The case for an immunologic cause of obesity

Associations of serum C-peptide level with body fat distribution and ever stroke in nondiabetic subjects

BACKGROUND

Although elevated serum C-peptide level as an indicator of insulin resistance increases the obesity-associated risk of cardiovascular disease among diabetic patients, evidence indicating that serum C-peptide level is associated with stroke in nondiabetic subjects is limited. The aim of this study is to evaluate the association between serum C-peptide level and ever stroke in nondiabetic subjects and investigated the associations of serum C-peptide level with body fat distribution and stroke events among nondiabetic subjects.

METHODS

This study was a population-based cross-sectional study that included 7030 participants aged 12-85 years. Body fat distribution was determined by dual-energy X-ray absorptiometry. Serum C-peptide level was measured using the radioimmunoassay method. The association between serum C-peptide level and body fat distribution was evaluated by multiple linear regression models. Logistic regression analysis was performed to calculate the odds ratio (OR) of serum C-peptide level being associated with ever stroke.

RESULTS

A total of 103 nondiabetic subjects reported having a stroke. Logistic regression analysis revealed a high-serum C-peptide level significantly associated with ever stroke among nondiabetic subjects (OR: 3.71, 95% confidence interval: 1.78-7.75). Meanwhile, in multiple linear regression analysis, serum C-peptide level was positively associated with total and regional fat distribution among nondiabetic subjects.

CONCLUSION

The serum C-peptide level is strongly associated with the ever stroke in nondiabetic subjects and significantly associated with total and regional body fat distribution.

Unraveling the directional link between adiposity and inflammation: a bidirectional Mendelian randomization approach

CONTEXT

Associations between adiposity and circulating inflammation markers are assumed to be causal, although the direction of the relationship has not been proven.

OBJECTIVE

The aim of the study was to explore the causal direction of the relationship between adiposity and inflammation using a bidirectional Mendelian randomization approach.

METHODS

In the PROSPER study of 5804 elderly patients, we related C-reactive protein (CRP) single nucleotide polymorphisms (SNPs) (rs1800947 and rs1205) and adiposity SNPs (FTO and MC4R) to body mass index (BMI) as well as circulating levels of CRP and leptin. We gave each individual two allele scores ranging from zero to 4, counting each pair of alleles related to CRP levels or BMI.

RESULTS

With increasing CRP allele score, there was a stepwise decrease in CRP levels (P for trend < 0.0001) and a 1.98 mg/liter difference between extremes of the allele score distribution, but there was no associated change in BMI or leptin levels (P >or= 0.89). By contrast, adiposity allele score was associated with 1) an increase in BMI (1.2 kg/m(2) difference between extremes; P for trend 0.002); 2) an increase in circulating leptin (5.77 ng/ml difference between extremes; P for trend 0.0027); and 3) increased CRP levels (1.24 mg/liter difference between extremes; P for trend 0.002).

CONCLUSIONS

Greater adiposity conferred by FTO and MC4R SNPs led to higher CRP levels, with no evidence for any reverse pathway. Future studies should extend our findings to other circulating inflammatory parameters. This study illustrates the potential power of Mendelian randomization to dissect directions of causality between intercorrelated metabolic factors.

Microbiota and SCFA in lean and overweight healthy subjects

Obesity has recently been linked to the composition of human microbiota and the production of short chain fatty acids (SCFAs). However, these findings rely on experimental studies carried out using rather small and defined groups of volunteers or model animals. Our aim was to evaluate differences within the human intestinal microbiota and fecal SCFA concentration of lean and obese subjects. A total of 98 subjects volunteered to take part in this study. The BMI in kg/m(2) of 30 volunteers was within the lean range, 35 were overweight and 33 were obese. The fecal microbiota was characterized by real-time PCR analyses. With the primers used herein we were able to cover 82.3% (interquartile range of 68.3-91.4%) of the total microbiota detectable with a universal primer. In addition, the concentration of SCFA was evaluated. The total amount of SCFA was higher in the obese subject group (P = 0.024) than in the lean subject group. The proportion of individual SCFA changed in favor of propionate in overweight (P = 0.019) and obese subjects (P = 0.028). The most abundant bacterial groups in faeces of lean and obese subjects belonged to the phyla Firmicutes and Bacteroidetes. The ratio of Firmicutes to Bacteroidetes changed in favor of the Bacteroidetes in overweight (P = 0.001) and obese subjects (P = 0.005). Our results are in line with previous reports suggesting that SCFA metabolism might play a considerable role in obesity. However, our results contradict previous reports with regard to the contribution of various bacterial groups to the development of obesity and this issue remains controversial.

