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DNA Repair 12 (2013) 811– 816

Contents lists available at ScienceDirect

DNA Repair

jo ur nal home p age: www.elsev ier .com/ locate /dnarepai r

ini review

NA-repair in mild cognitive impairment and Alzheimer’s disease

ina Bucholtza, Ilja Demutha,b,∗

The Berlin Aging Study II; Research Group on Geriatrics; Charité – Universitätsmedizin Berlin, Berlin, GermanyInstitute of Medical and Human Genetics, Charité – Universitätsmedizin Berlin, Germany

r t i c l e i n f o

rticle history:eceived 6 July 2013ccepted 8 July 2013

a b s t r a c t

While the pathogenesis of the sporadic form of Alzheimer disease (late onset Alzheimer disease, LOAD)is not fully understood, it seems to be clear that a combination of genetic and environmental factorsare involved and influence the course of the disease. Among these factors, elevated levels of oxidative

vailable online 3 August 2013 stress have been recognized and individual differences in the capacity to deal with DNA damage causedby its effects have been the subject of numerous studies. This review summarizes the research on DNArepair proteins and genes in the context of LOAD pathogenesis and its possible prodromal stage, mildcognitive impairment (MCI). The current status of the research in this field is discussed with respect tomethodological issues which might have compromised the outcome of some studies and future directionsof investigation on this subject are depicted.

© 2013 Elsevier B.V. All rights reserved.

ontents

1. Alzheimer’s disease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8112. Activity and amounts of DNA-repair proteins in MCI and AD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8123. Polymorphisms in DNA-repair genes and AD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8144. Methodological issues and future directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 814

Conflicts of interest statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815

. Alzheimer’s disease

Alzheimer’s disease is one of the most prevalent and worryingiseases in old age. Its symptoms – the progressive impairmentf cognitive functioning and attendant psychotic symptoms – areombined with the fear of autonomy loss. Although treatments limited, therapeutic and preventive intervention can slow therogression of cognitive impairment and need for nursing care.

has been confirmed in various studies and it is likely that a com-bination of genetic, environmental and lifestyle factors is affectingthe process of AD (reviewed in [3]). Among these factors, oxida-tive stress has been confirmed in various studies to have a rolein the pathogenesis of AD [4,5]. Consequently, these results haveled to an intensive research on alterations in amounts and activ-ity of DNA-repair proteins of pathways involved in the repair ofoxidative stress induced lesions in patients with AD. Recent studies

herefore, early diagnosis is an important basis for arranging indi-idual treatment [1,2].

The etiology and pathogenesis of AD is not fully understood,owever, the impact of several genetic and environmental factors

∗ Corresponding author at: Charité – Universitätsmedizin Berlin, Institute of Med-cal and Human Genetics and The Berlin Aging Study II; Research Group on Geriatrics,ugustenburger Platz 1, 13353 Berlin, Germany. Tel.: +49 30 450 566 306;

ax: +49 30 450 566 904.E-mail address: ilja.demuth@charite.de (I. Demuth).

568-7864/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.dnarep.2013.07.005

on DNA-repair proteins also included patients with mild cognitiveimpairment (MCI). MCI, which is usually assessed by standardizedneuropsychological tests, can be a prodromal phase of dementia. Itsanalysis is therefore expected to result in a better understanding ofAD pathogenesis [6].

Another approach followed by many researchers in order to geta better understanding of the impact of DNA repair on AD patho-genesis is the analysis of single nucleotide polymorphisms (SNPs)

in DNA-repair genes in a case–control setting.

The aim of this review is to give an overview of current studiesinvestigating the role of different DNA repair capacity measures,

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ncluding the impact of DNA repair gene polymorphisms, in theathogenesis of AD and to compare results by taking different diag-ostic criteria and study designs into account.

. Activity and amounts of DNA-repair proteins in MCI andD

Most studies analysing DNA repair capacity in the context of ADocus on proteins of the base excision repair pathway, especiallyhe enzyme 8-oxoguanine glycosylase 1 (OGG1) (Table 1). Thisrotein catalyses the incision of DNA at sites of the oxidationroduct, 8-hydroxy-2′-deoxyguanosine (8-OHdG). Several studies

nvestigated the OGG1 activity of protein extracts from MCI andate onset AD (LOAD) patients. In these experiments 32P-labeledligonucleotid duplexes containing an oxidized guanine (8-OHdG)ere incubated with tissue lysates of different brain regions

xtracted from MCI, LOAD or control donors. The enzyme activityas then determined by densitometric analysis of autoradio-

raphic signals resulting from DNA molecules of different gelobility. A reduced OGG1 activity was consistently reported from

tudies employing this strategy on protein extracts from both, MCInd AD patients [7–9].

