Differential Cytokine Responses of APOE3 and APOE4 Blood-brain Barrier Cell Types to SARS-CoV-2 Spike Proteins

SARS-CoV-2 spike proteins have been shown to cross the blood-brain barrier (BBB) in mice and affect the integrity of human BBB cell models. However, the effects of SARS-CoV-2 spike proteins in relation to sporadic, late onset, Alzheimer's disease (AD) risk have not been extensively investigated. Here we characterized the individual and combined effects of SARS-CoV-2 spike protein subunits S1 RBD, S1 and S2 on BBB cell types (induced brain endothelial-like cells (iBECs) and astrocytes (iAstrocytes)) generated from induced pluripotent stem cells (iPSCs) harboring low (APOE3 carrier) or high (APOE4 carrier) relative Alzheimer's risk. We found that treatment with spike proteins did not alter iBEC integrity, although they induced the expression of several inflammatory cytokines. iAstrocytes exhibited a robust inflammatory response to SARS-CoV-2 spike protein treatment, with differences found in the levels of cytokine secretion between spike protein-treated APOE3 and APOE4 iAstrocytes. Finally, we tested the effects of potentially anti-inflammatory drugs during SARS-CoV-2 spike protein exposure in iAstrocytes, and discovered different responses between spike protein treated APOE4 iAstrocytes and APOE3 iAstrocytes, specifically in relation to IL-6, IL-8 and CCL2 secretion. Overall, our results indicate that APOE3 and APOE4 iAstrocytes respond differently to anti-inflammatory drug treatment during SARS-CoV-2 spike protein exposure with potential implications to therapeutic responses.

Maternal and Fetal Expression of ATP-Binding Cassette and Solute Carrier Transporters Involved in the Brain Disposition of Drugs

Evidence from preclinical and clinical studies demonstrate that pregnancy is a physiological state capable of modifying drug disposition. Factors including increased hepatic metabolism and renal excretion are responsible for impacting disposition, and the role of membrane transporters expressed in biological barriers, including the placental- and blood-brain barriers, has received considerable attention. In this regard, the brain disposition of drugs in the mother and fetus has been the subject of studies attempting to characterize the mechanisms by which pregnancy could alter the expression of ATP-binding cassette (ABC) and solute carrier (SLC) transporters. This chapter will summarize findings of the influence of pregnancy on the maternal and fetal expression of ABC and SLC transporters in the brain and the consequences of such changes on the disposition of therapeutic drugs.

Canthin-6-one (CO) from Picrasma quassioides (D.Don) Benn. ameliorates lipopolysaccharide (LPS)-induced astrocyte activation and associated brain endothelial disruption

BACKGROUND

Canthin-6-one (CO) is an active ingredient found in Picrasma quassioides (D.Don) Benn. (PQ) that displays various biological activities including anti-inflammatory properties. Several studies reported PQ displayed neuroprotective activities, but its effects on astrocytes have not yet been investigated. Astrocytes are crucial regulators of neuroinflammatory responses under pathological conditions in the central nervous system (CNS). Proinflammatory astrocytes can induce the blood-brain barrier (BBB) breakdown, which plays a key role in the progression of neurodegenerative disorder (ND).

PURPOSE

This study aims to investigate the anti-neuroinflammatory effects of CO in LPS-induced astrocyte activation and its underlying mechanisms in protecting the blood-brain barrier (BBB) in vitro.

METHODS

Mouse astrocytes (C8-D1A) were activated with lipopolysaccharide (LPS) with or without CO pretreatment. Effects of CO on astrocyte cell viability, secretions of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), interleukin-1β (IL-1β) and nitric oxide (NO) were determined. Intracellular transcriptions and translations of proinflammatory mediators, molecular signaling, [Ca²⁺] and the levels of reactive oxygen species (ROS) were evaluated by RT-PCR, western blotting, and flow cytometry, respectively. Astrocyte-conditioned medium (ACM) was further prepared for incubating endothelial monolayer (bEnd.3) grown on transwell. Endothelial disruptions were evaluated by transendothelial electrical resistance (TEER), FITC-dextran permeability and monocyte adhesion assays. Endothelial tight junctions (TJs) and molecular signaling pathways were evaluated by immunofluorescence staining and western blotting.

