Serum elevated gamma glutamyltransferase levels may be a marker for oxidative stress in Alzheimer's disease.

Abstract

Gamma glutamyltransferase (GGT) plays a role in cellular glutathione uptake, which is an important element of antioxidant mechanisms. An increase in serum GGT is thought to be an early and sensitive marker of oxidative stress. Oxidative stress has a role in the pathogenesis of Alzheimer's disease (AD). The aim of this study was to investigate the GGT levels in AD.
In this cross-sectional study, 132 patients with AD (mean age: 74.1 +/- 7.4, female 62.9%) and 158 age- and gender-matched normal controls (mean age: 74.5 +/- 6.3, female 67.1%) were evaluated. For cognitive assessment, MMSE and clock drawing tests were performed; DSM-IV and NINCDS-ADRDA criteria were used. Serum GGT, aspartate aminotransferase, alanine aminotransferase and alkaline phosphatase concentrations were determined.
Median (min-max) GGT levels were 18 (9-70) in AD group and 17 (5-32) in normal controls. Mann-Whitney U test showed that GGT levels were significantly higher in AD patients (p = 0.012). Linear regression analysis revealed AD was an independent correlate of elevated GGT levels. Hypertension, diabetes mellitus, total cholesterol, and low density lipoprotein cholesterol were not associated with GGT levels.
GGT levels were increased significantly in AD patients. To evaluate the role of GGT as a marker of oxidative stress in AD, further studies are needed.

Full text

Page 1

International Psychogeriatrics: page 1 of 9 C ?2008 International Psychogeriatric Association
doi:10.1017/S1041610208006790
Serum elevated gamma glutamyltransferase
levels may be a marker for oxidative stress
in Alzheimer’s disease
..............................................................................................................................................................................................................................................................................
Burcu Balam Yavuz,1Bunyamin Yavuz,2Meltem Halil,1
Mustafa Cankurtaran,1Zekeriya Ulger,1
Eylem Sahin Cankurtaran,3Kudret Aytemir4
and Servet Ariogul1
1Hacettepe University Faculty of Medicine, Department of Internal Medicine, Division of Geriatric Medicine,
Ankara, Turkey
2Kecioren Research Hospital, Department of Cardiology, Ankara, Turkey
3Ankara Oncology Hospital, Department of Psychiatry, Ankara, Turkey.
4Hacettepe University Faculty of Medicine, Department of Cardiology, Ankara, Turkey
ABSTRACT
Background: Gamma glutamyltransferase (GGT) plays a role in cellular
glutathione uptake, which is an important element of antioxidant mechanisms.
An increase in serum GGT is thought to be an early and sensitive marker of
oxidative stress. Oxidative stress has a role in the pathogenesis of Alzheimer’s
disease (AD). The aim of this study was to investigate the GGT levels in AD.
Method: In this cross-sectional study, 132 patients with AD (mean age:
74.1±7.4, female 62.9%) and 158 age- and gender-matched normal controls
(mean age: 74.5±6.3, female 67.1%) were evaluated. For cognitive assessment,
MMSE and clock drawing tests were performed; DSM-IV and NINCDS-
ADRDA criteria were used. Serum GGT, aspartate aminotransferase, alanine
aminotransferase and alkaline phosphatase concentrations were determined.
Results: Median (min-max) GGT levels were 18 (9–70) in AD group and
17 (5–32) in normal controls. Mann-Whitney U test showed that GGT
levels were significantly higher in AD patients (p=0.012). Linear regression
analysis revealed AD was an independent correlate of elevated GGT levels.
Hypertension, diabetes mellitus, total cholesterol, and low density lipoprotein
cholesterol were not associated with GGT levels.
Conclusion: GGT levels were increased significantly in AD patients. To evaluate
theroleofGGTasamarkerofoxidativestress inAD,furtherstudiesareneeded.
Key words: Alzheimer’s disease, gamma glutamyltransferase, marker, oxidative stress, vascular risk
factor
Correspondence should be addressed to: Dr. Burcu Balam Yavuz, Hacettepe University, Faculty of Medicine, Department
of Internal Medicine, Division of Geriatric Medicine, Sihhiye, 06100, Ankara, Turkey. Phone: +903123053071;
Fax: +903123051538. Email: bbyavuz@hacettepe.edu.tr. Received 13 Nov 2007; revision requested 12 Dec 2007; revised
version received 17 Dec 2007; accepted 18 Dec 2007.
1

