Synergistic effect of polymorphisms of uncoupling protein 1 and beta3-adrenergic receptor genes on autonomic nervous system activity

Non-pharmacological and pharmacological strategies of brown adipose tissue recruitment in humans

Humans maintain core temperature through a complex neuroendocrine circuitry, coupling environmental thermal and nutritional cues to heat-producing and dissipating mechanisms. Up to 40% of resting energy expenditure contributes to thermal homeostasis maintenance. Recent re-discovery of thermogenic brown adipose tissue (BAT) has brought the relation between ambient temperature, thermogenesis and systemic energy and substrate metabolism to the forefront. In addition to well-known pituitary-thyroid-adrenal axis, new endocrine signals, such as FGF21 and irisin, orchestrate crosstalk between white adipose tissue (WAT), BAT and muscle, tuning non-shivering and shivering thermogenesis responses. Cold exposure modulates the endocrine milieu, and cold-induced hormones cause bioenergetics transformation sufficient to impact whole body metabolism. This review will appraise the nature of human BAT and the basis of BAT-centred therapeutics, highlighting how the interaction between hormones and adipose tissue impacts metabolic responses. Non-pharmacological and pharmacological strategies of BAT recruitment and/or fat browning for metabolic benefits will be discussed.

Meta-analysis reveals the association of common variants in the uncoupling protein (UCP) 1-3 genes with body mass index variability

Background

The relationship between uncoupling protein (UCP) 1–3 polymorphisms and susceptibility to obesity has been investigated in several genetic studies. However, the impact of these polymorphisms on obesity is still under debate, with contradictory results being reported. Until this date, no meta-analysis evaluated the association of UCP polymorphisms with body mass index (BMI) variability. Thus, this paper describe a meta-analysis conducted to evaluate if the -3826A/G (UCP1); -866G/A, Ala55Val and Ins/Del (UCP2) and -55C/T (UCP3) polymorphisms are associated with BMI changes.

Methods

A literature search was run to identify all studies that investigated associations between UCP1-3 polymorphisms and BMI. Weighted mean differences (WMD) were calculated for different inheritance models.

Results

Fifty-six studies were eligible for inclusion in the meta-analysis. Meta-analysis results showed that UCP2 55Val/Val genotype was associated with increased BMI in Europeans [Random Effect Model (REM) WMD 0.81, 95% CI 0.20, 1.41]. Moreover, the UCP2 Ins allele and UCP3-55T/T genotype were associated with increased BMI in Asians [REM WMD 0.46, 95% CI 0.09, 0.83 and Fixed Effect Model (FEM) WMD 1.63, 95% CI 0.25, 3.01]. However, a decreased BMI mean was observed for the UCP2-866 A allele in Europeans under a dominant model of inheritance (REM WMD −0.18, 95% CI −0.35, −0.01). There was no significant association of the UCP1-3826A/G polymorphism with BMI mean differences.

Conclusions

The meta-analysis detected a significant association between the UCP2-866G/A, Ins/Del, Ala55Val and UCP3-55C/T polymorphisms and BMI mean differences.

Brown adipose tissue in adult humans: a metabolic renaissance

Brown adipose tissue (BAT) plays a key role in energy homeostasis and thermogenesis in animals, conferring protection against diet-induced obesity and hypothermia through the action of uncoupling protein 1 (UCP1). Recent metabolic imaging studies using positron emission tomography computerized tomography (PET-CT) scanning have serendipitously revealed significant depots of BAT in the cervical-supraclavicular regions, demonstrating persistence of BAT beyond infancy. Subsequent cold-stimulated PET-CT studies and direct histological examination of adipose tissues have demonstrated that BAT is highly prevalent in adult humans. BAT activity correlates positively with increment of energy expenditure during cold exposure and negatively with age, body mass index, and fasting glycemia, suggesting regulatory links between BAT, cold-induced thermogenesis, and energy metabolism. Human BAT tissue biopsies express UCP1 and harbor inducible precursors that differentiate into UCP1-expressing adipocytes in vitro. These recent discoveries represent a metabolic renaissance for human adipose biology, overturning previous belief that BAT had no relevance in adult humans. They also have implications for the understanding of the pathogenesis and treatment of obesity and its metabolic sequelae.

