PHYSIOLOGY, PSYCHOLOGY, AND GENETICS OF OBESITY
, Head, Unit on Growth and Obesity
David Savastano, PhD, Postdoctoral Fellow
Joan Han, MD, Clinical Fellow, Endocrine Training Program
Mary Roberts, MD, Clinical Fellow, Endocrine Training Program
Lisa Yanoff, MD, Clinical Fellow, Endocrine Training Program
Sheila Brady, RN, FNP, Nurse Practitioner
Diane Adler-Wailes, MS, Biologist
Marian Tanofsky-Kraff, PhD, Volunteer
Deborah Glasofer, BA, Graduate Student
Jenna Checchi, BS, Postbaccalaureate Fellow
Jennifer Gustafson, BS, Postbaccalaureate Fellow
Rebecca Levinn, BA, Postbaccalaureate Fellow
Lisa Ranzenhofer, BS, Postbaccalaureate Fellow
Ethan Sanford, BA, Postbaccalaureate Fellow
Natascha Schvey, BS, Postbaccalaureate Fellow
Rachel Sorg, BA, Postbaccalaureate Fellow
The prevalence of overweight and obesity in children and adults has tripled during the past 30 years. The alarming rise in body weight has likely occurred because the current environment affords easy access to calorie-dense foods and requires relatively less voluntary energy expenditure. However, this environment leads to obesity only in those individuals whose systems of body weight regulation are not able to control body adiposity with sufficient precision in our high-calorie/low-activity environment, thus suggesting that some subgroups in the United States have a uniquely high susceptibility to weight gain under prevailing environmental conditions. Our research is primarily directed at increasing our understanding of the metabolic and behavioral factors involved in determining body weight regulation and body composition during childhood, with a special emphasis on minority populations. Our ongoing research program prospectively evaluates risk factors for the development of obesity and its complications in children, studies the effects of medications on body weight and obesity-related comorbid conditions in children, examines potential methods for modulating thermogenesis in children and adults, and seeks to identify the genetic and environmental factors important for the markedly greater incidence of obesity and its comorbid conditions in some U.S. minority populations.
Molecular studies of factors important for childhood body weight regulation
To identify gene variants that affect the body composition of African American and Caucasian children with different frequencies, we have been examining polymorphisms in genes involved in the leptin-signaling pathway. Genes include those encoding proopiomelanocortin (POMC); POMC processing enzymes; the melanocortin receptors 3, 4, and 5; neuropeptide Y and its receptors; brain-derived neurotrophic factor (BDNF); and the type 2 neurotrophic receptor TrkB. We previously studied genes important for energy expenditure, such as those encoding the mitochondrial uncoupling proteins, and genes potentially involved in cortisol metabolism that may affect intra-abdominal adipose tissue, such as 11-beta-hydroxysteroid dehydrogenase. We are currently studying a variant melanocortin 3 receptor (MC3R) that is associated with adiposity in children and may have functional significance for MC3R signal transduction. We found two mis-sense sequence variants—Thr6Lys and Val81Ile—that, in 355 children, showed marked linkage disequilibrium. Therefore, we categorized the genotypes based on a combination of the two variants. African American children were more likely to carry the variant alleles than Caucasian children such that 15.8 percent of African Americans (versus 1.7 percent of Caucasians) were homozygous for both polymorphisms. Among both African American and Caucasian children, those homozygous for both MC3R alleles had significantly greater BMI-SD (body mass index-standard deviation) scores, fat mass and body circumference, and plasma levels of insulin and leptin than “wild-type” or heterozygous children.
