Microalgae

The symbiotic microalga Symbiodinium sp., which is a type of symbiotic zooxanthellae, is found in a wide range of marine invertebrates. Dinofla-gellates are widely known to be a rich source of biologically active and structurally unique secondary metabolites (Kita and Uemura, 2005, 2006; Uemura, 2006). Some dinoflagellates were cultured under artificial conditions with seawater medium, and the alga body was then centrifuged and extracted with 80% aqueous EtOH to collect metabolites. Symbioimines (Kita et al., 2004,2005), symbiodinolide (Kita et al., 2007), and symbiospirols (Tsunematsu et al., 2009) have been isolated from the same strain of Sym-biodinium sp. derived from the marine acoel flatworm. One of these compounds, symbioimine (Fig. 34.1), an amphoteric iminium metabolite, has been shown to be an antiresorptive and anti-inflammatory drug (Kita et al., 2005). Its ability to suppress osteoclast differentiation (EC50 = 44 mM) was demonstrated in RAW264 cells. In addition, symbioimine (10 mM) also inhibited cyclooxygenase-1 and -2 activities by 5% and 32%, respectively.

The zoanthamine alkaloids are a structurally unique family of natural products that exhibit antiosteoporotic, antibiotic, anti-inflammatory, and cytotoxic biological activities. Although they are isolated from soft coral of the order zoantharia, symbiotic algae may play an important role in their biosynthesis. Norzoanthamine (Fig. 34.2) was isolated along with some analogs from a Zoanthus species collected off the Ayamaru coast of the Amami Islands in Japan (Fukuzawa et al., 1995). Norzoanthamine and its hydrochloride salt have been shown to prevent bone loss in ovariecto-mized mice, a pharmaceutical model for postmenopausal osteoporosis (Kuramoto et al., 1996). As ovariectomized mice do not produce sufficient estrogen, they quickly lose bone mass and strength within a few weeks. However, oral treatment of mice with norzoanthamine HCl at doses of ncn -

FIGURE 34.1 Structure of symbioimine. Symbioimine, an amphoteric iminium compound, was isolated from symbiotic algae of the marine acoel flatworm Amphiscolops sp. which was collected at Sesoko Island, Okinawa, Japan.

FIGURE 34.1 Structure of symbioimine. Symbioimine, an amphoteric iminium compound, was isolated from symbiotic algae of the marine acoel flatworm Amphiscolops sp. which was collected at Sesoko Island, Okinawa, Japan.

FIGURE 34.2 Structure of norzoanthamine. Norzoanthamine, an antiosteoporotic marine alkaloid, was isolated along with some analogs from a Zoanthus species collected off the Ayamaru coast of the Amami Islands in Japan.

0.08-2.0 mg/kg/day for 4 weeks led to a significantly higher retention of femur weight than in the control group (Kuramoto et al., 1996, 1998; Uemura, 2006). Further, these preventive effects were not accompanied by an increase in uterine weight, which is a serious side effect of treatment with 17b-estradiol (Yamaguchi et al., 1999). In vitro studies with nor-zoanthamine showed that it had no effect on the formation of osteoclasts, and the suppression of IL-6 secretion, which has been suggested by in vitro experiments (Kuramoto et al., 2000), has not yet been demonstrated in vivo (Behenna et al., 2008). Further investigations will be needed to elucidate the mechanism of the antiosteoporosis action of norzoanthamine.

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