OBJECTIVE—Adiponectin is an adipocyte-specific secretory protein found in circulation in several different forms and is present at significantly lower levels in the plasma of diabetic patients compared with that of insulin-sensitive individuals. We wanted to test whether insulin per se is a contributing factor toward lower plasma adiponectin concentrations and, if so, whether the splanchnic bed contributes to this phenomenon.

RESEARCH DESIGN AND METHODS—We sampled femoral artery and hepatic venous samples and measured the high–molecular weight (HMW) and low–molecular weight (LMW) fractions of adiponectin in 11 type 2 diabetic and 7 nondiabetic subjects matched for age, sex, and BMI during basal conditions and during a hyperglycemic (∼9.5 mmol/l) hyperinsulinemic (∼700 pmol/l) clamp.

RESULTS—Under these conditions, total arterial adiponectin, HMW, and the ratio of HMW to total adiponectin all were lower (P < 0.01) in the diabetic versus nondiabetic subjects, whereas the LMW form did not significantly differ. Under hyperinsulinemic conditions, total adiponectin levels dropped, primarily due to a reduction of the HMW form, whereas LMW forms were not significantly affected.

CONCLUSIONS—HMW adiponectin and the ratio of HMW to total adiponectin are lower in individuals with diabetes than in nondiabetic subjects. We conclude that HMW adiponectin is downregulated in hyperinsulinemia and type 2 diabetes.

Adiponectin is a secretory protein uniquely produced by adipocytes (1) and accepted as a marker for systemic insulin sensitivity, particularly as an indicator of hepatic insulin sensitivity and lipid content (2). Decreased levels correlate well with cardiovascular and atherosclerotic disease, and negative correlation with proinflammatory markers makes it one of the most promising biomarkers for the metabolic syndrome. Studies with recombinant protein and, more importantly, analysis of a number of mouse models with altered adiponectin levels have demonstrated potent hepatic insulin-sensitizing and anti-atherosclerotic activities (3,4).

Several articles have clarified relevance of the observation that adiponectin circulates as a mixture of several different complexes. The sexual dimorphism causing higher levels of adiponectin in females is primarily due to higher levels of the high–molecular weight (HMW) form, a complex of at least 18 subunits of adiponectin (5). A number of studies have taken advantage of the potent predictive potential that measurement of the HMW offers and have further strengthened the strong correlations with the metabolic syndrome and insulin sensitivity previously revealed with measurements of total adiponectin (6,7).

A small study in patients suggested that during hyperinsulinemic-euglycemic clamp, plasma adiponectin levels were significantly decreased (8). Patients carrying mutant insulin receptor genes that lead to functionally impaired receptors or subjects with anti-insulin receptor autoantibodies present with very high levels of adiponectin (9). This lends further support to the hypothesis that insulin and its receptor exert potent repressive effects on adiponectin expression. The present studies were done to examine the distribution of the different adiponectin complexes in insulin-sensitive and insulin-resistant subjects under both basal and hyperinsulinemic conditions across the splanchnic bed. The results reveal a potent repressive effect of insulin on circulating adiponectin levels, particularly the HMW form.

After approval from the Mayo institutional review board, 7 nondiabetic and 11 type 2 diabetic subjects gave informed written consent to participate in the study. This is a subset of the 14 nondiabetic and 12 diabetic subjects studied as part of another protocol, previously published (10). In brief, all subjects were in good health and on no medications at the time of study other than either thyroxine or hormone replacement therapy. Oral hypoglycemic agents were discontinued 3 weeks before study. Subjects were instructed to follow a weight maintenance diet for at least 3 days before the day of study. Nondiabetic and diabetic subjects were matched for age (66 ± 2 vs. 65 ± 1 years), BMI (29 ± 2 vs. 32 ± 1 kg/m2), fat-free mass (53 ± 3 vs. 53 ± 4 kg), and body fat (36 ± 3 vs. 39 ± 3%) (11).

