Therapeutic potential of d-limonene in rheumatoid arthritis: Modulation of inflammatory, anti-inflammatory cytokines, and prostaglandin E2.

Rheumatoid arthritis (RA) is a persistent autoimmune disorder predominantly affecting the joint structures, eliciting inflammatory responses, and ultimately leading to degenerative changes without proper medical intervention. Ultimately, this can severely impair joint function and impact the patient's quality of life. Current treatment approaches include disease-modifying anti-rheumatic drugs, non-steroidal anti-inflammatory drug, corticosteroids, and biologic therapies for RA management. The current study contributes to the ongoing advancements in RA treatment. d-Limonene is a monocyclic monoterpene. It is present in essential oils of various aromatic plants, such as Lippia alba and Artemisia dracunculus, and in citrus fruits such as lemon and orange. It has reported anti-inflammatory and anti-nociceptive properties and was selected for the current study as a potential anti-arthritic candidate. It was administered at three dosages (25, 50, 100 mg/kg, b.w., p.o) in Complete Freund's adjuvant-induced arthritic rats over 28 days. The efficacy of the compound was compared to piroxicam, a widely used standard drug for treating RA. The anti-arthritic activity of the compound was assessed by measuring arthritic scoring and plethysmometry at both baseline and post-intervention stages. Additional confirmation of the investigation was sought by performing biochemical and hematological activities. Moreover, quantitative polymerase chain reaction was employed to determine the levels of messenger RNA expression for transcription factors such as tumor necrosis factor-α, interleukin (IL)-1β, nuclear factor-κB, matrix metalloproteinase-3, IL-6, and IL-4 in the blood. The levels of PGE2 were evaluated by enzyme-linked immunosorbent assay. The histopathological and radiographic studies were also carried out for further confirmation. The results of these findings supported our assertion regarding the anti-arthritic potential of the compound.