Shawn Barton, MD, PhD

All Publications

• COVID-19 infection in myasthenia gravis: Clinical course and outcomes. Muscle & nerve Thomas, E. V., Bou, G., Barton, S., Hutto, S., Garcia-Santibanez, R. 2023; 68 (2): 171-175

  Abstract

  Myasthenia gravis (MG) patients have been predicted to have high rates of coronavirus disease-2019 (COVID-19) complications due to frequent involvement of respiratory muscles in MG and frequent use of immunosuppressive therapies. We investigated outcomes of MG patients infected with SARS-CoV-2 to identify risk factors for exacerbation and severe disease.This was a retrospective analysis of 39 MG patients with SARS-CoV-2 infection from January March 1, 2020 to October 25, 2021 at Emory University. Patients' records were queried for demographic data, MG history, and COVID-19 treatments and hospitalizations.At the time of infection, 8 of 39 were vaccinated, 30 of 39 unvaccinated, and 1 unknown. Average age was 52.6 years. Twenty-seven patients were receiving immunomodulatory treatments at the time of infection. Thirty-five of 39 were symptomatic, 21 were hospitalized, and 7 required ventilations. MG exacerbations occurred in 5 and were treated with therapeutic plasma exchange (n = 1), intravenous immunoglobulin (IVIg) (n = 1), and prednisone taper (n = 5). Four hospitalized patients died from COVID-related lung injuries. No deaths were attributed to MG exacerbation; however, one patient receiving IVIg for MG exacerbation had a pulmonary embolism. There were no deaths in fully vaccinated patients, and only one vaccinated patient was admitted to the intensive care unit.High rates of COVID-19 complications and death were observed in this cohort of MG patients. Some patients with MG and COVID-19 also had an exacerbation during infection. Further studies are needed to determine whether MG patients are at higher risk for complications than the rest of the population.

  View details for DOI 10.1002/mus.27919

  View details for PubMedID 37326164

• Inhalable Thioflavin S for the Detection of Amyloid Beta Deposits in the Retina. Molecules (Basel, Switzerland) Barton, S. M., To, E., Rogers, B. P., Whitmore, C., Uppal, M., Matsubara, J. A., Pham, W. 2021; 26 (4)

  Abstract

  We present an integrated delivery technology herein employing the aerosolized method to repurpose thioflavin S for imaging amyloid beta (Abeta) deposits in the retina as a surrogate of Abeta in the brain for early detection of Alzheimer's disease. The data showed that wild type (WT) mice also have Abeta deposits in the retinae, albeit much less than 5XFAD mice. Further, only in 5XFAD mice, significant Abeta deposits were found associated with retinal ganglion cells (RGCs) in whole-mount and cross-section data. Furthermore, the fluorescent signal depicted from thioflavin S corroborates with Abeta immunohistochemistry staining information. Overall, this probe delivery via inhalation method is also applicable to other Abeta-binding molecules, such as Congo red, curcumin, and thioflavin T. The advantage of imaging retinal amyloid deposits compared to the brain counterparts is that the eye is easily accessible by in vivo imaging and it reduces the effort to design a probe that must cross the formidable blood-brain barrier.

  View details for DOI 10.3390/molecules26040835

  View details for PubMedID 33562625

  View details for PubMedCentralID PMC7915734

• Lipopolysaccharide Induced Opening of the Blood Brain Barrier on Aging 5XFAD Mouse Model. Journal of Alzheimer's disease : JAD Barton, S. M., Janve, V. A., McClure, R., Anderson, A., Matsubara, J. A., Gore, J. C., Pham, W. 2019; 67 (2): 503-513