Page 2

2
B. B. Yavuz et al.
Introduction
Gamma glutamyltransferase (GGT) plays a role in cellular glutathione uptake
and extracellular catabolism of glutathione (Onat et al., 2006; Paolicchi et al.,
2006). These mechanisms are important elements of intracellular protective
antioxidantmechanisms(Onatetal.,2006).Glutathioneisanimportantelement
in antioxidant mechanisms, and GGT is therefore thought to have a role in
oxidative mechanisms and is regarded as an early and sensitive marker of
oxidative stress (Onat et al., 2006). Lim et al. have stated that modest increases
in serum GGT activity within normal range may be an early marker of cellular
oxidative stress (Lim et al., 2004). Oxidative stress is one of the mechanisms
which are thought to be involved in the pathogenesis of Alzheimer’s disease
(AD). Accumulation of free radicals and oxidative stress may have a role in the
pathology of AD by leading to lipid peroxidation and neuronal degeneration
in the brain (Sano et al., 1997). Therefore, we hypothesized that as GGT is a
marker for oxidative stress it may also be a marker for AD.
Gamma glutamyltransferase is also regarded as a cardiovascular risk factor
and has been identified as a predictor of cardiovascular mortality (Wannamethee
et al., 1995; Emdin et al., 2001; Paolicchi et al., 2006). Elevated GGT was found
to be associated with the presence of many cardiovascular risk factors such as
hypercholesterolemia, hypertension, diabetes mellitus, myocardial infarction,
metabolic syndrome, and obesity (Betro et al., 1973; Nilssen et al., 1990;
Wannamethee et al., 1995; Daeppen et al., 1998; Nakanishi et al., 2004; Kim
et al., 2005; Onat et al., 2006). Vascular factors have gained importance in the
pathogenesis of AD (Launer, 2002; Pansari et al., 2002). It was found that
vascular risk factors also increase the risk of AD (Seshadri, 2002; Reitz et al.,
2004). Starting from these points, we hypothesized that elevated levels of GGT
might be associated with AD as a vascular risk factor.
The aim of this study was to investigate the GGT levels in AD and control
groups as a possible marker of oxidative stress and as a vascular risk factor.
Methods
Subjects and Cognitive Assessment
In this cross-sectional study, following comprehensive geriatric assessment and
cognitive assessment, 132 AD patients and 158 control patients with normal
cognitive status aged 65 years and over admitted to our geriatric medicine
outpatient clinic for routine medical care were enrolled in this study. For
cognitive assessment, Mini-mental State Examination (MMSE) (Folstein et al.,
1975) and clock drawing tests (Stahelin et al., 1997) were performed. The
diagnosis of AD was made according to DSM-IV (American Psychiatric
Association, 1994) and NINCDS-ADRDA (McKhann et al., 1984) criteria after
cognitive assessment and neuroimaging performed using magnetic resonance
(MR). Clinical Dementia Rating Scale (CDR) scores of the patients with AD
were1andover(Hughesetal.,1982).Age-andgender-matchedpatientswithout
memory complaint, with normal neuropsychiatric test results (MMSE and clock

