The peroxisome proliferator-activated receptor-gamma2 Pro12Ala polymorphism

Genetics of type 2 diabetes mellitus

The clinical picture of type 2 diabetes mellitus (T2DM) is formed by impairment in insulin secretion and resistance to insulin action. As a result of intensive efforts of the scientists around the world mutations and polymorphisms in a number of genes were linked with monogenic and polygenic forms of T2DM. Two major strategies were used in this research: genome scanning and the candidate gene approach. Monogenic forms, despite their rarity, constitute a field where substantial progress has been made in the dissection of the molecular background of T2DM. Monogenic forms of T2DM with profound defect in insulin secretion include subtypes of maturity onset diabetes of the young (MODY), maternally inherited diabetes with deafness (MIDD) caused by mitochondrial mutations, and rare cases resulting from insulin gene mutations. The majority of proteins associated with MODY are transcription factors, such as hepatocyte nuclear factor 4alpha (HNF-4alpha), HNF-1alpha, insulin promoter factor-1 (IPF-1), HNF-1beta, and NEUROD1. They influence expression of the other genes through regulation of mRNA synthesis. Only MODY2 form is associated with glucokinase, a key regulatory enzyme of the beta cell. There are striking differences in the clinical picture of MODY associated with glucokinase and MODY associated with transcription factors. Three monogenic forms of T2DM characterized by severe insulin resistance are the consequence of mutations in the PPARgamma, ATK2, and insulin receptor genes. Patients with monogenic T2DM, particularly with MODY, sometimes, develop discrete extra-pancreatic phenotypes; for example, lipid abnormalities or a variety of cystic renal diseases. Efforts aiming to identify genes responsible for more common, polygenic forms of T2DM were less effective. These forms of T2DM have a middle/late age of onset and occur with both impaired insulin secretion and insulin resistance. Their clinical picture is created by the interaction of environmental and genetic factors, such as frequent polymorphisms of many genes, not just of one. These polymorphisms may be localized in the coding or regulatory parts of the genes and are present, although with different frequencies, in T2DM patients as well as in healthy populations. Sequence differences in a few genes have been associated, so far, with complex, polygenic forms of T2DM, for example, calpain 10, PPARgamma, KCJN11, and insulin. In addition, some evidence exists that genes, such as adiponectin, IRS-1, and some others may also influence the susceptibility to T2DM. It is expected that in the nearest future more T2DM susceptibility genes will be identified.

Molecular mechanisms of insulin resistance

Currently, we observe an epidemic expansion of diabetes mellitus. In subjects with Type 2 diabetes the resistance of fat, muscle and liver to insulin is the central pathophysiological event in the development of this disease. Genetic and environmental factors play a major role in this process, although the precise pathogenesis of insulin resistance and Type 2 diabetes is still largely unknown. However, recent studies have contributed to a deeper understanding of the molecular mechanisms underlying this process. In this review we therefore summarize the current developments in understanding the pathophysiological process of insulin resistance and Type 2 diabetes. Among the many molecules involved in the intracellular processing of the signal provided by insulin, insulin receptor substrate (IRS)-2, the protein kinase B (PKB)-beta isoform and the forkhead transcription factor Foxo1a (FKHR) are of particular interest in this context as recent data have provided strong evidence that dysfunction of these proteins results in insulin resistance in-vivo. Furthermore, we have now increasing evidence that the adipose tissue not only produces free fatty acids that contribute to insulin resistance, but also acts as a relevant endocrine organ producing mediators (adipokines) that can modulate insulin signalling. The identification of the molecular pathophysiological mechanisms of insulin resistance and Type 2 diabetes is essential for the development of novel and more effective therapies to better treat our patients with insulin resistance and Type 2 diabetes.

Peroxisome proliferator-activated receptor-gamma2 P12A polymorphism and risk of coronary heart disease in US men and women

OBJECTIVE

Activation of the peroxisome proliferator-activated receptor-gamma (PPARgamma) improves insulin sensitivity and exerts antiatherogenic effects. A common alanine for proline substitution at codon 12 in the PPARG2 gene is related to lower receptor activity. Studies suggest that the A12 allele is associated with reduced risk of type 2 diabetes; however, data on the risk of coronary heart disease (CHD) are scarce and controversial.

METHODS AND RESULTS

We examined the relationship between PPARG2 P12A and CHD risk in women (Nurses' Health Study) and men (Health Professionals Follow-Up Study) in nested case control settings. Among participants free of cardiovascular disease at baseline, 249 women and 266 men developed nonfatal myocardial infarction (MI) or fatal CHD during 8 and 6 years of follow-up, respectively. Using risk-set sampling, controls were selected 2:1 matched on age, smoking, and date of blood draw. The relative risk (RR) of nonfatal MI or fatal CHD of carriers compared with noncarriers of the A12 allele was 1.17 (95% CI, 0.82 to 1.68) among women and 1.44 (95% CI, 1.00 to 2.07) among men (pooled RR, 1.30 [95% CI, 1.00 to 1.67]). We found a significantly increased risk associated with the A12 allele among individuals with a body mass index > or =25 kg/m2 (women: RR, 1.88; 95% CI, 1.01 to 3.50; men: RR, 1.55; 95% CI, 0.92 to 2.60; pooled: RR, 1.68; 95% CI, 1.13 to 2.50) but not among those <25 kg/m2 (pooled RR, 0.86; 95% CI, 0.37 to 1.97; P heterogeneity overweight versus nonoverweight 0.16).

CONCLUSIONS

These data do not support the hypothesis that the A12 allele is associated with a decreased risk of CHD. The potential interaction between PPARG2 P12A, overweight, and increased CHD risk needs further evaluation.

[Genetics of type 2 diabetes]

In the last years type 2 diabetes has reached almost epidemic proportions. More than 170 million individuals are affected worldwide, about 6 million in Germany. Manifestation of type 2 diabetes is determined by both environmental factors such as lack of physical exercise and overeating and a genetic predisposition. Despite enormous efforts in medical research to identify susceptibility loci and high risk alleles, the genetics of common type 2 diabetes (non-MODY) remain unknown. To date, only a few susceptibility genes have been identified (such as PPARG, KCNJ11, CAPN10). However, replication of initial studies is often difficult. This can be explained by both locus and allelic heterogeneity as well as ethnic differences between different populations. Studies in genetically isolated populations such as the Pima Indians are advantageous to identify susceptibility alleles. Despite some recent advances, it is not possible to predict an individual's risk of type 2 diabetes based on the presence of a certain disease-risk allele.

