Effects of apolipoprotein E genotype on blood lipid composition and membrane platelet fluidity in Alzheimer's disease.

The blood lipid composition (plasma, platelets and leukocytes), platelet membrane fluidity, apolipoproteins A and B in the plasma of AD patients and control subjects with distinct Apo E genotypes were investigated. No significant differences were found between the Apo E genotype and the cholesterol, phospholipids, triglycerides and Apo B levels in the plasma; cholesterol and phospholipids levels in platelet and leukocyte membranes; and platelet membrane fluidity of AD and control groups. However, the phospholipid levels in the leukocyte membranes of the control subgroup with the genotypes epsilon3/epsilon3 and epsilon3/epsilon4 and the AD subgroups with the genotypes epsilon2/epsilon3 and epsilon3/epsilon3, epsilon3/epsilon4 and epsilon4/epsilon4 were significantly lower than those observed in the control subgroup with the genotype epsilon2/epsilon3. Moreover, the cholesterol and phospholipid levels in the platelet membranes of the AD subgroup with the epsilon2 allele were significantly higher than those in the AD subgroup without the epsilon2 allele and the control subgroups with and without the epsilon2 allele. A strong correlation was found between cholesterol and phospholipids levels in the platelet membranes of the AD and control subgroups without the epsilon2 allele, but the residual cholesterol level in the platelet membranes of the AD subgroup was twice that observed in the control subgroup. Furthermore, the Apo A levels in the plasma of the AD subgroup with the epsilon3 allele were significantly lower than those observed in the AD subgroup without the epsilon3 allele and the control subgroup with the epsilon3 allele. The results are discussed in terms of involvement of lipid metabolism in the etiopathogenesis of AD.     

Role of apolipoprotein E in renal damage protection

It is well-known that nephrotic syndrome and chronic renal failure are associated with lipid and lipoprotein abnormalities. For a long time, it has been thought that hyperlipidemia is a secondary and insignificant condition of these renal injuries. Recently, it has been shown that dyslipidaemia may contribute to the development and progression of chronic kidney disease. Apolipoprotein E (apoE) null mice are a very popular model for studying spontaneous hypercholesterolemia, but only limited data are available for the role of apolipoprotein E in kidney disease. The purpose of this study is to evaluate kidney disease in apolipoprotein E deficient mice. For this study, apoE null mice and control mice at different ages (6 weeks and 15 months) were used. Kidney morphological damage and proteins involved in oxidative stress and aging (TNF-α and NF-kB) were analyzed. ApoE deficient mice have morphological alterations that are the hallmark of kidney pathogenesis, which increase with the age of the animals. In apoE null mice kidneys, there is also increased oxidative stress as compared to control mice at the same age and fewer antioxidant enzymes. Our findings add to the growing list of protective effects that apoE possesses.     

Oxidative damage to catalase induced by peroxyl radicals: functional protection by melatonin and other antioxidants

Thermal decomposition by the azo initiator 2,2' azobis-(2-amidinopropane) dihydrochloride (AAPH) has been widely used as a water-soluble source of free radical initiators capable of inducing lipid peroxidation and protein damage. Here, in a lipid-free system, AAPH alone (40 mM) rapidly induced protein modification and inactivation of the enzyme catalase (EC 1.11.1.6). Using SDS-PAGE, it was shown that protein band intensity is dramatically reduced after 4 h of incubation with AAPH, leading to protein aggregation. Several antioxidants including melatonin, glutathione (GSH) and trolox prevented catalase modification when used at a 250 μM concentration whereas ascorbate was only effective at 1 mM concentration. All the antioxidants tested reduced carbonyl formation although melatonin was the most effective in this regard. Enzyme inactivation caused by AAPH was also significantly reduced by the antioxidants and again melatonin was more efficient than the other antioxidants used in this study. Results shown here demonstrate that alkyl peroxyl radicals inactivate catalase and reduce the effectiveness of cells to defend against free radical damage; the damage to catalase can be prevented by antioxidants, especially melatonin.     

