The blood-brain barrier (BBB) tightly controls entry of molecules and cells into the brain, restricting the delivery of therapeutics. Blood-brain barrier opening (BBBO) utilizes reversible disruption ...of cell-cell junctions between brain microvascular endothelial cells to enable transient entry into the brain. Here, we demonstrate that melittin, a membrane active peptide present in bee venom, supports transient BBBO. From endothelial and neuronal viability studies, we first identify the accessible concentration range for BBBO. We then use a tissue-engineered model of the human BBB to optimize dosing and elucidate the mechanism of opening. Melittin and other membrane active variants transiently increase paracellular permeability via disruption of cell-cell junctions that result in transient focal leaks. To validate the results from the tissue-engineered model, we then demonstrate that transient BBBO can be reproduced in a mouse model. We identify a minimum clinically effective intra-arterial dose of 3 μM min melittin, which is reversible within one day and neurologically safe. Melittin-induced BBBO represents a novel technology for delivery of therapeutics into the brain.
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•Membrane active peptide, melittin, supports blood-brain barrier opening (BBB) opening.•A reversible dosing regime is determined using a tissue-engineered BBB model.•BBB opening occurs due to transient increases in paracellular permeability.•Intra-arterial injections in mice induce reversible and neurologically safe BBB opening.
Purpose
To develop a quantitative MRI method to estimate cerebrovascular reactivity (CVR) in mice.
Methods
We described an MRI procedure to measure cerebral vasodilatory response to acetazolamide ...(ACZ), a vasoactive agent previously used in human clinical imaging. Vascular response was determined by cerebral blood flow (CBF) measured with phase‐contrast or pseudo‐continuous arterial spin labeling MRI. Vasodilatory input intensity was determined by plasma ACZ level using high‐performance liquid chromatography. We verified the source of the CVR MRI signal by comparing ACZ injection to phosphate‐buffered saline injection and noninjection experiments. Dose dependence and feasibility of regional CVR measurement were also investigated.
Results
Cerebral blood flow revealed an exponential increase following intravenous ACZ injection, with a time constant of 1.62 min. In contrast, phosphate‐buffered saline or noninjection exhibited a slow linear CBF increase, consistent with a gradual accumulation of anesthetic agent, isoflurane, used in this study. When comparing different ACZ doses, injections of 30, 60, 120, and 180 mg/kg yielded a linear increase in plasma ACZ concentration (p < 0.0001). On the other hand, CBF changes under these doses were not different from each other (p = 0.50). The pseudo‐continuous arterial spin labeling MRI with multiple postlabeling delays revealed similar vascular responses at different postlabeling delay values. There was a regional difference in CVR (p = 0.005), with isocortex (0.81 ± 0.17%/μg/ml) showing higher CVR than deep‐brain regions. Mice receiving multiple ACZ injections lived for a minimum of 6 months after the study without noticeable aberrant behavior or appearance.
Conclusions
We demonstrated the proof‐of‐principle of a new quantitative CVR mapping technique in mice.
Since the inception of CEST MRI in the 1990s, a number of compounds have been identified as suitable for generating contrast, including paramagnetic lanthanide complexes, hyperpolarized atom cages ...and, most interesting, diamagnetic compounds. In the past two decades, there has been a major emphasis in this field on the identification and application of diamagnetic compounds that have suitable biosafety profiles for usage in medical applications. Even in the past five years there has been a tremendous growth in their numbers, with more and more emphasis being placed on finding those that can be ultimately used for patient studies on clinical 3 T scanners. At this point, a number of endogenous compounds present in tissue have been identified, and also natural and synthetic organic compounds that can be administered to highlight pathology via CEST imaging. Here we will provide a very extensive snapshot of the types of diamagnetic compound that can generate CEST MRI contrast, together with guidance on their utility on typical preclinical and clinical scanners and a review of the applications that might benefit the most from this new technology.
In the past two decades, there has been a major emphasis in CEST MRI on the identification and application of diamagnetic compounds which have suitable biosafety profiles for their usage in medical applications. In this review, we provide a very extensive snapshot of the types of diamagnetic compounds that can generate CEST MRI contrast, together with guidance on their utility on typical preclinical and clinical scanners and review of the applications which might benefit the most from this new technology. Shown in the figure are select compounds whose MTRasym spectra display labile protons resonating from ‐10 ppm to +10 ppm from water.
