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UCLA Division of Digestive Diseases


Meet the Team


Daniel Hommes, MD, PhD
Director, Clinical Care & Clinical Research, UCLA Center for Inflammatory Bowel Diseases
Director, Quality Initiative Program

Dr. Hommes is a medical specialist whose professional aims include the improvement of the quality of life of patients suffering from inflammatory bowel diseases (IBD) through basic science, translational research and healthcare delivery innovations. 

He is a board-certified internist and gastroenterologist specializing in inflammatory bowel diseases (IBD). After completing medical school at the University of Amsterdam, he spend many years working in the Academic Medical Center (Amsterdam) where he qualified as an internist (2000) and later as a gastroenterologist (2002). His PhD thesis (1994) dealt with novel drug targets for IBD, supervised by Prof Dr Sander van Deventer and Prof Dr Guido Tytgat. In 2001, he was appointed Head of the IBD department in the Academic Medical Center in Amsterdam.

In 2006, Dr. Hommes moved to Leiden, the Netherlands, to become Chair of the Department of Gastroenterology and Hepatology at the Leiden University Medical Center (LUMC). In 2007, he was appointed full professor of Gastroenterology and Hepatology at the University of Leiden. He successfully reorganized the department, focusing on IBD, liver diseases (including liver transplantation) and colorectal cancer. He established a clinical trial center as well as a basic research lab with 4 post-docs and 12 PhD students. In addition, he designed 'CuraRata' (www.curarata.com), a platform for personalized medicine successfully piloted in IBD patients and officially launched by the Dutch Minister of Health.

Nationally, Dr. Hommes was one of the founders of the Dutch Academic IBD Society ICC which he chaired from 2003 until 2007. Also, he initiated the Pearl String Initiative (PSI) in 2006, a national academic biobanking infrastructure between the eight Dutch University Medical Centers for eight disease areas, supported by a € 35 million Dutch Government funding program. Internationally, Daniel served, since 2001, as primary investigator in numerous IBD programs and studies and was invited to act as both a consultant and member of advisory boards on many occasions for a wide variety of biomedical industry. He has authored well over 210 peer-reviewed papers and has lectured all around the globe. His interest and expertise in integrating biobanking into healthcare led to a number of consultancies in Europe and the US. In addition, he serves as reviewer and editor for medical journals. From 2004 to 2008, he chaired the Scientific Committee of the European Crohn´s and Colitis Organisation ECCO, and from 2010 until 2012 he served as ECCO's President.

In 2011, Dr. Hommes moved to Los Angeles where he was appointed Professor of Medicine in the UCLA Division of Digestive Diseases. He serves as director of the Center for Inflammatory Bowel Diseases, being responsible for both the clinical programs as translational research. In addition, he will implement a quality program across the entire division as the Director of the Quality Initiative. Dr. Hommes designed and successfully piloted a Value-based health care delivery program in over 500 IBD patients. This program integrates a number of different aspects of modern health care, like home care, biobanking, a mental reinforcement program, patient education and much more. This is demonstrated in two YouTube videos: Vision http://youtu.be/da7dRLSQPEI; Operations: http://youtu.be/HdmsL7GVmMg).


Harry Pothoulakis, MD
Director, IBD Basic Science Center & Basic Research Integration, UCLA Center for Inflammatory Bowel Diseases

Dr. Pothoulakis' research program is primarily focused on the role of neuropeptides and hormones in several disease states, including inflammatory bowel diseases, clostridium difficile infection, and irritable bowel syndrome. His recent projects also involve the neuropeptide-dependent mechanisms by which communication between the intestinal mucosa and the fat depots affect the pathogenesis of intestinal inflammation. He is an author of over 157 original articles and numerous reviews and book chapters and served in the Editorial Board of several biomedical journals, including Gastroenterology, and American Journal of Physiology. He has also been a member of Hormones, Transmitters, Growth Factors and Receptors, and Inflammatory Bowel Disease Sections of the American Gastroenterological Association. Dr. Pothoulakis' research projects have been supported by grants from the National Institutes of Health, the Broad Foundation, The Martin Blinder Foundation for Crohn's Disease, and the Knapp Foundation.

