Selective Acetyl- and Butyrylcholinesterase Inhibitors Reduce Amyloid-β Ex Vivo Activation of Peripheral Chemo-cytokines From Alzheimer’s Disease Subjects: Exploring the Cholinergic Anti-inflammatory Pathway

Abstract

Increasing evidence suggests that the early pathogenesis of Alzheimer’s disease (AD) is driven by elevated production and/or reduced clearance of amyloid-β peptide (Aβ), which is derived from the larger Aβ precursor protein (APP). Aβ aggregates to form neurotoxic soluble oligomers that trigger a cascade of events leading to neuronal dysfunction, neurodegeneration and, ultimately, clinical dementia. Inflammation, both within the brain and systemically, together with a deficiency in the brain neurotransmitter acetylcholine, which underpinned the development of anticholinesterases for the symptomatic treatment of AD, are invariable hallmarks of the disease. The inter-relation between Aβ, inflammation and cholinergic signaling is complex, with each feeding back onto the others to drive disease progression. To elucidate these interactions plasma samples and peripheral blood mononuclear cells (PBMCs) were evaluated from healthy control (HC) subjects and AD patients. Plasma levels of acetyl- (AChE) and butyrylcholinesterase (BuChE) as well as Aβ were significantly elevated in AD vs. HC subjects, and acetylcholine showed a trend towards reduced levels. Aβ challenge of the AD and HC PBMCs resulted in greater release of inflammatory cytokines interleukin-1β (IL-1β), monocyte chemotactic protein-1 (MCP-1) and tumor necrosis factor-alpha (TNF-α) from AD vs. HC subjects, with IL-10 expression being similarly affected. THP-1 monocytic cells, a cell culture counterpart of PBMCs and brain microglial cells, responded similarly to Aβ as well as to phytohaemagglutinin (PHA) challenge, to allow preliminary analysis of the cellular and molecular pathways that underpin Aβ-induced changes in cytokine expression. In light of prior studies demonstrating that APP expression was regulated by specific cytokines and anticholinesterase drugs, the latter were evaluated on Aβ- and PHA-induced chemo-cytokine expression. Co-incubation with selective inhibitors, such as the acetylcholinesterase (AChE)-inhibitor (−)-phenserine and the butyrylcholinesterase (BuChE)-inhibitor (−)-cymserine analogues mitigated the rise in cytokine levels, and suggest that augmentation of the cholinergic anti-inflammatory pathway may prove valuable in AD.

(−)‐Phenserine tartrate (PhenT) as a treatment for traumatic brain injury

“…As illustrated in Figure , CCI‐induced modTBI resulted in a phenotypic change in microglial cell morphology and number vs sham (unchallenged animals), resulting in an activated condition that is sometimes termed a M1 reactive state. PhenT at a clinically translatable dose reversed this, in line with anti‐inflammatory actions demonstrated in other models, and reduced the percent of microglia expressing an activated state from 64.3 ± 3.39% in CCI + saline animals to 25.1 ± 3.59% in CCI + PhenT mice which was reflected in a reduction in the CCI TBI‐induced contusion volume and size of the lateral ventricles (Figure ) …”

“…All achieve brain levels that vary between 7‐ and 1.25‐fold higher than concomitant plasma ones (Figure ) and, in concentration‐dependent relationships (EC 50 s = 26 to 100 nmol/L), produce a range of pharmacological benefits relevant to TBI and AD neuropathologies. Notably, PhenT provides protection from PNCD, anti‐inflammatory, and antioxidative stress; its actions include augmenting neurotrophic factor levels, brain acetylcholine levels, and neuronal stem cell survival and differentiation, as well as inhibiting APP and Aβ generation, as recently reviewed . PhenT is well tolerated across preclinical animal models, and in human studies (645 subjects) for up to 1 year, positively impacted markers of efficacy in AD; importantly, it also mitigates multiple sequelae instigated by TBI and brain injury …”

Targeting Tumor Necrosis Factor Alpha for Alzheimer’s Disease

“…Similarly, challenging human THP-1 and peripheral blood mononuclear cells with Aβ induced the synthesis of pro-inflammatory cytokines, including TNF-α [158]. This increase was mitigated by infusing the cells with AChE inhibitors [158].…”

“…Similarly, challenging human THP-1 and peripheral blood mononuclear cells with Aβ induced the synthesis of pro-inflammatory cytokines, including TNF-α [158]. This increase was mitigated by infusing the cells with AChE inhibitors [158]. Furthermore, it was recently shown that anti-ACh drugs exacerbate systemic inflammation in a mouse model of tauopathy [93], though the exact molecular mechanisms remain to investigate.…”

Status of Acetylcholinesterase and Butyrylcholinesterase in Alzheimer's Disease and Type 2 Diabetes Mellitus

“…Moreover, levels of β-amyloid are on average about 2-times higher in AD patients compared to normal, healthy subjects [42, 43]. Likewise, the activities of both AChE and BuChE are found to be higher in diabetic patients versus normal controls [44, 45].…”