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 less voluntary energy expenditure. However, today’s environment leads to obesity only in those individuals whose body-weight regulatory systems are not able to control body adiposity with sufficient precision in our high-calorie/low-activity environment, thereby suggesting that some subgroups in the United States have a uniquely high susceptibility to weight gain under the 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 special emphasis on minority populations. The ongoing research program prospectively evaluates risk factors for the development of obesity and its complications in children, investigates the effects of medications on body weight and obesity-related co-morbid conditions in children, examines potential methods for modulating thermogenesis in children and adults, and seeks the genetic and environmental factors important for the markedly greater incidence of obesity and its co-morbid conditions in some U.S. minority populations.
Molecular studies of factors important for childhood body-weight regulation
Feng, Koo, Adler-Wailes, Ning, Han, El-Gharbawy, Tanofsky-Kraff, Theim, Ranzenhofer, Taylor, Yanovski J; in collaboration with Aguilera, Hochberg, Leibel, O’Rahilly, Westphal
In attempting to identify gene variants affecting body composition with different frequency in African American and Caucasian children, we are using classical association studies to investigate polymorphisms in genes involved in the leptin signaling pathway. Genes currently under study include those encoding proopiomelanocortin (POMC), POMC processing enzymes, the melanocortin receptors 3, 4, and 5, neuropeptide Y and its receptors, and brain-derived neurotrophic factor (BDNF) and its receptor, the type 2 neurotrophic receptor TrkB. We have also studied genes important for energy expenditure, such as 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 found that an intronic polymorphism in the 11-beta-hydroxysteroid dehydrogenase gene is associated with several features of the metabolic syndrome in children. We also identified polymorphisms in the POMC sequence that are more prevalent in African American than in Caucasian children.
We are currently studying a variant melanocortin 3 receptor (MC3R) that appears to have functional significance for MC3R signal transduction and is associated with adiposity in a large cohort of children. By sequencing the human MC3R gene in 88 lean and obese children, we found two previously identified missense sequence variants: C17A (Thr6Lys) and G241A (Val81Ile). Of 355 children who were studied by restriction fragment length polymorphism (RFLP) analysis, nearly half carried at least one of the mutant alleles. The two variants showed marked linkage disequilibrium. Therefore, we characterized the genotypes based on the combination of the two variants. African American children were more likely to carry the variant alleles. Specifically, about 68 percent of African Americans (versus about 20 percent of Caucasians) carried at least one mutant allele, and about 16 percent of African Americans (versus about two percent of Caucasians) were homozygous for both polymorphisms. Overweight children had higher frequencies of the variants than normal-weight children. Children homozygous for both variants were identified only among children at risk for overweight (about eight percent) or already overweight (about 14 percent). 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 measurements and higher plasma levels of insulin and leptin than wild-type or heterozygous children.
To study the functional consequences of the MC3R missense variants, we transiently expressed both single- and double-variant MC3R receptors in HEK293 cells and compared ligand affinity and cAMP generation with that of the wild-type receptor. The doubly mutant Thr6Lys and Val81Ile MC3R bound to approximately 60 percent less 125I-NDP-alpha-MSH than the wild-type receptor, although the affinity for the single- or double-variant MC3R was not significantly different from the wild type. However, the level of surface expression, as reflected by the estimated maximum binding, was significantly lower for the double-mutant MC3R than for the wild-type MC3R, suggesting that cells expressing the double-mutant receptor have fewer available alpha-MSH binding sites. We assessed the function of the mutants by examining coupling to adenylyl cyclase upon stimulation by NDP-alpha-MSH. The double-mutant MC3R caused significantly lower maximal intracellular cAMP generation than wild-type MC3R. We also studied the function of the mutant MC3R in LVIP2.0Zc cells that were stably transfected with a cAMP-responsive beta-galactosidase reporter gene. Upon stimulation by NDP-alpha-MSH, the double-mutant MC3R produced significantly less maximal beta-galactosidase activity, paralleling the changes in intracellular cAMP accumulation. To study translational efficiency, we transiently expressed MC3R-GFP fusion proteins in LVIP2.0Zc cells, finding decreased protein expression. In sum, we determined that the co-occurrence of two previously identified variants was associated with impaired cAMP generation in vitro and with greater BMI-SD and body fat mass and higher plasma insulin and leptin levels in African American and Caucasian children. This is the first report of a significant relationship between these variants and pediatric obesity. Homozygocity for the double-mutant MC3R may contribute to the greater prevalence of overweight, particularly in African Americans. Ongoing studies attempt to understand the mechanisms by which these sequence alterations affect body weight. We are currently developing transgenic knockin mouse models of the human wild-type and double-mutant MC3R.
