PPAR-gamma2 Pro12Ala variant is associated with greater insulin sensitivity in childhood obesity

PPARs in Clinical Experimental Medicine after 35 Years of Worldwide Scientific Investigations and Medical Experiments

This year marks the 35th anniversary of Professor Walter Wahli's discovery of the PPARs (Peroxisome Proliferator-Activated Receptors) family of nuclear hormone receptors. To mark the occasion, the editors of the scientific periodical Biomolecules decided to publish a special issue in his honor. This paper summarizes what is known about PPARs and shows how trends have changed and how research on PPARs has evolved. The article also highlights the importance of PPARs and what role they play in various diseases and ailments. The paper is in a mixed form; essentially it is a review article, but it has been enriched with the results of our experiments. The selection of works was subjective, as there are more than 200,000 publications in the PubMed database alone. First, all papers done on an animal model were discarded at the outset. What remained was still far too large to describe directly. Therefore, only papers that were outstanding, groundbreaking, or simply interesting were described and briefly commented on.

G Allele of the rs1801282 Polymorphism in PPARγ Gene Confers an Increased Risk of Obesity and Hypercholesterolemia, While T Allele of the rs3856806 Polymorphism Displays a Protective Role Against Dyslipidemia: A Systematic Review and Meta-Analysis

BACKGROUND

The relationships between the rs1801282 and rs3856806 polymorphisms in nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) gene and obesity indexes as well as serum lipid levels have been extensively investigated in various studies, but the results were inconsistent and even contradictory.

METHODS

PubMed, Google Scholar, Embase, Cochrane Library, Web of Science, Wanfang, CNKI and VIP databases were searched for eligible studies. The random-effTPDEects model was used, and standardized mean difference (SMD) with 95% confidence interval (CI) was calculated to estimate the differences in obesity indexes and serum lipid levels between the subjects with different genotypes in a dominant model. Heterogeneity among studies was assessed by Cochran's x²-based Q-statistic test. Publication bias was identified by using Begg's test.

RESULTS

One hundred and twenty studies (70,317 subjects) and 33 studies (18,353 subjects) were identified in the analyses for the rs1801282 and rs3856806 polymorphisms, respectively. The G allele carriers of the rs1801282 polymorphism had higher levels of body mass index (SMD = 0.08 kg/m², 95% CI = 0.04 to 0.12 kg/m², p < 0.001), waist circumference (SMD = 0.12 cm, 95% CI = 0.06 to 0.18 cm, p < 0.001) and total cholesterol (SMD = 0.07 mmol/L, 95% CI = 0.02 to 0.11 mmol/L, p < 0.01) than the CC homozygotes. The T allele carriers of the rs3856806 polymorphism had lower levels of low-density lipoprotein cholesterol (SMD = -0.09 mmol/L, 95% CI = -0.15 to -0.03 mmol/L, p < 0.01) and higher levels of high-density lipoprotein cholesterol (SMD = 0.06 mmol/L, 95% CI = 0.02 to 0.10 mmol/L, p < 0.01) than the CC homozygotes.

CONCLUSIONS

The meta-analysis suggests that the G allele of the rs1801282 polymorphism confers an increased risk of obesity and hypercholesterolemia, while the T allele of the rs3856806 polymorphism displays a protective role against dyslipidemia, which can partly explain the associations between these polymorphisms and cardiovascular disease.

SYSTEMATIC REVIEW REGISTRATION

https://www.crd.york.ac.uk/prospero/, identifier [CRD42022319347].

PPARγ2 Pro12Ala Polymorphism is Associated in Children With Traits Related to Susceptibility to Type 2 Diabetes

Peroxisome proliferator-activated receptor gamma (PPARγ) is a ligand-activated nuclear receptor that regulates glucose and lipid metabolism. Pharmacological activators of PPARγ are being used as a treatment of obesity related disorders such as dyslipidaemia and type 2 diabetes, but questions remain open regarding the effects of PPARγ on traits related to the development of type 2 diabetes. In our study, we have analyzed the relationship of the common variant Pro12Ala in the human PPARγ2 gene with the presence of obesity and with insulin, HOMA and lipid profile in a representative sample of 6-to 8-year-old children free from the confounding factors associated with adults. We found that Ala12Ala genotype was significantly more frequent in females with obesity than in those without obesity, with Ala12Ala carriers having significantly higher weight and body mass index (BMI), however the association disappeared when adjusting by leptin concentrations. The Ala12Ala genotype was associated with significantly higher HDL-cholesterol and apoA-I levels in males but not in females, independently of BMI. In a recessive model, in females, leptin levels appeared higher in Ala12Ala carriers. Although no apparent differences were observed in any sex when analyzing insulin levels and HOMA among genotypes without adjusting, lower insulin levels and lower HOMA appeared associated with Ala12Ala carriers when adjusting for BMI and leptin levels. In summary, our data showed that leptin seems to be having an effect on the association between the PPARγ2 Pro12Ala and BMI. Besides, after controlling for BMI and leptin, a protective effect of the Ala12Ala variant of the PPARγ2 Pro12Ala polymorphism on insulin sensitivity is evident already in prepubertal children.

