The effects of poststroke captopril and losartan treatment on cerebral blood flow autoregulation in SHRsp with hemorrhagic stroke

Headache in Pregnancy: Preeclampsia and Intracerebral Hemorrhage

Preeclampsia is a type of hypertensive disorder of pregnancy that can cause significant maternal and perinatal morbidity and mortality. Hypertension and proteinuria are the keystones of the disease, though systemic end-organ dysfunction may follow. The pathogenesis is multifactorial, with known influences by placental, vascular, renal, and immunological dysfunction. This is a case of preeclampsia complicated by preterm delivery and antepartum intracerebral hemorrhage secondary to aneurysm rupture, presenting as dull headaches and blurry vision, commonly associated with severe features.

Plasma Kallikrein Contributes to Intracerebral Hemorrhage and Hypertension in Stroke-Prone Spontaneously Hypertensive Rats

Plasma kallikrein (PKa) has been implicated in contributing to hemorrhage following thrombolytic therapy; however, its role in spontaneous intracerebral hemorrhage is currently not available. This report investigates the role of PKa on hemorrhage and hypertension in stroke-prone spontaneously hypertensive rats (SHRSP). SHRSP were fed with a high salt-containing stroke-prone diet to increase blood pressure and induce intracerebral hemorrhage. The roles of PKa on blood pressure, hemorrhage, and survival in SHRSP were examined in rats receiving a PKa inhibitor or plasma prekallikrein antisense oligonucleotide (PK ASO) compared with rats receiving control ASO. Effects on PKa on the proteolytic cleavage of atrial natriuretic peptide (ANP) were analyzed by tandem mass spectrometry. We show that SHRSP on high-salt diet displayed increased levels of PKa activity compared with control rats. Cleaved kininogen was increased in plasma during stroke compared to SHRSP without stroke. Systemic administration of a PKa inhibitor or PK ASO to SHRSP reduced hemorrhage and blood pressure, and improved neurological function and survival compared with SHRSP receiving control ASO. Since PKa inhibition was associated with reduced blood pressure in hypertensive rats, we investigated the effects of PKa on the cleavage of ANP. Incubation of PKa with ANP resulted in the generation fragment ANP_5-28, which displayed reduced effects on blood pressure lowering compared with full length ANP. PKa contributes to increased blood pressure in SHRSP, which is associated with hemorrhage and reduced survival. PKa-mediated cleavage of ANP reduces its blood pressure lowering effects and thereby may contribute to hypertension-induced intracerebral hemorrhage.

The role of the brain renin-angiotensin system (RAS) in mild traumatic brain injury (TBI)

There is considerable interest in traumatic brain injury (TBI) induced by repeated concussions suffered by athletes in sports, military personnel from combat-and non-combat related activities, and civilian populations who suffer head injuries from accidents and domestic violence. Although the renin-angiotensin system (RAS) is primarily a systemic cardiovascular regulatory system that, when dysregulated, causes hypertension and cardiovascular pathology, the brain contains a local RAS that plays a critical role in the pathophysiology of several neurodegenerative diseases. This local RAS includes receptors for angiotensin (Ang) II within the brain parenchyma, as well as on circumventricular organs outside the blood-brain-barrier. The brain RAS acts primarily via the type 1 Ang II receptor (AT₁R), exacerbating insults and pathology. With TBI, the brain RAS may contribute to permanent brain damage, especially when a second TBI occurs before the brain recovers from an initial injury. Agents are needed that minimize the extent of injury from an acute TBI, reducing TBI-mediated permanent brain damage. This review discusses how activation of the brain RAS following TBI contributes to this damage, and how drugs that counteract activation of the AT₁R including AT₁R blockers (ARBs), renin inhibitors, angiotensin-converting enzyme (ACE) inhibitors, and agonists at type 2 Ang II receptors (AT₂) and at Ang (1-7) receptors (Mas) can potentially ameliorate TBI-induced brain damage.

