Adiponectin and adiponectin receptors

Serum adiponectin is a predictor of coronary heart disease: a population-based 10-year follow-up study in elderly men

CONTEXT

Cross-sectional and nested case-control studies indicate a relationship between adiponectin, obesity, and coronary heart disease (CHD).

OBJECTIVE

Our objective was to investigate whether adiponectin could predict CHD in a population-based cohort of elderly men.

DESIGN AND SETTING

From 1991-1995 a baseline investigation was carried out in 832 healthy men aged 70 yr in the Uppsala Longitudinal Study of Adult Men (ULSAM study). They were followed up to 10.4 yr using Swedish national registry data. The baseline investigation included anthropometry, blood pressure, smoking, serum lipids, a euglycemic insulin clamp, and fasting serum adiponectin.

MAIN OUTCOME MEASURES

Main outcome measures were defined as death or first-time hospitalization for CHD (n = 116), recorded in the Cause of Death Registry or in the Hospital-Discharge Registry of the National Board of Health and Welfare, Sweden. Associations were analyzed using Cox's proportional hazards regression, presented as hazard ratios (HR) with 95% confidence intervals (CI) for 1 sd increase in the predictor variable.

RESULTS

In a multivariable analysis including total cholesterol (HR, 1.24; CI, 1.02-1.50), high-density lipoprotein cholesterol (HR, 0.72; CI, 0.58-0.89), smoking (HR, 1.39; CI, 0.91-2.14), and systolic blood pressure (HR, 1.26; CI, 1.05-1.52), serum adiponectin was associated with lower risk for CHD (HR, 0.81; CI, 0.66-0.99). The association was independent of BMI and remained significant after adjustment for insulin sensitivity index.

CONCLUSIONS

In this population-based cohort of healthy men, elevated serum levels of adiponectin were associated with a lower risk for CHD. Importantly, the association between adiponectin and CHD was independent of other well-known risk factors.

Adiponectin deficiency protects mice from chemically induced colonic inflammation

BACKGROUND & AIMS

Adiponectin (APN) is an adipokine that regulates insulin sensitivity and is anti-inflammatory in atherosclerosis. The goal of this study was to investigate the role of APN in intestinal inflammation.

METHODS

APN knockout (KO) mice and their wild-type (WT) littermates received dextran sulfate sodium (DSS) or trinitrobenzene sulfonic acid (TNBS) to induce intestinal inflammation. Clinical and histologic scores and proliferation of epithelial cells were assessed. Cytokines and APN levels were measured. Expression of APN and heparin binding epidermal growth factor (HB-EGF) was analyzed by immunohistochemistry. Expression of APN and its receptors, HB-EGF, and basic fibroblast growth factor (bFGF) messenger RNA was assessed by reverse-transcription polymerase chain reaction. Association of serum APN with HB-EGF and bFGF was studied by coimmunoprecipitation.

RESULTS

APN KO mice are protected from chemically induced colitis; administration of APN restores inflammation. APN is expressed in the colon, luminal APN associates with colonic epithelial cells. In vitro, APN increases production of proinflammatory cytokines from colonic tissue. Expression of colonic APN overlaps with that of bFGF and HB-EGF, which play a protective role in colitis. Circulating APN binds to bFGF and HB-EGF, likely inhibiting their protective activity. Inhibition of EGF receptor signaling, which is required for biologic activity of HB-EGF, restores inflammation in APN KO mice.

CONCLUSIONS

APN deficiency is associated with protection from chemically induced colitis. APN exerts proinflammatory activities in the colon by inducing production of proinflammatory cytokines and inhibiting bioactivity of protective growth factors. Thus, in colitis, APN exerts an opposite role compared with atherosclerosis.

Mechanisms regulating energy metabolism by adiponectin in obesity and diabetes

Nutritional control of molecular events has become of great interest given the increased incidence of diet-induced obesity, and consequently Type 2 (non-insulin-dependent) diabetes, in recent years. The altered adipose tissue content in obese individuals results in an altered profile of circulating adipokines, and here we focus on adiponectin, whose circulating levels decrease in obese individuals. Adiponectin is a 30 kDa protein but circulates primarily as hexameric, oligomeric and, to a lesser extent, trimeric forms. Full-length adiponectin can also be cleaved to produce a fragment containing the globular domain that exerts potent metabolic effects. Adiponectin has insulin-mimetic and -sensitizing actions including stimulation of glucose uptake in skeletal muscle and suppression of glucose production in liver. Hence, adiponectin has attracted great interest as an antidiabetic agent. Adiponectin acts via two receptor isoforms, AdipoR1 (adiponectin receptor 1) and AdipoR2, which have distinct tissue distributions and affinities for recognition of the various adiponectin forms. Expression of AdipoR isoforms can be regulated by hyperinsulinaemia and hyperglycaemia with the consequence of increased sensitivity or resistance to specific forms of adiponectin. In summary, regulation of adiponectin or AdipoR expression may be of great importance in the development of metabolic perturbations characteristic of Type 2 diabetes in obese individuals.

The dual peroxisome proliferator-activated receptor alpha/gamma activator muraglitazar prevents the natural progression of diabetes in db/db mice

There are two major defects in type 2 diabetes: 1) insulin resistance and 2) insulin deficiency due to loss of beta-cell function. Here we demonstrated that treatment with muraglitazar (a dual peroxisome proliferator-activated receptor alpha/gamma activator), when initiated before or after the onset of diabetes in mice, is effective against both defects. In study 1, prediabetic db/db mice were treated for 12 weeks. The control mice developed diabetes, as evidenced by hyperglycemia, hyperinsulinemia, reduced insulin levels in the pancreas, blunted insulin response to glucose, and impaired glucose tolerance. The muraglitazar-treated mice had normal plasma glucose, and insulin levels, equivalent or higher pancreatic insulin content than normal mice, showed a robust insulin response to glucose and exhibited greater glucose tolerance. In study 2, diabetic db/db mice were treated for 4 weeks. The control mice displayed increased glucose levels, severe loss of islets, and their isolated islets secreted reduced amounts of insulin in response to glucose and exendin-4 compared with baseline. In muraglitazar-treated mice, glucose levels were reduced to normal. These mice showed reduced loss of islets, and their isolated islets secreted insulin at levels comparable to baseline. Thus, muraglitazar treatment decreased both insulin resistance and preserved beta-cell function. As a result, muraglitazar treatment, when initiated before the onset of diabetes, prevented development of diabetes and, when initiated after the onset of diabetes, prevented worsening of diabetes in db/db mice.

Adiponectin sensitizes insulin signaling by reducing p70 S6 kinase-mediated serine phosphorylation of IRS-1

Adiponectin functions as an insulin sensitizer, and yet the underlying molecular mechanism(s) remains largely unknown. We found that treating C2C12 myotubes with adiponectin or rapamycin enhanced the ability of insulin to stimulate IRS-1 tyrosine phosphorylation and Akt phosphorylation, concurrently with reduced p70 S6 kinase phosphorylation at Thr389 as well as IRS-1 phosphorylation at Ser302 and Ser636/639. Overexpression of dominant-negative AMP kinase (AMPK), but not dominant-negative p38 MAPK, reduced the insulin-sensitizing effect of adiponectin. Rapamycin, but not adiponectin, enhanced insulin-stimulated Akt phosphorylation in HeLa cells, which lack LKB1, and exogenous expression of LKB1 in HeLa cells rescued the insulin-sensitizing effect of adiponectin. Finally, overexpression of wild-type Rheb (Ras homology-enriched in brain) or the TSC2 mutant lacking the AMPK phosphorylation site (TSC2S1345A) inhibited the insulin-sensitizing effect of adiponectin in C2C12 cells. These results indicate that activation of the LKB1/AMPK/TSC1/2 pathway alleviates the p70 S6 kinase-mediated negative regulation of insulin signaling, providing a mechanism by which adiponectin increases insulin sensitivity in cells.