Case-control single-marker and haplotypic association analysis of pedigree data

Related individuals collected for use in linkage studies may be used in case-control linkage disequilibrium analysis, provided one takes into account correlations between individuals due to identity-by-descent (IBD) sharing. We account for these correlations by calculating a weight for each individual. The weights are used in constructing a composite likelihood, which is maximized iteratively to form likelihood ratio tests for single-marker and haplotypic associations. The method scales well with increasing pedigree size and complexity, and is applicable to both autosomal and X chromosomes. We apply the approach to an analysis of association between type 2 diabetes and single-nucleotide polymorphism markers in the PPAR-gamma gene. Simulated data are used to check validity of the test and examine power. Analysis of related cases has better power than analysis of population-based cases because of the increased frequencies of disease-susceptibility alleles in pedigrees with multiple cases compared to the frequencies of these alleles in population-based cases. Also, utilizing all cases in a pedigree rather than just one per pedigree improves power by increasing the effective sample size. We demonstrate that our method has power at least as great as that of several competing methods, while offering advantages in the ability to handle missing data and perform haplotypic analysis.

Type 2 diabetes: principles of pathogenesis and therapy

Type 2 diabetes mellitus has become an epidemic, and virtually no physician is without patients who have the disease. Whereas insulin insensitivity is an early phenomenon partly related to obesity, pancreas beta-cell function declines gradually over time already before the onset of clinical hyperglycaemia. Several mechanisms have been proposed, including increased non-esterified fatty acids, inflammatory cytokines, adipokines, and mitochondrial dysfunction for insulin resistance, and glucotoxicity, lipotoxicity, and amyloid formation for beta-cell dysfunction. Moreover, the disease has a strong genetic component, but only a handful of genes have been identified so far: genes for calpain 10, potassium inward-rectifier 6.2, peroxisome proliferator-activated receptor gamma, insulin receptor substrate-1, and others. Management includes not only diet and exercise, but also combinations of anti-hyperglycaemic drug treatment with lipid-lowering, antihypertensive, and anti platelet therapy.

The common PPAR-gamma2 Pro12Ala variant is associated with greater insulin sensitivity

Several genetic variants of peroxisome proliferator-activated receptor-gamma2 (PPAR-gamma2) have been identified, among which Pro12Ala, a missense mutation in exon 2, is highly prevalent in Caucasian populations. Up to now, conflicting results with regard to the association between this mutation and complex traits, such as obesity, insulin sensitivity and Type 2 diabetes, have been reported. We investigated the influence of the Pro12Ala polymorphism of PPAR-gamma2 on insulin sensitivity in a large Italian population sample, n=1215, in whom extensive clinical and biochemical analyses were performed. To estimate the insulin sensitivity status, the homeostasis model assessment of insulin resistance (HOMA-IR) was calculated; in the obese/overweight subjects an oral glucose tolerance test (OGTT) was also performed and the Matsuda insulin sensitivity index (ISI) calculated. The insulin secretion index (homeostasis model assessment of percent beta-cell function, HOMA-beta%) was utilized to evaluate beta-cell function. The effect of the Pro12Ala polymorphism on quantitative variables was tested using multiple linear regression analysis. X12Ala (either Pro12Ala or Ala12Ala) genotype was associated with significantly lower fasting insulin levels compared to Pro/Pro (P=0.01 after correction for multiple comparisons) in all subjects. Consistent with this finding, significantly lower HOMA-IR was observed in X12Ala carriers (P=0.013 after correction for multiple comparisons) in all cohort. Moreover, no significant interaction effect was observed between body mass index and X12Ala polymorphism and between gender and X12Ala polymorphism in modulating insulin sensitivity. Our observations substantially extend previous findings and demonstrated that X12Ala variant is significantly associated with greater insulin sensitivity.

Implication of the Pro12Ala polymorphism of the PPAR-gamma 2 gene in type 2 diabetes and obesity in the French population

Background

The Pro12Ala Single Nucleotide Polymorphism (SNP) of the Peroxisome Proliferator-Activated Receptor gamma 2 (PPAR-gamma 2) has been associated with insulin resistance and type 2 diabetes (T2D) and also inconsistently with obesity. The aim of this study was to evaluate the impact of this SNP with regards to T2D and childhood and adult obesity in the French Caucasian population.

Methods

We conducted three independent case/control studies encompassing 2126 cases and 1124 controls.

Results

We found a significant association between PPAR-gamma 2 Pro12Ala SNP and T2D (p = 0.04, OR = 1.37), which was stronger when the T2D cohort was stratified according to the obesity status (p = 0.03, OR = 1.81 in obese T2D subjects). In contrast, there was no association between the Pro12Ala SNP and childhood and adulthood obesity. In normal glucose tolerant obese adults (but not in lean subjects), the Pro12 allele was associated with a significant increase in fasting insulin levels (p = 0.01), and in insulin resistance estimated by the Homeostasis Model Assessment of Insulin Resistance (HOMA-IR) (p = 0.003), after adjustment for age, gender and BMI. We didn't detect evidence for an interaction effect between the Pro12Ala SNP and the obesity status with respect to the HOMA-IR index in normal glucose tolerant children, but we found a borderline interaction (p = 0.06) in normal glucose tolerant adults.

Conclusion

Our results showed that the Pro12Ala polymorphism is not associated with childhood or adult obesity in the French Caucasian population. In contrast, we confirm a contribution of the PPAR-gamma 2 Pro12 allele in the genetic risk forT2D, especially in obese subjects, where this allele worsens insulin resistanceand increases fasting insulin levels.

[Visceral, subcutaneous or intramuscular fat: where is the problem?]

The adipose tissue is a dynamic organ that secrets several factors, denominated adipokines. They are associated, directly or indirectly, in a process that contributes to atherosclerosis, hypertension, insulinic resistance and diabetes type 2, dyslipidemias, presenting the link between adiposity, metabolic syndrome and cardiovascular diseases. In the obesity, body fat depots are increased, presenting eventual elevation in the adipokines expression and secretion. The different fat depots, visceral, abdominal subcutaneous, gluteal-femoral subcutaneous and intramuscular adipose tissue, have different metabolic and endocrine degrees, interfering, therefore, with specific form in the process associated with body adiposity in obese and diabetics subjects. The present study seeks to discuss the endocrine and metabolic role of each adipose tissue compartment, by way to assess their contribution to the complications linked to obesity.

Evaluation of glucose metabolism and reproductive hormones in polycystic ovary syndrome on the basis of peroxisome proliferator-activated receptor (PPAR)-γ2 Pro12Ala genotype

BACKGROUND

Peroxisome proliferator-activated receptor (PPAR)-gamma2 Pro12Ala polymorphism has been suggested as a protective factor for polycystic ovary syndrome (PCOS). In this study, we aimed to investigate metabolic features and reproductive hormones in women with PCOS and compare these features with control women on the basis of Pro12Ala genotype.

METHODS

This study involved 60 randomly selected women with PCOS and 60 controls. Main outcome measures were anthropometric measures, variables of glucose metabolism and reproductive hormones. All the patients were genotyped for Pro12Ala variant of PPAR-gamma2 gene.