Page 3

Gamma glutamyltransferase and Alzheimer’s disease
3
drawing tests), who did not meet the criteria for dementia (American Psychiatric
Association, 1994) or mild cognitive impairment (Petersen et al., 1999), and
whose CDR scores were 0 were enrolled in a normal cognitive status control
group. In addition, information from a knowledgeable informant was obtained
to ensure there was no change in cognitive function for the normal cognitive
status group.
Exclusion criteria were: alcohol consumption; GGT levels over 100 U/L;
serum aspartate aminotransferase (AST) and serum alanine aminotransferase
(ALT) levels over 40 U/L; and alkaline phosphatase (ALP) concentrations
greater than three times the upper limit of the reference range. Hepatitis C
virus antibody (antiHCV) and hepatitis B virus surface antigen (HBs Ag) were
measured and patients with positive results were also excluded.
Blood pressure was measured in the left arm twice by a standardized mercury
sphygmomanometerfollowingapproximatelyfiveminutesofseatedrest.Patients
withbloodpressureexceeding140/90mmHgwerediagnosedwithhypertension.
The study protocol was consistent with the Declaration of Helsinki and
informed consent was obtained prior to enrollment.
Laboratory tests
Following an overnight fast, blood samples were obtained by antecubital
venipuncture and analyzed immediately. Serum ALP, ALT and AST
concentrations were determined using enzymatic methods. Serum GGT levels
were assayed by the kinetic procedure using gamma-glutamyl-p-nitroanilide as
substrate and glycylglycine as acceptor with a Roche/Hitachi analyzer. Plasma
concentrations of total cholesterol (TC), triglyceride (TG), and low density
lipoprotein cholesterol (LDL-C) were determined by the enzymatic chemistry.
Statistical analysis
Categorical variables are given as percentages, normal distributed continuous
variables as mean±SD, and skew distributed continuous variables as median
(minimum-maximum). In order to make comparisons between the AD and
control groups, the t-test was used for normally distributed continuous variables,
the Mann-Whitney U-test for skew distributed continuous variables, and the
χ2test for comparing categorical variables. A correlation analysis to examine
the correlation between GGT concentrations and MMSE scores in the AD
group was performed by Spearman correlation test. In order to find the
independent correlation between GGT levels and AD, linear regression analysis
was performed with the variables AD, age, gender, hypertension, diabetes
mellitus, TC, LDL, TG, ALP, ALT and AST levels. A p value<0.05 was
considered to be statistically significant. The statistical package SPSS 10.0 for
Windows was used to perform the statistical analysis.

Page 4

4
B. B. Yavuz et al.
Results
One hundred and thirty-two patients with AD (mean age: 74.1±7.4, female
62.9%) and 158 normal controls (mean age: 74.5±6.3, female 67.1%) were
evaluated. Mean age and gender were similar between groups. The demographic
properties and general characteristics of the study population are depicted in
Table 1.
Median (min-max) GGT levels were 18 (9–70) in AD group, 17 (5–32)
in normal controls. The Mann-Whitney U test showed that GGT levels were
significantly higher in AD patients (p=0.012). The laboratory test results
are given in Table 1. Correlation between MMSE scores and GGT levels
were analyzed in the AD group and no significant correlation was determined
(r=0.08, p=0.39).
Fifty-five patients were found to have diabetes mellitus. Serum GGT levels of
the patients with and without diabetes mellitus were compared and the Mann-
Whitney U test revealed no difference (p=0.28). GGT levels of the patients
with and without hypertension were also compared and no significant difference
was detected (p=0.59, Mann-Whitney U test).
A multivariate linear regression analysis was performed in order to assess
the independent effect of AD on GGT levels. AD, age, gender, hypertension,
diabetes mellitus, ALT, AST, ALP, TC, TG and LDL-C levels were put
Table 1. General characteristics and laboratory results of the study population
A L Z H E I M E R’ S
D I S E A S E ( N =132)
C O N T R O L
( N =158)
P
.............................................................................................................................................................................................................................................
Age74.1±7.4
Gender (M/F)49/83
MMSE score22.9±6.5
SBP (mmHg)140±24
DBP (mmHg) 82±12
GGT (U/L)18 (9; 70)
ALP (U/L) 149.7±66.2
ALT (U/L)18.1±6.9
AST (U/L)19.5±6.4
Diabetes mellitus 19 (14.4%)
Hypertension75 (56.8%)
TC (mg/dL) 208.5 (97.0; 337.0)
TG (mg/dL) 121.0 (43.0; 501.0)
LDL (mg/dL)125.0 (40.4; 265.0)
74.5±6.3
52/106
26.6±3.6
148±20
87±13
17 (5; 32)
135.5±76.9
17.5±6.9
20.9±6.1
36 (22.8%)
122 (77.7%)
205.5 (7.7; 377.0)
111.0 (19.0; 448.0)
125.6 (33.4; 240.0)
0.35
0.45
<0.001
0.003
0.002
0.012
0.08
0.67
0.05
0.07
<0.001
0.18
0.026
0.42
Categorical variable age is given as n, normal distributed continuous variables are demonstrated as
mean±SD, and skew distributed continuous variables as median (minimum-maximum).
P values were derived by t-test for normally distributed continuous variables, by Mann-Whitney U test
for skew distributed continuous variables, and by χ2test for categorical variables.
M/F=male/female; MMSE=Mini-mental State Examination; SBP=systolic blood pressure; DBP=
diastolicbloodpressure;GGT=gammaglutamyltransferase;ALP=alkalinephosphatase;ALT=alanine
aminotransferase; AST=aspartate aminotransferase; TC=total cholesterol; TG=triglyceride; LDL=
low density lipoprotein.