Neuroprotective Effects of Casein-Derived Peptide Met-Lys-Pro (MKP) in a Hypertensive Model

We have previously reported that casein hydrolysate, CH-3, from bovine milk and casein-derived tripeptide Met-Lys-Pro (MKP) has ACE inhibitory activity and reduces blood pressure. In this study, we investigated the therapeutic effects of MKP in a hypertensive rat model (7-week-old male SHRSP/Izm rats). For long term evaluation, rats were fed either a diet containing CH-3 or normal diet. The survival rate of SHRSP rats was significantly improved by intake of CH-3 for 181 days. For short term evaluation, rats were orally administered synthetic tripeptide MKP or distilled water for 4 weeks. MRI study demonstrated that hemorrhagic lesions were observed in two of five rats in the control group, while no hemorrhagic lesions were observed in the MKP group. Volumetric analysis using MRI revealed that MKP administration inhibited atrophy of diencephalic regions. Histological examinations revealed that hemorrhage areas and astrogliosis in the hippocampus and cerebral cortex were lower in the MKP group than in the control group. Gene expression analysis indicated that MKP administration reduced expression of genes related to cerebral circulation insufficiency such as immune responses (Cd74 and Prkcd), response to hypoxia (Ddit4, Apold1, and Prkcd), reactive oxygen species metabolic process (Ddit4 and Pdk4), and apoptotic process (Ddit4, Prkcd, and Sgk1), suggesting that MKP administration prevented cerebral ischemia associated with hypertension. In addition, some genes encoding responses to hormone stimulus (Fos, Dusp1, and Sik1) were also downregulated. Serum aldosterone and corticosterone levels were also significantly decreased following MKP administration. The present study indicates that MKP shows neuroprotective effects in SHRSP rats by regulating cerebral circulation insufficiency and corticoid levels. MKP administration may therefore be a potential therapeutic strategy for hypertensive brain diseases such as cerebrovascular disease.

The Role of Sartans in the Treatment of Stroke and Subarachnoid Hemorrhage: A Narrative Review of Preclinical and Clinical Studies

Background: Delayed cerebral vasospasm (DCVS) due to aneurysmal subarachnoid hemorrhage (aSAH) and its sequela, delayed cerebral ischemia (DCI), are associated with poor functional outcome. Endothelin-1 (ET-1) is known to play a major role in mediating cerebral vasoconstriction. Angiotensin-II-type-1-receptor antagonists such as Sartans may have a beneficial effect after aSAH by reducing DCVS due to crosstalk with the endothelin system. In this review, we discuss the role of Sartans in the treatment of stroke and their potential impact in aSAH. Methods: We conducted a literature research of the MEDLINE PubMed database in accordance with PRISMA criteria on articles published between 1980 to 2019 reviewing: "Sartans AND ischemic stroke". Of 227 studies, 64 preclinical and 19 clinical trials fulfilled the eligibility criteria. Results: There was a positive effect of Sartans on ischemic stroke in both preclinical and clinical settings (attenuating ischemic brain damage, reducing cerebral inflammation and infarct size, increasing cerebral blood flow). In addition, Sartans reduced DCVS after aSAH in animal models by diminishing the effect of ET-1 mediated vasoconstriction (including cerebral inflammation and cerebral epileptogenic activity reduction, cerebral blood flow autoregulation restoration as well as pressure-dependent cerebral vasoconstriction). Conclusion: Thus, Sartans might play a key role in the treatment of patients with aSAH.

Repurposed molecules for antiepileptogenesis: Missing an opportunity to prevent epilepsy?

