A new paradigm for the treatment of Alzheimer's disease: targeting vascular activation.

No disease-modifying therapies are currently available for Alzheimer's disease (AD), a neurodegenerative disorder that affects more than 36 million people worldwide. Although cardiovascular risk factors such as hypertension and diabetes are increasingly implicated as contributing to the development of AD, the mechanisms whereby these factors influence pathological processes in the AD brain have not been defined. Here we propose, for the first time, vascular activation as a relevant mechanism in AD pathogenesis. We explore this hypothesis in two transgenic AD animal models: AD2576APPSwe (AD2576) and LaFerla 3xTg (3xTgAD) mice using the vascular activation inhibitor sunitinib. Our data show that in both AD animal models, the cerebrovasculature is activated and overexpresses amyloid beta, thrombin, tumor necrosis factor alpha, interleukin-1 beta, interleukin-6, and matrix metalloproteinase 9. Oral administration of sunitinib significantly reduces vascular expression of these proteins. Furthermore, sunitinib improves cognitive function, as assessed by several behavioral paradigms, in both AD animal models. Finally, oxidant injury of brain endothelial cells in culture, resulting in expression of inflammatory proteins, is mitigated by sunitinib. The current data, as well as published studies showing cerebrovascular activation in human AD, support further exploration of vascular-based mechanisms in AD pathogenesis. New thinking about AD pathogenesis and novel, effective treatments are urgently needed. Identification of "vascular activation" as a heretofore unexplored target could stimulate translational investigations in this newly defined area, leading to innovative therapeutic approaches for the treatment of this devastating disease.

Purification of endothelial cells from rat brain.

Endothelial cells make up a minor population of cells in a tissue, but play a major role in tissue homeostasis, as well as in diverse pathologies. To understand the biology of cerebral endothelium, purification and characterization of the cerebrocortical endothelial cell population is highly desirable. For this purpose, rat brains are mechanically minced and subsequently digested enzymatically with collagenase. In this protocol, the capillary fraction (microvessels) and the fraction enriched in small arterioles and arteries (resistance vessels) are separated. Each produces its own homogenous endothelial culture, namely, MV-EC and RV-EC. The endothelial origin of these cells is identified by positive immunofluorescent staining for the endothelial cell surface antigen Factor VIII. Unlike MV-EC, RV-EC cultures are capable of serial cultivation for up to 15 passages. Primary MV-ECs are able to retain their characteristic endothelial morphology for 6-8 weeks.

Sunitinib enhances neuronal survival in vitro via NF-κB-mediated signaling and expression of cyclooxygenase-2 and inducible nitric oxide synthase.

BACKGROUND: Angiogenesis is tightly linked to inflammation and cancer. Regulation of angiogenesis is mediated primarily through activation of receptor tyrosine kinases, thus kinase inhibitors represent a new paradigm in anti-cancer therapy. However, these inhibitors have broad effects on inflammatory processes and multiple cell types. Sunitinib is a multitarget receptor tyrosine kinase inhibitor, which has shown promise for the treatment of glioblastoma, a highly vascularized tumor. However, there is little information as to the direct effects of sunitinib on brain-derived neurons. The objective of this study is to explore the effects of sunitinib on neuronal survival as well as on the expression of inflammatory protein mediators in primary cerebral neuronal cultures. METHODS: Primary cortical neurons were exposed to various doses of sunitinib. The drug-treated cultures were assessed for survival by MTT assay and cell death by lactate dehydrogenase release. The ability of sunitinib to affect NF-κB, COX2 and NOS2 expression was determined by western blot. The NF-κB inhibitors dicoumarol, SN50 and BAY11-7085 were employed to assess the role of NF-κB in sunitinib-mediated effects on neuronal survival as well as COX2 and NOS2 expression. RESULTS: Treatment of neuronal cultures with sunitinib caused a dose-dependent increase in cell survival and decrease in neuronal cell death. Exposure of neurons to sunitinib also induced an increase in the expression of NF-κB, COX2 and NOS2. Inhibiting NF-κB blunted the increase in cell survival and decrease in cell death evoked by sunitinib. Treatment of cell cultures with both sunitinib and NF-κB inhibitors mitigated the increase in COX2 and NOS2 caused by sunitinib. CONCLUSIONS: Sunitinib increases neuronal survival and this neurotrophic effect is mediated by NF-κB. Also, the inflammatory proteins COX2 and NOS2 are upregulated by sunitinib in an NF-κB-dependent manner. These data are in agreement with a growing literature suggesting beneficial effects for inflammatory mediators such as NF-κB, COX2 and NOS2 in neurons. Further work is needed to fully explore the effects of sunitinib in the brain and its possible use as a treatment for glioblastoma. Finally, sunitinib may be useful for the treatment of a range of central nervous system diseases where neuronal injury is prominent.

