Original Research Article Dement Geriatr Cogn Disord 2009;28:507–512 DOI: 10.1159/000255051
Accepted: October 22, 2009 Published online: December 7, 2009
Increased Serum IL-1 Level in Alzheimer’s Disease and Mild Cognitive Impairment Orestes Vicente Forlenza a Breno Satler Diniz a Leda Leme Talib a Vanessa Amaral Mendonça b Elida B. Ojopi a Wagner Farid Gattaz a Antonio Lucio Teixeira b a
Laboratory of Neuroscience (LIM 27), Department and Institute of Psychiatry, Faculty of Medicine, University of São Paulo, São Paulo, and b Group of Neuroimmunology, Laboratory of Immunopharmacology, Institute of Biological Sciences and School of Medicine, Federal University of Minas Gerais, Belo Horizonte, Brazil
Key Words Alzheimer’s disease ⴢ Mild cognitive impairment ⴢ Cognition ⴢ Interleukin-1 ⴢ Neuroinflammation
Abstract Background/Aims: Abnormal inflammatory response has been associated to the pathogenesis of Alzheimer’s disease (AD) and may be a marker of an ongoing neurodegenerative process. The aim of this study was to evaluate the serum levels of interleukin-1 (IL-1) in patients with mild cognitive impairment (MCI) and AD. Methods: One hundred and sixtythree older adults (58 with mild to moderate AD, 74 with MCI and 31 healthy controls) were recruited for this study. Serum IL-1 levels were measured by ELISA. Patients with MCI were subcategorized in single-domain amnestic (aMCI), nonamnestic (naMCI), and multiple-domain (mdMCI) subtypes. Results: Patients with AD and MCI (all subtypes) had a significant increase in serum IL-1 levels as compared to controls (p = 0.03). Patients with mdMCI had serum IL-1 levels comparable to those with AD, and significantly higher than those observed in aMCI and naMCI (p = 0.02). Discussion: The present study provides evidence that inflammatory mechanisms, represented by elevated IL-1, are observed in patients with
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MCI, specifically in those with impairment in multiple cognitive domains. As these patients are at higher risk of conversion to dementia, we propose that an increased serum IL-1 level is a stage marker of the ongoing brain neurodegeneration in the continuum between normal ageing and AD. Copyright © 2009 S. Karger AG, Basel
Introduction
Although the increased inflammatory response observed in Alzheimer’s disease (AD) has long been considered as secondary to the deposition of -amyloid in the brain, a growing body of evidence supports the direct involvement of inflammatory mechanisms in this process [1]. For instance, human postmortem studies showed that activated microglial cells and astrocytes as well as increased tissue levels of proinflammatory cytokines, such as interleukin-1 (IL-1), tumor necrosis factor-␣ (TNF␣), and interferon-, have been described in the vicinities of amyloid plaques and may precede the formation of neurofibrillary tangles [2, 3]. Proinflammatory cytokines may trigger or accelerate ongoing neurodegenerative processes in mice [4], and high levels of TNF-␣ receptors Orestes Vicente Forlenza Laboratory of Neuroscience (LIM 27), Department and Institute of Psychiatry Faculty of Medicine, University of São Paulo São Paulo 05403-010 (Brazil) Tel. +55 11 306 97283, Fax +55 11 306 30698 010, E-Mail forlenza @ usp.br
(sTNF-R1 and sTNF-R2) are present in the cerebrospinal fluid of patients with mild cognitive impairment (MCI) who progress to AD upon follow-up [5]. Increased inflammatory response may be observed in the ageing brain as a consequence of modifications of the physiological state, resulting in increased levels of proinflammatory cytokines that may predispose to several age-related medical disorders, including AD [6]. Gender may also influence the levels of proinflammatory cytokines, as older women may have higher low-grade inflammatory status as compared to older men [7]. In addition, abnormal inflammatory response may also occur in certain psychiatric disorders, such as major depression and schizophrenia [8, 9]. Thus, inflammation may have a major role in the pathophysiology of many central nervous system-related disorders. Among the proinflammatory cytokines, IL-1 may play a major role in the chronic neuroinflammatory processes observed in AD. IL-1 may be secreted and/or overexpressed by reactive microglia due to A42 deposition [10]. This cytokine determines neuronal dysfunction and death, and can also induce higher production of inflammatory cytokines, leading to a self-sustaining and selfamplifying inflammation in the brain. Indeed, previous studies demonstrated overexpression of IL-1 in the brain of AD patients [11, 12]. Moreover, IL-1 polymorphisms responsible for higher production of the cytokine were also associated with an increased risk for AD [13, 14]. MCI is a clinical syndrome characterized by cognitive decline, adjusted for age and education level, with global preservation of intellectual abilities and no or minimal interference with activities of daily life [15]. As patients with MCI have a higher risk to progress to AD upon follow-up, it is expected that several pathological features associated with AD, including the peripheral markers of elevated inflammatory activity, may be detected in patients with MCI [16, 17]. Few studies have addressed ADrelated inflammatory mechanisms in these high-risk subjects. Therefore, the aim of the present study was to assess serum levels of IL-1 in patients with MCI, as compared to AD patients and cognitively preserved older adults, and to determine its correlation with cognitive performance in these subjects. Methods Patients’ Assessment The present sample comprises participants of an ongoing study on cognitive ageing carried out at the Institute of Psychiatry of the University of São Paulo, Brazil. A total of 163 elderly sub-
