Publications by authors named "Tun-Li Shen"

8 Publications

  • Page 1 of 1

Oxygen-to-Oxygen Silyl Migration of α-Siloxy Sulfoxides and Oxidation-Triggered Allicin Formation.

Org Lett 2021 May 19;23(9):3741-3745. Epub 2021 Apr 19.

Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States.

Oxidation of α-siloxy thioethers leads to the formation of the corresponding sulfoxides as unstable intermediates, which undergo an intramolecular oxygen-to-oxygen silyl migration to break the C-S linkage. This process produces silyl protected sulfenic acids and subsequently thiosulfinates. It was used to develop oxidation-triggered allicin donors.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.orglett.1c01149DOI Listing
May 2021

Placental Trophoblast-Inspired Lipid Bilayers for Cell-Free Investigation of Molecular Interactions.

ACS Appl Mater Interfaces 2020 Jul 6;12(28):31099-31111. Epub 2020 Jul 6.

School of Engineering, Center for Biomedical Engineering, Brown University, Providence, Rhode Island 02912, United States.

The placenta plays a key role in regulating the maternal-fetal transport but it is a difficult organ to study due to a lack of existing in vitro models. Lipid bilayers inspired by the placenta can provide a facile new in vitro tool with promise for screening molecular transport across this important organ. Here we developed lipid bilayers that mimic the composition of human placental trophoblast cells at different times during the course of pregnancy. Mass spectrometry identified five major lipid classes (phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine, and sphingomyelin) present at varying concentrations in trophoblasts representative of the first and third trimesters and full-term placenta. We successfully developed supported and suspended lipid bilayers mimicking these trophoblast lipid compositions and then demonstrated the utility of these synthetic placenta models for investigating molecular interactions. Specifically, we investigated the interactions with di(2-ethylhexyl) phthalate (DEHP), a common plasticizer and environmental toxicant, and amphotericin B, a common yet toxic, antifungal therapeutic. Overall, we observed that DEHP adsorbs and potentially embeds itself within all placental lipid bilayers, with varying levels of interaction. For both amphotericin B and a liposomal formulation of amphotericin B, AmBisome, we noted lower levels of permeation in transport studies with bilayers and trophoblast cells compared with DEHP, likely driven by differences in size. AmBisome interacted less with both the supported and suspended placental lipid bilayers in comparison to amphotericin B, suggesting that drug delivery carriers can vary the impact of a pharmaceutical agent on these lipid structures. We found that the apparent permeability observed in suspended bilayers was approximately an order of magnitude less than those observed for trophoblast monolayers, which is typical of lipid bilayers. Ultimately, these placenta mimetic lipid bilayers can serve as a platform for the rapid initial screening of molecular interactions with the maternal-fetal interface to better inform future testing.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.0c06197DOI Listing
July 2020

Genetic manipulation of the pigment pathway in a sea urchin reveals distinct lineage commitment prior to metamorphosis in the bilateral to radial body plan transition.

Sci Rep 2020 02 6;10(1):1973. Epub 2020 Feb 6.

Department of Molecular Biology, Cellular Biology, and Biochemistry, Brown University, Providence, RI, 02912, USA.

Echinoderms display a vast array of pigmentation and patterning in larval and adult life stages. This coloration is thought to be important for immune defense and camouflage. However, neither the cellular nor molecular mechanism that regulates this complex coloration in the adult is known. Here we knocked out three different genes thought to be involved in the pigmentation pathway(s) of larvae and grew the embryos to adulthood. The genes tested were polyketide synthase (PKS), Flavin-dependent monooxygenase family 3 (FMO3) and glial cells missing (GCM). We found that disabling of the PKS gene at fertilization resulted in albinism throughout all life stages and throughout all cells and tissues of this animal, including the immune cells of the coelomocytes. We also learned that FMO3 is an essential modifier of the polyketide. FMO3 activity is essential for larval pigmentation, but in juveniles and adults, loss of FMO3 activity resulted in the animal becoming pastel purple. Linking the LC-MS analysis of this modified pigment to a naturally purple animal suggested a conserved echinochrome profile yielding a pastel purple. We interpret this result as FMO3 modifies the parent polyketide to contribute to the normal brown/green color of the animal, and that in its absence, other biochemical modifications are revealed, perhaps by other members of the large FMO family in this animal. The FMO modularity revealed here may be important in the evolutionary changes between species and for different immune challenges. We also learned that glial cells missing (GCM), a key transcription factor of the endomesoderm gene regulatory network of embryos in the sea urchin, is required for pigmentation throughout the life stages of this sea urchin, but surprisingly, is not essential for larval development, metamorphosis, or maintenance of adulthood. Mosaic knockout of either PKS or GCM revealed spatial lineage commitment in the transition from bilaterality of the larva to a pentaradial body plan of the adult. The cellular lineages identified by pigment presence or absence (wild-type or knock-out lineages, respectively) followed a strict oral/aboral profile. No circumferential segments were seen and instead we observed 10-fold symmetry in the segments of pigment expression. This suggests that the adult lineage commitments in the five outgrowths of the hydropore in the larva are early, complete, fixed, and each bilaterally symmetric. Overall, these results suggest that pigmentation of this animal is genetically determined and dependent on a population of pigment stem cells that are set-aside in a sub-region of each outgrowth of the pentaradial adult rudiment prior to metamorphosis. This study reveals the complex chemistry of pigment applicable to many organisms, and further, provides an insight into the key transitions from bilateral to pentaradial body plans unique to echinoderms.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41598-020-58584-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7005274PMC
February 2020

