Yukio Arita

Plasma Concentrations of a Novel, Adipose-Specific Protein, Adiponectin, in Type 2 Diabetic Patients

Adiponectin is a novel, adipose-specific protein abundantly present in the circulation, and it has antiatherogenic properties. We analyzed the plasma adiponectin concentrations in age- and body mass index (BMI)-matched nondiabetic and type 2 diabetic subjects with and without coronary artery disease (CAD). Plasma levels of adiponectin in the diabetic subjects without CAD were lower than those in nondiabetic subjects (6.6+/-0.4 versus 7.9+/-0.5 microg/mL in men, 7.6+/-0.7 versus 11.7+/-1.0 microg/mL in women; P<0.001). The plasma adiponectin concentrations of diabetic patients with CAD were lower than those of diabetic patients without CAD (4.0+/-0.4 versus 6.6+/-0.4 microg/mL, P<0.001 in men; 6.3+/-0.8 versus 7.6+/-0. 7 microg/mL in women). In contrast, plasma levels of leptin did not differ between diabetic patients with and without CAD. The presence of microangiopathy did not affect the plasma adiponectin levels in diabetic patients. Significant, univariate, inverse correlations were observed between adiponectin levels and fasting plasma insulin (r=-0.18, P<0.01) and glucose (r=-0.26, P<0.001) levels. In multivariate analysis, plasma insulin did not independently affect the plasma adiponectin levels. BMI, serum triglyceride concentration, and the presence of diabetes or CAD remained significantly related to plasma adiponectin concentrations. Weight reduction significantly elevated plasma adiponectin levels in the diabetic subjects as well as the nondiabetic subjects. These results suggest that the decreased plasma adiponectin concentrations in diabetes may be an indicator of macroangiopathy.

Novel Modulator for Endothelial Adhesion Molecules Adipocyte-Derived Plasma Protein Adiponectin

BACKGROUND Among the many adipocyte-derived endocrine factors, we recently found an adipocyte-specific secretory protein, adiponectin, which was decreased in obesity. Although obesity is associated with increased cardiovascular mortality and morbidity, the molecular basis for the link between obesity and vascular disease has not been fully clarified. The present study investigated whether adiponectin could modulate endothelial function and relate to coronary disease. METHODS AND RESULTS For the in vitro study, human aortic endothelial cells (HAECs) were preincubated for 18 hours with the indicated amount of adiponectin, then exposed to tumor necrosis factor-alpha (TNF-alpha) (10 U/mL) or vehicle for the times indicated. The adhesion of human monocytic cell line THP-1 cells to HAECs was determined by adhesion assay. The surface expression of vascular cell adhesion molecule-1 (VCAM-1), endothelial-leukocyte adhesion molecule-1 (E-selectin), and intracellular adhesion molecule-1 (ICAM-1) was measured by cell ELISA. Physiological concentrations of adiponectin dose-dependently inhibited TNF-alpha-induced THP-1 adhesion and expression of VCAM-1, E-selectin, and ICAM-1 on HAECs. For the in vivo study, the concentrations of adiponectin in human plasma were determined by a sandwich ELISA system that we recently developed. Plasma adiponectin concentrations were significantly lower in patients with coronary artery disease than those in age- and body mass index-adjusted control subjects. CONCLUSIONS These observations suggest that adiponectin modulates endothelial inflammatory response and that the measurement of plasma adiponectin levels may be helpful in assessment of CAD risk.

Diet-induced insulin resistance in mice lacking adiponectin/ACRP30

Here we investigated the biological functions of adiponectin/ACRP30, a fat-derived hormone, by disrupting the gene that encodes it in mice. Adiponectin/ACRP30-knockout (KO) mice showed delayed clearance of free fatty acid in plasma, low levels of fatty-acid transport protein 1 (FATP-1) mRNA in muscle, high levels of tumor necrosis factor-α (TNF-α) mRNA in adipose tissue and high plasma TNF-α concentrations. The KO mice exhibited severe diet-induced insulin resistance with reduced insulin-receptor substrate 1 (IRS-1)-associated phosphatidylinositol 3 kinase (PI3-kinase) activity in muscle. Viral mediated adiponectin/ACRP30 expression in KO mice reversed the reduction of FATP-1 mRNA, the increase of adipose TNF-α mRNA and the diet-induced insulin resistance. In cultured myocytes, TNF-α decreased FATP-1 mRNA, IRS-1-associated PI3-kinase activity and glucose uptake, whereas adiponectin increased these parameters. Our results indicate that adiponectin/ACRP30 deficiency and high TNF-α levels in KO mice reduced muscle FATP-1 mRNA and IRS-1-mediated insulin signaling, resulting in severe diet-induced insulin resistance.

