Enhancing extracellular vesicle cargo loading and functional delivery by engineering protein-lipid interactions.

Naturally generated lipid nanoparticles termed extracellular vesicles (EVs) hold significant promise as engineerable therapeutic delivery vehicles. However, active loading of protein cargo into EVs in a manner that is useful for delivery remains a challenge. Here, we demonstrate that by rationally designing proteins to traffic to the plasma membrane and associate with lipid rafts, we can enhance loading of protein cargo into EVs for a set of structurally diverse transmembrane and peripheral membrane proteins. We then demonstrate the capacity of select lipid tags to mediate increased EV loading and functional delivery of an engineered transcription factor to modulate gene expression in target cells. We envision that this technology could be leveraged to develop new EV-based therapeutics that deliver a wide array of macromolecular cargo.

HaloTag display enables quantitative single-particle characterisation and functionalisation of engineered extracellular vesicles.

Extracellular vesicles (EVs) play key roles in diverse biological processes, transport biomolecules between cells and have been engineered for therapeutic applications. A useful EV bioengineering strategy is to express engineered proteins on the EV surface to confer targeting, bioactivity and other properties. Measuring how incorporation varies across a population of EVs is important for characterising such materials and understanding their function, yet it remains challenging to quantitatively characterise the absolute number of engineered proteins incorporated at single-EV resolution. To address these needs, we developed a HaloTag-based characterisation platform in which dyes or other synthetic species can be covalently and stoichiometrically attached to engineered proteins on the EV surface. To evaluate this system, we employed several orthogonal quantification methods, including flow cytometry and fluorescence microscopy, and found that HaloTag-mediated quantification is generally robust across EV analysis methods. We compared HaloTag-labelling to antibody-labelling of EVs using single vesicle flow cytometry, enabling us to measure the substantial degree to which antibody labelling can underestimate proteins present on an EV. Finally, we demonstrate the use of HaloTag to compare between protein designs for EV bioengineering. Overall, the HaloTag system is a useful EV characterisation tool which complements and expands existing methods.

Effects of intermittent senolytic therapy on bone metabolism in postmenopausal women: a phase 2 randomized controlled trial.

Preclinical evidence demonstrates that senescent cells accumulate with aging and that senolytics delay multiple age-related morbidities, including bone loss. Thus, we conducted a phase 2 randomized controlled trial of intermittent administration of the senolytic combination dasatinib plus quercetin (D + Q) in postmenopausal women (n = 60 participants). The primary endpoint, percentage changes at 20 weeks in the bone resorption marker C-terminal telopeptide of type 1 collagen (CTx), did not differ between groups (median (interquartile range), D + Q -4.1% (-13.2, 2.6), control -7.7% (-20.1, 14.3); P = 0.611). The secondary endpoint, percentage changes in the bone formation marker procollagen type 1 N-terminal propeptide (P1NP), increased significantly (relative to control) in the D + Q group at both 2 weeks (+16%, P = 0.020) and 4 weeks (+16%, P = 0.024), but was not different from control at 20 weeks (-9%, P = 0.149). No serious adverse events were observed. In exploratory analyses, the skeletal response to D + Q was driven principally by women with a high senescent cell burden (highest tertile for T cell p16 (also known as CDKN2A) mRNA levels) in which D + Q concomitantly increased P1NP (+34%, P = 0.035) and reduced CTx (-11%, P = 0.049) at 2 weeks, and increased radius bone mineral density (+2.7%, P = 0.004) at 20 weeks. Thus, intermittent D + Q treatment did not reduce bone resorption in the overall group of postmenopausal women. However, our exploratory analyses indicate that further studies are needed testing the hypothesis that the underlying senescent cell burden may dictate the clinical response to senolytics. ClinicalTrials.gov identifier: NCT04313634 .

Transition Metal Complexes with Appended Benzimidazole Groups for Sensing Dihydrogenphosphate.

