Akiko Sakata

Cognitive Deficit in Amyloid-β–Injected Mice Was Improved by Pretreatment With a Low Dose of Telmisartan Partly Because of Peroxisome Proliferator-Activated Receptor-γ Activation

The pathological hallmark of Alzheimer disease is deposition of amyloid-&bgr; protein (A&bgr;) in the brain. Telmisartan is a unique angiotensin II receptor blocker with peroxisome proliferator-activated receptor-&ggr; (PPAR-&ggr;)–stimulating activity. Activation of PPAR-&ggr; is expected to prevent inflammation and A&bgr; accumulation in the brain. We investigated the possible preventive effect of telmisartan on cognitive decline in an Alzheimer disease mouse model via PPAR-&ggr; activation. Here, male ddY mice underwent ICV injection of A&bgr; 1-40. Cognitive function was evaluated by the Morris water maze test. A low dose of telmisartan (0.35 mg/kg per day) was administered in drinking water with or without GW9662, a PPAR-&ggr; antagonist. Cerebral blood flow was evaluated by laser speckle flowmetry. Inflammatory cytokine levels were measured by quantitative RT-PCR. A&bgr; 1-40 ICV injection significantly impaired cognitive function. Pretreatment with telmisartan improved this cognitive decline to a similar level to that in control mice. Cotreatment with GW9662, a PPAR-&ggr; antagonist, attenuated this telmisartan-mediated improvement of cognition. Treatment with telmisartan enhanced cerebral blood flow and attenuated the A&bgr;-induced increase in expression of cytokines, such as tumor necrosis factor-&agr; and inducible NO synthase in the brain. Interestingly, coadministration of GW9662 cancelled these beneficial effects of telmisartan. A&bgr; 1-40 concentration in the brain was significantly decreased by treatment with telmisartan, whereas administration of GW9662 attenuated the decrease in telmisartan-mediated A&bgr; 1-40 concentration. Taken together, our findings suggest that even a low dose of telmisartan had a preventive effect on cognitive decline in an Alzheimer disease mouse model, partly because of PPAR-&ggr; activation.

Telmisartan prevented cognitive decline partly due to PPAR-γ activation

Telmisartan is a unique angiotensin receptor blocker (ARB) and partial agonist of peroxisome proliferator-activated receptor (PPAR)-gamma. Here, we investigated the preventive effect of telmisartan on cognitive decline in Alzheimer disease. In ddY mice, intracerebroventricular injection of Abeta 1-40 significantly attenuated their cognitive function evaluated by shuttle avoidance test. Pretreatment with a non-hypotensive dose of telmisartan significantly inhibited such cognitive decline. Interestingly, co-treatment with GW9662, a PPAR-gamma antagonist, partially inhibited this improvement of cognitive decline. Another ARB, losartan, which has less PPAR-gamma agonistic effect, also inhibited Abeta-injection-induced cognitive decline; however the effect was smaller than that of telmisartan and was not affected by GW9662. Immunohistochemical staining for Abeta showed the reduced Abeta deposition in telmisartan-treated mice. However, this reduction was not observed in mice co-administered GW9662. These findings suggest that ARB has a preventive effect on cognitive impairment in Alzheimer disease, and telmisartan, with PPAR-gamma activation, could exert a stronger effect.

Direct stimulation of angiotensin II type 2 receptor enhances spatial memory

We examined the possibility that direct stimulation of the angiotensin II type 2 (AT2) receptor by a newly generated direct AT2 receptor agonist, Compound 21 (C21), enhances cognitive function. Treatment with C21 intraperitoneal injection for 2 weeks significantly enhanced cognitive function evaluated by the Morris water maze test in C57BL6 mice, but this effect was not observed in AT2 receptor-deficient mice. However, C21-induced cognitive enhancement in C57BL6 mice was attenuated by coadministration of icatibant, a bradykinin B2 receptor antagonist. Administration of C21 dose dependently increased cerebral blood flow assessed by laser speckle flowmetry and hippocampal field-excitatory postsynaptic potential (f-EPSP) determined by electrophysiological techniques in C57BL6 mice. Furthermore, activation of the AT2 receptor by C21 promoted neurite outgrowth of cultured hippocampal neurons prepared from fetal transgenic mice expressing green fluorescent protein. Finally, we investigated the pathologic relevance of C21 for spatial learning using an Alzheimers disease mouse model with intracerebroventricular injection of amyloid-β (1 to 40). We observed that treatment with C21 prevented cognitive decline in this model. These results suggest that a direct AT2 receptor agonist, C21, enhances cognitive function at least owing to an increase in CBF, enhancement of f-EPSP, and neurite outgrowth in hippocampal neurons.

