1 Introduction Friedman, 1993; Gressner, 1995; Lieber, 1999 Wu et al., 1998 Gressner, 1995 Maher and Bissell, 1993 Friedman, 1999; Geerts, 2001 Houglum et al., 1997; Maher et al., 1997; Horie et al., 2003; Canbay et al., 2002; Song et al., 2003 Lahaye and Kaeffer, 1997; Kloareg and Quatrano, 1988 Lahaye and Kaeffer, 1997; Kloareg and Quatrano, 1988; Mabeau et al., 1990 Fucus vesiculosus Boisson-Vidal et al., 1995; Saito et al., 2006 Xue et al., 2001; McCaffrey et al., 1994 2 Materials and methods 2.1 Reagents 4 4 4 2.2 Animals and experimental protocols All of the experimental protocols conformed to the ethics guidelines of the Graduate School of Pharmaceutical Sciences, Osaka University. Male Sprague–Dawley rats (200–250 g) and male ddy mice (6 weeks old) were obtained from SLC (Shizuoka, Japan). The mice were housed in an environmentally controlled room (lights on from 8:00 to 20:00; temperature, 23 ±1.5 °C). Animals had free access to water and commercial chow (Type MF, Oriental Yeast, Tokyo, Japan). 4 4 2.3 Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) assays Serum AST and ALT levels were measured using commercially available kits (Mitsubishi Kagaku Iatron Inc., Tokyo, Japan) according to the manufacturer's instructions. 2.4 Analysis of fibrosis Liver specimens were fixed with 10% formaldehyde and embedded in paraffin. Tissue sections were mounted on slides, and Azan staining was performed to analyze the extent of fibrosis. After establishing a background for each micrograph, the number of pixels showing a blue color (stained collagen fibers) was determined with Scion Image (National Institutes of Health, Bethesda, MD), and the percentage of fibrosis in the liver was calculated as the ratio of the blue-colored area to the total area of the liver. 2.5 Isolation of hepatocytes and assay of viability Seglen, 1976 5 2 4 2.6 Isolation of hepatic stellate cells and assay of viability Kawada et al., 1993 5 2 Mosmann, 1983 3 Results 3.1 Effect of fucoidan on acute liver injury 4 4 4 Fig. 1 4 3.2 Effect of fucoidan on chronic liver injury 4 Fig. 2 Fig. 2 Fig. 2 Fig. 2 4 Fig. 2 3.3 Effect of fucoidan on hepatocytes and stellate cells Gressner, 1995; Gutierrez-Reyes et al., 2007 Fig. 3 4 4 4 4 4 4 Fig. 3 4 4 Discussion l Boisson-Vidal et al., 1995; Berteau and Mulloy, 2003; Saito et al., 2006 Senoo et al., 1998 Tsukamoto, 1999 4 Boisson-Vidal et al., 1995; McCaffrey et al., 1994; Xue et al., 2001 4 Weiler-Normann et al., 2007 4 Canbay et al., 2002; Song et al., 2003; Iredale, 2001; Iredale et al., 1998; Issa et al., 2001 F. vesiculosus Nishino et al., 1994 Patel et al., 2002 Haroun-Bouhedja et al., 2000 In summary, we found that fucoidan prevents hepatocyte cell death and induces the death of hepatic stellate cells in an animal model of hepatic fibrosis. Future studies will examine the molecular mechanisms of fucoidan in hepatocytes and hepatic stellate cells. This is the first report that fucoidan has anti-fibrotic activity and that it is a promising lead for the development of anti-fibrotic agents. Identification of the molecular target and the active structure of fucoidan may lead to the development of novel anti-fibrotic agents.