"H" for Heterogeneity in the Algorithm for Type 2 Diabetes Management

PURPOSE OF REVIEW

Genetic, socioeconomic and clinical features vary considerably among individuals with type 2 diabetes (T2D) influencing disease development, progression and response to therapy. Although a patient-centred approach to pharmacologic therapy of T2D is widely recommended, patients are often treated similarly, irrespective of the differences that may affect therapeutic response. Addressing the heterogeneity of T2D is a major task of diabetes research to lower the high rate of treatment failure as well as to reduce the risk of long-term complications.

RECENT FINDINGS

A pathophysiology-based clustering system seems the most promising to help in the stratification of diabetes in terms of complication risk and response to treatment. This urges for clinical studies looking at novel biomarkers related to the different metabolic pathways of T2D and able to inform about the therapeutic cluster of each patient. Here, we review the main settings of diabetes heterogeneity, to what extent it has been already addressed and the current gaps in knowledge towards a personalized therapeutic approach that considers the distinctive features of each patient.

Wrist circumference is a biomarker of adipose tissue dysfunction and cardiovascular risk in children with obesity

PURPOSE

To evaluate the relationship between wrist circumference, markers of adipose dysfunction, and cardiovascular risk in youths with obesity.

METHODS

In this cross-sectional study, we measured body mass composition by dual-energy X-ray absorptiometry, wrist circumference, waist-to-height ratio, fasting blood insulin, glucose, lipid profile, adiponectin, and leptin in 280 children with overweight/obesity and without diabetes (age: 7-18 years). Cardiovascular risk was estimated by "metabolic syndrome score" (MetS score).

RESULTS

Study participants had median [25th-75th percentile] wrist circumference of 17.5 [16.7-18.5] cm and waist-to-height ratio of 0.62 [0.59-0.67]. Lower adiponectin-leptin ratio was found among subjects in the upper 50th percentiles of wrist circumference [0.17 (0.09-0.36) vs. 0.38 (0.16-0.79); p < 0.001]. Wrist circumference was independently associated with MetS score (r = 0.5 p < 0.001). Among MetS score components, an independent association between wrist circumference HDLc, triglycerides, and systolic blood pressure was found (r = - 0.253 p < 0.001; r =+ 0.204 p < 0.001; r = + 0.403 p = < 0.001, respectively). The coefficient of determination for MetS score was nominally higher when considering wrist circumference as independent variable (Adj-R² = 0.30) then when considering body mass index SD (Adj-R² = 0.28), waist-to-height ratio (Adj-R² = 0.26) or truncal fat percentage (Adj-R² = 0.01). The addition of wrist circumference in age and gender adjusted models, accounting to any other anthropometric parameters, resulted in a significant improvement of the Adj-R² (p < 0.001 for all).

CONCLUSIONS

Our study shows that wrist circumference independently relates to adiponectin-leptin ratio and to the prediction of cardiovascular risk, suggesting it as an efficient and adjunctive anthropometric marker of cardiometabolic risk in children with obesity.

Insulin Resistance in Children

Insulin resistance (IR) is a pathological condition strongly associated with obesity. However, corticosteroids or growth hormone therapy and genetic diseases may affect insulin sensitivity lifelong. In obese children and adolescents of any age there is an evident association between IR and an increased prevalence of type 2 diabetes (T2D) and other elements contributing to the metabolic syndrome, leading to a higher cardiovascular risk. Therefore, early diagnosis and interventions in the attempt to prevent T2D when glycemia values are still normal is fundamental. The gold standard technique used to evaluate IR is the hyperinsulinemic euglycemic clamp, however it is costly and difficult to perform in clinical and research sets. Therefore, several surrogate markers have been proposed. Although the treatment of insulin resistance in children is firstly targeted to lifestyle interventions, in selected cases the integration of a pharmacological intervention might be taken into consideration. The aim of this review is to present the current knowledge on IR in children, starting with an outline of the recent evidences about the congenital forms of deficiency in insulin functioning and therefore focusing on the physiopathology of IR, its appropriate measurement, consequences, treatment options and prevention strategies.

Association of the variants in the PPARG gene and serum lipid levels: a meta-analysis of 74 studies

Considerable studies have been carried out to investigate the relationship between the polymorphisms of PPARG (Pro12Ala, C161T and C1431T) and serum lipid levels, but the results were inconclusive. Hence, we conducted a meta-analysis to clarify the association. MEDLINE, EMBASE and the Cochrane Library databases were searched systematically. The subgroup analysis was performed based on ethnicity. Seventy-four studies with 54,953 subjects were included in this meta-analysis. In Pro12Ala, the group with the ‘PP’ (C/C genotype) genotype group had lower levels of total cholesterol (TC) (mean difference, MD: −0.02, P < 0.00001; I² = 28%), low-density lipoprotein cholesterol (LDL-C) (MD: −0.02, P < 0.00001; I² = 30%) and higher levels of triglyceride (TG) (MD: 0.06, P < 0.00001; I² = 30%) than the combined ‘PA+AA’ (PA = C/G genotype, AA = G/G genotype) genotype group in Asian population, and the group with the ‘PP’ genotype had higher levels of TG (MD: 0.07, P < 0.02; I² = 67%) than the combined ‘PA+AA’ genotype group in non-Asian population. No statistically significant differences in the levels of TC, TG, high-density lipoprotein cholesterol, LDL-C were detected between different genotypes in C161T(Asian or non-Asian) and C1431T(Asian) polymorphisms. This meta-analysis was a renewed and confirmed study to assess the association between PPARG polymorphisms and serum lipid levels in Asian and non-Asian populations. There is a prominent association between Pro12Ala polymorphism and the levels of TC, LDL-C and TG in Asian population. No statistically significant differences in serum lipid levels were detected between different genotypes in C161T and C1431T polymorphisms.