Lipid homeostasis and apolipoprotein E in the development and progression of Alzheimer's disease

Extracellular amyloid plaques, intracellular neurofibrillary tangles, and loss of basal forebrain cholinergic neurons in the brains of Alzheimer's disease (AD) patients may be the end result of abnormalities in lipid metabolism and peroxidation that may be caused, or exacerbated, by beta-amyloid peptide (Abeta). Apolipoprotein E (apoE) is a major apolipoprotein in the brain, mediating the transport and clearance of lipids and Abeta. ApoE-dependent dendritic and synaptic regeneration may be less efficient with apoE4, and this may result in, or unmask, age-related neurodegenerative changes. The increased risk of AD associated with apoE4 may be modulated by diet, vascular risk factors, and genetic polymorphisms that affect the function of other transporter proteins and enzymes involved in brain lipid homeostasis. Diet and apoE lipoproteins influence membrane lipid raft composition and the properties of enzymes, transporter proteins, and receptors mediating Abeta production and degradation, tau phosphorylation, glutamate and glucose uptake, and neuronal signal transduction. The level and isoform of apoE may influence whether Abeta is likely to be metabolized or deposited. This review examines the current evidence for diet, lipid homeostasis, and apoE in the pathogenesis of AD. Effects on the cholinergic system and response to cholinesterase inhibitors by APOE allele carrier status are discussed briefly.     

Apolipoprotein E genotype is related to nitric oxide production in platelets

The presence of the epsilon4 allele of apolipoprotein E (APOE) is considered a risk factor for sporadic Alzheimer's disease (AD). Our recent data demonstrated that the systemic modulation of oxidative stress in platelets and erythrocytes is disrupted in aging and AD. In this study, the relationship between APOE genotype and oxidative stress markers, both in AD patients and controls, was evaluated. The AD group showed an increase in the content of thiobarbituric acid-reactive substances (TBARS) and in the activities of nitric oxide synthase (NOS) and Na, K-ATPase, when compared to controls. Both groups had a similar cGMP content and superoxide dismutase activity. APOE epsilon4 allele carriers showed higher NOS activity than non-carriers. These results suggest a possible influence of APOE genotype on nitric oxide (NO) production that might enhance the effects of age-related specific factor(s) associated with neurodegenerative disorders.     

Oxidative DNA damage in mild cognitive impairment and late-stage Alzheimer's disease

Increasing evidence supports a role for oxidative DNA damage in aging and several neurodegenerative diseases including Alzheimer's disease (AD). Attack of DNA by reactive oxygen species (ROS), particularly hydroxyl radicals, can lead to strand breaks, DNA–DNA and DNA–protein cross-linking, and formation of at least 20 modified bases adducts. In addition, α,β-unsaturated aldehydic by-products of lipid peroxidation including 4-hydroxynonenal and acrolein can interact with DNA bases leading to the formation of bulky exocyclic adducts. Modification of DNA bases by direct interaction with ROS or aldehydes can lead to mutations and altered protein synthesis. Several studies of DNA base adducts in late-stage AD (LAD) brain show elevations of 8-hydroxyguanine (8-OHG), 8-hydroxyadenine (8-OHA), 5-hydroxycytosine (5-OHC), and 5-hydroxyuracil, a chemical degradation product of cytosine, in both nuclear and mitochondrial DNA (mtDNA) isolated from vulnerable regions of LAD brain compared to age-matched normal control subjects. Previous studies also show elevations of acrolein/guanine adducts in the hippocampus of LAD subjects compared to age-matched controls. In addition, studies of base excision repair show a decline in repair of 8-OHG in vulnerable regions of LAD brain. Our recent studies show elevated 8-OHG, 8-OHA, and 5,6-diamino-5-formamidopyrimidine in both nuclear and mtDNA isolated from vulnerable brain regions in amnestic mild cognitive impairment, the earliest clinical manifestation of AD, suggesting that oxidative DNA damage is an early event in AD and is not merely a secondary phenomenon.     