Low dose of telmisartan prevents ischemic brain damage with peroxisome proliferator-activated receptor-γ activation in diabetic mice

Background Telmisartan is a unique AT1 receptor blocker with a peroxisome proliferator-activated receptor gamma (PPAR-γ) agonistic action. Activation of PPAR-γ could prevent inflammation and brain damage. Method We investigated the beneficial effect of telmisartan on ischemic brain damage via PPAR-γ activation as well as AT1 receptor blockade. Eight-week-old male KK-Ay mice were subjected to middle cerebral artery occlusion. Before middle cerebral artery occlusion, they were administered telmisartan or losartan, with or without GW9662, a PPAR-γ antagonist, for 2 weeks. Ischemic area, neurological score, oxidative stress, inflammation and cerebral blood flow were assessed 24 h after middle cerebral artery occlusion. Results Administration of telmisartan, losartan, GW9662 and these AT1 receptor blockers with GW9662 had no significant effect on blood pressure. KK-Ay mice exhibited a significant increase in the ischemic area compared with C57BL6 mice. Treatment with telmisartan decreased the ischemic area and improved the neurological score compared with the no-treatment group, with an increase in cerebral blood flow and a reduction in superoxide production and expression of inflammatory cytokines. These protective effects of telmisartan were partially attenuated by coadministration of GW9662, although GW9662 treatment alone had no significant effect on ischemic area. Losartan treatment showed a reduction in ischemic area compared with nontreated KK-Ay mice. However, coadministration of GW9662 had no effect on the losartan-mediated reduction in ischemic area. Conclusion These results suggest that telmisartan has a beneficial effect on stroke partly due to activation of PPAR-γ as well as AT1 receptor blockade.

Sex-different effect of angiotensin II type 2 receptor on ischemic brain injury and cognitive function

We previously reported that angiotensin II type 2 (AT(2)) receptor signaling prevents neural damage and cognitive impairment after focal cerebral ischemia. We investigated the possible roles of the AT(2) receptor in the sex difference, focusing on cognitive function and ischemic brain damage using AT(2) receptor-deficient mice (Agtr2(-)). In Agtr2(-), spatial memory evaluated by the Morris water maze test was impaired in female compared with that in male Agtr2(-) and female wild-type (Agtr2(+)), while no significant sex-different change was observed in Agtr2(+). Interestingly, bromodeoxyuridine incorporation assay showed a significant decrease of hippocampal neurogenesis in female Agtr2(-) compared with that in female Agtr2(+). In contrast, ischemic area after middle cerebral artery (MCA) occlusion was significantly increased in male compared with female mice in Agtr2(-), while no significant sex-different change was observed in Agtr2(+). Male Agtr2(-) mice showed higher AT(1) receptor expression and significantly impaired cerebral blood flow (CBF) in the ipsilateral side 24 hours after MCA occlusion compared with female Agtr2(-) mice. In conclusion, deletion of the AT(2) receptor showed a sex-different effect such as a severe cognitive impairment with a decrease of hippocampal neurogenesis in females and a larger ischemic brain damage with a decrease of CBF in males.

