title: Sodium lactate increases LPS-stimulated MMP and cytokine expression in U937 histiocytes by enhancing AP-1 and NF-kappaB transcriptional activities.
abstract: The plasma lactate concentration in patients with obesity and type 2 diabetes is often higher than that in nondiabetic individuals. Although it is known that increased lactate concentration is an independent risk factor for developing type 2 diabetes, the underlying mechanisms are not well understood. Because inflammation plays an important role in the development of type 2 diabetes, we postulated that increased lactate level might contribute to the pathogenesis of type 2 diabetes by enhancing inflammation. In the present study, we demonstrated that preexposure of U937 macrophage-like cells to sodium lactate increased LPS-stimulated matrix metalloproteinase (MMP)-1, IL-1beta, and IL-6 secretion. Augmentation of LPS-stimulated MMP-1 secretion was diminished when sodium lactate was replaced by lactic acid that reduced pH in the culture medium. Furthermore, quantitative real-time PCR indicated that the increased secretion of MMP-1, IL-1beta, and IL-6 was due to increased mRNA expression. To explore the underlying signaling mechanism, blocking studies using specific inhibitors for NF-kappaB and MAPK cascades were performed. Results showed that blocking of either NF-kappaB or MAPK pathways led to the inhibition of MMP-1, IL-1beta, and IL-6 expression stimulated by sodium lactate, LPS, or both. Finally, electrophoretic mobility shift assays showed a synergy between sodium lactate and LPS on AP-1 and NF-kappaB transcriptional activities. In conclusion, this study has demonstrated for the first time that sodium lactate and LPS exert synergistic effect on MMP and cytokine expression through NF-kappaB and MAPK pathways and revealed a novel mechanism potentially involved in the development of type 2 diabetes and its complications.
authors.affiliation: Ralph H. Johnson Veterans Affairs Medical Center, Charleston, South Carolina, USA.
authors.forename: Alena
authors.initials: A
authors.lastname: Nareika
authors.forename: Lin
authors.initials: L
authors.lastname: He
authors.forename: Bryan A
authors.initials: BA
authors.lastname: Game
authors.forename: Elizabeth H
authors.initials: EH
authors.lastname: Slate
authors.forename: John J
authors.initials: JJ
authors.lastname: Sanders
authors.forename: Steven D
authors.initials: SD
authors.lastname: London
authors.forename: Maria F
authors.initials: MF
authors.lastname: Lopes-Virella
authors.forename: Yan
authors.initials: Y
authors.lastname: Huang
mesh_terms: D016207:Cytokines / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004789:Enzyme Activation / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D006801:Humans; D008070:Lipopolysaccharides / Q000008:administration & dosage*; D020782:Matrix Metalloproteinases / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism*; D019354:Sodium Lactate / Q000008:administration & dosage*; D018808:Transcription Factor AP-1 / Q000378:metabolism*; D015533:Transcriptional Activation / Q000187:drug effects / Q000502:physiology; D020298:U937 Cells
chemical_list: D016207:Cytokines; D008070:Lipopolysaccharides; D016328:NF-kappa B; D018808:Transcription Factor AP-1; D020782:Matrix Metalloproteinases; D019354:Sodium Lactate