Shao et al. explored the possibility of a reduced amount of OGG1rotein by western blot analysis of nuclear and mitochondrial frac-ions of the tissue material used for the activity assays. Indeed,hey found reduced OGG1 protein in both, MCI and AD frontal lobe

aterial, and in AD brain tissue of the parietal lobe. No differencesn OGG1 amounts were detected in mitochondrial fractions fromhe same individuals. Interestingly, a comparison of OGG1 proteinevels from MCI cerebellar nuclear fractions revealed a significantGG1 increase when compared to control lysates. The authors con-luded that decreased OGG1 activity occurs early in the progressionf AD, which can not completely be explained by reduced OGG1rotein levels [8]. Dezor et al. analyzed OGG1 protein levels byestern blot of lysates from peripheral blood lymphocytes. They

ound significantly decreased OGG1 levels in AD patients, however,hen considering the extent of dementia they observed increasedGG1 levels in AD patients with mild dementia when compared

o patients with a moderate stage of AD [10]. Unfortunately theesults of this study are difficult to be reconstructed by the readerecause of lacking information, e.g. on the numbers of AD patients

n different dementia groups classified by the mini mental statexam. In a different approach to measure OGG1 protein abundance,ida et al. used an antibody specifically recognizing the mitochon-rial form of OGG1 (hOGG1-2a) in immunhistochemical analysis.his revealed decreased OGG1 staining in paraffin sections of therbitofrontal gyrus and the entorhinal cortex from LOAD patientshen compared to controls [11].

The DNA polymerase beta (POLB) is another key enzyme ofhe BER-pathway and two studies have analyzed its role in theathogenesis of AD. Copani et al. assessed POLB levels in autop-ic brain specimen in a total of 23 samples, including controls andD patients grouped according to the Braak score, by western blotnalysis. They found a progressive increase of POLB amounts withncreasing Braak scores from 0 to III/IV in cortical brain samples.he group with Braak scores V/VI showed reduced POLB abundancehen compared with the signals from samples with Braak scores

II/IV. In the same study immunhistochemical analysis showededuced neuron POLB staining in temporal cortex AD brain sectionsnd no difference in astrocyte staining when compared to controlections from non AD donors [12]. Reduced POLB levels were also

ound in LOAD brain cerebellum lysates which was accompaniedy a significantly reduced single nucleotide gap-filling activity [9].

Two immunohistochemical studies provide evidence for aole of APEX1 (APE1/REF-1) in the pathogenesis of AD. This

pair 12 (2013) 811– 816

protein is also part of the BER-pathway and functions as 5′-apurinic/apyrimidinic endonuclease. APEX1 has also a role in theactivation of transcription factors in response to oxidative stressvia a redox-based mechanism (reviewed in [13]). Both studiesfound increased APEX1 staining in AD brain sections of the hip-pocampus and surrounding temporal cortex or cerebral cortex,respectively [14,15]. It is somewhat inconsistent, that Marcon et al.yielded their positive results only from analysis of bioptic samples,whereas no differences in APEX1 staining were observed in post-mortem samples. In contrast, Tan et al. found increased APEX1staining in post-mortem samples. However, both groups inter-preted their results in the context of the dual APEX1 function –the APEX1 increase in AD as a adaptive response to oxidative stressin order to repair resulting DNA-damage or, alternatively, to regu-late the expression of oxidative stress induced transcription factors.Western blot analysis on APEX1 expression in brain tissue yieldedcontradictory results. Whereas LOAD and control lysates from infe-rior parietal lobule and cerebellum were similar in APEX1 signalintensity [9], APEX1 was significantly increased in AD midfrontalcortex samples [16].

The Nucleotide excision repair pathway efficiently eliminatescyclobutane pyrimidine dimers and (6-4) photoproducts pro-duced by UV light, but also a broad spectrum of bulky chemicaladducts and oxidative DNA-damage (reviewed in [17]). Westernblot analysis of post-mortem brain tissue (frontal lobe, cerebel-lum, parietal lobe, temporal lobe, occipital lobe) from 10 relativelyyoung AD patients (58.7 ± 5.7 years) and the same number ofcontrols revealed significantly increased amounts of NER proteinsERCC2 (XPD) and ERCC3 (XPB) in all brain regions analyzed, aresult which was discussed as a consequence of ongoing DNAdamage [18].

Limited information on proteins involved in the repair of DNA-double strand breaks (DSBs) in the context of MCI and AD isavailable. A study investigated the role of DNA-dependent proteinkinase (DNA-PK) in AD by western blot analysis using antibod-ies specifically recognizing its subunits KU70, KU80 and DNA-PKCS(PRKDC). While the comparison of DNA-PK protein amounts did notreveal a significant difference between 7 control and 39 AD samples[16], the extension of this study by adding 7 AD and 6 control sam-ples revealed significantly reduced DNA-PKCS protein levels in theAD lysates. The DNA-PKCS abundance was significantly correlatedwith the end joining activity [19]. Another western blot study oncomponents of the DSB repair, the proteins of the MRN-complex,revealed substantially reduced amounts of MRE11, RAD50 and NBNin neurons of LOAD cortex samples. Immunohistochemical analy-sis of cerebellum sections from identical AD and control individualsfor NBN expression indicated, that the reduction of MRN complexproteins is specific to the cortex, the brain region primarily affectedby the neuropathological alterations in AD [20].

O-6-methylguanine-DNA methyltransferase (MGMT) is a cel-lular molecule that repairs methylated guanine in DNA bystoichiometrically transferring the methyl group at the O-6 positionto a cysteine of itself (reviewed in [21]).

Edwards et al. compared the MGMT activity in lymphocytes of19 LOAD patients with the activity of the enzyme in 19 age matchedcontrols. The assay used a substrate DNA that has been alkylatedwith [3H]methylnitrosourea at the O6 position followed by incu-bation with extracts prepared from the lymphocytes. The MGMTactivity was determined then as an equivalent of the radioactivityof the methylated protein. This strategy did not, however, revealedany significant differences between the LOAD and control group[22].

