In vitro protective activity of South Australian marine sponge and macroalgae extracts against amyloid beta (Aβ _1–42) induced neurotoxicity in PC-12 cells

South Australia is a biodiversity hotspot of marine sponges and macroalgae. This study aimed to evaluate the potential neuroprotective activity of extracts from these two marine sources by reducing the toxicity of human amyloid beta Aβ_1–42 in a cell model assay using PC-12 cells. A total of 92 extracts (43, 13, 16, and 20 extracts from sponge of 8 orders and 17 families, green algae of 3 orders and 4 families, brown algae of 6 orders and 8 families, and red algae of 5 orders and 10 families, respectively) were initially screened at three different concentrations (0.25, 2.5 and 25 μg/mL) to evaluate their toxicity using the MTT assay. About half of these extracts (26, 6, 5, and 10 extracts from sponge, green algae, brown algae, and red algae, respectively) showed some cytotoxicity, and were hence excluded from further assays. The rest of extracts (45 extracts in total) at 0.25 and 25 μg/mL were subsequently screened in a neuroprotection assay against Aβ_1–42 cytotoxicity. A cell viability reduction of 30% was observed in the MTT assay when the cells were treated with 1 μM Aβ_1–42. 29 extracts (13, 4, 7, and 5 extracts from sponge, green algae, brown algae, and red algae, respectively) reduced the toxicity induced by Aβ_1–42 (P < 0.05), indicating neuroprotective activity. These results demonstrate that marine sponge and macroalgae form a broad spectrum are promising sources of neuroprotective compounds against the hallmark neurotoxic protein in Alzheimer's disease (AD).