Studying progression from glucose intolerance to type 2 diabetes in obese children

AIM

Identification of metabolic and genetic factors capable to mediate progression from normal glucose tolerance (NGT) through impaired glucose tolerance (IGT) to type 2 diabetes (T2D) in childhood obesity.

PATIENTS AND METHODS

Three groups of obese children with NGT (n=54), IGT (n=35), and T2D (n=62) were evaluated. A control group of non-obese normal children (n=210) was also studied. In obese patients, an oral glucose tolerance test (OGTT) was performed. Insulin resistance (IR) was assessed using HOMA-IR index. Insulin sensitivity (IS) was assessed according to the Matsuda formula. Genomic DNA from obese and control children was genotyped for genetic variants of PPARG, ADIPOQ, ADIPOR1, FTO, TCF7L2, and KCNJ11 using a real-time PCR strategy. The unpaired Student's t-test and Kruskal-Wallis one-way test were used to compare quantitative data in two and more groups. To assess the extent to which the various genetic variants were associated with pathology, ORs (odds ratios) and 95% CI (confidence interval) were estimated.

RESULTS

In T2D children, HOMA-IR value (7.5±3.1) was significantly (P<0.001) higher than that in IGT (4.21±2.25) and NGT (4.1±2.4) subjects. The Matsuda IS index was significantly increased in normoglycemic patients compared to IGT individuals (2.8±1.75 vs. 2.33±1.2, P<0.05). The Pro12Ala polymorphism of PPARG was significantly associated with obesity (OR=1.74, 95% CI=1.19-2.55, P=0.004) and T2D in obesity (OR=2.01, 95% CI=1.24-3.26, P=0.004).

CONCLUSION

IR is a major risk factor that mediates progression from NGT to clinical T2D in Russian obese children. This progression may be genetically influenced by the Pro12Ala variant of PPARG.

Effect of the PPARγ C161T gene variant on serum lipids in ischemic stroke patients with and without type 2 diabetes mellitus

Peroxisome proliferator-activated receptor γ (PPARγ) is a ligand-activated transcription factor involved in the regulation of lipid metabolism, diabetes, obesity, atherogenesis and inflammation. PPARγ genetic variation has been associated with metabolic and cardiovascular diseases. The aim of this study was to explore, for the first time, the relationship between PPARγ C161T polymorphism and the risk of ischemic stroke (IS) among patients with type 2 diabetes mellitus (T2DM). A total of 196 patients with IS (117 diabetics and 79 nondiabetics) and 192 controls were recruited to enroll in this study. PPARγ C161T genotyping was performed by PCR-RFLP technique. The 161T allele as compared with C allele was found to be higher in controls than in IS patients (with or without T2DM). After adjusting for multiple risk factors, the T allele carriers had significantly reduced IS risk (OR=0.575, 95% CI 0.348-0.951, p=0.030) compared to the CC homozygotes which increased significantly the risk in IS patients with T2DM (OR=1.85, 95% CI 1.23-2.62). Moreover, the triglycerides (TG) and ApoB levels in CC homozygote carriers were significantly higher than those in T allele carriers. These results indicate that the C161T of PPARγ may reduce the risk of IS by modulation of adipose metabolism especially TG and ApoB in IS patients with T2DM.

The Rate of Decline of Glomerular Filtration Rate May Not Be Associated with Polymorphism of the PPARγ2 Gene in Patients with Type 1 Diabetes and Nephropathy

The aim of the study was to investigate whether a Pro12Ala polymorphism in the peroxisome proliferator-activated receptor gamma 2 (PPARγ2) gene is associated with the progress of diabetic nephropathy in patients with type 1 diabetes. 197 Caucasian patients with type 1 diabetes and ethnically matched 151 normal healthy controls were genotyped for this polymorphism. Results showed that there were no significant differences in the frequencies of the genotypes and alleles of the polymorphism between groups. Multiple regression analysis in 77 patients demonstrated that the rate of decline in renal function in terms of glomerular filtration rate was significantly correlated to the baseline level of cholesterol (P = 0.0014), mean diastolic blood pressure during follow-up period (P = 0.019), and baseline level of HbA1c (P = 0.022) adjusting for the effect of diabetes duration and gender, but no significant association was found between the polymorphism and the progression of diabetic nephropathy in our studied population. In summary, our results show that the PPARγ2 polymorphism is unlikely to be associated with the development and progression of the diabetic nephropathy in patients with type 1 diabetes. Further studies in different populations may be warranted to confirm our findings as the sample size in our study was relatively small.

Type 2 diabetes mellitus in children and youth

Type 2 diabetes mellitus (T2DM) which used to be a disease of adults is now seen commonly at an early age in children and adolescents. T2DM is now an important diagnostic consideration in children who present with signs and symptoms of diabetes. The emerging epidemic of obesity in children throughout the world and the resultant insulin resistance contributes to the increasing prevalence of T2DM in this population. The recommended treatment options include metformin and insulin. Optimal glycemic control is essential considering the lifelong nature of the disease and therefore, the increased risk of long term complications - both microvascular and macrovascular. This review article summarizes the classification, diagnosis, pathogenesis, management, complications and screening of T2DM in children, incorporating and contextualizing guidelines from various professional associations.

