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author:("Li, lingquan")
1.  A new method to detect contaminants in heparin using radical depolymerization and liquid chromatography-mass spectrometry 
Analytical chemistry  2013;86(1):326-330.
Heparin is a critically important anticoagulant drug that was contaminated with a persulfonated polysaccharide in 2008, resulting in a number of severe adverse reactions, some leading to death. Controversy remains as to the precise composition of the 2008 contaminant and new information suggests that heparin may now be subject to adulteration with a new, difficult to detect, contaminant, N-sulfo oversulfated chondroitin sulfate. This study synthesizes this new potential contaminant and describes the use of radical depolymerization followed by liquid chromatography-mass spectrometry to detect N-sulfo oversulfated chondroitin sulfate and to confirm the structure of the 2008 contaminant as oversulfated chondroitin sulfate and not oversulfated heparan sulfate.
PMCID: PMC3927312  PMID: 24364596
heparin; oversulfated chondroitin sulfate; oversulfated heparan sulfate; N-sulfated oversulfated chondroitin sulfate; contaminant; radical depolymerization; mass spectrometry
2.  Assays for determining heparan sulfate and heparin O-sulfotransferase activity and specificity 
O-sulfotransferases (OSTs) are critical enzymes in the cellular biosynthesis of the biologically and pharmacologically important heparan sulfate and heparin. Recently, these enzymes have been cloned and expressed in bacteria for application in the chemoenzymatic synthesis of glycosaminoglycan-based drugs. OST activity assays have largely relied on the use of radioisotopic methods using [35S] 3'-phosphoadenosine-5'-phosphosulfate and scintillation counting. Herein, we examine alternative assays that are more compatible with a biomanufacturing environment. A high throughput microtiter-based approach is reported that relies on a coupled bienzymic colorimetric assay for heparan sulfate and heparin OSTs acting on polysaccharide substrates using arylsulfotransferase-IV and p-nitrophenylsulfate as a sacrificial sulfogroup donor. A second liquid chromatography-mass spectrometric assay, for heparan sulfate and heparin OSTs acting on structurally defined oligosaccharide substrates, is also reported that provides additional information on the number and positions of the transferred sulfo groups within the product. Together, these assays allow quantitative and mechanistic information to be obtained on OSTs that act on heparan sulfate and heparin precursors.
PMCID: PMC3901155  PMID: 24271188
enzymes; mass spectrometry; bioassays; sulfotransferases; coupled assay; heparin; heparan sulfate
3.  Excited States and Photodebromination of Selected Polybrominated Diphenyl Ethers: Computational and Quantitative Structure—Property Relationship Studies 
This paper presents a density functional theory (DFT)/time-dependent DFT (TD-DFT) study on the lowest lying singlet and triplet excited states of 20 selected polybrominateddiphenyl ether (PBDE) congeners, with the solvation effect included in the calculations using the polarized continuum model (PCM). The results obtained showed that for most of the brominated diphenyl ether (BDE) congeners, the lowest singlet excited state was initiated by the electron transfer from HOMO to LUMO, involving a π–σ* excitation. In triplet excited states, structure of the BDE congeners differed notably from that of the BDE ground states with one of the specific C–Br bonds bending off the aromatic plane. In addition, the partial least squares regression (PLSR), principal component analysis-multiple linear regression analysis (PCA-MLR), and back propagation artificial neural network (BP-ANN) approaches were employed for a quantitative structure-property relationship (QSPR) study. Based on the previously reported kinetic data for the debromination by ultraviolet (UV) and sunlight, obtained QSPR models exhibited a reasonable evaluation of the photodebromination reactivity even when the BDE congeners had same degree of bromination, albeit different patterns of bromination.
PMCID: PMC4307296  PMID: 25569092
Polybrominateddiphenyl ethers; theoretical study; excited states; photodebromination; quantitative structure-property relationship; artificial neural network
4.  Ultrasensitive detection and quantification of acidic disaccharides using capillary electrophoresis and quantum dot-based fluorescence resonance energy transfer 
Analytical chemistry  2013;85(19):10.1021/ac402242v.