To study the functional consequences of the MC3R mis-sense variants, we transiently expressed both single- and double-variant MC3R receptors in HEK293 cells. Saturation curves for binding of 125-I-NDP-alpha-MSH showed that the double-mutant Thr6Lys and Val81Ile MC3R bound approximately 60 percent less 125I-NDP-alpha-MSH than the wild-type receptor; a Scatchard analysis showed that the Kd for the single- or double-variant MC3R was not significantly different from the wild type. However, the level of surface expression was significantly lower for the double-mutant MC3R than for the wild-type MC3R. The Val81Ile+Thr6Lys double-mutant MC3R generated significantly lower maximal intracellular cAMP than wild-type MC3R. We then transiently expressed MC3R–GFP fusion proteins in LVIP2.0Zc cells and found decreased protein expression. Our work represents the first report of a significant relationship between these MC3R variants and pediatric obesity.
Homozygocity for the MC3R double mutant may contribute to the greater prevalence of overweight, particularly among African Americans. Ongoing studies are attempting to understand the mechanisms by which these sequence alterations may affect body weight. We are currently developing transgenic “knockin” mice expressing the human wild-type and human double-mutant MC3R. We have also recently investigated the relevance of the BDNF-TrkB pathway to body mass in children. We measured serum BDNF in 328 children, age 3 to 19 years, many of whom were extremely obese. BDNF was lower in overweight children; multiple-regression analyses showed that BMI and body fat were negatively associated with BDNF. The data suggest that some obese individuals with low serum BDNF for age and platelet count may have mutations that alter BDNF function.
In collaboration with Sadaf Farooqi and Stephen O’Rahilly, we found that individuals with heterozygous TrkB mutations do not have unusually high circulating BDNF, and we identified a child with hyperphagia and severe obesity associated with functional loss of one copy of the BDNF gene. The child had a de novo chromosomal inversion, 46,XX,inv(11)(p13p15.3), a region encompassing the BDNF gene. The patient’s genomic DNA was heterozygous for a common coding polymorphism in BDNF, but we observed monoallelic expression in peripheral lymphocytes. The patient’s serum BDNF was markedly lower than that in age- and BMI-matched control subjects. Haploinsufficiency for BDNF was associated with increased ad libitum food intake and severe early-onset obesity. These findings provide direct evidence for the role of BDNF in human energy homeostasis. We are undertaking an initiative that will assess the role of BDNF haploinsufficiency as a cause of obesity in patients with syndromes attributable to deletions in the vicinity of 11p14.1, where the human BDNF gene is found. We will verify a comparative genomic hybridization approach with in situ hybridization and PCR-based assays and examine genotype-phenotype relationships in patients with 11p deletion syndromes.
El-Gharbawy A, Adler-Wailes DC, Mirch MC, Theim KR, Ranzenhofer LM, Tanofsky-Kraff M, Yanovski JA. Serum brain-derived neurotrophic factor concentrations in lean and overweight children and adolescents. J Clin Endocrinol Metab 2006;91:3548-52.
Feng NP, Young SF, Aguilera G, Puricelli E, Adler-Wailes DC, Sebring NG, Yanovski JA. Co-occurrence of two partially inactivating polymorphisms of MC3R is associated with pediatric-onset obesity. Diabetes 2005;54:2663-7.
Gray J, Yeo GSH, Cox JJ, Keogh JM, Morton J, Adlam A, Yanovski JA, El Gharbawy A, Han JC, Tung YCL, Hodges J, Raymond FL, O’Rahilly S, Farooqi IS. Hyperphagia, severe obesity, impaired cognitive function, and hyperactivity associated with functional loss of one copy of the BDNF gene. Diabetes 2006;55:3366-71.
Ning C, Yanovski JA. Endocrine disorders associated with pediatric obesity. In: Goran MI, Sothern MS, eds. Handbook of Pediatric Obesity, Chapter 9. CRC Press, 2006;135-55.
