Jae Kweon Park

Effects of the Molecular Weight and the Degree of Deacetylation of Chitosan Oligosaccharides on Antitumor Activity

Effects of the degree of deacetylation (DDA) and the molecular mass of chitosan oligosaccharides (CTS-OS), obtained from the enzymatic hydrolysis of high molecular weight chitosan (HMWC), on antitumor activity was explored. The DDA and molecular weights of CTS-OS were determined by matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-TOF MS) analysis. The CTS-OS were found to be a mixture of mainly dimers (18.8%), trimers (24.8%), tetramers (24.9%), pentamers (17.7%), hexamers (7.1%), heptamers (3.3%), and octamers (3.4%). The CTS-OS were further fractionated by gel-filtration chromatography into two major fractions: (1) COS, consisting of glucosamine (GlcN)n, n = 3–5 with DDA 100%; and (2) HOS, consisting of (GlcN)5 as the minimum residues and varying number of N-acetylglucosamine (GlcNAc)n, n = 1–2 with DDA about 87.5% in random order. The cytotoxicities, expressed as the concentration needed for 50% cell death (CC50), of CTS-OS, COS, and HOS against PC3 (prostate cancer cell), A549 (lung cancer cell), and HepG2 (hepatoma cell), were determined to be 25 μg·mL−1, 25 μg·mL−1, and 50 μg·mL−1, respectively. The HMWC was approximately 50% less effective than both CTS-OS and COS. These results demonstrate that the molecular weight and DDA of chitosan oligosaccharides are important factors for suppressing cancer cell growth.

Immunostimulating activity of polyhydric alcohol isolated from Taxus cuspidata

A polyhydric alcohol (PAL) was isolated from Taxus cuspidata and its immunostimulatory activities were assessed. The primary monosaccharide composition of the PAL was determined to be glucose, where HPAEC analysis showed no significant amount of any other sugars. However, glycerol and xylitol were identified as the main sugar alcohols. Fourier-transform infrared (FT-IR) analysis indicated that the purified PAL is a complex glycitol, which structurally contains significant amount of hydroxyl groups. MALDI-TOF mass spectroscopy also demonstrated that PAL is a complex glycitol built in hexose polymerization. Enzyme linked immunosorbent assay showed that the PAL stimulates the release of the proinflammatory cytokines TNF-α and IL-6 in a dose-dependent manner. Furthermore, treatment of RAW 264.7 cells with PAL for 24h remarkably increased the phosphorylation levels of ERK, p38 and JNK in a dose-dependent manner, whereas the total protein levels of ERK (t-ERK), p38 (t-p38) and JNK (t-JNK) remained unchanged. These results clearly demonstrate that PAL stimulates the immune response in RAW 264.7 cells through the activation of MAPKs (ERK, p38 and JNK) signaling pathway. To the best of our knowledge, this is the first study to demonstrate the primary structure and immune-stimulating activities of PAL from the fruit of T. cuspidata.

Neuroprotective effects of N-acetylglucosamine against hydrogen peroxide-induced apoptosis in human neuronal SK-N-SH cells by inhibiting the activation of caspase-3, PARP, and p38

Neuroprotective effects of N-acetylglucosamine (GlcNAc), a monosaccharide derivative of glucose, against H2O2-induced neurotoxicity and its underlying mechanism in human SK-N-SH neuroblastoma cells were investigated. Pretreatment of GlcNAc prior to exposure of cells to H2O2 stress significantly reduced the H2O2-mediated neuronal cell death and apoptosis. The GlcNAc dose-dependently decreased the level of intracellular reactive oxygen species (ROS) in H2O2-treated cells and also effectively inhibited H2O2-induced apoptotic features such as DNA fragmentation, caspase-3, and poly ADP-ribose polymerase (PARP) cleavages, and p38 phosphorylation. These results suggested that GlcNAc might potentially serve as agents for prevention of neurodegenerative diseases caused by oxidative stresses and this effect may be associated with the suppression of caspase-3, PARP, and p38 activation.

Purification and characterization of a polysialic acid-specific sialidase from Pseudomonas fluorescens JK-0412

An enzyme with polySia degrading activity was purified from a culture filtrate of Pseudomonas fluorescens JK-0412 to apparent homogeneity using DEAE-Sepharose CL-6B column chomatography and fast performance liquid chomatography separation on a Mono-Q column. The molecular mass of the purified enzyme (tentatively named Endo-PS) was approximately 20 kDa on SDS-PAGE and 120 kDa on native-PAGE gels, suggesting that the active form is a hexamer. Although 12 residues of the Endo-PS N-terminal amino acid sequence showed 75% homology to the 21 kDa chitin binding protein (CBP21) of Serratia marcescens 2170, no significant similarity to other known proteins was observed. Apparent Km and Vmax values of Endo-PS toward the artificial substrate 4-methylumbelliferyl-sialic acid (4-MU-Neu5Ac) were 0.08 mM and 16 nmol/mg/min, respectively. The enzyme was maximally active at 37°C and pH 8.0. Interestingly, the enzyme was shown to hydrolyze the natural substrate, α2,8-linked polySia (colominic acid), in an endo-acting manner. However, no activity toward α2,3- or α2,6-sialyllactose was observed. Under optimal conditions, oligoSia ranging from 2 to 30 residues long were liberated by the cleavage of polySia, as identified by HPAEC-PED. Therefore, the purified enzyme Endo-PS was found to be a polySia-specific sialidase. This is the first report to describe the properties of a bacterial polySia-specific sialidase. Therefore, this enzyme may be a useful tool for both industrial oligoSia production and research on the structure and biological functions of polySia in nature.