Blood–brain barrier P-glycoprotein function decreases in specific brain regions with aging: A possible role in progressive neurodegeneration

Exploratory Study of Sex Differences in P-Glycoprotein Function at the Blood-Brain Barrier

Permeability-glycoprotein (P-gp), a crucial efflux pump transporter encoded by the ABCB1 gene, plays a pivotal role in drug disposition at the blood-brain barrier (BBB) and is involved in the pharmacokinetics of numerous therapeutic agents. This study investigates differences in P-gp function at the BBB between males and females in a cohort of older (55+) healthy volunteers (HV) using [18F]MC225 and PET. Twenty HV (11 males and 9 females), free from medications that affect P-gp function and without a history of neurological or psychiatric disorders, underwent [18F]MC225 PET scans with manual arterial blood sampling. Tissue time-activity curves (TAC) were extracted using the Hammers maximum-probability atlas. Whole-blood TAC was derived from the internal carotid arteries, calibrated using manual arterial samples, and adjusted for the plasma-to-whole blood ratio and plasma parent fraction to obtain the image-derived input function. The volume of distribution (VT) was estimated using a reversible two-tissue compartment model, yielding the parameter of interest. Statistical analysis revealed no significant differences in P-gp function between sexes, based on VT values across various brain regions (Cohen's d < 0.2). Furthermore, the arterial blood concentration, plasma parent fraction, and microparameters demonstrated no statistical differences between male and female participants. These findings suggest that P-gp function at the BBB does not exhibit substantial sex-related variability in healthy older adults (55+). For future [18F]MC225 PET studies, a mixed-sex population can serve as an appropriate age-matched control group for neurodegenerative studies. Further research is needed to explore sex-related differences in younger populations, particularly with respect to hormonal cycles.

Senescence-associated microvascular endothelial dysfunction: A focus on the blood-brain and blood-retinal barriers

The blood-brain barrier (BBB) and blood-retinal barrier (BRB) constitute critical physiochemical interfaces, precisely orchestrating the bidirectional communication between the brain/retina and blood. Increased permeability or leakage of these barriers has been demonstrably linked to age-related vascular and parenchymal damage. While it has been suggested that the gradual aging process may coincide with disruptions in these barriers, this phenomenon is significantly exacerbated in individuals with age-related neurodegenerative disorders (ARND). This review focuses on the microvascular endothelium, a key constituent of BBB and BRB, highlighting the impact of endothelial senescence on barrier dysfunction and exploring recent discoveries regarding core pathways implicated in its breakdown. Subsequently, we address the "vascular senescence hypothesis" for ARND, with a particular emphasis on Alzheimer's disease and age-related macular degeneration, centered on endothelial senescence. Finally, we discuss potential senotherapeutic strategies targeting barrier dysfunction.

Enhancing of cerebral Abeta clearance by modulation of ABC transporter expression: a review of experimental approaches

Clearance of amyloid-beta (Aβ) from the brain is impaired in both early-onset and late-onset Alzheimer's disease (AD). Mechanisms for clearing cerebral Aβ include proteolytic degradation, antibody-mediated clearance, blood brain barrier and blood cerebrospinal fluid barrier efflux, glymphatic drainage, and perivascular drainage. ATP-binding cassette (ABC) transporters are membrane efflux pumps driven by ATP hydrolysis. Their functions include maintenance of brain homeostasis by removing toxic peptides and compounds, and transport of bioactive molecules including cholesterol. Some ABC transporters contribute to lowering of cerebral Aβ. Mechanisms suggested for ABC transporter-mediated lowering of brain Aβ, in addition to exporting of Aβ across the blood brain and blood cerebrospinal fluid barriers, include apolipoprotein E lipidation, microglial activation, decreased amyloidogenic processing of amyloid precursor protein, and restricting the entrance of Aβ into the brain. The ABC transporter superfamily in humans includes 49 proteins, eight of which have been suggested to reduce cerebral Aβ levels. This review discusses experimental approaches for increasing the expression of these ABC transporters, clinical applications of these approaches, changes in the expression and/or activity of these transporters in AD and transgenic mouse models of AD, and findings in the few clinical trials which have examined the effects of these approaches in patients with AD or mild cognitive impairment. The possibility that therapeutic upregulation of ABC transporters which promote clearance of cerebral Aβ may slow the clinical progression of AD merits further consideration.

Emerging Role of ABC Transporters in Glia Cells in Health and Diseases of the Central Nervous System

ATP-binding cassette (ABC) transporters play a crucial role for the efflux of a wide range of substrates across different cellular membranes. In the central nervous system (CNS), ABC transporters have recently gathered significant attention due to their pivotal involvement in brain physiology and neurodegenerative disorders, such as Alzheimer's disease (AD). Glial cells are fundamental for normal CNS function and engage with several ABC transporters in different ways. Here, we specifically highlight ABC transporters involved in the maintenance of brain homeostasis and their implications in its metabolic regulation. We also show new aspects related to ABC transporter function found in less recognized diseases, such as Huntington's disease (HD) and experimental autoimmune encephalomyelitis (EAE), as a model for multiple sclerosis (MS). Understanding both their impact on the physiological regulation of the CNS and their roles in brain diseases holds promise for uncovering new therapeutic options. Further investigations and preclinical studies are warranted to elucidate the complex interplay between glial ABC transporters and physiological brain functions, potentially leading to effective therapeutic interventions also for rare CNS disorders.

Association of variants in the ABCB1, CYP2C19 and CYP2C9 genes for Juvenile Myoclonic Epilepsy

Juvenile myoclonic epilepsy (JME) is the most common of the generalized genetic epilepsies, with multiple causal and susceptibility genes; however, its etiopathogenesis is mainly unknown. The toxic effects caused by xenobiotics in cells occur during their metabolic transformation, mainly by enzymes belonging to cytochrome P450. The elimination of these compounds by transporters of the ABC type protects the central nervous system, but their accumulation causes neuronal damage, resulting in neurological diseases. The present study has sought the association between single nucleotide genetic variants of the CYP2C9, CYP2C19, and ABCB1 genes and the development of JME in patients compared to healthy controls. The CC1236 and GG2677 genotypes of ABCB1 in women; allele G 2677, genotypes GG 2677 and CC 3435 in men; the CYP2C19*2A allele, and the CYP2C19*3G/A genotype in both sexes were found to be risk factors for JME. Furthermore, carriers of the TTGGCC genotype combination of the ABCB1 gene (1236/2677/3435) have a 10.5 times higher risk of developing JME than non-carriers. Using the STRING database, we found an interaction between the proteins encoded by these genes and other possible proteins. These findings indicate that the CYP450 system and ABC transporters could interact with other genes in the JME.

Approaches for Increasing Cerebral Efflux of Amyloid-β in Experimental Systems

Amyloid protein-β (Aβ) concentrations are increased in the brain in both early onset and late onset Alzheimer's disease (AD). In early onset AD, cerebral Aβ production is increased and its clearance is decreased, while increased Aβ burden in late onset AD is due to impaired clearance. Aβ has been the focus of AD therapeutics since development of the amyloid hypothesis, but efforts to slow AD progression by lowering brain Aβ failed until phase 3 trials with the monoclonal antibodies lecanemab and donanemab. In addition to promoting phagocytic clearance of Aβ, antibodies lower cerebral Aβ by efflux of Aβ-antibody complexes across the capillary endothelia, dissolving Aβ aggregates, and a "peripheral sink" mechanism. Although the blood-brain barrier is the main route by which soluble Aβ leaves the brain (facilitated by low-density lipoprotein receptor-related protein-1 and ATP-binding cassette sub-family B member 1), Aβ can also be removed via the blood-cerebrospinal fluid barrier, glymphatic drainage, and intramural periarterial drainage. This review discusses experimental approaches to increase cerebral Aβ efflux via these mechanisms, clinical applications of these approaches, and findings in clinical trials with these approaches in patients with AD or mild cognitive impairment. Based on negative findings in clinical trials with previous approaches targeting monomeric Aβ, increasing the cerebral efflux of soluble Aβ is unlikely to slow AD progression if used as monotherapy. But if used as an adjunct to treatment with lecanemab or donanemab, this approach might allow greater slowing of AD progression than treatment with either antibody alone.

