Relationship between Serum Resistin Concentrations and Insulin ...

8 downloads 0 Views 141KB Size Report
(Humulin, Eli Lily & Co., Indianapolis, IN) and glucose (Dextrose 20,. Baxter ..... Savage DB, Sewter CP, Klenk ES, Segal DG, Vidal-Puig A, Considine RV,.
0021-972X/04/$15.00/0 Printed in U.S.A.

The Journal of Clinical Endocrinology & Metabolism 89(4):1844 –1848 Copyright © 2004 by The Endocrine Society doi: 10.1210/jc.2003-031410

Relationship between Serum Resistin Concentrations and Insulin Resistance in Nonobese, Obese, and Obese Diabetic Subjects L. K. HEILBRONN, J. ROOD, L. JANDEROVA, J. B. ALBU, D. E. KELLEY, E. RAVUSSIN, S. R. SMITH

AND

Pennington Biomedical Research Center (L.K.H., J.R., L.J., E.R., S.R.S.), Baton Rouge, Louisiana 70808; Obesity Research Center, St. Luke’s Roosevelt Hospital (J.B.A.), New York, New York 10025; and Department of Medicine, University of Pittsburgh (D.E.K.), Pittsburgh, Pennsylvania 15213 Early reports suggested that resistin is associated with obesity and insulin resistance in rodents. However, subsequent studies have not supported these findings. To our knowledge, the present study is the first assessment in human subjects of serum resistin and insulin sensitivity by the insulin clamp technique. Thirty-eight nonobese subjects [age, 23 ⴞ 4 yr; body mass index (BMI), 25.4 ⴞ 4.3 kg/m2], 12 obese subjects (age, 54 ⴞ 8 yr; BMI, 33.0 ⴞ 2.5 kg/m2), and 22 obese subjects with type 2 diabetes (age, 59 ⴞ 7 yr; BMI, 34.0 ⴞ 2.4 kg/m2) were studied. Serum resistin concentrations were not different among nonobese (4.1 ⴞ 1.7 ng/ml), obese (4.2 ⴞ 1.6 ng/ml), and obese diabetic subjects (3.7 ⴞ 1.2 ng/ml), and were not significantly correlated to glucose disposal rate during a hyperinsulinemic

A

DIPOSE TISSUE, in addition to storing energy, secretes numerous factors implicated in modulating insulin sensitivity and energy balance, such as leptin, adiponectin, TNF␣, and resistin (1). Resistin was recently identified during an in vitro screening for genes up-regulated during adipocyte differentiation and down-regulated by peroxisome proliferator-activated receptor ␥ agonists (2). Further research by this group revealed that serum resistin and resistin mRNA expression from adipose tissue were increased in obese mouse models, increased by a high fat diet, and decreased by rosiglitazone treatment. Furthermore, blocking resistin (by specific antibodies), reduced 2-deoxyglucose uptake in 3T3-L1 cells, and ip administration of resistin increased peak blood glucose levels after a glucose tolerance test (2). Taken together, these results led to the hypothesis that resistin promotes insulin resistance. Two other groups independently identified resistin (3, 4). Kim et al. (3) observed that resistin inhibited adipocyte differentiation by 80% in 3T3-L1 cells. This suggests that resistin may promote insulin resistance by increasing the storage of triglycerides in muscle and liver instead of adipose tissue. Indeed, failure of adipocyte differentiation has been proposed as a cause of type 2 diabetes, possibly through an ectopic overload of fatty acids and lipotoxicity of nonadipose tissues (5, 6). Other groups have observed the opposite results of these Abbreviations: BMI, Body mass index; CT, computed tomography. JCEM is published monthly by The Endocrine Society (http://www. endo-society.org), the foremost professional society serving the endocrine community.

