licoflavone-c and 8-prenylnaringenin

Flavonoids display several biological activities, but exhibit poor oral absorption and rapid metabolism. To improve their pharmacological profile four C8-prenyl flavonoids, structurally related to the anti-inflammatory lead apigenin, were synthesized, and the two least cytotoxic (IC(50)>30 microM) compounds [8-prenylnaringenin (8-PN) and 8-prenylapigenin (8-PA)] in RAW 264.7 murine macrophages were assayed against a panel of biological targets. The anti-inflammatory properties of these compounds were evaluated in an in vitro model of inflammation [cells exposed to 0.1 microg/ml lipopolysaccharide (LPS) for 24h]. Both 8-PN and 8-PA were equally effective and potent in inhibiting the LPS-induced gene expression [tumor necrosis factor (TNF)-alpha, inducible nitric oxide synthase (iNOS), cyclooxygenase (COX)-2] (RT-PCR) and release (ELISA) of pro-inflammatory mediators [TNF-alpha, NO, prostaglandin (PG)E(2)], through mechanisms involving the inhibition of nuclear factor-kappaB (NF-kappaB) activation (EMSA) and reactive oxygen species accumulation [2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) determination]. One-digit nM concentrations of 8-PN or 8-PA induced a significant increase in the basal production of the atheroprotective prostacyclin (PGI(2)) by human umbilical vein endothelial cells (HUVEC), with maximal effects at 10 nM. Both NS-398, a specific COX-2 inhibitor, and ICI 182 780, a non-selective estrogen receptor antagonist, abolished the activity of these compounds, suggesting a COX- and estrogen receptor-dependent mechanism of activity. 8-PA, a weaker estrogenic compound than 8-PN, resulted only 2-fold less potent than 8-PN in potentiating PGI(2) production by HUVEC, qualifying this C8-prenyl flavonoid as a lead for the rational design of new anti-inflammatory and vascularprotective compounds.

Topics: Animals; Anti-Inflammatory Agents; Antioxidants; Blood Vessels; Cell Line; Cyclooxygenase 1; Cyclooxygenase 2; Dinoprostone; Endothelial Cells; Epoprostenol; Flavanones; Flavones; Gene Expression Regulation; Humans; Mice; NF-kappa B; Nitric Oxide; Nitric Oxide Synthase Type II; Prenylation; Tumor Necrosis Factor-alpha

The female flowers of hops are used throughout the world as a flavoring agent for beer. Recently, there has been increasing interest in the potential estrogenic properties of hop extracts. Among the possible estrogenic compounds in hops, 8-prenylnaringenin is perhaps most significant due to its high in vitro potency exceeding that of other known phytoestrogens. Since data regarding the pharmacokinetic properties of this compound are lacking, we investigated the in vitro metabolism of 8-prenylnaringenin by human liver microsomes. A total of 12 metabolites were identified, and biotransformation occurred on the prenyl group and the flavanone skeleton. The major site of oxidation was on the terminal methyl groups, and of the two possible isomers, the transisomer was more abundant. The double bond on the prenyl group was also oxidized to an epoxide that was opened by intramolecular reaction with the neighboring hydroxyl group. On the flavanone skeleton, the major site of oxidation was at 3'position on the B ring. Other metabolites included oxidation at carbon-3 as well as desaturation of the C ring to produce 8-prenylapigenin. An unusual hydroxy quinone product formed by ipso hydroxylation of the B ring of 8-prenylnaringenin was also detected. This product was probably an intermediate for the B ring cleavage product, 8-prenylchromone.

Topics: Chromatography, Liquid; Flavanones; Flavones; Humans; Humulus; In Vitro Techniques; Isoflavones; Kinetics; Mass Spectrometry; Microsomes, Liver; Phytoestrogens; Plant Preparations