Click here to learn more about our research »


Jennifer Choi, MD
Associate Director, Educational Affairs, UCLA Center for Inflammatory Bowel Diseases

Dr. Choi graduated from the Massachusetts Institute of Technology (MIT) in Cambridge, Massachusetts, before attending the Chicago Medical School, where she earned her medical degree and Dean's Award.  She completed her internship and residency training in Internal Medicine at the Cedars-Sinai Medical Center and spent an additional year as a post-doctoral researcher under the guidance of her mentor, Dr. Stephan Targan, at the Cedars-Sinai Inflammatory Bowel Disease (IBD) Center.
In 2008, Dr. Choi served as a Visiting IBD Fellow to the Mayo Clinic in Rochester, Minnesota, with support from the Crohn's & Colitis Foundation of America (CCFA).  After completing her fellowship training in gastroenterology/digestive diseases at the University of California, Los Angeles (UCLA), she then joined the UCLA faculty.  She is board-certified in Gastroenterology and Internal Medicine, and fluent in Spanish.
Dr. Choi is the Associate Director for the UCLA Center for Inflammatory Bowel Diseases, where she specializes in the value-based care of patients with Crohn's disease and ulcerative colitis.  She is also the co-Chair for the Los Angeles Chapter Medical Advisory Committee for the Crohn's and Colitis Foundation of America (CCFA).

Dr. Choi was recently recognized as one of 18 clinicians demonstrating outstanding IBD patient care across the United States by the American Gastroenterological Association 2013-2014 Bridges to Excellence (BTE) IBD Care Recognition program.  She was also named as a 2013 Super Doctors Rising Star by LA Magazine. 

Chrisina Ha MD Ulcerative Colitits Crohn's Disease UCLA

Christina Ha, MD
Associate Director, Clinical Affairs, UCLA Center for Inflammatory Bowel Diseases

Dr. Ha graduated from Harvard University and earned her medical degree from Albert Einstein College of Medicine. She completed both her internal medicine residency and gastroenterology fellowship at Washington University in St. Louis School of Medicine. Following GI fellowship, she spent a year as the Present-Levison Inflammatory Bowel Disease Fellow at the Mount Sinai School of Medicine in New York. Subsequently, she joined the faculty at The Johns Hopkins School of Medicine as part of the Meyerhoff Inflammatory Bowel Disease Center prior to joining the UCLA Division of Digestive Diseases in 2013. Her areas of clinical interest are in the inflammatory bowel diseases, Crohn's disease and ulcerative colitis. Her research is also centered around Crohn's disease and ulcerative colitis with a particular focus in the natural history and clinical outcomes of IBD in the elderly.


Daniel Hollander, MD
Director, Fellowship Research Program in Gastroenterology

Dr. Hollander is a board certified gastroenterologist specializing in diagnosis and therapy of Crohn's disease and Ulcerative Colitis. He is a professor of medicine at the University of California, Los Angeles (UCLA) School of Medicine. His major research area is intestinal inflammation and intestinal absorption of nutrients. Before joining UCLA, he was the director of The Broad Foundation inflammatory bowel disease research. In the past he held academic positions as the president/CEO of the Los Angeles Biomedical Research Institute. Dr. Hollander has also held several academic leadership positions including executive dean and professor of medicine at the University of Kansas School of Medicine and head of the Division of Gastroenterology at the University of California, Irvine (UCI). While at UCI, he also served as associate dean for research and program development, associate dean for academic affairs and senior associate dean for clinical affairs.

