Chi Chun Wong

Publications (12)41.24 Total impact

• Article: Carrier-mediated transport of quercetin conjugates: involvement of organic anion transporters and organic anion transporting polypeptides.

  Chi Chun Wong, Yasutoshi Akiyama, Takaaki Abe, Jonathan D Lippiat, Caroline Orfila, Gary Williamson
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  ABSTRACT: Flavonoids modulate cell signaling and inhibit oxidative enzymes. After oral consumption, they circulate in human plasma as amphiphilic glucuronide or sulfate conjugates, but it is unknown how these physiological metabolites permeate into cells. We examined the mechanisms of uptake of these conjugates into hepatocellular carcinoma (HepG2) cells, and found that uptake of quercetin-3'-O-sulfate was saturable and temperature-dependent, indicating the involvement of carrier-mediated transport. Quercetin-3-O-glucuronide was taken up predominantly via passive diffusion in these cells. Quantitative real-time PCR analysis showed high expression of OATP4C1, followed by OAT2, OAT4 and low expression of OATP1B1 in HepG2 cells, and addition of inhibitors of OATs and OATPs resulted in a significant reduction in quercetin-3'-O-sulfate uptake. The accumulation of quercetin-3'-O-sulfate was further evaluated in HEK293 cells expressing OAT2, OAT4 and OATP4C1. Uptake of quercetin-3'-O-sulfate was 2.3- and 1.4-fold higher in cells expressing OAT4 and OATP4C1 at pH 6.0, respectively, than in control HEK293 cells. siRNA knockdown of OATP4C1 expression in HepG2 cells reduced uptake of quercetin-3'-O-sulfate by ∼40%. This study highlights a role for OATs and OATPs in the cellular uptake of biologically active flavonoid conjugates.
  Biochemical pharmacology 05/2012; 84(4):564-70. · 4.25 Impact Factor
• Article: First chemical synthesis and in vitro characterization of the potential human metabolites 5-o-feruloylquinic acid 4'-sulfate and 4'-O-glucuronide.

  Candice Menozzi-Smarrito, Chi Chun Wong, Walter Meinl, Hansruedi Glatt, René Fumeaux, Caroline Munari, Fabien Robert, Gary Williamson, Denis Barron
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  ABSTRACT: Feruloylquinic acids are a major class of biologically active phenolic antioxidants in coffee beans, but their metabolic fate is poorly understood. The present study investigated the phase II metabolism of feruloylquinic acids with selected human sulfotransferases (SULT1A1 and SULT1E1) and uridine 5'-diphosphoglucuronosyltransferases (UGT1A1 and UGT1A9). For unequivocal metabolite identification, the chemical synthesis of two potential human metabolites of 5-O-feruloylquinic acid, the 4'-sulfated and 4'-O-glucuronidated conjugates, has been performed for the first time. Following incubation with human SULT1A1 or SULT1E1, formation of 5-O-feruloylquinic acid 4'-O-sulfate was confirmed by matching its HPLC and MS data with those of the authentic standard. On the other hand, no glucuronide conjugates were detected after incubation with human uridine 5'-diphosphoglucuronosyltransferases. These results suggest that sulfation can take place on the ferulic acid moiety of feruloylquinic acids and may be a major metabolic pathway for feruloylquinic acids in humans.
  Journal of Agricultural and Food Chemistry 03/2011; 59(10):5671-6. · 2.82 Impact Factor
• Article: Flavonoid conjugates interact with organic anion transporters (OATs) and attenuate cytotoxicity of adefovir mediated by organic anion transporter 1 (OAT1/SLC22A6).

