Association of abdominal circumference with serum nitric oxide concentration in healthy population

OBJECTIVES

We determined the relationship between abdominal circumference and the concentration of nitric oxide (NO), an endothelial cell product known to play an important role in the regulation of vascular tone and thrombocyte activations.

METHODS

Subjects were 177 men and 339 women aged 40 or over who were free from a history of diabetes or malignancy. Analysis of covariance was applied to examine the gender-specific and smoking-status-specific associations of abdominal fat volume measured as waist circumference, waist-hip ratio, and waist-to-stature ratio, with serum NO level represented by the concentration of NO metabolites (NOx; nitrate plus nitrite).

RESULTS

Although men showed no statistical association between abdominal fat accumulation and NOx concentration, abdominal adiposity seemed to inversely affect the serum NOx concentration of never- and current-smoking women.

CONCLUSION

Our results suggest that a reduction in NO bioactivity occurs with abdominal fat accumulation in women. The underlying biological mechanism might involve adipocytokines secreted from visceral fat, but is yet to be elucidated.

Omentin as a novel biomarker of metabolic risk factors

BACKGROUND

Omentin is an adipocytokine that is abundantly expressed in visceral fat tissue. We investigated the association of omentin with the number of metabolic risk factors.

FINDING

The study population comprised 201 Japanese men who underwent annual health checkups. Plasma omentin levels were determined by enzyme-linked immunosorbent assay. We divided the subjects into 4 groups according to omentin levels. A reduction of plasma omentin levels significantly correlated with an increase in the mean number of metabolic risk factors such as increased waist circumference, dyslipidemia, high blood pressure and glucose intolerance.

CONCLUSIONS

Circulating omentin levels negatively correlated with the multiplicity of metabolic risk factors, suggesting that omentin acts as a biomarker of metabolic disorders.

Influence of elevated liver fat on circulating adipocytokines and insulin resistance in obese Hispanic adolescents

OBJECTIVE

We performed this study to examine the metabolic differences arising from higher liver fat accumulation in obese Hispanic adolescents, with a particular focus on circulating levels of adipocytokines and insulin resistance.

METHODS

Forty-one obese Hispanic adolescents (15.3 ± 1.0 years, body mass index percentile: 97.0 ± 3.9) were assessed for: visceral adipose tissue (VAT), subcutaneous adipose tissue (SAT) and hepatic fat fraction (HFF) by magnetic resonance imaging; fasting measures of serum glucose, insulin and adipocytokines; homeostasis model assessment of insulin resistance (HOMA-IR); and insulin sensitivity (SI) and the acute insulin response to glucose (AIR) by intravenous glucose tolerance test. Subjects with normal levels of HFF (below 5%; n = 25) were compared to those with HFF > 5% (n = 16).

RESULTS

The two groups differing in HFF were similar for total body fat, VAT and SAT. The group with HFF > 5% had significantly (P < 0.05) higher interleukin-8 (IL-8) (6.1 ± 1.6 vs. 3.2 ± 0.4 pg mL(-1) ), NGF (30.2 ± 9.9 vs. 13.9 ± 1.6 pg mL(-1) ), HOMA-IR (8.8 ± 1.1 vs. 5.5 ± 0.5), AIR (1869 ± 206 vs. 1092 ± 165) and a tendency for lower SI (1.2 ± 0.4 vs. 2.1 ± 0.3; P = 0.06), with no significant differences in any of other factors measured.

CONCLUSIONS

These data suggest that elevated liver fat is most closely associated with elevated serum IL-8 and NGF levels as well as increased AIR and HOMA-IR. These elevated factors may play significant roles in the metabolic abnormalities associated with elevated liver fat in obese Hispanics.

Adipocytokines and obesity-linked disorders

Obesity is closely associated with an increased risk for metabolic and cardiovascular diseases. Adipose tissue produces a number of secretory bioactive substances, also known as adipocytokines or adipokines, which directly affect adjacent or distant organs. Most adipocytokines are pro-inflammatory, thereby promoting the obesity-linked disorders. In contrast, there are a small number of adipocytokines that exhibit antiinflammatory properties. It is now recognized that dysregulated production or secretion of adipocytokines caused by adipocyte dysfunction leads to the development of obesity-linked complications. In this review, we focus on the functional role of several adipocytokines in metabolic and cardiovascular diseases.

Visfatin/PBEF/Nampt: A New Cardiovascular Target?

In the last years, a growing interest has emerged toward understanding the role of adipocytokines in the development of cardio-metabolic complications. Five years ago, visfatin/PBEF/Nampt was identified as a novel adipocytokine. In the context of metabolic disorders, extracellular visfatin/PBEF/Nampt was initially claimed as a potentially beneficial molecule due to its insulin-mimetic and glucose-lowering properties. Nevertheless, growing evidence has since then unveiled that visfatin/PBEF/Nampt may rather be a biomarker of inflammation and endothelial damage, and also a direct regulator of the cardiovascular system that modulates cell proliferation and survival, extracellular matrix, vascular reactivity, and inflammation. On one side, the blockade of the deleterious cardiovascular actions of visfatin/PBEF/Nampt is being regarded as a potential approach to prevent and treat, not only cardio-metabolic complications, but also other pathologies implying excessive angiogenesis. Conversely, the administration of visfatin/PBEF/Nampt has shown beneficial effects in different ischemic conditions. Further research is required to evaluate the real value of visfatin/PBEF/Nampt as a pharmacological target.