Thrombin, a mediator of cerebrovascular inflammation in AD and hypoxia.

Considerable evidence implicates hypoxia and vascular inflammation in Alzheimer's disease (AD). Thrombin, a multifunctional inflammatory mediator, is demonstrable in the brains of AD patients both in the vessel walls and senile plaques. Hypoxia-inducible factor 1α (HIF-1α), a key regulator of the cellular response to hypoxia, is also upregulated in the vasculature of human AD brains. The objective of this study is to investigate inflammatory protein expression in the cerebrovasculature of transgenic AD mice and to explore the role of thrombin as a mediator of cerebrovascular inflammation and oxidative stress in AD and in hypoxia-induced changes in brain endothelial cells. Immunofluorescent analysis of the cerebrovasculature in AD mice demonstrates significant (p < 0.01-0.001) increases in thrombin, HIF-1α, interleukin-6 (IL-6), monocyte chemoattractant protein-1 (MCP-1), matrix metalloproteinases (MMPs), and reactive oxygen species (ROS) compared to controls. Administration of the thrombin inhibitor dabigatran (100 mg/kg) to AD mice for 34 weeks significantly decreases expression of inflammatory proteins and ROS. Exposure of cultured brain endothelial cells to hypoxia for 6 h causes an upregulation of thrombin, HIF-1α, MCP-1, IL-6, and MMP2 and ROS. Treatment of endothelial cells with the dabigatran (1 nM) reduces ROS generation and inflammatory protein expression (p < 0.01-0.001). The data demonstrate that inhibition of thrombin in culture blocks the increase in inflammatory protein expression and ROS generation evoked by hypoxia. Also, administration of dabigatran to transgenic AD mice diminishes ROS levels in brain and reduces cerebrovascular expression of inflammatory proteins. Taken together, these results suggest that inhibiting thrombin generation could have therapeutic value in AD and other disorders where hypoxia, inflammation, and oxidative stress are involved.

Neurovascular unit and the effects of dosage in VEGF toxicity: role for oxidative stress and thrombin.

Bidirectional communication between neurons and vascular cells is important to the maintenance of the central nervous system (CNS) milieu. Vascular endothelial growth factor (VEGF), through its ability to affect both vascular and neuronal cells, is likely a key protein in this process. Despite considerable literature documenting a neuroprotective function for VEGF, overexpression of this protein has also been shown in a wide variety of CNS diseases, including Alzheimer's disease (AD). Increased oxidative stress and elevated thrombin levels have also been documented in AD, specifically in the microvasculature. The aim of the current study is to examine endothelial cells and neurons in vitro to determine the effects of oxidative stress and thrombin on VEGF release as well as the effects of low and high dose VEGF on neuronal viability. The data show that microvessels isolated from AD patients secrete significantly higher levels of VEGF compared to control-derived vessels. Exposure of brain endothelial cells to oxidative stress (sodium nitroprusside, menadione, or hydrogen peroxide) or thrombin significantly increases VEGF expression. Exposure of cultured neurons to oxidative stress increases expression of thrombin. Treating rat cortical neurons with high dose VEGF (≥500 ng/ml) decreases neuronal survival and expression of the anti-apoptotic protein Bcl-2 while increasing proapoptic proteins caspase 3 and phosphorylated p38 MAPK. High dose VEGF also negates the decrease in amyloid-ß evoked by low dose VEGF. These results suggest that despite literature supporting neuroprotective effects of this protein, caution is warranted prior to implementation of VEGF as a therapeutic in the brain.

