Immunomodulatory effects of nicotine on interleukin 1β activated human astrocytes and the role of cyclooxygenase 2 in the underlying mechanism

Abstract

BackgroundThe cholinergic anti-inflammatory pathway (CAP) primarily functions through acetylcholine (ACh)-alpha7 nicotinic acetylcholine receptor (α7nAChR) interaction on macrophages to control peripheral inflammation. Interestingly, ACh can also bind α7nAChRs on microglia resulting in neuroprotective effects. However, ACh effects on astrocytes remain elusive. Here, we investigated the effects of nicotine, an ACh receptor agonist, on the cytokine and cholinesterase production of immunocompetent human astrocytes stimulated with interleukin 1β (IL-1β) in vitro. In addition, the potential involvement of prostaglandins as mediators of nicotine was studied using cyclooxygenase 2 (COX-2) inhibition.MethodsCultured human fetal astrocytes were stimulated with human recombinant IL-1β and treated simultaneously with nicotine at different concentrations (1, 10, and 100 μM). Cell supernatants were collected for cytokine and cholinesterase profiling using ELISA and MesoScale multiplex assay. α7nAChR expression on activated human astrocytes was studied using immunofluorescence. For the COX-2 inhibition studies, enzyme activity was inhibited using NS-398. One-way ANOVA was used to perform statistical analyses.ResultsNicotine treatment dose dependently limits the production of critical proinflammatory cytokines such as IL-6 (60.5 ± 3.3, %inhibition), IL-1β (42.4 ± 1.7, %inhibition), and TNF-α (68.9 ± 7.7, %inhibition) by activated human astrocytes. Interestingly, it also inhibits IL-8 chemokine (31.4 ± 8.5, %inhibition), IL-13 (34.243 ± 4.9, %inhibition), and butyrylcholinesterase (20.8 ± 2.8, %inhibition) production at 100 μM. Expression of α7nAChR was detected on the activated human astrocytes. Importantly, nicotine’s inhibitory effect on IL-6 production was reversed with the specific COX-2 inhibitor NS-398.ConclusionsActivation of the cholinergic system through α7nAChR agonists has been known to suppress inflammation both in the CNS and periphery. In the CNS, earlier experimental data shows that cholinergic activation through nicotine inhibits microglial activation and proinflammatory cytokine release. Here, we report similar anti-inflammatory effects of cholinergic activation on human astrocytes, at least partly mediated through the COX-2 pathway. These results confirm the potential for cholinergic neuroprotection, which is looked upon as a promising therapy for neuroinflammation as well as neurodegenerative diseases and stroke. Our data implicates an important role for the prostaglandin system in cholinergic regulatory effects.

Dysregulated repair and inflammatory responses by e‐cigarette‐derived inhaled nicotine and humectant propylene glycol in a sex‐dependent manner in mouse lung

“…In the human 3D EpiAirway tissue model, we found that nicotine significantly downregulated IL‐6 secretion by tissues from healthy subjects, while it increased by tissues from COPD subjects. This is in line with nicotine‐mediated inhibition of IL‐6 production in human brain astrocytes in a dose‐dependent manner . PG with or without nicotine induced significant IL‐8 release by both healthy and COPD donors compared to untreated controls, while no changes in PGE 2 in any of the groups were observed.…”

Don't forget astrocytes when targeting Alzheimer's disease

“…Astrocytes have functional nicotinic and muscarinic receptors and (controversially) may express butyrylcholinesterase ( Bche/ BuChE) and Ache . Levels of expression and catalytic function appear to vary depending on the stage of development/age and species investigated (Anderson et al, ; Elhusseiny, Cohen, Olivier, Stanimirovic, & Hamel, ; Pabst et al, ; Revathikumar et al, ; Teaktong et al, ; Thullbery, Cox, Schule, Thompson, & George, ). In AD pathology, the number of glial fibrillary acidic protein (GFAP) immunopositive astrocytes in the hippocampus and cortex with nicotinic receptor subtype α7 (α7 nAChR )‐immunoreactivity is increased from 40 –100% in sporadic AD and 50–60% in Swedish amyloid precursor protein (APPswe) 670/671 AD cases, compared to less than 50% in non‐symptomatic patient controls (Teaktong et al, ; Yu, Guan, Bogdanovic, & Nordberg, ).…”

“…Choline receptor stimulation via AChEIs or nicotine agonists can reduce many pro‐inflammatory signals (Tabet, )—making them an appealing target. When activated by IL‐1β, cultured fetal human astrocytes up‐regulated many pro‐inflammatory cytokines (Revathikumar et al, ). Pretreating cultures with nicotine prior to IL‐1β stimulation leads to a reduction in IL‐6, TNF‐α, IL‐1β, IL‐8, and IL‐13 production.…”

“…However, this decreased level of cytokine production never returned to non‐stimulated baselines, suggesting ACh stimulation may only modestly attenuate pro‐inflammatory responses. Additionally, no differences were detected for IFNγ, IL‐2, IL‐44, IL‐10, and IL‐12p70 secretion, and therefore, modulation of these inflammatory cytokines may not be universal (Revathikumar et al, ). One should also be wary of such investigations completed in serum‐containing culture conditions, as astrocyte cultures maintained in serum‐containing growth media irreversibly change the transcriptome and several functions of astrocytes (Foo et al, ).…”

“…Therefore, if microglia‐related inflammation decreases, so too would astrocyte reactivity (Liddelow et al, ; Yun et al, ). Given that ACh attenuates microglial cytokine production, anti‐inflammatory and neuroprotective pathways would be promoted (Liu et al, ; Revathikumar et al, ; Tabet, ). Under these parameters, the cholinergic system may be considered a modulator of astrocyte‐associated neuroinflammation both directly and indirectly (Revathikumar et al, ).…”