Hop bitter acids efficiently block inflammation independent of GRalpha, PPARalpha, or PPARgamma.
Hop (Humulus lupulus L.) is an essential ingredient of beer, where it provides the typical bitter taste, but is also applied in traditional folk medicine for sedative and antibacterial purposes. In this study, we demonstrate and compare the anti-inflammatory effect of various classes of hop bitter acids (HBA), including alpha-acids (AA), beta-acids (BA), and iso-alpha-acids (IAA), in fibroblasts, which are important players in the inflammatory response. All three studied classes of HBA blocked the tumor necrosis factor alpha (TNF)-induced production of the cytokine IL6, and inhibited the transactivation of the pro-inflammatory transcription factors nuclear factor kappa B (NF-kappaB), activator protein-1 (AP-1), and cAMP-response element-binding protein (CREB). In this respect, the six-membered ring compounds AA and BA showed equal potency, whereas the five-membered ring compounds, IAA, were effective only when used at higher concentrations. Furthermore, with regard to the mechanism of NF-kappaB suppression, we excluded a possible role for glucocorticoid receptor alpha (GRalpha), peroxisome proliferators-activated receptor alpha/gamma (PPARalpha or PPARgamma), nuclear receptors (NRs) that are also known to inhibit inflammation by directly interfering with the activity of pro-inflammatory transcription factors. Interestingly, combining hop acids and selective agonists for GRalpha, PPARalpha, or PPARgamma resulted in additive inhibition of NF-kappaB activity after TNF treatment, which may open up new avenues for combinatorial anti-inflammatory strategies with fewer side effects. Finally, systemic administration of HBA efficiently inhibited acute local inflammation in vivo.
Van Cleemput
Marjan
M
Laboratory of Eukaryotic Gene Expression and Signal Transduction (LEGEST), Department of Physiology, Ghent University, Gent, Belgium.
Heyerick
Arne
A
Libert
Claude
C
Swerts
Katrien
K
Philippé
Jan
J
De Keukeleire
Denis
D
Haegeman
Guy
G
De Bosscher
Karolien
K
D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology*; D045744:Cell Line, Tumor; D017362:Cyclic AMP Response Element-Binding Protein / Q000502:physiology; D005260:Female; D006801:Humans; D027582:Humulus / Q000737:chemistry*; D015850:Interleukin-6 / Q000096:biosynthesis; D051379:Mice; D008810:Mice, Inbred C57BL; D016328:NF-kappa B / Q000037:antagonists & inhibitors; D047493:PPAR alpha / Q000502:physiology*; D047495:PPAR gamma / Q000502:physiology*; D011965:Receptors, Glucocorticoid / Q000502:physiology*; D018808:Transcription Factor AP-1 / Q000502:physiology; D014158:Transcription, Genetic / Q000187:drug effects
D000893:Anti-Inflammatory Agents; D017362:Cyclic AMP Response Element-Binding Protein; D015850:Interleukin-6; D016328:NF-kappa B; D047493:PPAR alpha; D047495:PPAR gamma; D011965:Receptors, Glucocorticoid; D018808:Transcription Factor AP-1; C411470:glucocorticoid receptor alpha