articles
nature publishing group
Intervention and Prevention
In Central Obesity, Weight Loss Restores Platelet Sensitivity to Nitric Oxide and Prostacyclin Isabella Russo1, Monica Traversa1, Katia Bonomo1, Alessandro De Salve1, Luigi Mattiello1, Paola Del Mese1, Gabriella Doronzo1, Franco Cavalot1, Mariella Trovati1 and Giovanni Anfossi1 Central obesity shows impaired platelet responses to the antiaggregating effects of nitric oxide (NO), prostacyclin, and their effectors—guanosine 3′,5′-cyclic monophosphate (cGMP) and adenosine 3′,5′-cyclic monophosphate (cAMP). The influence of weight loss on these alterations is not known. To evaluate whether a diet-induced body‑weight reduction restores platelet sensitivity to the physiological antiaggregating agents and reduces platelet activation in subjects affected by central obesity, we studied 20 centrally obese subjects before and after a 6-month diet intervention aiming at reducing body weight by 10%, by measuring (i) insulin sensitivity (homeostasis model assessment of insulin resistance (HOMAIR)); (ii) plasma lipids; (iii) circulating markers of inflammation of adipose tissue and endothelial dysfunction, and of platelet activation (i.e., soluble CD-40 ligand (sCD-40L) and soluble P-selectin (sP-selectin)); (iv) ability of the NO donor sodium nitroprusside (SNP), the prostacyclin analog Iloprost and the cyclic nucleotide analogs 8-bromoguanosine 3′,5′-cyclic monophosphate (8-Br-cGMP) and 8-bromoadenosine 3′,5′-cyclic monophosphate (8-Br-cAMP) to reduce platelet aggregation in response to adenosine-5-diphosphate (ADP); and (v) ability of SNP and Iloprost to increase cGMP and cAMP. The 10 subjects who reached the body-weight target showed significant reductions of insulin resistance, adipose tissue, endothelial dysfunction, and platelet activation, and a significant increase of the ability of SNP, Iloprost, 8-Br-cGMP, and 8-Br-cAMP to reduce ADP-induced platelet aggregation and of the ability of SNP and Iloprost to increase cyclic nucleotide concentrations. No change was observed in the 10 subjects who did not reach the body-weight target. Changes of platelet function correlated with changes of HOMAIR. Thus, in central obesity, diet-induced weight loss reduces platelet activation and restores the sensitivity to the physiological antiaggregating agents, with a correlation with improvements in insulin sensitivity. Obesity (2010) 18, 788–797. doi:10.1038/oby.2009.302
Introduction
Obesity—a classical condition of insulin resistance—is a relevant risk factor for cardiac, cerebral, and lower limb vascular events (1,2). The INTERHEART and the Norfolk cohort studies underlined the role of central obesity in the risk of coronary heart disease, compelling to conclude that waist circumference should be preferred to BMI in the evaluation of the cardiovascular risk (3,4). This recommendation has a biological basis. Actually, abdominal fat deposition is characterized by a greater ability to release cytokines and free fatty acids than subcutaneous fat deposition, and therefore is more deeply involved in the pathogenesis of both atherothrombosis and insulin resistance (5,6). Central obesity has been considered by the International Diabetes Federation as an essential component of the metabolic
syndrome, a cluster of cardiovascular risk factors also including glucose and lipid abnormalities and arterial hypertension (7). Also, the role of central obesity in the pathogenesis of atherothrombosis, however, is played independently of the other components of the metabolic syndrome, because central obesity per se induces endothelial dysfunction and a prothrombotic state at least in part attributable to platelet defects (1). Platelets play a pivotal influence in atherothrombosis not only for their central role in hemostasis, but also through the release of cytokines, chemokines, growth factors, and proinflammatory mediators (8,9). Thus, platelets are also involved in inflammation, which is one of the most important pathogenetical mechanisms of atherogenesis (10). Persistent platelet activation has been observed in obese subjects, involving an increased synthesis of proaggregating isoprostanes as a
Department of Clinical and Biological Sciences, Internal Medicine Unit, University of Turin, San Luigi Gonzaga Hospital, Orbassano, Italy. Correspondence: Mariella Trovati (
[email protected])
1
Received 26 February 2009; accepted 26 July 2009; published online 15 October 2009. doi:10.1038/oby.2009.302 788
VOLUME 18 NUMBER 4 | april 2010 | www.obesityjournal.org