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Dement Geriatr Cogn Disord 2009;28:507–512
jects were included in this study (58 with mild-to-moderate AD, 74 with MCI, and 31 older adults with no evidence of cognitive decline, i.e. controls). Detailed information of recruitment criteria and strategy, clinical and cognitive assessment as well as diagnostic procedures can be found elsewhere [18]. In brief, all patients and controls underwent a comprehensive clinical and cognitive evaluation with the administration of the CAMDEX interview [19], which included the Cambridge Cognitive Test (CAMCOG) [20], the Mini-Mental State Examination (MMSE) [21], the Clock Drawing Test [22], verbal fluency (animal and fruit categories), the Rivermead Behavioral Memory Test [23], the Fuld Object Memory Evaluation (FOME) [24], the Trail A and B [25], and the Short Cognitive Test [26, 27]. The diagnosis of AD was established according to the NINCDSADRDA criteria [28]. The diagnosis of MCI and its subtypes was made according to the Petersen’s criteria [29, 30], yielding 3 subgroups of patients according to the affected cognitive domains, i.e. multiple-domain amnestic MCI (mdMCI), single-domain amnestic MCI (aMCI) and nonamnestic MCI (naMCI). Subjects without evidence of cognitive or psychiatric disorders were regarded as control subjects. All patients and subjects were living in the community at the time of cognitive and laboratory assessment and had no evidence of uncontrolled clinical diseases, including cardiovascular diseases, diabetes, metabolic syndrome, abnormal cholesterol levels, rheumatologic diseases or other chronic inflammatory conditions. Also, the patients with MCI, AD and the control subjects had no statistical differences in the distribution of clinical diseases (data not shown). This study was approved by the local ethical committee and was conducted according to the Helsinki Declaration. All patients and control subjects agreed to enroll in the psychogeriatric unit and blood samples were collected for biochemical analysis. Laboratory Assessment Blood samples were collected in the morning and all patients had been fasting for approximately 10 h. Blood samples were centrifuged at 515 g for 15 min at 20 ° C in acid citrate dextrose solution and serum aliquots were prepared and immediately stored at –70 ° C until analysis. The concentration of serum IL-1 was measured using highly sensitive colorimetric sandwich ELISA according to the procedure supplied by the manufacturer (Quantikine; R&D Systems, Minneapolis, Minn., USA). All samples were assayed in duplicate. The detection limits for these assays were 0.10 pg/ml. All coefficients of variation were under 5%. Standards and samples were added to the polystyrene microplate coated with a mouse monoclonal antibody against IL-1. After a 3-hour period of incubation, the microplate was washed. Polyclonal antibody against IL-1 conjugated to alkaline phosphatase was added and incubated for 2 h. A new wash was done. Nicotinamide adenine dinucleotide phosphate was then added followed by amplifier enzymes, and the reaction was allowed to develop for 30 min. The reaction was stopped with the addition of 2 N sulfuric acid. The absorbance was read on a plate reader at 490 nm wavelength (Emax; Molecular Devices, Minneapolis, Minn., USA). Apolipoprotein E Genotyping Genomic DNA was isolated from whole blood from each subject and the apolipoprotein E (APOE) genotyping was performed
Forlenza /Diniz /Talib /Mendonça /Ojopi / Gattaz /Teixeira
Table 1. Sociodemographic and clinical variables and the scores on neurocognitive tests in controls, MCI and
AD patients Controls (n = 31) Gender, F/Ma APOE 4 Age, years Educational level, years CAMCOG MMSE CDT VF animal VF fruits RBMT screening RBMT profile FOME total recall FOME late recall Trail A, s Trail B, s SKT
20/11 62.5% 69.986.7 14.085.3 98.783.9 29.281.0 9.783.9 20.084.1 16.785.7 10.581.3 22.281.9 45.482.7 9.480.9 49.6814.2 103.8836.7 2.381.7
MCI (n = 74) 55/19 22% 70.7810.3 10.185.1 88.487.0 27.082.2 8.783.1 14.384.2 12.982.9 7.982.2 17.983.9 39.086.6 8.081.7 68.1832.0 175.0870.6 4.383.3
AD (n = 58) 48/10 18% 76.386.5 7.385.1 64.1812.4 19.383.7 5.682.5 9.484.6 9.382.5 2.982.9 7.286.0 21.2812.4 3.682.9 121.7863.8 248.8899.1 11.3784.2
p 0.073