Serum levels of adipokines resistin and leptin in patients with colon cancer

Adipose tissue displays characteristics of an endocrine organ releasing a number of adipocyte-specific factors known as adipocytokines. It has been recently suggested that adipocytokines may play a role in pathogenesis and progression of certain cancers, in particular in colorectal cancer. The aim of this study was to investigate the association between several blood adipocytokine levels and clinicopathological characteristics of colon cancer patients undergoing surgery. The study group comprised of 29 patients who underwent surgical resection for colon cancer at Emergency University Hospital Bucharest and 27 healthy volunteers. The serum levels of adipocytokines were measured using multianalyte xMap profiling technology (Luminex). Resistin levels were significantly higher in colon cancer patients while leptin serum levels were significantly lower as compared to controls. Leptin levels decreased gradually with tumor stage and aggressiveness. Taken together, these results of this study suggest that adipokines, in particular resistin and leptin may be involved in development and progression of colon cancer.

Correlation of the leptin:adiponectin ratio with measures of insulin resistance in non-diabetic individuals

AIMS/HYPOTHESIS

Obesity is the dominant cause of insulin resistance. In adult humans it is characterised by a combination of adipocyte hypertrophy and, to a lesser extent, adipocyte hyperplasia. As hypertrophic adipocytes secrete more leptin and less adiponectin, the plasma leptin:adiponectin ratio (LAR) has been proposed as a potentially useful measure of insulin resistance and vascular risk. We sought to assess the usefulness of the LAR as a measure of insulin resistance in non-diabetic white adults.

METHODS

Leptin and adiponectin levels were measured in 2,097 non-diabetic individuals from the Ely and European Group for the Study of Insulin Resistance (EGIR) Relationship between Insulin Sensitivity and Cardiovascular Risk (RISC) study cohorts. LAR was compared with fasting insulin and HOMA-derived insulin sensitivity (HOMA-S) in all individuals and with the insulin sensitivity index (M/I) from hyperinsulinaemic-euglycaemic clamp studies in 1,226 EGIR RISC participants.

RESULTS

The LAR was highly correlated with HOMA-S in men (r = -0.58, p = 4.5 x 10(-33) and r = -0.65, p = 1.1 x 10(-66) within the Ely and EGIR RISC study cohorts, respectively) and in women (r = -0.51, p = 2.8 x 10(-36) and r = -0.61, p = 2.5 x 10(-73)). The LAR was also strongly correlated with the clamp M/I value (r = -0.52, p = 4.5 x 10(-38) and r = -0.47, p = 6.6 x 10(-40) in men and women, respectively), similar to correlations between HOMA-S and the M/I value.

CONCLUSIONS/INTERPRETATION

The leptin:adiponectin ratio is a useful measure of insulin resistance in non-diabetic white adults. These data highlight the central role of adipocyte dysfunction in the pathogenesis of insulin resistance. Given that variations between fasting and postprandial leptin and adiponectin levels tend to be small, the leptin to adiponectin ratio might also have potential value in assessing insulin sensitivity in the non-fasted state.

Cardioprotective effect of adiponectin is partially mediated by its AMPK-independent antinitrative action

Adiponectin (APN) exerts its metabolic regulation largely through AMP-dependent protein kinase (AMPK). However, the role of AMPK in APN's antiapoptotic effect in ischemic-reperfused (I/R) adult cardiomyocytes remains incompletely understood. The present study was designed to determine the involvement of AMPK in the antiapoptotic signaling of APN. Cardiomyocytes from adult male mice overexpressing a dominant-negative alpha(2)-subunit of AMPK (AMPK-DN) or wild-type (WT) littermates were subjected to simulated I/R (SI/R) and pretreated with 2 microg/ml globular domain of APN (gAPN) or vehicle. SI/R-induced cardiomyocyte apoptosis was modestly increased in AMPK-DN cardiomyocytes (P < 0.05). Treatment with gAPN significantly reduced SI/R-induced apoptosis in WT cardiomyocytes as well as in AMPK-DN cardiomyocytes, indicating that the antiapoptotic effect of gAPN is partially AMPK independent. Furthermore, gAPN-induced endothelial nitric oxide synthase (eNOS) phosphorylation was significantly reduced in AMPK-DN cardiomyocytes, suggesting that the APN-eNOS signaling axis is impaired in AMPK-DN cardiomyocytes. Additional experiments demonstrated that treatment of AMPK-DN cardiomyocytes with gAPN reduced SI/R-induced NADPH oxidase overexpression, decreased superoxide generation, and blocked peroxynitrite formation to the same extent as that observed in WT cardiomyocytes. Collectively, our present study demonstrated that although the metabolic and eNOS activation effect of APN is largely mediated by AMPK, the superoxide-suppressing effect of APN is not mediated by AMPK, and this AMPK-independent antioxidant property of APN increased nitric oxide bioavailability and exerted significant antiapoptotic effect.