Adiponectin, an Adipocyte-Derived Plasma Protein, Inhibits Endothelial NF-κB Signaling Through a cAMP-Dependent Pathway

BackgroundAmong the many adipocyte-derived endocrine factors, we found an adipocyte-derived plasma protein, adiponectin, that was decreased in obesity. We recently demonstrated that adiponectin inhibited tumor necrosis factor-&agr; (TNF-&agr;)–induced expression of endothelial adhesion molecules and that plasma adiponectin level was reduced in patients with coronary artery disease (Circulation. 1999;100:2473–2476). However, the intracellular signal by which adiponectin suppressed adhesion molecule expression was not elucidated. The present study investigated the mechanism of modulation for endothelial function by adiponectin. Methods and ResultsThe interaction between adiponectin and human aortic endothelial cells (HAECs) was estimated by cell ELISA using biotinylated adiponectin. HAECs were preincubated for 18 hours with 50 &mgr;g/mL of adiponectin, then exposed to TNF-&agr; (10 U/mL) or vehicle for the times indicated. NF-&kgr;B–DNA binding activity was determined by electrophoretic mobility shift assays. TNF-&agr;–inducible phosphorylation signals were detected by immunoblotting. Adiponectin specifically bound to HAECs in a saturable manner and inhibited TNF-&agr;–induced mRNA expression of monocyte adhesion molecules without affecting the interaction between TNF-&agr; and its receptors. Adiponectin suppressed TNF-&agr;–induced I&kgr;B-&agr; phosphorylation and subsequent NF-&kgr;B activation without affecting other TNF-&agr;–mediated phosphorylation signals, including Jun N-terminal kinase, p38 kinase, and Akt kinase. This inhibitory effect of adiponectin is accompanied by cAMP accumulation and is blocked by either adenylate cyclase inhibitor or protein kinase A (PKA) inhibitor. ConclusionsThese observations raise the possibility that adiponectin, which is naturally present in the blood stream, modulates the inflammatory response of endothelial cells through cross talk between cAMP-PKA and NF-&kgr;B signaling pathways.

Association of Hypoadiponectinemia With Coronary Artery Disease in Men

Background—Adiponectin is an adipocyte-derived plasma protein that accumulates in the injured artery and has potential antiatherogenic properties. This study was designed to determine whether a decreased plasma adiponectin level (hypoadiponectinemia) can be independently associated with the prevalence of coronary artery disease (CAD). Methods and Results—The consecutive 225 male patients were enrolled from inpatients who underwent coronary angiography. Voluntary blood donors (n=225) matched for age served as controls. Plasma adiponectin levels in the CAD patients were significantly lower than those in the control subjects. Multiple logistic regression analysis including plasma adiponectin level, diabetes mellitus, dyslipidemia, hypertension, smoking habits, and body mass index revealed that hypoadiponectinemia was significantly and independently correlated with CAD (P <0.0088). The entire study population was categorized in quartiles based on the distribution of plasma adiponectin levels. The interquartile cutoff points were 4.0, 5.5, and 7.0 &mgr;g/mL. The multivariate-adjusted odds ratios for CAD in the first, second, and third quartiles were 2.051 (95% confidence interval [CI], 1.288 to 4.951), 1.221 (95% CI, 0.684 to2.186), and 0.749 (95%CI, 0.392 to 1.418), respectively. Conclusions—Male patients with hypoadiponectinemia (<4.0 &mgr;g/mL) had a significant 2-fold increase in CAD prevalence, independent of well-known CAD risk factors.