Low-grade chronic inflammation in the relationship between insulin sensitivity and cardiovascular disease (RISC) population: associations with insulin resistance and cardiometabolic risk profile

OBJECTIVE

Low-grade chronic inflammation has been hypothesized to underlie the constellation of cardiometabolic risk factors, possibly by inducing insulin resistance. In the present study, we investigated associations between inflammation markers, insulin sensitivity (expressed as the ratio of the M value to the mean plasma insulin concentrations measured during the final 40 min of the clamp [M/I]), and a range of cardiometabolic risk factors in a large, healthy population.

RESEARCH DESIGN AND METHODS

The Relationship between Insulin Sensitivity and Cardiovascular Disease (RISC) cohort includes 1,326 nondiabetic European men and women, aged between 30 and 60 years. We measured cardiometabolic risk factors and performed a hyperinsulinemic-euglycemic clamp. We determined total white blood cell count (WBC) and erythrocyte sedimentation rate (ESR) as markers of chronic inflammation.

RESULTS

WBC and ESR were both strongly associated with M/I. WBC and ESR were further associated with a range of cardiometabolic risk factors. Associations between WBC and HDL cholesterol, triglycerides, heart rate, fasting C-peptide, and insulin and 2-h insulin in men and women and between WBC and 2-h glucose in women remained significant after adjustment for both M/I and waist circumference. Associations between ESR and HDL cholesterol, heart rate, fasting, and 2-h insulin in men and women and between ESR and fat mass in women remained significant after adjustment for M/I and waist circumference.

CONCLUSIONS

This study showed that low-grade chronic inflammation is associated with the cardiometabolic risk profile of a healthy population. Insulin resistance, although strongly associated with inflammation, does not seem to play a large intermediary role.

The role of impaired mitochondrial lipid oxidation in obesity

Obesity represents a disruption in balancing fuel intake with energy expenditure in favor of energy conservation. Adiposity is known to be carefully regulated and, over time, highly resistant to major changes, raising questions about how energy homeostasis can become dysregulated in favor of fat accumulation. In obesity, the excess lipid accumulation represents a surfeit of energy, but those who are obese often experience rapid fatigue and decreased physical endurance, reflecting an energy deficiency. To develop an explanation for this apparent contradiction in energy homeostasis and the chronic overeating relative to energy used in obesity, a review of the literature was conducted. The resulting model of obesity is based on a growing body of research demonstrating that altered mitochondrial energy production, particularly in skeletal muscles, is a major anomaly capable of setting off a chain of metabolic events leading to obesity. Alterations in skeletal muscle mitochondria distribution and their oxidative and glycolytic energy capacities in obesity are described. The metabolic responses of obese and normal individuals to exercise are contrasted, and the effects of weight loss on energy production are presented. The effect of altered fat oxidation is considered in relation to energy regulation by the central nervous system and the development of major obesity comorbidities, including systemic inflammation, insulin resistance and diabetes, and cardiovascular disease. Recommendations for clinical intervention and additional research are proposed based on the model presented of impaired mitochondrial function in obesity.

Obesity and Heart Failure

Current statistics on global obesity are staggering. In 2002, the International Obesity Task Force estimated that worldwide, nearly 1 billion (6%) people were overweight or obese. The American Heart Association's 2002: "Top 10" Research Advances for the Treatment of Heart Disease include obesity as a strong and independent risk factor for developing heart failure. This article outlines national and world statistics, cardiac risk factors, and pathophysiologic theories outlining the cellular mechanisms that associate obesity and heart failure. Access to guidelines for effective screening, evaluation, and treatment of obesity are also provided.