Association of adiponectin with coronary heart disease and mortality: the Rancho Bernardo study

Hypoadiponectinemia has been implicated in the development of obesity-related conditions, including dyslipidemia and coronary heart disease (CHD). In this study, the authors examined the association of adiponectin with CHD prevalence, incidence, and mortality among 1,513 community-dwelling men and women aged 50-91 years who were followed from 1984-1987 through 2004. In cross-sectional analyses, adiponectin concentrations were positively related to female sex, age, and high density lipoprotein cholesterol level and inversely related to waist girth, triglyceride level, and fasting plasma glucose level (all p's < 0.001). Adiponectin levels in the highest sex-specific quintile, as compared with the lowest, were associated with 44% decreased odds of prevalent CHD (p for trend = 0.03); adjustment for high density lipoprotein cholesterol and/or triglycerides eliminated this association. In 20-year prospective analyses, higher adiponectin concentrations predicted reduced risk of nonfatal myocardial infarction in men only; adiponectin was not associated with fatal incident CHD events or 20-year CHD mortality (n = 215 deaths) in either sex. Adiponectin levels in the highest sex-specific quintile, as compared with lower levels, were associated with almost 40% increased risks of cardiovascular disease death (n = 441) and death from all causes (n = 925), independent of age, sex, waist girth, lipid levels, and glucose level (both p's < 0.001). These results suggest that use of adiponectin for cardiovascular disease risk stratification is premature.

Adiponectin modulates the glycogen synthase kinase-3beta/beta-catenin signaling pathway and attenuates mammary tumorigenesis of MDA-MB-231 cells in nude mice

Adiponectin is an adipokine that has pleiotropic beneficial roles in systemic insulin resistance and inflammation. Several recent clinical studies suggest that low serum levels of adiponectin are associated with increased risks of breast cancer. Here, we investigated the direct effects of adiponectin on breast cancer development in vitro and in vivo. Our results showed that adiponectin significantly attenuated the proliferations of two typical human breast cancer cells, MDA-MB-231 and T47D, in a cell type-specific manner. Further analysis revealed that adiponectin could induce apoptosis and arrest the cell cycle progression at G(0)-G(1) phase in MDA-MB-231 cells. Prolonged treatment with adiponectin in this cell line blocked serum-induced phosphorylation of Akt and glycogen synthase kinase-3beta (GSK-3beta), suppressed intracellular accumulation of beta-catenin and its nuclear activities, and consequently reduced expression of cyclin D1. Adiponectin-mediated suppression of cyclin D1 expression and attenuation of cell proliferation was abrogated by the GSK-3beta inhibitor lithium chloride. These results suggest that the inhibitory role of adiponectin on MDA-MB-231 cell growth might be attributed to its suppressive effects on the GSK-3beta/beta-catenin signaling pathway. Furthermore, our in vivo study showed that both supplementation of recombinant adiponectin and adenovirus-mediated overexpression of this adipokine substantially reduced the mammary tumorigenesis of MDA-MB-231 cells in female nude mice. Taken together, these data support the role of adiponectin as a negative regulator of breast cancer development and also suggest that adiponectin might represent a novel therapeutic target for this disease.

Adiponectin in severe preeclampsia

AIMS

Adiponectin is an adipokine with insulin-sensitizing, anti-atherogenic, anti-inflammatory and angiogenic properties. The aims of this study were to determine whether maternal plasma adiponectin concentrations differ between patients with severe preeclampsia and those with normal pregnancies, and to explore the relationship between plasma adiponectin and the results of Doppler velocimetry of the uterine arteries.

METHODS

This case-control study included two groups: (1) patients with severe preeclampsia (n=50) and (2) patients with normal pregnancies (n=150). Pulsed-wave and color Doppler ultrasound examination of the uterine arteries were performed. Plasma adiponectin concentrations were determined by ELISA. Non-parametric statistics were used for analysis.

RESULTS

(1) Patients with severe preeclampsia had a higher median plasma concentration of adiponectin than that of normal pregnant women. (2) The median plasma adiponectin concentration did not differ between women with severe preeclampsia who had a high impedance to blood flow in the uterine arteries and those with normal impedance to blood flow. (3) Among patients with normal pregnancies, plasma adiponectin concentrations were negatively correlated with BMI in the first trimester and at sampling.

CONCLUSIONS

Women with severe preeclampsia have a higher median plasma concentration of adiponectin than that of normal pregnant women. This may reflect a compensatory feedback mechanism to the metabolically-altered, anti-angiogenic and pro-atherogenic state of severe preeclampsia.

Adiponectin and adiponectin receptor gene variants in relation to resting metabolic rate, respiratory quotient, and adiposity-related phenotypes in the Quebec Family Study

BACKGROUND

Despite adiponectin's presumed role in fatty acid oxidation and energy homeostasis, little is known about the effect of gene variants on substrate oxidation, energy expenditure, and adiposity-related phenotypes.

OBJECTIVE

We examined the effects of genetic variation in adiponectin (ADIPOQ) and adiponectin receptors 1 and 2 (ADIPOR1 and ADIPOR2) on resting metabolic rate, respiratory quotient (RQ), and adiposity-related phenotypes.

DESIGN

We studied the associations of ADIPOQ, ADIPOR1, and ADIPOR2 polymorphisms with resting metabolic rate, RQ, and body mass index, percentage body fat, sum of 6 skinfold thicknesses, waist circumference, and total, subcutaneous, and visceral fat in 759 participants in the Québec Family Study.

RESULTS

The ADIPOQ 45T-->G single-nucleotide polymorphism (SNP) was significantly (P = 0.0002 to 0.04) associated with overall adiposity and abdominal adiposity; the rare homozygotes (G/G) had a leaner phenotype than did the carriers of the common allele. One SNP each in the putative promoter of ADIPOR1 (ie, -3882T-->C) and ADIPOR2 (ie, IVS1 -1352G-->A) was associated with RQ (P = 0.03 and 0.04, respectively), and the association was even stronger in nonobese persons (P = 0.02 and 0.003). Carriers of the common alleles (ADIPOR1 T and ADIPOR2 G alleles) had a lower RQ than did the rare homozygotes. A significant genotype-by-genotype interaction (P = 0.0002 to 0.02) was found between SNPs in the promoters of ADIPOQ (-3971A-->G) and ADIPOR1 (-3882T-->C). Subjects carrying the minor ADIPOQ allele (G allele) who were rare homozygotes (C/C) for the ADIPOR1 SNP had a higher RQ (P = 0.003) and greater overall (P < 0.03) and abdominal (P < 0.05) adiposity than did persons with other genotype combinations.

CONCLUSIONS

Previous findings that the ADIPOQ 45T-->G variant contributes to overall fatness and abdominal obesity are confirmed. Moreover, variants in the promoter region of both ADIPOR genes contribute to substrate oxidation.

Plasma adiponectin levels and endometrial cancer risk in pre- and postmenopausal women

BACKGROUND

Adiponectin, an adipocytokine secreted by adipose tissue, is decreased in obesity, insulin resistance, type 2 diabetes, and polycystic ovary syndrome, all of which are well-established risk factors for endometrial cancer.

METHODS

We conducted a case-control study nested within the European Prospective Investigation into Cancer and Nutrition to examine the relation between prediagnostic plasma adiponectin levels and endometrial cancer risk. Among pre- and postmenopausal women who were not currently using exogenous hormones, 284 women developed incident endometrial cancer during an average of 5.1 yr of follow-up. Using risk set sampling, 548 control subjects were selected, matched on center, age, menopausal status, phase of menstrual cycle, time of blood draw, and fasting status. Conditional logistic regression models were used to estimate relative risks and 95% confidence intervals.

RESULTS

Adiponectin levels were inversely associated with endometrial cancer risk [body mass index-adjusted relative risk for the top vs. bottom quartile = 0.56 (95% confidence interval 0.36-0.86), P(trend) = 0.006]. There was evidence of a stronger inverse association among obese women than among nonobese women (P(heterogeneity) = 0.03). The inverse association also appeared stronger for women who were postmenopausal or perimenopausal than premenopausal at baseline, but this was not statistically significantly heterogeneous (P(heterogeneity) = 0.51). The association remained statistically significant after separate adjustment for other obesity-related physiological risk factors such as C-peptide, IGF binding protein-1, IGF binding protein-2, SHBG, estrone, or free testosterone but only marginally statistically significant after simultaneous adjustment for these factors.

CONCLUSIONS

High circulating adiponectin levels are associated with reduced endometrial cancer risk, largely independent of other obesity-related risk factors.

