Inhibitory effects of cucurbitacin R on lymphocyte proliferation and cytokine production

Cucurbitacin R (CCR) isolated from tayuya roots reduced both the acute and subchronic inflammation in different experimental models [1]. In addition, its acetyl-derivative showed inhibitory effects in a model of adjuvant-induced arthritis [2]. In order to gain insight into the mechanism of action of CCR, we studied its effect not only on lymphocyte proliferation induced by phytohemagglutinin (PHA), but also on the lymphocyte cell cycle. In addition, we examined its influence on the production of cytokines, and the effects on cyclins A₁, B₁, D₂ and E₂ and the transcription factors involved in inflammation. CCR strongly inhibited lymphoproliferation with an IC₅₀ value of 16µM, arresting the cell cycle in the G₀ phase. Inhibition of lymphoproliferation and on cell cycle disappeared with time. Western blot analysis was used to show CCR's effects on assayed cyclins. The production of mediators such as IL-2, IL-4, IL-10, TNF-α and IFN-γ by human lymphocytes was also significantly inhibited by CCR, with IC₅₀ values of 18µM for interleukins, 12µM for IFN-γ, and 15µM for TNF-α. The PCR analysis showed a clear inhibition of all these cytokines. In Jurkat cells, a total inhibition of the nuclear factor of T activated cells (NF-AT) was observed at a 50µM concentration of CCR. AP-1 remained unaffected. These results indicate that lymphocyte proliferation is inhibited by CCR through NF-AT blocking, which reduces cytokine production.

Acknowledgements: J.M.E. is recipient of a grant from the Generalitat Valenciana. This work was supported by the Spanish Government (SAF2002–00723)

References: 1. Recio, M.C. et al. (2004), Planta Med. 70: 414–420. 2. Escandell, J. et al. (2006), Eur. J. Pharmacol. 532:145–154.