Apolipoprotein E genotype and association between smoking and early onset Alzheimer's disease.

OBJECTIVE--To investigate the hypothesis that differential survival between smokers and non-smokers leading to a decrease in the frequency of the e4 allele of the apolipoprotein E gene may explain the inverse relation between smoking history and early onset Alzheimer''s disease. DESIGN--A population based case-control study. SETTING--The four northern provinces of the Netherlands and metropolitan Rotterdam. SUBJECTS--175 patients with early onset Alzheimer''s disease and two independent control groups of 159 and 457 subjects. MAIN OUTCOME MEASURES--Frequencies of the apolipoprotein e4 allele and relative risk of early onset Alzheimer''s disease. RESULTS--The inverse association between smoking history and early onset Alzheimer''s disease could not be explained by a decrease in the frequency of the apolipoprotein e4 allele. Among carriers of this allele with a family history of dementia subjects with a history of smoking had a strongly reduced risk of early onset Alzheimer''s disease (odds ratio 0.10 (95% confidence interval 0.01 to 0.87)). CONCLUSIONS--The results suggest that the inverse relation between smoking history and early onset Alzheimer''s disease cannot be explained by an increased mortality in carriers of the apolipoprotein e4 allele who smoke. The association is strongly modified by the presence of the apolipoprotein e4 allele as well as by a family history of dementia.     

Oxidative nerve cell death in Alzheimer's disease and stroke: antioxidants as neuroprotective compounds

Many neurodegenerative disorders and syndromes are associated with an excessive generation of reactive oxygen species (ROS) and oxidative stress. The pathways to nerve cell death induced by diverse potential neurotoxins such as peptides, excitatory amino acids, cytokines or synthetic drugs commonly share oxidative downstream processes, which can cause either an acute oxidative destruction or activate secondary events leading to apoptosis. The pathophysiological role of ROS has been intensively studied in in vitro and in vivo models of chronic neurodegenerative diseases such as Alzheimer's disease (AD) and of syndromes associated with rapid nerve cell loss as occuring in stroke. In AD, oxidative neuronal cell dysfunction and cell death caused by protofibrils and aggregates of the AD-associated amyloid beta protein (Abeta) may causally contribute to pathogenesis and progression. ROS and reactive nitrogen species also take part in the complex cascade of events and the detrimental effects occuring during ischemia and reperfusion in stroke. Direct antioxidants such as chain-breaking free radical scavengers can prevent oxidative nerve cell death. Although there is ample experimental evidence demonstrating neuroprotective activities of direct antioxidants in vitro, the clinical evidence for antioxidant compounds to act as protective drugs is relatively scarce. Here, the neuroprotective potential of antioxidant phenolic structures including alpha-tocopherol (vitamin E) and 17beta-estradiol (estrogen) in vitro is summarized. In addition, the antioxidant and cytoprotective activities of lipophilic tyrosine- and tryptophan-containing structures are discussed. Finally, an outlook is given on the neuroprotective potential of aromatic amines and imines, which may comprise novel lead structures for antioxidant drug design.     

Influence of apolipoprotein E genotype on the transmission of Alzheimer disease in a community-based sample.

The epsilon 4 allele of the apolipoprotein E locus (APOE) has been found to be an important predictor of Alzheimer disease (AD). However, linkage analysis has not clarified the role of APOE in the transmission of AD. The results of the current study provide evidence that the pattern of transmission of memory disorders differs in nuclear families in which the AD-affected proband did carry an epsilon 4 allele versus those families in which the AD-affected proband did not carry an epsilon allele. Further, risk of AD due to APOE genotype in the probands is modified by family history of memory disorders, suggesting gene-by-gene interactions. Family history remained a significant predictor of AD for affected probands with some, but not all, APOE genotypes in a logistic regression analysis. Though nonadditive in the prediction of AD, APOE genotype and family history acted additively in the prediction of age at AD onset. The results of complex segregation analysis were inconsistent with Mendelian segregation of memory disorders both in families of affected probands who did or did not carry an epsilon 4 allele, yet these two groups had significantly different parameter estimates for their transmission models. These results are consistent with gene-by-gene interactions, but also could result from common elements in the familial environment.     