Dr. Hollander's research has centered on intestinal absorption mechanisms of nutrients by the small intestine, and on paracellular transport. He began his studies of the pathophysiology of inflammatory bowel diseases by studying the intestinal permeability of patients with Crohn's disease and their family members and spouses. Since then, his studies have centered on the role of the intestinal tight junctions in intestinal inflammation and in IBD pathogenesis.

Currently, Dr. Hollander is teaching and providing care to patients with IBD at the Ronald Reagan UCLA Medical Center.


Bennett Roth, MD
Director, Educational Programs and Medical Procedure Units, Division of Digestive Diseases
Chief, Gastrointestinal Endoscopy

Dr. Roth received his medical degree from Hahnemann Medical College, completed his residency in internal medicine at the University of Pennsylvania and his fellowship in gastroenterology at UCLA. He served as the Chief of Clinical Gastroenterology at UCLA for 17 years and is currently Chief of Gastrointestinal Endoscopy. He is former president of the American Society for Gastrointestinal Endoscopy (ASGE).

  Jonathan Sack, MD
Associate Clinical Professor of Surgery, UCLA Department of Surgery

Dr. Sack is a board-certified Colon and Rectal Surgeon with over 25 years experience. He has a focused interest in treating patients with inflammatory bowel diseases, with special interest in laparoscopic reconstructive surgery for chronic ulcerative colitis (restorative proctocolectomy with ileal pouch anal anastomosis) and minimally invasive treatment of complicated Crohn's disease with bowel preservation techniques.

David Ziring, MD
Director, UCLA Pediatric IBD Center

Dr. Ziring has dedicated his life to helping children with inflammatory bowel disease (IBD). He received his medical degree from the Chicago Medical School concurrently with earning his Master's degree in Clinical Immunology. His thesis topic was the current state of understanding of the immune system in IBD. Dr. Ziring went on to receive his residency training in Pediatrics at Children's Hospital Orange County. He then pursued subspecialty training in Pediatric Gastroenterology at UCLA David Geffen School of Medicine with Dr. Marvin Ament and associated faculty, concentrating his research efforts on the regulation of the immune system in IBD with his research mentor, Dr. Jonathan Braun.

Dr. Ziring was instrumental in discovering an IBD-associated gene, working with collaborators at Cedars-Sinai Medical Center.  He has since migrated his research interests from working in the laboratory with animal models to studies involving patients with IBD.  He was recently awarded a Broad Medical Research Program grant to study the immunomodulatory effects of large doses of vitamin D in children with Crohn's disease.
Besides his research and direct patient care, Dr. Ziring works closely with the IBD community. He serves on the medical advisory board for the IBD Support Foundation, a non-profit organization developed to provide support to patients with IBD. Dr. Ziring is the medical director of the CCFA's national Team Challenge Half-Marathons, with events in Napa, San Antonio, Miami, and Hawaii that have raised more than 30 million dollars to date. He has been a volunteer physician for the last six years with the CCFA's summer program (Camp Oasis) at Paul Newman's Painted Turtle camp, caring for more than 120 children with IBD each summer. Dr. Ziring serves as the primary investigator and UCLA's representative for the CCFA's national Pediatric Research Network (PRO-KIIDS). He is a member of the IBD Committee for the North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition (NASPGHAN). He has given lectures on topics as diverse as skeletal health in children with IBD to the successful transition of care of teens with IBD at regional academic centers.  And he continues to publish extensively, from a recent review on the cutting-edge research being done in pediatric IBD to the discovery of a new IBD-associated gene (CNR2, a gene involved in the endocannabinoid system) and the importance of this system in regulating the immune system in IBD.


Angelos Oikonomopoulos, PhD
IBD Post-Doctoral Fellow

Angelos earned a Master's Degree and a PhD degree in Molecular Medicine in 2011 from the University of Crete. Dr. Oikonomopoulos has been fascinated by stem cell biology since his early undergraduate studies. Currently, his focus is on stem cell therapeutic applications and particularly on the potential of mesenchymal stromal stem cells for IBD treatment.