Prevention of epilepsy is a great unmet need. Acute central nervous system (CNS) insults such as traumatic brain injury (TBI), cerebrovascular accidents (CVA), and CNS infections account for 15%-20% of all epilepsy. Following TBI and CVA, there is a latency of days to years before epilepsy develops. This allows treatment to prevent or modify postinjury epilepsy. No such treatment exists. In animal models of acquired epilepsy, a number of medications in clinical use for diverse indications have been shown to have antiepileptogenic or disease-modifying effects, including medications with excellent side effect profiles. These include atorvastatin, ceftriaxone, losartan, isoflurane, N-acetylcysteine, and the antiseizure medications levetiracetam, brivaracetam, topiramate, gabapentin, pregabalin, vigabatrin, and eslicarbazepine acetate. In addition, there are preclinical antiepileptogenic data for anakinra, rapamycin, fingolimod, and erythropoietin, although these medications have potential for more serious side effects. However, except for vigabatrin, there have been almost no translation studies to prevent or modify epilepsy using these potentially "repurposable" medications. We may be missing an opportunity to develop preventive treatment for epilepsy by not evaluating these medications clinically. One reason for the lack of translation studies is that the preclinical data for most of these medications are disparate in terms of types of injury, models within different injury type, dosing, injury-treatment initiation latencies, treatment duration, and epilepsy outcome evaluation mode and duration. This makes it difficult to compare the relative strength of antiepileptogenic evidence across the molecules, and difficult to determine which drug(s) would be the best to evaluate clinically. Furthermore, most preclinical antiepileptogenic studies lack information needed for translation, such as dose-blood level relationship, brain target engagement, and dose-response, and many use treatment parameters that cannot be applied clinically, for example, treatment initiation before or at the time of injury and dosing higher than tolerated human equivalent dosing. Here, we review animal and human antiepileptogenic evidence for these medications. We highlight the gaps in our knowledge for each molecule that need to be filled in order to consider clinical translation, and we suggest a platform of preclinical antiepileptogenesis evaluation of potentially repurposable molecules or their combinations going forward.

The Application of Non-linear Flow Resistance in Cerebral Artery: Compared with Windkessel Model based on Genetic Algorithm

Continuous blood pressure is measured from various extracranial body sites, with difference in amplitude and phase with intracranial blood pressure. Consequent influences on the accuracy of Windkessel model need further investigation. Between blood pressure and intracranial flow rate, a model with non-linear flow resistance (R-DT) was proposed and compared with the 3-element Windkessel (RCR) model. From the measured blood flow velocity in middle cerebral artery, the blood pressure was estimated by R-DT and RCR models respectively. The parameters in the models were optimized by genetic algorithm. The accuracies of R-DT and RCR models were compared based on their estimation errors to the measured blood pressure. The capacitance element in RCR model indicated limited ability to take the time shift into account. Compared with RCR model, R-DT model had less error (averaged relative error: 5.19% and 2.49% for RCR and RDT models). The non-linear flow resistance was applicable in simulating cerebral arteries.

The angiotensin II type I receptor contributes to impaired cerebral blood flow autoregulation caused by placental ischemia in pregnant rats

BACKGROUND

Placental ischemia and hypertension, characteristic features of preeclampsia, are associated with impaired cerebral blood flow (CBF) autoregulation and cerebral edema. However, the factors that contribute to these cerebral abnormalities are not clear. Several lines of evidence suggest that angiotensin II can impact cerebrovascular function; however, the role of the renin angiotensin system in cerebrovascular function during placental ischemia has not been examined. We tested whether the angiotensin type 1 (AT1) receptor contributes to impaired CBF autoregulation in pregnant rats with placental ischemia caused by surgically reducing uterine perfusion pressure.

METHODS

Placental ischemic or sham operated rats were treated with vehicle or losartan from gestational day (GD) 14 to 19 in the drinking water. On GD 19, we assessed CBF autoregulation in anesthetized rats using laser Doppler flowmetry.

RESULTS

Placental ischemic rats had impaired CBF autoregulation that was attenuated by treatment with losartan. In addition, we examined whether an agonistic autoantibody to the AT1 receptor (AT1-AA), reported to be present in preeclamptic women, contributes to impaired CBF autoregulation. Purified rat AT1-AA or vehicle was infused into pregnant rats from GD 12 to 19 via mini-osmotic pumps after which CBF autoregulation was assessed. AT1-AA infusion impaired CBF autoregulation but did not affect brain water content.

CONCLUSIONS

These results suggest that the impaired CBF autoregulation associated with placental ischemia is due, at least in part, to activation of the AT1 receptor and that the RAS may interact with other placental factors to promote cerebrovascular changes common to preeclampsia.

Choices for long-term hypertensive control in patients after first-ever hemorrhagic stroke: a nationwide cohort study

Background

To compare the long-term clinical outcomes of different antihypertensive drugs in stable patients after acute hemorrhagic stroke (HS).