Obesity and eating behaviour in children and adolescents: contribution of common gene polymorphisms

The prevalence of childhood obesity is increasing in many countries and confers risks for early type 2 diabetes, cardiovascular disease and metabolic syndrome. In the presence of potent 'obesogenic' environments not all children become obese, indicating the presence of susceptibility and resistance. Taking an energy balance approach, susceptibility could be mediated through a failure of appetite regulation leading to increased energy intake or via diminished energy expenditure. Evidence shows that heritability estimates for BMI and body fat are paralleled by similar coefficients for energy intake and preferences for dietary fat. Twin studies implicate weak satiety and enhanced food responsiveness as factors determining an increase in BMI. Single gene mutations, for example in the leptin receptor gene, that lead to extreme obesity appear to operate through appetite regulating mechanisms and the phenotypic response involves overconsumption and a failure to inhibit eating. Investigations of robustly characterized common gene variants of fat mass and obesity associated (FTO), peroxisome proliferator-activated receptor (PPARG) and melanocortin 4 receptor (MC4R) which contribute to variance in BMI also influence the variance in appetite factors such as measured energy intake, satiety responsiveness and the intake of palatable energy-dense food. A review of the evidence suggests that susceptibility to childhood obesity involving specific allelic variants of certain genes is mediated primarily through food consumption (appetite regulation) rather than through a decrease in activity-related energy expenditure. This conclusion has implications for early detection of susceptibility, and for prevention and management of childhood obesity.

PPAR Genomics and Pharmacogenomics: Implications for Cardiovascular Disease

The peroxisome proliferator-activated receptors (PPARs) consist of three related transcription factors that serve to regulate a number of cellular processes that are central to cardiovascular health and disease. Numerous pharmacologic studies have assessed the effects of specific PPAR agonists in clinical trials and have provided insight into the clinical effects of these genes while genetic studies have demonstrated clinical associations between PPAR polymorphisms and abnormal cardiovascular phenotypes. With the abundance of data available from these studies as a background, PPAR pharmacogenetics has become a promising and rapidly advancing field. This review focuses on summarizing the current state of understanding of PPAR genetics and pharmacogenetics and the important implications for the individualization of therapy for patients with cardiovascular diseases.

The contribution of vitamin A to autocrine regulation of fat depots

Morbidity and mortality associated with increased white fat accumulation in visceral fat depots have focused attention on the pathways regulating the development of this tissue during embryogenesis, in adulthood, and while under the influence of obesogenic diets. Adipocytes undergo clonal expansion, differentiation (adipogenesis) and maturation through a complex network of transcriptional factors, most of which are expressed at similar levels in visceral and subcutaneous fat. Rigorous research attempts to unfold the pathways regulating expression and activity of adipogenic transcription factors that act in a fat-depot-specific manner. Peroxisome proliferator-activated receptor-γ (PPARγ) is the master regulator of adipogenesis, and is expressed at higher levels in subcutaneous than in visceral depots. PPARγ expression in adipogenesis is mediated by CCAAT/enhancer binding proteins (C/EBPs) and several transcription factors acting in conjunction with C/EBPs, although alternative pathways through zinc-finger protein-423 (ZFP423) transcription factor are sufficient to induce PPARγ expression and adipogenesis. Vitamin A and its metabolites, retinaldehyde and retinoic acid, are transcriptionally-active molecules. Retinoic acid is generated from retinaldehyde in adipose tissue by the aldehyde dehydrogenase-1 family of enzymes (Aldh1). In this review, we discuss the role of Aldh1 enzymes in the generation of retinoic acid during adipogenesis, in the regulation of the transcriptional network of PPARγ in a fat-depot-specific manner, and the important contribution of this autocrine pathway in the development of visceral obesity. This article is part of a Special Issue entitled Retinoid and Lipid Metabolism.

Association between C1431T polymorphism in peroxisome proliferator-activated receptor-γ gene and coronary artery disease in Chinese Han population

The C1431T polymorphism in peroxisome proliferator-activated receptor-γ (PPARγ) has been shown to be associated with diabetes, obesity, and metabolic syndrome. However, it is unclear whether this polymorphism is associated with coronary artery disease (CAD). Therefore, we conducted a hospital-based case-control study with 864 CAD patients and 1008 controls to explore the association between the PPARγ C1431T polymorphism and risk of CAD in Chinese Han population. Subjects with the variant genotypes (CT + TT) had a 39% decreased risk of CAD relative to CC carriers (adjusted odds ratio, 0.61; 95% confidence interval, 0.49-0.76). Our results suggested that the C1431T polymorphism was associated with a higher body mass index in both CAD patients and controls. Moreover, this polymorphism was also found to be associated with a higher HDL cholesterol level and a lower blood glucose level in CAD patients. In stratified analyses, the T allele was significantly associated with reduced risk of CAD in males, subjects with age <62 years, and non-smokers. In conclusion, the PPARγ C1431T polymorphism is associated with decreased risk of CAD in Chinese Han population.