Impact of UCP1 and β3AR gene polymorphisms on age-related changes in brown adipose tissue and adiposity in humans

BACKGROUND

Brown adipose tissue (BAT) is involved in the regulation of whole-body energy expenditure and adiposity. The activity and prevalence of BAT decrease with age in humans.

OBJECTIVE

To examine the effects of single nucleotide polymorphisms of the genes for uncoupling protein 1 (UCP1) and β3-adrenergic receptor (β3AR), key molecules of BAT thermogenesis, on age-related decline of BAT activity and accumulation of body fat in humans.

METHODS

One hundred ninety-nine healthy volunteers (20-72 years old (y.o.)) underwent fluorodeoxyglucose-positron emission tomography (FDG-PET) and computed tomography (CT) after 2-h cold exposure to assess BAT activity. The visceral and subcutaneous fat areas at the abdominal level were estimated from the CT images. They were genotyped for -3826 A/G polymorphism of the UCP1 gene and 64 Trp/Arg mutation of the β3AR gene.

RESULTS

BAT was detected in 88 subjects out of 199 (44%), more in younger (30 y.o., 55%) than older subjects (>40 y.o., 15%). BAT prevalence of older subjects tended to be lower in the UCP1 G/G group than the A allele group (A/A and A/G), and also in the β3AR Arg allele group (Trp/Arg and Arg/Arg) than the Trp/Trp group. When compared subjects who had two or more base substitutions on the two genes (the 2-4 allele group) with those who had less than two base substitutions (the 0-1 allele group), BAT prevalence was comparable in younger subjects (62% vs 50%) but lower in older subjects (0% vs 24%, P<0.05). Visceral fat area of the 2-4 allele group was higher than that of the 0-1 allele group (P<0.05) in older subjects, but not in younger subjects.

CONCLUSION

UCP1 -3826 A/G and β3AR 64 Trp/Arg substitutions accelerate age-related decrease in BAT activity, and thereby may associate with visceral fat accumulation with age.

The polymorphisms of UCP1 genes associated with fat metabolism, obesity and diabetes

Uncoupling protein 1 (UCP1), a 32-kDa protein located in the inner mitochondrial membrane, is abundant in brown adipose tissue, as a proton transporter in mitochondria inner membrane which uncouples oxidative metabolism from ATP synthesis and dissipates energy through the heat. UCP1 has been reported to play important roles for energy homeostasis in rodents and neonate of larger mammals including human. Recently, numerous candidate genes were searched to determine the genetic factors implicated in the pathogenesis of obesity, related metabolic disorders and diabetes. UCP-1, which plays a major role in thermogenesis, was suggested to be one of the candidates. This review summarizes data supporting the existence of brown adipocytes and the role of UCP1 in energy dissipation in adult humans, and the genetic variety association with the fat metabolism, obesity and diabetes.

Alterations of autonomic nervous activity and energy metabolism by capsaicin ingestion during aerobic exercise in healthy men

We investigated whether capsaicin ingestion (150 mg) enhances substrate oxidation associated with thermogenic sympathetic activity as an energy metabolic modulator without causing prolongation of the cardiac OT interval during aerobic exercise in humans. Ten healthy males [24.4 (4.3) y] volunteered for this study. The cardiac autonomic nervous activities evaluated by means of heart rate variability of power spectral analysis, energy metabolism, and ECG QT interval were continuously measured during 5-min rest and 30-min exercise at 50% of maximal ventilatory threshold (50% VT(max)) on a stationary ergometer with placebo or capsaicin oral administration chosen at random. The results indicated that there were no significant differences in heart rate during rest or exercise between the two trials. Autonomic nervous activity increased in the capsaicin tablet trial during exercise, but the difference did not reach statistical significance. Capsaicin, however, significantly induced a lower respiratory gas exchange ratio [0.92 (0.02) vs. 0.94 (0.02), means (SE), p < 0.05] and higher fat oxidation [0.17 (0.04) vs. 0.12 (0.04) g/min, means (SE), p < 0.05] during exercise. On the other hand, the data on the cardiac OT interval showed no significant difference, indicating that oral administration of capsaicin did not cause any adverse effect on cardiac depolarization-repolarization. In conclusion, it may be considered that capsaicin consumption 1 h before low intensity exercise (50% VT(max)) is a valuable supplement for the treatment of individuals with hyperlipidemia and/or obesity because it improves lipolysis without any adverse effects on the cardiac depolarization and repolarization process.

