Genotype-environment interaction in human obesity

Trefoil Factor Family Member 2: From a High-Fat-Induced Gene to a Potential Obesity Therapy Target

Obesity has its epidemiological patterns continuously increasing. With controlling both diet and exercise being the main approaches to manage the energy metabolism balance, a high-fat (HF) diet is of particular importance. Indeed, lipids have a low satiety potential but a high caloric density. Thus, focusing on pharmacologically targetable pathways remains an approach with promising therapeutic potential. Within this context, trefoil factor family member 2 (Tff2) has been characterized as specifically induced by HF diet rather than low-fat diet. TFF2 has also been linked to diverse neurological mechanisms and metabolic patterns suggesting its role in energy balance. The hypothesis is that TFF2 would be a HF diet-induced signal that regulates metabolism with a focus on lipids. Within this review, we put the spotlight on key findings highlighting this line of thought. Importantly, the hypothetical mechanisms pointed highlight TFF2 as an important contributor to obesity development via increasing lipids intestinal absorption and anabolism. Therefore, an outlook for future experimental activities and evaluation of the therapeutic potential of TFF2 inhibition is given. Indeed, its knockdown or downregulation would contribute to an antiobesity phenotype. We believe this work represents an addition to our understanding of the lipidic molecular implications in obesity, which will contribute to develop therapies aiming to manage the lipidic metabolic pathways including the absorption, storage and metabolism via targeting TFF2-related pathways. We briefly discuss important relevant concepts for both basic and clinical researchers.

Precision Nutrition and Childhood Obesity: A Scoping Review

Environmental exposures such as nutrition during life stages with high developmental plasticity-in particular, the in utero period, infancy, childhood, and puberty-may have long-lasting influences on risk of chronic diseases, including obesity-related conditions that manifest as early as childhood. Yet, specific mechanisms underlying these relationships remain unclear. Here, we consider the study of 'omics mechanisms, including nutrigenomics, epigenetics/epigenomics, and metabolomics, within a life course epidemiological framework to accomplish three objectives. First, we carried out a scoping review of population-based literature with a focus on studies that include 'omics analyses during three sensitive periods during early life: in utero, infancy, and childhood. We elected to conduct a scoping review because the application of multi-'omics and/or precision nutrition in childhood obesity prevention and treatment is relatively recent, and identifying knowledge gaps can expedite future research. Second, concomitant with the literature review, we discuss the relevance and plausibility of biological mechanisms that may underlie early origins of childhood obesity identified by studies to date. Finally, we identify current research limitations and future opportunities for application of multi-'omics in precision nutrition/health practice.

Dietary fat and total energy intake modifies the association of genetic profile risk score on obesity: evidence from 48 170 UK Biobank participants

BACKGROUND

Obesity is a multifactorial condition influenced by both genetics and lifestyle. The aim of this study was to investigate whether the association between a validated genetic profile risk score for obesity (GPRS-obesity) and body mass index (BMI) or waist circumference (WC) was modified by macronutrient intake in a large general population study.

METHODS

This study included cross-sectional data from 48 170 white European adults, aged 37-73 years, participating in the UK Biobank. Interactions between GPRS-obesity and macronutrient intake (including total energy, protein, fat, carbohydrate and dietary fibre intake) and its effects on BMI and WC were investigated.

RESULTS

The 93-single-nucleotide polymorphism (SNP) GPRS was associated with a higher BMI (β: 0.57 kg m^-2 per s.d. increase in GPRS (95% confidence interval: 0.53-0.60); P=1.9 × 10^-183) independent of major confounding factors. There was a significant interaction between GPRS and total fat intake (P_{(interaction)}=0.007). Among high-fat-intake individuals, BMI was higher by 0.60 (0.52, 0.67) kg m^-2 per s.d. increase in GPRS-obesity; the change in BMI with GPRS was lower among low-fat-intake individuals (β: 0.50 (0.44, 0.57) kg m^-2). Significant interactions with similar patterns were observed for saturated fat intake (high β: 0.66 (0.59, 0.73) versus low β: 0.49 (0.42, 0.55) kg m^-2, P_{(interaction)}=2 × 10^-4) and for total energy intake (high β: 0.58 (0.51, 0.64) versus low β: 0.49 (0.42, 0.56) kg m^-2, P_{(interaction)}=0.019), but not for protein intake, carbohydrate intake and fibre intake (P_{(interaction)} >0.05). The findings were broadly similar using WC as the outcome.

CONCLUSIONS

These data suggest that the benefits of reducing the intake of fats and total energy intake may be more important in individuals with high genetic risk for obesity.

Stable intergenerational associations of childhood overweight during the development of the obesity epidemic

OBJECTIVE

The obesity epidemic may have developed as a response to the obesogenic environment among the genetically predisposed. This investigation examined whether the intergenerational resemblances in childhood overweight changed across the development of the obesity epidemic in groups of children born to parents with and without childhood overweight.

METHODS

The study population was from the Copenhagen School Health Records Register, which includes age- and sex-specific body mass index (BMI; kg/m(2) ) of children. This study used BMI values from 7-year-old children born 1952-1989 and from their parents at ages 7 and 13 years. The available number of parent-child pairs ranged from 17,926 through 42,184. The odds ratios of childhood overweight (BMI z-score >90th percentile) were calculated using logistic regression by parental BMI groups (BMI > or ≤90th percentile) and child birth year intervals.

RESULTS

Stable levels in parent-child overweight associations were observed across child BMI groups born to parents with and without childhood overweight. A slight upward odds ratio trend was observed across time in children born to two overweight parents at age 13, but not at age 7 years.

CONCLUSIONS

Parent-child resemblance in childhood overweight showed small changes during the development of the obesity epidemic, suggesting that the obesogenic environment inducing the epidemic in Denmark influenced children irrespective of their familial predisposition.

