Alterations in blood-brain barrier ICAM-1 expression and brain microglial activation after lambda-carrageenan-induced inflammatory pain

Cardio-metabolic risk factors and cortical thickness in a neurologically healthy male population: Results from the psychological, social and biological determinants of ill health (pSoBid) study

INTRODUCTION

Cardio-metabolic risk factors have been associated with poor physical and mental health. Epidemiological studies have shown peripheral risk markers to be associated with poor cognitive functioning in normal healthy population and in disease. The aim of the study was to explore the relationship between cardio-metabolic risk factors and cortical thickness in a neurologically healthy middle aged population-based sample.

METHODS

T1-weighted MRI was used to create models of the cortex for calculation of regional cortical thickness in 40 adult males (average age = 50.96 years), selected from the pSoBid study. The relationship between cardio-vascular risk markers and cortical thickness across the whole brain, was examined using the general linear model. The relationship with various covariates of interest was explored.

RESULTS

Lipid fractions with greater triglyceride content (TAG, VLDL and LDL) were associated with greater cortical thickness pertaining to a number of regions in the brain. Greater C reactive protein (CRP) and intercellular adhesion molecule (ICAM-1) levels were associated with cortical thinning pertaining to perisylvian regions in the left hemisphere. Smoking status and education status were significant covariates in the model.

CONCLUSIONS

This exploratory study adds to a small body of existing literature increasingly showing a relationship between cardio-metabolic risk markers and regional cortical thickness involving a number of regions in the brain in a neurologically normal middle aged sample. A focused investigation of factors determining the inter-individual variations in regional cortical thickness in the adult brain could provide further clarity in our understanding of the relationship between cardio-metabolic factors and cortical structures.

Estradiol attenuates spinal cord injury-induced pain by suppressing microglial activation in thalamic VPL nuclei of rats

In our previous study we showed that central pain syndrome (CPS) induced by electrolytic injury caused in the unilateral spinothalamic tract (STT) is a concomitant of glial alteration at the site of injury. Here, we investigated the activity of glial cells in thalamic ventral posterolateral nuclei (VPL) and their contribution to CPS. We also examined whether post-injury administration of a pharmacological dose of estradiol can attenuate CPS and associated molecular changes. Based on the results,in the ipsilateral VPL the microglial phenotype switched o hyperactive mode and Iba1 expression was increased significantly on days 21 and 28 post-injury. The same feature was observed in contralateral VPL on day 28 (P<.05). These changes were strongly correlated with the onset of CPS (r(2)=0.670). STT injury did not induce significant astroglial response in both ipsilateral and contralateral VPL. Estradiol attenuated bilateral mechanical hypersensitivity 14 days after STT lesion (P<.05). Estradiol also suppressed microglial activation in the VPL. Taken together, these findings indicate that selective STT lesion induces bilateral microglia activation in VPL which might contribute to mechanical hypersensitivity. Furthermore, a pharmacological dose of estradiol reduces central pain possibly via suppression of glial activity in VPL region.

Tempol modulates changes in xenobiotic permeability and occludin oligomeric assemblies at the blood-brain barrier during inflammatory pain

Our laboratory has shown that λ-carrageenan-induced peripheral inflammatory pain (CIP) can alter tight junction (TJ) protein expression and/or assembly leading to changes in blood-brain barrier xenobiotic permeability. However, the role of reactive oxygen species (ROS) and subsequent oxidative stress during CIP is unknown. ROS (i.e., superoxide) are known to cause cellular damage in response to pain/inflammation. Therefore, we examined oxidative stress-associated effects at the blood-brain barrier (BBB) in CIP rats. During CIP, increased staining of nitrosylated proteins was detected in hind paw tissue and enhanced presence of protein adducts containing 3-nitrotyrosine occurred at two molecular weights (i.e., 85 and 44 kDa) in brain microvessels. Tempol, a pharmacological ROS scavenger, attenuated formation of 3-nitrotyrosine-containing proteins in both the hind paw and in brain microvessels when administered 10 min before footpad injection of λ-carrageenan. Similarly, CIP increased 4-hydroxynoneal staining in brain microvessels and this effect was reduced by tempol. Brain permeability to [(14)C]sucrose and [(3)H]codeine was increased, and oligomeric assemblies of occludin, a critical TJ protein, were altered after 3 h CIP. Tempol attenuated both [(14)C]sucrose and [(3)H]codeine brain uptake as well as protected occludin oligomers from disruption in CIP animals, suggesting that ROS production/oxidative stress is involved in modulating BBB functional integrity during pain/inflammation. Interestingly, tempol administration reduced codeine analgesia in CIP animals, indicating that oxidative stress during pain/inflammation may affect opioid delivery to the brain and subsequent efficacy. Taken together, our data show for the first time that ROS pharmacological scavenging is a viable approach for maintaining BBB integrity and controlling central nervous system drug delivery during acute inflammatory pain.

