Emerging data indicate that neurological complications occur as a consequence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. The blood-brain barrier (BBB) is a critical ...interface that regulates entry of circulating molecules into the CNS, and is regulated by signals that arise from the brain and blood compartments. In this review, we discuss mechanisms by which SARS-CoV-2 interactions with the BBB may contribute to neurological dysfunction associated with coronavirus disease of 2019 (COVID-19), which is caused by SARS-CoV-2. We consider aspects of peripheral disease, such as hypoxia and systemic inflammatory response syndrome/cytokine storm, as well as CNS infection and mechanisms of viral entry into the brain. We also discuss the contribution of risk factors for developing severe COVID-19 to BBB dysfunction that could increase viral entry or otherwise damage the brain.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Brain endothelial cells (BEC) of the vascular blood-brain barrier (BBB) interact with many different cell types in the brain, including microglia, the brain's resident immune cells. Physical ...associations of microglia with the BBB and the importance of these interactions in health and disease are an emerging area of study and likely involved in neuroimmune communication. In this mini-review, we consider how microglia and the BBB are intrinsically linked in the developing brain, discuss possible mechanisms that attract microglia to the vasculature in healthy physiological conditions, and examine the known microglial-vascular associated changes in systemic infection and various disease states. Our findings shed light on the complexities of microglial-vascular interactions and highlight the contributions of microglia to the functions of the neurovascular unit.
•Microglial–vascular associations are pleiotropic and context-dependent.•Up to 30% of microglia are anatomically associated with the BBB in healthy adults.•Microglia migrate to the BBB in response to inflammation and injury.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Systemic inflammation has been implicated in the progression of Alzheimer's disease (AD); however, less is understood about how existing AD pathology contributes to adverse outcomes following acute ...inflammatory insults. In the present study, our goal was to determine how AD-associated amyloid beta (Aβ) pathology influences the acute neuroinflammatory and behavioral responses to a moderate systemic inflammatory insult. We treated 16-18-month-old female Tg2576 (Tg) mice, which overproduce human Aβ and develop plaques, and age-matched wild-type (WT) littermate mice with an intraperitoneal injection of 0.33 mg/kg lipopolysaccharide (LPS) or saline. Mice were then evaluated over the next 28 h for sickness/depressive-like behaviors (food intake, weight loss, locomotion, and sucrose preference), systemic inflammation (serum amyloid A, SAA), blood-brain barrier (BBB) disruption, astrogliosis (glial fibrillary acidic protein/GFAP), Aβ, and cytokine levels in the brain. We found that LPS caused a larger reduction in body weight in Tg vs. WT mice, but that other behavioral responses to LPS did not differ by genotype. BBB disruption was not apparent in either genotype following LPS. Concentrations of the systemic inflammatory marker, SAA, in the blood and brain were significantly increased with LPS but did not significantly differ by genotype. GFAP was increased in Tg mice vs. WT but was not significantly affected by LPS in either genotype. Finally, LPS-induced increases of eight cytokines (IL-1β, IL-6, IL-12 (p40), IL-10, IL-17A, MIP-1α/CCL3, MIP-1β/CCL4, and RANTES/CCL5) were found to be significantly higher in Tg mice vs. WT. In summary, our data show that Aβ pathology exacerbates the neuroinflammatory response to LPS and identifies cytokines that are selectively regulated by Aβ. The association of worse neuroinflammation with greater weight loss in Tg mice suggests that Aβ pathology could contribute to poor outcomes following a systemic inflammatory insult.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The blood–brain barrier (BBB) is a critical physiochemical interface that regulates communication between the brain and blood. It is comprised of brain endothelial cells which regulate the BBB’s ...barrier and interface properties and is surrounded by supportive brain cell types including pericytes and astrocytes. Recent reports have suggested that the BBB undergoes dysfunction during normative aging and in disease. In this review, we consider the effect of cellular senescence, one of the nine hallmarks of aging, on the BBB. We first characterize known normative age–related changes at the BBB, and then evaluate changes in neurodegenerative diseases, with an emphasis on if/how cellular senescence is influencing these changes. We then discuss what insight has been gained from in vitro and in vivo studies of cellular senescence at the BBB. Finally, we evaluate mechanisms by which cellular senescence in peripheral pathologies can indirectly or directly affect BBB function.
