Jin Zhou

Angiotensin II AT1 Receptor Blockade Reverses Pathological Hypertrophy and Inflammation in Brain Microvessels of Spontaneously Hypertensive Rats

Background and Purpose— The spontaneously hypertensive rat (SHR) is vulnerable to brain ischemia and stress and exhibits a chronically stimulated brain angiotensin II system, cerebrovascular hypertrophy, and inflammation. Pretreatment with angiotensin II type 1 (AT1) receptor antagonists protects from brain ischemia and from stress and prevents the development of stress-induced gastric ulcers in part by reducing inflammation in the gastric mucosa. We studied whether AT1 receptor antagonists could exert antiinflammatory effects in the brain vasculature as a mechanism for their protective effects against ischemia. Methods— Ten-week-old SHR and normotensive Wistar-Kyoto male rats received the AT1 receptor antagonist candesartan (0.3 mg/kg per day) or vehicle for 28 days via osmotic minipumps. We studied AT1 receptors, intercellular adhesion molecule-1 (ICAM-1), endothelial nitric oxide synthase (eNOS), and number of macrophages by immunohistochemistry and Western blots. Results— We found increased endothelial AT1 receptor expression of brain microvessels and middle cerebral artery of SHR. Brain AT1 receptor inhibition reversed the pathological vascular hypertrophy, increased and normalized eNOS expression, and decreased ICAM-1 expression and the number of adherent and infiltrating macrophages in cerebral vessels of SHR. Conclusions— The antiinflammatory effects of AT1 receptor antagonists may be an important mechanism in protecting against ischemia.

Angiotensin II AT1 Receptor Blockade Abolishes Brain Microvascular Inflammation and Heat Shock Protein Responses in Hypertensive Rats

Endothelial dysfunction and inflammation enhance vulnerability to hypertensive brain damage. To explore the participation of Angiotensin II (Ang II) in the mechanism of vulnerability to cerebral ischemia during hypertension, we examined the expression of inflammatory factors and the heat shock protein (HSP) response in cerebral microvessels from spontaneously hypertensive rats and their normotensive controls, Wistar Kyoto rats. We treated animals with vehicle or the Ang II AT1 receptor antagonist candesartan, 0.3 mg/kg/day, via subcutaneously implanted osmotic minipumps for 4 weeks. Spontaneously hypertensive rats expressed higher Angiotensin II AT1 receptor protein and mRNA than normotensive controls. Candesartan decreased the macrophage infiltration and reversed the enhanced tumor necrosis factor-α and interleukin-1β mRNA and nuclear factor-κB in microvessels in hypertensive rats. The transcription of many HSP family genes, including HSP60, HSP70 and HSP90, and heat shock factor-1 was higher in hypertensive rats and was downregulated by AT1 receptor blockade. Our results suggest a proinflammatory action of Ang II through AT1 receptor stimulation in cerebral microvessels during hypertension, and very potent antiinflammatory effects of the Ang II AT1 receptor antagonist. These compounds might be considered as potential therapeutic agents against ischemic and inflammatory diseases of the brain.

AT1 Receptor Blockade Regulates the Local Angiotensin II System in Cerebral Microvessels From Spontaneously Hypertensive Rats

Background and Purpose— Blockade of angiotensin II AT1 receptors in cerebral microvessels protects against brain ischemia and inflammation. In this study, we tried to clarify the presence and regulation of the local renin-angiotensin system (RAS) in brain microvessels in hypertension. Methods— Spontaneously hypertensive rats (SHR) and Wistar Kyoto (WKY) controls were treated with an AT1 receptor antagonist (candesartan, 0.3 mg/kg per day) via subcutaneous osmotic minipumps for 4 weeks. The expression and localization of RAS components and the effect of AT1 receptor blockade were assessed by Affymetrix microarray, qRT-PCR, Western blots, immunohistochemistry and immunofluorescence. Results— We found transcripts of most of RAS components in our microarray database, and confirmed their expression by qRT-PCR. Angiotensinogen (Aogen), angiotensin-converting enzyme (ACE) and AT1 receptors were localized to the endothelium. There was no evidence of AT2 receptor localization in the microvascular endothelium. In SHR, (pro)renin receptor mRNA and AT1 receptor mRNA and protein expression were higher, whereas Aogen, ACE mRNA and AT2 receptor mRNA and protein expression were lower than in WKY rats. Candesartan treatment increased Aogen, ACE and AT2 receptor in SHR, and increased ACE and decreased Aogen in WKY rats, without affecting the (pro)renin and AT1 receptors. Conclusions— Increased (pro)renin and AT1 receptor expression in SHR substantiates the importance of the local RAS overdrive in the cerebrovascular pathophysiology in hypertension. AT1 receptor blockade and increased AT2 receptor stimulation after administration of candesartan may contribute to the protection against brain ischemia and inflammation.