Welmoed van Deen, MD
IBD Post-Doctoral Fellow

Welmoed received her medical degree at the University of Leiden in The Netherlands in 2011. After graduation she moved to Los Angeles where she is working at the Center for Inflammatory Bowel Diseases as a research fellow. Her main research interest is in value-based healthcare and she is currently researching ways to generate a sustainable and value based health care system for the IBD population. She hopes to finalize her PhD thesis on value based healthcare in 2015. 


Martijn van Oijen, PhD
Adjunct Associate Professor of Medicine
Dr. Van Oijen received a dual Master of Science in Biomedical Health Science (epidemiology and health technology assessment) from Radboud University Nijmegen. At Radboud, he also received his PhD in Medicine, based on his thesis titled 'Balancing Gastrointestinal and Cardiovascular Outcomes in Low-Dose Aspirin Users.' After completing his PhD, Dr. Van Oijen worked as a post-doc for a nationwide project aiming at developing an IBD research database connecting input from medical records, patient reported outcomes and bio-banking. In 2010, he became assistant professor in GI Epidemiology, department of Gastroenterology and Hepatology, at University Medical Center Utrecht. Dr. Van Oijen was also head of the departmental clinical trial bureau, and supervised a team of PhD students on topics covering the whole disease spectrum of gastroenterology and hepatology. 
Dr. Van Oijen has advanced skills in database analysis, cost-effectiveness analysis and epidemiology.

Laurin Eimers, RN, BSN
IBD Nurse Specialist

Laurin graduated nursing school from the Medical College of Georgia. After graduation, she worked in pediatric oncology for two years at the Medical University of South Carolina. After Charleston, Laurin did travel nursing for two years in pediatric oncology and pediatric inflammatory bowel diseases. Laurin joined UCLA in the pediatric oncology center but joined the IBD team when it formed.


Ellen Kane, RN, BS, CCRP
Research Nurse Manager

Ellen came from Minnesota in 2008 after working more than 30 years in various nursing positions including 12+ years in research. After landing in LA she immediately went to work in IBD research at Cedars-Sinai Medical Center until 2012 where she joined the newly formed IBD team at UCLA. Ellen is in charge of overseeing all IBD research.

  Lisette Macias, RN, BSN
Clinical Nurse Manager - Pediatrics

Lisette holds a baccalaureate degree in nursing from Azusa Pacific University. Her areas of clinical expertise include pediatrics, gastroenterology, and critical care. Currently, she is a pediatric clinical nurse working with Dr. David Ziring, a pediatric inflammatory bowel disease expert. She collaboratively manages and coordinates the care of patients with ulcerative colitis and Crohn's disease.
  Nancee Jaffe
Registered Dietician

Nancee graduated from California State University, Los Angeles, where she earned her Master's of Science degree in Nutrition. She completed her dietetic internship at Cedars-Sinai Medical Center and at the University of California, Los Angeles. Nancee works with all gastrointestinal disorders, including irritable bowel syndrome, inflammatory bowel disease, celiac disease, short bowel syndrome and idiopathic or functional bowel diseases.
Adriana Centeno
Assistant Director, Division of Digestive Diseases

She received a Bachelor's of Art in Sociocultural Anthropology from UCLA and recently graduated from the Executive Education Program at the UCLA Anderson School of Management.


Leticia Gutierrez
Administrative Assistant

Leticia began her employment in the Pediatric Allergy Immunology Division at UCLA as a high school student in 1986 and has made the medical field at UCLA her home. Working in GI the past 12 years, she was told about the exciting plans with the new IBD Program and was honored to become part of the team December 2011.


Tony Lopez
Administrative Assistant

Tony has been with UCLA Health for more than 10 years working for a variety of specialities. He was promoted to team leaders for internal medicine and gastroenterology clinic where he began working closely with IBD physicians. When the Center for Inflammatory Bowel Diseases was established, he joined the dynamic team.

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