Efficacy of marine bioactive compound fucoidan for bone regeneration and implant fixation in sheep

The need for a substitute for allograft and autograft is rising as bone graft surgeries exceed available supplies. We investigated the efficacy of the low-molecular weight marine bioactive compound fucoidan (FUC) on bone regeneration and implant fixation in seven female sheep, as FUC has shown great promise as a bone substitute. Titanium implants were inserted bilaterally in the distal femurs to test three hydroxyapatite/fucoidan (HA/FUC) groups and compared to allograft. The HA was coated with either 500 or 1500 μg of FUC, obtained by microwave-assisted chemical extraction, or 500 μg of FUC obtained by an enzyme-assisted extraction method. The concentric 2-mm gap around the implant was filled with either one of the HA/FUCs or allograft from the donor sheep. After 12 weeks, implant-bone blocks were harvested and divided into three parts for mechanical push-out testing, immunohistochemistry, and micro-CT and histomorphometry. Pronounced bone formations were observed by micro-CT and histomorphometry in all groups, but higher bone volume fractions were seen in the allograft group compared to the three HA/FUC groups. The trabecular thickness, trabecular separation, and architectural anisotropy were all significantly higher in the allograft group compared to the three HA/FUC groups. In conclusion, adequate bone formation was observed in all groups, although the bone formation was significantly greater in the allograft group. Also, no significant differences existed in the shear mechanical properties between groups, suggesting that the combination of HA and FUC can achieve a similar fixation strength to allograft in this model.

Influence of Fucoidan Extracts from Different Fucus Species on Adult Stem Cells and Molecular Mediators in In Vitro Models for Bone Formation and Vascularization

Fucoidans, sulfated polysaccharides extracted from brown algae, are marine products with the potential to modulate bone formation and vascularization processes. The bioactivity and safety of fucoidans are highly associated with their chemical structure, which may vary with algae species and extraction method. Thus, in depth evaluation of fucoidan extracts in terms of endotoxin content, cytotoxicity, and their detailed molecular biological impact on the individual cell types in bone is needed. In this study, we characterized fucoidan extracts from three different Fucus species including Fucus vesiculosus (Fv), Fucus serratus (Fs), and Fucus distichus subsp. evanescens (Fe) for their chemical features, endotoxin content, cytotoxicity, and bioactive effects on human outgrowth endothelial cells (OEC) and human mesenchymal stem cells (MSC) as in vitro models for bone function and vascularization. Extracts contained mainly high molecular weight (HMW) fucoidans and were free of endotoxins that may cause inflammation or influence vascularization. OEC tolerated fucoidan concentrations up to 200 µg/mL, and no indication of cytotoxicity was observed. The inflammatory response, however, investigated by real-time PCR (RT-PCR) and enzyme-linked immunosorbent assay (ELISA) and endothelial barrier assessed by impedance measurement differed for the individual extracts. MSC in comparison with endothelial cells were more sensitive to fucoidans and showed partly reduced metabolic activity and proliferation at higher doses of fucoidans. Further results for MSC indicated impaired osteogenic functions in alkaline phosphatase and calcification assays. All tested extracts consistently lowered important molecular mediators involved in angiogenesis, such a VEGF (vascular endothelial growth factor), ANG-1 (angiopoietin 1), and ANG-2 (angiopoietin 2), as indicated by RT-PCR and ELISA. This was associated with antiangiogenic effects at the functional level using selected extracts in co-culture models to mimic bone vascularization processes during bone regeneration or osteosarcoma.