Honey gold nanoparticles attenuate the secretion of IL-6 by LPS-activated macrophages

PLOS ONE RESEARCH ARTICLE Honey gold nanoparticles attenuate the secretion of IL-6 by LPS-activated macrophages John Benjamin W. Duncan1¤, Swarna Basu2*, Pavithra Vivekanand ID1* 1 Department of Biology, Susquehanna University, Selinsgrove, Pennsylvania, United States of America, 2 Department of Chemistry, Susquehanna University, Selinsgrove, Pennsylvania, United States of America a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Duncan JBW, Basu S, Vivekanand P (2023) Honey gold nanoparticles attenuate the secretion of IL-6 by LPS-activated macrophages. PLoS ONE 18(9): e0291076. https://doi.org/ 10.1371/journal.pone.0291076 Editor: Divakar Sharma, Lady Hardinge Medical College, INDIA Received: June 16, 2023 Accepted: August 22, 2023 Published: September 8, 2023 Copyright: © 2023 Duncan et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting information files. Funding: Funding for this research was provided by Susquehanna University. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist. ¤ Current address: Department of Microbiology, Immunology, and Cancer Biology, University of Virginia, Charlottesville, Virginia, United States of America * (SB); (PV) Abstract Interleukin-6 (IL-6) is a pleiotropic cytokine that coordinates host immune responses to infection. Though essential to the acute phase response, prolonged IL-6-mediated recruitment of mononuclear cells has been implicated in chronic inflammatory diseases such as rheumatoid arthritis, psoriasis, and Crohn’s disease. Accordingly, identifying novel therapeutics that diminish circulating IL-6 levels could benefit individuals suffering from chronic inflammation. In immunocompetent hosts, bacterial lipopolysaccharide (LPS) recognition by toll-like receptor 4 (TLR4) activates the transcription factor NF-κB, driving macrophage production of IL-6. Interestingly, both citrate-stabilized and ‘green’ synthesized gold nanoparticles (AuNPs) have been shown to modulate the cytokine responses of LPS-activated macrophages. Here we demonstrate that AuNPs, synthesized with commercial and locally sourced honey, downregulate LPS-induced macrophage secretion of IL-6. Compared to LPS-only controls, inhibition of IL-6 levels was observed for all three types of honey AuNPs. The effect was likely driven by honey AuNP-mediated perturbation of the TLR4/NF-κB signaling pathway, as evidenced by a reduction in the phosphorylation of IκB. Further investigation into the anti-inflammatory properties of honey AuNPs may yield novel therapeutics for the treatment of chronic inflammation. Introduction Innate immunity is a powerful first line of defense against infection in which tissue-resident macrophages detect invading pathogens and coordinate effective immune responses. Macrophage cell-surface receptors facilitate pathogen detection via recognition of associated molecular components [1]. These interactions of the pathogen-derived ligands stimulate signaling cascades within macrophages, ultimately inducing the secretion of soluble pro-inflammatory cytokines [2]. In the case of gram-negative bacterial encounter, macrophage toll-like receptor 4 (TLR4) recognizes the lipid A subregion of bacterial lipopolysaccharide (LPS) [3]. LPS-stimulation of TLR4 recruits myeloid differentiation factor 88 (MyD88), thus activating the PLOS ONE | https://doi.org/10.1371/journal.pone.0291076 September 8, 2023 1 / 14 PLOS ONE Honey gold nanoparticles attenuate IL-6 secretion MyD88-dependent signaling cascade [4]. Upon its association with TLR4, MyD88 recruits interleukin-1 receptor-associated kinase 4, prompting a signaling cascade that culminates in the activation of IκB kinase (IKK). IKK phosphorylates IκB, resulting in the polyubiquitination and degradation of IκB by the proteasome. Since IκB sequesters NF-κB, its degradation enables NF-κB to translocate to the nucleus. There, NF-κB promotes the transcriptional activation of proinflammatory cytokines such as tumor necrosis factor (TNF), interleukin 1 beta (IL-1β), and interleukin 6 (IL-6) [4]. TNF is processed into TNF-α, which promotes inflammation at the site of infection via vasodilation [5]. IL-1β is a critical inflammatory mediator that stimulates macrophage production of other proinflammatory cytokines [6, 7]. IL-6 is a pleiotropic cytokine with paradoxical proinflammatory and anti-inflammatory properties that initiates innate immunity’s acute phase response [8, 9]. Since the dysregulation of each proinflammatory cytokine has been implicated in chronic inflammatory diseases like rheumatoid arthritis and Crohn’s disease, numerous immunomodulatory medications targeting the dysregulated cytokines have been developed [10, 11]. However, modern immunosuppressant drugs are accompanied by a host of deleterious side effects such as increased risk of infection and malignancy [12]. Fortunately, advances in the field of nanobiotechnology have enabled the development of novel therapeutics that circumvent many of these clinical challenges. Due to their small sizes, high surface areas, and relative tunabilities, nanomaterials have emerged as invaluable diagnostic tools, drug-carrying vehicles, and therapeutic agents [13–15]. Within the last two decades, gold nanoparticles (AuNPs) have shown promise in a wide array of biological applications including photothermal cancer therapy [15, 16], bone tissue engineering [17], and antiseptic intervention [18]. As previously summarized by Vines et al., early whole-body photothermal therapies lacked the tissue specificity and penetrative capacity necessary to consistently improve clinical outcomes for cancer patients [16]. Both challenges were overcome using AuNPs, which passively accumulate at the tumor site due to vascular redistribution [19, 20], and can be activated by tissue penetrating near infrared (NIR) light to induce localized hyperthermia [15, 16]. Additionally, surface conjugations of epidermal growth factor receptor antibodies and polyethylene glycol, have enabled AuNPs to target solid tumors and remain undetected by the reticuloendothelial system in circulation, respectively [21, 22]. Finally, morphological modifications to AuNPs have improved their extinction coefficients for more efficient NIR activation in photothermal therapies [23]. Similar translational investigations have shed light onto the relationship between AuNP structure and function both in vitro and in vivo. It has been well documented that AuNPs accumulate in malignant cell lines and induce cell death to varying degrees depending upon the (...truncated)