Pioglitazone, a Thiazolidinedione Derivative, Attenuates Left Ventricular Hypertrophy and Fibrosis in Salt-Sensitive Hypertension

353 Hypertens Res Vol.31 (2008) No.2 p.353-361 Original Article Pioglitazone, a Thiazolidinedione Derivative, Attenuates Left Ventricular Hypertrophy and Fibrosis in Salt-Sensitive Hypertension Minori NAKAMOTO1), Yusuke OHYA1), Tomoko SHINZATO1), Rieko MANO1), Masanobu YAMAZATO1), Atsushi SAKIMA1), and Shuichi TAKISHITA1) Thiazolidinediones, which stimulate peroxisome proliferator–activated receptor γ, have been shown to prevent cardiovascular injury. However, little is known about their effects on salt-sensitive hypertension. We thus investigated whether or not pioglitazone affects left ventricular (LV) hypertrophy in Dahl salt-sensitive rats, then compared its effects to those of an angiotensin II receptor blocker, candesartan. Rats were used at 16 weeks of age after they had been fed either a low-salt (0.3%; DSL) or high-salt (8%; DSH) diet for 10 weeks; some of the DSH rats were treated with pioglitazone (10 mg/kg/day) or candesartan (4 mg/kg/day). Both drugs decreased the elevated blood pressure in DSH rats, although it was still higher than in DSL rats. Both drugs decreased plasma insulin levels, but neither affected plasma glucose levels. The thiobarbituric acid reactive substance level in the LV was decreased by both drugs. LV hypertrophy evaluated by echocardiography in DSH rats was nearly normalized by both drugs, whereas only candesartan decreased LV diameter. In histological analysis, both drugs ameliorated LV fibrosis and myocardial cell hypertrophy. Both drugs decreased elevated gene expression levels of transforming growth factor-β1 and collagen type I, although the pioglitazone action was slightly modest. The metalloproteinase activity was increased in DSH rats, but both drugs decreased this level. Taken together, these findings indicate that pioglitazone reduced LV hypertrophy and fibrosis in salt-sensitive hypertension. Improvement in blood pressure, insulin level, and oxidative stress may be associated with this beneficial action of pioglitazone. (Hypertens Res 2008; 31: 353–361) Key Words: salt-sensitive hypertension, peroxisome proliferator–activated receptorγ, cardiac fibrosis, reninangiotensin system Introduction Left ventricular (LV) hypertrophy appears with sustained hypertension, and is a predictor of cardiovascular morbidity and mortality in patients with hypertension. The regression of LV hypertrophy by means of antihypertensive treatment is associated with improvement in the prognoses of patients with hypertension (1, 2). LV hypertrophy initially occurs as a compensatory response to pressure overload, but gradually changes to induce inadequate remodeling, finally leading to cardiac dysfunction, including systolic and diastolic heart failure (3, 4). LV hypertrophy is characterized by hypertrophy of the cardiomyocytes and LV fibrosis and increased deposition of extracellular matrix (ECM) including collagen. The disproportionate synthesis and degradation of ECM plays an important role in the transition from LV hypertrophy to LV dysfunction (5, 6). ECM synthesis is mainly regulated by myofibroblasts, which secrete ECM molecules in response to various cytokines and growth factors including transforming From the 1)Department of Cardiovascular Medicine, Nephrology and Neurology, School of Medicine, University of the Ryukyus, Okinawa, Japan. Address for Reprints: Yusuke Ohya, M.D., Department of Cardiovascular Medicine, Nephrology and Neurology, School of Medicine, University of the Ryukyus, 207 Uehara, Nishihara-cho, Okinawa 903–0215, Japan. E-mail: Received January 4, 2007; Accepted in revised form September 6, 2007. Hypertens Res Vol. 31, No. 2 (2008) growth factor-β1 (TGF-β1) and connective tissue growth factor (CTGF) (7, 8). Together with these factors that regulate ECM synthesis, matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMP) also participate in the regulation of ECM remodeling (6, 9, 10). It has also been reported that the renin-angiotensin-aldosterone system has an important role in the upstream of these pathways for ECM regulation (11–13). A peroxisome proliferator–activated receptor (PPAR) γ, a member of the nuclear receptor superfamily of ligand-activated transcription, plays a crucial role in adipogenesis and insulin resistance. A PPAR γ is highly expressed in adipose tissue, but several recent studies have shown that PPAR γ exists in myocytes, vascular smooth muscle cells, and macrophages/monocytes, as well as in adipocytes (14, 15) Thiazolidinediones, which are PPAR γ activators, improve insulin sensitivity and are used as an anti-diabetic drug. This category of drug has also been shown to exert anti-inflammatory and anti-fibrotic actions in animal models of cardiovascular diseases, including atherosclerosis, vascular inflammation, and cardiac failure (14–16). The mechanisms underlying these actions are explained in part by insulin sensitization or PPAR γ–activation induced by these drugs. However, information is limited regarding the effects of thiazolidinediones on LV fibrosis. In addition, no study has examined cardiovascular organ damage in salt-sensitive hypertension. Dahl salt-sensitive (DS) rats, a model for salt-sensitive hypertension, develop severe hypertension and exhibit hypertensive target organ damage, such as cardiac hypertrophy and cardiac failure (17, 18). Volume retention, the local renin-angiotensin system, oxidative stress, and tissue inflammation have been suggested as mechanisms of LV failure in this model (19–23). In the present study, we investigated whether or not pioglitazone, a thiazolidinedione, has beneficial effects on LV hypertrophy and fibrosis in salt-loaded DS rats, then compared its effects to those of candesartan, an angiotensin II receptor blocker. Methods Experimental Animals and Treatment All experimental procedures were performed according to the National Institutes of Health guidelines for the care and use of laboratory animals. This experiment was approved by the Animal Care and Use Committee, University of the Ryukyus. Male DS rats were purchased from Seac Yoshitomi (Fukuoka, Japan). Rats (6 weeks old) were assigned randomly to four groups: a low-salt group (fed 0.3% NaCl rat chow; DSL, n = 6), a high-salt group (fed 8% NaCl rat chow; DSH, n = 8), a pioglitazone group (fed 8% NaCl rat chow and pioglitazone; DSH/pio, n= 8), and a candesartan group (fed 8% NaCl rat chow and candesartan; DSH/can, n= 8). Pioglitazone (10 mg/ kg/day) was administered orally by mixing with high-salt rat chow. Candesartan (4 mg/kg/day) was administered by dissolving it in drinking water. To adjust the doses, the amount (mmHg) Systolic blood pressure 354 240 DSL 220 200 DSH DSH/pio DSH/can 180 160 140 120 100 6 8 10 12 14 16 weeks Fig. 1. Time course changes in systolic blood pressure measured by the tail-cuff method in Dahl salt-sensitive (DS) rats. Data represent means ± SEM. DSL, DS rats fed with low salt (n= 6); DSH, DS rats fed with high salt (n= 8); DSH/pio, DSH tr (...truncated)