Central and Systemic Inflammation in Alzheimer's Disease

Introduction: Alzheimer's disease (AD) is characterized by abnormal β-amyloid deposition associated with Tau-based neurofibrillary tangles. The metabolism of these proteins is modulated by the individuals physiological background. In addition to genetic factors, early brain inflammation and the presence of a spontaneous beta amyloid (Aβ)-specific immune response are likely to have an important influence on amyloid pathogenesis, as demonstrated in recent neuropathological and experimental studies. In vivo measurements of the β-amyloid load and brain inflammation have become available with the development of new tracers for positron emission tomography (PET) imaging. So far, tracers for brain inflammation have had a limited ability to detect changes in the expression of peripheral benzodiazepine receptors (PBR), which are mainly present on the surface of activated microglial cells. The recently developed [18F]DPA-714 was found to be a better ligand for PBR than previous tracers. Inflammatory and immune anti-Aβ responses (I2ARs) are likely to occur very early in the pathogenic protein cascade. They could thus constitute early markers for AD diagnosis and also play key roles in its phenotypic presentation and as prognostics. Comparing sporadic AD and familial forms of AD caused by APP, PSEN1 or PSEN2 mutations (in both symptomatic and at-risk non-symptomatic relatives) will aid in establishing the chronology of pathological events and defining their clinical impact.

The main objective of this study is to investigate the central and peripheral inflammatory, as well as the spontaneous Aβ-specific, immune responses at the asymptomatic stage and early stages of AD by combining molecular imaging techniques with blood biomarker analyses. The early and preclinical stages of AD will be studied in the relatives of patients with PSEN1, PSEN2 or APP mutations that are at-risk (50%) to be mutation carriers.

The secondary objectives are

1. to investigate the specificity of the central inflammatory response (DPA PET scan) and the peripheral I2AR (blood markers) by analyzing their correlation with amyloid-binding radiotracer (PIB PET scan);

2. to evaluate the prognostic value of central and peripheral I2ARs on disease evolution over a 2 year follow-up;

3. to compare central and peripheral I2ARs in sporadic and genetic cases of AD;

4. to correlate the initial amyloid load with disease evolution in sporadic and genetic cases of AD

5. to correlate I2AR biomarkers with CSF biomarkers (Aβ1-42, tau and phosphorylated tau) when consent for lumbar puncture is obtained (optional). Each patient will then be invited to participate in a long-term follow-up study and will be informed of the possibility of brain donation for research purposes. A library of blood samples will also be collected and stored at the Platform for Biological Resources at the Salpetriere Hospital, to allow for future collaborations on new diagnostic and prognostic biomarkers based on novel techniques.

Methodology : We propose to conduct a multimodal study, first transversal, then longitudinal with a two year follow-up, based on

1. molecular PET imaging by coupling [18F]DPA-714, a marker of central inflammation, and PIB, a marker of amyloid deposition;

2. peripheral I2AR analysis (blood markers);

3. analysis of genetic factors;

4. measurement of regional cortical atrophy by MRI. A group of patients at an early stage of AD (CDR = 0.5), defined by a new diagnostic criteria (Dubois et al, 2007), will be compared to a group of moderate AD patients as defined by the criteria of NINCDS AIREN (CDR = 1 or 2), a group of patients with another type dementia (frontotemporal dementia) and a control group.

Recruitment of sporadic AD patients and controls will occur at the Pitie-Salpetriere Hospital. Teams of geneticists from Paris and Rouen will recruit patients with known mutations and at-risk asymptomatic first-degree relatives. Every subject will undergo the following examinations: (a) at the Pitie-Salpetriere Hospital, a clinical and neuropsychological assessment, a 3T multimodal research MRI, and a blood draw 8 for studying a panel of plasmatic markers, measuring the blood level of anti-Aβ antibodies, evaluating Aβ-specific T lymphocyte responses and studying potential genetic modifiers; and (b) at the ORSAY Hospital, two PET scans will be performed on the same day: first an [11C]-PIB PET scan, followed 3 hours later by an [18F]DPA-714 imaging. Clinical follow-ups will be conducted annually for two years and will include an MRI and a blood draw on the last visit.

The previous study BIOMAGE, funded by the French National Research Agency (ANR 2007), has demonstrated the logistical feasibility of the project as well as the efficiency of patient and control recruitment. The subjects that were included in BIOMAGE will be invited to participate in this research project, thus utilizing this cohort for DPA imaging and I2AR markers. The duration of the research will be four years.

Expected results and perspectives: This study will evaluate the contribution of I2ARs in AD progression. Inclusion of sporadic and familial forms of AD will aid in studying the chronology of pathological events. We expect I2ARs to appear in the early stages of the disease and to constitute new prognostic factors. I2ARs could also become therapeutic markers for the assessment of novel anti-amyloid treatments and may offer new insights to the development of Aβ-specific immunotherapy strategies.