An age-dependent diet-modified effect of the PPARγ Pro12Ala polymorphism in children

Variation in the peroxisome proliferator-activated receptor γ gene alters the risk for adiposity in adults, with evidence of interaction with diet. We investigated the age-related association between the Pro12Ala variant (rs1801282) and diet in obesity-related traits in children. The Pro12Ala variant was assayed in 2102 young children aged 1 to 6 years and in 794 periadolescent children aged 10 to 12 years of Greek origin. In both cohorts, no differences were found in obesity traits between the Ala allele carriers and Pro/Pro homozygotes. Sex-stratified analysis showed that, in periadolescent boys, Ala carriers exhibited lower measures of skinfolds (triceps: 16.9 ± 6.9 vs 19.4 ± 7.9 mm, P = .01; subscapular: 9.6 ± 4.5 vs 11.2 ± 5.4 mm, P = .02). On the other hand, young girls who were Ala carriers presented higher measures of triceps skinfold thickness (10.5 ± 3.0 vs 9.9 ± 2.8 mm, P = .04). Nominal gene-diet interactions were revealed in periadolescents for saturated fatty acid (SFA) intake and skinfolds (P for interaction = .05). In Pro/Pro homozygous young girls, SFA and total fat (TF) intake was positively associated with higher body mass index (BMI) (P = .01), waist circumference (P = .02), and skinfold thickness (triceps-SFA: P = 10⁻⁵, triceps-TF: P = 10⁻⁹, subscapular-SFA: P = 10⁻⁶, subscapular-TF: P = 10⁻⁴). For Pro/Pro homozygotes, unsaturated fat intake was inversely associated with BMI (P = .04) in young girls, and with BMI (P = .03), waist circumference (P = .03), and triceps (P = .02) in periadolescent boys. Our results suggest that adiposity in children is influenced by the Pro12Ala polymorphism in a sex-specific and age-dependent manner. We also demonstrate evidence of an age-dependent gene-diet (SFA, TF) interaction, suggesting that the type of fat intake modifies the effect of the Pro12 allele on obesity-related measures.

PPAR-gamma2 pro12Ala polymorphism is associated with post-challenge abnormalities of glucose homeostasis in children and adolescents with obesity

AIM

The aim of the study was to investigate the association between PPAR-gamma2 Pro12Ala polymorphism and laboratory characteristics of carbohydrate metabolism in children and adolescents with obesity. In addition, serum levels of tumor necrosis factor (TNF)-alpha, and soluble form of its receptors (sTNFR1 and sTNFR2) were assessed.

METHODS

In a cross-sectional study, 79 obese children and adolescents of Caucasian origin were investigated. PPAR-gamma2 Pro12Ala polymorphism was determined using polymerase chain reaction--restriction fragment length polymorphism technique. Serum levels of TNF-alpha, sTNFR1 and sTNFR2 were measured by enzyme amplified sensitivity immunoassay.

RESULTS

The minor Ala allele frequency was found to be 14.56% in our cohort. No significant differences in age, BMI, waist circumference, blood pressure, serum lipid, uric acid, TNF-alpha, sTNFR1 and sTNFR2 values were found between carriers of the Ala allele (Pro/Ala and Ala/Ala; n=21) vs. homozygous carriers of the Pro allele (Pro/Pro; n=58). However, post-challenge (120 min) plasma glucose and insulin values were significantly lower in Ala allele carriers vs. homozygous Pro allele carriers (6.56 +/- 0.26 vs. 7.36 +/- 0.25 mmol/L and 65.9 +/- 13.8 vs. 111.8 +/- 20.7 microU/mL, respectively; p < 0.05); while no significant differences were found at fasting state.

CONCLUSIONS

The association between PPAR-gamma2 Prol2Ala polymorphism and glucose metabolism is already present in children and adolescents with obesity who might be at the very beginning of the natural course of type 2 diabetes. At this stage, higher insulin sensitivity can be detected in Ala allele carriers compared to homozygous Pro subjects at post-challenge but not in fasting state; however, the TNF-system seems not to be involved in the alteration of glucose homeostasis due to PPAR-gamma2 Pro12Ala polymorphism.

Insulin resistance in children: consensus, perspective, and future directions

OBJECTIVE

Emerging data indicate that insulin resistance is common among children and adolescents and is related to cardiometabolic risk, therefore requiring consideration early in life. However, there is still confusion on how to define insulin resistance, how to measure it, what its risk factors are, and whether there are effective strategies to prevent and treat it. A consensus conference was organized in order to clarify these points.

PARTICIPANTS

The consensus was internationally supported by all the major scientific societies in pediatric endocrinology and 37 participants.

EVIDENCE

An independent and systematic search of the literature was conducted to identify key articles relating to insulin resistance in children.

CONSENSUS PROCESS

The conference was divided into five themes and working groups: background and definition; methods of measurement and screening; risk factors and consequences; prevention; and treatment. Each group selected key issues, searched the literature, and developed a draft document. During a 3-d meeting, these papers were debated and finalized by each group before presenting them to the full forum for further discussion and agreement.

CONCLUSIONS

Given the current childhood obesity epidemic, insulin resistance in children is an important issue confronting health care professionals. There are no clear criteria to define insulin resistance in children, and surrogate markers such as fasting insulin are poor measures of insulin sensitivity. Based on current screening criteria and methodology, there is no justification for screening children for insulin resistance. Lifestyle interventions including diet and exercise can improve insulin sensitivity, whereas drugs should be implemented only in selected cases.