Huperzine A and donepezil protect rat pheochromocytoma cells against oxygen-glucose deprivation

Huperzine A (HupA) and donepezil, two novel selective acetylcholinesterase inhibitors available for Alzheimers disease, were tested for their ability to alleviate injury from oxygen-glucose deprivation (OGD) in the rat pheochromocytoma line PC12 cells. OGD for 30 min triggered death in more than 50% of cells, along with major changes in morphology and biochemistry including elevated levels of lipid peroxide, superoxide disamutase activity and lactate. Cells pretreated for 2 h with HupA or donepezil showed improved survival and reduced biochemical and morphologic signs of toxicity (statistically significant over the range from 10 microM down to 1.0 and 0.1 microM, respectively). Our results indicated that HupA and donepezil protected PC12 cells against OGD-induced toxicity, most likely by alleviating disturbances of oxidative and energy metabolism.

Huperzine A attenuates cognitive deficits and hippocampal neuronal damage after transient global ischemia in gerbils

The protective effects of huperzine A on transient global ischemia in gerbils were investigated. Five min of global ischemia in gerbils results in working memory impairments shown by increased escape latency in a water maze and reduced time spent in the target quadrant. These signs of dysfunction are accompanied by delayed degeneration of pyramidal hippocampal CA1 neurons and by decrease in acetylcholinesterase activity in the hippocampus. Subchronic oral administration of huperzine A (0.1 mg/kg, twice per day for 14 days) after ischemia significantly reduced the memory impairment, reduced neuronal degeneration in the CA1 region, and partially restored hippocampal choline acetyltransferase activity. The ability of huperzine A to attenuate memory deficits and neuronal damage after ischemia might be beneficial in cerebrovascular type dementia.

Brain angiotensin II, an important stress hormone: regulatory sites and therapeutic opportunities.

Abstract: The presence of a brain Angiotensin II (Ang II) system, separated from and physiologically integrated with the peripheral, circulating renin‐angiotensin system, is firmly established. Ang II is made in the brain and activates specific brain AT1 receptors to regulate thirst and fluid metabolism. Some AT1 receptors are located outside the blood‐brain barrier and are sensitive to brain and circulating Ang II. Other AT1 receptors, located inside the blood‐brain barrier, respond to stimulation by Ang II of brain origin. AT1 receptors in the subfornical organ, the hypothalamic paraventricular nucleus (PVN), and the median eminence are involved in the regulation of the stress response. In particular, AT1 receptors in the PVN are under glucocorticoid control and regulate corticotrophin‐releasing hormone (CRH) formation and release. In the PVN, restraint elicits a fast increase in AT1 receptor mRNA expression. The expression of paraventricular AT1 receptors is increased during repeated restraint and after 24 h of isolation stress, and their stimulation is essential for the hypothalamic‐pituitary‐adrenal axis activation, the hallmark of the stress response. Peripheral administration of an AT1 receptor antagonist blocks peripheral and brain AT1 receptors, prevents the sympathoadrenal and hormonal response to isolation stress, and prevents the gastric stress ulcers that are a characteristic consequence of cold‐restraint stress. This evidence indicates that pharmacologic inhibition of the peripheral and brain Ang II system by AT1 receptor blockade has a place in the prevention and treatment of stress‐related disorders.

Tacrine attenuates hydrogen peroxide-induced apoptosis by regulating expression of apoptosis-related genes in rat PC12 cells

The present studies investigated the effects of tacrine, a selective acetylcholinesterase (AChE) inhibitor and promising anti-dementia agent, on hydrogen peroxide (H(2)O(2))-induced apoptosis and the expression of apoptosis-related genes in rat pheochromocytoma line PC12 cells. Transient exposure of the cells to H(2)O(2) (100 microM) triggered typical apoptosis as evidenced by chromatin condensation, nuclei fragmentation and DNA laddering. RT-PCR studies showed upregulated p53 and bax mRNA levels with H(2)O(2) treatment. The results were further confirmed at protein levels by immunocytochemistry with specific antibodies. Preincubation with tacrine significantly attenuated H(2)O(2)-induced injury, prevented the cells from apoptosis and attenuated H(2)O(2)-induced overexpression of bax and p53. The present findings suggest that tacrine exert significant protection against H(2)O(2)-induced apoptosis possibly through inhibiting expression of pro-apoptosis genes.