Adrenergic receptor polymorphisms and autonomic nervous system function in human obesity

Adrenergic receptors (ARs) are cell-surface G-protein-coupled receptors for catecholamines. They are essential components of the sympathetic nervous system, organized within the autonomic nervous system (ANS), which controls various physiological functions, including energy homeostasis and metabolism of glucose and lipids. An impairment of ANS function in metabolism is considered to be one of the pathological states associated with human obesity and related metabolic diseases; thus, alterations in AR function might be implicated in the pathophysiology of these diseases. Several studies have suggested an association between obesity phenotypes and some AR polymorphisms. In vitro and human clinical studies indicate that some of these polymorphisms have functional and pathophysiological significance, including the linkage to ANS function. This review summarizes present knowledge of AR polymorphisms related to human obesity, and their association with ANS function.

Autonomic nervous system activity in the late luteal phase of eumenorrheic women with premenstrual symptomatology

The majority of women of reproductive age experience a regular recurrence of various symptoms in the premenstrual phase. The etiopathogenesis of premenstrual symptomatology, however, remains inconclusive. The present study was proposed to evaluate whether the activity of the autonomic nervous system (ANS), which largely contributes to the relative stability of a human's internal environment, is altered during the menstrual cycle of women with premenstrual symptomatology. Thirty eumenorrheic young women participated in this study. All subjects were investigated during the follicular and late luteal phases. The ANS activity was assessed by means of heart rate variability power spectral analysis during supine rest. No intramenstrual cycle differences in the ANS activity were found in women experiencing no or small increases in premenstrual symptoms. In contrast, the sympathetic nervous system (SNS) activity significantly increased and the parasympathetic nervous system (PNS) activity apparently decreased in the late luteal phase in subjects whose premenstrual symptomatology was not unbearable, but substantially increased (> 20%) compared to the symptom-free follicular phase. The women with greater degrees of premenstrual distress possessed higher SNS activity and lower PNS activity in the late luteal phase than the women with less symptomatology. The ANS activity in the follicular phase did not differ among the subjects regardless of their premenstrual symptoms. Although causes and consequences continue to elude, the present study provides additional intriguing evidence that the altered functioning of ANS in the late luteal phase could be associated with diverse psychosomatic or behavioral symptoms appearing premenstrually.

Electrophysiology and kinesiology for health and disease

This paper summarizes my Basmajian keynote presentation at the 2004 International Society of Electrophysiology and Kinesiology Conference. I dedicate this paper to Dr. Herbert A. deVries, the mentor of my research career. The following topics will be covered from the standpoint of Electrophysiology and Kinesiology for health and disease: (1) electromechanical manifestations of neuromuscular fatigue and muscle soreness, (2) cardiac depolarization-repolarization characteristics of normal and patients, (3) etiology of obesity and diabetes and autonomic nervous system, and (4) functional electrical stimulation for health and disease, respectively.

T393C polymorphism of GNAS1 associated with the autonomic nervous system in young, healthy Japanese subjects

