Antiobesity effects of seaweeds

Over the past few decades, several studies have focused on fucoxanthin contained in seaweed. Fucoxanthin, a characteristic carotenoid of brown algae, has a unique structure that includes an unusual allenic bond and 5,6-monoepoxide. Wakame (U. pinnatifida), an edible seaweed, is rich in fucoxanthin.

Maeda et al. (2005) reported that fucoxanthin has an antiobesity effect by modifying uncoupling protein 1 (UCP1) expression in white adipose tissue (WAT) in KKAy mice, an animal model of type 2 diabetes with obesity. When fucoxanthin is orally administered to mice, it is metabolized to fucoxanthinol, which is further converted into amarouciaxanthin A (Asai et al., 2004; Sugawara et al., 2002). Fucoxanthin and its metabolite fucoxanthinol have been shown to reduce the expression of peroxisome proliferator-activated receptor (PPAR) g in 3T3-L1 preadipocytes, which in turn inhibits differentiation to mature adipocytes (Maeda et al., 2006), suggesting that fucoxanthin inhibits adipocyte maturation and stimulates UCP1 expression in WAT.

In addition, Maeda et al. (2009) reported that fucoxanthin-rich wakame lipids (WLs) had antiobesity and antidiabetic effects on HFD-induced obesity in mice. The increased expression of monocyte chemoattractant protein-1 (MCP-1) mRNA in HF mice was normalized by ingestion of WL with a HFD. Moreover, the HF-WL diet may ameliorate alterations in lipid metabolism and insulin resistance induced by a HFD by promoting the expression of |b3-adrenergic receptor (Adrb3) mRNA in WAT and glucose transporter 4 (GLUT4) mRNA in skeletal muscle tissues. These results suggest that there is a biochemical and nutritional basis for the application of fucoxanthin-rich WLs for the treatment of obesity and diabetes-related disorders.

The effects of fucoxanthin-rich seaweed extract (Fx-SEE) on body weight gain and lipid metabolism in HF-fed C57BL/6J mice were investigated by Jeon et al. (2010). They demonstrated that Fx-SEE affects the plasma and hepatic lipid profile, fecal lipids, and body fat mass, and alters hepatic cholesterol metabolism, FA synthesis, and lipid absorption in mice.

The antiobesity and antidiabetic effects of some allenic compounds including fucoxanthin were reported by Miyashita et al. (2011). These compounds improved insulin resistance and decreased blood glucose levels through the regulation of cytokine secretions from WAT by inducing UCP1. The key structures of these activities were thought to be an allenic bond and two hydroxyl groups.

Some reports have focused on the alginate contained in seaweed. Sodium alginate from the brown seaweed Laminaria digitata (LD) is currently marketed as a weight-loss supplement, but its effects on gastric motor functions and satiation are unknown. Odunsi et al. (2010) clinically investigated the effects of 10 days of treatment with alginate or placebo on gastric function, satiation, appetite, and gut hormones associated with satiety in overweight or obese adults. They found that treatment with alginate for 10 days had no effect on any of the above parameters. These results suggested that the daily continuous intake of alginates may be required to prevent obesity.

"Tororokombu" (TK) is a traditional Japanese food that is made by shaving Laminaria (kombu) very thinly. Miyata et al. (2009) first investigated the effects of NSK (non-shaved kombu) and TK on the absorption of TGs in the intestine by an oil-loading test in female SD rats (7 weeks old). One feature of this study is the improved efficiency of dissolution of the active component. SD rats were first divided into three groups: distilled water-treated, NSK-treated, and TK-treated groups. Next, corn oil (5 ml/ kg) was administered orally. The elevation of the serum TG level in the NSK- and TK-treated groups was significantly lower than that in the normal rat group.