Ghrelin prevents disruption of the blood-brain barrier after traumatic brain injury

Significant effort has been focused on reducing neuronal damage from post-traumatic brain injury (TBI) inflammation and blood-brain barrier (BBB)-mediated edema. The orexigenic hormone ghrelin decreases inflammation in sepsis models, and has recently been shown to be neuroprotective following subarachnoid hemorrhage. We hypothesized that ghrelin modulates cerebral vascular permeability and mediates BBB breakdown following TBI. Using a weight-drop model, TBI was created in three groups of mice: sham, TBI, and TBI/ghrelin. The BBB was investigated by examining its permeability to FITC-dextran and through quantification of perivascualar aquaporin-4 (AQP-4). Finally, we immunoblotted for serum S100B as a marker of brain injury. Compared to sham, TBI caused significant histologic neuronal degeneration, increases in vascular permeability, perivascular expression of AQP-4, and serum levels of S100B. Treatment with ghrelin mitigated these effects; after TBI, ghrelin-treated mice had vascular permeability and perivascular AQP-4 and S100B levels that were similar to sham. Our data suggest that ghrelin prevents BBB disruption after TBI. This is evident by a decrease in vascular permeability that is linked to a decrease in AQP-4. This decrease in vascular permeability may diminish post-TBI brain tissue damage was evident by decreased S100B.

Targeting blood-brain barrier changes during inflammatory pain: an opportunity for optimizing CNS drug delivery

The blood-brain barrier (BBB) is the most significant obstacle to effective CNS drug delivery. It possesses structural and biochemical features (i.e., tight-junction protein complexes and, influx and efflux transporters) that restrict xenobiotic permeation. Pathophysiological stressors (i.e., peripheral inflammatory pain) can alter BBB tight junctions and transporters, which leads to drug-permeation changes. This is especially critical for opioids, which require precise CNS concentrations to be safe and effective analgesics. Recent studies have identified molecular targets (i.e., endogenous transporters and intracellular signaling systems) that can be exploited for optimization of CNS drug delivery. This article summarizes current knowledge in this area and emphasizes those targets that present the greatest opportunity for controlling drug permeation and/or drug transport across the BBB in an effort to achieve optimal CNS opioid delivery.

Age and 17β-estradiol effects on blood-brain barrier tight junction and estrogen receptor proteins in ovariectomized rats

Age and estrogen levels alter blood-brain barrier (BBB) tight junction (TJ) regulation, impacting brain homeostasis and pathological outcomes. This examination evaluated BBB TJ and estrogen receptor (ER) protein expression changes in young (8-10 week) and middle-aged (10-12 month) ovariectomized female Fisher-344 rats with chronic 17β-estradiol or placebo treatment. Middle-aged rats showed decreased protein expression of occludin with 17β-estradiol (55 kDa band) or placebo (45, 55, 60 kDa bands) treatment compared to respective young. In young animals, 17β-estradiol treatment increased expression of the occludin 55 kDa band over placebo; however, this effect was lost in the middle-aged animals. In both young and middle-aged animals, expression of claudin-5 (23, 32 kDa bands) and ERα (66 kDa) increased with 17β-estradiol treatment, while junctional adhesion molecule-A showed no change across all groups. However, ERα expression (66 kDa) was significantly reduced in the middle-aged animals compared to young placebo treated animals. Measurement of BBB TJ permeability via in situ perfusion of (14)C-sucrose showed no change with age or treatment. Our results show that increasing age and 17β-estradiol treatment alters the expression of ERα and distinct BBB TJ protein isoforms without altering functional paracellular permeability.