Age-related decrease in cerebrovascular-derived neuroprotective proteins: effect of acetaminophen.

As the population ages, the need for effective methods to maintain brain function in older adults is increasingly pressing. Vascular disease and neurodegenerative disorders commonly co-occur in older persons. Cerebrovascular products contribute to the neuronal milieu and have important consequences for neuronal viability. In this regard vascular derived neuroprotective proteins, Such as vascular endothelial growth factor (VEGF), pigment epithelium-derived factor (PEDF), and pituitary adenylate cyclase activating peptide (PACAP) are important for maintaining neuronal viability, especially in the face of injury and disease. The objective of this study is to measure and compare levels of VEGF, PEDF and PACAP released from isolated brain microvessels of Fischer 344 rats at 6, 12, 18, and 24 months of age. Addition of acetaminophen to isolated brain microvessels is employed to determine whether this drug affects vascular expression of these neuroprotective proteins. Experiments on cultured brain endothelial cells are performed to explore the mechanisms/mediators that regulate the effect of acetaminophen on endothelial cells. The data indicate cerebrovascular expression of VEGF, PEDF and PACAP significantly decreases with age. The age-associated decrease in VEGF and PEDF is ameliorated by addition of acetaminophen to isolated brain microvessels. Also, release of VEGF, PEDF, and PACAP from cultured brain endothelial cells decreases with exposure to the oxidant stressor menadione. Acetaminophen treatment upregulates VEGF, PEDF and PACAP in brain endothelial cells exposed to oxidative stress. The effect of acetaminophen on cultured endothelial cells is in part inhibited by the selective thrombin inhibitor hirudin. The results of this study suggest that acetaminophen may be a useful agent for preserving cerebrovascular function. If a low dose of acetaminophen can counteract the decrease in vascular-derived neurotrophic factors evoked by age and oxidative stress, this drug might be useful for improving brain function in the elderly.

p38 MAPK: a mediator of hypoxia-induced cerebrovascular inflammation.

Vascular perturbations and hypoxia are increasingly implicated in Alzheimer's disease (AD) pathogenesis. Cerebral hypoxia induces a large number of inflammatory proteins in brain endothelial cells via signaling pathways that have not been defined. The p38 mitogen-activated protein kinase (MAPK) signaling system has been implicated in endothelial injury and inflammation. The objective of this study is to examine p38 MAPK levels in the cerebromicrovasulature in AD and AD animal models and determine the role of p38 MAPK signaling in hypoxia-mediated effects on brain endothelial cells. Western blot analysis of isolated human brain microvessels show that the phosphorylated (active) form of p38 MAPK (pp38 MAPK) is increased in vessels derived from AD brains compared to control-derived vessels. Similarly, immunofluorescent analysis reveals an increase in cerebrovascular pp38 MAPK as well as inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in transgenic AD mice. Exposure of brain endothelial cells to hypoxia (2-6 hours) shows a time-dependent increase in pp38 MAPK. Examination of these cultures at 6 hours hypoxia shows that iNOS and COX-2 are significantly elevated and that the selective p38 MAPK inhibitor SB203580 significantly reduces the hypoxia-mediated increase in their expression. Inhibition of p38 MAPK in cultured brain endothelial cells also significantly decreases the hypoxia-induced increase in the inflammatory proteins, matrix metalloproteinase-2 and angiopoietin-2. These data demonstrate that pp38 MAPK is a key regulator of hypoxia in the cerebrovasculature and suggest that control of this signaling pathway could have therapeutic value in AD and other disorders where hypoxia is involved.

Vascular signaling abnormalities in Alzheimer disease.