PPARgamma gene C161T substitution alters lipid profile in Chinese patients with coronary artery disease and type 2 diabetes mellitus

Background

Peroxisome proliferator-activated receptor γ (PPARγ) is a ligand-activated transcription factor, which regulates gene expression of the key proteins involved in lipid metabolism, vascular inflammation, and proliferation. PPARγ may contribute to attenuating atherogenesis and postangioplasty restenosis. PPARγ C161→T substitution is associated with a reduced risk of coronary artery disease (CAD). Whether or not the gene substitution alters the risk of CAD in type 2 diabetes mellitus (T2DM) patients remains unclear.

Methods

A total of 556 unrelated subjects from a Chinese Han population, including 89 healthy subjects, 78 CAD patients, 86 T2DM patients, and 303 CAD combined with T2DM patients, were recruited to enroll in this study. PPARγC161→T gene polymorphism was determined by polymerase chain reaction and restriction fragment length polymorphisms. Plasma levels of lipoproteins, apolipoproteins, glucose, and insulin were measured by ELISA or radioimmunoassay (RIA). The coronary artery lesions were evaluated by coronary angiography.

Results

The frequency of the 161T allele in CAD, T2DM, and CAD combined with T2DM patients was similar to that observed in the healthy control group. However, in CAD combined with T2DM patients, the group with angiographically documented moderate stenoses had a higher frequency of the 161T allele in comparison to the group with severe stenoses (P < 0.05). Moreover, in CAD with T2DM patients, the triglyceride levels and apoB in CC homozygote carriers were significantly higher than those in "T" allele carriers.

Conclusions

PPARγC161→T genotypes weren't significantly associated with the risk of CAD, but were markedly correlated with severity of disease vessels in patients with CAD and T2DM. Furthermore, PPARγC161→T substitution was associated with an altered adipose, but not glucose metabolism. These results indicate that the PPARγ C161→T polymorphism may reduce the risk of severe atherogenesis by modulation of adipose metabolism, especially triglycerides and apoB, in Chinese patients with CAD and T2DM.

The PPAR-gamma Pro12Ala polymorphism associates with weight gain during GH-treatment in short children born small for gestational age

CONTEXT

Short children born small for gestational age (SGA) have a lean phenotype with lower insulin sensitivity and higher blood pressure. GH treatment results in weight gain, and a decrease in blood pressure and insulin sensitivity. However, not all children respond in the same way. The Pro12Ala polymorphism of the peroxisome proliferator-activated receptor (PPAR-gamma) gene is inversely associated with body mass index (BMI), changes in BMI and the risk to develop type 2 diabetes mellitus.

OBJECTIVE

To analyze the contribution of the PPAR-gamma Pro12Ala polymorphism to GH induced changes in determinants of metabolic and cardiovascular disease in short SGA children.

METHODS

PPAR-gamma was genotyped in 238 Caucasian short SGA children (mean age 7.5 years). Height, weight, blood pressure, and serum lipids were measured before start and during 4 years of GH treatment. In addition, glucose homeostasis by homeostasis model assessment insulin resistance ratio (HOMA-IR) (n=148) and by frequently sampled i.v. glucose tolerance test (n=51), and body composition by dual energy X-ray absorptiometry (n=79) were measured.

RESULTS

At baseline, the Ala12 allele was not associated with any determinant of metabolic and cardiovascular disease. After 4 years of GH treatment, the increase in weight for height SDS and BMI SDS was significantly greater in carriers of an Ala12 allele than in noncarriers. The change in all other parameters was not associated with Pro12Ala genotype.

CONCLUSION

The Ala12 variant of the PPAR-gamma gene is associated with higher weight gain during GH treatment but not with changes in determinants of metabolic and cardiovascular diseases in Caucasian subjects born SGA.

PPARγ2 polymorphism and human health

The nuclear hormone receptor peroxisome proliferator activated receptor gamma (PPARγ) is an important transcription factor regulating adipocyte differentiation, lipid and glucose homeostasis, and insulin sensitivity. Numerous genetic mutations of PPARγ have been identified and these mutations positively or negatively regulate insulin sensitivity. Among these, a relatively common polymorphism of PPARγ, Pro12Ala of PPARγ2, the isoform expressed only in adipose tissue has been shown to be associated with lower body mass index, enhanced insulin sensitivity, and resistance to the risk of type 2 diabetes in human subjects carrying this mutation. Subsequent studies in different ethnic populations, however, have revealed conflicting results, suggesting a complex interaction between the PPARγ2 Pro12Ala polymorphism and environmental factors such as the ratio of dietary unsaturated fatty acids to saturated fatty acids and/or between the PPARγ2 Pro12Ala polymorphism and genetic factors such as polymorphic mutations in other genes. In addition, this polymorphic mutation in PPARγ2 is associated with other aspects of human diseases, including cancers, polycystic ovary syndrome, Alzheimer disease and aging. This review will highlight findings from recent studies.

An update in prevention and treatment of pediatric obesity

BACKGROUND

Obesity prevalence is growing as well as its severity with increasing morbidity and mortality. This "globesity" also affects developing countries where under nutrition and stunting frequently coexist with overweight and obesity. One third of obese adults began to be so in the pediatric ages. There are two main types of prevention: general one representing greater actions from health authorities and the individual one carried out by the pediatrician and the patient at risk. Once the state of obesity is reached (relative body mass index, rBMI >121%) the longer lasting care becomes more complex and frequently unsuccessful. The treatment of obesity is aimed to care for the present and silent disorders and for preventing its further tracking to adulthood.