Genotype by energy expenditure interaction and body composition traits: The Portuguese Healthy Family Study

Background and Aims. Energy expenditure has been negatively correlated with fat accumulation. However, this association is highly variable. In the present study we applied a genotype by environment interaction method to examine the presence of Genotype x by Total Daily Energy Expenditure and Genotype x by Daily Energy Expenditure interactions in the expression of different body composition traits. Methods and Results. A total of 958 subjects from 294 families of The Portuguese Healthy Family Study were included in the analysis. TDEE and DEE were assessed using a physical activity recall. Body fat percentages were measured with a bioelectrical impedance scale. GxTDEE and GxDEE examinations were performed using SOLAR 4.0 software. All BC traits were significantly heritable, with heritabilities ranging from 21% to 34%. The GxTDEE and GxDEE interaction models fitted the data better than the polygenic model for all traits. For all traits, a significant GxTDEE and GxDEE interaction was due to variance heterogeneity among distinct levels of TDEE and DEE. For WC, GxTDEE was also significant due to the genetic correlation function. Conclusions. TDEE and DEE are environmental constraints associated with the expression of individuals' BC genotypes, leading to variability in the phenotypic expression of BC traits.

Genotype-environment interactions for quantitative traits in Korea Associated Resource (KARE) cohorts

Background

Due to the lack of statistical power and confounding effects of population structure in human population data, genotype-environment interaction studies have not yielded promising results and have provided only limited knowledge for exploring how genotype and environmental factors interact to in their influence onto risk.

Results

We analyzed 49 human quantitative traits in 7,170 unrelated Korean individuals on 326,262 autosomal single nucleotide polymorphisms (SNPs) collected from the KARE (Korean Association Resource) project, and we estimated the statistically significant proportion of variance that could be explained by genotype-area interactions in the supra-iliac skinfold thickness trait (hGE2 = 0.269 and P = 0.00032), which is related to abdominal obesity. Data suggested that the genotypes could have different effects on the phenotype (supra-iliac skinfold thickness) in different environmental settings (rural vs. urban areas). We then defined the genotype groups of individuals with similar genetic profiles based on the additive genetic relationships among individuals using SNPs. We observed the norms of reaction, and the differential phenotypic response of a genotype to a change in environmental exposure. Interestingly, we also found that the gene clusters responsible for cell-cell and cell-extracellular matrix interactions were enriched significantly for genotype-area interaction.

Conclusions

This significant heritability estimate of genotype-environment interactions will lead to conceptual advances in our understanding of the mechanisms underlying genotype-environment interactions, and could be ultimately applied to personalized preventative treatments based on environmental exposures.

Association of single nucleotide polymorphism Rs2236518 in PRDM16 gene with BMI in Chinese males

AIM

PRD1-BF-1-RIZ1 homologous domain containing protein-16 (PRDM16) is a cell-autonomous transcriptional component that stimulates the development of brown fat cells. The aim of this study was to investigate the contribution of genetic variants of PRDM16 to obesity-related phenotype variations in Chinese.

METHODS

A total of 3204 subjects (consisting of 400 male-offspring nuclear families, 401 female-offspring nuclear families, and 729 unrelated older males) were recruited. Ten tag single nucleotide polymorphisms (SNPs) within the PRDM16 gene were genotyped using multiplex quantitative real-time PCR by Taqman assay. Body compositions were measured by dual-energy X-ray absorptiometry (DXA). The associations of the SNPs with the obesity-related phenotypes were analyzed using the quantitative transmission disequilibrium test (QTDT), GLM-ANOVA and PLINK statistical methods.

RESULTS

Rs2236518 was the only SNP that was associated with BMI in young (aged 20-40 years) males (P=0.011) using QTDT, and in the older men (aged 50-80 years) (P=0.003) using GLM-ANOVA. No significant associations were detected in the females. Nor was a relationship found between any haplotype and obesity-related phenotypes. When PLINK was used, no significant relationship was detected between 10 SNPs and obesity-related phenotypes in any of the studied cohorts.

CONCLUSION

Rs2236518 is associated with BMI in the young males (using QTDT), and the older males (using GLM-ANOVA).However, the result is not confirmed using PLINK. The discrepancy needs to be further addressed.

Association Between Body Fat Response to Exercise Training and MultilocusADRGenotypes

OBJECTIVE

To examine the contribution of adrenergic receptor (ADR) gene polymorphisms and their gene-gene interactions to the variability of exercise training-induced body fat response.

RESEARCH METHODS AND PROCEDURES

This was an intervention study that used a volunteer sample of 70 healthy, sedentary men (n = 29) and postmenopausal women (n = 41) 50 to 75 years of age, with a BMI < or = 37 kg/m2, from the Washington, DC, metropolitan area. Participants completed 6 weeks of dietary stabilization (American Heart Association diet) before 24 weeks of supervised aerobic exercise training. Diet was maintained throughout the intervention. Change in percent total body fat, percent trunk fat, and fat mass by DXA in ADR genotype groups (Glu12/Glu9 alpha2b-ADR, Trp64Arg beta3-ADR, and Gln27Glu beta2-ADR) at baseline and after 24 weeks of aerobic exercise training was measured.

RESULTS

In multivariate analysis (covariates: age, gender, and baseline value of phenotype), best fit models for percent total body and trunk fat response to exercise training retained main effects of all three ADR gene loci and the effects of each gene-gene interaction (p = 0.009 and 0.003, respectively). Similarly, there was a trend for the fat mass response model (p = 0.03). The combined genetic factors explained 17.5% of the overall model variability for percent total body fat, 22% for percent trunk fat, and 10% for fat mass.

DISCUSSION

The body fat response to exercise training in older adults is associated with the combined effects of the Glu12/Glu9 alpha2b-, Trp64Arg beta3-, and Gln27Glu beta2-ADR gene variants and their gene-gene interactions.

Variance-Component Analysis of Obesity in Type 2 Diabetes Confirms Loci on Chromosomes 1q and 11q

To study genetic loci influencing obesity in nuclear families with type 2 diabetes, we performed a genome-wide screen with 325 microsatellite markers that had an average spacing of 11 cM and a mean heterozygosity of approximately 75% covering all 22 autosomes. Genotype data were obtained from 562 individuals from 178 families from the Breda Study Cohort. These families were determined to have at least two members with type 2 diabetes. As a measure of obesity, the BMI of each diabetes patient was determined. The genotypes were analyzed using variance components (VCs) analysis implemented in GENEHUNTER 2 to determine quantitative trait loci influencing BMI. The VC analysis revealed two genomic regions showing VC logarithm of odds (LOD) scores > or =1.0 on chromosome 1 and chromosome 11. The regions of interest on both chromosomes were further investigated by fine-mapping with additional markers, resulting in a VC LOD score of 1.5 on chromosome 1q and a VC LOD of 2.4 on chromosome 11q. The locus on chromosome 1 has been implicated previously in diabetes. The locus on chromosome 11 has been implicated previously in diabetes and obesity. Our study to determine linkage for BMI confirms the presence of quantitative trait loci influencing obesity in subjects with type 2 diabetes on chromosomes 1q31-q42 and 11q14-q24.

