Ashbrook M J, McDonough K L, Pituch J J, Christopherson P L, Cornell T T, Selewski D T, Shanley T P, Blatt N B
Divisions of Pediatric Nephrology, University of Michigan, Ann Arbor, MI, USA.
Pediatric Critical Care, Department of Pediatrics and Communicable Diseases, University of Michigan, Ann Arbor, MI, USA.
Clin Exp Immunol. 2015 Jun;180(3):520-30. doi: 10.1111/cei.12591. Epub 2015 Apr 19.
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.
柠檬酸作为细胞代谢的核心成分，因其具有螯合钙的能力而被广泛用作抗凝剂。三磷酸腺苷（ATP）-柠檬酸裂解酶负责代谢柠檬酸，已被证明对炎症至关重要，但外源性柠檬酸影响炎症信号级联反应的能力在很大程度上仍不清楚。我们假设柠檬酸作为细胞代谢物和钙螯合剂会调节炎症反应，并通过确定临床相关水平的柠檬酸如何调节人急性单核细胞白血病细胞系（THP-1）中单核细胞对脂多糖（LPS）的促炎反应来验证这一假设。在正常培养基（0.4 mM钙）中，柠檬酸抑制LPS诱导的肿瘤坏死因子（TNF）-α和白细胞介素（IL）-8转录本，而在补充钙（1.4 mM）的培养基中，TNF-α和IL-8水平升高，且似乎与钙螯合无关。使用IL-8-荧光素酶质粒构建体，在IL-8启动子区域的激活中观察到相同的增强反应，提示存在转录调控。三羧甲基戊酸是ATP-柠檬酸裂解酶的抑制剂，它阻断了柠檬酸增强TNF-α的能力，将柠檬酸的增强作用与其通过ATP-柠檬酸裂解酶的代谢联系起来。在柠檬酸存在的情况下，在THP-1细胞的TNF-α和IL-8启动子区域观察到组蛋白乙酰化增加。我们观察到柠檬酸可通过调节炎症基因反式激活来增强和抑制促炎细胞因子的产生。这些发现表明，柠檬酸抗凝可能通过与炎症反应的复杂相互作用改变免疫功能。