1. T393C polymorphism of the gene encoding the Gs-protein alpha-subunit (GNAS1) has been reported recently to be associated with hypertension in which dysfunctions of the autonomic nervous system (ANS) are closely involved. In the present study, the association of this polymorphism with ANS activity was investigated in young, healthy Japanese males. 2. Four hundred and one subjects were genotyped for the T393C polymorphism of GNAS1 by polymerase chain reaction-restriction fragment length polymorphism. Autonomic nervous system activity during supine rest and when standing was assessed in 137 subjects by electrocardiogram R-R interval power spectral analysis. 3. One hundred and fifty-four subjects (38.4%) were homozygous for the T allele (TT), 188 (46.9%) were heterozygous (TC) and 59 (14.7%) were homozygous for the C allele (CC). There were no significant differences as to genotype among the clinical characteristics investigated. In power spectral analysis of heart rate variability, the high-frequency component and parasympathetic nervous system (PNS) index during supine rest were significantly lower in TT and TC carriers than in CC carriers. Furthermore, the increase in heart rate and the responsiveness of sympathetic nervous system index and PNS index to postural change from supine rest to standing were significantly lower in TT and TC carriers than in CC carriers. 4. These observations suggest that the GNAS1 T393C polymorphism is associated with ANS activity in youth, so that it may be useful as a genetic marker for future pathogenesis of hypertension. Follow-up studies are necessary to clarify the prevalence rates of hypertension among 393T allele carriers in the present study.

The effects of uncoupling protein-1 genotype on lipoprotein cholesterol level in Korean obese subjects

Uncoupling protein-1 (UCP-1) plays a major role in thermogenesis, and has been implicated in the pathogenesis of obesity and metabolic disorders. The purpose of this study was to estimate the effects of A-3826G polymorphism of the UCP-1 gene on the plasma lipid profiles in 190 Korean obese subjects with a body mass index (BMI) more than 30 kg/m2. Height, weight, BMI, wait-to-hip ratio (WHR), obesity index, and body composition were measured and genotype of UCP-1 was analyzed by polymerase chain reaction (PCR) restriction fragment length polymorphism (RFLP) method. Serum concentrations of fasting glucose, total cholesterol, high-density lipoprotein (HDL) cholesterol, and triglyceride were measured. The frequencies of UCP-1 genotypes were AA type, 22.1%; AG type, 53.7%; and GG type, 24.2%; and the frequency of G allele was 0.51. Among many parameters, diastolic blood pressure (DBP) (P = .023) and low-density lipoprotein (LDL) cholesterol (P = .011) were significantly higher in AG and GG types compared with AA type, whereas HDL cholesterol was significantly lower in GG type compared with other types (P < .05). Atherogenic index was significantly higher in GG type compared with AA type (P = 0.027). LDL-to-HDL cholesterol ratio was significantly increased in the order of AA < AG < GG types (P = .001). When the subjects were divided into a normal group and a hyper-LDL cholesterolemia group by LDL cholesterol level of 3.626 mmol/L (140 mg/dL), the frequency of hyper-LDL cholesterolemia was significantly higher in GG type compared with other types by Fisher's exact (chi-square) test (P = .05). When logistic regression analysis was conducted to find the risk factors of hyper-LDL cholesterolemia, the odds ratio was 4.115 (P = .03) for GG type of UCP-1 gene. These results suggest that the GG type of the UCP-1 gene has a strong association with increased LDL cholesterol level and might be a significant risk factor for hyper-LDL cholesterolemia among Korean obese subjects.

Genómica de la regulación del peso corporal: mecanismos moleculares que predisponen a la obesidad

Obesity has become a worldwide public health problem which affects millions of people. Substantial progress has been made in elucidating the pathogenesis of energy homeostasis over the past few years. The fact that obesity is under strong genetic control has been well established. Twin, adoption and family studies have shown that genetic factors play a significant role in the pathogenesis of obesity. Human monogenic obesity is rare in large populations. The most common form of obesity is considered to be a polygenic disorder. New treatments are currently required for this common metabolic disease and type 2 diabetes. The identification of physiological and biochemical factors that underlie the metabolic disturbances observed in obesity is a key step in developing better therapeutic outcomes. The discovery of new genes and pathways involved in the pathogenesis of such a disease is critical to this process. However, identification of genes that contribute to the risk of developing the disease represents a significant challenge since obesity is a complex disease with many genetic and environmental causes. A number of diverse approaches have been used to discover and validate potential new genes for obesity. To date, DNA-based approaches using candidate genes and genome-wide linkage analysis have not had a great success in identifying genomic regions or genes involved in the development of these diseases. Recent advances in the ability to evaluate linkage analysis data from large family pedigrees (using variance components-based linkage analysis) show great promise in robustly identifying genomic regions associated with the development of obesity. Studying rare mutations in humans and animal models has provided fundamental insight into a complex physiological process, and has complemented population-based studies that seek to reveal primary causes. Remarkable progress has been made in both fronts and the pace of advance is likely to accelerate as functional genomics and the human genome project expand and mature. Approaches based on Mendelian and quantitative genetics may well converge, and ultimately lead to more rational and selective therapies.

