apigenin and hesperetin

Recent in vivo studies in humans have shown a dramatic effect of grapefruit juice in blocking the oxidation of dihydropyridine calcium channel blockers. The flavonoid naringin is the most abundant natural product specific for grapefruit and related citrus--the aglycone naringenin, known to be readily formed from naringin in humans, was found to inhibit the oxidation of the dihydropyridines nifedipine and felodipine in human liver microsomal preparations. These observations were of interest in light of the knowledge that the same human liver cytochrome P450 (IIIA4) appears to be a major catalyst in both nifedipine oxidation and aflatoxin B1 activation. Several flavones inhibited the in vitro activation of aflatoxin B1 in a system employing umuC gene activation due to DNA damage in Salmonella typhimurium TA1535/pSK1002, with naringenin being as effective as any. The high concentration of derivatives of naringenin in certain citrus fruits may be of relevance to cancer chemoprevention involving those carcinogens that are activated by cytochrome P-450IIIA4.

Topics: Aflatoxins; Chamomile; Chromatography, High Pressure Liquid; Dihydropyridines; Felodipine; Flavanones; Flavins; Flavonoids; Gene Expression Regulation; Hesperidin; Humans; In Vitro Techniques; Kaempferols; Microsomes, Liver; Oils, Volatile; Plants, Medicinal; Quercetin; Transcriptional Activation

Strains of Rhizobium leguminosarum biovar viciae specifically make an abundant protein (Rhi) in free-living culture but not in bacteroids. Genes needed for Rhi synthesis are on a Sym plasmid and here we show that one of these genes, rhiA, is the structural gene that specifies this polypeptide. Transcription of rhiA requires a regulatory gene, rhiR, located close to rhiA and to nod genes involved in nodulation. Mutations in rhiA or rhiR do not appear to affect symbiotic nitrogen fixation. Transcription of rhiA is repressed in cells grown in the presence of the flavanone hesperetin or the flavone apigenin, both of which are potent inducers of transcription of nod genes. This was deduced from the use of rhiA-lacZ fusions; however, when the Rhi polypeptide was detected in SDS gels, there was no apparent difference in the intensity of its staining in extracts obtained from cells grown with or without these flavanoid nod gene inducer molecules. However, a mutation in a nodulation gene, nolR, also closely linked to the nod and rhi genes, caused a severe depression in the amount of Rhi (as seen on gels) that was made in cells grown in the presence of inducer flavanoids.

Topics: Bacterial Proteins; Chamomile; Flavonoids; Gene Expression Regulation; Genes; Genes, Bacterial; Genes, Regulator; Hesperidin; Nitrogen Fixation; Oils, Volatile; Plants, Medicinal; Plasmids; Restriction Mapping; Rhizobium; Transcription, Genetic