The neuroinflammatory hypothesis of delirium

Delirium is a neuropsychiatric syndrome characterized by a sudden and global impairment in consciousness, attention and cognition. It is particularly frequent in elderly subjects with medical or surgical conditions and is associated with short- and long-term adverse outcomes. The pathophysiology of delirium remains poorly understood as it involves complex multi-factorial dynamic interactions between a diversity of risk factors. Several conditions associated with delirium are characterized by activation of the inflammatory cascade with acute release of inflammatory mediators into the bloodstream. There is compelling evidence that acute peripheral inflammatory stimulation induces activation of brain parenchymal cells, expression of proinflammatory cytokines and inflammatory mediators in the central nervous system. These neuroinflammatory changes induce neuronal and synaptic dysfunction and subsequent neurobehavioural and cognitive symptoms. Furthermore, ageing and neurodegenerative disorders exaggerate microglial responses following stimulation by systemic immune stimuli such as peripheral inflammation and/or infection. In this review we explore the neuroinflammatory hypothesis of delirium based on recent evidence derived from animal and human studies.

Inflammatory hyperalgesia induces essential bioactive lipid production in the spinal cord

Lipid molecules play an important role in regulating the sensitivity of sensory neurons and enhancing pain perception, and growing evidence indicates that the effect occurs both at the site of injury and in the spinal cord. Using high-throughput mass spectrometry methodology, we sought to determine the contribution of spinal bioactive lipid species to inflammation-induced hyperalgesia in rats. Quantitative analysis of CSF and spinal cord tissue for eicosanoids, ethanolamides and fatty acids revealed the presence of 102 distinct lipid species. After induction of peripheral inflammation by intra-plantar injection of carrageenan to the ipsilateral hind paw, lipid changes in cyclooxygenase (COX) and 12-lipoxygenase (12-LOX) signaling pathways peaked at 4 h in the CSF. In contrast, changes occurred in a temporally disparate manner in the spinal cord with LOX-derived hepoxilins followed by COX-derived prostaglandin E(2), and subsequently the ethanolamine anandamide. Systemic treatment with the mu opioid agonist morphine, the COX inhibitor ketorolac, or the LOX inhibitor nordihydroguaiaretic acid significantly reduced tactile allodynia, while their effects on the lipid metabolites were different. Morphine did not alter the lipid profile in the presence or absence of carrageenan inflammation. Ketorolac caused a global reduction in eicosanoid metabolism in naïve animals that remained suppressed following injection of carrageenan. Nordihydroguaiaretic acid-treated animals also displayed reduced basal levels of COX and 12-LOX metabolites, but only 12-LOX metabolites remained decreased after carrageenan treatment. These findings suggest that both COX and 12-LOX play an important role in the induction of carrageenan-mediated hyperalgesia through these pathways.

The blood-brain barrier in neurodegenerative disease: a rhetorical perspective

Recent studies suggest that the function of the blood-brain barrier (BBB) is not static under normal physiologic conditions and is likely altered in neurodegenerative disease. Prevailing thinking about CNS function, and neurodegenerative disease in particular, is neurocentric excluding the impact of factors outside the CNS. This review challenges this perspective and discusses recent reports suggesting the involvement of peripheral factors including toxins and elements of adaptive immunity that may not only play a role in pathogenesis, but also progression of neurodegenerative diseases. Central to this view is neuroinflammation. Several studies indicate that the neuroinflammatory changes that accompany neurodegeneration affect the BBB or its function by altering transport systems, enhancing immune cell entry, or influencing the BBB's role as a signaling interface. Such changes impair the BBB's normal homeostatic function and affect neural activity. Moreover, recent studies reveal that alterations in BBB and its transporters affect the entry of drugs used to treat neurodegenerative diseases. Incorporating BBB compromise and dysfunction into our view of neurodegenerative disease leads to the inclusion of peripheral mediators in its pathogenesis and progression. In addition, this changing view of the BBB raises interesting new therapeutic possibilities for drug delivery as well as treatment strategies designed to reinstate normal barrier function.