Astroglial regulation of apolipoprotein E expression in neuronal cells. Implications for Alzheimer's disease

Although apolipoprotein (apo) E is synthesized in the brain primarily by astrocytes, neurons in the central nervous system express apoE, albeit at lower levels than astrocytes, in response to various physiological and pathological conditions, including excitotoxic stress. To investigate how apoE expression is regulated in neurons, we transfected Neuro-2a cells with a 17-kilobase human apoE genomic DNA construct encoding apoE3 or apoE4 along with upstream and downstream regulatory elements. The baseline expression of apoE was low. However, conditioned medium from an astrocytic cell line (C6) or from apoE-null mouse primary astrocytes increased the expression of both isoforms by 3-4-fold at the mRNA level and by 4-10-fold at the protein level. These findings suggest that astrocytes secrete a factor or factors that regulate apoE expression in neuronal cells. The increased expression of apoE was almost completely abolished by incubating neurons with U0126, an inhibitor of extracellular signal-regulated kinase (Erk), suggesting that the Erk pathway controls astroglial regulation of apoE expression in neuronal cells. Human neuronal precursor NT2/D1 cells expressed apoE constitutively; however, after treatment of these cells with retinoic acid to induce differentiation, apoE expression diminished. Cultured mouse primary cortical and hippocampal neurons also expressed low levels of apoE. Astrocyte-conditioned medium rapidly up-regulated apoE expression in fully differentiated NT2 neurons and in cultured mouse primary cortical and hippocampal neurons. Thus, neuronal expression of apoE is regulated by a diffusible factor or factors released from astrocytes, and this regulation depends on the activity of the Erk kinase pathway in neurons.     

Oxidative damage to E. coli membranes caused by superoxide radicals]

The effects of bacterial membranes of active oxygen species photochemically generated by riboflavin-histidine systems were studied. According to SDS-PAAG data, the formation of high molecular weight protein aggregates and the appearance of fluorochromes whose fluorescence is seen in the longwave length region of the spectrum (lambda excit = 350 nm, lambda emis = 400-500 nm) and which are bound to the proteins, are suggestive of membrane oxidation consisting in the chemical modification of protein components. The presence in E. coli membranes of endogenous photosensitizers which upon illumination with visible light induce the oxidation of membrane proteins, was established.     

The role of apolipoprotein E in Alzheimer's disease: pharmacogenomic target selection

The association of inheritance of different apolipoprotein E (APOE, gene; apoE, protein) alleles with the risk and rate of onset of Alzheimer's disease (AD) is now well established and widely confirmed. While there are now a collection of hypotheses concerning the specific relationship of APOE polymorphisms to various phenotypic manifestations of AD, no single compelling theory has been tested and universally accepted. The only clear fact emerging during the past 6 years is that differences in APOE genotype affect the average rate of disease onset as a predictable function of the inheritance of this polymorphic gene. Methods now exist to enable experimental designs to study the metabolic effects of inheriting different APOE alleles, addressing what differences that may be present for many years, perhaps over the entire lifetime, can lead to earlier or later manifestations of the disease and are therapeutically tractable. This review summarizes part of an experimental approach to identify biological pathways influenced by the different APOE polymorphisms that are relevant to the pathogenesis of AD.     

Oxidative damage to mitochondrial DNA is inversely related to maximum life span in the heart and brain of mammals.

