OBJECTIVE -- To test whether weight loss may improve endothelial dysfunction in human obesity, we recruited 28 healthy obese subjects, aged 30-46 years, with BMI 30-43 kg/[m.sup.2].
RESEARCH DESIGN AND METHODS -- Endothelium-dependent and -independent vasodilation were investigated by intra-arterial infusion of increasing doses of acetylcholine (ACh; 7.5, 15, and 30 [micro]g * [ml.sup.-1] * [min.sup.-1]) and sodium nitroprusside (0.8, 1.6, and 3.2 [micro]g * [ml.sup.-1] * [min.sup.-1]). Insulin resistance was estimated by homeostasis model assessment (HOMA). Weight loss was obtained by caloric restriction and physical activity.
RESULTS -- We observed a significant reduction in BMI (from 33.1 [+ or -] 4.2 to 27.5 [+ or -] 4.5 kg/[m.sup.2], - 16.9%, P <0.0001) and in waist circumference (from 108.2 [+ or -] 12.1 to 96.8 [+ or -] 12.9 cm, - 10.5%, P < 0.0001). Weight loss was also associated with a significant increase in ACh-stimulated forearm blood flow (FBF), from 7.4 [+ or -] 2.8 to 12.9 [+ or -] 3.4 ml * 100 [ml.sup.-1] of tissue * [min.sup.-1] kg/[m.sup.2] (P < 0.0001). Multivariate regression analysis demonstrated that the only independent predictor of FBF was HOMA, accounting for 44.5% of the variation, whereas the addition of BMI explained another 2.3% of the variation.
CONCLUSIONS -- Our data demonstrate that energy-restricted diet associated with physical activity induce a significant and clinically relevant improvement in ACh-stimulated vasodilation in obese healthy subjects.
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We recently reported that obesity and abdominal fat distribution are inversely related to endothelium-dependent vasodilation. We have also demonstrated that indexes of insulin sensitivity, which are linearly related to BMI and waist-to-hip ratio (WHR), predict the depressed acetylcholine (ACh)-stimulated forearm blood flow (FBF) in obese subjects (1). These findings are of considerable clinical importance because endothelial dysfunction is considered the early manifestation of the atherosclerotic process (2-4). Impaired endothelium-dependent vasodilation, caused by insulin resistance (IR), maybe the mechanism by which obesity confers increased risk for cardiovascular morbidity and mortality. In fact, IR represents a major underlying abnormality driving coronary and extracoronary atherosclerosis and cardiovascular diseases, which are the principal worldwide causes of morbidity and mortality (5). Our previous observations (1) led us to hypothesize that weight loss might be useful in both improving endothelial d ysfunction and reducing the risk of subsequent cardiovascular events. This hypothesis is also supported by recent evidence showing that both coronary (6,7) and forearm (8) endothelial dysfunction predict long-term atherosclerotic disease progression and cardiovascular event rates. Endothelial dysfunction associated with obesity is a very important medical problem in light of the evidence that the prevalence of obesity has significantly increased over the last few decades in developed and developing countries (9,10), becoming a major global public health problem (10). Many adverse clinical features associated with obesity are reversible with weight loss, but the effect of weight loss on ACh-stimulated vasodilation in human obesity is still unsettled.
In this study, we investigated the effect of weight loss on impaired endothelium-dependent vasodilation in obese subjects. In addition, we evaluated whether the increase in ACh-stimulated vasodilation is related to weight loss and reduction of IR.
RESEARCH DESIGN AND METHODS--Of a total of 76 Caucasian healthy obese subjects previously reported (1), 39 accepted to participate in this study. Inclusion and exclusion criteria were previously described. In addition, subjects were considered eligible if they lost >10% of their initial body weight. None of the subjects had a history of hypertension, diabetes, hyperlipidemia, peripheral vascular disease, or coagulopathy. Valvular, primary myocardial, and coronary artery diseases were excluded by history, physical examination, and standard diagnostic procedures. Other exclusion criteria were the presence of hematological, renal, or hepatic disease. All subjects were clinically evaluated and were required to be able to understand and comply with diet and physical activity guidelines. Eligible participants were aged 30-46 years (42.6 [+ or -] 7.5 [mean [+ or -] SD]) with a BMI between 30 and 43 kg/[m.sup.2] (33.1 [+ or -] 4.2). To avoid underestimation of FBF measurements, the forearm circumference was required to be <28 cm in all subjects. The institutional ethical committee approved the study, and all participants gave written informed consent.
