Intercellular adhesion molecule-1 K469E gene polymorphism and Alzheimer’s disease

Neurobiology of Aging 24 (2003) 385–387

Brief communication

Intercellular adhesion molecule-1 K469E gene polymorphism and Alzheimer’s disease Roberto Pola a,b,∗ , Andrea Flex a,c , Eleonora Gaetani a,c , Angelo Santoliquido c , Michele Serricchio c , Paolo Pola c , Roberto Bernabei b a

Laboratory of Vascular Biology and Genetics, Istituto di Patologia Speciale Medica, Università Cattolica del Sacro Cuore, A. Gemelli University Hospital, L. go A. Gemelli 8, 00168 Rome, Italy b Department of Geriatric Medicine, A. Gemelli University Hospital, Università Cattolica del Sacro Cuore, 00168 Rome, Italy c Department of Internal Medicine, A. Gemelli University Hospital, Università Cattolica del Sacro Cuore, 00168 Rome, Italy Received 17 January 2002; received in revised form 29 April 2002; accepted 10 June 2002

Abstract Inflammatory processes are considered important in the pathogenesis of Alzheimer’s disease (AD). Intercellular adhesion molecule-1 (ICAM-1) is an important mediator of inflammatory response and immune cell activation, is expressed on cerebrovascular endothelium and neuritic plaques in brain of AD patients, and seems to be implicated in the process of neuro-degeneration. A common polymorphism of the ICAM-1 gene (K469E) has been recently reported. In this case-control study, we evaluated the distribution of E/K alleles and genotypes of the ICAM-1 gene in 98 patients affected by sporadic AD and 115 age- and sex-matched controls. The frequency of the EE genotype was significantly higher in AD patients (P < 0.01). Logistic regression analysis indicated that the presence of EE genotype significantly increased the risk of AD (odds ratio 3.01 [1.1–8.0], P < 0.05). This study shows for the first time an association between ICAM-1 E/K gene polymorphism and AD, suggesting that polymorphisms of the ICAM-1 gene may be clinically important and confirming that inflammatory mechanisms may be crucial in the pathophysiology of neuro-degenerative diseases. © 2002 Elsevier Science Inc. All rights reserved. Keywords: ICAM-1; Gene polymorphism; Alzheimer’s disease; Inflammation

1. Introduction A role for inflammation in the pathogenesis of neurodegenerative disorders has been proposed [11]. Especially in Alzheimer’s disease (AD), inflammatory reactions are thought to be important contributors to the neuronal loss [11]. Intercellular adhesion molecule-1 (ICAM-1) is a member of the immunoglobulin (Ig) superfamily and the principal ligand for the leukocyte function-associated antigen-1 (LFA-1), a member of the integrin superfamily. One function of the ICAM-1/LFA-1 adhesion system is to assist leukocyte movement into tissue: in combination with selectins, other integrins, and immunoglobulins, LFA-1 positive leukocytes are induced to adhere to ICAM-1-positive endothelial surface [6,18] and then to pass through the basement membrane into tissue [15,21]. LFA-1 is constitutively expressed by brain microglia cells and is up-regulated in pathologic conditions associated with microglia reaction [1]. Similarly, ∗

Corresponding author. Tel.: +39-06-30154846; fax: +39-06-35500486. E-mail address: rob [email protected] (R. Pola).

ICAM-1 expression has been reported in AD neuritic plaque, in capillaries of normal [16] and AD tissues [7], and in cultured astrocytes from AD patients [2]. In addition, it has been proposed that ICAM-1 expression in the brain might depend on the specific site of amyloid beta production [22]. Recently, the K469E polymorphism of the ICAM-1 gene has been described [24]. This polymorphism occurs in exon 6 of the ICAM-1 gene and results in a change from glutamic acid to lysine in Ig-like domain 5, which has been reported to affect the interactions between ICAM-1 and LFA-1 and to influence B-cell adhesion [19]. In this study, we evaluated whether this polymorphism is associated with sporadic AD.

