Utilization of the By-Product of Corn: Guided Identification of Bioactive Terpenoids from Stigma Maydis (Corn Silk)

Stigma maydis (corn silk) (S. maydis) is a food-based by-product of maize and possesses great nutritional and pharmaceutical value. This study aimed to explore bioactive components from S. maydis. By the guidance of bioactivity-guided approach and Global Natural Products Social (GNPS) molecular networking, 12 terpenoids were discovered from S. maydis. The structures of 11 undescribed compounds (1-11) were determined by detailed spectroscopic analyses, single-crystal X-ray diffraction analysis, specific rotation calculations, electronic circular dichroism (ECD) calculations, and NMR calculations. The neuroprotective and acetylcholinesterase (AChE) inhibitory effects of 1-12 were examined, and most of them showed significant or moderate activities. The underlying neuroprotective mechanism of 4 and 5 was revealed by Hoechst 33258, AO-EB, and JC-1 staining assays. This work illustrated the potential of S. maydis as a prospective natural source of bioactive compounds in food and pharmaceutical industries.

Purification, Identification and Characterization of Antioxidant Peptides from Corn Silk Tryptic Hydrolysate: An Integrated In Vitro-In Silico Approach

Corn silk (CS) is an agro-by-product from corn cultivation. It is used in folk medicines in some countries, besides being commercialized as health-promoting supplements and beverages. Unlike CS-derived natural products, their bioactive peptides, particularly antioxidant peptides, are understudied. This study aimed to purify, identify and characterize antioxidant peptides from trypsin-hydrolyzed CS proteins. Purification was accomplished by membrane ultrafiltration, gel filtration chromatography, and strong-cation-exchange solid-phase extraction, guided by 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt radical cation (ABTS^•+) scavenging, hydrogen peroxide scavenging, and lipid peroxidation inhibition assays. De novo sequencing identified 29 peptides (6–14 residues; 633–1518 Da). The peptides consisted of 33–86% hydrophobic and 10–67% basic residues. Molecular docking found MCFHHHFHK, VHFNKGKKR, and PVVWAAKR having the strongest affinity (−4.7 to −4.8 kcal/mol) to ABTS^•+, via hydrogen bonds and hydrophobic interactions. Potential cellular mechanisms of the peptides were supported by their interactions with modulators of intracellular oxidant status: Kelch-like ECH-associated protein 1, myeloperoxidase, and xanthine oxidase. NDGPSR (Asn-Asp-Gly-Pro-Ser-Arg), the most promising peptide, showed stable binding to all three cellular targets, besides exhibiting low toxicity, low allergenicity, and cell-penetrating potential. Overall, CS peptides have potential application as natural antioxidant additives and functional food ingredients.

Terpenoids from stigma maydis (Zea mays L.) alleviate hydrogen peroxide-induced SH-SY5Y cell injury by activating Nrf2

Five terpenoids (1-5), including three new ent-kaurane diterpenoids (1-3), one new ent-rosane type diterpenoid (4) and one known triterpenoid (5), were isolated from stigma maydis (Zea mays L.). The structures of the compounds were elucidated by comprehensive spectroscopic analyses. The relative configurations of stigmanes A-D (1-4) were determined by NOESY experiments. In addition, the relative configuration of stigmane D (4) was further established by NMR calculations. The absolute configurations of these compounds were identified by a comparison of experimental and calculated specific rotations. The neuroprotective effects of these compounds against H₂O₂-induced injury in human neuroblastoma SH-SY5Y cells were evaluated, and the results showed that among the compounds, 2 exhibited the most significant neuroprotection. Further study demonstrated that 2 could activate nuclear factor E2-related factor (Nrf2), downregulate apoptosis and reactive oxygen species (ROS) generation, and increase antioxidant enzyme activities in SH-SY5Y cells. However, the neuroprotective effect was reversed when Nrf2 was silenced. In conclusion, this study suggested that terpenoids from stigma maydis exerted neuroprotective effects through Nrf2 activation.