Introduction
Depression is becoming more and more common worldwide, with approximately 1 in 30 people being affected by the illness1. Resulting from a combination of genetic, social and psychological factors, depression impacts one’s quality of living and can range in severity, from affecting their motivation for daily tasks to being completely debilitating. Modern medicine’s impact on treating mental illness has thus far been limited due to our incomplete understanding of the complex pathophysiology involved. As such, more research is necessary to elucidate underlying mechanisms of mental illness and develop effective therapies, which in turn is poised to improve quality of life.
Inflammation can contribute to the pathophysiology of depression. In a recent study published in the British Journal of Pharmacology, Xiang Xu and colleagues looked at a potential mechanism of depression in relation to two inflammatory signaling pathways (high-mobility group box 1 (HMGB1)/ Toll Like Receptor 4 (TLR4)/ Nuclear factor-κB (NF-κB) and Tumor Necrosis Factor-α (TNF-α)/ Tumor Necrosis Factor Receptor 1 (TNFR1)/NF-κB signaling pathways).
One biomolecule that is thought to be a potential drug candidate in the treatment of depression is arctigenin (AG), a bioactive component of Fructus arctii. However, the mechanism of AG’s antidepressant effects remains elusive. The goal of the study was to understand how AG exerts antidepressant effects by investigating its impact on the HMGB1/TLR4/NF-κB and TNF-α/TNFR1/NF-κB signaling pathways in a rodent model. A key component of this study was the use of OpenSPR™ for investigating the inhibitory capacity of AG on key interactions in these inflammatory pathways. This study exemplifies Nicoya’s mission of improving human life by helping scientists succeed.
Using mouse models for looking at the efficacy of AG to treat depression
Mice were subjected to various stressors each day, a procedure known as chronic unpredictable mild stress (CUMS), to induce a depressive state. The mice were then divided into 5 groups and administered various treatments to look at the efficacy of a particular treatment. These treatments included a vehicle/placebo, AG at 3 different concentrations, and sertraline hydrochloride (SERT), which is a common antidepressant drug. A group of mice that did not undergo the CUMS procedure acted as a control. Behavioural tests were then used to evaluate the depressive behaviour of each group.
The CUMS procedure resulted in an increase in depressive behaviours. This effect was mitigated via the administration of AG in a dose-dependent manner. This decrease in depressive behaviours was comparable to those mice that were administered SERT.
Using protein quantification to study inflammation factors
The mice were then sacrificed and the relative concentration of inflammatory factors was measured through immunohistochemistry and protein quantification (co-IPs, and western blots). Mice subjected to CUMS showed an increase in a variety of inflammatory factors including ionized calcium binding adapter molecule 1 (Iba-1) and HMGB1, which are both contributors to inflammation and suggest excessive microglia activation. This may be a contributing factor to the depressive behaviours observed in the mice. AG and SERT both reduced the concentration of these factors relative to the vehicle group, which suggests that AG and SERT resulted in less inflammation relative to the control.
Using LSPR to quantify binding interactions
To determine whether AG was having a direct effect on the HMGB1/TLR4/NF-κB and/or the TNF-α/TNFR1/NF-κB signaling pathways, binding studies were performed on the OpenSPR. This allowed the authors to determine the effect of AG on the binding affinity of HMGB1 to TLR4 and TNF-α to TNFR1.
First, the binding affinity between each protein-protein and protein-small molecule pair was determined. TLR4 or TNFR1 was covalently immobilized onto carboxyl sensors using EDC/NHS chemistry. Then, the proteins (HMGB1 and TNF-α) or small molecules (AG and SERT) were injected over the sensor from low to high concentrations. BSA was used as a negative control. The purpose of this was to see relative binding affinities between each ligand-receptor interaction, and to see whether AG would influence the binding affinity of the receptor for its native ligand via a competition assay, where HMGB1 + AG was injected onto TLR4 and TNF-α + AG was injected onto TNFR1.
Localized Surface Plasmon Resonance (LSPR) confirmed the interaction between HMGB1/TLR4 and AG/TLR4 as well as TNF-α/TNFR1 and AG/TNFR1 with varying affinities. The competition assay confirmed that the presence of AG resulted in reduced affinity of each native ligand for its receptor.
This reduction in binding seen via LSPR, along with the reduction in inflammatory factors seen with AG treatment in mice via Western Blot analysis, suggests that AG is a potential drug candidate for treating depression.
Summary
In this publication, Xu et al. were able to provide evidence for the potential efficacy of Arctigenin (AG) in the treatment of depression. They observed a reduction of inflammation factors in mice that received AG as treatment, as well as used OpenSPR to confirm that AG disrupts the interaction between inflammatory factors that are elevated in depressive mice. This suggests that AG contributes to a reduction in inflammation, and thus has potential antidepressant effects.
In keeping with our mission to improve human life, we strive to help scientists like Xiang Xu succeed in their research by providing them with affordable and accessible technology. Platforms like OpenSPR and Alto enable researchers with powerful binding data right at their benchtop, helping them make new discoveries and important breakthroughs in their work to solve some of today’s biggest healthcare challenges.
References
- “Global, Regional, and National Incidence, Prevalence, and Years Lived with Disability for 354 Diseases and Injuries for 195 Countries and Territories, 1990–2017: A Systematic Analysis for the Global Burden of Disease Study.” 2018. The Lancet 392 (10159): 1789–1858. https://doi.org/10.1016/S0140-6736(18)32279-7.
- Xu X, Piao HN, Aosai F, Zeng XY, Cheng JH, Cui YX, Li J, Ma J, Piao HR, Jin X, et al. 2020. “Arctigenin Protects against Depression by Inhibiting Microglial Activation and Neuroinflammation via HMGB1/TLR4/NF‐κB and TNF‐α/TNFR1/NF‐κB Pathways.” British Journal of Pharmacology 177 (22): 5224–45. https://doi.org/10.1111/bph.15261.