Feng NP, Adler-Wailes D, Elberg J, Chin J, Fallon E, Carr A, Fraser del Llado T, Yanovski JA. Sequence variants of the proopiomelanocortin (POMC) gene and their associations with body composition in lean and overweight children. Obes Res 2003;11:619-624.
Feng NP, Young SF, Aguilera G, Puricelli E, Adler-Wailes DC, Sebring NG, Yanovski JA. Partial inactivation of the melanocortin 3 receptor in pediatric-onset obesity. Diabetes 2005;54:2663-2667.
Gelernter-Yaniv L, Feng NP, Sebring NG, Hochberg Z, Yanovski JA. Associations between a polymorphism in the 11-beta-hydroxysteroid dehydrogenase type I gene and body composition. Int J Obes 2003;27:983-986.
Physiology, metabolism, and psychology of childhood body-weight regulation
Tanofsky-Kraff, Ning, Roberts, Han, Taylor, Glasofer, Mirch, Theim, Ranzenhofer, Mirza, McDuffie, Uwaifo, Yanovski J; in collaboration with Arslanian, Cox, Field, Gorbach, Hubbard, Levine, Malley, Reynolds, Salaita, Schoeller, Sebring, Walsh, Wilfley, Yanovski S, Young-Hyman
To define the physiological, metabolic, and psychological factors that identify children at risk for undue weight gain, we are optimizing the measurement of psychopathology, insulin sensitivity, and changes in both body composition and energy expenditure. Thus, we found that measurements of body fat by noninvasive air displacement plethysmography are highly correlated with results from dual-energy x-ray absorptiometry. Furthermore, the hyperglycemic clamp procedure is highly correlated with the more technically demanding euglycemic hyperinsulinemic clamp study and therefore is suitable for assessing insulin sensitivity in children.
We found that African American children secrete more insulin and demonstrate greater prevalence of acanthosis nigricans and less insulin sensitivity than Caucasian children of similar body composition. The results suggest that the relationship between visceral fat and the complications of obesity may differ between African Americans and Caucasians. The susceptibility to weight gain in African Americans may also result from differences in metabolic efficiency. Thus, we also 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. Our studies suggest that the differences are not explained by differences in the hormone leptin but instead are driven by variations in body composition and can be explained primarily by the greater appendicular lean body mass of African Americans, which is relatively metabolically inactive at rest. We have also studied the effects of adiposity on skeletal maturation in both groups, finding that a substantial portion of the advancement of sexual and skeletal maturation found in African American children may be explained by the children’s greater adiposity. Recent investigations have also documented a greater prevalence of fractures and muskuloskeletal complaints in significantly overweight children as well as a greater degree of valgus misalignment of the lower extremities, which may contribute to further weight gain.
Our evaluations concentrating on binge eating in children suggest that such behaviors also are associated with adiposity in children. Ongoing investigations suggest that binge-eating and dieting behaviors may predict future weight gain in children at risk for overweight. We recently found that children who report binge-eating episodes during childhood have greater adiposity than those not reporting such episodes. We also measure food consumption of children during meals to elucidate differences in the calorie and macronutrient content of meals and in the circulating hormones related to hunger and satiety in children who either endorse binge-eating behaviors or report no such behaviors. We hypothesize that differences in these factors will predict the development of obesity in the populations studied and may be of great importance in developing rational approaches for the prevention and treatment of obesity in the diverse U.S. population.
