Collagen and its peptides exhibit remarkable antioxidant activity, superior biocompatibility, and water solubility, making them a significant research focus in skin care. Hence, the recombinant humanized collagen types I, III, and XVII complexed with niacinamide were developed to address damage in human foreskin fibroblasts (HFF-1) caused by ultraviolet radiation and to evaluate basement membrane proteins in a rat skin model. The Cell Counting Kit-8 (CCK-8) assay showed that higher concentrations of the complex increased the survival of damaged cells by approximately 10% and 22%, respectively, compared to the normal group after 16 and 48 h of treatment. Further biochemical analyses using ELISA and immunofluorescence (IF) confirmed that the complex enhanced the expression of collagen type IV, laminin, P63, and transforming growth factor-β (TGF-β) in the damaged cells. Additionally, the complex boosted the activity of the basement membrane in rat skin and stimulated the secretion of integrin, laminin, and perlecan. Overall, the recombinant humanized collagen complex effectively reinforced the skin’s basement membrane.

Marine-derived bioactive peptides have attracted increasing attention as value-added functional ingredients. In this study, peptides (<3 kDa) were prepared from yellowfin tuna processing by-products and further fractionated by Sephadex G-25 gel filtration. The major fraction (TBP-MF) exhibited markedly improved compositional homogeneity compared with the unfractionated hydrolysate (TBP), providing a well-defined peptide system for subsequent characterization and biological evaluation. Physicochemical analyses demonstrated that TBP-MF possessed enhanced thermal stability and a more ordered secondary structure, characterized by pronounced β-sheet enrichment, as revealed by TGA/DSC, FTIR, and circular dichroism analyses. Morphological and colloidal characterization further showed that TBP-MF formed relatively uniform lamellar and fibrous assemblies with a narrower particle size distribution and reduced electrostatic stabilization, indicating a higher tendency toward ordered self-association. Peptidomic profiling combined with in silico analysis revealed that TBP-MF was enriched in short peptides with relatively higher PeptideRanker scores and a functional motif distribution containing relatively more neuro-related annotations, although angiotensin-converting enzyme (ACE)- and dipeptidyl peptidase IV (DPP-IV)-related motifs remained predominant in both groups. In differentiated PC12 cells, TBP-MF exhibited excellent cytocompatibility and induced a stable, concentration-dependent increase in the Cell Counting Kit-8 (CCK-8) readout (OD₄₅₀), indicating enhanced cellular metabolic activity and/or increased cell number. In addition, TBP-MF significantly increased intracellular levels of key neurochemical factors associated with sleep-related regulation, including tetrahydrobiopterin (BH4), serotonin (5-HT), and γ-aminobutyric acid (GABA). Overall, this study highlights yellowfin tuna by-products as a promising marine resource for bioactive peptides and suggests that fractionation-driven structural refinement is associated with neuro-related biological activity in differentiated PC12 cells. These findings support the potential application of marine by-product-derived peptides as functional ingredients in health-related fields.

The compact muscle architecture and poor aqueous dispersibility of Sthenoteuthis oualaniensis protein limit its use as a food ingredient. This study developed a gel filtration chromatography (GFC)-guided papain–alcalase sequential hydrolysis strategy using target-window peak area ($A_{\mathrm{target}}$) as a peptide-distribution response. Box–Behnken optimization identified an enzyme dosage of 1110 U/g, a papain/alcalase mass ratio of 3:5, and 8 h hydrolysis, yielding an $A_{\mathrm{target}}$ of 0.0648 ± 0.0012 a.u. O-phthaldialdehyde (OPA)-derived degree of hydrolysis (DH) values were 10.72 ± 0.08%, 35.32 ± 0.12%, and 25.03 ± 0.37% for SPH-Pap, SPH-Alc, and SPH-opt, respectively, showing that the highest $A_{\mathrm{target}}$ did not coincide with the highest DH. The essential-to-total amino acid ratio remained 38.18–39.20%, while lysine and methionine changed modestly. SPH-opt maintained high solubility across a broad pH range and exhibited a peptide profile distinct from those of the single-enzyme hydrolysates. Radical-scavenging capacity was assessed only post-optimization. At 5 mg/mL, SPH-opt showed DPPH and ABTS scavenging rates of 23.75% and 22.84%, respectively; without external standards, these values support only relative within-study comparisons. Overall, $A_{\mathrm{target}}$ and DH provided complementary information on peptide distribution and bond cleavage, and no causal relationship between $A_{\mathrm{target}}$ and radical-scavenging capacity was established.

Marine by-products represent a promising source of bioactive peptides. This study aimed to isolate and characterize a low-molecular-weight peptide fraction with antioxidant activity from Argentine shortfin squid carcass by-products, and to evaluate in vitro its cytocompatibility and protective effects against corticosterone (CORT)-induced oxidative injury in rat adrenal pheochromocytoma (PC12) cells and human astrocyte (hACs) cells. Argentine squid antioxidant peptide (PASN) was obtained by size-exclusion chromatography and fractionation-based screening. PASN exhibited the strongest overall free-radical-scavenging activity and consisted predominantly of components below 1 kDa (211.73–1013.48 Da). Spectroscopic analyses indicated that enzymatic hydrolysis transformed its structure from a rigid triple-helix conformation to a more flexible conformation dominated by β-turns (50.78%) and random coils (17.38%). In addition, thermogravimetric analysis confirmed its excellent thermal stability, with an onset decomposition temperature as high as 244.81 °C, supporting its potential applicability in high-temperature food-processing matrices. In vitro assays demonstrated that PASN exhibited high biocompatibility and promoted proliferation of both PC12 cells and hACs, while significantly improving cell viability under CORT challenge. PASN also reduced lactate dehydrogenase (LDH) leakage (hACs: 38.31%; PC12: 31.17%) in both cell models and restored total superoxide dismutase (T-SOD) activity (hACs: 69.46%, PC12: 66.40%). Immunofluorescence further revealed that PASN rescued the expression of brain-derived neurotrophic factor (BDNF) (hACs: 35.23%, PC12: 12.50%) and glutamate decarboxylase (GAD1/2) (hACs: 102.66%, PC12: 31.31%), key markers associated with synaptic plasticity and GABAergic sleep regulation. Collectively, PASN is a thermally stable squid-derived peptide fraction that exerts antioxidant and cytoprotective effects in neural cell models in vitro and represents a promising sustainable candidate for nutraceutical development.