RESULTS

Patients with Pro12Ala polymorphism were more obese in both groups. Furthermore, they had lower fasting insulin levels, were less insulin-resistant and were less glucose-intolerant as demonstrated by 2 h glucose concentrations. However, there was no difference in reproductive hormone levels on the basis of Pro12Ala genotype.

CONCLUSIONS

Both control women and women with PCOS had significant differences in glucose metabolism on the basis of PPAR-gamma2 Pro12Ala polymorphism. Pro12Ala variant may break the process that leads to PCOS in susceptible women, instead of being a direct causal relationship between Pro12Ala polymorphism and PCOS.

Peroxisome proliferator-activated receptor-??2 Pro12Ala and endothelial nitric oxide synthase-4a/b gene polymorphisms are not associated with hypertension in diabetes mellitus type 2

OBJECTIVE AND DESIGN

The Pro12Ala and the 4a/b polymorphisms of the peroxisome proliferator-activated receptor gamma (PPARgamma) and the endothelial nitric oxide-synthase (eNOS) genes, respectively, have been associated with hypertension in some but not all studies. The purpose of this study was to investigate the association between these polymorphisms and hypertension in patients with diabetes mellitus type 2 (DM2).

METHODS

We determined, by polymerase chain reaction (PCR), the Pro12Ala PPARgamma2 and the eNOS 4a/b gene polymorphisms in a total of 395 patients with diabetes mellitus 2 (DM2) (225 men and 170 women) from the LIANCO (Lipid-Analytic-Cologne) study. Hypertension was defined as known or newly diagnosed hypertension according to current national guidelines. Associations were determined using chi-square statistics. The influence of genotype and other parameters on blood pressure was determined by analysis of variance (ANOVA) and multivariate analyses.

RESULTS

The genotype frequencies of the Pro12Ala polymorphism were 3% AlaAla, 23% ProAla and 74% ProPro and of the eNOS 4a/b polymorphism 3% a/a, 25% b/a and 72% b/b. There were 65% patients with, and 35% without hypertension. A total of 77% of the patients with hypertension were under pharmacological treatment. The mean systolic and diastolic blood pressure (SBP, DBP) was 148 +/- 22 and 84 +/- 11 mmHg in patients with, and 131 +/- 12 and 79 +/- 8 mmHg in patients without, hypertension. There was no difference in the occurrence of hypertension among ProAla and AlaAla subjects compared with ProPro subjects (P = 0.98). There was also no difference between a-allele carriers and non-carriers of the eNOS polymorphism (P = 0.42). There were no differences between men and women in the associations. Analysis of variance did neither identify an influence on systolic or diastolic blood pressure by the presence of the Ala or the a-allele of the respective genotypes nor a significant interaction of the two.

CONCLUSIONS

In DM2 the Pro12Ala and 4a/b gene polymorphisms of the PPARgamma2 and eNOS genes, respectively, are not associated with systolic or diastolic blood pressure, either in men or in women. Our results in a large cohort fail to confirm reports of recent studies suggesting an association of lower blood pressure in patients with DM2 and carriers of Pro12Ala polymorphism.

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

Several genetic variants of peroxisome proliferator-activated receptor-gamma2 (PPAR-gamma2), a molecule known to be involved in transcription of target genes, have been identified. Pro12Ala, a missense mutation in exon 2 of the gene, is highly prevalent in Caucasian populations. Conflicting conclusions about the association between this mutation and complex traits such as obesity, insulin sensitivity, and T2DM have been reported. We have investigated the association of PPAR-gamma2 Pro12Ala polymorphism with measures of insulin sensitivity in a population of Italian obese children (n = 200; mean age, 10.38 +/- 2.8 y) in whom clinical and biochemical analyses were performed. To estimate the insulin sensitivity status, the homeostasis model assessment of insulin resistance (HOMA-IR) was calculated in all subjects. The effect of the Pro12Ala polymorphism on quantitative variables was tested using multiple linear regression analysis. The frequency of Ala carriers was 17%, similar to that reported in other adult Caucasian populations. The X12Ala (either Pro12Ala or Ala12Ala) genotype was associated with significantly lower fasting insulin levels compared with Pro/Pro (p = 0.008). Consistent with this finding, significantly lower HOMA-IR was observed in X12Ala carriers (p = 0.023). In conclusion, our observations demonstrate that the X12Ala variant is significantly associated with greater insulin sensitivity in childhood obesity. Because obesity is one of the most important risk factors for cardiovascular diseases and type 2 diabetes, obese children, who are presumably at a higher risk, may be protected from these diseases by the phenotypic effect of the Ala 12 allele on insulin resistance.

Peroxisome proliferator-activated receptor-gamma calls for activation in moderation: lessons from genetics and pharmacology

The peroxisome proliferator-activated receptor gamma (PPARgamma) is a prototypical member of the nuclear receptor superfamily and integrates the control of energy, lipid, and glucose homeostasis. PPARgamma can bind a variety of small lipophilic compounds derived from metabolism and nutrition. These ligands, in turn, determine cofactor recruitment to PPARgamma, regulating the transcription of genes in a variety of metabolic pathways. PPARgamma is the main target of the thiazolidinedione class of insulin-sensitizing drugs, which are currently a mainstay of therapy for type 2 diabetes. However, this therapy has a number of side effects. Here, we review the clinical consequences of PPARgamma polymorphisms in humans, as well as several studies in mice using general or tissue-specific knockout techniques. We also discuss the recent pharmacological literature describing a variety of new PPARgamma partial agonists and antagonists, as well as pan-PPAR agonists. The results of these studies have added to the understanding of PPARgamma function, allowing us to hypothesize a general mechanism of PPARgamma action and speculate on future trends in the use of PPARgamma as a target in the treatment of type II diabetes.

Serum adiponectin in young adults--interactions with central adiposity, circulating levels of glucose, and insulin resistance: the CARDIA study

PURPOSE

To study adiponectin, a circulating adipocytokine secreted by adipocytes inversely associated with diabetes and insulin resistance, and factors affecting its levels in the Coronary Artery Risk Development in Young Adults (CARDIA) study.

METHODS

Adiponectin in serum was measured by radioimmunoassay in 3355 participants (ages: 23-45 years) categorized by fasting glucose levels as normal, impaired fasting glucose, or diabetes mellitus.

RESULTS

Levels of adiponectin were higher in women, in white participants, and with age. Waist circumference, estimating visceral fat, strongly and inversely correlated with levels of adiponectin, more than body mass index. Adiponectin values adjusted for gender and race were lower with higher fasting glucose values in the normal range and still lower with impaired fasting glucose and untreated diabetes mellitus, even further adjusting for waist circumference and fasting insulin levels (p < 0.0001). Gender- and race-adjusted adiponectin levels were inversely associated with insulin resistance at year 15 and with insulin resistance measured 15 years previously and with its change from baseline to year 15 (p < 0.0001).