As a transcription factor the tumor suppressor protein p53 isinvolved in cell cycle regulation, DNA-repair, apoptosis and othercellular processes (reviewed in [23]). A comparison of the p53 levelas measured by western blot analysis of extracts prepared from

N. Bucholtz, I. Demuth / DNA Repair 12 (2013) 811– 816 813

Table 1Expression and activity of DNA-repair proteins in MCI and AD in case–control studies.

Protein DNA-repairpathway

Phenotypestudieda

Number ofcases/controls

Major findings Reference

OGG1 BER MCI 8/6 OGG1 activity (incision capacity) was reduced in nuclearpreparations of frontal, temporal and parietal lobes, and inmitochondria of temporal lobes; the amount of nuclearOGG1 protein was reduced in parietal lobes

[8]

OGG1 BER MCI 9/10 Linear decrease of OGG1 activity (incision capacity) andsingle-nucleotide gap filling activity with the severity ofthe clinical diagnosis

[9]

OGG1 BER AD 7/6 OGG1 activity (incision capacity) was reduced in nuclearpreparations of frontal, temporal and parietal lobes and inmitochondria of frontal and temporal lobes; the amount ofnuclear OGG1 protein was reduced in frontal and parietallobes

[8]

OGG1 BER LOAD 10/10 Reduced OGG1 activity (incision capacity) in cases,unaltered AP-site incision and protein amount

[9]

OGG1 BER AD 41/51 OGG1 protein amount was not significantly altered inlymphocytes of AD patients (western blot not shown);when analyzed with respect to the degree of dementiathey found OGG1 increased in moderate dementia whencompared to mild dementia

[10,48]

OGG1 BER LOAD 8/6 The mitochondrial form of OGG1 (hOGG1-2a) wasdecreased in the orbitofrontal gyrus and the entorhinalcortex in AD when compared to controls

[11]

OGG1 BER LOAD 10/8 Significant decrease of OGG1 activity (incision capacity)and elevated DNA helicase activity was found in four andthree analyzed brain regions, respectively

[7]

POLB BER AD 19/4 The expression level of POLB differed between groups withdifferent Braak scores (western blot). Reducedimmunohistochemical neuron POLB staining in temporalcortex AD brain sections, but no difference in astrocytestaining when compared to control sections from non ADdonors was found

[12]

APEX1 BER AD 39/7 APEX1 was increased in AD midfrontal cortex brain tissue [16]APEX1 BER LOAD 10/10 APEX1 levels were similar in cerebellum and inferior

parietal lobule in AD and controls[9]

APEX1 BER AD 5/4 Elevated APEX1 immunoreactivity in AD brain sectionswhen compared to controls

[15]

APEX1 BER AD 6/3 Increased APEX1 in nuclei of bioptic samples (not inautoptic) when compared to controls

[14]

POLB BER LOAD 10/10 Reduced POLB amount and reduced single nucleotide gapfilling activity in cases

[9]

ERCC2 (XPD) NER AD 10/10 All analyzed AD brain samples (five individual brainregions) showed higher levels of ERCC2 protein in westernblots when compared to control samples

[18]

ERCC4 (XPF) NER AD 10/10 All analyzed AD brain samples (five individual brainregions) showed higher levels of ERCC4 protein in westernblots when compared to control samples

[18]

DNA-PK DSB-Repair (NHEJ) AD 46/13 Reduced DNA-end joining activity in AD cortical cellextracts, corresponding to a reduction in PRKDC-protein(western blot)

[19]

DNA-PK DSB-Repair (NHEJ) AD 39/7 KU70, KU80 and DNA-PK expression in AD midfrontalcortex brain tissue not altered

[16]

MRN-complex DSB-Repair(NHEJ/HR)

LOAD 18/12 Reduced MRE11, RAD50 and NBN in AD brain sampleswhen compared to controls (western blot) and a reductionspecific for the brain cortex (immunohistochemistry)

[20]

p53 Regulates cellcycle, DNA-repairand apoptosis

AD 41/51 Elevated p53 protein level in peripheral lymphocytes(western blot not shown)

[10]

PARP various AD 39/7 PARP expression not altered in AD midfrontal cortex braintissue

[16]

PARP various AD 20/10 PARP and poly(ADP-ribose)-immunolabelled cells weredetected in a higher proportion in AD brains than incontrol brains

[25]

MGMT DirectDNA-damagereversal

LOAD 19/19 MGMT-activity in AD lymphocytes not altered [22]

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a MCI, mild cognitive impairment; AD, Alzheimer’s disease, studied cohort may coonset at age of 65 or later).

ymphoblasts of 41 AD patients and a group of 51 control individ-

als did not show any differences [10].

Poly(ADP-ribosyl)ation is a posttranslational modification car-ied out by members of the poly(ADP-ribose) polymerases familyPARPs) and is a immediate cellular response to various types of

patients with the familial form of the disease; LOAD, late onset Alzheimer’s disease

DNA-damage including oxidative stress induced lesions (reviewed

in [24]). In an immunohistological study Love et al. detected PARPand poly(ADP-ribose)-immunolabled cells in sections of frontal andtemporal lobe from autopsy material of AD patients with a sig-nificant higher proportion than in samples from control subjects,

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ndicating enhanced PARP activity in Alzheimer’s disease [25]. Asart of the above mentioned study on the expression of severalNA-repair proteins Davydov et al. found decreased amounts ofARP proteins in AD samples which also showed reduced expres-ion of KU70 and KU80 in western blot analysis [16].