RESULTS

CO attenuated LPS-induced expression of astrocytic proinflammatory mediators (TNF-α, IL-1β, IL-6, NO) and inhibited deleterious molecular activities including inducible nitric oxide synthase (iNOS), p-NFκB and p-STAT3 in astrocytes. Incubation of ACM collected from CO-treated astrocytes significantly ameliorated endothelial disruptions, reduced expressions of endothelial cytokine receptors (IL-6R, gp130 (IL-6RB), TNFR and IL-1R), suppressed proinflammatory pathways, MAPKs (p-AKT, p-MEK, p-ERK, p-p38, p-JNK) and p-STAT3, restored endothelial stabilizing pathways (p-Rac 1) and upregulated beneficial endothelial nitric oxide synthase (eNOS).

CONCLUSION

Our study demonstrates for the first time CO exhibited potent protective effects against astrocyte-mediated proinflammatory responses and associated endothelial barrier disruptions.

Three-dimensional co-culture of blood-brain barrier-composing cells in a culture insert with a collagen vitrigel membrane

The blood-brain barrier (BBB) is a structure located in brain capillaries that protects the brain from toxic substances in blood due to its high barrier function. The brain capillaries form a layered structure with pericytes, neurons, glial cells, and extracellular matrix proteins that is called neurovascular unit, and the structure is important to express the high barrier function of BBB. Here, we propose a method to construct a three-dimensional BBB tissue using three human BBB-composing cells, including brain endothelial cells, pericytes, and astrocytes, that mimics the in vivo BBB-like layered structure. Primary human brain endothelial cells were plated on the back side (outside) of the collagen vitrigel membrane of a culture insert, pericytes were plated on the upper side (inside), and astrocytes mixed in Matrigel were plated on the pericyte layer. The layered structure was maintained for at least 2 wk. The BBB tissue-loaded collagen vitrigel membrane can be detached from the insert frame using acetone with the tissue fixed intact and used for vertical cryosectioning to analyze the tissue interior. We also measured transendothelial electrical resistance (TEER) in the three-dimensional BBB co-culture to investigate barrier function of the brain endothelial cells. We believe that our co-culture method is useful to study engineered BBB tissues and develop reliable in vitro human BBB models in the future.

Estrogen deficiency is associated with brain iron deposition via upregulation of hepcidin expression in aged female mice

The total iron level in the brain increases with age, and excess iron is associated with neurodegenerative diseases; however, the mechanism of brain iron deposition is unknown. In peripheral cells, the expression of hepcidin, a master regulator of iron homeostasis, is regulated by estrogen. This study aimed to determine whether hepcidin was involved in iron deposition in the brain and brain endothelial cells of estrogen-deficient aged female mice. Aged mice showed increased levels of hepcidin and ferritin in the brain and brain microvessels compared with young mice, and these levels were reduced by estrogen replacement in ovariectomized aged mice. In the brain endothelial cell line bEnd.3, the lipopolysaccharide (10 ng/mL)-induced increases of hepcidin mRNA and protein levels, the number of Prussian blue-positive cells, and free radicals were reduced after estrogen treatment. These results suggest that estrogen deficiency with an increase of hepcidin is partly responsible for iron deposition in the brain and brain endothelial cells and that hepcidin can be a target to prevent brain aging and neurodegeneration in postmenopausal women.

The effects of Vitis vinifera L. phenolic compounds on a blood-brain barrier culture model: Expression of leptin receptors and protection against cytokine-induced damage

ETHNOPHARMACOLOGICAL RELEVANCE

The medicinal properties of grapes (Vitis vinifera L.) are well known since ancient times. Ethnobotanical grape preparations, like the Ayurvedic Darakchasava are used as cardiotonic and for the treatment of cardiovascular diseases. Dried grape products are also applied in Iranian traditional medicine for memory problems, which are linked to the pathology of brain microvessels, a special part of the cardiovascular system. The anti-inflammatory and protective effects of these traditional preparations on the cardiovascular system are related to their bioactive phenolic compounds.

