Scientists have identified a natural plant compound that could offer a surprising new approach in the fight against rheumatoid arthritis. In experiments on rats, the substance reduced joint swelling, protected cartilage, and calmed harmful immune activity. Researchers also discovered that it works through an unexpected mechanism involving the way the body processes fat.
The results, published in the journal Engineeringcentered on a compound called obakulactone (OL), a natural tetracyclic triterpenoid extracted from Phellodendrial cortexa type of plant bark. Tetracyclic triterpenoids are plant chemicals characterized by a structure containing four interconnected rings.
Researchers have found that obakulactone helps restore the balance of unsaturated fatty acids, which play an important role in cellular function and inflammation. It does this by promoting the degradation of a protein called acyl coenzyme A thioesterase 1 (ACOT1), using the cell’s natural protein removal system, known as the ubiquitin-proteasome pathway.
By identifying this previously underexplored molecular target, the study suggests that changing the way cells process fatty acids could become a new strategy for treating rheumatoid arthritis (RA).
Natural compound reduces inflammation from arthritis and joint damage
To study the effects of this compound, scientists created a rat model of rheumatoid arthritis using complete Freund’s adjuvant (CFA), a substance that triggers a strong inflammatory response resembling certain characteristics of the disease.
The animals received obakulactone for 21 days at three different daily doses: low (50 mg·kg⁻¹·d⁻¹), medium (100 mg·kg⁻¹·d⁻¹), and high (200 mg·kg⁻¹·d⁻¹). These quantities were calculated based on body weight.
The results were encouraging. Rats treated with the compound showed significantly less joint swelling, while the structure of their cartilage and synovium returned to normal. The synovium is the thin membrane that covers the joints and produces a lubricating fluid and can become seriously inflamed in rheumatoid arthritis.
The treatment also improved disease-related changes in the thymus and spleen, two organs that play important roles in the immune system.
Beyond these physical improvements, researchers observed major changes in immune activity. Obakulactone reduced elevated levels of CD3⁺ T cells and CD68⁺ macrophages in joint tissues. These immune cells normally help defend the body, but they can contribute to persistent inflammation and tissue damage when the immune system becomes overactive.
The compound also shifted macrophages from an inflammation-promoting M1 state (CD86) to an M2 state (CD206) that better resolves inflammation. At the same time, it suppressed the development of CD4⁺ T cells into Th17 cells, a type of immune cell associated with autoimmune inflammation.
Blood tests provided additional evidence of these effects. Obakulactone reduced several inflammatory signaling proteins, including IL-1β, IL-6, IL-17, and TNF-α. These proteins, called cytokines, help immune cells communicate, but can also intensify inflammation when produced in excessive amounts.
The treatment also reduced blood markers linked to rheumatoid arthritis, including rheumatoid factor (RF), anti-cyclic citrullinated peptide antibodies (CCP-Ab), C-reactive protein (CRP), and matrix metalloproteinase-3 (MMP-3). The reductions became more pronounced as the dose increased.
Scientists discover surprising link between fat metabolism and arthritis
One of the study’s most intriguing findings involved fatty acids, molecules typically associated with nutrition and energy storage, but which also influence inflammation throughout the body.
Using several advanced analytical methods, including metabolomics, MALDI mass spectrometry imaging, and proteomics, researchers examined how obakulactone affected chemical processes inside tissues.
These techniques allowed them to study changes in small molecules, map their distribution in tissues, and measure differences in protein levels.
The analysis revealed that the compound helped correct abnormalities in the production and breakdown of unsaturated fatty acids (e.g., arachidonic acid, linoleic acid, and α-linolenic acid).
These fatty acids are important components of cell membranes and may serve as raw materials for molecules that regulate inflammation. Arachidonic acid, in particular, is involved in the production of several powerful inflammatory signals.
In rats with arthritis, obakulactone helped bring these disrupted metabolic processes back to a healthier balance. This suggests that its benefits go beyond simply suppressing immune activity.
