Of Epigenetic Modulation by Valproic Acid in Traumatic Brain Injury – What We

TITLE PAGE Title: The ‘Omics’ of Epigenetic Modulation by Valproic Acid in Traumatic Brain Injury – What We Know and What the Future Holds Short title: The ‘Omics’ of Valproic Acid treatment for TBI Authors: Umar F. Bhatti, MD; Aaron M. Williams, MD; Patrick E. Georgoff, MD; Hasan B. Alam, MD Affiliations: Department of Surgery, University of Michigan, Ann Arbor, MI, USA. Address for correspondence: Hasan B. Alam, MD Norman Thompson Professor of Surgery, and Head of General Surgery University of Michigan Hospital 2920 Taubman Center/5331 University of Michigan Hospital 1500 E. Medical Center Drive This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/prca.201900068. This article is protected by copyright. All rights reserved. Ann Arbor, MI 48109-5331 [email protected] Abbreviations: VPA = Valproic acid HAT = Histone Acetylase HDAC = Histone Deacetylase TBI = Traumatic Brain Injury HS = Hemorrhagic Shock PBMC = Peripheral Blood Mononuclear Cells NEFL = Neurofilament Light ELISA = Enzyme-linked Immunosorbent Assay PCR = Polymerase Chain Reaction LINCS = Library of Integrated Network-based Cellular Signatures Keywords: epigenetic modulation, valproic acid, omics, traumatic brain injury, clinical trial No. of words: 2485 words This article is protected by copyright. All rights reserved. ABSTRACT Traumatic brain injury is a heterogeneous injury that is a major cause of morbidity and mortality worldwide. Epigenetic modulation via acetylation by valproic acid has shown promise as an effective pharmacological treatment for TBI; however, the mechanisms by which it improves clinical outcomes are not well-described. In recent years, omics technologies have emerged as a promising strategy to detect molecular changes at the cellular level. This review highlights the use of omics technologies in advancing the understanding of epigenetic modulation by VPA in TBI. It also describes the future role of omics techniques in developing a point of care test to guide patient selection for VPA administration. Introduction Traumatic brain injury remains a major health problem around the world.[1] It is the leading cause of morbidity and mortality in young adults. [2] In the United States alone, TBI affects nearly 1.5 to 2.0 million each year,[3] resulting in approximately 250,000 hospitalizations. As a result, 50,000 Americans die yearly, and 90,000 experience long-term disability. [4] Furthermore, according to the Center for Disease Control and Prevention, the estimated economic cost of TBI in 2010 was approximately $76.5 billion. [5] Despite recent advances in medical care, there is a lack of effective pharmacologic treatment options for TBI. However, valproic acid, a histone deacetylase inhibitor, has shown promise in animal models of TBI.[6] [7] The Nature of Traumatic Brain Injury TBI is a heterogeneous injury.[8] The many classification systems for TBI include those based on injury severity,[9] anatomy of the injured region,[10] mechanism of injury,[11]pathophysiology.[12] and prognostic modelling. [13] Although previously considered to be a single event, TBI is a disease process that starts with the inciting injury and may progress secondary to insults such as hypoxia and This article is protected by copyright. All rights reserved. hypotension. TBI may even progress many years after the primary injury. [14] Due to its heterogeneous nature, development of pharmacologic interventions for TBI is challenging. [15] [16] Role of Epigenetic Modulation in TBI Recently, acetylation of proteins (histone and non-histone) has gained attention as a therapeutic strategy for a variety of diseases, including cancer and trauma.[17] Histone acetylase and histone deacetylase (HDAC) are two enzymes that influence the acetylation status of a cell.[18] An imbalance between these key enzymes may result in modification of critical activator and silencer proteins involved in gene transcription. In an inactive form, the chromatin (complex of DNA and proteins within nucleus) is in a condensed conformation. Acetylation of these proteins promotes chromatin relaxation, allowing transcription factors to bind to chromosomes and thereby promoting gene expression.[19] Valproic Acid (VPA) – A Histone Deacetylase Inhibitor VPA, an FDA-approved drug for epilepsy, is an inhibitor of the enzyme histone deacetylase (HDAC).[20] By inhibiting HDAC and promoting acetylation of histones, VPA can alter gene expression. This action of VPA has proven beneficial in a variety of pathological states, including TBI.