Diabetes-Associated Cognitive Impairment Is Improved by a Calcium Channel Blocker, Nifedipine

Nifedipine, a calcium channel blocker, has been reported to exert pleiotropic effects on atherosclerosis, mainly through its antioxidative properties. However, the effect of the calcium channel blocker on cognitive impairment associated with type 2 diabetes mellitus is not well known. Here, we examined the possibility that a calcium channel blocker could improve cognitive function in a type 2 diabetic mouse model, KK-Ay. KK-Ay mice subjected to 20 trials of a passive avoidance task every week from 7 weeks of age exhibited impairment of the increase in avoidance rate and, moreover, exaggeration of its age-dependent decline, especially after 12 weeks of age. Oral administration of nifedipine at a nonhypotensive dose (0.001% in laboratory chow) to KK-Ay mice from 10 weeks of age improved cognitive function. Nifedipine treatment decreased serum insulin level to one fifth of that in KK-Ay mice without nifedipine. Moreover, nifedipine treatment significantly reduced superoxide anion production in the brain. Furthermore, treatment with nifedipine markedly reduced the mRNA level of Id-1, inhibitor of neural differentiation, in the brain hippocampus. We also observed the increase in blood flow in the brain in KK-Ay mice with nifedipine treatment compared with nontreated mice. Taken together, our findings suggest that nifedipine ameliorates impaired cognitive function in type 2 diabetic mice, at least because of attenuation of hyperinsulinemia and superoxide production in the brain and possible upregulation of the neural differentiation-controlling gene, Id-1.

Temporary pretreatment with the angiotensin II type 1 receptor blocker, valsartan, prevents ischemic brain damage through an increase in capillary density.

Background and Purpose— We investigated the effect of temporary treatment with a nonhypotensive dose of valsartan on ischemic brain damage in C57BL/6 mice. Methods— We separated the mice into 3 groups of valsartan treatment before middle cerebral artery (MCA) occlusion: (1) for 4 weeks: Val (2W, 2W); (2) for 2 weeks followed by its cessation for 2 weeks: Val (2W, -); and (3) no treatment for 4 weeks: Val (-, -). Results— Ischemic volume, DNA damage, superoxide production, and mRNA levels of monocyte chemoattractant protein-1 and tumor necrosis factor-&agr; on the ipsilateral side after 24 hours of MCA occlusion were significantly reduced in both Val (2W, 2W) and Val (2W, -) mice compared with those in Val (-, -) mice, whereas these parameters were larger in Val (2W, -) mice than in Val (2W, 2W) mice. Moreover, mice in both the Val (2W, 2W) and Val (2W, -) groups exhibited an increase in cerebral blood flow in the peripheral territory of the MCA 1 hour after MCA occlusion, with increases in endothelial nitric oxide synthase activation and nitric oxide production. Before MCA occlusion, treatment with valsartan did not influence superoxide production or mRNA levels of monocyte chemoattractant protein-1 and tumor necrosis factor-&agr; in the brain. However, the capillary density in the brain in both Val (2W, 2W) and Val (2W, -) mice was increased before MCA occlusion. Conclusions— Our results suggest that temporary valsartan treatment could protect against ischemic brain damage even after its cessation, at least in part due to an increase in capillary density.

Inhibition of cognitive decline in mice fed a high-salt and cholesterol diet by the angiotensin receptor blocker, olmesartan

The metabolic syndrome is closely related to dietary habits and seems to be associated with impairment of cognitive function in humans. Angiotensin receptor blockers are widely used with the expectation of preventing cardiovascular events and stroke and potential amelioration of the metabolic syndrome. We examined the diet-induced changes of cognitive function in mice treated with a high-salt and high-cholesterol diet. C57BL/6J mice were fed a high-salt (2% NaCl in drinking water) and high-cholesterol (1.25% cholesterol, 10% coconut oil) diet (HSCD) or a normal diet (ND), and subjected to 20 trials of a passive avoidance task every week from 8weeks of age. An age-dependent decline of the avoidance rate starting from 10weeks of age was observed in HSCD mice, whereas the avoidance rate gradually increased in the ND group. Oral administration of an angiotensin receptor blocker, olmesartan, at a dose of 3mg/kg per day in drinking water from 8weeks of age prevents this decline of avoidance rate in HSCD mice (49% vs. 82% at 12weeks of age). Treatment with olmesartan significantly decreased serum glucose and cholesterol levels in HSCD mice, with a slight decrease in blood pressure. Administration of olmesartan in HSCD-fed mice showed a 1.6-fold increase in mRNA expression of a neuroprotective factor, MMS2, compared to HSCD-fed mice without olmesartan. Olmesartan attenuated the increase in superoxide anion production detected by dihydroethidium staining in the brain of HSCD mice. Our results suggest that olmesartan could be therapeutically effective in preventing the impairment of quality of life in persons on a high-fat and high-salt diet.

