Alfalfa isoflavones

Cooper, J.D., Qiu, F., and Paiva, N.L., Biotransformation of an exogenously supplied isoflavo-noid by transgenic tobacco cells expressing alfalfa isoflavone reductase. Plant Cell Rep., 20, 876, 2002. 

Oommen A, Dixon RA, Paiva NL. 1994. The elicitor-inducible alfalfa isoflavone reductase promoter confers different patterns of developmental expression in homologous and heterologous transgenic plants. Plant Cell 6 1789-1803. 

Recently, the crystal structure of one such SMOMT from alfalfa, isoflavone OMT (IOMT), was solved.37 The likely reaction mechanism of this OMT, deduced from the crystal structure, involves the base-assisted deprotonation of the acceptor s hydroxyl group, followed by a nucleophilic attack by the subsequent phenolate anion on the reactive methyl group of SAM. Modeling of related SMOMTs using the crystal structure of IOMT has also proven useful in understanding the evolution of... 

Paiva, N.L. et al. (1991) Stress responses in alfalfa Medicago sativa L.) 11. Molecular cloning and expression of alfalfa isoflavone reductase, a key enzyme of isoflavonoid phytoalexin biosynthesis. Plant Mol. Biol. 17, 653-667... 

An inverse correlation between thyroid cancer risk and phytoestrogens was recently proposed as a result of a multi-ethnic population-based case control study conducted in the San Francisco Bay Area (Hom-Ross et al., 2002). In this study, dietary habits and phytoestrogen consumption were assessed by a food-frequency questionnaire and by a nutrient database. The outcome of the study was that soy-based foods and alfalfa sprouts were associated with a reduction of thyroid cancer risk, whereas a Western diet did not influence cancer risk. No difference was observed between American and Asian women or between pre- and postmenopausal women. Furthermore, among the few compounds examined, the isoflavones genistein and daidzein and the lignan secoisolariciresinol were the phytoestrogens most frequently associated with risk reduction (Horn-Ross et al., 2002). 

The three main classes of phytoestrogens (and common food sources) are isoflavones (soybeans), lignans (cereals and oilseeds such as flaxseed), and coumestans (alfalfa sprouts). The biologic potency of phytoestrogens varies and is less than that of synthetic estrogen. 

He X-Z, Dixon RA. 2000. Genetic manipulation of isoflavone 7-O-methyltransferase enhances biosynthesis of 4 -0-methylated isoflavonoid phytoalexins and disease resistance in alfalfa. Plant Cell 12 1689-1702. 

HE, X.-E., REDDY, J.T., DIXON, R.A., Stress responses in alfalfa (Medicago saliva L.). XXII. cDNA cloning and characterization of an elicitor-inducible isoflavone 7-O-methyltransferase. Plant Mol. Biol., 1998,36,43-54. 

HE, X.Z., DIXON, R.A., Affinity chromatography, substrate/product specificity, and amino acid sequence analysis of an isoflavone O-methyltransferase from alfalfa (Medicago sativa L.), Arch. Biochem. Biophys., 1996,336,121-129. 

Coumestrol (89) from alfalfa, Medicago sativa, and clover, Trifolium repens, is a more active estrogenic compound than simple isoflavones. Although it is 30 times more active than genistein (43) or formononetin (82), coumestrol occurs at lower concentrations and has less total effect (McClure, 1975 Wong, 1975). 

Barz and Welle, 1992). In both instances, an NADPH isoflavone oxidoreductase reduces a 2 - or 5 -hydroxyisofla-vone to the corresponding isoflavanone. This reaction is followed by the formation of pterocarpans catalyzed by ptero-carpan synthase. The pathways in soybean, pea (pisatin), and alfalfa (medicarpin) all reflect a high degree of homology (Barz and Welle, 1992). 

Clinical trials have supported the efficacy of isoflavones such as genistein, found in soymilk and other soy products, in prevention of breast tumours and other cancers, as well as alleviating hot flushes and other symptoms associated with the menopause (Albert et al. 2002). Isoflavones are also found in liquorice (Glycyrrhiza glabra), alfalfa Medicago sativa), black cohosh (Cimicifuga racemosa) and red clover (Trifolium pratense). 

Some commercial solid extracts of red clover have been reported to contain traces of cannabinol, caffeine, scopolamine, isocou-marin, phenylpentadienal, phenylhexadiene, and nepetalactone (see alfalfa) Contents of the major isoflavone constituents show wide variability. 

Red clover has shown estrogenic properties in animals that are due to its isoflavones (see alfalfa). Oral administration of a red... 

The three major chemical types of phytoestrogens that have been identified are flavones, isoflavones, and coumestans. The estrogenic potency of these com pounds is variable. The flavones are weak estrogens. The methoxyflavone, tricin, is a constituent of alfalfa and weakly estrogenic in the mouse. 

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