articles Intervention and Prevention consequence of an increased oxidative stress (11). This fact confirms the pivotal role of reactive oxygen species in platelet activation (11). Platelet function, however, is the result of a balance between pro- and antiaggregating mechanisms (8,12). In our laboratory, we mainly investigated the relationships between obesity and platelet sensitivity to antagonists, and we described that platelets from obese subjects are resistant to physiological antiaggregating agents, i.e., nitric oxide (NO) and prostacyclin, and to their effectors, i.e., the cyclic nucleotides guanosine 3′,5′-cyclic monophosphate (cGMP) and adenosine 3′,5′-cyclic monophosphate (cAMP) (13–15). We observed in more detail a multistep resistance to antiaggregation, including the ability of insulin to increase NO production (16), the ability of NO to increase cGMP synthesis, and the ability of cGMP to reduce platelet aggregation (16) in obese subjects. Similarly, we observed in obese subjects an impaired ability of prostacyclin to increase cAMP synthesis, and an impaired ability of cAMP to reduce platelet function (14,15). It is known that NO increases cAMP via cGMP, because cGMP inhibits a specific cAMP phosphodiesterase (16). In this light, we also observed a reduced ability of NO to increase cAMP in platelets from obese subjects (14). Other authors observed that obese subjects show a reduction in the ability of insulin to inhibit platelet interactions with collagen (17,18). The simultaneous presence of platelet activation and platelet resistance to antiaggregating agents can be considered as a “platelet dysfunction” characterizing human obesity (19). Interestingly, we observed that platelet resistance to the physiological antiaggregating agents is independently correlated with a measure of insulin resistance, the homeostasis model assessment (HOMAIR) index, suggesting a close relationship between platelet dysfunction and body sensitivity to insulin (14,15). The influence of lifestyle interventions aiming to reduce body weight by diet and exercise on obesity-related health complications is a matter of great interest (20). It has been observed that intentional weight loss reduces total mortality and cardiovascular events (21), likely through a beneficial influence on lipids, such as high-density lipoprotein (HDL) cholesterol and triglycerides (22), blood pressure (23), endothelial dysfunction (24), low-grade inflammation (25), and type 2 diabetes mellitus development (26,27). So far, few studies have evaluated whether weight loss also modifies the prothrombotic tendency of obese subjects. It has been observed in obese women that weight loss reduces the synthesis of prothrombotic isoprostanes (11), but it is not known whether weight loss also increases platelet sensitivity to the physiological antiaggregating agents. This study has been designed to evaluate whether a 6-month diet-intervention program aiming to reduce body weight of at least 10% in subjects affected by central obesity not only reduces insulin resistance, adipose tissue and endothelial dysfunction, and inflammation, but also reduces platelet activation and restores platelet sensitivity to NO and prostacyclin and to their effectors cGMP and cAMP. obesity | VOLUME 18 NUMBER 4 | april 2010
Methods and Procedures Subjects Among the obese subjects attending our metabolic clinic to loose weight, we chose 20 consecutive subjects (9 men and 11 women, aged 39.6 ± 1.25 years), affected by central obesity—defined as waist circumference >88 cm in women and 102 cm in men (28)—who were not taking any drug that could influence platelet function in the previous 4 weeks, were not smokers, did not follow diet-reduction programs during the past 6 months, did not have a family history of diabetes mellitus, and were otherwise healthy on the basis of medical history, physical examination, and standard diagnostic procedures; in particular, they did not present arterial hypertension, impaired fasting glucose, or impaired glucose tolerance. As controls for baseline parameters, we employed 15 healthy normal-weight volunteers (8 men; 7 women, aged 40.9 ± 2.1 years). Anthropometric measurements and biochemical parameter determinations were carried out as described below. Subjects’ characteristics are evidenced in Table 1. Patients and controls gave their informed consent to the biochemical investigations and the study was approved by our institutional review committee. Intervention study After the initial evaluation, obese patients followed our standard policy for weight reduction for 6 months, receiving detailed oral and written advices explaining how to follow a diet aiming to induce a weight reduction ≥10%. All information were enforced at the subsequent monthly visits carried out by the same trained physician. The intervention program consisted of a hypocaloric diet (1,200– 1,800 kcal/day) with personal goal settings, advising to increase consumption of vegetables, fresh fruit, grains, low-fat dairy products, fish, legumes, poultry, lean meats and to avoid foods high in saturated fats. The recommended diet composition was 50–60% complex carbohydrates, 15–20% proteins,
