Modifications of IL-6 by Hypochlorous Acids: Effects on Receptor Binding

Lori I Robins; Erika K Keim; Deborah B Robins; John S Edgar; John S Meschke; Philip R Gafken; Jeffrey F Williams

doi:10.1021/acsomega.1c05297

Modifications of IL-6 by Hypochlorous Acids: Effects on Receptor Binding

ACS Omega. 2021 Dec 14;6(51):35593-35599. doi: 10.1021/acsomega.1c05297. eCollection 2021 Dec 28.

Authors

Lori I Robins¹, Erika K Keim², Deborah B Robins³, John S Edgar⁴, John S Meschke², Philip R Gafken⁵, Jeffrey F Williams⁶

Affiliations

¹ Department of Physical Sciences, University of Washington Bothell, 18115 Campus Way NE, Bothell, Washington 98011, United States.
² Department of Environmental and Occupational Health Sciences, University of Washington, 4225 Roosevelt Way NE, Suite 100, Seattle, Washington 98195, United States.
³ Issaquah High School, 700 2nd Ave SE, Issaquah, Washington 98027, United States.
⁴ Department of Medicinal Chemistry, University of Washington, H172 Health Science Building, Seattle, Washington 98195, United States.
⁵ Fred Hutchinson Cancer Research Center, 1100 Fairview Ave N, Seattle, Washington 98109, United States.
⁶ Briotech Inc., 14120 NE 200th St, Woodinville, Washington 98072, United States.

Abstract

Interleukin-6 (IL-6) has been implicated in the pathogenesis of inflammatory events including those seen with COVID-19 patients. Positive clinical responses to monoclonal antibodies directed against IL-6 receptors (IL-6Rs) suggest that interference with IL-6-dependent activation of pro-inflammatory pathways offers a useful approach to therapy. We exposed IL-6 to hypochlorous acid (HOCl) in vitro at concentrations reported to develop in vivo. After HOCl treatment, binding of IL-6 to IL-6R was reduced in a dose-dependent manner using a bioassay with human cells engineered to provide a luminescence response to signal transduction upon receptor activation. Similar results followed the exposure of IL-6 to N-chlorotaurine (NCT) and hypobromous acid (HOBr), two other reactive species produced in vivo. SDS-PAGE analysis of HOCl-treated IL-6 showed little to no fragmentation or aggregation up to 1.75 mM HOCl, suggesting that the modifications induced at concentrations below 1.75 mM took place on the intact protein. Mass spectrometry of trypsin-digested fragments identified oxidative changes to two amino acid residues, methionine 161 and tryptophan 157, both of which have been implicated in receptor binding of the cytokine. Our findings suggest that exogenous HOCl and NCT might bring about beneficial effects in the treatment of COVID-19. Further studies on how HOCl and HOBr and their halogenated amine derivatives interact with IL-6 and related cytokines in vivo may open up alternative therapeutic interventions with these compounds in COVID-19 and other hyperinflammatory diseases.