ORIGINAL PAPER Comparative proteome analysis of the tear samples in patients with low-grade keratoconus Fatih Yenihayat . O ¨ zgu ¨l Altıntas ¸ . Murat Kasap . Gu ¨rler Akpınar . Nil Gu ¨zel . Onur Sinan C ¸ elik Received: 20 May 2017 / Accepted: 1 August 2017 Ó Springer Science+Business Media B.V. 2017 Abstract Purpose To elucidate the metabolic processes play- ing roles in the formation of keratoconus (KC). Methods Tears samples were collected using capil- lary glass tubes without stimulation and without prior anesthesia from 17 patients and 16 controls. Proteomic analysis by fluorescent 2D gel electrophoresis (DIGE) coupled with MALDI-TOF/TOF was performed. The identified proteins that were differentially regulated were subjected to Ingenuity Pathway Analysis (IPA). Corneal topography analyses with Sirius topogra- phy system (Costruzioni Strumenti Oftalmici, Flor- ence, Italy) were performed on all participants. The steepest keratometry index was lower than 50 diopters in all keratoconus patients. Results DIGE analysis showed changes in abundance of nine proteins. Six of these proteins, namely serum albumin, Keratin Type II Cytoskeletal 1, IgG gamma chain-1, GAPDH, alpha-1 antitrypsin and ApoA-I, were down-regulated in the KC samples in comparison with the controls. In addition, we detected up-regulation of lysozyme C, keratin type I cytoskeletal 10 and lipocalin. The subsequent IPA predicted that NADH repair pathway is activated in the KC patients. This pathway involves generation of NADHX as a by-product via catalysis by GAPDH. NADHX is an inhibitor of several dehydrogenases and must be removed. Conclusion The involvement of NADHX repair pathway in KC should be investigated, since prelim- inary clues obtained in this study point to that direction. In particular, showing the presence of ATP-dependent NAD(P)H-hydrate dehydratase that eliminates NADHX would strengthen our findings and would be a major step toward understanding KC. Keywords Tear proteome Á Keratoconus Á DIGE Á MALDI-TOF/TOF Introduction Keratoconus is a primary corneal ectasia, with gener- ally progressive and bilateral stromal thinning and F. Yenihayat (&) Department of Ophthalmology, Kocaeli State Hospital, 41100 Kocaeli, Turkey e-mail: fthynhyt@hotmail.com O ¨ . Altıntas ¸ Department of Ophthalmology, Medical School, Acıbadem University, Istanbul, Turkey M. Kasap Á G. Akpınar DEKART Proteomics Laboratory, Medical School, Kocaeli University, Kocaeli, Turkey N. Gu ¨zel Department of Medical Biology, Medical School, Kocaeli University, Kocaeli, Turkey O. S. C ¸ elik Department of Ophthalmology, Tunceli State Hospital, Tunceli, Turkey 123 Int Ophthalmol DOI 10.1007/s10792-017-0672-6