Camineralization via osteoblastic differentiation

Calcium level contributes to be crucial in the strengthening of bone and bone homeostasis. Investigations to find out natural products that promote Ca-mineralization are interesting nowadays. Marine algae have displayed a promising natural resource for this strategy, for example, unicellular coccolithophorid algae produce elaborate calcified scales called coccolith, which consist of fine pieces of CaCO3 (calcite) crystals, known as one of the representative biominerals. A novel polysaccharide named coccolith matrix acidic polysaccharide (CMAP) was isolated from the coccolith of a coccolithophorid alga, Pleurochrysis haptonemofera, by Ozaki et al. (2007). By using chemical analysis and NMR spectroscopy including COSY, TOCSY, HMQC, and HMBC, the structure of CMAP was determined to be a polysaccharide composed of the following unit: [L-iduronic acid (a1 ! 2), mesotartaric acid (3 ! 1), glyoxylic acid (1!)]n (Fig. 33.1). The investigation showed that CMAP has a strong inhibitory activity on CaCO3 precipitation and suggest that it serves as a regulator in the calcification of the coccolith. However, the effects of this compound on Ca-mineralization of osteoblasts were yet to be investigated.

Phlorotannins are the group of tannins and are found only in brown algae. Phlorotannins are oligomeric compounds using phloroglucinol (1,3,5-trihydroxybenzene) as a basic unit. Some phlorotannins have been identified as the bioactive components in Ecklonia species such as Ecklonia cava, Ecklonia kurome, and Ecklonia stolonifera (Ham et al., 2007). The compounds eckol, 2 dieckol, 6,6'-bieckol, and 1-(3',5'-dihydrox-yphenoxy)-7-(2'',4'',6''-trihydroxyphenoxy)-2,4,9-trihydroxydibenzo-1,4,-dioxin (Fig. 33.2) were isolated from E. cava by Ryu et al. (2009), who investigated the potent effect of these compounds on a host of commonly

Structure Glyoxylic Acid
FIG. 33.1 Probable repeating structure of CMAP: [l-iduronic acid (al ! 2), mesotartaric acid (3 ! 1), glyoxylic acid (1 ! )]n.
Adipates Structure

FIG. 33.2 Structures of phlorotannins from Ecklonia cava (1: dieckol; 2:1-(3',5'-dihy-droxyphenoxy)-7-(2",4" ,6"-trihydroxyphenoxy)-2,4,9-trihydroxydibenzo-1,4-dioxin).

FIG. 33.2 Structures of phlorotannins from Ecklonia cava (1: dieckol; 2:1-(3',5'-dihy-droxyphenoxy)-7-(2",4" ,6"-trihydroxyphenoxy)-2,4,9-trihydroxydibenzo-1,4-dioxin).

occurring diseases which possess an inflammatory component, including osteoarthritis, atherosclerosis, cancer, etc. These results suggested that the compounds help to stimulate the osteoblast differentiation at various stages and further confirmed that these compounds might have a therapeutic potential for the patients with osteoarthritis by stimulating production of proteoglycan. The phlorotannin derivatives showed the regulation of osteosarcoma differentiation by increasing ALP activity, mineralization, total protein, and collagen synthesis in human osteosarcoma cell (MG-63 cells). In addition, the phlorotannin derivatives could attenuate inflammatory response via MAPK pathway in chronic articular diseases.

Fucodiphlorethol G (Fig. 33.3), a new compound isolated from the methanol extract of E. cava, a brown alga, collected offshore in Jeju Island by Ham et al. (2007). By the examination of XH and 13C NMR data, it was found that the structure of the compound is similar to that of trimeric phlorotannin triphlorethol-A (Fig. 33.3). Although these studies evidenced that these compounds can stimulate osteoblast differentiation at various stages, there is no clear demonstration of whether the phlorotan-nin compound, Fucodiphlorethol G, has direct effect on osteoblast differentiation.

