Background/Purpose:

Smoking represents an independent risk factor for rheumatoid arthritis (RA) (1). In response to infectious agents, neutrophil granulocytes can extrude their nuclear contents as nucleoprotein threads, known as neutrophil extracellular traps (NETs) (4). Recently, it has been shown that RA neutrophils show a vastly greater propensity to form NETs than those from normal controls (2,3). Since NETs are pro-inflammatory and immuno-stimulatory, and neutrophils show increased activity in inflammatory lung conditions, we investigated the responsiveness of peripheral blood neutrophils in RA and controls to cigarette smoke exposure.

Methods:

Regular smokers without (n=8) and with (n=6) RA were examined at baseline and after a 16 hour abstinence from smoking. Then they smoked two cigarettes within 10 min and measurements were repeated at 30, 60 and 120 min. Parameters measured were exhaled carbon monoxide (CO), myeloperoxidase (MPO), neutrophil elastase (NE) and cell free nucleosomes by ELISA. Routine laboratory tests included blood counts, CRP, BSR and clotting parameters. In addition, neutrophils from healthy donors were incubated with cigarette smoke extract (CSE) for assessing NET formation by SytoxGreen extracellular DNA staining and combined immunohistochemistry (ICH) with anti-MPO, anti-cit-H3 and DAPI.

Results:

RA smokers started from higher baseline CO levels, but showed similar courses as the controls after re-exposure to cigarette smoke. They exhibited higher baseline MPO, NE and nucleosomes compared to controls. Re-exposure caused a pronounced increase of peripheral blood leucocytes and neutrophils in RA smokers compared to controls. No changes were observed concerning parameters of inflammation and clotting.

Re-exposure of RA patients to cigarette smoke led to a 3- fold rise of MPO und NE at 30 minutes after exposure and a subsequent gradual reduction of serum levels up to 120 min. Unexpectedly, this was paralleled by a sharp reduction in circulatory cell free nucleosomes with a decrease to the baseline at 120 min.

Freshly isolated control neutrophils showed diminished PMA-driven NET release in vitro after 3 hours of treatment with CSE. This was confirmed by MPO and citrullinated H3 ICH and morphometric analysis. Activated neutrophils with a delobulated citH3 positive nuclear phenotype were also remarkably higher in CSE-treated neutrophils.

Conclusion:

RA smokers show increased peripheral blood markers of neutrophil pre-activation compared to non-RA smokers. Cigarette smoking causes a rapid increase of MPO and NE, indicating the systemic release of neutrophil granular contents, and a rapid concomitant decrease of cell free nucleosomes. This is paralleled by the in vitro reduction of CSE-induced NET formation. Our findings provide evidence that cigarette smoking in RA patients provokes the immediate release of toxic neutrophil granular enzymes into the circulation and that NET formation is transiently reduced in the immediate aftermath of smoke inhalation.

References

1. Katrina AI et al., 2014

2. Khandpur R et al., 2013

3. Sur Chowdhury C et al., 2014

4. Amulic B et al., 2012

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/immediate-release-of-peripheral-neutrophil-myeloperoxidase-and-elastase-and-formation-of-extracellular-traps-to-cigarette-smoking-in-rheumatoid-arthritis/