Elberg J, McDuffie JR, Sebring NG, Salaita C, Keil M, Robotham D, Reynolds JC, Yanovski JA. Comparison of methods to assess change in children’s body composition. Am J Clin Nutr 2004;80:64-69.
McDuffie J, Adler-Wailes D, Elberg J, Fallon E, Steinberg E, Tershakovec A, Arslanian S, Delany J, Bray G, Yanovski JA. Prediction equations for resting energy expenditure in overweight and non-overweight Black and White children. Am J Clin Nutr 2004;80:365-373.
Mirza NM, Kadow K, Palmer M, Solano H, Rosche C, Yanovski JA. Prevalence of overweight among inner city Hispanic-American children and adolescents. Obes Res 2004;12:1298-1310.
Tanofsky-Kraff M, Yanovski SZ, Wilfley DE, Marmarosh C, Morgan CM, Yanovski JA. Eating disordered behaviors, body fat, and psychopathology in overweight and normal weight children. J Consult Clin Psychol 2004;72:53-61.
Tanofsky-Kraff M, Yanovski SZ, Yanovski JA. Comparison of child interview and parent reports of children’s eating disordered behaviors. Eat Behav 2005;6:95-99.
Treatment of children and adolescents with co-morbid conditions associated with obesity
Tanofsky-Kraff, Yanoff, Roberts, Ranzenhofer, Adler-Wailes, Mirch, Theim, Menzie, Taylor, Mirza, McDuffie, Yanovski J; in collaboration with Booth, Calis, Drinkard, Hubbard, Krakoff, Reynolds, Rolls, Salaita, Sebring, Young-Hyman
Given the rapid increase in the prevalence of obesity, the development of treatments for obesity in childhood is urgently needed. We completed a pilot study demonstrating that severely overweight adolescents can lose weight when enrolled in a comprehensive weight management program that includes the novel gastrointestinal lipase inhibitor orlistat as an adjunct to a behavioral modification program. However, the program may be more effective in Caucasians than in African Americans. We also found evidence 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 will determine whether orlistat improved the weight loss of African American and Caucasian children and adolescents with obesity-related co-morbidities.
In the course of these studies, we also evaluated cardiorespiratory fitness in significantly overweight children. We hypothesized that severely overweight adolescents have difficulty with sustained exercise mostly because the metabolic costs of moving excess mass result in the use of a high proportion of their total oxygen reserve. We thus compared results from a maximal cycle ergometry fitness test in severely overweight adolescents with results from nonoverweight adolescents. We compared oxygen uptake at three times: during a four-minute period of unloaded cycling (ULVO2), at the lactate threshold estimated by gas exchange (LTVO2), and at maximal exertion (VO2 max). We obtained 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 nonoverweight children 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 nonoverweight 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 nonoverweight adolescents. D12 was negatively related to BMI-SD and to ULVO2. Thus, overweight and nonoverweight 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 the metabolic cost of their excess mass burdens overweight adolescents. 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 while focusing on activities that keep demands below the lactate threshold so that exercise can be sustained.
We are also recruiting children for a study to examine the mechanism by which metformin affects the body weight of younger children with hyperinsulinemia who are therefore at risk for later development of type 2 diabetes.
Cohen ML, Tanofsky Kraff M, Young-Hyman D, Yanovski JA. Weight and its relationship to adolescent perceptions of their providers (WRAP): a qualitative and quantitative assessment of teen weight-related preferences and concerns. J Adol Health 2005;7:163.
McDuffie JR, Calis KA, Uwaifo GI, Freedman RJ, Sebring NG, Fallon EM, Frazer TE, Hubbard VS, Yanovski JA. Efficacy of orlistat as an adjunct to behavioral treatment in overweight African American and Caucasian adolescents with obesity-related co-morbid conditions. J Pediatr Endocrinol Metab 2004;17:307-319.
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-e696.
