Release, Cytokine

Cytokines are small, soluble molecules secreted by cells to enable intercellular communication. Cytokines may act on the cells that secrete them (autocrine action), on nearby cells (paracrine action), as well as on distant cells (endocrine action). Cytokines can act synergistically or antagonistically, and secretion from one cell can trigger upregulation of a further range of cytokines from the same cell or others ^[1]. Most cells in the body are able to secrete them, and several subfamilies belong to the group of cytokines, such as chemokines, interferons, interleukins, tumor necrosis factors (TNF), transforming growth factors (TGF) and colony-stimulating factors. They are important players in modulating fundamental biological processes, including body growth, adiposity, lactation, hematopoiesis, and also inflammation and immunity^[2]. Damaged cells, such as apoptotic cells, can trigger the upregulation and release of cytokines to induce the inflammatory response. An important receptor responsible for cell death-related cytokine regulation is Fas, a cell surface glycoprotein which belongs to the tumor necrosis factor (TNF) receptor family. The role of Fas in the onset of inflammation by upregulating inflammatory cytokines is increasingly discussed. Fas-activation can trigger the production of MCP-1 and IL-8 and its associated chemotaxis of phagocytes toward apoptotic cells^[3].

TNF-α is an inflammatory mediator that can be secreted by many cell types, including hepatocytes and Kupffer cells. TNF-induced cytokines and chemokines, such as IL-6, IL-8, GMCSF, CXCL1, and RANTES, can trigger immune responses by producing acute phase proteins and recruitment of inflammatory cells such as neutrophils, macrophages, and basophils to the site of inflammation. Moreover, an increased production of monocytes/macrophages from bone marrow is triggered^[3].

On the other hand, inflammation can be suppressed by cytokines and mediators such as IL-10 and TGF-β. In the liver, TGF-β1 is the most abundant isoform and is secreted by immune cells, stellate cells, and epithelial cells. IL-10 inhibits T cell-, monocyte-, and macrophage-mediated functions and has been detected in several liver cells, in¬cluding hepatocytes, stellate cells, and Kupffer cells ^[2].

Methods that have been previously reviewed and approved by a recognized authority should be included in the Overview section above. All other methods, including those well established in the published literature, should be described here. Consider the following criteria when describing each method: 1. Is the assay fit for purpose? 2. Is the assay directly or indirectly (i.e. a surrogate) related to a key event relevant to the final adverse effect in question? 3. Is the assay repeatable? 4. Is the assay reproducible?

mRNA expression levels of inflammatory cytokines can be determined by using real-time PCR as described in ^[4]. Equally, In Situ Hybridization of mRNA in liver tissue can be used ^[5].

Plasma levels of pro-inflammatory cytokines, or levels in cell supernatants can be analysed by enzyme linked immunosorbent assay (ELISA) using commercial kits ^[6][3]. A more advanced system was described recently by using a multiplex immunoassay platform. In a 96 well plate format the authors describe the analysis of blood, urine and breath samples of human volunteers in a Meso Scale Discovery (MSD) multiplex electrochemiluminescent immunoassay system ^[7].

^[4][6][5]: mouse ^[3][7]: human

1. ↑ Zhang JM, An J. Cytokines, inflammation, and pain. Int Anesthesiol Clin. 2007 Spring;45(2):27-37
2. ↑ ^{2.0 2.1} Braunersreuther V, Viviani GL, Mach F, Montecucco F. Role of cytokines and chemokines in non-alcoholic fatty liver disease. World J Gastroenterol. 2012 Feb 28;18(8):727-35
3. ↑ ^{3.0 3.1 3.2 3.3} Cullen SP, Henry CM, Kearney CJ, Logue SE, Feoktistova M, Tynan GA, Lavelle EC, Leverkus M, Martin SJ. Fas/CD95-induced chemokines can serve as "find-me" signals for apoptotic cells. Mol Cell. 2013 Mar 28;49(6):1034-48
4. ↑ ^{4.0 4.1} Cui Y, Liu H, Zhou M, Duan Y, Li N, Gong X, Hu R, Hong M, Hong F. Signaling pathway of inflammatory responses in the mouse liver caused by TiO2 nanoparticles. 2011; J. Biomed. Mater. Res. - Part A 96 A:221–229
5. ↑ ^{5.0 5.1} Faouzi S, Burckhardt BE, Hanson JC, Campe CB, Schrum LW, Rippe RA, Maher JJ. Anti-Fas induces hepatic chemokines and promotes inflammation by an NF-kappa B-independent, caspase-3-dependent pathway. J Biol Chem. 2001 Dec 28;276(52):49077-82
6. ↑ ^{6.0 6.1} Ma L, Zhao J, Wang J, Liu J, Duan Y, Liu H, Li N, Yan J, Ruan J, Wang H, Hong F. The Acute Liver Injury in Mice Caused by Nano-Anatase TiO2. Nanoscale Res Lett. 2009 Aug 1;4(11):1275-85
7. ↑ ^{7.0 7.1} Stiegel MA, Pleil JD, Sobus JR, Morgan MK, Madden MC. Analysis of inflammatory cytokines in human blood, breath condensate, and urine using a multiplex immunoassay platform. Biomarkers. 2015 Feb;20(1):35-46