Effect of daidzein in rats on cadmium excretion

Abstract

Cadmium (Cd) is a very toxic contaminant that has a long biological half-life in both humans and animals. This toxic metal can lead to itai-itai disease (Friberg et al., 1986), kidney tubular dysfunction (Friberg et al., 1984, 1986; Om et al., 2002) and cancer (Waalkers et al., 1999; Itokawa et al., 1978). Among these characteristic symptoms, Cd typically gives rise to renal dysfunction since the kidneys are a main route of excretion. Recently, there have been several reports on Cd exposure to humans in Korea (http://www.hani.co.kr). As a result, there has been increased public awareness and concern for cadmium exposure among the public. There have been many studies on Cd detoxification and excretion by protein (Ryu and Kim, 1996), dietary fiber (Bae et al., 1997), and minerals such as calcium (Walter et al., 2000; Whelton et al., 1997), copper (Glover and Hogstrand, 2003; Reeves and Chaney, 2001), and zinc (Glover and Hogstrand, 2003; Reeves and Chaney, 2001) as well as vitamins (Brzoska et al., 2001; Kurata et al., 2001). Moreover, some natural products have been potentially used to inhibit heavy metal accumulation and intoxication by stimulating excretion from the body. Recently, green tea catechin has shown effects on reduction in heavy metal accumulation and intoxification by promoting excretion from the body (Choi et al., 2003). Like catechin, genistein has polyphenol rings that are believed to play a role in binding them to hydroxyl groups in its structure. Paik et al. (2003) had a study on the effect of genistein on female OVX rats treated with 50 ppm of Cd. It demonstrated that genistein has detoxification effects on inhibiting the absorption of Cd as well as increasing its excretion.

Cd can act as an endocrine disruptor by altering the homeostatic balance of a variety of hormones (Takiguchi and Yoshihara, 2006). In particular, acute exposure of female rats to Cd can also decrease progesterone production, and this effect is dependent on the stage of the estrus cycle (Piasek and Laskey, 1994, 1999). More recent work has shown that Cd may have estrogenic properties (Hall et al., 2001) that share certain similar cellular pathways to estrogen. Furthermore, Cd can also alter the hormonal balance and may exert estrogenic effects via interaction with ERs. Accordingly, Pillet et al. (2006) suggest that females may be at a greater risk than males for Cd-induced immunomodulation.

Most studies on soy isoflavones are done with genistein. Genistein (5,7,4-trihydroxyisoflavone) and daidzein (7,4-dihydroxyisoflavone) have weak estrogen activity as phytoestrogens which have a similar structure to estrogen. It is believed that daidzein may bind with metal ions to form an insoluble complex-ionic salt used to remove heavy metals by a hydroxyl group and polyphenol (Joseph and Michael, 1999). However, few studies have been conducted with daidzein to examine its detoxification effect particularly using OVX rats.

Therefore, this study was undertaken to investigate the influence of daidzein on Cd excretion in 50 ppm of Cd-treated OVX rats. The data obtained may provide basal information about prevention of cadmium toxicity in the interest of public health.