Physiology, metabolism, and psychology of childhood body weight regulation
Our studies are directed at understanding the physiological, psychological, and metabolic factors that place children at risk for undue weight gain. To that end, we have examined how best to measure psychopathology, insulin sensitivity, changes in body composition, and energy expenditure in children. We have found that African American children secrete more insulin, evidence a greater prevalence of acanthosis nigricans, and exhibit less sensitivity to insulin, but have less visceral adipose tissue, than Caucasian children of similar body composition. These results imply that the relationship between visceral fat and the complications of obesity may be different in African Americans and Caucasians. The susceptibility to weight gain in African Americans may also result from differences in metabolic efficiency; we found that resting energy expenditure is approximately 90 kcal/d less in African American than in Caucasian normal-weight and overweight boys and girls; we verified the results in overweight children, developing new equations for predicting resting energy expenditure in African American and Caucasian children. Our studies suggest that these differences are not explained by differences in the hormone leptin but rather are driven by variations in body composition and may be explained primarily by the greater appendicular lean body mass observed in African Americans, which is relatively metabolically inactive at rest. Leptin, however, is an important predictor of weight gain in children; longitudinal studies show that those with high leptin gain even more weight.
Recent investigations have documented a greater prevalence of fractures and musculoskeletal complaints in significantly overweight children, along with a greater degree of valgus misalignment of the lower extremities that may contribute to (1) difficulties with exercise, and thus further weight gain in overweight youth, and (2) marked effects of obesity on adolescents’ quality of life. Our evaluations concentrating on binge-eating behaviors in children suggest that such behaviors are also associated with adiposity in children. We have found that binge-eating and dieting behaviors may predict future weight gain in children at risk for overweight; over an observation period of 4.2±1.8 years, children reporting binge-eating behaviors gained, on average, an additional 15 percent fat mass compared with children who do not binge-eat. Recent data also suggest that children engaging in binge eating consume more energy during meals. Actual intake during buffet meals averaged 400 kcal more in children with binge eating; nonetheless, such children reported shorter-lived satiety than children without binge-eating episodes. The ability to consume large quantities of palatable foods, especially when coupled with decreased subsequent satiety, may play a role in the greater weight gain in binge-eating children.
In two ongoing protocols designed to determine the factors that are most important for the development of obesity complications in African American and Caucasian youth, we are studying normal-weight African American and Caucasian children and adolescents, already obese African American and Caucasian children, and the non-obese African American and Caucasian children of obese parents. We examine body composition, metabolic rate, insulin sensitivity, glucose disposal, and genetic factors believed to regulate metabolic rate and body composition, along with psychological and behavioral factors such as propensity to engage in binge eating. We are studying children longitudinally into adulthood. In a third protocol, we are studying actual food consumption of children during meals in order to elucidate differences in the caloric and macronutrient content of meals and the circulating hormones related to hunger and satiety in those who either engage in binge eating or report no such behaviors. We hypothesize that differences in these factors predict the development of obesity in the populations studied and may be of great importance in developing rational approaches to the prevention and treatment of obesity in the diverse U.S. population. A new pilot clinical protocol will examine the effects of a targeted interpersonal therapy intervention on body weight change in adolescents who engage in binge-eating behaviors.
Fleisch AF, Agarwal N, Roberts MD, Han JC, Theim KR, Vexler A, Troendle J, Yanovski SZ, Yanovski JA. Influence of serum leptin on weight and body fat growth in children at high risk for adult obesity. J Clin Endocrinol Metab 2007;92:948-54.
Mirch M, McDuffie J, Yanovski S, Schollnberger M, Tanofsky-Kraff M, Theim K, Krakoff J, Yanovski JA. Effects of binge eating on satiation, satiety, and energy intake of overweight children. Am J Clin Nutr 2006;84:732-8.
Tanofsky-Kraff M, Cohen ML, Yanovski SZ, Cox C, Theim KR, Keil M, Reynolds JC, Yanovski JA. A prospective study of psychological predictors of body fat gain among children at high risk for adult obesity. Pediatrics 2006;117:1203-9.
Tanofsky-Kraff M, Haynos AF, Kotler LA, Yanovski SZ, Yanovski JA. Laboratory-based studies of eating during meals among children and adolescents. Curr Nutr Food Sci 2007;3:55-74.