  Abstract

  The development of neurotherapeutics for many neurodegenerative diseases has largely been hindered by limited pharmacologic penetration across the blood-brain barrier (BBB). Previous attempts to target and clear amyloid-β (Aβ) plaques, a key mediator of neurodegenerative changes in Alzheimer's disease (AD), have had limited clinical success due to low bioavailability in the brain because of the BBB. Here we test the effects of inducing an inflammatory response to disrupt the BBB in the 5XFAD transgenic mouse model of AD. Lipopolysaccharide (LPS), a bacterial endotoxin recognized by the innate immune system, was injected at varying doses. 24 hours later, mice were injected with either thioflavin S, a fluorescent Aβ-binding small molecule or 30 nm superparamagnetic iron oxide (SPIO) nanoparticles, both of which are unable to penetrate the BBB under normal physiologic conditions. Our results showed that when pretreated with 3.0 mg/kg LPS, thioflavin S can be found in the brain bound to Aβ plaques in aged 5XFAD transgenic mice. Following the same LPS pretreatment, SPIO nanoparticles could also be found in the brain. However, when done on wild type or young 5XFAD mice, limited SPIO was detected. Our results suggest that the BBB in aged 5XFAD mouse model is susceptible to increased permeability mediated by LPS, allowing for improved delivery of the small molecule thioflavin S to target Aβ plaques and SPIO nanoparticles, which are significantly larger than antibodies used in clinical trials for immunotherapy of AD. Although this approach demonstrated efficacy for improved delivery to the brain, LPS treatment resulted in significant weight loss even at low doses, resulting from the induced inflammatory response. These findings suggest inducing inflammation can improve delivery of small and large materials to the brain for improved therapeutic or diagnostic efficacy. However, this approach must be balanced with the risks of systemic inflammation.

  View details for DOI 10.3233/JAD-180755

  View details for PubMedID 30584141

  View details for PubMedCentralID PMC9026569

• Specific Molecular Recognition as a Strategy to Delineate Tumor Margin Using Topically Applied Fluorescence Embedded Nanoparticles Barton , S., Li, B., Siuta , M., Janve , V., Song , J., Holt , C., Tomono , T., Ukawa , M., Kumagai , H., Tobita , E., Wilson , K., Sakuma , S., Pham , W. Precision Nanomedicine 1.3. 2018 194-207
• Aerosol Delivery of Curcumin Reduced Amyloid-β Deposition and Improved Cognitive Performance in a Transgenic Model of Alzheimer's Disease. Journal of Alzheimer's disease : JAD McClure, R., Ong, H., Janve, V., Barton, S., Zhu, M., Li, B., Dawes, M., Jerome, W. G., Anderson, A., Massion, P., Gore, J. C., Pham, W. 2017; 55 (2): 797-811

  Abstract

  We report a novel approach for the delivery of curcumin to the brain via inhalation of the aerosol for the potential treatment of Alzheimer's disease. The percentage of plaque fraction in the subiculum and hippocampus reduced significantly when young 5XFAD mice were treated with inhalable curcumin over an extended period of time compared to age-matched nontreated counterparts. Further, treated animals demonstrated remarkably improved overall cognitive function, no registered systemic or pulmonary toxicity associated with inhalable curcumin observed during the course of this work.

  View details for DOI 10.3233/JAD-160289

  View details for PubMedID 27802223

  View details for PubMedCentralID PMC5848215

• RNA structure. Structure of the HIV-1 RNA packaging signal. Science (New York, N.Y.) Keane, S. C., Heng, X., Lu, K., Kharytonchyk, S., Ramakrishnan, V., Carter, G., Barton, S., Hosic, A., Florwick, A., Santos, J., Bolden, N. C., McCowin, S., Case, D. A., Johnson, B. A., Salemi, M., Telesnitsky, A., Summers, M. F. 2015; 348 (6237): 917-21

  Abstract

  The 5' leader of the HIV-1 genome contains conserved elements that direct selective packaging of the unspliced, dimeric viral RNA into assembling particles. By using a (2)H-edited nuclear magnetic resonance (NMR) approach, we determined the structure of a 155-nucleotide region of the leader that is independently capable of directing packaging (core encapsidation signal; Ψ(CES)). The RNA adopts an unexpected tandem three-way junction structure, in which residues of the major splice donor and translation initiation sites are sequestered by long-range base pairing and guanosines essential for both packaging and high-affinity binding to the cognate Gag protein are exposed in helical junctions. The structure reveals how translation is attenuated, Gag binding promoted, and unspliced dimeric genomes selected, by the RNA conformer that directs packaging.

