Inhibitory effects of polyphenols from grape pomace extract on collagenase and elastase activity.

Breakdown and disorganization of extracellular matrix proteins like collagen, fibronectin and elastin are main characteristics of skin aging due to the enhanced activation of proteolytic enzymes such as collagenases and elastases. Inhibition of their enzymatic activities by natural plant compounds might be a promising approach to prevent extrinsic skin aging. Especially polyphenols are supposed to interact with those enzymes due to their molecular nature. In our investigation, extracts of pomace from Riesling grapes were analyzed for their inhibitory properties on collagenase as well as elastase. Crude grape pomace extract showed a dose-dependent inhibitory activity against both enzymes with IC50-values of 20.3µg/ml and 14.7µg/ml for collagenase and elastase activity, respectively. The extracts were fractionated into four fractions containing phenolic compounds differing in chemical structure and polarity. Except for the stilbene containing fraction, all other fractions showed inhibitory effects on both enzyme activities. The most pronounced impact was found for the hydrophilic low molecular weight polyphenols containing the free phenolic acids. In particular, gallic acid showed considerable inhibition values. EGCG was used as a positive control and showed a dose-dependent inhibition of collagenase activity (IC50=0.9mM).

Oxidative metabolism of the mycotoxins alternariol and alternariol-9-methyl ether in precision-cut rat liver slices in vitro.

SCOPE: Monohydroxylation of alternariol (AOH) and alternariol-9-methyl ether (AME) has previously been reported as a prominent metabolic route under cell-free conditions. This pathway gives rise to several catechol metabolites and may therefore be of toxicological relevance. METHODS AND RESULTS: To clarify whether hydroxylation of AOH and AME occurs under in vivo-like conditions in the presence of conjugation reactions, the metabolism of the Alternaria toxins has now been studied in precision-cut rat liver slices. Four catechol metabolites of AOH and two of AME, together with several of their O-methylation products, as catalyzed by catechol-O-methyl transferase, were clearly identified after incubation of the liver slices with AOH and AME. These metabolites were predominantly present as conjugates with glucuronic acid and/or sulfate. In preliminary studies with bile duct-cannulated male rats dosed with AOH by gavage, the four monohydroxylated metabolites of AOH could also be demonstrated in the bile either as catechols or as O-methyl ethers. CONCLUSION: These experiments clearly show that AOH and AME undergo catechol formation in vivo and warrant closer examination of the toxicological significance of this metabolic pathway.