Four new complexes [Ru(bpy)2(bbib)](PF6)2, [Ru(phen)2(bbib)](PF6)2, [Re(CO)3(bbib)(py)](PF6) and [Ir(ppy)2(bbib)](PF6) [where bbib = 4,4'-bis(benzimidazol-2-yl)-2,2'-bipyridine] have been prepared and their photophysical properties determined. Their behaviour has been studied with a variety of anions in acetonitrile, DMSO and 10% aquated DMSO. Acetate and dihydrogenphosphate demonstrate a redshift in the bbib ligand associated absorptions suggesting that the ligand is strongly interacting with these anions. The 3MLCT emissive state is sensitive to the introduction of small quantities of anion (sub-stoichiometric quantities) and significant quenching is typically observed with acetate, although this is less pronounced in the presence of water. The emissive behaviour with dihydrogenphosphate is variable, showing systematic changes as anion concentration increases with several distinct interactions evident . 1H NMR and 31P NMR titrations in a 10% D2O - D6-DMSO mixture suggest that with dihydrogenphosphate, the imidazole group able to act as both a proton acceptor and donor. It appears that all four complexes can form a {[complex]2-H2PO4} "dimer", a one-to-one species (which the X-ray crystallography study suggests is dimeric in the solid-state), and a complex with a combined bis(dihydrogenphosphate) complex anion. The speciation relies on complex equilibria dependent on several factors including the complex charge, the hydrophobicity of the associated ligands, and the solvent.

Effects of self- and experimenter-administered cocaine on subsequent ethanol drinking in rhesus monkeys.

BACKGROUND: One possible reason for the lack of FDA-approved pharmacotherapies to treat cocaine use disorder (CUD) is that, although cocaine is typically used in combination with alcohol, it is studied in isolation in preclinical studies. A better understanding of the cocaine-alcohol interactions that promote polysubstance use (PSU) will improve animal models of CUD and hasten pharmacotherapy development. We used a rhesus monkey model of cocaine-alcohol PSU to investigate one possible mechanism: that alcohol is used to mitigate negative effects associated with termination of cocaine use. METHODS: In 6 adult male rhesus monkeys, the relationship between self-administered cocaine intake and oral ethanol intake 2hours later was examined during self-administration of cocaine (0.0003-0.3mg/kg per injection, i.v.) under a fixed-ratio 30 schedule (FR30) or a progressive-ratio (PR) schedule. Next, ethanol consumption was measured 0-120minutes after experimenter-administered cocaine (0.3-1.7mg/kg, i.v.). RESULTS: Self-administered cocaine intake under both FR30 and PR schedules was unrelated to oral ethanol intakes 2hours later. When cocaine was administered non-contingently, cocaine decreased ethanol intake as well as intake of a non-alcoholic solution in monkeys who never consumed ethanol (n=4) in a time- and dose-dependent manner. CONCLUSIONS: Taken together, the results do not provide evidence for cocaine-induced increases in ethanol consumption. By extension, the results do not support the hypothesis that cocaine users drink alcohol to counteract negative effects that occur after terminating use. This finding implies either that such effects do not exist or that such effects exist but are unaffected by ethanol.

Marrow Adipocyte Senescence in the Pathogenesis of Bone Loss.

PURPOSE OF REVIEW: Beyond aging, senescent cells accumulate during multiple pathological conditions, including chemotherapy, radiation, glucocorticoids, obesity, and diabetes, even earlier in life. Therefore, cellular senescence represents a unifying pathogenic mechanism driving skeletal and metabolic disorders. However, whether senescent bone marrow adipocytes (BMAds) are causal in mediating skeletal dysfunction has only recently been evaluated. RECENT FINDINGS: Despite evidence of BMAd senescence following glucocorticoid therapy, additional evidence for BMAd senescence in other conditions has thus far been limited. Because the study of BMAds presents unique challenges making these cells difficult to isolate and image, here we review issues and approaches to overcome such challenges, and present advancements in isolation and histological techniques that may help with the future study of senescent BMAds. Further insights into the roles of BMAd senescence in the pathogenesis of skeletal dysfunction may have important basic science and clinical implications for human physiology and disease.

