In Vivo Induction of P-Glycoprotein Function can be Measured with [18F]MC225 and PET

Unveiling the impact of aging on BBB and Alzheimer's disease: Factors and therapeutic implications

Alzheimer's disease (AD) is a highly prevalent neurodegenerative condition that has devastating effects on individuals, often resulting in dementia. AD is primarily defined by the presence of extracellular plaques containing insoluble β-amyloid peptide (Aβ) and neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau protein (P-tau). In addition, individuals afflicted by these age-related illnesses experience a diminished state of health, which places significant financial strain on their loved ones. Several risk factors play a significant role in the development of AD. These factors include genetics, diet, smoking, certain diseases (such as cerebrovascular diseases, obesity, hypertension, and dyslipidemia), age, and alcohol consumption. Age-related factors are key contributors to the development of vascular-based neurodegenerative diseases such as AD. In general, the process of aging can lead to changes in the immune system's responses and can also initiate inflammation in the brain. The chronic inflammation and the inflammatory mediators found in the brain play a crucial role in the dysfunction of the blood-brain barrier (BBB). Furthermore, maintaining BBB integrity is of utmost importance in preventing a wide range of neurological disorders. Therefore, in this review, we discussed the role of age and its related factors in the breakdown of the blood-brain barrier and the development of AD. We also discussed the importance of different compounds, such as those with anti-aging properties, and other compounds that can help maintain the integrity of the blood-brain barrier in the prevention of AD. This review builds a strong correlation between age-related factors, degradation of the BBB, and its impact on AD.

Cardiac PET Imaging of ATP Binding Cassette (ABC) Transporters: Opportunities and Challenges

Adenosine triphosphate binding cassette (ABC) transporters are a broad family of membrane protein complexes that use energy to transport molecules across cells and/or intracellular organelle lipid membranes. Many drugs used to treat cardiac diseases have an affinity for these transporters. Among others, P-glycoprotein (P-gp) plays an essential role in regulating drug concentrations that reach cardiac tissue and therefore contribute to cardiotoxicity. As a molecular imaging modality, positron emission tomography (PET) has emerged as a viable technique to investigate the function of P-gp in organs and tissues. Using PET imaging to evaluate cardiac P-gp function provides new insights for drug development and improves the precise use of medications. Nevertheless, information in this field is limited. In this review, we aim to examine the current applications of ABC transporter PET imaging and its tracers in the heart, with a specific emphasis on P-gp. Furthermore, the opportunities and challenges in this novel field will be discussed.

Quantification of P-glycoprotein function at the human blood-brain barrier using [18F]MC225 and PET

INTRODUCTION

P-glycoprotein (P-gp) is one of the most studied efflux transporters at the blood-brain barrier. It plays an important role in brain homeostasis by protecting the brain from a variety of endogenous and exogeneous substances. Changes in P-gp function are associated both with the onset of neuropsychiatric diseases, including Alzheimer's disease and Parkinson's disease, and with drug-resistance, for example in treatment-resistant depression. The most widely used approach to measure P-gp function in vivo is (R)-[11C]verapamil PET. (R)-[11C]verapamil is, however, an avid P-gp substrate, which complicates the use of this tracer to measure an increase in P-gp function as its baseline uptake is already very low. [18F]MC225 was developed to measure both increases and decreases in P-gp function.

AIM

The aim of this study was (1) to identify the pharmacokinetic model that best describes [18F]MC225 kinetics in the human brain and (2) to determine test-retest variability.

METHODS

Five (2 male, 3 female) of fourteen healthy subjects (8 male, 6 female, age 67 ± 5 years) were scanned twice (injected dose 201 ± 47 MBq) with a minimum interval of 2 weeks between scans. Each scanning session consisted of a 60-min dynamic [18F]MC225 scan with continuous arterial sampling. Whole brain grey matter data were fitted to a single tissue compartment model, and to reversible and irreversible two tissue-compartment models to obtain various outcome parameters (in particular the volume of distribution (VT), Ki, and the rate constants K1 and k2). In addition, a reversible two-tissue compartment model with fixed k3/k4 was included. The preferred model was selected based on the weighted Akaike Information Criterion (AIC) score. Test-retest variability (TRTV) was determined to assess reproducibility.

RESULTS

Sixty minutes post-injection, the parent fraction was 63.8 ± 4.0%. The reversible two tissue compartment model corrected for plasma metabolites with an estimated blood volume (VB) showed the highest AIC weight score of 34.3 ± 17.6%. The TRVT of the VT for [18F]MC225 PET scans was 28.3 ± 20.4% for the whole brain grey matter region using this preferred model.

CONCLUSION

[18F]MC225 VT, derived using a reversible two-tissue compartment model, is the preferred parameter to describe P-gp function in the human BBB. This outcome parameter has an average test-retest variability of 28%.

TRIAL REGISTRATION

EudraCT 2020-001564-28 . Registered 25 May 2020.

Imaging blood–brain barrier disruption in neuroinflammation and Alzheimer’s disease

The blood–brain barrier (BBB) is the neurovascular structure that regulates the passage of cells and molecules to and from the central nervous system (CNS). Alzheimer’s disease (AD) is a neurodegenerative disorder that is associated with gradual breakdown of the BBB, permitting entry of plasma-derived neurotoxins, inflammatory cells, and microbial pathogens into the CNS. BBB permeability can be visualized directly in AD patients using imaging technologies including dynamic contrast-enhanced and arterial spin labeling magnetic resonance imaging, and recent studies employing these techniques have shown that subtle changes in BBB stability occur prior to deposition of the pathological hallmarks of AD, senile plaques, and neurofibrillary tangles. These studies suggest that BBB disruption may be useful as an early diagnostic marker; however, AD is also accompanied by neuroinflammation, which can complicate these analyses. This review will outline the structural and functional changes to the BBB that occur during AD pathogenesis and highlight current imaging technologies that can detect these subtle changes. Advancing these technologies will improve both the diagnosis and treatment of AD and other neurodegenerative diseases.

