title: Citrate modulates lipopolysaccharide-induced monocyte inflammatory responses.
abstract: Citrate, a central component of cellular metabolism, is a widely used anti-coagulant due to its ability to chelate calcium. Adenosine triphosphate (ATP)-citrate lyase, which metabolizes citrate, has been shown to be essential for inflammation, but the ability of exogenous citrate to impact inflammatory signalling cascades remains largely unknown. We hypothesized that citrate would modulate inflammatory responses as both a cellular metabolite and calcium chelator, and tested this hypothesis by determining how clinically relevant levels of citrate modulate monocyte proinflammatory responses to lipopolysaccharide (LPS) in a human acute monocytic leukaemia cell line (THP-1). In normal medium (0.4 mM calcium), citrate inhibited LPS-induced tumour necrosis factor (TNF)-α and interleukin (IL)-8 transcripts, whereas in medium supplemented with calcium (1.4 mM), TNF-α and IL-8 levels increased and appeared independent of calcium chelation. Using an IL-8-luciferase plasmid construct, the same increased response was observed in the activation of the IL-8 promoter region, suggesting transcriptional regulation. Tricarballylic acid, an inhibitor of ATP-citrate lyase, blocked the ability of citrate to augment TNF-α, linking citrate's augmentation effect with its metabolism by ATP-citrate lyase. In the presence of citrate, increased histone acetylation was observed in the TNF-α and IL-8 promoter regions of THP-1 cells. We observed that citrate can both augment and inhibit proinflammatory cytokine production via modulation of inflammatory gene transactivation. These findings suggest that citrate anti-coagulation may alter immune function through complex interactions with the inflammatory response.
authors.affiliation: Divisions of Pediatric Nephrology, University of Michigan, Ann Arbor, MI, USA.
authors.forename: M J
authors.initials: MJ
authors.lastname: Ashbrook
authors.affiliation: Pediatric Critical Care, Department of Pediatrics and Communicable Diseases, University of Michigan, Ann Arbor, MI, USA.
authors.forename: K L
authors.initials: KL
authors.lastname: McDonough
authors.affiliation: Divisions of Pediatric Nephrology, University of Michigan, Ann Arbor, MI, USA.
authors.forename: J J
authors.initials: JJ
authors.lastname: Pituch
authors.affiliation: Divisions of Pediatric Nephrology, University of Michigan, Ann Arbor, MI, USA.
authors.forename: P L
authors.initials: PL
authors.lastname: Christopherson
authors.affiliation: Pediatric Critical Care, Department of Pediatrics and Communicable Diseases, University of Michigan, Ann Arbor, MI, USA.
authors.forename: T T
authors.initials: TT
authors.lastname: Cornell
authors.affiliation: Divisions of Pediatric Nephrology, University of Michigan, Ann Arbor, MI, USA.
authors.forename: D T
authors.initials: DT
authors.lastname: Selewski
authors.affiliation: Pediatric Critical Care, Department of Pediatrics and Communicable Diseases, University of Michigan, Ann Arbor, MI, USA.
authors.forename: T P
authors.initials: TP
authors.lastname: Shanley
authors.affiliation: Divisions of Pediatric Nephrology, University of Michigan, Ann Arbor, MI, USA.
authors.forename: N B
authors.initials: NB
authors.lastname: Blatt
mesh_terms: D000107:Acetylation; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D045744:Cell Line, Tumor; D019343:Citric Acid / Q000378:metabolism* / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D006657:Histones / Q000378:metabolism; D006801:Humans; D007249:Inflammation / Q000235:genetics / Q000276:immunology* / Q000378:metabolism*; D016209:Interleukin-8 / Q000235:genetics / Q000378:metabolism; D008070:Lipopolysaccharides / Q000276:immunology*; D009000:Monocytes / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics; D015533:Transcriptional Activation; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism
chemical_list: D006657:Histones; D016209:Interleukin-8; D008070:Lipopolysaccharides; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D019343:Citric Acid; D002118:Calcium
keywords: citrate; epigenetics; inflammation; monocytes