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New research provides expanded insights into the brain's response to opioids

June 21, 2018

(Philadelphia, PA) - Opioids are powerful painkillers that act on the brain, but they have a range of harmful side effects including addiction. Researchers from the Max Planck Institute of Biochemistry (MPIB) in collaboration with researchers from the Medical University of Innsbruck, Austria, University of Innsbruck, and the Lewis Katz School of Medicine at Temple University (LKSOM), have developed a tool that gives deeper insights into the brain's response to opioids. Using mass spectrometry, they determined changes of proteins' phosphorylation patterns - the molecular switches of proteins - in five different regions of the brain and assigned them to the desired and the undesired effects of opioid treatment. Their results, which are published in the journal Science, will lead the way for identification of novel drug targets and design of a new class of painkillers with fewer side effects.

The LKSOM team's participation in this research was led by Lee-Yuan Liu-Chen, PhD, Professor of Pharmacology in the Center for Substance Abuse Research. Other researchers contributing to the study from LKSOM are Chongguang Chen, a research technologist and Yi-Ting Chiu, a former postdoctoral fellow, in Dr. Liu-Chen's group in the Center for Substance Abuse Research.

The signal cascades that are used by cells to respond to external stimuli resemble the chain of command of a company. Activation of a receptor, which acts as the head of the company, gives instruction to other proteins inside the cells, which act as groups of subordinates. This information is then passed down to lower levels of the organizational structure via signal cascades of other interacting proteins. Like the employees who perform different tasks to keep a company running, proteins are the molecular machines that conduct majority of functions in the cells. In cells, instructions are passed along to other proteins by changing the function of these 'cellular employees'. One way to change the function is by "phosphorylations" - the attachment of a phosphate molecule to proteins. By analyzing all the molecular switches at the same time, activity of signaling pathways in cells or an organ can be determined. Studying this chain of command gives a more precise insight into the currently occurring processes within cells than studying the DNA, the genetic "blueprint", which is almost identical in all cells.

Snapshot of protein activities

Researchers in the laboratory of MPIB director and co-corresponding author on the study, Matthias Mann, use mass spectrometry - a method that determines the identity and quantity of proteins in a sample - to describe phosphorylation patterns of thousands of proteins in many organ specimens, a term coined as phosphoproteomics. In the recent study, they analyzed the activation of signaling pathways in different regions of the brain, responding to opioid-like drugs. To achieve this goal, the researchers used a recently developed method named EasyPhos.

To understand how drugs like opioids work, researchers must know their influence on the brain. "With phosphoproteomics, we can analyze more than 50,000 phosphorylation sites at once and get a snapshot of all pathways that are active in the brain samples during that time. We found more than 1,000 changes after exposure to an opioid-like drug, showing a global effect of these drugs on signaling in the brain," says Jeffrey Liu, the lead author of the study. Previous methods could not capture protein phosphorylations at a comparable scale and missed many important signaling pathways that were switched on or off.

Phosphoproteomics - a versatile tool

"In our study, we looked at activation of pathways in the brain that are responsible for desired effects of opioids like painkilling. In contrast, the parallel activation of other pathways causes undesired side effects", says Liu. The researchers used phosphoproteomics to measure how active these beneficial and side effects-causing pathways were. Christoph Schwarzer from the Medical University in Innsbruck, who collaborated with Liu and Mann for this study, focuses his research on these opioid-activated signaling cascades in the brain. During the development of new drugs, these data can be used to identify potential substances that give strong therapeutic benefits and have few side effects. In addition, this study also shows the promise of reducing side effects by interfering with signal cascades. So this study introduces a novel concept for opioid-based therapeutics. Current drugs of the opioid family are potent painkillers but quickly lead to addiction. Thus, there is an urgent need for novel non-addictive opioids.

Imagining the proteins in the brain as a company, phosphoproteomics allows the researchers to follow the activity of all employees at once instead of focusing on a selected few. Mass spectrometry can be a powerful tool to study drug targets in the brain or other organs. The mass spectrometry expert Matthias Mann says, "The current epidemic of opioid-related deaths in the US is a shocking example for the potential consequences of prescription drugs with strong side effects like addiction. With mass spectrometry, we can get a global view of the effects of drugs and streamline the development of new drugs with fewer side effects." Mann explains that the design of new drugs is just one of many potential applications of phosphoproteomics and predicts that the method can also be used to generate knowledge on how cells use their chains of command to process information and the effects on drugs in other organs.

Dr. Liu-Chen's group performed behavior experiments using two drugs and found that they have similar analgesic effects, but very different levels of side effects. Brains of animals treated with the two drugs were analyzed by MPIB for phosphoproteomic differences, which were found to belong to a few signaling pathways. Inhibition of one of the identified pathways greatly reduced some of the side effects.
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About Temple Health

Temple University Health System (TUHS) is a $2.1 billion academic health system dedicated to providing access to quality patient care and supporting excellence in medical education and research. The Health System consists of Temple University Hospital (TUH), ranked among the "Best Hospitals" in the region by U.S. News & World Report; TUH-Episcopal Campus; TUH-Northeastern Campus; Fox Chase Cancer Center, an NCI-designated comprehensive cancer center; Jeanes Hospital, a community-based hospital offering medical, surgical and emergency services; Temple Transport Team, a ground and air-ambulance company; and Temple Physicians, Inc., a network of community-based specialty and primary-care physician practices. TUHS is affiliated with the Lewis Katz School of Medicine at Temple University, and Temple University Physicians, which is Temple Health's physician practice plan comprised of more than 500 full-time and part-time academic physicians in 20 clinical departments.

The Lewis Katz School of Medicine (LKSOM), established in 1901, is one of the nation's leading medical schools. Each year, the School of Medicine educates approximately 840 medical students and 140 graduate students. Based on its level of funding from the National Institutes of Health, the Katz School of Medicine is the second-highest ranked medical school in Philadelphia and the third-highest in the Commonwealth of Pennsylvania. According to U.S. News & World Report, LKSOM is among the top 10 most applied-to medical schools in the nation.

Temple Health refers to the health, education and research activities carried out by the affiliates of Temple University Health System (TUHS) and by the Katz School of Medicine. TUHS neither provides nor controls the provision of health care. All health care is provided by its member organizations or independent health care providers affiliated with TUHS member organizations. Each TUHS member organization is owned and operated pursuant to its governing documents.

About the Max Planck Institute of Biochemistry

The Max Planck Institute of Biochemistry (MPIB) belongs to the Max Planck Society, an independent, non-profit research organization dedicated to top-level basic research. As one of the largest Institutes of the Max Planck Society, about 800 employees from 45 nations work here in the field of life sciences. In currently about 35 departments and research groups, the scientists contribute to the newest findings in the areas of biochemistry, cell biology, structural biology, biophysics and molecular science. The MPIB in Munich-Martinsried is part of the local life-science-campus in close proximity to the Max Planck Institute of Neurobiology, a Helmholtz Center, the Gene-Center, several bio-medical faculties of the Ludwig-Maximilians-Universität München and the Innovation and Founding Center Biotechnology (IZB). (http://biochem.mpg.de)

Temple University Health System

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