Childhood overweight: prevention strategies for parents

In recent years, childhood obesity has become a worldwide issue. The growing list of negative outcomes associated with its occurrence is constantly increasing the need for prevention and intervention. Although there is still much to learn about the causes and outcomes associated with childhood obesity, current empirical information is already available and should be used to influence good parenting practices. Observing good nutrition during pregnancy and prenatal monitoring; breastfeeding for 7 months and longer, if possible; introducing young children to healthy food in a positive context; and choosing physical activities are all important strategies for parents in preventing childhood obesity.

Interaction of FTO and physical activity level on adiposity in African-American and European-American adults: the ARIC study

Physical inactivity accentuates the association of variants in the FTO locus with obesity-related traits but evidence is largely lacking in non-European populations. Here we tested the hypothesis that physical activity (PA) modifies the association of the FTO single-nucleotide polymorphism (SNP) rs9939609 with adiposity traits in 2,656 African Americans (AA) (1,626 women and 1,030 men) and 9,867 European Americans (EA) (5,286 women and 4,581 men) aged 45-66 years in the Atherosclerosis Risk in Communities (ARIC) study. Individuals in the lowest quintile of the sport activity index of the Baecke questionnaire were categorized as low PA. Baseline BMI, waist circumference (WC), and skinfold measures were dependent variables in regression models testing the additive effect of the SNP, low PA, and their interaction, adjusting for age, alcohol use, cigarette use, educational attainment, and percent European ancestry in AA adults, stratified by sex and race/ethnicity. rs9939609 was associated with adiposity in all groups other than AA women. The SNP × PA interaction was significant in AA men (P ≤ 0.002 for all traits) and EA men (P ≤ 0.04 for all traits). For each additional copy of the A (risk) allele, WC in AA men was higher in those with low PA (β(lowPA): 5.1 cm, 95% confidence interval (CI): 2.6-7.5) than high PA (β(highPA): 0.7 cm, 95% CI: -0.4 to 1.9); P (interaction) = 0.002). The interaction effect was not observed in EA or AA women. FTO SNP × PA interactions on adiposity were observed for AA as well as EA men. Differences by sex require further examination.

[Advances in pathophysiological concepts of obesity]

Obesity is defined as an increase in fat mass, which reflects the inefficiency of the system regulating energy homeostasis to resist against the pressure of environmental and genetic factors. Obesity constitutes itself into several phases to reach a real pathology of adipose tissue, seat of large functional alterations. There is a continuum of obesity forms, from purely genetic forms to purely environmental forms. Within this continuum, genetic and environmental determinants interaction is the rule. The role of gut flora has become a new interesting line of research in the pathophysiology of obesity.

Epidemiological study designs to investigate gene-behavior interactions in the context of human obesity

The epidemiology of obesity suggests that, for the majority of individuals, the disorder arises from an interaction between genetic predisposition and lifestyle behaviors such as dietary intake and physical activity. Unravelling the molecular basis of such interactions is complex but is becoming a realistic proposition as evidence emerges from whole genome association studies of genetic variants that are definitively associated with obesity. A range of possible study designs is available for investigating gene-lifestyle interaction, and the strengths and weaknesses of each approach are discussed in this article. Given the likely small main effect of common genetic variants and the difficulties in demonstrating associations of lifestyle factors with future risk of obesity, we would favor an analytical approach based on the clear specification of prior probabilities to reduce the likelihood of false discovery. Mixed approaches combining data from large-scale observational studies with smaller intervention trials may be ideal. In designing new studies to investigate these issues, a key choice is how precisely to quantify the important, but difficult to measure lifestyle behaviors. It is clear from power calculations that an approach based on enhancing precision of measurement of diet and physical activity is critical.

Changing prevalence of obesity in a rural community between 1977 and 2003: a multiple cross-sectional study

OBJECTIVE

To determine the changes in the prevalence of obesity in a rural community between 1977 and 2003.

STUDY DESIGN

A multiple cross-sectional study.

METHODS

The analysis was based on data from four cross-sectional surveys of adults aged 25-59 years, conducted in the town of Humboldt, Saskatchewan in 1977, 1983, 1993 and 2003. People with a body mass index (BMI) > or =30 kg/m(2) were considered to be obese.

RESULTS

Average body weight increased by 8 kg for both men and women during the study period. The increase in BMI was greater in adults aged 25-39 years compared with older age groups. The prevalence of obesity increased from 24% in 1977 to 38% in 2003 for men, and from 16% to 32% for women. The change was more pronounced from 1993 to 2003 than from 1977 to 1993, especially among younger adults. Standardized to the 2003 study population by sex, age and smoking status, the prevalence of obesity was 16.8% in 1977, 22.7% in 1983, 24.7% in 1993 and 34.5% in 2003, and was much higher than the Canadian national average (16% in 2003).

CONCLUSION

There was a dramatic increase in the prevalence of obesity in rural adults, and this was greater in younger adults. Changes in cigarette smoking did not explain the increase. There is an urgent need to identify and implement effective interventions to slow if not reverse the trend, particularly in rural populations.

Association between BBS6/MKKS gene polymorphisms, obesity and metabolic syndrome in the Greek population

OBJECTIVE

To investigate the relationship between MKKS gene variations, obesity-related traits and features of the metabolic syndrome (MS) in the Greek population.

DESIGN AND SUBJECTS

Genotype and haplotype analysis was carried out for six known MKKS gene polymorphisms (534C>T, 985+16T>G, 985+33C>G, 986-29A>T, 1161+58A>G and 1595G>T) in 220 obese subjects (body mass index > or =30 kg/m(2)) and 330 non-obese controls.