2. Methods A total of 98 patients with sporadic AD were studied (mean age 77.6 ± 5.5 years, male:female ratio 40:58). Diagnosis of dementia was performed according with the DSM-III criteria [3] and diagnosis of probable AD was made in accordance with the NINCDS-ADRDA guidelines

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[12]. All patients underwent brain imaging evaluation by CT scan, structured interview, formal neuro-psychological testing, and mini-mental state examination (MMSE). The Hachinski ischemic score (HIS) was also used to aid in distinguishing between AD and multi-infarct dementia (MID) [8]. Patients were recruited among subjects consecutively admitted to the Departments of Geriatric Medicine and Internal Medicine at the “A. Gemelli” University Hospital of Rome, Italy, from November 2000 to October 2001. Control subjects were 115 age- and sex-matched individuals, admitted to the same Departments in the same period of time, not affected by dementia. The presence of cognitive deterioration in control subjects was clinically and instrumentally excluded by Mini-mental state examination (MMSE) and CT scan of the brain. The mean age of controls at the time of assessment was 76.0 ± 6.4 years. The male:female ratio in controls was 55:60. All patients and controls were Caucasians from central and southern Italy and belonged to independent pedigrees. Subjects with MID, suspected mixed dementia (MID and AD), or dementia of metabolic origin were excluded. In both patient and control groups, subjects affected by tumors, chronic inflammatory diseases, and autoimmune diseases were excluded as well. The study protocol was accepted by the Ethics Committee of our University Hospital. DNA was extracted from peripheral blood and assayed by PCR-RFLP for the detection of ICAM-1 gene, as previously described [13]. Genotype and allele frequencies between groups were compared by χ 2 test. Odds ratios were calculated with 95% CI. To estimate the association between genotype and AD, a logistic regression model was used (STATA software). Statistical significance was established at P < 0.05.

3. Results The distribution of ICAM-1 genotypes and alleles in cases and controls is shown in Table 1. Genotypes were in Hardy-Weinberg equilibrium. In the 98 patients with AD, the genotype distribution was 26 EE, 51 EK, 21 KK, and was significantly different from that observed in the 115 control

Table 1 ICAM-1 genotype and allele distribution between groups AD Patients, n (%) Genotypes E/E E/K K/K Alleles E K a ∗

26 (26.6)a 51 (52.0) 21 (21.4) 103 (52.6) 93 (47.4)

Numbers in parentheses are % of total. P < 0.01

Controls, n (%) 15 (13.0)∗ 64 (55.6) 36 (31.4) 94 (40.9)∗ 136 (59.1)∗

Table 2 Risk factors of AD based on logistic regression analysis

E/E genotype E/K genotype Sex M Age Smoking (current) Smoking (former) ∗

Odds ratio

95% CI

3.0 1.4 1.0 1.0 0.8 0.5

1.13–7.98∗ 0.69–3,08 0.49–2.08 1.01–1.12 0.28–2.46 0.23–1.29

P < 0.05

subjects (15 EE, 64 EK, 36 KK). The frequency of the EE genotype in patients with AD (26.6%) was significantly higher than in controls (13.0%) (P < 0.01). Similarly, allele distribution was significantly different between the two groups: the E allele was detected in 52.6% of patients with AD and in 40.9% of control subjects (P < 0.01), while the K allele was detected in 47.4% of patients with AD and in 59.1% of controls (P < 0.01). A logistic analysis (Table 2) showed that the EE genotype is an independent risk factor for AD in our population. Patients carrying the EE genotype have a risk 3 times higher than KK homozygous patients to develop AD (odds ratio 3.0 [1.13–7.98], P < 0.05).