DNA damage is considered of paramount importance in aging. Among causes of this damage, free radical attack, particularly from mitochondrial origin, is receiving special attention. If oxidative damage to DNA is involved in aging, long-lived animals (which age slowly) should show lower levels of markers of this kind of damage than short-lived ones. However, this possibility has not heretofore been investigated. In this study, steady-state levels of 8-oxo-7, 8-dihydro-2'-deoxyguanosine (8-oxodG) referred to deoxyguanosine (dG) were measured by high performance liquid chromatography (HPLC) in the mitochondrial (mtDNA) and nuclear (nDNA) DNA from the heart of eight and the brain of six mammalian species ranging in maximum life span (MLSP) from 3.5 to 46 years. Exactly the same digestion of DNA to deoxynucleosides and HPLC protocols was used for mtDNA and nDNA. Significantly higher (three- to ninefold) 8-oxodG/dG values were found in mtDNA than in nDNA in all the species studied in both tissues. 8-oxodG/dG in nDNA did not correlate with MLSP across species either in the heart (r=-0.68; P<0.06) or brain (r = 0.53; P<0.27). However, 8-oxodG/dG in mtDNA was inversely correlated with MLSP both in heart (r=-0.92; P<0.001) and brain (r=-0.88; P<0.016) tissues following the power function y = a(.)x(b), where y is 8-oxodG/dG and x is the MLSP. This agrees with the consistent observation that mitochondrial free radical generation is also lower in long-lived than in short-lived species. The results obtained agree with the notion that oxygen radicals of mitochondrial origin oxidatively damage mtDNA in a way related to the aging rate of each species.-Barja, G., Herrero, A. Oxidative damage to mitochondrial DNA is inversely related to maximum life span in the heart and brain of mammals.     

Time-dependent changes to lipids and antioxidants in plasma and aortas of apolipoprotein E knockout mice.

Oxidation of lipoproteins is thought to be an early event in atherogenesis. To evaluate whether aortic lipoprotein lipid (per)oxidation contributes to atherosclerosis, we investigated the time-dependent changes to lipids and antioxidants in plasma and aortas of apolipoprotein E gene knockout (apoE-/-) mice receiving a high fat diet, and compared these changes with lesion development. Circulating buoyant lipoproteins and associated cholesterol (C), cholesteryl esters (CE), and alpha-tocopherol (alpha-TOH) increased within 1 month then remained largely constant up to 6 months. Coenzyme Q (CoQ) remained unchanged for the first 3 months and increased marginally after 6 months. With increasing duration of the diet, plasma lipids showed an increased propensity to undergo peroxyl radical-induced (per)oxidation. Absolute concentrations of aortic C, hydroperoxides and hydroxides of CE (CE-O(O)H) and alpha-TOH increased gradually while aortic CE increased more markedly with changes to cholesteryl linoleate being most pronounced. Aortic CoQ remained largely unchanged. Overall, the extent of aortic CE (per)oxidation remained low (相似文献   

Effect of the brain-derived neurotrophic factor and the apolipoprotein E polymorphisms on disease progression in preclinical Alzheimer's disease

Genetic factors, such as apolipoprotein E (ApoE) polymorphisms, are thought to play an important role in the etiology of Alzheimer's disease (AD). Recent association studies have suggested that the Val66Met polymorphism in the brain-derived neurotrophic factor ( BDNF ) gene could play a role in the development of AD. To identify genotypic effects of the BDNF and the ApoE genes on disease progression in preclinical AD, we assessed morphological changes using serial magnetic resonance imaging during the preclinical period of AD in 35 individuals. When all subjects were analyzed as one group, progressive atrophy was noted in the limbic, paralimbic and neocortical areas. Individuals of the BDNF Val/Val genotype showed progressive atrophy in the left medial temporal areas, whereas the BDNF Met allele carriers showed additional changes in the anterior cingulate cortex (ACC), posterior cingulate cortex (PCC) and the precuneus. An interaction between the BDNF genotype and progressive morphological changes was found in the PCC. The noncarriers for the ApoE ɛ4 allele showed progressive atrophy in the bilateral medial temporal areas. In addition to changes in the medial temporal areas, ɛ4 carriers showed progressive atrophy in the PCC, ACC and precuneus. An interaction between the ApoE genotype and progressive morphological change was noted in the right medial temporal area. The present preliminary study indicates that polymorphisms of the ApoE and the BDNF genes could affect disease progression in preclinical AD and implies that the Met-BDNF polymorphism could be an additional risk factor for rapid disease progression in preclinical AD.     

