Hyun-Dae Lim

Cytoprotective and anti-inflammatory effects of melatonin in hydrogen peroxide-stimulated CHON-001 human chondrocyte cell line and rabbit model of osteoarthritis via the SIRT1 pathway.

Abstract:  Melatonin has potent antioxidant, analgesic, and antinociceptive properties. However, the effects of melatonin against oxidative stress‐induced cytotoxicity and inflammatory mediators in human chondrocytes remain poorly understood. This study examined the effects and underlying mechanism of melatonin in hydrogen peroxide (H2O2)‐stimulated human chondrocytes and rabbit osteoarthritis (OA) model. Melatonin markedly inhibited hydrogen peroxide (H2O2)‐stimulated cytotoxicity, iNOS, and COX‐2 protein and mRNA expression, as well as the downstream products, NO and PGE2. Incubation of cells with melatonin decreased H2O2‐induced Sirtuin 1 (SIRT1) mRNA and protein expression. SIRT1 inhibition by sirtinol or Sirt1 siRNA reversed the effects of melatonin on H2O2‐mediated induction of pro‐inflammatory cytokines (NO, PGE2, TNF‐α, IL‐1β, and IL‐8) and the expression of iNOS, COX‐2, and cartilage destruction molecules. Melatonin blocked H2O2‐induced phosphorylation of PI3K/Akt, p38, ERK, JNK, and MAPK, as well as activation of NF‐κB, which was reversed by sirtinol and SIRT1 siRNA. In rabbit with OA, intra‐articular injection of melatonin significantly reduced cartilage degradation, which was reversed by sirtinol. Taken together, this study shows that melatonin exerts cytoprotective and anti‐inflammatory effects in an oxidative stress‐stimulated chondrocyte model and rabbit OA model, and that the SIRT1 pathway is strongly involved in this effect.

The regulatory mechanism of 4-phenylbutyric acid against ER stress-induced autophagy in human gingival fibroblasts

Endoplasmic reticulum (ER) stress is closely connected to autophagy. When cells are exposed to ER stress, cells exhibit enhanced protein degradation and form autophagosomes. In this study, we demonstrate that the chemical chaperone, 4-phenylbutyric acid (4-PBA), regulates ER stressinduced cell death and autophagy in human gingival fibroblasts. We found that 4-PBA protected cells against thapsigargin-induced apoptotic cell death but did not affect the reduced cell proliferation. ER stress induced by thapsigargin was alleviated by 4-PBA through the regulation of several ER stress-inducible, unfolded protein response related proteins including GRP78, GRP94, C/EBP homologous protein, phospho-eIF-2α, eIF-2α, phospho-JNK1 (p46) and phospho-JNK2/3 (p54), JNK1, IRE-1α, PERK, and sXBP-1. Compared with cells treated with thapsigargin alone, cells treated with both 4-PBA and thapsigargin showed lower levels of Beclin-1, LC-3II and autophagic vacuoles, indicating that 4-PBA also inhibited autophagy induced by ER stress. This study suggests that 4-PBA may be a potential therapeutic agent against ER stress-associated pathologic situations.

4-phenylbutyric Acid Regulates Collagen Synthesis and Secretion Induced by High Concentrations of Glucose in Human Gingival Fibroblasts.

High glucose leads to physio/pathological alterations in diabetes patients. We investigated collagen production in human gingival cells that were cultured in high concentrations of glucose. Collagen synthesis and secretion were increased when the cells were exposed to high concentrations of glucose. We examined endoplasmic reticulum (ER) stress response because glucose metabolism is related to ER functional status. An ER stress response including the expression of glucose regulated protein 78 (GRP78), C/EBP homologous protein (CHOP), inositol requiring enzyme alpha (IRE-1α) and phosphoreukaryotic initiation factor alpha (p-eIF-2α) was activated in the presence of high glucose. Activating transcription factor 4 (ATF-4), a downstream protein of p-eIF-2α as well as a transcription factor for collagen, was also phosphorylated and translocalized into the nucleus. The chemical chaperone 4-PBA inhibited the ER stress response and ATF-4 phosphorylation as well as nuclear translocation. Our results suggest that high concentrations of glucose-induced collagen are linked to ER stress and the associated phosphorylation and nuclear translocation of ATF-4.

Iron chelator differentially activates macrophage inflammatory protein-3α/CCL20 in immortalized and malignant human oral keratinocytes

Macrophage inflammatory protein-3alpha (MIP-3alpha or CCL20) is an intriguing molecule in cancer immunotherapy, but MIP-3alpha expression and signalling are not well understood in oral cancer cells. We investigated CCL20 expression and signal transduction by treating immortalized human oral keratinocyte (IHOK) and oral cancer (HN4) cells with deferoxamine (DFO) and examined the mRNA expression of CCL20 using RT-PCR and ELISA. IHOK and HN4 cells treated with DFO showed increased mRNA and protein expression of CCL20, and the upregulation of DFO-induced CCL20 expression was higher in IHOK cells than in HN4 cells. Selective inhibitors of p38 and ERK1/2 abolished DFO-induced CCL20 expression in both IHOK and HN12 cells, and p38 and ERK1/2 inhibitors prevented DFO-induced degradation of I-kappaB and NF-kappaB activation. Activation of c-fos and c-jun also occurred following DFO treatment in IHOK and HN4 cells. Collectively, these results suggest that DFO-induced MIP-3alpha, which is involved in the MAP kinase, c-fos, c-jun, and NF-kappaB pathways, may be an important mediator of the antitumour immune response in oral keratinocytes and warrants consideration as a target molecule for oral cancer treatment.

Evaluation of Quality of Life according to Temporomandibular Disorder Symptoms in Dental Hospital Worker

Temporomandibular disorder(TMD) is relatively prevalent disease, and quality of life may be impaired in TMD patients. Like general population, dental hospital workers are also exposed to the risk of TMD. But, many of them tend to overlook or tolerate their symptoms for lack of time and interest. Therefore, problems may become more serious, causing interference of performing task and decrease of quality of life. The aim of this study were to obtain data for TMD prevalence in dental hospital workers and to evaluate quality of life according to TMD symptoms. Subjects were recruited from Wonkwang University Dental Hospital. After consent, subjects completed quality of life questionnaire and were evaluated for subjective and objective signs and symptoms of TMD. Subjects were classified into 4 groups : (1) normal group (2) joint disorder group, (3) local myalgia group, and (4) myofascial pain group. The result of the study indicated that TMD negatively influences the quality of life in dental hospital worker. TMD symptoms can deteriorate quality of life in dental hospital worker. Future effort to make protocol for proper management is needed.

N-Nitrosodimethylamine induced lung fibroblast cell death is associated with JNK activation

N-Nitrosodialkylamines are considered a potential health hazard for humans. Among various N-nitrosodialkylamines compound, N-nitrosodimethylamine (NDMA), was applied to lung cells, MLG. In order to examine the effect of NDMA in lung cells, cell death was first examined. NDMA induced cell death in a dose-dependent manner. Mitogen activated protein kinase (MAPK) involvement was tested using SP600125 for JNK, SB203580 for P38 MAPK, or PD98059 for ERK. SP compound induced a significant reduction of cell death, compared with other inhibitors. NDMA induced an increase in expression of ER stress response proteins, including GRP78, IRE-1α, CHOP, GRP94, p-eIF2α, p-JNK, or sXBP-1. Pretreatment with SP compound regulated expression of CHOP, the transcription factor associated with proapoptotic gene induction. This study showed that NDMA-induced cell death was resulted due to JNK activation. ER stress was also induced in the toxic situations. Study of the meaning of ER stress will be necessary in the near future.