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Publications (8)

  • Source
    Binnian Wei · June Feng · Imran J Rehmani · [...] · Lanqing Wang
    [Show abstract] [Hide abstract] ABSTRACT: Background: Most sample preparation methods characteristically involve intensive and repetitive labor, which is inefficient when preparing large numbers of samples from population-scale studies. Methods: This study presents a robotic system designed to meet the sampling requirements for large population-scale studies. Using this robotic system, we developed and validated a method to simultaneously measure urinary anatabine, anabasine, nicotine and seven major nicotine metabolites: 4-Hydroxy-4-(3-pyridyl)butanoic acid, cotinine-N-oxide, nicotine-N-oxide, trans-3'-hydroxycotinine, norcotinine, cotinine and nornicotine. We analyzed robotically prepared samples using high-performance liquid chromatography (HPLC) coupled with triple quadrupole mass spectrometry in positive electrospray ionization mode using scheduled multiple reaction monitoring (sMRM) with a total runtime of 8.5 min. Results: The optimized procedure was able to deliver linear analyte responses over a broad range of concentrations. Responses of urine-based calibrators delivered coefficients of determination (R(2)) of >0.995. Sample preparation recovery was generally higher than 80%. The robotic system was able to prepare four 96-well plate (384 urine samples) per day, and the overall method afforded an accuracy range of 92-115%, and an imprecision of <15.0% on average. Conclusions: The validation results demonstrate that the method is accurate, precise, sensitive, robust, and most significantly labor-saving for sample preparation, making it efficient and practical for routine measurements in large population-scale studies such as the National Health and Nutrition Examination Survey (NHANES) and the Population Assessment of Tobacco and Health (PATH) study.
    Full-text Article · Jun 2014 · Clinica Chimica Acta
  • Imran Rehmani · Fange Liu · Aimin Liu
    [Show abstract] [Hide abstract] ABSTRACT: Cell signaling and transcription is a tightly regulated process, integrating the activities of multiple interlinked pathways to respond in a precise manner to changes in the cellular environment. Many pathological conditions can be traced to defects in one or more of these regulatory mechanisms, which illustrates the requirement for exactness in which, when, and how genes are expressed. Considering this, it may seem unusual to consider the role of reactive oxygen species (ROS) in cell signaling. ROS were initially characterized as the undesirable byproducts of aerobic metabolism and earned a reputation for being destructive molecules that necessitated the existence of antioxidant enzymes to keep them from accumulating. How could these molecules, which literally have “reactive” in their name, have a role in a process that requires tight regulation and specificity? As decades of surprising research has revealed, ROS are an indispensable aspect of cell signaling and are mediators of crosstalk between different pathways. While they are reactive and capable of damaging biological molecules, their chemical properties give them a preference for specific molecules and structural features with which they react. The conservation and recurrence of these redox-sensitive structural features throughout nature has made ROS relevant to practically every level of eukaryotic cell signaling, from the mediation of growth factor receptor activity on the cell's plasma membrane to the regulation of transcription factors in the nucleus. ROS have come a long way from their initial characterization as a threat to life and will likely continue to be involved at the forefront of medical and biochemical research for many years to come. This chapter highlights some of the best-characterized mechanisms of ROS and oxygen signaling, especially those metal-dependent, in both prokaryotes and eukaryotes. We will start by briefly introducing the reactive properties of ROS and the most common structural features seen in redox-sensitive proteins. The types of simple redox and oxygen sensors found in bacteria will be reviewed with emphasis on a recently characterized transcription factor with a novel metal-catalysis mechanism, followed by a more in-depth discussion of the signaling systems found in metazoans (multicellular eukaryotes lacking a cell wall). Finally, the roles of redox and oxygen signaling in our understanding of disease will be highlighted.