Anthropometric measurements
The same trained examiner (F.S.) collected anthropometric measurements at baseline and after weight loss. We used waist circumference as the best anthropometric correlate of the distribution of visceral adipose tissue because it provides a crude index of the absolute amount of abdominal fat and avoids misleading information provided by changes in only WHR (11). The waist was measured at its smallest point with the abdomen relaxed.
Dietary intervention
The weight loss was obtained by an individual dietary program to reduce energy intake by 600-800 kcal, based on a macronutrient content <30% fat and 15% protein as recommended by the World Health Organization (12). The aim of this dietary intervention was to achieve at least a 10% weight loss in 10-16 weeks. At the initial interview with a dietitian, obese subjects were given verbal and written instructions on how to keep diet records, with food weighed and measured. Dietary intake was monitored by the same dietitian (F.S.). Obese subjects were instructed to substitute low-fat alternatives for typical high-fat foods, to increase the consumption of vegetables and fresh fruits, and to substitute complex carbohydrates, such as whole-grain bread and cereals, according to the Mediterranean diet. The prescribed energy intake ranged between 1,200 and 1,700 kcal/day. Finally, an extra 30 min walking per day, for at least 3 days weekly, was recommended, with advice on behavioral modification. Dietetic help was given e very 2 weeks by the dietitian when anthropometric measurements were performed; in addition, each subject was seen by a physician monthly to perform a clinical evaluation, standard electrocardiogram, and measurement of blood pressure (BP) and heart rate.
IR
IR was estimated using the previously validated homeostasis model assessment (HOMA) (13). HOMA was calculated from the fasting glucose and insulin concentrations according to the following equation: HOMA = [insulin ([micro]U/ml) X glucose (mmol/l)]/22.5.
Measurements of FBF
All studies were performed at 9:00 A.M. after subjects had fasted overnight, with the subjects lying supine in a quiet air-conditioned room (22-24[degrees]C). Patients underwent an evaluation of vascular function before and after weight loss during a weight-stable period to avoid a possible interference between the hypocaloric diet and insulin and glucose levels. We used the protocol previously described by Panza et al. (14) and subsequently used by ourselves (1).
Briefly, the FBF was measured as the slope of the change in the forearm volume. The mean of at least three measurements was calculated at each time point. Forearm vascular resistance (VR), expressed in arbitrary units, was calculated by dividing mean BP by FBF.
Vascular function
Endothelium-dependent and-independent vasodilation
All subjects rested at least 30 mm after artery cannulation to obtain a stable baseline before data collection; FEF and VR were repeated every 5 mm until stable. Endothelium-dependent and -independent vasodilation was assessed by the dose-response curve to intra-arterial infusions at increasing doses of ACh (7.5, 15, and 30 [micro]g [ml.sup.-1] * [min.sup.-1], each for 5 min) and sodium nitroprusside (SNP; 0.8,1.6, and 3.2 [micro]g * [ml.sup.-1] * [min.sup.-1], each for 5 min), respectively. The drug infusion rate, adjusted for the forearm volume of each subject, was 1 ml/min.
Oxidative stress and vascular function
To evaluate the effect of oxygen free radicals on endothelium-dependent and-independent vasodilation, both ACh and SNP were infused with either saline solution or vitamin C (24 mg/min), administered intrabrachially 5 mm before the agonists, and continued throughout the study. This vitamin C concentration has been shown to both protect human plasma from free radical-mediated lipid peroxidation (15) and improve impaired ACh-stimulated vasodilation in patients with various cardiovascular risk factors (16-18).
