Purpose: Dipeptidyl peptidase-4 inhibitors, including linagliptin, prevent inflammation. However, the in vitro effects of linagliptin are unclear. Moreover, although linagliptin inhibits lipopolysaccharide (LPS)-induced inflammation, the anti-inflammatory effects of linagliptin in this context are not concentration-dependent. In the absence of LPS-binding protein (LBP), the pro-inflammatory effects of LPS involve pathways other than the Toll-like receptor (TLR) 4 pathway. Here, we aimed to determine the anti-inflammatory mechanisms of linagliptin in an experimental model in which LBP was added to the medium.
Methods: Human U937 monocytes were cultured at 1 × 10⁶ cells/mL in Roswell Park Memorial Institute medium and differentiated into macrophages using phorbol myristate acetate. All processes were carried out in medium containing 10% fetal bovine serum (FBS). After 48 hrs of culture, we replaced the medium and pretreated the cells with 100, 250, 500, or 2500 nM linagliptin for 1 hr. We exchanged the medium again, and the cells were treated with 1 ng/mL LPS with or without 100, 250, 500, or 2500 nM linagliptin. Interleukin (IL)-6 and LBP in the supernatant, nuclear factor (NF)-κB/p65 in the nucleus, and reactive oxygen species (ROS) in the cells, as important markers of the mechanism of inflammation induction by LPS, were measured using enzyme-linked immunosorbent assay kits.
Results: Linagliptin significantly prevented LPS-stimulated IL-6 production and intranuclear NF-κB/p65 levels in a concentration-dependent manner. LPS-induced intracellular ROS levels were significantly decreased by linagliptin at all concentrations. LBP levels were markedly higher in FBS-containing medium than in medium without FBS. However, LBP levels did not change following administration of linagliptin and/or LPS.
Conclusion: Concentration-dependent and -independent inflammatory suppression was observed following linagliptin treatment in the context of LPS-induced pro-inflammatory responses. Thus, our findings suggested that linagliptin induced two different mechanisms to repress inflammation, i.e., TLR4-dependent and -independent mechanisms.

Keywords: linagliptin, lipopolysaccharide-binding protein, interleukin-6, intranuclear subunit of nuclear factor-κB/p65, reactive oxygen species




中文翻译：

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利格列汀以依赖性和非依赖性方式抑制脂多糖诱导的炎症浓度。

目的：二肽基肽酶 4 抑制剂，包括利格列汀，可预防炎症。然而，利格列汀的体外作用尚不清楚。此外，尽管利格列汀抑制脂多糖 (LPS) 诱导的炎症，但在这种情况下，利格列汀的抗炎作用不依赖于浓度。在没有 LPS 结合蛋白 (LBP) 的情况下，LPS 的促炎作用涉及除 Toll 样受体 (TLR) 4 途径以外的途径。在这里，我们旨在确定利格列汀在将 LBP 添加到培养基中的实验模型中的抗炎机制。
方法：人 U937 单核细胞以 1 × 10 ^6培养细胞/mL 在罗斯威尔公园纪念研究所培养基中，并使用佛波醇肉豆蔻酸酯醋酸酯分化成巨噬细胞。所有过程均在含有 10% 胎牛血清 (FBS) 的培养基中进行。培养 48 小时后，我们更换培养基并用 100、250、500 或 2500 nM 利格列汀预处理细胞 1 小时。我们再次更换培养基，用 1 ng/mL LPS 处理细胞，加或不加 100、250、500 或 2500 nM 利格列汀。测定了上清液中的白细胞介素 (IL)-6 和 LBP、细胞核中的核因子 (NF)-κB/p65 和细胞中的活性氧 (ROS) 作为 LPS 诱导炎症机制的重要标志物。使用酶联免疫吸附测定试剂盒。
结果：Linagliptin 以浓度依赖性方式显着阻止 LPS 刺激的 IL-6 产生和核内 NF-κB/p65 水平。利格列汀在所有浓度下均显着降低 LPS 诱导的细胞内 ROS 水平。含 FBS 的培养基中的 LBP 水平明显高于不含 FBS 的培养基。然而，LBP 水平在利格列汀和/或 LPS 给药后没有改变。
结论：在 LPS 诱导的促炎反应的情况下，利格列汀治疗后观察到浓度依赖性和非依赖性炎症抑制。因此，我们的研究结果表明，利格列汀诱导了两种不同的抑制炎症的机制，即依赖于 TLR4 和不依赖于 TLR4 的机制。

关键词：利格列汀，脂多糖结合蛋白，白细胞介素6，核因子-κB/p65的核内亚基，活性氧