Rapid and highly sensitive detection of the carbohydrate components of glycoconjugates is critical for advancing glycobiology. Fluorescence (or Forster) resonance energy transfer (FRET) is commonly used in detection of DNA, in protein structural biology, and in protease assays, but is less frequently applied to glycan analysis due to difficulties in inserting two fluorescent tags into small glycan structures. We report an ultrasensitive method for the detection and quantification of a chondroitin sulfate disaccharide based on FRET, involving a CdSe-ZnS core-shell nanocrystal quantum dot (QD)-streptavidin conjugate donor and a Cy5 acceptor. The disaccharide was doubly labeled with biotin and Cy5. QDs then served to concentrate the target disaccharide, enhancing the overall energy transfer efficiency, with unlinked QDs and Cy5-hydrazide producing nearly zero background signal in capillary electrophoresis using laser-induced fluorescence detection with two different band-pass filters. This method is generally applicable to the ultrasensitive analysis of acidic glycans and offers promise for the high-throughput disaccharide analysis of glycosaminoglycans.
PMCID: PMC3813904  PMID: 23985015
Fluorescence resonance energy transfer; quantum dots; glycosaminoglycans; ultrasensitive detection; capillary electrophoresis
5.  N-sulfotestosteronan, a novel substrate for heparan sulfate 6-O-sulfotransferases and its analysis by oxidative degradation 
Biopolymers  2013;99(10):10.1002/bip.22263.
Testosteronan, an unusual glycosaminoglycan first isolated from the microbe Comamonas testosteroni, was enzymatically synthesized in vitro by transferring uridine diphosphate sugars on β-p-nitrophenyl glucuronide acceptor. After chemically converting testosteronan to N-sulfotestosteronan it was tested as a substrate for sulfotransferases involved in the biosynthesis of the glycosaminoglycan, heparan sulfate. Studies using 35S-labeled 3′-phosphodenosine-5′-phosphosulfate (PAPS) showed that only 6-O-sulfotransferases acted on N-sulfotestosteronan. An oxidative depolymerization reaction was explored to generate oligosaccharides from 34S-labeled 6-O-sulfo-N-sulfotestosteroran using 34S-labeled PAPS because testosteronan was resistant to all of the tested glycosaminoglycan-degrading enzymes. Liquid chromotography-mass spectrometric analysis of the oxidatively depolymerized polysaccharides confirmed the incorporation of 34S into ~14% of the glucosamine residues. Nuclear magnetic resonance spectroscopy also showed that the sulfo groups were transferred to ~20% of the 6-hydroxyl groups in the glucosamine residue of N-sulfotestosteronan. The bioactivity of 6-O–sulfo-N-sulfotestosteronan was examined by performing protein-binding studies with fibroblast growth factors and antithrombin III using a surface plasmon resonance competition assay. The introduction of 6-O-sulfo groups enhanced N-sulfotestosteronan binding to the fibroblast growth factors, but not to antithrombin III.
PMCID: PMC3819802  PMID: 23606289
bacterial polysaccharide; sulfotransferases; protein-binding; sulfonation; heparan sulfate
6.  Immobilized enzymes to convert N-sulfo, N-acetyl heparosan to a critical intermediate in the production of bioengineered heparin 
Journal of biotechnology  2013;167(3):241-247.
Heparin is a critically important anticoagulant drug that is prepared from pig intestine. In 2007-2008, there was a crisis in the heparin market when the raw material was adulterated with the toxic polysaccharide, oversulfated chondroitin sulfate, which was associated with 100 deaths in the U.S. alone. As the result of this crisis, our laboratory and others have been actively pursuing alternative sources for this critical drug, including synthetic heparins and bioengineered heparin. In assessing the bioengineering processing costs it has become clear that the use of both enzyme-catalyzed cofactor recycling and enzyme immobilization will be needed for commercialization. In the current study, we examine the use of immobilization of C5-epimerase and 2-O-sulfotransferase involved in the first enzymatic step in the bioengineered heparin process, as well as arylsulfotransferase-IV involved in cofactor recycling in all three enzymatic steps. We report the successful immobilization of all three enzymes and their use in converting N-sulfo, N-acetyl heparosan into N-sulfo, N-acetyl 2-O-sulfo heparin.
PMCID: PMC3780768  PMID: 23835156
immobilized enyzmes; 2-O-sulfotransferase; C5-Epimerase; Aryl sulfotransferase IV; heparosan; bioengineered heparin
7.  An internal disulfide bond acts as a switch for intein activity 
Biochemistry  2013;52(34):5920-5927.