Methods

From January 2001 to December 2013, patients with first-ever primary HS were identified in the National Health Insurance Research Database, Taiwan. Patients with traumatic intracerebral hemorrhage and secondary HS were excluded. Those with first-ever HS were recruited and classified into three groups: (1) angiotensin-converting enzyme inhibitor/angiotensin receptor blocker (ACEI/ARB); (2) calcium channel blocker (CCB); and (3) other antihypertensive drugs (comparison) groups. Propensity score matching was used to balance the distribution of baseline characteristics, stroke severity, and medications between any two of the three groups. A validation study was performed using the databank of the Stroke Registry in Chang-Gung Healthcare System to reduce the bias. Primary outcomes were recurrent HS, ischemic stroke, any stroke, and all-cause mortality.

Results

Compared to the comparison group, the ACEI/ARB group [35.4% versus 39.3%; hazard ratio (HR), 0.84; 95% confidence interval (CI), 0.74-0.95] and CCB group (33.0% versus 41.9%; HR, 0.72; 95% CI, 0.64-0.81) had a lower risk of all-cause mortality during long-term follow up. The CCB group had a similar risk of all-cause mortality to the ACEI/ARB group. Risks of recurrent HS, ischemic stroke, or any stroke were not different between the study groups.

Conclusions

Antihypertensive drug class could be important to long-term outcomes in HS patients in addition to the target control of blood pressure. Both ACEIs/ARBs and CCBs are associated with lower risks of all-cause mortality. Our results may be applied to inform future research on hypertensive control in HS patients.

Vasomodulatory effects of the angiotensin II type 1 receptor antagonist losartan on experimentally induced cerebral vasospasm after subarachnoid haemorrhage

BACKGROUND

Cerebral vasospasm following subarachnoid haemorrhage (SAH) remains one of the major factors contributing to poor overall patient outcome. Prostaglandin F2-alpha (PGF2a) induces vasoconstriction. After SAH, PGF2a leads to cerebral inflammation and enhanced vasoconstriction, resulting in cerebral vasospasm. Losartan is already known to have beneficial effects in stroke models and also on several cerebral inflammatory processes. Therefore, the aim of the study was to analyse the effect of losartan on PGF2a-enhanced vasoconstriction after SAH.

METHODS

To investigate the effect of losartan on PGF2a-enhanced vasoconstriction after SAH, cerebral vasospasm was induced by a double-haemorrhage model. Rats were killed on day 3 and 5 after SAH followed by measurement of the isometric force of basilar artery ring segments in an organ bath.

RESULTS

PGF2a induced a dose-dependent contraction. After pre-incubation with losartan, the maximum contraction (E_max) for sham-operated animals was significantly lowered [E_max 6% in losartan 3 × 10^-4 molar (M) vs. 56% without losartan]. Also, after induced SAH, PGF2a induced no vasoconstriction in pre-incubated vessels with losartan 3 × 10^-4 M on day 3 (d3) as well as on day 5 (d5). For the vasorelaxative investigations, vessel segments were pre-incubated with PFG2a. Cumulative application of losartan completely resolved the pre-contraction in sham-operated animals (non SAH: 95% relaxation). After SAH, losartan not only resolved the pre-contraction (d5: 103%), but also exceeded the pre-contraction (d3: 119%). Therefore, a statistically significantly increased and earlier relaxation was calculated for all losartan concentrations [E_max (d3/d5) and pD₂ (d3/d5)] compared with the solvent control group.

CONCLUSION

In a physiological and pathophysiological setup, losartan reduces a PGF2-induced vasoconstriction and reverses a PGF2a-precontraction completely. This fact can be integrated in pushing forward further concepts trying to antagonise/prevent cerebral vasospasm after SAH.

Elastin microfibril interface-located protein 1, transforming growth factor beta, and implications on cardiovascular complications