  View details for DOI 10.1126/science.aaa9266

  View details for PubMedID 25999508

  View details for PubMedCentralID PMC4492308

• Database proton NMR chemical shifts for RNA signal assignment and validation. Journal of biomolecular NMR Barton, S., Heng, X., Johnson, B. A., Summers, M. F. 2013; 55 (1): 33-46

  Abstract

  The Biological Magnetic Resonance Data Bank contains NMR chemical shift depositions for 132 RNAs and RNA-containing complexes. We have analyzed the (1)H NMR chemical shifts reported for non-exchangeable protons of residues that reside within A-form helical regions of these RNAs. The analysis focused on the central base pair within a stretch of three adjacent base pairs (BP triplets), and included both Watson-Crick (WC; G:C, A:U) and G:U wobble pairs. Chemical shift values were included for all 4(3) possible WC-BP triplets, as well as 137 additional triplets that contain one or more G:U wobbles. Sequence-dependent chemical shift correlations were identified, including correlations involving terminating base pairs within the triplets and canonical and non-canonical structures adjacent to the BP triplets (i.e. bulges, loops, WC and non-WC BPs), despite the fact that the NMR data were obtained under different conditions of pH, buffer, ionic strength, and temperature. A computer program (RNAShifts) was developed that enables convenient comparison of RNA (1)H NMR assignments with database predictions, which should facilitate future signal assignment/validation efforts and enable rapid identification of non-canonical RNA structures and RNA-ligand/protein interaction sites.

  View details for DOI 10.1007/s10858-012-9683-9

  View details for PubMedID 23180050

  View details for PubMedCentralID PMC3555346

• NMR detection of structures in the HIV-1 5'-leader RNA that regulate genome packaging. Science (New York, N.Y.) Lu, K., Heng, X., Garyu, L., Monti, S., Garcia, E. L., Kharytonchyk, S., Dorjsuren, B., Kulandaivel, G., Jones, S., Hiremath, A., Divakaruni, S. S., LaCotti, C., Barton, S., Tummillo, D., Hosic, A., Edme, K., Albrecht, S., Telesnitsky, A., Summers, M. F. 2011; 334 (6053): 242-5

  Abstract

  The 5'-leader of the HIV-1 genome regulates multiple functions during viral replication via mechanisms that have yet to be established. We developed a nuclear magnetic resonance approach that enabled direct detection of structural elements within the intact leader (712-nucleotide dimer) that are critical for genome packaging. Residues spanning the gag start codon (AUG) form a hairpin in the monomeric leader and base pair with residues of the unique-5' region (U5) in the dimer. U5:AUG formation promotes dimerization by displacing and exposing a dimer-promoting hairpin and enhances binding by the nucleocapsid (NC) protein, which is the cognate domain of the viral Gag polyprotein that directs packaging. Our findings support a packaging mechanism in which translation, dimerization, NC binding, and packaging are regulated by a common RNA structural switch.

  View details for DOI 10.1126/science.1210460

  View details for PubMedID 21998393

  View details for PubMedCentralID PMC3335204

• Major groove width variations in RNA structures determined by NMR and impact of 13C residual chemical shift anisotropy and 1H-13C residual dipolar coupling on refinement. Journal of biomolecular NMR Tolbert, B. S., Miyazaki, Y., Barton, S., Kinde, B., Starck, P., Singh, R., Bax, A., Case, D. A., Summers, M. F. 2010; 47 (3): 205-19

  Abstract

  Ribonucleic acid structure determination by NMR spectroscopy relies primarily on local structural restraints provided by (1)H- (1)H NOEs and J-couplings. When employed loosely, these restraints are broadly compatible with A- and B-like helical geometries and give rise to calculated structures that are highly sensitive to the force fields employed during refinement. A survey of recently reported NMR structures reveals significant variations in helical parameters, particularly the major groove width. Although helical parameters observed in high-resolution X-ray crystal structures of isolated A-form RNA helices are sensitive to crystal packing effects, variations among the published X-ray structures are significantly smaller than those observed in NMR structures. Here we show that restraints derived from aromatic (1)H- (13)C residual dipolar couplings (RDCs) and residual chemical shift anisotropies (RCSAs) can overcome NMR restraint and force field deficiencies and afford structures with helical properties similar to those observed in high-resolution X-ray structures.

  View details for DOI 10.1007/s10858-010-9424-x

  View details for PubMedID 20549304

  View details for PubMedCentralID PMC2929647