RESULTS

Genotype frequencies of the 985+16T>G, 986-29A>T and 1595G>T SNPs were significantly different between obese and non-obese individuals (P=0.0016, 0.0196 and 0.0069, respectively). Obese carriers of the risk alleles of the above three polymorphisms had a significantly increased prevalence of arterial hypertension. Furthermore, obese carriers of the G allele for the 985+16T>G polymorphism had an increased prevalence of type 2 diabetes mellitus and of MS component traits. A new polymorphism was detected, namely a C to T substitution at position 1129 (1129C>T or N377N). Frequency of the T allele for the 1129C>T polymorphism was significantly higher in control individuals than in obese subjects (P=0.0253). Haplotype TGTGT was more prevalent in obese than in controls (P=0.0002) and was associated with increased prevalence of the MS in obese subjects (P<0.0001).

CONCLUSION

Our results suggest that genetic variation in the MKKS gene may play a role in the development of obesity and the metabolic syndrome.

The role of exercise and PGC1alpha in inflammation and chronic disease

Inadequate physical activity is linked to many chronic diseases. But the mechanisms that tie muscle activity to health are unclear. The transcriptional coactivator PGC1alpha has recently been shown to regulate several exercise-associated aspects of muscle function. We propose that this protein controls muscle plasticity, suppresses a broad inflammatory response and mediates the beneficial effects of exercise.

Physical activity as a mediator of the impact of chronic conditions on quality of life in older adults

BACKGROUND

Chronic conditions could negatively affect the quality of life of older adults. This may be partially due to a relative lack of physical activity. We examined whether physical activity mediates the relationship between different chronic conditions and several health outcomes that are important to the quality of life of older adults.

METHODS

The data were taken from the Canadian Community Health Survey (cycle 1.1), a cross-section survey completed in 2001. Only respondents who were 65 years or older were included in our study (N = 22,432). The Health Utilities Index Mark 3 (HUI3) was used to measure overall quality of life, and to measure selected health outcomes (dexterity, mobility, pain, cognition, and emotional wellbeing) that are considered to be of importance to the quality of life of older adults. Leisure-time physical activity was assessed by determining weekly energy expenditure (Kcal per week) based on the metabolic equivalents of self-reported leisure activities. Linear and logistic regression models were used to determine the mediating effect of leisure-time physical activity while controlling for demographic variables (age and sex), substance use (tobacco use and alcohol consumption), and obesity.

RESULTS

Having a chronic condition was associated with a relative decrease in health utility scores and a relative increase in mobility limitations, dexterity problems, pain, emotional problems (i.e., decreased happiness), and cognitive limitations. These negative consequences could be partially attributed to a relative lack of physical activity in older adults with a chronic condition (14% mediation for the HUI3 score). The corresponding degree of mediation was 18% for mobility limitations, 5% for pain, and 13% for emotional wellbeing (statistically significant mediation was not observed for the other health attributes). These values varied with respect to the different chronic conditions examined in our study.

CONCLUSION

Older adults with chronic conditions are less likely to engage in leisure-time physical activities of at least 1,000 Kcal per week, and this association partially accounts for some negative consequences of chronic conditions, including mobility limitations, pain, and emotional problems. These findings provide support for health promotion programs that facilitate or encourage increased leisure-time physical activity in older people with chronic conditions.

Metabolic syndrome in youths

The metabolic syndrome (MetS), characterized by a clustering of cardiovascular disease and type 2 diabetes (T2DM) risk factors, has become prevalent in children and adolescents in recent years. However, the reported prevalence data on the MetS in youths has varied markedly, in large part, because of the disagreement among the variously proposed definitions of the MetS. Obesity is defined by using body mass index, waist circumference, or percent overweight, pointing to the need for standardized use of anthropometric variables to define obesity with a well-defined reference year for each ethnic population. In addition, slightly different cutoff values are used for triglycerides, high-density lipoprotein cholesterol, blood pressure, and fasting plasma glucose. Therefore, International Diabetes Federation recently proposed unified, easy-to-use criteria for diagnosing the MetS in youths. To provide insight into the mechanisms underlying the MetS in youths, the degree of insulin sensitivity/resistance and its correlation with the serum lipid and blood pressure levels have been evaluated. In addition, the serum levels of adipocytokines, such as adiponectin, leptin, tumor necrosis factor-alpha, resistin, interleukin-6, plasminogen activator inhibitor-1, and their correlation with childhood obesity have been extensively investigated. Recommendations for future research include exploring ways to assess visceral adiposity, to identify better biochemical markers for prediction of T2DM and disease progression, and to effectively intervene to prevent the MetS in youths.

The role of proopiomelanocortin (POMC) neurones in feeding behaviour

The precursor protein, proopiomelanocortin (POMC), produces many biologically active peptides via a series of enzymatic steps in a tissue-specific manner, yielding the melanocyte-stimulating hormones (MSHs), corticotrophin (ACTH) and β-endorphin. The MSHs and ACTH bind to the extracellular G-protein coupled melanocortin receptors (MCRs) of which there are five subtypes. The MC3R and MC4R show widespread expression in the central nervous system (CNS), whilst there is low level expression of MC1R and MC5R. In the CNS, cell bodies for POMC are mainly located in the arcuate nucleus of the hypothalamus and the nucleus tractus solitarius of the brainstem. Both of these areas have well defined functions relating to appetite and food intake. Mouse knockouts (ko) for pomc, mc4r and mc3r all show an obese phenotype, as do humans expressing mutations of POMC and MC4R. Recently, human subjects with specific mutations in β-MSH have been found to be obese too, as have mice with engineered β-endorphin deficiency. The CNS POMC system has other functions, including regulation of sexual behaviour, lactation, the reproductive cycle and possibly central cardiovascular control. However, this review will focus on feeding behaviour and link it in with the neuroanatomy of the POMC neurones in the hypothalamus and brainstem.

Genomics, nutrition, obesity, and diabetes

PURPOSE

To present evidence of genetic and environmental interactions as they relate to nutrition, diabetes, and obesity.

METHODS

A review of seminal literature related to genetics, obesity, and diabetes.

FINDINGS

Multifactorial interactions are important in the development of nutrition-related disorders, but the challenge remains to explain how these interactions are expressed. Treating subpopulations of people might be important and useful to some extent at present, but in the future treating people of given genetic predispositions and other personal and environmental factors will have greater effects on quality-of-life indicators and life expectancies.

