Effect of Chlorella pyrenoidosa on fecal excretion and liver accumulation of polychlorinated dibenzo-p-dioxin in mice

Abstract

The effect of Chlorella pyrenoidosa on fecal excretion and liver accumulation of polychlorinated dibenzo-p-dioxin in C57BL/6N mice administered dioxin was examined. Mice were administered 2.2 μg of 1,2,3,4,7,8-hexachlorodibenzo-p-dioxin (H₆CDD) dissolved in corn oil once after a period of acclimatization, after which they were fed either a basal diet, a 10% C. pyrenoidosa diet, or a 10% Spinach diet, for five weeks. Among mice fed the 10% C. pyrenoidosa diet, cumulative fecal excretion of H₆CDD over the first week following administration was significantly greater (9.2-fold) than that observed among mice fed the basal diet. Moreover, excretion during the fifth week following administration of H₆CDD was still significantly greater (3.1-fold) among mice fed the 10% C. pyrenoidosa diet than among mice fed the basal diet. Five weeks after administration of H₆CDD, liver accumulation of H₆CDD in mice fed the 10% C. pyrenoidosa diet was significantly less than that observed among mice fed either the basal diet and the Spinach diet (by 27.9% and 34.8%, respectively).

These findings suggest that C. pyrenoidosa may be useful in inhibiting the absorption of dioxins via food and the reabsorption of dioxins stored already in the body in the intestinal tract, thus preventing accumulation of dioxins within the body.

Introduction

Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and co-planar polychlorinated biphenyls (Co-PCBs) are collectively referred to as dioxins. Dioxins are non-intentional by-products produced during industrial processing as a result of combustion reactions, such as those that occur during rubbish incineration and iron manufacturing. They are also produced during the manufacture and use of chloride-containing chemicals (Olie et al., 1983). Dioxins that have been released into the environment can be present in the air, soil, and water. As dioxins display an extremely high chemical stability and are lipid soluble, these chemicals are primarily introduced into the body through food, as a result of biomagnification in the food chain. Approximately 90% of dioxin intake in humans reportedly occurs through food, and in Japan, 60–80% of this intake is through seafood (Takayama et al., 1991, Tsutsumi et al., 2001). Conversely, in Europe and North America, the primary sources of dioxin are meat, eggs, and dairy products (Brimingham et al., 1989, Schecter et al., 1994, Schecter et al., 1995, Jensen and Bolger, 2001). Moreover, daily exposure of humans to dioxin via food has been estimated to range from 0.3 to 3.2 pg of the toxic equivalency quantity (TEQ)/kg body weight/day among the above studies. However, it is understood that the intake of dioxins varies according to the local environment.

Dioxins are absorbed from the digestive tract along with lipids in food due to their lipophilic nature. It has been reported that the digestive tract absorption of the tetra- to hexa-congeners in adult humans via food and in infants via breast milk were also 60–90% of intake (Jödicke et al., 1992, Abraham et al., 1996, Schlummer et al., 1998, Moser and McLachlan, 2001). Furthermore, absorption of 50–90% of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in vegetable oil has been reported in rats, guinea pigs and hamsters (Piper et al., 1973, Rose et al., 1976, Nolan et al., 1979). The biological and toxicological effects of dioxins have been extensively examined in experimental animals, wildlife and humans. TCDD causes both acute and chronic toxicity and has carcinogenic, teratogenic, and immunosuppressive effects in animals (Landers and Bunce, 1991). The effects of dioxins on human health has been investigated in cases of known exposure, such as the Yusho incident in Japan in 1968, and the Yu-Cheng incident in Taiwan in 1979, both of which resulted from the consumption of cooking oil contaminated with dioxins (Hsu et al., 1985, Masuda et al., 1985, Yamashita and Hayashi, 1985). Moreover, it has been reported that the IQs and reading ability of children with a history of high dioxin exposure in utero, following maternal ingestion of contaminated fish from lake Michigan in the USA, were inferior relative to children with low dioxin exposure in utero (Jacobson and Jacobson, 1996). In general, children are more susceptible to dioxin accumulation. Dioxins appear to transfer to fetus via placenta and concentrate within the breast milk, resulting in high pre- and peri-natal exposure. As things stand at the present time, it is difficult for humans to avoid exposure to dioxins, since they are pervasive in the environment. Consequently, in order to prevent health disorders as a consequence of dioxin exposure in humans, dietary measures which both inhibit absorption and promote the excretion of dioxins are a potentially effective means by which to reduce dioxin accumulation. With regard to the promotion of the excretion of lipophilic contaminants, several studies of dietary supplements, such as cholestyramine, mineral oil, hexadecane, and dietary fiber, in laboratory animals have been reported (Boylan et al., 1978, Rozman et al., 1981, Rozman et al., 1982, Morita et al., 1997b). In addition, Moser et al. reported that the enhancing effect of the non-absorbable lipid substitute olestra on the fecal excretion of PCDD/DFs and PCBs in the body in humans (Moser and McLachlan, 1999).

Chlorella pyrenoidosa is one of the supplements or health food widely utilized in Japan, the USA, Europe, and other countries. C. pyrenoidosa is a unicellular green algae that grows in fresh water. It has the highest concentration of chlorophyll and protein of any known plant, and also contains high concentrations of certain vitamins, minerals, dietary fiber, as well as nucleic acid. The protein contained within of C. pyrenoidosa contains all of the essential amino acids required for normal growth and maintenance of health in humans. This algae has a strong cell wall, so that the nutritive components in Chlorella can only be sufficiently digested by humans after breaking the cell wall (Mitsuda et al., 1977). A number of scientific reports have shown that broken cell wall preparations or extracts of C. pyrenoidosa, as well as other Chlorella species, promote human health, stimulate the immune system, thereby protecting the host from infection, and enhancing anticancer activity, when given orally or injected (Konishi et al., 1985, Komiyama et al., 1986, Tanaka et al., 1986, Miyazawa et al., 1988, Merchant et al., 1990).

The purpose of this study was to investigate the effects of C. pyrenoidosa on the fecal excretion and hepatic accumulation of H₆CDD in mice administered H₆CDD, as well as the relation of the fecal excretion of H₆CDD and sterols. The effect of C. pyrenoidosa was compared with those of Spinach, green vegetable.