glucose clamp across groups. Serum resistin was, however, inversely related to insulin sensitivity in nonobese subjects only (r ⴝ ⴚ0.35; P ⴝ 0.05), although this association was lost after adjusting for percent body fat. Serum resistin was not related to percent fat, BMI, or fat cell size. A strong correlation was observed between serum resistin and resistin mRNA expression from abdominal sc adipose tissue in a separate group of obese subjects (r ⴝ 0.62; P < 0.01; n ⴝ 56). Although the exact function of resistin is unknown, we demonstrated only a weak relationship between resistin and insulin sensitivity in nonobese subjects, indicating that resistin is unlikely to be a major link between obesity and insulin resistance in humans. (J Clin Endocrinol Metab 89: 1844 –1848, 2004)

initial findings (2), showing that resistin expression was down-regulated in rodent models of obesity (7–9), suppressed by free fatty acids (10), and stimulated by peroxisome proliferator-activated receptor ␥ agonists (7). Thus, evidence that supports resistin as a mediator of insulin resistance remains highly controversial. In humans, the role of resistin in regulating insulin sensitivity is also unclear. Serum resistin was related to fat mass (by bioelectrical impedance analysis) in young, healthy subjects and was significantly higher in women than in men (11). However, in another group of younger lean individuals or middle-aged overweight individuals, resistin was not related to body mass index (BMI), percent body fat, or insulin sensitivity, as determined by homeostasis model assessment (12). Resistin mRNA expression was shown to be higher in morbidly obese subjects compared with lean control subjects, although no association was observed with BMI (13). Increased expression of resistin was also found in abdominal depots (sc, n ⫽ 19; omental, n ⫽ 10) compared with thigh depots (n ⫽ 9), suggesting increased risk for type 2 diabetes due to central obesity and higher resistin (14). However, abdominal/gluteal resistin mRNA expression was not different in a larger cohort of 58 nondiabetic subjects (15). The goals of this study were 1) to determine the relationship between serum resistin and insulin sensitivity, fat distribution, fat cell size (a marker for adipocyte differentiation), and ectopic fat deposition in subjects with wide variations in adiposity and insulin sensitivity, including subjects with type 2 diabetes; and 2) to determine the relationship between

1844

Heilbronn et al. • Resistin and Insulin Sensitivity

serum resistin and resistin expression from abdominal sc adipocytes. Subjects and Methods The population for the current study was comprised of participants from three separate clinical trials. These studies were approved by the institutional review board of Pennington Biomedical Research Center, and all participants gave their written informed consent.

Study 1 Twelve obese, but otherwise healthy, subjects were matched by age, sex, and BMI to 22 obese subjects with well controlled type 2 diabetes [must have had fasting glucose concentrations ⬍180 mg/dl and not be receiving insulin or thiazolidinedione therapy to qualify for the study, which is an ancillary study of the Look AHEAD trial (16)]. Subjects were admitted to the in-patient unit and fed a standard dinner at 1800 h. The following morning, adipose tissue was collected by needle biopsy (superficial sc adipose tissue lateral to the umbilicus) to determine fat cell size. Fasting blood samples were taken, and participants underwent a 3-h hyperinsulinemic clamp to assess insulin sensitivity. Blood samples were drawn again at the end of the clamp. Fat distribution and ectopic fat deposition were determined by computed tomography (GE, High Speed Plus, General Electric, Fairfield, CT). Visceral adipose tissue was measured by multislice computed tomography (CT) scanning as previously described (17). Fat area and muscle attenuation characteristics of midthigh were also measured (x-ray attenuation value, Houndsfield units) (18). Liver fat was measured by CT scanning with splenic CT attenuation values, determined as an intrascan control and for the purposes of expressing values for liver fat as the ratio of liver to spleen CT attenuation values (19).

Study 2 Thirty-eight nonobese, nondiabetic subjects were fed a standard diet (35% fat) for 3 d. Subjects arrived at the in-patient unit at 0630 h after a 12-h fast, and serum samples were drawn. Abdominal sc adipose tissue was collected to determine fat cell size, followed by a hyperinsulinemic clamp to assess insulin sensitivity. Subjects were then fed a high fat diet for 3 d (50% fat by energy), and fasting blood samples were redrawn. In both studies 1 and 2, body composition (QDR 4500A, Hologics, Inc., Bedford, MA) was determined within 3 d of the clamp.