Synthesis and Characterization of a Magnetically Active F Molecular Beacon.

Bioconjug Chem 2018 02 9;29(2):335-342. Epub 2018 Jan 9.

Center for Biomedical Engineering, ‡Department of Molecular Pharmacology, Physiology, and Biotechnology, §Department of Chemistry, ∥School of Engineering, and ⊥Department of Orthopaedics, Brown University , Providence, Rhode Island 02912, United States.

Gene expression is used extensively to describe cellular characteristics and behaviors; however, most methods of assessing gene expression are unsuitable for living samples, requiring destructive processes such as fixation or lysis. Recently, molecular beacons have become a viable tool for live-cell imaging of mRNA molecules in situ. Historically, beacon-mediated imaging has been limited to fluorescence-based approaches. We propose the design and synthesis of a novel molecular beacon for magnetic resonance detection of any desired target nucleotide sequence. The biologically compatible synthesis incorporates commonly used bioconjugation reactions in aqueous conditions and is accessible for laboratories without extensive synthesis capabilities. The resulting beacon uses fluorine (F) as a reporter, which is broadened, or turned "off", via paramagnetic relaxation enhancement from a stabilized nitroxide radical spin label when the beacon is not bound to its nucleic acid target. Therefore, the F NMR signal of the beacon is quenched in its hairpin conformation when the spin label and the F substituent are held in proximity, but the signal is recovered upon beacon hybridization to its specific complementary nucleotide sequence by physical separation of the radical from the F reporter. This study establishes a path for magnetic resonance-based assessment of specific mRNA expression, providing new possibilities for applying molecular beacon technology in living systems.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.bioconjchem.7b00671DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5821531PMC
February 2018

The KIM-family protein-tyrosine phosphatases use distinct reversible oxidation intermediates: Intramolecular or intermolecular disulfide bond formation.

J Biol Chem 2017 05 7;292(21):8786-8796. Epub 2017 Apr 7.

From the Departments of Molecular Pharmacology, Physiology and Biotechnology,

The kinase interaction motif (KIM) family of protein-tyrosine phosphatases (PTPs) includes hematopoietic protein-tyrosine phosphatase (HePTP), striatal-enriched protein-tyrosine phosphatase (STEP), and protein-tyrosine phosphatase receptor type R (PTPRR). KIM-PTPs bind and dephosphorylate mitogen-activated protein kinases (MAPKs) and thereby critically modulate cell proliferation and differentiation. PTP activity can readily be diminished by reactive oxygen species (ROS), HO, which oxidize the catalytically indispensable active-site cysteine. This initial oxidation generates an unstable sulfenic acid intermediate that is quickly converted into either a sulfinic/sulfonic acid (catalytically dead and irreversible inactivation) or a stable sulfenamide or disulfide bond intermediate (reversible inactivation). Critically, our understanding of ROS-mediated PTP oxidation is not yet sufficient to predict the molecular responses of PTPs to oxidative stress. However, identifying distinct responses will enable novel routes for PTP-selective drug design, important for managing diseases such as cancer and Alzheimer's disease. Therefore, we performed a detailed biochemical and molecular study of all KIM-PTP family members to determine their HO oxidation profiles and identify their reversible inactivation mechanism(s). We show that despite having nearly identical 3D structures and sequences, each KIM-PTP family member has a unique oxidation profile. Furthermore, we also show that whereas STEP and PTPRR stabilize their reversibly oxidized state by forming an intramolecular disulfide bond, HePTP uses an unexpected mechanism, namely, formation of a reversible intermolecular disulfide bond. In summary, despite being closely related, KIM-PTPs significantly differ in oxidation profiles. These findings highlight that oxidation protection is critical when analyzing PTPs, for example, in drug screening.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1074/jbc.M116.774174DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5448105PMC
May 2017

Effects of red wine and vodka on collateral-dependent perfusion and cardiovascular function in hypercholesterolemic swine.