Our laboratory has documented that brain microvessels derived from patients with Alzheimer disease (AD) express or release a myriad of factors that have been implicated in vascular activation and angiogenesis. In addition, we have documented that signaling cascades associated with vascular activation and angiogenesis are upregulated in AD-derived brain microvessels. These results are consistent with emerging data suggesting that factors and processes characteristic of vascular activation and angiogenesis are found in the AD brain. Despite increases in proangiogenic factors and signals in the AD brain, however, evidence for increased vascularity in AD is lacking. Cerebral hypoperfusion/hypoxia, a potent stimulus for vascular activation and angiogenesis, triggers hypometabolic, cognitive, and degenerative changes in the brain. In our working model, hypoxia stimulates the angiogenic process; yet, there is no new vessel growth. Therefore, there are no feedback signals to shut off vascular activation, and endothelial cells become irreversibly activated. This activation results in release of a large number of proteases, inflammatory proteins, and other gene products with biologic activity that can injure or kill neurons. Pathologic activation of brain vasculature may contribute noxious mediators that lead to neuronal injury and disease processes in AD brains. This concept is supported by preliminary experiments in our laboratory, which show that pharmacologic blockade of vascular activation improves cognitive function in an animal model of AD. Thus, "vascular activation" could be a novel, unexplored therapeutic target in AD.

Brain microvasculature and hypoxia-related proteins in Alzheimer's disease.

Alzheimer's disease (AD) is a progressive, neurodegenerative disease of increasing incidence. The pathologic processes that underlie this disorder are incompletely understood, however, hypoperfusion/hypoxia is thought to contribute to disease pathogenesis. Hypoxia inducible factor 1-alpha (HIF-1α), a key regulator of cellular responses to hypoxia, is elevated in the microcirculation of AD patients. Cerebral hypoxia is a potent stimulus for vascular activation and angiogenesis. Microvessels isolated from the brains of AD patients express a large number of angiogenic proteins. Despite considerable data in human tissues regarding vascular expression of hypoxia-related angiogenic proteins, there is little information regarding these proteins in the brain vasculature of transgenic AD mice. The objectives of this study were to determine expression of HIF-1α, angiogenic proteins, angiopoietin-2 (Ang-2), and matrix metalloproteinase 2 (MMP2), and survival/apoptotic proteins (Bcl-xL, caspase 3) in the cerebromicrovasculature of AD transgenic mice and to determine the direct effect of hypoxia on cerebral endothelial expression of these proteins in vitro. Cultured brain endothelial cells were subjected to hypoxia for 4-6 h and analyzed by western blot and immunofluorescence. Our results demonstrated that HIF-1α is induced in cultured brain endothelial cells exposed to hypoxia and that expression of Ang-2, MMP2 and caspase 3 was elevated and the anti-apoptotic protein Bcl-xL decreased. Brain sections from AD and control mice showed that HIF-1α, Ang-2, MMP2 and caspase 3 are elevated and Bcl-xL decreased in the microvasculature of AD mice. These data suggest the cerebromicrovasculature is an important target for the effects of hypoxia in the AD brain.

Cerebrovascular expression of proteins related to inflammation, oxidative stress and neurotoxicity is altered with aging.

BACKGROUND: Most neurodegenerative diseases are age-related disorders; however, how aging predisposes the brain to disease has not been adequately addressed. The objective of this study is to determine whether expression of proteins in the cerebromicrovasculature related to inflammation, oxidative stress and neurotoxicity is altered with aging. METHODS: Brain microvessels are isolated from Fischer 344 rats at 6, 12, 18 and 24 months of age. Levels of interleukin (IL)-1ß and IL-6 RNA are determined by RT-PCR and release of cytokines into the media by ELISA. Vessel conditioned media are also screened by ELISA for IL-1α, monocyte chemoattractant protein-1 (MCP-1), tumor necrosis factor-α, (TNFα), and interferon γ (IFNγ). Immunofluorescent analysis of brain sections for IL-1ß and IL-6 is performed. RESULTS: Expression of IL-1ß and IL-6, both at RNA and protein levels, significantly (p < 0.01) decreases with age. Levels of MCP-1, TNFα, IL-1α, and IFNγ are significantly (p < 0.05-0.01) lower in 24 month old rats compared to 6 month old animals. Immunofluorescent analysis of brain vessels also shows a decline in IL-1ß and IL-6 in aged rats. An increase in oxidative stress, assessed by increased carbonyl formation, as well as a decrease in the antioxidant protein manganese superoxide dismutase (MnSOD) is evident in vessels of aged animals. Finally, addition of microvessel conditioned media from aged rats to neuronal cultures evokes significant (p < 0.001) neurotoxicity. CONCLUSIONS: These data demonstrate that cerebrovascular expression of proteins related to inflammation, oxidative stress and neurotoxicity is altered with aging and suggest that the microvasculature may contribute to functional changes in the aging brain.