4. Discussion Neuro-degenerative disorders are characterized by focal inflammatory reaction, involving activation of microglia [14], astrocytes reaction, activation of the complement system, production of cytokines [10], and release of oxygen free radicals [23]. In AD, inflammation occurs in response to the deposition of beta-amyloid protein in the brain parenchyma and macrophage activation is associated with the up-regulation of specific surface antigens, including ICAM-1 [26]. Similarly, ICAM-1 is expressed on endothelial cells and macrophages during Wallerian degeneration and inflammatory demyelinating diseases of peripheral nerves [5,20]. Additionally, a recent study has revealed impaired macrophage recruitment after peripheral nerve transection in ICAM-1 deficient mice [25]. ICAM-1 is also aberrantly expressed in other diseases of the central nervous system, such as multiple sclerosis, allergic encephalomyelitis, and AIDS dementia complex. In addition, ICAM-1 has been found to induce expression of several other proinflammatory cytokines, such as IL-1 alpha, IL-1 beta, IL-6, and TNF alpha specifically in astrocytes [9]. Regarding the distribution of ICAM-1 in the brain, this molecule has been found in AD neuritic plaques and AD tissues [7]. Taken together, these data suggest an important role for ICAM-1 in various kinds of neuro-degenerative disorders. Our study evaluates for the first time the association between a common polymorphism of the ICAM-1 gene and

R. Pola et al. / Neurobiology of Aging 24 (2003) 385–387

AD. We studied the distribution of E/K alleles and genotypes of the ICAM-1 gene in subjects with sporadic AD and correspondent controls. In the control group, we found that ICAM-1 alleles and genotypes were distributed consistently with the results reported in previous studies evaluating the ICAM-1 E/K gene polymorphism in the Italian population [4,17]. In contrast, in AD patients, the frequency of the E allele and the EE genotype was significantly higher. We also show, by using a logistic regression analysis, that subjects carrying the E allele have increased risk of AD. In particular, subjects EE homozygous have a risk 3 times higher to develop the disease, when compared to KK homozygous patients. These results confirm a role for ICAM-1 in AD and are consistent with the hypothesis that inflammation and inflammatory mediators are crucial in the pathogenesis of neuro-degenerative diseases. This study has some potential limitations. It is a case-control study and a possible survival bias cannot be excluded for the group of patients with AD. The size of the studied population is relatively small and our findings need to be confirmed in larger samples. Likewise, the association between ICAM-1 gene polymorphism and AD should be tested in groups of different ethnic origin. Finally, we cannot exclude that the observed association depends on a gene in linkage disequilibrium with the ICAM-1 gene or on the effect of ICAM-1 on an other peptide. In conclusion, we show that the K469E polymorphism of the ICAM-1 gene is associated with sporadic AD in an Italian population. These results suggest that genetic polymorphisms of ICAM-1 might be clinically important in the development and progression of AD and confirm a role for ICAM-1 in the pathophysiology of neuro-degenerative disorders, with potential important therapeutic implications. References [1] Akiyama H, McGeer PL. Brain microglia constitutively express beta-2 integrins. J Neuroimmunol 1990;30:81–93. [2] Akiyama H, Kawamata T, Yamada T, Tooyama I, Ishii T, McGeer PL. Expression of intercellular adhesion molecule (ICAM)-1 by a subset of astrocytes in Alzheimer disease and some other degenerative neurological disorders. Acta Neuropathol 1993;85:628–34. [3] American Psychiatric Association Diagnostic and Statistical Manual of Mental Disorders. 3rd edn. (revised), American Psychiatric Association, Washington DC 1987. [4] Boiardi L, Salvarani C, Casali B, et al. Intercellular adhesion molecule-1 gene polymorphisms in Behcet’s disease. J Rheumatol 2001;28:1283–7. [5] Brown HC, Castano A, Fearn S, Townsend M, Edwards G, Streuli C, et al. Adhesion molecules involved in macrophage responses to Wallerian degeneration in the murine peripheral nervous system. Eur J Neurosci 1997;9:2057–63. [6] Dunn SM, Hillam AJ, Stomski F, Jin BQ, Lucas CM, Boyd AW, et al. Leukocyte adhesion molecules involved in inflammation. Transplant Proc 1989;21:31–4.

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