Yanovski JA, Yanovski SZ. Treatment of pediatric and adolescent obesity. JAMA 2003;289:1851-1852.
Genetic and acquired lipodystrophies
McDuffie, Adler-Wailes, Feng, Theim, Mirch, Yanovski J; in collaboration with Calis, Gordon, Leibel, Londos, Manganiello
We are studying the pathophysiology underlying the metabolic defects observed in individuals with lipodystrophy; by definition, such individuals are leptin-insufficient. We are examining the effects of exogenous leptin on satiety and satiation. Eight females with hypoleptinemia and lipodystrophy (most due to congenital causes) received subcutaneous injections of A-100 (recombinant human leptin) (maximal dose 200 percent of that predicted to normalize serum leptin) for four months. We determined satiation and satiety before and during treatment. Satiation was measured as the time to voluntary cessation of eating from a standardized food array following a 12-hour fast. Satiety was determined as the time to hunger sufficient to consume a full meal after consumption of a standardized preload. During leptin treatment, satiation time decreased, satiety time increased, energy consumed to produce satiation decreased, and the amount of food desired in the post-absorptive state decreased. Ghrelin concentrations also decreased during leptin administration. We concluded that increased leptin in patients with lipodystrophy resulted in less caloric, shorter, more satiating meals and longer-lived satiety. The data support the hypothesis that leptin plays an important, permissive role in human appetite regulation.
An ongoing collaborative study examines the metabolic phenotype of patients with Hutchinson-Gilford progeria syndrome, a disorder caused by mutations in the Lamin A gene, previously known to be mutated in those with Dunnigan partial lipodystrophy. We are also interested in the pathogenesis of HIV-associated lipodystrophy. Several of the aspartic acid protease inhibitors used to treat HIV infection increase basal lipolysis in adipocytes, but the cellular mechanisms leading to such augmentation remain poorly understood. We therefore studied the effects of chronic exposure to the HIV protease inhibitor ritonavir on the lipolytic cascade in 3T3-L1 adipocytes. Our experiments showed that ritonavir decreases the activity of phosphodiesterase 3B and the expression of the lipid droplet–protective perilipin protein, affecting both basal and catecholamine-stimulated lipolysis in 3T3-L1 adipocytes. Ongoing studies include a microarray examination of gene expression in adipocytes treated with ritonavir and assessment of lipogenesis and re-esterification of fatty acids. Preliminary data suggest upregulation of genes important for de novo lipogenesis and support the hypothesis that protease inhibitors stimulate cycling of fatty acids both into and out of intracellular triglyceride storage pools.
Adler-Wailes DC, Liu H, Ahmad F, Feng N, Londos C, Manganiello V, Yanovski JA. Effects of the HIV-protease inhibitor ritonavir on catecholamine-stimulated lipolysis. J Clin Endocrinol Metab 2005;90:3251-3261.
McDuffie JR, Riggs PA, Calis KA, Freedman RJ, Oral EA, DePaoli AM, Yanovski JA. Effects of exogenous leptin on satiety and satiation in patients with lipodystrophy and leptin insufficiency. J Clin Endocrinol Metab 2004;89:4258-4263.
Environmental factors affecting weight gain
Yanoff, Menzie, McDuffie, Parikh, Uwaifo, Yanovski J; in collaboration with Gorbach, Salaita, Sebring, Yanovski S
We are also interested in assessing the impact of the environment on body-weight gain. We found that the only time during which weight changes significantly is the fall-winter holiday season between Thanksgiving and New Year’s Day, with implications for individuals attempting to control their weight. We have also studied the impact of chemotherapy on weight gain in women with breast cancer, finding redistribution of body mass from lean tissues to fat mass during the first year after chemotherapy. In addition, we noted that the development of estrogen deficiency attributable to chemotherapy is a risk factor for weight change in such women.
