Determination of the Lethal Concentrations of Two Phenolic Acid Derivatives Originated From the Edible Red Marine Macroalga ( Bangia fuscopurpurea ) Using the In Vivo Zebrafish Eleutheroembryo Model and Their In Silico Structure–Toxicity Relationship Study

ABSTRACT A 2023 study identified two phenolic acid derivatives (HBP2–3) in the extract from the edible macroalga ( Bangia fuscopurpurea ), and we previously demonstrated the in vitro neuroprotective effects of HBP2–3. However, the appropriate starting experimental concentration range for HBP2–3 in animals remained unclear, and it was uncertain which compound might carry a lower toxicity risk. This study assessed the in vivo lethal dose of HBP2–3 and analyzed their in silico toxicological profiles to support a structure–toxicity relationship (STR) analysis. We predicted their LD 50 using the tools GUSAR and DL‐AOT, and determined their lethal concentrations (LC) using the in vivo zebrafish eleutheroembryo model. We predicted their toxicological properties using the tools (ADMETlab 3.0, TISBE, and embryoTox). An in vitro model was further selected to assess their toxicity. In in silico models, HBP2–3 showed potential to treat 12 parkinsonian syndromes, and HBP2 exhibited a higher rat oral LD 50 than HBP3. In the in vivo zebrafish eleutheroembryo model, HBP2 (0.1–200 μM) and HBP3 (0.1–10 μM) did not induce mortality, and median LC (LC 50 ) of HBP3 was estimated to be 115.48 μM. Compared with HBP3, HBP2 exhibited the following in silico advantages: (a) lower probabilities of nephrotoxicity and neurotoxicity; and (b) a reduced risk of developmental toxicity. In in vitro human neuronal IMR‐32 cells, HBP3 exhibited greater cytotoxicity, potentially associated with the downregulation of Bcl‐2 and the activation of caspase‐3. These advantages of HBP2 may be associated with an increased degree of hydroxylation.