Adiponectin and leptin up-regulate extracellular matrix production by dermal fibroblasts

Adipocytes were recently shown to secrete adipocytokines, such as adiponectin and leptin, which may have an endocrine role. Subcutaneous adipose tissue lies just beneath the dermis, and dermal condition is correlated with body mass index (BMI). However, it is not clear whether adipocytokines released by adipocytes in subcutaneous adipose tissue influence the adjacent dermis. We found that human dermal fibroblasts express genes encoding receptors for adiponectin and leptin, and that those cytokines both significantly increase production of hyaluronic acid (HA), a major extracellular matrix component (ECM) of dermis, by dermal fibroblasts. This effect is accompanied with up-regulation of HA synthase 2 gene expression. Moreover, adiponectin significantly increases production of collagen, the most abundant component of ECM in dermis, by dermal fibroblasts. These results suggest that subcutaneous adipocytes influence dermal condition by up-regulating collagen and HA production by dermal fibroblasts via secretion of adiponectin and leptin.

Hypoadiponectinemia, dyslipidemia, and impaired growth in children with HIV-associated facial lipoatrophy

OBJECTIVE

To compare growth, lipids and adipocytokines in HIV-positive children with and without lipoatrophy.

PATIENTS

Eleven HIV-positive children with facial lipoatrophy, and 22 age- and sex-matched HIV-positive controls without signs of fat abnormality.

METHODS

Clinical data including height, physical examination findings, medications, markers of viral control, cholesterol, and triglycerides were retrieved from the medical charts. Serum samples were analyzed for adiponectin, inflammatory markers, and high density lipoprotein cholesterol (HDL).

RESULTS

Lipoatrophy was associated with higher triglycerides (330 vs 133 mg/dl, p = 0.0003), lower HDL (33 vs 48 mg/dl, p = 0.02), and a greater frequency of hypercholesterolemia (total cholesterol > 200 mg/dl; 64% vs 23%, p < 0.03). Adiponectin was 53% lower in patients with lipodystrophy (6.9 microg/ml vs 14.8 microg/ml, p = 0.005), however there was no difference in the inflammatory markers soluble TNFa receptor 2 or interleukin 6. Strikingly, despite similar BMI z-scores and virological control, lipoatrophic patients were shorter by 1 standard deviation score (p = 0.03).

CONCLUSIONS

The presence of facial lipoatrophy in a child with HIV infection is a marker for significant metabolic derangements including dyslipidemia and hypoadiponectinemia, and suggests the need for careful growth evaluation.

Metabolic syndrome increases the risk of ischemic stroke in women

BACKGROUND

Metabolic syndrome is a characterized by a cluster of cardiovascular risk factors, including visceral obesity, insulin resistance, dyslipidemia, and hypertension. The criteria for diagnosing metabolic syndrome differ among ethnic groups, due in part to differences in eating habits and body build. Little is known about the relationship between metabolic syndrome and ischemic stroke in Asian countries. The aim of this study was to investigate the relationship between metabolic syndrome and first-time ischemic strokes.

SUBJECTS & METHODS

Study subjects were 1,493 Japanese adults aged 55 years-old or older with no diabetes mellitus, no history of stroke and no neurological abnormalities, who participated in a voluntary neurological health screening at the Institute of Shimane Health Science, Japan (767 men, 62.0 +/- 5.9 years old at entry and 726 women, 61.8 +/- 5.1 years old at entry). All subjects were given an annual clinical stroke questionnaire. Clinical details of patients who reported strokes were confirmed with the attending physicians. Each subject was evaluated for an average of 6.4 +/- 3.8 years. Metabolic syndrome was defined using the modified criteria for Japanese population published in April 2005.

RESULTS

Metabolic syndrome was diagnosed in 11.0% of men and 1.1% of women. Adjusting for age and smoking, female subjects with metabolic syndrome had a 23.1-fold increased risk of suffering ischemic strokes [95% confidence interval (CI), 2.7-196], whereas metabolic syndrome did not increase the risk of ischemic stroke in men.

CONCLUSIONS

Metabolic syndrome is more likely to influence a risk for ischemic stroke in women than in men.

Intrahepatic insulin resistance in a murine model of steatohepatitis: effect of PPARgamma agonist pioglitazone

Hepatic insulin resistance is associated with hepatic steatosis and is thought to play an important role in the pathogenesis of steatohepatitis. Using a murine model of steatohepatitis (mice fed a diet deficient in methionine and choline-MCD diet), we tested the effects of the insulin-sensitising, PPARgamma agonist drug pioglitazone (PGZ) on systemic and intrahepatic insulin sensitivity and on liver pathology. Compared to controls, mice fed the MCD diet develop a significant steatohepatitis, have enhanced glucose tolerance and enhanced systemic response to insulin. PGZ did not affect the systemic insulin sensitivity in control or MCD-fed mice as assessed in vivo by intraperitoneal glucose or insulin dynamic tests. However, PGZ prevented hepatic fat accumulation and steatohepatitis induced by the MCD diet. This effect was associated with an increased mass of adipose tissue and increased expression and release of adiponectin, while hepatic acyl co-enzyme A oxidase and acyl-co-enzyme A carboxylase, regulating hepatic beta-oxidation of fatty acid, remained unchanged. Steatohepatitis in MCD-diet-fed mice was associated with intrahepatic insulin resistance as shown by a reduced phosphorylation of hepatic insulin receptor, and Akt in response to an insulin stimulus. PGZ to MCD-fed mice restored the activation of the insulin receptor and of the Akt pathway in response to insulin. In conclusion, PGZ alleviates steatosis and steatohepatitis induced by the MCD diet, an effect associated with correction of intrahepatic insulin resistance.

Plasma adiponectin concentrations in non-pregnant, normal and overweight pregnant women

AIMS

Adiponectin is an adipokine that has anti-diabetic, anti-atherogenic, anti-inflammatory and angiogenic properties. This hormone has been implicated in both the physiological adaptation to normal pregnancy and in obstetrical complications. The aims of this study were to determine normal maternal plasma concentrations of adiponectin throughout gestation and to explore the relationships between plasma adiponectin concentration, pregnancy, and maternal overweight.

METHODS

A cross-sectional study was designed to include normal pregnant (normal weight and overweight; 11-42 weeks of gestation), and non-pregnant women. Plasma adiponectin concentration was determined by immunoassay. Non-parametric statistics were used for analysis.

RESULTS

(1) Adiponectin was detectable in the plasma of all patients; (2) there was no significant differences in the median adiponectin concentration between pregnant and non-pregnant women; (3) plasma adiponectin concentrations were negatively correlated with gestational age only among normal weight pregnant women; and (4) overweight patients had significantly lower plasma adiponectin concentrations than normal weight women.

CONCLUSIONS

Consistent with the increased insulin resistance and weight gain that occur in pregnancy, adiponectin concentrations were negatively correlated with gestational age. The results of this study and the nomogram herein presented, can serve as the basis to explore the relationship between adiponectin and pregnancy complications and facilitate the clinical use of this important adipokine.

Chronic treatment with pioglitazone does not protect obese patients with diabetes mellitus type II from free fatty acid-induced insulin resistance

CONTEXT

Thiazolidinediones increase peripheral insulin sensitivity and decrease plasma free fatty acids (FFA). However, their exact mechanism of action has not been fully elucidated.

OBJECTIVE

We studied the protective effect of pioglitazone on FFA-induced insulin resistance and the effects on intramyocellular glycosphingolipids.

DESIGN

We studied glucose metabolism in the basal state and during a hyperinsulinemic euglycemic clamp by using stable isotopes. Studies were performed at baseline and after 4 months of treatment with pioglitazone. Patients were then studied on a third occasion during infusion of a lipid emulsion to increase plasma FFA to pretreatment levels. All studies were combined with muscle biopsies to measure intramyocellular ceramide and glycosphingolipids.

PATIENTS

Patients were obese with poorly controlled type 2 diabetes mellitus.

INTERVENTION

Patients were treated with 30 mg pioglitazone once daily.

MAIN OUTCOME MEASURE

The change in peripheral insulin sensitivity after treatment with pioglitazone and during the infusion of the lipid emulsion was the main outcome measure.