CONCLUSIONS

These data suggest complex and significant physiologic interactions among circulating levels of adiponectin and measures of insulin action throughout young adulthood, even from several years earlier. Central obesity, as measured with waist circumference, is a primary factor affecting levels of circulating adiponectin. Furthermore, levels of glucose and levels of adiponectin may directly influence one another.

Genetic variation in PPARG encoding peroxisome proliferator-activated receptor gamma associated with carotid atherosclerosis

BACKGROUND AND PURPOSE

Peroxisome proliferator-activated receptor gamma is a crucial molecule in atherogenesis because it is associated with metabolic risk factors such as obesity and diabetes and also plays a key role in subcellular metabolism of arterial wall macrophage foam cells. Genetic variation in PPARG has been associated with metabolic and cardiovascular end points.

METHODS

We investigated the relationship between 2 common PPARG polymorphisms, namely P12A and c.1431C>T, and carotid atherosclerosis in a sample of 161 Canadian aboriginal people. Dependent variables were carotid intima media thickness (IMT), assessed using B-mode ultrasonography, and total carotid plaque volume (TPV), assessed using 3D ultrasound.

RESULTS

Using multivariate analysis, we found that subjects with > or =1 PPARG A12 allele had less carotid IMT than others (0.72+/-0.03 versus 0.80+/-0.02 mm; P=0.0045), with no between-genotype difference in TPV. In contrast, subjects with the PPARG c.1431T allele had greater TPV than others (124+/-18.4 versus 65.1+/-23.7 mm3; P=0.0079), with no between-genotype difference in IMT.

CONCLUSIONS

The findings show an association between PPARG genotypes and carotid arterial phenotypes, and further reflect the prevailing view that the PPARG A12 allele protects against deleterious phenotypes. Also, whereas IMT and TPV are somewhat correlated with each other, they might also represent distinct traits with discrete determinants representing different stages of atherogenesis.

Expression and functional activity of PPARgamma in pancreatic beta cells

Rosiglitazone is an agonist of peroxisome proliferator activated receptor-gamma (PPARgamma) and ameliorates insulin resistance in type II diabetes. In addition, it may also promote increased pancreatic beta-cell viability, although it is not known whether this effect is mediated by a direct action on the beta cell. We have investigated this possibility. Semiquantitative real-time reverse transcription-polymerase chain reaction analysis (Taqman) revealed that freshly isolated rat islets and the clonal beta-cell line, BRIN-BD11, express PPARgamma, as well as PPARalpha and PPARdelta. The levels of expression of PPARgamma were estimated by reference to adipose tissue and were found to represent approximately 60% (islets) and 30% (BRIN-BD11) of that found in freshly isolated visceral adipose tissue. Western blotting confirmed the presence of immunoreactive PPARgamma in rat (and human) islets and in BRIN-BD11 cells. Transfection of BRIN-BD11 cells with a PPARgamma-sensitive luciferase reporter construct was used to evaluate the functional competence of the endogenous PPARgamma. Luciferase activity was modestly increased by the putative endogenous ligand, 15-deoxy-Delta12,14 prostaglandin J2 (15dPGJ2). Rosiglitazone also caused activation of the luciferase reporter construct but this effect required concentrations of the drug (50-100 microm) that are beyond the expected therapeutic range. This suggests that PPARgamma is relatively insensitive to activation by rosiglitazone in BRIN-BD11 cells. Exposure of BRIN-BD11 cells to the lipotoxic effector, palmitate, caused a marked loss of viability. This was attenuated by treatment of the cells with either actinomycin D or cycloheximide suggesting that a pathway of programmed cell death was involved. Rosiglitazone failed to protect BRIN-BD11 cells from the toxic actions of palmitate at concentrations up to 50 microm. Similar results were obtained with a range of other PPARgamma agonists. Taken together, the present data suggest that, at least under in vitro conditions, thiazolidinediones do not exert direct protective effects against fatty acid-mediated cytotoxicity in pancreatic beta cells.

Intramyocellular lipids and insulin resistance

Lipids are stored not only in adipocytes but also 'ectopically' in tissues such as muscle, liver, beta cells and others. From a metabolic perspective, intramyocellular lipids (IMCLs) have recently become a focus of interest. This review summarizes history, measurement techniques and interpretation of muscle lipid data. Problems in biopsies with the separation of those metabolically active lipid droplets in the cytoplasm of myocytes from further lipids in adipocytes are discussed as well as considerations important for analysis of correlations between IMCL content and insulin sensitivity under various circumstances. The relatively new approach to non-invasive assessment of the IMCL content by magnetic resonance spectroscopy (MRS) is described in detail and exemplary spectra from different skeletal muscle types in humans are presented. The MRS technique allows human examinations of large cohorts for a detailed assessment of the interactions among metabolic parameters such as age, measures of adiposity, hormonal and ethnic factors and insulin resistance. IMCLs are generally positively correlated with measures of obesity and negatively with insulin sensitivity. Paradoxically, physical fitness (maximal aerobic capacity) increases both IMCL content and insulin sensitivity and therefore has to be taken into account as a confounding factor. Intervention studies with MRS further allowed to elucidate the regulation of IMCL. Molecular mechanisms and potential genetic factors on IMCL regulation are discussed as well as possible mechanisms of current treatment strategies for improving insulin sensitivity.

Interactions between peroxisome proliferator-activated receptor-γ2 gene polymorphisms and size at birth on blood pressure and the use of antihypertensive medication

OBJECTIVE

The combination of small birth size and the Pro12Pro variant of the peroxisome proliferator-activated receptor-gamma 2 (PPAR-gamma 2) gene has been shown to be associated with insulin resistance, which is linked to hypertension. We examined whether the association between small body size at birth and adult blood pressure is modulated by PPAR-gamma 2 gene polymorphism, and whether the use of any class of antihypertensive medication is related to birth size.

DESIGN AND METHODS

A total of 500 subjects from an original epidemiological cohort of 7086 men and women aged 65-75 years attended a clinical study. Two hundred and eight of them (73 men and 135 women) were taking antihypertensive medication and are included in this study. The Pro12Ala polymorphism of the PPAR-gamma 2 gene was determined using the polymerase chain reaction single-strand conformation polymorphism method.

RESULTS AND CONCLUSIONS

Hypertensive subjects with low birth weight or short length at birth and the Pro12Pro variant had raised systolic blood pressure. We suggest that insulin resistance enhances the regulatory responses of the renin-angiotensin system, leading to raised blood pressure levels. Those hypertensive subjects who had small birth size and the Pro12Pro variant tended to use angiotensin-converting enzyme inhibitors or angiotensin-receptor blockers (ACEI/ARB). This could be because insulin resistance interacts with the renin-angiotensin system in ways that make ACEI/ARB an effective therapy. Alternative explanations include more severe and treatment resistant hypertension, leading to application of ACEI/ARB, or co-morbid conditions, such as myocardial infarction and type 2 diabetes, known to be linked to low birth weight.

