title: Mechanisms underlying the inhibitory actions of the pentacyclic triterpene alpha-amyrin in the mouse skin inflammation induced by phorbol ester 12-O-tetradecanoylphorbol-13-acetate.
abstract: The present study evaluated some of the mechanisms through which alpha-amyrin, a pentacyclic triterpene isolated from Protium Kleinii and other plants, exerts its effects against 12-O-tetradecanoylphorbol-acetate (TPA)-induced skin inflammation in mice. Topical application of alpha-amyrin (0.1-1 mg/ear) dose-dependently inhibited TPA-induced increase of prostaglandin E2 (PGE2) levels. In contrast with the selective cyclooxygenase (COX)-1 SC560 [5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-trifluoromethylpyrazole] or COX-2 rofecoxib inhibitors, alpha-amyrin failed to alter either COX-1 or COX-2 activities in vitro. Western blot analysis revealed that alpha-amyrin dose-dependently inhibited TPA-induced COX-2 expression in the mouse skin. The evaluation of nuclear factor-kappaB (NF-kappaB) pathway revealed that topical treatment with alpha-amyrin is able to prevent IkappaB alpha degradation, p65/RelA phosphorylation and NF-kappaB activation. Moreover, alpha-amyrin given topically dose-dependently inhibited the activation of upstream protein kinases, namely extracellular signal-regulated protein kinase (ERK), p38 mitogen-activated protein kinase (MAPK) and protein kinase C (PKC)alpha, following topical TPA treatment. Collectively, present results suggest that topical skin application of alpha-amyrin exerts a strong and rapid onset inhibition of TPA-induced inflammation. These effects seem to be associated with the suppression of skin PGE2 levels by mechanisms involving the suppression of COX-2 expression, via inhibition of upstream protein kinases--namely ERK, p38 MAPK and PKCalpha--and blocking of NF-kappaB activation. These results indicate that alpha-amyrin-derivative could be potentially relevant for the development of a topical agent for the management of inflammatory diseases.
authors.affiliation: Departamento de Farmacologia, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina, Florianópolis, SC, Brazil.
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Medeiros
authors.forename: Michel F
authors.initials: MF
authors.lastname: Otuki
authors.forename: Maria Christina W
authors.initials: MC
authors.lastname: Avellar
authors.forename: João B
authors.initials: JB
authors.lastname: Calixto
mesh_terms: D000287:Administration, Topical; D000818:Animals; D000893:Anti-Inflammatory Agents / Q000008:administration & dosage / Q000494:pharmacology* / Q000627:therapeutic use; D051545:Cyclooxygenase 1 / Q000378:metabolism; D051546:Cyclooxygenase 2 / Q000096:biosynthesis; D003877:Dermatitis, Contact / Q000209:etiology / Q000378:metabolism / Q000517:prevention & control*; D015232:Dinoprostone / Q000378:metabolism; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D004790:Enzyme Induction / Q000187:drug effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D020672:I-kappa B Proteins / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D016328:NF-kappa B / Q000378:metabolism; D009828:Oleanolic Acid / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000627:therapeutic use; D010766:Phosphorylation; D051571:Protein Kinase C-alpha / Q000378:metabolism; D012867:Skin / Q000187:drug effects* / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate; D013997:Time Factors; D051996:Transcription Factor RelA / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D000893:Anti-Inflammatory Agents; D020672:I-kappa B Proteins; D008565:Membrane Proteins; D016328:NF-kappa B; D051996:Transcription Factor RelA; D009828:Oleanolic Acid; D051545:Cyclooxygenase 1; D051546:Cyclooxygenase 2; C496512:Ptgs1 protein, mouse; D051571:Protein Kinase C-alpha; D048049:Extracellular Signal-Regulated MAP Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D015232:Dinoprostone; C036380:beta-amyrin; D013755:Tetradecanoylphorbol Acetate