. Polymorphisms in DNA-repair genes and AD

Based on the experimental data showing increased oxidativeamage, increased DNA-damage and aberrant activity or amountsf proteins involved in the repair of DNA-lesions in AD, numeroustudies have investigated the role of single nucleotide polymor-hisms (SNPs) located within DNA-repair genes in AD. An overviewf these studies is presented in Table 2. As mentioned before oxida-ive base damage was found dramatically increased in AD brainshen compared to controls. Consequently, and similarly to the

tudies on DNA repair proteins in AD, most association studiesocused on polymorphisms in genes participating in the pathwayrominent in the repair of this type of DNA damage, the base exci-ion repair pathway (BER). Two independent analyses were done on

polymorphism in the OGG1 gene resulting in Ser326Cys. This poly-orphism has earlier been shown to interfere with protein function

26,27] and potentially confers an increased risk to develop differ-nt types of cancer [28]. No association between Ser326Cys andporadic AD was observed in both studies of 178 and 91 cases andimilar numbers of control cases [29,30].

A different strategy to evaluate the impact of variations inhe OGG1 gene was used by Mao et al. They isolated genomicNA from brain regions of 14 AD patients and 10 controls fol-

owed by the amplification of all 7 OGG1 exons and flankingequences by PCR. Sequence analysis of PCR products with anberrant migration pattern in single strand conformation analy-is (SSCP) revealed a heterozygous deletion of one nucleotide inwo patients, c.796del, altering the coding frame and resultingn a protein differing from the wild type protein in amino acidomposition and size. The authors showed experimentally thathe resulting protein has essentially no 8-oxoG glycosylase activ-ty. Two other variations found in the OGG1 gene of AD patients

ithin this study result in amino acid substitutions, Ala53Thr andla288Val. The 8-oxo glycosylase activity of the corresponding pro-

eins was shown to be significantly reduced when compared tohe activity of the wild type protein [31]. While the NCBI databasebSNP lists Ala288Val as a variant with an allele frequency of about% or higher in at least tree populations of different ethnicity, thether two variants in this study can be considered as mutations.his variation was found in 2 of 14 unrelated AD patients analyzed,uggesting that it might be present with a higher frequency in ADatients, however, it was not reported again in any other study oratabase.

Three studies analyzed the impact of polymorphisms in anotherER gene, XRCC1, on the risk to develop LOAD. There is experimentalvidence that all three polymorphisms investigated in this con-ext, Arg194Trp, Arg280His and Arg399Gln, affect protein functionreviewed in [32]). Two studies focused on Arg194Trp, and analyzed8 and 212 cases and a similar number of controls. No significantssociation with an increased risk to develop LOAD was detectedn both groups, however, the larger case control study reached

p-value close to significance, p = 0.056, for the 194Trp allele33,34]. The third study investigated the XRCC1 polymorphismsrg280His and Arg399Gln in 91 patients and 93 controls, however,o association with LOAD risk was detected [30]. This study also

nalyzed the association of a polymorphism in the APEX1 (APE1)ene. This gene encodes an endonuclease involved in the initiationf repair of apurinic/apyrimidinic sites as part of the BER pathway.espite clear experimental evidence for functional relevance of the

pair 12 (2013) 811– 816

analyzed polymorphism Asp148Glu (reviewed in [35]) no associa-tion was found with LOAD risk [30].

ERCC2 (XPD) and ERCC4 (XPF) are members of the nucleotideexcision repair (NER) pathway. However, no significant asso-ciations between the analyzed polymorphisms in ERCC2 (XPD),Lys751Gln and g.22541C > A (silent) as well as in ERCC4 (XPF),g.30028T > C (silent) and LOAD risk could be demonstrated byinvestigating samples from 97 AD patients and 101 control subjects[36].

The PARP proteins and among them, PARP1, are involved inthe regulation of different cellular processes including severalpathways of DNA-damage repair (reviewed in [24,37]). Liu et al.investigated the role of two silent polymorphisms within the PARP1coding region, c.414C > T and c.2456 T > C in a group of 120 LOADpatients and 111 healthy controls. While there was no AD risk asso-ciation for either of the two polymorphisms, they found that twohaplotypes (414T – 2456T and 414C – 2456C) were significantlyoverrepresented in the LOAD group whereas the haplotype 414T –2456C showed a protective effect [38].

4. Methodological issues and future directions

Oxidative stress has been linked to AD many years ago andbased on the data published on this association the involvementof oxidative stress in the pathogenesis and progression of AD andits primary stages diagnosed as MCI is widely accepted. Numerousstudies aimed to investigate the relationship between the activityand abundance of proteins involved in the repair of DNA-damageproduced by oxidative stress and pathogenesis of AD and MCI.However, as summarized here, these studies yielded conflictingresults and we are far away from a clear picture. The situation isfurther complicated by the fact, that the increase, as well as thedecrease of DNA repair protein abundance and/or activity, can beinterpreted in the context of AD pathogenesis. Since increasedoxidative stress is a feature of AD, increased activity and abun-dance of proteins involved in cellular stress response, includingDNA repair proteins, are the consequential response to deal withincreased cellular damage. On the other hand a reduction in DNArepair protein abundance and activity might be due to genetic fac-tors, including DNA repair gene polymorphisms, or a consequenceof AD progression, as indicated by several studies showing DNArepair protein alterations in specific AD brain regions [7,8,20].Most of the genetic studies did not reveal a significant associationbetween polymorphisms in DNA repair genes and AD (Table 2).