Implementation of blood-brain barrier on microfluidic chip: recent advance and future prospects

The complex structure of the blood-brain barrier (BBB) hinders its modeling and the treatment of brain diseases. The microfluidic technology promotes the development of BBB-on-a-chip platforms, which can be used to reproduce the complex brain microenvironment and physiological reactions. Compared with traditional transwell technology, microfluidic BBB-on-a-chip shows great technical advantages in terms of flexible control of fluid shear stress in the chip and fabrication efficiency of the chip system, which can be enhanced by the development of lithography and three-dimensional (3D) printing. It is convenient to accurately monitor the dynamic changes of biochemical parameters of individual cells in the model by integrating an automatic super-resolution imaging sensing platform. In addition, biomaterials, especially hydrogels and conductive polymers, solve the limitations of microfluidic BBB-on-a-chip by compounding onto microfluidic chip to provide a 3D space and special performance on the microfluidic chip. The microfluidic BBB-on-a-chip promotes the development of basic research, including cell migration, mechanism exploration of neurodegenerative diseases, drug barrier permeability, SARS-CoV-2 pathology. This study summarizes the recent advances, challenges and future prospects of microfluidic BBB-on-a-chip, which can help to promote the development of personalized medicine and drug discovery.

Dysfunction of ABC Transporters at the Surface of BBB: Potential Implications in Intractable Epilepsy and Applications of Nanotechnology Enabled Drug Delivery

Epilepsy is a chronic neurological disorder affecting 70 million people globally. One of the fascinating attributes of brain microvasculature is the (BBB), which controls a chain of distinct features that securely regulate the molecules, ions, and cells movement between the blood and the parenchyma. The barrier's integrity is of paramount importance and essential for maintaining brain homeostasis, as it offers both physical and chemical barriers to counter pathogens and xenobiotics. Dysfunction of various transporters in the (BBB), mainly ATP binding cassette (ABC), is considered to play a vital role in hampering the availability of antiepileptic drugs into the brain. ABC (ATP-binding cassette) transporters constitute a most diverse protein superfamily, which plays an essential part in various biological processes, including cell homeostasis, cell signaling, uptake of nutrients, and drug metabolism. Moreover, it plays a crucial role in neuroprotection by out-flowing various internal and external toxic substances from the interior of a cell, thus decreasing their buildup inside the cell. In humans, forty-eight ABC transporters have been acknowledged and categorized into subfamilies A to G based on their phylogenetic analysis. ABC subfamilies B, C, and G, impart a vital role at the BBB in guarding the brain against the entrance of various xenobiotic and their buildup. The illnesses of the central nervous system have received a lot of attention lately Owing to the existence of the BBB, the penetration effectiveness of most CNS medicines into the brain parenchyma is very limited (BBB). In the development of neurological therapies, BBB crossing for medication delivery to the CNS continues to be a major barrier. Nanomaterials with BBB cross ability have indeed been extensively developed for the treatment of CNS diseases due to their advantageous properties. This review will focus on multiple possible factors like inflammation, oxidative stress, uncontrolled recurrent seizures, and genetic polymorphisms that result in the deregulation of ABC transporters in epilepsy and nanotechnology-enabled delivery across BBB in epilepsy.

Dose-response assessment of cerebral P-glycoprotein inhibition in vivo with [18F]MC225 and PET

The Blood-Brain Barrier P-glycoprotein (P-gp) function can be altered in several neurodegenerative diseases and due to the administration of different drugs which may cause alterations in drug concentrations and consequently lead to a reduced effectiveness or increased side-effects. The novel PET radiotracer [¹⁸F]MC225 is a weak P-gp substrate that may show higher sensitivity to detect small changes in P-gp function than previously developed radiotracers. This study explores the sensitivity of [¹⁸F]MC225 to measure the dose-dependent effect of P-gp inhibitor tariquidar. Twenty-three rats were intravenously injected with different doses of tariquidar ranging from 0.75 to 12 mg/kg, 30-min before the dynamic [¹⁸F]MC225-PET acquisition with arterial sampling. Tissue and blood data were fitted to a 1-Tissue-Compartment-Model to obtain influx constant K₁ and distribution volume V_T, which allow the estimation of P-gp function. ANOVA and post-hoc analyses of K₁ values showed significant differences between controls and groups with tariquidar doses >3 mg/kg; while applying V_T the analyses showed significant differences between controls and groups with tariquidar doses >6 mg/kg. Dose-response curves were fitted using different models. The four-parameter logistic sigmoidal curve provided the best fit for K₁ and V_T data. Half-maximal inhibitory doses (ID₅₀) were 2.23 mg/kg (95%CI: 1.669-2.783) and 2.93 mg/kg (95%CI: 1.135-3.651), calculated with K₁ or V_T values respectively. According to the dose-response fit, differences in [¹⁸F]MC225-K₁ values could be detected at tariquidar doses ranging from 1.37 to 3.25 mg/kg. Our findings showed that small changes in the P-gp function, caused by low doses of tariquidar, could be detected by [¹⁸F]MC225-K₁ values, which confirms the high sensitivity of the radiotracer. The results suggest that [¹⁸F]MC225 may allow the quantification of moderate P-gp impairments, which may allow the detection of P-gp dysfunctions at the early stages of a disease and potential transporter-mediated drug-drug interactions.

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.