RANTES upregulation in the Alzheimer's disease brain: a possible neuroprotective role.

Numerous studies demonstrate inflammatory proteins in the brain and microcirculation in Alzheimer's disease (AD) and implicate inflammation in disease pathogenesis. However, emerging literature suggests that neuroinflammation can also be neuroprotective. The chemokine RANTES has been implicated in neurodegenerative diseases including AD. The objectives of this study are to determine the expression of RANTES in AD microvessels, its regulation in endothelial cells and its effects on neuronal survival. Our data show elevated expression of RANTES in the cerebral microcirculation of AD patients. Treatment of neurons in vitro with RANTES results in an increase in cell survival and a neuroprotective effect against the toxicity of thrombin and sodium nitroprusside. Oxidative stress upregulates RANTES expression in rat brain endothelial cells. Developing strategies to augment neuroprotection and diminish inflammatory activation of multifunctional mediators such as RANTES holds promise for the development of novel neuroprotective therapeutics in AD.

RANTES release contributes to the protective action of PACAP38 against sodium nitroprusside in cortical neurons.

Pituitary adenylate cyclase activating polypeptide (PACAP), a promising neuroprotective peptide, plays an important role during development of the nervous system and in regeneration after injury. PACAP directly promotes survival via multiple signaling systems in neurons. This neuropeptide also has immuno-modulatory properties and can regulate the expression of various inflammatory mediators such as chemokines in nonneuronal cells. Chemokines and their G protein-coupled receptors are widely distributed in the brain, suggesting important functions for these inflammatory proteins in the CNS. The ability of brain endothelial cells and glia to release chemokines has been well documented, whether neurons are also a source for these mediators is unclear. The objective of this study is to determine whether PACAP38 affects expression of regulated on activation normal T expressed and secreted (RANTES) and macrophage inflammatory protein 1-alpha (MIP-1alpha) in cultured neurons and if these chemokines contribute to the neuroprotective effect of PACAP38. The data show that incubation of neuronal cultures with both PACAP38 and sodium nitroprusside (SNP) reduces the neuronal cell death evoked by SNP alone. PACAP38 dose-dependently increases immunodetectable levels of both RANTES and MIP-1alpha released in the media by cultured neurons. Co-treatment with a neutralizing antibody to RANTES decreases the PACAP38-mediated protection against SNP. Although RANTES treatment of neurons increased MIP-1alpha levels in the media and MIP-1alpha supports neuronal survival in unstressed cultures, MIP-1alpha does not protect neurons from SNP-induced toxicity. Furthermore, co-treatment with a MIP-1alpha neutralizing antibody did not affect PACAP38-induced protection against SNP. These results show that the protective effect of PACAP38 on cultured neurons is mediated, in part, by release of RANTES. The ability of PACAP to directly enhance neuronal survival through multiple intracellular signaling pathways as well as via the release of neuroprotective mediators such as RANTES highlights its utility as a potential therapeutic agent for the treatment of neurodegenerative diseases.

Acetaminophen inhibits neuronal inflammation and protects neurons from oxidative stress.

