Siaw Wei Ng

University of Oxford, Oxford, England, United Kingdom

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Publications (10)56.34 Total impact

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    Jenab N Sidhapuriwala · Siaw Wei Ng · Madhav Bhatia ·
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    ABSTRACT: Hydrogen sulfide (H(2)S), a gaseous mediator plays an important role in a wide range of physiological and pathological processes. H(2)S has been extensively studied for its various roles in cardiovascular and neurological disorders. However, the role of H(2)S in inflammation is still controversial. The current study was aimed to investigate the therapeutic potential of sodium hydrosulfide (NaHS), an H(2)S donor in in vivo model of acute pancreatitis in mice. Acute pancreatitis was induced in mice by hourly caerulein injections (50 mug/kg) for 10 hours. Mice were treated with different dosages of NaHS (5 mg/kg, 10 mg/kg or 15 mg/kg) or with vehicle, distilled water (DW). NaHS or DW was administered 1 h before induction of pancreatitis. Mice were sacrificed 1 h after the last caerulein injection. Blood, pancreas and lung tissues were collected and were processed to measure the plasma amylase, myeloperoxidase (MPO) activities in pancreas and lung and chemokines and adhesion molecules in pancreas and lung. It was revealed that significant reduction of inflammation, both in pancreas and lung was associated with NaHS 10 mg/kg. Further the anti-inflammatory effects of NaHS 10 mg/kg were associated with reduction of pancreatic and pulmonary inflammatory chemokines and adhesion molecules. NaHS 5 mg/kg did not cause significant improvement on inflammation in pancreas and associated lung injury and NaHS 15 mg/kg did not further enhance the beneficial effects seen with NaHS 10 mg/kg. In conclusion, these data provide evidence for anti-inflammatory effects of H(2)S based on its dosage used.
    Journal of Inflammation 12/2009; 6(1):35. DOI:10.1186/1476-9255-6-35 · 2.02 Impact Factor
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    Joseph Di Capite · Siaw Wei Ng · Anant B Parekh ·
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    ABSTRACT: Cytoplasmic Ca(2+) oscillations are a universal signaling mode that activates numerous cellular responses [1, 2]. Oscillations are considered the physiological mechanism of Ca(2+) signaling because they occur at low levels of stimulus intensity [3]. Ca(2+) oscillations are proposed to convey information in their amplitude and frequency, leading to activation of specific downstream targets [4-6]. Here, we report that the spatial Ca(2+) gradient within the oscillation is key. Ca(2+) oscillations in mast cells evoked over a range of agonist concentrations in the presence of external Ca(2+) were indistinguishable from those in the absence of Ca(2+) when plasmalemmal Ca(2+) extrusion was suppressed. Nevertheless, only oscillations with accompanying Ca(2+) entry through store-operated CRAC channels triggered gene expression. Increased cytoplasmic Ca(2+) buffering prevented oscillations but not gene activation. Local Ca(2+) influx and not global Ca(2+) oscillations therefore drives gene expression at physiological levels of stimulation. Rather than serving to maintain Ca(2+) oscillations by replenishing stores, we suggest that the role of oscillations might be to activate CRAC channels, thereby ensuring the generation of spatially restricted physiological Ca(2+) signals driving gene activation. Furthermore, we show that the spatial profile of a Ca(2+) oscillation provides a novel mechanism whereby a pleiotropic messenger specifically activates gene expression.
    Current biology: CB 05/2009; 19(10):853-8. DOI:10.1016/j.cub.2009.03.063 · 9.57 Impact Factor

