrome: an apparent relationship

Down syndrome (DS) is not usually thought of in association with significant infantile liver disease. We present clinical and histopathologic data from 10 patients with DS who presented with severe liver disease at birth or within the first few weeks of life, and summarize the findings of eight previously reported cases. The liver disease was fatal in all but one case. Diffuse lobular fibrosis surrounding proliferating ductular elements and residual hepatocytes characterized the pathologic findings in the liver in all patients. A large number of megakaryocytes were present in the liver in nine of 12 patients. The phenotype of "perinatal hemochromatosis" was documented in eight of nine cases in which the presence of iron was investigated. Since only a fraction of the patients with this phenotype have DS, the patients we describe seem to represent a relatively well-defined subset of the perinatal hemochromatosis phenotype. The existence of such a subset suggests that the perinatal hemochromatosis phenotype does not represent a single etiopathogenetic disorder. The association between DS, megakaryocytic infiltrates in the liver, and fatal subacute/chronic liver disease gives rise to the speculation that fibrosis-promoting factors and/or metabolic abnormalities, such as those resulting from a gene dosage effect, may play a role in the genesis of the liver disease, perhaps due to a particular susceptibility of fetal liver.

Excess brain protein oxidation and enzyme dysfunction in normal aging and in Alzheimer disease

The relationship between Alzheimer disease (AD) and aging is not currently known. In this study, postmortem frontal- and occipital-pole brain samples were obtained from 16 subjects with AD, 8 age-matched controls, and 5 young controls. These samples were analyzed both for protein oxidation products (carbonyl) and the activities of two enzymes vulnerable to mixed-function oxidation, glutamine synthetase and creatine kinase. Glutamine synthetase is more sensitive to mixed-function oxidation than creatine kinase. Carbonyl content rises exponentially with age, at double the rate in the frontal pole compared with the occipital pole. Compared with young controls, both aged groups (AD and age-matched controls) have increased carbonyl content and decreased glutamine synthetase and creatine kinase activities, which are more marked in the frontal than occipital pole in all instances. We conclude that protein oxidation products accumulate in the brain and that oxidation-vulnerable enzyme activities decrease with aging in the same regional pattern (frontal more affected than occipital). However, only glutamine synthetase activity distinguishes AD from age-matched controls: Because glutamine synthetase activity is differentially reduced in the frontal pole in AD, we suggest that AD may represent a specific brain vulnerability to age-related oxidation.

Current developments in the understanding of mental retardation. Part I: Biological and phenomenological perspectives

During the past decade, noteworthy advances have taken place within the field of mental retardation. The application of advanced biological techniques in such areas as molecular genetics and neuroimaging has substantially improved our ability to identify the biological factors that underlie the origin and pathogenesis of an increasing number of mental retardation syndromes. Refined genetic and psychosocial assessments have highlighted the impressive degree of heterogeneity that is present within and across many mental retardation syndromes, stimulating increasing interest and study. This, the first of a two-part review, will focus on recent developments in biological and phenomenological aspects of mental retardation.