Study 3 Fifty-six healthy obese subjects participated in this study (BMI range, 27.1– 42.3 kg/m2). After a 12-h fast, abdominal sc adipose tissue (to measure resistin mRNA expression) and blood samples (to measure serum resistin) were collected.

Hyperinsulinemic-euglycemic clamp An iv catheter was placed in an antecubital vein for infusion of insulin (Humulin, Eli Lily & Co., Indianapolis, IN) and glucose (Dextrose 20, Baxter, Deerfield, IL). A second catheter was placed retrograde in a dorsal vein of the contralateral hand for blood withdrawal. The hand was placed in a heating pad for arterialization of venous blood. Three blood samples were collected before a primed continuous insulin infusion (80 mU/m2䡠min) was started. Arterialized glucose was measured at 5-min intervals (YSI, Inc., Yellow Springs, OH), and a variable infusion of exogenous glucose was given to maintain glucose concentrations. Glucose was clamped at 100 mg/dl (study 1) and 90 mg/dl (study 2).

Fat cell size Fat cell size was determined as previously described (20). Briefly, adipose tissue was fixed in osmium tetrachloride/collidine-HCl after disassociation by urea digestion. Cells were counted on a Multisizer-3 (Beckman Coulter, Fullerton, CA) using a 400-␮m aperture (dynamic linear range, 12–320 ␮m). Adipocyte cell number (cells per milligram wet weight of tissue) was then determined from the amount of sample

J Clin Endocrinol Metab, April 2004, 89(4):1844 –1848 1845

(milliliters), the quantity of cells (per milliliter), and the tissue weight (milligrams).

Resistin mRNA in adipose tissue Total RNA was isolated from 50 mg frozen tissue using TRIzol (Life Technologies, Gaithersburg, MD). The primer-probe set and methods for amplification of human resistin mRNA were described previously (15). Briefly, forward primer (5⬘-AGCCATCAATGAGAGGATCCA-3⬘), reverse primer (5⬘-TCCAGGCCAATGCTGCTTA-3⬘), and the probe (5⬘6-carboxyfluorescein-TCGCCGGCTCCCTAATATTTAGGGCA-bhq-1– 3⬘; Biosearch Technologies, Inc., Novato, CA) were designed, and resistin mRNA levels were normalized to cyclophilin mRNA levels.

Biochemical analysis Serum resistin was measured in duplicate using a commercially available kit (BioVendor, Brno, Czech Rebublic; intra- and interassay coefficients of variation, 4.3 and 7.2%, respectively). The antibodies in the ELISA have no detectable cross-reactivity to mouse resistin or other cytokines in human serum. Glucose was analyzed using a glucose oxidase electrode (Syncron CX7, Beckman, Brea, CA). Insulin was measured using an immunoassay (DPC 2000, Diagnostic Products Corp., Los Angeles, CA).

Statistical analysis All data are presented as the mean ⫾ sd. Statistics were performed using SPSS for Windows version 11.0.1. Correlations were performed using Pearson’s correlation coefficient. Differences between groups were compared by one-way ANOVA. The glucose disposal rate was normalized for fat-free mass. Due to differences in methodology of the hyperinsulinemic clamp (duration and glucose concentrations), subjects from studies 1 and 2 were analyzed separately. Resistin was log-transformed to normalize distribution.

Results

The anthropometrics and metabolic characteristics of subjects from studies 1 and 2 are described in Table 1. Briefly, nondiabetic and diabetic subjects from study 1 were well matched with respect to age, weight, BMI, and percent fat. As expected, fasting glucose was lower, and glucose disposal rate was higher in nondiabetic subjects. Subjects from study 2 were younger than subjects from study 1 (P ⬍ 0.001) and had significantly lower fasting insulin concentrations than the obese diabetic subjects from study 1 (P ⬍ 0.05). Despite wide variations in adiposity and insulin sensitivity across groups, serum resistin concentrations were not different among nonobese (4.1 ⫾ 1.7 ng/ml), obese (4.2 ⫾ 1.6 ng/ml), and diabetic subjects (3.7 ⫾ 1.2 ng/ml). Furthermore, serum resistin was not related to percent body fat in either males or females. However, serum resistin was negatively related to glucose disposal rate in nonobese subjects (Fig 1A; r ⫽ ⫺0.35; P ⫽ 0.05), although this association was no longer significant after adjusting for percent body fat (P ⫽ 0.22). We repeated the analysis after removing an outlier (unremarkable, slightly overweight male, aged 20 yr, with glucose and insulin concentrations within normal ranges). Removing this observation from the analysis reduced the significance of the finding before and after adjusting for percent fat (P ⫽ 0.06 and P ⫽ 0.19). Serum resistin was not related to insulin sensitivity in obese and obese diabetic subjects (r ⫽ 0.02; P ⫽ 0.7). In nonobese men only, we observed a direct relationship between fasting insulin and resistin (r ⫽ 0.42; P ⫽ 0.04). However, serum resistin was not different between men and women, and other associations (when present) were similar