Inteins are intervening polypeptides that catalyze their own removal from flanking exteins, concomitant to the ligation of the exteins. The intein that interrupts the DP2 (large) subunit of DNA Polymerase II from Methanoculleus marisnigri (Mma) can promote protein splicing. However, protein splicing can be prevented or reduced by over-expression under non-reducing conditions, due to the formation of a disulfide bond between two internal intein Cys residues. This redox sensitivity leads to differential activity in different strains of E. coli as well as in different cell compartments. The redox-dependent control of in vivo protein splicing in an intein derived from an anaerobe that can occupy multiple environments hints at a possible physiological role for protein splicing.
PMCID: PMC3801215  PMID: 23906287
8.  Towards the chemoenzymatic synthesis of heparan sulfate oligosaccharides: Oxidative cleavage of p-nitrophenyl group with ceric ammonium salts 
Tetrahedron letters  2013;54(33):4471-4474.
We have developed an efficient chemoenzymatic synthesis of heparan sulfate oligosaccharides employing the para-nitrophenyl (p-NP) β-glucuronide as an acceptor compatible with enzymatic elongation and one that significantly simplifies oligosaccharide purification on C-18 resin. Employing ceric ammonium nitrate as oxidative reagent to remove the p-NP group unexpectedly also removed the glucuronic acid residue at the reducing-end, affording a smaller oligosaccharide. The application of ceric ammonium sulfate allowed the removal of the p-NP without concomitant loss of the adjacent glucuronic acid offering a route to longer heparin sulfate oligosaccharide products.
PMCID: PMC3733400  PMID: 23929984
Heparan sulfate oligosaccharides; chemoenzymatic synthesis; para-nitrophenyl glucuronic acid; ceric ammonium salt; deprotection
9.  On-line separation and characterization of hyaluronan oligosaccharides derived from radical depolymerization 
Carbohydrate polymers  2013;96(2):503-509.
Hydroxyl radicals are widely implicated in the oxidation of carbohydrates in biological and industrial processes and are often responsible for their structural modification resulting in functional damage. In this study, the radical depolymerization of the polysaccharide hyaluronan was studied in a reaction with hydroxyl radicals generated by Fenton Chemistry. A simple method for isolation and identification of the resulting non-sulfated oligosaccharide products of oxidative depolymerization was established. Hyaluronan oligosaccharides were analyzed using ion-pairing reversed phase high performance liquid chromotography coupled with tandem electrospray mass spectrometry. The sequence of saturated hyaluronan oligosaccharides having even- and odd-numbers of saccharide units, afforded through oxidative depolymerization, were identified. This study represents a simple, effective ‘fingerprinting’ protocol for detecting the damage done to hyaluronan by oxidative radicals. This study should help reveal the potential biological outcome of reactive-oxygen radical-mediated depolymerization of hyaluronan.
PMCID: PMC3711257  PMID: 23768593
Hyaluronan; oligosaccharides; free radical depolymerization; mass spectrometry
10.  Development of Virus-Specific CD4+ and CD8+ Regulatory T Cells Induced by Human Herpesvirus 6 Infection 
Journal of Virology  2014;88(2):1011-1024.
Human herpesvirus 6 (HHV-6) is an important immunosuppressive and immunomodulatory virus. The mechanisms by which HHV-6 establishes latency and immunosuppression in its host are not well understood. Here we characterized HHV-6-specific T cells in peripheral blood mononuclear cells (PBMCs) from HHV-6-infected donors. Our results showed that HHV-6 infection could induce both CD4+ and CD8+ HHV-6-specific regulatory T (Treg) cells. These HHV-6-specific Treg cells had potent suppressive activity and expressed high levels of Treg-associated molecules CD25, FoxP3, and GITR. Both CD4+ and CD8+ Treg cells secreted gamma interferon (IFN-γ) and interleukin-10 (IL-10) but little or no IL-2, IL-4, or transforming growth factor β (TGF-β). Furthermore, HHV-6-specifc Treg cells not only could suppress naive and HHV-6-specific CD4+ effector T cell immune responses but also could impair dendritic cell (DC) maturation and functions. In addition, the suppressive effects mediated by HHV-6-specific Treg cells were mainly through a cell-to-cell contact-dependent mechanism but not through the identified cytokines. These results suggest that HHV-6 may utilize the induction of Treg cells as a strategy to escape antivirus immune responses and maintain the latency and immunosuppression in infected hosts.
