Protective effects of angiotensin II type 1 receptor blocker on cerebral circulation independent of blood pressure.
ABSTRACT Angiotensin II type 1 receptor (AT1R) blocker (ARB) has been reported to modify hypertensive cerebrovascular changes; however, it is not clear whether its protective effects are independent of blood pressure. The aim of this study was to clarify the role of AT1R-mediated signals in cerebral circulation by the chronic treatment with telmisartan, an ARB, at a dose that did not lower the blood pressure. Male spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY) were treated for 4 weeks from 16 weeks of ages with telmisartan (SHR-L: 0.3 mg/kg/day, SHR-H: 3 mg/kg/day, WKY-H: 3 mg/kg/day) or vehicle (SHR-V, WKY-V). Superoxide measured by a chemiluminescent assay or dihydroethidium fluorescence and vascular morphology were examined for the thoracic aorta (Ao), common carotid (CCA), middle cerebral (MCA) and basilar arteries (BA). After 4 weeks of treatment, the blood pressure significantly declined in SHR-H but not in SHR-L in comparison to SHR-V. The lower limit of cerebral blood flow (CBF) autoregulation, evaluated by hemorrhagic hypotension, was significantly lower in SHR-L and SHR-H than SHR-V. In both SHR and WKY, the superoxide levels in the arteries were significantly attenuated by both doses of ARB. ARB also reversed vascular hypertrophy in Ao, CCA and BA and the inward remodeling in MCA. These results suggest that chronic treatment with telmisartan may therefore improve CBF autoregulation with a restoration of the vascular structure and an attenuation of superoxide generation, even at a dose that does not lower the blood pressure.
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ABSTRACT: Telmisartan is an angiotensin receptor blocker with high lipid solubility, also called metabosartan, which exerts a special protective effect on both acute brain damage and chronic neurodegeneration. We examined the effects of telmisartan on oxidative stress by advanced glycation end product (AGE) and 4-hydroxynonenal (4-HNE) assays and the accumulation of phosphorylated α-synuclein (pSyn) in the brain of stroke-resistant spontaneously hypertensive rats (SHR-SR). At the age of 12 weeks, SHR-SR received transient middle cerebral artery occlusion (tMCAO) for 90 minutes and were divided into the following 3 groups: the vehicle group, the low-dose telmisartan group (.3 mg/kg/day), and the high-dose telmisartan group (3 mg/kg/day, postoperatively). Immunohistologic analysis was performed when rats were 6, 12, and 18 months old. AGE, 4-HNE, and pSyn-positive cells (per square millimeter) increased with age in the cerebral cortex and hippocampus of the vehicle group, in the low-dose telmisartan group, these parameters decreased without lowering blood pressure (BP), and in the high-dose telmisartan group, these parameters increased with lowering BP. The present study suggests that a persistent hypertension after tMCAO caused a progressive oxidative stress with the abnormal accumulation of pSyn, and that telmisartan reduced oxidative stress and the accumulation of pSyn without lowering BP (low dose) or improved these conditions with a reduction in BP (high dose) via its pleiotropic effects through a potential peroxisome proliferator-activated receptor gamma stimulation in the brain of SHR-SR.Journal of stroke and cerebrovascular diseases: the official journal of National Stroke Association 04/2014;
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ABSTRACT: Previously, we reported that reactive oxygen species and signaling molecules of angiotensin II produced lipid peroxides, degenerated proteins, and injured DNA after cerebral ischemia in normotensive Wistar rats. Here, we investigated the long-term effect of the angiotensin II type I receptor blocker telmisartan on oxidative stress and hyperphosphorylated α-synuclein accumulation in stroke-resistant spontaneously hypertensive rats (SHR-SR). At the age of 3 months, SHR-SR were divided into 3 treatment groups: SHR-SR vehicle (SHR/Ve), SHR-SR low-dose telmisartan (.3 mg/kg/day) (SHR/low), and SHR-SR high-dose telmisartan (3 mg/kg/day) (SHR/high). Immunohistologic analyses were conducted in these groups and Wistar rats at the age of 6, 12, and 18 months. The SHR/Ve group demonstrated more progressive increase in advanced glycation end product (AGE)-, 4-hydroxy-2-nonenal (4-HNE)-, and phosphorylated α-synuclein (pSyn)-positive cells in the cerebral cortex and hippocampus compared with the Wistar group at 18 months. These expressions were reduced in the SHR/low group even without lowering blood pressure (BP), and expressions were dramatically suppressed in the SHR/high group with lowering of BP. These data suggest that persistent hypertension in SHR-SR strongly potentiate the markers of oxidative damage (AGEs and 4-HNE) and abnormal accumulation of pSyn, which were greatly suppressed by telmisartan in a dose-dependent manner without and with lowering of BP.Journal of stroke and cerebrovascular diseases: the official journal of National Stroke Association 01/2014;
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ABSTRACT: We have shown that Goto-Kakizaki (GK) rats, a lean model of type 2 diabetes, develop significant cerebrovascular remodeling by 18 weeks of age, which is characterized by increased media thickness and matrix deposition. While early glycemic control prevents diabetes-mediated remodeling of the cerebrovasculature, whether the remodeling can be reversed is unknown. Given that angiotensin II Type 1 receptor blockers (ARBs) reverse pathological vascular remodeling and function independent of changes in blood pressure in other vascular beds, we hypothesized that azilsartan medoxomil, a new ARB, is vasculoprotective by preventing and reversing cerebrovascular remodeling in diabetes. Control Wistar and diabetic GK rats (n=6-8/group), were treated with vehicle (water) or azilsartan medoxomil (3 mg/kg/day) from 14 to 18 or 18 to 22 weeks of age before or after vascular remodeling is established, respectively. Blood glucose and blood pressure were monitored and middle cerebral artery structure and function were evaluated using pressurized arteriography. Blood glucose was higher in GK rats compared to Wistar rats. Azilsartan treatment lowered blood glucose in diabetes with no effect on blood pressure. Diabetic animals exhibited lower myogenic tone, increased wall thickness, and cross sectional area compared to controls, which were corrected by azilsartan treatment when started at the onset of diabetes or later after vascular remodeling is established. Azilsartan medoxomil offers preventive and therapeutic vasculoprotection in diabetes-induced cerebrovascular remodeling and myogenic dysfunction and this is independent of blood pressure.Translational Research. 01/2014;