We are also interested in the role of dietary calcium in body-weight change. One hypothesis for how calcium intake may affect body adiposity is that it might alter plasma concentrations of calcitropic hormones such as 1,25 dihydroxy vitamin D. 1,25 dihydroxy vitamin D has been found to stimulate lipogenesis in vitro. It is widely thought that deficient calcium intake stimulates parathyroid hormone and promotes conversion of 25 hydroxy vitamin D to 1,25 dihydroxy vitamin D, thereby stimulating lipogenesis and leading to greater body weight. We determined that 1,25 dihydroxy vitamin D concentrations are not elevated in overweight and obese adults; rather, we observed vitamin D deficiency (and lower 1,25 dihydroxy vitamin D concentrations) among severely obese adults. An ongoing randomized controlled trial will answer important questions about the value of calcium supplementation for the prevention of future weight gain.
Freedman RJ, Aziz N, Albanes D, Hartman T, Danforth D, Hill S, Sebring N, Reynolds JC, Yanovski JA. Weight and body composition changes during and after adjuvant chemotherapy in women with breast cancer. J Clin Endocrinol Metab 2004;88:2248-2253.
Parikh SJ, Edelman M, Uwaifo GI, Freedman RJ, Semega-Janneh M, Reynolds J, Yanovski JA. The relationship between obesity and serum 1,25 dihydroxy vitamin D concentrations in healthy adults. J Clin Endocrinol Metab 2004;89:1196-1199.
Parikh SJ, Yanovski JA. Calcium intake and adiposity. Am J Clin Nutr 2003;77:281-287.
Collaborators
Greti Aguilera, MD, Developmental Endocrinology Branch, NICHD, Bethesda, MD
Silva Arslanian, MD, Pittsburgh Children’s Hospital, Pittsburgh, PA
Sarah Booth, PhD, USDA, Tufts University, Boston, MA
Karim Calis, PharmD, Pharmacy Department, Warren G. Magnuson Clinical Center, NIH, Bethesda, MD
Christopher Cox, PhD, The Johns Hopkins University, Baltimore, MD
Bart Drinkard, PT, Rehabilitation Medicine Department, Warren G. Magnuson Clinical Center, NIH, Bethesda, MD
Alison Field, DSc, Channing Laboratory, Brigham and Women’s Hospital, Boston, MA
Alexander Gorbach, PhD, Diagnostic Radiology Department, Warren G. Magnuson Clinical Center, NIH, Bethesda, MD
Leslie B. Gordon, MD, PhD, Tufts University School of Medicine, Boston, MA
Zeev Hochberg, MD, Rambam Children’s Hospital, Haifa, Israel
Van S. Hubbard, MD, PhD, Division of Nutritional Research Coordination, NIDDK, Bethesda, MD
Jonathan Krakoff, MD, Clinical Diabetes and Nutrition Section/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
Constantine Londos, DDS, PhD, Laboratory of Cellular and Developmental Biology, NIDDK, Bethesda, MD
James D. Malley, PhD, Center for Information Technology, Bethesda, MD
Vincent Manganiello, MD, Pulmonary Critical Care Medicine Branch, NHLBI, Bethesda, MD
Stephen O’Rahilly, MD, Cambridge Institute of Medical Research, Cambridge, UK
James Reynolds, MD, Nuclear Medicine, Warren G. Magnuson Clinical Center, NIH, Bethesda, MD
Barbara J. Rolls, PhD, Pennsylvania State University, University Park, PA
Christine Salaita, MS, RD, Nutrition Department, Warren G. Magnuson Clinical Center, NIH, Bethesda, MD
Dale A. Schoeller, PhD, University of Wisconsin, Madison, WI
Nancy Sebring, MEd, RD, Nutrition Department, Warren G. Magnuson Clinical Center, NIH, Bethesda, MD
B. Timothy Walsh, PhD, Columbia University College of Physicians and Surgeons, New York, NY
Heiner Westphal, MD, Laboratory of Mammalian Genes and Development, 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
Debra Young-Hyman, PhD, Center for Scientific Review, NIH, Rockville, MD
For further information, contact yanovskj@cc1.nichd.nih.gov.