Gook-Hyun Chung

The antioxidant, rather than prooxidant, activities of quercetin on normal cells: quercetin protects mouse thymocytes from glucose oxidase-mediated apoptosis.

The bioflavonoid quercetin is a dietary anticancer chemical that is capable of inducing apoptosis in tumor cells. Although the activity of quercetin is believed to be due to its antioxidative properties, it has recently been suggested that quercetin also has prooxidant activities, which might effect cytotoxicity directly. In this study, we used mouse thymocytes to investigate whether quercetin behaved as a protector against oxidative stress or as a cytotoxic agent. Quercetin treatment did not induce oxidative damage, but protected mouse thymocytes from glucose oxidase (GO)-mediated apoptosis in a dose-dependent manner. Furthermore, electrophoretic mobility shift assays revealed that quercetin (50 microM) treatment suppressed the GO-mediated DNA binding activity of redox state-sensitive transcription factors, such as NF-kappaB, AP-1, and p53. This result suggests that quercetin has antioxidative effects on thymocytes. More interestingly, quercetin treatment alone (50 microM) increased the DNA-binding activity of AP-1, which consisted of heterodimer of c-Jun and Fra-2. Finally, the antioxidant activity of quercetin was confirmed using a cell-free system of radical generation. Our findings suggest that quercetin protects mouse thymocytes from oxidative stress-mediated apoptosis and modulates the intracellular redox state through its antioxidant activity.

Lipoteichoic acid-induced nitric oxide production depends on the activation of platelet-activating factor receptor and Jak2

NO production by macrophages in response to lipoteichoic acid (LTA) and a synthetic lipopeptide (Pam3CSK4) was investigated. LTA and Pam3CSK4 induced the production of both TNF-α and NO. Inhibitors of platelet-activating factor receptor (PAFR) blocked LTA- or Pam3CSK4-induced production of NO but not TNF-α. Jak2 tyrosine kinase inhibition blocked LTA-induced production of NO but not TNF-α. PAFR inhibition blocked phosphorylation of Jak2 and STAT1, a key factor for expressing inducible NO synthase. In addition, LTA did not induce IFN-β expression, and p38 mitogen-activated protein serine kinase was necessary for LTA-induced NO production but not for TNF-α production. These findings suggest that Gram-positive bacteria induce NO production using a PAFR signaling pathway to activate STAT1 via Jak2. This PAFR/Jak2/STAT1 signaling pathway resembles the IFN-β, type I IFNR/Jak/STAT1 pathway described for LPS. Consequently, Gram-positive and Gram-negative bacteria appear to have different but analogous mechanisms for NO production.

Antioxidant property of an active component purified from the leaves of paraquat-tolerant Rehmannia glutinosa

Abstract Acteoside extracted from the leaves of Rehmannia glutinosa was examined to determine the mechanism(s) of its antioxidant properties. The deoxyribose assay system showed that acteoside has a high redox potential as electron donor, which generates hydroxyl radicals in an Fe3+-dependent manner similar to ascorbic acid. However, the antioxidant properties of acteoside differ from those of ascorbic acid in that the superoxide anion-mediated reduction of nitroblue tetrazolium was actively inhibited by acteoside but not by ascorbic acid. Acteoside protected cells against glucose oxidase-mediated cytotoxicity and apoptosis in a dose-dependent manner. In addition, acteoside had immune stimulating effects, as shown by the acteoside-mediated increase in the level of DNA synthesis, viability, and cytokine secretion in mouse splenocytes. Moreover, acteoside inhibited the gelatinolytic activity of MMP proteins in a dose-dependent manner. Considering these results and the fact that acteoside is a water-soluble natural product, acteoside might have potential as a preventative treatment for oxidative stress-mediated diseases and have possibilities in the cosmetic industry.

Modulation of antigen-specific immune responses by the oral administration of a traditional medicine, Bo-Yang-Hwan-O-Tang

ABSTRACT Bo-yang-hwan-o-tang (BHT) has long been used to treat cancer in traditional Korean medicine and is believed to have immune-modulating activity. This study investigated the effect of BHT on the induction of antigen-specific immune responses using hen egg-white lysozyme (HEL) as a model antigen system. Oral administration of BHT enhanced both HEL-specific humoral and lymphocyte proliferative responses in HEL low-responder mice. Feeding BHT to the mice increased INF-γ levels, but did not change IL-4 levels. Interestingly, however, the oral BHT feeding significantly increased HEL-specific antibodies of the IgG1, IgG2b, and IgG3 subtypes, which are associated with the direct stimulation of B cells. This indicates that BHT treatment enhances anti-HEL-specific humoral immune responses via the direct stimulation of B lymphocytes rather than by selective priming of specific subtypes of the helper T-cell population. This conclusion was supported by in vitro experiments, in which the presence of BHT significantly augmented B-cell mitogen-mediated proliferation of mouse splenocytes. This augmentation was closely associated with a glycoprotein with a molecular weight of around 100 kDa. The results suggest that BHT modulates antigen-specific immune responses, and might be used as a therapeutic agent for patients who need enhanced immune function.

