Metformin Suppresses MHC-Restricted Antigen Presentation by Inhibiting Co-Stimulatory Factors and MHC Molecules in APCs

Metformin is widely used for T2D therapy but its cellular mechanism of action is undefined. Recent studies on the mechanism of metformin in T2D have demonstrated involvement of the immune system. Current immunotherapies focus on the potential of immunomodulatory strategies for the treatment of T2D. In this study, we examined the effects of metformin on the antigen-presenting function of antigen-presenting cells (APCs). Metformin decreased both MHC class I and class II-restricted presentation of OVA and suppressed the expression of both MHC molecules and co-stimulatory factors such as CD54, CD80, and CD86 in DCs, but did not affect the phagocytic activity toward exogenous OVA. The class II-restricted OVA presentation-regulating activity of metformin was also confirmed using mice that had been injected with metformin followed by soluble OVA. These results provide an understanding of the mechanisms of the T cell response-regulating activity of metformin through the inhibition of MHC-restricted antigen presentation in relation to its actions on APCs.

Immunomodulatory Effects of Dioscoreae Rhizome Against Inflammation through Suppressed Production of Cytokines Via Inhibition of the NF-kappaB Pathway

Dioscoreae Rhizome (DR) has been used in traditional medicine to treat numerous diseases and is reported to have anti-diabetes and anti-tumor activities. To identify a bioactive traditional medicine with anti-inflammatory activity of a water extract of DR (EDR), we determined the mRNA and protein levels of proinflammatory cytokines in macrophages through RT-PCR and western blot analysis and performed a FACS analysis for measuring surface molecules. EDR dose-dependently decreased the production of NO and pro-inflammatory cytokines such as IL-1beta, IL-6, TNF-alpha, and PGE2, as well as mRNA levels of iNOS, COX-2, and pro-inflammatory cytokines, as determined by western blot and RT-PCR analysis, respectively. The expression of co-stimulatory molecules such as B7-1 and B7-2 was also reduced by EDR. Furthermore, activation of the nuclear transcription factor, NF-kappaB, but not that of IL-4 and IL-10, in macrophages was inhibited by EDR. These results show that EDR decreased pro-inflammatory cytokines via inhibition of NF-kappaB-dependent inflammatory protein level, suggesting that EDR could be a useful immunomodulatory agent for treating immunological diseases.

Role of Salvia miltiorrhiza for Modulation of Th2-derived Cytokines in the Resolution of Inflammation

BACKGROUND: Salvia miltiorrhiza (SM) has been used to treat inflammatory diseases including edema and arthritis; however, the anti-inflammatory mechanism of SM action remains unresolved. METHODS: The effects of an ethanol extract of SM (ESM) on pro-inflammatory cytokines such as TNF-alpha, IL-1beta, IL-6, and NO, on anti-inflammatory cytokines including IL-4, IL-10, TGF-beta, and IL-1Ra have been studied in an attempt to elucidate the anti-inflammatory mechanism in murine macrophages. RESULTS: ESM inhibited the production of pro-inflammatory cytokines via down-regulation of gene and protein expression whereas it increased the anti-inflammatory cytokines. Furthermore, ESM inhibited the expression of the chemokines, RANTES and CX3CL1, as well as of inflammatory mediators such as TLR-4 and 11beta-HSD1. CONCLUSION: These results indicated that the regulatory effects of ESM may be mediated though the suppression of pro-inflammatory cytokines as well as the induction of anti-inflammatory cytokines. Consequently, we speculate that ESM has therapeutic potential for inflammation-associated disorders.

Role of Salvia miltiorrhiza for Modulation of Th2-derived Cytokines in the Resolution of Inflammation

BACKGROUND: Salvia miltiorrhiza (SM) has been used to treat inflammatory diseases including edema and arthritis; however, the anti-inflammatory mechanism of SM action remains unresolved. METHODS: The effects of an ethanol extract of SM (ESM) on pro-inflammatory cytokines such as TNF-alpha, IL-1beta, IL-6, and NO, on anti-inflammatory cytokines including IL-4, IL-10, TGF-beta, and IL-1Ra have been studied in an attempt to elucidate the anti-inflammatory mechanism in murine macrophages. RESULTS: ESM inhibited the production of pro-inflammatory cytokines via down-regulation of gene and protein expression whereas it increased the anti-inflammatory cytokines. Furthermore, ESM inhibited the expression of the chemokines, RANTES and CX3CL1, as well as of inflammatory mediators such as TLR-4 and 11beta-HSD1. CONCLUSION: These results indicated that the regulatory effects of ESM may be mediated though the suppression of pro-inflammatory cytokines as well as the induction of anti-inflammatory cytokines. Consequently, we speculate that ESM has therapeutic potential for inflammation-associated disorders.