PMCID: PMC3911638  PMID: 24198406
11.  Isolation of bovine corneal keratan sulfate and its growth factor and morphogen binding 
The FEBS journal  2013;280(10):2285-2293.
Keratan sulfate (KS) is an important glycosaminoglycan that is found in cartilage, reproductive, and neural tissues. Corneal KS glycosaminoglycan is found N-linked to lumican, keratocan, and mimecan proteoglycans and has been widely studied by investigators interested in corneal development and diseases. Recently, the availability of corneal KS has become severely limited due to restricted the shipment of bovine central nervous system by-products across international borders in efforts to prevent additional cases of mad cow disease. We report a simple method for the purification of multi-milligram quantities of bovine corneal KS and characterize its structural properties. We also examined its protein-binding properties and discovered that corneal KS bound with high affinity to fibroblast growth factor-2 and sonic hedgehog, a growth factor and a morphogen involved in corneal development and healing.
PMCID: PMC3651742  PMID: 23402351
keratan sulfate; cornea; sonic hedgehog; fibroblast growth factor; interaction
12.  Neutralizing the anticoagulant activity of ultra-low molecular weight heparins using N-acetylglucosamine 6-sulfatase 
The FEBS journal  2013;280(10):10.1111/febs.12169.
Heparin has been the most commonly used anticoagulant drug for nearly a century. The drug heparin is generally categorized into three forms according to its molecular weight (MW), unfractionated (UF, average MW 13,000), low molecular weight (LMW, average MW 5,000), and ultra-low molecular weight heparin (ULMWH, average MW 2,000). Overdose of anticoagulant heparin can lead to very dangerous bleeding in patients. Protamine sulfate can be administered as an antidote to reverse heparin’s anticoagulant effect. There is not an effective antidote for ULMWH. In the current study, we examine human N-acetylglucosamine 6-sulfatase (NG6S), expressed in Chinese hamster ovary cells as a reversal agent for ULMWH. NG6S removes a single 6-O-sulfo group at the non-reducing end of the ULMWH Arixtra® (fondaparinux) effectively removing its ability to bind to antithrombin and preventing its inhibition of coagulation factor Xa. These results pave the way to develop human NG6S as an antidote for neutralizing the anticoagulant activity of ULMWHs.
PMCID: PMC3864854  PMID: 23374371
13.  Altered Expression Profile of Renal α1D-Adrenergic Receptor in Diabetes and Its Modulation by PPAR Agonists 
Journal of Diabetes Research  2014;2014:725634.
Alpha1D-adrenergic receptor (α1D-AR) plays important roles in regulating physiological and pathological responses mediated by catecholamines, particularly in the cardiovascular and urinary systems. The present study was designed to investigate the expression profile of α1D-AR in the diabetic kidneys and its modulation by activation of peroxisome proliferator-activated receptors (PPARs). 12-week-old Zucker lean (ZL) and Zucker diabetic fatty (ZD) rats were treated with fenofibrate or rosiglitazone for 8–10 weeks. Gene microarray, real-time PCR, and confocal immunofluorescence microscopy were performed to assess mRNA and protein expression of α1D-AR in rat kidney tissue. Using microarray, we found that α1D-AR gene was dramatically upregulated in 22-week-old ZD rats compared to ZL controls. Quantitative PCR analysis verified a 16-fold increase in α1D-AR mRNA in renal cortex from ZD animals compared to normal controls. Chronic treatment with fenofibrate or rosiglitazone reduced renal cortical α1D-AR gene. Immunofluorescence staining confirmed that α1D-AR protein was induced in the glomeruli and tubules of diabetic rats. Moreover, dual immunostaining for α1D-AR and kidney injury molecule-1 indicated that α1D-AR was expressed in dedifferentiated proximal tubules of diabetic Zucker rats. Taken together, our results show that α1D-AR expression is upregulated in the diabetic kidneys. PPAR activation suppressed renal expression of α1D-AR in diabetic nephropathy.