RESULTS

Peripheral glucose uptake (Rd) increased significantly, but returned to baseline levels after increasing plasma FFA to pretreatment levels. Insulin-mediated suppression of FFA was increased significantly. Intramyocellular ceramide concentrations were higher during the hyperinsulinemic clamp after treatment with pioglitazone, but not in the basal state. The intramyocellular content of glycosphingolipids and plasma concentrations of ceramide and glycosphingolipids did not change.

CONCLUSIONS

Pioglitazone increases Rd and insulin-mediated suppression of plasma FFA, but does not protect patients with type 2 diabetes mellitus from FFA-induced insulin resistance. This effect of pioglitazone is not attained via a decrease in intramyocellular concentrations of ceramide or glycosphingolipids.

The metabolic syndrome: A high-risk state for cancer?

The metabolic syndrome is composed of cardiovascular risk factors including increased body mass index/waist circumference, blood pressure, plasma glucose, and triglycerides, as well as decreased high-density lipoprotein cholesterol. The essence of the metabolic syndrome lies in the clustering of these risk factors, which are associated with cardiovascular disease. Interestingly, most of the components of the metabolic syndrome have individually been linked in some way to the development of cancer. However, epidemiological studies linking the metabolic syndrome to cancer are scarce. Nevertheless, two such studies indicate that the clustering of metabolic syndrome components significantly increases the risk of colon cancer mortality compared with the individual components. The purpose of this review is to further explore the potential relationship between the metabolic syndrome and cancer risk. Specifically, we examine the hypothesis that individual components of the metabolic syndrome contribute to the development of several processes, including insulin resistance, aromatase activity, adipokine production, angiogenesis, glucose utilization, and oxidative stress/DNA damage, which can work together to increase cancer risk beyond that of the individual components alone. We propose that the metabolic syndrome be considered as a high-risk state for certain types of cancer and that this relationship should be systematically explored across cancer types.

High molecular weight, rather than total, adiponectin levels better reflect metabolic abnormalities associated with childhood obesity

CONTEXT

Japanese are prone to obesity-induced metabolic derangement, which is linked to serum adipocytokine profile even in children.

OBJECTIVE

The objective of the study was to determine whether high molecular-weight adiponectin (H-Adn) more specifically relates to metabolic derangement in obese children than total adiponectin (T-Adn).

DESIGN AND SETTING

A case (n = 59) control (n = 28) study was performed at the pediatric clinic of a university hospital.

PATIENTS

Japanese obese children (38 boys and 21 girls) were consecutively enrolled. The ages ranged from 5 to 15 (10.3 +/- 0.3; mean +/- sem) yr. Nonobese children (15 boys and 13 girls) were assigned as age-matched controls.

MAIN OUTCOME MEASURES

Serum adiponectin multimeric complexes were assayed by an ELISA kit. The relationship of adiponectin to metabolic abnormalities was evaluated.

RESULTS

T-Adn (5.1 +/- 0.2 vs. 8.8 +/- 0.4 microg/ml), H-Adn (1.3 +/- 0.1 vs. 4.8 +/- 0.4 microg/ml), and medium molecular weight-Adn were significantly lower in obese than in control children. After adjustment for age and sex, both T- and H-Adn were inversely correlated with insulin and homeostasis model of assessment-insulin resistance, whereas H-Adn (but not T-Adn) inversely correlated with visceral fat area, as determined by computed tomography. Seven obese children were estimated to have metabolic syndrome and showed selective decrease in H-Adn and H/T-Adn.

CONCLUSION

H-Adn reflects metabolic abnormalities due to obesity better than T-Adn in children. H-Adn is associated with the development of metabolic syndrome, even in childhood.

Effects of pioglitazone and metformin on plasma adiponectin in newly detected type 2 diabetes mellitus

OBJECTIVE

This prospective study evaluates the effect of insulin sensitizers, pioglitazone (PGZ) and metformin (MET) on plasma adiponectin and leptin levels in subjects newly diagnosed with type 2 diabetes mellitus (T2DM).

DESIGN

Double blind, randomized, active control, dose escalation study of 12 weeks treatment duration.

PATIENTS

Thirty apparently healthy, treatment-naive T2DM patients diagnosed within the past 6 months.

MEASUREMENTS

Plasma adiponectin and leptin levels were estimated by enzyme-linked immunosorbent assay (ELISA), and insulin resistance by the homeostasis model of assessment (HOMA-IR).

RESULTS

Baseline plasma levels of adiponectin were lower in diabetic (n = 30) subjects than matched controls (n = 10, 6.6 +/- 1.1 vs 10.4 +/- 4.2 microg/ml, P = 0.021). The 12-week treatment with PGZ significantly increased adiponectin concentrations (6.6 +/- 1.1-17.9 +/- 7.4 microg/ml, P < 0.001) with no alteration in the MET treated group (6.8 +/- 1.5-6.7 +/- 2.8 microg/ml, P = 0.9). A significant decrease in plasma leptin levels was observed in the MET treated group (32.0 +/- 28.9-21.4 +/- 23.3 ng/ml, P = 0.024) but not in the PGZ treated group (23.9 +/- 24.1-22.4 +/- 25.4 ng/ml, P = 0.69). The alterations in plasma adiponectin and leptin levels were not associated with any change in body mass index (BMI). PGZ therapy improved insulin sensitivity to a greater degree (P = 0.007 and P = 0.001 for fasting plasma insulin (FPI) and HOMA-IR, respectively) than MET (P = 0.75 and P = 0.02 for FPI and HOMA-IR, respectively) but this improvement was not significantly different from that of MET at the end of 12 weeks (P = 0.146 and P = 0.09 for FPI and HOMA-IR, respectively). However, improvement in insulin sensitivity with PGZ was not commensurate with the increase in adiponectin. Better control of postbreakfast plasma glucose (PBPG) as well as decrease in serum triglycerides (TGs) were also seen with PGZ (PBPG, P < 0.001; TGs, P = 0.013). The rest of the parameters were comparable. Adverse reactions reported were minor and did not result in treatment discontinuation.

CONCLUSIONS

Pioglitazone therapy appears to be better in achieving glycaemic control and increasing plasma adiponectin and insulin sensitivity in newly detected type 2 diabetics.

Brain adipocytokine action and metabolic regulation

Adipose tissue secretes factors that control various physiological systems. The fall in leptin during fasting mediates hyperphagia and suppresses thermogenesis, thyroid and reproductive hormones, and immune system. On the other hand, rising leptin levels in the fed state stimulate fatty acid oxidation, decrease appetite, and limit weight gain. These divergent effects of leptin occur through neuronal circuits in the hypothalamus and other brain areas. Leptin also regulates the activities of enzymes involved in lipid metabolism, e.g., AMP-activated protein kinase and stearoyl-CoA desaturase-1, and also interacts with insulin signaling in the brain. Adiponectin enhances fatty acid oxidation and insulin sensitivity, in part by stimulating AMP-activated protein kinase phosphorylation and activity in liver and muscle. Moreover, adiponectin decreases body fat by increasing energy expenditure and lipid catabolism. These effects involve peripheral and possibly central mechanisms. Adipose tissue mediates interconversion of steroid hormones and secretes proinflammatory cytokines, vasoactive peptides, and coagulation and complement proteins. Understanding the actions of these "adipocytokines" will provide insight into the pathogenesis and treatment of obesity and related diseases.

A new type of orally active anti-diabetic Zn(II)-dithiocarbamate complex

In order to find orally active Zn(II) complexes that can treat diabetes mellitus (DM) at low doses, four new Zn(II)-dithiocarbamate complexes with Zn(II)-sulfur coordination bonds were prepared and their in vitro insulinomimetic activity and in vivo anti-diabetic ability were evaluated. Among the Zn(II)-dithiocarbamate complexes, the bis(pyrrolidine-N-dithiocarbamate)zinc(II) (Zn(pdc)(2)) complex was found to be the most effective in terms of inhibiting free fatty acid-release and enhancing glucose-uptake in adipocytes. After oral administration of the Zn(pdc)(2) complex to KK-A(y) mice with obesity and type 2 DM, we observed that the high blood glucose levels in the mice were lowered from approximately 500 mg/dL to 350 mg/dL within 6 days, and the effect was maintained during the administration period. Also, indicators of insulin resistance such as serum insulin, leptin, and triglyceride levels were also reduced compared with those in untreated mice. Moreover, the Zn(pdc)(2) complex improved not only the hypertension in the mice, but also the adiponectin level in the serum. On the basis of the results, the Zn(pdc)(2) complex is proposed to improve hyperglycemia and insulin resistance in type 2 DM animals on daily oral administrations.