Administration of sesamol improved blood-brain barrier function in streptozotocin-induced diabetic rats

Uncontrolled or poorly controlled blood glucose during diabetes is an important factor in worsened vascular function. While evidence suggests that hyperglycemia-induced oxidative stress plays a prominent role in development of microangiopathy of the retina, kidney, and nerves, the role oxidative stress plays on blood-brain barrier (BBB) function and structure has lagged behind. In this study, a natural antioxidant, sesamol, was administered to streptozotocin (STZ)-induced diabetic rats to examine the role that oxidative stress plays on BBB structure and function. Experiments were conducted at 56 days after STZ injection. Male Sprague-Dawley rats randomly were divided into four treatment groups CON--control; STZ--STZ-induced diabetes; CON + S--control + sesamol; STZ + S--STZ-induced diabetes + sesamol. Functional and structural changes to the BBB were measured by in situ brain perfusion and western blot analysis of changes in tight junction protein expression. Oxidative stress markers were visualized by fluorescent confocal microscopy and assayed by spectrophotometric analysis. Results demonstrated that the increased BBB permeability observed in STZ-induced diabetic rats was attenuated in STZ + S rats to levels observed in CON. Sesamol treatment reduced the negative impact of STZ-induced diabetes on tight junction protein expression in isolated cerebral microvessels. Oxidative stress markers were elevated in STZ as compared to CON. STZ + S displayed an improved antioxidant capacity which led to a reduced expression of superoxide and peroxynitrite and reduced lipid peroxidation. In conclusion, this study showed that sesamol treatment enhanced antioxidant capacity of the diabetic brain and led to decreased perturbation of hyperglycemia-induced changes in BBB structure and function.

Transforming growth factor-beta signaling alters substrate permeability and tight junction protein expression at the blood-brain barrier during inflammatory pain

Our laboratory has shown that peripheral inflammatory pain induced by lambda-carrageenan (CIP) can increase blood-brain barrier (BBB) permeability and alter tight junction (TJ) protein expression leading to changes in BBB functional integrity. However, the intracellular signaling mechanisms involved in this pathophysiologic response have not been elucidated. Transforming growth factor (TGF)-beta signaling pathways are known to regulate vascular integrity and permeability. Therefore, we examined the function of TGF-beta signaling at the BBB in rats subjected to CIP. During CIP, serum TGF-beta1 and protein expression of the TGF-beta receptor activin receptor-like kinase-5 (ALK5) were reduced. Brain permeability to (14)C-sucrose was increased and expression of TJ proteins (i.e., claudin-5, occludin, zonula occluden (ZO-1)) were also altered after 3 h CIP. Pharmacological inhibition of ALK5 with the selective inhibitor SB431542 further enhanced brain uptake of (14)C-sucrose, increased TJ protein expression (i.e., claudin-3, claudin-5, occludin, ZO-1), and decreased nuclear expression of TGF-beta/ALK5 signaling molecules (i.e., Smad2, Smad3), which suggests a role for TGF-beta/ALK5 signaling in the regulation of BBB integrity. Interestingly, administration of exogenous TGF-beta1 before CIP activated the TGF-beta/ALK5 pathway and reduced BBB permeability to (14)C-sucrose. Taken together, our data show that TGF-beta/ALK5 signaling is, in part, involved in the regulation of BBB functional integrity.

Global gene expression analysis in the mouse brainstem after hyperalgesia induced by facial carrageenan injection--evidence for a form of neurovascular coupling?

