Thomas Chung-Wai Mak

Publications of Thomas Chung-Wai Mak

• Gestational and lactational transfer of melamine following gavage administration of a single dose to rats.

  Authors: Judy Yuet Wa Chan, Chau Ming Lau, Tai Lun Ting, Thomas Chung Wai Mak, Michael Ho Ming Chan, Christopher Wai Kei Lam, Chung Shun Ho, Chi Chiu Wang, Tai Fai Fok, Kwok Pui Fung

  Food and chemical toxicology : an international journal published for the British Industrial Biological Research Association. 03/2011; 49(7):1544-8.

  Melamine contamination in an infant formula manufactured by a firm in China was reported in September 2008. Maternal transfer of melamine during pregnancy and through breast-feeding are possible waysMelamine contamination in an infant formula manufactured by a firm in China was reported in September 2008. Maternal transfer of melamine during pregnancy and through breast-feeding are possible ways of introduction. This study aims to evaluate the maternal transfer of melamine into amniotic fluid and breast milk through oral intake by pregnant and lactating rats, respectively. The quantity of melamine in the dam's sera, amniotic fluid, breast milk as well as in fetal whole body extract was measured. Our results showed that, after administration of single dose of 21.4 mg/kg per body weight of melamine to pregnant rats (16-18 days of gestation) by gavage, about 80% of melamine was found in dam's serum in 0.5 h. Melamine further reached the fetuses through placental transfer as it was found that peak melamine level of 7.15 ppm (∼30%) was detected in the fetuses after 2h and 4.36 ppm (∼20%) was shown in amniotic fluid after 3h of maternal intake. In the lactating rats, about 40% of maternal intake of melamine was transferred to breast milk and peaked at 3h. The results of this study confirmed the maternal transfer of melamine to fetuses in utero and infants through breast feeding.

• Pheophorbide a, an active component in Scutellaria barbata, reverses P-glycoprotein-mediated multidrug resistance on a human hepatoma cell line R-HepG2.

  Authors: Patrick Ming-Kuen Tang, Judy Yuet-Wa Chan, Dong-Mei Zhang, Shannon Wing-Ngor Au, Wing-Ping Fong, Siu-Kai Kong, Stephen Kwok-Wing Tsui, Mary Mui-Yee Waye, Thomas Chung-Wai Mak, Kwok-Pui Fung

  Cancer biology & therapy. 05/2007; 6(4):504-9.

  Scutellaria barbata, a Traditional Chinese Medicine native in southern China, has been widely used for treating liver diseases. In this study, the anti-proliferative effect of Pheophorbide a (Pa), anScutellaria barbata, a Traditional Chinese Medicine native in southern China, has been widely used for treating liver diseases. In this study, the anti-proliferative effect of Pheophorbide a (Pa), an active component from S. barbata, was examined on a multi-drug resistant (MDR) human hepatoma cell line R-HepG2. Our study showed that Pa could significantly inhibit the growth of R-HepG2 cells with an IC50 value at 25.0 microM after 48 hours treatment. When compared with the parental HepG2 cells, Pa showed weak resistance to R-HepG2. Efflux of Pa out of R-HepG2 cells was not observed as its cellular uptake level showed no significant difference comparing with HepG2 cells. Interestingly, significant reduction of P-glycoprotein expression on Pa-treated R-HepG2 cells was found at both transcriptional and translational levels, leading to reduction of P-glycoprotein activity. In addition, mechanistic study elucidated that Pa induced cell cycle arrest at G2/M phase and inhibited the expressions of G2/M phase cell cycle regulatory proteins, cyclin-A1 and cdc2 in a dose-dependent manner.

• Pheophorbide a, an active compound isolated from Scutellaria barbata, possesses photodynamic activities by inducing apoptosis in human hepatocellular carcinoma.

  Authors: Patrick Ming-Kuen Tang, Judy Yuet-Wa Chan, Shannon Wing-Ngor Au, Siu-Kai Kong, Stephen Kwok-Wing Tsui, Mary Mui-Yee Waye, Thomas Chung-Wai Mak, Wing-Ping Fong, Kwok-Pui Fung

  Cancer biology & therapy. 10/2006; 5(9):1111-6.