  • Gastroenterology 05/2009; 136(5). DOI:10.1016/S0016-5085(09)62496-3 · 16.72 Impact Factor
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    ABSTRACT: The role of nitric oxide (NO) has been increasingly implicated in the pathophysiology of acute pancreatitis (AP). Studies have shown increased NO production in AP although not all are agreeable on whether NO is beneficial or detrimental in AP. This study aims to profile NO production and NO synthase (NOS) expression in the pancreas and lungs in the progression of AP in mice to gain insights to the role played by different NOS isoforms. AP was induced in mice by hourly administration of cerulein. NO production was determined by measuring the total nitrite and nitrate (NOx) content while NOS expression was measured by Western blot. Pancreatic NO production increased sharply and was sustained throughout AP. iNOS expression was greatly increased while eNOS was downregulated at the later stages. In the lungs, there was an unexpected early increase in the constitutive NOS expression; however iNOS was also significantly overexpressed at the later time point along with a significant increase in NO. Acinar cells were found to overproduce NO in response to cerulein hyperstimulation with iNOS again being the major contributor. These data show that NO production and NOS expression are differentially regulated temporally and in magnitude in the pancreas and lungs in response to cerulein hyperstimulation which suggests differing roles for each NOS isoform. and IAP.
    Pancreatology 04/2009; 9(1-2):150-9. DOI:10.1159/000178886 · 2.84 Impact Factor
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    ABSTRACT: Mast cell activation involves cross-linking of IgE receptors followed by phosphorylation of the non-receptor tyrosine kinase Syk. This results in activation of the plasma membrane-bound enzyme phospholipase Cgamma1, which hydrolyzes the minor membrane phospholipid phosphatidylinositol 4,5-bisphosphate to generate diacylglycerol and inositol trisphosphate. Inositol trisphosphate raises cytoplasmic Ca2+ concentration by releasing Ca2+ from intracellular stores. This Ca2+ release phase is accompanied by sustained Ca2+ influx through store-operated Ca2+ release-activated Ca2+ (CRAC) channels. Here, we find that engagement of IgE receptors activates Syk, and this leads to Ca2+ release from stores followed by Ca2+ influx. The Ca2+ influx phase then sustains Syk activity. The Ca2+ influx pathway activated by these receptors was identified as the CRAC channel, because pharmacological block of the channels with either a low concentration of Gd3+ or exposure to the novel CRAC channel blocker 3-fluoropyridine-4-carboxylic acid (2',5'-dimethoxybiphenyl-4-yl)amide or RNA interference knockdown of Orai1, which encodes the CRAC channel pore, all prevented the increase in Syk activity triggered by Ca2+ entry. CRAC channels and Syk are spatially close together, because increasing cytoplasmic Ca2+ buffering with the fast Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis failed to prevent activation of Syk by Ca2+ entry. Our results reveal a positive feedback step in mast cell activation where receptor-triggered Syk activation and subsequent Ca2+ release opens CRAC channels, and the ensuing local Ca2+ entry then maintains Syk activity. Ca2+ entry through CRAC channels therefore provides a means whereby the Ca2+ and tyrosine kinase signaling pathways can interact with one another.
    Journal of Biological Chemistry 10/2008; 283(46):31348-55. DOI:10.1074/jbc.M804942200 · 4.57 Impact Factor
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    ABSTRACT: Sepsis is a complex clinical syndrome resulting from a harmful host inflammatory response to infection. Similarly, lipopolysaccharide (LPS) induced endotoxemia is marked by the activation of inflammatory responses, which can lead to shock, multiple organ damage and even death. Inflammatory mediator, chemokines are known to play an important role in the pathogenesis of sepsis and endotoxemia. Monocyte chemoattractant protein (MCP)-1, a prototype of CC chemokines, is a potent chemoattractant and a regulatory mediator involved in a variety of inflammatory diseases. The objective of this study is to investigate the role of MCP-1, by using bindarit, a blocker of MCP-1 synthesis, in murine models of sepsis and endotoxemia. Treatment with bindarit both prophylactically and therapeutically significantly (P<0.05) reduced MCP-1 levels in the lungs and liver in both sepsis and endotoxemia. In addition, prophylactic and therapeutic treatment with bindarit significantly (P<0.05) protected mice against sepsis and endotoxemia, as evidenced by the attenuation in lung and liver myeloperoxidase (MPO) activity, an indicator of neutrophil recruitment. The protective effect of bindarit was further confirmed by histological examination of lung and liver sections. Treatment with bindarit reduced lung and liver injury as indicated by decreased thickening of alveolar and neutrophil infiltration in CLP-induced sepsis and LPS-induced endotoxemia. Considering these results, we propose that anti-MCP-1 strategies may be of potential therapeutic value in the treatment of sepsis and endotoxemia.
    International Immunopharmacology 07/2008; 8(6):810-8. DOI:10.1016/j.intimp.2008.01.033 · 2.47 Impact Factor
