Redox Shift from Antioxidant to Pro-Oxidant Activity Induced by Nanoencapsulated α-tocopherol in Diets for Shrimp (Litopenaeus vannamei)

Shrimp farming has seen significant growth in recent years, with increased production leading to intensification that requires less area to achieve higher yields. Intensive shrimp farming increases susceptibility to oxidative stress due to hypoxia and thermal fluctuations, compromising productivity and survival. Although α-tocopherol is widely used as a dietary antioxidant, its bioavailability and stability are limited along the intestinal tract. In this study, α-tocopherol was nanoencapsulated in chitosan via ionic gelation to enhance systemic delivery of α-tocopherol in Litopenaeus vannamei, resulting in nanoparticles with a diameter of 150 nanometers. For two weeks, four dietary treatments with five replicates were fed different nanoencapsulated α-tocopherol levels, (0, 2, 3, and 4 mg kg-1). A system of 20-aquariums was used, each aquarium defined as the experimental unit (EU). Prior to the experiment, nanoparticles labeled with fluorescent FITC were used to confirm whether they crossed the intestinal barrier. Gene expression analysis revealed a dose-dependent catalase (CAT) modulation of antioxidant enzymes, such as superoxide dismutase (MnSOD), glutathione peroxidase (GPX), and glutathione S-transferase (GST) in the hepatopancreas, with transcriptional downregulation (qRT-PCR) at higher concentrations, suggesting reduced oxidative pressure or a shift toward pro-oxidant signaling. Despite the short length of the experimental procedure, these findings suggest that nanoencapsulated α-tocopherol not only enhances delivery efficiency but also unveils a redox transition threshold, highlighting the dual antioxidant/pro-oxidant nature of α-tocopherol in vivo. Nanotechnology with biomaterials such as chitosan presents a promising approach to mitigate oxidative stress by enhancing the stability and release of essential antioxidants. Furthermore, this work provides mechanistic insight into nanonutraceutical strategies for oxidative stress management in aquaculture. The pro-oxidant shift under longer experimental procedures is discussed.