Comparing artificial intelligence guided image assessment to current methods of burn assessment.

Appropriate identification of burn depth and size is paramount. Despite the development of burn depth assessment aids [e.g., laser doppler imaging (LDI)], clinical assessment, which assesses partial thickness burn depth with 67% accuracy, currently remains the most consistent standard of practice. We sought to develop an image-based artificial intelligence system that predicts burn severity and wound margins for use as a triaging tool in thermal injury management. Modified EfficientNet architecture trained by 1684 mobile-device-captured images of different burn depths were previously utilized to create a convoluted neural network (CNN). The CNN was modified to a novel Boundary-Attention Mapping (BAM) algorithm using elements of saliency mapping, which was utilized to recognize the boundaries of burns. For validation, 144 patient charts that included clinical assessment, burn location, total body surface area, and LDI assessment were retrieved for a retrospective study. The clinical images underwent CNN-BAM assessment and were directly compared with the LDI assessment. CNN using a four-level burn severity classification achieved an accuracy of 85% (micro/macro-averaged ROC scores). The CNN-BAM system can successfully highlight burns from surrounding tissue with high confidence. CNN-BAM burn area segmentations attained a 91.6% accuracy, 78.2% sensitivity, and 93.4% specificity, when compared to LDI methodology. Results comparing the CNN-BAM outputs to clinical and LDI assessments have shown a high degree of correlation between the CNN-BAM burn severity predictions to those extrapolated from LDI healing potential (66% agreement). CNN-BAM algorithm gives equivalent burn-depth detection accuracy as LDI with a more economical and accessible application when embedded in a mobile device.

Mycobacterium dormancy and antibiotic tolerance within the retinal pigment epithelium of ocular tuberculosis.

Tuberculosis (TB) is a leading cause of death among infectious diseases worldwide due to latent TB infection, which is the critical step for the successful pathogenic cycle. In this stage, Mycobacterium tuberculosis resides inside the host in a dormant and antibiotic-tolerant state. Latent TB infection can also lead to multisystemic diseases because M. tuberculosis invades virtually all organs, including ocular tissues. Ocular tuberculosis (OTB) occurs when the dormant bacilli within the ocular tissues reactivate, originally seeded by hematogenous spread from pulmonary TB. Histological evidence suggests that retinal pigment epithelium (RPE) cells play a central role in immune privilege and in protection from antibiotic effects, making them an anatomical niche for invading M. tuberculosis. RPE cells exhibit high tolerance to environmental redox stresses, allowing phagocytosed M. tuberculosis bacilli to maintain viability in a dormant state. However, the microbiological and metabolic mechanisms determining the interaction between the RPE intracellular environment and phagocytosed M. tuberculosis are largely unknown. Here, liquid chromatography-mass spectrometry metabolomics were used to illuminate the metabolic state within RPE cells reprogrammed to harbor dormant M. tuberculosis bacilli and enhance antibiotic tolerance. Timely and accurate diagnosis as well as efficient chemotherapies are crucial in preventing the poor visual outcomes of OTB patients. Unfortunately, the efficacy of current methods is highly limited. Thus, the results will lead to propose a novel therapeutic option to synthetically kill the dormant M. tuberculosis inside the RPE cells by modulating the phenotypic state of M. tuberculosis and laying the foundation for a new, innovative regimen for treating OTB. IMPORTANCE: Understanding the metabolic environment within the retinal pigment epithelium (RPE) cells altered by infection with Mycobacterium tuberculosis and mycobacterial dormancy is crucial to identify new therapeutic methods to cure ocular tuberculosis. The present study showed that RPE cellular metabolism is altered to foster intracellular M. tuberculosis to enter into the dormant and drug-tolerant state, thereby blunting the efficacy of anti-tuberculosis chemotherapy. RPE cells serve as an anatomical niche as the cells protect invading bacilli from antibiotic treatment. LC-MS metabolomics of RPE cells after co-treatment with H2O2 and M. tuberculosis infection showed that the intracellular environment within RPE cells is enriched with a greater level of oxidative stress. The antibiotic tolerance of intracellular M. tuberculosis within RPE cells can be restored by a metabolic manipulation strategy such as co-treatment of antibiotic with the most downstream glycolysis metabolite, phosphoenolpyruvate.

