*2.3. Oxidative Stress Protection*

Oxidative stress protection by sulfated fucans from brown seaweed was already shown before for OMM-1 with *Fucus vesiculosus* sulfated fucan from Sigma-Aldrich [16] and with sulfated fucans from other seaweed, especially from SL, which was also protective for ARPE-19 [11]. So, these two cellular model systems are suitable for testing LH sulfated fucans.

Starting with the melanoma cell line OMM-1, stress induction with 1 mM H2O2 led to decreased cell viability of between 49% and 57% (Figure 6). The addition of 1–100 μg/mL Fuc2 showed no protection. The same outcome was achieved via treatment with Fuc3, which significantly reduced viability at 100 μg/mL (44% ± 9%, *p* < 0.05). Also, 50 μg/mL Fuc3 showed a slightly antiproliferative effect which was not significant. Only the sulfated fucan with the highest molecular weight, Fuc1, had significant protective effects at 10 μg/mL (65% ± 7%, *p* < 0.05).

RPE cells have the important role of protecting the cells of the retina against oxidative burden [7]. The RPE cell line ARPE19 was described to be rather resistant against hydrogen peroxide [17]. However, treatment with 0.5 mM *tert*-butyl hydroperoxide (TBHP) has a significant, consistent effect on the cell viability of ARPE-19 after 24 h, as previously shown [11].

**Figure 6.** OMM-1 cell viability after treatment with Fuc1 (**a**), Fuc2 (**b**), and Fuc3 (**c**) and stress insult after 30 min incubation with the sulfated fucans. The oxidative agen<sup>t</sup> was 1 mM H2O2, which reduced cell viability to under 60% in all cases. Viability was tested via MTS assay and is shown as the mean and standard deviation in relation to an untreated control (100%). The 10 μg/mL Fuc1 showed significant protective e ffects for the cell line. Significance was evaluated via ANOVA; \*/ + *p* < 0.05, versus 0 μg/mL sulfated fucan + 1 mM H2O2 (*n* = 4).

Cell viability was e ffectively lowered to nearly 30% through oxidative stress with TBHP, but all LH sulfated fucans lowered the viability additionally to a lesser extent (Figure 7); the strongest e ffect was from 100 μg/mL of the Fuc3 sulfated fucan, which lowered the viability even further down to 18% ± 1% (*p* < 0.05).

**Figure 7.** ARPE-19 cell viability after treatment with Fuc1 (**a**), Fuc2 (**b**), and Fuc3 (**c**) and stress insult after 30 min incubation with the sulfated fucans. The oxidative agen<sup>t</sup> was 0.5 mM *tert*-butyl hydroperoxide (TBHP), which reduced cell viability to nearly 30% in all cases. Viability was tested via MTS assay and is shown as the mean and standard deviation in relation to an untreated control (100%). No sulfated fucan showed a significant protective e ffect for the RPE cell line. Significance was evaluated with ANOVA; \* *p* < 0.05, \*\* *p* < 0.01, \*\*\* *p* < 0.001, versus 0 μg/mL sulfated fucan + 0.5 mM TBHP (*n* = 4).