The present study was carried out to examine global gene expression in the brainstem, in a mouse facial carrageenan injection model of orofacial pain. Mice that received facial carrageenan injection showed increased mechanical allodynia, demonstrated by increased responses to von Frey hair stimulation of the face. The brainstem was harvested at 3 days post-injection, corresponding to the time of peak responses, and analyzed by Affymetrix Mouse Genome 430 2.0 microarrays. We sought to identify common genes that are changed in the respective sides of the brainstem after either right- or left-sided facial carrageenan injection. The result is a relatively small list of genes (22 genes), which were then classified using DAVID software. Many of them fell into the categories of "response to stress", "defence response", "response to biotic stimulus", "cell adhesion" and "leukocyte adhesion". Of these, increased expression of P-selectin, ICAM-1 and CCL12 after carrageenan injection could be verified by real-time RT-PCR on both the right and left sides, and increased in P-selectin and ICAM-1 further verified by Western blot analysis. P-selectin and ICAM-1 were immunolocalized to endothelial cells, and were double labelled with von Willebrand factor. Intraperitoneal injection of the P-selectin inhibitor KF38789 significantly reduced mechanical allodynia in the facial carrageenan-injected mice. P-selectin mediates the capturing of leukocytes from the bloodstream and rolling of leukocytes along the endothelial surface. We hypothesize that increased nociceptive input to the brainstem could attract circulating macrophages into the brain, resulting in neuroinflammation and pain.

Monocyte chemoattractant protein-1 in the choroid plexus: a potential link between vascular pro-inflammatory mediators and the CNS during peripheral tissue inflammation

During peripheral tissue inflammation, inflammatory processes in the CNS can be initiated by blood-borne pro-inflammatory mediators. The choroid plexus, the site of cerebrospinal fluid (CSF) production, is a highly specialized interface between the vascular system and CNS, and thus, this structure may be an important element in communication between the vascular compartment and the CNS during peripheral tissue inflammation. We investigated the potential participation of the choroid plexus in this process during peripheral tissue inflammation by examining expression of the small inducible cytokine A2 (SCYA2) gene which codes for monocyte chemoattractant protein-1 (MCP-1). MCP-1 protein was previously reported to be induced in a variety of cells during peripheral tissue inflammation. In the basal state, SCYA2 is highly expressed in the choroid plexus as compared with other rat CNS tissues. During hind paw inflammation, SCYA2 expression was significantly elevated in choroid plexus, whereas it remained unchanged in a variety of brain regions. The SCYA2-expressing cells were strongly associated with the choroid plexus as vascular depletion of blood cells by whole-body saline flush did not significantly alter SCYA2 expression in the choroid plexus. In situ hybridization suggested that the SCYA2-expressing cells were localized to the choroid plexus stroma. To elucidate potential molecular mechanisms of SCYA2 increase, we examined genes in the nuclear factor-kappa B (NF-kappaB) signaling cascade including tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta) and inhibitor of kappa B alpha (IkappaBalpha) in choroid tissue. Given that we also detected increased levels of MCP-1 protein by ELISA, we sought to identify potential downstream targets of MCP-1 and observed altered expression levels of mRNAs encoding tight junction proteins TJP2 and claudin 5. Finally, we detected a substantial up-regulation of the transcript encoding endothelial leukocyte adhesion molecule 1 (E-selectin), a molecule which could participate in leukocyte recruitment to the choroid plexus along with MCP-1. Together, these results suggest that profound changes occur in the choroid plexus during peripheral tissue inflammation, likely initiated by blood-borne inflammatory mediators, which may modify events in CNS.