The impact of YabG mutations on C. difficile spore germination and processing of spore substrates.

YabG is a sporulation-specific protease that is conserved among sporulating bacteria. C. difficile YabG processes cortex destined proteins preproSleC into proSleC and CspBA to CspB and CspA. YabG also affects synthesis of spore coat/exosporium proteins CotA and CdeM. In prior work that identified CspA as the co-germinant receptor, mutations in yabG were found which altered the co-germinants required to initiate spore germination. To understand how these mutations in the yabG locus contribute to C. difficile spore germination, we introduced these mutations into an isogenic background. Spores derived from C. difficile yabG C207A (catalytically inactive), C. difficile yabG A46D, C. difficile yabG G37E, and C. difficile yabG P153L strains germinated in response to TA alone. Recombinantly expressed and purified preproSleC incubated with E. coli lysate expressing wild type YabG resulted in the removal of the pre sequence from preproSleC. Interestingly, only YabGA46D showed any activity towards purified preproSleC. Mutation of the YabG processing site in preproSleC (R119A) led to YabG shifting its processing to R115 or R112. Finally, changes in yabG expression under the mutant promoters were analyzed using a SNAP-tag and revealed expression differences at early and late stages of sporulation. Overall, our results support and expand upon the hypothesis that YabG is important for germination and spore assembly and, upon mutation of the processing site, can shift where it cleaves substrates.

Hdac3-deficiency increases senescence-associated distention of satellite DNA and telomere-associated foci in osteoprogenitor cells.

Histone deacetylase 3 (Hdac3) is an epigenetic regulator of gene expression and interacts with skeletal transcription factors such as Runx2. We previously reported that conditional deletion of Hdac3 in Osterix-Cre recombinase-expressing osteoprogenitor cells (Hdac3 CKOOsx) caused osteopenia and increased marrow adiposity, both hallmarks of skeletal aging. We also showed that Runx2+ cells within osteogenic cultures of Hdac3-depleted bone marrow stromal cells (BMSCs) contain lipid droplets (LDs). Cellular senescence, a non-proliferative metabolically active state, is associated with increased marrow adiposity, bone loss and aging. In this study, we sought to determine if Hdac3 depleted Runx2+ pre-osteoblasts from young mice exhibit chromatin changes associated with early cellular senescence and how these events correlate with the appearance of LDs. We first confirmed that BMSCs from Hdac3 CKOOsx mice have more Runx2 + LD+ cells compared to controls under osteogenic conditions. We then measured senescence-associated distention of satellite DNA (SADS) and telomere-associated foci (TAFs) in Hdac3 CKOOsx and control BMSCs. In situ, Runx2+ cells contained more SADs per nuclei in Hdac3 CKOOsx femora than in controls. Runx2+ BMSCs from Hdac3 CKOOsx mice also contained more SADS and TAFs per nuclei than Runx2+ cells from age-matched control mice in vitro. SADs and TAFs were present at similar levels in Runx2 + LD+ cells and Runx2 + LD- cells from Hdac3 CKOOsx mice. Hdac inhibitors also increased the number of SADS in Runx2 + LD+ and Runx2 + LD- wildtype BMSCs. Senolytics reduced viable cell numbers in Hdac3 CKOOsx BMSC cultures. These data demonstrate that depletion of Hdac3 in osteochondral progenitor cells triggers LD formation and early events in cellular senescence in Runx2+ BMSCs through mutually exclusive mechanisms.

