Background/Purpose: Rheumatoid arthritis (RA) and related autoimmune joint disease patients exhibit cyclic episodes of resolution and exacerbation of joint inflammation, referred to as flares. Fibroblast-like synoviocytes (FLSs) that are epigenetically and metabolically transformed by chronic inflammation are implicated as the orchestrators of these flares. The tricarboxylic acid cycle (TCA) is the primary energy-producing metabolic pathway that occurs in the mitochondria. Biomolecules (enter the TCA cycle as acetyl-CoA to undergo a series of enzymatic reactions leading to the production of ATP. Another lesser investigated, but highly significant role of the TCA cycle is that its intermediate enzymatic byproducts, like alpha-ketoglutarate (AKG), enter the nucleus to function as an epigenetic modifier that has the potential to inhibit the expression of pro-inflammatory genes. We hypothesized that AKG can be developed as a drug to inhibit the deregulated metabolic and epigenetic state of the RA FLSs and effectively treat RA flares.

Methods: We isolated FLSs from the synovial joints of a transgenic mouse model of inducible human Tumor Necrosis Factor alpha expression (iTNF-tg). We further generated disease states equivalent to homeostasis, inflammatory, and resolution phases of arthritis pathology to mimic the characteristics of the flare pathology in RA patients. We studied the effect of AKG treatment on FLSs from various disease phases. Outcome measures included histological, immunohistochemical, ATP generation, gene expression, epigenetic regulation, cell cycle, and oxidative stress measurements.

Results: Our in vitro results in FLSs from the homeostasis, inflammatory, and resolution phase of the iTNF-tg mouse FLSs showed that AKG inhibited the expression of inflammatory genes. We utilized a luminescence-based assay to measure ATP and reactive oxygen species in live FLSs. Our data suggests that treatment with AKG inhibited the amount of ATP produced by FLSs from all stages. However, the anti-inflammatory and metabolic effects of AKG were maximal during the resolution phase. Our cell cycle analysis and found that AKG did not change the proliferation rate of FLSs. These results suggest that treatment with AKG inhibits inflammation and changes ATP production without altering cell proliferation. We will further discuss the results of our ongoing epigenetic and transcriptomic studies evaluating the in vivo effect of two different forms of dietary AKG treatment (cell-permeable and non-cell-permeable dietary forms) on the inflammatory arthritis features of the iTNF-tg mouse model.

Conclusion: AKG may inhibit RA FLSs’ inflammation by downregulating pro-inflammatory gene expression. AKG may show its most effective inhibition of the pathological of RA FLSs during the resolution phase of the disease. Mechanistically, these inhibitory effects may act via blocking the NF-kappaB signaling pathway and cellular senescence pathways. AKG supplementation during the resolution phase of RA may serve as an effective co-treatment with current disease-modifying anti-rheumatic drugs to prevent the epigenetic deregulation of RA FLSs and thereby the onset of subsequent flares.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/effect-of-alpha-ketoglutarate-on-synovial-fibroblasts-mediated-inflammation-in-arthritis/