Considering reported specifics on diagnostic criteria for AD10 of the 23 presented studies refer particularly to LOAD (seeTables 1 and 2), whereas more than half of the studies refer to AD ingeneral. For instance, in the study of Hermon et al. no informationof specific AD diagnosis is provided [18]. Though, as the mean ageof the patients with AD is 58.7 years in this study, it can be assumedthat cases with LOAD as well as early onset AD (EOAD) have beenincluded. However, when analyzing the impact of etiologic factorsdifferent forms of AD should be distinguished. Mutations in threedeterministic, autosomal dominant genes encoding amyloid pre-cursor protein (APP) presenilin 1 (PSEN1) and presenilin 2 (PSEN2),have been identified to result in early onset AD (EOAD). Mutationsin either of the three genes were found in about 13% of EOADpatients [39]. There is no evidence, however, that mutations inthese genes play a role in sporadic, late onset AD (LOAD), albeitassociations with risk genes as APOE could be confirmed in variousstudies [39]. Hence, it is likely that the role of DNA repair in AD dif-fers in EOAD and LOAD. The lack of differentiation between EOAD

and LOAD in most of the studies may have lead to heterogenoussamples and ambiguous results.

Similarly, MCI is not a homogenous phenotype. Impairment canaffect different cognitive domains. Winblad et al. distinguish (a)

N. Bucholtz, I. Demuth / DNA Repair 12 (2013) 811– 816 815

Table 2Case–control studies evaluating the association of variants in DNA-repair genes and AD.

Gene Role inDNA-repair

Phenotypestudieda

Number ofcases/controls

GroupDifferencesdetectable (%)b

Studied polymor-phisms/sequences

Major findings Reference

OGG1 BER AD 178/146 16 Ser326Cys No significant association [29]OGG1 BER AD 14/10 53 Sequencing of OGG1

coding sequence andflanking splice sitesbased on SSCP results

Detection of the common variant,delC796 (2 cases) and missensevariants G157A (Ala53Thr), C863T(Ala288Val) (1 case each), resulting incomplete loss of 8-oxoG glycosylaseactivity or in a significant reduction ofglycosylase activity

[31]

OGG1 BER LOAD 91/93 21 Ser326Cys No significant association [30]XRCC1 BER LOAD 98/101 20 Arg194Trp No significant association [33]XRCC1 BER LOAD 212/203 14 Arg194Trp No significant association [34]XRCC1 BER LOAD 91/93 21 Arg280His, Arg399Gln No significant association [30]APEX1 (APE1) BER LOAD 91/93 21 Asp148Glu No significant association [30]ERCC2 (XPD) NER LOAD 97/101 20 Arg156Arg, Lys751Gln No significant association [30]ERCC4 (XPF) NER LOAD 97/101 20 Ser824Ser No significant association [36]PARP1 various LOAD 91/93 21 Asp81Asp, Val762Ala Two haplotypes were significantly

associated with LOAD, but not singlepolymorphisms

[38]

a AD, Alzheimer’s disease, studied cohort may contain patients with the familial form of the disease; LOAD, late onset Alzheimer’s disease (onset at age of 65 or later).d wit

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b Estimation of the difference between cases and controls which can be detecteQuery 3/STATCON).

mnestic and nonamnestic subtypes and (b) if cognitive capacity ismpaired in one or multiple domains [6]. Epidemiological studiesave indicated that risk of AD is higher for patients with amnesticCI and impairment in multiple domains than for patients with

on-amnestic impairments [40–42]. Consequently, the two stud-es analyzing DNA repair capacity in MCI have considered amnestic

CI subtypes. For the diagnostic criteria both referred to Petersent al. who defined MCI as memory impairment or amnestic MCIespectively [43,44]. However, only Shao et al. also gave informa-ion on the operationalization of memory impairment. In the studyf Weissmann et al. details on applied neuropsychological mea-urements to assess memory impairment were not reported [8,9].

In addition it needs to be considered that the value of MCI in pre-icting AD is limited. It has been shown that associations betweenon amnestic subtypes of MCI and cognitive impairment in all MCIubtypes can remain stable or even be reversible [6,40]. Besides,tudy results regarding MCI and MCI subtypes are influenced byperationalization criteria, e.g. the choice of cognitive test or cutffs [45,46]. Further studies therefore should also consider specificsf operationalization. Additionally, as MCI is not a prodromal stagef AD, in any case longitudinal studies are necessary. Again, hetero-eneity of the samples analyzed might produce ambiguous results.