Histone deacetylase 3 (Hdac3) is an enzyme within cells that binds factors in cell nuclei like Runx2 to regulate the expression of genes and control cellular functions. Deleting Hdac3 in cells responsible for bone formation causes bone loss and increases fat in the bone marrow, both hallmarks of skeletal aging. We observed that Hdac3-deletion causes Runx2+ bone marrow stromal cells (BMSCs) to store fats in lipid droplets (LD) even though the cultures were stimulated to become bone cells. Here, we investigated whether these Runx2 + LD+ cells exhibit signs of cellular senescence, which is a zombie-like state associated with increased marrow fat, bone loss and aging. We found that Hdac3-depleted Runx2+ cells showed chromatin changes linked to early cellular senescence alongside the formation of LDs. These findings suggest that Hdac3 plays a crucial role in preventing skeletal aging via regulating both LD formation and cellular senescence in osteochondral progenitor cells.

Pediatric Leukemia Roadmaps Are a Guide for Positive Metastatic Bone Sarcoma Trials.

ALL cures require many MRD therapies. This strategy should drive experiments and trials in metastatic bone sarcomas.

2024 AHA/ASA Performance and Quality Measures for Spontaneous Intracerebral Hemorrhage: A Report From the American Heart Association/American Stroke Association.

The American Heart Association/American Stroke Association released a revised spontaneous intracerebral hemorrhage guideline in 2022. A working group of stroke experts reviewed this guideline and identified a subset of recommendations that were deemed suitable for creating performance measures. These 15 performance measures encompass a wide spectrum of intracerebral hemorrhage patient care, from prehospital to posthospital settings, highlighting the importance of timely interventions. The measures also include 5 quality measures and address potential challenges in data collection, with the aim of future improvements.

Barriers to Esketamine Nasal Spray Treatment Among Adults With Treatment-Resistant Depression.

Background: Under a risk evaluation and mitigation strategy program, esketamine nasal spray CIII requires self administration at a certified treatment center. Our objective was to identify factors associated with esketamine initiation and continuation.Methods: A retrospective observational cohort study was conducted among US adults who met treatment-resistant depression (TRD) criteria. Cases (n = 966) initiated esketamine between October 11, 2019, and February 28, 2022, and were compared to controls (n = 39,219) with TRD but no esketamine use. Outcomes included initiation, induction (8 administrations within 45 days), and interruptions (30-day treatment gap). Comorbid psychiatric conditions were identified using International Classification of Diseases, Tenth Revision, Clinical Modification, codes.Results: Cases resided significantly closer to treatment centers (8.9 vs 20.3 miles). Compared to 0-9 miles, initiation rate decreased by 11.9%, 50.8%, 68.1%, 75.9%, and 92.8% for individuals residing 10-19, 20-29, 30-39, 40-49, and 50+ miles from a center. After adjustment, factors associated with increased likelihood of initiation were posttraumatic stress disorder, major depressive disorder with suicidal ideation, and male sex, while increasing distance, substance use disorder, Medicaid, Charlson Comorbidity Index (CCI), and older age were associated with lower likelihood. Factors associated with lower likelihood of completing induction were Medicaid, low socioeconomic status (SES), CCI, and Hispanic communities. Factors associated with increased likelihood of interruption were alcohol use disorder, distance, and minority communities, while generalized anxiety disorder and Medicaid were associated with lower likelihood.Conclusions: Travel distance, insurance, low SES, and minority communities are potential barriers to treatment. Alternative care models may be needed to ensure adequate access to care.J Clin Psychiatry 2024;85(2):23m15102.

Theophylline-based control of repA on a Clostridioides difficile plasmid for use in allelic exchange.