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    ABSTRACT: Hydrogen sulphide (H(2)S), a novel gasotransmitter, has been recognized to play an important role in inflammation. Cystathionine-gamma-lyase (CSE) is a major H(2)S synthesizing enzyme in the cardiovascular system and DL-propargylglycine (PAG) is an irreversible inhibitor of CSE. Substance P (SP), a product of preprotachykinin-A (PPT-A) gene, is a well-known pro-inflammatory mediator which acts principally through the neurokinin-1 receptor (NK-1R). We have shown an association between H(2)S and SP in pulmonary inflammation as well as a pro-inflammatory role of H(2)S and SP in acute pancreatitis. The present study was aimed to investigate the interplay between pro-inflammatory effects of H(2)S and SP in a murine model of caerulein-induced acute pancreatitis. Acute pancreatitis was induced in mice by 10 hourly intraperitoneal injections of caerulein (50 (g/kg). PAG (100 mg/kg, i.p.) was administered either 1 hr before (prophylactic) or 1 hr after (therapeutic) the first caerulein injection. PAG, given prophylactically as well as therapeutically, significantly reduced plasma H(2)S levels and pancreatic H(2)S synthesizing activities as well as SP concentrations in plasma, pancreas and lung compared with caerulein-induced acute pancreatitis. Furthermore, prophylactic as well as therapeutic administration of PAG significantly reduced PPT-A mRNA expression and NK-1R mRNA expression in both pancreas and lung when compared with caerulein-induced acute pancreatitis. These results suggest that the pro-inflammatory effects of H(2)S may be mediated by SP-NK-1R pathway in acute pancreatitis.
    Journal of Cellular and Molecular Medicine 04/2008; 12(2):580-90. DOI:10.1111/j.1582-4934.2007.00131.x · 4.01 Impact Factor
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    Siaw Wei Ng · Huili Zhang · Akhil Hegde · Madhav Bhatia ·
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    ABSTRACT: Endotoxemia is a life-threatening, inflammatory condition that involves multiple organ injury and dysfunction. Preprotachykinin-A (PPT-A) gene products, substance P (SP), and neurokinin-A have been shown to play an important role in neurogenic inflammation. To investigate the role of PPT-A gene products on multiple organ injury in LPS-induced endotoxemia, endotoxemia was induced by LPS administration (10 mg/kg, i.p.) in PPT-A gene-deficient mice (PPTA(-/-)) and the wild-type (WT) control mice (PPT-A+/+). I.p. administration of LPS to WT mice caused a significant increase in circulating levels of SP as well as in liver, lung, and kidney. PPT-A gene deletion significantly protected against liver, pulmonary, and renal injury following LPS-induced endotoxemia, as evidenced by tissue myeloperoxidase activities, plasma alanine aminotransferase, aspartate aminotransferase levels, and histological examination. Furthermore, PPT-A(-/-) mice had significantly attenuated chemokines, proinflammatory cytokines, and adhesion molecule levels in the liver, lung, and kidney. These results show that PPT-A gene products are critical proinflammatory mediators in endotoxemia and the associated multiple organ injury. In addition, the data suggest that deletion of the PPT-A gene protected mice against organ damage in endotoxemia by disruption in neutrophil recruitment.
    Journal of Leukocyte Biology 03/2008; 83(2):288-95. DOI:10.1189/jlb.0807575 · 4.29 Impact Factor
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    ABSTRACT: Hydrogen sulfide (H2S) has been shown to induce the activation of neurogenic inflammation especially in normal airways and urinary bladder. However, whether endogenous H2S would regulate sepsis-associated lung inflammation via substance P (SP) and its receptors remains unknown. Therefore, the aim of the study was to investigate the effect of H2S on the pulmonary level of SP in cecal ligation and puncture (CLP)-induced sepsis and its relevance to lung injury. Male Swiss mice or male preprotachykinin-A gene knockout (PPT-A-/-) mice and their wild-type (PPT-A+/+) mice were subjected to CLP-induced sepsis. DL-propargylglycine (50 mg/kg i.p.), an inhibitor of H2S formation was administered either 1 h before or 1 h after the induction of sepsis, while NaHS, an H2S donor, was given at the same time as CLP. L703606, an inhibitor of the neurokinin-1 receptor was given 30 min before CLP. DL-propargylglycine pretreatment or posttreatment significantly decreased the PPT-A gene expression and the production of SP in lung whereas administration of NaHS resulted in a further rise in the pulmonary level of SP in sepsis. PPT-A gene deletion and pretreatment with L703606 prevented H2S from aggravating lung inflammation. In addition, septic mice genetically deficient in PPT-A gene or pretreated with L703606 did not exhibit further increase in lung permeability after injection of NaHS. The present findings show for the first time that in sepsis, H2S up-regulates the generation of SP, which contributes to lung inflammation and lung injury mainly via activation of the neurokinin-1 receptor.
    The Journal of Immunology 10/2007; 179(6):4153-60. DOI:10.4049/jimmunol.179.6.4153 · 4.92 Impact Factor
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    ABSTRACT: Preprotachykinin-A (PPT-A) gene products substance P and neurokinin-A have been shown to play an important role in neurogenic inflammation. To investigate the role of PPT-A gene products in lung injury in sepsis, polymicrobial sepsis was induced by cecal ligation and puncture in PPT-A gene-deficient mice (PPT-A(-/-)) and the wild-type control mice (PPT-A(+/+)). PPT-A gene deletion significantly protected against mortality, delayed the onset of lethality, and improved the long-term survival following cecal ligation and puncture-induced sepsis. PPT-A(-/-) mice also had significantly attenuated inflammation and damage in the lungs. The data suggest that deletion of the PPT-A gene may have contributed to the disruption in recruitment of inflammatory cells resulting in protection against tissue damage, as in these mice the sepsis-associated increase in chemokine levels is significantly attenuated.
    The Journal of Immunology 04/2006; 176(6):3813-20. DOI:10.4049/jimmunol.176.6.3813 · 4.92 Impact Factor

Publication Stats

386 Citations
56.34 Total Impact Points


  • 2008-2009
    • University of Oxford
      • Department of Physiology, Anatomy and Genetics
      Oxford, England, United Kingdom
    • National University of Singapore
      Tumasik, Singapore