Toll-Like Receptor-dependent immunomodulatory activity of Pycnogenol. Pycnogenol

Background: Pycnogenol® (PYC), a patented herbal extract of French maritime pine bark, consists of a complex mixture of bioflavonoids. The main constituents of PYC are procyanidins; biopolymers consisting of units of catechin (CAT) and epicatechin. PYC is shown to exert immunomodulatory properties, nevertheless its underlying mechanisms are not yet fully elucidated. Methods: In this study, the effect of PYC and its constituent CAT on membrane Toll like receptor (TLR) activity was examined using stably transfected Human Embryonic Kidney cells. The Human monocytic leukaemia cell line THP-1 was used to examine the effect of PYC and CAT on pro-inflammatory cytokine release.Findings: We showed that non-metabolised PYC acts as agonist of TLR1/2, TLR2/6 and a partial agonist of TLR5, which resulted in the induction of pro-inflammatory cytokine secretion from THP-1 macrophages as well as activation of Nf-κB transcription factor. This effect was altered due to gastrointestinal metabolism, which revealed immuno-suppressive potential against TLR 1/2 and TLR 2/6 of the retentate fraction compared to the control sample. Moreover, the dialysed fraction did not show potential to induce pro-inflammatory cytokine secretion by THP-1 macrophages but the capacity to induce anti-inflammatory IL-10. Moreover, we showed that PYC on its own does not activate TLR4 but the formation of complexes with lipopolysaccharides (LPS) is required to stimulate the TLR4 receptor. We found that PYC and PYC-LPS complexes to the same extend dose-dependently increase pro-inflammatory cytokine levels (IL-8, IL-1β and TNF) and upregulate phosphorylation of the transcription factor NF-ĸB. No effects for CAT were observed on TLR activation and pro-inflammatory cytokine production levels. Conclusions: Our study stresses the importance of metabolism for biological activity of PYC compounds. Moreover our results suggest that bot non-metabolised as well as metabolised PYC acts via TLR 1/2 and TLR 2/6 next to TLR4.