Historically, mutagenesis in the non-model enteropathogenic bacterium Clostridioides difficile has been challenging. Developing a versatile and reliable method of generating targeted mutations in C. difficile is important to further our understanding of its pathogenesis. Some of the most common targeted mutagenesis systems rely on allelic exchange mediated by either uracil auxotrophy combined with a toxic uracil precursor, a toxin/anti-toxin system, group II introns, or CRISPR/Cas mutagenesis. However, each of these methods suffers from its own issues. Here, we develop and test an allelic exchange strategy which better facilitates screening for integration and selecting for excision than previous systems. This is achieved by controlling plasmid replication with a theophylline-dependent riboswitch cloned upstream of repA, the gene whose product controls plasmid replication. This allows efficient mutant generation, can be performed in a wild-type strain of C. difficile, does not have the off-target effects inherent to group II introns, and alleviates the problem of testing multiple gRNA targets in CRISPR mutagenesis.

Cultural humility and racial microaggressions in cross-racial clinical supervision: A moderated mediation model.

Cultural humility is important in supervision; however, studies have primarily sampled White supervisees. Racially and ethnically minoritized trainees experience microaggressions during their training, yet cross-racial supervision is less often studied. We examined a moderated mediation model to test whether the supervisory working alliance mediated the relationship between frequency of racial microaggressions and satisfaction with supervision, and whether the impact of racial microaggressions on the supervisee and supervisor cultural humility moderated the relationship between racial microaggression frequency and the supervisory working alliance. In a sample of supervisees of color (N = 102; majority cisgender women, 86.2%, and heterosexual, 59.8%; 35.3% Black/African American, 28.4% Asian/Pacific Islander, 18.6% Hispanic/Latine) receiving clinical supervision from White supervisors, we found that racial microaggression frequency was negatively associated with satisfaction with supervision, and this relationship was fully accounted for by the supervisory working alliance. Racial microaggressions in supervision were found to be detrimental to the supervisory working alliance, which was then related to lower satisfaction with supervision. Further, racial microaggression impact and cultural humility moderated the relationship between racial microaggression frequency and the supervisory working alliance; this relationship was strongest when racial microaggression impact was high and cultural humility was average or high. The social bond hypothesis suggests we are more likely to allow ourselves to be vulnerable when we assess cultural humility to be high. We posit that the observed moderation effect may be due to supervisees experiencing greater shock when experiencing racial microaggressions from supervisors whom they perceived to be culturally humble. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Sexual dimorphism and the multi-omic response to exercise training in rat subcutaneous white adipose tissue.

Subcutaneous white adipose tissue (scWAT) is a dynamic storage and secretory organ that regulates systemic homeostasis, yet the impact of endurance exercise training (ExT) and sex on its molecular landscape is not fully established. Utilizing an integrative multi-omics approach, and leveraging data generated by the Molecular Transducers of Physical Activity Consortium (MoTrPAC), we show profound sexual dimorphism in the scWAT of sedentary rats and in the dynamic response of this tissue to ExT. Specifically, the scWAT of sedentary females displays -omic signatures related to insulin signaling and adipogenesis, whereas the scWAT of sedentary males is enriched in terms related to aerobic metabolism. These sex-specific -omic signatures are preserved or amplified with ExT. Integration of multi-omic analyses with phenotypic measures identifies molecular hubs predicted to drive sexually distinct responses to training. Overall, this study underscores the powerful impact of sex on adipose tissue biology and provides a rich resource to investigate the scWAT response to ExT.

The immune response to RNA suppresses nucleic acid synthesis by limiting ribose 5-phosphate.

During infection viruses hijack host cell metabolism to promote their replication. Here, analysis of metabolite alterations in macrophages exposed to poly I:C recognises that the antiviral effector Protein Kinase RNA-activated (PKR) suppresses glucose breakdown within the pentose phosphate pathway (PPP). This pathway runs parallel to central glycolysis and is critical to producing NADPH and pentose precursors for nucleotides. Changes in metabolite levels between wild-type and PKR-ablated macrophages show that PKR controls the generation of ribose 5-phosphate, in a manner distinct from its established function in gene expression but dependent on its kinase activity. PKR phosphorylates and inhibits the Ribose 5-Phosphate Isomerase A (RPIA), thereby preventing interconversion of ribulose- to ribose 5-phosphate. This activity preserves redox control but decreases production of ribose 5-phosphate for nucleotide biosynthesis. Accordingly, the PKR-mediated immune response to RNA suppresses nucleic acid production. In line, pharmacological targeting of the PPP during infection decreases the replication of the Herpes simplex virus. These results identify an immune response-mediated control of host cell metabolism and suggest targeting the RPIA as a potential innovative antiviral treatment.