    Chapter · Jun 2013
  • Source
    Fange Liu · Imran Rehmani · Shingo Esaki · [...] · Aimin Liu
    [Show abstract] [Hide abstract] ABSTRACT: Pirin is a nuclear nonheme Fe protein of unknown function present in all human tissues. Here we describe that pirin may act as a redox sensor for the nuclear factor κB (NF-κB) transcription factor, a critical mediator of intracellular signaling that has been linked to cellular responses to proinflammatory signals and controls the expression of a vast array of genes involved in immune and stress responses. Pirin's regulatory effect was tested with several metals and at different oxidations states, and our spectroscopic results show that only the ferric form of pirin substantially facilitates binding of NF-κB proteins to target κB genes, a finding that suggests that pirin performs a redox-sensing role in NF-κB regulation. The molecular mechanism of such a metal identity- and redox state-dependent regulation is revealed by our structural studies of pirin. The ferrous and ferric pirin proteins differ only by one electron, yet they have distinct conformations. The Fe center is shown to play an allosteric role on an R-shaped surface area that has two distinct conformations based on the identity and the formal redox state of the metal. We show that the R-shaped area composes the interface for pirin-NF-κB binding that is responsible for modulation of NF-κB's DNA-binding properties. The nonheme Fe protein pirin is proposed to serve as a reversible functional switch that enables NF-κB to respond to changes in the redox levels of the cell nucleus.
    Full-text Article · May 2013 · Proceedings of the National Academy of Sciences
  • [Show abstract] [Hide abstract] ABSTRACT: The development of pulmonary hypertension is a common accompaniment of congenital heart disease (CHD) with increased pulmonary blood flow. Our recent evidence suggests that asymmetric dimethylarginine (ADMA)-induced mitochondrial dysfunction causes endothelial nitric oxide synthase (eNOS) uncoupling secondary to a proteasome-dependent degradation of GTP cyclohydrolase I (GCH1) that results in a decrease in the NOS cofactor tetrahydrobiopterin (BH(4)). Decreases in NO signaling are thought to be an early hallmark of endothelial dysfunction. As l-carnitine plays an important role in maintaining mitochondrial function, in this study we examined the protective mechanisms and the therapeutic potential of l-carnitine on NO signaling in pulmonary arterial endothelial cells and in a lamb model of CHD and increased pulmonary blood flow (Shunt). Acetyl-l-carnitine attenuated the ADMA-mediated proteasomal degradation of GCH1. This preservation was associated with a decrease in the association of GCH1 with Hsp70 and the C-terminus of Hsp70-interacting protein (CHIP) and a decrease in its ubiquitination. This in turn prevented the decrease in BH(4) levels induced by ADMA and preserved NO signaling. Treatment of Shunt lambs with l-carnitine also reduced GCH1/CHIP interactions, attenuated the ubiquitination and degradation of GCH1, and increased BH(4) levels compared to vehicle-treated Shunt lambs. The increases in BH(4) were associated with decreased NOS uncoupling and enhanced NO generation. Thus, we conclude that L-carnitine may have a therapeutic potential in the treatment of pulmonary hypertension in children with CHD with increased pulmonary blood flow.
    Article · Apr 2012 · Free Radical Biology and Medicine
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    [Show abstract] [Hide abstract] ABSTRACT: We showed that nitric oxide (NO) signaling is decreased in the pulmonary vasculature before the development of endothelial dysfunction in a lamb model of congenital heart disease and increased pulmonary blood flow (Shunt). The elucidation of the molecular mechanism by which this occurs was the purpose of this study. Here, we demonstrate that concentrations of the endogenous NO synthase (NOS) inhibitor, asymmetric dimethylarginine (ADMA), are elevated, whereas the NOS cofactor tetrahydrobiopterin (BH4) is decreased in Shunt lambs. Our previous studies demonstrated that ADMA decreases heat shock protein-90 (Hsp90) chaperone activity, whereas other studies suggest that guanosine-5′-triphosphate cyclohydrolase 1 (GCH1), the rate-limitingenzyme in the generation of BH4, may be a client protein for Hsp90. Thus, we determined whether increases in ADMA could alter GCH1 protein and activity. Our data demonstrate that ADMA decreased GCH1 protein, but not mRNA concentrations, in pulmonary arterial endothelial cells (PAECs) because of the ubiquitination and proteasome-dependent degradation of GCH1. We also found that Hsp90-GCH1 interactions were reduced, whereas the association of GCH1 with Hsp70 and the C-terminus of Hsp70-interacting protein (CHIP) increased in ADMA-exposed PAECs. The overexpression of CHIP potentiated, whereas a CHIP U-box domain mutant attenuated, ADMA-induced GCH1 degradation and reductions in cellular BH4 concentrations.Wealso found in vivo that Hsp90/GCH1 interactions are decreased, whereas GCH1-Hsp70 and GCH1-CHIP interactions and GCH1 ubiquitination are increased. Finally, we found that supplementation with L-arginine restored Hsp90-GCH1 interactions and increased both BH4 and NOx concentrations in Shunt lambs. In conclusion, increased concentrations of ADMA can indirectly alter NO signaling through decreased cellular BH4 concentrations, secondary to the disruption of Hsp90-GCH1 interactions and the CHIP-dependent proteasomal degradation of GCH1.
