Retinoid X receptor agonists inhibit hypertension-induced myocardial hypertrophy by modulating LKB1/AMPK/p70S6K signaling pathway.

BACKGROUND: Retinoid X receptor (RXR) has been demonstrated to play an important role in cardiac development and has been implicated in cardiovascular diseases. This study aimed to examine the effects of RXRα agonist bexarotene on pathological left ventricular hypertrophy (LVH) in a spontaneously hypertensive rat (SHR) model and the underlying mechanism. METHODS: WKY rats served as controls. SHRs were randomized into 3 groups at the age of 4 weeks and were treated (once daily for 12 weeks) with either bexarotene (30 or 100mg/kg body weight) or vehicle alone. Echocardiography was performed to determine cardiac structure and function. Neonatal cardiomyocytes were treated with AngII (10(-7) mmol/L) with or without the indicated concentration of RXRα ligand 9-cis-RA. The protein abundances of ß-actin, RXRα, LKB1, phospho-LKB1, AMPK, phospho-AMPK, P70S6K, phospho-P70S6K, ACE, and AT1 receptor were measured along with blood pressure, body weight and angiotensin II (Ang II) levels. The effects of LKB1 downregulation by LKB1 small, interfering RNA were examined. RESULTS: Treatment of SHRs with bexarotene resulted in significant inhibition of LVH without eliminating hypertension. Immunoblot with heart tissue homogenates from SHRs revealed that bexarotene activated the LKB1/AMPK signaling pathway and inhibited p70S6K. However, the increased Ang II levels in SHR serum and heart tissue were not reduced by bexarotene treatment. Treatment of cardiomyocytes with Ang II resulted in significantly reduced LKB1/AMPK activity and increased p70S6K activity. 9-cis-RA antagonized Ang II-induced LKB1/AMPK and p70S6K activation changes in vitro. CONCLUSIONS: RXR agonists prevent the inhibition of the LKB1/AMPK/p70S6K pathway and regulate protein synthesis to reduce LVH. This antihypertrophic effect of bexarotene is independent of blood pressure.

Long-term prehypertension treatment with losartan effectively prevents brain damage and stroke in stroke-prone spontaneously hypertensive rats.

Prehypertension has been associated with adverse cerebrovascular events and brain damage. The aims of this study were to investigate ⅰ) whether short­ and long-term treatments with losartan or amlodipine for prehypertension were able to prevent blood pressure (BP)-linked brain damage, and ⅱ) whether there is a difference in the effectiveness of treatment with losartan and amlodipine in protecting BP-linked brain damage. In the present study, prehypertensive treatment with losartan and amlodipine (6 and 16 weeks treatment with each drug) was performed on 4-week­old stroke-prone spontaneously hypertensive rats (SHRSP). The results showed that long-term (16 weeks) treatment with losartan is the most effective in lowering systolic blood pressure in the long term (up to 40 weeks follow-up). Additionally, compared with the amlodipine treatment groups, the short­ and long-term losartan treatments protected SHRSP from stroke and improved their brains structurally and functionally more effectively, with the long-term treatment having more benefits. Mechanistically, the short­ and long-term treatments with losartan reduced the activity of the local renin-angiotensin-aldosterone system (RAAS) in a time-dependent manner and more effectively than their respective counterpart amlodipine treatment group mainly by decreasing AT1R levels and increasing AT2R levels in the cerebral cortex. By contrast, the amlodipine treatment groups inhibited brain cell apoptosis more effectively as compared with the losartan treatment groups mainly through the suppression of local oxidative stress. Taken together, the results suggest that long-term losartan treatment for prehypertension effectively protects SHRSP from stroke-induced brain damage, and this protection is associated with reduced local RAAS activity than with brain cell apoptosis. Thus, the AT1R receptor blocker losartan is a good candidate drug that may be used in the clinic for long-term treatment on prehypertensive populations in order to prevent BP-linked brain damage.

Effects of Losartan and Amlodipine on Left Ventricular Remodeling and Function in Young Stroke-Prone Spontaneously Hypertensive Rats.

BACKGROUND: The purpose of this study was to evaluate the effects of prehypertensive losartan and amlodipine administration on left ventricular (LV) remodeling and function in spontaneously hypertensive rats-stroke prone (SHRSP). METHODS: Spontaneously hypertensive rats-stroke prone were prehypertensively administered losartan, amlodipine, or vehicle. Wistar-Kyoto rats were used as a control. Blood pressure of the rats was determined by tail-cuff method, and LV structure and function were measured by echocardiography and LV cannulation. Collagen volume fraction was analyzed by picrosirius red staining. Protein expressions of brain natriuretic peptide (BNP) and angiotensin II type 1 (AT1R) and type 2 (AT2R) receptors were determined by use of the Western blotting method. RESULTS: Although both drugs downregulated BNP protein expression, the LV remodeling and function were more improved with losartan than with amlodipine treatment. Losartan upregulated AT1R and downregulated AT2R protein expression. CONCLUSIONS: Both drugs inhibited LV remodeling and improved LV function in prehypertensively treated SHRSP. Losartan provided better continued heart protection, potentially due to its persistent inhibition of AT1R and activation of AT2R in the myocardium. KEY WORDS: Amlodipine; Blood pressure; Heart; Losartan; Prehypertension.

Differential effects of antihypertensive treatments on apoptosis, oxidative stress, and expression of angiotensin receptors in the cerebral cortex from the onset of prehypertension and hypertension in stroke-prone spontaneous hypertensive rats.

To investigate the effects of losartan and amlodipine on cell apoptosis in the cerebral cortex of stroke-prone spontaneously hypertensive rats (SHRSP) from the onset of prehypertension or hypertension. SHRSP were randomly divided into five experimental groups that were administered losartan, amlodipine (n=8 in each group; 4 weeks old or 10 weeks old), or vehicle, respectively. Wistar-Kyoto rats were used as control animals. Systolic blood pressure was measured using the tail-cuff method every 2 weeks. At 20 weeks of age, apoptosis was analyzed by TdT-mediated dUTP-biotin nick end labeling, and the level of angiotensin II was measured by radioimmunoassay. Protein expressions of gp91(phox), superoxide dismutase, and angiotensin II type 1 (AT1R) and type 2 (AT2R) receptors in the cerebral cortex were detected by western blot. Losartan and amlodipine effectively delayed the progression of systolic blood pressure elevation, especially from the onset of prehypertension, and they had no obvious effects on the level of angiotensin II. In addition, treatment with losartan or amlodipine significantly decreased cell apoptosis, downregulated the protein expression of gp91(phox), and upregulated the protein expression of superoxide dismutase. The protein expressions of AT1R and AT2R were decreased by the administration of both drugs. No difference was found in the expression of AT1R among the drug treatment groups, whereas the expression of AT2R was increased in rats with increased blood pressure. Amlodipine, especially from the onset of prehypertension, was more effective than losartan in reducing apoptosis in the cerebral cortex in SHRSP. This may be related to the antioxidative stress properties of amlodipine.