1846

J Clin Endocrinol Metab, April 2004, 89(4):1844 –1848

Heilbronn et al. • Resistin and Insulin Sensitivity

TABLE 1. Characteristics of subjects from studies 1 and 2

No. (female/male) Age (yr) Weight (kg) Height (m) BMI (kg/m2) Body fat (%) Insulin mU/liter pmol/liter Glucose mg/dl mmol/liter GDR (mg/kg FFM䡠min) Resistin (ng/ml)

Obese (study 1)

Obese diabetic (study 1)

Nonobese (study 2)

12 (8/4) 54 ⫾ 8 94.8 ⫾ 13.8 1.69 ⫾ 0.9 33.0 ⫾ 2.5 39.3 ⫾ 7.6

22 (12/10) 59 ⫾ 7 97.6 ⫾ 8.8 1.69 ⫾ 0.9 34.0 ⫾ 2.4 37.4 ⫾ 6.7

38 (11/27) 23 ⫾ 4a 76.8 ⫾ 13.8a 1.74 ⫾ 0.8 25.4 ⫾ 4.1a 23.7 ⫾ 8.1a

9.4 ⫾ 1.8 65.2 ⫾ 12.5

12.4 ⫾ 4.5 86.1 ⫾ 31.2

7.6 ⫾ 4.9b 52.7 ⫾ 34.0b

101 ⫾ 7 5.6 ⫾ 0.4 6.1 ⫾ 1.9c 4.2 ⫾ 1.6

147 ⫾ 29a 8.1 ⫾ 1.6a 3.7 ⫾ 1.5a 3.7 ⫾ 1.2

94 ⫾ 7 5.0 ⫾ 0.4 9.1 ⫾ 3.9 4.1 ⫾ 1.7

Values are the mean ⫾ SD. GDR, Glucose disposal rate, adjusted for fat-free-mass (FFM). a P ⬍ 0.01 (lower than obese diabetic group). b P ⫽ 0.03 (lower than obese diabetic group). c P ⫽ 0.05 (lower than obese diabetic group).

FIG. 1. Association between insulin sensitivity and serum resistin concentrations in nonobese subjects (study 2) before high fat feeding (r ⫽ ⫺0.35; P ⫽ 0.05). GDR, Glucose disposal rate, adjusted for fat-free mass.

between men and women. Serum resistin was not associated with fat cell size, im fat, intrahepatic fat, or fasting glucose (correlation coefficients ranged from r ⫽ 0.05– 0.28; all P ⬎ 0.2). Serum resistin was modestly increased after 3 h of insulin infusion (measured only in subjects from study 1; n ⫽ 34; P ⫽ 0.05; Fig. 2A), but was unchanged after 3 d of high fat feeding (measured only in subjects from study 2; n ⫽ 38; P ⫽ 0.13; Fig. 2B). Resistin mRNA expression levels were measured only in subjects from study 3 (17 women and 39 men, all nondiabetic, 42 ⫾ 11 yr, 97.2 ⫾ 13.8 kg, 32.4 ⫾ 3.7 kg/m2). We observed that fasting serum resistin concentrations were directly related to the adipose expression levels of resistin (Fig. 3; r ⫽ 0.62; P ⬍ 0.001). Discussion

Resistin was inversely associated with the glucose disposal rate in nonobese subjects. However, serum resistin was not

FIG. 2. A, Serum resistin concentration before and after 3 h of insulin infusion (80 mU/mg䡠kg) in obese subjects with and without type 2 diabetes (study 1; *, P ⫽ 0.05; n ⫽ 34). B, Serum resistin before and after high fat feeding in nonobese subjects (study 2; P ⫽ 0.13; n ⫽ 38).

