Obakulactone reduces joint swelling in arthritis-model rats

Obakulactone reduced joint swelling and inflammatory markers over 21 days in rats given three dose levels, according to a Higher Education Press research release dated Oct. 21 and posted by ScienceDaily Oct. 22.

Evidence grade: Early (small, animal, cell or preprint). The result matters because rheumatoid arthritis affects approximately 1% of people worldwide, but the compound has been tested in rats and laboratory cells, not in patients.

The findings were published in the journal _Engineering_, according to the release. Obakulactone, or OL, is a naturally occurring tetracyclic triterpenoid, a plant chemical with four connected ring structures, extracted from _Phellodendri cortex_, a type of plant bark.

Researchers used complete Freund's adjuvant, a substance that triggers a strong inflammatory response, to create a rat model that resembles some features of rheumatoid arthritis. The release said obakulactone-treated rats had less joint swelling and joint tissue that moved closer to normal appearance.

The study also reported changes in the synovium, the thin tissue lining a joint, and cartilage, which can be damaged in rheumatoid arthritis. The thymus and spleen, two immune-system organs, also showed improvement in disease-related changes, according to the release.

The immune findings were broad but preclinical. Obakulactone reduced CD3+ T cells and CD68+ macrophages in joint tissue, shifted macrophages away from an inflammation-promoting M1 state toward an inflammation-resolving M2 state, and suppressed development of CD4+ T cells into Th17 cells, which are associated with autoimmune inflammation.

Blood measures moved in the same direction, according to the release. The compound reduced inflammatory cytokines, which are immune-signaling proteins, including IL-1β, IL-6, IL-17 and TNF-α. It also lowered rheumatoid factor, anti-cyclic citrullinated peptide antibodies, C-reactive protein and matrix metalloproteinase-3, with larger reductions at higher dose levels.

The proposed mechanism centers on fatty acid metabolism. Using metabolomics, MALDI mass spectrometry imaging and proteomics, the researchers reported that obakulactone helped correct abnormalities in unsaturated fatty acids, including arachidonic acid, linoleic acid and α-linolenic acid.

Further cell experiments used rheumatoid arthritis synovial fibroblasts, cells that help maintain the joint lining but can become inflammatory and tissue-damaging in the disease. Obakulactone slowed their growth, reduced cytokine production and encouraged apoptosis, the controlled removal of unwanted or damaged cells, according to the release.

The researchers identified acyl coenzyme A thioesterase 1, or ACOT1, as a direct molecular target. Binding tests produced dissociation constants of (6.18 ± 0.26) μmol·L⁻¹ by microscale thermophoresis and (6.34 ± 0.38) μmol·L⁻¹ by surface plasmon resonance. A dissociation constant describes binding strength between two molecules, with lower values generally indicating tighter binding.

The release said obakulactone promoted ACOT1 breakdown through the ubiquitin-proteasome pathway, the cell system that marks proteins for disposal. That was linked to lower stearoyl-CoA desaturase-1 activity and reduced signaling through JAK-STAT and PI3K-AKT pathways, which help control cell survival, growth and inflammatory responses.

The study cannot show that obakulactone is safe or effective for people with rheumatoid arthritis. The release did not provide the number of rats, absolute effect sizes, human dosing information, funding details or declared conflicts. Animal models and isolated cells can identify biological targets, but they often fail to predict clinical benefit.

The finding applies to a complete Freund's adjuvant rat model and rheumatoid arthritis synovial fibroblasts, not to adults or children living with rheumatoid arthritis. The next step described in the release is additional research to determine whether the compound can be developed safely and effectively for humans.

Source: research release, Higher Education Press via ScienceDaily, Oct. 22.

Atlas360 reports health research and does not provide medical advice.