Another downside of several studies in the context of AD andNA-repair is the size of the collectives analyzed. We estimated

he power of the genetic case–control studies evaluating the asso-iation of variants in DNA-repair genes and AD as shown in Table 2.his revealed that most of the studies have not been capable toetect differences between cases and controls smaller than 20%.he impact of polymorphisms in DNA repair genes on the progres-ion of AD can be expected to be rather small, most likely belowhis value. In the case of AD it would be essential to investigatearger numbers of cases/controls in order to increase the chance todentify associations with smaller effect sizes, especially because

eta-analyses of existing studies is hindered by the different orot precise definitions of AD diagnosis used. Similarly, in studies

nvestigating the expression and activity of DNA repair proteins higher number of analyzed patients would be desirable. Since

he techniques used in these studies are often time-consumingnd patient samples are limited, future studies should considerhe design of completed properly conducted studies to allow theombined analysis of several smaller studies.

h a power of 80% and a 5% level of significance (calculated by using the software

With respect to the analysis of DNA repair gene polymor-phisms in MCI, the evaluation of large study cohorts with a welldefined construct, differentiation of MCI subtypes and standardizedoperationalization, e.g. using the test battery of the Consortium toEstablish a Registry of Alzheimer’s Disease (CERAD) [47], would besuitable to get more insight into the role of interindividual differ-ences in DNA repair genes in MCI. The study of DNA repair factorsin MCI would most likely also benefit from the use of longitudi-nal data from large cohort studies allowing the identification of thepatients presenting a conversion from MCI to AD and their sep-aration from patients who developed other types of dementia orshowed no progression in cognitive decline after the initial MCIdiagnosis.

Conflicts of interest statement

The authors declare that there are no conflicts of interest.

Acknowledgements

We thank Werner Hopfenmüller for helpful discussions on sta-tistical issues. The work was supported by the German FederalMinistry of Education and Research (grant number #16SV5536K).

References

[1] J. Hort, J.T. O’Brien, G. Gainotti, T. Pirttila, B.O. Popescu, I. Rektorova, S.Sorbi, P. Scheltens, E.S.P.O. Dementia, EFNS guidelines for the diagnosis andmanagement of Alzheimer’s disease, European Journal of Neurology: The Offi-cial Journal of the European Federation of Neurological Societies 17 (2010)1236–1248.

[2] APA Work Group on Alzheimer’s Disease and other Dementias, P.V. Rabins, D.Blacker, B.W. Rovner, T. Rummans, L.S. Schneider, P.N. Tariot, D.M. Blass, Steer-ing Committee on Practice Guidelines, J.S. McIntyre, S.C. Charles, D.J. Anzia,I.A. Cook, M.T. Finnerty, B.R. Johnson, J.E. Nininger, B. Schneidman, P. Summer-grad, S.M. Woods, J. Berger, C.D. Cross, H.A. Brandt, P.M. Margolis, J.P. Shemo,B.J. Blinder, D.L. Duncan, M.A. Barnovitz, A.J. Carino, Z.Z. Freyberg, S.H. Gray,T. Tonnu, R. Kunkle, A.B. Albert, T.J. Craig, D.A. Regier, L.J. Fochtmann, Amer-ican Psychiatric Association practice guideline for the treatment of patients

with Alzheimer’s disease and other dementias. Second edition, The AmericanJournal of Psychiatry 164 (2007) 5–56.

[3] P.D. Barreto, Alzheimer’s disease learning from the past, looking to the future,American Journal of Alzheimer’s Disease and Other Dementias 28 (2013)304–305.

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[

[

[

[

[

[

[

[

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[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

[

16 N. Bucholtz, I. Demuth / D

[4] S. Bennett, M.M. Grant, S. Aldred, Oxidative stress in vascular dementia andAlzheimer’s disease: a common pathology, Journal of Alzheimer’s Disease: JAD17 (2009) 245–257.

[5] I.V. Murray, J.F. Proza, F. Sohrabji, J.M. Lawler, Vascular and metabolic dysfunc-tion in Alzheimer’s disease: a review, Experimental Biology and Medicine 236(2011) 772–782.

[6] B. Winblad, K. Palmer, M. Kivipelto, V. Jelic, L. Fratiglioni, L.O. Wahlund, A.Nordberg, L. Backman, M. Albert, O. Almkvist, H. Arai, H. Basun, K. Blennow,M. de Leon, C. DeCarli, T. Erkinjuntti, E. Giacobini, C. Graff, J. Hardy, C. Jack, A.Jorm, K. Ritchie, C. van Duijn, P. Visser, R.C. Petersen, Mild cognitive impair-ment – beyond controversies, towards a consensus: report of the InternationalWorking Group on Mild Cognitive Impairment, Journal of Internal Medicine256 (2004) 240–246.

[7] M.A. Lovell, C. Xie, W.R. Markesbery, Decreased base excision repair andincreased helicase activity in Alzheimer’s disease brain, Brain Research 855(2000) 116–123.

[8] C. Shao, S. Xiong, G.M. Li, L. Gu, G. Mao, W.R. Markesbery, M.A. Lovell,Altered 8-oxoguanine glycosylase in mild cognitive impairment and late-stageAlzheimer’s disease brain, Free Radical Biology & Medicine 45 (2008) 813–819.

[9] L. Weissman, D.G. Jo, M.M. Sorensen, N.C. de Souza-Pinto, W.R. Markesbery, M.P.Mattson, V.A. Bohr, Defective DNA base excision repair in brain from individ-uals with Alzheimer’s disease and amnestic mild cognitive impairment, NucleicAcids Research 35 (2007) 5545–5555.

10] M. Dezor, J. Dorszewska, J. Florczak, B. Kempisty, J. Jaroszewska-Kolecka, A.Rozycka, A. Polrolniczak, R. Bugaj, P.P. Jagodzinski, W. Kozubski, Expressionof 8-oxoguanine DNA glycosylase 1 (OGG1) and the level of p53 and TNF-alphalpha proteins in peripheral lymphocytes of patients with Alzheimer’sdisease, Folia neuropathologica/Association of Polish Neuropathologists andMedical Research Centre, Polish Academy of Sciences 49 (2011) 123–131.