CONCLUSIONS

Individualization coupled with multifactorial interactions will lead to new and more effective preventive and treatment modalities of nutrition-related disorders. With obesity and diabetes, genomics will bridge the traditional use of diet, exercise, and weight reduction with other environmental factors, ultimately leading to healthier lives.

Effect of a selective OX1R antagonist on food intake and body weight in two strains of rats that differ in susceptibility to dietary-induced obesity

An orexin-1 receptor antagonist decreases food intake whereas orexin-A selectively induces hyperphagia to a high-fat diet. In the present study, we evaluated the effect of an orexin antagonist in two strains of rats that differ in their sensitivity to becoming obese while eating a high-fat diet. Male Osborne-Mendel (OM) and S5B/Pl (S5B) rats were treated acutely with an orexin-1 receptor antagonist (SB-334867), after adaptation to either a high-fat (56% fat energy) diet or a low-fat (10% fat energy) diet that were equicaloric for protein (24% energy). Ad libitum fed rats were injected intraperitoneally with SB-334867 at doses of 3, 10 or 30 mg/kg, or vehicle at the beginning of the dark cycle, and food intake and body weight were measured. Hypothalamic prepro-orexin and orexin-1 receptor mRNA expression were analyzed in OM and S5B rats fed at a high-fat or low-fat diet for two weeks. SB-334867 significantly decreased food intake in both strains of rats eating the high-fat diet but only in the OM rats eating the low fat diet. The effect was greatest at 12 and 24 h. Body weight was also reduced in OM rats 1d after injection of SB-334867 but not in the S5B rats. Prepro-orexin and orexin-1 receptor expression levels did not differ between strains or diets. These experiments demonstrate that an orexin antagonist (SB-334867) reduces food intake and has a greater effect in a rat strain that is susceptible to dietary-induced obesity, than in a resistant strain.

Role of interaction between variants in the PPARG and interleukin-6 genes on obesity related metabolic risk factors

The combined effect of Peroxisome proliferator-activated receptor gamma (PPARG) Pro/Ala and interleukin-6 G174C gene variants, was evaluated in 429 Caucasian subjects in order to determine whether subjects carrying both variants were at different risk for obesity. In particular, the combined contribution of these two variants (both independent and interaction effects) to the total variation of obesity-related factors was estimated. All subjects were genotyped for codon 12 Pro/Ala locus variability and for the interleukin-6-174 C/G promoter polymorphism. Subjects with the Ala variant had significantly lower BMI, insulin resistance, triglyceride levels than those without. Furthermore, subjects with Ala variant had significantly lower IL-6 levels (0.88 +/- 0.9 vs 1.61 +/- 2.25 pg/ml; p = 0.041). In contrast, the IL6-C variant was significantly associated with lower plasma IL-6 and with lower total cholesterol levels but was not significantly associated with any other obesity risk factors. Indeed, subjects carrying both PPARG and IL-6 gene variants, had a clearly more favourable profile of obesity related risk factors than subjects with one variant, having Ala+/C+ carriers lower BMI (22.8 +/- 2.3 vs 24.14 +/- 1.9; f = 5.31; p < 0.005), insulin resistance (1.49 +/- 0.70 vs 2.13 +/- 0.92; f = 4.342; p = 0.038) and triglyceride levels (79.15 +/- 32.9 vs 98 +/- 6.73 mg/dl; f = 3.120; p < 0.005). These findings suggest that the effect of the two genetic variants on 'obesity related' factors is additive.

Genes, lifestyles and obesity

OBJECTIVE

To review the role of genes and lifestyle factors, particularly dietary habits and physical activity patterns, in obesity risk as well as their potential interactions.

DESIGN AND MEASUREMENTS

A descriptive report of a number of genes definitely ascribed or potentially implicated in excessive fat accumulation leading to obesity as assessed by different research approaches (Mendelian transmission, genetic animal models, epidemiological association/linkage studies and genome-wide scans). Also, the involvement of macronutrient intake and composition (fat/carbohydrate) as well as the role of activity-linked energy expenditure in obesity onset is reviewed.

RESULTS

Examples of the role of the genotype as well as of the dietary macronutrient composition/intake and sedentary/low energy cost of physical activities in obesity prevalence are reported.

CONCLUSIONS

Both genes and everyday life environmental factors such as cultural and social mediated food intake and reduced domestic and living work activities are involved in the obesity pandemia. The occurrence of gene x gene and gene x environmental factors interactions makes it more difficult to interpret the specific roles of genetics and lifestyle in obesity risk.

The yellow agouti mutation alters some but not all responses to diet and exercise

OBJECTIVE

Effects of ectopic expression of the agouti signaling protein were studied on responses to diet restriction and exercise in C57BL/6J (B6) mice and obese B6 mice congenic for the yellow agouti mutation [B6.Cg-Ay (Ay)].

RESEARCH METHODS AND PROCEDURES

Adult male Ay mice were either kept sedentary or exercised on a running wheel and fed ad libitum or diet restricted until weight matched to ad libitum-fed B6 control mice. Body composition, plasma lipids, leptin, and adiponectin were measured. mRNA levels for leptin, adiponectin, lipoprotein lipase, and pyruvate dehydrogenase kinase 4 were measured in a visceral (epididymal) and a subcutaneous (femoral) fat depot by real-time polymerase chain reaction.

RESULTS

Correlations among traits exhibited one of three patterns: similar lines for B6 and Ay mice, different slopes for B6 and Ay mice, and/or different intercepts for B6 and Ay mice. Correlations involving plasma leptin, mesenteric and epididymal adipose weights, or low-density lipoprotein-cholesterol were most likely to have different slopes and/or intercepts in B6 and Ay mice. mRNA levels for leptin, Acrp30, pyruvate dehydrogenase kinase 4, and lipoprotein lipase in epididymal adipose tissue were not correlated with corresponding levels in femoral adipose tissue.

DISCUSSION

The agouti protein interferes with leptin signaling at melanocortin receptors in the hypothalamus of Ay mice. Our results are consistent with the hypothesis that the melanocortin portion of the leptin-signaling pathway mediates effects primarily on certain fat depots and on some, but not all, components of cholesterol homeostasis.