[11C]metoclopramide is a sensitive radiotracer to measure moderate decreases in P-glycoprotein function at the blood-brain barrier

The efflux transporter P-glycoprotein (P-gp) at the blood-brain barrier limits the cerebral uptake of various xenobiotics. To assess the sensitivity of [11C]metoclopramide to measure decreased cerebral P-gp function, we performed [11C]metoclopramide PET scans without (baseline) and with partial P-gp inhibition by tariquidar in wild-type, heterozygous Abcb1a/b(+/-) and homozygous Abcb1a/b(-/-) mice as models with controlled levels of cerebral P-gp expression. Brains were collected to quantify P-gp expression with immunohistochemistry. Brain uptake of [11C]metoclopramide was expressed as the area under the brain time-activity curve (AUCbrain) and compared with data previously obtained with (R)-[11C]verapamil and [11C]N-desmethyl-loperamide. Abcb1a/b(+/-) mice had intermediate P-gp expression compared to wild-type and Abcb1a/b(-/-) mice. In baseline scans, all three radiotracers were able to discriminate Abcb1a/b(-/-) from wild-type mice (2.5- to 4.6-fold increased AUCbrain, p ≤ 0.0001). However, only [11C]metoclopramide could discriminate Abcb1a/b(+/-) from wild-type mice (1.46-fold increased AUCbrain, p ≤ 0.001). After partial P-gp inhibition, differences in [11C]metoclopramide AUCbrain between Abcb1a/b(+/-) and wild-type mice (1.39-fold, p ≤ 0.001) remained comparable to baseline. There was a negative correlation between baseline [11C]metoclopramide AUCbrain and ex-vivo-measured P-gp immunofluorescence (r = -0.9875, p ≤ 0.0001). Our data suggest that [11C]metoclopramide is a sensitive radiotracer to measure moderate, but (patho-)physiologically relevant decreases in cerebral P-gp function without the need to co-administer a P-gp inhibitor.

Targeting the blood-brain barrier to delay aging-accompanied neurological diseases by modulating gut microbiota, circadian rhythms, and their interplays

The blood-brain barrier (BBB) impairment plays a crucial role in the pathological processes of aging-accompanied neurological diseases (AAND). Meanwhile, circadian rhythms disruption and gut microbiota dysbiosis are associated with increased morbidity of neurological diseases in the accelerated aging population. Importantly, circadian rhythms disruption and gut microbiota dysbiosis are also known to induce the generation of toxic metabolites and pro-inflammatory cytokines, resulting in disruption of BBB integrity. Collectively, this provides a new perspective for exploring the relationship among circadian rhythms, gut microbes, and the BBB in aging-accompanied neurological diseases. In this review, we focus on recent advances in the interplay between circadian rhythm disturbances and gut microbiota dysbiosis, and their potential roles in the BBB disruption that occurs in AAND. Based on existing literature, we discuss and propose potential mechanisms underlying BBB damage induced by dysregulated circadian rhythms and gut microbiota, which would serve as the basis for developing potential interventions to protect the BBB in the aging population through targeting the BBB by exploiting its links with gut microbiota and circadian rhythms for treating AAND.

Effects of anti-tau immunotherapy on reactive microgliosis, cerebral endotheliopathy, and cognitive function in an experimental model of cerebral malaria

Cerebral malaria (CM), a potentially fatal encephalopathy caused primarily by infection with Plasmodium falciparum, results in long-term adverse neuro-psychiatric sequelae. Neural cell injury contributes to the neurological deficits observed in CM. Abnormal regulation of tau, an axonal protein pathologically associated with the formation of neurofibrillary lesions in neurodegenerative diseases, has been linked to inflammation and cerebral microvascular compromise and has been reported in human and experimental CM (ECM). Immunotherapy with a monoclonal antibody to pathological tau (PHF-1 mAB) in experimental models of neurodegenerative diseases has been reported to mitigate cognitive decline. We investigated whether immunotherapy with PHF-1 mAB prevented cerebral endotheliopathy, neural cell injury, and neuroinflammation during ECM. Using C57BL/6 mice infected with either Plasmodium berghei ANKA (PbA), which causes ECM, Plasmodium berghei NK65 (PbN), which causes severe malaria, but not ECM, or uninfected mice (Un), we demonstrated that when compared to PbN infection or uninfected mice, PbA infection resulted in significant memory impairment at 6 days post-infection, in association with abnormal tau phosphorylation at Ser202 /Thr205 (pSer202 /Thr205 ) and Ser396-404 (pSer396-404 ) in mouse brains. ECM also resulted in significantly higher expression of inflammatory markers, in microvascular congestion, and glial cell activation. Treatment with PHF-1 mAB prevented PbA-induced cognitive impairment and was associated with significantly less vascular congestion, neuroinflammation, and neural cell activation in mice with ECM. These findings suggest that abnormal regulation of tau protein contributes to cerebral vasculopathy and is critical in the pathogenesis of neural cell injury during CM. Tau-targeted therapies may ameliorate the neural cell damage and subsequent neurocognitive impairment that occur during disease.

Nanowired delivery of antibodies to tau and neuronal nitric oxide synthase together with cerebrolysin attenuates traumatic brain injury induced exacerbation of brain pathology in Parkinson's disease

Concussive head injury (CHI) is one of the major risk factors for developing Parkinson's disease in later life of military personnel affecting lifetime functional and cognitive disturbances. Till date no suitable therapies are available to attenuate CHI or PD induced brain pathology. Thus, further exploration of novel therapeutic agents are highly warranted using nanomedicine in enhancing the quality of life of veterans or service members of US military. Since PD or CHI induces oxidative stress and perturbs neurotrophic factors regulation associated with phosphorylated tau (p-tau) deposition, a possibility exists that nanodelivery of agents that could enhance neurotrophic factors balance and attenuate oxidative stress could be neuroprotective in nature. In this review, nanowired delivery of cerebrolysin-a balanced composition of several neurotrophic factors and active peptide fragments together with monoclonal antibodies to neuronal nitric oxide synthase (nNOS) with p-tau antibodies was examined in PD following CHI in model experiments. Our results suggest that combined administration of nanowired antibodies to nNOS and p-tau together with cerebrolysin significantly attenuated CHI induced exacerbation of PD brain pathology. This combined treatment also has beneficial effects in CHI or PD alone, not reported earlier.

Generation and characterization of a zebrafish knockout model of abcb4, a homolog of the human multidrug efflux transporter P-glycoprotein

The ATP-binding cassette subfamily B member 1 (ABCB1), encoding a multidrug transporter referred to as P-glycoprotein (Pgp), plays a critical role in the efflux of xenobiotics in humans and is implicated in cancer resistance to chemotherapy. Therefore, developing high-throughput animal models to screen for Pgp function and bioavailability of substrates and inhibitors is paramount. Here, we generated and validated a zebrafish knockout line of abcb4, a human Pgp transporter homolog. CRISPR/Cas9 genome editing technology was deployed to generate a frameshift mutation in exon 4 of zebrafish abcb4. The zebrafish abcb4 homozygous mutant exhibited elevated accumulation of fluorescent rhodamine 123, a substrate of human Pgp, in the intestine and brain area of embryos. Moreover, abcb4 knockout embryos were sensitized toward toxic compounds such as doxorubicin and vinblastine compared to the WT zebrafish. Immunostaining for zebrafish Abcb4 colocalized in the endothelial brain cells of adult zebrafish. Transcriptome profiling using Gene Set Enrichment Analysis uncovered that the 'cell cycle process,' 'mitotic cell cycles,' and 'microtubule-based process' were significantly downregulated in the abcb4 knockout brain with age. This study establishes and validates the abcb4 knockout zebrafish as an animal model to study Pgp function in vivo. Unexpectedly it reveals a potentially novel role for zebrafish abcb4 in age-related changes in the brain. The zebrafish lines generated here will provide a platform to aid in the discovery of modulators of Pgp function as well as the characterization of human mutants thereof.