Taylor ED, Theim KR, Mirch MC, Ghorbani S, Tanofsky-Kraff M, Adler-Wailes DC, Brady S, Reynolds JC, Calis KA, Yanovski JA. Orthopedic complications of overweight in children and adolescents. Pediatrics 2006;117:2167-74.
Treatment of obesity and the co-morbid conditions associated with obesity
Given the rapid increase in the prevalence of obesity, the development of treatments for childhood obesity is urgently needed. In three ongoing clinical protocols, we are studying approaches for the control of body weight in children. We conducted a pilot program demonstrating that severely overweight adolescents can lose weight when enrolled in a comprehensive weight management program that includes the gastrointestinal lipase inhibitor orlistat as an adjunct to a behavioral modification program. We found that the program may be more effective in Caucasians than in African Americans and that one mechanism through which orlistat may affect body weight is by changing the hedonic value of dietary fat. An ongoing placebo-controlled randomized trial, for which all the required 220 participants have been recruited, will determine whether the use of orlistat improves the weight loss of African American and Caucasian children and adolescents with obesity-related comorbidities.
In the course of our studies, we evaluated cardiorespiratory fitness in significantly overweight children. We hypothesized that most of the difficulty with sustained exercise experienced by severely overweight adolescents is attributable to the metabolic costs of moving excess mass, resulting in use of a high proportion of the adolescents’ total oxygen reserve. We compared results from a maximal cycle ergometry fitness test in 129 severely overweight adolescents, with BMI 41.5±9.7 kg/m2, and in 34 non-overweight adolescents, with BMI 20.1±2.9 kg/m2. We compared oxygen uptake (VO2) at three times: during a 4-minute period of unloaded cycling (ULVO2), at the lactate threshold estimated by gas exchange (LTVO2), and at maximal exertion (VO2 max). We measured heart rate at rest and at VO2 max. Subjects also completed a 12-minute walk/run performance test to obtain distance traveled (D12) and heart rate. Absolute LTVO2 and VO2 max, and LTVO2 as a percentage of VO2 max, did not differ in overweight and non-overweight subjects during the cycle test. However, absolute ULVO2 was significantly greater in overweight adolescents. Resting heart rate before initiating the cycle test was significantly greater in overweight than in non-overweight adolescents. However, maximal heart rate during the cycle test was significantly lower in overweight adolescents. During the walk/run test, mean D12 was significantly shorter for overweight than for non-overweight adolescents and was negatively related to BMI and ULVO2. Thus, overweight and non-overweight children exhibited similar absolute VO2 at the lactate threshold and at maximal exertion, suggesting that overweight adolescents are more limited by the increased cardiorespiratory effort required to move their larger body mass through space than by cardiorespiratory deconditioning. The higher percentage of oxygen consumed during submaximal exercise indicates that overweight adolescents are burdened by the metabolic cost of their excess mass. Their greater oxygen demand during an unloaded task predicted poorer performance during sustained exercise. The data suggest that exercise prescriptions for overweight adolescents should account for the limited exercise tolerance imposed by excess body mass, focusing on activities that keep demands below lactate threshold so that exercise can be sustained.
A second study examines the mechanism by which metformin may affect the body weight of younger children with hyperinsulinemia, which puts such children at risk for later development of Type 2 diabetes. We have recruited all 100 children required for this study. A third study examines the role played by central nervous system histamine in controlling food intake at meals. Subjects are randomized to take a placebo or one of several doses of betahistine; food intake at meals is measured.
Fallon EM, Tanofsky-Kraff M, Norman AC, McDuffie JR, Taylor ED, Cohen ML, Young-Hyman D, Keil M, Kolotkin R, Yanovski JA. Health-related quality of life in overweight and non-overweight black and white adolescents. J Pediatr 2005;147:443-50.
Glasofer DR, Tanofsky-Kraff M, Eddy KT, Yanovski SZ, Theim KR, Mirch MC, Ghorbani S, Ranzenhofer LM, Haaga D, Yanovski JA. Binge eating in overweight treatment-seeking adolescents. J Pediatr Psychol 2007;32:95-105.