Physiopathologie de l’insulinorésistance

AMONG THE BIOLOGICAL MEDIATORS OF INSULIN RESISTANCE: two compounds released by the adipocyte are found, such as free fatty acids and tumor necrosis factor-alpha. They are incriminated in the deleterious role of visceral adiposity on the metabolic parameters. INTRA-CELL CORTISOL: Attention is also focused on the potential implication of cortisol in the genesis of metabolic syndrome, because cortisol is a potent antagonist of the effect of insulin and its presence in excess enhances visceral obesity and insulin resistance. GENETIC ASPECTS: Although no major locus has yet been identified, recent findings of several mutations or polymorphisms in genes acting in different regulation systems (adiponectin, PPARgamma2) also provide an interesting insight into the pathogenesis of this syndrome. Moreover, there is growing epidemiological evidence that intra-uterine factors could induce a so-called programming of the individual that may, at least in part, account for the difficulties encountered by the classical genetic approach.

Changes in insulin sensitivity in response to troglitazone do not differ between subjects with and without the common, functional Pro12Ala peroxisome proliferator-activated receptor-gamma2 gene variant: results from the Troglitazone in Prevention of Diabetes (TRIPOD) study

OBJECTIVE

We have tested whether the Pro12Ala variant of the peroxisome proliferator-activated receptor (PPAR)-gamma nuclear receptor involved in thiazolidinedione (TZD) action accounted for the failure of troglitazone to increase insulin sensitivity in nondiabetic Hispanic women with previous gestational diabetes treated in the Troglitazone in Prevention of Diabetes (TRIPOD) study.

RESEARCH DESIGN AND METHODS

Ninety-three women assigned to troglitazone had intravenous glucose tolerance tests at randomization and after 3 months of treatment with troglitazone, 400 mg/day, and were genotyped for the Pro12Ala variant of the PPAR-gamma gene. Subjects were divided into tertiles based on their change in minimal model insulin sensitivity (S(i)) during the first 3 months of troglitazone treatment.

RESULTS

The mean changes in S(i) in the bottom, middle, and top tertiles of S(i) response were -0.21 +/- 0.57, 0.91 +/- 0.26, and 2.58 +/- 1.32 min(-1) per microU/ml. 10(-4), respectively. Frequencies of the Ala/- genotype were 30, 22, and 26% in the same three tertiles (P = 0.77). Analysis of phenotypes by genotype revealed only small differences between the Pro/Pro and Ala/- groups, respectively, in baseline S(i) (2.76 +/- 0.19 vs. 2.33 +/- 0.33 x 10(-4) min(-1) per microU/ml; P = 0.27), the change in S(i) after 3 months of troglitazone treatment (1.19 +/- 0.17 vs. 0.93 +/- 0.30; P = 0.46), and the cumulative incidence of diabetes during a median follow-up of 30 months (13 vs. 17%; P = 0.66).

CONCLUSIONS

Among young Hispanic women at high risk for type 2 diabetes, the Pro12Ala variant of the PPAR-gamma receptor gene did not explain the failure of approximately 1/3 of subjects to increase their insulin sensitivity when placed on troglitazone at a dose of 400 mg/day.

The Arg972 variant in insulin receptor substrate-1 is associated with an increased risk of secondary failure to sulfonylurea in patients with type 2 diabetes

OBJECTIVE

The aim of this study was to investigate whether diabetic patients carrying the Arg(972) insulin receptor substrate-1 (IRS-1) variant are at increased risk for secondary failure to sulfonylurea.

RESEARCH DESIGN AND METHODS

A total of 477 unrelated Caucasian type 2 diabetic patients were recruited according to the following criteria: onset of diabetes after age 35 years, absence of ketonuria at diagnosis, and anti-GAD(-) antibody. Type 2 diabetes was diagnosed according to the American Diabetes Association criteria. Patients with secondary sulfonylurea failure were defined as those requiring insulin due to uncontrolled hyperglycemia (fasting plasma glucose >300 mg/dl) despite sulfonylurea-metformin combined therapy, appropriate diet, and absence of any conditions causing hyperglycemia.

RESULTS

Of the total patients, 53 (11.1%) were heterozygous for the Arg(972) IRS-1 variant, 1 (0.2%) was homozygous, and the remainder (88.7%) were homozygous for the wild-type allele. The genotype frequency of the Arg(972) IRS-1 variant was 8.7% among diabetic patients well controlled with oral therapy and 16.7% among patients with secondary failure to sulfonylurea (odds ratio 2.1 [95% CI 1.18-3.70], P = 0.01). Adjustment for age, sex, BMI, metabolic control, age at diagnosis, duration of diabetes, and Pro12Ala polymorphism of peroxisome proliferator-activated receptor-gamma2 gene in a logistic regression analysis with secondary failure to sulfonylurea as a dependent variable did not change this association (2.0 [1.38-3.86], P = 0.038).

CONCLUSIONS

These data demonstrate that the Arg(972) IRS-1 variant is associated with increased risk for secondary failure to sulfonylurea, thus representing a potential example of pharmacogenetics in type 2 diabetes.

Desaturase activities in rat model of insulin resistance induced by a sucrose-rich diet

A sucrose-rich diet, as compared with a similar starch diet, induces a time-dependent typical noninsulin-dependent diabetes syndrome characterized by insulin resistance in rats. Within the first 3 wk, there was glucose intolerance associated with hyperinsulinemia, hypertriglyceridemia, and high plasma FFA. In this study, we examined the effect of the sucrose-rich diet vs. the starch diet during short- (3 wk) and longterm treatment (6 mon) on hepatic delta9, delta6, and delta5 desaturases. These enzymes modulate monounsaturated FA and PUFA biosynthesis, respectively. Sucrose feeding (3 wk) caused an initial hyperinsulinemia that was normalized within 6 mon. In the early period (3 wk), stearoyl-CoA desaturase-1 (SCD-1) mRNA and activity were decreased, whereas delta6 desaturase mRNA abundance and delta6 and delta5 desaturase activities remained unchanged. After 6 mon of sucrose feeding, activities of the delta9, delta6, and delta5 desaturases were each increased. The SCD-1 and delta6 desaturase mRNA were also correspondingly higher. These increases were consistent with an increase in oleic acid, the 20:4/18:2 ratio, and 22:4n-6 and 22:5n-6 acids in liver and muscle lipids. On the other hand, the percentage of 22:6n-3 acid was decreased. In conclusion, a sucrose-rich diet after 6 mon induces an increase in rat liver SCD-1 and delta6 desaturase mRNA and enzymatic activities that are opposite to the changes reported in insulin-dependent diabetes mellitus. It appears that neither blood insulin levels nor insulin resistance is a factor affecting the delta9, delta6, and delta5 desaturase changes in mRNA and activity found with the sucrose-rich diet.