PMCID: PMC3977090  PMID: 24772448
14.  Structural Characterization of Pharmaceutical Heparins Prepared from Different Animal Tissues 
Journal of pharmaceutical sciences  2013;102(5):10.1002/jps.23501.
Although most pharmaceutical heparin used today is obtained from porcine intestine, heparin has historically been prepared from bovine lung and ovine intestine. There is some regulatory concern about establishing the species origin of heparin. This concern began with the outbreak of mad cow disease in the 1990s and was exacerbated during the heparin shortage in the 2000s and the heparin contamination crisis of 2007–2008. Three heparins from porcine, ovine, and bovine were characterized through state-of-the-art carbohydrate analysis methods with a view profiling their physicochemical properties. Differences in molecular weight, monosaccharide and disaccharide composition, oligosaccharide sequence, and antithrombin III-binding affinity were observed. These data provide some insight into the variability of heparins obtained from these three species and suggest some analytical approaches that may be useful in confirming the species origin of a heparin active pharmaceutical ingredient.
PMCID: PMC3866627  PMID: 23526651
bioanalysis; glycosaminoglycans; heparin; LC–MS; NMR; mass spectomery; surface plasmon resonance; antithrombin III
15.  Signal Amplification by Glyco-qPCR for Ultrasensitive Detection of Carbohydrates: Applications in Glycobiology** 
Tiny amounts of carbohydrates (ca. 1 zmol) can be detected quantitatively by a real-time method based on the conjugation of carbohydrates with DNA markers (see picture). The proposed method (glyco-qPCR) provides uniform, ultrasensitive detection of carbohydrates, which can be applied to glycobiology, as well as carbohydrate-based drug discovery.
PMCID: PMC3544480  PMID: 23073897
carbohydrates; DNA; glycoconjugates; signal amplification; ultrasensitive detection
16.  Top-down approach for the direct characterization of low molecular weight heparins using LC-FT-MS 
Analytical chemistry  2012;84(20):8822-8829.
Low molecular heparins (LMWHs) are structurally complex, heterogeneous, polydisperse, and highly negatively charged mixtures of polysaccharides. The direct characterization of LMWH is a major challenge for currently available analytical technologies. Electrospray ionization (ESI) liquid chromatography-mass spectrometry (LC-MS) is a powerful tool for the characterization complex biological samples in the fields of proteomics, metabolomics and glycomics. LC-MS has been applied to the analysis of heparin oligosaccharides, separated by size exclusion, reversed phase ion-pairing chromatography and by chip-based amide hydrophilic interaction chromatography (HILIC). However, there have been limited applications of ESI-LC-MS for the direct characterization of intact LMWHs (top-down analysis) due to their structural complexity, low ionization efficiency and sulfate loss. Here we present a simple and reliable HILIC-Fourier transform (FT)-ESI-MS platform to characterize and compare two currently marketed LMWH products using the top-down approach requiring no special sample preparation steps. This HILIC system relies on cross-linked diol rather than amide chemistry, affording highly resolved chromatographic separations using a relatively high percentage of acetonitrile in the mobile phase, resulting in stable and high efficiency ionization. Bioinformatics software (GlycerSoft 1.0) was used to automatically assign structures within 5-ppm mass accuracy.
PMCID: PMC3479637  PMID: 22985071
Low molecular weight heparin Top-down glycomics; Hydrophilic interaction chromatography; High-resolution mass spectrometry
17.  Intramolecular Disulfide Bond between Catalytic Cysteines in an Intein Precursor 
Protein splicing is a self-catalyzed and spontaneous post-translational process in which inteins excise themselves out of precursor proteins while the exteins are ligated together. We report the first discovery of an intramolecular disulfide bond between the two active site cysteines, Cys1 and Cys+1, in an intein precursor composed of the hyperthermophilic P. abyssi PolII intein and extein. The existence of this intramolecular disulfide bond is demonstrated by the effect of reducing agent on the precursor, mutagenesis, and liquid chromatography–mass spectrometry (LC-MS) with tandem MS (MS/MS) of the tryptic peptide containing the intramolecular disulfide bond. The disulfide bond inhibits protein splicing, and splicing can be induced by reducing agents such as tris (2-carboxyethyl) phosphine (TCEP). The stability of the intramolecular disulfide bond is enhanced by electrostatic interactions between the N- and C-exteins but is reduced by elevated temperature. The presence of this intramolecular disulfide bond may contribute to the redox control of splicing activity in hypoxia and at low temperature and point to the intriguing possibility that inteins may act as switches to control extein function.