Mirch M, McDuffie J, Yanovski S, Schollnberger M, Tanofsky-Kraff M, Theim K, Krakoff J, Yanovski JA. Effects of binge eating on satiation, satiety, and energy intake of overweight children. Am J Clin Nutr 2006;84:732-8.
Norman AC, Drinkard B, McDuffie JR, Ghorbani S, Yanoff LB, Yanovski JA. The influence of excess adiposity on exercise fitness and performance in overweight children and adolescents. Pediatrics 2005;115:e690-6.
Environmental factors affecting weight gain
We are interested in assessing the impact of the environment on body weight gain. To determine the role of seasonal variation in weight change, we prospectively studied 200 U.S. adults, following them longitudinally. We found that the only time during which weight changes significantly is the fall-winter holiday season between Thanksgiving and New Year’s Day. These findings have implications for individuals attempting to control their weight. We also studied the impact of chemotherapy on weight gain in women with breast cancer. We found that redistribution of body mass from lean tissues to fat mass occurs during the first year after chemotherapy and that development of estrogen deficiency following chemotherapy poses another risk for weight change.
In view of the claims made by some epidemiological studies that those with greater calcium intake gain less weight over time, we are interested in the role played by dietary calcium in determining body weight changes. One hypothesis holds that calcium intake may affect body adiposity by altering plasma concentrations of calcitropic hormones such as 1,25 dihydroxy vitamin D. Some researchers have found that 1,25 dihydroxy vitamin D stimulates lipogenesis in vitro. Others have hypothesized that deficient calcium intake stimulates parathyroid hormone and promotes conversion of 25 hydroxy vitamin D [25(OH)D] to 1,25 dihydroxy vitamin D, thereby stimulating lipogenesis and leading to greater body weight in humans. We determined that 1,25 dihydroxy vitamin D concentrations are not elevated in overweight and obese adults; rather, vitamin D deficiency (and lower 1,25 dihydroxy vitamin D concentrations) is observed among severely obese adults. These studies led us to examine the prevalence of vitamin D deficiency in obese African American and Caucasian Americans. Because both obesity and African American race have been associated with a higher risk of vitamin D deficiency and secondary hyperparathyroidism, we hypothesized that the risk of hypovitaminosis D would be extraordinarily high in obese African American adults. In a study of 379 adults whose BMI ranged from 19.9 to 58.2 kg/m2, obese African American subjects had lower mean 25(OH)D than did obese Caucasians, non-obese African Americans, and non-obese Caucasians. The prevalence of hypovitaminosis D increased with increasing BMI and was greater in African Americans than in Caucasians within all BMI categories examined. Among subjects with BMI equal to or greater than 35 kg/m2, 59 percent of African Americans versus 18 percent of Caucasians had hypovitaminosis D. iPTH was negatively correlated with 25(OH)D, suggesting that those with hypovitaminosis D had a clinically important vitamin D deficiency with secondary hyperparathyroidism. Slightly more than one-third of African Americans met the criteria for secondary hyperparathyroidism as compared with just under 10 percent of Caucasians. These findings have clinical implications for physicians, who should consider routinely supplementing hyperparathyroidism patients with vitamin D or screening them for hypovitaminosis D.
For a recently completed protocol, we enrolled 340 subjects—39 percent overweight, 61 percent obese, and 72 percent female—to examine the impact of dietary calcium supplementation on body weight. Comparing subjects randomized to take calcium to those given a placebo, we found no significant differences in body weight change, BMI change, or body fat mass change over a two-year period. Supplementation with 1,500 mg/d calcium carbonate thus did not significantly improve body composition of overweight and obese adults.
Clinical initiatives that study modifiable factors affecting body weight are now addressing how to augment non-exercise activity thermogenesis in children and methods for improving body heat dissipation during physical activity in adults.