Polymorphism of stress protein HSP70-2 gene in Tunisians: susceptibility implications in type 2 diabetes and obesity

OBJECTIVES

Tumor necrosis factor alpha (TNFalpha) is expressed primarily in adipocytes and elevated levels of this cytokine have been linked to obesity and insulin resistance. Several studies have shown statistical evidence of linkage between obesity and the chromosomal region encompassing the TNFalpha gene, suggesting that TNF alpha and/or a nearby gene is involved in the pathogenesis of obesity. Recently we analyzed the -308 TNFalpha polymorphism and that of HSP70-2 gene in Tunisian patients with obesity and no significant difference in allele frequencies of the -308 TNFalpha polymorphism was found between obese patients and controls. In contrast, polymorphism in HSP70-2 gene was found to be highly associated with obesity. Both TNFalpha and HSP70-2 genes have been mapped within the major histocompatibility complex (MHC). We designated a case-controlled study to investigate a potential association of genetic variation of the TNFalpha and that of the heat shock protein 70-2 (HSP70-2) with type 2 diabetes.

METHODS

We used the polymerase chain reaction and restriction enzyme to characterize the variation of the TNFalpha promoter region and that of the HSP70-2 gene in 280 unrelated Tunisian patients with type2 diabetes and 274 healthy control subjects.

RESULTS

Analysis of the -308 TNFalpha polymorphism in patients with type 2 diabetes and in control subjects revealed that the heterozygous TNF1/TNF2 genotype was significantly less frequent in the patient group (p=0.003), suggesting that TNF1/TNF2 may be considered as a protective marker against type 2 diabetes (OR=0.58). In contrast, a significant relative risk of type 2 diabetes was found associated with the P2-HSP70-2 homozygous genotype in non obese diabetic subjects (OR=1.97; p=0.0012).

CONCLUSION

These results along with those showing high frequency of P2-HSP70-2 genotype in obese Tunisians, suggest that HSP70-2 polymorphism has susceptibility implications in both obesity and diabetes.

Psychiatric aspects of child and adolescent obesity: a review of the past 10 years

OBJECTIVE

To review the past 10 years of published research on psychiatric aspects of child and adolescent obesity and highlight information mental health professionals need for preventing obesity in youths and diagnosing and treating it.

METHOD

Researchers performed computerized and manual searches of the literature and summarized the most relevant articles.

RESULTS

The growing epidemic of child and adolescent obesity deserves attention for its immediate mental health and long-term medical complications. Mental health professionals working with obese youths should be aware of recent advances in neuroscience, genetics, and etiologies associated with obesity. Those who assess and treat obese youth should view obesity as a chronic disease. Currently, no approved pharmacological or surgical approaches exist to treat childhood obesity.

CONCLUSIONS

Health care providers should focus on modest weight-loss goals that correlate with significant health benefits. The most effective treatments include substantial parental involvement. Mental health professionals should help obese children build self-esteem to help them lead full lives regardless of weight.

Genome-wide screen in obese pedigrees with type 2 diabetes mellitus from a defined Dutch population

A genome scan was performed in obese type 2 diabetes mellitus pedigrees to identify susceptibility loci involved in obesity-driven type 2 diabetes mellitus. We studied the 20% most obese diabetes pedigrees from a confined Dutch population from around the town of Breda. Previously we, and others, have already shown that a susceptibility locus influencing obesity in diabetes may reside on chromosome 18p11. We now report evidence to also suggest linkage for type 2 diabetes in these obese pedigrees on chromosome regions 11p (genome-wide P-value </= 0.061) and 12q (genome-wide P-value </= 0.029), thereby confirming previous findings from corresponding regions. The linkage found in the Breda Cohort of type 2 diabetes patients is influenced by obesity. This supports the notion that a genetic predisposition to obesity is probably intertwined with a genetic predisposition to type 2 diabetes. Further efforts should address the question of how, on a genetic level, these two factors interact.

Increasing trends of obesity in Sweden between 1996/97 and 2000/01

BACKGROUND

During the last two decades, obesity has reached epidemic proportions in industrialised societies such as Sweden.

OBJECTIVE

The first aim of this study is to examine whether the body mass index (BMI) and obesity increased between 1996/97 and 2000/01 in different subgroups in the Swedish population. The second aim is to examine whether there were any differences in BMI between subgroups of the population, characterised by age, gender, educational status, smoking habits, degree of urbanisation, and country of birth. The third aim is to examine whether BMI increased between the two periods after adjustment for all the explanatory variables.

METHODS

This study is based on two cross-sectional, random samples of the entire population aged 16-84 y, the first from 1996/97 including 5622 men and 5940 women and the second from 2000/01 including 5515 men and 5838 women. To investigate the possible change in obesity between the two periods, a logistic model adjusted for age was applied, after stratification by gender. To study the relationship between BMI and the explanatory variables, and the possible change in the subgroups of the population between the two periods, a linear regression model was used.

RESULTS

The total BMI mean increased by 0.4 units from 1996/97 to 2000/01 for both men and women. The prevalence of obesity also increased to about 10% in 2000/01. In some subgroups, the prevalence of obesity was especially high, for example, men and women aged 55-74 y, men with middle educational status, women with low educational status, former smokers, and Finnish-born men and women.

CONCLUSIONS

These findings illustrate that both BMI and obesity increased in the Swedish population between 1996/97 and 2000/01. This increase in BMI and obesity is most likely due to environmental factors, such as diet and a sedentary lifestyle. Health interventions need to target both certain subgroups and the whole population.

Studies of natural allele effects in mice can be used to identify genes causing common human obesity

Although genes causing rare Mendelian forms of human obesity have provided much useful information about underlying causes of obesity, these genes do not explain significant proportions of common obesity. This review presents evidence that animal models can be used to uncover subtle genetic effects on obesity and can provide a powerful rigorous compliment to human association studies. We discuss the advantages of animal models of obesity, various approaches to discovering obesity genes, and the future of mapping and isolating naturally occurring alleles of obesity genes. We review evidence that it is important to map naturally occurring obesity genes using quantitative trait locus (QTL) mapping, instead of mutagenesis and knockout models because the latter do not allow study of interactions and because naturally occurring obesity alleles can interfere with cloning from mutagenesis projects. Because a substantial percentage of human obesity results from complex interactions, the underlying genes can only be identified by direct studies in humans, which are still very difficult, or by studies in mice that begin with QTL mapping. Finally, we emphasize that animal model studies can be used to prove that a specific gene, only associated with obesity in humans, can indeed be the underlying cause of obesity in mammals.

