Linagliptin Inhibits Lipopolysaccharide-Induced Inflammation Concentration-Dependently And -Independently

Abstract

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

Abbreviations

LPS, lipopolysaccharide; LBP, LPS-binding protein; TLR, Toll-like receptor; FBS, fetal bovine serum; IL, Interleukin; NF, nuclear factor; ROS, reactive oxygen species; DPP-4, Dipeptidyl peptidase-4; Loxo, loxoprofen sodium salt dihydrate.

Author Contributions

Naoki Sato, Yuya Nakamura, and Masahiro Inagaki devised the study concept and design. Shiho Yamadera, Sachiyo Kenmotsu, and Hiroshi Saito performed the experiments and collected the data. Naoki Sato, Yuya Nakamura, Masahiro Inagaki, and Shiho Yamadera analyzed the data. Yuya Nakamura interpreted the data. Yuya Nakamura searched the literature. Naoki Sato, Yuya Nakamura, and Shiho Yamadera drafted the manuscript. Naoki Sato, Yuya Nakamura, Shiho Yamadera, Masahiro Inagaki, Sachiyo Kenmotsu, Hiroshi Saito, Tatsunori Oguchi, Mayumi Tsuji, Hirokazu Chokki, Isao Ohsawa, Hiromichi Gotoh, Shinichi Iwai, and Yuji Kiuchi contributed to substantial revisions to the manuscript. Finally, all authors made substantial contributions to conception and design, acquisition of data, and analysis and interpretation of data; took part in drafting the article or revising it critically for important intellectual content; gave final approval of the version to be published; and agree to be accountable for all aspects of the work.

Disclosure

The authors report no conflicts of interest in this work.