Circulation 2012 Sep;126(11 Suppl 1):S65-72

Division of Cardiothoracic Surgery, Warren Alpert School of Medicine, Brown University, Providence, RI 02905, USA.

Background: Moderate consumption of alcohol, particularly red wine, has been shown to decrease cardiac risk. We used a hypercholesterolemic swine model of chronic ischemia to examine the effects of 2 alcoholic beverages on the heart.

Methods And Results: Yorkshire swine fed a high-cholesterol diet underwent left circumflex ameroid constrictor placement to induce chronic ischemia at 8 weeks of age. One group (HCC, n=9) continued on the diet alone, the second (HCW, n=8) was supplemented with red wine (pinot noir, 12.5% alcohol, 375 mL daily), and the third (HCV, n=9) was supplemented with vodka (40% alcohol, 112 mL daily). After 7 weeks, cardiac function was measured, and ischemic myocardium was harvested for analysis of perfusion, myocardial fibrosis, vessel function, protein expression, oxidative stress, and capillary density. Platelet function was measured by aggregometry. Perfusion to the ischemic territory as measured by microsphere injection was significantly increased in both HCW and HCV compared with HCC at rest, but in only the HCW group under ventricular pacing. Microvessel relaxation response to adenosine 5'-diphosphate was improved in the HCW group alone as was regional contractility in the ischemic territory, although myocardial fibrosis was decreased in both HCW and HCV. Expression of proangiogenic proteins phospho-endothelial nitric oxide synthase and vascular endothelial growth factor was increased in both HCW and HCV, whereas phospho-mammalian target of rapamycin was increased only in the HCV group. Expression of Sirt-1 and downstream antioxidant phospho-FoxO1 was increased only in the HCW group. Protein oxidative stress was decreased in the HCW group alone, whereas capillary density was increased only in the HCV group. There was no significant difference in platelet function between groups.

Conclusion: Moderate consumption of red wine and vodka may reduce cardiovascular risk by improving collateral-dependent perfusion through different mechanisms. Red wine may offer increased cardioprotection related to its antioxidant properties.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1161/CIRCULATIONAHA.111.082172DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3448932PMC
September 2012

Efficacy of a non-hypercalcemic vitamin-D2 derived anti-cancer agent (MT19c) and inhibition of fatty acid synthesis in an ovarian cancer xenograft model.

PLoS One 2012 3;7(4):e34443. Epub 2012 Apr 3.

Molecular Therapeutics Laboratory, Program in Women's Oncology, Department of Obstetrics and Gynecology, Women and Infants' Hospital of Rhode Island, Alpert Medical School, Brown University, Providence, Rhode Island, United States of America.

Background: Numerous vitamin-D analogs exhibited poor response rates, high systemic toxicities and hypercalcemia in human trials to treat cancer. We identified the first non-hypercalcemic anti-cancer vitamin D analog MT19c by altering the A-ring of ergocalciferol. This study describes the therapeutic efficacy and mechanism of action of MT19c in both in vitro and in vivo models.

Methodology/principal Finding: Antitumor efficacy of MT19c was evaluated in ovarian cancer cell (SKOV-3) xenografts in nude mice and a syngenic rat ovarian cancer model. Serum calcium levels of MT19c or calcitriol treated animals were measured. In-silico molecular docking simulation and a cell based VDR reporter assay revealed MT19c-VDR interaction. Genomewide mRNA analysis of MT19c treated tumors identified drug targets which were verified by immunoblotting and microscopy. Quantification of cellular malonyl CoA was carried out by HPLC-MS. A binding study with PPAR-Y receptor was performed. MT19c reduced ovarian cancer growth in xenograft and syngeneic animal models without causing hypercalcemia or acute toxicity. MT19c is a weak vitamin-D receptor (VDR) antagonist that disrupted the interaction between VDR and coactivator SRC2-3. Genome-wide mRNA analysis and western blot and microscopy of MT19c treated xenograft tumors showed inhibition of fatty acid synthase (FASN) activity. MT19c reduced cellular levels of malonyl CoA in SKOV-3 cells and inhibited EGFR/phosphoinositol-3kinase (PI-3K) activity independently of PPAR-gamma protein.

Significance: Antitumor effects of non-hypercalcemic agent MT19c provide a new approach to the design of vitamin-D based anticancer molecules and a rationale for developing MT19c as a therapeutic agent for malignant ovarian tumors by targeting oncogenic de novo lipogenesis.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0034443PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3317945PMC
August 2012

Liquid chromatography-mass spectrometry and tandem mass spectrometry of peptides and proteins.

Methods Mol Biol 2004 ;251:111-40

Department of Chemistry, Brown University, Providence, RI, USA.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1385/1-59259-742-4:111DOI Listing
March 2004