N.Y. Research Team Discovers How Antidepressants And Cocaine Interact With Brain Cell Targets
Breakthrough Findings from Columbia University Medical Center and Weill Cornell Medical College May Lead to New Therapies for Mental Illnesses, Addiction NEW YORK (July 28, 2008) -- In a first, scientists from Columbia University Medical Center and Weill Cornell Medical College, have described the specifics of how brain cells process antidepressant drugs, cocaine and amphetamines. These novel findings could prove useful in the development of more targeted medication therapies for a host of psychiatric diseases, most notably in the area of addiction.
Dr. Jonathan Javitch Their breakthrough research, featured as the cover story in a recent issue of Molecular Cell, describes the precise molecular and biochemical structure of drug targets known as neurotransmitter-sodium symporters (NSSs), and how cells use them to enable neural signaling in the brain. A second study, published in the latest issue of Nature Neuroscience, pinpoints where the drug molecules bind in the neurotransmitter transporter -- their target in the human nervous system.
To make their observations, the research team led by Dr. Jonathan Javitch, senior author of the Molecular Cell study and contributing author to the Nature Neuroscience study, and professor of Psychiatry and Pharmacology in the Center for Molecular Recognition at Columbia University Medical Center, stabilized different structural states of the neurotransmitter-sodium-symporter molecule that relate to steps in its function. This allowed the team to study how substrates and inhibitors affect the transition between these different states, and thus to understand the way in which its function is accomplished.
"Crystallography had allowed the identification of only one structural form of the molecule, but our experiments and computations were able to identify how this form changes and thereby add an understanding of the functional role of the different forms that the molecule must adopt to accomplish transport activity," says Dr. Javitch.
"These findings are so clear and detailed at the level of molecular behavior that they will be most valuable to developing more effective therapies for mood disorders and neurologic and psychiatric diseases, and to direct effective treatments for drug addiction to cocaine and amphetamines," says co-lead author Dr. Harel Weinstein, Chairman and Maxwell M. Upson Professor of Physiology and Biophysics, and director of the Institute for Computational Biomedicine at Weill Cornell Medical College. "This research may also open the door to the development of new therapies for dopamine-neurotransmitter disorders such as Parkinson's disease, schizophrenia, and anxiety and depression."
The main surprise was the realization that two binding sites on the transporter molecule need to be filled simultaneously and cooperate in order for transport to be driven across the cell membrane. For these studies, the scientists used the crystal structure of a bacterial transporter that is very similar to human neurotransmitter transporters. They performed computer simulations to reveal the path of the transported molecules into cells. Laboratory experimentation was used to test the computational predictions and validate the researchers' inferences.
Together, these procedures revealed a finely-tuned process in which two sodium ions bind and stabilize the transporter molecule for the correct positioning of the two messenger molecules -- one deep in the center of the protein, and the other closer to the entrance. Like a key engaging a lock mechanism, this second binding causes changes in the transporter throughout the structure, allowing one of the two sodium molecules to move inward, and then release the deeply bound messenger and its sodium partner into the cell.
In the bacterial transporter studied, antidepressant molecules bind in the outer one of two sites, and stop the transport mechanism, leaving the messenger molecule outside the cell.
The second team of researchers, involving a collaboration of the Javitch and Weinstein labs with colleagues in Denmark (the labs of Ulrik Gether and Claus Loland), found that in the human dopamine transporter cocaine binds in the deep site, unlike the antidepressant binding in the bacterial transporter. Therefore, the researchers conclude that anti-cocaine therapy will be more complicated, because interfering with cocaine binding also means interference with the binding of natural messengers.
"This finding might steer anti-cocaine therapy in a completely new direction," says Dr. Weinstein.
Molecular understanding at this level of structural and dynamic detail is rare in the world of drug development, the authors note. Only about 15 percent of all drugs have a known molecular method-of-action, even though the effects of these drugs within the body -- after very stringent and controlled laboratory testing -- are well understood pharmacologically.
Contributing authors to the Molecular Cell study include Dr. Matthias Quick from Columbia University Medical Center and the New York State Psychiatric Institute, who had a major role in the experimental component; Dr. Yongfang Zhao from Columbia University Medical Center; and Dr. Lei Shi from Weill Cornell Medical College, who had a major role in the computational simulations. Lead authors of the Nature Neuroscience study are first author Dr. Thijs Beuming of Weill Cornell Medical College and senior authors Drs. Claus Loland and Ulrik Gether of The Panum Institute of the University of Copenhagen, Denmark. Additional co-authors include Drs. Julie Kniazeff, Marianne Bergmann and Klaudia Raniszewska of The Panum Institute of the University of Copenhagen; Drs. Lei Shi and Luis Gracia of Weill Cornell; and Dr. Amy Hauck Newman of the National Institute on Drug Abuse (NIDA).
The NIH supported these studies, and it is noteworthy that both the Molecular Cell and the Nature Neuroscience study share an NIH funding source, a Program Project grant awarded by the National Institute on Drug Abuse and directed by Dr. Weinstein, with Drs. Javitch and Gether each directing one of the projects. Additional support came from the Danish Medical Research Council, the Lundbeck Foundation, the Novo Nordisk Foundation and the Maersk Foundation -- all in Europe.
Columbia University Medical Center Columbia University Medical Center provides international leadership in basic, pre-clinical and clinical research, in medical and health sciences education, and in patient care. The medical center trains future leaders and includes the dedicated work of many physicians, scientists, public health professionals, dentists, and nurses at the College of Physicians & Surgeons, the Mailman School of Public Health, the College of Dental Medicine, the School of Nursing, the biomedical departments of the Graduate School of Arts and Sciences, and allied research centers and institutions. Established in 1767, Columbia's College of Physicians & Surgeons was the first institution in the country to grant the M.D. degree and is now among the most selective medical schools in the country. Columbia University Medical Center is home to the largest medical research enterprise in New York City and state and one of the largest in the United States. For more information, please visit www.cumc.columbia.edu.
Weill Cornell Medical College Weill Cornell Medical College, Cornell University's medical school located in New York City, is committed to excellence in research, teaching, patient care and the advancement of the art and science of medicine, locally, nationally and globally. Weill Cornell, which is a principal academic affiliate of NewYork-Presbyterian Hospital, offers an innovative curriculum that integrates the teaching of basic and clinical sciences, problem-based learning, office-based preceptorships, and primary care and doctoring courses. Physicians and scientists of Weill Cornell Medical College are engaged in cutting-edge research in areas such as stem cells, genetics and gene therapy, geriatrics, neuroscience, structural biology, cardiovascular medicine, transplantation medicine, infectious disease, obesity, cancer, psychiatry and public health -- and continue to delve ever deeper into the molecular basis of disease in an effort to unlock the mysteries of the human body in health and sickness. In its commitment to global health and education, the Medical College has a strong presence in places such as Qatar, Tanzania, Haiti, Brazil, Austria and Turkey. Through the historic Weill Cornell Medical College in Qatar, the Medical College is the first in the U.S. to offer its M.D. degree overseas. Weill Cornell is the birthplace of many medical advances -- including the development of the Pap test for cervical cancer, the synthesis of penicillin, the first successful embryo-biopsy pregnancy and birth in the U.S., the first clinical trial of gene therapy for Parkinson's disease, the first indication of bone marrow's critical role in tumor growth, and most recently, the world's first successful use of deep brain stimulation to treat a minimally-conscious brain-injured patient. For more information, visit www.med.cornell.edu.