The -3826 A-->G variant of the uncoupling protein-1 gene diminishes postprandial thermogenesis after a high fat meal in healthy boys

This study investigated whether the -3826 A-->G nucleotide variant of the uncoupling protein-1 (UCP1) gene is correlated with postprandial thermogenesis after a high fat meal in children. Healthy boys, aged 8-11 yr, were examined for resting energy expenditure and the thermic effect of a meal (TEM), which were measured by indirect calorimetry for 180 min after a high fat (70% fat, 20% carbohydrate, and 10% protein, providing 30% of the daily energy requirement) and a high carbohydrate meal (20% fat, 70% carbohydrate, and 10% protein). The sympatho-vagal activities were assessed by means of spectral analysis of the heart rate variability during the same period. Children were genotyped for UCP1 polymorphism by applying a PCR-restriction fragment length polymorphism using buccal samples. There was no reaction of sympathetic activity to the high carbohydrate meal in either the GG allele or the AA+AG group and no significant difference in TEM. However, after the high fat meal, sympathetic responses were found in both groups; further, the GG allele group showed significantly lower TEM than the AA+AG group. In conclusion, despite fat-induced sympathetic stimulation, GG allele carriers have a lowered capacity of TEM in response to fat intake, suggesting that such impaired UCP1-linked thermogenesis can have adverse effects on the regulation of body weight.

Beta-adrenoceptor polymorphisms

There can be no doubt that beta(1)-, beta(2)- and beta(3)-adrenoceptor genes have genetic polymorphisms. Two single nucleotide polymorphisms have been described for the beta(1)- (Ser49Gly; Gly389Arg), three for the beta(2)- (Arg16Gly; Gln27Glu; Thr164Ile) and one for the beta(3)-adrenoceptor subtype (Trp64Arg) that might be of functional importance. The possibility that changes in expression or properties of the beta-adrenoceptors due to single nucleotide polymorphisms might have phenotypic consequences influencing their cardiovascular or metabolic function or may contribute to the pathophysiology of several disorders like hypertension, congestive heart failure, asthma or obesity is an idea that has attracted much interest during the last 10 years. At present, it appears that these beta-adrenoceptor polymorphisms are very likely not disease-causing genes, but might be risk factors, might modify disease and/or might influence progression of disease. The aim of this review is to provide an overview of the functional consequences of such beta-adrenoceptor polymorphisms in vitro, ex vivo and in vivo.

Phenotypic linkage between single-nucleotide polymorphisms of beta3-adrenergic receptor gene and NADH dehydrogenase subunit-2 gene, with special reference to eating behavior

The beta(3)-adrenergic receptor gene (BAR-3) allelic variant (Trp64Arg and Arg64Arg) is correlated with obesity or non-insulin-dependent diabetes mellitus. The mitochondrial NADH dehydrogenase subunit-2 gene (ND2) variant (Mt5178A) is associated with longevity or less susceptibility to adult-onset diseases. The frequencies of both the variants are high among the Japanese population. Cross-sectional analysis of these variants was conducted to determine if they correlated well with life-style-related phenotypes and nutrient intake. The body fat rate in the BAR-3 variant+ND2 variant group was higher than those rates in the BAR-3 normal+ND2 variant, BAR-3 normal+ND2 normal. The BAR-3 normal+ND2 variant group preferred much carbohydrate and less animal protein compared with other three groups. A combination of SNPs of the nuclear BAR-3 and the mitochondrial ND2 genes may affect eating behavior besides the biochemical and metabolic process of signal transduction and electron transfer system.