Elastin microfibril interface-located protein 1 (EMILIN1), a glycoprotein, is associated with elastin in the extracellular matrix (ECM) of arteries, lymph vasculature, and other tissues. EMILIN1 particularly has a niche role in elastin fiber biogenesis (elastogenesis) by aiding with the fusion of elastin fibers, rendering them more ordered. In addition to elastogenesis, EMILIN1 has been shown to have roles in maintenance of vascular cell morphology, smooth muscle cell adhesion to elastic fibers, and transforming growth factor (TGFβ) regulation, by inhibiting TGFβ activation via blocking the proteolytic production of the latency-associated peptide/active TGFβ complex. The increased TGFβ signaling induced during EMILIN1 deficiency alters TGFβ activity, resulting in vascular smooth muscle cell growth and vascular remodeling. The increasing systemic blood pressure associated with TGFβ signaling may be closely linked to the activity of other mediators that affect cardiovascular homeostasis, such as angiotensin II. The increase in prevalence of hypertension and other cardiovascular diseases in other disease states likely involve a complex activation of TGFβ signaling and ECM dysfunction. Thus, the interaction of TGFβ and ECM components appears to be integrative involving both structural alterations to vessels through EMILIN1 and changes in TGFβ signaling processes. This review summarizes the current knowledge on the EMILIN1-TGFβ relationship; the specific roles of EMILIN1 and TGFβ in blood pressure regulation, their synergistic interaction, and in particular the role of TGFβ (in conjunction with ECM proteins) in other disease states altering cardiovascular homeostasis.

Abnormal myosin phosphatase targeting subunit 1 phosphorylation and actin polymerization contribute to impaired myogenic regulation of cerebral arterial diameter in the type 2 diabetic Goto-Kakizaki rat

The myogenic response of cerebral resistance arterial smooth muscle to intraluminal pressure elevation is a key physiological mechanism regulating blood flow to the brain. Rho-associated kinase plays a critical role in the myogenic response by activating Ca²⁺ sensitization mechanisms: (i) Rho-associated kinase inhibits myosin light chain phosphatase by phosphorylating its targeting subunit myosin phosphatase targeting subunit 1 (at T855), augmenting 20 kDa myosin regulatory light chain (LC₂₀) phosphorylation and force generation; and (ii) Rho-associated kinase stimulates cytoskeletal actin polymerization, enhancing force transmission to the cell membrane. Here, we tested the hypothesis that abnormal Rho-associated kinase-mediated myosin light chain phosphatase regulation underlies the dysfunctional cerebral myogenic response of the Goto-Kakizaki rat model of type 2 diabetes. Basal levels of myogenic tone, LC₂₀, and MYPT1-T855 phosphorylation were elevated and G-actin content was reduced in arteries of pre-diabetic 8-10 weeks Goto-Kakizaki rats with normal serum insulin and glucose levels. Pressure-dependent myogenic constriction, LC₂₀, and myosin phosphatase targeting subunit 1 phosphorylation and actin polymerization were suppressed in both pre-diabetic Goto-Kakizaki and diabetic (18-20 weeks) Goto-Kakizaki rats, whereas RhoA, ROK2, and MYPT1 expression were unaffected. We conclude that abnormal Rho-associated kinase-mediated Ca²⁺ sensitization contributes to the dysfunctional cerebral myogenic response in the Goto-Kakizaki model of type 2 diabetes.

Development of a stretch-induced neurotrauma model for medium-throughput screening in vitro: identification of rifampicin as a neuroprotectant

BACKGROUND AND PURPOSE

We hypothesized that an in vitro, stretch-based model of neural injury may be useful to identify compounds that decrease the cellular damage in neurotrauma.

EXPERIMENTAL APPROACH

We screened three neural cell lines (B35, RN33B and SH-SY5Y) subjected to two differentiation methods and selected all-trans-retinoic acid-differentiated B35 rat neuroblastoma cells subjected to rapid stretch injury, coupled with a subthreshold concentration of H₂ O₂ , for the screen. The model induced marked alterations in gene expression and proteomic signature of the cells and culminated in delayed cell death (LDH release) and mitochondrial dysfunction [reduced 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) conversion]. Follow-up studies utilized human stem cell-derived neurons subjected to rapid stretch injury.

KEY RESULTS

From screening of a composite library of 3500 drugs, five drugs (when applied in a post-treatment regimen relative to stretch injury) improved both LDH and MTT responses. The effects of rifampicin were investigated in further detail. Rifampicin reduced cell necrosis and apoptosis and improved cellular bioenergetics. In a second model (stretch injury in human stem cell-derived neurons), rifampicin pretreatment attenuated LDH release, protected against the loss of neurite length and maintained neuron-specific class III β-tubulin immunoreactivity.