Biological agents and the aging brain: glial inflammation and neurotoxic signaling

Neuroinflammation is a universal characteristic of brain aging and neurological disorders, irrespective of the disease state. Glial inflammation mediates this signaling, through astrocyte and microglial polarization from neuroprotective to neurotoxic phenotypes. Glial reactivity results in the loss of homeostasis, as these cells no longer provide support to neurons, in addition to the production of chronically toxic pro-inflammatory mediators. These glial changes initiate an inflammatory brain state that injures the central nervous system (CNS) over time. As the brain ages, glia are altered, including increased glial cell numbers, morphological changes, and either a pre-disposition or inability to become reactive. These alterations induce age-related neuropathologies, ultimately leading to neuronal degradation and irreversible damage associated with disorders of the aged brain, including Alzheimer's Disease (AD) and other related diseases. While the complex interactions of these glial cells and the brain are well studied, the role additional stressors, such as infectious agents, play on age-related neuropathology has not been fully elucidated. Both biological agents in the periphery, such as bacterial infections, or in the CNS, including viral infections like SARS-CoV-2, push glia into neuroinflammatory phenotypes that can exacerbate pathology within the aging brain. These biological agents release pattern associated molecular patterns (PAMPs) that bind to pattern recognition receptors (PRRs) on glial cells, beginning an inflammatory cascade. In this review, we will summarize the evidence that biological agents induce reactive glia, which worsens age-related neuropathology.

Generation and characterization of a zebrafish knockout model of abcb4, a homolog of the human multidrug efflux transporter P-glycoprotein

The ATP-binding cassette subfamily B member 1 (ABCB1), encoding a multidrug transporter referred to as P-glycoprotein (Pgp), plays a critical role in the efflux of xenobiotics in humans and is implicated in cancer resistance to chemotherapy. Therefore, developing high throughput animal models to screen for Pgp function and bioavailability of substrates and inhibitors is paramount. Here, we generated and validated a zebrafish knockout line of abcb4 , a human Pgp transporter homolog. CRISPR/Cas9 genome editing technology was deployed to generate a frameshift mutation in exon 4 of zebrafish abcb4 . The zebrafish abcb4 homozygous mutant exhibited elevated accumulation of fluorescent rhodamine 123, a substrate of human Pgp, in the intestine and brain area of embryos. Moreover, abcb4 knockout embryos were sensitized toward toxic compounds such as doxorubicin and vinblastine compared to the WT zebrafish. Immuno-staining for zebrafish Abcb4 colocalized in the endothelial brain cells of adult zebrafish. Transcriptome profiling using Gene Set Enrichment Analysis (GSEA) uncovered that the 'cell cycle process,' 'mitotic cell cycles,' and 'microtubule-based process' were significantly downregulated in the abcb4 knockout brain with age. This study establishes and validates the a bcb4 knockout zebrafish as an animal model to study Pgp function in vivo. Unexpectedly it reveals a potentially novel role for zebrafish abcb4 in age-related changes in the brain. The zebrafish lines generated here will provide a platform to aid in the discovery of modulators of Pgp function as well as the characterization of human mutants thereof.

CRTC1 is a potential target to delay aging-induced cognitive deficit by protecting the integrity of the blood-brain barrier via inhibiting inflammation

Aging can cause attenuation in the functioning of multiple organs, and blood-brain barrier (BBB) breakdown could promote the occurrence of disorders of the central nervous system during aging. Since inflammation is considered to be an important factor underlying BBB injury during aging, vascular endothelial cell senescence serves as a critical pathological basis for the destruction of BBB integrity. In the current review, we have first introduced the concepts related to aging-induced cognitive deficit and BBB integrity damage. Thereafter, we reviewed the potential relationship between disruption of BBB integrity and cognition deficit and the role of inflammation, vascular endothelial cell senescence, and BBB injury. We have also briefly introduced the function of CREB-regulated transcription co-activator 1 (CRTC1) in cognition and aging-induced CRTC1 changes as well as the critical roles of CRTC1/cyclooxygenase-2 (COX-2) in regulating inflammation, endothelial cell senescence, and BBB injury. Finally, the underlying mechanisms have been summarized and we propose that CRTC1 could be a promising target to delay aging-induced cognitive deficit by protecting the integrity of BBB through promoting inhibition of inflammation-mediated endothelial cell senescence.

Safety and Tolerability of Antimicrobial Agents in the Older Patient

Older patients are at high risk of infections, which often present atypically and are associated with high morbidity and mortality. Antimicrobial treatment in older individuals with infectious diseases represents a clinical challenge, causing an increasing burden on worldwide healthcare systems; immunosenescence and the coexistence of multiple comorbidities determine complex polypharmacy regimens with an increase in drug-drug interactions and spread of multidrug-resistance infections. Aging-induced pharmacokinetic and pharmacodynamic changes can additionally increase the risk of inappropriate drug dosing, with underexposure that is associated with antimicrobial resistance and overexposure that may lead to adverse effects and poor adherence because of low tolerability. These issues need to be considered when starting antimicrobial prescriptions. National and international efforts have been made towards the implementation of antimicrobial stewardship (AMS) interventions to help clinicians improve the appropriateness and safety of antimicrobial prescriptions in both acute and long-term care settings. AMS programs were shown to decrease consumption of antimicrobials and to improve safety in hospitalized patients and older nursing home residents. With the abundance of antimicrobial prescriptions and the recent emergence of multidrug resistant pathogens, an in-depth review of antimicrobial prescriptions in geriatric clinical practice is needed. This review will discuss the special considerations for older individuals needing antimicrobials, including risk factors that shape risk profiles in geriatric populations as well as an evidence-based description of antimicrobial-induced adverse events in this patient population. It will highlight agents of concern for this age group and discuss interventions to mitigate the effects of inappropriate antimicrobial prescribing.

The role of the efflux transporter, P-glycoprotein, at the blood-brain barrier in drug discovery

The blood-brain barrier (BBB) expresses a high abundance of transporters, particularly P-glycoprotein (P-gp), that regulate endogenous and exogenous molecule uptake and removal of waste. This review discusses key drug metabolism and pharmacokinetic considerations for the efflux transporter P-gp at the BBB in drug discovery and development. We highlight the differences in P-gp expression and protein levels across species but the limited observations of species-specific substrates. Given the impact of age and disease on BBB biology, we summarise the modulation of P-gp for several neurological disorders and ageing and exemplify several disease-specific hurdles or opportunities for drug exposure in the brain. Furthermore, the review includes observations of CNS-related drug-drug interactions due to the inhibition or induction of P-gp at the BBB in animal studies and humans and the need for continued evaluation especially for compounds with a narrow therapeutic window. This review focusses primarily on small molecules but also considers the impact of new chemical entities, particularly beyond Ro5 molecules and their potential to be recognised as P-gp substrates as well as advanced drug delivery systems which offer an alternative approach to achieve and sustain central nervous system exposure.

A Novel Huntington's Disease Assessment Platform to Support Future Drug Discovery and Development

Huntington's disease (HD) is a lethal neurodegenerative disorder without efficient therapeutic options. The inefficient translation from preclinical and clinical research into clinical use is mainly attributed to the lack of (i) understanding of disease initiation, progression, and involved molecular mechanisms; (ii) knowledge of the possible HD target space and general data awareness; (iii) detailed characterizations of available disease models; (iv) better suitable models; and (v) reliable and sensitive biomarkers. To generate robust HD-like symptoms in a mouse model, the neomycin resistance cassette was excised from zQ175 mice, generating a new line: zQ175^Δneo. We entirely describe the dynamics of behavioral, neuropathological, and immunohistological changes from 15-57 weeks of age. Specifically, zQ175^Δneo mice showed early astrogliosis from 15 weeks; growth retardation, body weight loss, and anxiety-like behaviors from 29 weeks; motor deficits and reduced muscular strength from 36 weeks; and finally slight microgliosis at 57 weeks of age. Additionally, we collected the entire bioactivity network of small-molecule HD modulators in a multitarget dataset (HD_MDS). Hereby, we uncovered 358 unique compounds addressing over 80 different pharmacological targets and pathways. Our data will support future drug discovery approaches and may serve as useful assessment platform for drug discovery and development against HD.