PMCID: PMC3279520  PMID: 22280304
intein; protein splicing; intramolecular disulfide bond; extein; catalytic cysteine; MS
18.  Glomerular Expression of Kidney Injury Molecule-1 and Podocytopenia in Diabetic Glomerulopathy 
American Journal of Nephrology  2011;34(3):268-280.
Studies have shown that kidney injury molecule-1 (KIM-1) is upregulated in damaged renal proximal tubules. In this study, we examined KIM-1 expression in glomerular epithelial cells in diabetic glomerulopathy.
Renal histology, immunostaining and Western blot for protein level, and real-time PCR for mRNA expression of KIM-1 and podocyte markers were evaluated in untreated or losartan-treated Zucker lean (Fa/+) and Zucker diabetic fatty (Fa/Fa) rats.
The diabetic rats showed an increased glomerular expression of KIM-1. KIM-1 staining was localized primarily in the hyperplastic parietal epithelium of Bowman's capsule in the early stages of diabetes with subsequent increase in KIM-1-positive cells in the glomerular tuft in the more advanced stages. The increase in glomerular KIM-1 was associated with a decrease in podocytes in Fa/Fa rats. Antiproteinuric treatment with losartan attenuated podocytopenia and decreased renal expression of KIM-1 in treated diabetic rats. In an in vitro study, albumin overload increased KIM-1 protein in the primary cultures of rat glomerular epithelial cells.
These results show that glomerular KIM-1 expression was increased, in proportion to the extent of proteinuria and podocytopenia in the diabetic animals, supporting that KIM-1 could be used as a potential biomarker for glomerular injury in proteinuric kidney disease.
PMCID: PMC3169370  PMID: 21822010
Albuminuria; Kidney injury molecule-1; Parietal epithelial cells; Podocytes; Glomerulopathy
19.  Proteoglycan sequence 
Molecular bioSystems  2012;8(6):1613-1625.
Proteoglycans (PGs) are among the most structurally complex biomacromolecules in nature. They are present in all animal cells and frequently exert their critical biological functions through interactions with protein ligands and receptors. PGs are comprised of a core protein to which one or multiple, heterogeneous, and polydisperse glycosaminoglycan (GAG) chains are attached. Proteins, including the protein core of PGs, are now routinely sequenced either directly using proteomics or indirectly using molecular biology through their encoding DNA. The sequencing of the GAG component of PGs poses a considerably more difficult challenge because of the relatively underdeveloped state of glycomics and because the control of their biosynthesis in the endoplasmic reticulum and the Golgi is poorly understood and not believed to be template driven. Recently, the GAG chain of the simplest PG has been suggested to have a defined sequence based on its top-down Fourier transform mass spectral sequencing. This review examines the advances made over the past decade in the sequencing of GAG chains and the challenges the field face in sequencing complex PGs having critical biological functions in developmental biology and pathogenesis.
PMCID: PMC3425375  PMID: 22513887
20.  Systemic Delivery of a Glucosylceramide Synthase Inhibitor Reduces CNS Substrates and Increases Lifespan in a Mouse Model of Type 2 Gaucher Disease 
PLoS ONE  2012;7(8):e43310.
Neuropathic Gaucher disease (nGD), also known as type 2 or type 3 Gaucher disease, is caused by a deficiency of the enzyme glucocerebrosidase (GC). This deficiency impairs the degradation of glucosylceramide (GluCer) and glucosylsphingosine (GluSph), leading to their accumulation in the brains of patients and mouse models of the disease. These accumulated substrates have been thought to cause the severe neuropathology and early death observed in patients with nGD and mouse models. Substrate accumulation is evident at birth in both nGD mouse models and humans affected with the most severe type of the disease. Current treatment of non-nGD relies on the intravenous delivery of recombinant human glucocerebrosidase to replace the missing enzyme or the administration of glucosylceramide synthase inhibitors to attenuate GluCer production. However, the currently approved drugs that use these mechanisms do not cross the blood brain barrier, and thus are not expected to provide a benefit for the neurological complications in nGD patients. Here we report the successful reduction of substrate accumulation and CNS pathology together with a significant increase in lifespan after systemic administration of a novel glucosylceramide synthase inhibitor to a mouse model of nGD. To our knowledge this is the first compound shown to cross the blood brain barrier and reduce substrates in this animal model while significantly enhancing its lifespan. These results reinforce the concept that systemically administered glucosylceramide synthase inhibitors could hold enhanced therapeutic promise for patients afflicted with neuropathic lysosomal storage diseases.