Amelioration of Cognitive Impairment in the Type-2 Diabetic Mouse by the Angiotensin II Type-1 Receptor Blocker Candesartan

Angiotensin II type-1 receptor blockers are widely used with the expectation of prevention of stroke, potential effects to ameliorate of type-2 diabetes, which seems to be closely associated with the impairment of cognitive function in humans. Recently, we have reported that an angiotensin II type-1 receptor blocker prevented cognitive impairment in mice after focal cerebral ischemia, at least partly through an angiotensin II type-2 receptor-mediated increase in a neuroprotective factor, methyl methanesulfonate sensitive-2. Here, we examined the possibility that an angiotensin II type-1 receptor blocker could improve cognitive function in a type-2 diabetic mouse model, KK-Ay. KK-Ay mice subjected to 20 trials of a passive avoidance task every week from 8 weeks exhibited a significantly impaired avoidance rate, and moreover, its age-dependent decline, especially after 14 weeks of age, compared with age-matched C57BL6 mice. Oral administration of candesartan at a nonhypotensive dose (0.005% in laboratory chow) in KK-Ay mice improved cognitive function and inhibited the impairment of cognitive decline. Methyl methanesulfonate sensitive-2 expression in the brain was lower in KK-Ay mice than in C57BL6 mice. Treatment with candesartan markedly increased mRNA expression of angiotensin II type-2 receptor and methyl methanesulfonate sensitive-2 in the brain in KK-Ay mice, determined by quantitative RT-PCR. In KK-Ay mice treated with candesartan, age-dependent increases in blood glucose and insulin were significantly suppressed. Our results suggest that candesartan ameliorates the impaired cognitive function in type-2 diabetes mice, at least because of an increased expression of methyl methanesulfonate sensitive-2, a neuroprotective factor, in addition to improvement of glucose intolerance.

Angiotensin II type 1 receptor-associated protein prevents vascular smooth muscle cell senescence via inactivation of calcineurin/nuclear factor of activated T cells pathway

Emerging new research suggests that the functions of the angiotensin (Ang) II type 1 (AT(1)) receptor are regulated in a complex manner. AT(1) receptor-associated protein (ATRAP) has been reported to reduce AT(1) receptor signaling with enhancement of AT(1) receptor internalization and to regulate the calcineurin/nuclear factor of activated T cells (NFAT) pathway. We examined the possibility that ATRAP could attenuate AT(1) receptor-mediated vascular senescence via inactivation with the calcineurin/NFAT pathway. Ang II stimulation significantly increased senescence-associated beta-galactosidase (SA-beta-gal)-stained cells, oxidative stress, and expression of p53 and p21 in wild-type (WT) vascular smooth muscle cells (VSMC). Moreover, in WT VSMC, Ang II stimulation enhanced NFAT transcriptional activity, which was prevented by CAML-siRNA treatment. NFAT-siRNA treatment attenuated Ang-II-increased SA-beta-gal activity and p53 and p21 expression. Treatment with a calcineurin activity inhibitor, cyclosporin A, reduced Ang-II-induced NFAT transcriptional activity and senescent VSMC. In contrast, VSMC prepared from ATRAP transgenic (ATRAP-Tg) mice exhibited attenuation of Ang-II-induced SA-beta-gal activity, oxidative stress, NFAT transcriptional activity, and expression of p53 and p21. Moreover, ATRAP-Tg VSMC showed a more reduction of Ang-II-induced NFAT transcriptional activity by CAML-siRNA treatment than WT VSMC. Furthermore, we demonstrated that in ATRAP-Tg VSMC, NFAT activity and senescent cells induced by ultraviolet irradiation were decreased compared with those in WT VSMC. Treatment with an AT(1) receptor blocker, valsartan, blocked these senescent cells but did not change NFAT activity in both cells. These results suggest that ATRAP negatively regulates VSMC senescence by reducing AT(1) receptor signaling, and that ATRAP-mediated inactivation of the calcineurin/NFAT pathway could be at least partly involved in prevention of VSMC senescence, irrespective of AT(1) receptor blockade in some conditions.