Regulation of P-Glycoprotein in the Brain

Maintenance of the tightly regulated homeostatic environment of the brain is facilitated by the blood-brain barrier (BBB). P-glycoprotein (P-gp), an ATP-binding cassette transporter, is expressed on the luminal surface of the endothelial cells in the BBB, and actively exports a wide variety of substrates to limit exposure of the vulnerable brain environment to waste buildup and neurotoxic compounds. Downregulation of P-gp expression and activity at the BBB have been reported with ageing and in neurodegenerative diseases. Upregulation of P-gp at the BBB contributes to poor therapeutic outcomes due to altered pharmacokinetics of CNS-acting drugs. The regulation of P-gp is highly complex, but unravelling the mechanisms involved may help the development of novel and nuanced strategies to modulate P-gp expression for therapeutic benefit. This review summarises the current understanding of P-gp regulation in the brain, encompassing the transcriptional, post-transcriptional and post-translational mechanisms that have been identified to affect P-gp expression and transport activity.

Elevated Cerebrospinal Fluid Proteins and Albumin Determine a Poor Prognosis for Spinal Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a heterogeneous disease, both in its onset phenotype and in its rate of progression. The aim of this study was to establish whether the dysfunction of the blood–brain barrier (BBB) and blood–spinal cord barrier (BSCB) measured through cerebrospinal fluid (CSF) proteins and the albumin-quotient (QAlb) are related to the speed of disease progression. An amount of 246 patients diagnosed with ALS were included. CSF and serum samples were determined biochemically for different parameters. Survival analysis based on phenotype shows higher probability of death for bulbar phenotype compared to spinal phenotype (p-value: 0.0006). For the effect of CSF proteins, data shows an increased risk of death for spinal ALS patients as the value of CSF proteins increases. The same model replicated for CSF albumin yielded similar results. Statistical models determined that the lowest cut-off value for CSF proteins able to differentiate patients with a good prognosis and worse prognosis corresponds to CSF proteins ≥ 0.5 g/L (p-value: 0.0189). For the CSF albumin, the QAlb ≥0.65 is associated with elevated probability of death (p-value: 0.0073). High levels of QAlb are a bad prognostic indicator for the spinal phenotype, in addition to high CSF proteins levels that also act as a marker of poor prognosis.

ABCB1 gene variants as risk factors and modulators of age of onset of demyelinating disease in Mexican patients

INTRODUCTION

The C1236T, G2677T/A, and C3435T variants of the ABCB1 gene alter the functioning of P-glycoprotein and the transport of endogenous and exogenous substances across the blood-brain barrier, and act as risk factors for some neurodegenerative diseases. This study aimed to determine the association between demyelinating disease and the C1236T, G2677T/A, and C3435T variants of ABCB1 and its haplotypes and combinations of genotypes.

METHODS

Polymerase chain reaction with restriction fragment length polymorphism analysis (PCR-RFLP) and Sanger sequencing were used to genotype 199 patients with demyelinating disease and 200 controls, all Mexicans of mixed race; frequencies of alleles, genotypes, haplotypes, and genotype combinations were compared between patients and controls. We conducted a logistic regression analysis and calculated chi-square values and 95% confidence intervals (CI); odds ratios (OR) were calculated to evaluate the association with demyelinating disease.

RESULTS

The TTT and CGC haplotypes were most frequent in both patients and controls. The G2677 allele was associated with demyelinating disease (OR: 1.79; 95% CI, 1.12-2.86; P =  .015), as were the genotypes GG2677 (OR: 2.72; 95% CI, 1.11-6.68; P =  .025) and CC3435 (OR: 1.82; 95% CI, 1.15-2.90; P =  .010), the combination GG2677/CC3435 (OR: 2.02; 95% CI, 1.17-3.48; P =  .010), and the CAT haplotype (OR: 0.21; 95% CI, 0.05-0.66; P =  .001). TTTTTT carriers presented the earliest age of onset (23.0 ± 7.7 years, vs 31.6 ± 10.7; P =  .0001).

CONCLUSIONS

The GG2677/CC3435 genotype combination is associated with demyelinating disease in this sample, particularly among men, who may present toxic accumulation of P-glycoprotein substrates. In our study, the G2677 allele of ABCB1 may differentially modulate age of onset of demyelinating disease in men and women.

The Ubiquitin E3 Ligase Nedd4 Regulates the Expression and Amyloid-β Peptide Export Activity of P-Glycoprotein

The ATP-binding cassette transporter, P-glycoprotein (P-gp), has been demonstrated to facilitate the clearance of amyloid-beta (Aβ) peptides, exporting the neurotoxic entity out of neurons and out of the brain via the blood–brain barrier. However, its expression and function diminish with age and in Alzheimer’s disease. P-gp is known to undergo ubiquitination, a post-translational modification that results in internalisation and/or degradation of the protein. NEDD4-1 is a ubiquitin E3 ligase that has previously been shown to ubiquitinate P-gp and reduce its cell surface expression. However, whether this effect translates into altered P-gp activity remains to be determined. siRNA was used to knockdown the expression of Nedd4 in CHO-APP cells. Western blot analysis confirmed that absence of Nedd4 was associated with increased P-gp protein expression. This was accompanied by increased transport activity, as shown by export of the P-gp substrate calcein-AM, as well as enhanced secretion of Aβ peptides, as shown by ELISA. These results implicate Nedd4 in the regulation of P-gp, and highlight a potential approach for restoring or augmenting P-gp expression and function to facilitate Aβ clearance from the brain.

The impact of advanced age on anticoagulant therapy for acute venous thromboembolism

INTRODUCTION

Management of venous thromboembolic events (VTE) has been completely changed after the introduction of direct oral anticoagulants (DOAC). VTE is common in the geriatric population, but the management of DOACs remains complex because of the lack of specific data in this polymedicated fragile population.An exhaustive search of anticoagulants in the indication of VTE was performed on PubMed, including data from clinical trials, observational studies, real-world data, drug-drug interaction studies, as well as various guidelines from scientific societies.

AREAS COVERED

The present review aims to summarize our current knowledge on the era of DOACs in the management of VTE in the elderly. This involves learning the pharmacokinetics/pharmacodynamics of drugs specific to geriatrics, the problem of drug-drug interactions, and the main randomized clinical trials validating the use of DOACs.

EXPERT OPINION

DOACs have become an essential part of the management of VTE in the elderly, both for their efficacy and safety. However, we are faced with a list of unmet needs, such as the relevance of DOACs in the very elderly, cancer patients, and those with renal impairment. Clinicians and pharmacists must remain cautious about comedications, as well as about the patient's comorbidities.

Analysis of ABC Transporter Gene Expression in Atherosclerosis

ABC transporters are a large family of membrane proteins that transport chemically diverse substrates across the cell membrane. Disruption of transport mechanisms mediated by ABC transporters causes the development of various diseases, including atherosclerosis. Methods: A bioinformatic analysis of a dataset from Gene Expression Omnibus (GEO) was performed. A GEO dataset containing data on gene expression levels in samples of atherosclerotic lesions and control arteries without atherosclerotic lesions from carotid, femoral, and infrapopliteal arteries was used for analysis. To evaluate differentially expressed genes, a bioinformatic analysis was performed in comparison groups using the limma package in R (v. 4.0.2) and the GEO2R and Phantasus tools (v. 1.11.0). Results: The obtained data indicate the differential expression of many ABC transporters belonging to different subfamilies. The differential expressions of ABC transporter genes involved in lipid transport, mechanisms of multidrug resistance, and mechanisms of ion exchange are shown. Differences in the expression of transporters in tissue samples from different arteries are established. Conclusions: The expression of ABC transporter genes demonstrates differences in atherosclerotic samples and normal arteries, which may indicate the involvement of transporters in the pathogenesis of atherosclerosis.