Deoxycytidine kinase (DCK) is a key enzyme for the activation of a broad spectrum of nucleoside-based chemotherapy drugs (e.g., gemcitabine); low DCK activity is one of the most important causes of ...cancer drug-resistance. Noninvasive imaging methods that can quantify DCK activity are invaluable for assessing tumor resistance and predicting treatment efficacy. Here we developed a "natural" MRI approach to detect DCK activity using its natural substrate deoxycytidine (dC) as the imaging probe, which can be detected directly by chemical exchange saturation transfer (CEST) MRI without any synthetic labeling. CEST MRI contrast of dC and its phosphorylated form, dCTP, successfully discriminated DCK activity in two mouse leukemia cell lines with different DCK expression. This dC-enhanced CEST MRI in xenograft leukemic cancer mouse models demonstrated that DCK(+) tumors have a distinctive dynamic CEST contrast enhancement and a significantly higher CEST contrast than DCK(-) tumors (AUC
= 0.47 ± 0.25 and 0.20 ± 0.13, respectively;
= 0.026, paired Student
test,
= 4) at 1 hour after the injection of dC. dC-enhanced CEST contrast also correlated well with tumor responses to gemcitabine treatment. This study demonstrates a novel MR molecular imaging approach for predicting cancer resistance using natural, nonradioactive, nonmetallic, and clinically available agents. This method has great potential for pursuing personalized chemotherapy by stratifying patients with different DCK activity. SIGNIFICANCE: A new molecular MRI method that detects deoxycytidine kinase activity using its natural substrate deoxycytidine has great translational potential for clinical assessment of tumor resistance and prediction of treatment efficacy.
Mixing of oppositely charged amphiphilic molecules (catanionic mixing) offers an attractive strategy to produce morphologies different from those formed by individual molecules. We report here on the ...use of catanionic mixing of anticancer drug amphiphiles to construct multiwalled nanotubes containing a fixed and high drug loading. We found that the molecular mixing ratio, the solvent composition, the overall drug concentrations, as well as the molecular design of the studied amphiphiles are all important experimental parameters contributing to the tubular morphology. We believe these results demonstrate the remarkable potential that anticancer drugs could offer to self-assemble into discrete nanostructures and also provide important insight into the formation mechanism of nanotubes by catanionic mixtures. Our preliminary animal studies reveal that the CPT nanotubes show significantly prolonged retention time in the tumor site after intratumoral injection.
Chemical exchange saturation transfer (CEST) MRI has recently emerged as a versatile molecular imaging approach in which diamagnetic compounds can be utilized to generate an MRI signal. To expand the ...scope of CEST MRI applications, herein, we systematically investigated the CEST properties of N‐aryl amides with different N‐aromatic substitution, revealing their chemical shifts (4.6–5.8 ppm) and exchange rates (up to thousands s−1) are favorable to be used as CEST agents as compared to alkyl amides. As the first proof‐of‐concept study, we used CEST MRI to detect the enzymatic metabolism of the drug acebutolol directly by its intrinsic CEST signal without any chemical labeling. Our study implies that N‐aryl amides may enable the label‐free CEST MRI detection of the metabolism of many N‐aryl amide‐containing drugs and a variety of enzymes that act on N‐aryl amides, greatly expanding the scope of CEST MR molecular imaging.
Enzyme detection: The chemical exchange saturation transfer (CEST) MRI properties of N‐aryl amides were systematically investigated. With relatively large chemical shifts and fast exchange rate, this type of diamagnetic, biocompatible compounds can be directly used as CEST agents for label‐free MRI detection of enzymatic activity and drug metabolism (see figure).