A deletion in the alpha2B-adrenergic receptor gene and autonomic nervous function in central obesity

OBJECTIVE

We investigated the impact of a three-amino acid deletion (12Glu9) polymorphism in the alpha(2B)-adrenergic receptor gene on autonomic nervous function. The short form (Glu(9)/Glu(9)) of the polymorphism has previously been associated with a reduced basal metabolic rate in obese subjects. Because autonomic nervous function participates in the regulation of energy metabolism, there could be a link between this polymorphism and autonomic nervous function.

RESEARCH METHODS AND PROCEDURES

Data of a 10-year follow-up study with 126 nondiabetic control subjects and 84 type 2 diabetic patients were used to determine the effects of the 12Glu9 polymorphism on autonomic nervous function. A deep breathing test and an orthostatic test were used to investigate parasympathetic and sympathetic autonomic nervous function. In addition, cardiovascular autonomic function was studied using power spectral analysis of heart rate variability.

RESULTS

No significant differences were found in the frequency of the 12Glu9 deletion polymorphism between nondiabetic and diabetic subjects. The nondiabetic men with the Glu(9)/Glu(9) genotype, especially those with abdominal obesity, had significantly lower total and low-frequency power values in the power spectral analysis when compared with other men. Furthermore, in a longitudinal analysis of 10 years, the decrease in parasympathetic function was greater in nondiabetic men with the Glu(9)/Glu(9) genotype than in the men with the Glu(9)/Glu(12) or Glu(12)/Glu(12) genotypes.

DISCUSSION

The results of the present study suggest that the 12Glu9 polymorphism of the alpha(2B)-adrenergic receptor gene modulates autonomic nervous function in Finnish nondiabetic men. In the nondiabetic men with the Glu(9)/Glu(9) genotype, the general autonomic tone is depressed, and vagal activity especially becomes impaired with time. Furthermore, this association is accentuated by central obesity.

Genetics of obesity

Obesity is a typical common multifactorial disease in which environmental and genetic factors interact. In rare cases of severe obesity with childhood onset, a single gene has a major effect in determining the occurrence of obesity, with the environment having only a permissive role in the severity of the phenotype. Exceptional mutations of the leptin gene and its receptor, pro-opiomelanocortine (POMC), prohormone convertase 1 (PC1) and more frequently, mutations in the melanocortin receptor 4 (1 to 4% of very obese cases) have been described. All these obesity genes encode proteins that are strongly connected as part of the same loop of the regulation of food intake. They all involve the leptin axis and one of its hypothalamic targets; the melanocortin pathway. Pathways of bodyweight regulation involved in monogenic forms of obesity might represent targets for future drug development. Successful leptin protein replacement in a leptin-deficient child has contributed to the validation of the usefulness of gene screening in humans. However, the individual variability in response to leptin treatment might be related to genetic variability. The efficiency of leptin itself or of small-molecule agonists of the leptin receptor should be studied in relation with genetic variations in the leptin gene promoter. The most common forms of obesity are polygenic. Two general approaches have been used to date in the search for genes underlying common polygenic obesity in humans. The first approach focuses on selected genes having some plausible role in obesity on the basis of their known or presumed biological role. This approach yielded putative susceptibility genes with only small or uncertain effects. The second approach attempts to map genes purely by position and requires no presumptions on the function of genes. Genome-wide scans identify chromosomal regions showing linkage with obesity in large collections of nuclear families. Genome-wide scans in different ethnic populations have localized major obesity loci on chromosomes 2, 5, 10, 11 and 20. Susceptibility gene(s) for obesity may be positionally cloned in the intervals of linkage. The candidate gene and positional cloning of major obesity-linked regions approaches are discussed in this paper.