First clinical assessment of [18F]MC225, a novel fluorine-18 labelled PET tracer for measuring functional P-glycoprotein at the blood-brain barrier

OBJECTIVE

5-(1-(2-[18F]fluoroethoxy))-[3-(6,7-dimethoxy-3,4-dihydro-1H-isoquinolin-2-yl)-propyl]-5,6,7,8-tetrahydronaphthalen ([18F]MC225) is a selective substrate for P-glycoprotein (P-gp), possessing suitable properties for measuring overexpression of P-gp in the brain. This is the first-in-human study to examine safety, radiation dosimetry and P-gp function at the blood-brain barrier (BBB) of [18F]MC225 in healthy subjects.

METHODS

[18F]MC225 biodistribution and dosimetry were determined in 3 healthy male subjects, using serial 2 h and intermittent 4 and 6 h whole-body PET scans acquired after [18F]MC225 injection. Dynamic [18F]MC225 brain PET (90 min) was obtained in 5 healthy male subjects. Arterial blood was sampled at various time intervals during scanning and the fraction of unchanged [18F]MC225 in plasma was determined. T1-weighted MRI was performed for anatomical coregistration. Total distribution volume (VT) was estimated using 1- and 2-tissue-compartment models (1-TCM and 2-TCM, respectively). VT was also estimated using the Logan graphical method (Logan plot) (t* = 20 min). Surrogate parameters without blood sampling (area-under the curve [AUC] of regional time-activity curves [TACs] and negative slope of calculated TACs) were compared with the VT values.

RESULTS

No serious adverse events occurred throughout the study period. Although biodistribution implied hepatobiliary excretion, secretion of radioactivity from liver to small intestine through the gallbladder was very slow. Total renal excreted radioactivity recovered during 6 h after injection was < 2%ID. Absorbed dose was the highest in the pancreas (mean ± SD, 203 ± 45 μGy/MBq) followed by the liver (83 ± 11 μGy/MBq). Mean effective dose with and without urination was 17 ± 1 μSv/MBq. [18F]MC225 readily entered the brain, distributing homogeneously in grey matter regions. 2-TCM provided lower Akaike information criterion scores than did 1-TCM. VT estimated by Logan plot was well correlated with that of 2-TCM (r2 > 0.9). AUCs of TACs were positively correlated with VT (2-TCM) values (r2: AUC0-60 min = 0.61, AUC0-30 min = 0.62, AUC30-60 min = 0.59, p < 0.0001). Negative slope of SUV TACs was negatively correlated with VT (2-TCM) values (r2 = 0.53, p < 0.0001).

CONCLUSIONS

This initial evaluation indicated that [18F]MC225 is a suitable and safe PET tracer for measuring P-gp function at the BBB.

Hypoxia, Oxidative Stress, and Inflammation: Three Faces of Neurodegenerative Diseases

The cerebral hypoxia-ischemia can induce a wide spectrum of biologic responses that include depolarization, excitotoxicity, oxidative stress, inflammation, and apoptosis, and result in neurodegeneration. Several adaptive and survival endogenous mechanisms can also be activated giving an opportunity for the affected cells to remain alive, waiting for helper signals that avoid apoptosis. These signals appear to help cells, depending on intensity, chronicity, and proximity to the central hypoxic area of the affected tissue. These mechanisms are present not only in a large list of brain pathologies affecting commonly older individuals, but also in other pathologies such as refractory epilepsies, encephalopathies, or brain trauma, where neurodegenerative features such as cognitive and/or motor deficits sequelae can be developed. The hypoxia inducible factor 1α (HIF-1α) is a master transcription factor driving a wide spectrum cellular response. HIF-1α may induce erythropoietin (EPO) receptor overexpression, which provides the therapeutic opportunity to administer pharmacological doses of EPO to rescue and/or repair affected brain tissue. Intranasal administration of EPO combined with other antioxidant and anti-inflammatory compounds could become an effective therapeutic alternative, to avoid and/or slow down neurodegenerative deterioration without producing adverse peripheral effects.

Donepezil and Rivastigmine: Pharmacokinetic Profile and Brain-targeting After Intramuscular Administration in Rats

Current palliative pharmacotherapy of Alzheimer's disease based on the cholinergic hypothesis led to the development of four cholinesterase inhibitors. These compounds can bring prolongation of the symptom-free period in some patients. This is the first report directly comparing donepezil and rivastigmine plasma and brain levels in in-vivo study. Donepezil and rivastigmine were applied i.m. to rats; the dose was calculated from clinical recommendations. The samples were analysed on an Agilent 1260 Series LC with UV/VIS detector. An analytical column (Waters Spherisorb S5 W (250 mm × 4.6 i.d.; 5 μm particle size)) with guard column (Waters Spherisorb S5 W (30 mm × 4.6 mm i.d.)) was used. The mobile phase contained acetonitrile and 50 mM sodium dihydrogen phosphate (17:83; v/v); pH 3.1. The LLOQ in rat plasma was 0.5 ng/mL for donepezil and 0.8 ng/mL for rivastigmine, and the LLOQ in rat brain was 1.0 ng/mL for donepezil and 1.1 ng/mL for rivastigmine. Both compounds showed ability to target the central nervous system, with brain concentrations exceeding those in plasma. Maximum brain concentration after i.m. administration was reached in the 36 (8.34 ± 0.34 ng/mL) and 17 minute (6.18 ± 0.40 ng/mL), respectively for donepezil and rivastigmine. The differences in brain profile can be most easily expressed by plasma/brain AUC_total ratios: donepezil ratio in the brain was nine-times higher than in plasma and rivastigmine ratio was less than two-times higher than in plasma.

Abundance of P-Glycoprotein and Other Drug Transporters at the Human Blood-Brain Barrier in Alzheimer's Disease: A Quantitative Targeted Proteomic Study

The human blood-brain barrier (BBB) transporter P-gp can efflux amyloid-β (Aβ) out of the central nervous system (CNS). Aβ is thought to be the causative agent for Alzheimer's disease (AD). Using positron emission tomography imaging, we have shown that BBB P-gp activity is reduced in AD, as quantified by the in vivo brain distribution of the P-gp probe [11 C]-verapamil. Therefore, the aim of this study was to determine whether this reduced BBB P-gp activity in AD was due to decreased P-gp abundance at the BBB. Using targeted proteomics, we quantified the abundance of P-gp and other drug transporters in gray matter brain microvessels isolated from 43 subjects with AD and 38 age-matched controls (AMCs) from regions affected by AD (hippocampus and the parietal lobe of the brain cortex) and not affected by AD (cerebellum). First, P-gp abundance was decreased in the BBB of the hippocampus vs. the cerebellum in both subjects with AD and AMCs, and therefore was not AD-related. In addition, gray matter BBB abundance of P-gp (and of other transporters) in the hippocampus and the parietal lobe was not different between AD and AMC. The gray matter BBB abundance of all drug transporters decreased with age, likely due to age-dependent decrease in the density of brain microvessels. Collectively, the observed reduced in vivo cerebral BBB P-gp activity in AD cannot be explained by reduced abundance of P-gp at the BBB. Nevertheless, the drug transporter abundance at the human gray matter BBB data provided here can be used to predict brain distribution of drugs targeted to treat CNS diseases, including AD.

Blood-Brain Barrier Dynamics to Maintain Brain Homeostasis

The blood-brain barrier (BBB) is a dynamic platform for exchange of substances between the blood and the brain parenchyma, and it is an essential functional gatekeeper for the central nervous system (CNS). While it is widely recognized that BBB disruption is a hallmark of several neurovascular pathologies, an aspect of the BBB that has received somewhat less attention is the dynamic modulation of BBB tightness to maintain brain homeostasis in response to extrinsic environmental factors and physiological changes. In this review, we summarize how BBB integrity adjusts in critical stages along the life span, as well as how BBB permeability can be altered by common stressors derived from nutritional habits, environmental factors and psychological stress.