AIM OF THE STUDY

The blood-brain barrier (BBB), formed by brain capillaries, is not only involved in inflammatory and other diseases of the central nervous system, but also in many systemic diseases with an inflammatory component. Dietary obesity is a systemic chronic inflammatory condition in which the peripheral and central vascular system is affected. Among the cerebrovascular changes in obesity defective leptin transport across the BBB related to central leptin resistance is observed. Our aim was to study the protective effects of grape phenolic compounds epicatechin (EC), gallic acid (GA) and resveratrol (RSV) and grape-seed proanthocyanidin-rich extract (GSPE) on a cytokine-induced vascular endothelial inflammation model. Using a culture model of the BBB we investigated cytokine-induced endothelial damage and changes in the expression of leptin receptors and leptin transfer.

MATERIALS AND METHODS

For the BBB model, primary cultures of rat brain endothelial cells, glial cells and pericytes were used in co-culture. Cells were treated by tumor necrosis factor-α (TNF-α) and interleukin-1 β (IL-1β) (10 ng/ml each) to induce damage. Cell toxicity was evaluated by the measurement of impedance. The expression of leptin receptors was assessed by RT-qPCR and western blot. The production of reactive oxygen species (ROS) and nitric oxide (NO) were detected by fluorescent probes.

RESULTS

GSPE (10 μg/ml), EC (10 μM), GA (1 μM) or RSV (10 μM) did not change the viability of brain endothelial cells. The gene expression of the short leptin receptor isoform, Ob-Ra, was up-regulated by GSPE, EC and RSV, while the mRNA levels of Lrp2 and clusterin, clu/ApoJ were not affected. The tested compounds did not change the expression of the long leptin receptor isoform, Ob-Rb. RSV protected against the cytokine-induced increase in albumin permeability of the BBB model. GSPE and EC exerted an antioxidant effect and GSPE increased NO both alone and in the presence of cytokines. The cytokine-induced nuclear translocation of transcription factor NF-κB was blocked by GSPE, GA and RSV. Cytokines increased the mRNA expression of Lrp2 which was inhibited by EC. RSV increased Ob-Ra and Clu in the presence of cytokines. Cytokines elevated leptin transfer across the BBB model, which was not modified by GSPE or RSV.

CONCLUSION

Our results obtained on cell culture models confirm that natural grape compounds protect vascular endothelial cells against inflammatory damage in accordance with the ethnopharmacological use of grape preparations in cardiovascular diseases. Furthermore, grape compounds and GSPE, by exerting a beneficial effect on the BBB, may also be considered in the treatment of obesity after validation in clinical trials.

Niosomes decorated with dual ligands targeting brain endothelial transporters increase cargo penetration across the blood-brain barrier

Nanoparticles targeting transporters of the blood-brain barrier (BBB) are promising candidates to increase the brain penetration of biopharmacons. Solute carriers (SLC) are expressed at high levels in brain endothelial cells and show a specific pattern at the BBB. The aim of our study was to test glutathione and ligands of SLC transporters as single or dual BBB targeting molecules for nanovesicles. High mRNA expression levels for hexose and neutral amino acid transporting SLCs were found in isolated rat brain microvessels and our rat primary cell based co-culture BBB model. Niosomes were derivatized with glutathione and SLC ligands glucopyranose and alanine. Serum albumin complexed with Evans blue (67 kDa), which has a very low BBB penetration, was selected as a cargo. The presence of targeting ligands on niosomes, especially dual labeling, increased the uptake of the cargo molecule in cultured brain endothelial cells. This cellular uptake was temperature dependent and could be decreased with a metabolic inhibitor and endocytosis blockers filipin and cytochalasin D. Making the negative surface charge of brain endothelial cells more positive with a cationic lipid or digesting the glycocalyx with neuraminidase elevated the uptake of the cargo after treatment with targeted nanocarriers. Treatment with niosomes increased plasma membrane fluidity, suggesting the fusion of nanovesicles with endothelial cell membranes. Targeting ligands elevated the permeability of the cargo across the BBB in the culture model and in mice, and dual-ligand decoration of niosomes was more effective than single ligand labeling. Our data indicate that dual labeling with ligands of multiple SLC transporters can potentially be exploited for BBB targeting of nanoparticles.