DATA SOURCES

Identification of pediatric population at risk which is the one with an rBMI of 111%-120% plus other risk factors. Specific individual actions include reduction of food intake, increase of energy expenditure, involvement of parents, and the child-adolescent himself in the prevention. Therapy is based on some principles plus the important medical and emotional approach.

RESULTS

A Cochrane study based on only 10 appropriate studies showed a predominant poor efficacy of the undergone preventive action. Treatment guides are presented after our own experience with a group of 400 kids with an average follow-up of 7 years and other individual prevention studies.

CONCLUSIONS

Involving motivated pediatricians with a minimum of time for visits and better follow-up in the frame of a general national preventive programme could be a rational outcome. Treatment of obesity should never be postponed whatever the clinical care is.

Nutrigenomics: concepts and applications to pharmacogenomics and clinical medicine

The maintenance of health and the prevention and treatment of chronic diseases are influenced by naturally occurring chemicals in foods. In addition to supplying the substrates for producing energy, a large number of dietary chemicals are bioactive--that is, they alter the regulation of biological processes and, either directly or indirectly, the expression of genetic information. Nutrients and bioactives may produce different physiological phenotypes among individuals because of genetic variability and not only alter health, but also disease initiation, progression and severity. The study and application of gene-nutrient interactions is called nutritional genomics or nutrigenomics. Nutrigenomic concepts, research strategies and clinical implementation are similar to and overlap those of pharmacogenomics, and both are fundamental to the treatment of disease and maintenance of optimal health.

Non-synonymous polymorphisms in melanocortin-4 receptor protect against obesity: the two facets of a Janus obesity gene

The melanocortin-4 receptor (MC4R) gene pathogenic mutations are the most prevalent forms of monogenic obesity, responsible for approximately 2% of obesity cases, but its role in common obesity is still elusive. We analyzed the contribution of non-synonymous mutations V103I (rs2229616, c.307G > A) and I251L (no rs, c.751A > C) to obesity in 16 797 individuals of European origin from nine independent case-control, population-based and familial cohorts. We observed a consistent negative association of I251L variant (prevalence ranging 0.41-1.21%) with both childhood and adult class III obesity [odds ratio (OR) ranging from 0.25 to 0.76, 0.001 < P-value < 0.05] and with modulation of body mass index (BMI) in general populations, in eight out of nine studies, whereas only one study showed an association between V103I and BMI. Meta-analyses of previous published data with the current ones provided strong evidence of the protective effect of I251L toward obesity (OR = 0.52, P = 3.58 10-5), together with a modest negative association between V103I and obesity (OR = 0.80, P = 0.002). Taken together, gain-of-function mutations I251L and V103I may be responsible for a preventive fraction of obesity of 2%, which mirrors the prevalence of monogenic obesity due to MC4R haploinsufficiency. These results also emphasize the importance of the MC4R signalling tonus to prevent obesity, even in the context of our current obesogenic environment.

Gene-diet interactions in childhood obesity: paucity of evidence as the epidemic of childhood obesity continues to rise

Childhood obesity is growing rapidly worldwide. Although there have been enormous advances in the genetic underpinnings of obesity in recent years, the pathways that lead to obesity are still not completely understood. One of the ongoing challenges is the lack of a comprehensive definition of the obese phenotype that encompasses intermediary phenotypic expressions of biological and behavioral nature. Interactions between genetic and environmental factors, including nutrient exposures and dietary behaviors, can influence the development of the obese phenotype. Specifically, genes play a decisive role in the etiology of childhood obesity under the permissive circumstances of an obesogenic environment (increase in energy intake with a decrease in physical activity). Like many diseases, the causes of obesity are complex and their investigation requires novel approaches. Given the many contributors to obesity (weight gain, weight loss, weight maintenance, variability in body composition), as well as the dynamic nature of this issue, genomic tools must continue to be employed to evaluate all dimensions of the obesity phenotype, such as biochemical characteristics, susceptibility markers, nutrient intake, feeding practices and gene-environment interactions. Fundamental knowledge of the types of genes involved and available gene-diet interaction studies in children's obesity are reviewed. Although there is a paucity of existing literature in this specific domain of childhood obesity, ongoing investigations utilizing large cohorts have potential for providing the knowledge needed for targeted interventions in the future.

The peroxisome proliferator-activated receptor gamma (PPAR-γ2) Pro12Ala polymorphism is associated with higher risk for Alzheimer's disease in octogenarians

Recent observations support the hypothesis that inflammatory processes at the brain level may contribute to the pathogenesis of Alzheimer's disease (AD). Peroxisome proliferator-activated receptor gamma (PPAR-gamma) is involved in such processes, so we thought it interesting to study the Pro12Ala polymorphism in exon 2 of the gene in a sample of late-onset AD patients. We found that Ala genotypes were significantly overrepresented among octogenarian patients compared to controls (p=0.034). Using logistic regression we observed that carrying the Ala allele significantly increased by nearly two-fold the risk of developing AD in subjects 80 years or older (OR=1.98; 95% CI 1.03-3.80, p=0.04). Though this difference was borderline significant after correction for multiple comparisons, our results suggest a possible involvement of the PPAR-gamma gene in susceptibility to late-onset AD in octogenarians.

The Pro12Ala Polymorphism in PPARγ2 Gene Affects Lipid Parameters in Greek Primary School Children: A Case of Gene-to-Gender Interaction

BACKGROUND

In the present study we sought to evaluate the impact of the PPAR-gamma2 Pro12Ala polymorphism on blood lipid levels of primary school children.