  Photodynamic therapy (PDT) is an effective treatment for cancer by inducing apoptosis or necrosis in the target cells. Pheophorbide a (Pa), a chlorophyll derivative, is a photosensitzier which canPhotodynamic therapy (PDT) is an effective treatment for cancer by inducing apoptosis or necrosis in the target cells. Pheophorbide a (Pa), a chlorophyll derivative, is a photosensitzier which can induce significant anti-proliferative effects in a number of human cancer cell lines. This study investigated the action mechanism of Pa-mediated photodynamic therapy (Pa-PDT) on the human hepatocellular carcinoma, Hep3B cells. Pa-PDT significantly inhibited the growth of Hep3B cells with an IC50 value of 1.5 microM. Intracellular ROS level was increased in Pa-PDT treated cells and the cytotoxic effect could be reversed when ascorbic acid was applied. Pa was found to be localized in the mitochondria and then induced the target cells to undergo apoptosis, which was confirmed by propidium iodide staining and DNA fragmentation assay. Pa-PDT treatment also led to the depolarization of mitochondrial membrane potential (Deltapim) and a release of cytochrome c from mitochondria to the cytosol. The caspase cascade was activated as shown by a significant decrease of procaspase-3 and -9 in Pa-PDT treated cells in a dose-dependent manner. Furthermore, in nude mice model, Pa-PDT treatment could reduce the tumor size by 57% after 14 days treatment.

• Pheophorbide a, a major antitumor component purified from Scutellaria barbata, induces apoptosis in human hepatocellular carcinoma cells.

  Authors: Judy Yuet-Wa Chan, Patrick Ming-Kuen Tang, Po-Ming Hon, Shannon Wing-Ngor Au, Stephen Kwok-Wing Tsui, Mary Mui-Yee Waye, Siu-Kai Kong, Thomas Chung-Wai Mak, Kwok-Pui Fung

  Planta medica. 02/2006; 72(1):28-33.

  Scutellaria barbata has long been used as a Chinese medicine for the treatment of liver diseases such as hepatitis and hepatocellular carcinoma. In the present study, a bioassay-guided method wasScutellaria barbata has long been used as a Chinese medicine for the treatment of liver diseases such as hepatitis and hepatocellular carcinoma. In the present study, a bioassay-guided method was used to isolate the most active components from Scutellaria barbata. The anti-proliferative effects on human hepatoma HepG2 and Hep3B cells of each fraction at every stage of the purification were monitored. An active component, which is 97% pure by high performance liquid chromatographic analysis, was isolated. Based on nuclear magnetic resonance (NMR) and mass spectrophotometric (MS) analysis, this active component was identified to be pheophorbide a (C35H36N4O5). Mechanistic studies showed that pheophorbide a induced apoptosis in Hep3B cells, a viral-induced hepatoma cell line. However, it was found to be non-toxic in normal human liver cells WRL-68. DNA fragmentation, sub-G1 cell cycle arrest, as well as suppression of the anti-apoptotic protein Bcl-2, release of cytochrome c to the cytosol, and activation of pro-caspase 3 and pro-caspase 9 were observed when Hep3B cells were treated with 40 microg/mL (i. e., 67.5 microM) pheophorbide a for 48 hours. In conclusion, this is the first report describing the isolation of pheophorbide a from Scutellaria barbata using a bioassay-guided isolation method. The anti-proliferative activity and possible mechanisms of action of pheophorbide a on hepatoma Hep3B cells are also discussed.

• Polyphyllin D is a potent apoptosis inducer in drug-resistant HepG2 cells.

  Authors: Jenny Yuen-Nei Cheung, Rose Chik-Ying Ong, Yick-Keung Suen, Vincent Ooi, Henry Nai-Ching Wong, Thomas Chung-Wai Mak, Kwok-Pui Fung, Biao Yu, Siu-Kai Kong

  Cancer letters. 01/2005; 217(2):203-11.

  In a search for new anticancer agents, we identified a novel compound polyphyllin D (PD) (diosgenyl alpha-L-rhamnopyranosyl-(1-->2)-(alpha-L-arabinofuranosyl)-(1-->4)]-[beta-D-glucopyranoside) thatIn a search for new anticancer agents, we identified a novel compound polyphyllin D (PD) (diosgenyl alpha-L-rhamnopyranosyl-(1-->2)-(alpha-L-arabinofuranosyl)-(1-->4)]-[beta-D-glucopyranoside) that induced DNA fragmentation and phosphatidyl-serine (PS) externalization in a hepatocellular carcinoma cell line HepG2 derivative with drug resistance (R-HepG2). PD is a saponin originally found in a tradition Chinese medicinal herb Paris polyphylla. It has been used to treat liver cancer in China for many years. We evaluated the cell-killing mechanisms of this compound in R-HepG2 and its parental cells. The mitochondrial apoptotic pathway was found to be involved in the PD-induced apoptosis because PD elicited depolarization of mitochondrial transmembrane potential (DeltaPsim), generation of H2O2, as well as release of cytochrome c and apoptosis-inducing factor in a dose- and time-dependent manner. In conclusion, we show for the first time that PD is a potent anticancer agent that can overcome drug resistance in R-HepG2 cells and elicit programmed cell death via mitochondrial dysfunction.