CONCLUSIONS AND IMPLICATIONS

We conclude that the current model is suitable for medium-throughput screening to identify compounds with neuroprotective potential. Rifampicin, when applied either in pre- or post-treatment, improves the viability of neurons subjected to stretch injury and protects against neurite loss. Rifampicin may be a candidate for repurposing for the therapy of traumatic brain injury.

LINKED ARTICLES

This article is part of a themed section on Inventing New Therapies Without Reinventing the Wheel: The Power of Drug Repurposing. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.2/issuetoc.

Alterations to the middle cerebral artery of the hypertensive-arthritic rat model potentiates intracerebral hemorrhage

Aims

We have recently created an age-dependent hypertensive-mono-arthritic animal model from the stroke-resistant spontaneously hypertensive rat to model populations with autoimmune disease who are hypertensive and are prone to stroke. The model exhibits signs of hemorrhagic stroke (HS) subsequent to chronic inflammation and hypertension. HS is also associated with the inability of middle cerebral arteries to undergo pressure dependent constriction (PDC). We investigated alterations in the cerebrovasculature of our hypertensive mono-arthritic animals that develop stroke.

Main Methods

Animals were fed either a high salt diet (HSD) (4% NaCl) or Purina chow (0.58% NaCl) from weaning. Complete Freund’s Adjuvant (CFA) was injected into the left hind paw at 21–28 weeks; controls received saline and histological and functional studies were performed.

Results

Brain damage was more prominent with the high salt, with inflammation exacerbating the damage. High salt alone significantly decreased middle cerebral artery’s (MCA’s) ability to undergo PDC. Inflammation significantly decreased the ability of cerebrovasculature to respond to pressure step in the regular salt diet. The responses to vasoactive peptides were also significantly attenuated in both inflamed groups regardless of diet.

Conclusion

Induction of chronic systemic inflammation increases brain damage, and affect the MCA’s vasogenic function, decreasing its ability to respond to intraluminal pressure. HSD further exacerbates organ damage associated with chronic inflammation, further compromising cerebrovascular function, and likely increasing the incidence of intracerebral hemorrhage and injury.

Renin-angiotensin system as a potential therapeutic target in stroke and retinopathy: experimental and clinical evidence

As our knowledge expands, it is now clear that the renin-angiotensin (Ang) system (RAS) mediates functions other than regulating blood pressure (BP). The RAS plays a central role in the pathophysiology of different neurovascular unit disorders including stroke and retinopathy. Moreover, the beneficial actions of RAS modulation in brain and retina have been documented in experimental research, but not yet exploited clinically. The RAS is a complex system with distinct yet interconnected components. Understanding the different RAS components and their functions under brain and retinal pathological conditions is crucial to reap their benefits. The aim of the present review is to provide an experimental and clinical update on the role of RAS in the pathophysiology and treatment of stroke and retinopathy. Combining the evidence from both these disorders allows a unique opportunity to move both fields forward.

Adjuvant-induced mono-arthritis potentiates cerebral hemorrhage in the spontaneously hypertensive rats

AIMS

Patients with rheumatoid arthritis (RA), have a higher incidence of hypertension and stroke than the normal population. Currently there exists no animal model to study the pathogenic interactions of hemorrhagic stroke (HS) subsequent to chronic inflammation and hypertension. We have created and defined a hypertensive-mono-arthritic animal model who demonstrate gros signs of cerebral hemorrhage in presence of mono-arthritis.

MAIN METHODS

Spontaneously hypertensive rats (SHR) were fed either a high salt diet (4% NaCl; HSD) or Purina chow (RD) from weaning. Complete Freund's adjuvant (CFA) was injected into the left hind paw at 21-28weeks (control groups received saline (SAL)). Degree of inflammation, joint swelling, weight and blood pressure were monitored for 21days. Animals were then sacrificed and their brain and left hind paw evaluated.

KEY FINDINGS

All groups were hypertensive throughout the experimental period (>180mmHg systolic), irrespective of diet. Both CFA groups produced significant local inflammatory response in their injected paw with associated joint degradation and cellular infiltrates. Systemic plasma TNF-α levels were significantly elevated in CFA groups, with significant increase in TNF-α at 7 and 14days, compared to SAL groups. Cerebral hemorrhage was visualized in the CFA groups but not SAL controls, with a higher severity in HSD-CFA group.