New Evidence for P-gp-Mediated Export of Amyloid-β PEPTIDES in Molecular, Blood-Brain Barrier and Neuronal Models

Defective clearance mechanisms lead to the accumulation of amyloid-beta (Aβ) peptides in the Alzheimer’s brain. Though predominantly generated in neurons, little is known about how these hydrophobic, aggregation-prone, and tightly membrane-associated peptides exit into the extracellular space where they deposit and propagate neurotoxicity. The ability for P-glycoprotein (P-gp), an ATP-binding cassette (ABC) transporter, to export Aβ across the blood-brain barrier (BBB) has previously been reported. However, controversies surrounding the P-gp–Aβ interaction persist. Here, molecular data affirm that both Aβ₄₀ and Aβ₄₂ peptide isoforms directly interact with and are substrates of P-gp. This was reinforced ex vivo by the inhibition of Aβ₄₂ transport in brain capillaries from P-gp-knockout mice. Moreover, we explored whether P-gp could exert the same role in neurons. Comparison between non-neuronal CHO-APP and human neuroblastoma SK-N-SH cells revealed that P-gp is expressed and active in both cell types. Inhibiting P-gp activity using verapamil and nicardipine impaired Aβ₄₀ and Aβ₄₂ secretion from both cell types, as determined by ELISA. Collectively, these findings implicate P-gp in Aβ export from neurons, as well as across the BBB endothelium, and suggest that restoring or enhancing P-gp function could be a viable therapeutic approach for removing excess Aβ out of the brain in Alzheimer’s disease.

Impaired Clearance From the Brain Increases the Brain Exposure to Metoclopramide in Elderly Subjects

The antiemetic and gastroprokinetic drug metoclopramide is a weak substrate of the blood‐brain barrier (BBB) efflux transporter P‐gp and displays central nervous system (CNS) side effects (i.e., extrapyramidal symptoms and tardive dyskinesia) caused by dopamine D₂ receptor blockade in the basal ganglia. These side effects occur with a higher incidence in elderly people. We used positron emission tomography to assess the brain distribution of [¹¹C]metoclopramide in young (n = 11, 26 ± 3 years) and elderly (n = 7, 68 ± 9 years) healthy men both after administration of a microdose (9 ± 7 µg) and a microdose co‐injected with a therapeutic dose of unlabeled metoclopramide (10 mg). For both doses, elderly subjects had a significantly higher total volume of distribution (V_T) of [¹¹C]metoclopramide in the basal ganglia than young subjects (microdose: +26%, therapeutic dose: +41%). Increases in V_T (= K₁/k₂) were caused by significant decreases in the transfer rate constant of [¹¹C]metoclopramide from brain into plasma (k₂, microdose: −18%, therapeutic dose: −30%), whereas the distributional clearance from plasma into brain (K₁) remained unaltered. This reduction in the clearance of [¹¹C]metoclopramide (k₂) from the brains of elderly subjects may be caused by an age‐related decrease in the activity of P‐gp at the BBB and may contribute to the higher incidence of CNS side effects of metoclopramide in the aged population. Our data suggest that an age‐associated decrease in the clearance properties of the BBB may modulate the CNS effects or side effects of clinically used P‐gp substrates.

Tau Protein and Its Role in Blood-Brain Barrier Dysfunction

The blood-brain barrier (BBB) plays a crucial role in maintaining the specialized microenvironment of the central nervous system (CNS). In aging, the stability of the BBB declines and the permeability increases. The list of CNS pathologies involving BBB dysfunction is growing. The opening of the BBB and subsequent infiltration of serum components to the brain can lead to a host of processes resulting in progressive synaptic, neuronal dysfunction, and detrimental neuroinflammatory changes. Such processes have been implicated in different diseases, including vascular dementia, stroke, Alzheimer's disease (AD), Parkinson's disease, multiple sclerosis, amyotrophic lateral sclerosis, hypoxia, ischemia, and diabetes mellitus. The BBB damage is also observed in tauopathies that lack amyloid-β overproduction, suggesting a role for tau in BBB damage. Tauopathies represent a heterogeneous group of around 20 different neurodegenerative diseases characterized by abnormal deposition of the MAPT in cells of the nervous system. Neuropathology of tauopathies is defined as intracellular accumulation of neurofibrillary tangles (NFTs) consisting of aggregated hyper- and abnormal phosphorylation of tau protein and neuroinflammation. Disruption of the BBB found in tauopathies is driven by chronic neuroinflammation. Production of pro-inflammatory signaling molecules such as cytokines, chemokines, and adhesion molecules by glial cells, neurons, and endothelial cells determine the integrity of the BBB and migration of immune cells into the brain. The inflammatory processes promote structural changes in capillaries such as fragmentation, thickening, atrophy of pericytes, accumulation of laminin in the basement membrane, and increased permeability of blood vessels to plasma proteins. Here, we summarize the knowledge about the role of tau protein in BBB structural and functional changes.

ABCB1 gene variants as risk factors and modulators of age of onset of demyelinating disease in Mexican patients

INTRODUCTION

The C1236T, G2677T/A, and C3435T variants of the ABCB1 gene alter the functioning of P-glycoprotein and the transport of endogenous and exogenous substances across the blood-brain barrier, and act as risk factors for some neurodegenerative diseases. This study aimed to determine the association between demyelinating disease and the C1236T, G2677T/A, and C3435T variants of ABCB1 and its haplotypes and combinations of genotypes.

METHODS

Polymerase chain reaction with restriction fragment length polymorphism analysis (PCR-RFLP) and Sanger sequencing were used to genotype 199 patients with demyelinating disease and 200 controls, all Mexicans of mixed race; frequencies of alleles, genotypes, haplotypes, and genotype combinations were compared between patients and controls. We conducted a logistic regression analysis and calculated chi-square values and 95% confidence intervals (CI); odds ratios (OR) were calculated to evaluate the association with demyelinating disease.

RESULTS

The TTT and CGC haplotypes were most frequent in both patients and controls. The G2677 allele was associated with demyelinating disease (OR: 1.79; 95% CI: 1.12-2.86; P=.015), as were the genotypes GG2677 (OR: 2.72; 95% CI: 1.11-6.68; P=.025) and CC3435 (OR: 1.82; 95% CI: 1.15-2.90; P=.010), the combination GG2677/CC3435 (OR: 2.02; 95% CI, 1.17-3.48; P=.010), and the CAT haplotype (OR: 0.21; 95% CI: 0.05-0.66; P=.001). TTTTTT carriers presented the earliest age of onset (23.0±7.7 years, vs. 31.6±10.7; P=.0001).

CONCLUSIONS

The GG2677/CC3435 genotype combination is associated with demyelinating disease in this sample, particularly among men, who may present toxic accumulation of P-glycoprotein substrates. In our study, the G2677 allele of ABCB1 may differentially modulate age of onset of demyelinating disease in men and women.

The Role of Neurovascular System in Neurodegenerative Diseases

The neurovascular system (NVS), which consisted of neurons, glia, and vascular cells, is a functional and structural unit of the brain. The NVS regulates blood-brain barrier (BBB) permeability and cerebral blood flow (CBF), thereby maintaining the brain's microenvironment for normal functioning, neuronal survival, and information processing. Recent studies have highlighted the role of vascular dysfunction in several neurodegenerative diseases. This is not unexpected since both nervous and vascular systems are functionally interdependent and show close anatomical apposition, as well as similar molecular pathways. However, despite extensive research, the precise mechanism by which neurovascular dysfunction contributes to neurodegeneration remains incomplete. Therefore, understanding the mechanisms of neurovascular dysfunction in disease conditions may allow us to develop potent and effective therapies for prevention and treatment of neurodegenerative diseases. This review article summarizes the current research in the context of neurovascular signaling associated with neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD). We also discuss the potential implication of neurovascular factor as a novel therapeutic target and prognostic marker in patients with neurodegenerative conditions. Graphical Abstract.

Stability of anticholinergic load in Australian community-dwelling older people: a longitudinal analysis

BACKGROUND

It is recommended that anticholinergic medication is avoided in older people, especially those with cognitive impairment.