11] T. Iida, A. Furuta, K. Nishioka, Y. Nakabeppu, T. Iwaki, Expression of 8-oxoguanine DNA glycosylase is reduced and associated with neurofibrillarytangles in Alzheimer’s disease brain, Acta Neuropathologica 103 (2002)20–25.

12] A. Copani, J.J. Hoozemans, F. Caraci, M. Calafiore, E.S. Van Haastert, R. Veer-huis, A.J. Rozemuller, E. Aronica, M.A. Sortino, F. Nicoletti, DNA polymerase-betais expressed early in neurons of Alzheimer’s disease brain and is loaded intoDNA replication forks in neurons challenged with beta-amyloid, The Journal ofNeuroscience: The Official Journal of the Society for Neuroscience 26 (2006)10949–10957.

13] G. Fritz, Human APE/Ref-1 protein, The International Journal of Biochemistry &Cell Biology 32 (2000) 925–929.

14] G. Marcon, G. Tell, L. Perrone, R. Garbelli, F. Quadrifoglio, F. Tagliavini, G.Giaccone, APE1/Ref-1 in Alzheimer’s disease: an immunohistochemical study,Neuroscience Letters 466 (2009) 124–127.

15] Z. Tan, N. Sun, S.S. Schreiber, Immunohistochemical localization of redox factor-1 (Ref-1) in Alzheimer’s hippocampus, Neuroreport 9 (1998) 2749–2752.

16] V. Davydov, L.A. Hansen, D.A. Shackelford, Is DNA repair compromised inAlzheimer’s disease? Neurobiology of Aging 24 (2003) 953–968.

17] W.L. de Laat, N.G. Jaspers, J.H. Hoeijmakers, Molecular mechanism of nucleotideexcision repair, Genes & Development 13 (1999) 768–785.

18] M. Hermon, N. Cairns, J.M. Egly, A. Fery, O. Labudova, G. Lubec, Expression ofDNA excision-repair-cross-complementing proteins p80 and p89 in brain ofpatients with Down Syndrome and Alzheimer’s disease, Neuroscience Letters251 (1998) 45–48.

19] D.A. Shackelford, DNA end joining activity is reduced in Alzheimer’s disease,Neurobiology of Aging 27 (2006) 596–605.

20] E. Jacobsen, T. Beach, Y. Shen, R. Li, Y. Chang, Deficiency of the Mre11 DNArepair complex in Alzheimer’s disease brains, Brain research. Molecular BrainResearch 128 (2004) 1–7.

21] S. Mitra, MGMT: a personal perspective, DNA Repair 6 (2007) 1064–1070.22] J.A. Edwards, L.G. Wang, R.B. Setlow, E. Kaminskas, O6-methylguanine-DNA

methyltransferase in lymphocytes of the elderly with and without Alzheimer’sdisease, Mutation Research 219 (1989) 267–272.

23] P.A. Muller, K.H. Vousden, p53 mutations in cancer, Nature Cell Biology 15(2013) 2–8.

24] A. Burkle, DNA repair and PARP in aging, Free Radical Research 40 (2006)1295–1302.

25] S. Love, R. Barber, G.K. Wilcock, Increased poly(ADP-ribosyl)ation of nuclearproteins in Alzheimer’s disease, Brain: A Journal of Neurology 122 (Pt 2) (1999)247–253.

26] J. Choi, D.Y. Kim, J.W. Hyun, S.H. Yoon, E.M. Choi, K.B. Hahm, K.H. Rhee, M.H.

Chung, Measurement of oxidative damage at individual gene levels by quan-titative PCR using 8-hydroxyguanine glycosylase (OGG1), Mutation Research523-524 (2003) 225–235.

27] P. Vodicka, R. Stetina, V. Polakova, E. Tulupova, A. Naccarati, L. Vodickova, R.Kumar, M. Hanova, B. Pardini, J. Slyskova, L. Musak, G. De Palma, P. Soucek, K.

[

pair 12 (2013) 811– 816

Hemminki, Association of DNA repair polymorphisms with DNA repair func-tional outcomes in healthy human subjects, Carcinogenesis 28 (2007) 657–664.

28] J.M. Weiss, E.L. Goode, W.C. Ladiges, C.M. Ulrich, Polymorphic variation inhOGG1 and risk of cancer: a review of the functional and epidemiologic lit-erature, Molecular Carcinogenesis 42 (2005) 127–141.

29] F. Coppede, M. Mancuso, A. Lo Gerfo, M.L. Manca, L. Petrozzi, L. Migliore, G.Siciliano, L. Murri, A Ser326Cys polymorphism in the DNA repair gene hOGG1is not associated with sporadic Alzheimer’s disease, Neuroscience Letters 414(2007) 282–285.

30] H. Parildar-Karpuzoglu, S. Dogru-Abbasoglu, H.A. Hanagasi, B. Karadag, H.Gurvit, M. Emre, M. Uysal, Single nucleotide polymorphisms in base-excisionrepair genes hOGG1, APE1 and XRCC1 do not alter risk of Alzheimer’s disease,Neuroscience Letters 442 (2008) 287–291.