BACKGROUND: Recent studies have demonstrated a link between the inflammatory response, increased cytokine formation, and neurodegeneration in the brain. The beneficial effects of anti-inflammatory drugs in neurodegenerative diseases, such as Alzheimer's disease (AD), have been documented. Increasing evidence suggests that acetaminophen has unappreciated anti-oxidant and anti-inflammatory properties. The objectives of this study are to determine the effects of acetaminophen on cultured brain neuronal survival and inflammatory factor expression when exposed to oxidative stress. METHODS: Cerebral cortical cultured neurons are pretreated with acetaminophen and then exposed to the superoxide-generating compound menadione (5 microM). Cell survival is assessed by MTT assay and inflammatory protein (tumor necrosis factor alpha, interleukin-1, macrophage inflammatory protein alpha, and RANTES) release quantitated by ELISA. Expression of pro- and anti-apoptotic proteins is assessed by western blots. RESULTS: Acetaminophen has pro-survival effects on neurons in culture. Menadione, a superoxide releasing oxidant stressor, causes a significant (p < 0.001) increase in neuronal cell death as well as in the release of tumor necrosis factor alpha, interleukin-1, macrophage inflammatory protein alpha, and RANTES from cultured neurons. Pretreatment of neuronal cultures with acetaminophen (50 microM) increases neuronal cell survival and inhibits the expression of these cytokines and chemokines. In addition, we document, for the first time, that acetaminophen increases expression of the anti-apoptotic protein Bcl2 in brain neurons and decreases the menadione-induced elevation of the proapoptotic protein, cleaved caspase 3. We show that blocking acetaminophen-induced expression of Bcl2 reduces the pro-survival effect of the drug. CONCLUSION: These data show that acetaminophen has anti-oxidant and anti-inflammatory effects on neurons and suggest a heretofore unappreciated therapeutic potential for this drug in neurodegenerative diseases such as AD that are characterized by oxidant and inflammatory stress.

Acetaminophen protects brain endothelial cells against oxidative stress.

Increasing evidence suggests that acetaminophen has unappreciated anti-oxidant and anti-inflammatory properties. Drugs that affect oxidant and inflammatory stress in the brain are of interest because both processes are thought to contribute to the pathogenesis of neurodegenerative disease. The objective of this study is to determine whether acetaminophen affects the response of brain endothelial cells to oxidative stress. Cultured brain endothelial cells are pre-treated with acetaminophen and then exposed to the superoxide-generating compound menadione (25 microM). Cell survival, inflammatory protein expression, and anti-oxidant enzyme activity are measured. Menadione causes a significant (p<0.001) increase in endothelial cell death as well as an increase in RNA and protein levels of tumor necrosis factor alpha, interleukin-1, macrophage inflammatory protein alpha, and RANTES. Menadione also evokes a significant (p<0.001) increase in the activity of the anti-oxidant enzyme superoxide dismutase (SOD). Pre-treatment of endothelial cell cultures with acetaminophen (25-100 microM) increases endothelial cell survival and inhibits menadione-induced expression of inflammatory proteins and SOD activity. In addition, we document, for the first time, that acetaminophen increases expression of the anti-apoptotic protein Bcl2. Suppressing Bcl2 with siRNA blocks the pro-survival effect of acetaminophen. These data show that acetaminophen has anti-oxidant and anti-inflammatory effects on the cerebrovasculature and suggest a heretofore unappreciated therapeutic potential for this drug in neurodegenerative diseases such as Alzheimer's disease that are characterized by oxidant and inflammatory stress.

Expression of macrophage inflammatory protein 1-alpha is elevated in Alzheimer's vessels and is regulated by oxidative stress.

Inflammatory mediators are highly expressed in the Alzheimer's disease (AD) brain. We have shown that in AD the cerebral microcirculation is a rich source of cytokines and chemokines including interleukins (IL) 1beta, IL-6, IL-8, tumor necrosis factor-alpha, and monocyte chemoattractant protein-1. However, the factors that regulate expression of these inflammatory proteins have not been defined. The objective of this study is to compare expression of macrophage inflammatory protein 1-alpha (MIP-1alpha) in brain microvessels isolated from AD patients to vessels from age-matched controls and further to determine whether expression of MIP-1alpha in brain endothelial cells is altered by oxidative stress. The data show that brain AD-derived microvessels express high levels of MIP-1alpha mRNA and release high levels of MIP-1alpha protein compared to brain microvessels isolated from controls. Treatment of brain endothelial cell cultures with menadione, a superoxide releasing compound, hydrogen peroxide, lipopolysacharride, or oxidatively modified low density lipoproteins (LDL) (Ox-LDL, HNE-LDL) results in a dose- dependent increase in MIP-1alpha mRNA levels and MIP-1alpha release into the media. These results suggest that oxidative and lipid insults to the brain microvasculature are likely to contribute to the inflammatory milieu of the AD brain.