Subjects were admitted to the Mayo Clinic Research Unit on the evening before the study and fed a standard 10 cal/kg meal at 1800 h. An 18-gauge catheter was inserted into a forearm vein, and an infusion of insulin was started at 1900 h in the diabetic subjects (100 units regular human insulin in 1 l of 0.9% saline containing 5 ml 25% human albumin) and saline in the nondiabetic subjects. The insulin infusion rate was adjusted to maintain overnight euglycemia in the diabetic subjects (∼5 mmol/l) (12).

At 0600 h on the following morning, subjects were taken to an interventional radiology suite where femoral artery and femoral and hepatic venous catheters were placed as previously described (13).

At ∼0900 h, [3-3H]glucose and a hormone cocktail containing somatostatin and replacement amounts of growth hormone and glucagon were started (time 0 min) and continued until the end of the study as part of a separate experiment (14). Insulin was infused at a rate of 0.78 mU · kg lean body wt−1 · min−1 from 0 to 180 min, then at 1.56 mU · kg lean body wt−1 · min−1 from 181 to 300 min, and then at 3.1 mU · kg lean body wt−1 · min−1 from 301 to 420 min. Dextrose containing [3-3H]glucose was also begun and the rate adjusted so as to maintain plasma glucose concentrations at ∼9.3 mmol/l (∼165 mg/dl) and keep specific activity constant over the next 7 h of study (15). These experiments offered us the opportunity to measure serum adiponectin and its HMW and low–molecular weight (LWM) fractions across the splanchnic bed for the 3.1 mU · kg lean body wt−1 · min−1 infusion.

Analytical techniques.

All samples were stored at −20°C until analysis. Plasma glucose was measured by a glucose oxidase method using a YSI glucose analyzer (Yellow Spring Instruments, Yellow Springs, OH). Plasma insulin was measured by chemiluminescence with the Access ultrasensitive immunoenzymatic assay system (Beckman, Chaska, MN). Body composition and lean body mass were measured using dual-energy X-ray absorptiometry (SmartScan, version 4.6; Hologic, Waltham, MA).Velocity sedimentation/gel filtration chromatography was used for separation of adiponectin complexes as previously described using a human adiponectin radioimmunoassay (Linco) (5,11). Measurements of adiponectin level and distribution were performed with approval from the Albert Einstein institutional review board.

Statistical analysis.

Data in the text and figures are expressed as means ± SEM and rates as micromol per kilogram lean body mass per minute. Response during the high-dose insulin infusion was determined by taking the mean of the results from 390 to 420 min. Student's nonpaired t test was used to compare results between groups (e.g., diabetic vs. nondiabetic subjects) and paired t test for within a group (e.g., basal vs. high-dose insulin infusion). P < 0.05 was considered statistically significant.

Plasma glucose and insulin concentrations.

Plasma glucose concentrations were higher (P < 0.001) in the diabetic than in the nondiabetic subjects (Fig. 1A) at baseline (8.0 ± 0.3 vs. 5.5 ± 0.1 mmol) but did not differ during the insulin infusion. Plasma insulin concentrations were slightly but not significantly higher in the diabetic compared with the nondiabetic subjects at baseline (48 ± 6 vs. 39 ± 5 pmol/l) and did not differ during the high-dose insulin infusions (Fig. 1B).

Total, HMW, and LMW adiponectin concentrations in femoral artery.