Occludin oligomeric assembly at tight junctions of the blood-brain barrier is disrupted by peripheral inflammatory hyperalgesia

Tight junctions (TJs) at the blood-brain barrier (BBB) dynamically alter paracellular diffusion of blood-borne substances from the peripheral circulation to the CNS in response to external stressors, such as pain, inflammation, and hypoxia. In this study, we investigated the effect of lambda-carrageenan-induced peripheral inflammatory pain (i.e., hyperalgesia) on the oligomeric assembly of the key TJ transmembrane protein, occludin. Oligomerization of integral membrane proteins is a critical step in TJ complex assembly that enables the generation of tightly packed, large multiprotein complexes capable of physically obliterating the interendothelial space to inhibit paracellular diffusion. Intact microvessels isolated from rat brains were fractionated by detergent-free density gradient centrifugation, and gradient fractions were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis/ Western blot. Injection of lambda-carrageenan into the rat hind paw produced after 3 h a marked change in the relative amounts of oligomeric, dimeric, and monomeric occludin isoforms associated with different plasma membrane lipid raft domains and intracellular compartments in endothelial cells at the BBB. Our findings suggest that increased BBB permeability (i.e., leak) associated with lambda-carrageenan-induced peripheral inflammatory pain is promoted by the disruption of disulfide-bonded occludin oligomeric assemblies, which renders them incapable of forming an impermeant physical barrier to paracellular transport.

Nociceptive inhibition prevents inflammatory pain induced changes in the blood-brain barrier

Previous studies by our group have shown that peripheral inflammatory insult, using the lambda-carrageenan inflammatory pain (CIP) model, induced alterations in the molecular and functional properties of the blood-brain barrier (BBB). The question remained whether these changes were mediated via an inflammatory and/or neuronal mechanism. In this study, we investigated the involvement of neuronal input from pain activity on alterations in BBB integrity by peripheral inhibition of nociceptive input. A perineural injection of 0.75% bupivacaine into the right hind leg prior to CIP was used for peripheral nerve block. Upon nerve block, there was a significant decrease in thermal allodynia induced by CIP, but no effect on edema formation 1 h post-CIP. BBB permeability was increased 1 h post-CIP treatment as determined by in situ brain perfusion of [(14)C] sucrose; bupivacaine nerve block of CIP caused an attenuation of [(14)C] sucrose permeability, back to saline control levels. Paralleling the changes in [(14)C] sucrose permeability, we also report increased expression of three tight junction (TJ) proteins, zonula occluden-1 (ZO-1), occludin and claudin-5 with CIP. Upon bupivacaine nerve block, changes in expression were prevented. These data show that the lambda-carrageenan-induced changes in [(14)C] sucrose permeability and protein expression of ZO-1, occludin and claudin-5 are prevented with inhibition of nociceptive input. Therefore, we suggest that nociceptive signaling is in part responsible for the alteration in BBB integrity under CIP.

Bacillus cereus induces permeability of an in vitro blood-retina barrier

Most Bacillus cereus toxin production is controlled by the quorum-sensing-dependent, pleiotropic global regulator plcR, which contributes to the organism's virulence in the eye. The purpose of this study was to analyze the effects of B. cereus infection and plcR-regulated toxins on the barrier function of retinal pigment epithelium (RPE) cells, the primary cells of the blood-retina barrier. Human ARPE-19 cells were apically inoculated with wild-type or quorum-sensing-deficient B. cereus, and cytotoxicity was analyzed. plcR-regulated toxins were not required for B. cereus-induced RPE cytotoxicity, but these toxins did increase the rate of cell death, primarily by necrosis. B. cereus infection of polarized RPE cell monolayers resulted in increased barrier permeability, independent of plcR-regulated toxins. Loss of both occludin and ZO-1 expression occurred by 8 h postinfection, but alterations in tight junctions appeared to precede cytotoxicity. Of the several proinflammatory cytokines analyzed, only interleukin-6 was produced in response to B. cereus infection. These results demonstrate the deleterious effects of B. cereus infection on RPE barrier function and suggest that plcR-regulated toxins may not contribute significantly to RPE barrier permeability during infection.