SIRT1 regulates adiponectin gene expression through Foxo1-C/enhancer-binding protein alpha transcriptional complex

Adiponectin is an adipose-derived hormone that plays an important role in maintaining energy homeostasis. Adiponectin gene expression is diminished in both obesity and type 2 diabetes. However, the mechanism underlying the impaired adiponectin gene expression remains poorly understood. Recent studies have indicated that forkhead transcription factor O1 (Foxo1) and silent information regulator 2 mammalian ortholog SIRT1 are involved in adipogenesis. Here we have shown that Foxo1 up-regulates adiponectin gene transcription through a Foxo1-responsive region in the mouse adiponectin promoter that contains two adjacent Foxo1 binding sites. Foxo1 interacts with CCAAT/enhancer-binding protein alpha (C/EBPalpha) to form a transcription complex at the mouse adiponectin promoter and up-regulates adiponectin gene transcription. Our study has revealed that C/EBPalpha accesses the adiponectin promoter through two Foxo1 binding sites and acts as a co-activator. Further, SIRT1 increases adiponectin transcription in adipocytes by activating Foxo1 and enhancing Foxo1 and C/EBPalpha interaction. Importantly, both Foxo1 and SIRT1 protein levels were significantly lower in epididymal fat tissues from db/db and high fat diet-induced obese mice compared with normal mice. We propose that low expression of SIRT1 and Foxo1 leads to impaired Foxo1-C/EBPalpha complex formation, which contributes to the diminished adiponectin expression in obesity and type 2 diabetes.

Differential regulation of adiponectin receptor gene expression by adiponectin and leptin in myotubes derived from obese and diabetic individuals

OBJECTIVE

This study aimed to investigate the regulation of adiponectin receptors 1 (AdipoR1) and 2 (AdipoR2) gene expression in primary skeletal muscle myotubes, derived from human donors, after exposure to globular adiponectin (gAd) and leptin.

RESEARCH METHODS AND PROCEDURES

Four distinct primary cell culture groups were established [Lean, Obese, Diabetic, Weight Loss (Wt Loss); n = 7 in each] from rectus abdominus muscle biopsies obtained from surgical patients. Differentiated myotube cultures were exposed to gAd (0.1 microg/mL) or leptin (2.5 microg/mL) for 6 hours. AdipoR1 and AdipoR2 gene expression was measured by real-time polymerase chain reaction analysis.

RESULTS

AdipoR1 mRNA expression in skeletal muscle myotubes derived from Lean subjects (p < 0.05) was stimulated 1.8-fold and 2.5-fold with gAd and leptin, respectively. No increase in AdipoR1 gene expression was measured in myotubes derived from Obese, Diabetic, or Wt Loss subjects. AdipoR2 mRNA expression was unaltered after gAd and leptin exposure in all myotube groups.

DISCUSSION

Adiponectin and leptin are rapid and potent stimulators of AdipoR1 in myotubes derived from lean healthy individuals. This effect was abolished in myotubes derived from obese, obese diabetic subjects, and obese-prone individuals who had lost significant weight after bariatric surgery. The incapacity of skeletal muscle of obese and diabetic individuals to respond to exogenous adiponectin and leptin may be further suppressed as a result of impaired regulation of the AdipoR1 gene.

Adiponectin and mortality in patients undergoing coronary angiography

CONTEXT

The adipokine adiponectin has been suggested to protect against coronary artery disease (CAD). However, studies addressing the association between adiponectin and mortality are sparse.

OBJECTIVE

The objective of the study was to elucidate the relationship between adiponectin and mortality.

DESIGN, SETTING, AND PARTICIPANTS

Adiponectin was determined in 2473 persons with and 673 persons without angiographic CAD. During a mean follow-up period of 5.45 yr, 427 persons with CAD and 55 persons without CAD died.

MAIN OUTCOME MEASURE

Hazard ratios for mortality according to adiponectin levels were measured.

RESULTS

Adiponectin was positively related to female gender, age, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, homocysteine, and N-terminal pro-B-type natriuretic peptide. It was inversely related to glomerular filtration rate, body mass index, and triglycerides and was low in diabetes mellitus and CAD. An increase of 1 sd in adiponectin was associated with unadjusted and fully adjusted hazard ratios for death from any cause of 1.31 [95% confidence interval (CI) 1.20-1.42] and 1.22 (95% CI 1.12-1.34), and for death from cardiovascular causes of 1.32 (95% CI 1.19-1.45) and 1.23 (95% CI 1.11-1.37), respectively. In angiographic CAD, stable CAD, and unstable CAD, the predictive value of adiponectin was similar to that in the entire cohort, but it did not attain statistical significance in persons without angiographic CAD. Adiponectin was also positively related to the risk of death from noncardiovascular causes.

CONCLUSIONS

Despite the common view about adiponectin as a protective molecule in cardiovascular disease, high adiponectin independently predicts all-cause, cardiovascular, and noncardiovascular mortality in individuals with CAD.

Adiponectin deficiency does not affect the inflammatory response to endotoxin or concanavalin a in mice

Adiponectin (APN) is an adipocyte-derived protein that regulates insulin sensitivity and displays antiinflammatory activities in a variety of experimental models. The present study aimed at investigating the effect of APN deficiency on the inflammatory response to endotoxin (lipopolysaccharide, LPS) and Concanavalin A (ConA) in vivo in mice. Administration of a high dose of LPS (100 microg/mouse) induced production of comparable amounts of IL-6, TNFalpha, and interferon-gamma in wild-type (WT) and APN knockout (KO) mice. Furthermore, LPS-induced hypoglycemia, anorexia, and body weight loss did not differ between WT and APN KO mice. Administration of a low dose of LPS (100 or 10 ng/g) in association with d-galactosamine induced equivalent mortality rates, hepatotoxicity, and serum IL-6 in WT and APN KO mice. Finally, ConA-induced cytokine production and hepatotoxicity were not significantly different between WT and APN KO mice. These data indicate that--despite its well-described role as an antiinflammatory molecule--endogenous APN does not play a critical role in modulating the inflammatory responses to LPS and ConA in mice.

Circulating concentrations of high-molecular-weight adiponectin are increased following Roux-en-Y gastric bypass surgery

AIMS/HYPOTHESIS

In addition to weight loss, bariatric surgery for severe obesity dramatically alleviates insulin resistance. In this study, we investigated whether circulating concentrations of the high-molecular-weight (HMW) form of adiponectin are increased following gastric bypass surgery. The HMW form is implicated as the multimer responsible for adiponectin's hepatic insulin-sensitising actions.

SUBJECTS AND METHODS

We studied 19 women who were undergoing Roux-en-Y gastric bypass surgery. Studies were conducted prior to, and 1 and 12 months after surgery.

RESULTS

One month after surgery, total plasma adiponectin concentrations were unchanged. Nevertheless, increases in both HMW (by 40+/-15%, p=0.006) and the proportion of adiponectin in the HMW form (from 40+/-2 to 50+/-2%, p<0.0001) were observed. At 12 months, total and HMW adiponectin concentrations were increased by 58+/-8% and 118+/-21%, respectively (both p<0.001). The majority (80%) of the increase of total adiponectin was due to an increase of the HMW form. After adjustment for covariates, increases of HMW and total adiponectin at 12 months were correlated with the decrease of fat mass (HMW, p=0.0076; total, p=0.0302). In subjects with improved insulin sensitivity at 12 months after surgery (n=18), the increase of HMW, but not that of total adiponectin, predicted the relative decrease of insulin resistance (HMW: p=0.0044; total: p=0.0775, after adjustment for covariates).

CONCLUSIONS/INTERPRETATION

These data suggest that the reduction of fat mass following gastric bypass surgery is an important determinant of the increase of HMW adiponectin concentrations, which in turn is associated with and may contribute to the resulting improvement of insulin sensitivity.

Lipocalin-2 is an inflammatory marker closely associated with obesity, insulin resistance, and hyperglycemia in humans

BACKGROUND

Lipocalin-2, a 25-kDa secreted glycoprotein, is a useful biomarker for early detection of various renal injuries. Because lipocalin-2 is abundantly expressed in adipose tissue and liver, we investigated its relevance to obesity-related pathologies.