31] G. Mao, X. Pan, B.B. Zhu, Y. Zhang, F. Yuan, J. Huang, M.A. Lovell, M.P. Lee, W.R.Markesbery, G.M. Li, L. Gu, Identification and characterization of OGG1 muta-tions in patients with Alzheimer’s disease, Nucleic Acids Research 35 (2007)2759–2766.

32] G. Ginsberg, K. Angle, K. Guyton, B. Sonawane, Polymorphism in the DNA repairenzyme XRCC1: utility of current database and implications for human healthrisk assessment, Mutation Research 727 (2011) 1–15.

33] S. Dogru-Abbasoglu, G. Aykac-Toker, H.A. Hanagasi, H. Gurvit, M. Emre, M.Uysal, The Arg194Trp polymorphism in DNA repair gene XRCC1 and the risk forsporadic late-onset Alzheimer’s disease, Neurological Sciences: Official Jour-nal of the Italian Neurological Society and of the Italian Society of ClinicalNeurophysiology 28 (2007) 31–34.

34] Y. Qian, W. Chen, J. Wu, T. Tao, L. Bi, W. Xu, H. Qi, Y. Wang, L. Guo, Association ofpolymorphism of DNA repair gene XRCC1 with sporadic late-onset Alzheimer’sdisease and age of onset in elderly Han Chinese, Journal of the NeurologicalSciences 295 (2010) 62–65.

35] B. Karahalil, V.A. Bohr, D.M. Wilson 3rd, Impact of DNA polymorphisms inkey DNA base excision repair proteins on cancer risk, Human & ExperimentalToxicology 31 (2012) 981–1005.

36] S. Dogru-Abbasoglu, M. Inceoglu, H. Parildar-Karpuzoglu, H.A. Hanagasi, B.Karadag, H. Gurvit, M. Emre, G. Aykac-Toker, M. Uysal, Polymorphisms in theDNA repair genes XPD (ERCC2) and XPF (ERCC4) are not associated with spo-radic late-onset Alzheimer’s disease, Neuroscience Letters 404 (2006) 258–261.

37] B.A. Gibson, W.L. Kraus, New insights into the molecular and cellular func-tions of poly(ADP-ribose) and PARPs, Nature Reviews. Molecular Cell Biology13 (2012) 411–424.

38] H.P. Liu, W.Y. Lin, B.T. Wu, S.H. Liu, W.F. Wang, C.H. Tsai, C.C. Lee, F.J. Tsai,Evaluation of the poly(ADP-ribose) polymerase-1 gene variants in Alzheimer’sdisease, Journal of Clinical Laboratory Analysis 24 (2010) 182–186.

39] J. Williamson, J. Goldman, K.S. Marder, Genetic aspects of Alzheimer disease,The Neurologist 15 (2009) 80–86.

40] T.F. Hughes, B.E. Snitz, M. Ganguli, Should mild cognitive impairment be sub-typed? Current Opinion in Psychiatry 24 (2011) 237–242.

41] A.J. Mitchell, M. Shiri-Feshki, Rate of progression of mild cognitive impair-ment to dementia – meta-analysis of 41 robust inception cohort studies, ActaPsychiatrica Scandinavica 119 (2009) 252–265.

42] R.C. Petersen, Mild cognitive impairment as a diagnostic entity, Journal of Inter-nal Medicine 256 (2004) 183–194.

43] R.C. Petersen, J.C. Morris, Clinical features, in: R.C. Petersen (Ed.), Mild CognitiveImpairment: Aging to Alzheimer’s Disease, Oxford University Press, Inc., NewYork, 2003.

44] R.C. Petersen, G.E. Smith, S.C. Waring, R.J. Ivnik, E.G. Tangalos, E. Kokmen, Mildcognitive impairment: clinical characterization and outcome, Archives of Neu-rology 56 (1999) 303–308.

45] A.J. Jak, M.W. Bondi, L. Delano-Wood, C. Wierenga, J. Corey-Bloom, D.P. Salmon,D.C. Delis, Quantification of five neuropsychological approaches to definingmild cognitive impairment, The American Journal of Geriatric Psychiatry: Offi-cial Journal of the American Association for Geriatric Psychiatry 17 (2009)368–375.

46] J.A. Schinka, D.A. Loewenstein, A. Raj, M.R. Schoenberg, J.L. Banko, H. Potter, R.Duara, Defining mild cognitive impairment: impact of varying decision crite-ria on neuropsychological diagnostic frequencies and correlates, The AmericanJournal of Geriatric Psychiatry: Official Journal of the American Association forGeriatric Psychiatry 18 (2010) 684–691.

47] J.C. Morris, A. Heyman, R.C. Mohs, J.P. Hughes, G. van Belle, G. Fillenbaum, E.D.Mellits, C. Clark, The Consortium to Establish a Registry for Alzheimer’s Dis-ease (CERAD). Part I. Clinical and neuropsychological assessment of Alzheimer’sdisease, Neurology 39 (1989) 1159–1165.

48] J. Dorszewska, B. Kempisty, J. Jaroszewska-Kolecka, A. Rozycka, J. Florczak, M.Lianeri, P.P. Jagodzinski, W. Kozubski, Expression and polymorphisms of gene8-oxoguanine glycosylase 1 and the level of oxidative DNA damage in periph-eral blood lymphocytes of patients with Alzheimer’s disease, DNA and CellBiology 28 (2009) 579–588.