Heilbronn et al. • Resistin and Insulin Sensitivity

FIG. 3. Association between resistin expression from sc adipose tissue and fasting serum concentrations of resistin in subjects from study 3 (n ⫽ 56; r ⫽ 0.6; P ⬍ 0.001).

different in nonobese, obese, and obese diabetic groups despite wide variations in insulin sensitivity. Previous studies in mice have shown that resistin administration impairs insulin sensitivity (2). Rajala et al. (9) observed that this was the result of impaired suppression of hepatic glucose production, rather than peripheral insulin resistance in rats. However, resistin decreased glucose uptake in skeletal muscle cells, although this effect was independent of insulin signaling pathways (glucose transporter-4 translocation, insulin receptor substrate-1 tyrosine phosphorylation, or phosphoinositol 3-kinase activity) (21). High concentrations of resistin have also been shown to inhibit adipocyte differentiation in vitro (3). Large fat cells are postulated to be a marker of impaired adipocyte differentiation and are a predictor of the development of type 2 diabetes (22). In this study, fat cell size was not related to serum resistin in nonobese, obese, or obese diabetic subjects, indicating that resistin may not affect sc abdominal adipocyte differentiation in humans. Increased ectopic fat deposition is also postulated to mediate insulin resistance, with increased intramyocellular lipids predicting the development of type 2 diabetes (23), and fatty liver contributing to increased hepatic glucose output and type 2 diabetes (24). In the present study resistin was not associated with increased intramyocellular or intrahepatic lipid (both measured by CT). Together, these results imply that resistin does not cause peripheral insulin resistance in humans, at least not through impaired adipocyte proliferation/differentiation or increasing ectopic fat deposition. Serum resistin concentrations were increased in response to supraphysiological doses of insulin (steady state insulin averaged 164 ⫾ 5 mU/ml). This effect was modest and was only measured in obese and obese diabetic subjects, but suggests that resistin expression may be acutely regulated by

J Clin Endocrinol Metab, April 2004, 89(4):1844 –1848 1847

insulin. It implies that subjects with higher fasting insulin concentrations will have higher serum concentrations of resistin. However, this relationship was only observed in nonobese men and thus may be masked in subjects with increased fat mass. Previous reports have found that the infusion of insulin increases the expression of resistin in Zucker rats and streptozotocin-induced diabetic mice (3, 7). However, in 3T3-L1 adipocytes physiological concentrations of insulin decreased resistin expression (25). We did not find an acute effect of high fat diet on serum resistin concentrations in nonobese humans. This contrasts the results observed in mice fed a high fat diet (2), but this diet was implemented for a longer time period (8 wk vs. 3 d). We also observed that serum resistin was highly correlated to sc abdominal mRNA expression of resistin. Two other groups were unable to consistently detect resistin mRNA from human sc adipose tissue (26, 27), suggesting that resistin expression from adipose tissue was due to the presence of mononuclear cells. However, McTernan et al. (14) conclusively showed that resistin mRNA expression and protein were detectable in sc and visceral abdominal adipocytes from lean and obese subjects and that expression was approximately 3-fold higher in preadipocytes compared with mature cells. Despite a strong correlation between serum concentrations and mRNA expression in the present study, we did not observe a correlation between serum resistin and percent body fat in nonobese, obese, or obese diabetics (or sc abdominal fat in obese and obese diabetics), indicating that resistin is not related to adiposity. However, nonobese subjects were significantly younger than our obese group, and this (or some other correlate of youth, such as physical fitness) could have affected the results. This result does contrast with a previous report in young, nonobese subjects (11), but is supported by a recently published study of more than 240 young and middle-aged subjects (12). Conclusion