Alpha(2B)-adrenergic receptor deletion polymorphism associates with autonomic nervous system activity in young healthy Japanese

Several polymorphisms of genes involved in autonomic nervous system (ANS) function have been reported to affect metabolic regulation. We have investigated the association of an alpha(2B)-adrenergic receptor (alpha(2B)AR) three-amino acid deletion polymorphism with ANS activity in young healthy subjects by means of electrocardiogram R-R interval power spectral analysis. Three hundred eighty-one young healthy Japanese males (mean +/- SE, 20.6 +/- 0.1 yr) were studied. One hundred sixty-eight (44.1%) were homozygotes of Long allele (Long/Long), 162 (42.5%) were heterozygotes (Long/Short), and 51 (13.4%) were homozygotes of Short allele (Short/Short). The allele frequency of Short allele was 0.35. No significant differences were observed in any of the characteristics investigated: body mass index, plasma glucose, plasma insulin, or family history of diabetes and obesity. In R-R spectral analysis of heart rate variability, carriers of Short/Short had significantly greater low frequency and very low frequency than Long/Long, as well as a higher sympathetic nervous system index. These findings suggest that the alpha(2B)AR deletion polymorphism might result in metabolic disorder by altering ANS function.

Potential association between endogenous leptin and sympatho-vagal activities in young obese Japanese women

Leptin is an adipocyte-derived hormone that decreases food intake and increases energy expenditure through the activation of the sympathetic nervous system (SNS). Notwithstanding recent intensive research, the underlying physiological mechanism of leptin as well as the etiology of obesity in humans remains elusive. The present study attempted to investigate the potential association between endogenous circulating leptin and sympatho-vagal activities in age- and height-matched obese and nonobese healthy young women. Plasma leptin concentrations were measured by radioimmunoassay. The autonomic nervous system activity was assessed during the resting condition by means of a recently devised power spectral analysis of heart rate variability, which serves to identify three separate frequency components, very low (VLO), low (LO), and high (HI). Plasma leptin concentrations were greater in the obese than in the control group (45.7 +/- 5.89 vs. 11.2 +/- 1.10 ng. ml(-1), P < 0.01). As to the contribution of endogenous leptin to SNS activity, both the ratios of the VLO frequency component reflecting thermoregulatory sympathetic function and the global SNS index [(VLO + LO)/HI] to plasma leptin concentration were markedly reduced in the obese compared to the control group (VLO per leptin: 5.9 +/- 1.39 vs. 37.8 +/- 8.1 ms(2). ml. ng(-1), P < 0.01; SNS index per leptin: 0.04 +/- 0.008 vs. 0.33 +/- 0.01 ml c. ng(-1), P < 0.01). Additionally, a nonlinear regression analysis revealed that these ratios exponentially decreased as a function of body fat content (VLO per leptin r(2) = 0.57, P < 0.01; SNS index per leptin r(2) = 0.53, P < 0.01). Our data suggest that reduced sympathetic responsiveness to endogenous leptin production, implying peripheral leptin resistance, might be a pathophysiological feature of obesity in otherwise healthy young women. The findings regarding the association of leptin, body fat content, and SNS activity further indicate that the 30% of total body fat, which has been used as a criterion of obesity, might be a critical point at which leptin resistance is induced.

The human obesity gene map: the 2001 update

This report constitutes the eighth update of the human obesity gene map, incorporating published results up to the end of October 2001. Evidence from the rodent and human obesity cases caused by single-gene mutations, Mendelian disorders exhibiting obesity as a clinical feature, quantitative trait loci (QTLs) uncovered in human genome-wide scans and in crossbreeding experiments in various animal models, association and linkage studies with candidate genes and other markers is reviewed. The human cases of obesity related in some way to single-gene mutations in six different genes are incorporated. Twenty-five Mendelian disorders exhibiting obesity as one of their clinical manifestations have now been mapped. The number of different QTLs reported from animal models currently reaches 165. Attempts to relate DNA sequence variation in specific genes to obesity phenotypes continue to grow, with 174 studies reporting positive associations with 58 candidate genes. Finally, 59 loci have been linked to obesity indicators in genomic scans and other linkage study designs. The obesity gene map depicted in Figure 1 reveals that putative loci affecting obesity-related phenotypes can be found on all chromosomes except chromosome Y. A total of 54 new loci have been added to the map in the past 12 months, and the number of genes, markers, and chromosomal regions that have been associated or linked with human obesity phenotypes is now above 250. Likewise, the number of negative studies, which are only partially reviewed here, is also on the rise.