OBJECTIVE

To investigate anticholinergic load (ACL) over time in older primary care patients with and without cognitive impairment.

METHODS

Community-dwelling general practice patients at baseline (n = 1768), at year one (n = 1373) and a restricted cohort (with possible or definite cognitive impairment) at year two (n = 370) had medication regimens documented by a research nurse during a home visit. Anticholinergic medicines were categorized as levels 1-3 (low-high potency) and summed for each participant as a measure of their ACL.

RESULTS

Most participants had no change in ACL over time, but there was some turnover in the anticholinergic medications used. The mean change in ACL was 0.012 ± 0.99 from baseline to 12 months and -0.04 ± 1.3 from baseline to 24 months. Cardiovascular drugs were the most commonly used level 1 anticholinergics, followed by antidepressants and opioids. Antidepressants and urologicals were the most commonly used level 3 anticholinergics. The rate of anticholinergic deprescribing was equivalent to the rate of anticholinergic initiation, and commonly involved the level 1 drugs warfarin, furosemide and temazepam, and the level 3 drugs amitriptyline and oxybutynin. People with dementia had a higher ACL at baseline and year one compared with other participants.

CONCLUSION

ACL of community-dwelling older people was very stable over time. This may represent lost opportunities for deprescribing as well as potentially inappropriate prescribing, particularly in those with cognitive impairment.

Dysfunction of ABC transporters at the blood-brain barrier: Role in neurological disorders

ABC (ATP-binding cassette) transporters represent one of the largest and most diverse superfamily of proteins in living species, playing an important role in many biological processes such as cell homeostasis, cell signaling, drug metabolism and nutrient uptake. Moreover, using the energy generated from ATP hydrolysis, they mediate the efflux of endogenous and exogenous substrates from inside the cells, thereby reducing their intracellular accumulation. At present, 48 ABC transporters have been identified in humans, which were classified into 7 different subfamilies (A to G) according to their phylogenetic analysis. Nevertheless, the most studied members with importance in drug therapeutic efficacy and toxicity include P-glycoprotein (P-gp), a member of the ABCB subfamily, the multidrug-associated proteins (MPRs), members of the ABCC subfamily, and breast cancer resistance protein (BCRP), a member of the ABCG subfamily. They exhibit ubiquitous expression throughout the human body, with a special relevance in barrier tissues like the blood-brain barrier (BBB). At this level, they play a physiological function in tissue protection by reducing or limiting the brain accumulation of neurotoxins. Furthermore, dysfunction of ABC transporters, at expression and/or activity level, has been associated with many neurological diseases, including epilepsy, multiple sclerosis, Alzheimer's disease, and amyotrophic lateral sclerosis. Additionally, these transporters are strikingly associated with the pharmacoresistance to central nervous system (CNS) acting drugs, because they contribute to the decrease in drug bioavailability. This article reviews the signaling pathways that regulate the expression and activity of P-gp, BCRP and MRPs subfamilies of transporters, with particular attention at the BBB level, and their mis-regulation in neurological disorders.

Age dependency of cerebral P-glycoprotein function in wild-type and APPPS1 mice measured with PET

P-glycoprotein (P-gp, ABCB1) is an efflux transporter at the blood-brain barrier (BBB), which mediates clearance of beta-amyloid (Aβ) from brain into blood. We used (R)-[¹¹C]verapamil PET in combination with partial P-gp inhibition with tariquidar to measure cerebral P-gp function in a beta-amyloidosis mouse model (APPtg) and in control mice at three different ages (50, 200 and 380 days). Following tariquidar pre-treatment (4 mg/kg), whole brain-to-plasma radioactivity concentration ratios (K_p,brain) were significantly higher in APPtg than in wild-type mice aged 50 days, pointing to decreased cerebral P-gp function. Moreover, we found an age-dependent decrease in cerebral P-gp function in both wild-type and APPtg mice of up to -50%. Alterations in P-gp function were more pronounced in Aβ-rich brain regions (hippocampus, cortex) than in a control region with negligible Aβ load (cerebellum). PET results were confirmed by immunohistochemical staining of P-gp in brain microvessels. Our results confirm previous findings of reduced P-gp function in Alzheimer's disease mouse models and show that our PET protocol possesses adequate sensitivity to measure these functional changes in vivo. Our PET protocol may find use in clinical studies to test the efficacy of drugs to induce P-gp function at the human BBB to enhance Aβ clearance.

Age-Related Functional and Expressional Changes in Efflux Pathways at the Blood-Brain Barrier

During the last decade, several articles have reported a relationship between advanced age and changes in the integrity of the blood-brain barrier (BBB). These changes were manifested not only in the morphology and structure of the cerebral microvessels but also in the expression and function of the transporter proteins in the luminal and basolateral surfaces of the capillary endothelial cells. Age-associated downregulation of the efflux pumps ATP-binding cassette transporters (ABC transporters) resulted in increased permeability and greater brain exposure to different xenobiotics and their possible toxicity. In age-related neurodegenerative pathologies like Alzheimer's disease (AD), the amyloid-β (Aβ) clearance decreased due to P-glycoprotein (P-gp) dysfunction, leading to higher brain exposure. In stroke, however, an enhanced P-gp function was reported in the cerebral capillaries, making it even more difficult to perform effective neuroprotective therapy in the infarcted brain area. This mini-review article focuses on the efflux functions of the transporters and receptors of the BBB in age-related brain pathologies and also in healthy aging.

Mind the Gaps: Ontogeny of Human Brain P-gp and Its Impact on Drug Toxicity

Available data on human brain P-glycoprotein ontogeny during infancy and childhood are limited. This review discusses the current body of data relating to maturation of human brain P-glycoprotein including transporter expression levels in post-mortem human brain samples, in vivo transporter activity using probe substrates, surrogate marker endpoints, and extrapolations from animal models. Overall, the data tend to confirm that human brain P-glycoprotein activity keeps developing after birth, although with a developmental time frame that remains unclear. This knowledge gap is a concern given the critical role of brain P-glycoprotein in drug safety and efficacy, and the vulnerable nature of the pediatric population. Future research could include the measurement of brain P-glycoprotein activity across age groups using positron emission tomography or central pharmacodynamic responses. For now, caution is advised when extrapolating adult data to children aged younger than 2 years for drugs with P-glycoprotein-dependent central nervous system activity.

Dynamic Contrast-Enhanced MRI Reveals Unique Blood-Brain Barrier Permeability Characteristics in the Hippocampus in the Normal Brain

We report a prospective dynamic contrast-enhanced MR imaging analysis of region-specific blood-brain barrier permeability in 5 healthy subjects. By means of standardized postprocessing and ROI sampling methods, the hippocampi revealed significantly elevated area under the dynamic contrast-enhanced curve and significantly increased blood-brain barrier permeability metrics (volume transfer constant and volume in the extravascular extracellular space) from model-based quantitation. These findings suggest unique blood-brain barrier permeability characteristics in the hippocampus, which are concordant with previous animal studies, potentially laying the groundwork for future studies assessing patient populations in which hippocampal pathology plays a role.

Nrf2 overexpression protects against paraquat-induced A549 cell injury primarily by upregulating P-glycoprotein and reducing intracellular paraquat accumulation

Paraquat (PQ) intoxication causes thousands of mortalities every year, worldwide. Its pulmonary-targeted accumulation and the acute lung injury it subsequently causes, remain a challenge for detoxification treatment. A previous study has demonstrated that the upregulation of nuclear factor erythroid-2 related factor 2 (Nrf2) prevents PQ toxicity in cell line and murine models. As Nrf2 target genes include a group of membrane transporters, the current study assessed the protective mechanism exerted by Nrf2 against PQ toxicity and intracellular PQ accumulation via its effects on P-glycoprotein (P-gp), a downstream transporter of Nrf2. Adenovirus vectors containing the Nrf2 gene were transfected into A549 cells. Cell proliferation was assessed by Cell Counting Kit-8. The levels of LDH, MDA, SOD, TNF-α, IL-6 levels were detected using their respective ELISA kits. In addition, the levels of Nrf2 and P-gp protein expression were detected by western blot analysis. The concentration of PQ was measured by HPLC. The results revealed that overexpressed Nrf2 significantly increased P-gp protein levels, decreased the intracellular accumulation of PQ and attenuated PQ-induced toxicity. However, the protective effects of Nrf2 overexpression on PQ-challenged A549 cells were abrogated following cyclosporine A treatment, a competitive inhibitor of P-gp, which also increased intracellular PQ levels. These data indicated that Nrf2 gene overexpression prevented PQ toxicity in A549 cells, potentially via the upregulation of P-gp activity and the inhibition of intracellular PQ accumulation. Thus, Nrf2 and P-gp may serve as potential therapeutic targets for the treatment of PQ-induced injury.