Repression of adenosine triphosphate-binding cassette transporter ABCG2 by estrogen increases intracellular glutathione in brain endothelial cells following ischemic reperfusion injury

The adenosine triphosphate-binding cassette efflux transporter ABCG2, which is located in the blood-brain barrier limits the entry of endogenous compounds and xenobiotics into the brain, and its expression and activity are regulated by estrogen. This study was aimed to define the role of ABCG2 in estrogen-mediated neuroprotection against ischemic injury. ABCG2 protein levels before and after ischemic stroke were increased in the brain of female mice by ovariectomy, which were reversed by estrogen replacement. In brain endothelial cell line bEnd.3, estrogen reduced the basal ABCG2 protein level and efflux activity and protected cells from ischemic injury without inducing ABCG2 expression. When bEnd.3 cells were transfected with ABCG2 small interfering RNA, ischemia-induced cell death was reduced, and the intracellular concentration of glutathione, an antioxidant that is transported by ABCG2, was increased. In addition, after ischemic stroke in ovariectomized mice, estrogen prevented the reduction of intracellular glutathione level in brain microvessels. These data suggested that the suppression of ABCG2 by estrogen is involved in neuroprotection against ischemic injury by increasing intracellular glutathione, and that the modulation of ABCG2 activity offers a therapeutic target for brain diseases in estrogen-deficient aged women.

Kynurenic acid and its derivatives are able to modulate the adhesion and locomotion of brain endothelial cells

The neuroprotective actions of kynurenic acid (KYNA) and its derivatives in several neurodegenerative disorders [characterized by damage to the cerebral endothelium and to the blood-brain barrier (BBB)] are well established. Cell-extracellular matrix (ECM) adhesion is supposedly involved in recovery of impaired cerebral endothelium integrity (endothelial repair). The present work aimed to investigate the effects of KYNA and its synthetic derivatives on cellular behaviour (e.g. adhesion and locomotion) and on morphology of the GP8 rat brain endothelial cell line, modeling the BBB endothelium. The effects of KYNA and its derivatives on cell adhesion were measured using an impedance-based technique, the xCELLigence SP system. Holographic microscopy (Holomonitor^™ M4) was used to analyse both chemokinetic responses and morphometry. The GP8 cells proved to be a suitable model cell line for investigating cell adhesion and the locomotion modulator effects of kynurenines. KYNA enhanced cell adhesion and spreading, and also decreased the migration/motility of GP8 cells at physiological concentrations (10^-9 and 10^-7 mol/L). The derivatives containing an amide side-chain at the C2 position (KYNA-A1 and A2) had lower adhesion inducer effects compared to KYNA. All synthetic analogues (except KYNA-A5) had a time-dependent inhibitory effect on GP8 cell adhesion at a supraphysiological concentration (10^-3 mol/L). The immobilization promoting effect of KYNA and the adhesion inducer activity of its derivatives indicate that these compounds could contribute to maintaining or restoring the protective function of brain endothelium; they also suggest that cell-ECM adhesion and related cell responses (e.g. migration/motility) could be potential new targets of KYNA.

Effects of flow on LOX-1 and oxidized low-density lipoprotein interactions in brain endothelial cell cultures

Fluid shear stress and uptake of oxidized low-density lipoprotein (ox-LDL) into the vessel wall both contribute to atherosclerosis, but the relationship between shear stress and ox-LDL uptake is unclear. We examined the effects of flow, induced by orbital rotation of bEnd.3 brain endothelial cell cultures for 1 wk, on ox-LDL receptor (LOX-1) protein expression, ox-LDL uptake and ox-LDL toxicity. Orbitally rotated cultures showed no changes in LOX-1 protein expression, ox-LDL uptake or ox-LDL toxicity, compared to stationary cultures. Flow alone does not modify ox-LDL/LOX-1 signaling in bEnd.3 brain endothelial cells in vitro, suggesting that susceptibility of atheroprone vascular sites to lipid accumulation is not due solely to effects of altered flow on endothelium.