Next, the antiobesity effects of NSK and TK were investigated by a long-term experiment on obese female ddY mice (4 weeks old) induced by a HFD for 63 days. Mice were divided into four groups: ND (normal diet), HFD, HFD-NSK (HFD containing 3% NSK), and HFD-TK (HFD containing 3% TK) groups. The body weights on the 63rd day after treatment started and the serum TC levels in both the HFD-NSK and the HFD-TK groups were significantly lower than those in the HFD

group. The parauterus adipose tissue weight, and hepatic TG, serum TG, and TC levels in the HFD-TK group were significantly less than those in the HFD-NSK group. The fecal TG and TC levels in the HFD-TK group were significantly higher than those in the HFD group, and fecal TG in the HFD-TK-group was significantly higher than that in the HFD-NSK group. Consequently, it was demonstrated that TK consumption reduced the accumulation of visceral fat caused by HFD, and this effect of TK was more powerful than that of NSK, due to TG and cholesterol excretion in the feces. This report concluded that alginate may be one of the active components in Laminaria sp. In previous reports, alginate has been reported to have hypoglycemic and cholesterol-lowering effects by acting as a viscous soluble dietary fiber (Kimura et al., 1996; Pasquier et al., 1996; Paxman et al., 2008).

The inhibitory activities of NSK and TK against lipase were examined. The inhibitory activities of TK were greater than those of NSK, as shown in Fig. 15.1. In addition, TK had significantly higher alginate content than NSK, as shown in Fig. 15.2. The effects of extracted alginate with weak alkaline solution on lipase activity are shown in Fig. 15.3. Based on these results, alginate was thought to contribute to the inhibition of lipase. A lipase inhibitor should inhibit TG absorption and have an antiobesity effect in vivo (Miyata et al., 2009).

120 r

120 r

Control NSK TK

FIGURE 15.1 Effect of non-shaved kombu (NSK) and tororokombu (TK) on pancreatic lipase activity in vitro. Pancreatic lipase (from porcine) activity was measured using a Lipase Kit S according to the manufacturer's protocol. Data are presented as the mean ± SE (n = 5). *p < 0.05, ***p < 0.005 versus control. #p < 0.05 NSK versus TK.

Control NSK TK

FIGURE 15.1 Effect of non-shaved kombu (NSK) and tororokombu (TK) on pancreatic lipase activity in vitro. Pancreatic lipase (from porcine) activity was measured using a Lipase Kit S according to the manufacturer's protocol. Data are presented as the mean ± SE (n = 5). *p < 0.05, ***p < 0.005 versus control. #p < 0.05 NSK versus TK.

FIGURE 15.2 Alginate content eluted into weak alkaline solution from non-shaved kombu (NSK) and tororokombu (TK). The uronic acid content was analyzed using total components eluted from NSK and TK into phosphate-buffered saline (pH 8.0) for the determination of alginate by the carbazole method. Data are presented as the mean ± SE (n = 3). ***p < 0.005 versus NSK.

Control

NSK AS

TK AS

FIGURE 15.3 Effect of weak alkaline-soluble fraction (AS) from non-shaved kombu (NSK) and tororokombu (TK) on pancreatic lipase activity in vitro. Lipase activity was measured using a Lipase Kit S according to the manufacturer's protocol. Data are presented as the mean ± SE (n = 5). p < 0.05, p < 0.005 versus control, ### p < 0.005 NSK AS versus TK AS.

Control

NSK AS

TK AS

FIGURE 15.3 Effect of weak alkaline-soluble fraction (AS) from non-shaved kombu (NSK) and tororokombu (TK) on pancreatic lipase activity in vitro. Lipase activity was measured using a Lipase Kit S according to the manufacturer's protocol. Data are presented as the mean ± SE (n = 5). p < 0.05, p < 0.005 versus control, ### p < 0.005 NSK AS versus TK AS.

These results suggest that TK, but not NSK, had an antiobesity effect. The shaving process alters the amount of active component that dissolves to cause physiological effects. The active component in the crude extract of Laminaria sp. can be considered to be an alginate.

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