PMCID: PMC3422338  PMID: 22912851
21.  SCD1 Inhibition Causes Cancer Cell Death by Depleting Mono-Unsaturated Fatty Acids 
PLoS ONE  2012;7(3):e33823.
Increased metabolism is a requirement for tumor cell proliferation. To understand the dependence of tumor cells on fatty acid metabolism, we evaluated various nodes of the fatty acid synthesis pathway. Using RNAi we have demonstrated that depletion of fatty-acid synthesis pathway enzymes SCD1, FASN, or ACC1 in HCT116 colon cancer cells results in cytotoxicity that is reversible by addition of exogenous fatty acids. This conditional phenotype is most pronounced when SCD1 is depleted. We used this fatty-acid rescue strategy to characterize several small-molecule inhibitors of fatty acid synthesis, including identification of TOFA as a potent SCD1 inhibitor, representing a previously undescribed activity for this compound. Reference FASN and ACC inhibitors show cytotoxicity that is less pronounced than that of TOFA, and fatty-acid rescue profiles consistent with their proposed enzyme targets. Two reference SCD1 inhibitors show low-nanomolar cytotoxicity that is offset by at least two orders of magnitude by exogenous oleate. One of these inhibitors slows growth of HCT116 xenograft tumors. Our data outline an effective strategy for interrogation of on-mechanism potency and pathway-node-specificity of fatty acid synthesis inhibitors, establish an unambiguous link between fatty acid synthesis and cancer cell survival, and point toward SCD1 as a key target in this pathway.
PMCID: PMC3310881  PMID: 22457791
22.  Growth, Mechanical, Thermal and Spectral Properties of Cr3+∶MgMoO4 Crystal 
PLoS ONE  2012;7(1):e30327.
This paper reports the growth, mechanical, thermal and spectral properties of Cr3+∶MgMoO4 crystals. The Cr3+∶MgMoO4 crystals with dimensions up to 30 mm×18 mm×14 mm were obtained by TSSG method. The absorption cross-sections of 4A2→4T1 and 4A2→4T2 transitions are 12.94×10−20 cm2 at 493 nm and 7.89×10−20 cm2 at 705 nm for E//Ng, respectively. The Cr3+∶MgMoO4 crystal shows broad band emission extending from 750 nm to 1300 nm with peak at about 705 nm. The emission cross-section with FWHM of 188 nm is 119.88×10−20 cm2 at 963 nm for E//Ng. The investigated results showed that the Cr3+∶MgMoO4 crystal may be regarded as a potential tunable laser gain medium.
PMCID: PMC3265461  PMID: 22291935
23.  Human Herpesvirus 6 Suppresses T Cell Proliferation through Induction of Cell Cycle Arrest in Infected Cells in the G2/M Phase▿ 
Journal of Virology  2011;85(13):6774-6783.
Human herpesvirus 6 (HHV-6) is an important immunosuppressive and immunomodulatory virus that primarily infects immune cells and strongly suppresses the proliferation of infected cells. However, the mechanisms responsible for the regulation and suppression mediated by HHV-6 are still unknown. In this study, we examined the ability of HHV-6A to manipulate cell cycle progression in infected cells and explored the potential molecular mechanisms. We demonstrated that infection with HHV-6A imposed a growth-inhibitory effect on HSB-2 cells by inducing cell cycle arrest at the G2/M phase. We then showed that the activity of the Cdc2–cyclin B1 complex was significantly decreased in HHV-6A-infected HSB-2 cells. Furthermore, we found that inactivation of Cdc2–cyclin B1 in HHV-6A-infected cells occurred through the inhibitory Tyr15 phosphorylation resulting from elevated Wee1 expression and inactivated Cdc25C. The reduction of Cdc2–cyclin B1 activity in HHV-6-infected cells was also partly due to the increased expression of the cell cycle-regulatory molecule p21 in a p53-dependent manner. In addition, HHV-6A infection activated the DNA damage checkpoint kinases Chk2 and Chk1. Our data suggest that HHV-6A infection induces G2/M arrest in infected T cells via various molecular regulatory mechanisms. These results further demonstrate the potential mechanisms involved in immune suppression and modulation mediated by HHV-6 infection, and they provide new insights relevant to the development of novel vaccines and immunotherapeutic approaches.