Exercise and gene expression: physiological regulation of the human genome through physical activity

The current human genome was moulded and refined through generations of time. We propose that the basic framework for physiologic gene regulation was selected during an era of obligatory physical activity, as the survival of our Late Palaeolithic (50 000-10 000 BC) ancestors depended on hunting and gathering. A sedentary lifestyle in such an environment probably meant elimination of that individual organism. The phenotype of the present day Homo sapiens genome is much different from that of our ancient ancestors, primarily as a consequence of expressing evolutionarily programmed Late Palaeolithic genes in an environment that is predominantly sedentary. In this sense, our current genome is maladapted, resulting in abnormal gene expression, which in turn frequently manifests itself as clinically overt disease. We speculate that some of these genes still play a role in survival by causing premature death from chronic diseases produced by physical inactivity. We also contend that the current scientific evidence supports the notion that disruptions in cellular homeostasis are diminished in magnitude in physically active individuals compared with sedentary individuals due to the natural selection of gene expression that supports the physically active lifestyle displayed by our ancestors. We speculate that genes evolved with the expectation of requiring a certain threshold of physical activity for normal physiologic gene expression, and thus habitual exercise in sedentary cultures restores perturbed homeostatic mechanisms towards the normal physiological range of the Palaeolithic Homo sapiens. This hypothesis allows us to ask the question of whether normal physiological values change as a result of becoming sedentary. In summary, in sedentary cultures, daily physical activity normalizes gene expression towards patterns established to maintain the survival in the Late Palaeolithic era.

A genomewide linkage scan for quantitative-trait loci for obesity phenotypes

Obesity is an increasingly serious health problem in the world. Body mass index (BMI), percentage fat mass, and body fat mass are important indices of obesity. For a sample of pedigrees that contains >10,000 relative pairs (including 1,249 sib pairs) that are useful for linkage analyses, we performed a whole-genome linkage scan, using 380 microsatellite markers to identify genomic regions that may contain quantitative-trait loci (QTLs) for obesity. Each pedigree was ascertained through a proband who has extremely low bone mass, which translates into a low BMI. A major QTL for BMI was identified on 2q14 near the marker D2S347 with a LOD score of 4.04 in two-point analysis and a maximum LOD score (MLS) of 4.44 in multipoint analysis. The genomic region near 2q14 also achieved an MLS >2.0 for percentage of fat mass and body fat mass. For the putative QTL on 2q14, as much as 28.2% of BMI variation (after adjustment for age and sex) may be attributable to this locus. In addition, several other genomic regions that may contain obesity-related QTLs are suggested. For example, 1p36 near the marker D1S468 may contain a QTL for BMI variation, with a LOD score of 2.75 in two-point analysis and an MLS of 2.09 in multipoint analysis. The genomic regions identified in this and earlier reports are compared for further exploration in extension studies that use larger samples and/or denser markers for confirmation and fine-mapping studies, to eventually identify major functional genes involved in obesity.

An obligation for primary care physicians to prescribe physical activity to sedentary patients to reduce the risk of chronic health conditions

Physical inactivity increases the risk of many chronic disorders. Numerous studies have convincingly demonstrated that undertaking and maintaining moderate levels of physical activity (eg, brisk walking 3 hours a week) greatly reduces the incidence of developing many chronic health conditions, most notably type 2 diabetes mellitus, obesity, cardiovascular disease, and many types of cancers. However, the underlying mechanistic details of how physical activity confers such protective effects are not well understood and consequently constitute an active area of research. Although changing an individual's ingrained behavior is commonly perceived to be difficult, encouraging evidence suggests that intensive and repeated counseling by health care professionals can cause patients to become more physically active. Therefore, counseling patients to undertake physical activity to prevent chronic health conditions becomes a primary prevention modality. This article summarizes the vast epidemiologic and biochemical evidence supporting the many beneficial health implications of undertaking moderate physical activity and provides a rationale for incorporating physical activity counseling as part of routine practice in the primary care setting.

Tumor necrosis factor-alpha--308 G/A polymorphism in obese Caucasians

OBJECTIVE

Tumor necrosis factor-alpha (TNF-alpha) is expressed primarily in adipocytes, and elevated levels of this cytokine have been linked to obesity and insulin resistance. Recently, the A allele of a polymorphism in the 5'-flanking region of the TNF-alpha gene (G-308A) has been reported to be more frequent in obese than in lean subjects and has also been associated with increased expression of this cytokine in fat tissue and influences fat mass and insulin resistance. We, therefore, examined the relationship between this variant and obesity in a German Caucasian population.

SUBJECTS AND METHODS

We genotyped 176 index subjects recruited within the framework of the BErG (Berlin Ernährung Geschwister)- Study for the TNF-alpha-G-308A polymorphism. Subjects were characterized for weight, height, waist and hip circumference, body mass index (BMI), body composition, glucose tolerance, leptin and angiotensinogen levels.

RESULTS

The frequency of the -308A allele (0.18) was similar to that reported previously and genotype distribution was in Hardy-Weinberg equilibrium (GG, n=118; GA, n=53; AA, n=5). There was a significant difference in allele frequencies of the polymorphism by BMI quartiles (I,<27.3 kg/m2; II, 27.3-31.9 kg/m2; III, 31.9-36.5 kg/m2; IV,>36.5 kg/m2, in each quartile n=44) with -308A allele carriers having a higher BMI than G allele carriers (P=0.013). Despite previous smaller studies that have related insulin resistance to the G-308A polymorphism, we found no relationship between glucose and insulin response during an oral glucose tolerance test (OGTT) and the polymorphism. Furthermore, none of the plasma parameters were related to the polymorphism.

CONCLUSION

Our findings support the hypothesis that the G-308A polymophism of the TNF-alpha gene is associated with BMI. The G-308A polymorphism may, therefore, represent a genetic marker for increased susceptibility for obesity in Caucasians.