Osteochondroprogenitor cells and neutrophils expressing p21 and senescence markers modulate fracture repair.

Cells expressing features of senescence, including upregulation of p21 and p16, appear transiently following tissue injury, yet the properties of these cells or how they contrast with age-induced senescent cells remains unclear. Here, we used skeletal injury as a model and identified the rapid appearance following fracture of p21+ cells expressing senescence markers, mainly as osteochondroprogenitors (OCHs) and neutrophils. Targeted genetic clearance of p21+ cells suppressed senescence-associated signatures within the fracture callus and accelerated fracture healing. By contrast, p21+ cell clearance did not alter bone loss due to aging; conversely, p16+ cell clearance, known to alleviate skeletal aging, did not affect fracture healing. Following fracture, p21+ neutrophils were enriched in signaling pathways known to induce paracrine stromal senescence, while p21+ OCHs were highly enriched in senescence-associated secretory phenotype factors known to impair bone formation. Further analysis revealed an injury-specific stem cell-like OCH subset that was p21+ and highly inflammatory, with a similar inflammatory mesenchymal population (fibro-adipogenic progenitors) evident following muscle injury. Thus, intercommunicating senescent-like neutrophils and mesenchymal progenitor cells were key regulators of tissue repair in bone and potentially across tissues. Moreover, our findings established contextual roles of p21+ versus p16+ senescent/senescent-like cells that may be leveraged for therapeutic opportunities.

Diffusion-Weighted Imaging Fluid-Attenuated Inversion Recovery Mismatch on Portable, Low-Field Magnetic Resonance Imaging Among Acute Stroke Patients.

OBJECTIVE: For stroke patients with unknown time of onset, mismatch between diffusion-weighted imaging (DWI) and fluid-attenuated inversion recovery (FLAIR) magnetic resonance imaging (MRI) can guide thrombolytic intervention. However, access to MRI for hyperacute stroke is limited. Here, we sought to evaluate whether a portable, low-field (LF)-MRI scanner can identify DWI-FLAIR mismatch in acute ischemic stroke. METHODS: Eligible patients with a diagnosis of acute ischemic stroke underwent LF-MRI acquisition on a 0.064-T scanner within 24 h of last known well. Qualitative and quantitative metrics were evaluated. Two trained assessors determined the visibility of stroke lesions on LF-FLAIR. An image coregistration pipeline was developed, and the LF-FLAIR signal intensity ratio (SIR) was derived. RESULTS: The study included 71 patients aged 71 ± 14 years and a National Institutes of Health Stroke Scale of 6 (interquartile range 3-14). The interobserver agreement for identifying visible FLAIR hyperintensities was high (κ = 0.85, 95% CI 0.70-0.99). Visual DWI-FLAIR mismatch had a 60% sensitivity and 82% specificity for stroke patients <4.5 h, with a negative predictive value of 93%. LF-FLAIR SIR had a mean value of 1.18 ± 0.18 <4.5 h, 1.24 ± 0.39 4.5-6 h, and 1.40 ± 0.23 >6 h of stroke onset. The optimal cut-point for LF-FLAIR SIR was 1.15, with 85% sensitivity and 70% specificity. A cut-point of 6.6 h was established for a FLAIR SIR <1.15, with an 89% sensitivity and 62% specificity. INTERPRETATION: A 0.064-T portable LF-MRI can identify DWI-FLAIR mismatch among patients with acute ischemic stroke. Future research is needed to prospectively validate thresholds and evaluate a role of LF-MRI in guiding thrombolysis among stroke patients with uncertain time of onset. ANN NEUROL 2024;96:321-331.