Hidden protein emerges as potential treatment target
To understand exactly how the compound works, the scientists conducted additional laboratory experiments on rheumatoid arthritis synovial fibroblasts (SF).
These cells help maintain the tissues lining the joints. However, in rheumatoid arthritis, they can become abnormally aggressive, multiplying excessively, releasing inflammatory substances, and contributing to cartilage damage and tissue scarring.
Obakulactone slowed the growth of these cells, reduced their production of inflammatory cytokines, and promoted apoptosis, the controlled process by which the body eliminates unwanted or damaged cells.
The researchers then studied which protein the compound acted directly on.
Using cellular thermal shift, microscale thermophoresis, and surface plasmon resonance assays, they identified ACOT1 as a direct molecular target of obakulactone.
Binding measurements produced a dissociation constant (Kd) (6.18 ± 0.26) μmol.L⁻¹ (analyzed by microscopic thermophoresis (MST)) and (6.34 ± 0.38) μmol.L⁻¹ (analyzed by surface plasmon resonance (SPR)).
These closely concordant results provided evidence that the compound physically interacts with ACOT1. A dissociation constant describes the strength with which two molecules bind to each other, with lower values generally indicating a tighter bond.
It is important to note that obakulactone did more than bind to the protein. It promoted the destruction of ACOT1 by the ubiquitin-proteasome system, a cellular mechanism that marks proteins for elimination and breaks them down.
This process reduced the activity of several downstream mechanisms associated with inflammation and abnormal cellular behavior.
How targeting a protein can disrupt inflammation
When ACOT1 was broken down, levels of another enzyme called stearoyl-CoA desaturase-1 (SCD1) also decreased. This enzyme helps regulate the production of certain unsaturated fatty acids.
The changes then suppressed two major cellular signaling networks: Janus kinase signal transducer (JAK) and activator of transcription (STAT) and phosphoinositide 3-kinase (PI3K)-protein kinase B (AKT).
These pathways act as internal communication systems, carrying signals that influence how cells grow, survive, and respond to their environment. When their activity becomes abnormal, they can contribute to inflammation and excessive tissue growth.
By interfering with these signals, obakulactone reduced inflammation and fibrosis, a process involving excessive accumulation of scar-like connective tissue, in rheumatoid arthritis synovial fibroblasts.
Additional experiments, including rescue assays and studies using molecular inhibitors, strengthened the evidence that ACOT1 was central to these effects.
The researchers confirmed that the compound’s ability to reduce inflammation, slow abnormal cell proliferation, and promote apoptosis depended on its influence on ACOT1, the arachidonic acid pathway, and downstream JAK-STAT/PI3K-AKT signaling pathways.
Together, the findings suggest a potential way to disrupt the biological processes that sustain arthritic inflammation rather than focusing exclusively on suppressing immune responses.
A potential new direction for the treatment of rheumatoid arthritis
Rheumatoid arthritis is a chronic autoimmune disease in which the immune system mistakenly attacks the body’s own tissues, particularly the joints. It affects about 1% of people worldwide and can cause persistent pain, swelling, stiffness and progressive joint damage.
Because it is a systemic disease, rheumatoid arthritis can also affect organs and tissues beyond the joints.
Although existing medications can reduce symptoms and slow the progression of the disease, they don’t work equally well for everyone and some can cause serious side effects. This makes the search for additional therapeutic approaches particularly important.
The new results suggest that obakulactone may become a candidate for future drug development against rheumatoid arthritis. They also identify ACOT1 as a potentially valuable therapeutic target and highlight the importance of unsaturated fatty acid metabolism in controlling inflammation.
However, the results remain preclinical. The compound has been tested in rats and laboratory cells, and further research will be needed to determine whether it is safe and effective in humans.
Even with this limitation, the finding opens up an intriguing possibility: targeting the metabolic machinery that helps trigger inflammation could provide another way to combat rheumatoid arthritis and potentially protect joints from lasting damage.
Gn Health