Selective priming of Th1-mediated antigen-specific immune responses following oral administration of mixed prescriptions of traditional Korean medicines.

BACKGROUND In previous studies, we showed that oral administration of traditional Korean medicines, Soamsan (SA) and Bo-yang-hwan-o-tang (BHT), modulated antigen-specific immune responses in mice. METHODS We attempted to strengthen cell-mediated immune responses in mice using two mixed prescriptions composed mainly of components used in SA and/or BHT. The effect of oral administration of the medicines on the induction of antigen-specific immune responses was investigated using hen egg-white lysozyme (HEL) as a model antigen system. RESULTS Following oral administration, HEL-specific cellular immune responses were enhanced in HEL low-responder mice, and the concentrations of gamma interferon (IFN-gamma), but not interleukin (IL)-4, increased significantly. In addition, the prescriptions decreased the level of HEL-specific antibodies of the immunoglobulin (Ig)G1 subtype, which is associated with helper T lymphocyte (Th2) cell stimulation. Moreover, the presence of the medicines in vitro significantly increased IFN-gamma production from mouse splenocytes, and the magnitude of the increase was closely associated with glycoprotein concentrations. CONCLUSIONS The Korean prescriptions enhanced anti-HEL-specific cellular immune responses by selectively priming specific subtypes of the helper T cell population. Consequently, they might be useful therapy for patients who need enhanced Th1, or to suppress Th2 immune responses.

Latent membrane protein 1 of Epstein-Barr virus plays an important role in the serum starvation resistance of Epstein-Barr virus-immortalized B lymphocytes

We have previously shown that SNU‐1103, which is a latency type III Epstein–Barr virus (EBV)‐transformed lymphoblastoid cell line (LCL) that was developed from a Korean cancer patient, resists serum starvation‐induced G1 arrest. In this study, we examined the role of latent membrane protein‐1 (LMP‐1) in serum starvation resistance, since LMP‐1 is known to be essential for EBV‐mediated immortalization of human B lymphocytes. The LMP‐1 gene from SNU‐1103 was introduced into the EBV‐negative BJAB cell line, and shown to be associated with resistance to G1 arrest during serum starvation. Western blot analyses of the LMP‐1‐transfected cells revealed several protein alterations as compared to vector‐transfected control cells. The expression of key cell‐cycle regulatory proteins was affected in the G1 phase: the expression of cyclin D3, CDK2, p27, and E2F‐4 was up‐regulated, and the expression of cyclin D2, CDK6, p21, and p103 was down‐regulated during serum starvation. These results imply that of the several EBV viral genes expressed in EBV‐negative B lymphoma cells, LMP‐1 mediates resistance to serum starvation‐induced G1 arrest. However, we cannot rule out the possibility that other EBV genes are also involved in the cell‐cycle progression of the EBV‐transformed LCL during serum starvation, since the altered protein expression profile of the LMP‐1 transfectants was distinct from that of the SNU‐1103 cells that expressed all of the EBV viral proteins.

Molecular characterization of pneumococcal surface protein K, a potential pneumococcal vaccine antigen

ABSTRACT The pneumococcal capsule is indispensable for pathogenesis in systemic infections; however, many pneumococcal diseases, including conjunctivitis, otitis media, and some systemic infections in immunocompromised patients, are caused by nonencapsulated Streptococcus pneumoniae (NESp). Null capsule clade 1 (NCC1), found in group 2 NESp, expresses pneumococcal surface protein K (PspK) and is becoming prevalent among pneumococcal organisms owing to the widespread use of pneumococcal conjugate vaccines. Despite its clinical importance, the molecular mechanisms underlying the prevalence of NCC1 have not been fully elucidated. Here, we investigated the role of the R3 domain of PspK in the epithelial cell adherence of NCC1. We found that the R3 domain of PspK mediated NCC1 adherence via its direct interaction with the epithelial surface protein annexin A2. Additionally, neutralization with purified recombinant PspK-R3 or rabbit anti-UD:R3 IgG inhibited binding of NESp to lung epithelial cells in vitro. Immunization with the ‘repeat’ domain of PspK-R3 or PspK-UD:R3 effectively elicited mucosal and systemic immune responses against PspK-R3 and provided protection against nasopharyngeal, lung, and middle ear colonization of NESp in mice. Additionally, we found that rabbit anti-UD:R3 IgG bound to PspC-R1 of the encapsulated TIGR4 strain and that UD:R3 immunization provided protection against nasopharyngeal and lung colonization of TIGR4 and deaths by TIGR4 and D39 in mice. Further studies using 68 pneumococcal clinical isolates showed that 79% of clinical isolates showed cross-reactivity to rabbit anti-UD:R3 IgG. About 87% of serotypes in the 13-valent pneumococcal conjugate vaccine (PCV) and 68% of non-vaccine serotypes were positive for cross-reactivity with rabbit anti-UD:R3 IgG. Thus, the R3 domain of PspK may be an effective vaccine candidate for both NESp and encapsulated Sp.