**5. Conclusions**

The aim of this study was to investigate the e ffects of three pure sulfated fucans from *Laminaria hyperborea*, which di ffered in their molecular size. The sulfated fucan origin and extraction method were the same, and they di ffered only in the molecular weight average (Fuc1 > Fuc2 > Fuc3), paving the way for comparable data. To test whether they are suitable for further testing for potential

treatment of, e.g., AMD, different tests regarding oxidative stress protection (MTS), cell viability (MTT/MTS), and VEGF interference (VEGF ELISA) in ocular cells (OMM-1, ARPE-19, and RPE) were performed. The cell viability of ARPE-19 and RPE was not influenced by up to three days of treatment; this is important for further studies because it excludes toxic effects. Fuc2 and Fuc3 lowered the cell viability of the melanoma cell line OMM-1 and should therefore be tested in further tumor cell lines as to whether this is cell line specific or in general for tumor cells, which could pave the way for anticancer studies. Fuc1, the biggest sulfated fucan, was the only one which showed protective effects against oxidative stress (in OMM-1). Fuc3 reduced VEGF secretion in ARPE19 but stimulated VEGF secretion in primary RPE cells. Conversely, Fuc2 and Fuc1 inhibited VEGF in ARPE-19 as well as in RPE, with the strongest effect seen for 50 μg/mL Fuc1. Altogether, the results showed that the biological activity of sulfated fucans is dependent on the molecular weight, and the desired effect for the treatment of ocular diseases increases with the size of the sulfated fucan.

**Author Contributions:** Conceptualization, A.K., G.K.; Methodology, A.K., G.K., P.D.; Validation, P.D.; Formal Analysis, P.D.; Investigation, G.K., P.D.; Resources, A.K., G.K., J.R.; Data Curation, A.K., P.D.; Writing—Original Draft Preparation, G.K., P.D.; Writing—Review and Editing, A.K., G.K., P.D.; Visualization, G.K., P.D.; Supervision, A.K., J.R.

**Funding:** This study is part of the FucoSan—Health from the Sea Project and is supported by EU InterReg– Deutschland–Denmark and the European Fund of Regional Development.

**Acknowledgments:** We thank Alginor ASA for the provision of the algae.

**Conflicts of Interest:** The authors declare no conflict of interest.
