Proteomics: Identifying Organ-Specific Blood Biomarkers for Acute Liver Injury

Oct. 6, 2016

3 Bullets:

  • Finding organ-specific blood biomarkers for disease that are clinically useful is challenging.
  • New study identifies organ-specific blood biomarkers for acute liver injury caused by over-exposure to acetaminophen.
  • ISB researchers use the powerful, targeted mass spectrometry approach of selected reaction monitoring (SRM) to identify proteins.

Adverse effects associated with therapeutic drugs are a serious health concern and a costly challenge for healthcare systems. Many drug-induced adverse effects target the liver due to their immediate exposure through first-pass pharmacokinetics and the liver’s active roles in metabolizing xenobiotics.

To assess probable injury to an organ, it is important to monitor biologic materials that originate exclusively or primarily in that organ, in this case, liver-enriched proteins. For decades, cellular integrity indicators, such as levels of the transaminases, alanine aminotransferase (ALT, GPT), and aspartate aminotransferase (AST, GOT) in serum, have been used to reflect liver injury. However, use of these enzymes as surrogate markers of liver injury is not ideal. Because they are ubiquitously expressed at similar levels in multiple organs, an interpretation of their change in levels in blood in response to a toxin can be complicated as a consequence of these enzymes originating from many tissues other than liver.

Finding blood biomarkers to reflect the status of specific pathological conditions has been a major focus in academia and industry. Various high-throughput approaches have been applied to gain comprehensive molecular profiles, although there have been little success translating the findings to clinically useful biomarkers. In developing diagnostic markers, the most common scheme is to first create a candidate panel by discovering molecules relevant to disease condition, assess the panel’s diagnostic performance, and then validate the panel on a different set of samples. To discover markers that represent biological networks and hence could be employed as proxies for toxin-perturbed changes in their cognate networks in a particular organ, we employed a different strategy by focusing on proteins enriched in disease-associated organs. We identified 131 liver-enriched proteins for mouse by comparative organ-rich transcript analyses, then determined which of the proteins encoded by these transcripts could be detected in the blood, and finally measured the concentration changes of these proteins by SRM in plasma samples from toxin-exposed mice. The same strategy was also used in serum samples from acetaminophen overdose patients.

Read more about the methods and results.

Blood bathes all organs of the body, which synthesize as well as secrete/release proteins and other molecules, including small molecules and nucleic acids, into blood. Under pathological conditions the profile of molecular exchange between organs and blood will be affected as a consequence of their cognate networks becoming perturbed by diseases (or toxins); therefore, analyzing the changes of molecular profiles in blood may serve as an informative window to distinguish health and disease and to provide basic insights into the pathophysiology of the disease. The approach we adopted by monitoring the change in the concentrations of organ-enriched proteins in blood is especially informative because these proteins specifically reflect disease-affected organs; hence, they provide direct insights into the pathophysiology and severity of the disease. Many new potential blood markers identified in this study performed better in reflecting drug-induced liver injury than traditional blood AST and ALT measurements. Using this approach, more informative and accurate blood markers can be identified. High-quality antibodies, aptamers, or synthetic capture agents against these proteins can then be developed and incorporated in devices to detect a set of diseases, including drug-induced injuries. The development of microfluidic devices offers the possibility of using a fraction of a droplet of blood for such assessment, thus making it easier to follow the dynamics of the disease with frequent blood samplings. These diagnostic platforms may provide the foundation for convenient, low-cost, point-of-care and even possibly self-administered tests, which is a key step toward the contemporary predictive, preventive, personalized, and participatory (P4) medicine.

Journal: Journal of Proteome Research
Title: Identification of Organ-Enriched Protein Biomarkers of Acute Liver Injury by Targeted Quantitative Proteomics of Blood in Acetaminophen- and Carbon-Tetrachloride-Treated Mouse Models and Acetaminophen Overdose Patients
Authors: Shizhen Qin, Yong Zhou, Li Gray, Ulrike Kusebauch, Laurence McEvoy, Daniel J. Antoine, Lucy Hampson, Kevin B. Park, David Campbell, Juan Caballero, Gustavo Glusman, Xiaowei Yan, Taek-Kyun Kim, Yue Yuan, Kai Wang, Lee Rowen, Robert L. Moritz, Gilbert S. Omenn, Munir Pirmohamed, and Leroy Hood