Cordyceps militaris Enhances MHC-restricted Antigen Presentation via the Induced Expression of MHC Molecules and Production of Cytokines

BACKGROUND: Cordyceps militarys water extract (CME) has been reported to exert antitumor and immunomodulatory activities in vivo and in vitro. However, the therapeutic mechanism has not yet been elucidated. In this study, we examined the effects of CME on the antigen presenting function of antigen presenting cells (APCs). METHODS: Dendritic cells (DCs) were cultured in the presence of CME, and then allowed to phagocytose microspheres containing ovalbumin (OVA). After washing and fixing the efficacy of OVA, peptide presentation by DCs were evaluated using CD8 and CD4 T cells. Also, we confirmed the protein levels of proinflammatory cytokines through western blot analysis. RESULTS: CME enhanced both MHC class I and class II-restricted presentation of OVA in DCs. In addition, the expression of both MHC class I and II molecules was enhanced, but there was no changes in the phagocytic activity of exogenous OVA. Furthermore, CME induced the protein levels of iNOS, COX-2, proinflammatory cytokines, and nuclear p65 in a concentration-dependent manner, as determined by western blot. CONCLUSION: These results provide an understanding of the mechanism of the immuno-enhancing activity of CME on the induction of MHC-restricted antigen presentation in relation to their actions on APCs.

Mizoribine Inhibits Production of Pro-inflammatory Cytokines and PGE2 in Macrophages

BACKGROUND: Mizoribine (MZR) is an imidazole nucleoside isolated from Eupenicillium brefeldianum. MZR is currently in clinical use for patients who have undergone renal transplantation. Therapeutic efficacy of MZR has also been demonstrated in rheumatoid arthritis and lupus nephritis. MZR has been shown to inhibit the proliferation of lymphocytes by interfering with inosine monophosphate dehydrogenase. Since the exact mechanism by which MZR benefits rheumatoid arthritis (RA) is not clear, we investigated the ability of MZR to direct its immunosuppressive influences on other antigen presenting cells, such as macrophages. METHODS: Mouse macrophage RAW264.7 cells were stimulated with lipopolysaccharide in the presence of MZR. To elucidate the mechanism of the therapeutic efficacy in chronic inflammatory diseases, we examined the effects of MZR on the production of pro-inflammatory cytokines, nitric oxide (NO) and prostaglandin E2 (PGE2) in macrophages. RESULTS: MZR dose-dependently decreased the production of nitric oxide and pro- inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha), interleukins 1beta (IL-beta) and IL-6 PGE2. Examination of gene expression levels showed that the anti-inflammatory effect correlated with the down-regulation of inducible nitiric oxide synthase expression, cycloxygenase-2 expression and TNF-alpha gene expression. CONCLUSION: In this work, we resulted whether MZR (1.25~10 microgram/ml) inhibited macrophage activation by inhibiting secretion of pro-inflammatory cytokines, NO and PGE2. These findings provide an explanation for the therapeutic efficacy of MZR in chronic inflammation- associated diseases.

Activation of Macrophages by the Components Produced from Cordyceps militaris

BACKGROUND: Cordyceps militaris have been reported to modify the immune and inflammatory responses both in vivo and in vitro. Macrophages play important roles in the innate immunity through the phagocytosis of antigens. This study examined the effects of Cordyceps militaris on the activation of murine macrophage RAW 264.7 cells and primary macrophages. METHODS: The components contained in culture broth of Cordyceps militaris were purified by propyl alcohol extraction and HP 20 column chromatography to CMDB, CMDBW, CMDB5P, and CMDB25P. The amounts of nitric oxide (NO) were determined by using ELISA, Griess reagent respectively. The amounts of some cytokines were determined by using ELISA, western blot, and RT-PCR. The expression levels of cell surface molecules (ICAM-1, B7-1 and B7-2) were measured by flow cytometric analysis. RESULTS: All the components of Cordyceps militaris produced significant amounts of NO. In particular, CMDB produced much more NO in RAW 264.7 cells and primary macrophages than other fractions of Cordyceps militaris. CMDB increased significantly the production of tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and IL-6 dose-dependently in RAW 264.7 cells. Examination of the gene expression level also showed that the enhanced production of cytokines was correlated with the up-regulation of i-NOS expression, cycloxygenase (COX)-2 expression, IL-1beta and IL-6 expression, and TNF-alpha expression on the expression of mRNAs by semi-quantitative RT-PCR. Western blot analysis also confirmed that CMDB enhances the expression level of these cytokines. CONCLUSION: These results show that CMDB stimulates the production of NO and pro-inflammatory cytokines and can also up-regulate the gene expression levels in macrophages.

Inhibition of Major Histocompatibility Complex (MHC)- Restricted Presentation of Exogenous Antigen in Dendritic Cells by Korean Propolis Components

BACKGROUND: Dendritic cells (DCs) play a critical role not only in the initiation of immune responses, but also in the induction of immune tolerance. In an effort to regulate immune responses through the modulation of antigen presenting cell (APC) function of DCs, we searched for and characterized APC function modulators from natural products. METHODS: DCs were cultured in the presence of propolis components, WP and CP, and then examined for their ability to present exogenous antigen in association with major histocompatibility complexes (MHC). RESULTS: WP and CP inhibited class I MHC-restricted presentation of exogenous antigen (cross-presentation) in a DC cell line, DC2.4 cells, and DCs generated from bone marrow cells with GM-CSF and IL-4. The inhibitory activity of WP and CP appeared to be due not only to inhibition of phagocytic activity of DCs, but also to suppression of expression of MHC molecules on DCs. We also examined the effects of WP and CP on T cells. Interestingly, WP and CP increased IL-2 production from T cells. CONCLUSION: These results demonstrate that WP and CP inhibit MHC-restricted presentation of exogenous antigen through down-regulation of phagocytic activity and suppression of expression of MHC molecules on DCs.