  Chi Chun Wong, Nigel P Botting, Caroline Orfila, Nawaf Al-Maharik, Gary Williamson
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  ABSTRACT: Flavonoids are conjugated by phase II enzymes in humans to form glucuronidated and sulfated metabolites that are excreted in urine via the kidney. In this study, we examined the interaction between metabolites of quercetin and isoflavonoids found in vivo with human organic anion transporters 1 (OAT1) and 3 (OAT3) and their potential in attenuating OAT-induced cytotoxicity of adefovir. Accumulation of flavonoid conjugates was studied in human embryonic kidney 293H cells overexpressing OAT1 or OAT3. OAT1-overexpressing cells exhibited an increased uptake of the sulfated conjugates, genistein-4'-O-sulfate and quercetin-3'-O-sulfate. OAT3-overexpressing cells demonstrated enhanced uptake of glucuronide conjugates, such as daidzein-7-O-glucuronide, genistein-7-O-glucuronide, glycitein-7-O-glucuronide and quercetin-3'-O-glucuronide. Position of conjugation was important since quercetin-3-O-glucuronide and quercetin-7-O-glucuronide were poorly transported. Kinetic analysis revealed high affinity uptake of quercetin-3'-O-sulfate by OAT1 (K(m)=1.73μM; V(max)=105 pmol/min/mg). OAT3 transported isoflavone glucuronides with lower affinity (K(m)=7.9-19.1 μM) but with higher V(max) (171-420 pmol/min/mg). Quercetin-3'-O-sulfate strongly inhibited OAT1-mediated p-aminohippuric acid uptake with an IC(50) of 1.22μM. Transport of 5-carboxyfluorescein by OAT3 was potently inhibited by quercetin-3-O-glucuronide, quercetin-3'-O-glucuronide and quercetin-3'-O-sulfate (IC(50)=0.43-1.31μM). In addition, quercetin-3'-O-sulfate was shown to effectively reduce OAT1-mediated cytotoxicity of adefovir, an antiviral drug, in a dose-dependent manner. These data suggest that OAT1 and OAT3 are responsible for basolateral uptake of flavonoid conjugates in kidney, and flavonoid conjugates inhibit OAT1 and OAT3 activity at physiologically relevant concentrations. Interaction with OATs limits systemic availability of flavonoids and may be a mechanism of food-drug interaction via inhibition of renal uptake.
  Biochemical pharmacology 01/2011; 81(7):942-9. · 4.25 Impact Factor
• Article: In vitro and in vivo conjugation of dietary hydroxycinnamic acids by UDP-glucuronosyltransferases and sulfotransferases in humans.

  Chi Chun Wong, Walter Meinl, Hans-Rudolf Glatt, Denis Barron, Angélique Stalmach, Heike Steiling, Alan Crozier, Gary Williamson
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  ABSTRACT: Hydroxycinnamic acids are a class of phenolic antioxidants found widely in dietary plants. Their biotransformation in the human organism primarily involves Phase II conjugation reactions. In this study, activities of UDP-glucuronosyltransferases (UGTs) and sulfotransferases (SULTs) towards major dietary hydroxycinnamic acids (caffeic, dihydrocaffeic, dihydroferulic, ferulic and isoferulic acids) were investigated. Conjugate formation was evaluated using human liver and intestinal S9 homogenates, and in vitro characterization was carried out using recombinant human UGTs and SULTs. Analysis of the kinetics of hydroxycinnamic acid conjugation in human S9 homogenates revealed that intrinsic clearance (V(max)/K(m)) is much greater for sulfation than for glucuronidation. Assessment of activity using a panel of recombinant human SULTs showed that SULT1A1 is most active in the sulfation of caffeic, dihydrocaffeic and isoferulic acids, while SULT1E1 is most active in the sulfation of ferulic and dihydroferulic acids. Only isoferulic acid was significantly glucuronidated by human liver S9 homogenates, explained by the high activity of liver-specific UGT1A9. Studies on the kinetics of active SULTs and UGTs demonstrated a markedly lower K(m) for SULTs. To further corroborate our findings, we carried out an intervention study in healthy humans to determine the hydroxycinnamic acid conjugates in urine after consumption of hydroxycinnamate-rich coffee (200 ml). Analysis showed that sulfates are the main conjugates in urine, with the exception of isoferulic acid, which is mainly glucuronidated. These data suggest that sulfates are the predominant hydroxycinnamic acid conjugates in humans, and that SULT mediated sulfation is a major factor determining the bioavailability of hydroxycinnamic acids in vivo.
  The Journal of nutritional biochemistry 11/2009; 21(11):1060-8. · 4.29 Impact Factor
• Article: Inhibition of mutagenic PhIP formation by epigallocatechin gallate via scavenging of phenylacetaldehyde.

  Ka-Wing Cheng, Chi Chun Wong, Jianfei Chao, Clive Lo, Feng Chen, Ivan K Chu, Chi-Ming Che, Chi-Tang Ho, Mingfu Wang
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  ABSTRACT: Chemical model investigation showed that both epigallocatechin gallate (EGCG) and its peracetate, which has all the hydroxyl groups acetylated, effectively reduced the formation of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), the most abundant mutagenic heterocyclic amine found in foods. Mechanistic study was subsequently carried out to characterize the probable inhibitory mechanism involved. GC-MS analysis showed that EGCG in only one-fourth molar quantity of phenylalanine reduced formation of phenylacetaldehyde, a key PhIP intermediate by nearly 90%. Its peracetate also showed similar inhibitory activity. This further supported the existence of an antioxidant-independent mechanism contributing to the inhibition of PhIP formation by EGCG. Subsequent LC-MS analyses of samples from a wide range of model systems consisting of PhIP precursors showed the generation of characteristic analytes with molecular weight corresponding to the sum of EGCG and phenylalanine fragment(s) only in models where phenylalanine and EGCG were simultaneously present. An isotope-labeling study revealed that these analytes all contained fragment(s) of phenylalanine origin. Direct reaction employing phenylacetaldehyde and EGCG further confirmed the capability of EGCG to form adducts with phenylacetaldehyde, thus reducing its availability for PhIP formation. Finally, an investigation of the time course of the generation of postulated adduction products supported EGCG as an effective inhibitor of PhIP formation in prolonged heating processes.
  Molecular Nutrition & Food Research 06/2009; 53(6):716-25. · 4.30 Impact Factor
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  Available from: Ka-Wing Cheng

  Article: Identification and characterization of molecular targets of natural products by mass spectrometry.