Interactions between variants in the beta3-adrenergic receptor and peroxisome proliferator-activated receptor-gamma2 genes and obesity

OBJECTIVE

Previous studies have reported modest associations between measures of obesity and the Trp64-Arg variant of the beta3-adrenergic receptor (ADRbeta3) and the Pro12Ala variant of the peronisome proliferator-activated receptor (PPAR)-gamma2. We hypothesized that these single gene variants may mark mutations that act through convergent pathways to produce synergistic effects on obesity.

RESEARCH DESIGN AND METHODS

The sample included 453 subjects from 10 large Mexican-American families participating in the population-based San Antonio Family Heart Study. The effects of each gene variant singly and jointly were estimated as fixed effects using the measured genotype approach framework. Analyses were conditioned on the pedigree structures to account for the correlations among family members. Statistical significance was evaluated by the likelihood ratio test with adjustment for age, sex and diabetes status.

RESULTS

The allele frequencies for the ADRbeta3 Trp64Arg and PPARgamma2 Pro12Ala variants were 18 and 12%, respectively. The ADRbeta3 variant was not significantly associated with any of the obesity-related traits, but subjects with the PPAR-gamma2 variant (n = 98) had significantly higher levels of lasting insulin (P = 0.03), leptin (P = 0.009), and waist circumference (P = 0.03) than those without. Subjects with the gene variants (n = 32) had significantly higher BMI, insulin, and leprtin levels than those with only the PPARgamma2 variant (n = 66) (P for interaction: 0.04, 0.02, and 0.01 for BMI, fasting insulin, and leptin, respectively).

CONCLUSIONS

Our results suggest that epistatic models with genes that have modest individual effects may be useful in understanding the genetic underpinnings of typical obesity in humans.

Modifier genes in mice and humans

An emerging theme of studies with spontaneous, engineered and induced mutant mice is that phenotypes often depend on genetic background, implying that genetic modifiers have a role in guiding the functional consequences of genetic variation. Understanding the molecular and cellular basis by which modifier genes exert their influence will provide insights into developmental and physiological pathways that are critical to fundamental biological processes, as well as into novel targets for therapeutic interventions in human diseases.

Diet effects on weight gain and body composition in high growth (hg/hg) mice

Nongenetic factors such as nutrition modulate the effects of genes responsible for overgrowth in animals. The goal of this study was to examine the importance of genotype x diet interactions on the effects of a major locus that regulates growth in the mouse. We have examined the phenotype of high growth (hg), a partially recessive autosomal locus that increases growth rate and mature body size. C57BL/6J (C57) and congenic C57BL/6J-hg/hg (HG) mice were fed three experimental diets differing in protein and energy content from 3 to 12 wk of age. HG mice grew faster and were, on average, 51% heavier than C57 at 12 wk of age. Feed intake was higher in HG mice but proportional to the increase in body weight. The magnitude of the differences in body size and composition between lines depended on the interaction between genotype and the protein/energy ratio of the diet. In C57, the diets modified the level of fatness without changing adult lean mass. However, in HG the diets differentially affected both linear growth and body composition. In general, HG had higher plasma levels of insulin-like growth factor I at 3 and 12 wk than C57. Plasma insulin did not differ between lines, but leptin was higher for C57 mice fed a high-energy diet. These results show that the effects of hg on growth are modulated by diet composition. Therefore, this mutation could be a valuable model with which to study the genetic and nutritional aspects of overgrowth disorders.

Waging war on modern chronic diseases: primary prevention through exercise biology

In this review, we develop a blueprint for exercise biology research in the new millennium. The first part of our plan provides statistics to support the contention that there has been an epidemic emergence of modern chronic diseases in the latter part of the 20th century. The health care costs of these conditions were almost two-thirds of a trillion dollars and affected 90 million Americans in 1990. We estimate that these costs are now approaching $1 trillion and stand to further dramatically increase as the baby boom generation ages. We discuss the reaction of the biomedical establishment to this epidemic, which has primarily been to apply modern technologies to stabilize overt clinical problems (e.g., secondary and tertiary prevention). Because this approach has been largely unsuccessful in reversing the epidemic, we argue that more emphasis must be placed on novel approaches such as primary prevention, which requires attacking the environmental roots of these conditions. In this respect, a strong association exists between the increase in physical inactivity and the emergence of modern chronic diseases in 20th century industrialized societies. Approximately 250,000 deaths per year in the United States are premature due to physical inactivity. Epidemiological data have established that physical inactivity increases the incidence of at least 17 unhealthy conditions, almost all of which are chronic diseases or considered risk factors for chronic diseases. Therefore, as part of this review, we present the concept that the human genome evolved within an environment of high physical activity. Accordingly, we propose that exercise biologists do not study "the effect of physical activity" but in reality study the effect of reintroducing exercise into an unhealthy sedentary population that is genetically programmed to expect physical activity. On the basis of healthy gene function, exercise research should thus be viewed from a nontraditional perspective in that the "control" group should actually be taken from a physically active population and not from a sedentary population with its predisposition to modern chronic diseases. We provide exciting examples of exercise biology research that is elucidating the underlying mechanisms by which physical inactivity may predispose individuals to chronic disease conditions, such as mechanisms contributing to insulin resistance and decreased skeletal muscle lipoprotein lipase activity. Some findings have been surprising and remarkable in that novel signaling mechanisms have been discovered that vary with the type and level of physical activity/inactivity at multiple levels of gene expression. Because this area of research is underfunded despite its high impact, the final part of our blueprint for the next millennium calls for the National Institutes of Health (NIH) to establish a major initiative devoted to the study of the biology of the primary prevention of modern chronic diseases. We justify this in several ways, including the following estimate: if the percentage of all US morbidity and mortality statistics attributed to the combination of physical inactivity and inappropriate diet were applied as a percentage of the NIH's total operating budget, the resulting funds would equal the budgets of two full institutes at the NIH! Furthermore, the fiscal support of studies elucidating the scientific foundation(s) targeted by primary prevention strategies in other public health efforts has resulted in an increased efficacy of the overall prevention effort. We estimate that physical inactivity impacts 80-90% of the 24 integrated review group (IRG) topics proposed by the NIH's Panel on Scientific Boundaries for Review, which is currently directing a major restructuring of the NIH's scientific funding system. Unfortunately, the primary prevention of chronic disease and the investigation of physical activity/inactivity and/or exercise are not mentioned in the almost 200 total subtopics comprising t