    Full-text Article · Jul 2011 · American Journal of Respiratory Cell and Molecular Biology
  • Conference Paper · May 2010
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    [Show abstract] [Hide abstract] ABSTRACT: Acute lung injury (ALI) is associated with severe alterations in lung structure and function and is characterized by hypoxemia, pulmonary edema, low lung compliance and widespread capillary leakage. Asymmetric dimethylarginine (ADMA), a known cardiovascular risk factor, has been linked to endothelial dysfunction and the pathogenesis of a number of cardiovascular diseases. However, the role of ADMA in the pathogenesis of ALI is less clear. ADMA is metabolized via hydrolytic degradation to l-citrulline and dimethylamine by the enzyme, dimethylarginine dimethylaminohydrolase (DDAH). Recent studies suggest that lipopolysaccharide (LPS) markedly increases the level of ADMA and decreases DDAH activity in endothelial cells. Thus, the purpose of this study was to determine if alterations in the ADMA/DDAH pathway contribute to the development of ALI initiated by LPS-exposure in mice. Our data demonstrate that LPS exposure significantly increases ADMA levels and this correlates with a decrease in DDAH activity but not protein levels of either DDAH I or DDAH II isoforms. Further, we found that the increase in ADMA levels cause an early decrease in nitric oxide (NO(x)) and a significant increase in both NO synthase (NOS)-derived superoxide and total nitrated lung proteins. Finally, we found that decreasing peroxynitrite levels with either uric acid or Manganese (III) tetrakis (1-methyl-4-pyridyl) porphyrin (MnTymPyp) significantly attenuated the lung leak associated with LPS-exposure in mice suggesting a key role for protein nitration in the progression of ALI. In conclusion, this is the first study that suggests a role of the ADMA/DDAH pathway during the development of ALI in mice and that ADMA may be a novel therapeutic biomarker to ascertain the risk for development of ALI.
    Full-text Article · Dec 2009 · Vascular Pharmacology
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    [Show abstract] [Hide abstract] ABSTRACT: Previous studies demonstrate impaired nitric oxide (NO) signaling in children and animal models with congenital heart defects and increased pulmonary blood flow. However, the molecular mechanisms underlying these alterations remain incompletely understood. The purpose of this study was to determine if early changes in arginine metabolic pathways could play a role in the reduced NO signaling demonstrated in our lamb model of congenital heart disease with increased pulmonary blood flow (Shunt lambs). The activities of the arginine recycling enzymes, argininosuccinate synthetase (ASS) and argininosuccinate lyase (ASL) were both decreased in lung tissues of Shunt lambs while arginase activity was increased. Associated with these alterations, lung L-arginine levels were decreased. These changes correlated with an increase in NO synthase-derived reactive oxygen species (ROS) generation. This study provides further insights into the molecular mechanisms leading to decreased NO signaling in Shunt lambs and suggests that altered arginine metabolism may play a role in the development of the endothelial dysfunction associated with pulmonary hypertension secondary to increased pulmonary blood flow.
    Full-text Article · Oct 2009 · Vascular Pharmacology