METHODS

81 male and 92 female schoolchildren were genotyped. Biochemical, anthropometric, and lifestyle variables were assessed.

RESULTS

14.1% females and 14.8% males were heterozygotes, while the rest of the subjects were homozygotes for the Pro allele. A significant interaction between the PPARgamma-2 gene and gender on blood lipid levels was detected. In particular, Pro/Pro females exhibited higher values of total cholesterol (194 +/- 32 vs 180 +/- 28 mg/dL, P = 0.06) and triglycerides (94 +/- 31 vs 77 +/- 11 mg/dL, P = 0.045) compared to Pro/Ala individuals. The gene-to-gender interaction term was highly significant (P < 0.001). On the other hand, Pro/Pro males showed higher values of HDL cholesterol (47 +/- 8 vs 43 +/- 9 mg/dL, P = 0.001), lower total cholesterol/HDL ratio (4.04 +/- 0.59 vs 4.45 +/- 0.61, P = 0.031), lower values of apoB (59.8 +/- 11.3 vs 66.8 +/- 6.6 mg/dL, P = 0.007) and lower values of apoB/apoA1 ratio (0.41 +/- 0.09 vs 0.48 +/- 0.08, P = 0.019) compared with Pro/Ala. Even after adjusting for body mass index (BMI), total energy intake, total fat intake and saturated fat intake, differences in total cholesterol/high-density lipoprotein (HDL) cholesterol and the apoB/apoA1 ratios remained significant. Regarding females, no differences were observed among genotypes concerning total cholesterol/HDL levels (P for gene-to-gender interaction = 0.001) and the apoB/apoA1 levels (P for gene-to-gender interaction = 0.029).

CONCLUSION

We show for the first time a gene-to-gender interaction on total cholesterol/HDL and apoB/apoA1 ratios, in male schoolchildren genotyped for PPAR-gamma2 Pro12Ala.

Dietary fat, genes and insulin sensitivity

Both insulin resistance and dyslipidaemia are determined by genetic and environmental factors. Depending on their expression and their function, gene variants may influence either insulin action or dyslipidaemia. The purpose of this review was to give some examples from recent studies of gene variants that influence insulin signalling and the interaction between gene and diet to predispose insulin resistance. Recent findings indicate a major role for genetic susceptibility to the insulin resistance syndrome. Nutrition also plays an important role in the development and progression of the condition. Genetic background may interact with habitual dietary fat composition, affecting predisposition to the insulin resistance syndrome and individual responsiveness to changes in dietary fat intake. Due to the complex nature of gene-environment interactions, therefore, therapeutic dietary therapy may require a 'personalized' nutrition approach in the future. Although results have not always been consistent, gene variants that affect primary insulin action or dyslipidaemia, and particularly their interaction with the environment, are important modulators of glucose metabolism and insulin resistance syndrome.

PPAR-gamma2 Pro12Ala variant, insulin resistance and plasma long-chain polyunsaturated fatty acids in childhood obesity

Pro12Ala variant of peroxisome-proliferator-activated receptor-gamma2 (PPAR-gamma2) may be linked to insulin sensitivity. This study examined whether an association of PPAR-gamma2 Pro12Ala with insulin resistance and plasma LCPUFAs may exist in obese children. One hundred and forty Italian normolipidemic obese children (58 girls and 82 boys, mean age [SD], 10.2 [2.7] y) entered the study. Obesity was defined according to International Obesity Task Force. BMI Z-scores were calculated. Fasting blood glucose, insulin, lipids and plasma fatty acids were measured. Insulin resistance was estimated by the homeostatic model assessment (HOMA-IR). The frequency of Ala allele was 9%. Mean [SD] values of fasting insulin and HOMA-IR in Pro/Pro versus Pro12Ala groups were: 19.3 [10.6] versus 14.1 [10.4] microU/mL (p = 0.017) and 4.2 [2.3] versus 3.0 [2.3] (p = 0.022). Mean [SD] values of plasma C20:3n-9 and of C20:4n-6, C20:5n-3, C22:6n-3 and n-6/n-3 LCPUFA in phospholipds in Pro/Pro versus Pro12Ala groups were: 0.15 [0.07] versus 0.12 [0.08] % (p = 0.014), 8.9 [1.9] versus 10.2 [2.6] % (p = 0.023), 0.34 [0.15] versus 0.42 [0.11] % (p = 0.005), 2.1 [0.9] versus 2.6 [0.9] % (p = 0.032) and 4.8 [1.2] versus 4.2 [0.7] (p = 0.017). Pro12Ala may be associated with higher insulin sensitivity and higher LCPUFAs, particularly n-3, levels in plasma phosholipids of obese children.

The human obesity gene map: the 2005 update

This paper presents the 12th update of the human obesity gene map, which incorporates published results up to the end of October 2005. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTL) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2005, 176 human obesity cases due to single-gene mutations in 11 different genes have been reported, 50 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 244 genes that, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 408. The number of human obesity QTLs derived from genome scans continues to grow, and we now have 253 QTLs for obesity-related phenotypes from 61 genome-wide scans. A total of 52 genomic regions harbor QTLs supported by two or more studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably, with 426 findings of positive associations with 127 candidate genes. A promising observation is that 22 genes are each supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. The electronic version of the map with links to useful publications and relevant sites can be found at http://obesitygene.pbrc.edu.