1 3 Arch Toxicol DOI 10.1007/s00204-016-1830-8 ORGAN TOXICITY AND MECHANISMS TLR4-mediated inflammation is a key pathogenic event leading to kidney damage and fibrosis in cyclosporine nephrotoxicity Cristian González-Guerrero 1,2 · Pablo Cannata-Ortiz 2,3 · Consuelo Guerri 4 · Jesús Egido 1,5 · Alberto Ortiz 1,2,5 · Adrián M. Ramos 1,2,6 Received: 16 June 2016 / Accepted: 24 August 2016 © Springer-Verlag Berlin Heidelberg 2016 also reduced tubular damage and drastically prevented the development of kidney fibrosis. In vivo and in vitro CsA promoted secretion of the TLR ligand HMGB1 by tubu- lar cells upstream of TLR4 activation, and prevention of HMGB1 secretion significantly reduced CsA-induced synthesis of MCP-1, suggesting that HMGB1 may be one of the mediators of CsA-induced TLR4 activation. These results suggest that TLR4 is a potential pharmacological target in CsA nephrotoxicity. Keywords Cyclosporine A · TLR4 · Innate immunity · Nephrotoxicity · Inflammation · Fibrosis Introduction Cyclosporine A (CsA) was the first calcineurin inhibi- tor (CNI) available in the clinic and is still extensively used throughout the world. In fact, CsA is the only CNI included in the last updated World Health Organization (WHO) list of essential medicines (WHO 2015). CsA was a breakthrough that increased organ and patient sur- vival. Moreover, CsA is routinely used to treat autoim- mune disorders (Ponticelli 2005). Unfortunately, chronic CsA therapy increases the risk of chronic nephrotoxicity (Naesens et al. 2009). Although acute renal side effects may be reversible and can be minimized through strate- gies to reduce drug exposure, this often does not prevent chronic nephrotoxicity, a subtle, non-reversible process leading to progressive organ fibrosis (Sawinski et al. 2016). Molecular mechanisms underlying CsA nephrotoxicity have been extensively researched, although they remain to be completely characterized. Inflammation encompasses adaptive and protective mechanisms set in motion to repair damaged tissues and eliminate invading microorganisms. Abstract Cyclosporine A (CsA) successfully prevents allograft rejection, but nephrotoxicity is still a dose-lim- iting adverse effect. TLR4 activation promotes kidney damage but whether this innate immunity receptor medi- ates CsA nephrotoxicity is unknown. The in vivo role of TLR4 during CsA nephrotoxicity was studied in mice co- treated with CsA and the TLR4 inhibitor TAK242 and also in TLR4 -/- mice. CsA-induced renal TLR4 expression in wild-type mice. Pharmacological or genetic targeting of TLR4 reduced the activation of proinflammatory signaling, including JNK/c-jun, JAK2/STAT3, IRE1α and NF-κB and the expression of Fn14. Expression of proinflammatory fac- tors and cytokines was also decreased, and kidney mono- cyte and lymphocyte influx was prevented. TLR4 inhibition Electronic supplementary material The online version of this article (doi:10.1007/s00204-016-1830-8) contains supplementary material, which is available to authorized users. * Adrián M. Ramos amramos@fjd.es 1 Laboratory of Nephrology and Vascular Pathology, IIS-Fundación Jiménez Díaz, School of Medicine, Madrid, Spain 2 REDINREN, Madrid, Spain 3 Pathology, IIS-Fundación Jiménez Díaz, School of Medicine, UAM, Madrid, Spain 4 Department of Cellular Pathology, Centro de Investigación Príncipe Felipe, Valencia, Spain 5 Fundación Renal Íñigo Álvarez de Toledo (FRIAT), Madrid, Spain 6 Laboratorio de Patología Renal y Vascular (Investigación, 4° planta), Instituto de Investigación Sanitaria-Fundación Jiménez Díaz, Av. Reyes Católicos N°2, CP28040 Madrid, Spain