  Ka-Wing Cheng, Chi-Chun Wong, Mingfu Wang, Qing-Yu He, Feng Chen
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  ABSTRACT: Natural products, and their derivatives and mimics, have contributed to the development of important therapeutics to combat diseases such as infections and cancers over the past decades. The value of natural products to modern drug discovery is still considerable. However, its development is hampered by a lack of a mechanistic understanding of their molecular action, as opposed to the emerging molecule-targeted therapeutics that are tailored to a specific protein target(s). Recent advances in the mass spectrometry-based proteomic approaches have the potential to offer unprecedented insights into the molecular action of natural products. Chemical proteomics is established as an invaluable tool for the identification of protein targets of natural products. Small-molecule affinity selection combined with mass spectrometry is a successful strategy to "fish" cellular targets from the entire proteome. Mass spectrometry-based profiling of protein expression is also routinely employed to elucidate molecular pathways involved in the therapeutic and possible toxicological responses upon treatment with natural products. In addition, mass spectrometry is increasingly utilized to probe structural aspects of natural products-protein interactions. Limited proteolysis, photoaffinity labeling, and hydrogen/deuterium exchange in conjunction with mass spectrometry are sensitive and high-throughput strategies that provide low-resolution structural information of non-covalent natural product-protein complexes. In this review, we provide an overview on the applications of mass spectrometry-based techniques in the identification and characterization of natural product-protein interactions, and we describe how these applications might revolutionize natural product-based drug discovery.
  Mass Spectrometry Reviews 04/2009; 29(1):126-55. · 10.46 Impact Factor
• Article: Comparative proteomic analysis of indioside D-triggered cell death in HeLa cells.

  Chi Chun Wong, Ying Wang, Ka-Wing Cheng, Jen-Fu Chiu, Qing-Yu He, Feng Chen
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  ABSTRACT: Medicinal plants represent a rich source of cancer drug leads. Indioside D, a furostanol glycoside isolated from Solanum mammosum, was found to possess antiproliferative activity toward a panel of human cancer cell lines. Proteomic analysis of indioside D-treated HeLa cells revealed profound protein changes related to energy production and oxidative stress, suggesting that mitochondria dysfunction plays a role in indioside D-induced apoptosis. Indioside D caused a rapid dissipation of mitochondrial transmembrane potential (DeltaPsim) and the generation of reactive oxygen species (ROS), leading to the activation of caspase-dependent apoptotic cell death. The Fas death receptor pathway was also activated following indioside D treatment, and triggered the activation of caspase-8 and cleavage of Bid, which also acted through the mitochondrial apoptosis pathway. These results suggest that indioside D induced apoptosis in HeLa cells via both intrinsic and extrinsic cell death pathways.
  Journal of Proteome Research 06/2008; 7(5):2050-8. · 5.11 Impact Factor
• Article: Unraveling the molecular targets of natural products: Insights from genomic and proteomic analyses.

  Chi Chun Wong, Ka Wing Cheng, Qing-Yu He, Feng Chen
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  ABSTRACT: Natural products and their derivatives have been an invaluable source of drug leads for the pharmaceutical industry over the past decades, especially for antibacterial and anticancer purposes. Nature products, with their chemical diversity and biochemical specificity, are ideal starting points of drug development. Rational drug design based on natural product scaffolds, however, was hindered by a lack of knowledge regarding their mechanisms of action. Advances in proteomic technologies hold the key to revolutionize the target identification of natural products. In this regard, chemical proteomics have demonstrated the capabilities to identify specific targets by screening against the proteome. On the other hand, high-throughput proteome analysis reveals the multiple impacts of drug-target interaction in a global context, providing insights for elucidation of signaling pathways involved in the drug response, and uncovering predictive markers of drug efficacy and toxicity. Increasingly, studies have exploited integration of transcriptome and proteome datasets, which offers additional information on regulation of molecular network at transcriptional and post-translational levels. In this review, we discuss major proteomic approaches applied to studying the mechanism of action of natural products and merits of combining datasets from proteomics and transcriptomics analysis.
  Proteomics. Clinical applications 03/2008; 2(3):338-54. · 1.97 Impact Factor
• Article: Evaluation of two methods for the extraction of antioxidants from medicinal plants.