METHODS

We used real-time PCR and in-house immunoassays to quantify the mRNA and serum concentrations of lipocalin-2 in C57BL/KsJ db/db obese mice and their age- and sex-matched lean littermates. We analyzed the association between serum lipocalin-2 concentrations and various metabolic and inflammatory variables in 229 persons (121 men and 108 women) recruited from a previous cross-sectional study, and we evaluated the effect of the insulin-sensitizing drug rosiglitazone on serum lipocalin-2 concentrations in 32 diabetic patients (21 men and 11 women).

RESULTS

Compared with the lean littermates, lipocalin-2 mRNA expression in adipose tissue and liver and its circulating concentrations were significantly increased in db/db diabetic/obese mice (P <0.001). These changes were normalized after rosiglitazone treatment. In humans, circulating lipocalin-2 concentrations were positively correlated (P <0.005) with adiposity, hypertriglyceridemia, hyperglycemia, and the insulin resistance index, but negatively correlated (P = 0.002) with HDL cholesterol. There was also a strong positive association between lipocalin-2 concentrations and high sensitivity C-reactive protein (hs-CRP), independent of age, sex, and adiposity (P = 0.007). Furthermore, rosiglitazone-mediated decreases in lipocalin-2 concentrations correlated significantly with increases in insulin sensitivity (r = 0.527; P = 0.002) and decreases in hs-CRP concentrations (r = 0.509; P = 0.003).

CONCLUSIONS

Lipocalin-2 is an inflammatory marker closely related to obesity and its metabolic complications. Measurement of serum lipocalin-2 might be useful for evaluating the outcomes of various clinical interventions for obesity-related metabolic and cardiovascular diseases.

Area postrema neurons are modulated by the adipocyte hormone adiponectin

Adiponectin is an adipocyte-derived peptide hormone involved in energy homeostasis and the pathogenesis of obesity, including hypertension. Area postrema (AP) lacks a blood-brain barrier and is a critical homeostatic integration center for humoral and neural signals. Here we investigate the role of AP in adiponectin signaling. We show that rat AP expresses AdipoR1 and AdipoR2 adiponectin receptor mRNA. We used current-clamp electrophysiology to investigate whether adiponectin influenced membrane properties of AP neurons and found that approximately 60% of rat AP neurons tested were sensitive to adiponectin. Additional electrophysiology experiments coupled with single-cell reverse transcription-PCR indicated that all neurons that expressed both subtypes of receptor were sensitive to adiponectin, whereas neurons expressing only one subtype were predominantly insensitive. Last, microinjection of adiponectin into AP caused significant increases in arterial blood pressure, with no change in heart rate, suggesting that adiponectin acts at AP to provide a possible link between control of energy homeostasis and cardiovascular function.

Adipokines and treatment with niacin

Adipokines may serve as an important etiologic link between atherosclerosis and obesity. Because adipose tissue is one site of action of the lipid-lowering drug niacin, we investigated whether niacin treatment would affect not only lipids but also adipokines. Twenty-four patients were treated with extended-release niacin. During the first 4 weeks the daily dose was increased at weekly intervals from 375 to 1000 mg, which was maintained for 4 weeks. Thereafter, the dose was 1500 mg for another 6 weeks. Adiponectin increased by 54% and 94%, respectively, resistin was lowered only moderately, and leptin not at all. Because adiponectin has repeatedly been shown to be negatively associated with atherosclerotic risk, its pronounced increase may bring about additional atheroprotection by niacin beyond its improvement in lipids.

Aldehyde oxidase 1 is highly abundant in hepatic steatosis and is downregulated by adiponectin and fenofibric acid in hepatocytes in vitro

Adiponectin protects the liver from steatosis caused by obesity or alcohol and therefore the influence of adiponectin on human hepatocytes was analyzed. GeneChip experiments indicated that recombinant adiponectin downregulates aldehyde oxidase 1 (AOX1) expression and this was confirmed by real-time RT-PCR and immunoblot. AOX1 is a xenobiotic metabolizing protein and produces reactive oxygen species (ROS), that promote cell damage and fibrogenesis. Adiponectin and fenofibric acid activate peroxisome proliferator-activated receptor-alpha (PPAR-alpha) and both suppress AOX1 protein and this is blocked by the PPAR-alpha antagonist RU486. Obesity is associated with low adiponectin, reduced hepatic PPAR-alpha activity and fatty liver, and AOX1 was found induced in the liver of rats on a high-fat diet when compared to controls. Free fatty acids and leptin, that are elevated in obesity, failed to upregulate AOX1 in vitro. The current data indicate that adiponectin reduces AOX1 by activating PPAR-alpha whereas fatty liver disease is associated with elevated hepatic AOX1. High AOX1 may be associated with higher ROS well described to induce fibrogenesis in liver tissue but may also influence drug metabolism and activity.

Adiponectin and adiponectin receptors in insulin resistance, diabetes, and the metabolic syndrome

Adiponectin is an adipokine that is specifically and abundantly expressed in adipose tissue and directly sensitizes the body to insulin. Hypoadiponectinemia, caused by interactions of genetic factors such as SNPs in the Adiponectin gene and environmental factors causing obesity, appears to play an important causal role in insulin resistance, type 2 diabetes, and the metabolic syndrome, which are linked to obesity. The adiponectin receptors, AdipoR1 and AdipoR2, which mediate the antidiabetic metabolic actions of adiponectin, have been cloned and are downregulated in obesity-linked insulin resistance. Upregulation of adiponectin is a partial cause of the insulin-sensitizing and antidiabetic actions of thiazolidinediones. Therefore, adiponectin and adiponectin receptors represent potential versatile therapeutic targets to combat obesity-linked diseases characterized by insulin resistance. This Review describes the pathophysiology of adiponectin and adiponectin receptors in insulin resistance, diabetes, and the metabolic syndrome.

Mechanisms of Disease: hepatic steatosis in type 2 diabetes--pathogenesis and clinical relevance

Hepatic steatosis is defined by an increased content of hepatocellular lipids (HCLs) and is frequently observed in insulin-resistant states including type 2 diabetes mellitus. A dietary excess of saturated fat contributes significantly to HCL accumulation. Elevated HCL levels mainly account for hepatic insulin resistance, which is probably mediated by partitioning of free fatty acids to the liver (fat overflow) and by an imbalance of adipocytokines (decreased adiponectin and/or increased proinflammatory cytokines). Both free fatty acids and adipocytokines activate inflammatory pathways that include protein kinase C, the transcription factor nuclear factor kappaB, and c-Jun N-terminal kinase 1 and can thereby accelerate the progression of hepatic steatosis to nonalcoholic steatohepatitis and cirrhosis. Proton magnetic resonance spectroscopy has made it possible to quantify HCL concentrations and to detect even small changes in these concentrations in clinical settings. Moderately hypocaloric, fat-reduced diets can decrease HCL levels by approximately 40-80% in parallel with loss of up to 8% of body weight. Treatment with thiazolidinediones (e.g. pioglitazone and rosiglitazone) reduces HCL levels by 30-50% by modulating insulin sensitivity and endocrine function of adipose tissue in type 2 diabetes. Metformin improves hepatic insulin action without affecting HCL levels, whereas insulin infusion for 67 h increases HCL levels by approximately 18%; furthermore, HCL levels positively correlate with the insulin dosage in insulin-treated type 2 diabetes. In conclusion, liver fat is a critical determinant of metabolic fluxes and inflammatory processes, thereby representing an important therapeutic target in insulin resistance and type 2 diabetes mellitus.

Diabetes mellitus and periodontal diseases

BACKGROUND

The purpose of this review is to provide the reader with practical knowledge concerning the relationship between diabetes mellitus and periodontal diseases. Over 200 articles have been published in the English literature over the past 50 years examining the relationship between these two chronic diseases. Data interpretation is often confounded by varying definitions of diabetes and periodontitis and different clinical criteria applied to prevalence, extent, and severity of periodontal diseases, levels of glycemic control, and complications associated with diabetes.

METHODS

This article provides a broad overview of the predominant findings from research published in English over the past 20 years, with reference to certain "classic" articles published prior to that time.