Our study did not demonstrate an independent association between resistin and insulin sensitivity. Furthermore, although resistin was up-regulated by insulin, this effect was modest and was not observed in all subjects. Although the exact function of resistin remains unclear, this study does not support a role for resistin as a major mediator of insulin sensitivity in humans. Acknowledgments Received August 12, 2003. Accepted December 19, 2003. Address all correspondence and requests for reprints to: Dr. Steven Smith, Pennington Biomedical Research Center, 6400 Perkins Road, Baton Rouge, Louisiana 70808. E-mail address: [email protected]. This work was supported by NIDDK Grant DK-60412-02, USDA Grant 2001-34323-10704, and General Clinical Research Center Grant M01-RR-00645.

References 1. Havel PJ 2002 Control of energy homeostasis and insulin action by adipocyte hormones: leptin, acylation stimulating protein, and adiponectin. Curr Opin Lipidol 13:51–59 2. Steppan CM, Bailey ST, Bhat S, Brown EJ, Banerjee RR, Wright CM, Patel HR, Ahima RS, Lazar MA 2001 The hormone resistin links obesity to diabetes. Nature 409:307–312

1848

J Clin Endocrinol Metab, April 2004, 89(4):1844 –1848

3. Kim K-H, Lee K, Moon YS, Sul HS 2001 A cysteine-rich adipose tissue-specific secretory factor inhibits adipocyte differentiation. J Biol Chem 276:11252–11256 4. Holcomb IN, Kabakoff RC, Chan B, Baker TW, Gurney A, Henzel W, Nelson C, Lowman HB, Wright BD, Skelton NJ, Frantz GD, Tumas DB, Peale J, Franklin V, Shelton DL, Hebert CC 2000 FIZZ1, a novel cysteine-rich secreted protein associated with pulmonary inflammation, defines a new gene family. EMBO J 19:4046 – 4055 5. Danforth E 2000 Failure of adipocyte differentiation causes type II diabetes mellitus? Nat Genet 26:13 6. McGarry JD 2002 Dysregulation of fatty acid metabolism in the etiology of type 2 diabetes. Diabetes 51:7–18 7. Way JM, Gorgun CZ, Tong Q, Uysal KT, Brown KK, Harrington WW, Oliver Jr WR, Willson TM, Kliewer SA, Hotamisligil GS 2001 Adipose tissue resistin expression is severely suppressed in obesity and stimulated by peroxisome proliferator-activated receptor gamma agonists. J Biol Chem 276:25651–25653 8. Milan G, Granzotto M, Scarda A, Calcagno A, Pagano C, Federspil G, Vettor R 2002 Resistin and adiponectin expression in visceral fat of obese rats: effect of weight loss. Obes Res 10:1095–1103 9. Rajala MW, Obici S, Scherer PE, Rossetti L 2003 Adipose-derived resistin and gut-derived resistin-like molecule-␤ selectively impair insulin action on glucose production. J Clin Invest 111:225–230 10. Juan CC, Au LC, Fang VS, Kang SF, Ko YH, Kuo SF, Hsu YP, Kwok CF, Ho LT 2001 Suppressed gene expression of adipocyte resistin in an insulin-resistant rat model probably by elevated free fatty acids. Biochem Biophys Res Commun 289:1328 –1333 11. Yannakoulia M, Yiannakouris N, Bluher S, Matalas AL, Klimis-Zacas D, Mantzoros CS 2003 Body fat mass and macronutrient intake in relation to circulating soluble leptin receptor, free leptin index, adiponectin, and resistin concentrations in healthy humans. J Clin Endocrinol Metab 88:1730 –1736 12. Lee JH, Chan JL, Yiannakouris N, Kontogianni M, Estrada E, Seip R, Orlova C, Mantzoros CS 2003 Circulating resistin levels are not associated with obesity or insulin resistance in humans and are not regulated by fasting or leptin administration: cross-sectional and interventional studies in normal, insulin-resistant, and diabetic subjects. J Clin Endocrinol Metab 88:4848 – 4856 13. Savage DB, Sewter CP, Klenk ES, Segal DG, Vidal-Puig A, Considine RV, O’Rahilly S 2001 Resistin/Fizz3 expression in relation to obesity and peroxisome proliferator-activated receptor-gamma action in humans. Diabetes 50: 2199 –2202 14. McTernan PG, McTernan CL, Chetty R, Jenner K, Fisher FM, Lauer MN, Crocker J, Barnett AH, Kumar S 2002 Increased resistin gene and protein expression in human abdominal adipose tissue. J Clin Endocrinol Metab 87: 2407 15. Smith SR, Bai F, Charbonneau C, Janderova L, Argyropoulos G 2003 A