SIGNIFICANCE

The mono-arthritic hypertensive animals are capable of developing HS upon induction of inflammatory insult. The HSD appears to exacerbate the inflammatory response and influence degree of the hemorrhage. Our novel, multi-disease model may provide an appropriate platform to study the pathogenesis of HS among arthritic patients.

Cardiac Output and Cerebral Blood Flow

Cerebral blood flow (CBF) is rigorously regulated by various powerful mechanisms to safeguard the match between cerebral metabolic demand and supply. The question of how a change in cardiac output (CO) affects CBF is fundamental, because CBF is dependent on constantly receiving a significant proportion of CO. The authors reviewed the studies that investigated the association between CO and CBF in healthy volunteers and patients with chronic heart failure. The overall evidence shows that an alteration in CO, either acutely or chronically, leads to a change in CBF that is independent of other CBF-regulating parameters including blood pressure and carbon dioxide. However, studies on the association between CO and CBF in patients with varying neurologic, medical, and surgical conditions were confounded by methodologic limitations. Given that CBF regulation is multifactorial but the various processes must exert their effects on the cerebral circulation simultaneously, the authors propose a conceptual framework that integrates the various CBF-regulating processes at the level of cerebral arteries/arterioles while still maintaining autoregulation. The clinical implications pertinent to the effect of CO on CBF are discussed. Outcome research relating to the management of CO and CBF in high-risk patients or during high-risk surgeries is needed.

Renal autoregulation in health and disease

Intrarenal autoregulatory mechanisms maintain renal blood flow (RBF) and glomerular filtration rate (GFR) independent of renal perfusion pressure (RPP) over a defined range (80-180 mmHg). Such autoregulation is mediated largely by the myogenic and the macula densa-tubuloglomerular feedback (MD-TGF) responses that regulate preglomerular vasomotor tone primarily of the afferent arteriole. Differences in response times allow separation of these mechanisms in the time and frequency domains. Mechanotransduction initiating the myogenic response requires a sensing mechanism activated by stretch of vascular smooth muscle cells (VSMCs) and coupled to intracellular signaling pathways eliciting plasma membrane depolarization and a rise in cytosolic free calcium concentration ([Ca(2+)]i). Proposed mechanosensors include epithelial sodium channels (ENaC), integrins, and/or transient receptor potential (TRP) channels. Increased [Ca(2+)]i occurs predominantly by Ca(2+) influx through L-type voltage-operated Ca(2+) channels (VOCC). Increased [Ca(2+)]i activates inositol trisphosphate receptors (IP3R) and ryanodine receptors (RyR) to mobilize Ca(2+) from sarcoplasmic reticular stores. Myogenic vasoconstriction is sustained by increased Ca(2+) sensitivity, mediated by protein kinase C and Rho/Rho-kinase that favors a positive balance between myosin light-chain kinase and phosphatase. Increased RPP activates MD-TGF by transducing a signal of epithelial MD salt reabsorption to adjust afferent arteriolar vasoconstriction. A combination of vascular and tubular mechanisms, novel to the kidney, provides for high autoregulatory efficiency that maintains RBF and GFR, stabilizes sodium excretion, and buffers transmission of RPP to sensitive glomerular capillaries, thereby protecting against hypertensive barotrauma. A unique aspect of the myogenic response in the renal vasculature is modulation of its strength and speed by the MD-TGF and by a connecting tubule glomerular feedback (CT-GF) mechanism. Reactive oxygen species and nitric oxide are modulators of myogenic and MD-TGF mechanisms. Attenuated renal autoregulation contributes to renal damage in many, but not all, models of renal, diabetic, and hypertensive diseases. This review provides a summary of our current knowledge regarding underlying mechanisms enabling renal autoregulation in health and disease and methods used for its study.

Should losartan be administered following brain injury?