Association of apolipoprotein E phenotypes with late onset Alzheimer's disease: population based study.

OBJECTIVE--To determine the association between the e4 allele of apolipoprotein E and Alzheimer''s disease in a randomly selected population sample. DESIGN--Cross sectional population based study. SUBJECTS--980 people aged 69 to 78 (349 men, 631 women). SETTING--Population of Kuopio, eastern Finland. MAIN OUTCOME MEASURES--Presence of e4 allele and diagnosis of Alzheimer''s disease by detailed neurological and neurophysiological evaluation. RESULTS--46 (4.7%) subjects were classified as having probable or possible Alzheimer''s disease. The frequency of the apolipoprotein E e4 allele was 0.359 in patients with Alzheimer''s disease and 0.165 subjects without dementia (P < 0.0001). The prevalence of Alzheimer''s disease was 2.9% in subjects with no e4 alleles, 7.6% in subjects with one e4 allele, and 21.4% in subjects with two e4 alleles of apolipoprotein E. CONCLUSIONS--Allele e4 of apolipoprotein is associated with Alzheimer''s disease in a dose-response fashion in a randomly selected elderly population.     

Oxidative stress and APO E polymorphisms in Alzheimer's disease and in mild cognitive impairment

Abstract

A number of evidences indicates oxidative stress as a relevant pathogenic factor in Alzheimer's disease (AD) and mild cognitive impairment (MCI). Considering its recognized major genetic risk factors in AD, apolipoprotein (APO E) has been investigated in several experimental settings regarding its role in the process of reactive oxygen species (ROS) generation. The aim of this work has been to evaluate possible relationships between APO E genotype and plasma levels of selected oxidative stress markers in both AD and MCI patients.

APO E genotypes were determined using restriction enzyme analysis. Plasma levels of oxidative markers, advanced oxidation protein products, iron-reducing ability of plasma and, in MCI, activity of superoxide dismutases were evaluated using spectrophotometric analysis.

We found, compared to controls, increased levels of oxidized proteins and decreased values of plasma-reducing capacity in both AD patients (p < 0.0001) and MCI patients (p < 0.001); the difference between AD and MCI patients was significant only for plasma-reducing capacity (p < 0.0001), the former showing the lowest values. Superoxide dismutase activity was reduced, although not at statistical level, in MCI compared with that in controls. E4 allele was statistically associated (p < 0.05) with AD patients. When comparing different APO E genotype subgroups, no difference was present, as far as advanced oxidation protein products and iron-reducing ability of plasma levels were concerned, between E4 and non-E4 carriers, in both AD and MCI; on the contrary, E4 carriers MCI patients showed significantly decreased (p < 0.05) superoxide dismutase activity with respect to non-E4 carriers.

This study, in confirming the occurrence of oxidative stress in AD and MCI patients, shows how it can be related, at least for superoxide dismutase activity in MCI, to APO E4 allele risk factor.     