Page 5

Gamma glutamyltransferase and Alzheimer’s disease
5
Table 2. Results of regression analysis – the effects of the parameters on elevated
GGT levels
B E TA
t
P
............................................................................................................................................................................................................................................
Alzheimer’s disease0.202
Age
−0.017
Gender (M/F)
−0.206
DM
−0.010
HT
−0.018
AST0.001
ALT 0.330
ALP0.059
TC 0.044
TG0.125
LDL-C
−0.098
DM=diabetes
aminotransferase; ALP=alkaline phosphatase; TC=total cholesterol; TG=triglyceride; LDL-C=low
density lipoprotein cholesterol.
3.782
−0.299
−3.833
−0.185
−0.327
0.020
6.233
1.098
0.770
2.307
−1.112
aminotransferase;
<0.001
0.77
<0.001
0.85
0.74
0.98
<0.001
0.27
0.44
0.022
0.27
mellitus; HT=hypertension; AST=aspartate ALT=alanine
into the equation to establish the independent correlates of GGT. Linear
regression analysis revealed that AD was significantly correlated with GGT
levels (beta: 0.2, t: 3.8, p<0.001, 95%CI: 1.822; 5.776). Other significant
independent covariates of serum GGT were gender (beta: −0.2, t: −3.8,
p<0.001, 95%CI=−6.090; −1.957), ALT levels (beta: 0.3, t: 6.2, p<0.001,
95%CI: 0.310; 0.595), and TG levels (beta=0.1, t: 2.3, p=0.022, 95%CI:
0.002; 0.029). Table 2 demonstrates results of linear regression analysis. This
analysis showed that gender, serum ALT and TG levels were significantly
correlated with GGT as well as AD.
Discussion
The present study is the first to examine whether GGT levels, as an early
marker of oxidative stress, are related to AD. It was found that serum GGT
concentrations are significantly increased in AD patients. This increment may
be a marker of oxidative stress in AD.
Serum GGT is proposed as an early and sensitive marker for oxidative
stress (Lee et al., 2004; Paolicchi et al., 2006; Onat et al., 2006). It has an
important role in maintaining intracellular glutathione transport into cells,
thus mediating intracellular protective antioxidant mechanisms (Kugelman et
al.,1994; Takahashi et al., 1997; Karp et al., 2001; Onat et al., 2006). As it has
a role in increasing glutathione transport into the cell, an increase in GGT
levels was thought to be a response to oxidative stress (Kim et al., 2005).
Increased levels of oxidative stress have been demonstrated in the brain of
AD patients (Zhu et al., 2004; 2005), and markers for oxidative stress such
as advanced glycation end products (AGE), glycoxidative end products and