[18] The downstream effects of VPA are considered to be ‘pro-survival’ as it can exploit innate pathways that promote cell growth and differentiation and inhibit apoptosis and inflammation. [21] Several pre-clinical studies have demonstrated VPA’s effects in TBI with and without haemorrhage [22] [23] and spinal cord injuries[24]. Swine models of TBI have been used to demonstrate that a single large dose of VPA (150 mg/kg) can decrease brain lesion size and swelling, minimize neurologic injury, and shorten the time to recovery.[6] Because of its robust effects in animals, VPA is This article is protected by copyright. All rights reserved. now being tested in humans. A phase I dose-escalation trial was recently finished, demonstrating the safety of high doses of VPA in healthy humans (ClinicalTrials.gov identifier NCT01951560). [25] The Emergence of ‘Omics’ Technologies Because of its marked effects in the treatment of TBI in preclinical studies, understanding VPA’s mechanisms of action in trauma has become an area of interest. Traditional laboratory techniques like western blot, enzyme-linked immune-sorbent assay (ELISA) and polymerase chain reaction (PCR) have proven to be limited in many ways. For example, western blot can only be performed if the protein of interest has a specific primary antibody available. Even if an antibody to the target protein is available, it may have off-target effects which may decrease the accuracy of results. [26] Antibody cross-reactivity may not only affect the results of western blot, but also of ELISA. [27] Also, when proteins are absorbed to plastic surfaces, the epitopes of these proteins can get denatured resulting in alterations in antigens, which is known as the surface effect. Such changes can limit the utility of enzyme immunoassays.[28] On the other hand, omics technologies have emerged as a promising strategy to discover biological changes. [29] Knowledge of the molecular and cellular changes has afforded correlation of cellular events and effects. Omics technologies, including next-generation DNA and RNA sequencing, proteomics, and metabolomics, have enhanced our understanding of disease states, including TBI. In rats subjected to lateral fluid-percussion injury, peri-lesional cortex demonstrated an increase in transcription factors Pax6, Tp73, Cebpd, and Myb. Library of Integrated Network-based Cellular Signatures analysis has shown that certain drugs already in clinical use can modulate the expression of these key regulatory transcription factors.[30] Another study that used fresh human brain biopsies for mass-spectrometry (MS)-based proteomic analysis showed that there are several proteomic alterations in these brains following TBI. This study also demonstrated that these alterations were more pronounced in patients This article is protected by copyright. All rights reserved. with widespread axonal injury when compared with focal injury, which may result in a rapid induction of secondary brain injury in these severely injured brains.[31] While the pathological changes associated with TBI have been studied extensively, a gap in knowledge remains as to how therapeutic interventions, such as VPA, may improve clinical outcomes following TBI. We, therefore, decided to utilize these omics techniques to advance the understanding of VPA’s mechanisms of action for the treatment of TBI. Here, we summarize our findings. Overview of our TBI model All the TBI models used in our experiments are highly reproducible and clinically relevant.[6] [7] In summary, female Yorkshire swine are acquired from Michigan State university, East Lansing, Michigan, USA, and allowed an acclimation period of five days. On the day of experiment, swine are anesthetized, and a transdermal fentanyl patch is placed for pain control. Prophylactic antibiotics are administered via peripheral venous catheters. Femoral vessels are cannulated for haemorrhage and blood pressure monitoring. A craniotomy is performed to expose the dura. A stereotactic computer- controlled cortical impact (CCI) device that is developed by the University of Michigan Innovation Centre is used to induce the TBI. VPA, at the dose of 150 mg/kg, is administered via a peripheral intravenous catheter. [6, 32] Details of the model are already published. [33] TBI Triggers a Genomic and Proteomic Storm Although genomic responses to injury remain an expanding area of research, the interest in epigenetic mechanisms involved in the pathogenesis of TBI has only recently gained attention. Recent studies demonstrate that TBI results in numerous genomic changes, including modifications in DNA, post-translational changes to histones, and variations at the level of non-coding RNA. [34] These changes are collectively referred to as ‘epigenetics’ and involve modulation

Load more