RESULTS

This article describes current diagnostic and classification criteria for diabetes and answers the following questions: 1) Does diabetes affect the risk of periodontitis, and does the level of metabolic control of diabetes have an impact on this relationship? 2) Do periodontal diseases affect the pathophysiology of diabetes mellitus or the metabolic control of diabetes? 3) What are the mechanisms by which these two diseases interrelate? and 4) How do people with diabetes and periodontal disease respond to periodontal treatment?

CONCLUSIONS

Diabetes increases the risk of periodontal diseases, and biologically plausible mechanisms have been demonstrated in abundance. Less clear is the impact of periodontal diseases on glycemic control of diabetes and the mechanisms through which this occurs. Inflammatory periodontal diseases may increase insulin resistance in a way similar to obesity, thereby aggravating glycemic control. Further research is needed to clarify this aspect of the relationship between periodontal diseases and diabetes.

Salivary gland epithelial cells: a new source of the immunoregulatory hormone adiponectin

OBJECTIVE

Adiponectin is an adipocytokine that displays insulin-sensitizing and immunoregulatory properties. Adipocyte development in association with fibrosis is frequently detected in primary Sjögren's syndrome lesions, connoting a healing process. The aim of this study was to examine the expression of adiponectin in minor salivary gland biopsy specimens obtained from patients with primary SS and controls.

METHODS

The expression of adiponectin in minor salivary gland biopsy specimens and in long-term-cultured non-neoplastic salivary gland epithelial cell (SGEC) lines obtained from patients with primary SS and control subjects was examined, using immunohistochemistry and immunoblotting, respectively. The expression of adiponectin, adiponectin receptor 1 (AdipoR1), and AdipoR2 messenger RNA (mRNA) by SGECs was investigated by reverse transcription-polymerase chain reaction.

RESULTS

Immunohistochemical analysis for adiponectin revealed positive staining of adipocytes from primary SS lesions as well as ductal epithelial cells from both patients with primary SS and controls. All of the SGEC lines tested were shown to express adiponectin, AdipoR1, and AdipoR2 mRNA, whereas adiponectin protein expression was detected by immunoblotting in SGECs from patients with primary SS but not in those from controls. The analysis of concentrated culture supernatants also revealed increased adiponectin expression by SGECs from patients with SS compared with controls.

CONCLUSION

Our findings provide novel evidence that adiponectin is produced by SGECs. The high constitutive expression of adiponectin by SGECs from patients with primary SS is likely attributable to aberrant activation of these cells. Although the significance of adiponectin expression remains unknown, it is possible that adiponectin functions in an autocrine manner, as suggested by concurrent expression of the relevant receptors.

Plane of nutrition prepartum alters hepatic gene expression and function in dairy cows as assessed by longitudinal transcript and metabolic profiling

Liver metabolism and health in dairy cows during the periparturient period are affected by plane of nutrition prepartum. Long-term adaptations in hepatic gene expression are important for complete understanding of liver function. We examined temporal gene expression profiles during the dry period and early lactation in liver of Holstein cows fed moderate dietary energy ad libitum or restricted during the entire dry period using a microarray consisting of 7,872 annotated cattle cDNA inserts and quantitative RT-PCR. We identified 85 genes with expression patterns that were affected by level of energy intake prepartum over time. Restricted energy intake prepartum resulted in more pronounced upregulation of genes with key functions in hepatic fatty acid oxidation ( CPT1A, ADIPOR2), gluconeogenesis ( PC), and cholesterol synthesis ( SC4MOL). Ad libitum feeding upregulated a number of genes associated with liver triacylglycerol synthesis ( DGAT1) and proinflammatory cytokines ( TNFAIP3). Genomic responses to ad libitum feeding were accompanied by increased incorporation of palmitate to esterified products in vitro and increased liver triacylglycerol concentration in vivo. Overall, gene expression profiles due to plane of nutrition prepartum partly explained differences in rates of liver palmitate metabolism, blood serum metabolite concentrations, and liver tissue triacylglycerol concentration. Our data show that moderate overfeeding of energy in the dry period, in the absence of obesity, results in transcriptional changes predisposing cows to fatty liver and perhaps compromising overall liver health during the periparturient period. In this context, controlled energy intake may confer an advantage to the cow by triggering hepatic molecular adaptations well ahead of parturition.

Reduced levels of adiponectin in sleep apnea syndrome

BACKGROUND

To investigate adiponectin levels in an obese population with and without obstructive sleep apnea syndrome (OSAS) and the acute modifications in adiponectin after a whole-night control by auto continuous positive air pressure (CPAP).

METHODS

46 obese subjects [22 males, 24 females, age 55.1+/-11.4 yr, body mass index (BMI) 38.9+/-6.5 kg/m2]: 11 OSAS with apnea/hypopnea index (AHI) from 10/h to 30/h, 14 OSAS with AHI >30/h and 21 without OSAS. Thirty-seven normal weight healthy subjects (20 males, 17 females, age 31.3+/-9.5 yr, BMI 21.5+/-1.8 kg/m2). Serum adiponectin levels, biochemical parameters, anthropometric measurements, pulmonary function, pulse-oxymetry and polisomnography.

RESULTS

The 3 groups of obese patients were comparable for gender, BMI, age, fat mass, fat free mass, hip and waist circumference, waist-to-hip ratio (WHR), systolic and diastolic blood pressure and glycometabolic parameters. Adiponectin levels were significantly reduced in obese patients compared to healthy normal weight subjects (8.1+/-3.5 vs 11.3+/-4.8 microg/ml p<0.001) In particular, adiponectin showed a trend to decrease according to the severity of OSAS. No differences in adiponectin levels were found after a whole-night control by Auto CPAP.

CONCLUSIONS

OSAS is associated with reduced levels of adiponectin independently of insulin-resistance and BMI. These low adiponectin levels may contribute to the increased mortality seen in such patients.

Adiponectin increases fatty acid oxidation in skeletal muscle cells by sequential activation of AMP-activated protein kinase, p38 mitogen-activated protein kinase, and peroxisome proliferator-activated receptor alpha

Adiponectin has recently received a great deal of attention due to its beneficial effects on insulin resistance and metabolic disorders. One of the mechanisms through which adiponectin exerts such effects involves an increase in fatty acid oxidation in muscle and liver. In the present study, we demonstrate that 5'-AMP-activated protein kinase (AMPK) and p38 mitogen-activated protein kinase (MAPK) are involved in the activation of peroxisome proliferator-activated receptor (PPAR)alpha by adiponectin in muscle cells. Adiponectin increases the transcriptional activity of PPARalpha and the expression of its target genes, including ACO, CPT1, and FABP3 in C2C12 myotubes. These effects were suppressed by the overexpression of a dominant-negative form of AMPK. Moreover, chemical inhibitors of AMPK and p38 MAPK potently repressed fatty acid oxidation and the induction of PPARalpha target gene expression by adiponectin. Interestingly, araA, an AMPK inhibitor, prevented the activation of p38 MAPK, whereas SB203580, a p38 MAPK inhibitor, did not affect AMPK activation, suggesting that p38 MAPK is a downstream signaling factor of AMPK. Taken together, these results suggest that adiponectin stimulates fatty acid oxidation in muscle cells by the sequential activation of AMPK, p38 MAPK, and PPARalpha.

Systemic and brain metabolic dysfunction as a new paradigm for approaching Alzheimer's dementia

Since its definition Alzheimer's disease has been at the centre of consideration for neurologists, psychiatrists, and pathologists. With John P. Blass it has been disclosed a different approach Alzheimer's disease neurodegeneration understanding not only by the means of neurochemistry but also biochemistry opening new scenarios in the direction of a metabolic system degeneration. Nowadays, the understanding of the role of cholesterol, insulin, and adipokines among the others in Alzheimer's disease etiopathogenesis is clarifying approaches valuable not only in preventing the disease but also for its therapy.