Adipocyte-Derived Plasma Protein, Adiponectin, Suppresses Lipid Accumulation and Class A Scavenger Receptor Expression in Human Monocyte-Derived Macrophages

Background —Excessive lipid accumulation in macrophages plays an important role in the development of atherosclerosis. Recently, we discovered an adipocyte-specific plasma protein, adiponectin, that is decreased in patients with coronary artery disease. We previously demonstrated that adiponectin acts as a modulator for proinflammatory stimuli and inhibits monocyte adhesion to endothelial cells. The present study investigated the effects of adiponectin on lipid accumulation in human monocyte-derived macrophages. Methods and Results —Human monocytes were differentiated into macrophages by incubation in human type AB serum for 7 days, and the effects of adiponectin were investigated at different time intervals. Treatment with physiological concentrations of adiponectin reduced intracellular cholesteryl ester content, as determined using the enzymatic, fluorometric method. The adiponectin-treated macrophages contained fewer lipid droplets stained by oil red O. Adiponectin suppressed the expression of the class A macrophage scavenger receptor (MSR) at both mRNA and protein levels by Northern and immunoblot analyses, respectively, without affecting the expression of CD36, which was quantified by flow cytometry. Adiponectin reduced the class A MSR promoter activity, as measured by luciferase reporter assay. Adiponectin treatment dose-dependently decreased class A MSR ligand binding and uptake activities. The mRNA level of lipoprotein lipase as a marker of macrophage differentiation was decreased by adiponectin treatment, but that of apolipoprotein E was not altered. Adiponectin was detected around macrophages in the human injured aorta by immunohistochemistry. Conclusions —The adipocyte-derived plasma protein adiponectin suppressed macrophage-to-foam cell transformation, suggesting that adiponectin may act as a modulator for macrophage-to-foam cell transformation.

Adiponectin Reduces Atherosclerosis in Apolipoprotein E-Deficient Mice

Background—Dysregulation of adipocyte-derived bioactive molecules plays an important role in the development of atherosclerosis. We previously reported that adiponectin, an adipocyte-specific plasma protein, accumulated in the injured artery from the plasma and suppressed endothelial inflammatory response and vascular smooth muscle cell proliferation, as well as macrophage-to-foam cell transformation in vitro. The current study investigated whether the increased plasma adiponectin could actually reduce atherosclerosis in vivo. Methods and Results—Apolipoprotein E-deficient mice were treated with recombinant adenovirus expressing human adiponectin (Ad-APN) or &bgr;-galactosidase (Ad-&bgr;gal). The plasma adiponectin levels in Ad-APN–treated mice increased 48 times as much as those in Ad-&bgr;gal treated mice. On the 14th day after injection, the lesion formation in aortic sinus was inhibited in Ad-APN–treated mice by 30% compared with Ad-&bgr;gal–treated mice (P <0.05). In the lesions of Ad-APN–treated mice, the lipid droplets became smaller compared with Ad-&bgr;gal–treated mice (P <0.01). Immunohistochemical analyses demonstrated that the adenovirus-mediated adiponectin migrate to foam cells in the fatty streak lesions. The real-time quantitative polymerase chain reaction revealed that Ad-APN treatment significantly suppressed the mRNA levels of vascular cell adhesion molecule-1 by 29% and class A scavenger receptor by 34%, and tended to reduce levels of tumor necrosis factor-&agr; without affecting those of CD36 in the aortic tissue. Conclusions—These findings documented for the first time that elevated plasma adiponectin suppresses the development of atherosclerosis in vivo.

Role of adiponectin in preventing vascular stenosis: The missing link of adipo-vascular axis

Obesity is more linked to vascular disease, including atherosclerosis and restenotic change, after balloon angioplasty. The precise mechanism linking obesity and vascular disease is still unclear. Previously we have demonstrated that the plasma levels of adiponectin, an adipose-derived hormone, decreases in obese subjects, and that hypoadiponectinemia is associated to ischemic heart disease. In current the study, we investigated the in vivorole of adiponectin on the neointimal thickening after artery injury using adiponectin-deficient mice and adiponectin-producing adenovirus. Adiponectin-deficient mice showed severe neointimal thickening and increased proliferation of vascular smooth muscle cells in mechanically injured arteries. Adenovirus-mediated supplement of adiponectin attenuated neointimal proliferation. In cultured smooth muscle cells, adiponectin attenuated DNA synthesis induced by growth factors including platelet-derived growth factor, heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF), basic fibroblast growth factor, and EGF and cell proliferation and migration induced by HB-EGF. In cultured endothelial cells, adiponectin attenuated HB-EGF expression stimulated by tumor necrosis factor α. The current study suggests an adipo-vascular axis, a direct link between fat and artery. A therapeutic strategy to increase plasma adiponectin should be useful in preventing vascular restenosis after angioplasty.