Localization of S100A8 and S100A9 expressing neutrophils to spinal cord during peripheral tissue inflammation

Investigation of hyperalgesia at the spinal transcriptome level indicated that carrageenan-induced inflammation of rat hind paws leads to a rapid but sustained increase in S100A8 and S100A9 expression, two genes implicated in the pathology of numerous inflammatory diseases including rheumatoid arthritis and gout. In situ hybridization revealed that the elevation occurred in neutrophils that migrate to the spinal cord vasculature during peripheral inflammation, not in spinal neurons or glial cells. Immunohistochemical analysis suggests, but does not prove, that these neutrophils abundantly release S100A8 and S100A9. Consistent with this, we detected an increase in ICAM and VCAM, both indicators of endothelial activation, a known trigger for secretion of S100A8 and S100A9. Migration of S100A8- and S100A9-expressing neutrophils to spinal cord is selective, since MCP-1- and CD68-expressing leukocytes do not increase in spinal cord vasculature during hind paw inflammation. Examination of many neutrophil granule mediators in spinal cord indicated that they are not regulated to the same degree as S100A8 and S100A9. Neutrophil migration also occurs in the vasculature of brain and pituitary gland during peripheral inflammation. Together, these findings suggest an interaction between a subpopulation of leukocytes and the CNS during peripheral tissue inflammation, as implied by an apparent release and possible diffusion of S100A8 and S100A9 through the endothelial blood-brain barrier. Although the present findings do not establish the neurophysiological or behavioral relevance of these observations to nociceptive processing, the data raise the possibility that selective populations of leukocytes may communicate the presence of disease or tissue damage from the periphery to cells in the central nervous system.

Peripheral inflammatory hyperalgesia modulates morphine delivery to the brain: a role for P-glycoprotein

P-glycoprotein (Pgp, ABCB1) is a critical efflux transporter at the blood-brain barrier (BBB) where its luminal location and substrate promiscuity limit the brain distribution of numerous therapeutics. Moreover, Pgp is known to confer multi-drug resistance in cancer chemotherapy and brain diseases, such as epilepsy, and is highly regulated by inflammatory mediators. The involvement of inflammatory processes in neuropathological states has led us to investigate the effects of peripheral inflammatory hyperalgesia on transport properties at the BBB. In the present study, we examined the effects of lambda-carrageenan-induced inflammatory pain (CIP) on brain endothelium regulation of Pgp. Western blot analysis of enriched brain microvessel fractions showed increased Pgp expression 3 h post-CIP. In situ brain perfusion studies paralleled these findings with decreased brain uptake of the Pgp substrate and opiate analgesic, [(3)H] morphine. Cyclosporin A-mediated inhibition of Pgp enhanced the uptake of morphine in lambda-carrageenan and control animals. This indicates that the CIP induced decrease in morphine transport was the result of an increase in Pgp activity at the BBB. Furthermore, antinociception studies showed decreased morphine analgesia following CIP. The observation that CIP modulates Pgp at the BBB in vivo is critical to understanding BBB regulation during inflammatory disease states.

The pathogenesis and treatment of acid sphingomyelinase-deficient Niemann-Pick disease

Patients with types A and B Niemann-Pick disease (NPD) have an inherited deficiency of acid sphingomyelinase (ASM) activity. The clinical spectrum of this disorder ranges from the infantile, neurological form that results in death by 3 years of age (type A NPD) to the non-neurological form (type B NPD) that is compatible with survival into adulthood. Intermediate cases also have been reported, and the disease is best thought of as a single entity with a spectrum of phenotypes. ASM deficiency is panethnic, but appears to be more frequent in individuals of Middle Eastern and North African descent. Current estimates of the disease incidence range from approximately 0.5 to 1 per 100,000 births. However, these approximations likely under estimate the true frequency of the disorder since they are based solely on cases referred to biochemical testing laboratories for enzymatic confirmation. The gene encoding ASM (SMPD1) has been studied extensively; it resides within an imprinted region on chromosome 11, and is preferentially expressed from the maternal chromosome. Over 100 SMPD1 mutations causing ASM-deficient NPD have been described, and some useful genotype-phenotype correlations have been made. Based on these findings, DNA-based carrier screening has been implemented in the Ashkenazi Jewish community. ASM 'knockout' mouse models also have been constructed and used to investigate disease pathogenesis and treatment. Based on these studies in the mouse model, an enzyme replacement therapy clinical trial has recently begun in adult patients with non-neurological ASM-deficient NPD.