The goal of this study was to develop a molecular biomarker for the detection of protein aggregation involved in Alzheimer's disease (AD) by exploiting the features of the water saturation transfer ...spectrum (Z-spectrum), the CEST signal of which is sensitive to the molecular configuration of proteins. A radial-sampling steady-state sequence based ultrashort echo time (UTE) readout was implemented to image the Z-spectrum in the mouse brain, especially the contributions from mobile proteins at the frequency offsets for the composite protein amide proton (+3.6 ppm) and aliphatic proton (−3.6 ppm) signals. Using a relatively weak radiofrequency (RF) saturation amplitude, contributions due to strong magnetization transfer contrast (MTC) from solid-like macromolecules and direct water saturation (DS) were minimized. For practical measure of the changes in the mobile protein configuration, we defined a saturation transfer difference (ΔST) by subtracting the Z-spectral signals at ±3.6 ppm from a control signal at 8 ppm. Phantom studies of glutamate solution, protein (egg white) and hair conditioner show the capability of the proposed scheme to minimize the contributions from amine protons, DS, and MTC, respectively. The ST signal at ±3.6 ppm of the cross-linked bovine serum albumin (BSA) solutions demonstrated that the ΔST signal can be used to monitor the aggregation process of the mobile proteins. High-resolution ΔST images of AD mouse brains at ±3.6 ppm of mouse brains showed significantly reduced ΔST (-3.6) signal compared to the age-matched wild-type (WT) mice. Thus, this signal has potential to serve as a molecular biomarker for monitoring protein aggregation in AD.
•A low-B1 radial-sampling steady-state MRI acquisition scheme was developed to acquire high-resolution saturation transfer difference (ΔST) maps.•Low B1 was used to focus on the chemical exchange saturation transfer from mobile proteins and minimize the direct water saturation and the magnetization transfer effects in tissue.•ΔST maps at offset frequencies of ±3.6 ppm from water reflected changes in protein aggregation, providing a novel imaging biomarker.•Detection of protein aggregation associated with Alzheimer's disease using a mouse model by a UTE-CEST sequence.
Objectives
To explore individual weight of cardiac magnetic resonance (CMR) metrics to predict mid-term outcomes in patients with dilated cardiomyopathy (DCM), and develop a risk algorithm for ...mid-term outcome based on CMR biomarkers.
Materials and methods
Patients with DCM who underwent CMR imaging were prospectively enrolled in this study. The primary endpoint was a composite of heart failure (HF) death, sudden cardiac death (SCD), aborted SCD, and heart transplantation.
Results
A total of 407 patients (age 48.1 ± 13.8 years, 331 men) were included in the final analysis. During a median follow-up of 21.7 months, 63 patients reached the primary endpoint. NYHA class III/IV (HR = 2.347 1.073–5.133,
p
= 0.033), left ventricular ejection fraction (HR = 0.940 0.909–0.973,
p
< 0.001), late gadolinium enhancement (LGE) > 0.9% and ≤ 6.6% (HR = 3.559 1.020–12.412,
p
= 0.046), LGE > 6.6% (HR = 6.028 1.814–20.038,
p
= 0.003), and mean extracellular volume (ECV) fraction ≥ 32.8% (HR = 5.922 2.566–13.665,
p
< 0.001) had a significant prognostic association with the primary endpoints (
C
-statistic: 0.853 0.810–0.896). Competing risk regression analyses showed that patients with mean ECV fraction ≥ 32.8%, LGE ≥ 5.9%, global circumferential strain ≥ − 5.6%, or global longitudinal strain ≥ − 7.3% had significantly shorter event-free survival due to HF death and heart transplantation. Patients with mean ECV fraction ≥ 32.8% and LGE ≥ 5.9% had significantly shorter event-free survival due to SCD or aborted SCD.
Conclusion
ECV fraction may be the best independently risk factor for the mid-term outcomes in patients with DCM, surpassing LVEF and LGE. LGE has a better prognostic value than other CMR metrics for SCD and aborted SCD. The risk stratification model we developed may be a promising non-invasive tool for decision-making and prognosis.
Clinical relevance statement
“One-stop” assessment of cardiac function and myocardial characterization using cardiac magnetic resonance might improve risk stratification of patients with DCM. In this prospective study, we propose a novel risk algorithm in DCM including NYHA functional class, LVEF, LGE, and ECV.
Key Points
•
The present study explores individual weight of CMR metrics for predicting mid-term outcomes in dilated cardiomyopathy.
•
We have developed a novel risk algorithm for dilated cardiomyopathy that includes cardiac functional class, ejection fraction, late gadolinium enhancement, and extracellular volume fraction.
•
Personalized risk model derived by CMR contributes to clinical assessment and individual decision-making.
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