Adipocyte-Derived Plasma Protein Adiponectin Acts as a Platelet-Derived Growth Factor-BB–Binding Protein and Regulates Growth Factor–Induced Common Postreceptor Signal in Vascular Smooth Muscle Cell

Background—Vascular smooth muscle cell proliferation plays an important role in the development of atherosclerosis. We previously reported that adiponectin, an adipocyte-specific plasma protein, accumulated in the human injured artery and suppressed endothelial inflammatory response as well as macrophage-to-foam cell transformation. The present study investigated the effects of adiponectin on proliferation and migration of human aortic smooth muscle cells (HASMCs). Methods and Results—HASMC proliferation was estimated by [3H] thymidine uptake and cell number. Cell migration assay was performed using a Boyden chamber. Physiological concentrations of adiponectin significantly suppressed both proliferation and migration of HASMCs stimulated with platelet-derived growth factor (PDGF)-BB. Adiponectin specifically bound to 125I-PDGF-BB and significantly inhibited the association of 125I-PDGF-BB with HASMCs, but no effects were observed on the binding of 125I-PDGF-AA or 125I-heparin–binding epidermal growth factor (EGF)–like growth factor (HB-EGF) to HASMCs. Adiponectin strongly and dose-dependently suppressed PDGF-BB–induced p42/44 extracellular signal–related kinase (ERK) phosphorylation and PDGF &bgr;-receptor autophosphorylation analyzed by immunoblot. Adiponectin also reduced PDGF-AA–stimulated or HB-EGF–stimulated ERK phosphorylation in a dose-dependent manner without affecting autophosphorylation of PDGF &agr;-receptor or EGF receptor. Conclusions—The adipocyte-derived plasma protein adiponectin strongly suppressed HASMC proliferation and migration through direct binding with PDGF-BB and generally inhibited growth factor–stimulated ERK signal in HASMCs, suggesting that adiponectin acts as a modulator for vascular remodeling.

Genomic structure and mutations in adipose-specific gene, adiponectin

BACKGROUND: Adiponectin is a collagen-like plasma protein specifically synthesized in adipose tissue. Plasma adiponectin concentrations are decreased in obesity whereas it is adipose-specific.OBJECTIVE: To clarify the significance of the genetic variations in adiponectin gene on its plasma concentrations and obesity.SUBJECTS: Two hundred and nineteen unrelated adult Japanese subjects (123 men and 96 women, age: 20–83 y, BMI: 16–43 kg/m2) including 77 obese subjects (BMI>26.4 kg/m2).MEASUREMENT: Human adiponectin gene was isolated from PAC DNA pools. Mutations in the adiponectin gene were screened by direct sequencing or restriction-fragment polymorphism. The levels of plasma adiponectin were determined by the enzyme-linked immunosorbent assay (ELISA).RESULTS: Adiponectin gene spanned 17 kb on chromosome 3q27, consisting of three exons and two introns. Within 2.1 kb of the 5′-flanking region, there were two octamer elements present in the promoter of adipsin. Two nucleotide changes were identified. One was a polymorphism (G/T) occurring in exon 2, and the other was a missense mutation (R112C) in exon 3. The mean plasma adiponectin levels of the subjects carrying G allele were low (G/G: 4.5 μg/ml; G/T: 5.9 μg/ml; and T/T: 6.3 μg/ml), but were not statistically significant. The allelic frequency between the obese and the non-obese showed no significant difference. The subject carrying R112C mutation showed markedly low concentration of plasma adiponectin.CONCLUSION: Two nucleotide changes have been identified in the adiponectin gene. G/T polymorphism in exon 2 was associated with neither plasma adiponectin concentrations nor the presence of obesity. A subject carrying missense mutation (R112C) showed markedly low plasma adiponectin concentration.