Urinary a1-Antichymotrypsin: A Biomarker of Prion Infection Gino Miele1¤*, Harald Seeger1, Denis Marino1, Ralf Eberhard1, Mathias Heikenwalder1, Katharina Stoeck1, Max Basagni2, Richard Knight3, Alison Green3, Francesca Chianini4, Rudolf P. Wu¨ thrich5, Christoph Hock6, Inga Zerr7, Adriano Aguzzi1* 1 Department of Pathology, Universita¨tsSpital Z u¨rich, Institute of Neuropathology, Zu¨ rich, Switzerland, 2 Prion Diagnostica Srl, Rho, Italy, 3 The National Creutzfeldt-Jakob Disease Surveillance Unit, Western General Hospital, Edinburgh, United Kingdom, 4 Moredun Research Institute, Pentlands Science Park, Edinburgh, United Kingdom, 5 Universita¨tsSpital Z u¨rich, Clinic for Nephrology, Zu¨ rich, Switzerland, 6 Division of Psychiatry Research, University of Zu¨ rich, Z u¨rich, Switzerland, 7 National TSE Reference Center, Department of Neurology, Medical Faculty, Georg-August University, Go¨ ttingen, Germany Abstract The occurrence of blood-borne prion transmission incidents calls for identification of potential prion carriers. However, current methods for intravital diagnosis of prion disease rely on invasive tissue biopsies and are unsuitable for large-scale screening. Sensitive biomarkers may help meeting this need. Here we scanned the genome for transcripts elevated upon prion infection and encoding secreted proteins. We found that a1-antichymotrypsin (a1-ACT) was highly upregulated in brains of scrapie-infected mice. Furthermore, a1-ACT levels were dramatically increased in urine of patients suffering from sporadic Creutzfeldt-Jakob disease, and increased progressively throughout the disease. Increased a1-ACT excretion was also found in cases of natural prion disease of animals. Therefore measurement of urinary a1-ACT levels may be useful for monitoring the efficacy of therapeutic regimens for prion disease, and possibly also for deferring blood and organ donors that may be at risk of transmitting prion infections. Citation: Miele G, Seeger H, Marino D, Eberhard R, Heikenwalder M, et al. (2008) Urinary a1-Antichymotrypsin: A Biomarker of Prion Infection. PLoS ONE 3(12): e3870. doi:10.1371/journal.pone.0003870 Editor: Manuel B. Graeber, Imperial College London, United Kingdom Received October 27, 2008; Accepted November 12, 2008; Published December 5, 2008 Copyright: 2008 Miele et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by a grant from the Swiss National Science Foundation (G.M.), and in part by grants from the UK Department of Environment, Food and Rural Affairs (A.A. & G.M.) an EU Framework Programme 6 STREP grant (A.A.) and Nationale TSE-Forschungsplattform: Etablierung einer nationalen CJD- Probenbank (BMBF, 01KO0101) and CJK-Netz (Forschungsnetz zur Verbesserung der Fr u¨h- und Differentialdiagnose der CJK und rasch progressiver Demenzen, BMBF 01 610 301) to Inga Zerr. Competing Interests: Max Bassagni has an interest in Prion Diagnostica Srl, which commercializes prion detection assays. All remaining authors declare no conflict of interests. * E-mail: g.miele@dundee.ac.uk (GM); adriano.aguzzi@usz.ch (AA) ¤ Current address: Translational Medicine Research Collaboration, Sir James Black Centre, University of Dundee, Dundee, United Kingdom Introduction The prion [1] is the infectious agent causing transmissible spongiform encephalopathies, which include sporadic (sCJD) and variant Creutzfeldt-Jakob disease (vCJD) in humans, scrapie in sheep, bovine spongiform encephalopathy (BSE) in cattle, and chronic wasting disease (CWD) in cervids [2]. Although prions may replicate in extraneural tissues [3,4], cellular damage is essentially limited to the central nervous system (CNS). The molecular mechanisms underlying prion replication and subse- quent neural damage are not entirely understood. No effective therapeutic strategies are available. An essential component of the prion is PrPSc, an abnormally folded, aggregated isoform of the host protein PrPC [5]. To date, all validated laboratory assays for prion diseases rely on the immunochemical detection of PrPSc. These methods are highly specific, but suffer from limited sensitivity as one infectious prion may be equivalent to ,102 aggregated PrPSc molecules [6] – which is much lower than the threshold of detection of most immunoassays. Additionally, the presence of excess PrPC in complex biological fluids may confound immunochemical detec- tion, even if biophysical detection methods are employed. Consequently, while positive detection of PrPSc suffices to establish a firm diagnosis of prion infection, its absence by no means rules out the presence of prion infectivity. The hundreds of iatrogenic transmissions through organ extracts [7], contaminated surgical instruments [8], and probably through blood transfusions [9,10] have tragically highlighted the current inability of diagnosing presymptomatic prion infections. While there has been recent progress in detecting low amounts of PrPSc in blood of experimentally inoculated hamsters by protein misfolding cyclic amplification [11], it is unknown whether this technology possesses adequate sensitivity and throughput for prion detection in human blood. The use of surrogate biomarkers represents a diagnostic strategy fundamentally different to those delineated above. Since they typically identify secondary host reactions, surrogate biomarkers of prion infection cannot aspire at matching the specificity of PrPSc detection. On the other hand, surrogate biomarkers may be useful for identifying subjects at risk, and specifying acceptance or deferral of blood donations. In such cases high sensitivity (i.e. the identification of all suspect individuals) is more important than absolute diagnostic specificity, as the latter can be supplied by confirmatory assays. PLoS ONE | www.plosone.org 1 December 2008 | Volume 3 | Issue 12 | e3870