Heilbronn et al. • Resistin and Insulin Sensitivity

16.

17.

18. 19. 20. 21. 22. 23.

24.

25. 26.

27.

promoter genotype and oxidative stress potentially link resistin to human insulin resistance. Diabetes 52:1611–1618 Look AHEAD Research Group: Ryan DH EM, Foster GF, Haffner SM, Hubbard VS, Johnson KC, Kahn SE, Knowler WC, Yanovski SZ 2003 Look AHEAD: Action for Health in Diabetes. Design and methods for a clinical trial of weight loss for the prevention of cardiovascular disease in type 2 diabetes. Control Clin Trials 24:610 – 628 Smith SR, Lovejoy JC, Greenway F, Ryan D, deJonge L, de la Bretonne J, Volafova J, Bray GA 2001 Contributions of total body fat, abdominal subcutaneous adipose tissue compartments, and visceral adipose tissue to the metabolic complications of obesity. Metabolism 50:425– 435 Goodpaster BH 2002 Measuring body fat distribution and content in humans. Curr Opin Clin Nutr Metab Care 5:481– 487 Ricci C, Longo R, Gioulis E, Bosco M, Pollesello P, Masutti F, Croce LS, Paoletti S, de Bernard B, Tiribelli C, Dalla Palma L 1997 Noninvasive in vivo quantitative assessment of fat content in human liver. J Hepatol 27:108 –113 Harris RBS, Ramsay TG, Smith SR, Bruch RC 1996 Early and late stimulation of ob mRNA expression in meal-fed and overfed rats. J Clin Invest 97:2020 – 2026 Moon B, Kwan JJ, Duddy N, Sweeney G, Begum N 2003 Resistin inhibits glucose uptake in L6 cells independently of changes in insulin signaling and GLUT4 translocation. Am J Physiol 285:E106 –E115 Weyer C, Foley JE, Bogardus C, Tataranni PA, Pratley RE 2000 Enlarged subcutaneous abdominal adipocyte size, but not obesity itself, predicts type II diabetes independent of insulin resistance. Diabetologia 43:1498 –1506 Jacob S, Machann J, Rett K, Brechtel K, Volk A, Renn W, Maerker E, Matthaei S, Schick F, Claussen CD, Haring HU 1999 Association of increased intramyocellular lipid content with insulin resistance in lean nondiabetic offspring of type 2 diabetic subjects. Diabetes 48:1113–1119 Ryysy L, Hakkinen AM, Goto T, Vehkavaara S, Westerbacka J, Halavaara J, Yki-Jarvinen H 2000 Hepatic fat content and insulin action on free fatty acids and glucose metabolism rather than insulin absorption are associated with insulin requirements during insulin therapy in type 2 diabetic patients. Diabetes 49:749 –758 Haugen F, Jorgensen A, Drevon CA, Trayhurn P 2001 Inhibition by insulin of resistin gene expression in 3T3–L1 adipocytes. FEBS Lett 507:105–108 Savage DB, Sewter CP, Klenk ES, Segal DG, Vidal-Puig A, Considine RV, O’Rahilly S 2001 Resistin Fizz3 expression in relation to obesity and peroxisome proliferator-activated receptor-␥ action in humans. Diabetes 50:2199 – 2202 Nagaev I, Smith U 2001 Insulin resistance and type 2 diabetes are not related to resistin expression in human fat cells or skeletal muscle. Biochem Biophys Res Commun 285:561–564

JCEM is published monthly by The Endocrine Society (http://www.endo-society.org), the foremost professional society serving the endocrine community.