Impact of aging, Alzheimer's disease and Parkinson's disease on the blood-brain barrier transport of therapeutics

Older people are at a greater risk of medicine-induced toxicity resulting from either increased drug sensitivity or age-related pharmacokinetic changes. The scenario is further complicated with the two most prevalent age-related neurodegenerative diseases, Alzheimer's disease (AD) and Parkinson's disease (PD). With aging, AD and PD, there is growing evidence of altered structure and function of the blood-brain barrier (BBB), including modifications to tight junctions and efflux transporters, such as P-glycoprotein. The subsequent impact on CNS drug exposure and risk of neurotoxicity from systemically-acting medicines is less well characterized. The purpose of this review, therefore, is to provide an overview of the multiple changes that occur to the BBB as a result of aging, AD and PD, and the impact that such changes have on CNS exposure of drugs, based on studies conducted in aged rodents or rodent models of disease, and in elderly people with and without AD or PD.

Spotlight on lorlatinib and its potential in the treatment of NSCLC: the evidence to date

The identification of anaplastic lymphoma kinase (ALK), an oncogenetic driver mutation, in lung cancer has paved the way for a new era in the treatment of non-small cell lung cancer (NSCLC). Targeting ALK using tyrosine kinase inhibitors (TKI) has dramatically improved the prognosis of patients with ALK-rearranged NSCLC. However, most patients relapse on ALK-TKI therapy within a few years because of acquired resistance. One mechanism of acquiring resistance is a second mutation on the ALK gene, and the representative mutation is L1996M in the gatekeeper residue. In particular, the solvent-front ALK G1202R mutation is the common cause of resistance against first- and second-generation ALK-TKIs. Another major concern regarding ALK-TKI is metastasis to the central nervous system, commonly observed in patients relapsing after ALK-TKI therapy. The next-generation ALK inhibitor lorlatinib (PF-06463922) has therefore been developed to inhibit resistant ALK mutations, including ALK G1202R, and to penetrate the blood–brain barrier. In a Phase I/II trial, the safety and efficacy of lorlatinib were demonstrated in patients with advanced ALK-positive NSCLC, most of whom had central nervous system metastases and had previous ALK-TKI treatment. In this review, we discuss the structure, pharmacodynamics, and pharmacokinetics of lorlatinib and compare its characteristics with those of other ALK inhibitors. Furthermore, clinical trials for lorlatinib are summarized, and future perspectives in the management of patients with ALK-rearranged NSCLC are discussed.

Emerging findings into molecular mechanism of brain metastasis

Brain metastasis is an important cause of morbidity and mortality in cancer patients. Hence, the need to develop improved therapies to prevent and treat metastasis to the brain is becoming urgent. Recent studies in this area are bringing about some advanced progress on brain metastasis. It was concluded that the occurrence and poor prognosis of brain metastasis have been mostly attributed to the exclusion of anticancer drugs from the brain by the blood-brain barrier. And several highly potent new generation targeted drugs with enhanced CNS distribution have been developed constantly. However, the noted "seed and soil" hypothesis also suggests that the outcome of metastasis depends on the relationship between unique tumor cells and the specific organ microenvironment. Moreover, increasing studies in multiple tumor types demonstrated that brain metastasis has great molecular differences between primary tumors and extracranial metastasis to a large extent. Here, the authors summarized the most common malignancies that could lead to brain metastasis-lung cancer, breast cancer and melanoma and their related mutated factors. Only by comprehending a deeper understanding of the molecular mechanisms, more effective brain-specific therapies will be developed for brain metastasis.

Imaging techniques to study drug transporter function in vivo

Transporter systems involved in the permeation of drugs and solutes across biological membranes are recognized as key determinants of pharmacokinetics. Typically, the action of membrane transporters on drug exposure to tissues in living organisms is inferred from invasive procedures, which cannot be applied in humans. In recent years, imaging methods have greatly progressed in terms of instruments, synthesis of novel imaging probes as well as tools for data analysis. Imaging allows pharmacokinetic parameters in different tissues and organs to be obtained in a non-invasive or minimally invasive way. The aim of this overview is to summarize the current status in the field of molecular imaging of drug transporters. The overview is focused on human studies, both for the characterization of transport systems for imaging agents as well as for the determination of drug pharmacokinetics, and makes reference to animal studies where necessary. We conclude that despite certain methodological limitations, imaging has a great potential to study transporters at work in humans and that imaging will become an important tool, not only in drug development but also in medicine. Imaging allows the mechanistic aspects of transport proteins to be studied, as well as elucidating the influence of genetic background, pathophysiological states and drug-drug interactions on the function of transporters involved in the disposition of drugs.

Age-dependent changes at the blood-brain barrier. A Comparative structural and functional study in young adult and middle aged rats

Decreased beta-amyloid clearance in Alzheimer's disease and increased blood-brain barrier permeability in aged subjects have been reported in several articles. However, morphological and functional characterization of blood-brain barrier and its membrane transporter activity have not been described in physiological aging yet. The aim of our study was to explore the structural changes in the brain microvessels and possible functional alterations of P-glycoprotein at the blood-brain barrier with aging. Our approach included MR imaging for anatomical orientation in middle aged rats, electronmicroscopy and immunohistochemistry to analyse the alterations at cellular level, dual or triple-probe microdialysis and SPECT to test P-glycoprotein functionality in young and middle aged rats. Our results indicate that the thickness of basal lamina increases, the number of tight junctions decreases and the size of astrocyte endfeet extends with advanced age. On the basis of microdialysis and SPECT results the P-gp function is reduced in old rats. With our multiparametric approach a complex regulation can be suggested which includes elements leading to increased permeability of blood-brain barrier by enhanced paracellular and transcellular transport, and factors working against it. To verify the role of P-gp pumps in brain aging further studies are warranted.

Preparation and characterization of universal Fe3O4@SiO2/CdTe nanocomposites for rapid and facile detection and separation of membrane proteins

The separation and enrichment of cell membrane proteins was achieved by the construction of bi-functional magnetic fluorescent nanoprobes.

Caloric restriction preserves memory and reduces anxiety of aging mice with early enhancement of neurovascular functions

Neurovascular integrity plays an important role in protecting cognitive and mental health in aging. Lifestyle interventions that sustain neurovascular integrity may thus be critical on preserving brain functions in aging and reducing the risk for age-related neurodegenerative disorders. Here we show that caloric restriction (CR) had an early effect on neurovascular enhancements, and played a critical role in preserving vascular, cognitive and mental health in aging. In particular, we found that CR significantly enhanced cerebral blood flow (CBF) and blood-brain barrier function in young mice at 5-6 months of age. The neurovascular enhancements were associated with reduced mammalian target of rapamycin expression, elevated endothelial nitric oxide synthase signaling, and increased ketone bodies utilization. With age, CR decelerated the rate of decline in CBF. The preserved CBF in hippocampus and frontal cortex were highly correlated with preserved memory and learning, and reduced anxiety, of the aging mice treated with CR (18-20 months of age). Our results suggest that dietary intervention started in the early stage (e.g., young adults) may benefit cognitive and mental reserve in aging. Understanding nutritional effects on neurovascular functions may have profound implications in human brain aging and age-related neurodegenerative disorders.