Identification of a novel mitochondrial protein ("mitoNEET") cross-linked specifically by a thiazolidinedione photoprobe

Thiazolidinediones address underlying causes of type 2 diabetes, although their mechanism of action is not clearly understood. The compounds are thought to function as direct activators of the nuclear receptor PPARgamma (peroxisome proliferator-activated receptor-gamma), although pioglitazone, the weaker agonist of the two thiazolidinediones now in clinical use, seems to have more useful effects on circulating lipids. We have used tritiated pioglitazone and a photoaffinity cross-linker to identify a novel binding site in mitochondria. A saturable binding site for [3H]pioglitazone was solubilized from the membranes with CHAPS and migrated as a large complex by size exclusion chromatography. The binding correlated with a <17-kDa protein (m17), marked by a photoaffinity cross-linker, in both subcellular location and selectivity of competition by analogs. The protein was isolated and identified by mass spectrometry analysis and NH2-terminal sequencing. Three synthetic peptides with potential antigenic properties were synthesized from the predicted nontransmembrane sequence to generate antibodies in rabbits. Western blots show that this protein, which we have termed "mitoNEET," is located in the mitochondrial fraction of rodent brain, liver, and skeletal muscle, showing the identical subcellular location and migration on SDS-PAGE as the protein cross-linked specifically by the thiazolidinedione photoprobe. The protein exists in low levels in preadipocytes, and expression increases exponentially in differentiated adipocytes. The synthetic protein bound to solid phase associated with a complex of solubilized mitochondrial proteins, including the trifunctional beta-oxidation protein. It is possible that thiazolidinedione modification of the function of the mitochondrial target may contribute to lipid lowering and/or antidiabetic actions.

Differential effects of the C1431T and Pro12Ala PPARgamma gene variants on plasma lipids and diabetes risk in an Asian population

We investigated the association of C1431T and Pro12Ala polymorphisms at the peroxisome proliferator-activated receptor gamma (PPARgamma) locus with plasma lipids and insulin resistance-related variables, according to diabetes status, in a large and representative Asian population from Singapore consisting of 2,730 Chinese, 740 Malays, and 568 Indians. Moreover, we estimated the diabetes risk and examined gene-nutrient interactions between these variants and the ratio of polyunsaturated fatty acid to saturated fat (SFA) in determining body mass index (BMI) and fasting insulin. We found differential effects of these gene variants. The Pro12Ala polymorphism was more associated with plasma lipids and fasting glucose concentrations, whereas the C1431T polymorphism was related to the risk of diabetes. Carriers of the 12Ala allele had higher HDL-cholesterol than did Pro12Pro homozygotes (P < 0.05), and the effect of the 12Ala allele on fasting glucose was modified by diabetes status (P < 0.001). After controlling for confounders, carriers of the T allele had decreased risk of diabetes compared with CC homozygotes [odds ratio (OR) 0.73, 95% confidence interval (CI) 0.58-0.93; P = 0.011]; this effect was stronger in Indians (OR 0.38, 95% CI 0.15-0.92; P = 0.032). For both polymorphisms, normal subjects carrying the less prevalent allele had higher BMI (P < 0.05). The PUFA/SFA did not modify the effect of these polymorphisms on BMI or insulin.

Genetic Basis of Metabolic Abnormalities in Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a common heterogeneous disorder characterized by hyperandrogenism and chronic anovulation. The syndrome is frequently associated with an increased risk for insulin resistance and type 2 diabetes mellitus; obesity exacerbates insulin resistance and favors the progression from impaired glucose tolerance to diabetes in these patients. In young women, precocious pubarche and hyperinsulinemia are early manifestations of PCOS. The familial clustering of women with PCOS suggests that heredity is implicated in the origin of the syndrome. However, genetic approaches to its pathogenesis have been hampered by the heterogeneity of phenotypic features within families, and the lack of uniform criteria for diagnosis. Currently, PCOS is considered a polygenic trait that might result from the interaction of susceptibility and protective genomic variants under the influence of environmental factors. Both linkage analysis and association studies are valid tools for the study of the genetics of PCOS. Candidate genes for PCOS include those related to androgenic pathways and metabolic associations of the syndrome. More recently, genes encoding inflammatory cytokines have been identified as target genes for PCOS, as proinflammatory genotypes and phenotypes are also associated with obesity, insulin resistance, type 2 diabetes, PCOS, and increased cardiovascular risk. This paper reviews the candidate genes involved in the metabolic pathways that are altered in patients with PCOS. Despite a significant amount of research in this area, none of the genes studied so far has been identified as the PCOS susceptibility gene for the majority of cases. PCOS is the first component of the metabolic syndrome to be detected in many women, so the identification and correct diagnosis of PCOS has important preventive and therapeutic implications for the affected women and their families. In the future, new therapeutic approaches to PCOS will rely on knowing the genes, environmental influences, and etiologic mechanisms associated with the disorder.

Exon 6 and 2 peroxisome proliferator-activated receptor-gamma polymorphisms in polycystic ovary syndrome

Obesity affects about 44% of women with polycystic ovary syndrome (PCOS). Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is one of the genes involved in the differentiation of adipose tissue. In an attempt to shed light on the high percentage of obesity in PCOS, we examined polymorphisms at exons 6 and 2 of the PPAR-gamma gene in 100 PCOS patients and in 100 healthy controls matched for age and body mass index (BMI). The T allele frequency of exon 6 was significantly higher (P < 0.05) in PCOS patients compared with control women. In addition, the BMI and leptin levels were significantly higher (P < 0.05) in PCOS patients carrying the C-->T substitution than in controls. There was no significant difference in leptin levels after normalization for BMI. The Pro(12)Ala polymorphism at exon 2 was unrelated to BMI and/or leptin levels in PCOS women. In conclusion, the higher frequency of the C-->T substitution in exon 6 of the PPAR-gamma gene in PCOS women suggests that it plays a role in the complex pathogenetic mechanism of obesity in PCOS, whereas the Pro(12)Ala polymorphism does not seem to affect BMI in PCOS women.

Combined effects of PPARγ2 P12A and PPARα L162V polymorphisms on glucose and insulin homeostasis: the Québec Family Study

Peroxisome proliferator-activated receptors gamma2 and alpha are nuclear factors known to be important regulators of lipid and glucose metabolism. Two polymorphisms, namely PPARgamma2 P12A and PPARalpha L162V, were investigated for their individual and interaction effects on glucose and insulin homeostasis. Genotypes were determined in 663 nondiabetic adults participating in the Québec Family Study and who underwent an oral glucose tolerance test (OGTT). The insulin and C-peptide areas under the curve (AUC) following the OGTT were higher in subjects carrying the PPARalpha V162 allele compared to homozygous for the L162 allele. When subjects were grouped according to both polymorphisms, higher levels of insulin and C-peptide during the OGTT were observed for those carrying the PPARalpha V162 allele except when they carry at the same time the PPARgamma2 A12 allele. Thus, the PPARgamma2 A12 allele seems protective against the deleterious effect of the PPARalpha V162 allele. Furthermore, a significant gene-gene interaction was observed for the acute (0-30 min) (p<0.001) and the total (p=0.05) C-peptide AUC following the OGTT. These results provide evidence of a gene-gene interaction in the regulation of plasma glucose-insulin homeostasis, and emphasize that these interactions need to be taken into account when dissecting the genetic etiology of complex disorders.