The fucans of brown algae, often called fucoidans, have shown biological activities such as antioxidative, anticoagulant, antithrombotic, anti-inflammatory, antitumoral, and antiviral activities (Cho et al., 2009). Berteau et al. (2003) studied the fucoidan derived from brown algae and other common fucoidans (Fig. 33.4). Although fucoidan was extracted from the numerous species of brown algae (Table 33.1), to the best of our knowledge, there are a few reports on beneficial effects of fucoidan on bone health or formation. Cho et al. (2009) extracted fucoidan from brown algae Undaria pinnatifida and showed that fucoidan significantly effects

Lignin Monomers
OH

3, Triphloretol-A

3, Triphloretol-A

FIG. 33.3 Structure of phlorotannin from Ecklonia cava (1: fucodiphlorethol G; 3: triphlorethol-A).

A Ascophyllum nodosum/Fucus vesiculosus/Fucus evanescens B Ecklonia kurome

Chemical Structure Fucoidan

FIG. 33.4 Common structures in fucoidans from brown algae. (A) The disaccharide repeating unit [4)-a-l-Fucp(2,3di-OSO^)-(1 ! 3)-a-l-Fucp(2OSO^)-(1] of a fraction of A. nodosum fucoidan representing the most abundant structural feature of fucoidans from both A. nodosum and F. vesiculosus. The same structure has been identified in the fucoidan of F. evanescens. (B) The 3-linked, preponderantly 4-sulfated fucoidan from E. kurome. (C) The quasirepeat unit identified in fucoidan from C. filum. Other substituents, such as O-acetyl, and branches are present in all these fucoidans and add considerably to their heterogeneity.

FIG. 33.4 Common structures in fucoidans from brown algae. (A) The disaccharide repeating unit [4)-a-l-Fucp(2,3di-OSO^)-(1 ! 3)-a-l-Fucp(2OSO^)-(1] of a fraction of A. nodosum fucoidan representing the most abundant structural feature of fucoidans from both A. nodosum and F. vesiculosus. The same structure has been identified in the fucoidan of F. evanescens. (B) The 3-linked, preponderantly 4-sulfated fucoidan from E. kurome. (C) The quasirepeat unit identified in fucoidan from C. filum. Other substituents, such as O-acetyl, and branches are present in all these fucoidans and add considerably to their heterogeneity.

TABLE 33.1 Brown algae containing fucoidan

Species

Order

Cladosiphon okamuranus

Chordariales

Chordaria flagelliformis, Ch. gracilis

Chordariales

Saundersella simplex

Chordariales

Desmarestia intermedia

Desmarestiales

Dictyosiphon foeniculaceus

Dictyosiphonales

Dictyota dichotoma

Dictyotales

Padina pavonica

Dictyotales

Spatoglossum schroederi

Dictyotales

Adenocystis utricularis

Ectocarpales

Pylayella littoralis

Ectocarpales

Ascophyllum nodosum

Fucales

Bifurcaria bifurcata

Fucales

Fucus.vesiculosus, F. spiralis, F. serratus, F. evanescens

Fucales

Himanthalia lorea

Fucales

Hizikia fusiforme

Fucales

Pelvetia canaliculata, P. wrightii

Fucales

Sargassum stenophyllum, S. horneri, S. Kjellmanium,

Fucales

S. muticum

Alaria fistulosa, A. marginata

Laminariales

Arthrothamnus bifidus

Laminariales

Chorda filum

Laminariales

Ecklonia kurome, E. cava

Laminariales

Eisenia bicyclis

Laminariales

Laminaria angustata, L. brasiliensis, L. cloustoni,

Laminariales

L. digitata, L. japonica, L. religiosa, L. saccharina

Macrocystis integrifolia, M. pyrifera

Laminariales

Nereocystis luetkeana

Laminariales

Undaria pinnatifida

Laminariales

Petalonia fascia

Scytosiphonales

Scytosiphon lomentaria

Scytosiphonales

osteoblastic cell differentiation. The level of ALP, osteocalcin, and BMP-2 were increased in the presence of fucoidan. It is suggested that fucoidan could be an agent to promote osteoblast differentiation and has possibility for its application in bone health supplement. Synytsya et al. (2010) determined the structure of fucoidan extracted from brown algae U. pinnatifida and concluded that this fucoidan is sulfated galactofucan containing p-D-galactopyranose and a-L-fucopyranose at near equal amounts (44.6 and 50.9 mol%).

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