Orphan nuclear receptors: therapeutic opportunities in skeletal muscle

Nuclear hormone receptors (NRs) are ligand-dependent transcription factors that bind DNA and translate physiological signals into gene regulation. The therapeutic utility of NRs is underscored by the diversity of drugs created to manage dysfunctional hormone signaling in the context of reproductive biology, inflammation, dermatology, cancer, and metabolic disease. For example, drugs that target nuclear receptors generate over $10 billion in annual sales. Almost two decades ago, gene products were identified that belonged to the NR superfamily on the basis of DNA and protein sequence identity. However, the endogenous and synthetic small molecules that modulate their action were not known, and they were denoted orphan NRs. Many of the remaining orphan NRs are highly enriched in energy-demanding major mass tissues, including skeletal muscle, brown and white adipose, brain, liver, and kidney. This review focuses on recently adopted and orphan NR function in skeletal muscle, a tissue that accounts for approximately 35% of the total body mass and energy expenditure, and is a major site of fatty acid and glucose utilization. Moreover, this lean tissue is involved in cholesterol efflux and secretes that control energy expenditure and adiposity. Consequently, muscle has a significant role in insulin sensitivity, the blood lipid profile, and energy balance. Accordingly, skeletal muscle plays a considerable role in the progression of dyslipidemia, diabetes, and obesity. These are risk factors for cardiovascular disease, which is the the foremost cause of global mortality (>16.7 million deaths in 2003). Therefore, it is not surprising that orphan NRs and skeletal muscle are emerging as therapeutic candidates in the battle against dyslipidemia, diabetes, obesity, and cardiovascular disease.

Association of sequence variations in the gene encoding adiponectin receptor 1 (ADIPOR1) with body size and insulin levels. The Finnish Diabetes Prevention Study

AIMS/HYPOTHESIS

Adiponectin is a circulating peptide derived from adipose tissue. It mediates its insulin-sensitising and anti-atherogenic effects on target tissues through two known receptors, adiponectin receptors 1 and 2 (ADIPOR1; ADIPOR2), which are encoded by the genes ADIPOR1 and ADIPOR2. Our aim was to study the association of ADIPOR1 gene variations with body size and risk of type 2 diabetes in subjects with impaired glucose tolerance, who participated in the Finnish Diabetes Prevention Study (DPS).

SUBJECTS AND METHODS

We selected seven single nucleotide polymorphisms (SNPs) of the ADIPOR1 gene to perform association studies with anthropometrics and metabolic parameters at baseline, and with the risk of type 2 diabetes during the 3-year follow-up in the DPS study population. Both single SNP analysis and haplotype effects were studied.

RESULTS

Three out of seven markers studied (rs10920534, rs22757538 and rs1342387) were significantly associated with various body size measurements including weight, height, waist and hip circumference, sagittal diameter and body mass index. Furthermore, three markers (rs10920534, rs12045862 and rs7539542), of which two were different from those associating with body size, were linked to fasting and 2-h insulin levels, particularly in men at baseline. The haplotype analysis with five markers revealed seven major haplotypes in the DPS study population. The haplotype effects on body size measures were in line with those of single SNP analysis. However, none of the markers were associated with the risk of type 2 diabetes.

CONCLUSIONS/INTERPRETATION

Our findings suggest that ADIPOR1 has a putative role in the development of body size, and that traits for central adiposity and insulin resistance may be dissociated from each other.

MKR mice are resistant to the metabolic actions of both insulin and adiponectin: discordance between insulin resistance and adiponectin responsiveness

Most rodent models of insulin resistance are accompanied by decreased circulating adiponectin levels. Adiponectin treatment improves the metabolic phenotype by increasing fatty acid oxidation in skeletal muscle and suppressing hepatic glucose production. Muscle IGF-I receptor (IGF-IR)-lysine-arginine (MKR) mice expressing dominant-negative mutant IGF-IRs in skeletal muscle are diabetic with insulin resistance in muscle, liver, and adipose tissue. Adiponectin levels are elevated in MKR mice, suggesting an unusual discordance between insulin resistance and adiponectin responsiveness. Therefore, we investigated the metabolic actions of adiponectin in MKR mice. MKR and ob/ob mice were treated both acutely (28 microg/g) and chronically (for 2 wk) with full-length adiponectin. Acute hypoglycemic effects of adiponectin were evident only in ob/ob mice but not in MKR mice. Chronic adiponectin treatment significantly improved both insulin sensitivity and glucose tolerance in ob/ob but not in MKR mice. Adiponectin receptor mRNA levels and adiponectin-stimulated phosphorylation of AMPK in skeletal muscle and liver were similar among MKR, wild-type, and ob/ob mice. Thus MKR mice are adiponectin resistant despite normal expression of adiponectin receptors and normal AMPK phosphorylation in muscle and liver. MKR mice may be a useful model for dissecting relationships between insulin resistance and adiponectin action in regulation of glucose homeostasis.

Effects of DGAT1 deficiency on energy and glucose metabolism are independent of adiponectin

Mice lacking acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1), an enzyme that catalyzes the terminal step in triacylglycerol synthesis, have enhanced insulin sensitivity and are protected from obesity, a result of increased energy expenditure. In these mice, factors derived from white adipose tissue (WAT) contribute to the systemic changes in metabolism. One such factor, adiponectin, increases fatty acid oxidation and enhances insulin sensitivity. To test the hypothesis that adiponectin is required for the altered energy and glucose metabolism in DGAT1-deficient mice, we generated adiponectin-deficient mice and introduced adiponectin deficiency into DGAT1-deficient mice by genetic crosses. Although adiponectin-deficient mice fed a high-fat diet were heavier, exhibited worse glucose tolerance, and had more hepatic triacylglycerol accumulation than wild-type controls, mice lacking both DGAT1 and adiponectin, like DGAT1-deficient mice, were protected from diet-induced obesity, glucose intolerance, and hepatic steatosis. These findings indicate that adiponectin is required for normal energy, glucose, and lipid metabolism but that the metabolic changes induced by DGAT1-deficient WAT are independent of adiponectin and are likely due to other WAT-derived factors. Our findings also suggest that the pharmacological inhibition of DGAT1 may be useful for treating human obesity and insulin resistance associated with low circulating adiponectin levels.

Adipose tissue as an endocrine organ

Adipose tissue plays a critical role in energy homeostasis, not only in storing triglycerides, but also responding to nutrient, neural, and hormonal signals and secreting adipokines that control feeding, thermogenesis, immunity, and neuroendocrine function. A rise in leptin signals satiety to the brain through receptors in hypothalamic and brainstem neurons. Leptin activates tyrosine kinase, Janus kinase 2, and signal transducer and activator of transcription 3, leading to increased levels of anorexigenic peptides, e.g., alpha-melanocyte stimulating hormone and cocaine- and amphetamine-regulated transcript, and inhibition of orexigenic peptides, e.g., neuropeptide Y and agouti-related peptide. Obesity is characterized by hyperleptinemia and hypothalamic leptin resistance, partly caused by induction of suppressor of cytokine signaling-3. Leptin falls rapidly during fasting and potently stimulates appetite, reduces thermogenesis, and mediates the inhibition of thyroid and reproductive hormones and activation of the hypothalamic-pituitary-adrenal axis. These actions are integrated by the paraventicular hypothalamic nucleus. Leptin also decreases glucose and stimulates lipolysis through central and peripheral pathways involving AMP-activated protein kinase (AMPK). Adiponectin is secreted exclusively by adipocytes and has been linked to glucose, lipid, and cardiovascular regulation. Obesity, diabetes, and atherosclerosis have been associated with reduced adiponectin levels, whereas adiponectin treatment reverses these abnormalities partly through activation of AMPK in liver and muscle. Administration of adiponectin in the brain recapitulates the peripheral actions to increase fatty acid oxidation and insulin sensitivity and reduce glucose. Although putative adiponectin receptors are widespread in peripheral organs and brain, it is uncertain whether adiponectin acts exclusively through these targets. As with leptin, adiponectin requires the central melanocortin pathway. Furthermore, adiponectin stimulates fatty acid oxidation and reduces glucose and lipids, at least in part, by activating AMPK in muscle and liver.

Role of adipose tissue as an inflammatory organ in human diseases

Reviews on the inflammatory role of adipose tissue outside the field of metabolism are rare. There is increasing evidence provided by numerous basic research studies from nearly all internal medicine subspecializations that adipocytes and adipocytokines are involved in primary inflammatory processes and diseases. Therefore, it is the aim of the present review to discuss and to summarize the current knowledge on the inflammatory role of adipocytokines and special types of regional adipocytes such as retroorbital, synovial, visceral, subdermal, peritoneal, and bone marrow adipocytes in internal medicine diseases. Future clinical and therapeutic implications are discussed.