Total adiponectin concentrations were significantly lower (P < 0.001) in diabetic than in nondiabetic subjects (Fig. 2A) both at baseline (8.2 ± 0.6 vs. 14.4 ± 2.8 μg/ml) and during the high-dose insulin infusion (5.0 ± 0.6 vs. 9.8 ± 1.4 μg/ml). There was a significant decrease in total adiponectin concentrations with increasing doses of insulin in the diabetic subjects (ANOVA P < 0.001), primarily due to a decrease in the HMW form (P < 0.001). A similar trend was observed in the nondiabetic subjects but failed to reach statistical significance, presumably because of the small sample size. HMW adiponectin concentrations were significantly lower (P < 0.001) in the diabetic than in the nondiabetic subjects (Fig. 2B) both at baseline (3.1 ± 0.2 vs. 11.0 ± 2.0 μg/ml) and during the high-dose insulin infusion (1.7 ± 0.2 vs. 5.1 ± 0.8 μg/ml). Similar to total adiponectin, the levels of the HMW form were significantly lower with increasing doses of insulin in both the diabetic (ANOVA P < 0.001) and nondiabetic subjects (ANOVA P < 0.01). Interestingly, the concentrations of the LMW fraction of adiponectin (Fig. 2C) did not differ in the diabetic and nondiabetic subjects either in the basal state (4.75 ± 0.52 vs. 5.27 ± 0.9 μg/ml) or during the high-dose insulin infusion (3.1 ± 0.4 vs. 4.7 ± 0.8 μg/ml). There was a very small but significant decrease (P < 0.05) in the LMW fraction adiponectin with increasing doses of insulin in the diabetic but not in the nondiabetic subjects. Combined, these data suggest that diabetic subjects have lower levels of adiponectin, predominantly due to differences at the level of the HMW form. Hyperinsulinemia has a significant negative impact on total adiponectin levels, primarily due to a decrease in the HMW form. This further highlights the relevance of the HMW form as the more sensitive of the circulating complexes.

Ratio of HMW to total adiponectin concentrations in the femoral artery.

The ratio of HMW to total adiponectin is used because it is considered a better index of insulin sensitivity than either total adiponectin levels or absolute levels of HMW (Fig. 3). This ratio is termed the adiponectin sensitivity index (SA). SA was significantly lower in the diabetic than in the nondiabetic subjects (P < 0.01) at baseline (0.4 ± 0.04 vs. 0.71 ± 0.05) and during the high-dose insulin infusion (0.36 ± 0.04 vs. 0.52 ± 0.02; P < 0.01). Importantly, hyperinsulinemia had less of an effect on SA in the diabetic than in the nondiabetic subjects. This indicates that in insulin-sensitive individuals, there is a disproportionate loss of the HMW form relative to total levels.

Total adiponectin, HMW adiponectin, and LMW adiponectin gradients across the splanchnic bed.

There were no significant differences in total adiponectin concentrations across the splanchnic bed; i.e., adiponectin levels in the femoral artery were comparable with those measured in the hepatic vein in the either diabetic or nondiabetic subjects at baseline (change [Δ] = 0.20 ± 1.0 vs. −0.19 ± 1.8 μg/ml) and during the high-dose insulin infusion (Δ = −0.9 ± 0.7 [diabetic] vs. −0.91 ± 1.5 μg/ml [nondiabetic]), indicating that there was no net release or uptake of adiponectin in the splanchnic bed in either group (Fig. 4A). On measuring the different complexes, the differences in the HMW forms did not reach statistical significance in the diabetic or the nondiabetic subjects at baseline (Δ = 0.33 ± 0.43 vs. 1.04 ± 1.54 μg/ml, respectively) or during the high-dose insulin infusion (Δ = 0.07 ± 0.4 vs. −0.41 ± 0.82 μg/ml, respectively) (Fig. 4B). Small but nonsignificant changes were seen for the LMW form at baseline for both the diabetic and nondiabetic subjects (Δ = −0.3 ± 0.5 vs. 0.5 ± 0.7 μg/ml, respectively) and during the high-dose insulin infusion (Δ = −1.1 ± 0.4 vs. −0.5 ± 0.8 μg/ml, respectively) (Fig. 4C). This suggests that in both the basal and insulin-stimulated states, the splanchnic bed does not make any significant net contributions toward systemic changes.

We report that the HMW form of adiponectin is prone to be reduced under hyperinsulinemic conditions, particularly among insulin-sensitive nondiabetic individuals. This has profound physiological implications. Hyperinsulinemia is frequently an indicator of insulin resistance. Hypoadiponectinemia is not only frequently associated with insulin resistance (16) but also may be directly causative for reduced insulin sensitivity (17). This suggests a vicious cycle during the initial stages of hyperinsulinemia, whereby high insulin levels lead to a downregulation of adiponectin levels, which in turn decreases insulin sensitivity further, prompting an even higher level of circulating insulin to maintain glucose homeostasis. Previous experiments in rodents (5) have demonstrated that the impact on HMW levels is primarily mediated through insulin and not hyperglycemia.

