Ortizo Rhessa Grace Guanga, Lai Ching-Shu, Anwar Choirul, Sharma Vishal, Sun Pei-Pei, Chen Chiu-Wen, Dong Cheng-Di, Tsai Mei-Ling
Department of Seafood Science, National Kaohsiung University of Science and Technology, Kaohsiung 811, Taiwan; College of Fisheries and Aquatic Sciences, Iloilo State University of Fisheries Science and Technology, Barotac Nuevo, Iloilo 5007, Philippines; Institute of Aquatic Science and Technology, National Kaohsiung University of Science and Technology, Kaohsiung 811, Taiwan.
Department of Seafood Science, National Kaohsiung University of Science and Technology, Kaohsiung 811, Taiwan.
Food Res Int. 2025 Nov;219:116986. doi: 10.1016/j.foodres.2025.116986. Epub 2025 Jul 8.
Dipeptidyl-peptidase (DPP)-IV inhibition by penultimate N-terminus Pro-containing peptides is a promising strategy for Type 2 diabetes (T2D) management, as it prevents the degradation of incretin hormones (DPP-IV substrates) like glucagon-like peptide-1 (GLP-1), thereby prolonging their half-life. However, the stability and bio-accessibility of these peptides are crucial to their efficacy in orally administered therapeutics. We previously identified LPCL and TPFLPDE peptides from tilapia viscera by-products hydrolysates, which exhibited significant DPP-IV inhibition in vitro and in situ while effectively preserving active GLP-1 levels after 2 h treatment in STC-1 cells under basal glucose conditions. In this study, we assessed the gastrointestinal (GI) stability of these peptides using a static in vitro GI digestion model and evaluated their DPP-IV inhibition capacity after post-GI digestion and post-DPP-IV pre-incubation. Our findings revealed that both peptides retained their DPP-IV inhibition capacity after GI digestion, with RP-HPLC and mass spectrometry confirming their intact forms. At post-DPP-IV pre-incubation, peptides exhibited decreased DPP-IV inhibition potency, indicating a substrate-type inhibition mechanism, forming N-terminal dipeptide fragments. Furthermore, we extended our previous findings by demonstrating that LPCL not only inhibits DPP-IV activity but also modulates GLP-1 expression and increases PepT1 protein levels in STC-1 cells. Unlike glycyl sarcosine, a known PepT1 substrate, LPCL effectively activates the PepT1 extracellular domain (ECD), leading to increased receptor expression and receptor-ligand interactions, as confirmed by molecular docking analysis. These results provide novel insights into the functional roles of LPCL in modulating DPP-IV activity and GLP-1 expression, potentially via PepT1 ECD conformational stabilization.
含倒数第二个N端脯氨酸的肽对二肽基肽酶（DPP）-IV的抑制作用是2型糖尿病（T2D）管理的一种有前景的策略，因为它可防止肠促胰岛素激素（DPP-IV底物）如胰高血糖素样肽-1（GLP-1）的降解，从而延长其半衰期。然而，这些肽的稳定性和生物可及性对其口服治疗的疗效至关重要。我们之前从罗非鱼内脏副产物水解物中鉴定出LPCL和TPFLPDE肽，它们在体外和原位均表现出显著的DPP-IV抑制作用，并且在基础葡萄糖条件下于STC-1细胞中处理2小时后能有效维持活性GLP-1水平。在本研究中，我们使用静态体外胃肠道消化模型评估了这些肽的胃肠道（GI）稳定性，并在胃肠道消化后和DPP-IV预孵育后评估了它们的DPP-IV抑制能力。我们的研究结果表明，两种肽在胃肠道消化后均保留了其DPP-IV抑制能力，反相高效液相色谱（RP-HPLC）和质谱证实了它们的完整形式。在DPP-IV预孵育后，肽表现出降低的DPP-IV抑制效力，表明存在底物型抑制机制，形成N端二肽片段。此外，我们扩展了之前的研究结果，证明LPCL不仅抑制DPP-IV活性，还调节GLP-1表达并增加STC-1细胞中肽转运体1（PepT1）蛋白水平。与已知的PepT1底物甘氨酰肌氨酸不同，LPCL有效地激活了PepT1细胞外结构域（ECD），导致受体表达增加和受体-配体相互作用增强，分子对接分析证实了这一点。这些结果为LPCL在调节DPP-IV活性和GLP-1表达中的功能作用提供了新的见解，可能是通过稳定PepT1 ECD构象实现的。