Loss of resistin ameliorates hyperlipidemia and hepatic steatosis in leptin-deficient mice

Resistin has been linked to components of the metabolic syndrome, including obesity, insulin resistance, and hyperlipidemia. We hypothesized that resistin deficiency would reverse hyperlipidemia in genetic obesity. C57Bl/6J mice lacking resistin [resistin knockout (RKO)] had similar body weight and fat as wild-type mice when fed standard rodent chow or a high-fat diet. Nonetheless, hepatic steatosis, serum cholesterol, and very low-density lipoprotein (VLDL) secretion were decreased in diet-induced obese RKO mice. Resistin deficiency exacerbated obesity in ob/ob mice, but hepatic steatosis was drastically attenuated. Moreover, the levels of triglycerides, cholesterol, insulin, and glucose were reduced in ob/ob-RKO mice. The antisteatotic effect of resistin deficiency was related to reductions in the expression of genes involved in hepatic lipogenesis and VLDL export. Together, these results demonstrate a crucial role of resistin in promoting hepatic steatosis and hyperlipidemia in obese mice.

Role of retinol-binding protein 4 in the pathogenesis of Type 2 diabetes

Retinol-binding protein (RBP)4 is a new adipocytokine that has been associated with insulin resistance. Both RBP4 mRNA expression in adipocytes and serum RBP4 levels are elevated in adipose-specific glucose transporter 4-knockout mice, and elevated circulating RBP4 levels cause insulin resistance by inhibiting phosphatidylinositol 3 kinase activity in skeletal muscle and increasing phosphoenolpyruvate carboxylase expression in liver. Several clinical cross-sectional studies have shown a significant negative association between circulating RBP4 levels and insulin sensitivity evaluated by the glucose clamp method, but it is unclear if RBP4 is associated with insulin resistance in humans because of many conflicting results. Drugs such as rosiglitazone, exercise and weight loss have been shown to decrease circulating RBP4 levels and improve insulin resistance, but contradictory results have been found in other studies. In addition, a recent clinical study has suggested that RBP4 is more closely related to visceral adiposity than subcutaneous adiposity. In summary, RBP4 is an adipocytokine that is especially associated with visceral fat and may be associated with insulin resistance in humans. However, this association remains uncertain and whether or not RBP4 is a new target for treatment of Type 2 diabetes remains to be determined.

The self-inhibited structure of full-length PCSK9 at 1.9 A reveals structural homology with resistin within the C-terminal domain

Mutations in proprotein convertase subtilisin/kexin type 9 (PCSK9) are strongly associated with levels of low-density lipoprotein cholesterol in the blood plasma and, thereby, occurrence or resistance to atherosclerosis and coronary heart disease. Despite this importance, relatively little is known about the biology of PCSK9. Here, the crystal structure of a full-length construct of PCSK9 solved to 1.9-A resolution is presented. The structure contains a fully folded C-terminal cysteine-rich domain (CRD), showing a distinct structural similarity to the resistin homotrimer, a small cytokine associated with obesity and diabetes. This structural relationship between the CRD of PCSK9 and the resistin family is not observed in primary sequence comparisons and strongly suggests a distant evolutionary link between the two molecules. This three-dimensional homology provides insight into the function of PCSK9 at the molecular level and will help to dissect the link between PCSK9 and CHD.

Whole-body proteolysis rate is elevated in HIV-associated insulin resistance

Type 2 diabetes is characterized by impaired glucose tolerance (IGT) and insulin resistance with respect to glucose metabolism but not amino acid metabolism. We examined whether whole-body leucine and protein metabolism are dysregulated in HIV-infected individuals with IGT. Glucose and leucine kinetics were measured under fasting insulin conditions and during euglycemic hyperinsulinemia using primed-constant infusions of 2H2-glucose and 13C-leucine in 10 HIV-seronegative control subjects, 16 HIV+ subjects with normal glucose tolerance, and 21 HIV+IGT subjects. Glucose disposal rate during hyperinsulinemia was lower in HIV+IGT than the other two groups. Absolute plasma leucine levels and rate of appearance (whole-body proteolysis) were higher in HIV+IGT at all insulin levels but declined in response to hyperinsulinemia in parallel to those in the other two groups. HIV+IGT had greater visceral adiposity, fasting serum interleukin (IL)-8 and free fatty acid levels, and higher lipid oxidation rates during the clamp than the other two groups. These findings implicate several factors in the insulin signaling pathway, which may be further dysregulated in HIV+IGT, and support the notion that insulin signaling pathways for glucose and leucine metabolism may be disrupted by increased proinflammatory adipocytokines (IL-8) and increased lipid oxidation. Increased proteolysis may provide amino acids for gluconeogenesis, exacerbating hyperglycemia in HIV.