We have recently demonstrated (18) that the endoplasmic reticulum chaperone pair ERp44 and Ero1 is critically involved in the assembly pathway of adiponectin higher-order complexes. The levels of these chaperones are subject to tight regulation, are lowered in diabetes, and are induced by peroxisome proliferator–activated receptor-γ agonists. The differential response is likely due to a differential impact of insulin on the levels of these chaperones in adipocytes from diabetic and nondiabetic subjects. Our observations that stimulation with peroxisome proliferator–activated receptor-γ agonists leads to an increase of circulating adiponectin, primarily due to an increase in the HMW form (11), have originally highlighted the potential importance of the HMW form. This HMW form of adiponectin is in many instances much more prone to regulation than other adiponectin complexes (1922). While we failed to detect net differences of adiponectin levels across the splanchnic bed, we cannot rule out contributions of the visceral fat depots toward a unique local profile of adiponectin complexes that subsequently are efficiently extracted by the liver.

The methodology used in these studies is able to effectively separate the HMW form from the other adiponectin forms; however, the assay is not designed to separate the hexameric from the trimeric forms (5,11). A number of recent articles have compared the correlation coefficients of various parameters with either absolute levels of HMW or the ratio of HMW to total adiponectin concentrations. It depends on the specific parameter examined as to which of the two adiponectin measurements prevails with better correlation coefficients. The fact that under a number of circumstances the ratio of HMW to total adiponectin concentration is a superior read out indeed suggests that a competitive relationship may exist between HMW and the other adiponectin forms. It is yet unknown whether these complexes individually bear any physiological meaning, and future experiments will be required to separate these forms.

Published ahead of print at http://diabetes.diabetesjournals.org on 18 May 2007. DOI: 10.2337/db07-0185.

U.B.P. is currently affiliated with the Department of Internal Medicine, Columbia University and New York-Presbyterian Hospital, New York, New York. P.E.S. is currently affiliated with the Touchstone Diabetes Center, Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

This study was supported by U.S. Public Health Service Grants DK 29953, RR-00585, and R03-EY014935; a Novo Nordisk research infrastructure grant; the Mayo Foundation; New York Regional Obesity Center Grant P30DK026687-25 (adipocyte physiology core); an American Diabetes Association mentor-based fellowship (to R.B.); and National Institutes of Health Medical Scientist Training Grant T32-GM07288 (to U.B.P.).

We thank B. Dicke and L. Heins for technical assistance, R. Rood for assistance with graphics, and J. Feehan and B. Norby for assistance in performing the studies.