Sebring NG, Denkinger BI, Menzie CM, Yanoff LB, Parikh SJ, Yanovski JA. Validation of three food frequency questionnaires to assess dietary calcium intake in adults. J Am Diet Assoc 2007;107:752-9.
Yanoff LB, Menzie CM, Denkinger BI, Sebring NG, McHugh T, Remaley AT, Yanovski JA. Inflammation and iron deficiency in the hypoferremia of obesity. Int J Obes (London) 2007;31:1412-9.
Yanoff LB, Parikh SJ, Spitalnik A, Denkinger B, Sebring NG, Remaley AT, Yanovski JA. High prevalence of hypovitaminosis D and secondary hyperparathyroidism in obese Black Americans. Clin Endocrinol (Oxf) 2006;64:523-9.
COLLABORATOR
Greti Aguilera, MD, Program in Developmental Endocrinology and Genetics, NICHD, Bethesda, MD
Sarah Booth, PhD, Human Nutrition Research Center on Aging at Tufts University, USDA, Boston, MA
Karim Calis, Pharm D, Pharmacy Department, NIH Clinical Center, Bethesda, MD
Kong Chen, PhD, Clinical Endocrinology Branch, NIDDK, Bethesda, MD
Christopher Cox, PhD, The Johns Hopkins University, Baltimore, MD
Blakeley Denkinger, MPH, RD, Nutrition Department, NIH Clinical Center, Bethesda, MD
Bart Drinkard, PT, Rehabilitation Medicine Department, NIH Clinical Center, Bethesda, MD
I. Farooqi, MD, Cambridge Institute for Medical Research, Cambridge, UK
Alison Field, DSc, Brigham and Women’s Hospital and Harvard Medical School, Boston, MA
Alexander Gorbach, PhD, Division of Bioengineering and Physical Science, ORS, NIH, Bethesda, MD
Leslie Gordon, MD, PhD, Hasbro Children’s Hospital, Providence, RI
Van S. Hubbard, MD, PhD, Division of Nutritional Research Coordination, NIDDK, Bethesda, MD
Michael J. Iadarola, PhD, Laboratory of Sensory Biology, NIDCR, Bethesda, MD
Merel Kozlosky, MS, RD, Nutrition Department, NIH Clinical Center, Bethesda, MD
Jonathan Krakoff, MD, Phoenix Epidemiology and Clinical Research Branch, NIDDK, Phoenix, AZ
Rudolph L. Leibel, MD, Columbia University College of Physicians and Surgeons, New York, NY
James Levine, MD, PhD, Mayo Clinic, Rochester, MN
Qing-Rong Liu, PhD, Molecular Neurobiology Branch, NIDA, Baltimore, MD
James D. Malley, PhD, Mathematical and Statistical Computing Laboratory, CIT, Bethesda, MD
Stephen O’Rahilly, MD, Cambridge Institute for Medical Research, Cambridge, UK
James Reynolds, MD, Nuclear Medicine, NIH Clinical Center, Bethesda, MD
Barbara J. Rolls, PhD, Pennsylvania State University, University Park, PA
Christine Salaita, MS, RD, Nutrition Department, NIH Clinical Center, Bethesda, MD
Dale A. Schoeller, PhD, University of Wisconsin, Madison, WI
Nancy Sebring, MEd, RD, Nutrition Department, NIH Clinical Center, Bethesda, MD
James Troendle, PhD, Biometry and Mathematical Statistics Branch, NICHD, Bethesda, MD
George R. Uhl, MD, PhD, Molecular Neurobiology Branch, NIDA, Baltimore, MD
B. Timothy Walsh, PhD, Columbia University College of Physicians and Surgeons, New York, NY
Heiner Westphal, MD, Program in Genomics of Differentiation, NICHD, Bethesda, MD
Denise E. Wilfley, PhD, Washington University School of Medicine, St. Louis, MO
Susan Z. Yanovski, MD, Obesity and Eating Disorders Program, NIDDK, Bethesda, MD
For further information, contact yanovskj@mail.nih.gov.
