Adiponectin is lower among African Americans and is independently related to insulin sensitivity in children and adolescents

Adiposity, the metabolic syndrome, and breast cancer in African-American and white American women

Breast cancer, the second most common cause of cancer-related deaths in American women, varies substantially in incidence and mortality according to race and ethnicity in the United States. Although the overall incidence of breast cancer among African-American (AA) women is lower than in white American women, this cancer is more common in young premenopausal AA women, and AA breast cancer patients of all ages are more likely to have advanced disease at diagnosis, higher risk of recurrence, and poorer overall prognosis. Epidemiological studies indicate that these differences may be attributable in part to variation in obesity and body fat distribution. Additionally, AA women more frequently exhibit breast cancer with an aggressive and metastatic phenotype that may also be attributable to the endocrine and metabolic changes associated with upper body obesity. These changes include both elevated estrogen and androgen bioactivity, hyperinsulinemia, and perturbations of the adipokines. Type 2 diabetes and the metabolic syndrome, which are more common in AA women, have also been associated with breast cancer risk. Moreover, each of the individual components of the syndrome has been associated with increased breast cancer risk, including low levels of the adipocytokine, adiponectin. This review explores the specific roles of obesity, body fat distribution (particularly visceral and sc adipose tissue), type 2 diabetes, metabolic syndrome, and adipocytokines in explaining the differential patterns of breast cancer risk and prognosis between AA and white American women.

Degree of obesity and glucose allostasis are major effectors of glucose tolerance dynamics in obese youth

OBJECTIVE

One of the signals for the beta-cell to maintain an adequate response to worsening insulin sensitivity is elevated ambient glycemia, namely the concept of "glucose allostasis." We examined whether glucose allostasis can be demonstrated using oral glucose tolerance tests (OGTTs) and the effects of the dynamics of beta-cell demand on longitudinal changes of glucose tolerance in obese youth.

RESEARCH DESIGN AND METHODS

A cross-sectional analysis of 784 OGTTs of obese youth was used to demonstrate the concept of allostasis, and a longitudinal assessment of 181 subjects was used to examine the effects of changes in beta-cell demand and the degree of obesity on glucose tolerance.

RESULTS

Glucose allostasis can be demonstrated using indexes derived from an OGTT. Increasing beta-cell demand and the degree of obesity at baseline were independently related to elevations in ambient glycemia over time. Baseline BMI Z score was a significant contributor to elevated glucose levels on the second OGTT, while the change in degree of obesity during follow-up was not.

CONCLUSIONS

Increasing beta-cell demand related to worsening insulin sensitivity and the degree of obesity per se have independent roles in the development of elevated glucose levels over time. This implicates that peripheral insulin sensitization and/or beta-cell enhancement alongside a significant reduction in obesity may be needed to prevent the development of altered glucose metabolism in obese youth.

Genetic determination of adiponectin and its relationship with body fat topography in multigenerational families of African heritage

Adiponectin, an adipose-specific protein, is negatively associated with adiposity, insulin sensitivity, and diabetes. Very few studies have examined the role of heredity in the regulation of adiponectin and its association with body fat among individuals of African heritage. Thus, we measured fasting serum adiponectin levels by radioimmunoassay and body composition by dual-energy x-ray absorptiometry (DEXA) in 402 individuals aged 18 to 103 years belonging to 7 multigenerational families of African heritage in the relatively homogeneous island population of Tobago. Heritability of adiponectin was 33.2% (P < .01), and age, sex, and body mass index explained 23.4% of the variance in adiponectin. Sex-specific heritability was significant in men (heritability, 34%; P < .05), but not in women. The inverse associations between body mass index and percentage of body fat and adiponectin, independent of age and height, were much stronger in women (all P values <.001) than in men. However, percentage of trunk fat was consistently strongly associated with adiponectin in both men (r = -0.40, P < .001) and women (r = -0.44, P < .001), independent of age and height. This study suggests that genetic factors are a significant source of interindividual differences in circulating adiponectin among Afro-Caribbeans. Adiponectin may serve as a promising quantitative intermediate trait in studies designed to map the genes underlying diabetes and obesity in this population.

Adiponectin in childhood and adolescent obesity and its association with inflammatory markers and components of the metabolic syndrome

CONTEXT

Adiponectin levels are lower in obese children and adolescents, whereas markers of inflammation and proinflammatory cytokines are higher. Hypoadiponectinemia may contribute to the low-grade systemic chronic inflammatory state associated with childhood obesity.

OBJECTIVE

We investigated whether C-reactive protein (CRP), the prototype of inflammation, is related to adiponectin levels independently of insulin resistance and adiposity.

DESIGN, SETTING, PARTICIPANTS, AND MAIN OUTCOME MEASURES

In a multiethnic cohort of 589 obese children and adolescents, we administered a standard oral glucose tolerance test and obtained baseline measurements for adiponectin, plasma lipid profile, CRP, IL-6, and leptin.

RESULTS

Stratifying the cohort into quartiles of adiponectin levels and adjusting for potential confounding variables, such as age, gender, ethnicity, body mass index z-score, pubertal status, and insulin sensitivity, the present study revealed that low levels of adiponectin are associated not only with higher CRP levels, but also with components of the metabolic syndrome, such as low high-density lipoprotein cholesterol and a high triglyceride-to-high-density-lipoprotein ratio.

CONCLUSIONS

The link between adiponectin levels and a strong marker of inflammation, CRP, is independent of insulin resistance and adiposity in obese children and adolescents. Adiponectin may be one of the signals linking inflammation and obesity. Thus, adiponectin may function as a biomarker of the metabolic syndrome in childhood obesity.

Development of type 2 diabetes in children and adolescents

Type 2 diabetes is emerging as a significant health problem in children and adolescents. The disease usually develops in obese insulin-resistant youth with a typical pattern of lipid partitioning characterized by increased lipid deposition in myocytes, the visceral compartment, and the liver. Unfavorable adipocytokine profiles, together with a state of low-grade inflammation, create an additional metabolic burden tightly coupled to other components of the metabolic syndrome. Insufficient beta-cell compensation promotes altered glucose metabolism.

Adiponectin is a candidate marker of metabolic syndrome in obese children and adolescents

The aim of this study was to compare the use of several biomarkers to identify obese children and adolescents with increased metabolic risk. One hundred sixty-two Caucasian obese children and adolescents (41% males, 9-18 years old) referred to the Istituto Auxologico Italiano between 2003 and 2004 underwent an oral glucose tolerance test. Circulating levels of adiponectin (AD), plasminogen activator inhibitor 1 (PAI-1), interleukin 18 (IL-18), C-reactive protein (CRP), fibrinogen, uric acid, lipids and insulin were measured. Twenty five percent of obese children had the MS defined using World Health Organization-derived child specific criteria. MS subjects had significantly lower AD (p<0.01) and higher log-PAI-1 (p<0.001), uric acid (p<0.0001), and IL-18 (p<0.001). Subjects with AD levels </=median value had a significantly increased risk of having the MS (p<0.0001), as did subjects with uric acid and PAI-1 levels greater than the median. There was no increased risk with elevated IL-18, CRP, or fibrinogen. Hypoadiponectinemia was independently associated with the MS risk (p<0.0001). In conclusion in obese children and adolescents AD is the best predictor of MS and thus of higher cardiovascular disease risk.