A natural compound called obakulactone (OL) may offer a new way to treat rheumatoid arthritis (RA), according to a study published in Engineering. OL is a tetracyclic triterpenoid isolated from Phellodendri cortex. Researchers found that it reduced signs of arthritis by promoting the breakdown of acyl coenzyme A thioesterase 1 (ACOT1) through the ubiquitin‒proteasome pathway and by restoring the balance of unsaturated fatty acids.
The findings help explain how OL acts on rheumatoid arthritis at the molecular level. They also identify ACOT1 as a possible new drug target and suggest that correcting disrupted fatty acid metabolism could become a useful strategy for treating RA.
Obakulactone Reduced Joint Swelling and Damage
Researchers tested OL in rats with rheumatoid arthritis triggered by complete Freund’s adjuvant (CFA). The animals received low (50 mg·kg-1·d-1), medium (100 mg·kg-1·d-1), and high (200 mg·kg-1·d-1) doses of OL for 21 days.
Treatment significantly reduced swelling in the joints. It also helped restore the normal structure of cartilage and the synovium, the tissue that lines the inside of joints. In addition, OL improved abnormal changes in immune organs including the thymus and spleen.
The compound also altered immune activity within the joints. It reduced the unusually high levels of CD3+ T cells and CD68+ macrophages. At the same time, it shifted macrophages away from the proinflammatory M1 (CD86) state and toward the anti-inflammatory M2 (CD206) state. OL also limited the development of CD4+ T cells into inflammation-promoting Th17 cells.
Blood tests showed that OL lowered several inflammatory molecules in a dose-dependent manner. These included IL-1β, IL-6, IL-17, and TNF-α. The treatment also reduced rheumatoid arthritis markers including RF, CCP-Ab, CRP, and MMP-3.
Restoring Disrupted Fatty Acid Metabolism
The researchers used multiomics techniques, including metabolomics, MALDI mass spectrometry imaging, and proteomics, to examine how OL affected biological processes throughout the body.
Their analysis showed that rheumatoid arthritis had disrupted the production and metabolism of several unsaturated fatty acids. OL helped correct these abnormalities, including changes involving arachidonic acid, linoleic acid, and α-linolenic acid.
Laboratory experiments also examined the effects of OL on RA synovial fibroblasts (SFs). These cells can grow excessively in rheumatoid arthritis and contribute to inflammation, thickening of joint tissue, and damage to cartilage and bone.
OL slowed the growth of the abnormal fibroblasts, encouraged them to undergo apoptosis, and reduced their release of inflammatory cytokines.
ACOT1 Identified as a Direct Target
A series of tests, including cellular thermal shift assays, microscale thermophoresis, and surface plasmon resonance experiments, showed that OL binds directly to ACOT1.
The researchers measured a dissociation constant (Kd) of (6.18 ± 0.26) μmol·L-1 (analyzed by microscale thermophoresis (MST)) and (6.34 ± 0.38) μmol·L-1 (analyzed by surface plasmon resonance (SPR)).
OL increased the ubiquitination-mediated proteasomal degradation of ACOT1. In this process, cells attach molecular tags to the protein and send it to the proteasome, the cellular machinery responsible for breaking down unwanted proteins.
Reducing ACOT1 also lowered levels of the downstream protein stearoyl-CoA desaturase-1 (SCD1). This, in turn, limited activation of the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) and phosphoinositide 3-kinase (PI3K)-protein kinase B (AKT) signaling pathways.
These pathways help regulate cell survival, growth, inflammation, and fibrosis. By suppressing their activity, OL reduced inflammatory and fibrotic changes in SFs.
Additional rescue experiments and studies using inhibitors supported the proposed mechanism. The results indicated that OL produced its anti-inflammatory, antiproliferative, and proapoptotic effects by targeting ACOT1, regulating the arachidonic acid pathway, and influencing the downstream JAK-STAT/PI3K-AKT signaling pathways.
A Potential New Rheumatoid Arthritis Strategy
RA is a chronic systemic autoimmune disease that affects approximately 1% of people worldwide. It occurs when the immune system mistakenly attacks healthy joint tissue, causing pain, swelling, stiffness, and progressive damage. Existing treatments do not work equally well for everyone and can sometimes cause serious adverse effects.
The new findings provide preclinical evidence that OL could serve as a potential therapeutic compound for rheumatoid arthritis. They also highlight ACOT1 and unsaturated fatty acid metabolism as promising targets for future drug development.
Because the research was conducted in rats and isolated cells, further studies will be needed to determine whether OL is safe and effective in humans.