Objective-Plasma concentration of adiponectin is positively correlated with high-density lipoprotein (HDL) cholesterol level. However, the role of adiponectin on HDL metabolism remains unknown. This prompted us to perform an in vivo kinetic study of apoA-I, the main apolipoprotein of HDL, using stable isotopes, in 22 subjects with a wide range of plasma adiponectin, including 11 patients with metabolic syndrome (8 with type 2 diabetes, 3 without type 2 diabetes) and 11 normal individuals. Methods and Results-In the 22 studied subjects, plasma adiponectin levels ranged from 2.57 to 14.44 g/mL and apoA-I fractional catabolic rate (FCR) values ranged from 0.142 to 0.340 day Ϫ1 . A strong negative correlation was found between adiponectin and apoA-I FCR (rϭϪ0.66, PϽ0.001) in the whole studied population and, to a similar extent, in patients with metabolic syndrome (rϭϪ0.73, Pϭ0.010) and normal subjects (rϭϪ0.68, Pϭ0.020), separately. In multivariable analysis, apoA-I FCR was associated negatively with adiponectin (Pϭ0.005) and positively with HDL triglycerides/cholesterol ratio (Pϭ0.006), but not with age, sex, body mass index (BMI), waist circumference, plasma triglycerides, HDL cholesterol, fasting glycemia, and QUICKI. Both adiponectin and HDL triglycerides/cholesterol ratio explained 62% of the variance of apoA-I FCR and adiponectin on its own explained 43%. Conclusions-Our kinetic study shows a strong negative correlation between adiponectin and apoA-I FCR, which can explain the positive link between HDL cholesterol and adiponectin. This association is independent of obesity, insulin resistance, and the content of triglycerides within HDL particles. These data suggest that adiponectin may have a direct role on HDL catabolism. Key Words: adiponectin Ⅲ apoA-I Ⅲ HDL cholesterol Ⅲ insulin-resistance Ⅲ kinetic A diponectin is a peptide predominantly synthesized in the adipose tissue that plays an important role in carbohydrate and lipid metabolism and vascular biology. 1,2 It has been suggested to be a link between obesity, insulin resistance, and cardiovascular disease. Plasma adiponectin levels are reduced in individuals with abdominal obesity, metabolic syndrome, and/or type 2 diabetes. 1,3-5 Adiponectin concentration has been found negatively correlated with abdominal obesity and insulin resistance in humans 6,7 and has been shown to predict the development of type 2 diabetes. 8,9 Furthermore, several studies indicate that plasma adiponectin levels are significantly decreased in patients with coronary heart disease 10,11 and high plasma adiponectin predict a lower risk of future myocardial infarction in nondiabetic 12 and diabetic individuals. 13 However, the link between adiponectin and cardiovascular disease could be partly mediated by its effects on lipids, because several studies indicate that the inverse association between adiponectin and coronary disease is importantly attenuated or no more significant after adjustment for lipids, particularly high-density lipoprotein (HDL) cholesterol. 12,13 Adiponectin ...

AIMS=HYPOTHESIS:Mechanisms responsible for the decreased high-density lipoprotein (HDL) cholesterol level associated with insulin resistance in obese patients are not clearly understood. To determine the influence of insulin resistance at an early stage on HDL metabolism, we performed a stable isotope kinetic study of apolipoprotein (apo) A-I, in five obese insulin resistant women with normal fasting triglycerides and without impaired glucose tolerance, and in five age-matched control women. METHODS: Each subject received a 16 h constant infusion of L-[1-13 C]leucine at 0.7 mg=kg=h following a primed bolus of 0.7 mg=kg. RESULTS: ApoA-I fractional catabolic rate (FCR) was significantly increased in insulin-resistant women compared to controls (0.316 AE 0.056 vs 0.210 AE 0.040 per day, P < 0.01), indicating a significant 50% increase of apoA-I catabolism, leading to an important reduction of plasma apoA-I residence time (3.25 AE 0.59 vs 4.92 AE 1.11, P < 0.01). ApoA-I production rate tended to be higher in insulin resistant women than in controls (364 AE 77 vs 258 AE 60 mg=l=day, P ¼ 0.13), but the difference was not statistically significant. ApoA-I FCR was correlated with triglycerides during the fed state (r ¼ 0.69; P ¼ 0.026) and HDL triglycerides -esterified cholesterol ratio (r ¼ 0.73; P ¼ 0.016), suggesting that alteration of apoA-I metabolism in insulin resistance may be partly related to HDL enrichment in triglycerides. CONCLUSIONS: Our kinetic study shows that patients, at an early stage of insulin resistance (without impaired glucose tolerance nor fasting hypertriglyceridaemia), already have a significant alteration of apoA-I metabolism (increased apoA-I catabolism), which is consistent with the increased risk of atherosclerosis in this population.