title: Soluble DPP-4 up-regulates toll-like receptors and augments inflammatory reactions, which are ameliorated by vildagliptin or mannose-6-phosphate.
abstract: OBJECTIVE
  Studies have shown that dipeptidyl peptidase-4 (DPP-4) inhibitors have anti-inflammatory effects. Soluble DPP-4 (sDPP-4) has been considered as an adipokine of which actions need to be further characterized.
  
  
  METHODS
  We investigated the pro-inflammatory actions of sDPP-4 and the anti-inflammatory effects of DPP-4 inhibition, using vildagliptin, as an enzymatic inhibitor, and mannose-6-phosphate (M6P) as a competitive binding inhibitor.
  
  
  RESULTS
  In lipopolysaccharide (LPS)-stimulated RAW264.7 cells, vildagliptin suppressed the increased expression of inducible nitric oxide synthase (iNOS) and phosphorylated JNK (pJNK), activation of the NF-κB pathway, and the resultant NO and proinflammatory cytokine production. Although sDPP-4 alone did not affect the protein level of iNOS or pJNK or the production of NO in RAW264.7 cells, it did amplify iNOS expression, NO responses, and proinflammatory cytokine production in LPS-stimulated RAW264 cells. As a probable mechanism, we found that sDPP-4 caused dose-dependent increases in the expression levels of toll-like receptor 4 (TLR4) and TLR2 in RAW264.7 cells, and that these alterations were inhibited by vildagliptin, M6P, or bisindolylmaleimide II, a protein kinase C inhibitor. Either vildagliptin or M6P suppressed iNOS expression and NO and cytokine production in LPS+DPP-4-co-stimulated macrophages, while combined treatment of the co-stimulated cells with both agents had increased anti-inflammatory effects compared with either treatment alone. Intravenous injection of sDPP-4 to C57BL/6J mice increased the expression of both TLRs in kidney and white adipose tissues.
  
  
  CONCLUSIONS
  Our findings suggest that sDPP-4 enhances inflammatory actions via TLR pathway, while DPP-4 inhibition with either an enzymatic or binding inhibitor has anti-inflammatory effects.
authors.affiliation: Department of Biomedical Chemistry, College of Health and Biomedical Science, Konkuk University, Chung-Ju, 27478, Republic of Korea.
authors.forename: Dong-Sung
authors.initials: DS
authors.lastname: Lee
authors.affiliation: College of Human Environmental Sciences, Department of Food Industry Convergence, Wonkwang University, Iksan, 54538, Republic of Korea; Hanbang Body Fluid Research Center, Wonkwang University, Iksan, 54538, Republic of Korea.
authors.forename: Eun-Sol
authors.initials: ES
authors.lastname: Lee
authors.affiliation: Tohoku University Graduate School of Medicine, Sendai-shi, 980-8575, Japan.
authors.forename: Md Morshedul
authors.initials: MM
authors.lastname: Alam
authors.affiliation: Department of Biochemistry, Inha University School of Medicine, Incheon, 22212, Republic of Korea.
authors.forename: Jun-Hyeog
authors.initials: JH
authors.lastname: Jang
authors.affiliation: Hanbang Body Fluid Research Center, Wonkwang University, Iksan, 54538, Republic of Korea; College of Oriental Medicine and Professional Graduate School of Oriental Medicine, Wonkwang University, Iksan, Jeonbuk, 54538, Republic of Korea.
authors.forename: Ho-Sub
authors.initials: HS
authors.lastname: Lee
authors.affiliation: Hanbang Body Fluid Research Center, Wonkwang University, Iksan, 54538, Republic of Korea; College of Pharmacy, Wonkwang University, Iksan, 54538, Republic of Korea.
authors.forename: Hyuncheol
authors.initials: H
authors.lastname: Oh
authors.affiliation: College of Human Environmental Sciences, Department of Food Industry Convergence, Wonkwang University, Iksan, 54538, Republic of Korea; Hanbang Body Fluid Research Center, Wonkwang University, Iksan, 54538, Republic of Korea; College of Pharmacy, Wonkwang University, Iksan, 54538, Republic of Korea.
authors.forename: Youn-Chul
authors.initials: YC
authors.lastname: Kim
authors.affiliation: Department of Microbiology and Immunology, School of Medicine, Jeju National University, Jeju, 690-756, South Korea.
authors.forename: Zahid
authors.initials: Z
authors.lastname: Manzoor
authors.affiliation: Department of Microbiology and Immunology, School of Medicine, Jeju National University, Jeju, 690-756, South Korea.
authors.forename: Young-Sang
authors.initials: YS
authors.lastname: Koh
authors.affiliation: Hanbang Body Fluid Research Center, Wonkwang University, Iksan, 54538, Republic of Korea; College of Oriental Medicine and Professional Graduate School of Oriental Medicine, Wonkwang University, Iksan, Jeonbuk, 54538, Republic of Korea. Electronic address: dgkang@wonkwang.ac.kr.
authors.forename: Dae-Gil
authors.initials: DG
authors.lastname: Kang
authors.affiliation: Hanbang Body Fluid Research Center, Wonkwang University, Iksan, 54538, Republic of Korea; Department of Internal Medicine, Wonkwang University School of Medicine and Hospital, Iksan, 54538, Republic of Korea. Electronic address: drhormone@naver.com.
authors.forename: Dae Ho
authors.initials: DH
authors.lastname: Lee
mesh_terms: D000218:Adamantane / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D018819:Dipeptidyl Peptidase 4 / Q000502:physiology*; D054873:Dipeptidyl-Peptidase IV Inhibitors / Q000494:pharmacology; D007249:Inflammation / Q000209:etiology*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008360:Mannosephosphates / Q000494:pharmacology*; D051379:Mice; D008810:Mice, Inbred C57BL; D016328:NF-kappa B / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II / Q000235:genetics; D009570:Nitriles / Q000494:pharmacology*; D011759:Pyrrolidines / Q000494:pharmacology*; D012333:RNA, Messenger / Q000032:analysis; D051193:Toll-Like Receptors / Q000235:genetics / Q000502:physiology*; D000077597:Vildagliptin
chemical_list: D054873:Dipeptidyl-Peptidase IV Inhibitors; D008070:Lipopolysaccharides; D008360:Mannosephosphates; D016328:NF-kappa B; D009570:Nitriles; D011759:Pyrrolidines; D012333:RNA, Messenger; D051193:Toll-Like Receptors; C027693:mannose-6-phosphate; D052247:Nitric Oxide Synthase Type II; D018819:Dipeptidyl Peptidase 4; D000077597:Vildagliptin; D000218:Adamantane
keywords: Dipeptidyl peptidase-4; Inflammation; Macrophages; Mannose-6-phosphate; Toll-like receptor; Vildagliptin