Plant flavonoids, estrogenic activity

In addition to steroids there are plant flavonoids (Box 21-E) that have estrogenic activity. These labile compounds are among the "environmental estrogens." In addition, there are many much more stable compounds, including the insecticides atrazine and DDT, PCBs, and phenolic softeners for plastics, that have weak estrogenic activity. Alarm has been sounded... 

A number of foodstuffs and plant-derived products, largely from soy, are available as nonprescription items and often are touted as providing benefits similar to those from compounds with established estrogenic activity. These products may contain flavonoids such as genistein, which display estrogenic activity in laboratory tests, albeit generally much less than that of estradiol. In theory, these preparations could produce appreciable estrogenic effects, but their efficacy at relevant doses has not been established in human trials. 

Miksicek, R.J., Commonly occurring plant flavonoids have estrogenic activity, A/o/. PharmacoL, 44, 37, 1993. 

Documented effects A tincture of the plant is used to treat arteriosclerosis in patients with normal blood pressure (Nuraliev 1989). In modem medicine this species is used as an expectorant, diuretic, and antiseptic (Khodzhimatov 1989). Metabolites of isoflavones found in the plant were found to protect against UV radiation-induced inflammation and immunosuppression (Widyarini et al. 2001). Isoflavones found in red clover inhibited COX enzyme activity in certain cancer cell types (Lam et al. 2004). Extracts of red clover and individual flavonoid constituents exhibited estrogenic activity in a variety of in vitro assays (Overk et al. 2005). 

Many plant phenolics are of pharmaceutical interest. Flavonoids, lignans, flavolignans, coumarins, phenyl pro-panoids, and other phenolic compounds show a wide variety of biological and pharmacological activities, such as anti-oxidant, anti-hepatotoxic, spasmolytic, cytotoxic, anti-fungal, and anti-bacterial. Some flavonoids improve capillary resistance while isoflavonoids found in soy and other legumes have estrogenic activity. 

Many plant extracts contain a complex mixture of flavonoids, some of which might contribute directly to particular biological properties of the extract, such as antioxidant, free radical scavenging, or estrogenic activity. The isolation of individual biologically active flavonoids from a complex mixture requires a systematic approach involving a carefully considered selection of solvents and chromatographic stationary supports. 

The mechanism of repulsion or negative chemotaxis in zoospores is not yet kiK)wn, but in bacteria Ix activities are mediated by the modification of common receptor and signal transduction pathways (29). Notably, while several isoflavones with structural similarity to daidzein functioned as chemoattractants for Ph, sojacy many related flavonoids had repellent activities (i9). The importance of flavonoids in the case of Ph. sojae, and estrogenic substances in the case of A. cochlioides, in deterring infection of nonhost plants, certainly warrants additional investigation. 

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