Mechanisms of the Anti-Ischemic Effect of Angiotensin II AT( 1 ) Receptor Antagonists in the Brain.

SUMMARY1. Circulating and locally formed Angiotensin II regulates the cerebral circulation through stimulation of AT1 receptors located in cerebrovascular endothelial cells and in brain centers controlling cerebrovascular flow.2. The cerebrovascular autoregulation is designed to maintain a constant blood flow to the brain, by vasodilatation when blood pressure decreases and vasoconstriction when blood pressure increases.3. During hypertension, there is a shift in the cerebrovascular autoregulation to the right, in the direction of higher blood pressures, as a consequence of decreased cerebrovascular compliance resulting from vasoconstriction and pathological growth. In hypertension, when perfusion pressure decreases as a consequence of blockade of a cerebral artery, reduced cerebrovascular compliance results in more frequent and more severe strokes with a larger area of injured tissue.4. There is a cerebrovascular angiotensinergic overdrive in genetically hypertensive rats, manifested as an increased expression of cerebrovascular AT1 receptors and increased activity of the brain Angiotensin II system. Excess AT1 receptor stimulation is a main factor in the cerebrovascular pathological growth and decreased compliance, the alteration of the cerebrovascular eNOS/iNOS ratio, and in the inflammatory reaction characteristic of cerebral blood vessels in genetic hypertension. All these factors increase vulnerability to brain ischemia and stroke.5. Sustained blockade of AT1 receptors with peripheral and centrally active AT1 receptor antagonists (ARBs) reverses the cerebrovascular pathological growth and inflammation, increases cerebrovascular compliance, restores the eNOS/iNOS ratio and decreases cerebrovascular inflammation. These effects result in a reduction of the vulnerability to brain ischemia, revealed, when an experimental stroke is produced, in protection of the blood flow in the zone of penumbra and substantial reduction in neuronal injury.6. The protection against ischemia resulting is related to inhibition of the Renin–Angiotensin System and not directly related to the decrease in blood pressure produced by these compounds. A similar decrease in blood pressure as a result of the administration of β-adrenergic receptor and calcium channel blockers does not protect from brain ischemia.7. In addition, sustained AT1 receptor inhibition enhances AT2 receptor expression, associated with increased eNOS activity and NO formation followed by enhanced vasodilatation. Direct AT1 inhibition and indirect AT2 receptor stimulation are associated factors normalizing cerebrovascular compliance, reducing cerebrovascular inflammation and decreasing the vulnerability to brain ischemia.8. These results strongly suggest that inhibition of AT1 receptors should be considered as a preventive therapeutic measure to protect the brain from ischemia, and as a possible novel therapy of inflammatory conditions of the brain.

Huperzine A attenuates apoptosis and mitochondria‐dependent caspase‐3 in rat cortical neurons

The neuroprotection of huperzine A against apoptosis was investigated. In cultures of rat primary cortical neurons, neuronal apoptosis was induced by serum deprivation for 24 h, which was accompanied by enhanced caspase‐3 activity and the release of cytochrome c into the cytosol from mitochondria. Pretreating the neurons for 2 h with huperzine A (0.1–10 μM) improved neuronal survival. Huperzine A at a concentration of 1 μM significantly attenuated apoptosis by inhibiting the mitochondria–caspase pathway directly and indirectly.

Huperzine A attenuates cognitive deficits and brain injury in neonatal rats after hypoxia-ischemia

The protective effects of huperzine A, a novel acetylcholinesterase inhibitor, on hypoxic-ischemic (HI) brain injury were investigated in neonatal rats. A unilateral HI brain injury was produced by the ligation of left common carotid artery followed by 1 h hypoxia with 7.7% oxygen in 7-day-old rat pups. After 5 weeks, HI brain injury in rat pups resulted in working memory impairments shown by increased escape latency in a water maze and reduced time spent in the target quadrant. The combination of common carotid artery ligation and exposure to a hypoxic environment caused the damage in the striatum, cortex, and hippocampus in the ipsilateral hemisphere, and the neuronal loss in the CA1 region. Huperzine A was administrated daily at the dose of 0.05 or 0.1 mg/kg i.p. for 5 weeks after HI injury. The significant protection against HI injury on behavior and neuropathology was produced by huperzine A at the dose of 0.1 mg/kg. These findings suggest that huperzine A might be beneficial in the treatment of hypoxic-ischemic encephalopathy in neonates.