Brain injury is a major health concern and associated with delayed neurological complications, including post-injury epilepsy, cognitive and emotional disabilities. Currently, there is no strategy to prevent post-injury delayed complications. We recently showed that dysfunction of the blood-brain barrier, often reported in brain injuries, can lead to epilepsy and neurodegeneration via activation of inflammatory TGF-β signaling in astrocytes. We further showed that the FDA approved angiotensin II type 1 receptor antagonist, losartan, blocks brain TGF-β signaling and prevents epilepsy in the albumin or blood-brain barrier breakdown models of epileptogenesis. Here we discuss the potential of losartan as an anti-epileptogenic and a neuroprotective drug, the rationale of its use following brain injury and the challenges of designing clinical trials. We highlight the urgent need to develop reliable biomarkers for epileptogenesis (and other complications) after brain injury as a pre-requisite to challenge neuroprotective therapies.

Etiologies of intracerebral hematomas

Intracerebral hemorrhage (ICH) remains a life-threatening disease that carries significant morbidity and mortality despite recent diagnostic and management advances. Various conditions are associated with increased risk of intracerebral hemorrhage. Understanding the etiology of these conditions and their pathophysiological contribution to ICH will likely lead to better therapeutic and preventative measures and improve the morbidity and mortality associated with intracerebral hemorrhage. We will review the current literature regarding important etiologies/risk factors of intracerebral hemorrhage.

Aldosterone and the mineralocorticoid receptor in the cerebral circulation and stroke

Ischemic stroke is a leading cause of morbidity and mortality worldwide. Elevated plasma aldosterone levels are an independent cardiovascular risk factor and are thought to contribute to hypertension, a major risk factor for stroke. Evidence from both experimental and human studies supports a role for aldosterone and/or the mineralocorticoid receptor (MR) in contributing to detrimental effects in the cerebral vasculature and to the incidence and outcome of ischemic stroke. This article reviews the evidence, including the protective effects of MR antagonism. Specifically, the effects of aldosterone and/or MR activation on cerebral vascular structure and on immune cells will be reviewed. The existing evidence suggests that aldosterone and the MR contribute to cerebral vascular pathology and to the incidence and outcome of stroke. We suggest that further research into the signaling mechanisms underlying the effects of aldosterone and MR activation in the brain and its vasculature, especially with regard to cell-specific actions, will provide important insight into causes and potential treatments for cerebrovascular disease and stroke.

Cognition and Hemodynamics

The relationship between cerebral hemodynamics and cognitive performance has increasingly become recognized as a major challenge in clinical practice for older adults. Both diabetes and hypertension worsen brain perfusion and are major risk factors for cerebrovascular disease, stroke and dementia. Cerebrovascular reserve has emerged as a potential biomarker for monitoring pressure-perfusion-cognition relationships. Endothelial dysfunction and inflammation, microvascular disease, and mascrovascular disease affect cerebral hemodynamics and play an important role in pathohysiology and severity of multiple medical conditions, presenting as cognitive decline in the old age. Therefore, the identification of cerebrovascular vascular reactivity as a new therapeutic target is needed for prevention of cognitive decline late in life.

Role of angiotensin II in the brain inflammatory events during experimental diabetes in rats

Hyperglycemia during diabetes is one of the causes of encephalopathy. However, diabetes causes chronic inflammatory complications and among them is peripheral neuropathy. Since, diabetes is one of the major risk factors for cerebrovascular disease, inflammatory process could take place in central nervous system (CNS). To test that hypothesis, experiments to determine inflammatory events in CNS during streptozotocin-induced diabetes were performed. Diabetes was induced by intravenous injection of streptozotocin (STZ). Brain angiotensin II (Ang II), monocyte/macrophage (ED-1 positive cells), CD8, the intercellular adhesion molecule-1 (ICAM-1), the lymphocyte function-associated antigen-1 (LFA-1) and superoxide anion were determined by hystochemical and immunohistochemical methods. Nitric oxide (NO), malondialdehyde (MDA) and catalase activity were measured in brain homogenates by enzymatic and biochemical methods. This research showed increased expressions of Ang II, ICAM-1, LFA-1 and CD8 positive cells in diverse zones of cerebrum and cerebellum of diabetic rats (week 8). Treatment of diabetic animals with losartan or enalapril reduced the expression of those molecules. Values of lipid peroxidation, nitrite content and superoxide anion expression remained similar to control rats. Only decreased activity of catalase was observed in diabetic animals, but losartan or enalapril failed to modify catalase activity. This study suggests the presence of Ang II-mediated brain inflammatory events in diabetes probably mediated by AT1 receptors.