Oxidative stress induced by lipid peroxidation products (LPP) accompanies aging and has been hypothesized to exacerbate the secondary cascade in traumatic brain injury (TBI). Increased oxidative ...stress is a contributor to loss of neural reserve that defines the ability to maintain healthy cognitive function despite the accumulation of neuropathology. ALDH2−/− mice are unable to clear aldehyde LPP by mitochondrial aldehyde dehydrogenase-2 (Aldh2) detoxification and provide a model to study mild TBI (mTBI), therapeutic interventions, and underlying mechanisms. The ALDH2−/− mouse model presents with elevated LPP-mediated protein modification, lowered levels of PSD-95, PGC1-α, and SOD-1, and mild cognitive deficits from 4 months of age. LPP scavengers are neuroprotective in vitro and in ALDH2−/− mice restore cognitive performance. A single-hit, closed skull mTBI failed to elicit significant effects in WT mice; however, ALDH2−/− mice showed a significant inflammatory cytokine surge in the ipsilateral hemisphere 24 h post-mTBI, and increased GFAP cleavage, a biomarker for TBI. Known neuroprotective agents, were able to reverse the effects of mTBI. This new preclinical model of mTBI, incorporating significant perturbations in behavior, inflammation, and clinically relevant biomarkers, allows mechanistic study of the interaction of LPP and neurotrauma in loss of neural reserve.
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•ALDH2−/− mice have elevated brain LPP adducts and mild cognitive impairment.•The effects of a “2nd hit” via LPS are exacerbated by LPP in vitro and in vivo.•ALDH2−/− mice + mTBI show amplified/prolonged cognitive deficits and neuroinflammation.•This new preclinical model for mTBI supports a role for LPP in reduced neural reserve.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Calpain inhibitors have been proposed as drug candidates for neurodegenerative disorders, with ABT‐957 entering clinical trials for Alzheimer's disease and mild cognitive impairment. The structure of ...ABT‐957 was very recently disclosed, and trials were terminated owing to inadequate CNS concentrations to obtain a pharmacodynamic effect. The multistep synthesis of an α‐ketoamide peptidomimetic inhibitor series potentially including ABT‐957 was optimized to yield diastereomerically pure compounds that are potent and selective for calpain‐1 over papain and cathepsins B and K. As the final oxidation step, with its optimized synthesis protocol, does not alter the configuration of the substrate, the synthesis of the diastereomeric pair (R)‐1‐benzyl‐N‐((S)‐4‐((4‐fluorobenzyl)amino)‐3,4‐dioxo‐1‐phenylbutan‐2‐yl)‐5‐oxopyrrolidine‐2‐carboxamide (1 c) and (R)‐1‐benzyl‐N‐((R)‐4‐((4‐fluorobenzyl)amino)‐3,4‐dioxo‐1‐phenylbutan‐2‐yl)‐5‐oxopyrrolidine‐2‐carboxamide (1 g) was feasible. This allowed the exploration of stereoselective inhibition of calpain‐1, with 1 c (IC50=78 nM) being significantly more potent than 1 g. Moreover, inhibitor 1 c restored cognitive function in amnestic mice.