Bacterial endophthalmitis: therapeutic challenges and host-pathogen interactions

Endophthalmitis is an infection of the posterior segment of the eye that frequently results in loss of vision. This devastating result occurs despite prompt and often aggressive therapeutic and surgical intervention. Over the past decade, research has centered on determining the bacterial and host factors involved in this potentially blinding disease. The initial focus on the bacterial factors responsible for intraocular virulence has recently expanded into analysis the inflammatory response to infection, including the molecular and cellular interactions between the pathogen and host. This review discusses the epidemiology and therapeutic challenges posed by endophthalmitis, as well as recent findings from the analysis of interactions between the host and pathogen. Based on these findings, a model for the pathogenesis of endophthalmitis is presented. A more comprehensive understanding of the molecular and cellular interactions taking place between pathogen and host during endophthalmitis will expose possible therapeutic targets designed to arrest the infection and prevent vision loss.

Pathophysiology of the blood-brain barrier: animal models and methods

The specialized cerebral microvascular endothelium interacts with the cellular milieu of the brain and extracellular matrix to form a neurovascular unit, one aspect of which is a regulated interface between the blood and central nervous system (CNS). The concept of this blood-brain barrier (BBB) as a dynamically regulated system rather than a static barrier has wide-ranging implications for pathophysiology of the CNS. While in vitro models of the BBB are useful for screening drugs targeted to the CNS and indispensable for studies of cerebral endothelial cell biology, the complex interactions of the neurovascular unit make animal-based models and methods essential tools for understanding the pathophysiology of the BBB. BBB dysfunction is a complication of neurodegenerative disease and brain injury. Studies on animal models have shown that diseases of the periphery, such as diabetes and inflammatory pain, have deleterious effects on the BBB which may contribute to neurological complications associated with these conditions. Furthermore, genetic and/or epigenetic abnormalities in constituents of the BBB may be significant contributing factors in disease etiology. Research that approaches the BBB as a dynamic system integrated with both the CNS and the periphery is therefore critical to understanding and treating diseases of the CNS. Herein, we review various methodological approaches used to study BBB function in the context of disease. These include measurement of transport between blood and brain, imaging-based technologies, and genomic/proteomic approaches.

Biphasic cytoarchitecture and functional changes in the BBB induced by chronic inflammatory pain

The blood-brain barrier (BBB) is a dynamic system which maintains brain homeostasis and limits CNS penetration via interactions of transmembrane and intracellular proteins. Inflammatory pain (IP) is a condition underlying several diseases with known BBB perturbations, including stroke, Parkinson's, multiple sclerosis and Alzheimer's. Exploring the underlying pathology of chronic IP, we demonstrated alterations in BBB paracellular permeability with correlating changes in tight junction (TJ) proteins: occludin and claudin-5. The present study examines the IP-induced molecular changes leading to a loss in functional BBB integrity. IP was induced by injection of Complete Freund's Adjuvant (CFA) into the plantar surface of the right hindpaw of female Sprague-Dawley rats. Inflammation and hyperalgesia were confirmed, and BBB paracellular permeability was assessed by in situ brain perfusion of [14C]sucrose (paracellular diffusion marker). The permeability of the BBB was significantly increased at 24 and 72 h post-CFA. Analysis of the TJ proteins, which control the paracellular pathway, demonstrated decreased claudin-5 expression at 24 h, and an increase at 48 and 72 h post-injection. Occludin expression was significantly decreased 72 h post-CFA. Expression of junction adhesion molecule-1 (JAM-1) increased 48 h and decreased by 72 h post-CFA. Confocal microscopy demonstrated continuous expression of both occludin and JAM-1, each co-localizing with ZO-1. The increased claudin-5 expression was not limited to the junction. These results provide evidence that chronic IP causes dramatic alterations in specific cytoarchitectural proteins and demonstrate alterations in molecular properties during CFA, resulting in significant changes in BBB paracellular permeability.