  Hua-Bin Li, Yue Jiang, Chi-Chun Wong, Ka-Wing Cheng, Feng Chen
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  ABSTRACT: The efficiencies of two traditional extraction methods used in Chinese medicine (the decoction method and the maceration method) were evaluated for the extraction of antioxidants from medicinal plants. A group of medicinal plants possessing nutritious and tonic functions were chosen as model plants. A commonly used extraction method was used as a reference method. The antioxidant capacities and total phenolic contents of the extracts were measured by ferric-reducing antioxidant power and Trolox equivalent antioxidant capacity assays as well as the Folin-Ciocalteu method, respectively. The results obtained indicated that the two traditional extraction methods could effectively extract antioxidants from medicinal plants. These extraction methods can be applied to the analysis and purification of antioxidants in plants, respectively. At home, people can use these methods to extract antioxidants from plants for consumption. In the food industry, these methods could be utilized to prepare crude extracts from plants containing antioxidants for use as food additives.
  Analytical and Bioanalytical Chemistry 06/2007; 388(2):483-8. · 3.78 Impact Factor
• Article: A systematic survey of antioxidant activity of 30 Chinese medicinal plants using the ferric reducing antioxidant power assay

  Chi-Chun Wong, Hua-Bin Li, Ka-Wing Cheng, Feng Chen
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  ABSTRACT: The antioxidant activities and total phenolic contents of 30 Chinese medicinal plants were evaluated using the ferric reducing antioxidant power assay and the Folin–Ciocalteu method, respectively. The Chinese medicinal plants were extracted by the traditional method, boiling in water and also in 80% methanol. A significant and linear correlation coefficient between the antioxidant activity and the total phenolic content was found in both aqueous (R2 = 0.7917) and methanol (R2 = 0.7584) extracts. Phenolic compounds are thus a major contributor of antioxidant activity. Comparing the extraction efficiency of the two methods, the boiling water method extracted phenolic compounds more efficiently, and antioxidant activity of the extract was higher. It was found that the Chinese medicinal plants Rhodiola sacra Fu, the stem of Polygonum multiflorum Thunb. and the root of P. multiflorum Thunb. possessed the highest antioxidant activities and thus could be potential rich sources of natural antioxidants.
  Food Chemistry.
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  Available from: Ka-Wing Cheng

  Article: Evaluation of antioxidant capacity and total phenolic content of different fractions of selected microalgae

  Hua-Bin Li, Ka-Wing Cheng, Chi-Chun Wong, King-Wai Fan, Feng Chen, Yue Jiang
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  ABSTRACT: In order to identify new sources of safe and inexpensive antioxidants, the antioxidant capacity and total phenolic content of different fractions of 23 microalgae were evaluated, using Trolox equivalent antioxidant capacity assay and the Folin–Ciocalteu method, respectively. The microalgae were extracted using hexane, ethyl acetate and water by a three-step sequential extraction procedure. Most of these microalgae were evaluated for the first time for their antioxidant activities. It was found that the microalgae Synechococcus sp. FACHB 283, Chlamydomonas nivalis and Nostoc ellipsosporum CCAP 1453/17 possessed the highest antioxidant capacities and thus could be potential rich sources of natural antioxidants. In addition, the correlation coefficients between the antioxidant capacities and the phenolic contents were very small in hexane (R2 = 0.0075), ethyl acetate (R2 = 0.5851) and water (R2 = 0.3599) fractions. Thus, phenolic compounds were not a major contributor to the antioxidant capacities of these microalgae. This was very different from many other plant species like fruits, vegetables and medicinal plants. The microalgae could contain different antioxidant compounds from other plants.
  Food Chemistry.
• Article: Antioxidant properties in vitro and total phenolic contents in methanol extracts from medicinal plants

  Hua-Bin Li, Chi-Chun Wong, Ka-Wing Cheng, Feng Chen
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  ABSTRACT: In order to find out new sources of safe and inexpensive antioxidants, the antioxidant capacities of 45 selected medicinal plants were evaluated using ferric reducing antioxidant power (FRAP) and Trolox equivalent antioxidant capacity (TEAC) assays, respectively, and the total phenolic contents of these plants were measured by the Folin–Ciocalteu method. Most of these plants were analyzed for the first time for their antioxidant activities. It was found that the plants Sargentodoxa cuneata Rehd. Et Wils, Fraxinus rhynchophylla Hance, Paeonia lactiflora Pall, Paeonia suffruticosa Andr and Scutellaria baicalensis Ceorgi possessed the highest antioxidant capacities and thus could be potential rich sources of natural antioxidants. A strong correlation between TEAC values and those obtained from FRAP assay implied that antioxidants in these plants were capable of scavenging free radicals and reducing oxidants. A high correlation between antioxidant capacities and their total phenolic contents indicated that phenolic compounds were a major contributor of antioxidant activity of these plants.
  LWT - Food Science and Technology.