PMCID: PMC3126536  PMID: 21525341
24.  Iminosugar-Based Inhibitors of Glucosylceramide Synthase Increase Brain Glycosphingolipids and Survival in a Mouse Model of Sandhoff Disease 
PLoS ONE  2011;6(6):e21758.
The neuropathic glycosphingolipidoses are a subgroup of lysosomal storage disorders for which there are no effective therapies. A potential approach is substrate reduction therapy using inhibitors of glucosylceramide synthase (GCS) to decrease the synthesis of glucosylceramide and related glycosphingolipids that accumulate in the lysosomes. Genz-529468, a blood-brain barrier-permeant iminosugar-based GCS inhibitor, was used to evaluate this concept in a mouse model of Sandhoff disease, which accumulates the glycosphingolipid GM2 in the visceral organs and CNS. As expected, oral administration of the drug inhibited hepatic GM2 accumulation. Paradoxically, in the brain, treatment resulted in a slight increase in GM2 levels and a 20-fold increase in glucosylceramide levels. The increase in brain glucosylceramide levels might be due to concurrent inhibition of the non-lysosomal glucosylceramidase, Gba2. Similar results were observed with NB-DNJ, another iminosugar-based GCS inhibitor. Despite these unanticipated increases in glycosphingolipids in the CNS, treatment nevertheless delayed the loss of motor function and coordination and extended the lifespan of the Sandhoff mice. These results suggest that the CNS benefits observed in the Sandhoff mice might not necessarily be due to substrate reduction therapy but rather to off-target effects.
PMCID: PMC3126858  PMID: 21738789
25.  Fenofibrate attenuates tubulointerstitial fibrosis and inflammation through suppression of nuclear factor-κB and transforming growth factor-β1/Smad3 in diabetic nephropathy 
Fibrates, the ligands of peroxisome proliferator-activated receptor-α, have been shown to have a renal protective action in diabetic models of renal disease, but the mechanisms underlying this effect are unknown. In the present study, we sought to investigate in greater detail the effect of fenofibrate and its mechanism of action on renal inflammation and tubulointerstitial fibrosis in an animal model of type 2 diabetes mellitus. Twelve-week-old non-diabetic Zucker lean (ZL) and Zucker diabetic fatty (ZD) rats were treated with vehicle or fenofibrate for 10 weeks. mRNA and protein analyses were performed by real-time polymerase chain reaction, Western blot and immunostaining. The diabetic condition of ZD rats was associated with an increase in collagen and α-smooth muscle actin accumulation in the kidney, which was significantly reduced by fenofibrate. Chronic treatment of ZD rats with fenofibrate attenuated renal inflammation and tubular injury as evidenced by a decrease in mRNA and protein expression of secreted phosphoprotein-1, monocyte chemotactic protein-1 and kidney injury molecule-1 in the kidneys. Renal interstitial macrophage infiltration was also significantly reduced in the kidneys of fenofibrate-treated diabetic animals. Moreover, renal nuclear factor (NF)-κB DNA-binding activity, transforming growth factor (TGF)-β1 and phospho-Smad3 proteins were significantly higher in ZD animals compared with ZL ones. This increase in NF-κB activity, TGF-β1 expression and Smad3 phosphorylation was greatly attenuated by fenofibrate in the diabetic kidneys. Taken together, fenofibrate suppressed NF-κB and TGF-β1/Smad3 signaling pathways and reduced renal inflammation and tubulointerstitial fibrosis in diabetic ZD animals.
PMCID: PMC3057137  PMID: 20404057
inflammation; kidney; peroxisome proliferator-activated receptor-α; renal injury; type 2 diabetes

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