Oxidative modification of citrate synthase by peroxyl radicals and protection with novel antioxidants

In mammals, aging is linked to a decline in the activity of citrate synthase (CS; E.C. 2.3.3.1), the first enzyme of the citric acid cycle. We used 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH), a water-soluble generator of peroxyl and alkoxyl radicals, to investigate the susceptibility of CS to oxidative damage. Treatment of isolated mitochondria with AAPH for 8–24?h led to CS inactivation; however, the activity of aconitase, a mitochondrial enzyme routinely used as an oxidative stress marker, was unaffected. In addition to enzyme inactivation, AAPH treatment of purified CS resulted in dityrosine formation, increased protein surface hydrophobicity, and loss of tryptophan fluorescence. Propyl gallate, 1,8-naphthalenediol, 2,3-naphthalenediol, ascorbic acid, glutathione, and oxaloacetate protected CS from AAPH-mediated inactivation, with IC₅₀ values of 9, 14, 34, 37, 150, and 160?μM, respectively. Surprisingly, the antioxidant epigallocatechin gallate offered no protection against AAPH, but instead caused CS inactivation. Our results suggest that the current practice of using the enzymatic activity of CS as an index of mitochondrial abundance and the use of aconitase activity as an oxidative stress marker may be inappropriate, especially in oxidative stress-related studies, during which alkyl peroxyl and alkoxyl radicals can be generated.     

MutY is Down-regulated by Oxidative Stress in E. coli

In Escherichia coli, MutM (8-oxoG DNA glycosylase/lyase or Fpg protein), MutY (adenine DNA glycosylase) and MutT (8-oxodGTPase) function cooperatively to prevent mutation due to 7, 8-dihydro-8-oxoguanine (8-oxoG), a highly mutagenic oxidative DNA adduct. MutM activity has been demonstrated to be induced by oxidative stress. Its regulation is under the negative control of the global regulatory genes, fur, fnr and arcA. However, interestingly the presence of MutY increases the mutation frequency in mutT- background because of MutY removes adenine (A) from 8-oxoG:A which arises from the misincorporation of 8-oxoG against A during DNA replication. Accordingly we hypothesized that the response of MutY to oxidative stress is opposite to that of MutM and compared the regulation of MutY activity with MutM under various oxidative stimuli. Unlike MutM, MutY activity was reduced by oxidative stress. Its activity was reduced to 30% of that of the control when E. coli was treated with paraquat (0.5 mM) or H₂O₂ (0.1 mM) and induced under anaerobic conditions to more than twice that observed under aerobic conditions. The reduced mRNA level of MutY coincided with its reduced activity by paraquat treatment. Also, the increased activity of MutY in anaerobic conditions was reduced further in E. coli strains with mutations in fur, fnr and arcA and the maximum reduction in activity was when all mutations were present in combination, indicating that MutY is under the positive control of these regulatory genes. Therefore, the down-regulation of MutY suggests that there has been complementary mechanism for its mutagenic activity under special conditions. Moreover, the efficacy of anti-mutagenic action should be enhanced by the reciprocal co-regulation of MutM.     

Diminution of singlet oxygen-induced DNA damage by curcmin and related antioxidants

Curcumin, the natural antioxidant from turmeric, an Indian spice, and its derivatives have significant abilities to protect plasmid pBR322 against single-strand breaks induced by singlet oxygen (¹O₂), a reactive oxygen species with potential genotoxic/mutagenic properties. ¹O₂ was generated at 37°C in an aqueous buffer system by the thermal dissociation of the endoperoxide of 3,3′-(1,4-naphthylene)dipropionate (NDPO₂). Among the compounds, tested, curcumin was the most effective inhibitor of DNA damage followed by desmethoxycurcumin, bisdesmethoxycurcumin and other derivatives. The observed antioxidant activity was both time-and concentration-dependent. The protectice ability of curcumin was higher than that of the well-known biological antioxidants lipoate, α-tocopherol and β-carotene. However, the highest protective ability with saturating concentrations of curcumin did not exceed 50%. The ability of curcumin and its derivatives to protect DNA against ¹O₂ seems to be related to their structures and may at least partly explain the therapeutic and other beneficial effects of these compounds including anticarcinogenic and antimutagenic properties.