Treatment with an acetylcholinesterase inhibitor in Alzheimer patients modulates the expression and production of the pro-inflammatory and anti-inflammatory cytokines

Abstract

Elevated levels of cytokines have been detected in brains of Alzheimer's disease (AD) patients, and altered peripheral levels of IL-1β, TNFα and IL-6 have been reported in these patients. We studied the ability of PBMC from patients with AD, matched with a control group, to release pro- and anti-inflammatory cytokines, and the effect of AChEI treatment on cytokine release. Our data indicates that AChEI treatment down-regulates IL-1, IL-6 and TNF, and up-regulates the expression and production of IL-4 in PBMC in AD patients, and that AChEI leads to the remodelling of the cytokine network, probably acting on the lymphocytic cholinergic system.

Introduction

Inflammatory mechanisms and immune activation have been hypothesized to play a role in the pathogenesis of age-associate disease O'Mahony et al., 1998, Gerli et al., 2000 and neurodegenerative processes such as dementia and atherosclerosis Benveniste, 1992, De Luca et al., 1998, Porrini et al., 1998, Bruunsgaard et al., 1999, Iarlori et al., 2000, Iarlori et al., 2002, Bruunsgaard and Pedersen, 2003.

Alzheimer's disease (AD) is a chronic neurodegenerative disorder causing progressive impairment of memory and cognitive function. The amyloid cascade hypothesis suggests that unregulated metabolism of the beta-amyloid (Aβ) precursor protein (APP) followed by subsequent formation of non-fibrillar and fibrillar Aβ deposits leads to glial activation and eventually to neurotoxicity, causing cognitive impairment (Maat-Schieman et al., 1997). Aβ up-regulates and activates astrocytes, microglia and monocytes to act as pro-inflammatory cells. These cells release a myriad of pro-inflammatory cytokines, including TNF, IL-1 and IL-6 (Meda et al., 1999). In AD, immune and inflammatory-related proteins have been implicated as mediators in response to brain injury. Elevated levels of cytokines have been detected in brains of AD patients. Altered peripheral levels of IL-1β, TNFα and IL-6 have been reported in patients with Alzheimer's disease (Licastro et al., 2000). Since the most recent successful therapeutic approach to AD involve acetylcholinesterase inhibitors (AChEI) Giacobini, 2001, Winblad et al., 2001, we investigated the ability of peripheral blood mononuclear cells from a group of patients with AD, matched with healthy controls (HC), to release pro- and anti-inflammatory cytokines, and studied if the stabilizing effect of AChEI treatment in vivo may relate to the cytokine release or inhibition.

Biologically, IL-1 and TNF are closely related, because of their multiple pro-inflammatory properties, these cytokines contribute to many diseases and have strategic importance to the initiation and progression of inflammation (Dinarello, 1997). IL-1, a key molecule in systemic immune responses in health and disease, has analogous roles in the brain where it may contribute to neuronal degeneration (Sheng et al., 1996) by triggering production of other cytokines and nitric oxide (Rossi and Bianchini, 1996); IL-1 promote Aβ deposition through increased expression and processing of amyloid precursor protein (APP) (Rothwell and Hopkins, 1995) and may facilitate dystrophic neuritic formation in diffuse non-neuritic plaques (Griffin et al., 1995). In Alzheimer's disease, TNF is up-regulated and increases the production of Aβ and inhibits the secretion of neuroprotective, soluble amyloid precursor protein (sAPPs). The up-regulation of Aβ and ApoE by TNF would then lead to increased neuritic plaque formation.(Perry et al., 2001). High levels of protease inhibitors induced by IL-1 and IL-6 were responsible for an abnormal processing of APP leading to high levels of insoluble Aβ (Del Bo et al., 1995). Over-expression of IL-6 in Alzheimer's microglia are associated with Aβ plaque (Huell et al., 1995), and plasma IL-6 concentrations in AD subjects was also significantly higher than that of the control cases (Shibata et al., 2002). The role of IL-4 in neurodegenerative disorders is still unclear; however, IL-4, such as other anti-inflammatory cytokines, regulates microglial responses to Aβ in primary murine microglia and in human monocyte cell line. IL-4 has been reported to regulate Aβ-induced production of the inflammatory cytokines, IL-1 and IL-6 (Szcepanik et al., 2001a). IL-4 is able to block or suppress IL-1, TNFα, IL-6 and IL-8 Conti and Dempsey, 1990, Lee et al., 1995. IL-4 activity may also be associated with the pathophysiology of AD (Abbas et al., 2002).

Our results demonstrate that, in AD patients the pro- and anti-inflammatory peripheral cytokine system is affected when compared with age/sex-matched HC, and that AChEI treatment modulates cytokine production. Thus, at this stage, we believe that AChEI treatment, besides restoring the cholinergic system, reverses the cytokine imbalances observed in AD.