Peroxisome proliferator-activated receptors and the cardiovascular system

Insulin resistance syndrome (also called syndrome X) includes obesity, diabetes, hypertension, and dyslipidemia and is a complex phenotype of metabolic abnormalities. The disorder poses a major public health problem by predisposing individuals to coronary heart disease and stroke, the leading causes of mortality in Western countries. Given that hypertension, diabetes, dyslipidemia, and obesity exhibit a substantial heritable component, it is postulated that certain genes may predispose some individuals to this cluster of cardiovascular risk factors. Emerging data suggest that peroxisome proliferator-activated receptors (PPARs), including alpha, gamma, and delta, are important determinants that may provide a functional link between obesity, hypertension, and diabetes. It has been well documented that hypolipidemic fibrates and antidiabetic thiazolidinediones are synthetic ligands for PPAR alpha and PPAR gamma, respectively. In addition, PPAR natural ligands, such as leukotriene B4 for PPAR alpha, 15-deoxy-delta 12,14-prostaglandin J2 for PPAR gamma, and prostacyclin for PPAR delta, are known to be eicosanoids and fatty acids. Studies have documented that PPARs are present in all critical vascular cells: endothelial cells, vascular smooth muscle cells, and monocyte-macrophages. These observations suggest that PPARs not only control lipid metabolism but also regulate vascular diseases such as atherosclerosis and hypertension. In this review, we present structure and tissue distribution of PPAR nuclear receptors, discuss the mechanisms of action and regulation, and summarize the rapid progress made in this area of study and its impact on the cardiovascular system.

Peroxisome proliferator-activated receptors: are they involved in atherosclerosis progression?

Peroxisome proliferator-activated receptors (PPAR) are nuclear receptors present in several organs and cell types. They are subdivided into PPAR alpha, PPAR gamma and PPAR delta (or beta). PPAR alpha and gamma are the two main categories of these receptors, which are both characterized by their ability to influence lipid metabolism, glucose homeostasis, cell proliferation, differentiation and apoptosis, as well as the inflammatory response, by transcriptional activation of target genes. PPAR alpha are activated by fatty acids, eicosanoids and fibrates, while PPAR gamma activators include arachidonic acid metabolites, oxidized low density lipoprotein and thiazolidinediones. Atherosclerosis is now considered a chronic inflammatory condition. Thus, PPAR activation appears a promising approach to favorably affect atherosclerosis development through both metabolic and anti-inflammatory effects. However, the clinical data in favor of an anti-atherosclerotic action of PPAR agonists are still scanty, and some experimental data would even indicate possible pro-atherogenic effects, or a lack of effect in the female sex. New controlled clinical studies will provide the information necessary to understand the true significance and usefulness of PPAR alpha, gamma and delta activators in the control of atherosclerotic disease.

A functional variant in the peroxisome proliferator-activated receptor gamma2 promoter is associated with predictors of obesity and type 2 diabetes in Pima Indians

Peroxisome proliferator-activated receptor gamma (PPARgamma)-2 is a member of the nuclear hormone receptor superfamily that is expressed predominantly in adipocytes and is thought to have a role in energy homeostasis, adipogenesis, and insulin sensitivity. A functional single nucleotide polymorphism (SNP) that predicts a proline to alanine substitution (Pro12Ala) within the coding region of this gene has previously been associated with obesity and type 2 diabetes in several populations. In this study, we identified several novel SNPs in the promoter region of PPARgamma2 and genotyped them, along with the previously identified Pro12Ala SNP. In 241 nondiabetic Pima subjects, the Pro12Ala was associated with whole-body insulin action (P = 0.05), hepatic insulin action (P = 0.03), and fasting plasma insulin concentrations (P = 0.01). One of the promoter SNPs positioned within a putative E2 box was in high linkage disequilibrium (/D'/ = 0.98) with the Pro12Ala. This promoter SNP was similarly associated with whole-body insulin action (P = 0.04) and hepatic insulin action (P = 0.05), but not fasting plasma insulin concentrations. Functional studies in transfected 3T3-L1 cells demonstrated that this single base substitution in the putative E2 box significantly altered transcriptional activity from a luciferase reporter construct. These data indicate that this promoter SNP, via its effect on PPARgamma2 expression, may also have functional consequences on PPARgamma2-activated pathways, and perhaps both the promoter SNP and the Pro12Ala contribute to PPARgamma2-related phenotypes.

Thiazolidinediones -- some recent developments

The role of thiazolidinediones (currently rosiglitazone and pioglitazone) in the treatment of Type 2 diabetes is firmly established. The mechanism of action involves binding to the peroxisome proliferator-activated receptor-gamma, a transcription factor that regulates the expression of specific genes especially in fat cells but also other cell types such as endothelial cells, macrophages and monocytes, vascular smooth muscle cells and colonic epithelium. Thiazolidinediones have been shown to interfere with expression and release of mediators of insulin resistance originating in adipose tissue (e.g., increased free fatty acids, decreased adiponectin) in a way that results in net improvement of insulin sensitivity (i.e., in muscle and liver). A direct or indirect effect on AMP-dependent protein kinase may also be involved. Prevention of lipid accumulation in tissues critical to glycaemia such as visceral adipocytes, liver, muscle and beta-cells at the expense of lipids accumulating at the less harmful subcutaneous site may be central to their net metabolic effect. The sustained beneficial effect of troglitazone on beta-cell function in women with previous gestational diabetes in addition to the insulin-sensitising properties point to an important role of this class of drugs in the prevention of Type 2 diabetes. Original safety concerns based on animal and in vitro studies (e.g., fatty bone marrow transformation, colonic cancer, adipogenic transdifferentiation of blood cells) remain theoretical issues but become less pressing practically with prolonged uneventful clinical use. Hepatotoxicity for troglitazone and fluid retention, which can aggravate pre-existing heart failure, are the most important side effects. In summary, with the thiazolidinediones, a novel concept for the treatment of insulin resistance and possibly preservation of beta-cell function is available that could become effective in the prevention of Type 2 diabetes. Moreover, their anti-inflammatory properties also make them interesting in the prevention and treatment of atherosclerosis and possibly other inflammatory conditions (e.g., inflammatory bowel disease). Long-term data will be necessary for a final risk-benefit assessment of these substances.