Transfer of opiorphin through a blood-brain barrier culture model

Opioid peptides are potent analgesics with therapeutic potential in the treatment of acute and chronic pain. Their efficacy is limited by peptidases (enkephalinases). Opiorphin pentapeptide (QRFSR) is the first characterized human endogenous inhibitor of enkephalinases. The peptide is able to increase the binding and affinity of endogenous opiates to mu opioid receptors; thus, the mechanism of opiorphin may provide a new therapeutic approach in pain management. The analgesic effect of opiorphin was proven in several earlier published in vitro and in vivo studies. Our aim was to test the transfer of opiorphin through a blood-brain barrier model for the first time. The flux of opiorphin was tested on a blood-brain barrier culture model consisting of rat brain endothelial, glial and pericyte cells. Brain endothelial cells in this triple co-culture model form tight monolayers characterized by transendothelial electrical resistance measurement. Relative quantity of the peptide was estimated by mass spectrometry. The transfer of opiorphin through the blood-brain barrier model was estimated to be ∼3%, whereas the permeability coefficient was 0.53 ± 1.36 × 10(-6) cm/s (n = 4). We also observed rapid conversion of N-terminal glutamine into pyroglutamic acid during the transfer experiments. Our results indicate that opiorphin crosses cultured brain endothelial cells in the absence of serum factors in a significant amount. This is in agreement with previous in vivo data showing potentiation of enkephalin-mediated antinociception. We suggest that opiorphin may have a potential as a centrally acting novel drug to treat pain.

Isobavachalcone attenuates lipopolysaccharide-induced ICAM-1 expression in brain endothelial cells through blockade of toll-like receptor 4 signaling pathways

Inflammation has been implicated in the pathogenesis of various cerebral diseases. Thus, control of brain inflammation is regarded as one of the important therapeutic strategies for the treatment of neurodegenerative diseases such as Alzheimer׳s disease and stroke. Isobavachalcone, a flavonoid from Psoralea corylifolia, is known to possess a wide spectrum of biological activities and is expected to be useful in preventing or treating neurodegenerative diseases. However, very little is known regarding its effects on cerebral inflammation. In this study, we examined the effect of isobavachalcone on leukocyte adhesion and intercellular adhesion molecule-1 (ICAM-1) expression in brain endothelial cells activated with lipopolysaccharide (LPS) and explored the possible mechanisms involved. Isobavachalcone significantly down-regulated LPS-induced ICAM-1 expression and leukocyte-endothelial cell adhesion and suppressed NF-κB activity which is implicated in the expression of ICAM-1. It attenuated ICAM-1 expression as well as NF-κB transcriptional activity induced by macrophage-activating lipopeptide 2-kDa (MALP-2) or polyriboinosinic polyribocytidylic acid (poly[I:C]). Isobavachalcone also down-regulated LPS or poly[I:C]-induced expression of IFN-β, which can indirectly activate NF-κB. These data imply that isobavachalcone can modulate both MyD88-dependent and TRIF-dependent signaling of toll-like receptor 4 (TLR4). Taken together, our data suggest that isobavachalcone inhibits LPS-induced ICAM-1 expression and leukocyte adhesion to brain endothelial cell by blocking TLR4 signaling and thus, has the potential to ameliorate neuronal injury in brain diseases associated with inflammation.

The blood-brain barrier in neuroimmunology: Tales of separation and assimilation

Neuroimmunology is concerned with the relations between the central nervous and immune systems and with the mechanisms that drive those relations. The blood-brain barrier (BBB) employs mechanisms that both separate and connect these two systems. In fact, the relative immune privilege of the central nervous system (CNS) is largely attributable to the BBB's ability to prevent the unregulated exchange of immune cells and their secretions between the CNS and blood. Having separated the two systems, the BBB then participates in mechanisms that allow them to influence, communicate, and interact with one another. Likewise, the BBB itself is influenced by immune events that are occurring in the periphery and in the CNS so that these three components (the BBB, the immune system, and the CNS) form neuroimmune axes that adapt to physiological and pathological conditions. To date, four major themes have emerged by which the BBB participates in these neuroimmune axes. The first of these four, the formation of the barrier, acts to separate the immune and central nervous systems. The other three themes provide mechanisms for re-establishing communication: response of the BBB to immunomodulatory molecules (e.g., prostaglandins, cytokines, chemokines, nitric oxide) secreted by immune and CNS cells; the controlled, regulated exchange of chemokines, cytokines, and immune cells between the CNS and the blood (i.e., transport across the BBB); the secretion of immunomodulatory molecules by the BBB, often in a polarized fashion. Taken together, these mechanisms reveal the BBB to be a dynamic, interactive, and adaptable interface between the immune system and the CNS, separating them on the one hand and fostering their interactions on the other hand, adjusting to physiological changes, while being a target for disease processes. This review examines specific examples by which the BBB plays an interactive, defining role in neuroimmunology.