Scherer PE, Williams S, Fogliano M, Baldini G, Lodish HF: A novel serum protein similar to C1q, produced exclusively in adipocytes.
J Biol Chem
Trujillo ME, Scherer PE: Adiponectin: journey from an adipocyte secretory protein to biomarker of the metabolic syndrome.
J Intern Med
Berg AH, Combs TP, Du X, Brownlee M, Scherer PE: The adipocyte-secreted protein Acrp30 enhances hepatic insulin action.
Nat Med
Yamauchi T, Kamon J, Waki H, Imai Y, Shimozawa N, Hioki K, Uchida S, Ito Y, Matsui J, Eto K, Komeda K, Tsunoda M, Murakami K, Ohnishih Y, Yamamura K, Ueyama Y, Froguel P, Kimura S, Nagai R, Kadowaki T: Globular adiponectin protected ob/ob mice from diabetes and apoE-deficient mice from atherosclerosis.
J Biol Chem
Pajvani UB, Du X, Combs TP, Berg AH, Rajala MW, Schulthess T, Engel J, Brownlee M, Scherer PE: Structure-function studies of the adipocyte-secreted hormone Acrp30/adiponectin.
J Biol Chem
Fisher FF, Trukillo ME, Hanif W, Barnett AH, McTernan PG, Scherer PE, Kumar S: Serum high molecular weight complex of adiponectin correlates better with glucose tolerance than total serum adiponectin in Indo-Asian males.
Tonelli J, Li W, Kishore P, Pajvani UB, Kwon E, Weaver C, CScherer PE, Hawkins M: Mechanisms of early insulin-sensitizing effects of thiazolidinediones in type 2 diabetes.
Mohlig M, Wegewitz U, Osterhoff M, Isken F, Ristow M, Pfeiffer AF, Spranger J: Insulin decreases human adiponectin plasma levels.
Horm Metab Res
Semple RK, Soos MA, Luan J, Mitchell CS, Wilson JC, Gurnell M, Cochran EK, Gorden P, Chatterjee VK, Wareham NJ, O'Rahilly S: Elevated plasma adiponectin in humans with genetically defective insulin receptors.
J Clin Endocrinol Metab
Basu R, Basu A, Johnson CM, Schwenk WF, Rizza RA: Insulin dose-response curves for stimulation of splanchnic glucose uptake and suppression of endogenous glucose production differ in nondiabetic humans and are abnormal in people with type 2 diabetes.
Pajvani UB, Hawkins M, Combs TP, Rajala MW, Doebber T, Berger JP, Wagner JA, Wu M, Knopps A, Xiang AH, Utzschneider KM, Kahn SE, Olefsky JM, Buchanan TA, Scherer PE: Complex distribution, no absolute amount of adiponectin, correlates with thiazolidinedione-mediated improvement in insulin sensitivity.
J Biol Chem
White NH, Skor D, Santiago JV: Practical closed-loop insulin delivery: a system for the maintenance of overnight euglycemia and the calculation of basal insulin requirements in insulin-dependent diabetics.
Ann Intern Med
Meek SE, Persson M, Ford GC, Nair KS: Differential regulation of amino acid exchange and protein dynamics across splanchnic and skeletal muscle beds by insulin in healthy human subjects.
Basu R, Singh RJ, Basu A, Chittilapilly EG, Johnson CM, Toffolo G, Cobelli C, Rizza RA: Splanchnic cortisol production occurs in humans: evidence for conversion of cortisone to cortisol via the 11-β hydroxysteroid dehydrogenase (11-β HSD) type 1 pathway.
Molina JM, Baron AD, Edelman SV, Brechtel G, Wallace P, Olefsky JM: Use of a variable tracer infusion method to determine glucose turnover in humans.
Am J Physiol
Matsuzawa Y, Shimomura I, Kihara S, Funahashi T: Importance of adipocytokines in obesity-related diseases.
Horm Res
Nawrocki AR, Rajala MW, Tomas E, Pajvani UB, Saha AK, Trumbauer ME, Pang Z, Chen AS, Ruderman NB, Chen H, Rossetti L, Scherer PE: Mice lacking adiponectin show decreased hepatic insulin sensitivity and reduced responsiveness to peroxisome proliferator-activated receptor gamma agonists.
J Biol Chem
Wang ZV, Schraw TD, Kim JY, Khan T, Rajala MW, Follenzi A, Scherer PE: Secretion of the adipocyte-specific secretory protein adiponectin critically depends on thiol-mediated protein retention.
Mol Cell Biol
Retnakaran R, Hanley AJG, Raif N, Connelly PW, Sermer M, Zinman B: Hypoadiponectinaemia in South Asian women during pregnancy: evidence of ethnic variation in adiponectin concentration.
J Biol Chem
Hara K, Horikoshi M, Yamauchi T, Yago H, Miyazaki O, Ebinuma H, Imai Y, Nagai R, Kadowaki T: Measurement of the high–molecular weight form of adiponectin in plasma is useful for the prediction of insulin resistance and metabolic syndrome.
Diabetes Care
Richards AA, Hickman IJ, Wang AY, Jones AL, Newell F, Mowry BJ, Whitehead JP, Prins JB, Macdonald GA: Olanzapine treatment is associated with reduced high molecular weight adiponectin in serum: a potential mechanism for olanzapine-induced insulin resistance in patients with schizophrenia.
J Clin Psychopharmacol
Ebinuma H, Miyazaki O, Yago H, Hara K, Yamauchi T, Kadowaki T: A novel ELISA system for selective measurement of human adiponectin multimers by using proteases.
Clin Chim Acta