Pro12Ala of the peroxisome proliferator-activated receptor-gamma2 gene is associated with lower serum insulin levels in nonobese African Americans: the Atherosclerosis Risk in Communities Study

Recent research suggests that the Pro12Ala variant in peroxisome proliferator-activated receptor-gamma2 (PPAR-gamma2) is associated with diabetes- and obesity-related traits, and that its effects may be modified by obesity status. We characterized this variant in a population-based sample of 1,441 middle-aged African-American individuals with respect to diabetes-, obesity-, and other cardiovascular-related traits, both cross-sectionally and prospectively. The overall frequency of Ala12 was 1.9% (95% CI 1.5-2.5%), significantly lower than in Caucasian populations. Consistent with previous findings in Caucasians, African Americans with type 2 diabetes tended to be less likely to have the Pro/Ala genotype than those without (odds ratio [OR] 0.64, 95% CI 0.34-1.20); however, this OR was not statistically significant. Among nonobese individuals, the Pro/Ala genotype was associated with significantly lower ln(insulin) (P = 0.001), lower ln(HOMA-IR) (homeostasis model assessment of insulin resistance) (P = 0.002), higher fasting glucose-to-insulin ratio (P = 0.005), and lower diastolic blood pressure (P = 0.02). Among overweight individuals (BMI 25-29.9 kg/m(2)), the Pro/Ala genotype was associated with greater BMI (P = 0.02), waist-to-hip ratio (P = 0.01), and waist circumference (P = 0.04). Among obese individuals, there was no association between any of the diabetes- or obesity-related traits and the Pro12Ala PPAR-gamma2 variant. We conclude that among nonobese African Americans, the Pro/Ala genotype is associated with markers of greater insulin sensitivity.

The genetics of adiponectin

Adiponectin encoded by the APMI gene is one of the adipocyte-expressed proteins that function in the homeostatic control of glucose, lipid, and energy metabolism. Its dysregulation has been suggested to be involved in disorders covering the metabolic X syndrome, such as insulin resistance, obesity, type 2 diabetes, and coronary artery disease. Recent data present evidence of a genetic modulation of the adiponectin level, and linkage of the 3q27 locus, where the APMI gene lies, with diabetes and features of the metabolic X syndrome playing a putative role of the APMI gene in this syndrome. In this article, we present an overview of the results available to date and discuss positive evidence for a role of genetic variants of the APMI gene and questions that genetic data raise.

Resistin: molecular history and prognosis

Obesity and diabetes have reached epidemic proportions worldwide. The antidiabetic thiazolidinedione (TZD) drugs are insulin-sensitizing agents now widely used in the treatment of type 2 diabetes. TZDs are ligands for the nuclear hormone receptor peroxisome proliferator activated receptor gamma, which is a master regulator of adipogenesis and adipocyte metabolism. The molecular mechanisms by which TZDs improve insulin sensitivity have not been fully identified. Here we consider a novel secreted factor first identified as a TZD-suppressible gene in mouse adipocytes, called resistin, and discuss what is currently known about resistin regulation and function in mouse and human.

Contributions of insulin-resistance and insulin-secretory defects to the pathogenesis of type 2 diabetes mellitus

Controlled clinical trials have shown that optimal glycemic control can prevent the microvascular complications of type 2 diabetes mellitus; considerable epidemiological data suggest that this may also be true for macrovascular complications. However, this is frequently not achieved. Consequently, research efforts have been undertaken to better understand the pathophysiology of this disorder. It is now well recognized that 2 factors are involved: impaired beta-cell function and insulin resistance. Prospective studies of high-risk populations have shown insulin-resistance and/ or insulin-secretory defects before the onset of impaired glucose tolerance. Thus, there has been a long-standing debate whether an alteration in insulin sensitivity or in insulin secretion is the primary genetic factor. Most of the available evidence favors the view that type 2 diabetes is a heterogeneous disorder in which the major genetic factor is impaired beta-cell function and insulin resistance is the major acquired factor. Superimposition of insulin resistance on a beta cell that cannot appropriately compensate leads to deterioration in glucose tolerance. Therefore, clinicians managing type 2 diabetes must reduce insulin resistance and augment and/or replace beta-cell function.

Assessing the shape of the glucose curve during an oral glucose tolerance test

OBJECTIVE

The oral glucose tolerance test (OGTT) is used to define the status of glucose tolerance based on the plasma glucose level at 120 min. The purpose of the present study was to identify parameters that determine the shape of the plasma glucose course measured at 0, 30, 60, 90, and 120 min during an OGTT.

RESEARCH DESIGN AND METHODS

OGTT data from 551 subjects (485 with normal glucose tolerance [NGT] and 66 with impaired glucose tolerance [IGT]) were analyzed. We distinguished between "monophasic," "biphasic," and unclassified glucose shapes. A "shape" index based on the extent and the direction of the plasma glucose change in the second hour allowed us to treat shape as a continuous variable.

RESULTS

In the biphasic group, the NGT-to-IGT ratio was slightly higher (173/20 vs. 209/40, P = 0.08) and the male-to-female ratio was lower (60/133 vs. 120/129, P = 0.0003). Subjects with a biphasic shape had significantly lower age, BMI, waist-to-hip ratio (WHR), HbA(1c), plasma glucose, and area under the insulin curve (insulin(AUC)) and a better estimated insulin sensitivity and secretion (using validated indexes) than monophasic subjects (all P < 0.05). By adjusting this shape index for glucose(AUC) (as continuous measure of glucose tolerance), correlations with age, BMI, WHR, HbA(1c), and insulin(AUC) were completely abolished. The adjusted shape index was still higher in female than in male subjects but lower in IGT than in NGT subjects (both P = 0.0003). Finally, we tested common polymorphisms in insulin receptor substrate (IRS)-1, IRS-2, calpain-10, hepatic lipase, and peroxisome proliferator-activated receptor-gamma for association with the shape index.

CONCLUSIONS

We conclude that the plasma glucose shape during an OGTT depends on glucose tolerance and sex. In addition, genetic factors seem to play a role. The shape index may be a useful metabolic screening parameter in epidemiological and genetic association studies.

Genetics of obesity: more complicated than initially thought

During the past several decades, there has been an explosion in the prevalence of obesity. Since our genes have not changed appreciably during that time, it stands to reason that the present epidemic is caused by our pervasive obesigenic environment, in which excess caloric intake and decreased physical activity conspire with one another. Despite an obesigenic environment, humans have great variability in their susceptibility to obesity, which is determined in large part by genetics. Current evidence suggests that genetic susceptibility to human obesity is the result of multiple genes, each with a modest effect, that inter-act with each other and with environmental provocations. Elucidation of obesity susceptibility genes through genome-wide and candidate gene approaches provides great promise in ultimately determining the genetic underpinnings of obesity. Further research will translate these new insights on the pathophysiological basis of obesity into new medications and diagnostic tests.