Don't forget: (R)‐1‐Benzyl‐N‐((S)‐4‐((4‐fluorobenzyl)amino)‐3,4‐dioxo‐1‐phenylbutan‐2‐yl)‐5‐oxopyrrolidine‐2‐carboxamide (1 c) is a potent and selective calpain‐1 inhibitor (IC50=78 nM) that restored memory in response to the blockade of cholinergic signaling by the mAChR antagonist scopolamine.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Histone deacetylase 8 (HDAC8) is a promising drug target for multiple therapeutic applications. Here, we describe the modeling, design, synthesis, and biological evaluation of a novel series of ...C1-substituted tetrahydroisoquinoline (TIQ)-based HDAC8 inhibitors. Minimization of entropic loss upon ligand binding and use of the unique HDAC8 “open” conformation of the binding site yielded a successful strategy for improvement of both HDAC8 potency and selectivity. The TIQ-based 3g and 3n exhibited the highest 82 and 55 nM HDAC8 potency and 330- and 135-fold selectivity over HDAC1, respectively. Selectivity over other class I isoforms was comparable or better, whereas inhibition of HDAC6, a class II HDAC isoform, was below 50% at 10 μM. The cytotoxicity of 3g and 3n was evaluated in neuroblastoma cell lines, and 3n displayed concentration-dependent cytotoxicity similar to or better than that of PCI-34051. The selectivity of 3g and 3n was confirmed in SH-SY5Y cells as both did not increase the acetylation of histone H3 and α-tubulin. Discovery of the novel TIQ chemotype paves the way for the development of HDAC8 selective inhibitors for therapeutic applications.
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IJS, KILJ, NUK, PNG, UL, UM, UPUK
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The inflammatory caspases (caspase-1, -4 and -5) are potential therapeutic targets for autoimmune and inflammatory diseases due to their involvement in the immune response upon ...inflammasome formation. A series of small molecules based on the 4-(piperazin-1-yl)-2,6-di(pyrrolidin-1-yl)pyrimidine scaffold were synthesized with varying substituents on the piperazine ring. Several compounds were pan-selective inhibitors of the inflammatory caspases, caspase-1, -4 and -5, with the ethylbenzene derivative CK-1–41 displaying low nanomolar Ki values across this family of caspases. Three analogs were nearly 10 fold selective for caspase-5 over caspase-1 and -4. The compounds display non-competitive, time dependent inhibition profiles. To our knowledge, this series is the first example of small molecule inhibitors of all three inflammatory caspases.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The calpain–cathepsin hypothesis posits a key role for elevated calpain-1 and cathepsin-B activity in the neurodegeneration underlying neurotrauma and multiple disorders including Alzheimer’s disease ...(AD). AD clinical trials were recently halted on alicapistat, a selective calpain-1 inhibitor, because of insufficient exposure of neurons to the drug. In contrast to neuroprotection, the ability of calpain-1 and cathepsin-B inhibitors to protect the blood–brain barrier (BBB), is understudied. Since cerebrovascular dysfunction underlies vascular dementia, is caused by ischemic stroke, and is emerging as an early feature in the progression of AD, we studied protection of brain endothelial cells (BECs) by selective and nonselective calpain-1 and cathepsin-B inhibitors. We show these inhibitors protect both neurons and murine BECs from ischemia–reperfusion injury. Cultures of primary BECs from ALDH2 –/– mice that manifest enhanced oxidative stress were sensitive to ischemia, leading to reduced cell viability and loss of tight junction proteins; this damage was rescued by calpain-1 and cathepsin-B inhibitors. In ALDH2 –/– mice 24 h after mild traumatic brain injury (mTBI), BBB damage was reflected by significantly increased fluorescein extravasation and perturbation of tight junction proteins, eNOS, MMP-9, and GFAP. Both calpain and cathepsin-B inhibitors alleviated BBB dysfunction caused by mTBI. No clear advantage was shown by selective versus nonselective calpain inhibitors in these studies. The lack of recognition of the ability of calpain inhibitors to protect the BBB may have led to the premature abandonment of this therapeutic approach in AD clinical trials and requires further mechanistic studies of cerebrovascular protection by calpain-1 inhibitors.
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IJS, KILJ, NUK, PNG, UL, UM, UPUK
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